Fused TiO2—Al2O3 microspheres through corona electrical arcs on TiO2 nanotubes surfaces of anodized titanium

Abstract

Microspheres based on TiO² and TiO²–Al²O³ were obtained by applying corona electrical discharges to the surfaces of anodized titanium. The high-voltage arc plasma, characterized by localized temperatures exceeding 3000 °C, melted and projected segments of the TiO² nanotube layer. During the brief flight in ambient air, the molten material underwent surface tension–driven spheroidization and rapid solidification, forming microspheres with diameters ranging from 45 to 300 nm. The nanotube layers, previously grown by anodization on sandblasted or polished industrial-grade Ti, exhibited distinct morphologies and compositions depending on the surface preparation. Sandblasting led to Al²O³ contamination from the abrasive media, resulting in Al incorporation into the fused microspheres. The spherical geometry of the products supports the occurrence of complete melting followed by rapid quenching. This work demonstrates a route for transforming non-uniform nanotube films into robust microspheres suitable for photocatalytic and environmental applications. The method bridges morphological control and material reuse by exploiting localized high-temperature plasma processing.