Papers by Author: Yi Zeng

Abstract: In the paper, the influence factors of electron channeling contrast imaging (ECCI) on crystalline material microstructure characterization by scanning electron microscopes (SEMs) were analyzed, such as electric current, accelerating voltage and sample material’s surface conditions. It was found that high current, appropriate accelerating voltage and smooth sample surface were more beneficial to obtaining an ideal channel effect pattern. In addition, the difference between the channel effect contrast and the EBSD technology was also investigated. And the results showed that the channel effect contrast image could qualitatively characterize grains with different orientations. However, it was far less sensitive than EBSD in characterizing small angle grain boundaries.

Abstract: By scanning electron microscope equipped (SEM) with energy dispersive spectroscopy (EDS) accessory, analysis can be performed simultaneously in the samples’ micromorphology observation and micro composition test. At present, EDS analysis is generally used high acceleration voltage, and the diffusion range of the incident electrons in sample is 3-5 μm. Therefore, the minimum area for the component analysis is several micrometers. The diffusion range of incident electrons can be reduced by reducing the acceleration voltage, and as a result, the nanometer-scale composition analysis in SEM can be achieved. Based on Monte Carlo simulation method, the incident electrons practical effect range can be estimated. While the acceleration voltage is reduced, X-ray yield rates of the B, C, N, O and other light elements will be increased. Thereby the measuring precision of EDS quantitative analysis of light elements can be improved.

Abstract: Scanning Electron Microscope (SEM) has been widely used in the observation of surface and cross section of materials. So it is important to prepare the cross section of various specimens. In this study, a novel cross section preparation method using argon ion beam (called argon ion beam cross-section polisher or CP) was introduced. This method can not only overcome the problem of artifacts caused by mechanical polishing on the polished surface, but also enable one to prepare a wider area of specimens than the Focused Ion Beam (FIB) method. The soft materials, composite materials with different hardness, multilayer films and powders were all easily polished with few artifacts using this method.

Abstract: Silicon-based materials have been widely applied in industrial fields, such as microelectronic and solar power, for the specific electronic properties. In the present work, free-standing thick silicon coatings were fabricated by air plasma spraying (APS) and vacuum plasma spraying (VPS) technologies. The microstructure and electrical property of the coatings were characterized. It was found that the electrical resistance of APS-Si coating was higher than that of VPS-Si coating. The impedance spectroscopy results showed there was significant difference in impedance curves of APS-Si and VPS-Si coatings. The grain boundary semicircle appeared in the plot of VPS-Si coating, while did not appeared in that of APS-Si coating. It was thought that the electrical property difference of the two kind coatings was related with the oxidation and microstructure difference of the coatings.

Abstract: Vacuum plasma sprayed (VPS) hydroxyapatite (HA) coatings with silver-loaded zirconium phosphate antimicrobial have been prepared on titanium substrate. Antibacterial effects of the coatings were studied by bacteria culturing using Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn) and Actinobacillus actinomycetemcomitans (Aa) as microorganisms. Simulated body fluid (SBF) test was carried out to evaluate the bioactivity of the coatings as well. The results obtained showed that the coatings exhibited a marked antibacterial effect against Pg, Fn and Aa when the content of antimicrobial was equal to or more than 5%. The antibacterial capability of the coatings decreased in the following order: Pg, Fn, Aa. Bone-like apatite layer was formed on the silver-containing HA coatings after immersed in SBF, suggesting that their bioactivities were not affected obviously by the addition of silver-zirconium phosphate antimicrobial. This study indicated that silver-containing VPS HA coating is a prospective candidate as dental material.

Abstract: The phase and microstructure of four kinds of plasma sprayed TiO2 coatings (P25, ST, NK, KT) were characterized by XRD (X-ray Diffraction), FE-SEM (Field Emission Scanning Electron Microscope) and TEM ( Transmission Electron Microscopy). Their photocatalytic properties were discussed in relation to phase composition and microstructure. The FE-SEM observation results reveal that there are quite a number of nanoparticles on the surfaces of all four kinds of plasma sprayed TiO2 coatings, which provide photocatalytic reactive sites. Based on the observation results of FE-SEM and TEM, the microstructure schematic of plasma sprayed TiO2 coatings using nanoparticles as feedstock is suggested. The best photocatalytic property of P25 coating among the four plasma sprayed TiO2 coatings is attributed to the combination of its fine “cauliflower” structure and the highest anatase content.

Abstract: Nanostructured and conventional Al2O3, ZrO2, and TiO2 were deposited using an atmospheric plasma spraying (APS). The size of commercial nano-ceramic powders was varied from 5nm up to 150nm. The microstructure and phase composition of the plasma sprayed coatings on metallic substrate were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that nano-sized ceramic powders enhanced the deposition efficiency on the metallic substrate rather than the micro-sized conventional commercial powders. Density and mechanical property such as microhardness were better in the case of the nano-sized ceramic powders than that of the conventional micro-sized ceramic powders, which are associated with the fine surface roughness and less size in pores of the coating layers. The wear rate of the nanostructured coating was lower than that of the conventional coating. The results were explained in terms of their microstructure of the coatings layers. Also, photocatalytic characterization of the plasma sprayed coatings, using nanocrystalline size TiO2 as feedstock with various powder sizes and shapes as well as adding with different photocatalytic oxides, was performed. The photocatalytic reactivity using plasma sprayed coating layers can be utilized into various applications.

Abstract: A novel TiO2−ZnFe2O4 coating was prepared by plasma spraying. The effects of spraying parameters and the composition of powders on the microstructure and surface morphology of plasma sprayed coatings are studied. The photocatalytic efficiency of the as-sprayed coatings was evaluated through the photo mineralization of methylene blue. It was found that TiO2 coatings can decompose methylene blue under the illumination of ultraviolet rays, and the degrading efficiency is improved with an increase in the content of FeTiO3 in the coatings. However, the presence of a large amount of ZnFe2O4 compound will substantially lower the photocatalytic efficiency of the TiO2−ZnFe2O4 coatings for the unfavorable photo-excited electron-hole transfer process.