Inorganic Precursor For Sol-gel Preparation Of Mullite

The progress of preparation of mullite powder and the phase changes during mullitization have been reviewed. For preparation of ultrafme powder, the mullite powder from sol-gel process with colloid silica and alumina sol was systemically investigated.The existence of the Si-O-Al bond and its changes in the oxide product under heat treatment were determined by infrared spectrum technique. The thermal changes and crystallization of the gel were measured by both thermal analysis and XRD. We also studied the mullite powder's properties with Particle size analyzer and BET.It is shown that to prepare the stable mullite sol, the solution's pH must blow 3. And We found that the gel structure influences the phase change from gel to mullite. The nucleus of the gel prepared by addition of hydrochloric acid were composed of the silica, and the A1J" ions may be in the absorption layer of the gel. They subsequently form the Si-O-Al bonds under heat treatment. By addition of ammonia basis or acetyl acetone, the A1JT ions are impossible to come into its absorption layer, therefore, the Si-O-Al bond is not formed under heat treatment.Only the oxide product with Si-O-Al bond can be crystallized out the mullite before 1000 癈. The higher temperature is required to crystallize out the mullite for oxide product without Si-O-Al bond.It is also shown that there are aluminum-rich phase and silica-rich phase in the oxide products from the above mentioned acidic, basic and acetyl acetone approaches. The aluminum-rich phase can cause the formation of the Si-Al spinel under heat treatment.We found the oxalic acid has some effect on separate mullite powder..Based on the above research works, we prepared highly pure and ultra fine mullite powders with micro order. The applications of the mullite geled powder inceramics were investigated.