Physical changes of sintered ceramics obtained from freeze-dried ZnO+(CH3COO)2Cu•H2O powders

Freeze-drying was used to produce highly homogeneous mixtures of powders containing ZnO and (CH3COO)2Cu.H2O (copper(II) acetate monohydrate, denoted by CuAcH2O). Mixtures of ZnO + CuAcH2O, in specific concentrations of Cu2+, i.e., ZnO + x mol% Cu (0.0 less than or equal to x less than or equal to 5.0) were obtained by freeze-drying. Due to the polymeric characteristic of CuAcH2O, pellets of those mixtures were compacted without any pressing additives. After sintering at temperature range 750-1150 degreesC 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 CuAcH2O increased. The mass loss was nearly independent of the sintering temperature, especially from 750 to 1050 degreesC, and directly proportional to the concentration of CuAcH2O. The mass loss was mainly related to dehydration and thermal decomposition of CuAcH2O, 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 Cu2O, for sintering temperature above 1050 degreesC. Shrinkage and density were nearly independent of the sintering temperature above 850 degreesC, which indicates that sintering (grain growth) may occur in that temperature range. Shrinkage and densification increased as the concentration of CuAcH2O increased, especially for ZnO+x mol% Cu (x>1.0). The presence of CuO, particles on the ZnO, surface, originated from thermal decomposition of CuAcH2O during heating, is believed to promote shrinkage and densification. (C) 2003 Elsevier Science B.V. All rights reserved.