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Nanoparticle generation by intensified solution crystallization using cold plasma
... Therefore, recent research works have focused on the effects of nano-scale particle size on sensitivity. A recrystallization process based on the rapid expansion of supercritical solutions (RESS) was developed [11], nanosized crystals of RDX were produced using cold plasma [12], and a technique based on bead milling was also established [13]. ...
The outstanding sensitivity of high-energetic materials such as cyclotrimethylenetrinitramine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) has prompted efforts by researchers in the production of less sensitive explosives by crystallization without compromising performance. One such endeavor is crystal-size reduction to nano-scales. The optimum operating conditions for producing nano-sized RDX were experimentally determined. Based on these results, computational fluid dynamics modeling and simulations were executed for scale-up purposes and identification of the influence of fluid dynamics, mixing, and heat transfer on crystal growth and production rate on commercial scales. As a result, a commercial plant was designed and operation data from the commercial crystallizers were compared with data obtained from scale-up tasks.
Aluminum particles (Al) inherently contain a natural oxide (Al2O3) coating that limits rates of diffusion-controlled energy release and can prevent complete conversion of the chemical energy available within an Al particle. Therefore, altering Al surface properties to reduce the oxide shell and/or transform shell chemistry are active areas of research. This study used atmospheric pressure plasmas to reduce the aluminum oxide shell, then examined the resulting changes in reactivity. Two plasma gas discharges were compared: argon (Ar) and helium (He). All plasma-treated particles were characterized using Powder X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). Results show Ar plasma treatment resulted in high concentrations of surface hydration, while He plasma treatment did not. Both plasma-treated Al particles show reduced oxidation barriers that result in increased reaction rate constants by an order of magnitude for oxidation reactions. The results further an understanding of the effects of surface modifications on reaction kinetics and energy release behavior of fuel particles.
Concomitant crystallization leads to process intensification through the synergistic combination of the partial processes of particle formation and encapsulation within a single process step. Both cooling and electrospray crystallization in multi-component solutions were used to create (sub-)micron sized particles of different crystalline materials. Concentrations were varied to control core and shell material. Depending on the relative initial concentrations used, concomitant electrospray crystallization of isonicotinamide and caffeine lead to encapsulated particles. Only limited encapsulation was achieved during concomitant cooling crystallization. Concomitant cooling crystallization of cyclotrimethylenetrinitramine (RDX) - 2,4,6-trinitrotoluene (TNT) resulted in separate RDX and TNT particles. Using electrospray crystallization, spherical nano-particles were produced, for which the component distribution within the particles could not be determined. Whereas crystallization from bulk solvent starts with a nucleus that grows gradually outward, whereby heterogeneous growth of a coating material on this core particle is not guaranteed, it appears that crystallization from evaporating solvent droplets starts at the surface of the droplets, and moves gradually inward. The resulting RDX-TNT powders have been tested for impact and friction sensitivity. The impact sensitivity has decreased compared to the raw materials, the friction sensitivity did not change.
Flexible carbon fiber fabrics of 1.7 μm diameter fiber were prepared by electrospray deposition (ESD) from phenolic resin/poly(vinyl butyral) and successive curing and carbonization. In the present study, phenolic resin (thermostable 3-dimensional cross-linked polymer) was used for ESD and successive carbonization. The bead-free fiber was obtained by ESD from a phenolic resin solution with concentration above 55 wt %. The as-deposited fabrics, however, were very brittle. The addition of poly (vinyl butyral) (Mw=110,000) improved the dimensional stability of the as-deposited fabrics. After carbonization of the as-deposited fabrics, the flexible carbon fiber fabrics were obtained. The carbon fiber fabrics showed relatively high electrical conductivity and a large specific surface area (BET surface area = 495 m2/g). This indicates that the flexible carbon fiber fabrics are applicable not only for adsorbent and composite materials but also for materials for electronic device use.
Dielectric-barrier discharges (silent discharges) combine the ease of atmospheric pressure operation with nonequilibrium plasma conditions suited for many plasma chemical processes. In most gases at this pressure the discharge consists of a large number of randomly distributed short-lived microdischarges. Their properties are discussed in detail. Traditionally mainly used for industrial ozone production, dielectric-barrier discharges have found addi- tional large volume applications in surface treatment, high-power CO2 lasers, excimer ultraviolet lamps, pollution control and, most recently, also in large-area flat plasma display panels. Future applications may include their use in greenhouse gas control technologies. Historical aspects, properties and applications of dielectric-barrier discharges are discussed.
This article attempts to give an overview of atmospheric plasma sources and their applications. The aim is to introduce, in a first part, the main scientific background concerning plasmas as well as the different atmospheric plasma sources (description, working principle). The second part focuses on the various applications of the atmospheric plasma technologies, mainly in the field of surface treatments.Thus this paper is meant for a broad audience: non-plasma-specialized readers will find basic information for an introduction to plasmas whereas plasma spectroscopists who are familiar with analytical plasmas may be interested in the synthesis of the different applications of the atmospheric pressure plasma sources.
The objective of this study was to explore the correlation among urbanisation, climate change and human health. Temporal variation of the prevalence of communicable diseases and the meteorological parameters were analysed, and relations among communicable diseases, meteorological parameters and socio-economic statistical data are discussed based on correlation analysis and stepwise regression. The results showed that both socio-economic development and regional climate change have effects on the prevalence of communicable diseases. Prevalence of blood-borne diseases and sexually transmitted diseases in Xiamen significantly increased during the 1990s. On the other hand, the prevalence of respiratory infectious diseases and gastrointestinal infectious diseases showed a decreasing trend with economic development. Climate has changed in the past 50 years, and particularly so in the last 30 years. The prevalence of gastrointestinal infectious diseases is linked to variation of annual average temperature and relative humidity. Annual average temperature, maximum temperature, minimum temperature and precipitation could be important determinants of the prevalence of insect-borne diseases.
Based on experimental results, numerical investigations of dielectric barrier discharges (DBDs) have been performed in three basic configurations: in the volume, coplanar and surface discharge arrangements. It is shown that the DBD dynamics is the same in all arrangements and it is determined by the development of a few principal constituents, i.e. cathode- and anode-directed streamers, discharge channel, cathode layer and surface charges. It is found that the anode- and cathode-directed streamers appear with a highly conductive channel in between. The interaction of the streamers with conductive and dielectric surfaces determines the filamentary or homogeneous appearance of the discharge and its properties. The cathode-directed streamer is a self-sustaining phenomenon, which moves in a gas gap or along an electrode driven by a positive loop-back between photoemission and electron multiplication. The anode-directed streamer plays a subsidiary role. Depending on the kind of gas (electronegative or electropositive) and/or the degree of development of the cathode-directed streamer, the field strength in the conductive channels changes significantly. When the cathode-directed streamer touches the electrode surface, a cathode layer appears with parameters close to those of normal glow discharges. In volume discharge arrangements the movement of the streamers results in the appearance of Lichtenberg figures on dielectric surfaces.
Nano- and submicron-sized crystals are too small to contain inclusions and are, therefore, expected to have a higher internal quality compared to conventionally sized particles (several tens to hundreds of microns). Using electrospray crystallization, nano- and submicron-sized crystals can be easily produced. With the aid of electrospray crystallization, a mist of ultrafine solution droplets is generated and subsequent solvent evaporation leads to crystallization of submicron-sized crystals. Using cyclotrimethylene trinitramine (RDX) solutions in acetone, the conditions for a stable and continuous jet were established. At relatively small nozzle diameters and relatively low potential differences, hollow spheres of RDX crystals were observed. At a higher nozzle diameter and potential difference and in the region of a continuous jet, RDX crystals with an average size of around 400 nm could be produced. In order to test the quality of the submicron-sized energetic material, impact and friction sensitivity tests were carried out. The test results indicate that the submicron-sized product had reduced friction sensitivity, indicating a higher internal quality of the crystalline product.
Recent advances in nanotechnology offer nano sized or nanostructured pharmaceutical particles, being as small as the size of cells such as receptors or nucleic acids, which can be engineered to pro-vide enhanced efficacy, solubility, or biocompatibility, and to administer at much lower dosages. However, industrial production of these particles is still challenging. Among different techniques, aerosol based ones might be favorable since they are considered as contamination free processes and do not interfere with complex molecules of drugs. We, in this review, consider liquid atomiza-tion, where droplet formation is followed by conversion into solid particles. The best candidate is a method, which not only produces mono sized droplets with a diameter smaller than the inside nozzle diameter but also generates small enough start up sizes. Such a method is found in: Electro-Hydrody-namic Atomization (EHDA) or Electrospraying. Electrospraying is now a well practiced technique for producing very fine monodisperse droplets from a liquid under the influence of electrical forces. By controlling the liquid flow rate and the electrostatic potential between the liquid and the counter electrode, droplets within a narrow size range can be generated, while the mean diameter ranges from nanometers up to several micrometers. Besides generating monodisperse droplets, electrosprays are also distinguished by their self dispersing nature due to Coulomb repulsion, the possibility of tra-jectory control of the produced charged droplets, and the reduced risk of nozzle clogging due to the large size of the orifice compared to the size of the droplets. We will discuss different spraying modes depending on the strength of the electric stresses relative to the surface tension stress on the liquid surface and on the inertia of the liquid leaving the nozzle. However, for the production of monodis-perse nanoparticles the so called cone-jet mode will be explained in depth. Scaling laws can be used to estimate the operational conditions for producing nanodroplets of a certain size. Hartman and co-workers refined the scaling laws for EHDA in the Cone-Jet mode using theoretically derived models for the cone, jet, and droplet size. By means of several examples, a generic way to produce nanopar-ticles, via scaling laws, from a multitude of different precursors will be discussed. Several examples of medicine particles with different properties made by EHDA will be given. Processes based on bipolar coagulation, where oppositely charged carrier particles and nano sized active agents are brought together to form composite drugs, will be discussed. Finally some attention will be given to challenges on out-scaling of EHDA methods for industrial production.
The measurements of electro-optical discharge characteristics and concentration of produced ozone were performed to evaluate
the efficiency of ozone production in an AC surface dielectric barrier discharge (SDBD) in pure oxygen at atmospheric pressure.
The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1kHz, variable discharge duty cycle
of 0.01–0.8 and oxygen flow rate of 2.5–10 slm. We observed asymmetric SDBD behaviour as evidenced by the variation in the
ratio of the OI/O2
+ emission intensities registered during the positive/negative half-periods and complemented by the transferred charge measurements
through the Lissajous figures. We also found a strong dependence of O3 concentration on the discharge duty cycle. The highest calculated ozone production yield reached 170g/kWh with a corresponding
energy cost of about 10eV/molecule when combining the lowest inspected duty cycle with the lowest AC high voltage amplitude.
KeywordsOzone-Surface DBD-Oxygen-Production efficiency
Nucleation is a stochastic phenomenon and the probability of observing the critical nuclei formation is very low. Our aim is to enhance nucleation in the metastable zone enabling us to locate and control it.The first step is to determine the nucleation rate, and thus the nucleation behavior of the molecule studied. The two usual methods for determining nucleation rate are measuring induction time by direct counting/observation and direct determination of the steady-state rate of homogeneous nucleation.The second step consists in acting on nucleation, to control, locate and observe it. We develop unusual approaches, adding an external field to the crystallization conditions or using confinement. Ultrasounds reduce induction time and increase the number of crystals. The light irradiation induces nucleation by forming radicals. The electric field tends to localize the nucleation near one electrode depending on the polarity of the molecule studied in acting locally on the density of the solution. Lastly confinement was tested, and results indicate that this approach is very promising for controlling nucleation spatially and generate one single crystal per droplet.
Spray drying technology is widely known and used to transform liquids (solutions, emulsions, suspension, slurries, pastes or even melts) into solid powders. Its main applications are found in the food, chemical and materials industries to enhance ingredient conservation, particle properties, powder handling and storage etc. However, spray drying can also be used for specific applications in the formulation of pharmaceuticals for drug delivery (e.g. particles for pulmonary delivery). Büchi is a reference in the development of spray drying technology, notably for laboratory scale devices. This study presents the Nano Spray Dryer B-90, a revolutionary new sprayer developed by Büchi, use of which can lower the size of the produced dried particles by an order of magnitude attaining submicron sizes. In this paper, results are presented with a panel of five representative polymeric wall materials (arabic gum, whey protein, polyvinyl alcohol, modified starch, and maltodextrin) and the potentials to encapsulate nano-emulsions, or to formulate nano-crystals (e.g. from furosemide) are also shown.
A macroscopic Coulomb crystal of solid particles in a plasma has been observed. Images of a cloud of 7-μm "dust" particles, which are charged and levitated in a weakly ionized argon plasma, reveal a hexagonal crystal structure. The crystal is visible to the unaided eye. The particles are cooled by neutral gas to 310 K, and their charge is >9800e, corresponding to a Coulomb coupling parameter Γ>20 700. For such a large Γ value, strongly coupled plasma theory predicts that the particles should organize in a Coulomb solid, in agreement with our observations.
Atmospheric-pressure plasmas are used in a variety of materials
processes. Traditional sources include transferred arcs, plasma torches,
corona discharges, and dielectric barrier discharges. In arcs and
torches, the electron and neutral temperatures exceed 3000°C and the
densities of charge species range from 10<sup>16</sup>-10<sup>19</sup>
cm<sup>-3</sup>. Due to the high gas temperature, these plasmas are used
primarily in metallurgy. Corona and dielectric barrier discharges
produce nonequilibrium plasmas with gas temperatures between
50-400°C and densities of charged species typical of weakly ionized
gases. However, since these discharges are nonuniform, their use in
materials processing is limited. Recently, an atmospheric-pressure
plasma jet has been developed, which exhibits many characteristics of a
conventional, low-pressure glow discharge. In the jet, the gas
temperature ranges from 25-200°C, charged-particle densities are 10
<sup>11</sup>-10<sup>12</sup> cm<sup>-3</sup>, and reactive species are
present in high concentrations, i.e., 10-100 ppm. Since this source may
be scaled to treat large areas, it could be used in applications which
have been restricted to vacuum. In this paper, the physics and chemistry
of the plasma jet and other atmospheric-pressure sources are reviewed
A review is presented of plasma chemical processes occurring in
the volume part of electrical nonequilibrium discharges. The role of
energetic electrons as initiators of chemical reactions in a cold
background gas is discussed. Different discharge types of (glow, corona,
silent, RF, and microwave discharges) are investigated with respect to
their suitability for plasma processing. Emphasis is placed on the
requirements of initiating and maintaining the discharge and, at the
same time, optimizing plasma parameters for the desired chemical
process. Using large-scale industrial ozone production as an example,
the detailed process of discharge optimization is described. Other
applications of volume plasma processing include other plasma chemical
syntheses as well as decomposition processes such as flue gas treatment
and hazardous waste disposal. The author only deals with plasmas which
are not in equilibrium
A novel approach to chemical process intensification based on microplasma reactor systems is presented. Microplasmas (plasmas generated in sub-mm volumes) possess a favorable reaction environment because of high densities of reactive ions, radicals, and electrons. Moreover, operation under atmospheric pressure and near-room temperature makes them convenient for implementation. Experiments utilized a microfabricated microplasma reactor to intensify the reforming of methanol into a hydrogen-rich product stream useful for energy applications such as combustion or fuel cells. A reaction model elaborates the key mechanisms and demonstrates that reaction rates in the microplasma environment surpass those of conventional plasma reactors. The outcome is that microplasma chemical processing is a viable approach for hydrocarbon reforming and merits consideration for other chemical reaction applications.
The highly unstable β-polymorph of hexahydro-1,3,5-trinitro-s-triazine (RDX), previously only visually observed by optical microscopy, was prepared in essentially pure form by evaporation of a thymol-RDX solution. The infrared spectrum of β-RDX was recorded by Fourier transform infrared spectroscopy. β-RDX appears to have higher molecular and/or site symmetry than does the stable polymorph of RDX, α-RDX. Although stability of β-RDX for several days was witnessed, β-RDX as a solid phase material is unlikely to play an important role in the decomposition or material properties of RDX.
The surface of high-performance poly(ethylene terephthalate) (PET) fibers is difficult to wet and impossible to chemically bond to different matrices. Sizing applied on the fiber surface usually improves fiber wetting, but prevents good adhesion between a matrix and the fiber surface. The present study demonstrates that the plasma treatment performed by Surface dielectric barrier discharge (Surface DBD) can lead to improved adhesion between sized PET fabric and polyurethane (PU) or poly(vinyl chloride) (PVC) coatings. Moreover, it points out that this plasma treatment can outperform current state-of-the-art adhesion-promoting treatment. Plasma treatment of sized fabric was carried out in various gaseous atmospheres, namely N2, N2 + H2O, N2 + AAc (acrylic acid) and CO2. The adhesion was assessed by a peel test, while wettability was evaluated using strike-through time and wicking rate tests. Changes in fiber surface morphology and chemical composition were determined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Only the CO2 plasma treatment resulted in improved adhesion. As indicated by the analyses, increased surface roughness and the incorporation of specific oxygen-containing groups were responsible for enhanced adhesion. The results presented were obtained using a plasma reactor suitable only for batch-wise treatment. As continuous treatment is expected to provide higher homogeneity and, therefore, even better adhesion, a scaled-up Surface DBD plasma system allowing continuous treatment is presented as well.
Process intensification (PI) is commonly seen as one of the most promising development paths for the chemical process industry and one of the most important progress areas for modern chemical engineering. Often illustrated with spectacular examples, process intensification struggles, however, with its definition and interpretation. Instead of narrowing the scientific discussion down to finding a commonly accepted definition of PI, it is more important to determine its position within chemical engineering and to identify its fundamentals. Accordingly, the paper presents a fundamental vision on process intensification. The vision encompasses four approaches in spatial, thermodynamic, functional, and temporal domains, which are used to realize four generic principles of PI. The approaches refer to all scales existing in chemical processes, from molecular to meso- and macroscale, and are illustrated with relevant examples with special attention given to the molecular scale.
This paper reviews the most commonly used methods for the generation of plasmas with special emphasis on non-thermal, low-temperature plasmas for technological applications. We also discuss various technical realizations of plasma sources for selected applications. This paper is further limited to the discussion of plasma generation methods that employ electric fields. The various plasmas described include dc glow discharges, either operated continuously (CW) or pulsed, capacitively and inductively coupled rf discharges, helicon discharges, and microwave discharges. Various examples of technical realizations of plasmas in closed structures (cavities), in open structures (surfatron, planar plasma source), and in magnetic fields (electron cyclotron resonance sources) are discussed in detail. Finally, we mention dielectric barrier discharges as convenient sources of non-thermal plasmas at high pressures (up to atmospheric pressure) and beam-produced plasmas. It is the main objective of this paper to give an overview of the wide range of diverse plasma generation methods and plasma sources and highlight the broad spectrum of plasma properties which, in turn, lead to a wide range of diverse technological and technical applications.
Measurements of the charge and size of heptane droplets generated by electrostatic sprays showed that the droplet charge-to-volume ratio is a monotonically decreasing function of size. In the useful range of electrospray operation, characterized by droplets smaller than the size of the orifice from which the liquid is issued, it was found that the larger were the droplets the closer they were to the Rayleigh limit. In particular, when droplets had charging levels between 70% and 80% of such limit, they were observed to rupture because the repulsive force due to surface charge evidently overcame surface tension. The rupture phenomenon, here termed Coulomb fission, was also captured in microphotographs that typically showed a droplet with one or two, diametrically opposed, conical protrusions terminating in a fine jet ejecting a stream of much smaller, apparently equisized offsprings. The process appeared swift and, yet, well ordered, quite different from the common view of a violent, convulsive explosion. Corroborating evidence on the disruption pattern was also gathered by quantitative measurements of the evolution of the droplet size distribution in evaporating sprays using phase Doppler anemometry (PDA). Implications of these findings are finally discussed in the context of a particular application of electrostatic sprays, electrospray ionization, a technique that is revolutionizing the mass-spectrometric analysis of large biomolecules
A new technique is proposed for the production and coating of nanoparticles, based on the dissociation of a volatile precursor in an atmospheric pressure, non-equilibrium (cold) plasma. The plasma is produced by a dielectric barrier discharge. Using this technique, nanoparticles were successfully produced from acetylene, ferrocene and hexamethyldisiloxane, using argon and helium as carrier gasses. Carbon nanoparticles were formed from acetylene when argon was used as a carrier gas, while in helium no particles were observed. The difference between the gasses is most likely due to the plasma structure. The argon plasma is filamentary, whereas in helium a homogeneous glow is observed. Using ferrocene, iron particles were produced, which rapidly oxidized to form iron oxide when exposed to ambient air. Preliminary experiments on particle coating suggest that coating by a silicon-based compound is possible.
Nanocrystalline Mg-Al layered double hydroxides with the particle size being 10-40 nm were firstly prepared by the technology
of the microwave-crystallization and the variable-speed addition of the alkali. The obtained samples were characterized by
TEM and XRD. The roles of the microwave and addition rate of the alkali were also discussed in the present work. The thermal
decomposition activation energy of the nano-LDHs was calculated according to their TG, DTG and DSC curves by the Ozawa method.
The results showed that the thermal decomposition of the nano-LDHs had four steps. Thereby the decomposition model of the
nano-LDHs was supposed according to the analysis of their thermal decomposition. After PS, ABS, HDPE and PVC were filled with
the nano-LDHs, their LOI values could be increased up to 28, 27, 26 and 33, respectively. When the fire-retardant coating
contained 1.9% of the nano-LDHs that was 0.27 times the dosage of the conventional TiO2, its fire endurance time reached 32.75min that was 7.05 min longer than that of the best coating containing TiO2 according to the model big-panel combustion test method.
Surface dielectric barrier discharges (SDBD), which find widespread industrial applications in ozone production, were used to hydrophilize light-weight polypropylene nonwoven fabric (PPNF) samples. The samples were treated in nitrogen plasma generated by SDBD at atmospheric pressure. The hydrophilicity of the samples was examined as a function of the storage time using a standard strike-through test. The surface chemical composition was characterized by X-ray photoelectron spectroscopy. Because of very short treatment times obtained (∼1 s) and its simplicity the method has the potential to be used in-line with standard high-speed PPNF production lines, laminating, printing and metal plating lines, etc.
The design of current industrial crystallizers is strongly focussed on optimization of known types of crystallization equipment. These crystallizers harbour various physical phenomena, which are strongly entangled. The application of generic principles of process intensification (PI) to crystallization processes requires individual control over physical phenomena. A new design method is applied that exploits elementary processing functions as building blocks for design instead of existing equipment, which enables the application of generic principles of PI. Innovations in the field of crystallization to manipulate shear forces, manipulate nucleation rates with external fields, and improve control over solvent removal with membranes are key technologies. A case study demonstrates the application of task-based design for solution crystallization. The results show how task-based design leads to high modularization of the process representation and model architecture. In addition, task-based design enables the application of generic PI principles, which results in a large flexibility to manipulate final product quality. Future needs include generalization of task-based design for crystallization and development of novel technologies for single task manipulation.
The paper presents an industrial view on the current developments in the field of reactive separations, particularly reactive distillation, reactive adsorption and membrane reactors, and their place in the intensification of chemical manufacturing and processing. Several cases of successfully commercialized reactive separation technologies are presented. Barriers hindering a wider introduction of reactive separations in the industry are discussed, together with the most likely scenarios of further developments in the field.
Partial oxidation of methane to methanol via post-plasma catalysis using a dielectric-barrier discharge was performed under mild reaction conditions. Air was used as the oxidizing co-reactant because of its economical practicality. Three catalysts impregnated with Pt, Fe2O3, CeO2 on ceramic supports located downstream of the discharge zone were examined for increased selectivity towards methanol. It was found that all three catalysts had no significant effect on the conversion of methane, but enhanced methanol selectivity, which could be explained by a two-stage reaction mechanism. The Fe2O3-based catalyst showed the best catalytic activity, and high stability in the reaction. The methanol selectivity of the Fe2O3-assisted plasma process was 36% higher than that of the non-catalytic system at a rather low catalyst temperature (150 °C). In addition, the effects of input power, discharge frequency, discharge gap distance, total flow rate, and methane/air ratio on methane conversion and methanol yield were also studied.
The Collison nebulizer is widely used to produce fine aerosols from a liquid supply. Details of its design and operating characteristics are given, including air and liquid consumption, aerosol output rate and droplet size distribution. An adaptor for the outlet of the nebulizer is also described. This is used when monodispersed aerosols are being generated and enables the output of particles to be increased.
Most plasma-assisted deposition methods currently available use gas discharges at pressures below 1 hPa. In many cases, the process temperature can be kept low due to the fact that the energy necessary for the initiation of chemical reactions is transferred via charged particles. However, a low pressure requires a large amount of vacuum equipment. Processes at atmospheric pressure are more favourable if results similar to those of existing methods can be achieved. Barrier discharges provide the basis for a new plasma-assisted deposition method at atmospheric pressure. These discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated.Starting with some basic considerations on the properties of microdischarges, the deposition of thin polymeric films on glass surfaces is described using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained if trains of voltage pulses are used. The parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.
IntroductionMass Flow and Core FlowThe Design PhilosophyShear Cell TestAnalysis of Shear Cell Test ResultsSummary of Design ProcedureDischarge AidsPressure on the Base of a Tall Cylindrical BinMass Flow RatesConclusions
Worked ExamplesTest YourselfExercises
A thin ceramic layer, either cylindrical or planar in form, is
sandwiched by a number of parallel strip-like discharge electrodes and a
film-like induction electrode. An AC exciting voltage of frequency 10
kHz and 10 kV peak-to-peak (p-p) is applied between the electrodes to
produce a stable high-frequency surface glow discharge for generation of
ozone. As a result of its high frequency, low exciting voltage, and
small size, a great reduction in cost is achieved in both the ozonizer
and its power supply. The presented ozonizer can easily produce a very
high ozone concentration (5000-15000 volume p.p.m. for air; 50-100000
volume p.p.m. for oxygen) without using a special enrichment means. Its
power efficiency can be made very high (170 gO/kWh for air) by proper
selection of operating parameters
Plasma generation and plasma Atmospheric pressure plasmas: a review
- M Conrads
- H Schmidt
- C Tendero
- C Tixier
- P Tristant
- J Desmaison
- P Leprince
M. Conrads, H. Schmidt, Plasma generation and plasma, Plasma Sources Science and Technology 9 (2000). [19] C. Tendero, C. Tixier, P. Tristant, J. Desmaison, P. Leprince, Atmospheric pressure plasmas: a review, Spectrochimica Acta Part B: Atomic Spectroscopy 61 (January (1)) (2006) 2–30.
Transform infrared spectroscopy study of an energetic material
- R J Karpowicz
- S T Serglo
- T B Brlll
R.J. Karpowicz, S.T. Serglo, T.B. Brlll, Transform infrared spectroscopy study of
an energetic material, Industrial and Engineering Chemistry Product Research
and Development 22 (2) (1983) 363-365.
March [14] principles task-based Intensification [15] processing, [16] Coatings [17] methanol and [18] and Zhang, Study on fire-retardant nanocrystalline Mg–Al layered double synthesized by micro-wave-crystallization method
- Tals
tals 48 [13] perspective, (March [14] principles task-based Intensification [15] processing, [16] Coatings [17] methanol and [18] and Zhang, Study on fire-retardant nanocrystalline Mg–Al layered double synthesized by micro-wave-crystallization method, Science in B 47 (6) (2004) 488
Plasma decontamination of surfaces pre-treated with mild disinfectant spray
- T Huijser
- Y L M Creyghton
- H F G Oudmaijer
T. Huijser, Y.L.M. Creyghton, H.F.G. Oudmaijer, Plasma decontamination of surfaces pre-treated with mild disinfectant spray, pp. 1-3.
DC biased AC corona charging
- R W Gundlach
R.W. Gundlach, DC biased AC corona charging, U.S. Patent U.S. Patent
6,349,0242002.
- U N Kobayashi
- Y T Fujiyoshi
U.N. Kobayashi, Y. T. Fujiyoshi, Acta Crystallographica 38 (1982) 356-362.