Solvent exchange in sulphoaluminate phases. Part I: ettringite

The change in the microstructure of ettringite and concomitant changes in volume due to the application of organic solvent exchange methods were investigated. Ettringite samples conditioned to 11% relative humidity were treated with methanol, ethanol and iso-propanol, and were examined using different analytical techniques (x-ray diffraction, Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy and nitrogen BET surface area measurement) to explore the limitations of using these organic solvents in the study of ettringite microstructure. The results suggest that methanol interacts with ettringite and therefore is not recommended for characterisation of this sulphoaluminate phase. Ethanol and iso-propanol did not significantly change the crystalline structure of ettringite, but did result in a higher surface area of the treated sample compared with the surface area of the untreated one. The length-change of ettringite in these alcohols was also determined and the results are presented.