Stability and transformation mechanism of weddellite nanocrystals studied by X-ray diffraction and infrared spectroscopy.

This study is focused on the stability of weddellite, the dihydrate phase of calcium oxalate [CaC(2)O(4)·(2 + x)H(2)O], mainly detected in kidney stones and in oxalate films found on the surfaces of several ancient monuments. Its occurrence is a critical issue since, at environmental conditions, weddellite is unstable and quickly changes into whewellite, the monohydrate phase of calcium oxalate (CaC(2)O(4)·H(2)O). New single crystal X-ray diffraction experiments have been carried out, which confirm the structural model of weddellite previously published. Synthesised nanocrystals of weddellite have been kept under different hygrometric conditions in order to study, by X-ray powder diffraction, the influence of humidity on their stability. Moreover, the mechanism of transformation of weddellite nanocrystals has been investigated by infrared spectroscopy using D(2)O as a structural probe.