Thermodynamic Properties of Non-Oxide Composite Refractories

For initiative application of non-oxides in refractories, it is essential to study thermodynamic properties of non-oxides. The stability and stable order of non-ox- ides under oxidized atmosphere are analyzed firstly and then a new process, “converse reaction sintering”, is proposed. The results of study on oxidation mechanism of silicon and aluminum nitrides indicate that the gaseous suboxides can be produced observably when the oxygen partial pressure is lower than “conversion oxygen partial pressure”. The suboxides can be deposited near the surface of composite to become a compact layer. This causes the material possessing a performance of “self-impedient oxidation”. Metal Si and Al are the better additives for increasing the density and width of compact layer and increasing the ability of anti-oxidation and anti-corrosion. The study on Si3 N4-Al2O3, Si3N4-MgO, Si3 N4-SiC systems is also enumerated as examples in the paper. The experimental results show that the converse reaction sintering is able to make high performance composites and metal Si and Al not only can promote the sintering but also increase the density and width of compact layer.