Papers by Author: Huang Chen

Abstract: The low temperature transformation of ZrO2-3 mol% Y2O3 coatings were investigated at 40 ~100oC using Raman spectroscopy. The results show that the low temperature transformation of ZrO2-3 mol% Y2O3 coatings is considerably effected by water temperature and mainly occurred on the coating surface. However, the transformation can be retarded by addition of Al2O3. The reasons lie in that the addition of Al2O3 can result in improvement of deposition efficiency and Young’s modulus of ZrO2-3 mol% Y2O3 coatings containing Al2O3.

Abstract: Plasma sprayed coatings have been widely applied in modifying surface properties of metal components. It is also useful to prevent various types of wear, corrosion, erosion and thermal. But the residual stress is still an important problem which can effect the properties of sprayed coating. So it’s necessary to find out the reason of residual stress and the relationship between plasma sprayed condition and residual stress. Plasma spray coating layers with conventional ZrO2 powder was examined to calculate residual stress by X-ray diffraction method with various coating thickness.

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: The sliding wear property of plasma sprayed TiO2 coatings with porosity of 4.2% and 5.4% mating against silicon nitride ball were comparatively investigated with a reciprocating tribometer under dry conditions. The results indicate that the wear resistance of the TiO2 coating with lower porosity is superior, which is attributed to its homogeneous microstructure and improved microhardness. The morphologies of the wear tracks of the two TiO2 coatings, as well as wear debris reveal the pore is the main location wear occur. The coefficients of friction of the two TiO2 coatings decrease with the increase of applied load, while the wear rates increase, which is attributed to the difference of the dependence of microhardness on load between the coating and the Si3N4 ball. No apparent dependence of wear resistance on sliding speed was found on these two coatings.

Abstract: The commercial nano-sized TiO2 powder (P25) was immobilized on foamed waste-glass substrates by using the plasma spraying technology. The immobilized TiO2 coatings were applied to treat both the green tide and the red tide under illumination of an UV light. Their photocatalytic characterizations were evaluated as functions of the number of residual algae, transmission as well as pH value with illumination time. It was found that the plasma sprayed nano-TiO2 coatings on foamed waste-glass show a higher photocatalytic activity, which was effective to treat the green tide and the red tide.

Abstract: Adhesion/cohesion is one of the most important properties for coatings. It is related with their durability and functionality of coatings. In this study, a series of TiO2 coatings were prepared by atmosphere plasma spraying under different deposition parameters. Their adhesion or cohesion was evaluated as a function of coating thickness as well as deposition parameters using the scratch test. In addition, the influence of deposition parameters on coating porosity, surface roughness, and microhardness is discussed. The results indicate that the deposition parameters investigated have a remarkable influence on coating porosity and microhardness as well as adhesion or cohesion, but no obvious influence was observed for surface roughness.

Abstract: Based on the strong inhibition of SiC particles on the grain growth of the Αl2O3 matrix, a mixture powder of α-Al2O3 and SiC was used as feedstock to deposit the nanocomposite coatings by plasma spraying. To determine the effect of plasma spraying gas on microstructure and mechanical properties of Al2O3–SiC nanocomposite coatings, primary Ar gas and secondary H2 gas were chosen, which have an effect on temperature and velocity of the flyingpowders at the time of impacting on substrate. The X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to characterize the microstructures of these coatings. Surface roughness was measured also.

Abstract: The influence of the two deposition parameters on microstructure, and microhardness of plasma sprayed TiO2 coatings were investigated. It was found that a higher spraying power and a shorter distance resulted in a lower porosity and a higher microhardness for the coatings. The anisotropy on the microstructure and microhardness of TiO2 coatings was also found. The denser microstructure is attributed to the higher degree of melting and higher velocity of the TiO2 powders during spraying. The improvement of microhardness is associated with the lower porosity. The difference of porosity and microhardness between surface and cross section resulted from their different microstructures.

Abstract: Plasma spraying technique was used to deposit thin TiO2-based photocatalytic coatings on a foamed aluminum. Before spraying, the composites of nano-TiO2 powder (P25) and nano- ZnO/CeO2/SnO2 powders were agglomerated into microsized powders by a spray-drying process. XRD, SEM, TEM, XPS and the photocatalytic activity evaluation by the decomposition of benzene were applied to characterize the starting powders and the coatings, respectively. The results showed that all the three plasma sprayed TiO2-based coatings were the mixture phases of anatase and rutile. The XPS spectra results revealed that the oxygen element was composed of three kinds of chemical states, i.e., crystal lattice oxygen, hydroxyl oxygen and physical-adsorbed oxygen. The plasma sprayed 90%TiO2-10%CeO2 coating and 90%TiO2-10%SnO2 coating exhibited similar photocatalytic activity, which was higher than that of 90%TiO2-10%ZnO coating.