Ku-Tak Lee,Boo-Hyun Choi,Jong-Un Woo,Jeong-Su Kang,Jong-Hoo Paik,Byoung-Uck Chu,Sahn Nahm
ZnS nanopowders annealed at low temperatures (≤550 °C) have a pure cubic structure, while a small amount of hexagonal phase formed in specimens annealed at temperatures ≥700 °C. The particle sizes of the ZnS nanopowders increased with the annealing temperature. ZnS ceramics that were sintered using ZnS nanopowders annealed at low temperatures (≤550 °C) exhibited low transmittance, because of their porous microstructure. ZnS ceramics that were synthesized using ZnS powders annealed at high temperatures (≥800 °C) containing large agglomerated particles, also exhibited low transmittance, due to the presence of a liquid phase. A carbonate absorption band was found from the ZnS ceramics with small grains, because carbon ions diffused from the graphite mold into the ZnS ceramics during sintering, probably through the grain boundaries, and formed carbonates. A ZnS ceramic that was sintered at 1020 °C using the nanopowders annealed at 750 °C exhibited dense microstructure, with a large transmittance, 68%, in the wavelength range 6.0–12 μm.
Boo-Hyun Choi,Dae-Su Kim,Ku-Tak Lee,Bum-Joo Kim,Jeong-Su Kang,Sahn Nahm
Hydrothermally synthesized ZnS nanopowders comprising small and large particles were used to synthesize ZnS ceramics. Small particles (200 nm) existed in the gaps between the large particles (0.7 μm) and assisted the densification of the ZnS ceramics. ZnS ceramics sintered at low temperatures (<1000°C) exhibited small grains with large grain-boundary areas that provided diffusion paths for carbon ions from the graphite mold, resulting in carbonate absorption bands. ZnS ceramics sintered at high temperatures (≥1000°C) for a long time (≥2.0 hours) exhibited a dense microstructure with very large grains (>500 μm). The ZnS liquid phase, which was formed at approximately 980°C, assisted the densification and grain growth of the ZnS ceramics. A 3.0-mm-thick ZnS ceramic sintered at 1000°C for 16 hours showed a high Knoop hardness (321 kgf/mm 2 ) and a high transmittance of 71% in the wavelength range 6.0-12 μm without carbonate absorption bands.
Chaoyu Li,Yubai Pan,Huamin Kou,Haohong Chen,Wei Wang,Tengfei Xie,Jiang Li
In this study, transparent ZnS ceramics were hot pressed from precipitated wurtzite nanopowders. Influences of sintering temperature on wurtzite-to-sphalerite phase transition and densification behavior have been investigated. Maximum sphalerite phase content and highest densification were simultaneously obtained in the sample hot pressed at 900°C with uniaxial pressure of 250 MPa for 2 h, which accounts for the highest transmittance above 55% and 70% in the range 2–5 μm and 5–13 μm, respectively. Preferred orientation of wurtzite grains in [002] direction paralleled to the press direction was also observed, which is supposed to be benefit to transmittance by reducing birefraction and second-phase scattering. Furthermore, second-phase scattering caused by wurtzite grains has been investigated. It is found that fine grains are conducive to hot-pressed ZnS ceramics with high transmittance, especially in the short-wavelength range.
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