Abstract: The chemical and electrical characteristics of the grain boundary of the polycrystalline semiconducting SrTiO3 ceramics, which were synthesized by hot-press sintering Na-coated semiconducting SrTiO3 powders, were investigated in terms of process parameters such as sintering temperature. Diffusion kinetic parameters such as diffusion coefficients and activation energy of diffusing ions at particular heat-treatment conditions were obtained by fitting experimental data with computer-simulated results as well as electrical features near the grain boundary of the ceramics.
Abstract: For usage of glass fertilizer, physical and dissolution properties were investigated
according to variation of the SiO2 and K2O contents in silicate glasses. In glass forming region, K2O/P2O5 0-0.24, SiO2/(SiO2+P2O5) 0-0.29 and CaO/P2O5 0-1.00 were fabricated as clear glass in K2O-CaO-SiO2-P2O5 glass system. The glass transition temperature (Tg) and softening temperature (Ts) were gradually shifted to the higher temperature range according to increase of SiO2 contents. The K2O contents, which could cause the structure change from network structure to polymeric chain structure, have direct proportion with the thermal expansion coefficient and inverse proportion with Tg and Ts. The change of the K2O/P2O5 ratio was a main factor to control chemical durability and physical properties such as density and hardness. In the abnormal glass properties such as fast dissolution in aqueous solution, it was presented that the glass can be a good candidate for agriculture fertilizer.
Abstract: Defect perovskite, La1-xMnO3-1.5x (x=0.00-0.10), was synthesized by conventional ceramic method and phase transition was measured by X-ray diffractometry, electrical conductivity, thermal diffusivity and thermal analysis. La1-xMnO3-1.5x (x=0.00-0.09) have single orthorhombic phase corresponding to GdFeO3 type perovskite structure at room temperature, while have rhombohedral structural at high temperature. The transition temperatures observed from electric conductivity, DSC, thermal diffusivity were mostly in agreement and they slightly decrease with increasing x.
Abstract: The synthesis of Sr1-XBaXAl2O4 :Eu 2+ (x = 0, 0.1, 0.2 and 0.3 mol) phosphor and its properties of photoluminescence and long-phosphorescence were investigated as a function of sintering condition. The single phase of SrAl2O4 was obtained by sintering the mixtures of SrCO3, BaCO3, Eu2 O3, Al2O3 and 3wt% B2 O3 powders over 1100°C in Ar/H2 atmosphere. Stuctural properties were analyzed by a X-ray diffractometer, microstructural properties by a SEM, and photoluminescent properties by a PL measuring system. The optimum sintering condition for the long-phosphorescent phosphor of Sr1-XBaXAl2O4:Eu2+ was found at 1400 °C. Substitution of Ba about 0.2mol in SrAl2O4
:Eu 2+ enhanced the photoluminescence and long-phosphorescence.
Abstract: Nb/Nb5Si3 in-situ composites are very attractive structural materials for these materials perform a good balance in mechanical properties, including a high strength at high temperature (>1373K) and reasonably high fracture toughness at room temperature. Metastable phase Nb3Si plays an important role in the properties of Nb/Nb5Si3 composites by affecting microstructure and volume fracture of ductile phase. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x=0,5,15) are prepared by arc melting and annealed at 1473K for 100h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The stability of metastable phase is analyzed by XRD. The room temperature fracture toughness of Nb-10Si is 10.47MPa(m)1/2 and higher than that of binary Nb-18Si alloys at near-eutectic compositions. The addition of Mo improves the fracture toughness of as cast Nb-Si alloys from 4.1 MPa(m)1/2 to 9.9MPa(m)1/2 at near-eutectic compositions and decreases it from 10.47 MPa(m)1/2 to 8.8MPa(m)1/2 at hypoeutectic compositions.
Abstract: In order to assess material properties and part homogeneity in carbon matrix
composite (CMC) brake disks we have performed nondestructive evaluation, which are originally developed for aerospace applications. In this paper we have adopted several ultrasonic techniques to evaluate carbon matrix composites for the material properties that are attributable to the manufacturing process. In a carbon matrix composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of the CMC composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Optical micrograph had been examined on the surface of the CMCs using a destructive way. Also a motorized system was adopted to measure ultrasonic velocity on the point of the CMC materials under the same coupling conditions. Manual results were compared with those obtained by the motorized system with using dry-coupling ultrasonics and through transmission method in immersion.
Abstract: Interfacial strength distribution and thermal residual stresses in multi-layered or
compositionally graded NiCrAlY/ZrO2 coatings are analyzed. These coatings are fabricated by detonation gun spraying using mechanically alloyed, plasma-spheroidized composite powders. The problems in design of functionally graded materials (FGMs) are outlined and their modeling approaches are reviewed. Due to the concentrational or structural gradients in FGMs, the normal approximations and models, used for traditional composites, are not directly applicable to graded materials. The goal is to show the efficiency of the simplest models to provide the most accurate estimates of the properties and even to make simple elasto-plastic analysis of FGM components without vast computations by finite element methods with an arbitrary non-linear distribution of phases and corresponding properties is presented. Results showed that bonding strengths increased gradually with increase of the composition of metals in the FGM coatings. The FGM coating was more stable on the mechanical properties than normal duplex composites. And, the maximum compressive radial stress is found to be at or near the surface of the specimen where surface cracking may be generated. The maximum axial stress is at the edge of the specimen where spallation may occur. The maximum shear stress is also at or close to the edge.
Abstract: A new approach for the CTE on the basis of Ashelby.s cutting and welding process was made for the analysis of the thermal expansion behaviors of Al-Si alloys and composites. In this theoretical approach, it was considered that relaxation of residual stress could create an elastoplastic zone in the matrix around a particle during cooling. A comparison of the measured CTEs with the calculated ones for the Al-Si-SiCp and Al-Si-Al2O3 composite systems was performed in terms of the volume percent and the size of reinforced phases. The calculated results revealed that the linear CTE of the both composite depends on the size of the reinforce phases, especially at the composite systems with a low volume percent of the reinforce phases. The increase in the volume percentages of Al2O3, SiCp and Si phase lowers the linear CTEs of the systems. The measured CTEs was deviated less than about ten percents from the calculated ones at composites with a high volume percent. The deviations of the CTEs of reinforced phases are about 4 - 6 vol% from real composite systems.
Abstract: Nanocompositesα-Fe/Fe3B/Y2O3 and ε-Fe3N/Y2O3 were prepared by a melt-spun
technique, and the subsequent hydrogenation, oxidation and nitrogenation treatments, respectively. The effective electromagnetic wave absorption (RL<-20 dB) was obtained in a frequency range of 2.7-6.5 GHz on resin composites of 80 wt% α-Fe/Fe3B/Y2O3 powders, with thickness of 6-3 mm; the ε-Fe3N/Y2O3 resin composites exhibited good microwave absorption properties in the 0.6-4.4 GHz range.