Study On Electrochemical Behavior Of Sm On Different Cathodes And The Alloys Formation Mechanism In Molten Salt

With the development the technology, rare earth alloys (such as Sm alloys) have been extensively used in automotive industry, steel industry and aerospace industry. Therefore, the demand of Sm alloys is increasing rapidly. Moreover, at present, the extraction of Sm element from spent nuclear fuel is an important research topic because Sm can absorb the neutrons in a large section and prevent the transmutable actinides to capture neutron, and hence reduce the efficiency of transmutation. In this article, we investigated the electrochemical behavior of Sm in LiCl-KCl melt on both inert and reactive electrodes and its alloy formation mechanism with M(M =Al, Ni, Cu and Zn). Sm-M alloys were prepared on reactive solid, whichs provide a feasible method for the reprocessing of Sm from spent nuclear fuel.In the first section of this thesis, we investigated the Sm(?) reduction process on a Mo electrode. We only observed the reduction process of Sm(?)/Sm(?) and did not observe the reduction process of Sm(?) to Sm. At 7731, the reduction potential of Sm(?)/Sm(?) is at about-0.62V on a Mo electrode in LiCl-KCl-SmCl3 (5wt.%) melt. Simultaneously, the reduction potential of Sm(?)/Sm(?) was also determined by square wave voltammtery (- 0.65V), open circuit chronopotentiometry (- 0.57V), steady-state polarization test (- 0.60V) and chronopotentiometry (- 0.64V), and the value was close to - 0.62V. Moreover, the reversibility of Sm(?)/Sm(?) was investigated via cyclic voltammtery in KCl-LiCl-SmCl3 (5wt.%) at 773K.The reduction of Sm(III)/Sm(II) was found to be reversibility under 0.2V·s-1. Using the square wave voltammogram gave a total number of electrons involved in the electrochemical system equal to 1.0, which indicates that the reduction of Sm(III) /Sm(II) is one electron transfer process.In KCl-LiCl-SmCl3 (5wt.%) melt, the diffusion coefficient of Sm(III) ions was calculated via cyclic voltammtery yielding Dsm(?)=3.65×10-5cm2·s-1 and via chronopotentiometry yielding DSm(?)=5.69×10-5cm2·s-1 and Dsm(?) =6.83×10-5cm2·s-1, respectively.In the second section of this thesis, we investigated the electrochemical behavior of Sm(?)on different reactive electrodes (Al, Ni, Cu and liquid Zn) via cyclic voltammtery, square wave voltammtery, steady-state polarization test and open circuit chronopotentiometry in LiCl-KCl-SmCl3 melt. On reactive electrodes, the deposition process of Sm(?) was observed.Because, Sm(?) can form into intermetallic compounds with reactive electrodes via underpotential deposition. Additionally, the formation potentials and the variety of intermetallic compounds were different on different reactive electrodes. Sm-M alloys were prepared via potentiostatic and galvanostatic electrolysis.In this thesis, the electrochemical reduction mechanism of Sm(?) was investigated on both inert and reactive electrodes. Sm-M alloys were prepared via potentiostatic and galvanostatic electrolysis on different reactive electrodes. The alloys formation mechanism was also studied,which not only provides reliable theoretical basis and technological process for rare earth alloys preparation, but also provides favorable basic data and extraction process for the reprocessing of spent nuclear fuel.