Rong Lin Wang

Influence of Oxygen Donor Alcohols on Non-Hydrolytic Sol-Gel Synthesis of MgAl2O4 Spinel Nanoparticles

Magnesium aluminate (MgAl2O4) spinel nanoparticles were prepared by non-hydrolytic sol-gel method using anhydrous alcohols as oxygen donor. XRD and FTIR were used to characterise the effect of anhydrous alcohols on synthesis of MgAl2O4 spinel nanoparticles.The results showed that when the oxygen donor used in stoichiometric ratio for synthesizing MgAl2O4, anhydrous ethanol was the more effective oxygen donor than anhydrous isopropanol. But there was no remarkable effect on synthesis of MgAl2O4 spinel when the amount of anhydrous ethanol exceeded the stoichiometric ratio. The mean particle size MgAl2O4 spinel nanoparticles was in the range of 40 to 50 nm.

Effect of Rare Earth Nano-Oxides on Sintering and Crystallization of Fused Quartz Ceramic Materials

Fused quartz powder (size<0.04mm) was used as raw material, nano-Y2O3, nano-CeO2 and nano-La2O3 (size<0.08μm) were dividedly used as additives with dosage of 2% each. Fused quartz ceramic materials were sintered in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1h. The effect of rare earth nano-oxides on sintering and crystallization of the fused quartz ceramic were researched by measurements of apparent porosity, bending strength and thermal expansion rate, and analyses of XRD and SEM. The results showed that additives nano-Y2O3, nano-CeO2and nano-La2O3 had obvious effect of inhibiting crystallization of fused quartz, and the samples added nano-Y2O3 and nano-La2O3 were better. Sample added nano-Y2O3 had least thermal expansion rate. Sample added nano-La2O3 had higher bending strength, and it showed that nano-La2O3 had better effect on sintering of fused quartz ceramic. It can be deduced that nano-La2O3 plays the excellent role as the crystallization inhibitor of fused quartz materials.

Phase Composition Analysis of Recycled MgO-C Ladle Lining Materials

With the iron and steel metallurgy, cement, ceramic and other industries making a rapid development, the refractory consumption in our country is quite large. So how to recycle the used refractory materials effectively is more and more important. In this experiment, the phase composition of ladle lining bricks at slag line, rampart and bottom were researched systematically, to determine the phase composition change between the unused and recycled materials. It turned out that the low melting point minerals CaMgSiO4 and Ca3Mg (SiO4)2 formed due to the reaction between MgO and the impurity compositions like SiO2 and CaO from the melted slag and liquid steel. On the one hand, the formation of these low melting point minerals was one of the main reason for the damage of the recycled MgO-C ladle lining bricks. On the other hand, the alkaline magnesium carbon bricks had purification effect for the liquid steel as a result of the content reduction of SiO2 and CaO.

Fabrication of Pressureless Sintered β-Sialon-ZrO2 Composites

β-sialon-ZrO2composites with Si5AlON7 or Si4Al2O2N6 bonding phase were prapared in N2 atmosphere at 1550°C with Si, Al2O3, AlN and ZrO2 (Ca) as raw materials by reaction in situ pressureless sintering. Effect of Z value and content of β-sialon batch on its sintering performance, phase composition, microstructure, and thermal expansion character were investigated. Results showed that the phase of Si5AlON7 was formed in samples with β-sialon designing Z=1, and phases of Si5AlON7 and Si4Al2O2N6 were formed in samples with β-sialon designed Z=2 and β-sialon designed Z=3, respectively and Bending strength of samples increase with content of β-sialon batch. When content of β-sialon batch equals 10wt%, 15wt% and 15% respectively, the samples with β-sialon designed Z=1, Z=2, and Z=3 have lower apparent porosity, microstructure of homogeneous and compact and lower thermal expansion coefficient, respectively.

Preparation and Performance of Zr(Ca)-Al-O-N Composites by Reaction Sintering of Al-ZrO2(Ca) in N2 Atmosphere

Zr(Ca)-Al-O-N composites were prepared with ZrO2(Ca) (i.e Ca-PSZ, d50 < 10 μm) and Al powder (d50 =7.5 μm, 29 μm, and 62 μm) as raw materials by in situ reaction sintering in N2 atmosphere at 1600 °C. Phase constiturion of the composites was affirmed by XRD and SEM-EDS, and effect of grain size and content of Al powder on sintering performance of the composites was investigated, and oxidation characteristic of the composites were analysed by measure increasing weight of oxidation. The results showed that major phases of the composites composed of (t+c)-ZrO2, ZrN, ZrAl3O3N and CaAl12O19, and Al powder of 5 wt% - 7 wt% d50 =7.5 μm and 3 wt% - 5 wt% d50 =29 μm were suitable for preparation of the composites and bendiing strength of its samples sintered at 1600 °C had 60-90MPa. In atmosphere, oxidation onset temperature of Zr(Ca)-Al-O-N composites were approximately 550 °C, and the end temperature of its oxidening were approximately 950 °C. Treating with antioxidation is a key for application of Zr(Ca)-Al-O-N composites.

Synthesis of ZrTiO4 and MgAl2O4 Powders via Non-Hydrolytic Sol-Gel Route Using Alcohol as Oxygen Donor

Zirconium titanate and magnesium aluminate spinel precursors were prepared by non-hydrolytic sol-gel method using ethanol as oxygen donor. The gels and calcined powders were investigated by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD). The results show that the ZrTiO4 and MgAl2O4 crystallized at low temperature of 550 °C and 700 °C, respectively. It indicated that the highly homogeneous zirconium titanate and magnesium aluminate gels were aslo obtained by nonhydrolytic sol-gel process using ethanol as oxygen donor. The particle size distribution measured by laser scattering exhibit that ZrTiO4 and MgAl2O4 powders were large soft agglomerates which could be broken through milling process.

Thermodynamical Analysis of the Reaction between AlN and ZrO2 and Experimental Substantiation

Two equations with discrepancies of solid-state displacement reactions between AlN and ZrO2 were analysed by thermodynamic calculation, and its results were substantiated by experiment. Results of thermodynamic calculation showed that the reaction equation of Bayer and Mocellin proposing could occured at 1411.26K, and it accord with TG-DTA and SEM analysis results, i.e. the reaction equation of Bayer and Mocellin proposing was true.

Research on Oxidation Reaction of AlN Powder

The process of non-isothermal oxidation of AlN powder (d50=15μm, 5μm and 0.5μm) were studied by TG-DTA and XRD in atmosphere of 80%N2 and 20%O2 mixture at flowrate of 55ml/min and heating rate of 10 /min. The experimental results reveal that the AlN powder obviously began to be oxidated and its weight increased at 900-1000°С . The process of dynamics of oxidation reaction between AlN and O2 was controlled alternately by reaction and diffusion. Non-isothermal oxidation dynamic parameters (activation energy E, reaction orders n and pre-exponential factor A) of d50=5μm AlN powder were obtained by the experimental data. E equals about 417.4kJ/mol, n about 2.9 and A about 3.47×1012. Due to smaller activation energy E and larger pre-exponential factor A in dynamic parameters of AlN powder non-isothermal oxidation, powdery AlN is easily oxidated at high temperature and in air and has a larger oxidation reaction rate. If AlN material with high thermal conductivity characteristics is introduced to prepare composite with high thermal shock resistance, the AlN powder must be treated for oxidation resistance.

Effect of Sintering Temperatures on the Sintering Performance and Thermal Shock Resistance of MgO-Al2O3-Fe2O3 Composite

The composites in the MgO-Al2O3-Fe2O3 system were prepared using high pure magnesia and alumina as raw materials and ferric oxide powder as additive. The effect of sintering temperatures on the sintering performance and thermal shock resistance of the composites was studied. The results showed that both the apparent porosity and linear change ratio of the samples decreased with the increase of sintering temperatures, and their bulk density and bending strength increased accordingly. The sample sintered at 1550°C exhibits excellent thermal shock resistance. The XRD and SEM results indicated that the crystal phase of the samples remained the same, but their microstructure became denser as the sintering temperatures increased from 1500°C to 1600°C. As a result, the composites could be sintered at about 1550°C, which has a potential application in cement rotary kiln linings.

Effect of Molar Ratio of Al2O3 to Fe2O3 on the Sintering and Thermal Shock Resistance of Al2O3-Fe2O3 Composite

The Al2O3-Fe2O3 composite was prepared at 1550°C for 3h with alumina powder and ferric oxide powder as raw materials and with magnesia powder as additive. The effect of molar ratio of Al2O3 to Fe2O3 on the sintering and thermal shock resistance of the composite materials was studied. The results showed that the apparent porosity and bulk density of the samples both decreased with the molar ratio of Al2O3 to Fe2O3 increase, as a result, the linear change ratio and bending strength both increased. When the molar ratio of Al2O3 to Fe2O3 equals to 3, the sample exhibits excellent thermal shock resistance. The XRD and SEM analysis results indicated that the mechanical and thermal proprieties are relative to the microstructure and crystal phases of the composite materials.