Wen Jie Yuan

Preparation and Hydration Resistance of MgO-MgAl2O4 Composite Refractory

Magnesia-magnesium aluminate (MA) spinel composite refractory was prepared by using fused magnesia, industrial alumina and AlCl3•6H2O as the raw materials. The effects of calcining temperature and holding time on phase compositions of MgO-MgAl2O4 system samples were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). With the increase of calcining temperature, the hydration mass increasing rate of the sample decreases significantly. The results show that MgO-MgAl2O4 composite refractory has quite excellent hydration resistance because of periclase grains with exsolved spinel phase.

Progress in the Synthesis of Ternary Carbide by Carbothermal Reduction from Natural Raw Material

Aluminum-containing ternary carbide, Al4SiC4-Al4Si2C5 composites, were synthesized using a mixture of bauxite, kaolin and carbon black as starting materials. The effects of raw materials ratio on the phase transformation and micromorphology of ternary carbide were investigated. The results indicated that the optimum condition for synthesizing Al4SiC4-Al4Si2C5 composites was 2 h sintering at 1900 °C in flowing argon atmosphere. Al4Si2C5, Al, Si and SiC formed when carbon black content was lower than stoichiometric amount. With increasing of carbon black content, the Al and Si content decreased and Al4Si2C5 content increased in the products. Al4SiC4 appeared when stoichiometric amount of carbon black was used, and about 20 mol% excess of carbon black promoted the formation of Al4SiC4.

In-Situ Reactions and Properties of Alumina-Magnesia Refractory Castables with Addition of TiO2

In the present work, the phase composition, apparent porosity, permanent linear change and microstructure were examined in castables containing 0–2 mass-% of TiO2 with and without magnesia to investigate the effect of TiO2 on in-situ reactions and properties in alumina-magnesia refractory castables after calcination at 1450°C/5 h. The results show that the addition of TiO2 can modify in-situ reactions and sintering processes. The amounts of spinel and calcium hexaaluminate (CA6) formed in overall castables increased with TiO2 addition, and the grain size of CA6 decreased gradually. The difference of the phase composition in overall and the matrix of castables indicated that the aggregates were involved in the CA6 formation. The permanent linear change and cold modulus of rupture of castables were dependent on TiO2 addition. For design of alumina-magnesia refractory castables, TiO2 could be used as an alternative to achieve good strength and certain expansion.

Effect of Particle Size on Properties of Novel Thermal Insulation Materials Synthesized by Molten Salt Method

Novel heat insulation materials were synthesized by molten salt method by using natural forsterite and NaSO4 molten salt. The insulation materials which have light weight and small size pore were obtained by using different particle size (44 μm, 74 μm and 250 μm) natural forsterite and NaSO4 molten salt at 1000 °C-1150 °C for 10 h after treating by distilled water. The effects of particle size of forsterite on phase composition, sintering porperties, physical property and microstructure were studied. The results showed that the main pahse in all samples was Mg2SiO4Fe2O3 and MgFe2O4 which indicate that the NaSO4 molten salt just play the role of Promoting particles sintering. The particle size of 74 μm have better bulk density and comprssive strength in all sample, at 1100 °C, the sample of bulk density is 1.54 g/cm3 and the apparent porosity is 0.498. In addition, the strength of the sample made of 44 μm forsterite materials was always higher than that used 74 μm forsterit, and was the lowest strength of sample used 250 μm forsterite.

Synthesis of Al4SiC4 Powders from Kaolin Grog, Aluminum and Activated Carbon as Raw Materials

In Al-Si-C system, there are many compounds, of which Al4SiC4 is useful as high-temperature structure material and the antioxidant in carbon-containing refractory. In this paper, Al4SiC4 powders were synthesized by using kaolin grog, aluminum and activated carbon as raw materials. The phase changes of the synthesized samples were examined by X-ray diffraction (XRD), and the microstructure was observed by scanning electron microscope (SEM). The effects of synthesis temperature and the proportion of aluminum on phase compositions of Al-Si-C system were investigated. The results show plate-like Al4SiC4 powders can be prepared with optimal ratio of starting materials and synthesis temperature.

Effects of Rare Earth Chlorides on Properties of Al 2 O 3 -MgO Castables

For the urgent requirements of high performance castables in iron and steel making industry, effects of rare earth chlorides on properties of Al2O3-MgO castables were addressed. The prepared castables were compared in terms of phase compositions, apparent porosity, bulk density, permanent linear change and strength. It was demonstrated that cerium chloride and yttrium chloride exhibited a positive influence on in-situ reactions and volumetric stability of castables. The cation inversion degree of spinel and solid-soluted content of spinel and CaAl12O19 (CA6) were both dependent on the temperature and addition. Cold modulus of rupture for castbles with rare earth chlorides additions calcined at 1450°C was similar to that for referenced castables though the former ones were relatively less at 1250 and 1350°C.

Effect of Adding Y2O3 on Synthesis of Al4SiC4 Powders

The reaction process of synthesis of Al4SiC4 from Al, Si and graphite powders and the effects of Y2O3 on synthesis and microstructure of Al4SiC4 were investigated in this paper. The results show that no substantial changes in the formation of Al4SiC4 content with or without addition of Y2O3. The addition of Y2O3 to Al, Si and carbon powder mixtures was found to be effective for obtaining tabular grains of Al4SiC4. Conversely, Al4SiC4 grains existed as irregular granules without addition of Y2O3.

Study on the Oxidation Kinetics of In Situ β-Sialon Bonded Al2O3-C Refractories

The oxidation behaviors and kinetics of in-situ β-Sialon bonded Al2O3-C refractories were investigated by TGA techniques via isothermal oxidation experiments at different temperatures. The results show that the oxidation process of in-situ β-Sialon bonded Al2O3-C refractories can be divided into three stages: oxidation reaction rate controlling stage, reaction and diffusion controlling stage, and diffusion controlling stage. The oxidation rate controlled by the reaction rate has no obvious changes as the temperature increases. The oxidation rate controlled by the reaction rate and the diffusion rate together has a trend of decline, so is the oxidation rate controlled by the diffusion rate.

Novel Synthesis and Characterization of Titanium Carbide Coatings on Graphite Flakes

Titanium carbide coatings were synthesized by reacting with titanium powders in NaF-NaCl based salt on surface of graphite at 1100-1400 °C in argon (Ar). The effect of temperature of heat treatment on TiC coatings properties was studied. Phase composition and microstructure of the TiC coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray spectroscopy (EDS). The “template-growth” mechanism plays a dominant role in the coating formation process.

Preparation of Zirconium Titanate Ceramics by Alloy Oxidation Method

In this paper, the investigations are presented for preparation of zirconium titanate ceramics by pressureless sintering of powders obtained by alloy oxidation method. ZrxTi1-xO2 (x=0.40-0.60) powders were prepared by the oxidation of Zr-Ti alloys. The zirconium titanate powders were sintered in the temperature range from 1400 to 1600 °C for 3 h by pressureless sintering. The relationships among the composition, the relative densities and microstructure of bulk ceramic were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the sintering and microstructure of single phase zirconium titanate ceramics varied with ZrO2 content. The relative density of samples reaches the maximum value of near 92% when sintering temperature is up to 1600 °C. Irregular pores distributed uniformly among the particles in the sintered ceramics with homogeneous microstructure.