Spectroscopic study of phase transitions in natural calcite mineral

The process and the formation of new minerals upon heating the carbonate rocks containing clay minerals, together with calcite are determined with thermal analysis, X-ray diffraction, infrared and Raman spectroscopy. The calcite-calcium oxide phase transition sequence was followed up to 947 degrees C in naturally occurring limestone samples. The spectral variations of the internal modes of the carbonate trigonal (nu(1), nu(2), nu(3) and nu(4)) were used to probe the structural phase transitions. The calcium oxide phase (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 degrees C was also characterized by the appearance of the infrared mode around 450 cm(-1). The minerals, which were formed upon heating the calcite, were calcium oxide and wollastonite.     

Spectroscopic characterization of natural corals

The FTIR, micro-Raman, NMR, and XPS spectra of 25 different natural corals have been compared. Reflectance and transmission absorbance IR and Raman data have been used as rapid and efficient means of classification of natural corals containing aragonite (non-precious white species), calcite (red, pink, precious white species), and organic material (black protein polymer). The combination of reflectance IR and infrared microscopy could serve as a rapid, non-destructive method for distinguishing natural corals from artificial, fake jewels.     

Thermoluminescence and chemical characterization of natural calcite collected from Kodwa mines

This paper reports the thermoluminescence (TL) and chemical characterization of natural calcite collected from Kodwa mines of the C.G. Basin. The sample was irradiated with a 10-Gy dose from an Sr-90 beta source. The heating rate used for TL measurements was 6.7 °/s. The sample had a good TL peak at approximately 127 °C and the corresponding kinetic parameter were calculated. The effect of annealing temperature is also described for natural calcite. The photoluminescence excitation spectrum at ~254 nm and the corresponding emission spectrum peak at 395 nm are reported. Inductively coupled plasma–activated emission spectroscopy (ICP–AES) was conducted to determine the percentages of elements in the calcite mineral.     

Aqueous suspensions of natural swelling clay minerals. 2. Rheological characterization

We report in this article a comprehensive investigation of the viscoelastic behavior of different natural colloidal clay minerals in aqueous solution. Rheological experiments were carried out under both dynamic and steady-state conditions, allowing us to derive the elasticity and yield stress. Both parameters can be renormalized for all sizes, ionic strength, and type of clay using in a first approach only the volume of the particles. However, applying such a treatment to various clays of similar shapes and sizes yields differences that can be linked to the repulsion strength and charge location in the swelling clays. The stronger the repulsive interactions, the better the orientation of clay particles in flows. In addition, a master linear relationship between the elasticity and yield stress whose value corresponds to a critical deformation of 0.1 was evidenced. Such a relationship may be general for any colloidal suspension of anisometric particles as revealed by the analysis of various experimental data obtained on either disk-shaped or lath- and rod-shaped particles. The particle size dependence of the sol-gel transition was also investigated in detail. To understand why suspensions of larger particles gel at a higher volume fraction, we propose a very simplified view based on the statistical hydrodynamic trapping of a particle by an another one in its neighborhood upon translation and during a short period of time. We show that the key parameter describing this hydrodynamic trapping varies as the cube of the average diameter and captures most features of the sol-gel transition. Finally, we pointed out that in the high shear limit the suspension viscosity is still closely related to electrostatic interactions and follows the same trends as the viscoelastic properties.     

Physicochemical characterization of the retardation of aqueous Cs+ ions by natural kaolinite and clinoptilolite minerals

The aim of this study was to carry out kinetic, thermodynamic, and surface characterization of the sorption of Cs+ ions on natural minerals of kaolinite and clinoptilolite. The results showed that sorption followed pseudo-second-order kinetics. The activation energies were 9.5 and 13.9 kJ/mol for Cs+ sorption on kaolinite and clinoptilolite, respectively. Experiments performed at four different initial concentrations of the ion revealed that the percentage sorption of Cs+ on clinoptilolite ranged from 90 to 95, compared to 28 to 40 for the kaolinite case. At the end of a 1 week period, the percentage of Cs+ desorption from clinoptilolite did not exceed 7%, while it amounted to more than 30% in kaolinite, indicating more stable fixation by clinoptilolite. The sorption data were best described using Freundlich and D-R isotherm models. Sorption showed spontaneous and exothermic behavior on both minerals, with deltaH(0) being -6.3 and -11.4 kJ/mol for Cs+ uptake by kaolinite and clinoptilolite, respectively. Expanding the kaolinite interlayer space from 0.71 to 1.12 nm using DMSO intercalation, did not yield a significant enhancement in the sorption capacity of kaolinite, indicating that the surface and edge sites of the clay are more energetically favored. EDS mapping and elemental analysis of the surface of kaolinite and clinoptilolite revealed more intense signals on the surface of the latter with an even distribution of sorbed Cs+ onto the surfaces of both minerals.     

Spectroscopic characterization of 2-naphthylcarbene

The 308 nm excimer laser flash photolysis of 2-naphthyldiazomethane produces triplet 2-naphthylcarbene (λ_max = 362 nm) which decays with the observed pseudo-first-order rate constants (k_exptl) of 5.54 ± 0.03 × 10⁶; 3.33 ± 0.4 × 10⁶; 1.64±0.02 × 10⁷; and 3.05±0.4 × 10⁶ s^-1 in n-pentane, 2,2,4-trimethylpentane (2,2,4-TMP), benzene and Freon 113 respectively. In hydrocarbon solvents the observed decay of triplet 2-naphthylcarbene is correlated with the pseudo-first-order growth of the 2-naphthylmethyl radical (λ_max = 378 nm). Direct kinetic measurements of the reaction of triplet 2-naphthylcarbene in 2,2,4-TMP with cyclohexane, styrene, methanol and carbon tetrachloride yielded bimolecular quenching rate constants of 1.48 ± 0.04 × 10⁶;4.33 ± 0.1 × 10⁷;7.25 ± 0.5 × 10⁶; and 3.35 ± 0.07 × 10⁶M^-1S^-1. It is also found that 2-naphthylcarbene reacts with acetonitrile (k_q = 5.28 ± 0.1 × 10⁵ M^-1 s^-1) to form a nitrile ylide intermediate with a λ_max = 372 nm. These results are interpreted in terms of a rapid singlet-triplet 2-naphthylcarbene equilibrium.     

Spectroscopic characterization of cobalt-containing mesoporous materials

Cobalt-containing mesoporous materials that have been prepared using different procedures have been comparatively characterized by transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDS), extended X-ray absorption fine structure spectroscopy (EXAFS), X-ray absorption near edge spectroscopy (XANES), and ultraviolet-visible (UV-vis), near-infrared (NIR), and mid-infrared (mid-IR) spectroscopies, and the results provide new insights into the local environment and properties of cobalt in this type of material. TEM/EDS analyses have shown that tetraethyl orthosilicate (TEOS) may be less appropriate as a silicon source during the syntheses of cobalt-containing mesoporous materials, because the distribution of cobalt throughout the framework may become uneven. EXAFS has been determined to be the most suitable method for direct verification of framework incorporation, by identifying silicon as the backscatterer in the second shell. Such a direct verification may not be obtained using UV-vis spectroscopy. From EXAFS analyses, it is also possible to distinguish between surface-bound and framework-incorporated cobalt. There is a good agreement between the results obtained from XANES and UV-vis regarding the coordination symmetry of cobalt in the samples. The presence of cobalt in the silica framework has been determined to create Lewis acid sites, and these acid sites are suggested to be located at tetrahedral cobalt sites at the surface.     

Spectroscopic and structural characterization of pascoite

Pascoite mineral having yellow-orange colour of Colorado, USA origin has been characterized by EPR, optical and NIR spectroscopy. The colour dark red-orange to yellow-orange colour of the pascoite indicates that the mineral contain mixed valency of vanadium. The optical spectrum exhibits a number of electronic bands due to presence of VO(II) ions in the mineral. From EPR studies, the parameters of g, A are evaluated and the data confirm that the ion is in distorted octahedron. Optical absorption studies reveal that two sets of VO(II) is in distorted octahedron. The bands in NIR spectra are due to the overtones and combinations of water molecules.     

Spectroscopic characterization of SnO2 gels

Excitation and dynamic emission spectra of Eu³⁺ ions were simultaneously used with FTIR and Raman spectroscopy to study the structural evolution during SnO₂ sol gel xerogel conversion. Results make evident an increase of the surroundings symmetry for the Eu³⁺ ions dissolved in SnO₂ matrix and a decrease of the amount of hydroxo groups (Sn-OH) during drying. These phenomena were associated to the pursuit of the condensation reaction after gelation.     

Simultaneous DTA-EGA of minerals and natural mineral mixtures

A DTA apparatus has been linked to non-dispersive infrared H₂O and CO₂ analyzers and an SO₂ analyzer based on an electrochemical cell, enabling evolution profiles of these three volatiles to be recorded simultaneously with the DTA curve. Examples are given of the use of the combined DTA-EGA method in the determination of the quantitative mineralogical composition of potential industrial raw materials.

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Zusammenfassung Ein DTA-Gerät wurde mit nicht-dispersiven Infrarot-Analysatoren für H₂O und CO₂ sowie mit einem auf einer elektrochemischen Zelle beruhenden SO₂-Analysator gekoppelt, welche die gleichzeitige Registrierung der Entwicklungsprofile dieser drei flüchtigen Substanzen und der DTA-Kurve gestatten. Beispiele zum Einsatz der kombinierten DTA-EGA-Methode bei der Bestimmung der quantitativen mineralogischen Zusammensetzung potentieller Rohstoffe der Industrie werden gegeben.

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Résumé On a couplé un appareil d'analyse thermique différentielle avec un spectromètre infrarouge non dispersif pour l'analyse d'H₂O et CO₂ et avec une cellule électrochimique pour l'analyse de SO₂, afin d'enregistrer simultanément la courbe ATD et le profil de dégagement de ces trois composés volatils. On donne des exemples d'application de ce couplage dans la détermination de la composition minéralogique quantitative de matières premières potentielles de l'industrie.

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H₂O ₂, - SO₂ , . - .

     

Spectroscopic characterization of acetylene-terminated sulfone resin

Fourier-transform infrared spectroscopy was used to characterize the thermal polymerization of the acetylene-terminated (AT) resin, bis[4-(3-ethynylphenoxy)phenyl]sulfone. Spectral processing techniques (including the method of factor analysis) were utilized in the analysis of the infrared data. The degree of cure was quantitatively monitored as the resin was thermally polymerized. Factor analysis indicated that only one reaction product is spectroscopically distinguishable. Further band analysis indicated the formation of predominantly trans conjugated polyene structures. No evidence for cyclotrimerization was found.     

AAS, XRPD, SEM/EDS, and FTIR characterization of Zn2+ retention by calcite, calcite-kaolinite, and calcite-clinoptilolite minerals

In this study, the sorption behavior of Zn2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the sorption capacity was enhanced with increasing amount of calcite in both types of mixtures. Under neutral-alkaline pH conditions and high loadings, the order of Zn2+ retention was observed as calcite>clinoptilolite>kaolinite. The experiments on the retention of Zn2+ by pure calcite under conditions of oversaturation showed that the uptake process proceeds via an initial adsorption mechanism (possibly ion-exchange type) followed by a slower mechanism that leads to the overgrowth of the hydrozincite phase, Zn5(OH)6(CO3)2.     

Distinguishing between natural and recarbonated calcite in oil shale ashes

Oil shale ashes from the PAMA demonstration power plant in the Negev region of Israel are produced by fluidized bed combustion (700–850°C) under short residence time. The FED is organic-rich calcareous raw material rich in carbonate rather than clays. Thus it is important to ascertain whether the calcite in the ashes is original natural calcite from the raw material or the product of recarbonation of lime. Three groups of ashes from the power plant, Ash Cooler (AC), Fly Ash (FAS) and Boiler Bank (BB) were examined using XRD, FT-IR, SEM and isotope analysis methods. The recarbonated calcite is distinguished from the natural original by smaller crystal size, lower degree of crystallinity and the presence of impurities. High negative δ¹³C values in oil shale ashes are explained by assuming recarbonation of lime with CO₂ originating from the combustion of the organic matter of the raw oil shale. Fly Ash, FAS, and BB, produced from organically-rich FED, contain more recarbonated calcite than bottom ash, AC. This observation can be explained by the larger grains of the AC, which do not reach the highest temperature area, and thus most of the original calcite does not decompose. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectroscopic characterization of solvent-induced crystallization of PET

Using recently developed quantitative FTIR methods, the gauche and trans conformer compositions have been measured for polyethylene terephthalate (PET) samples exposed to benzene and acetone. The kinetics of the primary and secondary isomerization stages of the solvent-induced crystallization process have been studied and compared with the thermally crystallized system. The Arrhenius activation energies of isomerization in the primary stage in which Fickian diffusion behavior is followed for the benzene- and acetone-induced PET systems are 8.2 ± 0.4 and 7.7 ± 0.4 kcal/mol, respectively.     

Spectroscopic characterization of some iron-containing pillared clays

Bentonites, when pillared with Al₂O₃-oxide clusters, can generate materials with BET surface area in the 290–310 m² g⁻¹ range having high cracking activity for gas oil conversion. The high coke make tendency of these catalysts has been attributed to their strong Lewis type acidity.Mössbauer and X-ray photoelectron spectroscopy have shown that iron in pillared clays can be found on the clay platelets, between the clay silicate layers or in the clay octahedral layer in substitution for Al. On heating, iron migration occurs. When iron is found near the pillars it can easily catalyze secondary cracking reactions and greatly enhances the already high coke make generation observed during gas oil conversion.     

Spectroscopic characterization of hydroxylated nanoballs in methanol

In this report, the photophysical properties of self-assembled [Cu(2)(5-OH-bdc)(2)L(2)](12) [where (5-OH-bdc)(2-) = 5-hydroxybenzene-1,3-dicarboxylate and L is a dimethyl sulfoxide, methanol, or water ligand] hydroxylated nanoballs (OH-nanoball) were examined in methanol using optical absorption and steady-state and time-resolved fluorescence methods. The optical spectrum of the OH-nanoball is dominated by ligand absorbance at 305 nm and a weaker Cu(2+)-to-ligand charge-transfer transition at approximately 695 nm, which are distinct from the absorption of either the free ligand (approximately 312 nm) or Cu(2+)(NO(3))(2) (>750 nm) in methanol. The corresponding emission spectrum of the OH-nanoball originates from the emission of the ligand and is centered at approximately 360 nm with a shoulder at approximately 390 nm. The emission from the OH-nanoball is significantly quenched relative to the free ligand [Phi(5-OH-H(2)bdc) = 0.014 and Phi(OH-nanoball) = (5.6 +/- 0.5) x 10-5]. The addition of bases such as imidazole results in an increase in the emission intensity of the OH-nanoball solution, indicating dissociation of the [Cu(2)(5-OH-bdc)(2)L(2)](12) units. Although the mechanism of (5-OH-bdc)(2-) quenching within the OH-nanoball is not clear, it is likely due to interactions between the ligand pi system and the Cu d orbitals. Fluorescence polarization studies further suggest that the OH-nanoball retains a spherical shape in solution. This is evident by the fact that the fluorescence anisotropy of the nanoball is nearly identical with that of the free ligand, suggesting rapid energy transfer (homogeneous fluorescence resonance energy transfer) between ligands within the OH-nanoball.     

Spectroscopic characterization of ambers and amber-like materials

Longitudinal acoustic (LA) phonon of Baltic, Dominican and Kuji ambers, amber-like rosin and synthetic acrylic resin has been investigated by means of Brillouin light scattering (BLS) at room temperature. We observed a pair of LA phonon peaks and a broad quasi-elastic scattering peak in backscattering spectra from ambers. The LA phonon frequencies were found to be 16.97–17.11 GHz for Baltic ambers, 17.23–17.68 GHz for Dominican ambers and 17.70–17.97 GHz for Kuji ambers, respectively. We would like to point out that the LA phonon frequency can be a good physical quantity to specify the amber-producing district. We also present a correlation between the BLS spectrum and infrared absorption spectrum of ambers and amber-like materials.     

Spectroscopic characterization of lithium doped borate glasses

B₂O₃-xLi₂O₃ (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B₂O₃ glass obtained by melting and quenching.     

Spectroscopic characterization of novel polycyclic aromatic polymers

A series of novel polyphenylenevinylene (PPV) derivative polymers were studied by absorption and photoluminescence spectroscopies. The effect of the sequential introduction of polycyclic aromatic ring substituents into the delocalized backbone was examined with relation to hypsochromatic and bathochromatic shifting. While the replacement of the phenyl units by naphthyl units results in a substantial hypsochromic shift of both the absorption and emission spectra, their subsequent substitution by anthryl units results in a bathochromic shift. The system is modeled according to, and is found to be consistent with, a previous study of donor-acceptor polyenes of varying length. The electronic structure of the backbone is found to be a balance between that of the high electron affinity polycyclic ring system and the contribution to conjugation across the linking vinyl unit. The model is adapted based on electron affinities of the constituent units, and a clear structure-property relationship for the absorption and emission properties of the system is elucidated. The Stokes shift is examined and is seen to be well-correlated with the vinyl contribution to the electron affinity total (EAtotal). The trends observed in the optical properties of the polymeric system are supported by Raman spectroscopy, whereby the spectral signature of the connecting vinyl bond is seen to soften in a fashion which is correlated with the modeled electron affinity parameters.