Thermal Decomposition Of Hydrocarbons Research Articles

PROCESSING OF LIQUID HIGH-ENERGY PRODUCTS WITH THE PRODUCTION OF GAS MIXTURES OF A GIVEN COMPOSITION

The article considers the problem of using waste as an energy resource. The possibility of processing liquid carbon-containing waste, which is formed during the processing of agricultural products, the use of fats in the food industry and oils in transport, is analyzed. An analysis of the volumes of such waste is presented. It is shown that sunflower processing is accompanied by the formation of about 7,000 tons/year of liquid carbon-containing waste. Technological processes of food industry generate about 1,000 tons of such waste per year. A significant source of waste generation is motor vehicle companies, the total resource of which for the introduction of competitive processing technology is currently about 100,000 tons of olives. A promising resource source for the proposed technology is the process of thermal destruction of used automobile tires, of which 250–300 thousand tons are generated annually in Ukraine. Possibilities of introducing the technology of thermal decomposition of liquid carbon-containing substances of various origins, as components of waste, to create gaseous products of a given composition with further use in the chemical industry and replacement of natural gas are considered. The thermal decomposition of hydrocarbons with stabilization of the process due to the introduction of a high-temperature plasma discharge source into it is among the most promising methods of performing such a task. The results of the development of the methodology for the analytical study of the composition of gaseous fuels are presented. The concept and schematic diagram of the experimental stand are presented. The results of test studies are presented. Bibl. 15, Fig. 5, Tabl. 5.

Cu-promoted Ni-LaCeOx/SBA-15 catalysts for ethanol steam reforming

Hydrogen is a globally recognized high-energy, clean, and ecofriendly fuel that is currently produced by means of electrocatalysis, biomass conversion, coal gasification, and thermal decomposition of hydrocarbons, with the steam reforming showing high potential. The present work is focused on Cu-promoted SBA-15-supported Ni-LaCeOx catalysts for ethanol steam reforming (ESR). The catalysts were prepared by incipient wetness impregnation and characterized by XRF, N2 adsorption-desorption, IR spectroscopy, SAXS, XRD, H2-TPR, Raman, and STA methods. The support features caused by the distribution of LaCeOx NPs and Cu promoter in proper ratios affect the conditions of formation of active dispersed Ni species to determine the catalyst performance and its reducibility. At 800 оС, the NiСu-LaCeOx/SBA-15 (1:1) catalyst demonstrates a 100 % ethanol conversion and 55 % hydrogen yield. Thus, the role of the Cu-containing promoter comprises both a significant decrease of carbon deposits on the catalyst surface and redirecting of the intermediate interactions towards the formation of the desired gaseous products.

Comparative analysis of industrial ethane pyrolysis methods for the ethylene production

The thermal decomposition of hydrocarbons in tubular furnaces is the main technology for the production of ethylene. Also, there are some alternative pyrolysis types, such as catalytic pyrolysis, oxidative dehydrogenation, pyrolysis with direct heating. This paper summarizes ethylene production via the most used pathways of this process and the comparison of pyrolysis methods is also discussed.

Emission of soot particles from the combustion of various fuels in boilers

According to modern estimates, the largest contribution to global warming is made by carbon dioxide, while its share is 60-70%. However, studies of the last decade also indicate a large impact on the planet’s climate of “short-lived climate pollutants”, which mean forcing substances with “lifetimes” in the atmosphere from several days to several years. These pollutants include black carbon. In the Russian Federation, black carbon refers to the substance “carbon (soot)”, which is a dispersed carbon product of incomplete combustion or thermal decomposition of hydrocarbons, consisting of particles of various shapes and having a black color. Soot is a strong carcinogen. It is the 2nd class harmful substance and carried by winds for thousands of kilometres. It has been found that black carbon retains several hundred times more heat than carbon dioxide does. Therefore, reducing black carbon emissions is one of the most important challenges in the fight against climate change. Therefore, the task arises of a comprehensive study of all aspects related to black carbon emissions. Based on this, experimental studies of the emissions of soot particles formed in the combustion chambers of boilers of various capacities and designs were carried out during the combustion of various solid, liquid and gaseous fuels. The structure, size and quantitative composition of soot particles, as well as their constituent elements, were studied using scanning electron microscopy. The research results made it possible to propose a more extended approach for choosing the values of specific soot emissions from the combustion of various fuels in heat generators, which should be used in the inventory of emissions of this pollutant.

Continuous synthesis of graphene nano-flakes by a magnetically rotating arc at atmospheric pressure

A novel approach for the preparation of few-layer graphene nano-flakes (GNFs) is presented in this paper. The GNFs are continuously synthesized by thermal decomposition of hydrocarbons using a magnetically rotating arc at atmospheric pressure. The effects of magnetic field, arc current, feedstock gas flow rate, and feedstock gas type on the morphologies and microstructures of pyrolysis products are investigated and discussed. Results show that the microscopic characteristics of pyrolysis products are affected by the operating parameters. High temperature and high hydrogen concentration are considered the essential condition for the formation of GNFs. The synthesized GNFs are agglomerative flakes, where each flake is between 50 and 300 nm. Material analyses indicates that the GNFs have excellent properties such as a good crystalline structure, a low number of layers, and a large specific surface area. This indicates that the GNFs could be applied in fuel cells and energy storages. This method is suitable for mass production of few-layer GNFs since it is a continuous process with a relatively high yield (∼14%) and a relatively low energy cost (∼0.4 kWh/g).

Analysis of graphene films grown on copper foil at 845 °C by intermediate pressure chemical vapor deposition

Chemical vapor deposition (CVD) is the widely accepted method for synthesis of large area graphene from thermal decomposition of hydrocarbons. However, the high temperature (above 1000 °C) requirement is the major drawback of this technique. The present study is an effort towards growing graphene on copper foil using methane at a temperature of 845 °C without incorporation of any additional energy sources. This is achieved by tailoring the growth parameters at 8 mbar in thermal chemical vapor deposition. The effect of total pressure and the effect of growth-supporting gases on the growth and number of layers of graphene were analyzed to select a favorable deposition condition. Graphene formation and its uniformity were examined by Raman spectroscopy, SEM, optical microscopy, AFM and TEM analysis. No studies till date, have reported a growth temperature as low as 845 °C for complete graphene coverage on copper by thermal CVD using methane as the precursor. The low temperature can reduce the thermal budget for graphene production to a certain extent.

Modeling of Block of Reactors of High-Temperature Pyrolysis Process Line

The results from mathematical modeling of a block of reactors of a high-temperature hydrocarbon pyrolysis line are presented. Models of tube furnaces for homogeneous pyrolysis with variously designed coils are described as ideal-displacement reactors. Application of a determinative approach to the reaction mechanism and determination of the kinetic parameters for thermal decomposition of hydrocarbons and their use for describing the processes occurring in SRT-1 and SRT-2 pyrolysis furnaces showed agreement between the calculated relationships and the experimental data.

Effect of Ni in the Anode on the Performance of Pulse-Jet Rechargeable Direct Carbon Fuel Cells

NTRODUCTION Solid Oxide Fuel Cells (SOFCs) operate at high temperature, and thus various fuels can be used due to internal reforming reactions of the fuel. Our research group previously developed Rechargeable Direct Carbon Fuel Cells (RDCFCs) in which the solid carbon deposited by thermal decomposition of hydrocarbon is used as fuel [1, 2]. We also developed Pulse Jet-Rechargeable Direct Carbon Fuel Cells (PJ-RDCFCs) as a new type of RDCFC [3, 4]. In a PJ-RDCFC, liquid hydrocarbon is supplied, thus enabling as fuel the use of hydrogen, lower hydrocarbons, and the solid carbon by thermal decomposition of the liquid hydrocarbon. The operating conditions of a PJ-RDCFC are broader because such conditions can be controlled by adjusting the fuel-supply interval time (T int), the amount in a single pulse (PJ vol), and the current density (j). The type of chemical species that react in a PJ-RDCFC can be selected by controlling these parameters [3]. Sulfur compounds contained in liquid fuel cause poisoning of the catalyst and increase the amount of deposited carbon, both of which cause catalyst degradation. Anode degradation can possibly be controlled, however, by adjusting the parameters in PJ-RDCFCs so that carbon-removal reactions occur selectivity [4]. Traditionally, Ni/GDC cermet anodes are used in PJ-RDCFCs, but the amount of Ni should be kept at a minimum because of the formation of NiCx. Only a slight difference existed between the power density (P) of RDCFCs with Ni and those without Ni, whereas the P of SOFCs with Ni/GDC was much smaller than those with GDC metal-free anodes [2]. In this research, to develop a metal-free anode that is tolerant against anode degradation, power generation characteristics of a PJ-RDCFC using a GDC metal-free anode and that using a Ni/GDC cermet anode were compared and the role of Ni in the anode was investigated. EXPERIMENTAL The electrolyte was a 8YSZ disk (0.25-mm thickness), the cathode was a (La0.8Sr0.2MnO3)/ScSZ composite, and the anodes were a Ni/GDC (Gd0.10Ce0.90O2-δ) composite and a GDC (Gd0.20Ce0.80O2-δ:Gd0.10Ge0.90O2-δ = 9:1) composite. Two different thicknesses of GDC were evaluated, 9- and 52-μm. The operating temperature was 900 °C and oxygen was introduced to the cathode at 60 sccm. Hydrogen was introduced to the anode at 200 sccm during the power generation of the SOFCs. In the power generation of a PJ-RDCFC, after 3 jet-pulses of isooctane as fuel followed by a 1-min wait, power generation at constant j was initiated. PJ vol was set to 1.2 μl. Charging was again carried out by pulse jetting at fixed T int (60 sec). After 15 power generation/charging cycles, pulse jetting was stopped. RESULT AND DISCUSSION Figure 1 shows the current density-terminal voltage (I-V) characteristics of the SOFCs fueled by hydrogen using (1) Ni/GDC (42-μm), (2) GDC (52-μm thickness) and (3) GDC (9-μm thickness). Their respective maximum P was (1) 225 mW/cm2, (2) 47.9 mW/cm2, (3) 132 mW/cm2 , and ohmic resistance was (1) 0.324 Ω/cm2, (2) 3.47 Ω/cm2, (3) 1.06 Ω/cm2. Lower electric conductivity in GDC leads to high ohmic resistance, and thus the maximum P using GDC anodes here was lower than using Ni/GDC. Ohmic resistance decreased, however, with the thinner GDC anode, resulting in a higher P. Figure 2 shows the power generation characteristics of PJ-RDCFCs using (1) Ni/GDC at j = 100 mA/cm2 and (2) GDC (9-μm thickness) at j = 15 mA/cm2. The average P were (1) 77.8 mW/cm2 and (2) 11.0 mW/cm2. The same V behavior was exhibited during each power generation of a single pulse (i.e., cyclic power generation), showing that steady power generation occurred using a GDC metal-free anode. With the Ni/GDC anode, V increased during a cyclic power generation, whereas with GDC, it increased just after pulse jetting and then decreased. In PJ-RDCFCs, V is affected by changes in the chemical species that contribute to the electrochemical and thermochemical reactions following increasing fuel utilization. Because Ni is thought to be mainly the catalyst of thermochemical reactions, the difference in power generation behavior with these two anodes apparently is due to the difference in such contribution by Ni to the thermochemical reactions. In conclusion, power generation of PJ-RDCFCs using a GDC metal-free anode was successful, and suggested that the difference in power generation characteristics is due to the presence of Ni, which is a catalyst of thermochemical reactions. REFERENCES [1]M. Ihara et al., Solid State Ionics, 175, 51 (2004) [2]Y. Tagawa et al., ECS Trans., 25 (2), 1133 (2009) [3] S. Sugiyama et al., ECS Trans., 58 (45), 21 (2014) [4] S. Hattori et al., ECS Trans., 64 (2), 211 (2014) Figure 1

Poisoning Effect of Sulfur Compounds in Pulse Jet-Rechargeable Direct Carbon Fuel Cells

INTRODUCTION Rechargeable Direct Carbon Fuel Cells (RDCFCs) use the solid carbon deposited on the anode by thermal decomposition of hydrocarbons as fuel [1-4]. One application of RDCFCs is Pulse Jet-Rechargeable Direct Carbon Fuel Cells (PJ-RDCFC) [5]. In a PJ-RDCFC, small amounts of a liquid hydrocarbon are supplied via pulse jet, thus allowing not only the solid carbon to be used as fuel but also hydrogen, methane and lower hydrocarbons by thermal decomposition of the liquid hydrocarbon. Operating conditions of PJ-RDCFCs can be controlled by adjusting the interval time of the pulse jet (T int), the amount in a single pulse (PJ vol) and the current density (j). Our group previously suggested that the chemical species contributing to an electrochemical reaction in PJ-RDCFCs can be controlled by adjusting T int, PJ vol and j[5]. Kerosene and gasoline are typical liquid hydrocarbon fuels that contain sulfur-based impurities, such as benzothiophene and its derivatives. Sulfur compounds are generally known to degrade the fuel anode in SOFCs because they can poison the catalyst of the anode. Some studies reported that the power density in SOFCs decreases dramatically when the supplied hydrogen contains 50 ppm hydrogen sulfide [6,7]. However, power generation characteristics of PJ-RDCFCs have not been evaluated when the supplied liquid hydrocarbon contains sulfur. In this study, the poisoning effect of sulfur compounds on the power generation characteristics of PJ-RDCFCs was investigated by measuring and then comparing these characteristics when the fuel was isooctane (the main component of gasoline) with and without benzothiophene. EXPERIMENTAL In the PJ-RDCFC used here, the electrolyte was an YSZ disk (8 mol% Y2O3 –stabilized 1 mol% ZrO2, 0.25-mm thickness, 20-mm diameter), the anode was a Ni/Gd0.10Ce0.90O2-δ composite, and the cathode was a La0.8Sr0.2MnO3/ScSZ composite. The operating temperature was 900ºC and oxygen was introduced to the cathode at STP 60 ccm. After 3 jet-pulses of fuel followed by a 1-min wait, power generation at constant j was initiated. Charging was again carried out by pulse jetting at fixed T int. After two or more and power generation/charging cycles, pulse jetting was stopped, and power generation was considered done when terminal voltage Vreached 0 V. First, power generation tests using isooctane without benzothiophene were performed at T int = 30 sec, PJ vol = 1.2 μl and j = 100 and 200 mA/cm2. Then, power generation tests using isooctane with 100 ppm sulfur adjusted by benzothiophene addition was performed at T int = 30 sec, PJ vol = 1.3μl and j = 100 and 200 mA/cm2. RESULTS AND DISCUSSION Figure 1 shows V as a function of time at j = 100 mA/cm2 and at Tint = 30 sec. For 15 minutes from the start of power generation, 30 pulses of fuel were supplied. After 15 minutes, residual fuel might have been either reformed or decomposed. When isooctane with sulfur was supplied, the average power density was 66.9 mW/cm2, a 13% decrease compared with that when only isooctane was supplied (76.7 mW/cm2). In addition, the power generation time was shorter when the supplied fuel was isooctane with sulfur 33.4 minutes than isooctane only 37.6 minutes. Figure 2 shows V as a function of time at j = 200 mA/cm2 and at T int = 30 sec for a PJ-RDCFC using supplied isooctane with and without 100 ppm sulfur. For 20 minutes from the start of power generation, 40 pulses of fuel were supplied. After 20 minutes, residual fuel might have been either reformed or decomposed. When isooctane with sulfur was supplied, the average power density was 110 mW/cm2, which is a 21% decrease compared with that when only isooctane was supplied (139 mW/cm2). In conclusion, the power density during power generation of PJ-RDCFCs under the normal operational conditions is lower when sulfur compounds are in the supplied liquid hydrocarbon. However, because PJ-RDCFCs can control electrochemical reactions contributing to the power generation, we can expect to find some operational conditions to prevent the degradation due to sulfur compounds. REFERENCES [1]M. Ihara et al., Solid State Ionics, 175, 51-54 (2004)[2]S. Hasegawa et al., J. Electrochem. Soc., 155, B58-B63 (2007)[3]Y. Tagawa et al., ECS Trans., 25(2) 1133-1142 (2009)[4]F. Ohba et al., ECS Trans., 33(40), 163 (2011)[5]A. Yabuki et al., ECS Trans., 41(12) 57-67 (2012)[6] S. Zha, et al., J. Electrochem. Soc., 154 (2) B201-B206 (2007)[7] K. Sasaki, et al., J. Electrochem. Soc., 153 (11) A2023-A2029 (2006)

Synthesis of superhydrophobic soot in the flame and its application

The hydrophobic properties of the fabric by means methods of mechanical and method of Obruchev with adding the synthesized superhydrophobic soot into soap solution were investigated. Thermal decomposition of hydrocarbons and their mixtures under dynamic conditions in a jetting setup was considered. The results showed that the fabric processing with method of Obruchev with the addition of soap solution synthesized superhydrophobic soot was more exceptional properties than waterproof superhydrophobic soot, also keep in for a long time. In this case, the wetting angle was more than 1700, which indicating that the superhydrophobic properties of the synthesized surface. It was shown that the addition of a hydrophobic soot filler in the polymer an amount of 4wt.% of the starting material gives the hydrophobic properties of the coating surface. The measured wetting angle is higher than 1500.

Isolation of disperse carbon from aerosol flows

The brief review considers features of the coagulation of disperse carbon in an aerosol flow on thermal decomposition of hydrocarbons. Analysis of the coagulation mechanisms and basic equations for calculation of the Brown, gradient, kinematic, and turbulent coagulation constants of disperse carbon aerosols is given. Methods for calculation of the precipitation of disperse carbon aerosols in a cyclone concentrator and fiberglass and granular filters are presented.

Production of Nanosized Carbon Black from Hydrocarbon by a Thermal Plasma

Thermal plasma conditions (optimal heat and radical sources for the thermal decomposition) can be used to accelerate thermodynamically favorable chemical reactions or provide the energy required for endothermic reforming processes. Direct thermal decomposition of hydrocarbon (methane, acetylene, and propane) was carried out using a thermal plasma system which is an environmentally favorable process. In case of thermal decomposition, high purity of the hydrogen and solidified nano-sized carbon can be achieved without any contaminant. The main product carbon produced by thermal decomposition can be either sequestered or used as a raw material and it can be applied for the varieties of industry fields. The morphology of the carbon was characterized by SEM and the particle size was determined by a particle size analyzer. It was observed that the carbon black particles were sphere particles with mainly several tens of nano-sized diameters, those are about 10–80 nm. It can be expected to be used as a raw material of laser printer toner which requires small sized carbon black particles; An average primary particle size of PRINTEX® L (Degussa Fillers & Pigment) used in a part of printing inks is 23 nm. In case of the XRD pattern of the produced carbon black from acetylene is of higher crystalline than the commercialized carbon black used for fuel cells. Also carbon species produced were characterized by EA and TGA.

Production of Nanosized Carbon Black from Hydrocarbon by a Thermal Plasma

Thermal plasma conditions (optimal heat and radical sources for the thermal decomposition) can be used to accelerate thermodynamically favorable chemical reactions or provide the energy required for endothermic reforming processes. Direct thermal decomposition of hydrocarbon (methane, acetylene, and propane) was carried out using a thermal plasma system which is an environmentally favorable process. In case of thermal decomposition, high purity of the hydrogen and solidified nano-sized carbon can be achieved without any contaminant. The main product carbon produced by thermal decomposition can be either sequestered or used as a raw material and it can be applied for the varieties of industry fields. The morphology of the carbon was characterized by SEM and the particle size was determined by a particle size analyzer. It was observed that the carbon black particles were sphere particles with mainly several tens of nano-sized diameters, those are about 10-80 nm. It can be expected to be used as a raw material of laser printer toner which requires small sized carbon black particles; An average primary particle size of PRINTEX L (Degussa Fillers & Pigment) used in a part of printing inks is 23 nm. In case of the XRD pattern of the produced carbon black from acetylene is of higher crystalline than the commercialized carbon black used for fuel cells. Also carbon species produced were characterized by EA and TGA.

Reaction Process in the Ni–ScSZ Anode for Hydrocarbon Fueled SOFCs

Hydrocarbon fueled cell reactions, which consist of thermal decomposition, reforming, and CO shift reactions, and electrochemical oxidation in the Ni–ScSZ anode of solid oxide fuel cells, were examined by electrochemical measurements and outlet gas analysis for several hydrocarbon fuels (, , , ). Examinations on the anode potential and its relation to observed outlet gas compositions have revealed that hydrogen molecules were mainly electrochemically oxidized even for hydrocarbon fuels. The electrode conductivities can be well correlated with the water vapor partial pressure for both hydrogen and hydrocarbons. Water vapor produced as a result of the electrochemical oxidation of hydrogen promotes the hydrogen-producing reactions in the vicinity of the electrochemically active site. A large difference in the thermal decomposition of hydrocarbons appeared in the anode potential and also in the maximum fuel utilization between methane and other hydrocarbons. A simple reaction model has been proposed to interpret consistently the electrode reactions as well as the reforming and the CO shift reactions with a focus on the oxygen atoms on Ni surfaces as a catalyst for both the electrode and the reforming reactions.

The use of a localized heating protocol in heterogeneous catalysis

The catalyzed decomposition of ethylene has been used as a probe reaction to ascertain the advantages of exclusive heating of a supported metal catalyst by a current stimulated technique. This approach has been found to result in the elimination of certain side reactions generally encountered in conventional catalytic reactor systems associated with thermal decomposition of gas phase molecules. We have found that by restricting the heated zone to the catalyst surface the ubiquitous formation of pyrolytic carbon arising from thermal decomposition of hydrocarbons can be effectively mitigated. In addition, major differences in the selectivity patterns were observed from the localized heating system compared to that found when the same catalyst was reacted in a conventional flow system. The difference in behavior of the catalyst under these diverse conditions is rationalized according to the notion that the flow of an electric current through the support not only served to resistively heat the sample, but also induced electronic perturbations in the metal surface atoms.

Modification of activated carbon fiber pore structure by coke deposition

The pore structure of activated carbons can be tailored to produce carbon molecular sieves (CMS), by vapour phase thermal decomposition of hydrocarbons. Thermal cracking of propylene at 700°C was used to deposit coke on activated carbon fibers. Pore structure development was studied by determining the adsorption isotherms of N 2 at 77 K and CO 2 at 298 K, while the molecular sieving properties were investigated by the kinetic uptake curves of CO 2 and CH 4 at room temperature. Coke deposition resulted in the decrease of surface area and the enhancement of molecular sieving properties during the early stages of hydrocarbon decomposition.

Scanning tunnelling microscopy (STM) imaging of carbon nanotubes

Carbon nanotubes prepared by thermal decomposition of hydrocarbons on supported Co catalysts were investigated by STM in air. An interpretation of the STM images is proposed which accounts for specific distortions taking place while scanning three-dimensional objects whose dimensions are of the order of the curvature radius of the tip. These distortions have both geometric and electronic origins, and cannot be neglected. The distortion mechanism was found to be different for nanotube diameters in the ranges of 1 nm and 10 nm. The 1 nm tubes are more strongly affected by their apparent broadening, reflecting the finite size of the tip apex. Here the distortion can reach up to 300% of the geometric diameter, whereas for 10 nm tubes the distortions are in the range of 50% of the geometric diameter. An apparent flattening of the nanotubes in the vertical direction was also found, which is attributed to differences in electronic densities of states between the substrate and the nanotube, and to an additional tunnelling barrier between the nanotube and the substrate. STM images with atomic resolution and line cut topographic profiles show similar structures as for the case of HOPG. However, the atomic corrugation was found to be five times smaller on the 1 nm diameter tubules than for the 10 nm family, the latter being close to the value obtained with HOPG. Coiled nanotubes have been imaged by STM for the first time. Here both the electrical resistance of the coiled nanotube and its elastic deformation play a significant role in the image formation process, these effects being more important than for straight nanotubes.

Development of fusion fuel cycle technology at the Tritium Laboratory Karlsruhe: the experiment CAPRICE

Abstract A facility carrying the acronym CAPRICE has been erected at the Tritium Laboratory Karlsruhe to demonstrate fuel clean-up technology for ITER with tritium. The clean-up process for the recovery of molecular and chemically bonded tritium and deuterium from all reactor exhaust streams is based on the combination of hydrogen isotope permeation through palladium-silver with catalytic process steps involving the thermal decomposition of hydrocarbons and the reduction of water vapour by carbon monoxide. On the basis of the CAPRICE process and from recent results on mathematical modelling of a permeator-catalyst combination, a simple continuous clean-up concept for ITER with low tritium inventories is proposed.

Co-pyrolysis of hydrocarbons and SiEt4for the synthesis of graduated SixC1–xceramic thin films by chemical vapour deposition

The thermal decomposition of hydrocarbons has been investigated under particular conditions in a low-pressure chemical vapour deposition reactor in order to select suitable carbon sources for the preparation of carbon-rich or graduated SixC1–x layers. Growth of pyrolitic carbon thin films (pyro-C) starts at ca. 1050 K and only above 1273 K using C6H5Pri and CH4, respectively. The microstructure of the pyro-C layers is more dependent on the deposition temperature than on the nature of hydrocarbons. Their co-pyrolysis with SiEt4 used as SiC precursor has been achieved in the temperature range 1050–1250 K. As expected, the film composition does not change significantly at 1173 K using CH4 as an additional C source. By contrast, the C content of the films deposited by co-pyrolysis of SiEt4 and C6H5Pri increases continuously from 0.48 to 1 by increasing the mole fraction ratio x(C6H5Pri)/[x(C6H5Pri)+x(SiEt4)] from 0 to 1. Multilayers and compositional gradient layers can be prepared by discrete or continuous changes of the gas-phase composition, respectively. These films were successfully used as interphase in ceramic–ceramic composite materials to weaken the fibre/matrix bond and to improve their ductility.

Preparation of coatings and surface modification by plasma and thermal processes

The application of various plasma and ion beam processes for the production of coatings and surface modification of materials, are reviewed. We describe, in particular, cold plasma techniques for the preparation of nitrides, carbides, oxides, bondes and so on and ion implantation techniques for modification of surfaces and interfaces by ion beam mixing to form alloys and chemical compounds on materials. Further, we present our recent collaborative studies on in situ coatings by a dc glow discharge of H 2 + CH 4 gas in torus devices. The carbon coatings deposited on surface probes at liner positions of TEXTOR and JIPPT-IIU are characterized in terms of depth composition profiles, chemical binding states and hydrogen concentration. Properties of these coatings produced by the dc glow discharge are compared with those by an ECR plasma and by a thermal decomposition of hydrocarbons at high temperature. Finally, our recent results on the formation of ceramics by the exposure of Tokamak plasmas and thermal heating will be discussed. TiC layers on a Ti-coated graphite probe and TiB x layers on a B-coated Ti probe were formed after the exposure to the scrape-off layer plasma in JIPPT-IIU, and TiC-TiN double layers on Ti-coated stainless steels were formed by vacuum heating at 600–1000°C.