Papers by Author: Zhi Fa Wang

Abstract: Fused silica particles and zirconyl chloride were used as main raw material. Meanwhile, ammonia was used as precipitator and polyethylene glycol as dispersant. Firstly, the composite powders were prepared by wet chemical synthesis. Then, fused silica/zirconia ceramic composites containing zirconia with different contents (5%, 15%, 25%, 35% and 45%) were fabricated in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1 h. The thermal expansion ratios and XRD of samples were examined. The analysis of XRD indicated that the cristobalite peaks intensity of sample with more zirconia is lower at the same sintering temperature, and the intensity of cristobalite was higher while sintered at higher temperature. Zircons were found in all samples’ XRD patterns. The results of thermal expansion ratios showed the ratios of samples with more zirconia were lower, especially at higher sintering temperature. So, existence of zirconia can inhibit crystallization of fused silica/zirconia ceramic composites effectively.

Abstract: Different dosages of BN-B₄C compound additive have been introduced for preparing specimen with fused quartz granule (d₅₀=10μm). Fused quartz ceramic materials were fabricated in reduction atmosphere at various temperatures for 1h. The characterizations were carried out by thermal expansion ratio, apparent porosity, cold modulus of rupture (CMOR) and SEM as well as by X-ray diffraction (XRD). The effect of BN-B₄C on the sintering, crystallization and properties of fused quartz was investigated. The result reveals that with increase of the temperature, the apparent porosity and CMOR of specimens decrease. The specimen C sintered at 1300°C possessed a maximum CMOR (22.31 MPa). The specimen C sintered at 1350°C has more compact microstructure. The lowest thermal expansion ratio of the specimens sintered at various temperatures was obtained when the dosages of compound additive is 3%. With increasing BN-B₄C content, the role on inhibiting crystallization was improved. The specimens containing 3 wt% BN-B₄C had obvious effect on inhibiting crystallization of the specimens sintered at various temperatures.

Abstract: Silicon carbide with diffierent granularity was used as raw material, quartz, silica fume, aluminum powder or alumina was used as additive with dosages of 1% (in mass, similarly hereinafter), 3% and 5%. Silicon carbide refractory material was prepared in oxidizing atmosphere at 1400 °C for 3 h. Performence of samples were researched by measurements of apparent porosity, bulk density, bending strength at room temperature, thermal shock resistance and thermal expansion rate, and analyzed by SEM. The results showed that samples added silica fume have low thermal expansion rate and apparent porosity, high bending strength and bulk density, good thermal shock resistance, compact texture as well. It can be deduced that 5% silica fume plays the excellent role to improve integrated performance of silicon carbide refractory material.

Abstract: Fused quartz granule (d50=10μm) was used as raw material, and Al₂O₃-AlN (1:1, in mass) was used as additive with dosages of 1 wt%, 2 wt% and 3 wt%. The crystallization characteristics of fused quartz ceramic fabricated in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1h has been investigated by thermal expansion ratio and XRD. The results showed that the crystallization characteristics were markedly improved by 1 wt% AI₂O₃-AIN compound additive. 1 wt% Al2O3-AIN had obvious effect on inhibiting crystallization of the samples sintered at various temperatures. The apparent porosity, bending strength and SEM of the samples were also examined. The results showed that the samples with 1 wt% AI₂O₃-AIN had the lowest apparent porosity among the samples containing Al₂O₃-AlN, the highest bending strength, and the sample AA1 sintered at 1350°C had more compact microstructure, which indicated that 1 wt% Al₂O₃-AlN was conducive to sintering of fused quartz ceramic materials. It can be deduced that the 1 wt% Al₂O₃-AIN compound additive plays the excellent role on inhibiting crystallization and promoting sintering of fused quartz ceramic materials.

Abstract: Fused quartz granule was used as raw material, and La2O3 nanopowder was used as additive with dosages of 1wt %, 2 wt % and 3 wt %. Fused quartz ceramic materials were fabricated in reduction atmosphere at 1300 °C, 1350 °C and 1400 °C for 1 h, respectively. The properties of samples including apparent porosity, bending strength and thermal expansion ratio were measured. The results show that the sample with 2 wt % La₂O₃ nanopowder has the lowest apparent porosity and the highest bending strength, and sample added 1% nano-La₂O₃ has the best inhibiting effect on crystallization of fused quartz. The samples with La₂O₃ nanopowder adding have lower thermal expansion ratio than blank sample. The XRD and SEM results show that the diffraction peak intensity of quartz phase decrease and the microstructure of the samples become more compact, after the La₂O₃ nanopowder was added into fused quartz ceramics. It indicated that La₂O₃ nanopowder has excellent inhibiting effect on crystallization of fused quartz and facilitating effect on sintering of fused quartz ceramics.

Abstract: The characteristics of grouting material for blast furnace lining crack repair were briefly introduced in this paper. The influences of matrix aggregates particle size grades on the properties of grouting materials for blast furnace lining crack repair were mainly discussed. Based on series of tests and experiments, the optimized matrix aggregates particle size grades were confirmed.

Abstract: Influencing effects of additives CaF₂, ZrB₂ and MoSi₂ on sintering performance and oxidation resistance of Zr-Al-O-N composites were investigated. The results showed that additives CaF2, ZrB2 and MoSi₂ were beneficial to improve sintering density of Zr(Ca)-Al-O-N composites, and additives CaF2 and ZrB2 were beneficial to improve obviously bending strength of samples Zr(Ca)-Al-O-N composites and MoSi2 was contrary. After additives CaF₂, ZrB₂ and MoSi₂ were introduced to Zr(Ca)-Al-O-N composites, oxidation resistance of Zr(Ca)-Al-O-N composites was improved, and relative superior or inferior of influence ranking of additives was MoSi₂, CaF₂, and ZrB₂.

Abstract: 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.

Abstract: Fused quartz granules (d₅₀=19 μm) were used as raw material, and Si₃N₄-Y₂O₃ (1:1, in mass) was used as additive with dosages of 1%, 2% and 3% (in mass). Fused quartz ceramic materials were fabricated in reduction atmosphere at 1300 °C, 1350 °C and 1400 °C for 1 h. The effect of Si₃N₄-Y₂O₃ on crystallization and sintering of the fused quartz ceramic materials were researched by measurements of apparent porosity, bending strength and thermal expansion rate (RT~1200 °C), and by the analyses of XRD and SEM. The results showed that the samples sintered at each temperature with 3% Si₃N₄-Y₂O₃ had the lowest apparent porosity, the highest bending strength and more compact microstructure. This indicated that 3% Si₃N₄-Y₂O₃ was conducive to sintering of fused quartz ceramic materials. The results of XRD and thermal expansion rate showed that addition of 3% Si₃N₄-Y₂O₃ compound had obvious effect on inhibiting crystallization of the samples sintered at various temperatures. It can be deduced that the Si3N4-Y2O3 compound plays the best role in inhibiting crystallization and facilitating sintering of fused quartz ceramic materials.

Abstract: An easy synthesis route of YSZ (Yttria-Stabilized Zirconia) nanopowder with the formation of Zr_0.92Y_0.08O_1.96 is synthetized by using thermal decomposition of ZrOCl₂ and Y(NO₃)₃, with polyvinyl alcohol (PVA) as surface active agent and with quantitative filter paper as carrier. The roasting temperature of YSZ precursor was 650oC. The results of SEM and XRD analysis showed that the pure ZrO₂ and YSZ powders prepared via thermal decomposition had better crystallinity, and YSZ powders had perfect crystalline t-ZrO₂ phase after heating at 650 °C, and changing the amount of PVA or the reaction precursors could obtain YSZ powders sized 20-50 nm.