A new model for the interpretation of dioctahedral mica infrared (IR) spectra in the OH stretching vibration region is proposed. It is based on the analysis of the main factors responsible for the observed sequence of the OH frequencies. In terms of this model, the simple analytical dependence between the OH frequencies and the mass and valency of cations bonded to OH groups has been found. The specific character of the interaction between octahedral Al and OH groups in the mica structures is assumed.

Integrated optical densities of the OH bands determined by the decomposition of the studied mica IR spectra are used for the quantitative analysis, that is, for the determination of a number of each type of octahedral cations per unit cell of the sample under study. A good agreement between the octahedral cation contents of 2:1 layers found from the IR spectra decomposition and the chemical analysis has shown that this technique may be used to study the local order-disorder of isomorphous cation distribution in mica structures.

The essential result obtained by the quantitative analysis of the mica IR spectra is the determination of Fe3+ cations in the tetrahedral sites of some samples. This means that the conventional presentation of structural formulae for Al-Fe3+-containing 2:1 layer silicates is unacceptable without consideration of tetrahedral Fe3+ by spectroscopic techniques and by the quantitative analysis of the IR spectra, in particular.

Synthetic hematites prepared in the presence of phosphate can incorporate phosphorus (P) in forms other than phosphate adsorbed by ligand-exchange on the crystal surface. To investigate the nature of such occluded P, which is also found in some natural specimens, we prepared 13 hematites by aging ferrihydrite precipitated from Fe(NO3)3-KH2PO4 solutions. The P/Fe atomic ratio of the resulting hematites ranged from 0 to 3% and all incorporated significant amounts of OH. As P content is raised, particle morphology changes from rhombohedral to spindle or ellipsoid-shaped. Despite the grainy appearance in transmission electron microscope images, X-ray diffraction data indicate that the particles are single crystals. Specific surface area ranged from 66 to 91 m2g−1, partly in micropores. The intensity of the absorption bands due to Fe3+ ligand field transition in the visible region, as measured by the second derivative of the Kubelka-Munk function, suggests that both OH and P contribute to an Fe deficiency in the structure. Such a deficiency is also apparent from the 104/113 peak intensity ratio in the X-ray diffraction patterns. The c unit-cell length increases with increasing P content. The infrared spectra exhibit four bands in the P-OH stretching region (viz., at 936, 971, 1005, and 1037 cm−1) which suggest that occluded PO4 possesses a low symmetry. Congruent dissolution of P and Fe was observed on acid treatment of the hematites, the dissolution rate being negatively correlated with the P content. All observations are consistent with the occluded P in the hematites being structural. A model is proposed where P occupies tetrahedral sites in the hematite structure, thus resulting in an Fe deficiency and facilitating proton incorporation.

Infrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3). Magnetic analyses showed that the thermal conversion began at about 175°C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic γ-Fe2O3 occurred at 200°C and was complete around 300°C. At higher temperatures, the maghemite converted into hematite (α-Fe2O3). Observation of the transformation from γ-FeOOH to γ-Fe2O3 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145°C and 155°C. The lag time between the onset of the breaking of OH bonds and the release of H2O from lepidocrocite around 175°C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219°C. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.

Alteration of the crystal structure of Mulhacén antigorite caused by dry, vibration grinding was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analyses (TG), grain-size distribution, and transmission and analytical electron microscopy (TEM, AEM). Grinding for 1 min reduces particles to a size ideal for IR and TG. With prolonged grinding, XRD and electron diffraction patterns showed that the crystal structure was affected mainly along the c axis, causing a partial loss of crystallinity. TG analyses revealed that vibration grinding modified mineral dehydration, accelerating the dehydroxylation process and transforming the structural OH to adsorbed water in the resulting matrix. IR spectra and AEM showed that grinding affected the tetrahedral sheet to a lesser extent than the octahedral sheet. Partial release of Mg by preferential destruction of the octahedral sheet after 10 min grinding produced an increase in the Si/Mg ratio in semi-crystalline particles, whereas the amorphous material product after 120 min showed the same composition as the initial antigorite. TEM and grain-size distribution results revealed that grinding led to a general decrease in particle size at the beginning of the experiment followed by the agglomeration of ultrafine particles as grinding proceeded.

A large and representative collection of clay-size dioctahedral mica minerals differing in their chemical compositions has been studied by infrared (IR) spectroscopy in the OH stretching vibration region. Decomposition of the IR spectra in the individual OH bands has provided unambiguous identification of the band positions for each defined pair of octahedral cations bonded to OH groups. The presence of pyrophyllite-like local structural environments in samples having a deficiency of K in interlayers has been established. A set of the relationships between the OH frequencies corresponding to pairs of cations having different valency and mass has been found.

Polarized micro-Raman spectra of a single large crystal of Keokuk kaolinite were recorded in the OH-stretching region with the laser beam directed along the different crystal axes. The Raman spectra are characterized by five OH-stretching bands at 3694, 3683, 3668, 3650 and 3620 cm−1 labeled A, Z, B, C and D, respectively. The relative intensities of these five bands depend on the orientation of the crystal and the scattering geometry. The spectra agree with the assertion that bands A and Z arise from out-of-plane vibrations, whereas band D corresponds to an in-plane vibration. The area ratios of the various bands were calculated from fitted curves of spectra recorded with the electric vector of the laser beam parallel to different crystallographic planes. The increments in the relative areas of bands B and C were parallel to those of bands A and Z and it appears that out-of-plane vibrations made considerable contributions to these bands also. From the change of area ratios with the change in the direction of the electric vector of the laser beam, bands A and Z were attributed to LO and TO frequencies of one inner-surface hydroxyl vibration. Bands A + Z, B, C and D were attributed to the vibrations of the hydroxyls assigned by Bish (1993) as OH(3), OH(4), OH(2) and OH(1), respectively. These observations were supported by photoacoustic and transmission IR spectra.

Diffuse reflectance spectra in the near-infrared region are presented for Li-saturated smectites heated up to 200°C. The smectites included three montmorillonites, an Fe-beidellite and a ferruginous smectite. Unheated samples showed a complex band near 7060 cm-1 assigned to the first overtone of the OH-stretching mode of structural hydroxyl groups and bound H2O. The OH combination bands appeared in the 4600-4300 cm-1 region. Spectra of heated montmorillonites showed an upward shift and splitting of the OH-overtone band into two components near 7170 and 7110 cm-1. The presence of a band near 7170 cm-1, assigned to the overtone of the AlMgLiOH-stretching vibration, implied that local trioctahedral domains were created upon Li(I) fixation in the previously vacant octahedral positions of montmorillonites. The OH combination bands were shifted to higher frequencies and a new band appeared near 4472 cm-1 in the spectra of montmorillonites heated to temperatures in excess of 130°C. No features indicating Li(I) in the structure of Fe-beidellite or ferruginous smectite were observed in the NIR spectra.

Infrared spectroscopy in the mid-IR region was used to follow the structural changes occurring in five Li-saturated dioctahedral smectites upon heating. The smectites included three montmorillonites, an Fe-beidellite and a ferruginous smectite. Fixation of Li+ ions in the structure even upon heating at 120°C caused the appearance of an AlMgLiOH-stretching band near 3670 cm–1 in the spectra of all three montmorillonites. This band confirmed the presence of Li(I) in the previously vacant octahedral positions in montmorillonites. No similar band was observed in the spectra of ferruginous heated smectites with prevailing tetrahedral charge. A gradual upward frequency shift and decrease in intensity of the AlAlOH-bending band showed that Li(I) present in the hexagonal cavities causes pronouncedperturbation of this OH-bending mode. The Li(I) present in the octahedral sheets causes small perturbations of the OH-bending mode near 850 cm–1 and activation of a new OH-bending mode near 803 cm–1. Reversible changes in the positions of the stretching Si–O and bending OH bands in the spectra of Fe-beidellite and a ferruginous smectite proved that Li was present in these minerals primarily in the hexagonal holes of the tetrahedral sheets.

From the early days of radiocarbon dating, the standard sample treatment has involved removal of contamination from carbonates and humic acids by washes in acid and base, respectively. A modification of this acid-base-acid (ABA) method has been suggested, especially for material older than 20,000 yr. However, the criticism of ABA and application of a more aggressive oxidizing method, such as wet oxidation (ABOX) or cellulose extraction, might only be needed in some special cases, for example, in the case of poorly preserved or chemically treated wood. Separation of cellulose seems to be the ultimate solution; however, it is not always applicable when samples contain small amounts of wood. As a part of studies focusing on the chronology of late Pleistocene sedimentary processes in the Venetian–Friulian Plain and Carnic Alps (NE Italy), 14C analyses were performed on old wood samples found in sedimentary deposits of pre-Last Glacial Maximum (LGM) age. Wood samples were treated by five methods: ABA, two modified ABA treatments (ABOX and ABA+Bleach), as well as two different cellulose separations. Infrared spectra of treated samples and 14C results show that in most cases the ABA method is sufficient in removing the contamination of naturally deposited wood, even when the wood is of very old age.

Our X-ray powder diffraction data determine that UTeO4 has an orthorhombic unit cell with parameters: a=10.115±0.003 Å, b=10.706±0.002 Å, c=7.833±0.002 Å, and v=848±0.40 (Å)3, i.e., the cell volume twice as large as that of UTeO5. IR spectral studies show that UTeO4 and UTeO5 have almost an identical molecular symmetry. In UTeO4, the effective environment of U and Te remains nearly the same as in UTeO5 and the UO2 group is noncentrosymmetric and nonlinear with little or no interaction with equatorial oxygen. Frequencies of the characteristic stretching bands of UTeO4 are (cm−1): νas (O=U=O)=945, νs (O=U=O)=880, νs (Te–O)eq=818, νas (Te–O)eq=749, νas (Te–O)ax=649, νs (Te–O)ax=561.