Low temperature sintering of .ALPHA.-cordierite ceramics with low thermal expansion using Li2O-Bi2O3 as a sintering additive

Abstract

Low temperature sintering of α-cordierite ceramics with low coefficient of thermal expansion was attained using Li2O–Bi2O3 sintering additive. High purity α-cordierite could be synthesized at 1270°C using high purity and fine amorphous silica, α-alumina and magnesium oxide powder mixture via the solid state reaction route. The mixture was calcined at 1240°C, pulverized, compacted, and at first sintered without sintering additive. High density and outstanding characteristics cordierite ceramics was obtained. However, sintering temperature reached 1430°C, which was extremely high. By adding 3 mass % of the additive, the sintering temperature could be lowered from 1430 to 1050°C. Its relative density reached 97%, its flexural strength, however, decreased from 243 to 120 MPa. Its thermal expansion coefficient (from R.T. to 800°C) decreased slightly from 1.8 × 10−6/K to 1.6 × 10−6/K. Its dielectric constant increased slightly from 4.9 to 5.2 accompanied with considerable increase in loss tangent from 1.3 × 10−4 to 6.1 × 10−4 at 14 GHz, which were, however, low enough at this high frequency range. These results indicated that the addition of Li2O–Bi2O3 sintering additive had negligibly small effects on the properties of the sintered sample except mechanical properties and the loss tangent. These properties were found more excellent or at least comparable compared with the best properties previously reported and suitable for substrate materials on micro-electronic applications.