Papers by Author: Chang Qing Hong

Abstract: Abstract. ZrB2-SiC ultra-high temperature ceramics (UHTCs) was hot-pressed at a temperature of 1900°C with the addition of carbon black as a reinforcing phase. Microstructure and mechanical properties were investigated. Analysis revealed that the amount of carbon black had a significant influence on the sinterability and mechanical properties of ZrB2-SiC ceramics. When a small amount ( < 10 vol.%) of carbon black was introduced, it may react with oxide impurities (i.e. ZrO2, B2O3 and SiO2) present on the surface of the starting powder, thus promote the densification and grain refining of ZrB2-SiC ceramics. As a result, the mechanical properties including flexural strength and fracture toughness were improved. However, with the further adoption of carbon black, mechanical properties were not improved much, which could be attributed to the redundant phase at grain boundaries. The results presented here point to a potential method for improving densification, microstructure and mechanical properties of ZrB2-based ceramic composites.

Abstract: Low density SiO2-xZrO2 aerogels with x=35wt%, 65wt%, 75wt%, 90wt%, 95wt% were prepared by CO2 supercritical drying technique with tetraethylorthosilicate (TEOS) and zirconyl nitrate dihydrate (ZrO(NO3)2 .2H2O) by hydrolytic polycondensation under different chemical conditions. The prepared aerogels are performed by X-ray Diffraction (XRD), Transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR) and BET surface areas to characterize and analyze the morphology and pore structure of SiO2-ZrO2 aerogels. The results showed that the SiO2-ZrO2 areogels are the typical of nano mesopores and the average pore size is about 50 nm. The specific surface areas varied from 345.5 to 615.5 m2/g with (SBET)MAX = 615.5 m2/g with 20wt% Zirconia; Moreover a mass of Si-O-Zr bands formed in the aerogels and the formation mechanism of Si-O-Zr bands are also discussed.

Abstract: The recrystallized carbon-ceramic composites were prepared from calcined coke, coal-tar pitch and Cr by hot-press to investigate the effects of Cr on the physical properties, mechanical properties and microstructure of recrystallized graphite. Experimental results showed that Cr doped recrystallized graphites exhibited higher bending strength and compressive strength and lower electrical resistivity when the Cr content is10wt% compared with pure graphite. Microstructural analyses revealed that the degree of graphitization of recrystallized graphite increased and the layers spacing of microcrystalline decreased with increasing the Cr concentration. XRD analysis indicated that Cr added to the carbon substrate was in the form of C, Cr2C3 and Cr2O3. The catalytic mechanism of Cr dopant to accelerate the graphitization of carbon substrates can be explained by the mechanism of decomposition of the carbide.

Abstract: Porous TiB2 ceramics with a three-dimensional interconnected skeleton were fabricated by high temperature pressureless sintering from fine TiB2 powders. The microstructure of the porous TiB2 ceramic was characterized by the enhanced neck growth between the initially touching particles. This neck growth was ascribed to the selective heating of TiB2 particles with different dimension. The porous structure prepared by the high-temperature sintering exhibited higher bending strength and fracture toughness in the present experiment. The improved mechanical properties of the sintered composites were attributable to the enhanced neck growth by surface diffusion.

Abstract: Highly Nano-porous SiO2-ZrO2 aerogels were manufactured with tetraethylorthosilicate (TEOS) and zirconyl nitrate dihydrate (ZrO(NO3)2 .5H2O) by the sol-gel method followed by supercritical drying technique. The prepared aerogels are performed by SEM, FT-IR and BET to characterize and analyze the morphology and pore structure of SiO2-ZrO2 aerogels. The results showed that:(i) The areogels are the typical of nano pores in the interval between 1

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