Determination of Tetrahedral Substitutions and Interlayer Surface Heterogeneity from Vibrational Spectra of Ammonium in Smectites

B. Chourabi and J. J. Fripiat
Centre de Recherche sur les Solides a Organisation Cristalline Imparfaite, C.N.R.S., 1B, Rue de la Férollerie, 45045 Orléans, Cedex, France

Abstract: Integrated intensities of the fundamental modes of vibrations of ammonium in heat-treated, NH4+-exchanged swelling minerals permits (1) a quantitative determination of the amount of tetrahedral substitutions of Si4+ by M3+ in dioctahedral smectites, and (2) an estimate of the degree of interlayer surface heterogeneity in trioctahedral minerals to be made. This is possible because NH4+ cations balancing the negative charge of tetrahedral sites that are not influenced by an excess positive charge of the octahedral layer have a symmetry lower (probably C3v) than the usual tetrahedral Td symmetry of NH4+. In C3v symmetry the ν1 band is infrared active whereas it is only Raman active in Td symmetry. Protons left after deammoniating dioctahedral smectites with tetrahedral substitutions form interlayer silanol groups, the stretching vibration of which give a band that is distinct from that of octahedral OH-stretching modes.

Key Words: Ammonium • Hofmann-Klemen effect • Infrared spectroscopy • Smectite • Tetrahedral substitution

Clays and Clay Minerals; August 1981 v. 29; no. 4; p. 260-268; DOI: 10.1346/CCMN.1981.0290403
© 1981, The Clay Minerals Society
Clay Minerals Society (www.clays.org)