NITRIDATION STUDY OF REACTION-BONDED SILICON-NITRIDE IN-SITU BY HIGH-TEMPERATURE X-RAY-DIFFRACTION

The reaction-bonded silicon nitride (RBSN) nitriding process has been studied using a high temperature X-ray diffractometer (HT-XRD) under i sothermal conditions in the temperature interval 1300-1400 degrees C. With HT-XRD, the nitridation reaction and phases formed could be monit ored almost instantaneously at temperature. The experimentally observe d kinetics of the nitriding reaction were found to be in fair agreemen t with a theoretical model which predicts that the nitriding reaction occurs predominantly by Knudsen diffusion of nitrogen molecules throug h channels in a layer of growing Si3N4. However, no single rate law is likely to describe the whole nitridation process. Observation of the microstructure ater nitridation indicates that the process occurs part ly by reaction of Si vapour with nitrogen gas but that inward diffusio n of nitrogen into particles also contributes significantly to the ove rall nitridation. The phase analysis showed that alpha-Si3N4 formation predominates over beta-Si3N4 formation but the proportion of beta-Si3 N4 increases as nitridation continues. (C) 1997 Elsevier Science Limit ed.