Sintering behavior of calcium lanthanum sulfide ceramics in field‐assisted consolidation

Abstract

In this study, calcium lanthanum sulfide (CaLa 2 S 4 , CLS) ceramics with the cubic thorium phosphate structure were sintered at different temperatures by fieldassisted sintering technique (FAST). Densification behavior and grain growth kinetics were studied through densification curves and microstructural characterizations. It was determined that the densification in the 850°C-950°C temperature range was controlled by a mixture of lattice or grain-boundary diffusion, and grain-boundary sliding. It was revealed that grain-boundary diffusion was the main mechanism controlling the grain growth between 950°C and 1100°C. The infrared (IR) transmittance of the FAST-sintered CLS ceramics was measured and observed to reach a maximum of 48.1% at 9.2 lm in ceramic sintered at 1000°C. In addition, it was observed that the hardness of the CLS ceramics first increased with increasing temperature due to densification, and then decreased due to a decrease in dislocations associated with grain growth. K E Y W O R D S

Processing of CaLa2S4 infrared transparent ceramics: A comparative study of HP and FAST/SPS techniques

“…This results in a negligible change in hardness values with regard to the standard deviation (Table ). These values are consistent with the ones reported in the literature …”

“…We retain, though, that FAST technique results in fragmentation of the CLS ceramics. Note that this issue was not mentioned in the work of Li et al, who reported comparable sintering conditions for commercial CLS powders. The difference between HP and FAST techniques lies in the way the heat is produced and transmitted to the material.…”

“…These values are consistent with the ones reported in the literature. 3,29 T A B L E 3 EDS analysis of ceramics HPed at 800°C (HP1), Figure 10 shows the IR transmission spectra of the HP ceramics (th = 1.9 mm) sintered at 800°C, 900°C, 1000°C, and 1100°C. One can observe that the influence of sintering temperature on the level of transmission is significant.…”

“…These precursors are subsequently sulfurized in H 2 S or CS 2 atmosphere and converted into pure CLS powders. Sintering of the powders is thereafter carried out by different sintering techniques: Hot pressing (HP), natural sintering in sulfurizing atmosphere followed by HIP, or Field‐Assisted Sintering Technique (FAST also denominated as spark plasma sintering (SPS)) for which, to the best of our knowledge, only two references have been published very recently …”

“…Sintering of the powders is thereafter carried out by different sintering techniques: Hot pressing (HP), 4,6,[24][25][26] natural sintering in sulfurizing atmosphere followed by HIP, 2,3,12,27 or Field-Assisted Sintering Technique (FAST also denominated as spark plasma sintering (SPS)) for which, to the best of our knowledge, only two references have been published very recently. 28,29 Reduction phenomena of CLS at high sintering temperatures, namely T ≥ 1000°C, are generally reported issues for sintered CLS ceramics. 4,6,10,13 [33][34][35]37 (they are noted La 3 S 4 :Ca for simplification).…”