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The epoxy-siloxane/Al composite coatings with low infrared emissivity for high temperature applications
Abstract
Low infrared emissivity coatings with good thermal resistance were prepared by using epoxy-siloxane and aluminum as adhesive and pigment, respectively. The influence of chemical composition, surface texture, roughness and thickness on the infrared emissivity was systematically investigated. The detailed results of experimental investigation indicate that the cured composite coatings could possess low emissivity value. Due to reducing infrared absorption and forming uniform and compact char construction, the infrared emissivity decreases obviously. Both the surface roughness and thickness have a critical value, respectively. Too large roughness or thickness would not contribute to the decrease of the emissivity. Moreover, the composite coatings were tested for thermal stability in air to explore the effect of high-temperature environment on the emissivity. The results indicate that the composite coatings, still possessing low emissivity after the test, exhibit favorable thermal ageing and thermal shock resistance.
... The emissivity simulated using the superposition T-matrix method is averaged over five generated configurations to obtain more realistic results. The dispersed coatings discussed in this study can be used in applications, such as radiative cooling [13,15] and infrared camouflage [17,44,45]. ...
... In the simulations, the parameters, including the materials, coating thicknesses, particle sizes, and volume fractions, are selected based on previous studies [13,15,17,22,44]. The single scattering properties of Al particles are significantly different from those of TiO 2 particles. ...
Particle dispersed coatings with gradient distributions, resulting from either gravity or artificial control, are frequently encountered in practical applications. However, most current studies investigating the optical properties of coatings use the uniform model (uniform single layer assumption), overlooking the gradient distribution effects. Given the pervasiveness of gradient distributions and the widespread use of the uniform model, it is imperative to evaluate applicability conditions of the uniform model in practical applications. In this work, we comprehensively investigate the quantitative performance of the uniform model in predicting the infrared optical properties of coatings with gradient distributions of particle volume fraction using the superposition T-matrix method. The results show that the gradient distribution of particle volume fraction has a limited impact on the emissivity properties of T i O 2 -PDMS coatings in the midwavelength-infrared (MWIR) and long-wavelength-infrared (LWIR) bands, which validates the uniform model for the gradient coatings with weakly scattering dielectric particles. However, the uniform model can yield significant inaccuracies in estimating the emissivity properties of Al-PDMS coatings with gradient distributions in the MWIR and LWIR bands. To accurately estimate the emissivity of such gradient coatings with the scattering metallic particles, meticulous modeling of the particle volume fraction distribution is essential.
... The main absorption peaks located at 3450 cm −1 and 1109 cm −1 belonged to the vibrations of Si-OH and Si-O-Si correspondingly, indicating most siloxanes had been hydrolyzed and polycondensation. The peak at 2969 cm −1 , 1260 cm −1 and 849 cm −1 belonged to the stretching vibrations of Si-O-C 2 H 5 [16], suggesting insufficient hydrolysis of siloxane monomer. Specifically, the peak at 2969 cm −1 was related to the C-H stretching vibration of residual CH 3 from non-hydrolyzed Si-O-C 2 H 5 groups, and the small peaks near and below 2969 cm −1 were assigned to asymmetric and symmetric C-H vibrations of CH 2 . ...
... The main absorption peaks located at belonged to the vibrations of Si-OH and Si-O-Si correspondingly anes had been hydrolyzed and polycondensation. The peak at 2 849 cm −1 belonged to the stretching vibrations of Si-O-C2H5 [16], hydrolysis of siloxane monomer. Specifically, the peak at 2969 cm H stretching vibration of residual CH3 from non-hydrolyzed Si-O small peaks near and below 2969 cm −1 were assigned to asymme vibrations of CH2. ...
In this paper, nano SiO2 particles modified organic silane coatings were successfully prepared to aim at the application of the self-cleaning coating on PMMA substrate for deep-sea optical windows. The chemicals, surface microstructure, wettability, hardness, adhesion, transparency, water scouring resistance as well as microorganism attachment rate of the coatings were investigated. The results showed that adding SiO2 nanoparticles into the organic silicon coating can effectively improve the hydrophobicity due to generating a micro-nano structure surface. However, excessive addition would result in a decrease in hydrophobicity, adhesion, as well as transparency, due to the inorganic SiO2 particle destroying the integrity of the organic coating. The optimal coating was obtained by adding 0.5 wt% nano SiO2 particles, which possessed a water contact angle of 114.2°, hardness of 4H, adhesion level of 0, and visible light transmittance of 0.886. After 40-h water scouring, the water contact angle decreased to 108.3° and the visible light transmittance decreased to 0.839, suggesting good water scouring resistance. The microorganism attachment rate of the S05 coating was 0.17% after a 6 h immersion test, which was about half that of the PMMA substrate.
... The reflection peaks around 410 nm and 550 nm are characteristic peaks The emissivity gradually decreases with IRS layer thickness increases and tends to a stable value of 0.525 when the thickness is beyond 40 μm. The emissivity ( ε em ) of coatings can be defined as the following [30]: ...
Here, we proposed a strategy of reducing the areal density and thickness of compatible stealth coatings by introducing silicone resin-based infrared stealth (IRS) coatings as the absorption peak modulation layer of a dual-layer absorber. The joint infrared-visual camouflage performance was achieved by employing Al powder and modified Cr2O3 (M-Cr2O3) hybrid filler in IRS coating. When the mass ratio of the above two pigments is 2:1, the coating exhibits a low emissivity value of 0.525 with green grass color. The radar wave-transmitting property and dielectric property of the infrared coating can be regulated by the mass ratio of Al powder to M-Cr2O3. By coating the Al/M-Cr2O3-filled layer on FeSiAl-based microwave absorption (MA) layer, enhanced MA performance was achieved due to the synergistic effect between the two layers. Outstandingly, introducing the Al/M-Cr2O3-filled IRS coating suppressed the thermal radiation of the double-layered structure by 41% and reduced the total thickness and areal density by 16% and 18.6%, respectively. The properties promote the service reliability and practicability of compatible stealth coatings on equipment.
Graphical abstract
... However, these preparation conditions were very stringent and high-cost. On the contrary, low-emissivity organic coatings have advantages such as simple operation, low-cost, and easy maintenance at room temperature [17,18]. The adhesion strength between organic coatings and CF/resin composites at room temperature could be improved using the activation treatment method for the CF surface, and research by Li et al. reported an improvement to 8.37 MPa [19]. ...
In this study, the adhesion strength between a low-emissivity Al/polysiloxane coating and the polyimide/carbon fiber substrate at high-temperatures was successfully enhanced. The surface microstructure, adhesion, thermal properties, and optical performance of the samples were measured by scanning electron microscopy, tensile testing, simultaneous thermal analysis, infrared spectroscopy, and infrared thermal imaging. The coating structural analysis results showed that the emissivity of the top of the coating was lower than that of the bottom owing to the high enrichment ratio of Al powder with good infrared reflectance on the top. The thermal stability of the polyimide/carbon fiber substrate was studied to explore the effects of high temperature on the substrate surface structure and composition. Moreover, the failure mechanism of the adhesion strength between the coatings and substrate was explained, and the adhesion strength after being heated at 500 °C for 30 min was successfully enhanced using a resin intermediate layer and thermal pre-treatment step. Substrate pre-treatment at 500 °C for 6 min increased the adhesion strength by 3.5 ± 0.4 MPa because of the polysiloxane resin intermediate layer. The adhesion strength increased from 0.5 ± 0.4 to 5.0 ± 0.4 MPa when the pre-treatment time of polyimide/carbon fiber increased from 0 to 6 min. The potential applications of carbon fiber on the infrared stealth and energy saving fields at high temperatures might be improved by adding high-temperature resistant low-emissivity organic coatings to reduce infrared absorption and radiation.
... A superhydrophobic coating can prevent the accumulation of dust, rust, and fungi due to its ability to repel water or the "lotus effect". High-solar-energy-reflective pigments can also reduce thermal shock caused by a change in temperature 6 and passively lower the indoor temperature when painted on a rooftop. 7 However, pigments with these properties are relatively scarce, and the available commercial pigments with high NIR reflectance are usually bland. ...
This research studies the physical, superhydrophobic, and optical properties of functionalized silica-coated copper phthalocyanine (CuPc) pigments. The silica coating was confirmed by the size increase and the atomic ratio of silicon and copper of the coated pigments. Under optimal conditions, the green and blue shades of the pigments were enhanced as indicated by the increase in solar reflectance at 450-540 nm for the CuPc green and 380-520 nm for the CuPc blue. The total near-infrared (NIR) reflectance of the CuPc green and blue also increases by 10.6 and 11.5% compared to the uncoated pigments, respectively. The functionalized silica layer also adds a superhydrophobic property to the pigments. The contact angles of the functionalized pigments with water and oil are 154.4 and 54.3° for the CuPc green pigment and 142.9 and 78.1° for the CuPc blue pigment, respectively. The improved optical and hydrophobic properties make the pigment suitable for outdoor applications as an advanced protection layer to slow down material degradations from heat and humidity.
... Our results are consistent with the reported for epoxy filled with CIP, in which the emissivity decreases monotonically from 0.87 to 0.76 for concentrations between 0 and 50% [49]. Using low emissivity fillers like Al or Cu, is possible to obtain large reductions in emissivity (more than 0.5) of composites as a function of concentration [50][51][52]. However, increases in concentration are not the only factor that influences changes in emissivity. ...
Composites made up of microparticles embedded in a polymeric matrix have attracted increasing attention due to the possibility of tailoring their physical properties by adding the adequate quantity of fillers. As the concentration of these fillers increases, their connectivity changes drastically at a given threshold and therefore the electrical, thermal and optical properties of these composites are expected to exhibit a percolation effect. In this work, the thermal and electrical conductivities along with the emissivity of composites composed of carbonyl-iron microparticles randomly distributed in a polyester resin matrix are measured, for volume fractions ranging from 0 to 0.55. It is shown that both the thermal and electrical conductivities increase with the particles’ concentration, such that their percolation threshold appears at volume fractions of 0.46 and 0.38, respectively. The emissivity, on the other hand, decreases as the fillers’ concentration increases, such that it exhibits a substantial decay at a volume fraction of 0.41. The percolation threshold of the emissivity is thus higher than that of the thermal conductivity, but lower than the electrical conductivity one. This dispersion on the percolation concentration is justified by the different physical mechanisms required to activate the electrical, thermal, and optical responses of the considered composites. The obtained results thus show that the percolation phenomenon can efficiently be used to enhance or reduce the physical properties of particulate composites.
... Research suggested that the paint coat possessed the lowest infrared emissivity and gloss performances at an 80 • C curing temperature. Hu et al. [15] made low infrared emissivity paint coats owning excellent heat resistance, choosing epoxy-siloxane and Al as the binder together with pigment. Detailed conclusions indicated that the cured composite paint coats still possess low emissivity, profitable heat ageing and anti-thermal shock after the stability test. ...
An Al powder filler, nano silica slurry and KH560 were mixed with a prepared waterborne UV-curable coating, and the coating was optimized by an orthogonal experiment. Influences of the Al powder concentration on the gloss, infrared emissivity, brightness, mechanical properties, corrosion resistance and other related properties of the coating were further discussed. The results show that the influence of the Al powder concentration on the gloss was more significant, followed by the UV curing time and nano silica slurry concentration. After studying the key role of the concentration of the Al powder, we found that as the concentration of the Al powder is augmented from 10.0% to 25.0%, the gloss lessened from 19.1% to 8.5%. As the concentration of the Al powder was augmented from 10.0% to 40.0%, the infrared emissivity lessened from 0.649 to 0.083 and the brightness L’ value of the coating was step-by-step augmented and inclined to be stable; in addition, the coating’s mechanical properties reached an excellent level. The coating containing 25.0% Al powder had the best corrosion resistance, surface morphology and comprehensive properties, which can potentially be used for infrared stealth technology.
... [18,19] The properties of the epoxy-based composites can be fine-tuned by choosing appropriate fillers and hardener. [20,21] Filler-reinforced epoxy resin adhesives are widely used in metal joints. The performance of these joints is significant for industrial products like automotive adhesives, aerospace and coatings. ...
Epoxy-based systems serve as excellent adhesives to join a wide range of substrates such as metal, ceramics, plastics, etc. The mechanical properties of such systems can be improved considerably by the addition of filler to the epoxy matrix. Herein, polymethylsilsesquioxane (PMS) and poly(methyl/vinyl)silsesquioxane (PMVS) nanosphere were synthesised by hydrolytic condensation of oraganosilane as a precursor in aqueous phase. The epoxy nanocomposite adhesives were prepared by adding different weight percentages (1–4 wt%) of the PS nanospheres. Tensile and compressive strength of the adhesive formulations were studied using the universal testing machine (UTM) and it was observed that the mechanical properties of the composites showed an increasing trend on increasing the filler loading. Adhesive strength of the epoxy composites on mild steel substrate was studied by conducting the lap shear test and EPV-4 exhibited a 31% increase in adhesive strength on the mild steel compared to the neat epoxy. Surface morphology of the epoxy composites were visualised from the SEM images and the composites also showed enhanced thermal conductivity. Higher mechanical and adhesive strength indicates the potential of the prepared nanocomposites to be used as an effective formulation in adhesive-based systems.
... Actually, the coatings based on metal powders as conductive fillers and polymers as binders can exhibit low infrared emissivity and excellent engineering behavior simultaneously at room temperature [6]. However, the metal powders could be oxidized rapidly and the conductivity usually decreases with increasing temperature, which will lead to the infrared emissivity increasing sharply [10][11][12][13]. In addition, the mechanical properties of the organic binders would also be damaged seriously at high-temperature [14]. ...
The CeO2 filler modified by different content (0, 1, 5 and 10 wt%) of polyethylene glycol (PEG) 400 and the inorganic silicate binder were introduced for preparation of coatings with excellent thermal shock resistance performance and low infrared emissivity at high-temperature. The influences of PEG 400 content on phase structure and morphology of CeO2 powders, and hence on thermal shock resistance behavior and high-temperature infrared emissivity of the corresponding coatings were investigated deeply in this work. The results show that the crystal structure of CeO2 remains unchanged after modification of PEG 400. The dispersity of CeO2 particles is improved with content of modifier PEG 400 increasing from 0 wt% to 5 wt% while it gets worse with PEG 400 content further rising to 10 wt%. Thermal shock resistance of the corresponding coatings enhances from 4 cycles to 31 cycles by increasing PEG 400 content from 0 wt% to 5 wt% while diminishes significantly to 1 cycle with PEG 400 content of 10 wt%. Simultaneously, the minimum emissivity of 0.348 is achieved at 600 °C in the coating with 5 wt% of PEG 400. The results suggest that the coating with CeO2 modified by 5 wt% of PEG 400 is a promising candidate for high-temperature infrared stealth due to both excellent thermal shock resistance and low infrared emissivity at high temperature.
... Based on the Stephen-Boltzmann's law, coating low infrared emissivity materials on the hot components is an effective and convenient way to reduce the infrared radiation [7] . In recent years, extensive work has been done to develop low infrared emissivity materials, such as nanosized silver colloids [8] , dielectric/metal multi-coatings [9] and epoxy-siloxane/Al composite coatings material [10] . The materials can exhibit low infrared emissivity values at room temperature, while the properties at high temperature of 400°C~600°C are still not satisfactory.Apparently, materials with low infrared emissivity at high temperature are urgently needed for infrared stealth of the hot components of strategic aircrafts. ...
The ceria powders co-doped with Ca²⁺ and Y³⁺ ions Ce0.8Y0.2−xCaxO2−δ were prepared by oxalate co-precipitation method. The crystal structure, morphology, conductivity and infrared emissivity of the pure and doped ceria were analyzed in detail. From the perspective of microstructure and conductivity, the reasons for the reduced infrared emissivity in ceria by co-doping Ca²⁺ and Y³⁺ ions are revealed. The results show that singe-phased ceria with cubic fluorite structure is obtained in all the samples with Y³⁺ or/and Ca²⁺ ions doping. The lattice parameter ‘a’ of ceria phase increases gradually with Ca²⁺ ions content increasing from x = 0 to x = 0.2 in the Ce0.8Y0.2−xCaxO2−δ. The grains become smaller and distributed more homogeneously after doping Y³⁺ or/and Ca²⁺ ions. The conductivity increases with temperature rising and Y³⁺ or/and Ca²⁺ ions doping, in which Ce0.8Y0.2−xCaxO2−δ with x = 0.05 possesses the highest conductivity among all the samples. Contributed by decreased grain aggregation and enhanced conductivity, lowest infrared emissivity value of 0.241 at 600 °C is achieved in the Ce0.8Y0.15Ca0.05O2−δ, which reduces nearly 33% compared to the un-doped ceria. It indicates that Y³⁺ and Ca²⁺ ions co-dopant has a decisive effect on reducing infrared emissivity of ceria at high-temperature, which provides an effective and convenient method to develop infrared stealth materials for high-temperature use.
... It has been reported that epoxy-modified silicone and flake aluminum powder can produce heat-resistant low emissivity coatings with an infrared emissivity of 0.22 after being heated to 500 • C for 50 h [8]. Guo [9] synthesized low infrared emissivity coatings using flake aluminum powder and pure silicone resin. ...
High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (ΔL) of the coatings were characterized by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA), respectively. The results show that thermal decomposition of the resin and mismatch of ΔL between the coating and the substrate facilitate the high temperature failure of the coating. A suitable amount of flake aluminum pigments could restrain the thermal decomposition of the resin and could increase the match degree of ΔL between the coating and substrate, leading to an enhanced thermal resistance of the coating. Our results find that a coating with a pigment to binder ratio (P/B ratio) of 1.0 could maintain integrity until 600 °C, and the infrared emissivity was as low as 0.27. Hence, a coating with high-temperature resistance and low emissivity was obtained. Such coatings can be used for infrared stealth technology or energy savings in high-temperature equipment.
... Finally, FTIR spectrographs for epoxy incorporating 0.0 wt.% (control), 0.5 wt.%, 2.0 wt.%, and 3.0 wt.% ANPs are presented in Fig. 9. Based on the FTIR results, the characteristic peaks of the synthesized siloxane-epoxy-ANP samples appeared at 3,150-3,550 cm −1 (ν O−H ); 2,780-2,980 cm −1 (ν sym and ν asym of C-H); 1,465 cm −1 (δ C-H , CH 2 and CH 3 ); 1,035-1,110 cm −1 (ν Si-O-Si and ν C-O-C ); 1,250 cm −1 (δ C-H in Si-CH 3 ); 560 cm −1 (δ Si-O-Si ); and epoxide ring at 830 cm −1 (Kwon et al. 2011;Wang et al. 2011;Byczyński et al. 2015). A peak appears near 1,610 cm −1 due to Si-C 6 H 5 vibrations (Hu et al. 2010). Comparing the O-H stretching bands of all epoxy-ANP nanocomposite spectra with that in the neat specimen, O-H bands of epoxy-ANP nanocomposites show lower absorption height with broader bands than those of the neat epoxy sample. ...
This study investigates the effect of alumina nanoparticles (ANPs) on tension and fracture characteristics of polymer concrete (PC). ANPs with a maximum particle size of 50 nm were used at 0.5, 1.0, 2.0, and 3.0 wt.% of epoxy resin. Tensile strength, tensile failure strain, and fracture toughness (KIC, GIC, and JIC) were determined experimentally. A PC with superior ductility showing a tensile failure strain of 4.89% (compared with 2.56% for neat PC) was observed at ANP content of 3.0 wt.%. Using ANPs in producing epoxy PC can significantly improve ductility (+60.6%) and fracture toughness (+131.8%) compared with neat PC. Scanning electron microscope (SEM), dynamic mechanical analyzer (DMA), and Fourier transform infrared (FTIR) observations were conducted to understand the role ANPs play to manifest the observed improvements in tension and fracture characteristics of PC.
... [17][18][19]. A peak appears near 1605 cm −1 due to Si-C6H5 vibrations [20]. The remaining epoxy groups (oxirane ring) appeared at 940 cm −1 . ...
... Furthermore, the results were identical with those of the emissivity tests. The results also coincide well with most researches (Hu et al. 2010) that the infrared emissivity of EPDM-based composite coatings is significantly dependent upon the properties of the pigment particles and the contact or porosity between particles. The infrared radiation is absolutely absorbed due to the presence of pores in the coating, and only a little radiation is reflected by the metallic particles, which are highly reflective. ...
Low-infrared-emissivity coatings were prepared using metallic particles (including Cu, Al, Ni, Ag, etc.) and an ethylene-propylene-diene monomer (EPDM) binder. The effects of size, shape, morphology, and content of metallic particles on infrared emissivity of the coatings were systematically investigated. The principles of the low-infrared-emissivity and low-solar-reflectance coatings are discussed in terms of reflection, emissions, and chemical structure. The thermal insulation performance of composite coatings is studied via a simulation model. Mechanical properties of composite coatings are studied by using circle-cut test and impact strength test. The composite coatings are also tested for corrosion behavior with potentiodynamic polarization. The results indicate that when the Cu particles and Al particles are flaky and high-leafing, they have the minimum coating emissivity, exhibiting infrared emissivity values of 0.33–0.40 and solar reflectance values of 0.38–0.53. The formation of low-infrared-emissivity coatings depends highly on the size and shape of the metallic particles. A simulation model is proposed to account for thermal insulation properties of the coatings, which indicates that an EPDM/ Cu-powder coating achieves good thermal insulation performance, with a 4°C relative temperature drop. The low-infrared-emissivity composite coatings also show excellent corrosion resistance and mechanical performance.
MXenes have attracted growing interest in electrochemical energy storage owing to their high electronic conductivity and editable surface chemistry. Besides, rendering MXenes with spectrum defense properties further broadens their versatile applications. However, the development of MXenes suffers from weak van der Waal interaction‐driven self‐restacking that leads to random alignment and inferior interface microenvironments. Herein, a nacre‐inspired MXene film is tailored by dual‐filling of 2‐ureido‐4[1H]‐pyrimidinone (UPy)‐modified polyvinyl alcohol (PVA‐UPy) and carbon nanotubes (CNTs). The dual‐nanofillers engineering endows the nanocomposite film with a highly ordered structure (a Herman's order value of 0.838), a high mechanical strength (139.5 MPa), and continuous conductive pathways of both the ab plane and c‐axis. As a proof‐of‐concept, the tailored nanocomposite film achieves a considerable capacitance of 508.2 F cm⁻³ and long‐term cycling stability without performance degradation for 10 000 cycles. It is efficient for spectra defense in radar and infrared bands, displaying a high electromagnetic shielding capacity (19186 dB cm² g⁻¹) and a super‐low infrared (IR) emissivity (0.16), with negligible performance decay after saving in the air for 1 year, responsible for the applications in specific and complex conditions. This interfacial dual‐filler engineering concept showcases effective nanotechnology toward sustainable energy applications with a long lifetime and safety.
In modern war of “find and destroy,” hiding the target is one of the essential means to improve battlefield survivability of personnel, weapons, and equipment. Infrared stealth technology started to emerge when hiding in the visible light band could no longer meet the protection requirements. With the rapid development of infrared detection technology, infrared stealth materials are gradually diversified. At present, infrared stealth technology no longer focuses only on low infrared emissivity, but from multiple perspectives to achieve target stealth, such as the tunability of optical properties, good thermal management, and multi‐spectral compatibility stealth. At the same time, the infrared stealth of the target is gradually shifted from passive to active, emphasizing dynamic integration of the target and the environment. This review summarizes research progress, development, and application of infrared stealth materials. Camouflage dye and infrared stealth coating are classified as traditional technologies, however new developments and novel processes from literature can be constantly retrieved over the years. In addition to dyeing/coating technologies, this review also highlights advanced infrared stealth materials such as thermal insulation materials, phase change materials, electrochromic materials, metamaterials, and bionic materials. Outlines of the advanced technologies are mainly focused on those published in recent years. Challenges and prospects for the future development of infrared stealth materials are presented at the end of the review.
Strong electromagnetic shielding coatings for aviation components are becoming more and more important as aerospace technology develops. In order to better understand the microstructural evolution, surface morphology, and thermal behaviour of ZrB 2 , Al 2 O 3 /ZrB 2 , Ag-ZrB 2 composites, Cu/Al-doped films, TiO 2 /Si/Ag(Cr)/TiN x films, and ZnO/Ag/ZnO structures, this work presents the creation and use of advanced coatings. Applying X-ray diffraction, X-ray photoelectron spectroscopy, and microstructural characterization, among other experimental investigations, the coatings’ performance is assessed in a virtual aircraft environment. This work contributes to a better knowledge of the elements impacting electromagnetic shielding durability and efficiency, which opens the door to the development of next-generation coatings that meet and even surpass the strict specifications needed for aerospace applications. The enhancement of this technology highlights the importance it is to maintain the dependability and safety of aircraft systems, which eventually helps both crew and passengers.
With the rapid development of infrared detection and tracking technology, the combat concealment and viability of various military targets are seriously threatened, and the demand for military infrared camouflage is increasingly urgent. Individual combatants, as small moving targets, have the characteristics of small size, strong mobility, complex and changeable background, etc. Their infrared camouflage is more flexible and accurate than the equipment and engineering camouflage. The infrared camouflage textile material is soft and portable, which is the main embodiment of the infrared camouflage technology for individual soldiers. It can be used for infrared camouflage clothing, military tents, sleeping bags, and other equipment. Its research and development have been highly valued by many countries. In this article, details of the working principle, preparation methods, and recent research progress of flexible infrared camouflage textile materials are summarized. First of all, from the military application of infrared technology and the principle of infrared camouflage, the development status of infrared camouflage textile materials is summarized, and the research results of near-infrared and thermal infrared camouflage textile materials are introduced. Secondly, the camouflage conditions and research directions of new multi-band recombination and adaptive infrared camouflage textile materials are discussed. Finally, the challenges and opportunities of the future development of infrared camouflage textile materials, especially adaptive infrared camouflage textile materials, are considered.
Perpetual advancements in modern detection techniques have augmented the requirement of infrared camouflage; however, its development is impeded by multiband compatible regulation and curved application targets. Here, a flexible wavelength-selective metasurface based on two metal-dielectric-metal resonators is experimentally demonstrated for infrared radiation regulation with thermal management utilizing magnetic polariton. Low emissivity in atmosphere windows (infrared stealth) and high emissivity in the wavelength of 5-8 μm nonatmospheric window (radiative cooling) are simultaneously achieved. In comparison with conventional hard substrates, it is for the first time the composite wavelength-length metasurface is successfully prepared directly on a flexible polyimide film via applying polyimide double-sided tapes and S1805/LOR5A bilayer stack lift-off technology. Not only does this method successfully overcome the debonding problem of photoresist on the flexible substrate, but it also solves the bulging problem of the substrate as well as the limitation of high temperature. Besides, the temperature and infrared radiation distributions of flexible wavelength-selective metasurfaces with different curvatures are first investigated. The compared results reveal that the metasurface with larger curvature has a better infrared camouflage performance. Furthermore, the cycle stability of the flexible metasurface is tested, and the results show that the infrared radiation regulation is stable after 30 cycles with essentially no change. This study provides a guideline for preparing flexible composite metasurfaces and avoids the trouble of replacing the metal/dielectric material of the initial structure with a flexible material to improve the structure for application to curved surfaces, thus broadening implications in enhancing the effective bonding of metasurfaces to target surfaces.
In order to meet the demand for infrared stealth materials in the military field, conjugated polymers containing Schiff base moieties were designed and prepared. Various dialdehyde monomers were introduced and their effect on the comprehensive properties were systematically characterized. The resulted polymers could be cast in solution to prepare polymer coatings. The coatings exhibited high thermal stability up to 400 °C at 5% weight loss, and excellent mechanical performance with high Young’s modulus and hardness. The infrared emissivity values varied from 0.587 to 0.627 at wavelength of 8–14 µm and ranged from 0.595 to 0.609 at wavelength of 2–22 µm. Specifically, it was found that the ATTPAL structure with carbazole moieties had a lower band gap and better electrical conductivity by photoelectric test and DFT theoretical analysis. Meanwhile, the infrared emissivity value of ATTPAL coating was the lowest compared with p-phenyl and pyridyl containing analogues, suggesting it was potential material for the future development of infrared stealth technology. The combined results showed that reducing the band gap and improving the electrical conductivity of the structure were both beneficial to the reduction of infrared emissivity. It would positively provide new ideas for the design of infrared stealth materials.
Low emissivity coatings were synthesized by using fine flake Aluminium (Al) powder as a filler within acrylic resin to from the desired composite coatings. In the current work, ball milling was applied to prepare Al with different shapes and sizes. The technical parameters of prepared Al powders with respect to the initial raw Al are characterized by scanning electron microscope (SEM), X-Ray diffraction (XRD), and Energy Dispersive X-Ray Analysis (EDX). Moreover, parameters that affect the emissivity of the coating was investigated; such as coating thickness, particle size, spin coating, ball milling time and the content of coated Al powder. The thermal signature is highly affected by the variation in Al content (5%, 20%, 25%, 35%, 40% and 60%) at different temperatures (50°C, 70°C, 90°C). The results indicate that the perfect percentage for the filler (Al) in the matrix within the range (35 wt. - 40 wt. %) and Al fine flake powder particle, which gives the lowest infrared emissivity of 0.385 μm and 0.412 μm for (3-5) μm, (8-12) μm, respectively.
Materials with significant infrared (IR) stealth effect have been of great importance for camouflage of military targets and thermal management of special environments. In this paper, we design a dual-working module IR stealth fabric with electroless silver plated fabric component and heat-absorbing component derived from a phase change material (PCM) coating. The aim of electroless silver plating is to reduce the IR emissivity to 0.692 (1-22 µm), 0.687 (8-14 µm) and 0.655 (3-5 µm), and the PCM coating provides a phase change latent heat of 128.5 J/g to further lower temperature. Temperature measurements show that the PCM coating can create a maximum actual temperature difference of 21.6°C with untreated fabric on a 65°C hot plate and maintain the surface actual temperature below 38℃ for 300 s. IR camera images show that the as-prepared IR stealth fabric can significantly shield or interfere with the IR heat signature of the target compared to the untreated fabric. In addition, related performance tests show that it can meet the fastness requirements for practical use. Benefiting from the modulation of the dual working modules and the good fastness, this IR stealth fabric has great potential for practical applications.
Composite coating materials or structures with low infrared emissivity and high radar transmittance are in urgent need in practical applications, among which binder is one of the important factors affecting the mechanical properties, infrared and dielectric properties of coatings. Acrylic acid (AA) and maleic anhydride (MAH) were used as graft monomers to modify ethylene propylene diene monomer (EPDM) binder. Composite coating with low infrared emissivity and low dielectric properties was prepared by using modified EPDM as binder, floating aluminum (Al) powder and antistatic carbonaceous fiber (CF) as filler. The effects of the type and amount of modified monomer on the mechanical properties, infrared emissivity and dielectric properties of the binder and the composite coating were systematically studied. The results show that the tensile strength (σb) and elongation at break (e) of the composite coating can be increased by 32% and 18%, respectively, by appropriate grafting modification of the binder. The infrared emissivity and the dielectric properties of the composite coating has a slight change with the increase of graft monomer content. Grafting modification of the binder improves the compatibility, wettability and interfacial bonding between filler and binder, which remarkably enhanced the mechanical and comprehensive properties of the composite coating. The effect mechanism of grafting modification of AA and MAH is disclosed from the aspects of polarity, branching and crosslinking. This work increases the selection range of binders needed to prepare low infrared emissivity materials.
This study focuses on the possibility of using siloxane resins with epoxy modification to delay corrosion of metal substrates for hydraulic applications. Formulations aimed at metal protection were designed, without including anticorrosive additives, and deposited on 11SMnPb37 steel. Thin monolayer films were obtained by dip coating in different process conditions, avoiding primers. The developed procedure was simple and able to provide solid and well-anchored coatings. They were characterized in terms of morphology, scratch and wear endurance, and resistance to a corrosive environment. The optimum formulation and deposition parameters were found. The selected coating showed remarkable adhesion to the substrate, good mechanical properties, and resistance in a saline environment, proving to be suitable as a protective barrier against corrosion. The protective effect was ensured not by additives but through the excellent adhesion of the coating and its endurance to scratch and wear.
The goal of this research was to obtain a coating with low-infrared emissivity and both good hydrophobic and mechanical properties. Using nano-SiO2 as the micro-nano structural modifier, a hydrogen-containing silicone oil (HCSO)-modified polyurethane (PU)/Al composite coating with super-hydrophobicity and low-infrared emissivity was prepared via a simple glass rod scraping method. Effects of the ratio of HCSO to PU, the total filler addition, and the ratio of Al powder and nano-SiO2 on the coating properties are systematically discussed. The results show that as the ratio of HCSO to PU increases, the surface energy of the coating decreases, and this significantly increases the hydrophobicity of the coating. When the ratio is 2:8, the coating has outstanding hydrophobic properties, the adhesion strength of the coating reaches grade 1, and the water contact angle (WCA) reaches 152°. The total filler addition has a significant impact on the coating performance. With an increase in the filler addition, the emissivity of the coating increases, and the glossiness decreases. When the total filler addition is 50 wt%, the coating surface forms an obvious papillary micro-nano rough structure, so that the coating has outstanding hydrophobic properties. The ratio of Al powder to nano-SiO2 obviously affects the emissivity and hydrophobic properties of the coating. When the ratio is 5.5:4.5, the coating has good overall performance. At this point, the emissivity of the coating is as low as 0.675; the glossiness and adhesion strength are 2.7 and grade 1, respectively; the WCA and sliding angle are 155° and 8°, respectively; and it has outstanding self-cleaning performance. Through the research in this paper, a low-infrared emissivity coating with outstanding super-hydrophobic properties and adhesion strength has been obtained and has important application value in the design and transformation of infrared stealth of various equipment.
TiN films were oxidized at different temperatures (300, 400, 500, and 600 °C) for different times (1, 10, 50, and100 h), and the effect of oxidation behavior on optical performance and infrared emissivity of TiN films was investigated. The results showed that TiN films were oxidized to the solid solution of TiON with the same crystal structure as TiN at 400 °C for 1 h. The films exhibited low reflectance and transmittance and the infrared emissivity changed little. With the extension of oxidation time, TiON gradually transformed into Ti2O3 and TiO2 and the infrared emissivity of the films went up. As the oxidation temperature rose above 500 °C, TiN films were oxidized quickly and the infrared emissivity increased to 0.8.
In this work, flaky aluminum was coated with bismuth oxide to obtain low reflection in near-infrared range and low emission in long-wave infrared stealth material. The composites were prepared through coprecipitation method, characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measured by ultraviolet spectrophotometer and dual band infrared emissometer. The morphology and microstructure show that the flaky aluminum was coated by bismuth oxide nanoparticles. The optimal reaction temperature was 50 °C, and the optimized amount of Al was 20 wt%. Meanwhile, the infrared emissivity in 8–14 μm infrared waveband range was 0.462 and the reflectivity was 39.1% at wavelength of 1.064 μm. In addition, it could also achieve good thermal insulation in a thinner thickness. When the temperature of heating platform reached 100 °C, the temperature of the disk with 0.30 mm thickness was 26.9 °C which was only 2.7 °C higher than that of the disk with 0.94 mm thickness. It may shed light on a new material design orientation to obtain high performance infrared and laser compatible stealth materials.
The earliest microwave absorbing materials (MAMs) are fabricated in the early 20th century for military purpose to inhibit radar detection. Currently, the application of MAMs has been existing in every part of human's life to prevent radiation and interference. The microwave absorbant and microwave absorbing coatings classified by composition including alloys, metal oxides, conductive polymers, carbon materials, ceramic materials both in traditional and innovative forms are introduced in this work. Considering the harsh and complex application environment, MAMs with high temperature resistance and infrared-compatible stealth performance are involved. Metamaterials, showing excellent electromagnetic properties which are far beyond that of the materials can achieve, including perfect absorber, digitally coded control metamaterials, bionic structural materials, and adjustable smart metamaterials, are also introduced specifically in this work. In addition, to investigate electromagnetic response of absorbant, the first-principles calculations works are overviewed. The electromagnetic properties, loss mechanisms, structure, fabrication method, regulation approaches, designing principles, current applications, and future prospects of MAMs are involved in this work. This work gives a comprehensively overview over the MAMs for their theoretical and experimental advances in recent years including the military radar (frequency range of 2–18 GHz) stealth materials, relevant infrared compatible (infrared-visible, infrared-radar, infrared-laser) stealth materials, and other stealth materials with multifrequency adaptability.
Infrared thermal radiation suppression techniques are vital to the survival of various vehicles/targets, and low-emissivity materials are conventionally employed to reduce infrared radiant power of targets. However, infrared radiant power depends not only on infrared emittance but also heavily on the temperature according to Steven-Boltzmann law (P=εσT⁴). In this work, it is for the first time, a novel type of infrared stealth material based on tailoring radiative properties in an ultra-broadband ranging from 0.4 µm to 14 µm is proposed. A low emittance in atmosphere window (3–5 µm, 8–14 µm) is achieved to suppress infrared radiation, and a high emittance from 5 to 8 µm is obtained to reduce temperature via radiative cooling from metamaterial surface to the atmosphere. Meanwhile, low absorptance in the solar spectra (0.4–2.5 µm) can help to resist the solar heat. As a result, the infrared radiant power in the atmospheric window is prominently reduced benefiting from low emittance and decreased temperature. This work helps guide the design of more effective infrared stealth materials and paves the way for the applications of metamaterials in infrared stealth applications.
Thermal expansion performance of Aluminum/polysiloxane/glass coatings with low infrared emissivity was improved by adding zinc powder. The influences of zinc powder on phase structure, composition, surface microstructure, thermal expansion, adhesion and infrared radiation of Aluminum/polysiloxane/glass coating was systematically studied. The thermal mechanical analysis indicated that thermal expansion coefficient can be adjusted by adding zinc powder in the coating. The tensile strength test results show that the matching of the thermal expansion could improve the adhesion strength of the coatings. As a result, compared with the coating without zinc powder, the adhesion strength was enhanced by 2.0 ± 0.4 MPa when the heat treatment temperature at 450 and 500 °C, and increased by 3.0 ± 0.4 MPa at 550 °C. Simultaneously, average infrared emissivity value of the coating with good thermal stability was about 0.20 in the 3–5 μm wavebands, and approximately 0.34 within 8–14 μm after heated at 550 ℃. These results indicated that the good thermal expansion performance and low infrared emissivity coatings were obtained by adding zinc powder.
Zirconium diboride exhibits high thermal conductivities and high melting point, which are beneficial for use in extreme environments. Examples including cutting tools, high-temperature electrodes and leading edges of hypersonic space vehicles. However, there is limited literature on the infrared properties of ZrB2 thin films. In this study, we report the results of infrared emissivity of sputter-deposited films and post-annealed films. X-ray diffraction shows promoted crystalline quality and grains growth for ZrB2 films with the increasing annealing temperature and time. The thin film exhibits high thermal stability and a low infrared emissivity of 0.01(8∼14 μm) after annealed at 1000℃ for 10 h. Besides, with an increase in annealing temperature and annealing time, film densification and grains growth were observed, leading to decrease of electrical resistivity and infrared emissivity.
In this study, low infrared emissivity coatings with good thermal stabilities were fabricated using silicone resin as adhesive, flake aluminum powder as pigment, and low-melting glass powder as functional filler. The effects of the low-melting glass powder on the adhesions, thermal expansions, and infrared emissivity of the coatings were systematically investigated. In addition, the surface microstructures and thermal stability mechanisms of the coatings were analyzed in detail. Mechanical tests showed that the addition of the low-melting glass powder to the Al/polysiloxane coating enhanced its adhesion after a high-temperature treatment due to the mechanical interlocking of the particles by the secondary film-forming low-melting glass. Thermal analysis indicated that the oxidation resistance of the coating could be improved by the film-forming low-melting glass powder. The low-emissivity coating with a low-melting glass powder content of approximately 15 wt.% and Al/polysiloxane ratio of 1.5 exhibited good thermal stability. The adhesion of the coating increased to 9.0 ± 0.4 MPa after heating at 500 °C. When the content of the low-melting glass was increased from 0 to 15 wt.%, the oxidation exothermic peak of the coating shifted from 590 to 625 °C at a pigment/binder ratio of 1.5. The infrared emissivity of the coating was 0.25 after heating at 600 °C.
Ge/TiO2 one-dimensional photonic crystals (1DPC), with low infrared-emissivity in the 8−14 μm band, were successfully designed and prepared by alternating the Ge and TiO2 layers on the quartz substrate using optical coating technology. The microstructure and spectral emissivity of the as-prepared 1DPC were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared spectrometry (FTIR), respectively. The microstructural analysis indicates that the as-prepared 1DPC has clear structural multilayer characteristics, and the thicknesses of Ge layer and TiO2 layer are very close or identical with the target values. The spectral emissivity shows the as-prepared 1DPC has low infrared emissivity in the 8−14 μm band. In fact, the average emissivity can be as low as 0.202, and meets the requirement of our design. The results of this paper show that low infrared emissivity materials can be prepared successfully using materials, which are not transparent for infrared light, via a suitable one-dimensional photonic structural design. This result increases the selection range of raw materials needed to prepare low infrared-emissivity materials.
A kind of novel ternary polyurethane (PU)/silver (Ag)/zinc oxide (ZnO) array composite coatings was fabricated by the growth of ZnO arrays onto the stainless steel substrates, the modification of Ag nanoparticles and following PU spinning. The structure, morphologies, wettability and mechanical properties of the PU/Ag/ZnO array composite coatings were measured by SEM, TEM, XRD, UV-vis, surface contact angle (CA) and nano indentation technology. The infrared emissivity values of the composites (8–14 μm) were estimated. The results showed that hexagonal wurtzite ZnO arrays and face-centered cubic Ag nanoparticles were in the composite coatings with good dispersion. The content and the density of the Ag and ZnO arrays can be varied by controlling the deposition time of the Ag and the concentration of the ZnO crystal growth solution, which remarkably had effect on the surface roughness properties of the coatings. By comparison with PU, the mechanical properties of PU/Ag/ZnO array coatings were obviously improved. The PU/Ag/ZnO coatings exhibited improved infrared emissivity property than that of pure PU and PU/ZnO due to the introduction of component Ag with high reflectivity.
Multi-layered AlCrN/Cr/AlCrN coatings were designed and deposited on Ni-based substrates by a cathodic arc ion plating system for low thermal emissivity applications. The multi-layered coatings annealed at different temperatures in air and vacuum were systematically investigated by GIXRD, EPMA, XPS, DSC, GDOES, FESEM, HR-TEM and scratch tester as well as the infrared properties evaluation. The as-deposited AlCrN layer was consisted of Cr2N nanocrystallites embedded in AlCrN amorphous matrix, inhibiting element diffusion and presenting higher infrared emissivity. The amorphous matrix began to crystallize as fcc-Cr(Al)N structure at 750 °C. The diffusion of Ni element from the substrate to the middle Cr layer was observed as well as the Cr-rich oxides were substituted by chrome‑aluminum oxides above 750 °C in air. The grain boundaries resulted from the crystallization of amorphous AlCrN layer could promote the penetration of O element from air and the diffusion of Ni element from the substrate. The AlCrN/Cr/AlCrN coatings vacuum-annealed above 750 °C performed lower infrared emissivity than the as-deposited one, while the coatings air-annealed above 750 °C showed higher infrared emissivity than vacuum-annealed ones due to the low extinction coefficient of oxides formed on the coating surface. The multi-layered AlCrN/Cr/AlCrN coating could be proposed for low infrared emissivity applications below 750 °C.
CoNi magnetic nanoparticles (NPs) and hybrid architectures have attracted tremendous attention from numerous applications. In this study, a facile approach based on one-step metal-organic chemical vapor deposition (MOCVD) was developed to fabricate CoNi/C core/shell NPs with an extremely small core size of [Formula: see text]3.7[Formula: see text]nm and an ultrathin shell thickness of 1–3[Formula: see text]nm. Only 10[Formula: see text]wt.% CoNi/C core/shell NP-filled composites with thickness of 1.6[Formula: see text]mm exhibit an optimal reflection loss value of [Formula: see text]25.7[Formula: see text]dB and an absorbing bandwidth value up to 6.2[Formula: see text]GHz. The extremely small core/shell NPs are demonstrated to have enhanced electromagnetic parameters (i.e., complex permittivity and permeability), reflection loss and broadened effective absorption bandwidth, as compared to the relatively larger NPs. The superior microwave absorbing performance should be attributed to the increased specific area with enriched interfacial polarization. The as-synthesized extremely small CoNi/C core/shell NPs are expected to be a fascinating candidate for efficient microwave absorption material with lightweight and thin thickness.
In this work, an Al powder was coated with antimony-doped tin oxide (ATO) to obtain an infrared-laser compatible stealth material. The composites are prepared via a coprecipitation method, characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measured by ultraviolet spectrophotometer and dual band infrared emissometer. The morphology and microstructure show that the flaky Al powder was coated by the ATO nanoparticles and doped into the SnO 2 rutile structure by an Sb ⁵⁺ ion . The optimal Al content was 20%, and the optimized Sn/Sb molar ratio was 10: 1. Meanwhile, the reflectivity of the composites was 43.454%, and the infrared emissivity in 8–14 μm far infrared waveband range was 0.708. It may shed light on a new material design orientation to obtain high performance laser-infrared compatible stealth materials.
CeO 2 powders with flaky morphology and high floating rate are fabricated successfully by ball-milling and stearic acid modification. The influences of ball-milling time and surfactant stearic acid content on the morphology, floating rate, infrared emissivity of CeO 2 powders as well as the CeO 2 /epoxy-silicone coatings have been investigated systematically. The results show that the CeO 2 powders transform from irregular grains with larger size to flake grains with smaller size by ball-milling for 4 h. The floating rate of CeO 2 enhances from 0 cm ² /g to 89.06 cm ² /g by increasing stearic acid content from 0 wt% to 1 wt% while diminishes to 60.477 cm ² /g with stearic acid content of 3 wt%. Ultimately, the coating with CeO 2 fillers ball-milled by 4 h and modified by 1 wt% of stearic acid exhibits the lowest emissivity value of 0.831 in the 8–14 μm waveband. The mechanisms for small and flaky fillers as well as high floating fillers to achieve low emissivity coatings are also fully revealed.
The effect of N 2 flow rate on structural, composition, deposition rate, electrical and infrared properties of the multi-layer AlCrN/Cr/AlCrN tandem coatings have been studied. The coatings were designed and prepared by a cathodic arc ion plating system at various N 2 flow rates for low emissivity applications. The results showed that the thickness of AlCrN layers decreased continuously with increasing N 2 flow rate. Structure and elemental composition of the deposited coatings strongly depended on N 2 flow rate. X-ray diffraction analysis showed that for 10–80 sccm, the coatings exhibited a single (fcc) phase, for 120–160 sccm, an amorphous phase was obtained. The phase formation has been confirmed by transmission electron microscopy diffraction patterns. As for electrical resistivity, the AlCrN layers turned from conductive, semiconductive, to dielectric behavior. In practice for low emissivity applications, the deposited multi-layer coatings exhibited emissivity values among 0.0748–0.1193, which rose with increased N 2 flow rate. Among all the phases, the coating with an amorphous AlCrN layer (160 sccm) presented an outstanding thermal stability and had an emissivity of 0.1194 even after annealing at 800 °C for 10 h in air. It was observed that the amorphous AlCrN layer effectively controlled the inward diffusion of O and the outward diffusion of Cr, Al and Ni from substrate, which rendered this multi-layer coating a potential material for low emissivity applications at high temperature.
Silicon-based polymers are outstanding materials for coating applications. These compounds have excellent properties, such as strong adhesion to most substrates, and high chemical, thermal and UV resistance. Additionally, they can be converted into ceramic materials (polymer-derived ceramics) by a heat treatment and, in some cases, by chemical reactions or radiation. Hence, ceramic coatings can be obtained after deposition of the polymers by simple lacquer techniques. The properties and composition of polymeric and ceramic coatings can be changed by tailoring the chemical structure of the precursors or by the addition of fillers. This enables the preparation of coatings with a great variety of properties for different applications. In this review paper, the main aspects of the use of silicon polymers for coatings are elucidated. The advantages and disadvantages of these materials, and the processing methods developed are discussed. Finally, a summary of the applications and the prospects for future research are presented.
PtOx
films have been prepared by reactive magnetron sputtering on glass substrates without external heating and characterized by x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The resulting PtOx
films mainly consisted of amorphous PtO and PtO2, and the composition largely depended on the O2 partial pressure during sputtering. In this study, the effects of the O2 partial pressure on the deposition rate, composition, surface morphology, structure, electrical resistivity, and infrared emissivity of the as-deposited PtOx
films were evaluated. It was found that, with increase in the O2 partial pressure, the O/Pt atomic ratio, resistivity, and infrared emissivity of the as-deposited PtOx
film increased, while the deposition rate first increased then decreased with increasing O2 partial pressure. In addition, the O2 partial pressure had little influence on the structure or surface morphology of the as-deposited PtOx
film.
PtOx films were deposited by direct current reactive magnetron sputtering in Ar/O2 mixture atmosphere. Subsequently, post-deposition heat treatments were conducted in air ambient at temperatures from 400 to 600 °C for 1 h with the heating rate of 10 °C/min. Effects of the annealing temperature on properties of PtOx films such as the structure, morphology, composition, electrical resistivity and infrared emissivity were studied. The as-deposited PtOx films mainly consisted of amorphous PtO and PtO2 compounds and decomposed to polycrystalline Pt slightly at 500 and 550 °C. As the annealing temperature increased, the films were decomposed completely at 600 °C. Due to the prompt release of oxygen at 600 °C, a great number of nano-scale pores were found on Pt films. The XPS analysis showed that the observed Pt 4f peaks would shift to lower binding energy with increasing the annealing temperature, which was consistent with the XRD analysis. The electrical resistivity and infrared emissivity of the films both increased when the annealing temperature was below 500 °C and decreased intensely at 550 and 600 °C.
In this paper, the aluminum/polymer composite coating was prepared and the infrared emitting properties and environmental stability performance of the as-prepared coating were studied. The factors, such as polymer binders, pigment/binder ratios, preparation technology and coating thickness were investigated in detail. Firstly, the study of the polymer binders indicated that modified fluorocarbon resin was the best candidate due to its low infrared emissivity and well-performed physical and chemical properties. Secondly, the optimal pigment/binder ratio was 1.25:1. Thirdly, the optimum coating thickness was 75 μm and the scrape coating method was suitable to prepare the coating. Finally, the optimized aluminum/polymer composite coating showed low infrared emissivity of 0.31. The adhesive force of the coating was first grade and the impact resistance was more than 50 kg cm. In addition, it exhibited excellent salt, acid and alkali resistance. The as-prepared aluminum/polymer composite coating can be used as infrared stealth coating in the wavelength of 8–14 μm.
Low infrared emissivity coating with good thermal resistance was prepared by using Ni20Cr alloy particles and inorganic silicate as pigments and binders, respectively. The effects of size, shape, and annealing temperature of Ni20Cr alloy particles on infrared emissivity of the coatings were systematically investigated. The results indicate that the composite coatings can exhibit low emissivity (0.49) and good thermal stability property. Ni20Cr alloy particles with tens of micron-sized, flaky, and fine crystal structure can be propitious for decreasing the infrared emissivity of the composite coatings. In addition, the thermal stability properties of the composite coatings were measured in air to explore the effect of high-temperature environment on the infrared emissivity. The measured results show that the composite coatings can exhibit a favorable thermal stability property below 800 °C and still possess low emissivity when the test temperature is below 500 °C, due to the Si–O–Si cross-linking network structure and the mechanical interlocking between the coating and substrate.
By use of the Kubelka-Munk theory, the Mie theory and the independent scattering approximation, we obtain the explicit expression of the emittance of an infrared coating attached to a radar absorber with a high emittance, in the 3~5μm window. Taking aluminum particles with spherical shape as the pigments within the coating, we give the dependence of the coating emittance with respect to the particle radius, the thickness of the coating. At a volume fraction of 0.05, we propose the optimum particle radius range of the pigment particles is around 0.35~0.6μm. When the thickness of the coating exceeds 300μm, the decrease of emittance at 4μm wavelength becomes negligible. Too much thickness of IR layer wouldn’t contribute to the decrease of emittance. We study the influence of the infrared coating on the performance of the radar absorber, and believe that not too much thick infrared coating consisting of spherical Al particles wouldn’t result in a remarkable deterioration of the absorbing ability of the radar absorber.
In the current study, we demonstrate that the modification of a commercial siloxane protective composition by the addition of silica nanoparticles substantially enhances its protective efficiency and renders the treated stone surface super-hydrophobic and self-cleaning. The extent of surface hydrophobization depends on nanoparticle concentration and reaches a maximum value of ~ 160° at 1% w/v of nanoparticles for the case of white Greek marbles (Naxos, Pentelic and Thassos) treated with the modified composition. The investigation of the surface morphology by scanning electron microscopy (SEM) reveals the presence of micron-sized protrusions (10–100 μm in diameter) formed by nanoparticle aggregates consolidated by the siloxane polymer. The diameter and surface density of the protrusions depend on nanoparticle concentration. The developed nanostructure of the protrusions was observed by atomic force microscopy (AFM). The nano-dimensions of the silica particles are essential for the superhydrophobization of the treated marble surfaces. In the case of micron-sized silica particles that were mixed with siloxane and were applied accordingly on similar white Greek marbles, the superhydrophobic effect was not achieved and the observed water contact angles were substantially lower.In the event that hydrophobicity is not the sole parameter of optimal stone and stone-monuments protection, other important parameters, such as water vapor permeability, water capillary absorption and stone color alterations, were also investigated and their dependence on nanoparticle concentration was established.
The field of nanoscience and nanotechnology is extending the applications of physics, chemistry, biology, engineering and technology into previously unapproached infinitesimal length scales. The polymer–nanoparticles/nanocomposites have been the exponentially growing field of research for developing the materials in last few decades and have been mainly focusing on the structure–property relationships and their development. Since the polymer–nanocomposites have been the staple of modern polymer industry, their durability under various environmental conditions and degradability after their service life are also essential fields of research. Thus, this article is intended to review the status of worldwide research in this aspect. Among various nanoparticulates, clay minerals and carbon nanotubes are more often used in enhancing physical, mechanical and thermal properties of polymers. In very few systems, the nanoparticulates have been incorporated into polymer as ‘nano-additives’ for both purposes: degradation and stabilization of polymers. The degradation and durability of polymers is reviewed in the presence of nanoparticles/nanocomposites under different environmental conditions. Nanoparticle-induced biodegradation of polymers is also discussed.
Infrared (IR) emissions from aircraft are used to detect, track, and lock-on to the target. MAN Portable Air Defence Systems (MANPADS) have emerged as a major cause of aircraft and helicopter loss. Therefore, IR signature studies are important to counter this threat for survivability enhancement, and are an important aspect of stealth technology. This paper reviews contemporary developments in this discipline, with particular emphasis on IR signature prediction from aerospace vehicles. The role of atmosphere in IR signature analysis, and relation between IR signature level and target susceptibility are illustrated. Also, IR signature suppression systems and countermeasure techniques are discussed, to highlight their effectiveness and implications in terms of penalties.
This study explores the relationship between the emissivity of aluminum alloy surfaces and surface roughness. Two methods are discussed which yield good overall predictions of the emissivity of rough surfaces. One method consists of using a mathematical multispectral radiation thermometry (MRT) model for the emissivity and determining both the surface temperature and the empirical constants in the emissivity model from radiance measurements. This method requires new emissivity constants to be determined for each surface topography. This study also presents an alternative method for determining the emissivity of rough surfaces. This method relies on determining the emissivity characteristics of a single reference surface and inferring the emissivity of any other rough surface of the same material by relating a surface roughness function (determined by surface topography instrumentation) of the rough surface to that of the reference surface. Using data for AL 7075 with various degrees of surface roughness, this method is shown to yield better accuracy than the first method.
The products of the thermal degradation of polydimethylsiloxane (PDMS) are determined by the heating conditions, since two competing mechanisms are involved.Cyclic oligomers are formed in the low degradation temperature range and during slow heating in programmed degradation. This involves molecular splitting of oligomers from loop conformations of the PDMS chain favoured by its flexibility, and assistance on the part of empty silicon d-orbitals.Methane and oligomers are formed in the high temperature range and during fast heating. This shows that homolytic scission of Si–CH3 also takes place and is followed by hydrogen abstraction.
The total hemisphere emissivity at 90°C and the normal spectral reflectance at room temperature of C/SiC composites were measured by using steady-state calorimeter method and Fourier infrared spectrometer (FTIR) respectively. The effect of fiber preform weaving mode, thickness of SiC coating and surface morphology on thermal radiation properties of C/SiC were investigated. The results show that thermal radiation properties of 3D C/SiC composites are superior to those of 2D C/SiC composites. Total emissivity of 2D C/SiC is 0.78, and total emissivity of 3D C/SiC is up to 0.82. The thickness of SiC coating has great effect on thermal radiation properties of C/SiC composites. With increase of SiC coating thickness, total emissivity of C/SiC firstly decrease, then increase, the largest emissivity may attain 0.85. Polished surface makes thermal radiation properties of C/SiC composites reduce with the result that total emissivity of 2D C/SiC and 3D C/SiC is 0.74 and 0.75 respectively.
Under precondition of high emissivity, the thickness of high emissivity ceramic coatings should be reduced to satisfy the requirement for mechanical property, which can also save raw materials and decrease the weight of the apparatus. So the relationship between emissivity and thickness of the coatings is important. In this paper, the coatings were prepared from Al2O3 sols and high emissivity fillers by spin and spray processes, respectively. The relationship between emissivity and thickness of coatings was examined, and the critical thickness of coatings was determined while the emissivity changes with the thickness rapidly. Based on Maxwell-Carnett theory, a new theoretical model about the relationship between emissivity and thickness of composite coatings is established. The emissivity values from the theoretical calculation are agree with the experimental data, which shows that the model can be used to predict the emissivity or the critical thickness of the composite coatings.
Thermal resistance coatings with low infrared emissivity were prepared by using polysiloxane and aluminum as adhesives and paint, respectively. The influence of the solidification temperature, content of Al powders and coating thickness on the infrared emissivity of the composite coatings was systematically investigated. The chemical composition, surface microstructure and thickness of composite coatings were characterized and the thermal stability was studied. These results indicate that the emissivity changes significantly with increasing solidification temperature. The optimum content of Al powders is around 30 wt.%, and the lowest emissivity value is ∼0.19. The emissivity decreases rapidly with increasing thickness and reaches to a saturation value when d > 50 μm. Moreover, we found that the emissivity was almost unchanged with thermal stability test maintaining a low value 0.19 at temperature below 600 °C. The thermal stability study shows that the composite coatings exhibit favorable thermal ageing and good thermal shock resistance.
In this research, novel organic–inorganic nanocomposite films of Konjac glucomannan (KGM) and CdS were prepared by one-step synthesis. As-prepared films were characterized by IR, TEM and SEM. The results indicated that hexagonal CdS nanoparticles with the sizes of 10 to 100 nm were well dispersed in KGM. The infrared emissivities of the films were characterized by IR-1 infrared emissivity instrument. As results showed, the KGM/CdS nanocomposite films had significantly lower infrared emissivity (8–14 μm), meanwhile when the size of KGM nanoparticles was between 10 and 20 nm and the mole ratio of CdS to KGM was 1.2:1, the film got the lowest infrared emissivity value of 0.011, which would be attributed to the strong synergism effect existing between KGM and CdS nanoparticles.
1000nm-thick Au film was sputter-deposited on two groups of nickel alloy substrates, in which one group (Group A) was oxidated at 800°C for 20h to form a oxide film before coating gold while another group (Group B) was unoxidated. The gold thin-film is applied to serve as a low emissivity coating to reflect thermal radiation. The gold-coated samples were heated in air at 600°C for 150h to explore the effect of high-temperature environment on the emissivity of coated Au film. After heat-treatment, the average thermal emissivity at the wavelength of 3–14μm of Group B greatly increased from 0.18 to 0.82 while that of Group A only increased a little. The diffusion between Au and other nickel alloy elements at 600°C also had been discussed in this paper.
In this study, polyurethane/titania (PU/TiO2) nanocomposites were prepared in ultrasonic process and characterized by fourier transform IR spectroscopy (FT-IR), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissivity analysis. The TEM and SEM results indicated that the nanoparticles were dispersed homogeneously in PU matrix on nanoscale. TGA-DSC confirmed that the heat stability of the composite was improved. Infrared emissivity study showed that the nanocomposite possessed lower emissivity value than those values of pure polymer and nanoparticles.
A combination of traditional kinetic formal treatments and computer simulation has been made to analyze polydimethylsiloxane (PDMS) thermal degradation. It was shown that PDMS thermally decomposes to cyclic oligomers through Si–O bond scission in a chain-folded cyclic conformation energetically favored by overlapping of empty silicon d-orbitals with orbitals of oxygen and carbon atoms. Kinetic treatment shows that PDMS thermal volatilization, as rate of heating increases, becomes dominated by rate of diffusion and evaporation of oligomers produced on its decomposition. At high heating rate (e.g. 100°Cmin−1.) thermal decomposition in nitrogen and in air tend to overlap because the rate of reaction between the material and oxygen is strongly reduced by low-oxygen solubility and high-thermal degradation rate. In nitrogen a small black residue is formed (silicon oxycarbide) which is produced by an alternative decomposition path leading to cyclic oligomers, made possible at high heating rate.
A new epoxy monomer, triglycidyloxy phenyl silane (TGPS) has been synthesized. By curing of TGPS, Epon 828 and DER 732, with 4,4-diaminodiphenyl methane (DDM), the curing rate and conversion efficiency of these epoxy resins are in the order of TGPS>Epon828>DER732. In the mixed epoxy system of TGPS/Epon 828/DDM, homogenous products are obtained from all proportions. In addition, the glass transition temperature of the blend decreases with increasing amount of TGPS from 140 to 100°C. By using TGA in a N2 environment, the onset decomposition temperature of silicone-containing epoxy resin system of TGPS is 80°C lower than that of Epon 828, and the decomposition of TGPS is a two-stage process with maxima weight loss rates at 330 and 430°C, respectively. The first stage involves the breaking of the silicone-containing group in TGPS and the second-stage is carbonization. In the second stage of carbonization, the temperature for maximum weight loss rate is 15°C higher than that of the Epon 828 in the first stage. This result indicates that the silicone-containing group is in favor of the carbonization mechanism and the solid char yield at 800°C for TGPS is 40wt%. Based on EDX analysis on the surface elements, the presence of Si and C is indicative of the above observation. In addition, the result by using TGA in an air environment shows that the silicon-containing carbon residue is superior in preventing oxidative burning. The high limiting oxygen index (LOI) of TGPS at 35 is considered as an excellent flame retardant in the epoxy system.
Evolution of volatile materials from pure poly(dimethylsiloxane) heated under temperature programmed conditions (10° min−1 under vacuum) is detectable at 343° and reaches a maximum at 443°. The volatile products comprise a continuous mixture of cyclic oligomers from trimer upwards. Replacement of the terminal hydroxyl by trimethyl silyl structures (end-blocking) results in a considerable increase in stability but no change in the distribution of products. The reaction is strongly accelerated by KOH and methane then appears as a significant product. Thermal gravimetry and molecular weight measurements confirm that the hydroxyl terminated polymer degrades in a stepwise fashion from chain ends. These observations are discussed from a mechanistic point of view. The reaction is accelerated by oxygen and cross-linking occurs.
We present experimental studies on the deposition and characterisation of ZnS/Ag/ZnS low-e coatings carried out to assess their optical performance and stability. Theoretical predictions of the coatings optical properties were combined with measured emissivity (ε) values to derive a figure of merit (η) defined as the ratio of luminous transmittance over emissivity. A coating consisting of 37.0nm ZnS/21.5nm Ag/37.0nm ZnS was found to maximise η. Long-term experiments on the produced ZnS/Ag/ZnS coatings, under solar irradiation have revealed that a moderate vacuum (10−2–10−3mbar) is required to avoid degradation of the film properties. Four-layer ZnS/Al/Ag/ZnS and five-layer ZnS/Ag/ZnS/Ag/ZnS coatings were produced and tested for thermal stability. They were both found to withstand heating at 300°C for 3h. The four-layer structures however, present low transmittance in the visible, due to absorption by the Al layer.
The relationship between internal stress of doped zinc oxide films and durability of doped zinc oxide/silver/doped zinc oxide low emissivity (low-e) coatings in humid environment was investigated. Aluminum, titanium, tin, chromium, silicon, gallium, magnesium, boron, barium, and calcium were chosen as a doping element in sputtering targets. Ratios of dopant/zinc in the oxide targets were 4/96–5/95 at.%. Films were formed by radio frequency sputtering. Doping of barium and calcium to the zinc oxide film led to a large increase in the internal stress. Doping of the other elements resulted in decreasing the internal stress. It was concluded that durability of the low-e coatings in humid environment closely correlated with the internal stress of the oxide layers.
Platinum films were sputter-deposited on polished nickel alloy substrates. The platinum thin films were applied to serve as low-emissivity layers to reflect thermal radiation. The platinum-coated samples were then heated in the air at 600°C to explore the effects of annealing time on the emissivity of platinum films. The results show that the grain size of the Pt films increased with the increasing annealing time while their dc electrical resistivity decreased. Besides, the IR emissivitiy of the films gradually decreased with the increasing annealing time. Especially, when the annealing time reached 150h, the average IR emissivity at the wavelength of 3–14μm was only about 0.1. Moreover, the chemical analysis indicated that the Pt films on Ni-based alloy exhibit a good resistance against oxidation at 600°C.
This study demonstrates the shielding effects of a silica-ash layer on the combustion of silicones and their possible applications on the fire retardancy of organic materials. The deposited silica-ash layer, formed on the surface of silicone materials during combustion, has shielding effects on the combustion of silicones. It insulates the burning surface from the radiant heat of flame, as well as from the radiant heat produced from the burning of adjacent materials. It also restricts the diffusion of fuels into the combustion zone and the access of oxygen to the unburned fuels. The shielding effects provide some of the fundamentals for the development of silicone-based fire retardants. © 1998 John Wiley & Sons, Ltd.
Annealing of pristine polypropylene blended with the organomontmorillonite (OMMT) at temperatures of 180–340 °C under a stream of nitrogen and of nitrogen–air mixtures is investigated. The oxidative annealing brings about the dispersion of the OMMT in the polypropylene and the formation of a nanocomposite structure. This is evidenced by the increase in the interlayer distance ‘d’ as measured by small angle XRD, with time of annealing and with the weight percent of air. This indicates progressive intercalation of the polymeric matrix into the clay gallery and subsequently exfoliation. The degree of exfoliation is estimated by the extent of migration determined spectroscopically on the surface of the annealed sample. The accumulated clay on the surface due to migration hinders the penetration of the oxygen into the annealing melt as expressed by the decrease in the rate of migration with the increase in the air concentration. This indicates the increase in ageing and storage stability of nanocomposites with increase in the extent of migration. The extent of migration is proportional to the polar carbonyl groups formed on the matrix. The energy of activation of the migration was found to be 37.82 kJ/mol indicating that the rate-determining step of migration is diffusion controlled reaction. The penetration of oxygen into the melt is the first of five steps, followed by oxidation, intercalation, exfoliation and migration. Monitoring the migration with increase in the temperature enables the observation at 275 °C of the transition of the nanocomposite structure to noncolloidal microcomposite. Increasing the annealing temperature above 300 °C brings about a slow, low-temperature combustion and formation of a new kind of char on the surface of the sample.
Phosphorus-containing polysilsesquioxane (PSSQ) was introduced into diglycidyl ether of bisphenol A epoxy (DGEBA) to generate a novel P/Si PSSQ nanocomposite. A series of nanocomposites was fabricated by changing the content of the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) monomer or P/Si PSSQ cured with DGEBA epoxy and modified epoxy. The structure, thermal properties and flame-retardancy of the P/Si PSSQ nanocomposites were characterized by FT-IR, solid-state 29Si NMR, thermogravimetric analysis (TGA) and limited oxygen index (LOI) instruments. The nano-sizes of the particles in P/Si PSSQ were approximately 30–50 nm, and the polarity of nanocomposites might generate the nanophase-separated structure from transmission electron microscopy (TEM). The urethane-like side group of the modified epoxy and the fabrication of oligomers in the curing reaction affected the Td5 values of nanocomposites. TGA and LOI results indicated that the char yield (29 wt%) increased and the nanocomposites were not very flammable (LOI = 30). The hybrid materials also exhibited high thermal stability, good flame-retardance and a lack of phase separation.
Polyimide/mesoporous silica composite films were prepared by direct mixing of polyamic acid solution and silylated mesoporous silica particles, or by condensation polymerization of dianhydride and diamine with silylated mesoporous silica particles in N,N-dimethylacetamide, followed with thermal imidization. Structure and glass transition temperatures of the composite films were measured with FTIR, SEM, EDX, XPS and DMTA. The results show that the silylated mesoporous silica particles in the composites tend to form the aggregation with a strip shape due to phase separation. The composite films exhibit higher glass transition temperature as comparing with that of pure polyimide. It is found that the composite films present lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value is related to the content of silylated mesoporous silica in the composite films. Inhibiting actions of silylated mesoporous silica on infrared emission of the composite films may be owing to presence of nanometer-scale pores in silylated mesoporous silica.Graphical abstract
Sheath-core bicomponent fibers were prepared by a general melt-spinning method with polypropylene chips and various particles. The melt-spun fibers were characterized by DSC and mass specific electrical resistance (MSER) apparatus. The electromagnetic constant was measured using a network analyzer and the absorbing wave effect was evaluated by an arch method. The results of the DSC thermogram indicated that the crystallinity of polypropylene containing particles in the core-part slightly increased first and then kept steadily with the particles content increase. Nanoparticles in the sheath-part did not make the crystallinity of fibers change markedly. The MSER of fibers rapidly decreased with the metal particles input. The complex permeability of fibers with Ba/Mn-Zn ferrite was improved compared with that of fiber with single Mn-Zn ferrite and the complex permittivity of fiber containing the 20 wt % Ba/Mn-Zn ferrite increased with the increasing bronze content. The fibers filled with the Ba/Mn-Zn ferrite and bronze particles had good radar absorbing effect. The input of Al particles in the sheath-part of the fibers showed a limited effect on the radar wave absorbing properties of the fibers. The lowest infrared emissivity of the fibers including 15 wt % Al particles in sheath-part reached 0.62. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2180–2186, 2007
The thermal degradation of polycarbonate (PC) containing methylphenyl-silicone with a branched structure (SFR-PC) was investigated by the thermogravimetric analysis (TGA). The decomposition activation energies were determined using the Ozawa method. It was found that the decomposition activation energy and the degradation residue of the SFR-PC at 800 °C in air atmosphere were much higher than those of the PC. The addition of methylphenyl-silicone enhanced the thermal stability of PC and promoted the formation of char. The silicone was found effective in retarding the combustion of the PC. The limited oxygen index of the PC containing 5 wt.% of methylphenyl-silicone was 34%. Surfaces of the SFR-PC before and after combustion were analyzed by energy dispersive X-ray analysis (EDX) and infrared (IR) spectroscopy. Based on these results obtained, the flame retarding mechanism of the SFR-PC was discussed.
Collagen/SiO2 composites were prepared in aqueous suspensions. Adsorption behaviors of collagen onto the surfaces of SiO2 spheres were studied. Structure and thermal properties were measured with FTIR, SEM, TEM, and TGA-DTA. The results showed that the self-aggregation of collagen macromolecules was taken place during the adsorption of collagen on SiO2 sphere. The morphology of collagen evolved from line to microfibrils with the increase in the concentration of collagen along with the distortion of SiO2. Interfacial interactions of electrostatic forces and hydrogen bonding between the collagen macromolecule and SiO2 sphere had a vital effect on the adsorption of collagen. The amount of the collagen adsorption was increased with the increase of the collagen concentration, yet decreased in increased pH value of the solution. It was found that the composites exhibited lower infrared emissivity values in the wavelength ranged from 8 to 14 μm than not only pure collagen but also SiO2 sphere, and the value of infrared emissivity was related to the adsorption amount of collagen in the composites.
Solar energy materials have properties tailored to meet requirements set by the spectral distribution, angle of incidence, and intensity of the electromagnetic radiation prevailing in our natural surroundings. Specifically, the optimization can be performed with regard to solar irradiation, thermal emission, atmospheric absorption, visible light, and photosynthetic efficiency. Materials for thermal and electrical conversion of solar energy in man-made collectors, as well as for energy-efficient passive design in architecture, are typical examples. This paper reviews solar energy materials with emphasis on the thermal applications of a variety of types. Electrical applications are given a more cursory exposition, the reason being that a systems perspective—rather that a materials perspective—is most fruitful in this case.
The flame retarding mechanism for polycarbonate (PC) by a trifunctional phenyl-rich silicone additive was studied by analytical
pyrolysis techniques. In order to clarify the actions of the silicone-based flame retardant for PC substrate during combustion,
the change in the chemical structure of the flame retarded PC with the silicone additive (FR-PC) after thermal treatment at
380 °C was investigated by pyrolysis-gas chromatography (Py-GC) in the presence of organic alkali. On the pyrogram of the
thermally treated FR-PC, which exhibited highly insoluble nature, the peaks reflecting the abnormal structures, formed through
the reaction between a silyl radical originating from the additive and an ether like oxygen atom in the carbonate linkage
of the PC chain accompanied by decarboxylation or Fries rearrangement, were clearly observed in much larger intensity than
those on the pyrogram of the thermally treated PC. On the basis of the observed results for the thermally treated FR-PC, it
was suggested that the formation of a char barrier on the surface of the FR-PC material was promoted during combustion to
reduce the radiant heat of flame and to restrict the diffusion of flammable degradation products into the combustion zone.
Thus formed cross-linking structure might surpress the thermal decomposition and confine the movements of the degradation
products.
The aim of this study was to investigate the characteristics and mechanism of the degradation of poly(siloxane-urethane) (PSiU) copolymers by thermogravimetric analysis (TGA) and TGA coupled with Fourier-transform infra-red spectroscopy (TG–FTIR). The PSiU copolymers consisted of 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (1,4-BD), and OH-terminated polydimethylsiloxane (PDMS). In TGA they exhibited a two-stage degradation at 250–650 °C. The two stages of degradation have been found to comprise eight degradation steps and two interchange reactions, as revealed by TG–FTIR analysis. The main decomposition products have been identified as CO2, tetrahydrofuran, cyclosiloxane, and macrocyclic species. In addition, the effects of hard segment content (HSC) on the degradation and thermal stability of PSiU copolymers have been investigated by means of TG and DTG curves; notably, a stability region at 410–470 °C is caused by the cyclosiloxane, as verified by TG–FTIR.
New mercaptan-terminated polythiourethanes were applied as curing agents for epoxy resin. The formulation studied consisted of a diglycidyl ether of bisphenol A epoxy resin, polythiourethane curing agent accelerated with primary or tertiary amine. The coating performance of the resins was tested by measurements of scratch resistance, pencil hardness, flexibility, adhesion and chemical resistance. The results show better properties of the polythiourethane-cured resin compared to standard epoxy formulation. It is observed that evaluation of the physico-mechanical and chemical resistance performance shows better results with the increased loading of polythiourethane hardener. In addition, polythiourethane hardeners revealed high reactivity toward curing of epoxy resins at low-temperature conditions (−10 °C). Polythiourethane-cured epoxy resins, thus stand as an effective surface coating material where high performance is needed in terms of physico-mechanical properties as well as chemical resistance.
This work is aimed at developing and investigating silane based organic–inorganic hybrid coatings possessing unique properties, which can be used to improve the performance of steel structures subjected to marine corrosion. These silane based sol–gel coatings were prepared by dip coating planar samples of mild steel in solution of an organically modified silica sol made from hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) in acid catalysis condition. Crack-free coatings were obtained on curing at 200 °C. On increasing the curing temperature to 400 °C, however, cracks developed in the plain organic–inorganic hybrid coatings. This observation was consistent with the visual observations where appearance of the coated specimen changed from colourless metallic to brownish grey on curing from 200 °C to 400 °C temperature. The coatings were further modified using SiO2 nanoparticles and cerium. The effect of change in the – temperature as well as – composition on the microstructural properties of the coatings was determined using optical microscopy, scanning electron microscopy and atom force microscopy. Additionally, Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR/FTIR) was carried out to show the formation of the Si–O–Si structural backbone of the hybrid material with the organic CH3 group incorporated into the silica network. The corrosion protection performance of these coatings was examined using potentiodynamic polarisation technique and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution. The polarization curves and corrosion resistance as measured by the bode plots suggested that the plain hybrid coatings offer good protection against corrosion. However, the SiO2 and cerium modified nano hybrid coatings exhibited superior performance to that displayed by plain hybrid coatings.
Polyurethane/Cu composite coatings with low infrared emissivity near to 0.10 at the wavelength of 8–14 μm were prepared by a simple and convenient process. The influences of the content of Cu powder, surface roughness, coating thickness and temperature on infrared emissivity of the coatings were systematically investigated. The results indicated that the emissivity decreases significantly with increasing content of Cu powder and coating thickness. The coatings with smooth surface exhibit lower emissivity values than those with rough coatings. Moreover, we found the relationship between the emissivity of coatings and temperature presents a “U” type, and the emissivity reaches to the minimum at about 380 K. The mechanisms of low emissivity were proposed by optical theories, which are found to be in a good agreement with the experimental results.
The present work is concerned with the effect of different bituminous coal chars pore surface structure on their combustion behavior. The chars were sampled in a semi-industrial coal jet flame of 2.5 MW thermal input. The solid samples from the jet flame were compared with samples tested in an isothermal plug flow reactor. For surface characterization, N2-adsorption and scanning electron microscopy were applied. Differences in the BET-surface area up to one order of magnitude were observed for char samples collected in both combustion facilities. It was concluded that the larger surface area of the plug flow reactor char samples was due to a micropore structure, which was developed during devolatilization. The higher the initial particle heating rate was, the larger was the micropore structure and thus larger pore surface area resulted. Thus chars were expected to show different intrinsic reactivities. Nevertheless, since the control of internal structure on char consumption decreases as the temperature grows, an attempt was made to model char burnout in the jet flame making use of the kinetic parameters derived from the plug flow reactor experiments. Theoretical burnout curves fit remarkably well the experimental data, revealing that the porous structure may play a minor role in pulverized fuel combustion processes. Diffusive transport and reaction rates were of the same order of magnitude. Thus bulk diffusion may play a significant role, governing the global rate so that the internal porous structure is not significantly involved in the combustion process.
Rate of heat release data for a range of silicones (fluids, elastomers, resins) were obtained using the cone calorimeter. These materials exhibit relatively low rates of heat release, a uniquely low dependence of rate of heat release on external heat flux, and low yields of carbon monoxide. The cone calorimeter provides a reliable, efficient methodology for the characterization of materials ranging from simple fluids to multicomponent elastomers and resins. Comparative data between silicones and organic-based materials were also obtained.
In this study, far infrared low-emissive coatings have been prepared using a spin-coated 2-μm layer of commercial inorganic binder under a spin-coat produced from nanosized silver solution, resulting in Ag films of thicknesses between 0.1 and 1 μm. The bilayer coatings were baked at various temperatures for 30 min in air. The 1-μm Ag film baked at 150 °C exhibited an extremely low emissivity of 0.04 in the far infrared range wavelengths of 8 to 14 μm. In addition, this nano-silver paint showed good adhesive strength and the capability to withstand a neutral salt test.
SiC/SiO2 nanocomposite coating was deposited by electron beam-physical vapor deposition (EB-PVD) through depositing SiC target on pre-oxidized 316 stainless steel (SS) substrate. High melting point component C remained and covered on the surface of ingot after evaporation. When SiC ingot was reused, remaining C had an effect on the composition, hardness and emissivity of SiC/SiO2 nanocomposite coating. The composition of ingot and coating was studied by X-ray photoelectron spectroscopy (XPS). The influence of remaining C on hardness and spectral normal emissivity of SiC/SiO2 nanocomposite coating was investigated by nanoindentation and Fourier transform infrared spectrum (FTIR), respectively. The results show that remaining C has a large effect on hardness and a minor effect on spectral normal emissivity of SiC/SiO2 nanocomposite coating.
A method for eliminating the mass transport limitation on biosensor surfaces is introduced. The measurement of macromolecular binding kinetics on plane surfaces is the key objective of many evanescent wave (e.g. total internal reflection fluorescence (TIRF)), and surface plasmon resonance (SPR) based biosensor systems, allowing the determination of binding constants within minutes or hours. However, these methods are limited in not being rigorously applicable to large macromolecules like proteins or DNA, since the on-rates are transport limited due to a Nernst diffusion layer of 5-10 microm thickness. Thus, for the binding of fibrinogen (340 kDa) to a surface current SPR biosensors will show a mass transport coefficient of ca. 2 x 10(-6) m/s. In a novel approach with an immiscible fluid vesicle (e.g. air bubble), it has been possible to generate nanoscopic fluid films of ca. 200 nm thickness on the sensor surface of an interfacial TIRF rheometer system. The thickness of the liquid film can be can be easily probed and measured by evanescent wave technology. This nanofilm technique increases the mass transport coefficient for fibrinogen to ca. 1 x 10(-4) m/s eliminating the mass transport limitation, making the binding rates reaction-rate limited. From the resulting exponential kinetic functions, lasting only 20-30s, the kinetic constants for the binding reaction can easily be extracted and the binding constants calculated. As a possible mechanism for the air bubble effect it is suggested that the aqueous fluid flow in the rheometer cell is separated by the air bubble below the level of the Nernst boundary layer into two independent laminar fluid flows of differing velocity: (i) a slow to stationary nanostream ca. 200 nm thick strongly adhering to the surface; and (ii) the bulk fluid streaming over it at a much higher rate in the wake of the air bubble. Surprising properties of the nanofluidic film are: (i) its long persistence for at least 30-60s after the air bubble has passed (2.5s); and (ii) the absence of solute depletion. It is suggested that a new liquid-liquid interface (i.e. a "vortex sheet") between the two fluid flows plays a decisive role, lending metastability to the nanofluidic film and replenishing its protein concentration via the vortices-thus upholding exponential binding kinetics. Finally, the system relaxes via turbulent reattachment of the two fluid flows to the original velocity profile. It is concluded that this technique opens a fundamentally novel approach to the construction of macromolecular biosensors.
- Hshieh