Effect of Heat Treatment on Far Infrared Emission Properties of Tourmaline Powders Modified with a Rare Earth

Abstract

Far infrared materials were prepared by precipitation method using natural tourmaline (XY 3 Z 6 Si 6 O 18 (BO 3 ) 3 W 4 , where X is Na + , Ca 2+ , K + , or vacancy; Y is Mg 2+ , Fe 2+ , Mn 2+ , Al 3+ , Fe 3+ , Mn 3+ , Cr 3+ , Ti 4+ or Li + ; Z is Al 3+ , V 3+ , Cr 3+ , or Mg 2+ ; and W is OH − , F − , or O 2− ) powders and cerium nitrate as raw materials. The results of Fourier transform infrared spectroscopy (FTIR) show that rare earth Ce can enhance the far infrared emission properties of tourmaline. Through characterization by transmission electron microscopy (TEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS), the mechanism by which rare earth Ce acts on the far infrared emission property of tourmaline was systematically studied. The XPS spectra show that the Fe 3+ ratio inside tourmaline powders after heat treatment can be raised by doping Ce. Moreover, it is showed that Ce 3+ is dominant inside the samples but its dominance is replaced by Ce 4+ outside. In addition, XRD results indicate the formation of CeO 2 crystallites during the heat treatment and further TEM observations show they exist as nanoparticles on the surface of tourmaline powders. Based on these results, we attribute the improved far infrared emission properties of Ce‐doped tourmaline to the enhanced unit cell shrinkage of the tourmaline arisen from the oxidation of Fe 2+ (0.074 nm in radius) to Fe 3+ (0.064 nm in radius) inside the tourmaline caused by the redox shift between Ce 4+ and Ce 3+ .