Papers by Author: Xiao Wen Zhang

Abstract: The presence of the colloid will affect uranium heap leaching. The objective of this study was the examination of the ability of colloid retardation to uranium by irons hydroxide colloids simulated heap leaching process. Batch studies have been carried by observing the effects of pH, contact time, uranium concentration. Iron hydroxide colloids can exist stably at pH 1.5-3.0. The size of the colloid samples is between 20 nm and 1000 nm. The sorption equilibrium was attained at 24 h. The load uranium capacity on iron hydroxide colloids are between 2.43×10^-3 and 3.84×10^-3 mmol/mol. The colloid morphology of before and after loaded uranium were identified using S-4800 scanning electron microscopy (SEM/EDS). The load uranium capacity on iron hydroxide colloids is least at pH=2, it implies that the appropriate pH of uranium heap leach is 2.0 on the point of retardation of colloid to uranium migration.

Abstract: In this paper, 0.95K0.5Na0.5NbO3-0.05LiTaO3 ceramics were synthesized by conventional mixed-oxide technique. To clarify the optimal sintering condition, three kinds of different temperature conditions were used. It was found that the samples sintered near 1130 °C had the best piezoelectric properties (d33~155 pC/N). In addition, sintering aid such as K5.4C1.3Ta10O29 was investigated to confirm whether it really benefited to the sintering process and increased the piezoelectric property of ceramics.

Abstract: (Na0.5Bi0.5)TiO3 (BNT) system ceramics are considered to be an excellent candidate for leadfree piezoelectric ceramics. In this paper, (1–x)Na0.5Bi0.5TiO3-xBaTiO3 (x = 0.03 ~ 0.10) was synthesized by conventional mixed-oxide technique. The powders were calcined at 950oC for 2 h and the pressed disks were sintered at 1145oC for 2 h in air atmosphere. The phase structure was investigated by X-ray diffraction technique (XRD). It is revealed that the morphotropic phase boundary (MPB) lies in a narrow composition range of x=0.05–0.08 but not a unique composition (x = 0.055 or 0.06) as shown before [1-4]. The microstructures of the ceramics were investigated by scanning electron microscopic. In addition, the piezoelectric and dielectric properties of this system were also investigated. It was indicated that both the piezoelectric and dielectric properties are better with the compositions lie near the tetragonal phase within the MPB than that whose compositions lie near the rhombohedral phase.

Abstract: A small piece of <110> orientated relaxor-based ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals was embedded in Pb(Mg1/3Nb2/3)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 (PMN-PNN-PT) polycrystalline matrix to form the fully dense disk by spark plasma sintering (SPS) technique. Specimens were subsequently annealed to promote the boundary migration of the template single-crystal through a process termed as solid-state single crystal growth. It was found that the addition of excess 5 wt% PbO can promote the crystal growth, and the 2D morphology with V-shaped single crystals of PMN-PNN-PT were also observed. The possible growth mechanism was discussed.

Abstract: Ceramics with the type of 0.50Pb(Ni1/3Nb2/3)O3-0.15PbZrO3-0.35PbTiO3 were synthesized by conventional mixed-oxide technique. The dielectric and ferroelectric properties of this composition were investigated in detail. Frequency dispersion and diffuse phase transition were observed in the dielectric behaviors. The revealed electrical properties are εm = 22388, Pr = 21.449 μC/cm2 and Ec = 5.191 kV/cm. XRD experiments demonstrate that this composition is within the MPB region, which may help to explain the super electrical properties discussed in this study.

Abstract: Ferroelectric ceramics of (1
x)(0.8PMN
0.2PNN)
xPT (x = 0.28
0.43) were synthesized by the columbite precursor method. Their phase structures as well as the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) results demonstrate that the morphotropic phase boundary (MPB) of this system lies in the composition range of x = 0.31–0.37. Examination of the dielectric behavior indicates that the ceramics exhibit high dielectric constants near the MPB compositions. In addition, the piezoelectric properties of the ceramics were found quite well around the MPB. The interrelated mechanism was also discussed.

Abstract: (1-x)(0.64PNN-0.36PT)-x(0.91PZN-0.09PT) ferroelectric ceramics with different x were synthesized by the columbite precursor method. The phase structure and piezoelectric properties were investigated. XRD profiles implied that with the increasing of x, samples could no longer maintain the pure perovskite phase. All the compositions were found to lie within the region of the morphotropic phase boundaries (MPBs) with different contents of rhombohedral and tetragonal phases. The piezoelectric coefficients for compositions with x £ 0.30 were obviously better than those for the rest ones and the composition with x = 0.15 exhibited the largest value of d33 among all the samples. The relationship between the structure and the piezoelectric properties was discussed.

Abstract: Fiber textured 0.70PMN-0.30PT ceramics was fabricated using the Templated Grain Growth (TGG) process. Tabular SrTiO3 particles synthesized in molten NaCl-KCl salts were used as templates and oriented in fine 0.70PMN-0.30PT matrix during rolling. Tabular SrTiO3 particles can stabilize in sintering by SPS technique and annealing. A degree of [001] texture (Lotgering factor ~ 0.38) was obtained by heteroepitaxial growth of oriented single PMN-PT on the SrTiO3 template particles.