Electrochemical Behavior Of Zr（Ⅳ）in LiCl-KCl Molten Salt And Preparation Of ZrO₂ Nanocrystals

Zirconium and its alloys have become important nuclear industry materials because of their low intercepting ability with neutrons,easy machining,good thermal stability,and low corrosion resistance.This paper mainly focuses on the electricity of Zr（IV）on inert tungsten electrode,copper electrode and yttrium electrode in the LiCl-KCl-K₂ZrF₆ molten salt system,respectively.The chemical behavior was studied and then the extraction of zirconium was explored by using galvanostatic electrolysis method.Nano-sized zirconia materials have some unique properties,such as insulators at normal temperature,and electrical conductivity,sensitivity,toughness,etc.at high temperatures.Therefore,it is popular in many different fields,such as ceramic pigments,engineering ceramics,gem industries,piezoelectric components,ion exchangers,and solid electrolytes.However,the traditional methods for preparing nano-sized zirconium dioxide has the disadvantages of complicated preparation process,long time-consuming,and non-recyclable raw materials.Therefore,a method for the rapid preparation of zirconia nanocrystals was explored in the LiCl-KCl-K₂ZrF₆ molten salt system.The reaction that may occur during the preparation process are discussed.1.At 873 K,a series of electrochemical test methods such as cyclic voltammetry,square wavevoltammetry,chronoamperometry,chronopotentiometryandopen-circuit chronopotentiometry were utilized in the LiCl-KCl eutectic molten salt system.The electrochemical behaviors of Zr（IV）on an inert tungsten electrode were examined.The test results show that the reduction mechanism of Zr（IV）on the inert tungsten electrode is a two-step 2-electron transfer process.At 873 K,the diffusion coefficient of Zr（IV）in the molten salt system was calculated to be 1.63×10^-5 cm² s^-1,and the diffusion activation energy was 35.46 KJ mol^-1.The electrochemical behavior of Zr（IV）on the active Cu electrode was studied in LiCl-KCl eutectic molten salt system at 873 K,and an electrochemical signal of Cu-Zr intermetallic compound was observed at-1.1 V.The electrochemical behavior of Zr（IV）on the active ruthenium electrode was investigated,and an electrochemical reduction signal of Bi-Zr intermetallic compound was observed at-0.03 V.Copper-zirconium alloy and yttrium-zirconium alloy were prepared by electrolysis on the active copper electrode and the ruthenium electrode using galvanostatic electrolysis at 0.05 A in the LiCl-KCl eutectic molten salt system,respectively.Finally,the obtained electrolysis products were characterized by XRD and SEM-EDS.The characterization results show that there are three Cu-Zr intermetallic compounds,namely Cu₅₁Zr₁₄,Cu₈Zr₃ and Cu₁₀Zr₇ in the prepared Cu-Zr alloys.However,in the electrolysis product obtained by using ruthenium as the active electrode,no Bi-Zr intermetallic compound was found.2.In the LiCl-KCl eutectic molten salt system,nano-sized zirconium dioxide was prepared by using oxygen in the air as an oxidant.The obtained samples were subjected to XRD,SEM-EDS and TEM analysis.The main component of the obtained product was analyzed by XRD technique as ZrO₂,and the corresponding standard card was JCPDS:37-1484,and no peak of other substances appeared in the XRD pattern.The three highest peaks were selected and their corresponding crystal faces were found to be（-1 1 1）,（1 1 1）and（0 2 2）.The results of SEM analysis showed that the prepared ZrO₂ was spherical.In order to further study its micromorphology and particle size,a transmission electron microscope was selected for its analysis.The transmission results show that the generated ZrO₂ is a crystal structure,and there are nanocrystals having a particle diameter of 15²0 nm.Simultaneously,the reaction that may occur during the process is surmised as following:+27)+(5=（5↓+7）.The temperature conditions were changed so that the reaction temperature was between 773 and 923 K.The same mass of K₂ZrF₆ was added to the molten salt system,and the conversion of zirconium in this temperature range was calculated.From the calculation results,it is known that zirconium in this temperature range,the conversion rate of Zr is between 77.3 and 85.1%,indicating that this method is suitable for preparing zirconium dioxide nanocrystals.