Advanced Materials Research Vols. 1004-1005

Abstract: In this study, the disadvantage that adhesive layer of piezoelectric bimorph actuator was ignored when model of actuator was developed by predecessors is indicated, according to the actual structure of actuator. Based on the thickness of adhesive layer and substrate, the improved model of adhesive layer that substrate and adhesive layer are combined as one layer called mid layer is proposed. Mathematical model of mid layer can be obtained with theory of composite material, which is then used to develop the model of actuator under electrical load. Another model of actuator is developed as a reference in the same way except with model of adhesive layer used by predecessors, and experiment is also presented later. Performance predicted by these two models of actuator and result measured in the experiment are compared, which comes to a conclusion that model of actuator developed with the improved model of adhesive layer conform to the physical model and is more precise in performance prediction.

Abstract: Fused quartz granules (d₅₀=19 μm) were used as raw material, and B₄C-Si₃N₄ (1:1, in mass) was used as additive with dosages of 1% (in mass, similarly hereinafter), 2% and 3%. Fused quartz ceramic materials were fabricated in reduction atmosphere at 1250 °C, 1300 °C, 1350 °C and 1400 °C for 1 h. The apparent porosity, bending strength and thermal expansion ratios of the samples were examined and they were analysed by means of XRD. The results showed that the sample sintered at each temperature with 1% B₄C-Si₃N₄ had the lowest apparent porosity, the highest bending strength. This indicated that 1% B₄C-Si₃N₄ was conducive to sintering of fused quartz ceramic materials. The results of XRD analysis and thermal expansion ratio analysis showed that 1% B₄C-Si₃N₄ compound additive had obvious effect on inhibiting crystallization of the samples sintered at various temperatures. It can be deduced that the 1% B₄C-Si₃N₄ compound additive plays the excellent role in inhibiting crystallization and facilitating sintering of fused quartz ceramic materials.

Abstract: In general, ceramic membranes consist of top layer possess structure a hygroscopic zone which acts as a separator while the following bottom layers form a porous nonhygroscopic zone which provides the permeation paths and acting as supporting structures. Thus, the combination of these two different multilayer systems will exhibit different water desorption behavior especially in ceramic membrane preparation. Experimentally, this water characteristic is defined through water retention curve (WRC). Since there is no detailed study on the fitting parameters that associated with WRC on membrane structure has yet been reported, therefore, this paper investigates the effects of various parameters used in WRC equation that represent material properties of the membrane structure using mathematical model. The results showed that hygroscopic material has higher α and n value with lower m value compared with nonhygroscopic material. Hence, understanding the variation of the fitting parameters in the WRC equation is essential for the configuration of WRC slope associated with the material properties especially during drying process of membrane.

Abstract: The processible and high yield polyborosilazane (PBSZ) precursor for SiBN ceramics was prepared by coammonolysis reaction of dichlorosilane and trichloroborazine. The synthesized PBSZ precursor was characterized by Fourier Transform Infrared spectroscopy (FTIR), ¹H, ¹¹B, and ²⁹Si Nuclear Magnetic Resonance (NMR), and its ceramic conversion chemistry was investigated by differential scanning calorimetric (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA). The PBSZ precursor is a viscous liquid and changes to an insoluble solid via a cross-linking reaction between the N-H group and Si-H group as post-heated from 60 to 180°C. The insoluble solid is transformed to Si₃N₄ and BN amorphous structures with an approximately 95% ceramic yield after being pyrolyzed to 1000°C.

Abstract: The XRD patterns of Strontium Titanate (SrTiO₃) prepared by direct current arc discharge plasma technique show that the well crystallized cubic structure. A Raman spectra study is performed to investigate SrTiO₃ ceramics and powders compared with earlier investigations. The observed Raman spectra in this work have been interpreted primarily as second order and derived from combinations, overtones and differences of phonon frequencies.

Abstract: A continuum field model describing the electrical characteristics of polycrystalline semiconductors ceramics is suggested. Taking into account the continuum theory, a static differential equation about electron level on the base of Poisson equation is established. The one-dimensional quantitative calculation is carried out using the Runge-Kutta method. The results show that as the applied voltage increases, the grain boundary barrier in the nonlinear zone drop drastically. The nonlinear characteristics of high temperature paraelectric phase is larger than that of room temperature ferroelectric phase.

Abstract: In this paper, the dielectric properties of ZnO-Bi₂O₃ based varistor ceramics doped with Li are investigated by Novocontrol wide band dielectric spectrometer. It is found that Lithium is an amphoteric impurity. If the content of Lithium is very low, It will enters into the interstitials and Lithium interstitial is formed as a donor. While with the increase of Lithium content, Zn is replaced with Li and Lithium substitution for Zinc as a acceptor is formed. If the content of Lithium increases further, Lithium interstitial is formed again with the redundant Lithium. Therefore, the concentrations of intrinsic point defects of Zinc interstitial and oxygen vacancy varies with the content of Lithium, which leads to the increase of Schottky barrier at grainboundary with Lithium.

Abstract: 0.65(K_0.5Bi_0.5)TiO₃–0.35BaTiO₃ (0.65 KBT-0.35 BT3) ceramic was synthesized using a conventional calcination process (CC-process), and using a two-step calcination process that combined hydrothermal and CC processes (HT-CC-process). The effects of these two different calcination processes on the physical and dielectric properties of 0.65 KBT-0.35 BT3 ceramics were recorded and analyzed. When the CC-process was used, secondary phases—namely, BaBi₄Ti₄O₁₅, K₂TiO₃, and K₄Ti₃O₈—were observed in the XRD patterns of 0.65 KBT-0.35 BT3 ceramics. When the HT-CC-process was used, only the (K_0.5Bi_0.5)TiO₃ (or (K_0.5Bi_0.5, Ba)TiO₃) phase was observed in the XRD patterns, with no secondary phases. Due to the secondary phases, the CC-process 0.65 KBT-0.35 BT3 ceramic had lower dielectric peaks and broader temperature-dielectric constant curve than the 0.65 KBT-0.35 BT3 ceramic synthesized using the HT-CC-process.

Abstract: In this study, the fracture toughness of ceramic materials such as Al₂O₃, SiC, Si₃N₄, ZrO₂ were measured by the SENB method and IF method respectively. The results shown that the value of fracture toughness obtained from the SENB method is significantly higher than the IF method. When the notch width is fixed, with the flexural strength of ceramic materials increasing, the error of fracture toughness from the SENB method compared to the IF method is increased. For example, the flexural strength of ZrO₂ is about 847MPa and the error of fracture toughness from the SENB method compared to the IF method is 50.14%, the flexural strength of Al₂O₃ is about 338MPa and the error of fracture toughness from the SENB method compared to the IF method is only 4.52%.

Abstract: The oxidation resistance of SiAlONs is one important property. In our work we present a test method to characterize its anti-oxidation property with the non-isothermal oxidation process using Thermo Gravimetric Analyzer (TGA). The oxidation starting temperature (T_s), maximum oxidation rate temperature (T_m) and the value of the oxidation weight gain per unit area (G_a) are three key parameters to describe the antioxidant properties of the material. Experimental results prove this test method is easy and reasonable and it will be developed as the national standard of China.