Li Hua Xu

Influence of different seeds on transformation of aluminum hydroxides and morphology of alumina grains by hot-pressing

The influence of different seeds on transformation of aluminum hydroxides and morphology of alumina grains was investigated. There are two kinds of alumina seeds used separately, alumina milling ball abrasive seeds and ultra-fine alumina powder seeds. Abrasive seeds were introduced to the starting materials by wet-grinding of high-purity alumina milling balls. The alumina powder seeds were directly added into raw materials. First, the introduction of different seeds can lower the transformation temperature from κ phase to α phase. The phase transformation from aluminum hydroxide to α-Al2O3 was completed at 1100 °C in 2 h when a certain amount of seeds were employed. Second, seeds also changed the sintering behaviour and microstructure of alumina ceramics. For the hot-pressed sample with alumina powder seeds added directly, the microstructure with platelets was observed. However, the anisotropic growth of alumina grains is favored in the presence of alumina abrasives as seeds. The elongated grains were developed in the sample with abrasive seeds introduced.

Microwave annealing of yttria stabilized zirconia ceramics

Abstracts are not published in this journal

Preparation of Eco-Friendly Composite Ceramic from Iron Ore Tailings

In this paper, the research mainly focused on utilization of iron ore tailing of Panzhihua region. Based on the analysis of its components, Carbothermal Reduction Nitridation (CRN) method was selected to synthesize eco-friendly composite material. Different additives were tried to improve the property of the samples. The influence of different sintering temperature, holding time and contents of additives were taken into account, and orthogonal design was employed to obtain the optimal parameters. It indicated that only when the temperature was 1450°C and the holding time was 5 hours, the samples with the bulk density of 3.42g/cm3 was obtained. The phase and surface morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Experimental results showed that the phases of the product were Fe3Si and TiC0.3N0.7. The research provided a novel recycling process for ore tailings.

Preparation of Sialon from Solid Wastes by Colloidal Process

Based on the slip casting and the preparation of sialon synthesized from clay, fly ash and gangue by the carbothermal reduction nitridation, the influences of compositions, dispersant additive and sintering process on the properties of materials have been investigated in present work. The experimental results indicate that disposal of fly ash via a pickling process can greatly reduce the content of iron, and the effect is obvious with increasing the concentrations of hydrochloric acid and pickling temperature. Therefore the component of the final product can be purified. It is also noted that the final density of the sintered body using colloidal process is superior to that of using conventional dry pressing, although the slightly higher green density is observed in dry pressing body because of high compaction pressure.

Reaction Processes and Thermodynamic Modeling for SiAlON Structural Ceramic Powders Synthesized from Nonmetallic Mine

SiAlON family matrix materials have been fabricated from nonmetallic mine. The process of Carbothermal Reduction and Nitridation (CRN) is selected on the basis of raw rocks containing various Si/Al ratios. Thermodynamic analysis of Si-Al-O-N system at different sintering temperatures indicates once the temperature is above 1673 K, a series of chemical reactions occur in sequence, SiO2, SiO, Si2N2O, SiO2+Al2O3, mullite, X-SiAlON, O′-SiAlON, β-SiAlON, SiAlON- polytypiods and Si3N4+AlN. Moreover, most of the reactions are exothermal and are promoted by further heating. The adding or in-situ formed SiC can reduce mullite and Al2O3 to produce O′- or β-SiAlON, and its reaction is surprisingly endothermic and is inhibited when further heated. Also, atmosphere is essential to affect the sintering process. Either raising N2 partial pressures or reducing CO partial pressures can accelerate CRN progress. Correspondingly, phase content and microstructure of the product converted from nonmetallic ore are in detail investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Slip Casting of Green Compact of SiAlON Multiphase Ceramics from River Sand

Green compact containing Yellow River sand and several additives was prepared by slip casting and the as-made compact was used to synthesize SiAlON multiphase ceramics by carbothermal reduction nitridation. The processing parameters of slip casting including the type and concentration of dispersant, solid loading, ball milling time, pH value and particle size distribution were optimized by orthogonal experiments. The results indicated that the raw materials could disperse uniformly in the suspension under the use of the mixed dispersant of skip liquid (SL, PT) and sodium carboxymethylcellulose (CMC). The green body with high bulk density of 1.86 g·cm-3 was obtained. After sintered in flowing N2, the compact could transform to SiAlON multiphase ceramics.

Colloidal Process of Magnesia-Carbon Refractory and Its Sintering Characteristic

Carbon-containing refractories are widely used in metallurgical industry due to their excellent thermal property and resistance to corrosion by molten iron. In the present work, slip casting colloidal process, which is used to fabricate high performance structural ceramics, has been introduced into the preparation for magnesia-carbon refractory with selection of suitable dispersant. The results indicated that the curve of zeta-potential of magnesia was similar with that of carbon just containing dispersant and the homogenized mixtures were attained under a controlling of low pH value. Three kinds of preparing routes for green bodies were designed, and all of the final densities and the resultant hardness of sintered bodies using colloidal process were superior to these of the specimen using conventional dry pressing, whereas its high green density can be plausibly observed in dry pressing body because of high compaction pressure used.

Effect of TiO2 on the Thermal Conductivity of Eco-Friendly Silica Bricks Fabricated by Yellow River Silt

Silt from the Yellow River was mixed with a certain amount of SiO2 powder to fabricate eco-friendly silica bricks and different amounts of TiO2 were added to ameliorate the thermal conductivity of the bricks. Results showed that the phases of as-fabricated silica bricks are cristobalite and tridymite with cristobalite predominating. With increasing amounts of TiO2, the bulk density and thermal conductivity of the samples increase. Although the bulk density (1.65~1.76 g/cm3 ) than the ideal density 1.85 g/cm3, the thermal conductivity is significantly ameliorated. The thermal conductivity of the sample with 1.5% TiO2 addition is 2.11 W/m.°C, which is nearly three times higher than that of commercial silica bricks (0.8 W/m.°C).

Silicon Nitride Ceramic Prepared by Colloidal Process

Advanced silicon nitride ceramic compact was prepared by colloidal process. The rheological behaviors of the Si3N4 powders were emphatically investigated. At the same time, the effects of the dispersant, pH value and ball milling time on the silicon nitride slurry were discussed. The results showed that the addition of the dispersant could shift the value of Zeta potential and improve the fluidity of silicon nitride slurries. The well fluidity can be achieved when the amount of the dispersant was 1.2wt%. Besides, a ball milling time of 8h was appropriate. Statistic pattern recognition was used to predict the processing parameters. Then the high density of green compact could be attained while the volume fraction of solid powders was up to 40%, and the fracture toughness of the sintered body reached 7.2MPa·m1/2. The microstructure of final sintered ceramic was observed by scanning electron microscope (SEM).

Synthesis of Sialon-Based Eco-Materials from Gold Mineral Tailings

Sialon-based eco-materials were synthesized by using the gold mineral tailings that containing abundant Si and Al elements as the major raw material with minor additives through the carbothermal reduction nitridation route. This study realized the conversion of eco-materials from solid waste, gold mineral tailings. The effects of sintering temperature, holding time and x value during carbothermal reduction nitridation process on the phase composition and microstructure of as-fabricated Sialon-based materials were explored. The XRD results indicated that when sintering temperature is 1550°C, holding time is 6h, and x value is 1.0, Ca-α-Sialon/SiC/Fe3Si composites was successfully synthesized. The relative content Subscript textof each phase in the products is I(α-Sialon): I(SiC): I(Fe3Si)=82:10:8. The SEM images showed the densificated microstructure and uniform grains with the long column shape.