Search

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.

We report that the corrosion resistance of Mg–8Sn–1Zn–1Al alloy is significantly improved by the application of a low-temperature indirect extrusion process utilizing artificial cooling. It was found that the corrosion rates, measured by immersion tests in 0.6 M NaCl solution at 25 °C, are 27.5 and 246.7 mm y−1 for the alloys extruded with and without artificial cooling, respectively. The remarkably improved corrosion resistance is mainly attributed to the reduced nobility of cathodic Al5Fe2 particles, which results in retarded microgalvanic corrosion in the corrosive condition. Metallurgical factors affecting the electrochemical nobility of Al5Fe2 particles are discussed.

We report that alloying with Y remarkably enhances the corrosion resistance of extruded Mg–Al–Ca-based alloy. The corrosion rates, measured by immersion tests in 0.6 M NaCl solution at 25 °C, were 0.31 and 1.84 mm y −1 for the Mg–6Al–1Zn–0.5Ca–0.3Mn (wt.%) alloys with and without 0.25 wt.% Y, respectively. The improved corrosion resistance is mainly attributed to a change in the type of Al-containing intermetallic particles toward reducing their electrochemical nobility, resulting in reduced H 2 evolution rate during corrosion.

Hexagonal wurtzite (HWZ) ZnS nanorods were formed in specimens with a S/Zn ratio of 1.3, synthesized at temperatures ≥200 °C in a solution containing 80 vol% water and 20 vol% of ethylenediamine (EN). In contrast, HWZ ZnS nanoparticles were formed in specimens synthesized at temperatures lower than 200 °C. Also, cubic zinc blende (CZB) ZnS nanoparticles were formed in specimen synthesized in water. The absorption peak for the HWZ nanorods and CZB ZnS nanoparticles was at wavelength of 325 nm and 339 nm, respectively, indicating that the band gap energy of the former is larger than that of the latter. Moreover, the HWZ ZnS exhibited two emission peaks at 474 nm and 580 nm. The peak at 474 nm is attributed to Zn vacancies but the origin of the peak at 580 nm remains undetermined. Since the intensity of the emission peak at 580 nm was significantly higher for the HWZ nanoparticles than for nanorods, this peak might be associated with defects in the HWZ ZnS nanoparticles.