Anti-corrosion Study Of Magnesia Ceramics And Zirconia Ceramics In Molten Salts

Ceramics is a kind of inorganic nonmetallic materials prepared by natural or synthetical compounds through molding and high-temperature sintering processes. Advanced ceramic material is rising as the production condition becomes increasingly rigorous. It has been using in many fields for its excellent performances, such as high melting point, high rupture strength, low creep rupture behavior at high temperature, fine thermal shock resistance, oxidation resistance and stable structural behavior.ZrO2and MgO are two kind of typical advanced oxide ceramic with stable chemical properties, excellent mechanical properties and anti-corrosion performance. Crucible made by ZrO2and MgO possesses outstanding thermochemical properties and satisfactory anti-erosion behavior in molten metal. Therefore, the crucible has been playing critical role in modern smelting industry, wildly using for smelting nonferrous metals and precious metals. Whereas, rare metals smelting method has never been confirmed, because electrolysis of molten salts, the wildly used method for smelting rare metals, uses graphite crucible, inwall of which is prone to flake away making the graphite proportion in produced metal high. The graphite in metal is difficult to be removed and this metal can't meet the demand in practice. It is suggested that graphite crucible be replaced by ceramic crucible made by ZrO2and MgO in view of excellent performances at high temperature.The thesis systematically studied the anti-corrosion behavior of magnesia ceramic and zirconia ceramic in molten salts of KCl,CaCl2and KF by captive test. The characterization method includes XRD,SEM and other mechanical property tests, etc.The anti-corrosion behavior of MgO in KCl is fine. The composition and morphology have no evident change and the small crystal grains integrated, making the sample much more compact and the rupture strength increased. Similarly, corrosion in molten CaCl2, strength is also slightly increased and composition is still unchanged. However, grain boundary is severely damaged and grains are appeared evidently. Corrosion in KF is much more severe with KMgF3produced. Round particles can be observed in morphology with amount of pores increased and corrosion pits appeared. Anti-corrosion performance of ZrO2in KCl is also satisfactory. Composition after corrosion is tetragonal phase zirconia (ZrO2(t)) and strength is decreased slightly. Morphology is observed in squama structure and the partially appeared grains are a little sharp. Besides, most area has no change. Composition after corrosion in CaCl2remains unchanged and rupture strength is obviously reduced with corrosion temperature increased. The morphology is similar to that corrupted in KCl. ZrO2ceramic is badly damaged in molten KF. Plenty of monoclinic phase zirconia(ZrO2(m)) and little amount of ZrF4are detected. It is phasetransformation that makes stress confused and the sample broke up after corrosion.In conclusion, anti-corrosion behaviors of magnesia ceramic and zirconia ceramic in molten salts of KCl,CaCl2is poor while that in KF is good. The performance of magnesia ceramics, in especial, is much better because recombination of small grains makes sample more compact and rupture strength increased. In one word, this study indicates that magnesia ceramics and zirconia ceramics have application potential in smelting rare metals by electrolysis of molten salts.