Preperation of Powders in the Al2O3-SiO2 System by Hydrothermal Treatment of Alkoxide

Aluminosilicate powders were obtained by hydrothermal treatment of mixed alkoxide solution containing Al2O3: SiO2 = 3: 2 (mol ratio) with distilled water at 300-600˚C under 10-100 MPa for 2 hr. Very fine crystalline pseudoboehmite (γ-Al00H)-like phase was formed at 300-500˚C under 10-100 MPa. Above 600˚C, instead of the pseudoboehmite-like phase, amorphous product was formed under 10 MPa, Al-Si spinel under 50 MPa, and hydralsite (2Al2O3.2SiO2.H2O), AS(H)-II (close to Al2SiO5), Al-Si spinel and a small amount of mullite (3Al3O3.2SiO2-2Al2O3-SiO2) under 100 MPa, respectively. Transmission electron microscope (TEM) revealed that the pseudoboehmite-like phase obtained at 300˚C under 50 MPa was thin plate of about 10 ran thick and 100 nm long, and contained homogeneously both Al and Si in the narrow area as a few hundreds nm2, by energy dispersive spectrometric (EDS) analysis. The organic solvent such as benzene and alcohol might stabilize the fine crystals of pseudoboehmite-like phase and prevent the crystalization of hydralsite or As(H)-II.