| It is of great significance to study the electroplating process of nickel-rhenium alloy in acid citrate system.Nickel-rhenium alloy electroplating has a certain application prospect in aerospace and petrochemical industry because of its excellent high temperature oxidation resistance and a series of excellent comprehensive properties.In this paper,the electroplating process of nickel-rhenium alloy in acid citrate system was determined.The effects of molar ratio of citric acid to Ni2+and nickel ion concentration on rhenium content and current efficiency of plating bath were studied.The effects of rhenium content on the surface morphology and microstructure of nickel-rhenium alloy coating were studied by three-dimensional microscopy and XRD.The corrosion resistance and oxidation resistance of Ni-Re alloy coatings were studied by oxidation kinetics curves of different coatings at 1000°C and Tafel curves in3.5%Nacl solution.The electrodeposition behavior of nickel-rhenium alloy was studied by means of steady-state cathodic polarization curve and cyclic voltammol/Letry curve.The reduction process and control steps of the alloy were speculated.The internal causes of the effect of bath composition and temperature on rhenium content in the nickel-rhenium alloy coating were analyzed.The main results were as follows:The optimum technological conditions for nickel-rhenium alloy plating in acid citrate system are as follows:current density Jc is 45A/dm2,temperature is 6070°C,pH=5,keeping ammol/Lonium rhenium rhenium 10 g/L,boric acid 30 g/L,saccharin 1g/L and sodium dodecyl sulfate 0.1g/L unchanged,by adjusting nickel ion concentration?30mmol/L450mmol/L?in plating bath,the Ni-Re alloy coating with Re content of 16wt%98wt%is obtained;nickel ion concentration in plating bath is 0240 mmol/L,nickel deposition catalyzes the reduction of rhenium.At CNi2+=240mmol/L,JRe=30.06 mA/cm2 and Re deposition current efficiency is 66.9%.The micro-surface of Ni-Re alloy coating with Re content less than 43 wt%is smooth and fine,and its XRD diffraction peak angle is similar to pure nickel,forming the crystal structure of replacement solid solution with Re as solute and Ni as solvent.When Re content is more than 52 wt%,Ni-Re alloy transforms into amorphous state.Coating.With the increase of Re content in the coating,the self-corrosion potential of Ni-Re alloy coating shifts positively,Ni-Re?80at%?and the corrosion current Icorr=1.467uA/cm2.The polarization resistance of Ni-Re alloy coating is four times that of Ni-Re?52 at%?.The oxidation weight gain rate constants of Ni-Re alloy coating and pure nickel coating are 0.1503 and 0.1918,respectively,indicating that the constant temperature oxidation resistance of Ni-Re alloy coating is better than that of pure nickel coating.At pH=4,5,the main complex form of nickel citrate in nickel-rehnium alloy plating solution is[NiCit]-,which accounts for 99.99%,Ni-Re alloy deposition processisNiCit-=Ni2++Cit3-,Ni2++2e=Ni,ReO4-+2H++2e+Ni0=ReO3-+H20+Ni0,ReO3-+6H++5e=Re+H20,the discharge process is irreversible,The nickel-rhenium alloy in acid citrate system belongs to abnormal codeposition because of the preferential precipitation of nickel with negative potential.In the interval of 0.65V-0.75V,the pre-formation of nickel citrate complex occurs mainlyIn the interval of-0.75V-0.85V,electrodeposition of the alloy mainly occurs;the cathode of different reaction zones at60°C The transfer coefficients are an1=0.2788 and an2=0.1967,respectively.The exchange current densities are j10=9.8362×10-7 and j20=1.0319×10-4,respectively,which indicates the control of pre-conversion to cathode reaction in Ni-Re alloy plating bath.Step,[NiCit]-the step of converting to free Ni2+determines the rate of reduction of Ni2+,ReO4-;the electrochemical behavior of Ni,Re alone deposited and co-deposited with different components of Ni-Re alloy indicates:an increase in nickel ion concentration The precipitation potential of the alloy gradually shifts positively,the nucleation overpotential decreases,and the polarization decreases.When the nickel ion concentration is greater than 240 mmol/L,the steady state polarization curve and the pure nickel phase It seems that the alloy is mainly deposited by Ni at this time. |
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