Effect of cristobalite formation on sinterability, microstructure and properties of glass/ceramic composites

Six glass/ceramic composite materials were prepared from pure alumina and borosilicate glass (BSG) with chemical composition of 99.0 Al2O3 and 80.5 SiO2, 12.9 B2O3, 3.8 Na2O, 2.2 Al2O3, 0.4 K2O and 0.2 CaO wt.%, respectively. These batches were sintered at different firing temperatures up to 1300 degreesC. XRD, microstructure and properties, namely thermal expansion, dielectric constant and hardness of prepared composites were examined, respectively. The results reveal that the crystallization of borosilicate glass in glass/alumina composite can be prevented by varying the alumina content in the glass matrix, by which the diffused aluminum ion change the structure of glass. When approximately greater than or equal to30 wt.% of allumina filler is added, the structure of glass changes enough to decrease the formation of cristobalite crystals and consequently decrease the thermal expansion coefficient and dielectric constant. In glass/alumina system, phase formation is influenced by firing temperature and alumina content as follows: (a) when alumina content and firing temperature are low, the precipitated phase is cristobalite, (b) at high temperature and high alumina content, mullite is formed in the glass phase. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.