Effect of Organic Additives on Silicon Combustion in Nitrogen
The work shows some peculiarities of silicon combustion in nitrogen in the presence of additives of organic compounds. Organic compounds with different composition were used. Combustion of samples was carried out in a constant-pressure bomb. The combustion products are composite powders and containing α-, β- Si3N4, SiC, Si2N2O. The addition of organic additives suppressed coagulation of Si particles, improved the extent of conversion, and promoted combustion of coarse Si powders which can’t be ignited by any other methods. Introduction of organic dopants to Si powders was found to intensify their combustion without significant influence on the combustion temperature. Active transition of silicon to the gas phase occurs in the low-temperature zone of the combustion wave at the temperature lower than the melting point of silicon. At the temperatures lower than the melting point of Si the quenched combustion products contain two types of crystals of SiC and Si3N4. SiC is formed within a low-temperature zone of the combustion wave. SiC is formed by fine crystals and large spherical particulates which are formed by a bunch of very thin web-like crystals. SiC and Si3N4 formation provides a protective coating on silicon particles. It prevents coagulation at the temperature increase. The experiments have proved that it is enough to introduce 1-7 M of the organic additive to 1000 M of silicon for the combustion initiation. Meanwhile, adding different inorganic salts, including ammonium chloride, did not promote combustion. After initiation of combustion to continue Si powder must contain additives or organic compounds or addition of carbon black; carbon black is necessary for keeping the combustion on.
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