Visible-light photoactive thermally sprayed coatings deposited from spray-dried (Na0.5Bi0.5)TiO3 microspheres

(Na0.5Bi0.5)TiO3 (NBT) ceramics are candidates to be used as coarse coatings in several applications including environmental remediation, alternative energies, electromechanical devices, etc. In this work, visible-light photoactive thermally sprayed coatings deposited from spray-dried NBT microspheres are reported. NBT powder was synthesized and processed by mixed oxides solid state reaction and milling. The spray drying process and sintering treatments to produce NBT microspheres were optimized to obtain a size distribution suitable to be used as a feedstock for flame spray deposition. The effect of spray drying and sintering parameters on the characteristics of NBT microspheres are presented and discussed. NBT microspheres with size distribution described by D-10 = 25 mu m and D-90 = 83 mu m were prepared in a design of experiments using a two-fluid nozzle spray dryer equipment varying nozzle size, atomizing pressure, feeding rate of the spray drying equipment, and the solid content (vol%) of the slurry formulation. NBT spray-dried agglomerates showed predominantly dense spheres with D-50 sizes in the range of 17-55 mu m NBT Pemvskite was confirmed by XRD in the synthesized powders and sintered microspheres. NBT powder was fed into a flame spray gun and a thick coating of approx. 100 mu m was deposited. Rapid solidification and high temperature of the flame spray process allowed to couple a heterojunction composed by NBT with small amounts of TiO2 in both, anatase and rutile phases. The hetero-junction showed a direct band gap of 1.93 eV, which makes the NBT + flame spray process an excellent combination to couple visible light photoactive NBT + TiO2 heterojunctions.

Automated summary

This study reports on the deposition of visible-light photoactive thermally sprayed coatings using spray-dried NBT microspheres. The optimization of spray drying and sintering processes allowed for the production of NBT microspheres suitable for flame spray deposition. The resulting heterojunction of NBT with TiO2 formed by the flame spray process showed a direct band gap of 1.93 eV, making it an excellent combination for visible light photoactive applications.