Effect of green density on the thermomechanical properties of a ceramic during sintering

The thermomechanical properties of a commercial barium titanate were experimentally or theoretically determined for samples with green densities ranging from 45% to 55%. For stresses less than 300 kPa, sample deformation was determined to be linear viscous for all three stages of sintering. The shrinkage rates at a given temperature can differ by up to ∼ 25% as the green density changes from 45% to 55%, and the maximum shrinkage rate increased with decreasing green density. The increase in shrinkage rate with lower green density samples persisted through the final sintering stage. The viscosity was determined by cyclic loading dilatometry to range from 5 to 6 GPa·s in the initial stage of sintering, to 2 GPa·s in the intermediate stage, and to increase to 10-20 GPa·s for all specimens in the final stage of sintering. Differences in the final-stage viscosity were attributed to grain size differences. Relaxation times for the sintering body were estimated to be less than 1 s, indicating that viscous behavior is dominant throughout the sintering process.