Investigation of the Calcium Sulphate-Water System by Infrared Spectroscopy

Bensted, J.; Prakash, Satya

doi:10.1038/219060a0

Cited by 60 publications

(45 citation statements)

References 3 publications

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“…However, the sulphate modes, which have the distinct characteristic vibrational modes in three phases, could give more information about the structural transitions. 10 As we can see from Figs 2(a) and 4, the mode l 1 (SO 4 ) at 1008 cm~1 in gypsum has undergone signiÐcant spectral variations at elevated temperatures. A new mode at 1026 cm~1 sets in around 388^5 K. The characteristic mode of gypsum also showed a small but deÐnite lower shift and became weaker.…”

Section: Gypsum-bassanite Transitionmentioning

confidence: 95%

Raman spectroscopic study of phase transitions in natural gypsum

Sarma

Prasad

Ravikumar

1998

J. Raman Spectrosc.

125

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The gypsum-bassanite-anhydrite phase transition sequence was followed up to 550 K at ambient pressure in a naturally occurring gypsum using Raman spectroscopy. The spectral variations of the internal (CaSO 4 AE 2H 2 O) modes of sulphate tetrahedra and were used to probe the structural phase transitions. A new Raman mode (m 1 m 2 ) emerged at 1026 cm-1, in the mode region, at around 388 » 5 K, indicating the onset of the bassanite m 1 phase. This mode became weaker after showing an initial increase. The anhydrite (CaSO 4 AE 0.5H 2 O) (CaSO 4 ) 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 mode clearly corroborate the transition sequence. m 2

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Section: Gypsum-bassanite Transitionmentioning

confidence: 95%

Raman spectroscopic study of phase transitions in natural gypsum

Sarma

Prasad

Ravikumar

1998

J. Raman Spectrosc.

125

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“…During dehydration the intensities of the POH.gypsum bands decrease strongly. Concomitantly, the UOHjlcmihydrat e bands (Bensted and Prakash, 1968) appear, first as a high-energy shoulder to the high-energy 1)OH.gy p .... band (Fig. 2b), then as distinct bands.…”

Section: Infrared Spectroscopymentioning

confidence: 99%

“…Of particular interest in our context is the work of Bensted and Prakash (1968) who investigated the possibility of the existence of two forms of hemihydrate (c~ and/3), but concluded that there are only three dehydration products of the dehydration of gyp- sum, namely hemihydrate, soluble (y), and insoluble (a) anhydrite. They listed the IR frequencies of all three forms in the range from 3600cm 1 to 650cm -1 and we use these data, together with those by Seidl et al (1969) in the range down l to 400cm-for the identification of the phases present in our experiments.…”

Section: Infrared Spectroscopymentioning

confidence: 99%

In situ IR spectroscopic and thermogravimetric study of the dehydration of gypsum

1990

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The dehydration of gypsum CaSO4.2H20 has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine whether intermediate phases (CaSO4.nH20) exist, other than the hemihydrate with n=0.5, and also to compare the mechanism of the dehydration process when measured by two techniques with very different correlation lengths. Thermogravimetry shows an apparently continuous water loss with an activation energy of 90.3 kJ.mol -~, with no changes in the activation energy as a function of the degree of dehydration. IR spectroscopy on the other hand, clearly shows the existence of three discrete phases, gypsum CaSO4.2H20, hemihydrate CaSO4.0.5H20 and y-CaSO4, with nucleation of each successive phase as dehydration proceeds. There is no evidence to suggest the presence of phases with any intermediate water content.

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“…Bensted was the pioneer in using Raman spectroscopy (1976a) to characterize cement minerals, following by Conjeaud and Boyer (1980). Most of the papers devoted to the application of Raman spectroscopy in cement chemistry concerns the characterization of clinker anhydrous minerals (Bensted, 1976a-Conjeaud and Boyer, 1980-Newman et al, 2005, identification of the various calcium sulfate forms: gypsum CaSO 4 ·2H 2 O, bassanite CaSO 4 ·½H 2 O and anhydrite CaSO 4 (Bensted, 1976b-Prasad, 2001), study of cement hydration by recording the decrease in intensity of the signals from the anhydrous silicate phases (Tarrida et al, 1995) and the effects of carbonation (Bensted, 1977-Martinez-Ramirez, 2003. However some studies report the use of Raman spectroscopy to investigate cementitious hydrates: namely to distinguish thaumasite Ca 6 Si 2 (OH) 12 ·(CO 3 ) 2 ·(SO 4 ) 2 ·24H 2 O from ettringite Ca 6 Al 2 (OH) 12 ·(SO 4 ) 3 ·26H 2 O, (Brough and Atkinson, 2001-Jallad et al, 2001-Sahu et al, 2002 and to characterize the C-S-H, calcium silicate hydrate, phase (Kirkpatrick et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

A Raman Study of the Sulfated Cement Hydrates: Ettringite and Monosulfoaluminate

Renaudin

Segni

Mentel

et al. 2007

ACT

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Ettringite (the AFt Ca 6 Al 2 (OH) 12 ·(SO 4 ) 3 ·26H 2 O compound) and monosulfoaluminate (the AFm Ca 4 Al 2 (OH) 12 ·SO 4 ·6H 2 O compound) phases were synthesised by the coprecipitation method and studied by micro-Raman spectroscopy. Hydrogen bond network, involving sulfate anions, ensures the cohesion of the structure of these two compounds; the columnar struture of ettringite as well as the lamellar structure of monosulfoaluminate. Raman spectroscopy has been used as a probe to investigate mainly the inter-columnar and the inter-lamellar regions of the structures. Raman spectra allowed the characterization of the local environment of sulfate anions and the hydrogen bond networks. A significant asset brought by Raman spectroscopy is the ability to work on hydrated cement products without specific sample preparation; i.e. without a risk to dammage these hydrated compounds. Several examples of the possibilities brought by Raman spectroscopy in cement chemistry are given in this paper. A space group redetermination of the ettringite structure was performed on the basis of the point symmetry of sulfate tetrahedra. The inter-columnar region of ettringite was compared to the inter-lamellar region of monosulfoaluminate as these two structural parts contain the same species. The thermal behaviors at the beginning of the dehydration (up to 390 K) and the iron substitution in ettringite were also investigated.

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Investigation of the Calcium Sulphate-Water System by Infrared Spectroscopy

Cited by 60 publications

References 3 publications

Raman spectroscopic study of phase transitions in natural gypsum

Raman spectroscopic study of phase transitions in natural gypsum

In situ IR spectroscopic and thermogravimetric study of the dehydration of gypsum

A Raman Study of the Sulfated Cement Hydrates: Ettringite and Monosulfoaluminate

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