Papers by Author: Guang Hui Min

Abstract: Equal channel angular pressing (ECAP) has been conducted on as-extruded Mg-Zn-Y alloy containing quasicrystal phase at a temperature of 523 K. The optical images indicate that after 8 ECAP passes through route BA, the grain size of the extruded alloy is decreased sharply; and the coarse eutectic icosahedral quasicrystal phases (I- phases) are broken and dispersed in the alloy; and the distributions of Zn and Y elements become more homogeneous. These can be attributed to the shear effect during the ECAP processing. TEM micrographs show the grain refinement, the evolution of broken and dispersed I- phases and dispersion precipitation of nano I-phases during 1- ,4- and 8- pass ECAPed Mg-Zn-Y alloy. And the mechanism of grain refinement is also discussed.

Abstract: Lanthanum hexaboride (LaB6) nanopowders were synthesized at 1200 for 2 hours in the vacuum hot resistor furnace with lanthanum chloride (LaCl3) and sodium borohydride (NaBH4). As-prepared nanopowders were surface modified first by silane coupling agent and then were used as fillers for PMMA to fabricate poly methyl methacrylate (PMMA)/LaB6 nanocomposites via melt extrusion using a twin-screw extruder. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) indicated a pure cubic phase with the average size of 70 nm. Fourier transform infrared spectra (FTIR) proved silane coupling agent was grafted onto nanoparticles. The comparision of field emission scanning electron microscopy (FESEM) of unmodified and modified nanoparticles showed that surface modification prevented agglomeration of nanoparticles, making more evenly-distributed inorganic nanoparticles within organic matrix as LaB6 mass fraction equaled 0.010%. In addition, LaB6 nanoparticles played a vital role in the absorption range from ultraviolet (UV) to NIR and the composite with a higher content of LaB6 was beneficial for rejecting heat.

Abstract: In this study, AZ91 and SiC particulates reinforced AZ91 (SiCp/AZ91) magnesium alloys were successfully fabricated using rapid solidification/powder metallurgy technique followed by hot extrusion. Microstructural evolution and mechanical properties of the monolithic AZ91 and SiCp/AZ91 magnesium alloys were evaluated. SiC particulates were well distributed with only few agglomerated particles. The porosity level and microhardness increased as SiCp content increased because the increased surface area of SiCp, harder ceramic phases and SiCp acted obstacles to the motion of dislocations. In addition, an increase in particulate reinforcement content was observed to decrease mechanical properties of the composite compared with the unreinforced counterpart due to increasing agglomerating regions and porosity, brittle interface debonding between matrix and SiCp.

Abstract: A simple sonochemical synthesis of tungsten trioxide hydrate with various morphologies has been developed by using tungsten hexachloride (WCl6) as precursor and water, ethanol and their mixture as solvent, followed by annealing in a tube furnace. The resulting products were structurally characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and differential thermal analysis (DTA). Results show that nanowhiskers emanating from the core of nanoparticles have been obtained with ethanol as solvent, and that nanoplates and nanosheets were formed when water and/or mixed ethanol and water was used as the solvent, respectively. The continuous changing supersaturation of tungsten trioxide may account for the formation of nanowhiskers. The formation of nanoplates or nanosheets may be associated with the selective adsorption of solvent molecules on the WO3 crystals. Due to a combination of the loss of chemical bonded water and crystal growth, the as-synthesized tungsten trioxide hydrate underwent apparent morphological evolution during thermal processing.