Dissolution of Alumina, Sintering, and Crystallization in Glass Ceramic Composites for LTCC

Abstract

Sintering and microstructure evolution of alkali‐free calcium–alumo–borosilicate glass/α‐Al 2 O 3 composites (mean particle size ca. 2 μm) for low‐temperature cofired ceramics were studied during heating at 5 K/min by heating microscopy, thermal analysis (DTA), X‐ray diffraction (XRD), and electron microscopy (SEM). Composites fully densify at ≈830°C, not essentially influenced by the dissolution of alumina and glass crystallization. Thus wollastonite, as first crystalline phase, was detectable at 840°C. Above 900°C, a pronounced crystallization of anorthite is evident, reaching 60 wt% at 1050°C. Rietveld analyses of XRD data revealed that anorthite precipitates at the expenses of alumina, which declines from ≈33 to <10 wt%, and wollastonite, which fully declines from its maximum of ≈19 wt%. Based on XRD, we discuss the evolution of crystal mass fractions, the residual glass composition, the glass viscosity, and the effective shear viscosity of the composites under study during heating.