Mechanical Activation of Diopside in CO2

The mechanical activation (MA) of diopside in a controlled CO₂ atmosphere was studied using different grinding facilities. The results demonstrate that diopside may sorb CO₂ by two mechanisms, depending on the nature of the MA process. If grinding is not accompanied by structure breakdown, the sorption process is similar to that reported for metal oxides, and the adsorbate consists of undistorted CO₃ ^2- groups. If the MA process leads to diopside amorphization, CO₂ is sorbed in the form of distorted carbonate groups, and the IR spectrum contains a split absorption band (1433 and 1522 cm^–1) similar to the CO₃ ^2- band in the spectra of carbonate-containing silicate glasses. After ball milling in an AL-1000 mechanical activator in CO₂ for 580 min, diopside contains up to 15 wt % CO₂. Subsequent heating ensures partial or complete removal of the carbonate. Acid treatment of diopside after MA in CO₂ leads to decomposition of the carbonate and almost complete leaching of the Ca and Mg cations.     

Mechanochemical interaction of Ca silicate and aluminosilicate minerals with carbon dioxide

Processes induced by mechanical activation (MA) in a planetary ball mill of natural diopside CaMgSi₂O₆ and plagioclase (CaAl₂Si₂O₈)_0.745·(2NaAlSi₃O₈)_0.209·(2KAlSi₃O₈)_0.046 in CO₂ atmosphere have been studied. Plagioclase like diopside consumes CO₂ during MA in the form of distorted carbonate groups resulting in appearance of the double IR absorption band in 1400-1600 cm^?1 region corresponding to the stretching vibrations of CO^2? ₃ group. The degree of spitting of the double carbonate band for plagioclase is markedly higher than that for diopside indicating increased distortion of CO^2? ₃ group in the mechanically activated plagioclase. According to the XRD data after 25 min of MA the diopside and plagioclase samples are almost totally amorphous. The carbonization degree of the plagioclase is lower than that of diopside after MA at the same conditions. The differences in the mechanically induced CO₂ sorption ability by silicates can be explained on the basis of simple thermodynamic considerations involving standard Gibbs free energies of reactions of the crystalline minerals with carbon dioxide producing crystalline carbonates, silica and alumina. The results on thermal relaxation of the activated samples have been reported.     

Oxide impurity absorptions in Ge-Se-Te glass fibres

Oxide impurity absorptions in Ge-Se-Te glass fibres and the cause of the absorption loss around 943 cm^–1, the frequency of the CO² laser, have been investigated. The oxygen in the glass bounds preferentially to germanium and causes the absorptions due to Ge-O bond vibrations at 765 cm^–1 (band I) and 1230cm^–1 (band II). The excess absorptions due to these bands were determined as 0.228cm^–1/P.p.m. wt O₂ for band-I and 0.006cm^–1 /p.p.m. wt O₂ for band II. The loss of the fibre at 943cm^–1 increased with the oxygen content. It was, however, revealed from the deconvolution of the IR spectra into the independent absorption components that the absorption tails of band I and band II did not affect the loss at 943 cm^–1. The content of the impurities except oxygen analysed by a mass spectroscopy was too low to affect the loss at 943 cm^–1.     

Precipitation of carbonate crystal on surface active glasses

Anions, such as CO₃ ^2– and SO₄ ^2– ions, in industrial wastewater can cause serious scale problem in drainage pipes and vessels, when combined with other metal ions in the water. In this study, it was attempted to remove CO₃ ^2– ions from an aqueous solution by using surface active glasses. Glasses with various compositions of SiO₂-Na₂O-B₂O₃-RO (R = Mg, Ca, Sr, Ba) system were reacted in a CO₃ ^2– ion-containing solution with various pH, then the glass surfaces were analyzed by XRD and SEM, and CO₃ ^2– ions in the reacted solution were also measured. CO₃ ^2– ions in the solution were combined with alkaline earth metal ions, which were leached out of the glass, and were precipitated on the glass surface as carbonate crystals. In this way, the carbonate ions could be removed from the solution. The removal capacity of CO₃ ^2– ions is closely related to the surface reactivity of the glass and solubility product constants of the newly formed carbonate crystals. Glass containing either SrO or BaO showed a strong uptake capacity of CO₃ ^2– ions from the solution.     

Formation of oxide phases in the system Fe2O3-NiO

Mixed metal oxides in the system Fe₂O₃-NiO were prepared by coprecipitation of Fe(OH)₃/Ni(OH)₂ and the thermal treatment of hydroxide coprecipitates up to 800 or 1100°C. X-ray diffraction showed the presence of -Fe₂O₃, NiO and NiFe₂O₄ in samples prepared at 800°C. The oxide phases -Fe₂O₃, NiO, NiFe₂O₄ and a phase with structure similar to NiFe₂O₄ were found in samples prepared at 1100°C. Fourier transform-infrared spectra of oxide phases formed in the system Fe₂O₃-NiO are discussed. Two very strong infrared bands at 553 and 475 cm^–1, a weak intensity infrared band at 383 cm^–1 and two shoulders at 626 and 441 cm^–1 were observed for -Fe₂O₃ prepared at 1100°C. NiFe₂O₄, prepared at the same temperature, showed two broad and very strong infrared bands at 602 and 411 cm^–1, while NiO showed a broad infrared band at 466 cm^–1. Fourier transform infrared spectroscopic results were in agreement with X-ray diffraction.     

Corrosion behaviour of some stainless steel alloys in molten alkali carbonates (I)

In the present work it is aimed to study the corrosion behaviour of two types of stainless steel alloys (one ferritic and two austenitic) in molten Li₂CO₃- Na₂CO₃- K₂CO₃ mixture. This mixture is of interest in corrosion studies because of its low melting point (397°C) and good electrical properties. In this investigation the following techniques of measurements are used: (i) open circuit-potential, (ii) galvanic current, (iii) impedance, (iv) atomic absorption spectroscopy for the determination of the amount of metals dissolved in the melt (v) corrosion tests, carried out on the oxide scales formed during the oxidation of stainless steel alloys in carbonate melt. In this melt the electrode Ag/AgCl was used as a reference electrode. In molten carbonates, the oxide ions originate by self-dissociation according to the equilibrium CO₃ ^2– CO₂ + O^2–. The oxide ions, O^2–, and carbonate ions, CO₃ ^2–, play an important role in the oxidation process of these alloys and their passivation in the carbonate melt. As previously mentioned in references it can be assumed that the oxide scales formed on the alloy surface consist mainly of LiCrO₂ and LiFeO₂. The cathodic path of the corrosion process may be the reduction of CO₂ and/or CO₃ ^2–. The resistance of alloys against corrosion in melt increases with the increase of temperature. This may be due to the increase of concentration of O^2– and CO₂, enhancing both the anodic and cathodic reactions. The activation energy was calculated and found to be 91.496, 23.412 and 37.956 kJ/mol for the alloys 1, 2 and 3 respectively. The above mentioned techniques of measurements showed that the oxide scales of the austenitic stainless steel alloys (2, 3) are more passive and protective than of ferritic stainless steel alloy (1). This means that the resistance against corrosion, in the carbonate melts, of austenitic stainless steel alloys is higher than that of ferritic one.     

The effects of various hydrothermal treatments on magnesium-aluminium hydrotalcites

Mg/Al hydrotalcites were synthesised by coprecipitation followed by hydrothermal treatment. The materials were characterised by XRD, infrared and Raman spectroscopy, electron microscopy and thermal analysis. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO₃ ^2–, with a basal distance of 23.5 Å. All possible CO₃ ^2– modes were observed in the infrared and Raman spectra, at 1068 cm^–1, 844 cm^–1, 1380 cm^–1, and 680 cm^–1. XRD, Infrared and Raman spectroscopy complimented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity and that treatment in water rather than in the mother liquid resulted in a more crystalline material. TEM showed that crystal size increased with aging, such that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. Thermal analysis showed 3 major weight losses corresponding to the loss of interparticle water, interlayer water, and dehydroxylation of the hydroxide layers and decarbonation of the interlayer region.     

Electron Paramagnetic Resonance Spectra of Carbonate Centers in Natural Apatites

The EPR spectra of carbonate centers in apatites of different compositions are measured in the range 77–290 K. The results indicate that the F^– : OH^– ratio on the 6₃ axis and the state of constitutional water (H₂O molecules) determine vibronic interactions in the CO₂ ^–, CO₃ ^–, and CO₃ ^3– centers and the parameters of their EPR spectra. Depending on the molecular water and OH^– contents, the spectra of the carbonate centers are isotropic or anisotropic, due to the dynamic or static Jahn-Teller effect. Computer simulation is used to estimate the contributions of the centers to the EPR spectrum.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 585–591.Original Russian Text Copyright © 2005 by Gilinskaya.     

An infrared study of the structure of GeO2-CeO2 thin films

The infrared spectra of amorphous thin films consisting of GeO₂ co-evaporated with CeO₂ are presented and interpreted in relation to the spectrum of the pure amorphous GeO₂ film. The lower frequency side of the broad absorption band within this spectrum peaking at 730 cm^–1 is believed to be due to defect centres similar to the O ₁ ^– and O ₃ ⁺ centres found in a-SiO₂. Absorption at higher frequencies within this band is due to the O stretch vibrations of the Ge-O-Ge linkage. After considering the vibrations of the O ₁ ^– and O ₃ ⁺ centres in detail, it is shown that the band at 495 cm^–1 cannot be due to either of these centres and must therefore by caused by some other reactive defect centres. The variation of the position of the 730 cm^–1 peak within the series of spectra is noted and probable explanations are offered. The optical absorption edge of a-GeO₂ thin film is compared with that of a-SiO and a possible explanation of the basic differences is proposed.     

CO<Subscript>2</Subscript> Sorption during Mechanical Activation of Sodium and Calcium Aluminosilicates

Data are presented on CO₂ sorption by natural Na- and Ca-containing aluminosilicates (plagio-clases) during mechanical activation in an AGO-2 centrifugal planetary mill filled with CO₂. IR spectroscopy, chemical analysis, x-ray diffraction, and thermal analysis are used to determine the amount of absorbed CO₂ and to elucidate the mechanism of its incorporation into the aluminosilicates during grinding. The results, similar in a number of aspects to those reported for Ca- and Mg-containing silicates, lend support to the conclusion made earlier that CO₂ absorption by silicate minerals during mechanical activation and CO₂ dissolution in silicate melts have many features in common.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 566–572.Original Russian Text Copyright © 2005 by Kalinkin, Kalinkina, Zalkind, Makarov.     

Infrared spectra and composition dependence investigations of the vitreous V2O5/P2O5 system

A series of glasses in the V₂O₅-P₂O₅ system was prepared and their compositions analysed. The glass densities and molar volumes were determined. The results obtained revealed three compositional regions. In addition, the infrared absorption spectra of these glasses were measured at room temperature in the frequency range 1600–200 cm^–1. The compositional dependence of the bands present, attributed to a given band and mode of vibration, was investigated. However, the infrared data confirmed the results obtained from the density and molar volume measurements.     

Preparation and characterization of magnesium/carbonate co-substituted hydroxyapatites

A new synthesis/processing method has been devised to produce magnesium/carbonate co-substituted hydroxyapatite ceramics that do not decompose to tricalcium phosphate (TCP) on sintering. Using this method, a series of magnesium/carbonate co-substituted hydroxyapatite (Mg/CO₃–HA) compositions, containing between 0 and 0.35 wt % Mg and approximately 0.9 wt % CO₃ were prepared. Sintering the Mg/CO₃–HA compositions in a CO₂/H₂O atmosphere yields a single crystalline phase that appears to be identical to stoichiometric HA. In contrast, when the compositions were prepared in the absence of carbonate and were sintered in air, the phase composition was a biphasic mixture of HA and TCP e.g. for 0.25 wt % Mg substitution the phase composition was approximately 60%HA/40% TCP. Clearly, both the synthesis route and the processing (i.e. sintering) route are of importance in the production of a single-phase Mg/CO₃–HA ceramic. Fourier transform infrared (FTIR) spectroscopy has indicated that the Mg/CO₃–HA ceramics still contained carbonate groups after sintering at 1200 °C. Chemical analysis by X-ray fluorescence spectroscopy (XRF) and C–H–N analysis has shown that the cation/anion molar ratio (i.e. [Ca+Mg]/[P+C/2]) of the different compositions were 1.68(±0.01), which is equivalent to the Ca/P molar ratio of stoichiometric HA. Although the magnesium/carbonate co-substitution had a positive effect in preventing phase decomposition during sintering, it appeared to have a negative effect on the densification of the MgCO₃–HA ceramics, compared to stoichiometric HA.     

Infrared and Structural Properties of Y1?xNdxBa2Cu3O7?δ (0 ≤ x ≤ 1)

Infrared and structural properties of Y_1–x Nd _x Ba₂Cu₃O_7– (0 x 1) were investigated using infrared absorption spectroscopy and X-ray powder diffraction. The unit cell parameters of the samples were defined using X-ray diffraction data. The resistance measurements showed that the samples revealed superconductivity in the temperature range of 80–100 K. It was observed that by the substitution of Nd to Y in YBa₂Cu₃O_{7 –} IR band at 573 cm^–1 that is assigned as Cu–O axial antisymmetric stretching mode shifts to 533 cm^–1 while the band at 620 cm^–1 that is due to Cu–O symmetric stretching mode in YBa₂Cu₃O_7– shifts to 588 cm^–1.     

FTIR investigation of structural modifications during low-temperature ageing of polycarbonate

Conformational changes are sought during low-temperature ageing of solution-cast films of BPA-polycarbonate, by observing the conformationally sensitive IR aromatic breathing band at 1600 cm^–1. Preliminary results using the carbonyl band at 1775 cm^–1 had shown some indication of ageing-induced changes in the distribution of conformations. The present results obtained on the 1600 cm^–1 band show no indication whatever of conformational rearrangements. This result, at variance with observations of conformational rearrangements accompanying sub-T _g annealing, lends support to the concept that sub-T _g annealing and low temperature ageing are two distinct processes.     

Solubilities of Carbon Dioxide in Aqueous Potassium Carbonate Solutions Mixed with Physical Solvents

The solubilities of carbon dioxide in aqueous potassium carbonate (K₂CO₃) solutions mixed with physical solvents were measured at 298.2 and 323.2 K with a CO₂ partial-pressure range of 5 kPa to 2 MPa. 1,2-propanediol and propylene carbonate were selected as physical solvents. The aqueous solutions treated in this study were 5 mass% K₂CO₃–15 mass% 1,2-propanediol, 5 mass% K₂CO₃–30 mass% 1,2-propanediol, 5 mass% K₂CO₃–7.5 mass% propylene carbonate, and 5 mass% K₂CO₃–15 mass% propylene carbonate. The experimental solubility results were presented by the mole ratio of CO₂ and K₂CO₃ contained in the liquid mixture. The addition of 1,2-propanediol to 5 mass% K₂CO₃ solution lowered the solubility of CO₂ at constant temperature and pressure conditions within the CO₂ partial-pressure range of 5 kPa to 2 MPa. In the case of propylene carbonate, the addition of propylene carbonate increased the experimental solubilities in the region of low CO₂ partial pressures and decreased as the CO₂ partial pressure was increased above atmospheric. The solubilities of CO₂ decreased with increasing temperature in the range of 298.2 to 323.2 K.     

Behavior of Np(VII,VI, V) in silicate solutions

Properties of Np(VII, VI, V) in silicate solutions were studied spectrophotometrically. In noncomplexing media, the Np(VII) cation transforms into the anionic species at pH 5.5–7.5. In the presence of carbonate ions, this rearrangement occurs at pH 10–11.5, and in silicate solutions, at pH 10.5–12.0. These data show that Np(VII) cation forms complexes with carbonate and silicate ions, the latter being stronger. From the competitive reactions of Np(VI) complex formation with carbonate and silicate ions, the stability of NpO₂SiO₃ complex was estimated (log = 16.5) using the known stability constant of NpO₂(CO₃) ₃ ^4– . Complexation of Np(V) with SiO ₃ ^2– ions was not detected by the methods used.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 527–530.Original Russian Text Copyright © 2004 by Shilov, Fedoseev, Yusov, Delegard.     

Raman microscopy study of basic aluminum sulfate Part II Raman microscopy at 77 K

The tridecameric aluminum polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate the tridecamer crystallised as the monoclinic basic aluminum sulfate Na_0.1[AlO₄Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)_3.55. These crystals have been studied using Raman microscopy at 300 and 77 K and compared to Na₂SO₄·xH₂O and Al₂(SO₄)₃·xH₂O. The Raman spectrum of basic aluminum sulfate is dominated by two broad bands, which are assigned to the ₂ and ₄SO₄ ^2– triplets at 446, 459 and 496 cm^–1 and 572, 614 and 630 cm^–1. The ₁ is observed as a single band at 990 cm^–1, partly overlapped by the ₃ triplet at 979, 1009 and 1053 cm^–1 of the sulfate group in the Al₁₃ sulfate structure. Furthermore the band at 726 cm^–1 is assigned to an Al–O mode of the polymerised Al–O–Al bonds in the Al₁₃ Keggin structure. For the first time the OH-stretching region of the basic aluminum sulfate has been reported. The 77 K spectrum shows the presence of 3 crystal water bands at 3035, 3138 and 3256 cm^–1 accompanied by 3 Al–H₂O bands at 3354, 3418 and 3498 cm^–1 and 4 Al-OH bands at 3533, 3584, 3671 and 3697 cm^–1.     

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1–x)P₂O₅ vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO ₄ ^3– and P₂O ₇ ^4– , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH₄H₂PO₄ by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P₂O₅, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm^–1, assigned to the bending and stretching modes in H₂O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1–x)P₂O₅ system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm^–1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb²⁺ takes place. The ionic character of the phosphate groups, P-O^(–), PO ₄ ^3– is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm^–1 respectively. The maximum intensity of the P-O^(–) band at 1120 cm^–1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO ₄ ^3– , P₂O ₆ ^2– and P₂O ₇ ^4– for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm^–1 region attributed to the v₃-mode in PO ₄ ^3– , suggests a gradual transformation of PO ₄ ^3– units to PO ₃ ^– groups in lead meta-phosphate glass and then their restoration to PO ₄ ^3– groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O^(–), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.     

Poly(ethylene glycol) interactions with alumina and silica powders determined via DRIFT

Diffuse reflection infrared spectroscopy (DRIFT) is used to determine interfacial interactions between poly(ethylene glycol) (PEG), alumina and silica powders. The interactions are created by grafting in high temperature and low moisture environments due to preferential adsorption between PEG and water. Under these grafting conditions, a shoulder appears on the C–O–C stretching band of the DRIFT spectrum. This is found to occur when PEG is in the presence of a hydrogen donor such as surface hydroxyls on alumina and silica. The shoulder is reported as an interaction band due to hydrogen bonding between the PEG etheric oxygen and the surface hydroxyls of alumina and silica. Specific band positions are measured when the PEG chain is interacting with alumina (1090 cm^–1), silica (1080 cm^–1), or water (1085 cm^–1).     

Investigation of Doped Inert Gas Solids for Cryogenic Lasers

Inert gas polycrystalline samples containing about 0.05–0.5% of dopants such as neutral excimers XeF, KrF, NeF, and ionic excimers Rb²⁺F^–, Cs²⁺F^–, Cs²⁺Cl^–, and also molecules CO-Hg, NO, N₂O and ¹³CO₂ are considered as active media for cryogenic lasers emitting in a broad wavelength range from VUV through VIS into far IR. A correlation between the values of the oscillator strength f in the range of 0.4–10^–6, the cross section for stimulated emission between 10^–15–10^–17 cm² and the pump energy density at laser threshold (10^–3–10^–2 J/cm³) confirms the lasing potential of the systems XeF/Ar (B-X, 411 nm) and of those emitting in IR in agreement with experiment. For the deep UV and VUV transitions B-X of alkalihalides in solid Ne (196.5 nm, 220.1 nm, 136 nm) high pumping thresholds are derived despite of high f values because of large line width.