Ceramic system based on ZnO•CuO obtained by freeze-drying

Compositions of powders containing ZnO and copper(II) acetate monohydrate [(CH3COO)(2)Cu.H2O, denoted CuAcH2O] equivalent to ZnO+x mol% Cu (x=0, 0.05, 0.5 and 5.0) were obtained by freeze-drying. The powders were characterised by thermogravimetry (TG) up to 700degreesC and differential scanning calorimetry (DSC) up to 1150degreesC, in static air with heating rate of 5degreesC/min. Pellets of the freeze-dried powders were compacted without pressing additives and sintered in air at 950degreesC/1 h. After crushing, the crystalline phases of the sintered samples were characterised by powder X-ray diffractometry (XRD). Microstructure and Cu-element mapping of sintered ZnO+5.0 mol% Cu samples were characterised by scanning electron microscopy (SEM) with microprobe apparatus. TG and DSC indicated the presence of three important thermal events. Event I: (100-190degreesC) corresponds to dehydration of CuAcH2O, giving rise to copper(II) acetate [(CH3COO)(2)Cu, denoted CuAc], with an endothermic peak at 125degreesC. Event II: (190-350degreesC) corresponds to thermal decomposition of CuAc giving rise to CuO, with two exothermic peaks at 237 and 261degreesC. In air, above 350degreesC, the ceramic system is ZnO.CuO. Event III: (800-1000degreesC) corresponds to a solid-state reaction involving ZnO.CuO, with an exothermic peak at 895degreesC. DSC, XRD and SEM indicated that, after sintering at 950degreesC/1 h, the resulting ceramic matrix is composedby Cu-doped ZnO grains (ZnO/Cu) for ZnO+x mol% Cu (xless than or equal to1) and by ZnO/Cu grains with CuO-inclusions (ZnO/Cu.CuO) for ZnO+x mol% Cu (xgreater than or equal to1). (C) 2003 Elsevier Science B.V All rights reserved.