Raman spectroscopic study of phase transitions in natural gypsum

• Published in: Journal of Raman spectroscopy Vol. 29; no. 9; pp. 851 - 856
• Main Authors: Sarma, L. P., Prasad, P. S. R., Ravikumar, N.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.09.1998
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/(SICI)1097-4555(199809)29:9<851::AID-JRS313>3.0.CO;2-S

The gypsum–bassanite–anhydrite phase transition sequence was followed up to 550 K at ambient pressure in a naturally occurring gypsum (CaSO4·2H2O) using Raman spectroscopy. The spectral variations of the internal modes of sulphate tetrahedra (ν1 and ν2) were used to probe the structural phase transitions. A new Raman mode emerged at 1026 cm‐1, in the ν1 mode region, at around 388±5 K, indicating the onset of the bassanite (CaSO4·0.5H2O) phase. This mode became weaker after showing an initial increase. The anhydrite (CaSO4) phase, with an onset temperature of around 448±5 K, was also characterized by the appearance of the Raman mode at 1016 cm‐1. From the Arrhenius‐type changes in the reduced intensity, the activation energies associated with the gypsum to bassanite and bassanite to anhydrite transitions were estimated to be 92.25 and 32.94 kJ mol‐1, respectively. The observed spectral anomalies in the ν2 mode clearly corroborate the transition sequence. © 1998 John Wiley & Sons, Ltd.