Papers by Author: Wei Pan

Abstract: In this study, hexagonal Boron Nitride-Aluminium Nitride composites were prepared by spark plasma sintering at 1700°C
for 4 min under the pressure of 25 MPa, varying the amount of BN from 0 to 30 wt.%. The dielectric constants and losses of the samples were measured from 100 Hz to 1 MHz at room temperature, and the results show that with the increment of BN content, the dielectric constants and losses of AlN-BN composites decrease. When the BN content is 20 wt.%, the dielectric constant and loss of the composites at 1 MHz are 6.18, 2.1 × 10-3 respectively.

Abstract: BaTiO3 powder was synthesized from BaCO3 and TiO2 using a domestic microwave oven. The samples were synthesized under different temperatures with various holding times. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the phase compositions and morphologies of the result samples. The main phase obtained at 950°C was BaTiO3, and the intermediate phases Ba2TiO4 and Ba4TiO9 were also detected. The pure, well-crystallized BaTiO3 powder could be obtained at 1050°C within 10 minutes and the particle size ranged from 300~500nm. In comparison with conventional synthesis, faster speed and finer grains could be achieved through microwave heating.

Abstract: Three rare earth zirconates (Sm2Zr2O7, Gd2Zr2O7 and Er2Zr2O7) were prepared by solid state reaction. The crystal structure and ionic conductivity of these zirconates were characterized by X-ray diffraction (XRD) and complex impedance spectroscopy. The results show that Sm2Zr2O7 exhibits single-phase pyrochlore structure and Er2Zr2O7 exhibits single-phase fluorite structure, while Gd2Zr2O7 has pyrochlore and fluorite structure. Among three zirconates, the ionic conductivity of Sm2Zr2O7 is highest, while that of Er2Zr2O7 is lowest.

Abstract: In this paper, the Ti(CN)-based cermets were fabricated with ultrafine Ti(CN) powders, additives WC, Cr2C3 and Mo, metal binder Ni by vacuum sintering and HIP treatment. The composition of the mixture was Ti(CN)-10Mo-20WC-xCr2C3-20Ni. Effect of Cr2C3 addition on microstructure and mechanical properties was investigated. Results indicated that with increasing Cr2C3 content, the relative densities after vacuum sintering decreased and the grain sizes of cermets increased. Cr2C3 addition to the cermets improved the hardness but had some negative effect on the performance of bending strength.

Abstract: The effect of V2O5 as additives of different content on the densification, microstructure and dielectric properties of Ba(Mg1/3Nb2/3)O3 (BMN) was investigated. The sintering temperature of the V2O5-doped BMN samples were lowered down to 1250 oC with 0.5wt% V2O5 compared to pure BMN ceramics where the sintering temperature was 1500 oC at least. The εr and τf was not influenced much, while the Q value was affected by the sintering temperature and the V2O5 additives. The Q value decreased with decrease of the sintering temperature and the V2O5 addition increasing due to the bulk density and the second phase. Good microwave dielectric properties of Q·f=42100GHz, εr =31.7 and temperature coefficient of resonance frequency (τf) =22.7ppm/ oC were obtained with 0.25 wt% V2O5 sintered at 1350 oC for 4h.

Abstract: In this paper, particular CVD processes of so-called Se method with solid substances as starting materials was investigated to fabricate ZnSe. On the basis of detailed experimental researches, the growth model and dominant regime of deposition rate were discussed. ZnSe of high optical properties was produced under optimized process conditions. The grain size of CVD ZnSe by Se method is less than 10μm, and its average transmittance in the wavelength range of 0.55~20μm is up to 70%.

Abstract: Using ultra-fine alumina powders as raw materials, the submicron transparent alumina with relative density more than 99.9% was fabricated by gelcasting and then sintering-HIP process. It was found that only the samples with relative density more than 95% after presintering could obtain fully densification by post-HIP treatment. The final grain sizes increased after post-HIP treatment and were decided by either HIPing temperature or presintering temperature, depending on which one is higher. The maximal strength can reach about 650MPa when grain size is about 1 μm.

Abstract: The uniform Sr0.5Ba0.5Bi4Ti4O15 thin films were prepared using a modified Sol-Gel technique and the influence of precursor on the microstructure and characterization of thin films were studied. The stability and uniformity of precursor solution is key issue for the quality of thin films. Ethanolamine is an effective complexation reagent of Bi3+, which could moderate the acidity of precursor. When pH value and concentration of precursor solution was about 3.5 and 0.35M respectively, the smooth and uniform Sr0.5Ba0.5Bi4Ti4O15 thin films could be obtained. The Bi-layered perovskite structure of Sr0.5Ba0.5Bi4Ti4O15 formed at 750°C. The morphology of the grains in Sr0.5Ba0.5Bi4Ti4O15 thin films was elliptoid and the grain size was about 90 ~ 100 nm.

Abstract: Densification behavior, microstructural developments and mechanical properties of 5 wt% SiC nano particulate toughened Al2O3 composites were prepared by using microwave sintering at different sintering temperatures. Densities of up to 97.5% of the theoretical value were achieved at temperature as low as 1380°C. Improvements in fracture toughness and bending strengths are of the order of 99% theoretical dense conventionally sintered composites. Surface heating was observed at the final stages of densification. No thermal runaway was observed in the nanocomposites due to presence of SiC spheroids.

Abstract: High purity polycrystalline titanium silicon carbide (Ti3SiC2) was synthesized by spark plasma sintering (SPS) with additive of Aluminum at low temperature of 1100~1300oC. XRD results showed that the content of Ti3SiC2 in the synthesized bulks increased with the addition of Aluminum, however, the lattice parameters of Ti3SiC2 samples with different amounts of additive exhibited scarcely change. With a starting powder of 1Ti/1.2Si/2TiC/0.1Al (molar ratios), dense Ti3SiC2 ceramic (98vol.%Ti3SiC2) was obtained by sintering at 1100oC for 5min under a pressure of 30MPa. Fine Plate-like grains of the samples with sizes of 2~6μm could be identified by scanning electronic microscope (SEM).