Influence of spark plasma sintering conditions on microstructure, carbon contamination, and transmittance of CaF2 ceramics

Commercial CaF2 powder was applied to fabricate transparent CaF2 ceramics by spark plasma sintering under various sintering conditions. The low sintering temperatures and high pressures caused serious carbon contamination, while the soak time had less influence on the carbon concentration in the ceramics. The highest carbon contamination occurred to the CaF2 ceramics sintered at 800 °C. A low sintering pressure suppressed carbon contamination but led to high porosity and large pore size. A high pre-loading pressure led to relatively high porosity and carbon concentration. Furthermore, the relatively fast densification in the edge region of the plates may cause the non-uniform distribution of porosity, thereby affecting the distribution of carbon concentration. The low pre-loading pressure and the high sintering pressure reduced porosity and carbon concentration to obtain dense transparent ceramic with uniform microstructure and high transmittance.