Abstract
During recent years a variety of silicon powders have been developed which are suitable for fabrication of sinterable Si 3N 4 powders. A selection of these powders, with different histories of preparation and variable impurity levels, was examined with respect to their particle size characteristics and reactivity to nitrogen. A comparative thermoanalytical study (thermogravimetry, differential thermogravimetry, and differential thermal analysis) of the nitridation process of these powders in nitrogen at atmospheric pressure, was performed to identify (a) the possible correlations between the silicon powder properties and their reactivity and (b) the specific features of these powders which can make them susceptible to a runaway nitridation rate. Using a low heating rate schedule within the temperature range of nitridation, the process of nitride formation was found to include two stages. The first stage was similar for all powders, and the nitrogen uptake could be related to the formation of a surface nitride layer. The thickness of this layer appeared to be approximately the same for powders of widely variable specific surface area. The starting temperature of the second (main) stage was lowered by the presence of metallic impurities. Some powders experienced a runaway nitridation rate at this stage, and this tendency could be correlated to the oxygen content and the particle characteristics of the respective powders. The relative ratio of α-Si 3N 4 to β-Si 3N 4 was determined after nitriding beyond the first and second stages of nitridation, and the results are discussed in the context of nitride nucleation and the properties of the starting silicon powders.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call