Jianwei Cao

Effect of P2O5 on evolution of microstructure of MgO–Al2O3–SiO2 glass ceramics

Abstract MgO–Al2O3–SiO2 (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P2O5 on microstructure MAS based glass ceramics. The results showed that P5+ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg4Al2Ti9O25 and the containing P5+ area at <900°C. Mg4Al2Ti9O25 and Mg3(PO4)2 in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P5+ in the residual glassy phase. However, P5+ inhibited the presence of cordierite when the heat treatment temperature was >900°C.

Spectroscopic Study of Optical Property and Structural State of Vanadium Ions in Lithium Aluminosilicate Glass-Ceramics

ABSTRACT The optical property and the structural states of vanadium ions were studied by multiple spectra (UV-visible, IR, Raman, and electron paramagnetic resonance (EPR)) in LAS glass and glass-ceramics. The color of glasses changed drastically from light yellow-green to claret during crystallization, the optical absorption in visible range is the characteristic absorption of V4+, and the variation of absorption region is mainly attributed to the change of vanadium ions coordination polyhedron during crystallization process. The V4+ ions, formed by reduction of V5+ ions, existed as the VO2+ complex in octahedral coordination with a tetragonal compression with C4v symmetry. Additionally, the V4+ ions partially replaced Li+ and occupied tetrahedral sites in beta-quartz solid solution.

Preparation of porous spodumene/zircon composite ceramics and its thermal and mechanical properties

Abstract Porous β-spodumene/zircon (ZrSiO4) composite ceramics were prepared by addition of zirconia to spodumene mineral using conventional solid reaction methods. The formation of the zircon was investigated by means of the differential scan calorimetry measurements and an X-Ray diffractometer. The microstructure of the composite ceramics was observed through a scanning electron microscope. The results show that the presence of zircon benefited the formation and stability of the porous structure and improved significantly the thermal endurance and mechanical properties of the spodumene matrix. The composites with 10–15% porosity exhibit an excellent thermal shock resistance, a low thermal expansion coefficient of approximately 1·4 × 10−6 K−1 in the range of 200–800°C and a high flexural strength about 100 MPa. It is found that the spodumene/zircon composites, widely used as a high temperature structure material, can be synthesised by a cost effective method.

Oxidation behavior of metallurgical silicon slag under non-isothermal and isothermal conditions

AbstractMetallurgical silicon slag is the by-product of metallic silicon industry. The utilization of silicon slag is very limited due to the absence of related researches. In this work, the oxidation behavior of metallurgical silicon slag was studied by means of phase variation under the non-isothermal and isothermal conditions. The crystal structure and phase composition of silicon slags were investigated by X-ray powder diffraction, simultaneous thermal analysis, scanning electron microscopy and thermogravimetry. During the oxidation process, the CO2 emission was progressively enhanced with increasing the oxidation temperature, and the exothermic oxidation primarily occurred above 700xa0°C. The non-isothermal oxidation of silicon slag powder was a complicated process, involving the oxidation, crystal precipitation and disproportionation processes. The graphite phase was completely removed at 1000xa0°C. The SiC and cristobalite phases greatly increased at 750xa0°C and decreased with further increasing the oxidation temperature. For the isothermal oxidation, the Si and SiC phases generally reduced with increasing the soaking time. The cristobalite and tridymite phases increased with the oxidation time. The mass change in slag powders suggested that the isothermal oxidation process consisted of the initial redox reaction and subsequent oxidation reaction.n