Depicting the dehydration and dehydroxylation processes in very rare hydrogen arsenate minerals

Autor: Petre Makreski, Gligor Jovanovski, Monika Stojanovska, Gjorgji Petrushevski, Jovica Todorov
Rok vydání: 2018
Předmět:
Zdroj: Journal of Thermal Analysis and Calorimetry. 135:2265-2276
ISSN: 1588-2926
1388-6150
DOI: 10.1007/s10973-018-7436-z
Popis: The work represents a pioneering attempt to couple TG analysis and hot-stage t-ATR-FTIR spectroscopy to describe the dehydration and dehydroxylation behaviors of very rare and complex hydrous Ca–hydrogen arsenate minerals [pharmacolite, CaHAsO4·2H2O, and picropharmacolite, Ca4Mg(AsO3OH)2(AsO4)2·11H2O]. The results are compared with the hydrous arsenate hydroxide mineral [pharmacosiderite, KFe4(AsO4)3(OH)4·6–7H2O] where OH groups are isolated from the arsenate units. The dehydration process in the hydrogen arsenate minerals (pharmacolite and picropharmacolite) reveals complete depletion of water molecules at higher temperatures (200–240 °C) explained by the structurally pronounced and stronger hydrogen bonding character in these systems compared to the arsenate sample (pharmacosiderite) where water removal was observed at 175 °C. More evident temperature disparity was obtained for the dehydroxylation process observed at 360 °C in pharmacolite compared to 210 °C in pharmacosiderite. On the other hand, the t-ATR-FTIR spectroscopy enabled to precisely assign the bands originating from the water and hydroxyl vibrations in the corresponding spectra, which is heavily demanding, especially for these compositionally and structurally complex minerals exhibiting a rich and perplexing IR spectral view. Thus, the assignment of the 3600–3000 cm−1 higher-wavenumber ν(OH) bands (from the OH group or H2O molecules) as well as the overlapping lower-wavenumber bands from δ(AsOH)/ν(AsOH)/H2O librations in the 820–600 cm−1 region was successfully resolved by a combination and correlation of the spectroscopic and thermoanalytical data.
Databáze: OpenAIRE
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