An X-ray powder diffraction study of damage produced in Ca(OH)2 and Mg(OH)2 by electron irradiation using the 2.5 MeV SIRIUS accelerator

Abstract

Two isomorphous hydrous minerals, Mg(OH)2 and Ca(OH)2, were exposed to the 2.5 MeV electron beam of the SIRIUS accelerator platform. Both compounds remain stable under the beam up to high doses, in the range of 3 -3.5 GGy. No decomposition is observed.But contrary to earlier statements, a net difference of reactivity between them is highlighted as a result of the present X-ray powder diffraction study: i) a significant dilatation is observed along the c -axis, more significant in brucite than in portlandite as already reported during thermal decomposition studies, ii) but a contraction is here revealed in the basal plane of brucite, along the aaxis, while a slight dilatation is still being observed in portlandite. Contraction in the basal plane seems a specific feature of electron irradiation only once previously observed by TEM in brucite. Moreover for brucite, the decreasing intensities of Bragg lines together with the appearance of a diffuse scattering over the whole angular range is compatible with the appearance of some static structural disorder induced by electron irradiation. Finally electron irradiation leads to a significant reduction in crystallite size with increasing dose, by a factor of 2 at the intermediate dose of 310 MGy in brucite, while for a comparable effect to occur an absorbed dose of 3.5 GGy should be attained in portlandite.

Ce‐Modified MgFe−LDH Supported Au Particles: An Efficient Catalyst for Base‐Free Selective Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

“…Consequently, the support maintains its clearly defined rhombohedral symmetry (3R) after deposition. [25][26][27] In addition, the identification of brucite-like peaks at a 2θ of 18.8°serves as evidence supporting the layered structure of LDHs. [28] Nevertheless, as a result of the larger ionic radius of Ce 3 + (1.02 Å) in contrast to Mg 2 + (0.86 Å) and Fe 3 + (0.55 Å), elevated concentrations of Ce induce structural distortion.…”

Behavior of Portlandite upon Exposure to Ionizing Radiation: Evidence of Delayed H2 Production

“…Interestingly, previous XRD analysis of Ca(OH) 2 samples irradiated at 300 MGy evidenced peaks broadening and shift to smaller angles. 10 Although not mentioned by the authors, this result could be attributed to deformation of the crystal due to trapped H 2 accumulation. The influence of the thermal treatment performed on the sample was tested to compare the evolution of the peak at 4.3 ppm with the H 2 release measured by micro gas chromatography (Figure 5).…”

H2 production under gamma irradiation of a calcium aluminate cement: An experimental study on both cement pastes and its stable hydrates

“…Compared to other hydrous minerals irradiated under similar conditions, gibbsite and katoite are found to be very resistant to irradiation, just like portlandite Ca(OH)2 and brucite Mg(OH)2 hydroxides (de Noirfontaine et al, 2018), but contrary to brushite CaHPO4.2H2O for which amorphization occurs even at very low irradiation doses (de Noirfontaine et al, 2021).…”