Journal of the American Ceramic Society, Vol.94, No.5, 1427-1433, 2011
Low-Temperature Sintering of High-Strength beta-Eucryptite Ceramics with Low Thermal Expansion Using Li2O-GeO2 as a Sintering Additive
Low-temperature sintering of high-strength beta-eucryptite ceramics with low positive coefficient of thermal expansion (CTE) was attained using Li2O-GeO2 sintering additive. High-purity beta-eucryptite could be synthesized using high-purity and fine amorphous silica, alpha-alumina, and lithium carbonate powder mixture at 950 degrees C via the solid-state reaction route. Accordingly, the mixture was calcined at 900 degrees C, pulverized, compacted, and sintered at 1020 degrees C for 2 h with the sintering additive. The sintering temperature could be lowered by about 300 degrees C, compared with the sintering temperature previously reported. The relative density of the sintered sample reached 99% of true density. Its flexural strength and indentation fracture toughness were 214 MPa and 2.5 MPa. m(1/2), respectively. Its CTE (from room temperature to 800 degrees C) was 1.2 x 10(-6)/K. Its dielectric constant was 5.5 with a loss tangent of 7.5 x 10(-3). However, prolonged sintering time resulted in large negative CTE and mechanical weakness in the sintered samples. Microcracks were introduced with prolonged sintering time, which caused their large negative CTE with mechanical weakness.