The effects of Fe and NH4Cl on silicon nitridation

Silicon nitride (Si3N4) with a high α-phase content is in demand due to its higher thermal conductivity for use in heat dissipation bases for electronic devices. However, more needs to be understood about its fibrous growth, therefore, rich fibrous morphologies were synthesized with the assistance of Fe powder and NH4Cl. The effects of these additives on the phase content and fiber morphologies of the products were investigated The results illustrate that the Si3N4 products possess upper and lower layers and that when the Fe powder content is 4 wt% and NH4Cl content is 5 wt%, the Si3N4 fibers have smooth surfaces, uniform diameters, and no floating particles. Moreover, the maximum α-Si3N4 content reached 94.8 wt%, demonstrating an increase in this phase. The double mechanisms of vapor-liquid-solid and vapor-solid are presented as the growth mechanism at the fiber.

Origin of dislocation loops in α-silicon nitride

Dislocation loops and stacking fault formation mechanism in α–Si3N4 have been studied by annealing α–Si3N4 powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si3N4. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si3N4 lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si3N4 fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si3N4 lattice arisen from the fact that the observed unit cell dimension of α–Si3N4 has a wide variation, and also to some related phenomena in processing of Si3N4.