Mingju Chao

Textured BaTi2O5 ceramic synthesized by laser rapid solidification method and its dielectric properties

Textured poly crystalline barium dititanate BaTi2O5 (BT2) ceramics with a preferred 〈010〉 orientation were synthesized by laser rapid solidification method, with a CO2 laser. The 〈010〉 orientation of the BT2 is along the laser incident direction, and the orientation factor (f) and relative density of the unannealed BT2 sample are 0.40 and 96.2%, respectively. The two quantities increase with increasing annealing time, and reach the maximum values of 0.42 (annealed at 1,000xa0°C for 12xa0h) and 97.5% (annealed at 1,000xa0°C for 24xa0h), respectively. The images of scanning electron microscopy reveal that the BT2 are composed of flake-like microstructures with the maximum thickness of 20xa0μm and dimension of 0.6xa0mm, which are parallel to the laser incident direction. The measured Curie temperature (Tc) and the maximum dielectric constant (εmax) are 443 and 6,000xa0°C, respectively.

Effects of synthesis condition and atomic group on conductivity of V2O5-doped ceria-based ceramics

The relationship between conductivity and activation energy was discussed in ceria-based ceramics. The conductivity of La-doped ceria solid solution with or without V2O5 additive was measured by AC impedance method and concluded that the conductivity and activation energy could be affected by a slight doping with extra atoms. The addition of V2O5 greatly improved the sintering characteristic of ceria solid solution and elevated about 15xa0% of relative density. The value of activation energy was also variable with the content of V2O5 addition. However, the minimum activation energy is consistent with the maximum conductivity not at random temperature. The intersection of the Arrhenius plot is moved to a lower temperature with increasing content of V2O5 below 0.05xa0mol% between the V2O5-doped and undoped samples. The total conductivity was lower than that of undoped sample at the low temperature but larger at a high temperature. Selecting suitable additive is considered as a useful method to prepared high-density and conductive ceramics.

Laser synthesised TaC for improving copper tribological property

Abstract To improve the wear resistance of copper through in situ synthesis of ceramic particulate reinforcement, laser surface modification on copper was performed using a powder mixture of Ni based alloy with (Ta2O5+C) doping. The microstructure, microhardness, wear resistance and bulk electrical conductivity of the integral material were investigated. The results indicated that the modified layer had a homogeneous fine microstructure containing TaC particles and Cr3C2 acicular phases dispersed uniformly in the matrix of γ (Ni,Fe) and (Cu,Ni,Fe) solid solutions. The modified layer exhibited higher hardness and better wear resistance than the Ni based alloy modified layer because of the presence and the uniform distribution of in situ synthesised TaC particles. However, the addition of TaC particles slightly decreased the electrical conductivity of the integral bulk.