Formation Mechanism of Zircon Phase in ZrB_2-SiC Ceramic Composites during Oxidation

Oxidation of ZrB2-20vol% ceramic composites in air was investigated,and the effects of oxygen partial pressure,oxidation temperature and holding time on the formation of zircon phase ZrSiO4 were analyzed.The formation mechanism of zircon during oxidation in air of zirconium diboride-silicon carbide ceramic composites is proposed.Active oxidation of SiC is the major reason to explain the appearance of zircon according to thermal dynamic calculation results.The experimental results indicate that the formation of zircon can be divided into two steps:(I) Nucleation,which is related to the active oxidation of SiC;(II) Crystal growth,which is fulfilled by the reactions between silicate glass and zirconia crystalline at the interface of the zircon nuclei / melt.Zircon particles with mean size of 100 μm can be observed after oxidation in air for 90 min.