Hydrothermal synthesis of high refractive index thin films from chromium slag

Abstract

Chromium slag is a hazardous waste, and its high-value-added comprehensive utilisation would be advantageous. High refractive index thin films were prepared on glass substrates by a hydrothermal method from chromium slag with different mineralisers. The samples were characterised by inductively coupled plasma, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, an atomic force microscope, a transmission electron microscope and by film thickness and refractive index. The results show that a few Fe2O3, FeOOH, Al2O3, AlOOH or MgO crystals are formed, and most compounds of iron, aluminium, magnesium and chromium are still in amorphous state. The film materials are combined with a glass substrate by a chemical bond. The coordination ability of mineraliser anion and metal ion affects the sediment reaction rates. With NaClO3 or NaHCO3 as a mineraliser, the film surface is a perfect threedimensional space orientation network sediment with fine twines and small pores. The thinner the film, bigger the refractive index will be. The films' refractive index is mainly related to the film structure and non crystalline phase. © The Institution of Engineering and Technology 2013.