Ji Kang Yan

Research on Dehydrogenation and Sintering Process of Titanium Hydride for Manufacture Titanium and Titanium Alloy

In this paper, unlike the traditional powder metallurgy technology, the titanium hydride is directly used as the starting material to manufacture the titanium and titanium alloy. Thermogravimetric and dilatometric techniques are performed to study the dehydrogenation and shrinkage of TiH2 powders with different particle sizes. The process factors such as the sintering temperature, the sintering time, the heating rate, the compaction density, the compaction methods, and the alloy system, would affect the sintering densification of TiH2 powders and TiH2-Al-V alloy powder. The results shown that the dehydrogenation temperature of the starting and ending of the ball milling TiH2 is lower than that of the coarse TiH2 powders, the finer the TiH2 powder, the lower the temperature. The densification of TiH2 powders is easy due to the combination of dehydrogenation and shrinkage of α-Ti in one process, which creates the fresh dehydrided titanium uniform during sintering, thus leads to rapid densification and very high sintering relative density, higher than 99%. In contrast, it is difficult to achieve a full densification of TiH2-Al-V alloy powder during sintering, which requires dissolution of alloy elements during sintering above its beta transformation temperature. The sintered microstructure of Ti-6Al-4V shows the typical lamellar shaped α+β characteristics, with a uniform alloy element distribution.

Low Temperature Co-Fired ZnNb2O6 Dielectric Ceramic Doped by B2O3

To lower the sintering temperature of ZnNb2O6 microwave dielectric ceramic, ZnNb2O6 doped with B2O3 were prepared by the traditional solid state reaction method. The effects of the amount of B2O3 (0.25-5.0wt.%) on the microstructure, density and electrical performances were investigated. The results show that a pure columbite ZnNb2O6 phase was obtained for all B2O3-doped ceramics. The microwave dielectric properties reached the maximum values of εr = 24.1, Q×f = 19502 GHz, τf = -52.19 ppm/°C for 1wt% B2O3-doped ZnNb2O6 ceramic sintered at 1050 °C for 4 h. All of evidences suggest that the enhancement of microwave dielectric properties is due to the enhanced ions-energy and ionic diffusion with the increase of sintering temperature. Furthermore, B2O3 doping can generate liquid phase and reduce the activation energy of diffusion to promote the materials sintering.

Study on the Second Phases of (Y,Nb)-Codoped TiO2 Ceramic

Microstructures and crystal structures of the second phases YNbO4 and YTiNbO6 in (Y,Nb)-codoped TiO2 ceramics were investigated at different sintering temperature and calcination temperature. The (Y,Nb)-codoped TiO2 ceramics and the second phase ceramic samples were prepared by the traditional electronic ceramic process. The microstructure, chemical composition and crystal structures of samples were characterized by SEM, EDS and XRD. The results show that there exist second phases of YNbO4 and YTiNbO6 in (Y,Nb)-codoped TiO2 ceramic. With the sintering temperature and calcination temperature rising, the second phase YNbO4 will transmit to YTiNbO6.

Photocatalytic Properties of (Fe, N)-Codoped TiO2

Fe, N)-codoped TiO2 were prepared by calcining the Fe-doped TiO2 samples accomplished by precipitation method in the nitrogen atmosphere, and the photocatalytic properties of (Fe, N)-codoped TiO2 at different temperatures were investigated. The samples were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and ultraviolet-visible (UV-vis). The results show that the (Fe, N)-codoped TiO2 powder samples calcined at 600°C are dispersed well with more hydroxyl groups on its surface. The absorption edge of the (Fe, N)-codoped TiO2 is 429nm due to the effects of mixed crystal, which means the improvement of photocatalytic capability.

Effects of Sintering Temperature on Microstructure and Properties in TiO2 Varistor Ceramics

The effects of sintering temperature on microstructure, micro-composition, barrier structure and electrical properties of TiO2 varistors ceramics were investigated. The microstructures and chemical compositions of grains in TiO2 ceramics were measured by SEM and EDS. Based on the thermo electronic emission theory, Grain boundaries barrier structure was calculated by analyzing electrical properties of samples. The sample sintered at 1350°C exhibits better microstructure and properties. The grains size of the TiO2 sample sintered at 1350°C is about 15m, and other electrical properties are as follows: solid solubility of donor doping Nb5+ cation solute in TiO2 grains of 1.49mol%, barriers height of 0.28ev, barriers width of 48nm, varistor voltages of 5.25V/mm, non-linear coefficient of 4.2 and relative dielectric constant of 1.1×104.

Effects of Paste Composition and Sintering Process on Performance of Silver Paste for Silicon Solar Cells

In order to study the effects of composition ratio of silver paste and the sintering process on the properties of the silver film after sintering, the effects of different ratios of silver powders, glass powders and organic carrier in silver paste and different sintering temperatures and sintering time on the adhesion force and square resistance of the silver film were studied. The morphology of the sintered silver film was observed by SEM. The results showed that the silver film sintered at 760°C for 6 seconds had better properties after sintering when the ratio of silver powders, glass powders and organic carrier in silver paste was 80:5:15 and the silver powders was composed of spherical silver powders and flake silver powders at the ratio of 94:6. The adhesion force and square resistance of the silver film were 8.25 N and 3.47mΩ /□, respectively.

Performance of (Y2O3,V2O5) Co-Doping TiO2 Ceramics

The present study investigated the effect of the sintering temperature and (Y2O3, V2O5) co-doping on the performance of TiO2 varistor ceramic which has lower varistor voltage and high nonlinear coefficient. The results showed that the TiO2-based varistor ceramic which doped with 0.35% mol and 0.25% mol of Y2O3 and V2O5 has good comprehensive electrical performance and excellent dielectric constant sintered at 1200°C. Its varistor voltage V1mA is 38.1V, nonlinear coefficient is 4.6.

Influence of Voltage on the Biological Performance of Micro-Arc Oxide Films Based on TC4 Titanium Alloy

The porous ceramic biologic films were prepared on the surface of Ti6Al4V (TC4) with micro-arc oxidation technology (MAO). The phase composition, microstructure and valence state of micro-arc oxide films were studied. The biological properties of the ceramic film were comprehensive evaluated through animal experiments. Results show that with increasing of the micro-arc oxidation voltage, the better biocompatible hydroxyapatite appears on the surface of titanium alloy (TC4). The high voltage promotes the surface pore size enlarge. The porous ceramic surface makes bone tissue early grow up. Pathological sections of bone tissue 24 w animal experiments indicates that the implants can form good biological combination with bone, no rejection and the higher the micro-arc oxidation voltage, the more new bone cells.

Influence of Voltage on Microstructure of Micro-Arc Oxide Films on TC4 Titanium Alloy

The porous ceramic biologic films were prepared on the surface of Ti6Al4V (TC4) with micro-arc oxidation technology (MAO). The phase composition, microstructure and cross section morphology, surface elements composition and valence state of micro-arc oxide films were studied. Results show that with increasing of the micro-arc oxidation voltage, the better biocompatible hydroxyapatite appears on the surface of titanium alloy (TC4). The high voltage promotes the surface pore size enlarge.

Effect of Thermal Oxidation Temperature on the Properties of Micro-Arc Oxidation Ceramic Coating on TC4 Alloy

The effect of thermal oxidation temperature on the properties of MAO ceramic coating was investigated, The phase composition and surface morphology of composite oxidation coating were analyzed by XRD and SEM. The micro-hardness of composite oxidation coating were tested by micro hardness tester. The results shown that the composite oxidation coating consists of rutile, anatase Ti and HA. With the thermal oxidation temperature increasing, the micro-hardness of composite oxidation coatings were improved, but when the thermal oxidation temperature rose from 600 °C to 700 °C, the micro-hardness of coating dropped from 575 HV to 505 HV. With the thermal oxidation temperature increasing, the numbers of micro-porous on coating surface was decreased , and the composite oxidation coating became more density.