A multi-technique characterisation of cronstedtite synthetized by iron-clay interaction in a step by step cooling procedure
Résumé
The cooling of steel containers in radioactive waste storages has been simulated by an original step by step experiment from 90°C to 40°C. Among newly formed clay minerals observed in run products, cronstedtite has been undoubtedly identified by different analytical techniques (XRD, TEM and SEM). This is the first time that cronstedtite is so abundant and well-crystallized in an iron-clay interaction experiment. The supersaturation of experimental solutions with respect to cronstedtite is due to the availability of Fe and Si in solution, as a result of the dissolution of iron metal powder, quartz and in a minor amount other silicates. Cronstedtite crystals are characterized by various morphologies: pyramidal (truncated or not) with a triangular base and conic with a rounded or hexagonal cross-section. The pyramidal crystals occur more frequently and their polytypes (2M1, 1M, 3T) have been identified by selected area electron diffraction (SAED) patterns and by automated diffraction tomography (ADT). Cronstedtite is stable within the 90°-60°C temperature range. At temperature ≤ 50°C, cronstedite crystals show evidences of alteration.
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