Establishing empirical relationships to predict porosity level and corrosion rate of atmospheric plasma-sprayed alumina coatings on AZ31B magnesium alloy

Plasma sprayed ceramic coatings are successfully used in many industrial applications,where high wear and corrosion resistance with thermal insulation are required.In this work,empirical relationships were developed to predict the porosity and corrosion rate of alumina coatings by incorporating independently controllable atmospheric plasma spray operational parameters(input power,stand-off distance and powder feed rate)using response surface methodology(RSM).A central composite rotatable design with three factors and five levels was chosen to minimize the number of experimental conditions.Within the scope of the design space,the input power and the stand-off distance appeared to be the most significant two parameters affecting the responses among the three investigated process parameters.A linear regression relationship was also established between porosity and corrosion rate of the alumina coatings.Further,sensitivity analysis was carried out and compared with the relative impact of three process parameters on porosity level and corrosion rate to verify the measurement errors on the values of the uncertainty in estimated parameters.

Prediction and optimization of process variables to maximize the Young’s modulus of plasma sprayed alumina coatings on AZ31B magnesium alloy

Like other manufacturing techniques,plasma spraying has also a non-linear behavior because of the contribution of many coating variables.This characteristic results in finding optimal factor combination difficult.Subsequently,the issue can be solved through effective and strategic statistical procedures integrated with systematic experimental data.Plasma spray parameters such as power,stand-off distance and powder feed rate have significant influence on coating characteristics like Young’s modulus.This paper presents the use of statistical techniques in specifically response surface methodology(RSM),analysis of variance,and regression analysis to develop empirical relationship to predict Young’s modulus of plasma-sprayed alumina coatings.The developed empirical relationships can be effectively used to predict Young’s modulus of plasma-sprayed alumina coatings at 95%confidence level.Response graphs and contour plots were constructed to identify the optimum plasma spray parameters to attain maximum Young’s modulus in alumina coatings.A linear regression relationship was established between porosity and Young’s modulus of the alumina coatings.

Effect of experimental parameters on the micro hardness of plasma sprayed alumina coatings on AZ31B magnesium alloy

Surface treatment of engineering materials has recently become important for serviceable engineering components.Many techniques such as thermal and thermo chemical surface treatments have been used to develop surface characteristics of materials.Hardness is the most important property,which influences considerably service life characteristics of coatings.In this investigation,alumina coatings were deposited by atmospheric plasma spray technique under different levels of power,stand-off distances and powder feed rates.Empirical relationship was developed to predict the micro hardness of alumina coatings by incorporating the plasma spray process parameters.The input power and the stand-off distance appeared to be the most significant two parameters affecting the hardness of the coating among the three investigated process parameters.Further,correlating the spray parameters with coating properties enables the identification of characteristics regime to achieve desired quality of coatings.

Development of Electrospray Laser Chemical Vapour Deposition for Homogenous Alumina Coatings

Electrospray,as a liquid source supply system,has been applied to chemical vapour deposition（CVD）.In thermal CVD,the microstructure of the obtained films changes from dense to coarse granular because of the decreasing surface temperature during deposition.Using the electrospray laser chemical vapour deposition method,we prepared homogenous alumina coatings.We found that laser irradiation was effective in compensating the surface temperature decrease,and an alpha-alumina coating with dense columnar microstructures was obtained at a deposition rate of 200 μm/h using 200 W Nd：YAG laser irradiation.

Laser Modification of Plasma Sprayed Alumina Coating

An alumina coating was developed on mild carbon steel by plasma spraying and then modified by laser remelting.Some characteristics of plasma sprayed ceramic coating before and after laser remelting,such as microstructure,wear resistance, heat shock resistance,hot corrosion property and bond strength,have been investigated in this paper.

Flame Pyrolysis Spraying of Alumina-Yttria Ceramic Coating

Alumina yttria composite oxide coating was obtained on the stainless steel through the pyrolysis of aluminium nitrate and yttrium nitrate by flame spraying in the open atmospheric environment. The isothermal oxidation behaviour of the specimens coated with alumina yttria was investigated in air at the temperature of 1273 K. The results show that coating can promote the selective oxidation of chromium in the alloy and improve the high temperature corrosion resistance of the stainless steel.

Structure of Laser Depositing of Al_(2)O_(3) Coating

A CO 2 laser with continuous wave was employed to deposite an alumina coating with a Ti Al transition coating on two kinds of steel substrates,i.e. steel Q235 and steel 45. Ti and Al could react with C in steel 45 substrate under the condition of laser depositing and form a thin reacting transition coating between the substrate and alumina coating,but the reaction did not occur on steel Q235 substrate because of its low carbon content.The quality and performance of the former were superior to that of the latter. The results were verified by SEM, XRD and Microhardness Tester.

SYNTHESIS OF DIARYL ETHERS THROUGH PHASE TRANSFER CATALYSIS WITH POTASSIUN FLUORIDE COATED ALUMINA AS A STRONG BASE

Seven diaryl ethers were synthesized with potassium fluoride coated alumina as a strong base and the addition of catalytic amount of PTC. The yield of diaryl ethers with addition of PTC was much higher than that without PTC.A discussion of the catalysis mechanism was given in this paper.

Phase Formation and Process Analysis of SiC-Al_2O_3-Al_6Si_2O_(13) Composite Powder via Carbothermal Reduction of Fly Ash at 1 550 ℃

Silicon carbide（SiC）-alumina（Al_2O_3）-mullite（Al_6Si_2O_（13）） composite powder was successfully synthesized at 1 550 ℃ for 5 h via carbothermal reduction reaction,and the effects of various mass ratios of active carbon to fly ash（0.38,0.44 and 0.58） on the phase composition and microstructure of products were investigated,and the formation process of the powder was also analyzed in detail.The products mainly consist ofβ-SiC,α-Al_2O_3,Al_6Si_2O_（13） and FeSi.Increasing carbon content favors the decomposition of Al_6Si_2O_（13） and formation of SiC.The average particle size of β-SiC andα-Al_2O_3 is about 1 μm and that of Al_6Si_2O_（13） is 5-10μm.The formation process of SiC-Al_2O_3-Al_6Si_2O_（13）powder includes the decomposition of mullite in fly ash and formation of SiC.

Reaction Mechanism and Thermal Insulation Property of Al-deposited 7YSZ Thermal Barrier Coating

To increase the performance and efficiency of thermal barrier coating （TBC）, it is important to improve the thermal insulation property. In this work, a columnar AI film was deposited at the top of 7 wt% yttria- stabilized zirconia （7YSZ） TBC by magnetron sputtering. A vacuum heat treatment was then carried out to improve the insulation property of Al-deposited TBC. Reaction mechanism of AI-ZrO2 system in AIdeposited TBC was studied by differential thermal analysis （DTA）. The phase structures of the assprayed TBC, the Al-deposited and vacuum-treated TBC were characterized. The microstructure evolution of M-deposited TBC was illustrated after vacuum heat treatment. And the insulation property of the assprayed TBC and treated TBC was compared. The results show that a multi-scaled layer, consisting of micron/ nano structured α-Al2O3 and AI3Zr grain was in situ synthesized at the top of 7YSZ coating via vacuum heat treatment. The TBC with the multi-scaled overlay has better insulation property than the asspraved TBC.

Preconcentration/Separation of Some Metal Ions Using Sodium Dodecyl Sulfate Coated Alumina Modified with Bis（5-bromo- 2-hydroxy-benzaldehyde）-2-methyl-1,5-pentane Diimine （BBHBPDI） Prior to Their Flame-AAS Determination

Preconcentration/separation of Co（II）, Fe（III）, Pb（II）, Cr（IIl）, Cu（II） and Cd（II） ions using bis（5-bromo- 2-hydroxy-benzaldehyde）-2-methy1-1,5-pentane diimine （BBHBPDI） on SDS coated alumina has been reported. The influences of the analytical parameters including pH, ligand and SDS amount, type and concentration of eluent and sample volume on metal ions recoveries were investigated. At optimum values of all variables the relative standard deviation are between 2.5-2.7 and preconcentration factor was 375, while recoveries for all understudy metal ions are higher than 95%, determination limits are between 1.5-2.7. The method has been successfully applied to determination of Co（II）, Fe（III）, Pb（II）, Cr（III）, Cu（II） and Cd（II） ions content in some real samples.

Metallurgy of aluminum-inspired formation of aluminosilicate-coated nanosilicon for lithium-ion battery anode

Modification of Si anode with various coating matrixes is a promising strategy to resolve the unsta-ble solid electrolyte interphase issues.However,the com-plex preparation process and inherently weak interaction between Si and other matrixes impede its practical appli-cation.Inspired by the metallurgical process of aluminum,an aluminosilicate matrix was prepared as coating layer on the surface of Si nanoparticles after heat treatment.Si nanoparticles with a uniform native oxide layer were used as seed crystals for the adsorption of aluminum hydroxide.The strong symbiosis and bond between alumina and silica,such as mullite(3Al_(2)O_(3)·2SiO_(2))or kaolin(Al2O_(3)·SiO_(2)·2H_(2)O),provide homogeneous and durable contact coating layer.The as-produced Si/SiO_(2)·Al_(2)O_(3)composite delivers a charge capacity of 1440 mAh·g^(-1)at 100 mA·g^(-1)and remains 879 mAh·g^(-1)at 3 A·g^(-1).After 200 cycles,the capacity retention remains high at 76%.The enhanced properties were ascribed to SiO_(2)·Al_(2)O_(3)syner-gistic composite coating layer,which could hinder the interfacial side chemical reaction and buffer volume change of Si.