Reactions with Oxygen-Containing Gases

4 CARBON REACTIONS WITH OXYGEN-CONTAINING GASES 

---

In this chapter, the theoretical background and different molecular simulation methods are introduced with stress on electronic structme methods, followed by a comprehensive review of studies on gas-carbon reactions using MS in the last four decades, which include the hydrogen-carbon reactions, carbon reactions with oxygen-containing gases, and metal-carbon interaction. 

Carbon Reactions with Oxygen-Containing Gases and the Unified Mechanism... 

In the past five decades there has been a large volume of literature in the study of carbon reactions with oxygen-containing gases, and the central issue is the determination of the active sites on carbon so that the kinetics of carbon can be correlated for different forms of carbon based on the active sites existing on these carbons. Since the groundbreaking work of Laine, Vastola, and Walker [7], this area has been somewhat dormant until recently, when further advances have been made [4-6,8,9,73-76]. 

The reaction level of aluminum depends on its particle size and the scattering conditions of explosion products. The decrease of aluminum powder grain size can increase the stability of explosive detonation, but it can cover other particles to hinder the reaction transmission if its size is too small. The typical used aluminum particle is 3-200 pm in diameter. Since aluminum are oxidized during its secondary reaction with oxygen-containing gas products from the first stage of explosion, the temperature of gas explosion products, the distribution of unreacted aluminum particles in the product, and the extended phase-contacting time all play important roles in the reaction level of aluminum powder. 

The oxidation reaction is generally described with Pt or Pd as catalyst, eventually on active coal, in aqueous alkaline solutions at temperature from 40°C to 100°C. The oxidation reaction is mostly carried out with oxygen or with an oxygen-containing gas such as air [17,18]. 

It is possible that the as-made nanowires contain some crystalline Si core, and subsequent reaction with oxygen in the air results in the formation of silica nanowires. Since hydrogen gas was used in the reaction, pure silicon nanowires were probably made first, followed by oxidation in air. In the following discussion, for simplicity reason we will assume that amorphous SiNW were made during catal)Tic reactions. 

Arsenic is oxidised, mainly to arsenious oxide, when heated in nitrous oxide 8 the reaction becomes appreciable at 250° to 270° C. and ignition occurs at 400° to 450° C. This reaction takes place specifically between arsenic and the nitrous oxide and is not due to reaction with oxygen after thermal decomposition of the nitrous oxide, as such decomposition does not occur below 400° C. and is very slight at 460° C. Nor does the reaction resemble that which occurs in oxygen, except that, like the reaction in the dark with the latter gas (see p. 47), it is a surface reaction. No chemi-luminescence is observed, however, and there is no upper critical oxidation pressure. At 360° C. the product contains at least 99 per cent, of pure arsenious oxide, and at 420° C. it contains about 5-8 per cent, of arsenic pentoxide. 

Because the details of processing in each class of CMCs (e.g., oxide, carbide, or nitride matrix) are slightly different, the appropriate thermochemical approach for each class may also be different. For example, in the formation of alumina matrix materials by directed metal oxidation, the alumina product grows from a molten aluminum alloy by reaction with an oxygen-containing gas phase. On the other hand, in the formation of platlet-reinforced zirconium carbide, the gas phase is not involved in the reaction at all, being inert to the reactants and products. Thus, a general approach to deal with the myriad of possible products formed by the... 

The produced hydrogen from SR is separated through a dense proton-conducting membrane to react with oxygen contained in an air stream. The exothermic reaction between H2 and O2 is used as heat source for ATR of methane. A 10% Ni supported on Y-AI2O3 catalyst is placed on top of the perovskitic membrane. Without the presence of catalysts, methane conversion is quite poor at 850 °C, less than 20%. As nickel supported catalysts is introduced into the system, the methane conversion increases to 88% (thermodynamic equilibrium conversion is around 96%). This phenomenon is related to the low contact time between gas and catalysts, because the gas flow rate used is high. 

A characteristic example of the phosgene-based process for manufacture of polycarbonates is the synthetic method used by Dow Chemical Co. A typical variation of the process uses bisphenol A, diphenyl carbonate, phosgene, cuprous chloride, and an oxygen-containing gas. Thus, when a phenol is reacted with phosgene, a diaryl carbonate is formed, which is then reacted with a bisphenol monomer to obtain a bisphenol polycarbonate and phenol, the latter of which after separation from the polycarbonate is reacted with more phosgene, and the diaryl carbonate thus produced is cycled back into the process for reaction with the bisphenol monomer. 

---