Reduction combustion synthesis

The third main type of CS is reduction combustion synthesis, described by the formula... 

The dependence of the combustion temperature of the Ti + 0.5 C samples with relative density of 58 2.5% on the PN2 is shown in Figure 11.8. Clearly, the undiluted samples had a high reaction temperature, but this was decreased by a reduction of PN2 or by the addition of diluent. The effect of carbon content on the combustion synthesis of titanium... 

Combustion synthesis of boron nitride powder, BN, was reported in one of the earliest works on SHS (Merzhanov and Borovinskaya, 1972). The mechanisms of combustion and product structure formation from elements were later investigated (Mukasyan and Borovinskaya, 1992). More recently, finely dispersed hexagonal boron nitride powder has been obtained from reduction-type reactions (Borovinskaya et fl/., 1991). 

The typical production technologies for combustion synthesis were described in Section II. It is evident that apparatus needed for synthesis is relatively simple, especially since no additional equipment is needed for bulk heating of the material (e.g., furnaces, plasma generators, etc.). In addition, it has been reported that replacing conventional furnaces with a CS apparatus leads to significant reduction in workspace requirements (Merzhanov, 1992). Finally, owing to low power requirements, combustion synthesis technology is one of the few methods of materials synthesis that is feasible in outer space (Hunter and Moore, 1994). 

The use of CeOs-based materials in catalysis has attracted considerable attention in recent years, particularly in applications like environmental catalysis, where ceria has shown great potential. This book critically reviews the most recent advances in the field, with the focus on both fundamental and applied issues. The first few chapters cover structural and chemical properties of ceria and related materials, i.e. phase stability, reduction behaviour, synthesis, interaction with probe molecules (CO. O2, NO), and metal-support interaction — all presented from the viewpoint of catalytic applications. The use of computational techniques and ceria surfaces and films for model catalytic studies are also reviewed. The second part of the book provides a critical evaluation of the role of ceria in the most important catalytic processes three-way catalysis, catalytic wet oxidation and fluid catalytic cracking. Other topics include oxidation-combustion catalysts, electrocatalysis and the use of cerium catalysts/additives in diesel soot abatement technology. 

From the viewpoint of chemical nature, three main types of CS processes can be distinguished. The first is a gasless CS from elements. The second type, the so-called as-so//d combustion synthesis, involves at least one gaseous reagent in the main combustion reaction. And the third type of CS is reduction CS. In this chapter, we consider the gas-solid type of CS, which in general can be described by the following overall reaction formula ... 

The reduction of porous silica with magnesium vapor is a highly exothermic reaction. The process with thermal moderators is an attractive route to generating highly mesoporous silicon (surface areas >500 m /g). Without thermal moderators, large batches of macroporous silicon can be generated by combustion synthesis. Electrochemical reduction with molten calcium or lithium salts rather than thermal reduction with magnesium is also under evaluation. The use of liquid aluminum to reduce mesoporous silica deserves much further study. 

Bera, P., Patil, K.C., Jayaram, V., Hegde, M.S., Subbana, G.N. Combustion synthesis of nano metal particles supported on a-AliOs CO oxidation and NO reduction cattdysts. J. Mater. Chem. 9, 1801-1805 (1999)... 

Of the various synthetic methods, combustion synthesis (GS) has special significance because CS processes are characterized by high temperatures, fast heating rates and short reaction times. These features make CS an attractive method for the manufacture of materials. In this method, the exothermicity of the redox (reduction-oxidation or electron transfer) chemical reaction is used to produce useful materials. - ... 

Since NO is a precursor in NDMA formation and high combustion temperatures (usually from 1500 to 1800 0) yield high reaction rates between oxygen and nitrogen, a decrease in NDMA formation can also be achieved by lowering the flame temperature. Excess air seems to be the most economic way to reduce flame temperature and NO synthesis. In a new type of burner developed on this principle the resulting air had only 0.05 - 0.1 mg NO /m as compared with 14 mg/m in conventional burners. Accordingly, malt dried with such burners contains only 1 to 3 mg/kg NDMA, a 15-30 fold reduction of the NDMA concentration. 

The finely divided hydride produced by pyrolysis is pyrophoric in air, while synthesis from the elements produces a substantially air-stable product [1]. That prepared by reduction of butylmagnesium bromide with lithium tetrahydroalumi-nate is pyrophoric and reacts violently with water and other protic compounds [2], The hydride produced from magnesium anthracene has a very large specific surface area and is pyrophoric [3], In the context of use of the hydride for energy storage purposes, ignition and combustion behaviour of 100-400 g portions were studied, as well as the reaction with water [4],... 

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