Viscous Flow as the Driving Force for the Densification of Low‐Temperature Co‐Fired Ceramics

Abstract

Filled glass–ceramic composites, like low‐temperature co‐fired ceramics (LTCC), must densify at temperatures <900°C. The densification mechanism of LTCC is often described by liquid‐phase sintering. The results of this paper clearly show that densification of ceramic‐filled glass–composites with a glass content above 60 wt% can be attributed to viscous sintering, which is decisively controlled by the viscosity of the glass during the heat treatment. This is demonstrated by the experimental determination of the viscosity of a MgO–Al2O3–B2O3–SiO2 glass dependent on temperature, by investigation of the wetting behavior of the glass on the ceramic filler mullite, and of the microstructural development. It was found that the glass does not wet the filler material in a temperature range up to 1000°C. Therefore, liquid‐phase sintering can be excluded. Independent of any wetting effect and therefore in the absence of capillary forces, densification starts at a temperature of 750°C, which corresponds to a viscosity of 109.5 dPa·s. This densification can be attributed to viscous flow of the glass matrix composite.

Preparation and properties of crystallizable Glass/Al2O3 composites for LTCC material

“…It was found that the glass does wet the filler material is very important by investigation of the wetting behavior of the glass on the ceramic filler, and of the micro structural development [13] .…”

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

“…Debido a que la sinterización es impulsada por las energías interfaciales de los poros y de los cristales dispersos en el fundido viscoso y que este proceso se desarrolla mediante un transporte de materia por flujo viscoso, a este mecanismo de sinterización también se le denomina "sinterización viscosa", incluso aún cuando no se produzca un buen mojado de las partículas rígidas por el vidrio [2]. La Figura 2.2 ilustra esquemáticamente los fenómenos clave de la sinterización viscosa de GMCs.…”

“…= tensión superficial del vidrio; η= viscosidad del vidrio; c=8 (2) 0,5 /3π; aS y LS = radio y longitud del cilindro del modelo Scherer; n*= concentración numérica de poros; rp = radio del poro y el subíndice "0" indica el inicio de sinterización.…”

Low-temperature sintering and dielectric properties of the Bi(Nb1−x Ta x )O4 system

“…It is, moreover, considered that the non-reactive liquid phase sintering (NPLS) occurred in this system [17,18]. The NLPS is one of the liquid-assisted sintering (LAS) [19]; LAS distinguishes between the NLPS, where a glass phase content of at least 20-40 vol.% is necessary for the densification and a reactive liquid phase sintering, where a glass content <20 vol.% is sufficient. The densification in the NLPS was proposed in three stages; the first stage is glass redistribution and local grain rearrangement where only slight densification occurs, the second is the main densification process including global rearrangement, glass redistribution, and closure of pores where the density from 65 to 90% of the theoretical density is accomplished, and the third is viscous flow where the residual porosity of about 10% is closed.…”