Abstract
Co-precipitate mixtures containing zinc and aluminum hydroxides were prepared by either heterogeneous and homogeneous co-precipitation. The co-precipitate mixtures were washed and dried, and both ZnO and ZnAl2O4 were formed with firing.The particle size of ZnO increased with increased firing temperature and/or with increased amount of ZnO in the powder, while the particle size of ZnAl2O4 was relatively small, being less than 0.5μm.These ZnO-Al2O3 powders prepared by co-precipitation were applied to zinc phosphate cement. It was found that the ZnO particles reacted with the phosphoric acid faster than the ZnAl2O4 particles when the experimental cement powders were mixed with a commercial zinc phosphate cement liquid. The experimental cement powders containing a large amount of ZnAl2O4 showed slow setting time, low compressive strength and high disintegration. The powder containing a large amount of ZnO also showed the same results, because a low powder/liquid ratio was needed to achieve a standard consistency despite the large particle size of ZnO. Therefore, the experimental cement powders containing 30〜50wt% Al2O3 showed good results and met acceptance criteria(JIS-T-6602). However, the disintegration of the experimental cements was 2 or 3 times as large as that of the commercial zinc phosphate cement, and the surface of the experimental cements exhibited slow neutralization because of slow setting reaction. On the other hand, the solubility in citric acid or lactic acid was nearly the same as that of the commercial zinc phosphate cement.
