Study On Electrochemical Reduction And Preparation Of Siliconized Layer On Niobium By Molten Salt Electrodeposition

With the purpose of improving oxidation resistance of pure niobium, siliconized layer was prepared on Nb by pulse electrodeposition in molten salt of Na Cl: KCl: Na F:Si O2=1:1:3:0.3(mole ratio). The effects of average current density, deposition temperature and time, duty cycle and frequency on deposition rate, composition,morphology and phase were studied by weight increase method, GDS, OM, SEM and XRD. The electrochemical reduction of Si(IV) on working electrodes in FCl Na K-Si O2 was studied through electrochemical measurement by using CV, CP and CA with threeelectrode system.The results showed that as average current density, deposition temperature and time increased, deposition rate increased, so did the siliconized layer; as duty cycle and frequency decreased, deposition rate increased, so did the layer got at small frequency;duty cycle had no effect on thickness. Grain sizes of siliconized layer were fine and no cracks when current density(10m A/cm2 up to 40 m A/cm2), duty cycle(10%, 20%), and frequencies(500Hz, 1000Hz) were small; grain sizes with no cracks increased if temperatures went up from 800℃ to 850℃ and times built up from 30 min to 150 min.Siliconized layer got under various process parameters consisted of single-phase Nb Si2 with preferred orientation of(111). Compaed with other methods, molten salt pulse electrodeposition could be implemented in common atmosphere environment. It needed simple devices and operated easily; its temperature was low, time was short; the layer firmly embedded in matrix was thick without holes or cracks. Si(â…£) on Mo and Nb electrodes in Na Cl-KCl-Na F-Si O2(800℃) were reduced into Si in a one-step process exchanging 4e:Si4++4eâ†'Si0; the process on Mo was quasi-reversible, while irreversible on Nb. This may due to difference of electrode properties. Crystallization process of Si conformed with hemispherical three-dimensional nucleus instantaneous nucleation theory.