Showing papers by "Ray L. Frost published in 2001"

Comparison of Raman spectra in characterizing gibbsite, bayerite, diaspore and boehmite

Abstract: High-quality Raman spectra were used for the characterization of alumina phases of gibbsite, bayerite, diaspore and boehmite. The Raman spectrum of gibbsite shows four strong, sharp bands at 3617, 3522, 3433 and 3364 cm in the hydroxyl stretching region. The spectrum of bayerite shows seven bands at 3664, 3652, 3552, 3542, 3450, 3438 and 3420 cm. Five broad bands at 3445, 3363, 3226, 3119 and 2936 cm and four broad and weak bands at 3371, 3220, 3085 and 2989 cm-1 are present in the Raman spectrum of the hydroxyl stretching region of diaspore and boehmite. The hydroxyl stretching bands are related to the surface structure of the minerals. The Raman spectra of bayerite, gibbsite and diaspore are complex whereas the Raman spectrum of boehmite shows only four bands in the low-wavenumber region. These bands are assigned to deformation and translational modes of the alumina phases. A comparison of the Raman spectrum of bauxite with those of boehmite and gibbsite showed the possibility of using Raman spectroscopy for on-line processing of bauxites that contain a mixture of alumina phases.

Porous Clays and Pillared Clays-Based Catalysts. Part 2: A review of the Catalytic and Molecular Sieve Applications

Abstract: Metal oxide pillared clay (PILC) possesses several interesting properties, such as large surface area, high pore volume and tunable pore size (from micropore to mesopore), high thermal stability, strong surface acidity and catalytic active substrates/metal oxide pillars. These unique characteristics make PILC an attractive material in catalytic reactions. It can be made either as catalyst support or directly used as catalyst. This paper is a continuous work from Kloprogge's review (J.T. Kloprogge, J. Porous Mater. 5, 5 1998) on the synthesis and properties of smectites and related PILCs and will focus on the diverse applications of clay pillared with different types of metal oxides in the heterogeneous catalysis area and adsorption area. The relation between the performance of the PILC and its physico-chemical features will be addressed.

Modification of Kaolinite Surfaces by Mechanochemical Treatment

Abstract: Kaolinite surfaces were modified by grinding kaolinite/quartz mixtures with mole fractions of 0.25 kaolinite and 0.75 quartz for periods of time up to 4 h. X-ray diffraction shows the loss of intensity of the d(001) spacing with mechanical treatment resulting in the delamination of the kaolinite. Thermogravimetric analyses show the kaolinite surface is significantly modified and surface hydroxyls are replaced with water molecules. Changes in the molecular structure of the surface hydroxyls of the kaolinite/quartz mixtures were followed by infrared spectroscopy. Kaolinite hydroxyls were lost after 2 h of grinding as evidenced by the decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm-1 and the deformation modes at 937 and 915 cm-1. Changes in the surface structure of the OSiO units were reflected in the SiO stretching and OSiO bending vibrations. The decrease in intensity of the 1056 and 1034 cm-1 bands attributed to kaolinite SiO stretching vibrations were concomitantly matched by the increase in intensity of additional bands at 1113 and 520 cm-1 ascribed to the new mechanically synthesized kaolinite surface. Mechanochemical treatment of the kaolinite results in a new surface structure.

Near-infrared spectroscopic study of basic aluminum sulfate and nitrate

Abstract: The tridecameric Al-polymer [AlO4Al12(OH)24(H2O)12]7+ was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2.2. Under slow evaporation crystals were formed of Al13-nitrate. Upon addition of sulfate the tridecamer crystallised as the monoclinic Al13-sulfate. These crystals have been studied using near-infrared spectroscopy and compared to Al2(SO4)3.16H2O. Although the near-infrared spectra of the Al13-sulfate and nitrate are very similar indicating similar crystal structures, there are minor differences related to the strength with which the crystal water molecules are bonded to the salt groups. The interaction between crystal water and nitrate is stronger than with the sulfate as reflected by the shift of the crystal water band positions from 6213, 4874 and 4553 cm−1 for the Al13 sulfate towards 5925, 4848 and 4532 cm−1 for the nitrate. A reversed shift from 5079 and 5037 cm−1 for the sulfate towards 5238 and 5040 cm−1 for the nitrate for the water molecules in the Al13 indicate that the nitrate-Al13 bond is weakened due to the influence of the crystal water on the nitrate. The Al-OH bond in the Al13 complex is not influenced by changing the salt group due to the shielding by the water molecules of the Al13 complex.

FT-IR and Raman microscopic study at 293 K and 77 K of celestine, SrS04, from the middle triassic limestone (Muschelkalk) in Winterswijk, The Netherlands

Abstract: This paper describes the Raman and infrared spectroscopy of SrSO4 or celestine from the Muschelkalk of Winterswijk, The Netherlands. The infrared absorption spectrum is characterised by the SO4 2-modes V1 at 991 cm-1, v3 at 1201, 1138 and 1091 cm-1, and v4 at 643 and 611 cm-1. An unidentified band is observed at 1248 cm-1. In the Raman spectrum at 293 K the V1 mode is found at 1000 cm-1 and is split in two bands at 1001 and 1003 cm-1 upon cooling to 77 K.The v2 mode, not observed in the infrared spectrum, is observed as a doublet at 460 and 453 cm-1. The v3 mode is represented by four bands in the Raman spectrum at 1187, 1158, 1110 and 1093 cm-1 and the v4 mode as three bands at 656, 638 and 620 cm-1. Cooling to 77 K results in a general decrease in bandwidth and a minor shift in frequencies. A decrease in intensities is observed upon cooling to 77 K due to movement of the Sr atom towards one or more of the oxygen atoms in the sulfate group.

Application of Near-Infrared Spectroscopy to the Study of Alumina Phases

Abstract: Near-infrared (IR) spectroscopy has been used to distinguish between alumina oxo and hydroxy phases. Two near-IR spectral regions are identified for this function: (1) the high-frequency region between 6400 and 7400 cm-1, attributed to the first overtone of the hydroxyl stretching mode, and (2) the 4000-4800 cm-1 region attributed to the combination of the stretching and deformation modes of the AlOH units. Near-IR spectroscopy allows the study and differentiation of the hydroxy and oxo(hydroxy) alumina phases, since each phase has its own characteristic spectrum. The spectrum of bayerite resembles that of gibbsite, whereas the spectrum of boehmite is similar to that of diaspore. Bayerite has four characteristic near-IR bands at 7218, 7128, 6996, and 6895 cm-1. Gibbsite shows five major bands at 7151, 7052, 6958, 6898, and 6845 cm-1. Boehmite displays three near-IR bands at 7152, 7065, and 6960 cm-1. Diaspore shows a prominent band at around 7176 cm-1. The use of near-IR reflectance spectroscopy to study alumina surfaces has a wide application, particularly with thin films and surfaces. The technique is rapid and accurate. Near-IR, because of its sensitivity, can be used in reflectance mode for the on-line processing of bauxitic minerals.

Raman spectroscopy of kaolinites using different excitation wavelengths

Abstract: The Raman spectra of both low- and high-defect kaolinites in the hydroxyl stretching and low-wavenumber region were obtained with excitation at three visible wavelengths of 633, 514 and 442 nm and a UV wavelength of 325 nm. The UV-excited spectra were comparable to those excited by the visible wavelengths. The Raman spectra show hydroxyl stretching bands at 3621 cm-1 attributed to the inner hydroxyl, at 3692 and 3684 cm-1 attributed to the longitudinal and transverse optic modes of the inner surface hydroxyls and at 3668 and 3653 cm-1 assigned to the out-of phase vibrations of the inner surface hydroxyls. Two bands were observed in the spectral profile at 3695 cm-1 for the high-defect kaolinite at 3698 and 3691 cm-1 and were assigned to TO/LO splitting. An increase in relative intensity of the transverse optic mode is observed with decrease in laser wavelength. The intensity of the out-of-phase vibrations at 3668 and 3653 cm-1 of the inner surface hydroxyls shows a linear relationship with the longitudinal and transverse optic modes. In the low-wavenumber region excellent correlation was found between the experimentally determined and the calculated band positions.

The PbCrO4-PbSO4 system and its mineralogical significance

Abstract: X-ray powder diffraction studies have shown that solid solution in the orthorhombic lead(II) chromate-orthorhombic lead(II) sulfate system, space group Pnma, is lacunar at 25°C, with the miscibility gap bounded by Pb(CrO ) (SO ) and Pb(CrO ) (SO ) . All Cr-rich compositions are metastable with respect to the monoclinic polymorph, corresponding to crocoite, space group P /n. The extent of solid solution of sulfate in crocoite at 25°C is Pb(CrO ) (SO ) . The transformation of orthorhombic Pb(CrO ) (SO ) to the monoclinic phase is slow in the solid state, as compared to when solid samples are allowed to remain in contact with the solution from which they crystallized. Recrystallization at ambient temperatures is acid-catalyzed and these effects explain a number of disparate reports concerning the stabilities of the various series in the literature. A value for the solubility product of orthorhombic lead(II) chromate has been determined using solution methods as logK (PbCrO ,s,orthorhombic, 298.2 K) = -10.71(12) and this has been used in turn to assess the nature of solid solution in Pb(CrO ) (SO ) (0

Raman spectroscopy of descloizite and mottramite at 298 and 77 K

Abstract: The Raman spectra of the isomorphous series descloizite [PbZn(VO4)(OH)] and mottramite [PbCu(VO4) (OH)] were obtained at 298 and 77 K. The Raman band at 844 cm-1, assigned to the 1 symmetric (VO4-) stretching mode for descloizite, is shifted to 814 cm-1 for mottramite. The 3 mode of descloizite is observed as a single band at 777 cm-1 but this mode is more complex for mottramite with three bands observed in the 77 K spectrum at 811, 785 and 767 cm-1. The bending mode (2) is observed at 437 cm-1 for descloizite and at 426 cm-1 for mottramite. The 3 region is complex for both minerals and this is attributed to symmetry reduction of the vanadate unit from Td to Cs. Collecting Raman spectra at 77 K allowed better band separation with observation of additional bands ascribed to the removal of degeneracy.

Separation of Adsorbed Formamide and Intercalated Formamide Using Controlled Rate Thermal Analysis Methodology

Abstract: Controlled rate thermal analysis (CRTA) has been used to separate adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. This separation is achieved by removal of the sample at the end of the controlled isothermal desorption step. The temperature of this isothermal desorption is dependent on the use of open or closed crucibles in the thermal analysis unit but is independent of the formamide/water ratio. X-ray diffraction shows that the formamide-intercalated kaolinite remains expanded after formamide desorption with a d(001) spacing of 10.09 A. Further heating to 300 °C results in the deintercalation of the formamide-intercalated kaolinite. DRIFT spectroscopy shows differences between the infrared spectra of the adsorbed and formamide-intercalated kaolinites. An intense band observed at 3629 cm-1 is attributed to the inner surface hydroxyls hydrogen bonded to the formamide. The adsorbed formamide-intercalated kaolinites contain adsorbed water and show intensity in the 1705 cm...

Infrared Emission Spectroscopic Study of the Dehydroxylation of Some Natural and Synthetic Saponites

Abstract: The infrared emission spectra of hydrothermally synthesized saponites have been compared to those of naturally occurring saponites. The spectra are very similar and only very minor differences are observed in the band positions and intensities. The OH-stretching region reveals for only the synthetic saponite a small band around 3040-3120cm ascribed to ammonium in the interlayer position. OH-stretching bands associated with adsorbed and interlayer water are observed around 3250 and 3425 cm. The strong band around 3600-3630 cm is ascribed to the Mg(Al, vac)-OH stretching mode whereas the band around 3670 cm is ascribed to the Mg-OH stretching mode. Upon heating the OH-stretching region shows firstly the disappearance of the interlayer water and secondly a decrease in intensity of the Mg(Al, vac)-OH hydroxyl-band. In contrast the Mg-(OH) hydroxyl-band decreases far less in intensity. A silanol band at 3778 cm is observed over the whole temperature range from room temperature to 750 °C in the spectra of all saponites. The MgAl-OH translation mode around 450 cm and deformation mode around 750cm decrease in intensity and are no longer observed in the 700 °C spectrum. Instead, a new band is observed around 730-740 cm ascribed to the restructuring of the octahedral layer and the formation of a new Al-O bond after the dehydroxylation. Because the dehydroxylation is not complete at 700-750 °C no new bands due to the formation of new Mg-O-Mg, Mg-O-Al or Mg-O-Si bonds are observed. Only a minor decrease in the Mg-OH bands is observed.

Thermoanalytical Investigation of Formamide Intercalated Kaolinites Under Quasi-isothermal Conditions

Abstract: The thermal behaviour of fully and partially expanded kaolinites intercalated with formamide has been investigated in nitrogen atmosphere under quasi-isothermal heating conditions at a constant, pre-set decomposition rate of 0.20 mg min−1 . With this technique it is possible to distinguish between loosely bonded (surface bonded) and strongly bonded (intercalated) formamide. Loosely bonded formamide is liberated in an equilibrium reaction under quasi-isothermal conditions at 118°C, while the strongly bonded (intercalated) portion is lost in an equilibrium, but non-isothermal process between 130 and 200°C. The presence of water in the intercalation solution can influence the amount of adsorbed formamide, but has no effect on the amount of the intercalated reagent. When the kaolinite is fully expanded, the amount of formamide hydrogen bonded to the inner surface of the mineral is 0.25 mol formamide/mol inner surface OH group. While the amount of surface bonded formamide is decreasing with time, no change can be observed in the amount of the intercalated reagent. With this technique the mass loss stages belonging to adsorbed and intercalated formamide can be resolved thereby providing a complex containing only one type of bonded (intercalated) formamide.

Raman microscopy of formamide-intercalated kaolinites treated by controlled-rate thermal analysis technology

Abstract: Raman spectroscopy of formamide-intercalated kaolinites treated using controlled-rate thermal analysis technology (CRTA), allowing the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites, is reported. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites, which display a combination of both intercalated and adsorbed formamide. An intense band is observed at 3629 cm-1, attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm-1, assigned to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl-stretching band of the inner hydroxyl is observed at 3621 cm-1 in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. Significant differences are observed in the CO stretching region between the adsorbed and intercalated formamide.

Thermogravimetric analysis-mass spectrometry (TGA-MS) of hydrotalcites containing CO32-, NO3-, Cl-, SO42- or ClO4-

Abstract: Mg/Al-hydrotalcites containing NO3-, Cl-, SO42- or ClO4- were synthesised under N2 to prevent incorporation of CO32-. The presence of the anions in the hydrotalcite structure was confirmed by infrared and Raman spectroscopy. The CO3- and the NO3-hydrotalcites contained both NO3- and CO32-, while the Cl-hydrotalcite also contained some CO32-. It is known that during thermal treatment of hydrotalcites dehydroxylation and decarbonisation strongly overlap. Mass spectrometry following TGA enables one to identify both reactions. For CO3-hydrotalcite CO2 is released simultaneously with water (dehydroxylation) around 335 degrees Celsius followed by NO around 365 and 500 degrees Celsius. The stability of the NO3-hydrotalcite is different showing a major loss of CO2 and H2O (dehydroxylation) around 410 degrees Celsius with losses of NO around 345 and 450 degrees Celsius. The Cl-hydrotalcite shows a similar behaviour for the H2O loss (dehydroxylation), but Cl is lost over a range from 400 to 900 degrees Celsius and CO2 comes off in steps around 360 and 500 degrees Celsius. Completely different is the thermal behaviour of SO4- and ClO4-hydrotalcites. SO4-hydrotalcite shows a gradual weight-loss due to dehydroxylation with two minor water peaks around 260 and 375 degrees Celsius, while the sulphate remains in the structure. The sulphate is not lost until heated to 900 degrees Celsius. The ClO4-hydrotalcite shows a complex thermal behaviour with 2 steps of water loss around 375 and 440 degrees Celsius, where the second step is accompanied by the loss of O2. A possible explanation is a redox reaction between perchlorate and the cations giving metal-chlorides and O2.

Raman spectroscopy of potassium acetate‐intercalated kaolinites over the temperature range 25–300,°C

Abstract: Raman spectra of the hydroxyl-stretching region of potassium acetate-intercalated kaolinite were obtained under an atmosphere of both air and nitrogen using a thermal stage over the temperature range 25–300 °C. At 25 °C, an additional band at 3606 cm−1 attributed to the inner surface hydroxyl hydrogen bonded to the acetate ion is observed with a concomitant loss of intensity in the bands attributed to the inner surface hydroxyls. Heating the intercalated complex to 50 °C results in two hydroxyl-stretching wavenumbers at 3594 and 3604 cm−1. At 100 °C, the bands shift to 3600 and 3613 cm−1. At temperatures from 100 to 300 °C, bands are observed in similar positions. Upon cooling in air to 25 °C, the acetate-bonded inner surface hydroxyl stretching wavenumber shifts back to 3606 cm−1. Upon heating the intercalated kaolinite to 300 °C under an atmosphere of nitrogen and upon cooling the acetate-bonded inner surface hydroxyl stretching wavenumber is observed at 3601 cm−1. Upon cooling to 150 °C and subsequently to 25 °C, two bands are observed at 3611 and 3600 cm−1. Upon rehydration, the hydroxyl stretching wavenumber returns to 3606 cm−1. The changes in the Raman spectra of the hydroxyl-stretching region during dehydration and rehydration are reversible. When the potassium acetate-intercalated kaolinite is heated to 300 °C and cooled to 25 °C, the inner-hydroxyl band is observed at 3630 cm−1. The shift in the wavenumber of the inner hydroxyl band is attributed to the insertion of the potassium ion in the ditrigonal cavity of the siloxane layer. Copyright © 2001 John Wiley & Sons, Ltd.

Comparison of the Raman spectra of Bayerite, Boehmite, Diaspore and Gibbsite

Abstract: Gibbsite and bayerite are alumina trihydrate (Al(OH) 3). Gibbsite occurs abundantly in nature, usually as a major mineral component in bauxite whereas bayerite is rarely found in nature. Boehmite and diaspore are alumina oxohydroxide (AlOOH) and are two other important minerals in bauxite. The Raman spectra of these four minerals were obtained using a Fourier transform Raman spectrometer operating at 1064 nm. Bayerite spectrum shows five absorption bands, 3652, 3542, 3449, 3438, and 3421 cm-1 and the gibbsite spectrum shows four strong and sharp absorption bands, 3619, 3523, 3433 and 3363 cm-1 in the hydroxyl stretching region. Four broad bands, 3426, 3365, 3229 and 2935 cm-1 and three weak bands, 3420, 3216 and 3090 cm-1 are present in this region for diaspore and boehmite, respectively. The Raman bands correspond well with the infrared absorption bands at 3620, 3525 cm-1 for gibbsite, 3365 cm-1 for diaspore and 3423, 3096 cm-1 for boehmite and these bands are assigned to be Raman and infrared active. The spectra of bayerite, gibbsite and diaspore are complex while the spectrum of boehmite only illustrates four absorption bands in the low frequency region. Common bands of RT-Raman spectra at 1019, 892, 816, 710, 568, 539, 506, 429, 395, 379, 321, 306, 255 and 242 cm-1 were observed for gibbsite, 1079, 1068, 898, 866, 545, 434, 388, 322, 292, 250 and 239 cm-1 for bayerite, 705, 608, 446, 260 and 216 cm-1 for diaspore, and 674, 495 and 360 cm-1 for boehmite. The differences in the vibrational spectra of bayerite, gibbsite, diaspore and boehmite are interpreted as being due to the differences in the molecular structure of these minerals.

The ageing of alumina hydrolysates synthesized from sec-butoxyaluminium(III)

Abstract: A combination of X-ray diffraction, thermal analysis and Raman spectroscopy was employed to characterise the ageing of alumina hydrolysates synthesised from the hydrolysis of anhydrous tri-sec-butoxyaluminium(III). X-Ray diffraction showed that the alumino-oxy(hydroxy) hydrolysates were pseudoboehmite. For boehmite the lamellar spacings are in the b direction and multiple d(020) peaks are observed for the un-aged hydrolysate. After 4 h of ageing, a single d(020) peak is observed at 6.53 A. Thermal analysis showed five endotherms at 70, 140, 238, 351 and 445 °C. These endotherms are attributed to the dehydration and dehydroxylation of the boehmite-like hydrolysate. Raman spectroscopy shows the presence of bands for the washed hydrolysates at 333, 355, 414, 455, 475, 495, 530 and 675 cm−1. These bands are attributed to pseudoboehmite. Ageing of the hydrolysates results in an increase in the crystallite size of the pseudoboehmite.