FTIR study of the thermal transformation of barium- exchanged zeolite A to celsian

In this study room temperature X-ray diffraction patterns and FTIR spectra of zeolite A in its Na form, Ba-exchanged zeolite A, hexacelsian, monoclinic celsian and Ba-exchanged zeolite A samples thermally treated at temperatures ranging from 200 to 1000degreesC are reported. The combined inspection of room temperature X-ray diffraction patterns and FTIR spectra reveals the following points. 1) The thermal collapse of the microporous zeolite structure goes to completion upon thermal treatment at 200-300degreesC; in the resulting amorphous phase the presence of the secondary building units of the zeolite A structure may be detected. 2) Thermal treatment in the temperature range 200-400degreesC results in a middle-range order which favours the crystallisation of small crystallites of monoclinic celsian at 500degreesC.3) The further evolution of the amorphous phase in the 500-800degreesC temperature range of thermal treatment instead of promoting the crystalline growth of monoclinic celsian, creates a middle-range order favourable to the crystallisation of hexacelsian which occurs at 1000degreesC.