Papers by Author: Jun Zhao

Abstract: It is very important for accurately grasping stress, strain, and metal flow during the hollow motor shaft rolling, and it is also foundation of forming regularity, rolling force and energy parameter. The cross wedge rolling process of hollow motor shaft was simulated through rigid-plastic finite element software deform-3D. According to the simulation results, the distribution of internal stress, strain field inside the second step of the motor shaft had been obtained, revealed the metal flow ruler for the second step during forming process and it could effected on the metal flow ruler for the first step.

Abstract: BaTiO3 nanopowders prepared by sol-gel process were used for multilayer PTCR ceramics in order to utilize grain boundary effect and lower sintering temperature. The precursor gel was calcined at different temperatures and the powders were characterized by XRD and TEM. The average grain size was about 26nm when calcined at 800°C for 2h. Effects of acceptor/donor concentration and sintering temperature on PTCR ceramics were also investigated. The optimal concentration of the donor was found to be 0.6mol with the acceptor concentration being 1/8 of the donor. Multilayer PTCR elements were fabricated by tape-casting technique. The jump ratio of PTCR chips sintered at 1240°C was above 103 with the average grain size smaller than 1~2 μm, which is suitable for the multilayer PTCR elements.

Abstract: The sintering dynamics, microstructures and microwave dielectric properties of Bi2O3 and MnO2 co-doped [(Pb,Ca) La](Fe,Nb)O3 (PCLFN) ceramics were investigated. Bi2O3 and MnO2 dopants effectively enhanced bulk densities and reduced sintering temperatures by about 100~140°C. Sintering procedure had significant effect on grain size and porosities of ceramics. Investigation of microstructures revealed that the grain growth was controlled by either volume diffusion or second-order interface mechanism in present ceramics. The potential microwave dielectric properties of εr=91.1,Qf=4870GHz and τf=18.5ppm/°C could be obtained when the mass ratio of Bi2O3/MnO2 (k) was 1, the doping content w=1wt% and sintered at 1050°C for 4h.

Abstract: The microstructures and microwave dielectric properties of temperature compensated composite ceramics (1-x)(Na0.5La0.5)TiO3+xCeO2 doped with 1wt%CuO were investigated. Dense and mixed phase samples were produced in the range of 0.1 ≤ x ≤ 0.9. As x value increases the Qf increases nonlinearly while the dielectric constant decreases almost linearly. The compensated τf value is obtained in 0.1(Na0.5La0.5)TiO3 + 0.9CeO2 + 1wt%CuO ceramic with the Qf and εr being 8240GHz and 32.0 respectively.

Abstract: In order to study the effect of coexistence of Nd2O3 and Sm2O3 on phase development in Ba4 (Sm0.7Nd0.3)9.33Ti18O54 ceramics, the calcination process was applied in one-step and two-step way. From the XRD patterns of one-step calcinated powders, the solid-state reactions were deduced. And the results indicated the coexistence of Nd2O3 and Sm2O3 would be helpful to form secondary phase Nd2Ti2O7, which would worsen the properties. The final tested results of sintered samples confirmed the advantages of two-step calcination. The εr was improved from 72.1 to 82.4 and Q.f was improved from 7200 GHz to 8300 GHz, while τf was still near zero.

Abstract: The microwave properties of (Ca1-xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ(0.0≤x≤0.2, CBLNZ) ceramics were investigated. A single phase with orthorhombic perovskite structure was obtained at x = 0.0 − 0.025. Both the εr and Qf value firstly increased with increasing Ba2+ content, and then began to decrease at x = 0.025. The τf value increased from −9.4 ppm/°C at x=0.0 to 18ppm/°C at x=0.2, which could be explained by the decrease of B-site bond valence in perovskite structure.