Haruyo NAKAGAWA

Effect of Aluminum Phosphate on the Properties of Silica Glass Prepared by Pulsed Electric Current Method

Kazumasa MATSUSHITA

Low expansion glass is important as substrate material of electronic devices. It is supposed that SiO2-Al2O3-P2O5 glasses have lower refractive index depending on the composition. Thus it is expected to apply these glasses to optical devices. But it is difficult to prepare these glasses of this system because of crystallization and high melting temperature. Therefore, it takes long time and consumes much energy to prepare these glasses.
The present study was to develop glass manufacture method that requiring only short time and low energy consumption. Pulsed electric current method was used to prepare SiO2-Al2O3-P2O5 glasses. The optical and thermal properties of the glasses were measured as a function of Al2O3 and P2O5 contents. As raw materials of aluminum phosphate, AlPO4 and Al(PO3)3 were used. Glasses were obtained in the composition ranges AlPO4:0-3.8mol% and Al(PO3)3:0-3.1mol%. In both series of raw material, it was founded density and refractive index increased linearly with increase of aluminum phosphate content. But thermal expansion coefficient increased parabolically. Those results show that the glass structure changes with composition. Infrared absorption spectrum was measured to analyze the glass structure. On Infrared absorption spectrum, Absorption Peak, which is caused by combination of Al or P, was observed clearly with increase of aluminum phosphate content. In result, it was supposed that "triclusters" exist in these SiO2- AlPO4 glasses. In triclusters one oxygen atom is bonded to three tetrahedra. Also it was supposed that P�|O�|P and P=O bonds exist in SiO2-Al(PO3)3 glass.
The glasses containing Al(PO3)3 were changed to yellow after heat-treatment. It is considered that coloring was caused by P-colloid, which followed phase separation and precipitation of crystal.