Papers by Author: Xuan Yong Liu

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: The in vitro attachment, spread, and proliferation behavior of osteoblast cells on the plasma-sprayed composite coating with 70wt% zirconia and 30wt% dicalcium silicate were studied. The composite coating shows good cytocompatibility. The human osteoblast cells attached, spread and proliferate well on the surface. The cytocompatibility of the coating was attributed to the incongruent dissolution of dicalcium silicate and the large amount of Si-OH functional groups produced on the surface. The released calcium and silicon ions are also positive to the proliferation of cells. All our results show that the composite coating possesses good cytocompatibility.

Abstract: In this paper, AlN powder and ceramic are prepared by microwave sintering under various sintering environments. The microstructures of the powder and the ceramic are characterized by scanning electron microscopy and X-ray diffraction technology. The mechanical and thermal properties of the ceramic are studied. It was found that the sintering environment has great influence on the material fabrication. The heat-assisted environment is beneficial to the synthesis of AlN powder. On the other hand, the carbothermal sintering environment has the two-sided influence to the sintering of AlN ceramic.

Abstract: TiO2 coatings on titanium alloy substrates were prepared by atmospheric plasma spraying using commercial nano-powders and followed by H2SO4 treatment. The bioactivity of coatings was evaluated by the simulated body fluid soaking test. Scanning electron microscopy and energy-dispersive X-ray spectrometry were used to characterize the surface morphologies and phase composition of the coating before and after soaking in simulated body fluid. The results obtained indicate that H2SO4-treated TiO2 coating can induce a bone-like apatite formation on its surface, however, no apatite appears on the surface of as-sprayed TiO2 coatings. The acid concentration and treated time affected the bioactivities of TiO2 coatings.

Abstract: In this work, nano-TiO2 powders were deposited onto Ti-6Al-4V substrates to produce coating using plasma spraying. The TiO2 coatings were respectively by acid, alkali and heat treatment to produce the bioactive surface. The bioactivity of TiO2 coating was examined by simulated body fluids test. The results obtained indicated apatite was formed on the surfaces of nano-TiO2 coatings treated by H2SO4, HCl and HF solutions, while it could not be formed on the surface of the nano-TiO2 coating treated by NaOH solution at low concentration. After alkali attack and heat treatment at 600°C, the bioactivity of nano-TiO2 coating disappeared.

Abstract: In this work, collagen type I was covalently grafted on the surface of plasma sprayed titania coatings to improve their biocompatibility. The plasma sprayed titania coatings were pretreated by sodium hydroxide to induce the formation of hydroxyl groups which can covalently graft collagen, rendering the collagen having good stability. The dependence of collagen grafting on the sodium hydroxide treatment conditions (concentration, time and temperature) was investigated by measuring the amount of collagen grafted on the titania surface. The biocompatibility of the titania coatings with grafted collagen was evaluated by in vitro cell culture. The results showed that the amount of collagen grafted on the titania coatings increased with the concentration of the sodium hydroxide and the treating temperature, while that on the coating is slightly dependent on the treatment time in sodium hydroxide. In vitro cell culture test proved the positive effects of collagen on the biocompatibility of the plasma sprayed titania coating.

Abstract: In this work, silicon coatings were deposited using VPS and APS technologies. Their structure and composition were characterized using XPS, SEM, and XRD. The porosity and surface-roughness of coatings were evaluated. The results showed that the VPS silicon coating possessed lower porosity compared with the APS silicon coating. The APS silicon coating surface was almost all covered by many small particles whose size is about 100 nm. The Si 2p XPS spectra indicated that silicon oxide existed in both coatings. The oxidation may have occurred during the plasma spray process. However, the VPS process could inhibit silicon from being oxidated.

Abstract: TiO2 coatings on titanium alloy substrates were prepared by atmospheric plasma spraying using commercial nano-powders. Then, as-sprayed coatings were treated using 10% hydrofluoric acid (HF) at room temperature for 30 seconds. As-sprayed and HF-treated titania coatings were soaked in simulated body fluid to investigate the formation of apatite on their surface. Field-emission scanning electron microscopy was used to observe the surface morphologies, and the phase composition of the as-sprayed coating and apatite were analyzed by X-ray diffraction and energy-dispersive X-ray spectrometry. As-sprayed titania coating is composed of rutile, anatase, and a small quantity of Ti3O5. It exhibited excellent adhesion between the TiO2 coatings and titanium alloy substrates, and the bonding strength was about 38 MPa. After in vitro experiment, a new substance containing calcium and phosphate was formed on the surface of HF-treated TiO2 coatings after being soaked in SBF, while the new substance was not formed on the surface of as-sprayed TiO2 coatings. The results indicated that the bioactivity can be induced to the surface of plasma sprayed TiO2 coatings by hydrofluoric acid treatment.

Abstract: The long-term stability of plasma-sprayed dicalcium silicate (C2S) composite coatings is determined by the phase composition, crystallinity, and other properties. Zirconia reinforcement and post-spraying heat treatment are applied to C2S coatings simultaneously in this work. The stability of the coating increases evidently by reinforcement with 70wt% zirconia and heat treatment at 800oC for 4 hours. SEM reveals that the smooth glassy surface of the as-sprayed coatings is replaced by randomly dispersed crystals. Tris-HCl immersion test results show that the dissolution rate of the composite coatings decreases after the heat treatment.