Papers by Author: Mei Ling Zhou

Abstract: A systematic investigation of the fabrication process, microstructure and treatment technology of the Rare earth oxide doped Mo cermet (REO-Mo in brief) on the secondary electron emission (SEE) mainly has been performed. The REO-Mo samples were fabricated by liquid-liquid, Liquid-Solid and Liquid-Liquid doping method and subsequently by the Spark Plasma Sintering (SPS) techniques. It was found that the uniform mixing of REO with Mo would have considerable benefit for enhancement of SEE coefficient (δ). Annealing the cathode in hydrogen (called as the pre-activation treatment) could greatly improve the SEE performance by removing the absorbed water and oxygen at the cathode surface which might cause the oxidation of molybdenum during cathode high temperature operation. It is found that the activation temperature of REO-Mo cathode annealed in hydrogen could decrease to 1000oC, about 300oC lower than that of the cathode without pre-activation treatment, which is favorable for the practical application.

Abstract: In-situ MgB2/Fe tapes were fabricated by the powder in tube (PIT) technology using Mg and B powders. The tapes were sintered by both an advanced spark plasma sintering (SPS) and a conventional vacuum furnace, respectively. The effects of these two sintering routes on the properties of the MgB2 tapes were investigated by the analysis of XRD, SEM and the magnetic Jc measurements. It was shown that at 10K, 0T, the magnetic Jc value of the tape sintered using SPS machine at 800°C for 15min under 30MPa were close to 106A/cm2, which was higher than that of the tapes annealed at 700°C for 2h under pressureless vacuum condition. It was found that the density and the homogeneity of the MgB2 core were strongly improved using SPS sintering process, which explained why the MgB2 tapes sintered by SPS method have a higher Jc value. Further enhancement of Jc in the tapes is expected for the understanding of the SPS sintering mechanism.

Abstract: It is well know that Ni-5at.% W(Ni5W) and Ni-9.3at.% W(Ni9W) alloy substrates are two kinds of promising materials to be employed in coated conductors. The Ni5W substrate is very easy to produce cube texture, while the Ni9W alloy has a lower magnetic property and higher strength. However, the pure cube texture are not capable to be obtained in Ni9W alloy. In this work, the preparation and texture development in both Ni5W and Ni9W alloy substrates have been reported. Highly biaxial textured Ni5W substrate was fabricated by cold rolling, followed by three different annealing routes. The texture analysis indicated that a sharp cube texture was formed after annealing at a wide temperature range of 800-1100°C in as rolled Ni5W substrate. The high quality of cube orientation was obtained after a two step annealing (TSA) with farthing twin boundaries analyzed by EBSD. Furthermore, in order to obtain a pure cube texture in Ni9W alloy substrate, a typical rolling process was performed and the deformation texture was optimized in these substrates. The designed deformation texture components were obtained in Ni9W alloy when pre-heating the ingot at 250 °C before performing a cold rolling, which shows a possibility to form cube texture in Ni9W alloy substrate after annealing.

Abstract: CeO2 has been considered as one of the most lattice compatible and chemically stable materials for YBa2Cu3O7-x coated conductors. In this paper, we presented the epitaxial growth of CeO2 thin film on both YSZ single crystal and cube textured Ni5W substrates by MOD method. Homogenous, crack-free and dense CeO2 thin films on both substrates with sharp biaxially cube texture were fabricated by post-annealing the precursor films at 1000-1150°C. For the CeO2 film on the textured Ni5W substrate, the FWHM values of (111) Phi-scan and (002) rocking curve were around 6°and 7°, respectively, the surface roughness was less than 2 nm over an area of 1μm×1μm observed by AFM. It was found that the CeO2 thin film improved both the in-plane orientation and surface roughness of the Ni5W substrate, indicating that the as deposited CeO2 films were suitable for the further growth of YBCO superconductor layer.

Abstract: The objective of this study was to investigate the inhibitory effect of the synthetic nanohydroxyapatite (HA) on dental caries. The nano-HA was synthesized by using the depositing reaction of Ca (H2PO4)2. The artificial dental caries was made by using sour solution and inoculating Streptococcus mutans (S.mutans) to the Sprague-Dawley (SD) rat’s mouth respectively. After mineralization of solution of nano-HA for 10 days, the hardness of enamel was measured. The inhibitory effect of the synthetic nano-HA on dental caries was detected by gargling way to rinse the rat tooth with the solution of nano-HA in the animal test. Transmission electron microscopy (TEM) revealed that the dried HA particles were needle-like with ф5-20nm×60nm and the sintered HA particles were spherical with less than 100nm. The remineralized test indicated that the solution of nano-HA with different shapes enhanced the hardness of artificial caries and improved the remineralization of artificial caries. The animal test showed that the dried nano-HA had the inhibitory effect on dental caries. The good absorptive effect of the nano-HA on both the saliva protein and the glucans leads to the development of interventions that could reduce or modify bacterial colonization of tooth surfaces.

Abstract: The molybdenum powder doped with rare earth oxide was processed by powder metallurgy method and a new style thin film cathode material was firstly processed by Spark Plasma Sintering (SPS) method in this paper. The secondary emission property of such kind of cathode materials were studied, the maxim secondary emission coefficient after the material was activated at 1600°C reached to 3.84 about double that of traditional cathode materials application in magneto. The microstructure, element analysis and phase constitution of materials before and after the secondary emission property was measured were studied through SEM, EDAX and XRD. The results show that a rare earth layer about 5um thickness was created after the material was activated at 1600°C. The material grain size is about 1 um or even smaller and the distribution of elements in such materials is even.

Abstract: YBa2Cu3O7-δ (YBCO) films were deposited on (100), (110) and (111) oriented silver single crystals and {100}<100>, {110}<211> , {110}<100>+{110}<011>， {110}<011> and {012}<100> textured Ag substrates using pulsed laser deposition. The relationship between the epitaxial growth YBCO film and silver substrate has been determined. It is shown that among polycrystalline Ag substrates, {110}<011> textured tape is suitable for the deposition of YBCO thin films having strong texture.

Abstract: The influence of the oxygen-content, the rolling method, the annealing method and the annealing temperature on the texture in silver have been studied. The results show that low oxygen-content in original material, annealing at a temperature higher than 700ı and annealing in an atmosphere such as inert gas, air or pure oxygen are beneficial to obtain the {110}<110> component. Textured Ag substrate in which the main components is {110}<110> has been obtained. The mechanism of texture-forming is studied using electron back-scattered diffraction (EBSD) method.

Abstract: YBa2Cu3O7-δ(YBCO) films with highly biaxial textures were deposited on SrTiO3 single crystal, textured polycrystalline Ag and NiO/Ni substrates using pulsed laser deposition, metal-organic decomposition and ultrasonic spray pyrolysis method. The microstrains in different specimens with strong textures were measured using x-ray diffractometer and were compared each other.