Ultrafine particles of the ZrO2-SiO2 system prepared by the spray-ICP technique

Ultrafine powders of the ZrO₂-SiO₂ system prepared by spraying aqueous mixed solutions of ZrO(NO₃)₂·2H₂O and silicone oil into an ultrahigh temperature inductively coupled plasma (the spray-ICP technique) have been investigated in connection with particle growth and phase change caused by heat treatment. The prepared powders were composed of roundish ultrafine particles 10 to 20 nm in size, and their components were tetragonal ZrO₂ (t-ZrO₂) and amorphous SiO₂ (a-SiO₂).a-SiO₂ alone did not crystallize below 1400° C, though the particles grew above 900° C.t-ZrO₂ converted to monoclinic ZrO₂ (m-ZrO₂) above 400° C, also followed by particle growth. On the other hand composite powders oft-ZrO₂ anda-SiO₂ exhibited no particle growth below 1200° C. Above 1200° Ct-ZrO₂ converted tom-ZrO₂, and its amount decreased with an increase in SiO₂ content. At 1400° C particle growth occurred, and the round particles of ZrO₂ were dispersed in ana-SiO₂ glass medium. These results indicate that ZrO₂ and SiO₂ mutually block particle growth, and that SiO₂ contributes to the quenching oft-ZrO₂ by keeping the particles of ZrO₂ within the critical particle size oft-ZrO₂.