SUPPRESSION OF CRYSTALLIZATION DURING SINTERING OF LEAD BOROSILICATE GLASS POWDERS

Cristobalite is formed when an initially amorphous lead borosilicate glass is sintered at temperatures ranging from 700 to 1000 degrees C. X-ray diffraction results show that with a sufficient amount of gallium oxide present, however, the precipitation of cristobalite is completely prevented. The amount of gallium oxide required to inhibit cristobalite formation decreases with increasing sintering temperature. The above results are further evidenced by the linear thermal expansion measurement, in which the thermal expansion of the cristobalite-free sample is much smaller than that with cristobalite. The resulting cristobalite-free glass composite has a thermal expansion coefficient of 3.5 X 10(-6) K-1 in the temperature range of 20-200 degrees C, and a dielectric constant of 5.1 at 1 MHz.