Thermal analysis, X-ray diffraction and infrared emission spectroscopy of the borate mineral meyerhofferite CaB3O3(OH)5·H2O
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Meyerhofferite is a calcium hydrated borate mineral with formula Ca2(H3B3O7)2·4H2O and occurs as white complex acicular to crude crystals in sedimentary or lake-bed borate deposits. Simultaneous thermogravimetric analysis (TG) and derivative thermal analysis were performed. The TG curve shows a main decomposition at 195 °C followed by a second decomposition centered at about 436 °C. The total loss of mass is 28.1 % upon heating up to 1000 °C. The decomposition of meyerhofferite is also followed by the infrared emission spectra. A very sharp peak is observed at 3614 cm−1 in the 100 °C spectrum, which is attributed to the stretching vibration of OH units. This band shows a red shift with increasing temperature. The intensity of this band is lost by 250 °C. X-ray powder diffraction of the product of heating at 200 and 650 °C shows an amorphous phase, and at temperature up to 1000 °C is observed a partial reordering of the crystal structure, including calcium hexaboride, boron oxide, calcium peroxide, as well as unidentified phases.
KeywordsThermogravimetry Infrared emission spectroscopy Borate Meyerhofferite Inyoite Colemanite
The financial and infrastructure support of the Discipline of Nanotechnology and Molecular Science, Science and Engineering Faculty of the Queensland University of Technology, is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation. R. Scholz thanks to CNPq and FAPEMIG (respectively, Grant No. 305284/2015-0 and Grant APQ-01448-15) and PROPP/UFOP.
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