Mining tailings as a raw material for glass-bonded thermally sprayed ceramic coatings: Microstructure and properties

Magnesium aluminate, MgAl₂O₄, spinel powders for thermal spraying, were synthesized from secondary raw materials by spray drying and subsequent reaction sintering. Talc ore mining tailings and aluminium hydroxide precipitate from aluminium anodizing process were studied. A stoichiometric MgAl₂O₄ spinel coating was prepared as a reference using pure raw materials. Atmospheric plasma spraying resulted in the formation of ceramic coatings. Microstructural investigations revealed that the reference coatings exhibited crystalline lamellar microstructure of MgAl₂O₄ but secondary coatings contained amorphous areas between the crystalline MgAl₂O₄ clusters. Abrasive wear test results revealed considerably lower wear rate for secondary coatings. It is suggested that the different structure of coatings, particularly the high degree of amorphous phase between the isolated crystalline MgAl₂O₄ clusters caused the higher abrasive wear resistance by changing the wear mechanism. The dielectric breakdown strength of the secondary coatings were at the same level, 24 V/μm, as compared to reference coating, 23 V/μm.