Electrochemical Behavior Of Y And Nd In LiCl-NaCl-MgCl₂ Molten Salts

Magnesium-aluminiun alloys have a wide application in aerial and auto industry for their lower density and higher specific strength. Rare earth elements can improve the mechanical properties of Mg-A1 alloys at room temperature and high temperature.So, the Mg-Al-RE alloys can be prepared at a low temperature by electrolysis in molten salts in this thesis. The details as follow:(1) The volatile loss of molten salt in the LiCl-NaCl-MgCl2 hand KCl-LiCl-MgCl2 melts were studied in the temperature range from 600 ? to 800 ? . The results show that the volatility of LiCl-NaCl-MgCl2 is much lower than the one of LiCl-KCl-MgCl2. Solubility of rare earth oxides in LiCl-NaCl-MgCl2 melts were investigated in the temperature range from 650 ? to 850 ?, and the Gibbs energy of rare earth oxides in the dissolved process were calculated.(2) The electrochemical behaviors of Y(III) ions and the mechanism of Mg-Al-Y alloys by co-reduction were studied in LiCl-NaCl-MgCl2 melts by cyclic voltammetry,chronopotentiometry and open circuit chronopotentiometry on a molybdenum electrode. Cyclic voltammetry indicates that Y(III) ions were reducted to Y atoms in a single step exchange 3 electons. Cyclic voltammetry with different scan rates indicate that the reduction of Y(?) ions are reversible process when the scan rate range from 100 mV s-1 to 300 mV s-1 and the diffusion coefficient of Y(III) ions was determined to be DY(?)?1.39 × 10-5 cm2 s-1. The alloy samples obtained by galvanostatic electrolysis were analyzed by inductively coupled plasma-atomic emission spectrometer (ICP-AES) and X-ray diffraction (XRD). Scanning electron microscopy(SEM) with energy dispersive spectrometry (EDS) analysis of deposits indicate that the element Y is distributed in grain, the element Mg mainly distributes within the grain and the Al both in grain boundary and grain. The effect of the temperature,electrolysis time as well as current density on the current efficiency has the same trend, i.e., the current efficiency ascends with increasing the temperature, electrolysis time as well as current density and then declines. The current efficiency has the maximum value of 73.8% when the temperature is 750 ? with a current density of-9.39 A cm-2 for 1.5h.(3)The electrochemical behaviors of Nd(?) ions and the mechanism of Mg-Al-Nd alloys by co-reduction were studied in LiCl-NaCl-MgCl2 melts by cyclic voltammetry, chronopotentiometry and open circuit chronopotentiometry on a molybdenum electrode as well. CV indicates that Nd(?) ions were reducted to Nd atoms in two steps exchange 3 electons which are Nd(?)+e-=Nd(?),Nd(?)+2e-=Nd(0), diffusion coefficients of Nd(?) is DNd(?)=4.92×10-5 cm2 s-1. The alloy samples performed by galvanostatic electrolysis were analyzed by ICP-AES and XRD. Results indicate that when the concentration of Nd2O3 is above 0.35 wt. %,Al2Nd and pure Mg phases exist in Mg-Al-Nd alloys. SEM-EDS analyses of sample indicate that the element Nd is distributed in grain, the element Mg mainly distributes within the grain and the Al both in grain boundary and grain. The effect of the temperature, electrolysis time as well as current density on the current efficiency has the same trend,i.e.,the current efficiency ascends with increasing the temperature,electrolysis time as well as current density and then declines. The current efficiency has the maximum value of 73.5% when the temperature is 750 ? with a current density of -9.39 A cm-2 for 1.5h.