Font Size: a A A

Study On The Electrodeposition Of Ti5Si3 Alloy And Its Reaction Mechanism In Chloride Molten Salt

Posted on:2022-04-16Degree:MasterType:Thesis
Country:ChinaCandidate:W TangFull Text:PDF
GTID:2481306722951339Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
As a typical intermetallic compound,Ti5Si3 has received a tremendous amount of attention due to its distinct properties,such as low density(4.32 g cm–3),low electrical resistivity(50~120μΩcm),high melting point(2130°C),excellent oxidation resistance and high specific strength,etc.At present,most of the preparation methods suffer from the problems such as high cost,high energy consumption,complex production process,limited product purity,etc.Herein,we report the successful demonstration of Ti5Si3 alloy electrodeposition in molten CaCl2-CaO containing titanium/silicon dioxides at a relatively low temperature(850°C).In this study,high temperature in-situ X-ray diffraction(in-situ XRD)and high temperature in situ Raman spectroscopy(in-situ Raman)were used to analyze the dissolution behavior and the structure of molten salt system.Besides,the formation mechanism of Ti5Si3 prepared by electrodeposition was analyzed based on cyclic voltammetry(CV)analysis,which may provide a theoretical guidance for the preparation of Ti5Si3 in CaCl2-CaO-SiO2-TiO2 system.In addition,three dimensional atomic probe(3DAP),transmission electron microscope(TEM)and electron backscatter diffraction(EBSD)were also used to analyze the phase,composition and crystal orientation of the products.The main results are as follows:(1)According to the in-situ XRD results,Ca4OCl6,Ca2SiO4 and Ca3SiO4Cl2 were formed in CaCl2-CaO-SiO2 system during the whole heating process,and Raman peaks were corresponding to[SiO4]4-.In the CaCl2-CaO-TiO2 system,Ca4OCl6 and Ca TiO3were formed,and their characteristic Raman peaks at 850℃were related to[TiO3]2-.When adding SiO2 and TiO2 into the molten CaCl2-CaO simultaneously,the in-situ XRD and in-situ Raman results showed that the phases and ions appeared in the molten salts were the same as that of CaCl2-CaO-SiO2 and CaCl2-CaO-TiO2,and no obvious changes have been observed.These three systems indicate that CaO can promote the solution processes of SiO2 and TiO2 in molten CaCl2.When adding SiO2 and TiO2 into the molten CaCl2-CaO simultaneously,the silicate ions and titanate ions coexist in the molten salts.(2)At 850℃,the reduction potential of Si(Ⅳ)in CaCl2-CaO-SiO2 system was determined at around-1.08 V,the reaction has been controlled by diffusion mass transfer,and the diffusion coefficient was calculated to be 3.31×10-5 cm2 s-1.In CaCl2-Ca2SiO4 system,the reaction Si(Ⅳ)→Si(0)proceeds a two-step reduction process.The reduction potentials were-1.1 V and-1.3 V,respectively,and the reaction processes were also controlled by diffusion mass transfer.Besides,the electrochemical behavior of Ti(IV)was also studied in CaCl2-CaO-TiO2 and CaCl2-Ca TiO3 systems.The potentials of the two-step reduction preocess of the two systems were about-1.4V,-1.6 V and-1.2 V,-1.4 V respectively,and the reduction processes were also controlled by diffusion mass transfer.The cyclic voltammetry curves of CaCl2-CaO-SiO2-TiO2 showed that the reduction potentials did not change when Ti(Ⅳ)and Si(Ⅳ)coexisted at the same time.However,due to the relative low solubility of TiO2 in CaCl2,one of the reduction peaks of TiO2 has not been observed.The reduction potentials of Ti(IV)and Si(IV)in CaCl2-Ca2SiO4-Ca TiO3 system shifted slightly.In addition,the reduction order of Si(IV)was prior to that of Ti(IV)in both of the systems.(3)The thickness of Ti5Si3 alloy film increased with the increasing electrodeposition time.The results also showed that the morphology of the products can be significantly influenced by current density.By controlling current density at the range from 10 m A cm–2 to 25 m A cm–2,Ti5Si3 products with different morphologies,i.e.,dendritic particles,dense films and porous powders can be obtained in a controlled manner.The general reaction mechanism of the electrodeposition of Ti5Si3 from CaCl2-CaO-SiO2-TiO2 molten salt system can be summarized as three periods,i.e.,(i)CaO-assisted dissolution of SiO2 and TiO2 in molten CaCl2 to form silicate ions(SiO44–)and titanate ions(TiO32–),respectively;(ii)the electrodeposition of Si and Ti from silicate ions and titanate ions,respectively;(iii)the formation of stable Ti5Si3 through Si,Ti→TixSiy→Ti5Si3.
Keywords/Search Tags:Molten salt electrodeposition, CaCl2-CaO-SiO2-TiO2, Molten salt structure, Ti5Si3 alloy, Dissolution-electrodeposition mechanism
PDF Full Text Request
Related items