Advanced Materials Research Vol. 1058

Abstract: A new sensor with Pt and Ag mixture paste on the surface to act as the sensing electrode (Ag) and catalyst (Pt) to oxidized SO₂ to SO₃ for sulfur dioxide was fabricated. The effect of auxiliary phase on the sensing properties has been investigated and the device with auxiliary phase showed better performance and the effect of operating temperature has also been studied. It shown that 500°C would be more suitable than 600°C for the device gas test.

Abstract: NASICON materials can be used as the solid electrolyte component in the sensor system, because they have excellent Na⁺ conductivity. This study prepares NASICON materials by solid state reaction method, and their phase, microstructure and electrical property will be characterized by XRD, SEM and EIS. Then an amperometric NO₂ sensor is fabricated to detect NO₂ gas in the level of ppb. The sensor current signal will be studied by changing different NO₂ concentrations, employing different materials on the counter electrode and using different applied voltages when the working temperature is 150°C.

Abstract: The effect of the limestone on the strength of the foam concrete is studied in this paper. The dry density of the foam concrete used in this experiment is 500 kg/m³, which is largely used in foam concrete for heat preservation in building. The experimental results reveal that the content of the limestone has great influence on the 3 d, 7 d and 28 d compressive strength and flexural strength of the foam concrete, but the fineness of the limestone has little influence on the 3 d, 7 d and 28 d compressive strength and flexural strength of the foam concrete, when the specific surface area is in the range of 210 cm²/g-440 cm²/g.

Abstract: The study of dye-sensitized solar cells (DSCs) based on nanocrystalline films of high band gap semiconductors is a progressive field of research that is being carried out by scientists in a wide range of laboratories. To improve the conversion efficiency of the DSCs, the SnO₂ nanorots photocurrent, the effect of controlling concentration on the properties of SnO₂ nanocrystalline were investigated via the hydrothermal method, and characterized by XRD, HRTEM, BET and Absorption spectrum. Though analysis the results, the conclusion is shown the pure SnO₂ is preparation, the prepared SnO₂ nanocrystalline under 0.05mol/L shows the particle-shape crystalline, the surface area of SnO₂ nanocrystalline is 102.1683m²/g. The prepared SnO₂ nanocrystalline under 1mol/L the fiber-shape crystalline, the surface area of SnO₂ nanocrystalline is 79.7591m²/g. The absorbance of SnO₂ nanocrystalline shows the strong absorption in the ultraviolet ray range, the absorbance of synthesized SnO₂ nanocrystalline under the concentration of SnCl₄ solution for 1mol/L shows the higher value.

Abstract: Charge density wave theory is used to investigate the dependence of dielectric loss of relaxor ferroelectrics on temperature, frequency and concentration of impurities. The dielectric loss originates from the local pinning. The competition between the local and collective pinning leads to a peak in the curve of dielectric loss v.s. temperature as well as the curve of dielectric constant v.s. temperature. The peak temperature of dielectric constant T_L, increases with increasing frequency and with decreasing concentration of impurities. The maximum dielectric loss is in proportion to T_L and in inverse proportion to the barrier height. Our theoretical results agree qualitatively with the experimental results.

Abstract: In this paper, A bipolar high voltage pulse with 20 ns rising time was employed to generate diffuse gas-liquid diffuse discharge in helium, and dielectric-free electrode configuration is used to generate room temperature plasma in small gas flow rate, which can be considered as a effective method to reduce the production cost. Discharge images, waveforms of pulse voltage and discharge current, and emission spectra of active species are measured.

Abstract: The hot deformation behaviors of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 350-500°C under strain rates of 0.01-10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 183.251 kJ/mol. The optimum hot working conditions for this material are suggested.

Abstract: SiC continuous fiber reinforced SiC ceramic matrix composites (SiC_f/SiC CMCs) and SiC fiber reinforced SiC micro ceramic matrix composites (SiC_f/SiC micro-CMCs) were prepared through polymer impregnation pyrolysis (PIP) progress, then the structures, mechanical properties and forming mechanisms of SiC_f/SiC CMCs were investigated. Results showed that volume shrinkage of SiC matrix occurred, and pyrolysates with bamboo-like layered structure were attached to the surface of SiC multifilament gradually. Furthermore, the mechanical properties of SiC_f/SiC micro-CMCs were consistent with SiC_f/SiC CMCs, so the PIP process parameters for the preparation of SiC_f/SiC CMC might be optimized primarily through SiC_f/SiC micro-CMCs, which could enhance the design and preparation efficiency of SiC_f/SiC CMCs obviously.Key word: polymer impregnation pyrolysis progress, micro ceramic matrix composites, forming mechanism

Abstract: The effect of MgO-Y₂O₃ additives on densification, microstructure and mechanical properties of hot-pressed Al₂O₃-TiCN composites was studied. The MgO-Y₂O₃ additions had little influence on densification of Al₂O₃-TiCN composites. The Al₂O₃-TiCN composites without additives had coarsening microstructure, whereas that containing 0.25wt%MgO-0.5wt%Y₂O₃ had a noticeable finer microstructure and good mechanical properties. The increase of fracture toughness were attributed to the addition of MgO and Y₂O₃ together with the TiCN particles to inhibit the abnormal grain growth of Al₂O₃.

Abstract: In this paper, centrifugal slip casting method was use to prepare carbon fiber/HA composites using the nanoHA particles and carbon fibers as initial materials. The morphology of the carbon fiber after modification of p-aminobenzoic acid was observed. The rheological characteristic of the carbon fibers/HA slurries was studied. The effects of the centrifugal acceleration on green density uniformity of carbon fiber/HA composites were analyzed. The bending strength and fracture toughness of carbon fiber/HA composites were measured. The results show the roughness of carbon fibers treated by p-aminobenzoic acid increases. At the pH of 10 and 5 wt% dispersant, the HA slurries with 3 vol% carbon fibers have good fluidity. After centrifuged at 2860 G for 30 min, the green compacts of HA composites have high and uniform the green density. After sintered at 1100°C for 1h, compared with carbon fiber/HA composites prepared by dry pressing, the modified carbon fiber/HA composites prepared by centrifugal slip casting have higher bending strength and fracture toughness of 89.4 MPa and 1.92MPa^1/2, respectively.