Characterization and humidity properties of MgAl2O4 powders synthesized in a mixed salt composed of KOH and KCl

Abstract

In this paper, we have tried to prepare MgAl₂O₄ spinel by molten salt synthesis using hydroxide as solvent. By controlling the amount of KCl in KOH, pure flower-like MgAl₂O₄ nanostructures could be synthesized at 1150 °C. Powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy were used to investigate the structures and morphologies of the obtained products. The results showed that the 3D flower-like nanostructures consisted of numerous 2D nanoflakes with a thickness of about several tens of nanometers. Further investigations on the possible formation mechanism revealed that a self-sacrificing template process dominated the formation of MgAl₂O₄ and the growth of the flower-like products was attributed to the competition between the growth rates along the directions perpendicular and parallel to the Al₂O₃ particle surfaces. Finally, an impedance-type humidity sensor was fabricated based on the flower-like MgAl₂O₄ nanostructures and tested for its humidity performance showing that the as-prepared MgAl₂O₄ nanostructures are suitable for high-performance humidity sensors.