Preparation of Lanthanum Zirconate Ceramics from Egyptian Black Sand Minerals for using in Emerging Electronic Applications

Abstract

Rare earth zirconates have received considerable attention due to its wide industrial applications such as solid oxide fuel cell electrode materials, fluorescence screens, thermal – barrier coatings, high temperature heating elements, and oxidation catalysts. Of particular interest, lanthanum zirconate, La2Zr2O7, (LZ) has been suggested as an alternative to the traditional NiCoCrAlY coating on super alloys as a thermal barrier in modern gas-turbine engines. LZ exhibits high thermal stability nearly up to its melting point at 2300 oC. LZ suffers from low thermal expansion coefficient, which makes the coating more susceptible to thermal stress due to the large thermal expansion mismatch with the metallic substrates.

The chemical processing Monazite concentrate was obtained from the physical processing of Rossitta black sand, Egypt. The material has in average 95% of monazite estimated using ICP technique. A sample portion of monazite concentrate was ground to < 300 mesh size followed by stirring with 50 Wt % NaOH solutions for 3hr at 170 0C using solid/liquid ratio of 1/1.5. The sample was then washed with distilled water and derided at 80 0C before it was treated with concentrate sulfuric acid 70% concentration at solid/liquid ratio 1:2 with agitation time 2h and leaching temperature 1100C. These conditions realized dissolution efficiency 99.4 % REEs and 99.8% Th. Thorium and REEs were then separated from U as their insoluble oxalates. Thorium with almost associated heavy REEs especially yttrium were then selectively separated from the prepared Th-REEs oxalate cake via their selective dissolution in ammonium carbonate solution at the optimum dissolution conditions