Effects of sintering additives on preparation of CaF2 transparent ceramics

Abstract

The effects of different sintering addictives on the preparation of CaF2 transparent ceramics were studied. Transparent CaF2 ceramics were fabricated by vacuum sintering and hot isostatic pressing (HIP) method, using CaF2 nanopowders synthesized by chemical precipitation method as raw materials. The nanopowders and transparent ceramics were studied using X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and spectrophotometer. The experimental results indicated that the obtained nanopowders presented normal distribution with grain size about 30 nm; transmittance of CaF2 transparent ceramics was 39% and 26% at 1100 nm for LiF and NaF as sintering addictives, respectively, with corresponding mean grain size 188 μm and 44 μm. Loss of transmission could be attributed to the residual closed porosity. Sintering mechanism was liquid-phase sintering at pre-stage, then solid-phase sintering at later stage, as well as solid solution of lithium ions and sodium ions in the CaF2 lattice structure.