Advanced Materials Research Vols. 634-638

Abstract: Al₈B₄C₇ ceramic powder was successfully synthesized via a gas-solid reaction method using aluminum, boron trioxide and activated carbon as the starting materials. The effects of synthesis temperature and the amount of B₂O₃ addition on synthesis of Al₈B₄C₇ were investigated. The results indicated that the optimized process for preparing the Al₈B₄C₇ was that the mixtures were heated at 1800 °C for 2 h in flowing argon atmosphere. With the heated temperature increasing, the Al₈B₄C₇ content was decreased in the products. And 0.5 molar excess of B₂O₃ addition promoted the formation of Al₈B₄C₇. The heating samples at 1800 °C had a hexagonal plate-like morphology with ~100 μm in size.

Abstract: In this paper, the synthesis of MgAl2O4-SiAlON composite powders by forsterite, alumina and carbon black was studied. The samples were calcined under nitrogen atmosphere at 1500 °C, 1600 °C, 1650 °C for 3 hrs respectively. The phase compositions and microstructure of the synthesized powders were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result shows that an optimal alumina/forsterite content was a molar ratio of 2.0:1.0, the products consisted mainly of MgAl2O4 and Si3Al3O3N5 at 1500 °C, MgAl2O4 and Mg1.25Si1.25Al2.5O3N3 at 1600 °C and 1650 °C. The temperature can improve the formation of the octahedral spinel and flakiness Mg1.25Si1.25Al2.5O3N3.

Abstract: Friction and wear tests of Al2O3 and SiC were conducted from room temperature to 1200°C both in air and in vacuum. Results show that the wear mechanism of Al2O3 is dominated by micro fracture, debris abrasive and delamination at temperatures below 600°C, while is controlled by plastic deformation and recrystallization among 600~1200°C, resulting in an obvious decrease of wear loss. The wear rate and surface microstructure of SiC are closely depending on the testing temperature, atmosphere and contact pressure. Oxidation of SiC at elevated temperatures plays important role on the wear rate. Self lubrication of both Al2O3 and SiC at high temperatures was observed, which is mainly depending on the formation of a specific surface layer composed of nano-particles or very thin glassy film.

Abstract: The effects of B₄C addition on the room temperature physical properties and hot mechanical properties of MgO-SiC based refractory castables were investigated using magnesia and SiC fines as starting materials and silica fume as a binder. The microstructure was characterized by scanning electron microscopy (SEM). The results showed that drying strength of MgO-SiC based castables decreased with the increase in B4C addition, the immediate temperature strength and hot temperature strength increased. The HMOR at 1400°C for 0.5h decreased. This is because B4C oxidized and produced a liquid phase during heating, contributing to sintering and making the material denser. So the cold strength increased. On the other hand, due to the formation of liquids, direct binding reduced and the HMOR decreased

Abstract: In this paper, the investigations are presented for preparation of zirconium titanate ceramics by pressureless sintering of powders obtained by alloy oxidation method. Zr_xTi_1-xO₂ (x=0.40-0.60) powders were prepared by the oxidation of Zr-Ti alloys. The zirconium titanate powders were sintered in the temperature range from 1400 to 1600 °C for 3 h by pressureless sintering. The relationships among the composition, the relative densities and microstructure of bulk ceramic were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the sintering and microstructure of single phase zirconium titanate ceramics varied with ZrO₂ content. The relative density of samples reaches the maximum value of near 92% when sintering temperature is up to 1600 °C. Irregular pores distributed uniformly among the particles in the sintered ceramics with homogeneous microstructure.

Abstract: AlN-CNTs composites were prepared by using hot pressed sintering. The microstructure of AlN-CNTs composites was observed by scanning electron microscope (SEM), and the dielectric property and thermal conductivity were measured using LCR and other specialized instruments. The experimental results showed that the variation of the electrical resistivity was consistent with the percolation theory, with the percolation threshold of the samples at about 1.4% CNTs, and that with increase of CNTs content both the dielectric constant and dielectric loss rise up, whereas the thermal conductivity goes down

Abstract: The sintering parameters of hot-pressing diamond drill bit mainly contains the sintering temperature, holding time, sintering pressure and the pressurized method. The length of holding time is directly related to the performance of diamond drill bit. This article mainly discusses the effect of holding time on the performance of diamond drill bit. First, a general formula of diamond drill bit is chosen. A group of samples in this parameter were loaded and sintered. Holding time is set as variable, while other parameters remain the same. The optimal holding time for this formula is obtained through the mechanical properties tests on the samples’ bending, tension, compression, and hardness, and fracture analysis using scanning electron microscopy (SEM).

Abstract: The silica matrix specimens were prepared by adding microsilica and MoSi2 powder. The mixture were pressed to cylinder and then sintered at 1200oC, 1250oC, 1300oC and 1400oC for 8h respectively. The phase compositions of specimens were analyzed by X-ray diffusion and the tridymite crystal morphology and grain sizes were observed by SEM. The results show that with the addition amount of MoSi2 powders increase, the intensity of tridymite diffraction peaks first strengthen slightly and then decrease, becoming more and more amorphous process, while the diffraction peaks of residual quartz phase enhance. When adding 2.5% MoSi2, the precipitation of CaMoO4 phase reduces the O/Si ratio in the liquid phase, and promotes the generation of tridymite, so the number of tridymite increase, but the crystal size decreases. With the sintering temperature increase, the intensity of tridymite diffraction peaks increase, the residual quartzite amount reduces.

Abstract: The theory of Hamiltonian system is introduced for the problems of laminated transversely isotropic magnetoelectroelastic plates. The partial differential equations of the magnetoelectroelastic solids are derived corresponding to the Lagrange density function and Legendre’s transformation. These equations are a set of the first-order Hamiltonian equations and expressed with displacements, electric potential and magnetic potential, as well as their dual variables--lengthways stress, electric displacement and magnetic induction in the symplectic geometry space. To obtain the solutions of the equations, the schemes of separation of variables and expansion of eigenvector of Hamiltonian operator matrix in the polar direction are implemented. The homogenous solutions of the equations consist of zero eigen-solutions and nonzero eigen-solutions. All the eigen-solutions of zero eigenvalue are obtained in the symmetric deformation. These solutions give the classical Saint-Venant’s solutions because the Hamiltonian matrix is symplectic. The method is rational, analytical method and does not require any trial functions.

Abstract: Stretch-oriented chrysophenine-doped poly(vinyl alcohol) (PVA) films were prepared at temperatures above the glass transition temperature of PVA. The optical absorption spectra of the stretch-oriented films exhibited a very high anisotropy (anisotropy ratio = 13). The third-order nonlinear optical properties of chrysophenine in stretch-oriented PVA films were measured by the resonant femtosecond degenerate four-wave mixing (DFWM) technique. The anisotropy ratio of the DFWM signal intensity was greater than 1000. The value of third-order nonlinear optical susceptibility of a uniaxially stretch-oriented chrysophenine-doped PVA film was 6.9×10^-13 esu.