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Influence of Sintering Conditions on the Microstructure and Properties of Alumina-Filled Borosilicate Glass
P.F. Araújo, L.B. Daros, M. Souza, D.E. García, D. Hotza, D. Hotza
Abstract
Alumina-filled borosilicate glass composites (1-x) glass + xAl2O3 (x = 0, 5, 10, 15, 20 vol%) were fabricated by means of conventional sintering at 800 and 850 °C and fast firing at temperatures between 850 and 950 °C. The effect of particle size, heating rate and holding time at maximum temperature on phase composition and densification was investigated. The effect of Al2O3 addition on microstructure, flexural strength, fracture toughness, electrical conductivity, and thermal expansion coefficient is reported. Al2O3 hinders the formation of cristobalite and enhances the mechanical properties of borosilicate glass. Composites containing 10 vol% alumina fabricated by means of conventional sintering exhibited 98 % TD, flexural strength of 175 MPa and fracture toughness of 1.9 MPa·m1/2. Crack path and fracture surface observations showed that crack deflection, crack bridging and pull-out by alumina particles were responsible for the increase in fracture toughness. Samples fabricated by means of fast firing exhibited a decrease in flexural strength of ∼ 50 % and an increase in fracture toughness of ∼ 40 % when compared to conventional sintering. This behaviour could be related to the presence of microcracks originating from β-to-α cristobalite transformation during rapid cooling from the sintering temperature. In conventionally sintered samples, the addition of 5 vol% alumina to borosilicate glass increases hardness from 4.7 to 5.6 GPa, and the dielectric constant from 5.5 to 6.5.
Keywords
Alumina, borosilicate glass, ceramic-filled glasses, fast firing, sintering
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