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Chuanxian Ding - One of the best experts on this subject based on the ideXlab platform.

  • Study on erosion-wear behavior and mechanism of plasma-sprayed alumina-based Coatings by a novel slurry injection method
    Tribology International, 2016
    Co-Authors: Kai Yang, Shunyan Tao, Huayu Zhao, Chenguang Liu, Jian Rong, Chuanxian Ding
    Abstract:

    In this paper, Al2O3-Cr2O3 composite Coating was fabricated by plasma spraying. It has better mechanical performances than Al2O3 Coating. Erosion-wear resistance of the Coatings was evaluated by a new type of solid particle impact test (slurry jet). Slurry was mixed with compressed air in the nozzle and eventually injected on Coating Surface at high velocity. Injected slurry on Coating Surface resulted in a wear progression (wear rate) proportionately to the erosion strength of the Coating material. Al2O3-Cr2O3 composite Coating possesses better erosion-wear resistance than pure Al2O3 Coating.

  • mechanism of apatite formation on wollastonite Coatings in simulated body fluids
    Biomaterials, 2004
    Co-Authors: Chuanxian Ding
    Abstract:

    Abstract The formation mechanism of apatite on the Surface of wollastonite Coating was examined. Plasma-sprayed wollastonite Coatings were soaked in a lactic acid solution (pH=2.4) to result in the dissolution of calcium from the Coating to form silanol (Si–OH) on the Surface. Some calcium-drained samples were soaked in a trimethanol aminomethane solution (pH=10) for 24 h to create a negatively charged Surface with the functional group (Si–O − ). These samples before and after treatment in a trimethanol aminomethane solution were immersed in simulated body fluids (SBF) to investigate the precipitation of apatite on the Coating Surface. The results indicate that the increase of calcium in the SBF solution is not the critical factor affecting the precipitation of apatite on the Surface of the wollastonite Coating and the apatite can only form on a negatively charged Surface with the functional group (Si–O − ). The mechanism of apatite formation on the wollastonite Coating is proposed. After the wollastonite Coatings are immersed into the SBF, calcium ions initially exchange with H + leading to the formation of silanol (Si–OH) on the Surface of the layer and increase in the pH value at the Coating–SBF interface. Consequently, a negatively charged Surface with the functional group (Si–O − ) forms on the Surface. Due to the negatively charged Surface, Ca 2+ ions in the SBF solution are attracted to the interface between the Coating and solution, thereby increasing the ionic activity of the apatite at the interface to the extent that apatite precipitates on the Coating Surface.

  • mechanism of apatite formation on wollastonite Coatings in simulated body fluids
    Biomaterials, 2004
    Co-Authors: Xuanyong Liu, Chuanxian Ding, Paul K Chu
    Abstract:

    The formation mechanism of apatite on the Surface of wollastonite Coating was examined. Plasma-sprayed wollastonite Coatings were soaked in a lactic acid solution (pH=2.4) to result in the dissolution of calcium from the Coating to form silanol (triple bond Si-OH) on the Surface. Some calcium-drained samples were soaked in a trimethanol aminomethane solution (pH=10) for 24h to create a negatively charged Surface with the functional group (triple bond Si-O(-)). These samples before and after treatment in a trimethanol aminomethane solution were immersed in simulated body fluids (SBF) to investigate the precipitation of apatite on the Coating Surface. The results indicate that the increase of calcium in the SBF solution is not the critical factor affecting the precipitation of apatite on the Surface of the wollastonite Coating and the apatite can only form on a negatively charged Surface with the functional group (triple bond Si-O(-)). The mechanism of apatite formation on the wollastonite Coating is proposed. After the wollastonite Coatings are immersed into the SBF, calcium ions initially exchange with H(+) leading to the formation of silanol (triple bond Si-OH) on the Surface of the layer and increase in the pH value at the Coating-SBF interface. Consequently, a negatively charged Surface with the functional group (triple bond Si-O(-)) forms on the Surface. Due to the negatively charged Surface, Ca(2+) ions in the SBF solution are attracted to the interface between the Coating and solution, thereby increasing the ionic activity of the apatite at the interface to the extent that apatite precipitates on the Coating Surface.

Aleksey Yerokhin - One of the best experts on this subject based on the ideXlab platform.

  • plasma electrolytic oxidation Coatings on cp mg with cerium nitrate and benzotriazole immersion post treatments
    Surface & Coatings Technology, 2018
    Co-Authors: Ming Sun, A Matthews, Aleksey Yerokhin
    Abstract:

    Abstract Cerium nitrate (Ce(NO3)3) and benzotriazole (BTA) were applied as immersion post-treatments for Plasma Electrolytic Oxidation (PEO) Coatings on commercially pure magnesium. The Surface morphology of the coated samples was characterised by Scanning Electron Microscopy (SEM), and it was found that the micro-pores on the Coating Surface can be effectively sealed by Ce(NO3)3 immersion post-treatment, whereas BTA did not show any significant effect on the Coating microstructure. The corrosion resistance behaviour of the coated samples was examined by electrochemical tests in a 3.5 wt% NaCl solution. According to the results, the Ce(NO3)3 immersion post-treatment showed the better effect in enhancing the corrosion resistance of the PEO Coating, compared with BTA immersion post-treatment. The insoluble Ce-containing compounds can provide both a sealing effect and continuous longer-term protection for the PEO-Ce(NO3)3 Coating. At the same time, BTA provides only a short-term improvement in the corrosion resistance, due to adsorption on the Coating Surface.

  • influence of sealing post treatments on the corrosion resistance of peo coated az91 magnesium alloy
    Applied Surface Science, 2018
    Co-Authors: Endzhe Matykina, Aleksey Yerokhin, B Mingo, R Arrabal, M Mohedano, Y Llamazares, A Pardo
    Abstract:

    Abstract The effect of three different post-treatments carried out on Plasma Electrolytic Oxidation (PEO) coated magnesium alloys are evaluated in terms of characterisation and corrosion resistance. Special interest is given to the role of a common additive (NaF) to the Coating properties. The post–treatments are based on immersion sealing processes in aqueous solutions of inorganic salts (cerium and stannate based salts) and alcoholic solution of an organic acid (octodecylphosphate acid, ODP). Sealing mechanisms for each post-treatment are proposed. Cerium and stannate sealings are based on filling of the pores with the products of dissolution/precipitation reactions, while the ODP acid sealing is based on the formation of a thin layer of ODP over the Coating through specific interactions between the polar part of the organic acid and the Coating Surface. All Coatings are evaluated by salt fog test and analysed by electrochemical impedance spectroscopy. All sealings show a slight increase in the corrosion resistance of the Coatings formed in the NaF-free electrolyte, but their positive influence is boosted in case of the Coatings obtained in the NaF-containing electrolyte. This is related to the chemical and morphological changes at the Coating Surface induced by the presence of NaF in the electrolyte.

  • Spectroscopic study of electrolytic plasma and discharging behaviour during the plasma electrolytic oxidation (PEO) process
    Journal of Physics D: Applied Physics, 2010
    Co-Authors: R. O. Hussein, X Nie, Aleksey Yerokhin, Derek O Northwood, Allan Matthews
    Abstract:

    In this study, a plasma electrolytic oxidation (PEO) process was used to produce oxide Coatings on commercially pure aluminium (1100 alloy) at a pulsed dc power mode. The effects of process parameters (i.e. current density and treatment time) on the plasma discharge behaviour during the PEO treatment were investigated using optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285–800 nm). The elements present in the plasma were identified. Stark shifts of spectral lines and line intensity ratios were utilized to determine the plasma electron concentrations and temperatures, respectively. The plasma electron temperature profile, Coating Surface morphology and Coating composition were used to interpret the plasma discharging behaviour. The different Coating morphologies and compositions at different Coating Surface regions are explained in terms of three types of discharge, which originate either at the substrate/Coating interface, within the upper layer, or at the Coating top layer. The high spike peaks on the plasma intensity and temperature profiles corresponded to discharges originated from the substrate/Coating interface, while the base line and small fluctuations were due to discharges at the Coating/electrolyte interface.

Xinyan Yue - One of the best experts on this subject based on the ideXlab platform.

  • ultra high temperature ceramic tab2 sic si Coating by impregnation and in situ reaction method to prevent graphite materials from oxidation and ablation
    Ceramics International, 2019
    Co-Authors: Yan Jiang, Tianyu Liu, Wei Wang, Cuiping Zhang, Xinyan Yue
    Abstract:

    Abstract A monolayer TaB2-SiC-Si protective Coating was fabricated by impregnation and in-situ reaction method on the Surface of graphite to prevent graphite materials from oxidation and ablation, and the microstructure, oxidative and ablative protection properties of the Coating were investigated. Experimental results revealed that the Coating could protect graphite from oxidation at 1020 °C and 1550 °C for more than 321 h and 168 h, respectively, and from ablation for 120 s with a heat flux of 2.38 MW/m2. The good oxidative protection performance was ascribed to the low oxygen diffusivity of the Coating and oxide film formed on the Coating Surface, which effectively inhibited oxygen diffusion to the graphite substrate. Under oxyacetylene flame, a Ta2O5 layer was gradually formed on the Coating Surface and acted as a protective layer, which weakened the erosion of flame to the inner Coating. The increase of ablative time promoted the fierce evaporation of gaseous Si and oxide phases, such as B2O3(g), SiO2(g), CO(g) and CO2(g), which resulted in the damage to the TaB2-SiC-Si Coating, leading to the reduction of anti-ablation property of the Coating.

Jie Weng - One of the best experts on this subject based on the ideXlab platform.

  • formation and characteristics of the apatite layer on plasma sprayed hydroxyapatite Coatings in simulated body fluid
    Biomaterials, 1997
    Co-Authors: Jie Weng, Qing Liu, J G C Wolke, Xingdong Zhang, K De Groot
    Abstract:

    Plasma-sprayed hydroxyapatite (HA) Coatings were incubated in simulated body fluids (SBFs) for different periods of time to investigate the nucleation and growth of apatite on their Surface. The layer that formed was recognized as having similarities to bone apatite because it is poorly crystallized, non-stoichiometric or calcium deficient, and contains carbonate and magnesium. Scanning electron microscopy (SEM) and infrared spectroscopy (IR) were employed to investigate the morphological changes of the Coating Surface and the structure of the grown layer respectively. In the first few hours, calcium and phosphate ions dissolved from the Coatings so as to increase their local supersaturation to a higher degree, thereafter followed by the nucleation and growth of apatite. The nucleation occurred firstly on the recessed regions, inside pores and cracks where the higher supersaturation was readily maintained. Only after 24 h incubation was a complete layer formed on the Surface of the Coating. There is no obvious interface between the grown layer and the underlying Coating. Heat treatment in the air made the apatite transform into biphasic calcium phosphate of HA and tricalcium phosphate, with a blue colour because of trace manganese ions. The heat-treated HA Coating showed no dissolution by SEM observation. This resulted in no precipitation on the Surface. When SBF was used with two-fold higher ion concentrations, the apatite layer formed slowly in 72 h without dissolution of the Coating Surface. This may mean that the microenvironment with a sufficiently high degree of supersaturation of calcium and phosphate ions is crucial for apatite to nucleate and grow in SBF, while the HA crystalline structure is not critical in the nucleation process, as expected.

Tooru Tsuru - One of the best experts on this subject based on the ideXlab platform.

  • electrochemical behavior of gradient polished Surface of hot dipped al si coated steel
    Electrochemistry, 2010
    Co-Authors: Chaiyaput Kruehong, Gamal A Elmahdy, Atsushi Nishikata, Tooru Tsuru
    Abstract:

    A novel method for Coating Surface polishing has been applied for a systematic study of the localized individual Coating regions of the Al–Si coated steel. Polarization, EPMA and corrosion potential measurements have been applied for determination the ability of each region for protection of underlying steel. The susceptibility of the Si rich region, interface region and Fe-rich region to pitting corrosion decreases in the following order: Si-rich region>Fe-rich region>interface region. The elemental distribution of Si and Fe plays an important role in the corrosion behavior of Coating film and influences its susceptibility to pitting process.

  • electrochemical corrosion monitoring of galvanized steel under cyclic wet dry conditions
    Corrosion Science, 2000
    Co-Authors: Gamal A Elmahdy, Atsushi Nishikata, Tooru Tsuru
    Abstract:

    Abstract The corrosion behavior of a galvanized steel was investigated under cyclic wet–dry environments using electrochemical techniques. The wet–dry cyclic was conducted by exposure to alternate conditions of 1 h-immersion in a 0.05 M NaCl solution (or Na 2 SO 4 solution) and 7 h-drying at 60% RH. The polarization resistance R p of the galvanized steel was monitored during the wet–dry cycles by AC impedance method. Simultaneously, the corrosion potential E corr was measured only when the specimen was immersed in the solution. The corrosion current density i corr of the zinc Coating was estimated from the monitored R p using Stern–Geary equation. The corrosion mass loss Δ M , which was obtained from the i corr vs time curve, was plotted vs the wet–dry cycle number. The average corrosion rate per cycle starts to decrease and the E corr shifts in the noble direction, immediately before the red rust (FeOOH) appears on the Coating Surface. It seems that the underlying steel corrosion commences when the zinc Coating does not act as sacrificial anode due to accumulation of zinc corrosion products on the Coating Surface. The electrochemical methods, such as impedance and corrosion potential measurements, are an effective tool for monitoring the degradation of metallic Coating under atmospheric environments.