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Construction of a smart active/barrier anti-corrosion system based on epoxy-ester/zinc intercalated kaolin nanocontainer for steel substrate
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In this study, for the first time, the corrosion mitigation ability of zinc intercalated kaolin (K) as an inorganic and cost-effective nanocontainer was studied. The impact of kaolin modification by zinc ions on the epoxy ester coating corrosion protection ability was surveyed by EIS (Electrochemical impedance spectroscopy) and salt spray tests. XRD (X-Ray diffraction) results showed that feeding the kaolin particles by zinc ions increased the interlayer space of the galleries. The Rct (charge transfer resistance) values obtained from the EIS analysis of the scratched coating were found to be around 9800, 34693, and 52188 Ω cm² for neat, K, and KZn (modified K particles with Zn ions) epoxy coated samples after 6 h from immersion. The physical and thermal-mechanical properties of the epoxy ester composite coating reinforced with.
KZn particles were assessed by DMTA and tensile tests. Results proved that the addition of modified kaolin particles had reinforced the mechanical characteristics, including the ultimate strength and Young’s modulus.
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... CPE is an alternative element for the ideal capacitance (C) since the surface of the metal is not homogenous, and it is porous. This element is composed of Y 0 (admittance) and n (exponent) [50][51][52][53][54][55]. ...
... (1)) and Neumann's (Eq. (2)) [32,[50][51][52]63]: ...
This study deals with the Mg-AZ31 alloy anticorrosion properties improvement via a novel surface treatment method. In this regard, the praseodymium (Pr)-based film formation on the Mg-alloy surface at different film formation conditions (i.e., pH, time, temperature) were investigated. The composition of the generated Pr-based film on the Mg-AZ31 alloy surface was characterized in depth using atomic/microscopic level techniques, i.e., X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and contact angle (CA) test. The influence of Pr film on the polyurethane (PU) coating adhesion properties and corrosion protection performance were studied by the pull-off test, neutral salt spray (NSS), and electrochemical impedance spectroscopy (EIS) analyses, respectively. FE-SEM micrographs revealed that the metal surface was covered with a Pr film, which has brought about a rough surface. Applying the Pr film to the Mg alloy surface has caused significant improvement in the corrosion resistance characteristics. A 94.84% corrosion retardation potency was recorded for the Pr-modified Mg alloy at the optimum surface chemical treatment condition. A significant improvement in the adhesion degree (about 64%) was obtained for the PU film on the Mg alloy modified by an optimized Pr film. Results have declared that the Pr-based film could improve the Mg alloy corrosion resistance by affecting the anodic/cathodic reactions through the formation of insoluble and electrically insulate inorganic film and enhancing the PU adhesion by providing a surface with high energy/wettability and micro-nano scales roughness.
... This enormous potential continues to stimulate research in corrosion prevention and the improvement of anticorrosion treatments. Various industries have a high interest in developing materials with higher corrosion resistance, such as reinforcements in construction [5][6][7][8], automotive [9][10][11][12][13][14], aeronautics [15][16][17], steel [18][19][20], and biomedical implants [21,22]. ...
The formation of cerium hydroxide was studied, and its capacity as a corrosion inhibitor on aluminum substrates was evaluated. These particles were deposited by immersing the substrate in a bath with cerium nitrate and hydrogen peroxide. Four different immersion times were used to determine the differences in behavior from low concentrations to an excess of particles on the surface. The coatings were analyzed morphologically by scanning electron microscope (SEM) and optical microscope, and chemically by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Electrochemical corrosion analysis was studied using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and electrochemical noise (EN). The results show that for 2 and 5 min of immersion, there was corrosion inhibition caused by the presence of cerium Ce3+ in the coating, but with excess cerium hydroxide particles, corrosion was favored. The presence of cerium particles favors corrosion at 30 s of immersion. This is the same case at 60 min, where corrosion was favored by the excess of Ce4+ particles on the surface.
... This encourages research in the area of corrosion prevention and continuous improvement of anticorrosion treatments. This leads various industries to have a great interest in developing materials with high corrosion resistance, mainly industries, such as construction [4][5][6][7], automotive [8][9][10][11][12][13], aeronautics [14][15][16], steel [17][18][19], ...
Corrosion is one of the main problems in materials science that represents a high cost to the world economy. Rare earth elements have attracted attention as corrosion inhibitors due to their excellent results and being environmentally friendly. Although its mechanism of action continues to be studied, the most accepted theory indicates that corrosion inhibition is based on the formation of insoluble oxides/hydroxides and requires specific conditions to be effective, which represents a problem in some applications. In recent years, various lanthanide salts have been investigated, their corrosion protection mechanism being widely reported, and the operation principle is the same for all rare earth elements. Cerium is the element that has been most extensively investigated among them, mainly for its abundance, low cost, favorable results attributed to the formation of oxides/hydroxides that block cathodic sites, and, in recent years, to developing coatings capable of self-healing. Despite not having reached extensive applications in real cases of protection against corrosion, the prospects of rare earth salts as corrosion inhibitors are promising and appear as a viable option for replacing processes involving chromium.
... Recent research has shown the use of encapsulation methods to store and confine the corrosion inhibitors into nanocontainers in order to minimize excessive leaching as well as to prevent unwanted reactions between the coating and the corrosion inhibitors. These nanocontainers when embedded into the coatings provide corrosion resistance by actively releasing the corrosion inhibitor in a controlled manner [5]. ...
Mild steel is an important material in construction, automobile, and other engineering applications. Long exposure to a corrosive environment causes damage to the material and makes it less efficient for usage. Various methodologies such as barrier coatings and self-healing coatings are employed to prevent corrosion to occur. To increase the performance of the coatings, modifications are carried out by the addition of corrosion inhibitors into the coating matrix. Direct addition leads to unwanted reactions with the coating matrix and loss of corrosion inhibitor itself. In order to prevent this problem, nanocontainers are used to encapsulate the self-healing agent/corrosion inhibitor. Therefore, recent corrosion prevention methods involve the fabrication of multifunctional coatings using different nanocontainers such as halloysite nanotubes, polymeric microcapsules, layered double hydroxide, etc. loaded with corrosion inhibitors. The release of corrosion inhibitors works on trigger mechanism arising due to change in external stimuli and thus increasing the durability of the coatings.
... The outcomes evidenced a continuous growth of the impedance and resistance with time because of the construction of inhibitive species over the scratched zones ( Figure 10.4). The role of bentonite, feldspar, and kaolin as the container for self-healing coatings has been rarely reported, though early outcomes have been hopeful [80][81][82][83]. Unlike the three mentioned compounds, zeolite and halloysite structures have been extensively studied in the literature to achieve active corrosion protection [84][85][86][87][88][89][90][91][92]. ...
During the past decade, the application of polymeric coatings with intrinsic self‐healing corrosion inhibition potency regarding metal substrates becomes a vital aspect for academic researches and industries. This chapter gives the recent advances and concise description regarding the potential applications of different kinds of micro/nano‐carriers of healing agents for the development of smart/intrinsic self‐healing anti‐corrosion polymeric coatings. The self‐healing materials/fillers classification, various techniques of the inhibitors loading in the carriers/containers, and their release/corrosion‐inhibition mechanisms are introduced and discussed. The nano‐containers are divided into five main categories with self‐healing activity which are: ion‐exchange based materials (i.e., clay, bentonite, montmorillonite, feldspar, layer double hydroxide (LDH), zeolite, halloysite, and kaolin), porous‐structure and metal oxide materials, conductive polymers, fibril materials and lamellar‐structure materials (i.e., graphene‐based materials). The latest achievements regarding the development of the self‐healing coatings based on these five groups of nano‐containers to corrosion control of the metallic substrates are reviewed. Moreover, healing using polymerizable agents and micro/ nano‐capsules is proposed.
... Moreover, as the exposure time prolonged, n values related to CPE dl continuously rose, indicating that the Mg alloy surface is becoming smoother by time. That is most likely due to the formation of insoluble metal-lawsone complexes upon the release of lawsone and filling of the active corroding sites on the Mg substrate [81]. It should be also noted that, at the end of 7-day immersion time, the R ct value of PCL-LS coating is much higher than those of uncoated Mg samples and the pure PCL coating. ...
The clinical application of magnesium (Mg)-based alloys as temporary orthopedic implants is highly limited by their rapid corrosion rate in the physiological environment. Herein, an anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone was prepared on AZ31 Mg alloy to improve its corrosion resistance. Lawsone was incorporated into the coating as a corrosion inhibitor to enhance the passive corrosion protection of the PCL coating through its strong chelation ability of dissolving Mg²⁺. Anti-corrosion properties of the coatings were assessed by electrochemical techniques and in vitro immersion tests, and the results demonstrated a remarkable improvement in corrosion resistance of the bare Mg alloy. In addition to the corrosion inhibition effect, incorporation of lawsone provided the coating with a strong antibacterial activity against Escherichia coli and Staphylococcus aureus bacterial strains. Moreover, the fabricated coating was cytocompatible (viability of > 85 %) toward human fetal osteoblast cells. The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants.
... 40 Corrosion resistance is a sought-after property of materials used in various industries, such as the construction, [41][42][43][44] automotive, 45-50 aeronautical 51-53 and steel industries. [54][55][56] These new technologies mainly search for materials capable of replacing those currently used with the benefits of being lighter, possession of various functional characteristics, having environmentally friendlier processes, the viability to be incorporated into production lines and all the cost advantages that these points involve. ...
The atmospheric pressure plasma jet (APPJ) has received attention in recent years due to its ease of incorporation into production lines, rapid application, low surface damage and use in a wide variety of materials (cardboard, textiles, metals, polymers and glass) and for being a more environmentally friendly technique than wet chemical techniques. Treatments with APPJ can be divided into two types: (a) surface modification with APPJ and (b) coating deposition with APPJ. These treatments decrease the hydrophobicity, change the surface composition and favor the growth of passive oxide films, while the coatings have excellent adhesion and good barrier properties. The APPJ-electrochemical link has been focused on the prevention of and protection against corrosion. Electrochemical studies show excellent results against corrosion, and APPJ treatment has the potential to replace procedures currently in use. This work describes the relationship between APPJ treatments and the electrochemical studies carried out on surfaces modified with this method.
... Detection of the Zr ions and N atoms in the EDS results is good evidence for the inhibitive film formation within the scratch region. The film formation mechanisms were explained before [110]. ...
For the first time, the UIO-66, NH2-UIO, and NH2-UIO particles covalently functionalized by Glycidyl Methacrylate (GMA@NH2-UIO), were utilized as the novel functional anti-corrosive fillers. The functionality, high surface area, phase composition, excellent thermal properties as well as chemical stability of the Zr-MOFs were proved by FT-IR, BET, XRD, TGA, and water stability tests, respectively. The smart pH-sensitive controlled-release activity of the corrosion inhibitors (i.e., Zr ions and organic compounds) from the prepared Zr-MOFs was proved by the water stability test of the Zr-MOFs particles in the acidic (pH = 2), neutral (pH = 7.5), and alkaline (pH = 12) solutions containing 3.5 wt% sodium chloride. The active inhibition properties of the Zr-MOFs were obtained in saline solution by two methods of (i) the solution phase and (ii) scratched epoxy coated samples containing Zr-MOFs by Tafel polarization method and EIS analysis. According to the EIS data, the excellent barrier (passive) properties of the composite film filled with GMA@NH2-UIO particles (G-UIN/EP) were proved by the highest impedance level at the lowest f (frequency) (log (|Z|10 mHz = 9.86 Ω.cm2), the lowest value of the breakpoint frequency (log (fb) = −1.42 Hz) and the highest coating undamaged index (85.93%) after 120 h of immersion. The salt spray (accelerated corrosion test) test (SST), pull-off (testing the strength of adhesion), and cathodic disbonding test (CDT) experiments showed excellent interfacial-adhesion properties of the G-UIN/EP sample in two dry (unexposed) and wet conditions. The hardness test showed that through the incorporation of the UIO, UIN, and G-UIN particles into the epoxy coating, the hardness, and scratch-resistance of the coating were notably improved.
Metals (Ms) and metal oxides (MOs) possess a strong tendency to coordinate and combine with organic polymers to form respective metal–polymer frameworks (MPFs) and metal oxide polymer frameworks (MOPFs). MPFs and MOPFs can be regarded as composites of organic polymers. MPFs and MOPFs are widely used for industrial and biological applications including as anticorrosive materials in the aqueous phase as well as in the coating conditions. The presence of the Ms and MOs in the polymer coatings improves the corrosion inhibition potential of MPFs and MOPFs by improving their self-healing properties. The Ms and MOs fill the micropores and cracks through which corrosive species such as water, oxygen, and corrosive ions and salts can diffuse and destroy the coating structures. Therefore, the Ms and MOs enhance the durability as well as the effectiveness of the polymer coatings. The present review article is intended to describe the corrosion inhibition potential of some MPFs and MOPFs of some most frequently utilized transition metal elements such as Ti, Si, Zn, Ce, Ag, and Au. The mechanism of corrosion inhibition of MPFs and MOPFs is also described in the presence and absence of metal and metal oxides.
Gallic acid modified and reduced graphene coated by polydopamine (DM-GO) is synthesized. The results show that gallic acid can reduce graphene oxide and promote the stable dispersion of graphene in solution, and repair some defects of graphene surface through π-π interactions. Polydopamine can effectively mitigate serious corrosion caused by graphene due to its high electrical conductivity. Because of the barrier effect of well-dispersed graphene and the presence of polydopamine, the addition of DM-GO into waterborne coating leads to the significant improvement of the adhesion and long-term corrosion resistance of coatings.
Organic resin-based coating is the most effective and cost-efficient method for preventing metal corrosion, but it is always plagued by its hydrophilicity, brittleness and preparation-induced pore flaws. In this study, a double-layer superhydrophobic anti-corrosion coating with concentration gradient variation was designed and prepared, using benzoxazine as the matrix and waste fly ash-prepared zeolite A as the inorganic filler. The upper layer of the designed coating with the low concentration of zeolite formed a superhydrophobic surface with a water contact angle of 158.8° ± 0.9°, while the high concentration of zeolite in the lower layer improved the adhesion of the coating to the metal substrate with a surface hardness of 5H and an adhesion of 5B, which were both significantly improved in comparison to the pure benzoxazine coating. In particular, the impedance value of our designed coating is 2.677 × 10⁸ Ω, which is 4 orders of magnitude greater than the pure benzoxazine coating. The benzoxazine/zeolite A (from fly ash) bilayer coatings developed mechanical properties, anti-fouling and corrosion resistance, which not only boosted the use of fly ash but also created a new type of anti-corrosion coating.
Na⁺-montmorillonite nanoplatelets were surface functionalized by triethoxyvinylsilane through sol-gel reactions. The functionalized, and pristine nanoplatelets were then impregnated by Octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, a primary phenolic antioxidant, to be used in an epoxy vinyl ester resin. The FTIR, Raman and, TGA results confirm that the functionalization reactions, and the antioxidant impregnation process have been successfully carried out. FE-SEM micrographs demonstrate that particle morphology significantly changed as a result of the processes. In the next step, three different concentrations of the obtained nanofillers were added to an epoxy vinyl ester resin, and the attained colloids underwent rheological assessment. Both steady-shear, and dynamic complex viscosity diagrams showed significantly increased values, by two orders of magnitude, for untreated Na⁺-montmorillonite compared to the other nanofillers, i.e. vinyl-functionalized, and antioxidant-loaded ones. It was then demonstrated that such an increase is most certainly attributed to a proposed theory as possible selective physisorption of lower molecular mass of epoxy vinyl ester chains on the untreated montmorillonite nanoplatelets.
Polymer coatings like epoxies (EP) are among the most used approaches to overcome corrosion loss in industries. But these coatings have porosities in their structure due to the evaporation of the solvent. This study aims to construct a nanocomposite epoxy coating incorporated with reduced graphene oxide (rGO) nanoparticles utilizing the aqueous Echium ammonium extract (EAE). The surface characterizations were conducted using X-ray photoelectron spectroscopy (XPS), Ultraviolet-visible spectroscopy (UV–Vis), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), dispersibility experiment, and field emission scanning electron microscope (FE-SEM). The anti-corrosion properties were scrutinized by electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSS). The surface analyses have proved the successful conversion of the carbonyl groups into CO bonds. The Rt value in the liquid phase has improved by time and reached its maximum after 24 h from immersion which was 66,566 Ω·cm². The high response of the rGO-EAE sample was attributed to the various chelates and complexes constructed by the allocation of the lone pairs of EAE molecules electrons to the vacant d-orbital of the Fe atom. The indirect use of EAE in EP has enriched the barrier function and constructed a protective layer inside the scratch, elucidating the self-healing operation. The EAE molecules have protected via absorbing on the active anodic zones. The presence of modified graphene oxide nanolayers in the epoxy coating not only brought about enhancement in the nanocomposite barrier function but also, owing to the delivery of EAE molecules to the anodic zones of the steel surface, a desirable grade of protection was provided through active inhibition of the anodic zones.
Various methods have been employed to protect metals in assets from corrosion damage, among which is the use of very efficient and economical organic coatings. The performance of organic coatings is often influenced by their inherent porosity, which provides pathways for corrosive species or results in vulnerability to mechanical damage. Nanomaterials (NMs) have a wide range of shapes and sizes that have been employed to improve the engineering performance of coatings. They have been shown to increase corrosion resistance and other properties of coatings through various mechanisms, some of which are not well known. Following an overview of the different types of anticorrosion coatings and their protective mechanisms in this article, we summarized the effects of different NMs on the performance of polymer-based coatings. It was observed that bio- and carbon-based nanomaterials are the most promising nanofillers to improve the barrier performance of organic coatings. Smart nanocomposite organic coatings were then examined, as they could be regulated to release repairing or protective agents, mainly to corrosion defects or damaged areas of the coating once triggered by external stimuli. Then, high-performance nanocomposite organic coatings, which provide long-lasting and superior corrosion protection, were examined. Subsequently, advanced characterization methods for studying nanocomposite organic coatings were briefly discussed. We concluded with a summary of the key findings and the research needs.
Polymer nanocomposite coatings (PNC) have been successfully utilized in hindering corrosion; scratching, biofouling, and so on. Inherent deficiencies accruable from usage of organic coatings in hindering or mitigating these environmental flaws are caused by their inherently porous micro-architecture which has defaulted in resisting attack of deteriorating elements, and damages from scratching, corrosion, surface abrasion, or wearing. Interestingly, these deficiencies have been overcome by PNC coatings. Potential techniques of enhancing impenetrability of organic coatings involve the inclusion of impermeable layered nanomaterials (NM). Amongst varying layered NM available, graphene (GN) (a twin-dimensional carbon layering), and nanoclay have presented unique behaviors capable of repressing surface faults due to their inherently elevated aspect ratios, superior mechanical and physical properties, in addition to their peculiar geometries and anti-microbial attributes. Hence, this paper elucidates recently emerging nanotechnological advancements in enhancing properties of polymer nanocomposite coatings (PNCs) including nano-silica and titanium dioxide coatings and mechanisms with special focus on graphene (GN), and nanoclay (PCN) coatings and mechanisms for effective surfacial mitigations and applications.
The intercalation of kaolinite through the insertion of ions or molecules amongst the structural aluminosilicate layers is a vital process in numerous clay-based applications and products. Layer neutrality and hydrogen bonding limits direct intercalation into
kaolinite, other than for small molecules. Synthesizing zirconia-intercalated kaolinite is not a straightforward matter. To overcome this barrier, raw Egyptian kaolin (UnK) or its acid-activated product (HK) was sonicated and impregnated in aqueous ZrOCl2·8H2O solution
followed by thermal treatment at various temperatures (100, 200, 300, and 500°C). The intercalation process was confirmed using various spectroscopic and analytical techniques. The direct intercalation of ZrO2 into the kaolinite layers was observed even through a mild thermal treatment (100, 200, and 300°C). The mechanism of intercalation was suggested to occur by binding ZrO2 to the Si/AlO groups with a preference for the acid-activated HK, causing variable enlargements of the basal spacing and producing very perturbed layers. Interestingly, the surface area increased by 250% as a result of zirconia intercalation. Scanning electron microscopy (SEM) images showed a remarkable improvement in the stacking order of the kaolinite particles. The impact of ZrO2 intercalation into kaolinite also enhanced its adsorption efficiency for Pb2+, Cu2+, and Cd2+ ions. Preliminary investigations showed that the zirconia-intercalated
HK demonstrated a removal efficiency, which is three times greater than that of pristine HK. The adsorption tendency toward Pb2+ ions was greater than those of Cu2+ and Cd2+ and followed the order: Pb2+ >> Cu2+>Cd2+. The study suggests that the chemical modification of kaolin by zirconia via a direct intercalation technique, which greatly improves its functionality as demonstrated by the selective sorption of heavy metal ions, is worthy of further study.
In this work, for the first time, the Satureja Hortensis leaves was extracted by ultra-pure water solution and then, the synergistic inhibition effect of various mixtures of Satureja Hortensis extract (SHE) and zinc cations on carbon steel corrosion in 3.5% saline (NaCl) solution was investigated. The proposed compounds' effectiveness in carbon steel corrosion mitigation was surveyed by polarization and EIS tests. The inhibition efficiency of 99.34% was recorded for 700 ppm Zn + 300 ppm SHE. Surface characterizations were conducted employing scanning electron microscope (SEM) equipped with EDX, ultraviolet-visible (UV-Vis) analysis, Fourier transmission infrared (FTIR) spectroscopy, grazing incidence X-ray diffraction (GIXRD), and contact angle (CA) analysis which vividly proved the results of the electrochemical investigation. A mixed protection behavior was observed according to the polarization test results. Molecular dynamics (MD) simulation results complemented the experimental findings in affording insights into the adsorption mechanism at the atomic/molecular scale.
With the development of nanotechnology, the application of new nanomaterials with unique properties and great versatility in different areas of science and industry has sharply increased in the last years. Among them, metal-organic frameworks (MOFs) have been one of the most widely used in many different areas, including analytical chemistry. Their particular characteristics and the ease to customize their synthesis, based on the requirements, have made them excellent candidates as sorbents in sample preparation procedures, as substrates for the preparation of stationary phases in chromatographic and electrophoresis separations, as well as modifiers or frameworks for the preparation of detection systems, including sensors. The aim of this chapter is providing an overview of the employment of MOFs in the field of analytical chemistry, summarizing the most remarkable approaches developed in the last 5 years (2016–20) and carrying out a thoroughly discussion about the use of such materials in this field.
Metal-organic frameworks (MOFs), which are advanced category of porous types of coordination polymers, are a novel genre of porous crystalline compounds constructed by assembling the organic ligands with metal ions. The growth in the MOF-based studies evokes important information related to numerous potential applications. Due to the unique properties of the MOFs, these materials have garnered the great attention of the researchers in the construction of high-performance composite materials. MOFs can be utilized whether as an inhibitor or a nanocarrier for the protective compounds in thin films and polymeric nanocomposites. Besides, due to inherent features, that is, excellent mechanical characteristics and high thermal stability, MOFs have been applied for the development of advanced composite materials with outstanding thermal/mechanical properties. This chapter describes and compiles diverse interesting characteristics of MOFs, synthesis approaches, different parameters affecting the stability of the frameworks in different conditions and environments, and the use of MOFs in the corrosion protection applications as well as in the construction of polymer-based composites with unique thermal/mechanical properties. The impact of MOF addition whether as an inhibitor or a nanocontainer on the corrosion protection and thermal–mechanical properties of the polymer composites have been thoroughly discussed.
In this study, the organic coating of epoxy zinc-chromate (E) and the two-layer coating of epoxy zinc-chromate-polyurethane (PU-E) was coated on the steel substrate using the spraying method. Then, their corrosion resistance was compared using electrochemical impedance spectroscopy (EIS) and dynamic polarization tests. Comparison of corrosion properties using parameters of, phase angle at a maximum frequency (100kHz), and breakpoint frequency (fb) were performed during 2, 4, and 8 weeks. A comparison of these three parameters showed that the corrosion resistance of the PU-E coating was higher than the E coating due to the behavior of the polyurethane coating barrier as well as the active protective behavior induced by the chromate pigments which was distributed on the epoxy coating. According to the test results, E and PU-E coatings had good hardness and scratch resistance and were resistant to pencil scratches with H and F hardness, respectively. The salt spray test for the two-layer coating showed no qualitative change, damaged area, blistering/delamination, or corrosion products on the coated sample. The results showed that both coatings were suitable candidates for use in various industries, including marine and power industries, and other industries that suffered from corrosion problems.
Hollow carbon spheres (HCS) are spherical forms of carbon materials that can be used as nanocontainers due to their empty cores. In this work, zinc cations were doped in HCS ([email protected]) from an aquatic solution of zinc nitrate salt. Corrosion inhibition of released zinc cations in saline solution on bare mild steel samples was assessed by EIS, polarization, and electrochemical noise measurements. The sample surfaces were characterized through FTIR spectroscopy and grazing incidence XRD analyses after exposure to the test solutions. The results showed improvement in the corrosion resistance in the presence of [email protected] in a long immersion period. [email protected] were also incorporated in organosilane coating up to 5%. The EIS results showed a significant improvement in corrosion resistance of the samples at 2.5% wt. of [email protected] FESEM and Raman mapping inspections of reinforced silane coatings approved morphological alteration of the coating surface in the form of severe heterogeneity and crack formation at 5% loading of [email protected] probably due to inappropriate nanocontainer dispersion.
Inhibition of steel corrosion in 3.5% sodium chloride (NaCl) by rice straw extract (RSE) was studied via weight loss method up to 42 days immersion. The corrosion inhibition efficiency (IE) showed a consistent value with the highest IE of 92% and low corrosion rate, 0.013 mm/y. RSE was able to reduce pitting corrosion by presenting small hysteresis loop via cyclic polarization measurement. The formation of ferric-RSE layer due to complexation was confirmed via surface analysis. The presence of corrosion products on steel was significantly reduced by immersion in RSE. The inhibitory mechanism was proposed to be achieved through interphase inhibition. © 2018 The Korean Society of Industrial and Engineering Chemistry
Corrosion inhibition of carbon steel in hydrochloric acid solution was inspected using newly Benzylidene-aniline derivatives namely: (E)-N(2-Chlorobenzylidene)-2-Fluorobenzenamine (NCF) and (E)-N(2-Chlorobenzylidene)-3-Chloro-2-Methylbenzenamine (NCCM), by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The experimental results showed that both NCF and NCCM are good inhibitors for carbon steel in 1 M HCl. The inhibition efficiency increases with inhibitors concentration rise, reaching a value up to 89.72% at 10⁻³ M for the inhibitor NCF. Electrochemical impedance data show a frequency distribution of the capacitance, simulated as constant phase element (CPE). Polarization curves study revealed that both inhibitors are mixed type. The adsorption on the carbon steel surface follows Langmuir isotherm model with negative values of ΔGads0. Thermodynamics data for the adsorption process are calculated and discussed. The effect of molecular structure on inhibition efficiency was investigated by quantum chemical calculations using density function theory (DFT). Furthermore, Monte Carlo simulation technique incorporating molecular mechanics and molecular dynamic was applied to search for the best configurationally space for (NCCM or NCF)/100H2O/α-Fe2O3 (1 1 1) systems. The results indicate that the adsorption energy of NCF was greater than NCCM which is in accordance with the experimentally determined inhibition efficiency.
Zn-Al layered double hydroxide (LDH) nanoparticles with carbonate as the charge balancing anion in the interlayer space were synthesized using co-precipitation method. Then, the carbonate base Zn-Al LDH nanoparticles were doped with phosphate ion via anion-exchange reaction to synthesize Zn-Al-[PO4³⁻]-[CO3²⁻]. The structure and composition were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric-differential thermal analysis (TG-DTA). Inductively coupled plasma-optical emission spectrometer (ICP-OES) was employed to measure the phosphate release ability of Zn-Al-[PO4³⁻]-[CO3²⁻] in the 3.5 wt% NaCl solution. Results showed that zinc cation can release along with phosphate anion during ion exchange process. Then, the corrosion inhibition of phosphate anion and zinc cation on mild steel specimens was assessed by electrochemical impedance spectroscopy (EIS) and polarization. Field emission-scanning electron microscopy (FE-SEM) was used to study the surface morphology of the mild steel specimens after exposure to the test solutions. The results indicated the significant impact of zinc and phosphorus concentration in test solution on the corrosion inhibition properties.
The temperature-humidity-bias (THB) test is the standard for accelerated stress testing with respect to corrosion and other humidity driven degradation mechanisms. Usually, 1000 h tests at 85°C and 85% relative humidity are used to predict up to 25 years of operation. The bias is usually limited to 80 V in order to fulfil the respective standards. Nevertheless, THB tests on 1700 V insulated-gate bipolar transistor (IGBT)-modules have shown that higher bias is a more severe test condition. The failure analysis confirmed Cu- and Ag-dendrites and corrosion of the aluminium (Al)-chip-metallisation as the relevant failure mechanisms. To determine the acceleration factor due to voltage, 1200 V IGBT modules were tested in THB at 780 V (65% of VCES) and 1080 V (90% of VCES). A characteristic degradation consisting of three phases has been identified. The second phase seems to be determined by Al corrosion and an acceleration factor of about two has been estimated from 780 to 1080 V. Within the third phase, the devices stabilised probably due to localised self-heating. Thus, this degradation mechanism is kind of self-limiting, but the higher leakage also increases the risk of thermal runaway especially when biased close to the rated collector-emitter voltage.
Experimental cation exchange capacities (CEC) of kaolinites were determined and compared to theoretical calculations of CEC. The comparison reveals that the exchangeable cations occur mostly on the edges and on the basal (OH) surfaces of the mineral. It also shows that permanent negative charge from isomorphous substitution of Al3+ for Si4+ is insignificant. The CEC of kaolinite strongly depends on the particle size (both thickness and diameter in the (00l plane) and pH value. Particle size is more important than crystallinity in affecting kaolinite CEC. This study shows that they hydroxyls on the exposed basal surfaces may be ionizable in aqueous solutions. The amount of negative charge on the edges and the exposed basal hydroxyls depends on pH and other ion concentrations. A higher pH value gives rise to more negative charges, which lead to a higher CEC value. This study indicates that charge from broken edges and exposed OH planes rather than charge from Al/Si substitution determines the kaolinite CEC, even at zero point charge. A high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals.
We produced novel nanocellulose particles made from cellulose fibers by periodate oxidation. For partial oxidation [degree of substitution (DS) <2], three products were generated after the periodate oxidized fibers were heat treated: fibrous cellulose, rod-like dialdehyde cellulose (DAC) nanofibers which we refer to as sterically stabilized nanocrystalline cellulose (SNCC), and dissolved DAC which is a copolymer of cellulose and DAC which we refer to as dialdehyde modified cellulose (DAMC). The products were separated by centrifugation and cosolvent addition. SNCC has similar dimension (100–200 nm in length and 5–8 nm in width) as conventional nanocrystalline cellulose (NCC) made by sulfuric acid hydrolysis. Several techniques were applied to characterize SNCC and its properties are compared to NCC. DAMC was found to be soluble in hot water or a few solvents (such as dimethyl formamide and dimethyl acetamide) at elevated temperature, but was insoluble in most common solvents at room temperature. The molecular weight of DAC (DS = 2) produced under various conditions (heating time and temperature) was determined by gel permeation chromatography. It was shown that the molecular weight decreased from 85.1 to 4.1 kDa with heating time and residence time when cooled down to room temperature.
A simple and flexible method has been developed to fabricate reversibly switchable nanocontainers (by layer by layer assembly) using zinc phosphate (ZP) nanoparticles as a core material and subsequent deposition of oppositely charged species of polyelectrolyte (polyaniline and polyacrylic acid) and organic corrosion inhibitor (immidazole). Immidazole was entrapped between polyaniline (PANI) and polyacrylic acid (PAA). The PAA nanovalve can control the access of immidazole molecules to and from the nanocontainers. The average particle size of the synthesized nanocontainer was found to be in the range of 250–500 nm. X-ray diffraction (XRD), particle size analysis (PSA), zeta potential, and fourier transform infrared spectroscopy (FTIR) analysis confirms the successful formation of the layered structure of nanocontainers. UV-vis spectroscopy was used to analyze the release rate of immidazole in media of different pH as a function of time. This core-shell nanostructure can have potential applications in corrosion inhibition paint formulation.
Nonmetallic (based on polymers or oxides) and metallic protective coatings are used to protect metal products against the harmful action of the corrosion environment. In recent years, self-healing coatings have been the subject of increasing interest. The ability of such coatings to self-repair local damage caused by external factors is a major factor contributing to their attractiveness. Polymer layers, silica-organic layers, conversion layers, metallic layers and ceramic layers, to mention but a few, are used as self-healing coatings. This paper presents the main kinds of self-healing coatings and explains their self-healing mechanisms.
The present work focuses on the use of layered double hydroxides (LDH) as containers for corrosion inhibitors in an epoxy coating. 2-Benzothiazolylthio-succinic acid (BTSA), used as corrosion inhibitor, was intercalated by co-precipitation in magnesium–aluminum layered double hydroxides. The obtained LDH–BTSA was characterized by infrared spectroscopy, X-ray diffraction and scanning electron microscopy. BTSA release from LDH–BTSA in NaCl solutions was investigated by UV–vis spectroscopy. The inhibitive action of LDH–BTSA on carbon steel corrosion was characterized by electrochemical methods and the protective properties of an epoxy coating containing LDH–BTSA were evaluated by electrochemical impedance spectroscopy. It was shown that the BTSA was intercalated in the layered double hydroxide and its loading was about 33%. The BTSA release was dependent on the NaCl concentration in the electrolyte. The polarization curves obtained on the carbon steel sample showed that the LDH–BTSA is an anodic inhibitor. Its efficiency was about 90% at a concentration of 3 g/l. The impedance results showed that the incorporation of LDH–BTSA (3%) in the epoxy matrix improved the corrosion protection of the carbon steel.
The influence of polyacrylic acid (PAA) and a blend of polyacrylic add with hexafluorozirconic acid treatments on the performance of anepoxylpolyester powder coating on a 1050 Al substrate has been studied and compared to the performance of the same system using a so-called chromate/phosphate conversion coating. The chemical interactions between pretreatments and Al substrates were examined using FTIR spectroscopy and various accelerated test methods were also employed. Two mechanical adhesion measurement methods were used under wet and dry conditions, namely a vertical pull-off test in the dry state and the tape test under dry and wet conditions . The water permeation of the differently pretreated powder coated samples was studied using a capacitance measurement method. FTIR results showed two modes of interaction: namely ionic and complex formation between COO- and Ala+. Various experiments revealed that PAA improved only the dry adhesion but as a standing alone treatment it did not provide an overall improvement in anti-corrosive performance . The water uptake measurements proved that pre- treatment does not considerably affect the properties of the coatings during water permeation stage. The use of various techniques revealed that relative- ly good performance of the powder coating is due to a high ohmic resistance of the coating prior to and after saturation with water, reasonably low water solubility and good adhesion to the substrate.
Enviromentally friendly calcium-exchange derived from naturally occurring sodium-bentonite clays (Wyoming) are shown to significantly enhance resistance to corrosion protection in organic coatings applied on aluminium under aggressive environment typical from industrial areas. Two pigments classified as ion-exchange were also studied for comparison (Shieldex® and Al-Zn-vanadate hydrotalcite) together with zinc chromate as reference corrosion protection pigment. Electrochemical impedance spectroscopy (EIS) is used to study the corrosion protection in the metal/coating interface of pigmented alkyd coatings and a blank coating (without corrosion inhibitor pigment) in combination with visual inspection. The protection performance of these specimens was studied using outdoor exposure (two atmospheres with different aggressiveness) and accelerated tests (condensing humidity, salt spray and Kesternich tests, respectively). Results have shown strong dependence of the coating performance with the aggressive environment (e.g. Cl⁻, H⁺, SO2) for all coatings formulated with ion-exchange pigments. The corrosion protection of the underlying aluminium substrate provided by calcium-exchange bentonite coating was shown under the presence of cationic aggressive agents in accelerated corrosion tests (specifically in Kesternich test). However, poor performance was observed for this coating using chlorides as an aggressive agent. Therefore, the presence of bentonite pigment improves the corrosion protection due to the cation-exchange mechanism.
The aim of this research was to investigate the influence of temperature variation on the formation and protective behavior of calcium carbonate scale deposited on steel electrodes in artificial seawater. Chronoamperometry measurement, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and x-ray diffraction (XRD) were employed for analysis. An increase in temperature from 20 to 50 °C accelerated the oxygen reduction reaction, which increased the nucleation/deposition rate. The chronoamperometry, SEM and XRD results indicated that complete coverage of the electrode surface was achieved at higher temperatures because a denser layer of scale deposits covered the entire surface of the metal and acted as a barrier against the passage of oxygen. The EIS results showed that better corrosion protection was obtained after deposition that included a stepwise decrease in temperature, indicating fewer pathways through the deposited layer onto the electrode surface.
In this study, Na-montmorillonite (MMT) was intercalated with the cerium cations. The Ce3+ cations intercalated sodium montmorillonite (Ce-MMT) nanoreservoirs were incorporated into the epoxy coating. The active inhibitive performance of the synthesized nanoreservoirs and their effect on the protective behavior of the epoxy coating was investigated in the present study. For this purpose, field emission scanning electron microscopy, Fourier transformation infrared spectroscopy, inductively coupled plasma optical emission spectroscopy and Xray diffraction analyses were employed to characterize the synthesized nanoreservoirs. Characterization results showed that the Ce3+ cations successfully intercalated into the MMT structure. The active anti-corrosion performance of the Ce-MMT was proved by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential, and salt spray tests. In the electrolyte phase, the obtained results showed that the corrosion resistance of the steel samples significantly improved in the presence of the Ce-MMT extract and the observed corrosion efficiency was about 93%. Also, the results of surface study confirmed the subsequent effect of the active nanoreservoirs on the chemical composition and surface morphology of the steel samples. In the coating phase, the result of the EIS and salt spray tests confirmed the enhanced inhibitive behavior of the epoxy coating in the presence of the Ce-MMT nanoreservoirs.
In this work, the effect of Zn2+ cations on the calcareous scales during the cathodic protection of mild steel was studied. The Zn2+ cations were introduced into the epoxy and alkyd coatings in the form of zinc chloride. Also, the influence of Zn2+ cations was investigated in the zinc -rich primer coated mild steel. The study was conducted in the electrolyte and coating phases. In the first stage, pure calcareous scales deposited from artificial seawater (AS) were compared with zinc containing calcareous scales deposited from the zinc containing AS solution. For this purpose, scanning electron microscopy equipped with the energy dispersive spectroscopy and X-ray diffraction analyses were used to characterize the calcareous scales. Also, chronoamperometric, electrochemical impedance spectroscopy, and potentiostatic polarization were conducted to investigate the effect of Zn2+ cations on the calcareous scales. Results indicated that the Zn2+ cations have influenced the calcareous scales through altering calcareous deposited phases and phase proportions. Moreover, according to the electrochemical results, with increase in the Zn2+
cations concentration, an increase in calcareous scales inhibition was observed. In the coating phase, the effect of Zn2+ cations presented in the organic coatings and zinc-rich primer was studied. To evaluate this effect, the coated samples with an artificial defect were exposed to AS. Results showed that the presence of Zn2+ cations in the coatings led to a decrease in the brucite content of the scales and stabilization of the hydrated calcium carbonate phases over aragonite phases. Furthermore, presence of the Zn2+ cations in the form of zinc-rich primer leads to the brucite phase elimination in the calcareous scales.
The secondary metabolites of Solanum trilobatum-L was extracted from its leaves and their components were separated by column chromatography as Fraction-A and Fraction-B. The functional groups of the extracts were identified by FT-IR spectroscopy. The inhibition efficiency of the extract and its fractions were tested for mild steel in 1 M HCl and 3% NaCl by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. Plant extracts act as mixed type inhibitors in all experimental conditions, and Fraction-A has more inhibition efficiency (I.E) than crude extract and Fraction-B. The protective layer of adsorbed extract constituents were confirmed by morphological study. The surface coverage and time constant for adsorption of extract molecules were calculated using Rct and Cdl values.
Various Standard methods such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization study (PDS) and atomic force microscopy (AFM) have been utilized to study the corrosion characteristics of reinforcing steel in concrete in without and with various concentrations of Ricinus communis (R. communis) in NaCl media in different time intervals. The ability of the plant extract to produce protective layer on steel surface in concrete and mixed mode (anodic as well as cathodic) inhibitive action have been established from the findings of electrochemical measurements (EIS & PDS). Further, the formation of protective layer on the steel surface by plant extract has been supported by surface morphology analysis (AFM). The adsorption of R. communis extract on steel surface followed the Temkin adsorption isotherm. The results of density functional theory (DFT) analysis brought out the active centers of major ingredients responsible for adsorption of molecules present in R. communis over the steel surface that influenced the anti-corrosion potential of plant extract. The increase in compressive strength and splitting tensile strength of concrete has been observed. The inhibitive mechanism of the R. communis extract against reinforcing steel corrosion in concrete in 3.5% NaCl media has also been proposed.
We reported the preparation of epoxy coatings incorporated with a composite filler of poly(styrenesulfonate)-polyaniline/reduced graphene oxide (PSS-PANI/rGO) and their performance on the mechanical and anticorrosion properties. The rGO platelets were first dispersed in the PSS solution, followed by in situ oxidative polymerization of aniline. The resulting PSS-PANI/rGO composite was then blended with a bisphenol-A type epoxy at different loadings by tri-roller mill, and was subsequently cured with a curing agent. The ultimate tensile strength and tensile toughness of the epoxy composite at a loading of only 0.5 wt% PSS-PANI/rGO were improved by 39% and 127%, respectively, when compared to the respective values of the pristine epoxy. This was ascribed to their strong interfacial bonding upon curing by the reaction between the PANI and epoxy. Furthermore, the potentiodynamic polarization of the carbon steels coated with the epoxy/PSS-PANI/rGO composite revealed that the anticorrosion performance was greatly improved when compared to those with the neat epoxy and epoxy/rGO coatings. The superior anticorrosion effect was attributed to its larger tortuosity of diffusion pathways, improved interfacial strength between the epoxy and filler, and the passivation layer formed by the presence of polyaniline which was confirmed by X-ray photoelectron spectroscopy. The improved anticorrosion and toughness would allow the coatings to withstand externally mechanical impact and prevent corrosion effectively.
The recent shortage of fossil fuel sources and the growing environmental concerns have considerably affected the necessity to search for alternative energy sources. The tremendous increase in energy demands in the transportation and industrial sectors has strengthened efforts to identify sustainable alternative fuel sources. In this regard, biodiesel can be considered a promising substitute for diesel. However, biodiesel is corrosive when it comes in contact with metals. The present study aims at investigating the sustainability of additive-doped biodiesel upon exposure of copper-based materials. A static immersion test was conducted at room temperature (25 °C–27 °C) for 2160 h. The metals used in the experiment were copper, leaded bronze, and phosphorous bronze. The investigated fuel was 100% palm biodiesel without and with additives (500 ppm), including tert-butylamine, benzotriazole, propyl gallate, pyrogallol, and butylated hydroxytoluene. The corrosion rate of the metals was determined at the end of the experiment via weight loss measurement. The metals were further characterized via scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction analysis. Results showed that the corrosion rate of copper was considerably higher than those of the other metals. X-ray diffraction analysis indicated the presence of copper carbonate and cupric oxide on the copper surface that was exposed to biodiesel. The occurrence of these compounds could be attributed to the high concentrations of carbon dioxide and oxygen in the biodiesel when additive was absent. Gas chromatography–mass spectrometry data showed that the unsaturated molecules in biodiesel could reduce the sustainability of metals upon exposure to biodiesel. However, metal surface degradation was significantly reduced in the presence of additives. In particular, benzotriazole and tert-butylamine considerably improved the sustainability of biodiesel by limiting metal surface degradation.
Titanium dioxide-decorated graphene oxide nanocomposite (TiO2-GO) was synthesized with the help of 3-aminopropyltriethoxysilane (APS) and characterized by Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results revealed that TiO2 was decorated to GO by chemical bonds. Then TiO2-GO nanocomposite was modified with γ- (2,3-epoxypropoxy) propyltrimethoxysilane (GPTMS) before introducing into epoxy resin to form an epoxy coating (TiO2-GO-f-EP) on AA-2024 aluminum alloy for good anticorrosion properties. The scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, salty spray and UV aging measurements were carried out to confirm that the TiO2-GO-f-EP coating exhibited good anti-corrosion performance. The corrosion current density of TiO2-GO-f-EP coating was nearly two orders of magnitude lower than that of pure epoxy coating and the adhesion loss after UV aging test changed 86%–57%, compared with pure epoxy coating. The superiority of TiO2-GO-f-EP coating is related to the TiO2-GO addition which can enhance anti-UV aging performance of the epoxy coating and the GPTMS modification that may ensure TiO2-GO nanocomposite's good dispersion into epoxy resin and improve the cross-linking density and adhesion strength of the epoxy coating.
This study reports an eco-friendly water-borne epoxy (EP) with enhanced corrosion protection performance by embedding graphene oxide (GO). For this purpose, the dispersion of the GO in ethanol is improved by modifying the GO nanosheets with hydrophilic dopamine (DA), owing to the π-π interactions between the GO and self-polymerized polydopamine (PDA) as well as the covalent bonding between DA and GO. Results obtained from transmittance electron microscopy (TEM), scanning probe microscopy (SPM) Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, UV–vis absorbance spectroscopy and X-ray photoelectron spectroscopy (XPS) reveal the successful modification of PDA on the surface of GO nanosheets. Besides, the GO/EP and GO-PDA/EP coatings are applied on the steel substrates and their corrosion protection performance is investigated via electrochemical measurements, scanning electron microscopy (SEM) and scanning vibration electrochemical technology (SVET). Results demonstrate that inclusion of well-dispersed GO-PDA nanosheets leads to the remarkable improvement in the corrosion protection performance of water-borne EP coating.
This work aims at revealing the key factors that limit the cleaner production level of a pickling process. By comparing the difference in their characteristics and the corrosion behaviors in an acidic medium, three kinds of sample, including the matrix steel (AS), the naturally-corroded carbon steel (NR) and the carbon steel treated under high temperature oxidation (OR), after immersed in the experimental solutions with or without hexamethylenetetramine (HA), were characterized with the methods, such as, electrochemical polarization, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated, no matter which kind of rust layers, the adsorption of HA on their surface all accorded with the same adsorption isotherm. Although the rust layers did not change the adsorption pattern of HA directly, but their steric effect would influence the adsorption potential of HA; the forming process of rust layers (under different environmental conditions) heavily influenced their composition, structure, and the interface roughness between the rust layer and the metal matrix, and also influenced the corrosion behavior of samples in an acidic medium, which were the key factors that limited the cleaner production level of a pickling process. These results indicated that an object-oriented pickling strategy should be adopted for a practical pickling process.
Low-cost, environmentally friendly, cation exchange pigments derived from naturally occurring bentonite clay are shown to significantly enhance resistance to corrosion-driven cathodic delamination in organic coatings adherent to iron surfaces. A scanning Kelvin probe (SKP) is used to study the delamination kinetics of pigmented and unpigmented poly-vinyl-butyral (PVB)-based coatings applied to polished iron substrates. The bentonite clay is used both in its native form and exhaustively exchanged with a range of divalent alkali earth and trivalent rare earth metal cations. For the best performing divalent cation-exchanged pigment, the dependence of coating delamination rate on pigment volume fraction is determined and compared with that of a conventional strontium chromate (SrCrO4) inhibitor. An inhibition mechanism is proposed for the bentonite pigments whereby underfilm cation release and subsequent precipitation of sparingly soluble hydroxides reduces the conductivity of the underfilm electrolyte.
An epoxy organic coating containing zinc aluminum polyphosphate (ZAPP) pigments with and without a hexafluorozirconic acid based conversion coating (ZrCC) pretreatment was applied on carbon mild steel (St 37) in order to investigate the corrosion resistance behavior and adhesion of the coating to substrate. Optimization of pigment volume concentration (PVC) and conversion coating application conditions was carried out and also the interaction of organic and conversion coating was studied using electrochemical impedance spectroscopy (EIS), salt spray and pull-off adhesion tests. Appropriate anti-corrosion properties was gained from organic coating samples with PVC = 30% and conversion coating applied from a solution with pH and acid concentration of 4.5 and 0.01 M, respectively. Results indicated that using conversion coating as a pretreatment before applying organic coating, improves adhesion of the coating to the substrate (by 1–2 MPa) and also provides an effective corrosion protection in long periods of immersion time. The highest corrosion resistance was obtained for pigmented organic coating sample with Zr conversion coating pretreatment after 4 weeks of immersion in NaCl 3.5 wt.%. Field emission scanning electron microscope and energy dispersive X-ray spectroscopy (FE-SEM/EDS) also proved the presence of about 5 wt.% of zirconium at the interface of coating and substrate not only at the onset of immersion but also after 4 weeks of immersion time. Results taken from this research, can clarify the key role of surface modification at interface of coating and substrate in adhesion and also the retention of anti-corrosion properties over the course of time even for an anti-corrosion pigment reinforced organic coating sample.
A protective coating was produced by dispersing mesoporous silica nanocontainers, loaded with sodium molybdate, as corrosion inhibitor, in an epoxy layer. The corrosion properties of the composite coatings were assessed by electrochemical impedance spectroscopy. Results showed remarkable corrosion resistance of epoxy/mesoporous silica loaded with corrosion inhibitor (epoxy/MSInh) and self-healing ability of coating in the chloride medium during eight weeks of immersion. Epoxy/MSInh had the greatest Rct values for all immersion times, which could be attributed to the release of molybdate ion from the nanocontainers as well as barrier resistance of these inorganic mesoporous silica particles. This value at the first day of immersion in the chloride medium was 318.4 kΩ cm2, while it was 71.3 and 23.5 kΩ cm2 for epoxy and epoxy/mesoporous silica (epoxy/MS), respectively. Rct for epoxy, epoxy/MS, and epoxy/MSInh after the last day of immersion (56 day) was determined as 10.1, 15.9, and 24.4 kΩ cm2, respectively. Corrosion inhibitors were released from nanocontainers in response to corrosion damage in the scratched zone. Besides, the analytical investigation showed the oxidation state of Mo was (Mo (VI)), which could be attributed to the formation of Fe2(MoO4)3 or molybdenum oxides.
Experimental cation exchange capacities (CEC) of kaolinites were determined and compared to theoretical calculations of CEC. The comparison reveals that the exchangeable cations occur mostly on the edges and on the basal (OH) surfaces of the mineral. It also shows that permanent negative charge from isomorphous substitution of AP + for Si 4+ is insignificant. The CEC of kaolinite strongly depends on the particle size (both thickness and diameter in the (00l plane) and pH value. Particle size is more important than crystallinity in affecting kaolinite CEC. This study shows that the hydroxyls on the exposed basal surfaces may be ionizable in aqueous solutions. The amount of negative charge on the edges and the exposed basal hydroxyls depends on pH and other ion concentrations. A higher pH value gives rise to more negative charges, which lead to a higher CEC value. This study indicates that charge from broken edges and exposed OH planes rather than charge from A1/Si substitution determines the kaolinite CEC, even at zero point charge. A high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals.
Mesoporous silica nanocontainer powders were applied as corrosion inhibitor hosts and dispersed in the polypyrrole matrix. Then, the release and corrosion resistance of these composite coatings were studied with and without inhibitor in NaCl solution. Results showed that in higher pHs and more aggressive chloride media, the release content of corrosion inhibitor is higher. OCP, ICP, XRD, EIS, and FTIR results showed that the substrates were better protected in the presence of released corrosion inhibitor from mesoporous silica compared to the coatings without inhibitor. Then, the corrosion inhibitor reacted with substrate and made a protective phase during corrosion.
Purpose
Kaolin is a soft white mineral which has a large array of uses. It is most commonly referred to as “China clay”. Sources of this mineral can be found all over the world, its uses are multiple and diverse. It is a mineral belonging to the group of alumino‐silicates with the chemical composition Al2Si2O5(OH)4. It is white, soft, plastic clay mainly composed of plate‐like particles. It is a unique industrial mineral, which remains chemically inert over a relatively wide pH range. The purpose of this paper is to study the difference in performances of untreated or natural kaolin, thermally treated kaolin or so‐called “calcined kaolin” and chemically treated kaolin using ammonium molybdate to convert the γ‐Al2O3 naturally found in kaolin to α‐Al2O3 which possesses one of the most known stable crystalline phases (corundum) in alkyd based anticorrosive paint formulations used for protection of steel.
Design/methodology/approach
The different kaolins were characterized using different analytical and spectro‐photometric techniques. The pigments were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Evaluation of these pigments using international standard testing methods (ASTM) was estimated. The extender pigments were then incorporated in solvent‐based paint formulations based on medium oil‐modified soya‐bean dehydrated castor oil alkyd resin. The physico‐mechanical properties of dry films and their corrosion properties using accelerated laboratory test in 3.5% NaCl for 28 days were tested.
Findings
The results of this work revealed that calcined kaolin was better in its performance in protection of steel than kaolin, while chemically treated kaolin varied in its performance according to the concentration of modifier or dopant.
Practical implications
Kaolin has a large array of uses. These pigments can be applied in other polymer composites, e.g. rubber and plastics as reinforcing agent.
Originality/value
The untreated and treated kaolins are environmentally friendly pigments which can impart high anticorrosive behaviour to paint films with concomitant cost saving.
A wide variety of inhibitive pigments is now being offered as possible alternatives to chromate and lead compounds for painted metals protection. Unfortunately, the most wide spread of these substitute pigments, zinc phosphate, has, at present, raised some environmental concern because phosphate causes the eutrophication of water courses and zinc itself is toxic. The aim of this research was to study the anticorrosive performance of a mixture consisting of zinc phosphate, modified zeolite and clay (bentonite) in order to diminish phosphate content in paints. The zeolite and the clay were exchanged with La(III) ions, as inorganic green inhibitor. In the first step, the anticorrosion protection by La(III) ions in solution was assessed by electrochemical tests. In the second step, an epoxy-polyamide paint formulated with the pigment mixture applied on galvanized panels was studied by salt spray test and electrochemical noise measurements (ENM). The results showed that it was possible to replace part of the zinc phosphate content in the paint with the exchanged zeolite and the clay.
Nanocomposite coatings which were applied on carbon steel panels based on epoxy cerium nitrate–montmorillonite (MMT) were synthesized and formulated. Nanoparticles were incorporated into epoxy resin by mechanical and sonication processes. The state of dispersion, dissolution, and incorporation were characterized by optical microscopy, sedimentation tests, X-ray diffraction, and transmission electron microscopy. To investigate anticorrosive properties of nanocomposite coatings, electrochemical impedance spectroscopy and salt spray tests were employed. The experimental results showed that epoxy cerium nitrate–MMT nanocomposite coatings were superior to the neat epoxy in corrosion protection effects. In addition, it was observed that the corrosion protection of nanocomposite coatings was improved as the clay loading was increased up to 4–2 wt% cerium nitrate.
Direct applicaion of a “modified” Scherrer equation, B = Kλ/D cos θ, is made in the determination of the mechanical thickness of thin highly oriented gold films. A relationship between the measured width at half intensity, B, of the observed x-ray diffraction profile, and the linear crystallite dimension, D (in this case the film thickness), is utilized. The constant K was evaluated experimentally to be 0.9118 from a series of gold films under 600 Å in thickness. From a rederivation of the equation, a value of K equal to 0.8859 is adopted for use in this study. The value obtained by Scherrer in the original formulation was 0.9394.Accuracy of this method is dependent on the success in measuring the actual width, at half intensity, of a diffraction peak obtaiend from the gold thin film. Broadening of the observed Au(111) peak profiles, used in the analysis, were found to be appreciable relative to bulk gold sample profiles. An empirical instrumental broadening correction was applied to the data to obtain improved results. Calculated film thicknesses were compared to those obtained by flame atomic absorption analysis and transmission/reflection visible spectroscopy and were found to be in good agreement. Results from a series of gold film thickness determinations is given, and a description of the methodology is provided regarding determinations of metal film thicknesses in the 100–500 Å range.
Strength and toughness are commonly two contradictory properties in polymer materials. For polymer elastomers, the addition of stiff filler frequently results in enhanced stiffness but reduced toughness and ductility. Inspired by biomimetic studies, here we demonstrate a new method that can simultaneously improve strength and toughness while maintaining the good ductility of polyurethane elastomers. This method constructs sacrificial bonds and hidden lengths at the interface of graphene nanosheet/polyurethane (GN/PU) composites by exploiting covalently and non-covalently functionalized GNs (HO-GNs). GNs are prepared by reduction of graphene oxide with hydrazine. The residual functional groups such as hydroxyl and epoxide groups on GNs enable PU oligomer chains to be covalently bonded to GNs by sequentially reacting with diisocyanate and polyethylene glycol oligomer. Non-covalently bonded PU oligomer chains are formed by the π–π interaction between GNs and pyrene derivatives. Both Fourier transform infrared spectra and thermogravimetric results provide direct evidence for the covalent bonding in HO-GNs while fluorescence spectra and decay curves confirm the existence of non-covalent bonding. The resulting HO-GNs exhibit a good dispersion capacity in organic solvents and the PU matrix, improving the load transfer and the particle mobility in GN/PU composites. Upon loading, both rupture of the π–π interaction (sacrificial bonds) and release of the hidden length (dissociation of H-bonds between the PU oligomer and polymer chains) enable the composite to exhibit high toughness and ductility nearly identical to the neat polyurethane (strain at break >900%). This approach is expected to be helpful for developing novel strong, tough and highly ductile polymer elastomers.
In order to obtain homogeneous dispersion and strong filler-matrix interface in epoxy resin, graphene oxide was functionalized via surface modification by hexachlorocyclotriphosphazene and glycidol and then incorporated into epoxy resin to obtain nanocomposites via in situ thermal polymerization. The morphology of nanocomposites was characterized by scanning electron microscopy and transmission electron microscopy, implying good dispersion of graphene nano-sheets. The incorporation of functionalized graphene oxide effectively enhanced various property performances of epoxy nanocomposites. The storage modulus of the epoxy nanocomposites was significantly increased by 113% (2% addition) and the hardness was improved by 38% (4% addition). Electrical conductivity was improved by 6.5 orders of magnitude. Enhanced thermal stability was also achieved. This work demonstrates a cost-effective approach to construct a flexible interphase structure, strong interfacial interaction and good dispersion of functionalized graphene in epoxy nanocomposites through a local epoxy-rich environment around graphene oxide sheets, which reinforces the polymer properties and indicates further application in research and industrial areas.
The exquisite structure of natural materials manifests the importance of particle mobility and load transfer in developing advanced polymer nanocomposites; however, it is difficult to concurrently meet these two mutually exclusive requirements. To address this issue, we demonstrate an approach that constructs a hierarchical, flexible interphase structure in epoxy nanocomposites through a local amine-rich environment around graphene sheets (GNs) and volume exclusion effect of grafting chains. Long-chain aromatic amines, which are chemically similar to the curing agent, are covalently bonded on the surface of GNs by diazonium addition. They play multifold roles in the structure formation of epoxy composites, (1) promoting the exfoliation and molecular level dispersion of GNs in the matrix, (2) serving as a linker between GNs and epoxy networks for improved load transfer, (3) modulating the stoichiometric ratio around GNs to construct a hierarchical structure that can dissipate more strain energy during fracture. With the addition of 0.6 wt% amine-functionalized GNs, the resulting composite exhibits significant mechanical improvements, 93.8 and 91.5% increases in fracture toughness and flexural strength, respectively. This approach affords a novel design strategy for developing high-performance structural composites.
Mg–Al layered double hydroxides, loaded with tungstate anions, were synthesized via the co-precipitation method. The obtained compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma (ICP), and transmission electron microscopy (TEM), respectively. The ICP results demonstrated the partial anion-exchange process, involving the release of tungstate anions from layered double hydroxide by the chloride anions. Polarization measurements showed that the filtrate as electrolyte possessed a low corrosion current density value of 3.042μA/cm2. The electrochemical impedance spectroscopy (EIS) exhibited that the coating could effectively protect the alloy from corrosion. The function of the layered double hydroxide loaded with tungstate doped in organic coating was also discussed.
The concepts of cation and anion exchange capacity, as applied to kaolinite, are critically examined. By attention to experimental detail it was possible to obtain reproducible measurements of ion uptake. Contrary to classical ideas the new data show no evidence for any definite cation exchange capacity. The cation uptake depends upon the cation chosen, the electrolyte concentration and pH, and on whether the experiment is done from aqueous or 95%-ethanol solvent. Apparent “capacities” as high as 25 μequiv/g of kaolinite were obtained with Ca2+ and Cs+ from the nonaqueous solvent and as low as 12 μequiv/g of kaolinite with Li+ from aqueous solutions. The data suggest complex ion exchange reactions on heterogeneous -SiOH and -A1OH sites. They do not support the simple model of isomorphous substitution charge plus basic edge sites so often assumed in the past.
We investigated the effect of silica nanoparticles on the mechanical property and fracture toughness of two epoxy systems cured by Jeffamine D230 (denoted J230) and 4,4′-diaminodiphenyl sulfone (denoted DDS), respectively. Toughening mechanisms were identified by a tailor-loaded compact tension method which quantitatively recorded the deformation of a damage zone in the vicinity of a sub-critically propagated sharp crack tip. 20wt% silica nanoparticles' fraction provided 40% improvement in Young's modulus for both systems; it improved the toughness of J230-cured epoxy from 0.73 to 1.68MPam1/2, and for the other system improved from 0.51 to 0.82MPam1/2. The nanoparticles not only stiffen, strengthen and toughen epoxy, but reduce the effect of flaws on mechanical performance as well. In both systems, nanosilica particle deformation, internal cavitation and interface debonding were not found, different to previous reports. This could be due to the various hardeners used or different identification techniques employed. The toughening mechanisms of the J230-cured nanocomposite were attributed to the formation and development of a thin dilatation zone and nanovoids, both of which were induced, constrained and thwarted by the stress fields of the silica nanoparticles. Regarding 10wt% silica-toughen epoxy cured by J230, a thicker and shorter dilatation zone was found, where neither nanoparticles nor nanovoids were observed. With regard to the DDS-cured system, much less dilatation and voids were found due to the hardener used, leading to moderately improved toughness.
A new thiomorpholine-functionalized nanoporous mesopore Mobil Composition of Matter No. 41 (MCM-41), abbreviated as TMMCM-41,
was synthesized and applied as a sensing material in construction of a cadmium carbon paste electrode. The electrode composition
of 20.1%wt TMMCM-41, 54.0% graphite powder, 25.9% paraffin oil showed the stable potential response to Cd2+ ions with the Nernstian slope of 28.6 mV decade−1 (±1.8 mV decade−1) over a wide linear concentration range of 10−6 to 10−2 mol L−1 with a detection limit of 6 × 10−7 mol L−1. The electrode has fast response time and long-term stability (more than 4 months). The proposed electrode was used to determine
the concentration of cadmium in tap water contaminated by this metal and cadmium electroplating waste water samples.
Development of a new generation of multifunctional coatings, which will possess not only passive functionality but also active and rapid feedback activity in response to changes in the local environment, is a key technology for fabrication of future high-tech products and functional surfaces. These new multifunctional coatings should combine passive components inherited from “classical” coatings (barrier layers) and active components, which provide fast responses of the coating properties to changes occurring either in the passive matrix of multifunctional coatings (e.g., cracks, local pH change) or in the local environment surrounding the coating (temperature, humidity). The coatings should also have several functionalities (e.g., antifriction, antifungal, and anticorrosion) exhibiting synergistic effects.
Two types of nanosilica (NS) particles with different average particle sizes (20nm and 80nm in diameter, respectively) were used to fabricate epoxy–silica nanocomposites (ESNs) in this study. No significant differences in fracture behavior were observed between the epoxies filled with 20nm NS particles and the epoxies filled with 80nm NS particles. Interestingly, both types of NS particles were found to be more efficient in toughening epoxies than micron size glass spheres. As with micron size glass spheres, the fracture toughness of the ESNs were affected by the crosslink density of the epoxy matrix, i.e. a lower crosslinked matrix resulted in a tougher ESN. The increases in toughness in both types of ESNs were attributed to a zone shielding mechanism involving matrix plastic deformation. Moreover, the use of Irwin's formalized plastic zone model precisely described the relationship between the fracture toughness, yield strength and the corresponding plastic zone size of the various ESNs examined.
We report the development of silica/polymer double-walled hybrid nanotubes, which consist of a hollow cavity, a porous silica inner wall, and a stimuli-responsive (pH, temperature, and redox) polymeric outer wall, as a novel nanocontainer system. The length, diameter, wall thickness, and aspect ratio of the hybrid nanotubes are precisely controlled in the range of 48-506 nm, 41-68 nm, 3-24 nm, and 1.2-7.6, respectively. The hybrid nanotubes loaded with active molecules exhibit morphology-dependent release and pH-, temperature-, redox-responsive release, which enable a wide range of applications from energy storage to drug delivery and self-healing coatings for metal corrosion protection.
Abstract This study fabricates Amine (NH2)-functionalized graphene oxide (GO)/polyimide(PI) composite films with high performance using in-situ polymerization. Linear poly(oxyalkylene)amines with two different molecular weights 400 and 2000 (D400 and D2000) have been grafted onto the GO surfaces, forming two types of NH2-functionalized GO (D400-GO/D2000-GO). NH2-functionalized GO, especially D400-GO, demonstrated better reinforcing efficiency in mechanical and thermal properties. The observed property enhancement are due to large aspect ratio of GO sheets, the uniform dispersion of the GO within the PI matrix, and strong interfacial adhesion due to the chemical bonding between GO and the polymeric matrix. The Young's modulus of the composite films with 0.3 wt% D400-GO loading is 7.4 times greater than that of neat PI, and tensile strength is 240% higher than as of neat PI. Compared to neat PI, 0.3 wt% D400-GO/PI film exhibits approximately 23.96 °C increase in glass transition temperature (Tg). The coefficients of thermal expansion below Tg is significantly decreased from 102.6 μm/°C (neat PI) to 53.81 μm/°C (decreasing 48% ) for the D400-GO/PI composites with low D400-GO content (0.1 wt%).This work not only provides a method to develop the GO-based polyimide composites with superior performances, but also conceptually provides a chance to modulate the interfacial interaction between GO and the polymer through designing the chain length of grafting molecules on NH2-functionalized GO.