Infrared emission properties of a kind of natural carbonate: interpretation from mineralogical analysis

Abstract

In recent years, infrared radiation materials have received extensive attention. In this study, a kind of natural carbonate rock was highlighted and its radiation mechanism investigated, using a series of mineralogical and spectroscopy studies such as optical microscope, varying-temperature X-ray diffraction (XRD), Raman spectroscopy, X-ray fluorescence spectrometer (XRF), inductively coupled plasma mass spectrometry (ICP-MS), electron microprobe analysis (EMPA), thermogravimetry, differential thermal analysis (TG/DTA), environment scanning electron microscopy (ESEM) and infrared absorption and emission spectroscopy (IR). Results indicated that micro-nanoscale calcite (95%), graphite (3%) and pyrite (0.1%) were the primary components. Additionally, Sr2+ and Mg2+ were found to substitute Ca2+ in calcite, whose content could reach 0.145% and 0.152% (wt%), respectively. On the basis of blackbody radiation theory and the radiation energy spectrum of samples from 400 to 2000 cm−1, the average emissivity of this rock, pure calcite, pyrite and graphite was calculated as 1.007, 0.986, 0.899 and 0.488, respectively, in the temperature range of 50–140 °C. Notably, the radiation energy spectrum calculated emissivity and emission spectrum of calcite showed high consistency with the natural carbonate at all temperatures, indicating that the radiation performance of the rock was principally contributed to calcite. The heat capacity of three components presented a positive correlation with their infrared emissivity values within the temperature and wavelength of this study. The highest heat capacity of calcite benefited the enhancement of the whole thermal radiation performance of carbonate rock. The vibration of C–O bonds in the narrow absorption band of emission spectrum (1350–1500 cm−1) would lead to relatively high radiation energy and emissivity. In addition, the substitution of Mg2+ and Sr2+ for Ca2+ improved the infrared radiation characteristics due to the 6–8% enhancement of average emissivity for pure MgCO3 and SrCO3 compared to CaCO3. This study can provide theoretical reference for infrared radiation material, using abundant and cheap natural minerals on the Earth as a source of raw materials for infrared functional materials.