Surface of powders of silicon nitride produced by self-propagating high-temperature synthesis

Conclusions The surface of a starting silicon powder used in the production of silicon nitride by the SHS method is covered with an oxide film whose thickness varies, depending on the method of comminution and time of storage of the powder, in the range 1–12 nm. During SHS the Si + SiO₂ reaction results in the formation of gaseous SiO, which becomes adsorbed on the cold walls of the reactor and then experiences disproportionation. This lowers the oxygen content of the resultant silicon nitride, but the overall purification effect achieved is small. After comminution, a 1- to 2-mm-thick layer of powdered silicon nitride produced by SHS consists of a silicon oxynitride with an oxygen content of 5–30 wt.%. Milling conditions do not significantly affect the concentration of oxygen inside the nitride particles, which does not exceed 0.4%. To obtain silicon nitride of low oxygen content, it is necessary to employ starting reactants of high purity.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 48–54, January, 1984.