The Basic Research Of Electrolysis Preparation Of Ni-Yb Master Alloy In Fluorine System

Ni-based alloy is a representative alloy material for preparing corrosion-resistant and temperature-resistant materials,catalysts and magnetic properties materials,and the addition of rare earth ytterbium?Yb?can effectively enhance the comprehensive performance of Ni-based alloys.Therefore,it is great significance to looking for a highly-efficient,energy-saving and environment-friendly,low-cost Ni-Yb master alloy preparation method.In this paper,the Ni-Yb master alloys were prepared by solid consumptive cathodic electrolysis using fluoride-oxide?LiF-CaF₂-Yb₂O₃?as molten salt electrolyte;the solubility of Yb₂O₃ in LiF-CaF₂ molten salt was studied by isothermal saturation method and the dissolution mechanism was analyzed.The melt physical property test equipment was used to investigate the effect of temperature and Yb₂O₃ addition on the physical properties of the molten salt.In combination with the electrochemical analysis method,the formation mechanism of the Ni-Yb master alloy prepared electrolysis was clearly defined;the products are characterized by X-Ray Diffraction?XRD?,Scanning Electron Microscope?SEM?,Energy Disperse Spectroscopy?EDS?analysis.The results show:At 1353 K,the dissolution equilibrium time of Yb₂O₃ in LiF-CaF₂ molten salt is about 2.5 h,and the saturated solubility is 1.26 wt%.After the solution reaches equilibrium,the solubility increases with the increase of temperature,andtheenthalpychange(?35?_fusH^?_Yb2O3)ofdissolutionreaction?Yb₂O₃?s??Yb₂O₃?dissolved??is approximately equal to 23.975 KJ?mol^-1,indicating that the dissolution of Yb₂O₃ in fluoride salts is an endothermic process.In combination with molten salt phase after dissolution equilibrium and theoretical analysis,it is inferred that the dissolution of Yb₂O₃ in LiF-CaF₂ molten salt exists physical dissolution,but the fluorination process is the main form of dissolution.The viscosity,density and surface tension in the molten salt system with increasing temperature all show a decreasing trend,while the increase in temperature can increase the conductivity of the molten salt,but the addition of Yb₂O₃ will not change the effect of temperature on the physical properties of the molten salt system.The viscosity and surface tension of the molten salt system will gradually increase as the amount of Yb₂O₃ increases.The conductivity of molten salt system decreases with the increase of Yb₂O₃ addition.However,the density of molten salt system increases first and then decreases with the addition of Yb₂O₃,and the density reaches the maximum when the addition amount is about 2.0 wt%.The electrochemical window for the electrolyte LiF-CaF₂ analysis is:-1.80-0.1 V?vs Pt?.Yb?III?on the W and Ni electrodes both have the redox process of Yb?III??Yb?II?,The reduction potentials are all around-0.8 V?vs Pt?.The alloying of Yb?III?on the active Ni electrode occurs through phase diffusion and interfacial reaction of the generated Yb?II?on the Ni cathode surface,resulting in under potential deposition.The alloy was separated from the cathode matrix to form a low-melting intermetallic compound with precipitation potentials of-1.2 V?vs Pt?and-1.5 V?vs Pt?.The characterization showed that the Ni-Yb master alloy was uniformly distributed on Ni substrate with Ni₂Yb and Ni₅Yb compound.With the temperature rises,the current fluctuation amplitude of the electrolysis process increases,and the product carbon inclusions,gas inclusions increase,the product of Ni₂Yb disappears,and the Ni-Yb-C ternary compound is in form of Yb₁₁Ni₆₀C₆ distributing in the grain boundary.