Processing of micro-components made of sintered reaction-bonded silicon nitride (SRBSN). Part 1: Factors influencing the reaction-bonding process

In order to establish a process for the manufacturing of injection moulded micro-components of sintered reaction-bonded silicon nitride (SRBSN) several process parameters were investigated with regard to their influence on the reaction-bonding step. One question to be answered was how the sintering aids affect the nitridation behaviour of a silicon green body. For the processing of micro-components it was of special interest to study, how a decreasing sample size and wall thickness would influence the rate of Si3N4 formation. By varying the added amounts of the sintering aids, it was found that increasing the Y2O3 and MgO contents both improved the nitridation rate, whereas an increase of Al2O3 content resulted in reduced nitridation rates. Within the investigated range of sample dimensions (0.2–4.0 g) the unexpected observation was made, that with decreasing sample weight the nitridation rate also decreased. This was explained by the exothermic nature of the reaction between Si and N2 and the fact that small samples with a large surface-to-volume ratio attain thermal equilibrium with their environment better than large samples which may be subject to local overheating.