Expansion behaviour of commercial vermiculites at 1000°C

Abstract

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 Fe²⁺ and Fe³⁺ contents and allowed identification of both tetrahedral and octahedral iron. The Fe²⁺ content was higher in type-2 vermiculites (with K⁺− or > 1 and/or Na⁺ and/or Ca²⁺ with or without Mg²⁺ as the principal interlayer cations) than in type-1 vermiculites (with Mg²⁺ or Mg²⁺ 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.