The Layer Silicates

The Vibrations of Protons in Minerals: hydroxyl, water and ammonium

The infrared spectrum of a mineral is a characteristic feature, which permits the identification of mineral species. The absorption bands arise from vibrations of the atoms or ions in the structure, and the frequencies of vibrations are dependent on the mass of the atoms, the restraining forces of the bonds, and the geometry of the structure. As a result, the spectrum of a mineral is sensitive to isomorphous replacements in its structure, as these affect both bond strengths and atom masses. The symmetry and regularity of a structure play an important part in determining the intensity and frequency of its vibrations, so that the infrared spectrum is often a sensitive indicator of the degree of order of a crystalline mineral. Amorphous structures absorb infrared radiation as strongly as crystalline structures, although their absorption bands are broader and show fewer distinctive features. Nevertheless, infrared spectroscopy is one of the few techniques which can yield information on the structure and composition of amorphous phases.

The Characterization of Soil Minerals by Infrared Spectroscopy

The nature of active sites on zeolites: II. Temperature dependence of the infrared spectra of hydrogen Y zeolite

To identify the far-infrared (FIR) absorption bands related to K cations in micas, spectra of muscovite, phlogopite, and biotite were compared with the spectra of pyrophyllite and talc, which have no compensating cations, and to the spectra of micas in which K is substituted by mono- and divalent cations. Dichroic experiments using single crystals of these micas showed that some of the bands or components related to K have a strong in-plane and out-of-plane dichroic character. These experimental data led to the assignment of the FIR bands at 110, 91, and 83 cm -~ for muscovite, phlogopite, and biotite, respectively, which have no in-plane and out-of-plane dichroic character, to the vibration of the double ring of oxygen atoms that constitutes the cage in which K is located (mode III). Bands at 146, t36, and 152 cm -I for muscovite, phlogopite, and biotite, respectively, which have a strong out-of-plane dichroic character, were assigned to the out-of-plane vibrations of K atoms (mode IV). Some of the components at 190, 158-153, and 145-124 cm l for muscovite, phlogopite, and biotite, respectively, which have a strong in-plane dichroic character, are possibly related to the in-plane vibrations of K atoms (modes I and II). The 165-cm ~ band of muscovite is a lattice mode of vibration. Frequencies of modes III and IV of the compensating cations of micas in which K was substituted by mono- and divalent cations exchanged as a function of ~ where Z is the charge and m the mass of the cation. Modes III and IV were well resolved and very sensitive to the crystallochemical properties of the structure (di- or trioctahedral character, Fe content, etc.). FIR spectroscopy may therefore be an important tool that uses compensating cations as probes to study the interactions between the cations and the structure of mica minerals.

Assignment of the far-infrared absorption bands of K in micas

Proton delocalization in micas

On a etudie l'effet de la temperature sur l'intensite des bandes de vibration de valence OH des solides suivants : micas, zeolites, boehmite, kaolinite, rnontmorillonite et gel de silice. ; Pour toutes ces substances, l'intensite de l'absorption diminue reversiblement en fonction de la temperature pour autant qu'on reste en-deca des conditions de deshydroxylation. La diminution est attribuee a une augmentation de la mobilite des protons dans la structure. Cette theorie a pu etre approfondie dans le cas assez simple de la boehmite ou l'on peut estimer raisonnablement les barrieres de potentiel separant les sites accessibles aux protons. La diminution d'intensite peut s'expliquer par la disparition des niveaux discrets de vibration au-dela d'un niveau d'energie ou la probabilite pour le proton de passer a travers la barriere de potentiel est proche de la frequence d'absorption. ; Certains mineraux, notamment la gibbsite, la bayerite et la brucite, ne manifestent pas de phenomene de delocalisation.

La délocalisation des protons dans les solides inorganiques

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Proton delocalization in micas

La délocalisation des protons dans les solides inorganiques