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. Mossbauer 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 degrees C for 1 min. (C) 2010 Elsevier B.V. All rights reserved.