The objective of MONAMIX project is to demonstrate the potential use of mixed REOs with naturally occurring composition, obtained from monazite concentrates, as dopant in the design of high temperature zirconia coatings and sintered materials. The naturally mixed REOs doped zirconia thermal barrier coatings (TBC) will be designed to increase the lifetime of Ni/Cr alloys or reduce the critical raw materials (CRMs) content in substrate alloys. Sintered natural mixed-REOs doped zirconia will be also designed as solid oxide fuel cells (SOFCs) with controlled ionic conductivity and low REO content. MONAMIX project addresses mainly the topic 2 of ERAMIN II call: Design: 2.1: Product design for increased raw material efficiency and 2.4: Product design for critical materials substitution .

      Monazite with generic formula (Ce, La, Nd, Th, Y, Dy, Sm)(PO4) is one of the most valuable natural resources of rare earth elements used as dopants with high added value applications in many areas, including catalysis, glassmaking, metallurgy, optoelectronics, batteries and coatings for extreme environments. Extraction of individual lanthanides from mining concentrates requires very complex and reagents consuming sequential processes: (1) to obtain firstly a hydroxides cake (containing Th, U and all lanthanides), (2) separate Th and U oxalate;(iii) separate Ce (3) by solvent extraction, and (4) separate individual lanthanides by solvent extraction using hundreds of mixer-settler stages, due to their very similar electronic configuration and physical-chemical properties. Afterward, lanthanides are used as oxides (further denominated REO) or metals in different applications. The complexity of the separation process is therefore reflected in the high price of the individual lanthanides.
      A hydro-chemical method for monazite concentrates purification by selective leaching and their usage for hydrothermal synthesis of mixed nanostructured zirconia doped with different REO/ZrO2 molar ratios by a cost efficient process will be developed. The mixed REO-ZrO2 materials obtained will be used as target material to obtain TBCs at TRL 4 and validated on industrial systems by RF sputtering and electron beam deposition and study their structural stability vs. mixed REO/ZrO2 molar ratios for TBCs aiming to increase the lifetime of Ni/Cr alloys or reduce the CRMs content in substrate alloys. Bulk mixed REO-ZrO2 will be obtained at ICMCB-CNRS, Bordeaux by using various innovative sintering techniques(TRL 4-6). Densification process and ionic conductivity will be optimized for SOFCs. Elimination of separation stages and mixed REO utilization instead of individual REO, if validated in applications, may reduce production costs along the whole fabrication cycle from raw materials to product, providing nanomaterials for high-tech applications in high temperature coatings (up to 1400-1500°C) and SOFCs with operating temperature around 400°C, with cost efficiency and sustainable production.