Advanced Materials Research Vols. 284-286

Abstract: The B₂O₃-CuO oxide mixture (abbreviated as BC) was selected to lower the sintering temperature of (Ca_0.9375Sr_0.0625)_0.25(Li_0.5Sm_0.5)_0.75TiO₃ (abbreviated as CSLST) microwave dielectric ceramics by solid sate reaction technique. The effects of BC doping amounts on the crystal structure, microstructure and microwave dielectric properties of the ceramics were investigated. For the ceramic sample with the composition of CSLST + 5 wt% BC, its sintering temperature was reduced to 1000 °C as compared to 1200 °C for pure CSLST. In addition to the obtained good microwave dielectric properties as follows: ε_r = 80.4, Q×f = 1380 GHz, τ_f = -32.89 ×10^-6/°C, this ceramic was a desirable high-permittivity microwave dielectric candidate for low-temperature cofired ceramic (LTCC) applications.

Abstract: Bismuth titanate Bi₄Ti₃O₁₂ powders had been successfully prepared from different starting materials by chemical methods and characterized by XRD, SEM and DTA. Our efforts in this paper were directed to disclose the influence of precursors on the particle characterization. It was shown that different precursors affected the crystalline temperature, particle nucleation and growth rate greatly, leading to different particle size and morphology. Excess addition of Bi₂O₃ was found to be dominant in lowing crystalline temperature while spherical particles was probably attributed to large growth rate and use of glacial acetic acid as a solvent medium.

Abstract: Plated-like Bi₄Ti₃O₁₂ particles with anisotropic properties were prepared by the NaCl-KCl molten salt method. The effect on microstructure and patterns of Bi₄Ti₃O₁₂ particles was investigated by adjusting salt quantities, calcined temperature and excessive Bi₂O₃ content. The results show that the size of Bi₄Ti₃O₁₂ particle and the degree of anisotropy of pure perovskite structure of Bi₄Ti₃O₁₂ particles prepared at 750°C simultaneously increased with the quantities of molten salt and the temperature of the calciner. Excessive Bi₂O₃ content also shows a positive effect to obtain the anisotropic Bi₄Ti₃O₁₂ particles whose preparation process was optimized.

Abstract: Using traditional experiment means on piezoelectric ceramic device has certain limitations due to the complicated boundary conditions and stress situation. In this paper, the finite element model of piezoelectric ceramics in line with the experiment results was established according to piezoelectric structure field and the coupling of the electric field, deformation of representative PZT piezoelectric ceramics under the voltage was analysed in using finite element analysis software ADINA according to establishing geometric model, defining boundary conditions and materials, Coupling calculation. Consistency between simulation results and experimental results is improved and lay the foundation for the realization of the piezoelectric ceramic shapes and vibration control.

Abstract: BaZr_0.25Ti_0.75O₃ (BZT) ceramics were prepared by conventional ceramic process at a relatively low sintering temperature and with an addition of Li₂O as the liquid-phase sintering aid. X-ray diffraction characterized results showed that the main crystal phase of the samples with 1.0wt% Li₂O additive sintered at 1050°C～1250°C for 4h presented perovskite structure. The dielectric properties of BZT ceramics have been investigated. The dielectric constant of 1.0wt% Li₂O doped BZT sintered at 1150°C decreased, and the dielectric loss increased by 0.0012 compared with that of the pure BZT sintered at 1450°C.

Abstract: In this study we report sintering behavior and microstructures of glass-added BaTi₄O₉ microwave dielectric ceramics with copper paste in reducing atmosphere. Experimental results show a buffer layer may form at the interface of Cu-electrode and BaTi₄O₉ microwave dielectric ceramics if the glass did not diffuse smoothly during sintering, and therefore materials exhibited different colors. X-ray results indicate that Cu reacted with Ba seriously to form complicated reaction products, and some BaTi₄O₉ transformed to barium titanate with various ration of Ba/Ti, which may degrade the dielectric properties of materials.

Abstract: Zirconium titanate and magnesium aluminate spinel precursors were prepared by non-hydrolytic sol-gel method using ethanol as oxygen donor. The gels and calcined powders were investigated by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD). The results show that the ZrTiO₄ and MgAl₂O₄ crystallized at low temperature of 550 °C and 700 °C, respectively. It indicated that the highly homogeneous zirconium titanate and magnesium aluminate gels were aslo obtained by nonhydrolytic sol-gel process using ethanol as oxygen donor. The particle size distribution measured by laser scattering exhibit that ZrTiO₄ and MgAl₂O₄ powders were large soft agglomerates which could be broken through milling process.

Abstract: Titanium sponge is used as anode, titanium plate as cathode and NaCl-KCl-TiClx molten salt as electrolyte, to prepare high purity titanium by molten-salt electrolysis at 900~980°C. The effects of feeding TiCl₄ temperature, electrolytic temperature, soluble titanium concentration and cathode current density on the content of impurities of cathode products have been studied. The results show that the impurities in product can be controlled when the temperature of feeding and electrolyte is higher. The final product with different morphology and degree of purity can be prepared by controlling the soluble titanium concentration and cathode current density.

Abstract: To explore reaction mechanisms and proper effects of aluminium in laser micro-molton pool, experiments of laser cladding (Ti+1-8%Al) on Ti-6Al-4V by pulsed Nd:YAG had been carried out. The microstructures, microhardness and phases of the cladding layers with different weight percentage of Al were investigated. The content of Al was quantitatively determinated when ordering α₂ ceramic phase (Ti₃Al matrix) were formed. And the friction and wear properties of the cladding layers were examined in atmosphere. It was found that the microstructure of the cladding layers included cellular crystals, columnar crystals, arborescent crystals and dispersive white granules. The α₂ ceramic phase was formed when the content of Al was 6%wt. With the increasing of weight percentage of Al, the number and size of arborescent crystals increased obviously, as well as the microhardness, the maximum was 957.9Hv, 1.3-1.5 times of the layers with below 6%wt Al. Inversely, the wear resistance of the laser cladding layers was improved gradually. Friction coefficient, wear extent and wear rate decreased. 0.55-0.7 times of the layers with below 6%wt Al.

Abstract: This study presents a numerical simulation, using the flow simulation of solidworks 2010; the results showed the flow speed trajectory, the variation of the shear stress and the flow pressure on different faces of the micro-asperities in relation with the face length. The simulation was done in steady state and with the no- slips condition in contact with the upper surface. The flow characteristics were found also with different flow speed. The turbulence area due to the micro-asperity geometry is localized. The flow characteristics (variation of shear stress and flow pressure) are analyzed for the prediction of the maximum wear area due to the skin friction or drag.