Expansion behaviour of commercial vermiculites at 1000°C

Commercial vermiculites from different places were studied in order to know the cause of their different behaviour after abrupt heating at 1000 °C. Mössbauer spectroscopy provided Fe ²⁺ and Fe ³⁺ contents and allowed identification of both tetrahedral and octahedral iron. The Fe ²⁺ content was higher in type-2 vermiculites (with K ⁺− or > 1 and/or Na ⁺ and/or Ca ²⁺ with or without Mg ²⁺ as the principal interlayer cations) than in type-1 vermiculites (with Mg ²⁺ or Mg ²⁺ and K ⁺ (< 1) as the principal interlayer cations). The higher iron content seemed to facilitate the fixing of potassium ions. This was responsible of the larger expansion after abrupt heating at 1000 °C for 1 min.