Preparation of zirconia mullite flakes via a plasma rapid solidification process using starting materials derived from a sol-gel technique

Flakes of zirconia-mullite with different zirconia contents varying from 3 to 24 wt% were produced from sol-gel derived raw materials via a plasma mel ting method followed by a rapid solidification process using a rotating cop per roll. The morphology, phase constitution and microstructure development of the as-prepared flakes and of the flakes after various heat treatments were investigated by means of X-ray diffraction (XRD), scanning electron mi croscopy (SEM), transmission electron microscopy (TEM) and energy dispersiv e spectroscopy (EDS). It was found that the starting materials could be tra nsformed from the initial irregular-shaped powders into flakes which consis ted of mullite, zirconia phase, a relatively large amount of glassy phase a nd pores. Using TEM, it was shown that the crystalline phases consisted of zirconia polymorphs and mullite. The glassy phases consisted of Al2O3-SiO2 solid solution supersaturated with zirconia. Firing at 1500 degreesC or 170 0 degreesC resulted in full crystallisation of the flakes and a fairly homo geneous distribution of zirconia particles in terms of size and shape dispe rsed in the mullite matrix, which contained both intra-granular and inter-g ranular precipitates. The microstructural characteristics of the flakes may provide promising physical properties for applications in high temperature thermal insulation materials. (C) 2001 Elsevier Science B.V. All rights re served.