Showing papers by "Ray L. Frost published in 1997"

The structure of an intercalated ordered kaolinite; a Raman microscopy study

Abstract: Changes in the molecular structure of a highly ordered kaolinite, intercalated with urea and potassium acetate, have been studied using Raman microscopy. A new Raman band, attributed to the inner surface hydroxyl groups strongly hydrogen bound to the acetate, is observed at 3605 cm (super -1) for the potassium acetate intercalate with the consequential loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm (super -1) . Remarkable changes in intensity of the Raman spectral bands of the low-frequency region of the kaolinite occurred upon intercalation. In particular, the 144 and 935 cm (super -1) bands increased by an order of magnitude and were found to be polarized. These spectroscopic changes provide evidence for the inner surface hydroxyl group-acetate bond being at an angle approaching 90 degrees to the 001 face. Decreases in intensity of the bands at 243, 271 and 336 cm (super -1) were observed. The urea intercalate shows additional Raman bands at 3387, 3408 and 3500 cm-1 which are attributed to N-H vibrations after formation of the urea-kaolinite complex. Changes in the spectra of the inserting molecules were also observed.

The structure of the kaolinite minerals — a FT-Raman study

Abstract: The Fourier transform Raman spectra of the kaolinite minerals have been measured in the 50–3800 cm−1 region using near infrared spectroscopy. Kaolinites are characterized by remarkably intense bands in the 120–145 cm−1 region. These bands, attributed to the O-Si-O and O-Al-O symmetric bending modes, are both polymorph and orientation dependent. The 200–1200 cm−1 spectral range is a finger-print region for clay minerals and each kaolinite clay has its own characteristic spectrum. The structure of clays is fundamentally determined by the position of hydroxyl groups. Fourier-transform Raman spectroscopy readily enables the hydroxyl stretching region to be examined allowing identification of the component bands. The advantages of FT-Raman spectroscopy are shown to enhance the study of the kaolinite structure.

Raman microprobe spectroscopy of halloysite

Abstract: The Raman spectra of a tubular halloysite originating from Matauri Bay, New Zealand, have been obtained using a Renishaw 1000 Raman microscope system. The Raman microprobe enables the Raman spectra of crystals as small as 0.8 mu m diameter to be obtained over the complete wavelength range and allows spectral variations along the different crystal axes to be studied. Three bands in the hydroxyl stretching region were observed at 3616.5, 3629.7 cm (super -1) and are attributed to the inner hydroxyls of the shared lower plane of the octahedral sheet of the halloysite. Two bands at 3698.2 and 3705 cm (super -1) were obtained for the outer hydroxyls of the unshared outer octahedral plane. The relative intensity of the 3629.7 cm (super -1) band varied according to the tube orientation. Lattice vibrations of the halloysite were also found to be orientation-dependent.

Kaolinite hydroxyls; a Raman microscopy study

Abstract: Raman microscopy of the kaolinite polymorphs was used to study single crystals and bundles of aligned crystals of kaolinite. The spectra of the hydroxyl stretching region were both sample and orientation dependent. Kaolinites can be classified into two groups according to the ratio of the intensities of the 3685 and 3695 cm (super -1) bands. No relationship was found between the d-spacing and the crystal domain size measurement from the 001 reflection and the Raman spectral intensities indicating the Raman spectra are independent of d-spacing and crystallinity. However, a relationship of the crystallinity in the a-b direction and intensities of the 3685 and 3695 cm (super -1) bands indicate that the relative position of one layer to the other determines the position of the inner surface hydroxyl groups and the hydrogen bonding with the oxygen of the opposite layer. A new hypothesis based on symmetric and non-symmetric hydrogen bonding of the inner surface hydroxyl groups is proposed to explain the two inner surface hydroxyl bands centred at 3685 and 3695 cm (super -1) . The bands at 3670 and 3650 cm (super -1) are described in terms of the out-of-phase vibrations of the in-phase vibrations at 3695 and 3685 cm (super -1) .

Intercalation of halloysite: a raman spectroscopic study

Abstract: Intercalates from an ordered halloysite with urea and potassium acetate were studied using Raman microscopy. The urea intercalate showed new Raman bands at 3387, 3410, 3497 and 3598 cm−1 which were attributed to the formation of a urea-Si2O5 complex. New Raman bands were observed at 3585 and 3602 cm−1 for the potassium acetate intercalate with concomitant loss of intensity of the bands at 3635, 3655, 3675 and 3696 cm−1. These new bands were attributed to the hydrogen bonds formed between the acetate and the inner surface hydroxyl groups. Remarkable changes in intensity in the lattice region of the halloysite were observed, the foremost being the reduction of the intensity of the bands at 243, 271 and 336 cm−1. Pronounced changes in the bands at 913 and 143 cm−1 attributed to the Al-OH librations were also observed. It is proposed that 2 distinct types of intercalation were present, as exemplified by: 1) urea intercalate, where the intercalating molecule hydrogen bonds to the Si-O of the halloysite layers and 2) potassium acetate intercalate, where the molecule is hydrogen-bonded to the inner surface hydroxyls of the halloysite layer and interacts with the tetrahedral sheet of the next adjacent halloysite layer. The Raman spectra of the intercalated halloysite strongly resembled that of an intercalated kaolinite.

Study of the structure and thermal behaviour of intercalated kaolinites

Abstract: Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration — reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 A halloysite present in the same mineral.

Fourier-Transform Raman Spectroscopy of Kaolinite

Abstract: The vibrational modes of clay minerals are uniquely accessible to FT Raman spectroscopy. Raman spectra in the 50–3800 cm -1 region were obtained for a suite of kaolinite clay minerals. The kaolinite clay minerals are characterized by intense bands centred at 142.7cm-1 with a prominent shoulder at 127 cm -1 and are attributed to the O-Al-O and O-Si-O symmetric bends. Differences in the lattice modes for the kaolinite clay minerals in the 200–1200 cm-1 region were obtained. Five hydroxyl bands were obtained for kaolinite at 3619, 3650, 3667, 3686, and 3695 cm-1; four OH bands were found for dickites at 3621, 3639, 3652 and 3703 cm-1.

Fourier-transform Infrared Emission Spectroscopy of Kaolinite Dehydroxylation

Abstract: The dehydroxylation of kaolinite has been investigated by Fourier-transform in situ infrared emission spectroscopy from 100 to 800 °C at 5 degree intervals. The major advantage lies in the ability to obtain vibrational spectroscopic information in situ at the elevated temperature. Dehydroxylation was determined by the loss of intensity of the hydroxyl bands in the 3550–3750 cm-1 emission spectra. No clay phase changes occur until after dehydroxylation takes place. The kaolinite layers lose their outer and inner hydroxyl groups simultaneously. It is proposed that the kaolinite dehydroxylation process takes place homogeneously and involves two mechanisms.

Drift Spectroscopy for Determination of Organic Acids on Montmorillonite

Abstract: This paper reports the application of diffuse reflectance Fourier-transform-infrared spectroscopy for the analysis of mixtures of organic acids adsorbed on montmorillonitic clays. Mixtures of several straight-chain homologues: ethanoic, propanoic, butanoic, pentanoic, hexanoic and octanoic acid and 3 iso-alkyl homologues: 2-methylpropanoic, 3-methylbutanoic, and 4-methylpentanoic acid were used. Acid concentrations were determined by using principal-components regression, with recoveries ranging from 89 to 123%.

Ft-raman spectroscopy of modified tetraisopropyltitanate hydrolysates

Abstract: Modification of metal alkoxides with complexing agents, such as carboxylic acids, which act both as a catalyst and a ligand, is commonly used in sol-gel processing to alter the hydrolysis and condensation rates of the alkoxide. Hydrolysates produced by the reaction of modified tetraisopropyltitanate with water were X-ray-amorphous but exhibited spectra similar to the spectrum of rutile; broad bands assigned to the E g and A1g Ti-O stretching modes of the “rutile-like” phase were observed at ca. 425 and 605 cm-1, respectively. During peptization of the hydrolysate with nitric acid at 60 °C, the intensity of these bands decreased substantially, and new peaks appeared at 154, 405, 515 and 630 cm-1 which were assigned to the \( {\delta _{O - Ti - O}}({E_g}),{\delta _{O - Ti - O}}({B_{1g}}),{ u _{Ti - O}}({A_{1g}}/{B_{1g}}) \) and \( {v_{Ti - O}}\left( {{E_g}} \right) \) modes, respectively, of anatase. However, the hydrolysates were also found to undergo a similar phase change when processed at the same temperature in the absence of peptizing agents, but the rate of transformation was slower. The carboxylic acid also had a significant influence on the induction time for the phase change, with the transformation occurring more slowly with increasing carboxylate chain length.

Kaolinite hydroxyls - a Raman study microscopy

Abstract: Raman microscopy of the kaolinite polymorphs was used to study single crystals and bundles of aligned crystals of kaolinite. The spectra of the hydroxyl stretching region were both sample and orientation dependent. Kaolinites can be classified into two groups according to the ratio of the intensities of the 3685 and 3695 cm -I bands. No relationship was found between the d-spacing and the crystal domain size measurement from the 001 reflection and the Raman spectral intensities indicating the Raman spectra are independent of d-spacing and crystallinity. However, a relationship of the crystallinity in the a-b direction and intensities of the 3685 and 3695 cm -1 bands indicate that the relative position of one layer to the other determines the position of the inner surface hydroxyl groups and the hydrogen bonding with the oxygen of the opposite layer. A new hypothesis based on symmetric and non-symmetric hydrogen bonding of the inner surface hydroxyl groups is proposed to explain the two inner surface hydroxyl bands centred at 3685 and 3695 cm -1, The bands at 3670 and 3650 cm -1 are described in terms of the out-of-phase vibrations of the in-phase vibrations at 3695 and 3685 cm -1.