Pressureless sintering of silicon nitride powders with Al2O3, MgO, MgF2 sintering aids

Silicon nitride based ceramics are of some specific characteristics, that is to say, hardening, abrasion resistance, oxidation resistance, perfect thermal shock resistance and they retain these properties at high temperatures. Thus, they are preferred in some specific areas. Due to the fact that Si3N4 ceramics have strong covalent bonds, their diffusion coefficient is low. Due to this reason, it is difficult to sinter pure silicon nitride. The properties of Si3N4 based ceramics change depending on preparation before sintering, additive, and sintering method. It is known that Si3N4 can be produced in full density using pressureless sintering method with various additives. However, pressureless sintering is both cheaper techniques and provides more complex result product comparing to other methods sintering methods.At this study, Silicon nitride powders were sintered with the addition of MgO, Al2O3, MgF2 at various temperatures and different compositions in nitrogen atmosphere using graphite furnace. Si3N4 powders were sintered with pressureless sintering technique with additives of MgO, Al2O3, MgF2 and nearly full dense results were achieved. The sintered Si3N4 ceramics density measurements were characterized by using archimedes method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were also carried out.Keywords: Silicon nitride, Liquid phase sintering