Physical changes of sintered ceramics obtained from freeze-dried ZnO+(CH 3COO) 2Cu·H 2O powders

Abstract

Freeze-drying was used to produce highly homogeneous mixtures of powders containing ZnO and (CH 3COO) 2Cu·H 2O (copper(II) acetate monohydrate, denoted by CuAcH 2O). Mixtures of ZnO+CuAcH 2O, in specific concentrations of Cu 2+, i.e., ZnO+ x mol% Cu (0.01≤ x≤5.0) were obtained by freeze-drying. Due to the polymeric characteristic of CuAcH 2O, pellets of those mixtures were compacted without any pressing additives. After sintering at temperature range 750–1150 °C in air for 1 h, physical changes such as mass loss, shrinkage and density were evaluated. The results showed that all physical changes increased as the concentration of CuAcH 2O increased. The mass loss was nearly independent of the sintering temperature, especially from 750 to 1050 °C, and directly proportional to the concentration of CuAcH 2O. The mass loss was mainly related to dehydration and thermal decomposition of CuAcH 2O, although the presence of water excess or sublimation of copper(II) acetate (CuAc) could not be neglected. In addition, contributions to mass loss were supposed to be related to sublimation of ZnO or reduction of CuO to Cu 2O, for sintering temperature above 1050 °C. Shrinkage and density were nearly independent of the sintering temperature above 850 °C, which indicates that sintering (grain growth) may occur in that temperature range. Shrinkage and densification increased as the concentration of CuAcH 2O increased, especially for ZnO+ x mol% Cu ( x>1.0). The presence of CuO particles on the ZnO surface, originated from thermal decomposition of CuAcH 2O during heating, is believed to promote shrinkage and densification.