Chang Sung Lim

Synthesis of ZnWO4 nanocrystalline powders, by the polymerized complex method

Abstract Nanocrystalline ZnWO 4 powders were successfully prepared by the polymerized complex method using zinc nitrate and tungstic acid as starting materials. The polymeric precursors were heat-treated at temperatures from 300 to 600 °C for 3 h. The precursors and heat-treated powders were evaluated for crystallization process, thermal decomposition, surface morphology and crystallite size. Crystallization of the ZnWO 4 powders was detected at 400 °C and entirely completed at a temperature of 600 °C. The particles heat-treated at 400 and 500 °C showed primarily co-mixed morphology with spherical and silkworm-like forms, while the particles heat-treated at 600 °C showed more homogeneous morphology with a narrow size distribution. The average crystalline sizes were 19.92–24.16 nm, showing an ordinary tendency to increase with the temperatures from 400 to 600 °C.

Microwave-Assisted Synthesis of MWO4 and MMoO4 (M = Ca, Ni) Nano-Powders Using Citrate Complex Precursor

Nano-sized MWO4 and MMoO4 (M = Ca, Ni) powders, which have scheelite and wolframite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heattreated at temperatures from 300 to 600 °C for 3 h. Crystallization of the MWO4 and MMoO4 precursors was detected at 400 °C and completed at a temperature of 500 °C. Most of the MWO4 and MMoO4 powders heat-treated between 300 and 600 °C showed primarily spherical and homogeneous morphology. The average crystallite sizes of MWO4 (M = Ca, Ni) were between 22 and 39 nm, and those for MMoO4 (M = Ca, Ni) were between 19 and 35 nm respectively, showing an ordinary tendency to grow with temperature.

Columnar inter-grains and toughening of SiC–AlN ceramics induced by addition of α-SiC

Abstract The fabrication of SiC–AlN solid solutions with columnar inter-grains using the addition of small amounts of α-SiC to an AlN–β-SiC mix was studied by hot-pressing under 2030°C. The appreciable amounts of α-SiC content for a reaction of AlN and β-SiC affected the SiC–AlN phase relationships and the microstructures by stabilizing a 2H phase. It could develop columnar inter-grains of 4H phase and the stable 2H phase with a uniform composition and grain size distributions. The α-SiC containing samples showed fracture toughness of 5.1–5.4 MPa m 1/2 . The fracture toughness was related to the amounts of 4H present. The enhanced fracture toughness was due to the reinforcement of the columnar inter-grains of 4H phase in the 2H phase induced by appreciable amounts of α-SiC.