The formation of Si and Al sols, and the micro-structural changes of the dual phase Si-Al gel in the in-situ crystallizing process were investigated by Laser Raman(LRa), Fourier Transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The results show that the disordered network structure is composed of Si—O…H and Al—O…H groups in the Si and Al sols, respectively. After the thermal treatment at 600℃, the dual phase Si-Al gel is obtained with non organic impurity phase. At 800 ℃, the amorphous structure of the Si-Al double gel apparently reorganizes, resulting in the formation of a small amount of AlO4 tetrahedron and AlO6 octahedral units. The Si-Al spinel was crystallized from the sample at 1 000 ℃. With the increase of temperature, the peak of Al-Si spinel enhances and then disappears in the XRD pattern. At 1 200 ℃, the characteristic FT-IR bands of mullite at 1 130 cm−1 and 1 170 cm−1 indicates that the Al—O—Si bond is formed, and the Raman bands at 310, 410, 600, 960, 1 037 and 1 129 cm−1 typical for mullite occur. When the temperature increases to 1 450℃, the main crystalline phases are identified as mullite with a small amount of Alumina, the spinel phase disappears. These results indicate mullite is formed from the Si-Al spinel, which is metastable phase at 1 200−1 400℃in the heating process of the dual phase gel.%借助Raman，FT-IR和XRD等技术探讨Si和Al溶胶的形成及Si-Al双相凝胶在原位受控晶化过程中微结构变化。研究结果表明：Si和Al溶胶分别以Si—O…H和Al—O…H基团构成的无序网络结构形式存在。经600℃热处理后，Si-Al双相凝胶中基本不存在有机杂相；当温度升至800℃，该非晶试样已开始网络结构重排，形成少量有序AlO4四面体区和AlO6八面体区；经1000℃热处理后，试样中开始析出Si-Al尖晶石相；随着温度进一步升高，Si-Al尖晶石相衍射峰增强，经1200℃热处理后，在1130 cm−1和1170 cm−1附近出现明显的红外吸收峰，表明莫来石(mullite)中Al—O—Si键形成，同时检测到莫来石的拉曼特征峰；温度继续升高至1450℃时，尖晶石相消失，除了莫来石相外，还有少量Al2O3析出。采用本方法制得的Si-Al双相凝胶首先形成Si-Al尖晶石相，然后在1200~1400℃下转化为纯的莫来石相。
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