An in situ method was designed to measure a continuous open circuit potential （OCP） curve of AZ31 magnesium alloy and to observe the morphology variation of Ni-P coating during the process of the electroless plating...An in situ method was designed to measure a continuous open circuit potential （OCP） curve of AZ31 magnesium alloy and to observe the morphology variation of Ni-P coating during the process of the electroless plating. The deposition mechanism of the electroless Ni-P plating on AZ31 Mg alloy was studied by OCP curve, scanning electron microscopy （SEM）, and energy dispersion spectroscopy （EDS）. The process of electroless Ni-P plating contains the coating formation stage and the coating growth stage. The formation stage includes three procedures, i.e., the nucleation and growth of Ni crystallites, the extension of the coating in two-dimensional （2D） direction and the coalescence of the coating along three-dimensional （3D） direction. SEM investigations demonstrate that the spherical nodules of the Ni-P coating are not only formed during the coating growth stage, but also generated in the initial deposition stage of electroless Ni-P plating. The variation of the coating rates at different deposition stages corresponds to the deposition mechanism of their respective deposition stage.展开更多
There are many factors that affect the phosphorus content in the electroless Ni-P coatings The effects of the compositions of plating solution,the PH values of plat ing solution and the deposition temperature on the p...There are many factors that affect the phosphorus content in the electroless Ni-P coatings The effects of the compositions of plating solution,the PH values of plat ing solution and the deposition temperature on the phosphorus content in Ni-P coatings were investigated in this paper It is found that the phosphorus content in Ni-P coatings increases and the deposition rate decreases with decreasing PH values,nickel sulphate NiSO4 content of plating solution and the deposition temperature.展开更多
Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart.Scanning electronic microscopy（SEM）, transmis...Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart.Scanning electronic microscopy（SEM）, transmission electronic microscopy（TEM）, X-ray diffraction spectrometer（XRD）, and differential scanning calorimeter（DSC） were used to examine surface morphology and microstructure of the coating.Corrosive investigation was carried out in 3%NaCl＋5%H2SO4 solution.The results showed that Ni-P coating had partial amorphous structure mixed with nanocrystals, whereas the Ni-P/CeO2 coating had perfect amorphous structure.In high temperature condition, Ni3P precipitation and Ni crystallization occurred in both coatings but at different temperatures, whereas the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels.The anticorrosion property and passivity were improved in the CeO2-containing coating due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart.During the co-deposition process, some Cen＋（n=3, 4） ions may be adsorbed to the metal/solution interface, hinder nickel＇s crystal-typed deposition and promote phosphorous deposition.The nano-CeO2 doping finally resulted in the coating＇ perfect amorphous structure and good anti-corrosive property.展开更多
The corrosion resistance of electroless Ni-P deposits with phosphorous contents from 12% to 14% in sodium chloride solutions was studied. The deposits were immersed in 3.5% NaCl solutions for 29 d to obtain the electr...The corrosion resistance of electroless Ni-P deposits with phosphorous contents from 12% to 14% in sodium chloride solutions was studied. The deposits were immersed in 3.5% NaCl solutions for 29 d to obtain the electrochemical parameters and were examined in a standard salt spray test for 15 d respectively. The corrosion resistance of the deposits was studied by poten- tio-dynamic scan, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and cold-field emission scanning electron microscopy (FE-SEM) equipped with an energy dispersive X-ray detector (EDX). The patterns of XRD and the results of FE-SEM showed that the prepared deposits were amorphous. But after a 15 d standard salt spray test, a few pinholes appeared on the surface of the deposit and the weight content of phosphorus on the surface of the deposit was higher (which was beneficial to the formation of the passivation films) than that before the standard salt spray test when the nickel content was lower because the dissolved weight of nickel was greater than that of phosphorus. The results from potentio-dynamic scan and EIS showed that passivation films formed on the Ni-P deposit after immersion in the NaCl solutions, which decreased the corrosion rate of Ni-P samples. The results of this work show their potential applications in marine corrosion.展开更多
The electroless Ni-P coatings on AZ91 D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the ...The electroless Ni-P coatings on AZ91 D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the deposition rate varies with the ternary ligand concentration in plating solution. The structural and morphological characteristics of the coatings were analyzed by XRD and SEM. The anticorrosion properties of the Ni-P coatings were evaluated in 3.5% NaCl solution by electrochemical impedance and potentiodynamic polarization methods. The amount of ternary ligands in electroless plating bath has an significant effect on the surface morphology and structure of Ni-P coatings. The decrease of crystallization temperature and increase of crystallization heat of all the deposits with an increase in ternary ligand concentration are found by DSC measurements. The coating obtained with 0.035 mol/L ternary ligand additive in plating bath can offer a better surface homogeneity and improve corrosion resistance.展开更多
Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated. In this paper, Ni-P coating was successfully prepared on AZ33 magnesium ...Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated. In this paper, Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg（OH）2 pre-treatment film by electroless plating. To investigate the role of MgF2 in Ni-P coating, the deposition procedures between Mg（OH）2 pre-treatment film and Mg（OH）2-MgF2 pre-treatment film （a traditional process） were compared. The surface morphology variations of coatings were observed with scanning electron microscopy and the compositions were analyzed by energy dispersive spectrometry. The results showed that during the plating, both MgF2 and Ni-P deposited at the initial stage, and MgF2 distributed in the bottom of the coating, forming a transitional interlayer with Ni- P. According to the heat quench test, a poor adhesion of the coating mainly occurred between the MgF2 and Ni-P coating.展开更多
基金Project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), China
文摘An in situ method was designed to measure a continuous open circuit potential （OCP） curve of AZ31 magnesium alloy and to observe the morphology variation of Ni-P coating during the process of the electroless plating. The deposition mechanism of the electroless Ni-P plating on AZ31 Mg alloy was studied by OCP curve, scanning electron microscopy （SEM）, and energy dispersion spectroscopy （EDS）. The process of electroless Ni-P plating contains the coating formation stage and the coating growth stage. The formation stage includes three procedures, i.e., the nucleation and growth of Ni crystallites, the extension of the coating in two-dimensional （2D） direction and the coalescence of the coating along three-dimensional （3D） direction. SEM investigations demonstrate that the spherical nodules of the Ni-P coating are not only formed during the coating growth stage, but also generated in the initial deposition stage of electroless Ni-P plating. The variation of the coating rates at different deposition stages corresponds to the deposition mechanism of their respective deposition stage.
文摘There are many factors that affect the phosphorus content in the electroless Ni-P coatings The effects of the compositions of plating solution,the PH values of plat ing solution and the deposition temperature on the phosphorus content in Ni-P coatings were investigated in this paper It is found that the phosphorus content in Ni-P coatings increases and the deposition rate decreases with decreasing PH values,nickel sulphate NiSO4 content of plating solution and the deposition temperature.
基金supported by the National Natural Science Foundation of China (29233011)the Natural Science Foundation of Jiangsu Province (07KJD430246)
文摘Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart.Scanning electronic microscopy（SEM）, transmission electronic microscopy（TEM）, X-ray diffraction spectrometer（XRD）, and differential scanning calorimeter（DSC） were used to examine surface morphology and microstructure of the coating.Corrosive investigation was carried out in 3%NaCl＋5%H2SO4 solution.The results showed that Ni-P coating had partial amorphous structure mixed with nanocrystals, whereas the Ni-P/CeO2 coating had perfect amorphous structure.In high temperature condition, Ni3P precipitation and Ni crystallization occurred in both coatings but at different temperatures, whereas the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels.The anticorrosion property and passivity were improved in the CeO2-containing coating due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart.During the co-deposition process, some Cen＋（n=3, 4） ions may be adsorbed to the metal/solution interface, hinder nickel＇s crystal-typed deposition and promote phosphorous deposition.The nano-CeO2 doping finally resulted in the coating＇ perfect amorphous structure and good anti-corrosive property.
文摘The corrosion resistance of electroless Ni-P deposits with phosphorous contents from 12% to 14% in sodium chloride solutions was studied. The deposits were immersed in 3.5% NaCl solutions for 29 d to obtain the electrochemical parameters and were examined in a standard salt spray test for 15 d respectively. The corrosion resistance of the deposits was studied by poten- tio-dynamic scan, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and cold-field emission scanning electron microscopy (FE-SEM) equipped with an energy dispersive X-ray detector (EDX). The patterns of XRD and the results of FE-SEM showed that the prepared deposits were amorphous. But after a 15 d standard salt spray test, a few pinholes appeared on the surface of the deposit and the weight content of phosphorus on the surface of the deposit was higher (which was beneficial to the formation of the passivation films) than that before the standard salt spray test when the nickel content was lower because the dissolved weight of nickel was greater than that of phosphorus. The results from potentio-dynamic scan and EIS showed that passivation films formed on the Ni-P deposit after immersion in the NaCl solutions, which decreased the corrosion rate of Ni-P samples. The results of this work show their potential applications in marine corrosion.
基金Project(21073027)supported by the National Natural Science Foundation of ChinaProject(DUT10LK26)supported by the Fundamental Research Funds for the Central Universities of China
文摘The electroless Ni-P coatings on AZ91 D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the deposition rate varies with the ternary ligand concentration in plating solution. The structural and morphological characteristics of the coatings were analyzed by XRD and SEM. The anticorrosion properties of the Ni-P coatings were evaluated in 3.5% NaCl solution by electrochemical impedance and potentiodynamic polarization methods. The amount of ternary ligands in electroless plating bath has an significant effect on the surface morphology and structure of Ni-P coatings. The decrease of crystallization temperature and increase of crystallization heat of all the deposits with an increase in ternary ligand concentration are found by DSC measurements. The coating obtained with 0.035 mol/L ternary ligand additive in plating bath can offer a better surface homogeneity and improve corrosion resistance.
基金the financial support of NSFC (No.51375379),Key State Lab.Foundation of China
文摘Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated. In this paper, Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg（OH）2 pre-treatment film by electroless plating. To investigate the role of MgF2 in Ni-P coating, the deposition procedures between Mg（OH）2 pre-treatment film and Mg（OH）2-MgF2 pre-treatment film （a traditional process） were compared. The surface morphology variations of coatings were observed with scanning electron microscopy and the compositions were analyzed by energy dispersive spectrometry. The results showed that during the plating, both MgF2 and Ni-P deposited at the initial stage, and MgF2 distributed in the bottom of the coating, forming a transitional interlayer with Ni- P. According to the heat quench test, a poor adhesion of the coating mainly occurred between the MgF2 and Ni-P coating.
