An X-Ray Investigation of the Thermal Decomposition of Portlandite

N. H. Brett
Department of Ceramics with Refractories Technology, University of Sheffield

Summary: The thermal decomposition of portlandite, Ca(OH)2, has been studied in air and in vacuum using X-ray single-crystal techniques. In air, the crystals were decomposed in situ on the goniometer arcs whilst X-ray reflections were simultaneously recorded. The transformation to CaO was not accompanied by topotaxy; this is attributed to the high nucleation rate of CaO crystallites in air. When Ca(OH)2 single crystals were decomposed under vacuum (and subsequently exposed to X-rays), some orientation of the CaO crystallites occurred. These results are compared with those of previous workers using electron-diffraction techniques. Decomposition of Ca(OH)2 single crystals commences at ∼ 450 °C in air and at ∼ 230 °C in a vacuum of 10−6 mmHg; reaction commences at crystal edges and surface defects, the reaction boundary moving inwards to the centre of the crystal. This observation is consistent with a homogeneous mechanism of decomposition.

Mineralogical Magazine; June 1969 v. 37; no. 286; p. 244-249; DOI: 10.1180/minmag.1969.037.286.13
© 1969, The Mineralogical Society
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