Stability under electron irradiation of some layered hydrated minerals

Abstract

The structural damages caused to some layered hydrated minerals by 2.5 MeV electron irradiation using the SIRIUS platform were studied by powder X-Ray diffraction and, in some cases, by ¹H MAS-NMR spectroscopy. It is clearly demonstrated that the radiation damages are distinguishable from the heating effects. It is shown that: i) in all cases electron irradiation leads to distortions of the unit cell and very limited volume expansion, compared to heating; ii) radiation damages increase with increasing the structural complexity of the mineral; iii) portlandite Ca(OH)₂ and brucite Mg(OH)₂ remain crystalline up to high doses (a few GGy), with appearance of stacking fault disorder especially in brucite; iv) brushite CaHPO₄.2H₂O and gypsum CaSO₄.2H₂O undergo a phase transformation of type amorphization for brushite involving the strongest intralayer H bond between the acidic proton and the phosphate tetrahedral, and decomposition for gypsum involving interlayer H bonds between water molecules.