Decomposition plasma processes

It could be concluded that thermal plasma process for methane decomposition is very effective for the production of high purity of the hydrogen as well as synthesis of the carbon black. 

Ogata, A., Mizuno, K., Kushiyama, S. and Yamamoto, T. (1998) Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor, Plasma Chem. Plasma Process 18, 363-73. 

Rudolph, R., Francke, K.P. and Miessner, H. (2002) Concentration dependence of VOC decomposition by dielectric barrier discharges, Plasma Chem. Plasma Process. 220, 401-12. 

Oda, T., Kato, T., Takahashi, T. et al. (1998) Nitric oxide decomposition in air by using nonthermal plasma processing with additives and catalyst, IEEE Trans. Ind. Appl. 34, 268-72. 

Non-equilibrium plasma processes are much less sensitive to reverse reactions, because of low temperature, and often don t require product quenching. For this reason, several direct halide decomposition processes have been effectively carried out in non-thermal discharges. 

Consider the kinetics of the plasma process starting with decomposition of hydrocarbons in low-pressure glow discharges, which initiates polymerization (Yensen, Bell, Soong, 1983 Ivanov Epstein, 1984 Ivanov, 1989 Ivanov, Rytova, Soldatova, 1990a Ivanov et al, 1990b). If the initial concentration of hydrocarbons mixed with an inert gas exceeds 10-20 vol %, dissociation of hydrocarbons is mostly due to electronic excitation by direct... 

Non-Thermal Plasma Synthesis of Formic Acid in CO2-H2O Mixture. Determine the minimum energy efficiency of the plasma-chemical HCOOH synthesis in the CO2-H2O mixture (9-60) required for effective hydrogen production in the double-step cycle (9-60) and (9-61). Assume that thermodynamically about 70% of the total energy required for hydrogen production from water should be consumed in this case for decomposition of formic acid (9-61) to form hydrogen and to recycle carbon dioxide back to the plasma process. 

These reactions may be stimulated to provide 80% decomposition by using a plasma process to excite the methane molecule. In this case, the molecular breakdown may occur in the plasma to produce charged species. Hydrocarbons other than methane may be used as the feedstock. The usual operating sequence involves flushing and evacuation, heating to temperature under the inert atmosphere, carburizing for a predetermined time followed by a diffusion anneal in a carbon-free atmosphere. This cycle is designed to provide the optimum surface carbon content and carburized depth. - ... 

UV/ozone treated parathion and paraoxon samples (treatment time = 5 min) were still toxic enough to kill all Drosophila in less than 12 hours in the culture bottle. In contrast, the Drosophila in the bottle containing the plasma-treated sample (treatment time = 10 sec) lived their full life cycle and laid eggs. Even the newly hatched larvae were able to develop into adult flies. These culture test results qualitatively demonstrate the efficacy of the atmospheric if plasma process for the complete decomposition and detoxification of OP nerve agents. 

Carbon black is the generic name for a family of small particle size carbon and their fused aggregates which are formed in the gas phase by the thermal decomposition of hydrocarbons. The numerous existing processes principally differ in the operating conditions. They can be classified into three categories partial combustion, thermal decomposition, and the more recent plasma process. - ... 

In the plasma process the energy required for the thermal decomposition of the hydrocarbon is delivered by a plasma generated by electrical energy in a plasma generator ... 

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

Newer high velocity thermal spray coating processes produce coatings in compression rather than tension because of the shot peening effect of the supersonic particles on impact. This has permitted coating as thick as 12,500 p.m without delamination as compared to older processes limited to 1,250 p.m. The reduced residence time of particles at temperature minimises decomposition of carbides present in conventional d-c plasma. This improves wear and hardness (qv) properties. 

The rates of these reactions bodr in the gas phase and on the condensed phase are usually increased as the temperature of die process is increased, but a substantially greater effect on the rate cati often be achieved when the reactants are adsorbed on die surface of a solid, or if intense beams of radiation of suitable wavelength and particles, such as electrons and gaseous ions with sufficient kinetic energies, can be used to bring about molecular decomposition. It follows drat the development of lasers and plasmas has considerably increased die scope and utility of drese thermochemical processes. These topics will be considered in the later chapters. 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

Additional confirmation of the approach can be found in the fact that mere thermal treatment of powder obtained from fluoride solutions by plasma chemical decomposition at 1000-1200K for 2-3 hours in air brings about a 100-300 fold reduction in fluorine content. Hence, the plasma chemical process and subsequent thermal treatment of the powder enables to obtain final products with fluorine contents as low as 10 2-10 3 % wt. 

The unique advantage of the plasma chemical method is the ability to collect the condensate, which can be used for raw material decomposition or even liquid-liquid extraction processes. The condensate consists of a hydrofluoric acid solution, the concentration of which can be adjusted by controlling the heat exchanger temperature according to a binary diagram of the HF - H20 system [534]. For instance, at a temperature of 80-100°C, the condensate composition corresponds to a 30-33% wt. HF solution. 

Investigations of the plasma chemical decomposition of tantalum-containing fluoride solutions indicated no significant differences in the process and product parameters compared to the corresponding decomposition of niobium-containing fluoride solution [529, 532]. The particle diameter, shape and specific surface area of both niobium oxide and tantalum oxide powders attest to a gas-phase mechanism of the interaction, with sequential condensation and agglomeration of the oxides. 

Amorphous Silicon (a-Si). Amorphous silicon is considered a promising new material.As mentioned above, only a very thin coating is necessary, since the amorphous structure is much better at absorbing sunlight than is the crystalline material. The most common process to produce a-Si is the decomposition of silane by plasma CVD (see Ch. 8). Thicknesses of a few micrometers can be deposited and,... 

Direct thermal decomposition of methane was carried out, using a thermal plasma system which is an environmentally favorable process. For comparison, thermodynamic equilibrium compositions were calculated by software program for the steam reforming and thermal decomposition. In case of thermal decomposition, high purity of the hydrogen and solidified carbon can be achieved without any contaminant. 

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