Synthesis of hollow SiC microglobules by a combustion method

Hollow β-SiC microglobules have been synthesized successfully by a combustion technique by using a Si + C starting mixture. In this process, a controlled amount of KClO₃ + 3Mg is mixed with Si + C to enable a self-sustaining combustion regime and to promote a carburization of the silicon. The structures and morphologies of the products were analyzed by X-ray diffractometry (XRD) and a scanning electron microscopy (SEM). This procedure provides an easy method for the synthesis of hollow microglobular assemblies with SiC composed of submicrometer size particles.     

The role of the reaction medium in the self propagating high temperature synthesis of nanosized tantalum powder

The high temperature combustion of the mixture Ta₂O₅ + 5 Mg has been investigated using a microthermocouple in the medium MgO and molten NaCl. The effect of varying the amounts of these two inorganic agents (MgO and NaCl) was examined. It was shown that using MgO as the reaction medium produces the complex oxide Mg_xTa_yO_z as an impurity in the Ta powder, whereas unagglomerated single-phase powder (particle size of 20-90 nm) of Ta was formed in the presence of NaCl. The approximate mechanism for forming the final product is discussed. The distributions of temperature, the rate of heat generation and degree of conversion in the combustion wave of the mixture Ta₂O₅ + 5Mg + NaCl were measured. The sizes of the combustion zones and the kinetics of reaction were derived.     

A study of tungsten nanopowder formation by self-propagating high-temperature synthesis

Molten salt-assisted self-propagating high-temperature synthesis of nanocrystalline W powder was studied experimentally. The technique involves the reduction of WO₃ in the presence of sodium chloride using three different reducing agents: magnesium (Mg), sodium azide (NaN₃), and sodium borohydride (NaBH₄). The effects of the mole fraction of sodium chloride on temperature distributions, combustion parameters, phase compositions, and morphology of the final products were determined. The sodium chloride-assisted method reported here has been found to be effective for lowering combustion temperature and producing uniform and spherical W nanopowders of average particle size around 20-200, 100-200, and 20-50 nm. The effect of combustion temperature on tungsten particle size is discussed, and a sketch describing the chemistry of combustion is proposed.     

Simple synthesis of nano-sized refractory metal carbides by combustion process

Combustion reactions of transition metal oxides (WO₃, MoO₃, Ta₂O₅, Nb₂O₅, ZrO₂, and TiO₂), magnesium, carbon, and sodium fluoride produce a range of nanostructured transition metal carbides (W₂C, Mo₂C, TaC, NbC, ZrC, and TiC) with low amounts of free carbon. Sodium fluoride improves unfavorable combustion regimes and facilitates the carburization of metal carbides. The average particle size of carbides prepared in this study was below 100 nm in pure phase. The carbides were characterized by X-ray diffraction, scanning electron microscopy, specific surface area analysis, and carbon analysis.     

Investigation of the thermal structure of a combustion wave by the microthermocouple method in the system titanium-carbon-chlorine-containing polymer

Erevan. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 6, pp. 43–45, November–December, 1992.