DESORDRE A COURTE DISTANCE DANS LES PHASES TRANSITOIRES RESULTANT DE L'ACTIVATION THERMIQUE DES MONTMORILLONITES

Transitory phases have been prepared by thermal activation of Ca- and Na- montmorillonites from 650 to 950~ and investigated by IR spectroscopy. The short-range disorder index, defined from both the broadening and the intensity of characteristic bands, reaches its maximum value with transitory phases obtained at 800~ and 820-850~ for the silica layer and the alumina one, respectively. This result has been correlated with data dealing with the dissolution of transitory phases either in dilute hydrofluoric acid or in a saturated calcium hydroxide solution. In addition, the particularly large increase in short-range disorder observed when the AI(V)--,AI(IV) transition occurs, experimentally confirms a previous hypothesis to explain the third endothermic effect observed on the DTA curve of montmorillonite between 800 ~ and 900~