1. College of Metallurgical Science and Engineering, Central South University, Changsha 410083, China 2. Key Laboratory for Nonferrous Metal Materials of the Ministry of Education，School of Materials Science and Engineering, Central South University, Changsha 410083, China
Abstract：The structural changes in the in-situ controlled crystallizing process of Si—Al—Zr—O(SAZ) amorphous bulk were investigated by laser Raman (LRa), infrared (IR) and X-ray diffraction (XRD) techniques. The structure of the amorphous network apparently reorganized at about 920 ℃, resulting in the formation of Si-rich and Al, Zr-rich regions. The t-ZrO2 was crystallized from the Zr-rich region at 920~950 ℃ and poorly defined Al—Si spinel was formed from the Al-rich regions. With the increase in temperature, the peak of Al—Si spinel was enhanced and then disappeared in the XRD pattern, and the characteristic IR band groups of mullite centered in the 1 200~1 100, 1 000~700 and 650~400 cm-1 could be observed. At 1 100~1 150 ℃, the Raman bands at 179 and 193 cm-1 typical for the m-ZrO2 occurred and cristobalite was detected, and the main crystalline phases were identified as t-ZrO2 and mullite. These results indicated that mullite was formed by reaction between amorphous silica and the Al—Si spinel which was metastable phase. During the heating process, t-ZrO2 was crystallized firstly and a portion was transformed to m-ZrO2 at high temperature, and the left amorphous silica was transformed to cristobalite.
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