Xiao Wen Wu

Influence of CeO2 additive on the phase transformations of zirconia from zircon ore by carbothermal reduction process

This paper mainly discusses the influences of heating temperatures and CeO2 additive contents on the phase transformations of zirconia from zircon ore by carbothermal reduction. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure of the product was characterized by scanning electron microscopy. The results show that without adding CeO2, the optimized heating temperature of zircon carbothermal reduction was 1600 °C and the main phases of the product were m-ZrO2, ZrC and β-SiC, t-ZrO2; After adding CeO2, the main phase of the products consists of t-ZrO2, m-ZrO2, ZrC and β-SiC when the heating temperature is 1600 °C. CeO2 additive can be introduced into zirconia lattice and can cause it to form cerium stabilized zirconia. Zirconia in the product would be turned into partially stabilized zirconia with cerium addition from 5 wt% to 20 wt%. However, the form of zirconia in the product is not changed greatly with the amount of CeO2 additive increase.

Effect of Er3+ Doped on Photocatalytic Properties of ZnO-TiO2 Nanofibers

Er3+ doped ZnO-TiO2 nanofibers with diameter of 100～200 nm were prepared by electrospinning mothed after calcined at high temperature, using polyvinylpyrrolidone(PVP), Zn(NO3)2·6H2O, Er(NO3)3·5H2O, Ti(OC4H9)4 asraw materials. The composite nanofibers were characterized by XRD, SEM, and UV-V respectively. Effects of different calcined temperatures on structure and photocatalytic degradation were investigated. The results indicated that the crystallinity becomes better with the increasing of calcination temperature. The composite nanofibers had the best effects of photocatalytic degradation of methylene blue, when Er3+ doping content was 0.3 wt.% and calcined temperature was 500 °C.

Preparation of Al2O3-SiC Composite Powder by Carbothermal Reduction of Coal Gangue and its Influence on Properties of Blast Furnace Stemming

Al2O3-SiC composite powders are prepared by carbothermal reduction method using coal gangue as raw material and carbonaceous materials (such as coke, anthracite, and carbon black) as reducing agents. The optimum conditions are as follows: when the addition of coke or anthracite is 50%, the temperature is at 1600 °C for 5 h, and adding 50% carbon black’s best temperature is at 1600 °C for 4 h. Based on the formula of stemming used in an iron and steel factory, Al2O3-SiC-C series blast furnace stemming refractory was prepared by adding Al2O3-SiC composite powder. The results show that the addition of Al2O3-SiC composite powders has a positive influence on the apparent porosity, volume density, and bending strength of the refractory. The effect of the amount of Al2O3-SiC composite powder on the slag corrosion resistance of the blast furnace stemming refractory was also studied by the static crucible method.

Preparation and Characterization of ZrO2 Nanofibers and Nanobelts by Electrospinning

ZrO2 fibers and belts have been fabricated by heat-treating the hybrid fibers and belts which were prepared by electrospinning method. Fiber and belt properties, for instance, surface morphology, diameter of fibers, crystallization formation, etc. were investigated by various techniques, scanning electron microscopy (SEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), energy dispersive spectrum (EDS) included. It was found that more belts and thicker fibers appeared with increasing PVP content. Using N,N,N-trimethyl-1-dodecanaminium bromide (DTAB) can avoid formation of belts and reduce the diameter of fibers from a range of 270 to 750 nm to a range of 90 to 150 nm. It all obtained monoclinic ZrO2 fibers and belts after heat-treating (respectively at 700, 800, 900 °C) hybrid fibers and belts. The higher temperature heat-treatment leads rougher fibers and belts.

Erosion wear behaviour of 3 mol-% yttria-stabilised zirconia ceramics by solid particle impact at elevated temperatures

Abstract The solid particle impact erosion wear behaviour of 3 mol-% yttria-stabilised zirconia ceramics is studied at elevated temperatures. The influence of erosive temperature on the erosion wear resistance and erosion mechanism of 3 mol-% yttria-stabilised zirconia ceramic at the impact angle of 90° is investigated. The results show that material removal rate of volume erosion wear of 3 mol-% yttria-stabilised zirconia ceramics increases with rising temperature. The erosion rate increases slowly between room temperature and 600°C. The 3 mol-% increases rapidly between 800 and 1200°C. The maximum erosion rate of 0·55 mm3 g−1 is found at 1200°C. The increase of the erosion wear rate is because of the decrease of the mechanical properties at high temperatures. The erosion wear mechanism of 3 mol-% yttria-stabilised zirconia ceramics is temperature-dependent, which is mainly plastic deformation below 800°C and mainly cracking in irregular crisscross patterns leading to the flaky exfoliation of material, between 800 and 1400°C. The results provide an insight into the mechanism of material damage and failure of advanced ceramics by high temperature erosion.

Performance and Phase Behavior of Quartz-Aluminum Matrix Composites

The performance and phase behavior of Quartz - Aluminum Matrix Composites at different temperatures were studied. Quartz aluminum matrix composites were prepared by powder metallurgy method. At the temperature that was less than 660.4°C(the melting point of aluminum), a portion of quartz was happened decomposition and revivification to silicon, most aluminum still existed in the form of metal aluminum. All quartz were happened at the temperature that was higher than 660.4°C. When the temperature is 700°C, the compressive strength of S5(added 40% quartz) is up to 46.02MP. The higher the value of compressive strength was, the less the amount of quartz were happened decomposition. At the temperature more than the melting point of aluminum, Quartz was revivification to silicon, aluminum is oxidized to Al2O3. When the amount of silica exceeded 10%, the mechanical properties of composites declined consequently.

Influence of Sintering Temperature on Phase Behavior of Products from Rutile and Quartz by Aluminothermic Reduction Nitridation

The effects of sintering temperatures on phase behavior of products from rutile and quartz by aluminothermic reduction nitridation (ARN) were investigated in this study. The crystalline phase and morphology of the samples were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), respectively. As the temperature was 1200 oC, the phases were corundum, TiN, Si and a small amount of cristobalite. Mullite were initially observed when it reached 1300 oC. A small amount of Si3Al3O3N5 was detected when the temperature rose to 1400 oC. More corundum, TiN and Si3Al3O3N5 were obtained at 1500 oC. The quantities of TiN and corundum increased slightly at 1550 oC while Si3Al3O3N5 reduced. In addition, the microstructure of well-developed β-Sialon crystals was long columnar and the TiN particles distributed in the composites.

The Effects of Mineral Composition and Sintering Temperature on Synthetic Mullite

Mullite material was prepared from quartz (SiO2) and industrial alumina (γ-Al2O3). The effects of mineral composition and sintering temperature on the final phase composition and physical properties of mullite were investigated. The results shown that a large number of mullite phase was emerged in samples when the ratio of alumina to silica (A/S) was 2.55. At 1500 oC and 1600 oC, the flexural strength of the samples reached to 87.13 MPa and 89.50 MPa, respectively. Consider the environmental protection and energy saving, the optimal sintering temperature was 1500 °C.

Microstructure, Mechanical Properties, and Electrical Resistivities of Mica Glass-Ceramics with Flake Phlogopite and Waste Glass

Mica glass-ceramics can be applied in all kinds of electrical equipment, locomotive internal circuits in high-speed rail, ordinary electric locomotive and subway locomotive. In this study, mica glass-ceramics were prepared by sintering process using flake mica and waste glass as the main raw material with low cost. Different mica glass-ceramic samples were fabricated by changing the formula of raw materials, molding process and sintering temperature. X-ray diffraction, scanning electron microscopy, three-point bending test, and balanced-bridge technique were applied to investigate the phase, microstructure, mechanical and electrical resistivities of the samples, respectively. The results show that the optimum sintering temperature is 900 to 1000 °C holding for two hours, the desirable ratio is 70 wt% of mica powder while 30 wt% of glass powder. In that condition the sample could be less porosity, high flexural strength (63.3 MPa) and eligible electrical resistivity (0.4×1013 Ω·cm).

Effects of CaO Additives on the Phase Evolution of ZrO2-SiC Composites from Zircon by Carbothermal Reduction

In this study, Ca2+ stabilized ZrO2-SiC composite materials were prepared via carbothermal reduction, using natural zircon ore as raw material, CaO as additive, and black carbon as the reducing agent. The effects of synthesis temperature and CaO content on the phase composition of the products were investigated by XRD. The microstructure and micro-area chemical analysis of the products were characterized by SEM and EDS. The results indicate that: (1) Ca2+ stabilized ZrO2-SiC composite materials could be prepared from natural zircon ore with CaO addition between 1500°C and 1600°C for 4 hours by carbothermal reduction process. (2) The synthetic temperature has an important influence on the phase composition of the carbothermal reduction products of zircon. The production of m-ZrO2 and t-ZrO2 got obviously enhanced with increasing temperature from 1500°C to 1600°C. (3) At the same synthetic temperature, Ca2+ stabilized ZrO2 got enhanced with increasing adding amount of CaO. The optimized synthesis condition of Ca2+ stabilized cubic-ZrO2/SiC composite materials is sintering at 1600°C for 4 hours with adding 40 mol% CaO as additive.