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Dehydration products of gypsum: positron annihilation and dielectric measurements

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Abstract

Bassanite (CaSO4·1/2 H2O) and anhydrite (CaSO4) are the low-temperature products of gypsum (CaSO4·2H2O) dehydration, which are obtained at about 373 and 433 K, respectively. These sulphates have non-centrosymmetric crystallographic point groups, but dielectric measurements do not reveal any piezo- or ferroelectric characteristic, and they practically behave like linear dielectrics. Positron lifetime spectra exhibit the existence of two different positron states, besides a free positron state. There is positronium formation in the three sulphates, and there is also evidence for the presence of a highly populated positron bound state which may be a complex state associated with positrons bound to SO 2−4 ions. Parameter S estimated from the Doppler curve and the average positron lifetime show unquestionably the sensitivity of positrons to the phase transitions gypsum-bassanite and bassanite-anhydrite.

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Authors and Affiliations

  1. Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 1184, Sofia, Bulgaria

    T. Troev & M. Petkov

  2. Instituto de Ciencia de Materiales (Sede A), CSIC, Serrano 144, 28006, Madrid, Spain

    C. Alemany

  3. Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Complutense, 28040, Madrid, Spain

    J. Serna

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  1. T. Troev
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  2. M. Petkov
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  3. C. Alemany
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  4. J. Serna
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Troev, T., Petkov, M., Alemany, C. et al. Dehydration products of gypsum: positron annihilation and dielectric measurements. JOURNAL OF MATERIALS SCIENCE 29, 865–869 (1994). https://doi.org/10.1007/BF00351403

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