Uniaxial viscosity of low-temperature cofired ceramic (LTCC) powder compacts determined by loading dilatometry

This paper reports on the experimental determination of the uniaxial viscosity of two commercially available low-temperature cofired ceramic (LTCC) powder compacts, Ceramtape GC (glass-ceramic) and Ferro A6M (glass), by loading dilatometry. Isothermal sintering of cylindrical green compacts was carried out at temperatures ranging from 720 to 840 °C and under varying uniaxial compressive loads of 0–50 N (corresponding to 0–0.5 MPa). Both instantaneous radial and axial strains were measured during sintering. These data were analyzed by using constitutive laws for a porous sintering body and the uniaxial viscosity was calculated as a function of relative density. The activation energy for viscosity was independent of relative density and showed an average value of 668±76 kJ/mol for the Ceramtape material but was not accessible for the Ferro material. The viscosity data were compared with several theoretical models.