Reaction Mechanisms in Talc under Ionizing Radiation: Evidence of a High Stability of H^• Atoms

The reactivity under ionizing radiation of synthetic and natural talc was studied. The two samples were chosen as models of nonswelling clays. H₂ production measurements evidenced that the H₂ yield in synthetic talc was of the same order of magnitude as in water, implying a very efficient production, and then recombination, of hydrogen atoms arising from the lysis of structural −OH groups. This yield was 30 times smaller in natural talc. The discrepancy between synthetic and natural talc is most likely related to transition elements cationic impurities in the latter. Even if they are present in very small amounts, they are able to efficiently scavenge the electrons and/or the hydrogen atoms. The produced defects in irradiated synthetic talc were investigated by means of electron paramagnetic resonance (EPR) spectroscopy, which enabled proposing reaction mechanisms. Lastly, the EPR spectra evidenced the presence, at 298 K, of hydrogen atoms, which were detected few days after irradiation in both types of talc. This surprisingly high stability was mainly attributed to the absence of water molecules. It is proposed that the hydrogen atoms are stabilized in octahedra between two tetraedra sheets.