Abstract
Effects of alumina on the devitrification kinetics and dielectric properties of a low-dielectric CaO-Al2O3-SiO2 glass powder have been investigated. Crystalline phases including pseudowollastonite, anorthite and cristobalite are formed during firing of the glass. The crystallization kinetics of crystalline phases follows the analyses of the Avrami equations. Combined with the results of reduced growth rate, the rate-controlling step appears to be alkali ion diffusion in the glass. With added alumina content greater than a critical value, the above crystalline phases are completely suppressed but anorthite is formed. This result is attributed to the dissolution of alumina into the glass which changes the composition of the glass. By using Avrami analysis, the rate-controlling mechanism changes to reaction-controlled kinetics which has an activation energy closely related to Al-O bonding. With increasing anorthite formed, the composites exhibit insignificant change in dielectric constant, but a significant decrease in dielectric loss.