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‐Al2O3 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.

Sintering and Foaming of Barium Silicate Glass Powder Compacts

“…As discussed in previous literature, different sources may contribute to foaming: gases encapsulated within the closed pore volume of the powder compact (Lim et al, 2006;Kim et al, 2007;Müller et al, 2009), gases adsorbed onto the glass powder surface (Hwang et al, 2002), glass volatilization (Lucchini et al, 1983), or effusing oxygen from the glass bulk (Hwang et al, 2002). Due to the strong effect of particle size on foaming activity (Figures 1 and 5), the latter two mechanisms should not dominate foaming in the present study.…”

“…Due to the decreased sintering pressure of larger pores, less gas is forced to dissolve into the glass melt, and low viscosity allows easy bubble growth. An analogous explanation was given by Kim et al (2007) for foaming of lead-free Bi2O3-B2O3-SiO2 solder glass powders and by Müller et al (2009) for LTCC model glass powders. Undesired porosity was also observed during sintering ashes for porcelain tile production, which was attributed to "some boiling and trapped gas effects" (Fernandes and Ferreira, 2007).…”

Wet chemical porosification of LTCC in phosphoric acid: Anorthite forming tapes

“…In alkali-free calcium-alumino-borosilicate glass, the accompanying consumption of the Al 2 O 3 during firing can reduce their amount from 33 wt% to approx. 10 wt% [38]. In 951 the densification starts at approx.…”

Sinterización de compactos de vidrio y de composites vidrio-circón. Mecanismo y cinética del proceso

“…En Especialmente a temperaturas elevadas, el mojado de la inclusión por el vidrio es elevado, incluso completo, y la disolución de los cristales y difusión de los iones resultantes en la matriz vítrea son también altos, lo que provoca un cambio sustancial de la composición de ésta última, facilitando con ello la precipitación de cristales secundarios. Dicho fenómeno se ha comprobado en composites de borosilicato de calcio/alúmina, en los que se forma anortita, hasta un 60%, coincidiendo con la disolución de corindón, a temperaturas comprendidas entre 900 y 1050ºC [39]. También son frecuentes los procesos de disolución de fases cristalinas en el fundido y la posterior cristalización de otras durante la cocción de vidriados cerámicos.…”