| Rare metals is absolutely necessary in the made of the precision guided, Radar and a variety of weapons, and also be used as the compositions of alloy or equipment used in metallurgy, machinery and new material. The solid oxide membrane (SOM) process has great potential to produce pure high-value metals directly from their oxides at low cost and in an environmental friendly fashion. Previously, efficient production of various metals (e.g. magnesium, tantalum, titanium, ytterbium, silicon) has been demonstrated by the SOM process. The oxide dissociated on the cathode which was protected by SOM from the fused salt, so that the oxygen diffuse through the solid oxide conducting membrane (referred to interchangeably as "SOM tube") to the anode, this way could improve the electrolysis efficiency by the high voltage electrolysis.Zirconia has been an important solid-electrolyte material, and stabilizing oxides such as CaO, MgO, Y2O3 or Ce2O3 are used for alloying pure zirconia to get the high oxygen-ion conductivity. But, one of the main problems in this structure is the progressive spontaneous transformation of zirconia from the metastable tetragonal phase into monoclinic when it was attacked by molten salts. Additionally, during this transformation a large volume increase (4-7%) occurs in the zirconia.This phenomenon make the failure of SOM and influence the oxygen-ion conductivity of its. To understand the cause of zirconia degradation and subsequently develop strategies to improve membrane stability, we designed the molten salt corrosion experiments under electric field.This paper mainly research the corrosion resistance of Y2O3ã€CaOã€CeO and MgO stabilized zirconia in the NaF-KF molten salt, and the factors influencing corrosion resistance.The result tells us that the corrosion rate reduces with the increase of corrosion time and the corrosion resistance is poor when the grain size is small. The molten salts destroy firstly the CSZ through the grain boundary, the grain boundary attack leads to ingress of the flux into the attacked boundaries and defect and the out diffusion of Ca from the calcia-stabilized lattice to molten-salts in grain boundary, followed by the phase transformation, grain break up, volume expansion and particles fall off. The results showed that the external voltage could greatly promote the corrosion rate, and the cathode sides of the membrane were damaged more seriously than anode. From the macrostructures of sample after corrosion tests, we knew corrosion layer outside the Ca-ZrO2 and Mg-ZrO2 ceramic tubes could fall off from the tubes, but the both sides of the Ce-ZrO2 ceramic tube increase and the organize becomes fluffy.The whole work tells us that CSZ and Mg-PSZ have good molten salts corrosion resistance in the NaF-KF molten salts, and it can be used as a SOM at a low decomposition voltage. |
