Interdependence between green compact property and powder agglomeration and their relation to the sintering behaviour of zirconia powder

Abstract

Interdependence of green density and corresponding powder agglomeration and their influence on the sintering behaviour of commercial fine zirconia powders under a constant rate of heating (non-isothermal sintering) were investigated. Agglomeration of the powder was controlled by different time periods of ball-milled processing and was defined as the size ratio of sedimentationally-measured particle size to the size of primary particles which were microscopically-determined (hereinafter termed agglomeration parameter or AP). Green compact density shows to be approximately linearly related to powder agglomeration under identical consolidation technique, which is decreased with increasing degree of agglomeration. Both the green density and powder agglomeration affect sintering behaviour over entire sintering schedule. For a given AP the shrinkage rate reduces with increasing green compact density and vice versa, which is consistent with the literatured reports. The experimental results also showed that compacts with identical starting density showed a lower shrinkage rate when the compacts contained less agglomeration (i.e. low AP) than does for high-AP compacts. However, a higher end-point density can be obtained for low-AP compacts, suggesting a better packing structure of the powders. The use of agglomeration parameter defined currently, which is taken as an indication of the level of powder agglomeration in commercial fine ceramic powders, is likely to provide some useful understanding in characterising the sintering behaviour and possibly potential evolution of sintered microstructure on sintering.