Advanced Materials Research Vol. 412

Abstract: The gas-sensing materials, CdFe₂O₄, were prepared by inverse titration chemical co-precipitation with FeSO₄⋅7H₂O and CdCl₂⋅2.5H₂O. After calcinations at 300° ~ 700°C for 1h, respectively, n-type semiconductor gas-sensing materials with inverse spinel structure were obtained. Effects of the calcining temperature on the phase constituents and microstructure were characterized. The crystallite size of powders sintered at 700°C for 1h is 82 nm and dispersity good. Sensors based on CdFe₂O₄ were fabricated, and the gas-sensing properties were determined for using reducing gases. The results demonstrated that the sensors based on CdFe₂O₄ had good sensitivity and good selectivity to C₂H₅OH at 400°C. The difference in response for various tested gases might be attributed to absorption of reducing gases and reaction between these gases and the absorbed oxygen.

Abstract: Al₂O₃ ceramic is prepared by spark plasma sintering (SPS) using two commercial α-Al₂O₃ powders at elevated sintering temperature. The relative density and average grain size of the prepared Al₂O₃ ceramics are measured and compared. One α-Al₂O₃ powder has good sintering property because the relative density of the prepared α-Al₂O₃ ceramic is higher than 97% while another α-Al₂O₃ powder has poor sintering property.

Abstract: Al₃BC₃-based porous ceramics are prepared by pressureless sintering using Al, B₄C, and graphite powders as the starting materials. The influences of molar ratio of starting materials on the purity, open porosity and pore size of the porous ceramics are investigated. Graphite is the main impurity of the Al₃BC₃-based porous ceramics and can be eliminated by adjusting the molar ratio of starting material. With the molar ratio of Al:B₄C:C = 3.2:0.25:2.30, high pure Al₃BC₃ porous ceramic is successfully fabricated by pressureless sintering in vacuum at 1800 °C for 2 h. The open porosity of the Al₃BC₃-based porous ceramics ranges from 36% to 47%. The pores are uniformly distributed.

Abstract: Porous acicular mullite ceramic was prepared by in-situ reaction sintering, using clay materials and Al (OH)₃) as the raw materials. The influences of different clay materials on the phase composition, formation of acicular grains and microstructure of prepared porous ceramics were investigated. Results show that the metal oxide impurities were beneficial for the synthesis of acicular mullite. The prepared porous ceramic from Longyan kaolin with high impurity content has the highest mullite content of 93.5%, and composed of interlaced acicular grains with high slenderness ratio of 26.4 and large average diameter of about 0.7μm when sintered 1400°C for 2h. The TEM analysis indicates that the growth direction of acicular grains is along the [001] direction (c axis) of orthorhombic mullite crystals.

Abstract: Lithium carbonate, zinc oxide and silica as the main raw materials, potassium oxide and sodium as flux, phosphorus pentoxide as nucleating agent, the glass in Li₂O-ZnO-SiO₂ was synthesized by conventional melt cooling method and then converted to glass-ceramics. The crystallization behavior, microstructure and thermal expansion coefficient of the resulting glass-ceramics were investigated by XRD, SEM and thermal performance test. The results show that the Tg of the matrix glass is about 508°C, initial crystallization temperature is about 620°C. When the crystallization temperature ranges from 650°C to 750°C, the main crystal phase is Li₂ZnSiO₄. Increasing crystallization temperature to 850°C, much cristobalite crystals is formed. Owing to the high TEC of the cristobalite, the glass-ceramics with TEC of 12.27×10^-6°C^-1 were obtained, which is matched with the TEC of stainless steel SAE 1010.

Abstract: The spectral transmittance of six kinds of Vita In-Ceram and Cercon all-ceramic core materials after veneering ceramic was determined. Based on the production method recommended by the manufacturer, specimens of the same thickness are made. PERKIN ELMER Spectrophotometer is adopted to measure the spectral transmittance of In-Ceram AL2 slip-casting glass/alumina composite, AL2 electroformed alumina, Z21 slip-casting glass/zirconia composite, Z21 electroformed zirconia, Cercon base color zirconia and Cercon base zirconia all-ceramic core materials, after veneering ceramic. The results show that, after veneering ceramic, Cercon base Zirconia has the highest spectral transmittance, followed by AL2 Electroformed Alumina and Z21 Electroformed Zirconia, whereas the transmittance of Z21 slip-casting Glass/Zirconia composite has the lowest. Statistical data show that, among the groups, In-Ceram slip-casting Glass/Alumina composite (AL2), Electroformed Alumina (AL2), Cercon base color Zirconia and Cercon base Zirconia have significant differences between every group. On the other hand, there is no significant difference between In-Ceram slip-casting Glass/Zirconia composite (Z21) and Electroformed Zirconia (Z21). Therefore, we should choose all-ceramic restoration materials based on the spectral transmittance of all-ceramic core materials after veneering ceramic and transparency of the remaining natural teeth of patients.

Abstract: The present paper probes into the effect of background color of different post-core materials on the core materials of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia, Cercon base color Zirconia, and Cercon base Zirconia. The spectrocolorimeter was used to measure colorimetric values of all groups of samples against the background of noble metal, nickel-chromium alloy, silver amalgam and resin, and to calculate the color difference among the groups. The result showed that the color difference of Cercon base color Zirconia viewed against different backgrounds was identifiable by human eyes (ΔE > 1.5). In contrast, the color differences of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia and Cercon base Zirconia viewed against different backgrounds were unidentifiable by human eyes (ΔE < 1.5). Based on this, it can be stated that Cercon base color Zirconia is significantly affected by background color. Thus, proper method to shelter the background color should be adopted. In addition, AL2 Electroformed Alumina, Z21 Electroformed Zirconia, and Cercon base color Zirconia are less influenced by the background color, thus it is not necessary to cover the background color.

Abstract: A series of Ba-Al-O/NSR supports were prepared by co-precipitation in this work. The effect of Al/Ba atomic ratio and calcination temperature on the structure and texture of the supports was investigated carefully. The XRD spectra show that Ba is mainly exist in the form of BaAl₂O₄, and Al exists in Al₂O₃. The results of S_BET indicate that the supports possess relative high specific surface area (70~150 m²/g). The effect of different parameters on the process of supports synthesized was investigated carefully. The results show that the structure and specific surface area of support is significantly depended on calcination temperature.

Abstract: A series of Ba-Al-O NSR supports and Pt/Ba-Al-O NSR catalysts are prepared by co-precipitation and impregnation method in this work. The catalyst and the support are characterized by XRD, SEM, S_BET performance testing. The structure and texture of the supports is observed and discussed. The results of S_BET indicate that the supports possess relative high specific surface area (94~110 m²/g). Temperature programmed reduction is characterized by means of H2-TPR.

Abstract: Graphite powders are important pore former, and widely used in the preparation of many kinds of porous ceramics. The dispersion of pore former controls the homogenous pore structure of porous ceramics, and deeply influences its properties. The dispersion and its influence factors of graphite powders in water and alcohol were systematically studied. The dispersion of graphite powders in water and alcohol were investigated by sedimentation method. It was found that alcohol as dispersion media can improve the dispersibility of graphite powders. In addition, the influence of different surfactants on the disperisibility was also studies. It can be confirmed that surfactant can prompt the dispersion of graphite powders in water. The zeta potential and particle size of graphite powders in different pH value were tested to understand its dispersion.