Preparation of Silicon Nitride and Oxonitride by Gas-Phase Pyrolysis of Hexamethyldisilazane

The technique was developed, the installation was done, and the conditions for the production of Si 3 N 4 and Si 2 N 2 O by the method of gas-phase pyrolysis of hexamethyldisilazane (CH 3 ) 3 -Si-NH-Si-(CH 3 ) 3 (HMDS) were experimentally studied. In the experiments, two different methods of inputting the raw material were used—the input of a vapor–gas mixture (bubbling feeder with heating to supply the HMDS vapor in a stream of carrier gases) and input as a gas-droplet stream (pneumatic nozzle). The effect of gas-dynamic synthesis conditions at temperatures up to 1100°C on the properties of silicon oxonitride and silicon nitride nanopowders was studied. The influence of the conditions of mixing the reactants, the volume ratio of nitrogen/ammonia, and the content of HMDS in the vapor–gas mixture on the yield of products was shown. The dependences of the degree of conversion of the feedstock on the gas flow rate and the concentration of ammonia in the gas phase were obtained. The optimal conditions for the pyrolysis process were found: temperature, the ratio of the components of the gas mixture, the conditions of mixing, and the contact times of the phases. X-ray amorphous Si 3 N 4 and Si 2 N 2 O powders with particle sizes of 50–200 nm and a specific surface area of up to 15 m 2 /g and powders of alpha modification of silicon nitride Si 3 N 4 in the form of threadlike crystals with a particle diameter of 50–200 nm were obtained.