Reaction Products from High Temperature Treatments of (La x Gd 1−x ) 2 Zr 2 O 7 System and Volcanic Ash Powder Mixtures

Rare-earth zirconate (REZ) pyrochlores, specifically (La,Gd) 2 Zr 2 O 7 , are promising alternatives to substitute 7YSZ in thermal barrier coatings (TBC) due to their increased phase stability and resistance to calcium-magnesium-aluminosilicate (CMAS)-based damage at high temperatures. This work analyses the reaction products of isothermal treatments at 1250°C of (La x Gd 1−x ) 2 Zr 2 O 7 powder mixtures in reaction with natural volcanic ashes (VAs) with different chemical compositions (Popocatepetl, Colima, and Eyjafjallajökull). The chemical composition in the (La x Gd 1−x ) 2 Zr 2 O 7 system showed a strong influence on the formation of reprecipitation products (Zr,Gd,La oxides), reactive crystallization products (La-Gd apatites, lanthanum silicates, zirconolite, and garnets), and intrinsic crystallization products (hematite-like structures). The formation of garnets, which enhances the mitigation effect against molten VAs/Si deposit damage, was observed more promptly on (La 0.5 Gd 0.5 ) 2 Zr 2 O 7 promoted by high contents of Fe, Ca, Ti, and Mg on VAs. Thus, the (La 0.5 Gd 0.5 ) 2 Zr 2 O 7 system stands as a possible candidate to overcome today’s threats for the integrity of current TBCs.