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Dissolution mechanisms of silicate minerals yielded by intercomparison with glasses and radiation damage studies |
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| Authors: | J -C Petit J -C Dran G Della Mea and A Paccagnella |
| Institution: | 1 SESD/LECALT, CEN-FAR, F-92265, Fontenay-aux-Roses Cédex, France 2 CSNSM/CNRS, F-91405, Orsay, France 3 Dipartimento di Ingegneria, Università di Trento, I-38050, Mesiano, Italy 4 Unità CISM-GNSM di Padova, I-35131, Padova, Italy |
| Abstract: | The behaviour of two silicates (albite and olivine) toward aqueous dissolution has been investigated with emphasis to two aspects: (1) similarities and differences with silicate glasses; and (2) influence of ion bombardment which transforms the initially crystalline structure to a glass-like one. The occurrence on leached materials of hydrated layers enriched with metallic elements is checked by using high-energy ion beam analytical techniques. It is shown that for both amorphous and crystalline silicates, dissolution involves competing processes responsible for either hydrated-layer generation (hydration by ion exchange and/or water permeation), or its destruction (hydrolysis of siloxane bonds and detachment of silica units). At moderate temperature ( |
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100°C), the latter processes dominate for crystalline silicates and the resulting dissolution is congruent. However, these silicates tend to behave like glasses upon ion bombardment above a critical dose. At higher temperature (> 200°C), hydration is markedly enhanced and thick altered layers are generated even on undamaged minerals such as albite and orthoclase, where alkali cations are easily exchangeable.