Xiaoru Zhao

Grain selection during casting Ni-base,single-crystal superalloys with spiral grain selector

The behavior of grain selection in a spiral grain selector during investment casting of a Ni-base, single-crystal (SX) superalloy, DD3, has been investigated by electron backscattered diffraction (EBSD) techniques and optical microscopy. The results indicated that the main function of starter block is to optimize the crystal orientation. During the process of grain selection in spiral passage, the grain near the inner wall of spiral passage was usually selected as the final single crystal. It was found that the dendrites near the inner wall could develop new tertiary dendritic arms that paralleled the primary dendrites from the secondary dendritic arms to overgrow the dendrites far away from the inner wall. The crystal orientation that was examined by X-ray diffraction revealed that (1) the crystal orientation did not change obviously with increasing spiral thickness or angle and (2) the crystal orientation could be optimized by increasing the withdrawal rate and ceramic mold temperature. The influence of pouring temperature on crystal orientation was also discussed.

Controlled synthesis of SnO2 nanostructures with different morphologies and the influence on photocatalysis properties

SnO2 nanoparticles, nanoflowers, and nanorods of highly crystalline were synthesized via a simple hydrothermal method. The size and morphology of the SnO2 nanostructures could be controlled by varying the NaOH concentration of the precursor solutions. The SnO2 structures appeared to be sphere-like nanoparticles with diameters in the range of 5–10 nm in lower NaOH concentrations. In higher NaOH concentrations, the nanostructures showed orientation growth behavior and were flower-like or rod-like in morphology. The sphere-like shape demonstrated that Ostwald ripening took effect only at lower NaOH concentration while the preferential growth behavior at higher NaOH concentration testified “oriented attachment” was more suitable under this condition. Photocatalysis experiments were carried out to study the influence of the morphology, size, and surface on photocatalytic activities of SnO2. The nanoparticles synthesized with the MNaOH:MSnCl4 = 4:1 showed the highest photolytic activities owing to their tiny si...

Effect of NaZn/Nai ratio on structural, optical, and electrical properties of Na-doped ZnO thin films

In this paper, Na-doped ZnO (NZO) thin films were prepared via a dip-coating sol-gel method with Na doping content in a range of 0 at. %–3 at. %. X-ray photoelectron spectroscopy analysis showed that the NaZn/Nai ratio ( r) increased with Na doping contents from 1 at. %–3 at. %. The effect of the NaZn/Nai ratio on the structural, optical, and electrical properties of NZO thin films was investigated. As the NaZn/Nai ratio increased, the lattice constant exhibited a continuous increase and resulted in the presence of increasing compressive stress in the NZO films. When the NaZn/Nai ratio was less than 1 ( r 1, it decreased. The Hall mobility was mainly limited by ionized impurity scattering and displayed a decrease trend with the increasing NaZn/Nai ratio. Due to the Burstein-Moss effect, the optical energy band gaps ( E g) of NZO films got slightly enlarged as compared with that of the undoped ZnO film. Considering the ...

Effects of Ga doped seed layer on microstructural and optical properties of ZnO nanorods

ZnO nanorods have been successfully grown on Ga doped (0, 1, 2, 3, 4, 5 wt%) ZnO seed layer by using simple hydrothermal method. The seed layer was coated on the substrate by using Dip coating technique. The effects of Ga doped seed layer on optical and structural morphology of ZnO nanorods are investigated in detail by using Field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Photo luminescence spectroscopy (PL). It has been observed that the Ga doped seed layer strongly affected the structural morphology of ZnO nanorods. XRD results show that all the samples have hexagonal wurtzite shape and [002] is preferred direction of growth. The intensity of (002) peak increases with increasing Ga concentration in seed layer indicating that the Ga doped seed layer has promoted growth of nanorods along [002]. SEM images show a decrease in diameter of ZnO nanorods with increasing Ga concentration in seed layer. The PL spectra of all the samples have two emission bands, UV and defect emission. UV emission shows a small blue shift with increasing Ga concentration in seed layer.