Raman spectroscopic studies on the sulfation of cerium oxide

In the present study, we have examined sulfation of cerium oxide via impregnation of (NH₄)₂SO₄, followed by heating in the temperature range of 220–720°C, using Raman Spectroscopy. Based on the SO and SO stretching frequencies in the range of 900–1400 cm⁻¹, a wide range of surface oxysulfur species and bulk cerium-oxy-sulfur species are identified. At 220°C, a mixture of (NH₄)₂SO₄ crystals, SO²⁻_4(aq) and HSO¹⁻_r(aq) is found to have formed on ceria's surface, whereas complete conversion of (NH₄)₂SO₄ to SO²⁻_4(aq) and HSO¹⁻_4(aq) occurs at 280°C. At 350°C, formation of a mixture of surface pyrosulfate S₂O²⁻_7(surf.0, consisting of two SO oscillators and a bulk type compound identified as Ce(IV)(SO₄)_x(SO₃)_2−x (0 < x < 2) have been observed. Upon introduction of moisture, the former transforms to HSO¹⁻_4(surf.), whereas the latter remains unchanged. At 400°C, only the bulk type compound can be observed. At 450°C, only Ce₂(SO₄)₃ is generated and remains stable until 650°C. Further increase in the temperature to 720°C results in the formation of CeOSO₄. The present study not only provides a more thorough understanding of the sulfation of cerium oxide at a molecular level, but also demonstrates that Raman spectroscopy is a highly effective technique to characterize sulfation of metal oxides.     

Mechanism of steel corrosion in concentrated NaOH solutions

A study has been made of the mechanism of corrosion of carbon steel in 1–19 N NaOH at 25–80°C. The polarization curves were obtained with a rotating steel disk electrode, and the rotating ring-hemisphere electrode technique was used to identify soluble corrosion products. It was found that at the active anodic dissolution potentials, steel dissolves to form HFeO⁻₂ ions. Both the anodic and cathodic polarization curves exhibited a well defined Tafel regime, and the electrokinetic parameters were obtained for the corrosion of steel. The results were interpreted with a corrosion mechanism based on the decomposition of molecular water to hydrogen at the cathodic sites, and the active dissolution of iron to HFeO⁻₂ ions via two adsorbed intermediates, FeOH_ads and Fe(OH)_2,ads, at the anodic sites. The theoretically derived anodic Tafel slope, anodic reaction order, corrosion potential, and corrosion current density agreed quantitatively with the experimental values. At the potentials above the anodic Tafel regime and in the neighborhood of the active—passive transition potential, steel dissolved to form both the bi-valent and tri-valent iron species, HFeO⁻₂ and FeO⁻₂ ions. The thermodynamic considerations revealed that FeO⁻₂ ion was formed from the oxidation of Fe(OH)_2,ads intermediate, rather than from the oxidation of HFeO⁻₂ ion on steel surface.     

Highly thiocyanate-selective membrane electrodes based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex as a neutral carrier

Some novel PVC membrane electrodes based on N,N′-bis-(benzaldehyde)-glycine metallic complexes of Cu(II), Ni(II), Zn(II) and Co(II) as neutral carriers are described. The results showed that the electrode based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex [Cu(II)-BBAG] had a near-Nernstian response to the thiocyanate ion ranging from 1.0×10⁻¹ to 9.0×10⁻⁷ M in a phosphate buffer solution of pH 4.0 with a detection limit of 7.0×10⁻⁷ M and a slope of −57.6 mV/decade at 25°C. The electrode displays an anti-Hofmeister selectivity sequence in the following order: SCN⁻>ClO⁻₄>Sal⁻>I⁻>Br⁻>NO⁻₂>NO⁻₃>SO²⁻₃>SO²⁻₄>Cl⁻>H₂PO The response mechanism is discussed in view of both AC impedance and UV spectroscopy techniques. The [Cu(II)-BBAG]-based electrode was successfully applied to the determination of the thiocyanate ion in wastewater and human saliva.     

Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

Infrared spectroscopy of carbonyl species in oxidised diesel distillates

The extent of molar carbonyl group formation in some diesel distillates has been shown, using semiquantitative infrared difference spectroscopy, to differ by about an order of magnitude for three different fuel aging conditions (100 °C/168 h/O₂ atmosphere: 95 °C/16 h/O₂ sparge; ambient storage ≈10⁻³: 10⁻⁴ 10⁻⁵ M). This may partly explain the known unreliability of accelerated oxidation techniques for predicting fuel storage stability. It has also been shown that C=O species present in steam-jet gum residues do not represent those in oxidised fuels prior to evaporation.     

The conductivity of hydrochloric acid in water—sulpholane mixtures at 35°C

Measurements are reported on the equivalent conductivity of dilute solutions of hydrochloric acid, at 35°C, in water—sulpholane mixtures over the entire solvent composition range. Data were analyzed by 1965 Fuoss-Onsager equations. A rapid decrease of anomalous proton mobility on adding sulpholane to water was observed. Ion pair association higher than expected was found in solvents of dielectric constant less than 61. In pure sulpholane a zero slope linear plot of −log Λ vs −log c was observed and related to the unilateral triple ion HCl⁻₂ formation. A first approximation value of hydrochloric acid dissociation constant which indicates that HCl is a very weak electrolyte in sulpholane, was calculated.     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia powder from sucrose derived organic precursors

An organic precursor synthesis of 8 mol% yttria stabilized zirconia (YSZ) powder from Zr–Y composite nitrate solution and sucrose has been studied. Oxidation of sucrose in Zr–Y composite nitrate solution containing excess nitric acid in situ generates hydroxy carboxylic acids that forms a white sol which showed peaks at 1640 cm⁻¹ and 1363 cm⁻¹ in IR spectrum corresponding to hydroxy carboxylic acid complexes of Zr and Y. Precursor mass obtained by drying the sol on calcinations at 600 °C produced loosely agglomerated particles of cubic YSZ. Deagglomerated YSZ contain submicron particles with D₅₀ value of 0.5 μm and the particles are aggregates of nanocrystallites of nearly 10 nm size. Compacts prepared by pressing the YSZ powder sintered to 96.7% TD at 1450 °C. The sintered YSZ ceramic showed an average grain size of 2.2 μm.     

Preparation of hollow alumina microspheres by microwave-induced plasma pyrolysis of atomized precursor solution

Hollow alumina microspheres have been prepared by microwave-induced (MI) plasma pyrolysis of atomized aerosols of precursor solutions and subsequent calcination at 1300 °C for 2 h. When an aqueous solution of 0.5 mol dm⁻³ Al(NO₃)₃ without any additives was used as a precursor, hollow -Al₂O₃ microspheres with a thick shell wall were prepared after post-calcination at 1300 °C. The addition of a polypropylene (PO)–polyethylene(EO) blockcopolymer (molecular weight: 2900–6500) to the precursor solution was effective for increasing the yield of hollow microspheres, but resulted in the formation of many cracks and holes in the thinned shell wall. Hollow alumina microspheres with a thin, but strong, shell layer could be prepared by the simultaneous addition of tetraethylorthosilicate.     

Preparation and sintering behaviour of ultrafine Mn/Fe and Fe/Co mixed oxides

Mn/Fe and Fe/Co mixed oxides with spinel structure were prepared by low-temperature (300–400°C) thermal decomposition of carbonate precursors. The oxide samples are cation-deficient phases with average oxidation state of the metal ions of ca. 3·0, and consist of fine particles (ca. 10 nm) which are single crystalline domains with few lattice distortions. Gas adsorption measurements reveal values of specific surface area between 30 and 120 m² g⁻¹ and the presence of an interparticle porous system. Pelletized aggregates of selected compositions sinter to almost theoretical densities at 1000°C and release oxygen excess from the spinel structure. The sintered pellets show little intergranular porosity.     

Monodispersed gold nanoparticles supported on γ-Al2O3 for enhancement of low-temperature catalytic oxidation of CO

Monodispersed nano-Au/γ-Al₂O₃ catalysts for low-temperature oxidation of CO have been prepared via a modified colloidal deposition route, which involves the deposition of dodecanethiolate self-assembled monolayer (SAM)-protected gold nanoparticles (C₁₂ nano-Au) in hexane on γ-Al₂O₃ at room temperature. The diameter of the gold nanoparticles deposited on the support is 2.5 ± 0.8 nm after thermal treatment, and their valence states comprise both the metallic and oxidized states. It is found that the thermal treatment temperature affects significantly the catalytic activity of the catalysts in the processing steps. The catalyst treated at 190 °C exhibits considerably higher activity as compared to catalysts treated at 165 and 250 °C. A 2.0-wt.% nano-Au/γ-Al₂O₃ catalyst treated at 190 °C for 15 h maintains the catalytic activity at nearly 100% CO oxidation for at least 800 h at 15 °C, at least 600 h at 0 °C, and even longer than 450 h at −5 °C. Evidently, the catalysts obtained using this preparation route show high catalytic activity, particularly at low temperatures, and a good long-term stability.     

Performance of La1−xSrxAl1−y−y′FeyMgy′O3−δ perovskites in methane combustion: effect of aluminum and magnesium content

Perovskites of different La_1−xSr_xAl_1−y−y′Fe_yMg_y′O_3−δ compositions (x=0, 0.1, 0.15, 0.2 and y=0.1, 0.3, 0.5, 0.8) were prepared from a reactive precursor slurry of hydrated oxides. Each sample was aged between 16 and 26 h up to 1473 K. Activity in methane combustion (1%/air) was determined in a plug-flow reactor, with 1 g catalyst and 24 l/h flowrate. Gradual decrease in activity due to thermal aging was observed, the degree of activity loss being composition dependent. Nevertheless, activity of samples aged at 1370 K was nearly independent of composition. The best thermal stability showed LaAl_0.65Fe_0.15Mg_0.2O₃ perovskite. None of the magnesium substituted perovskites performed better than a La_0.85Sr_0.15Al_0.87Fe_0.13O₃ reference sample.     

Naturally occurring 1.4 nm tobermorite and synthetic jennite: Characterization by Al and Si MASNMR spectroscopy and cation exchange properties

A naturally occurring 1.4 nm tobermorite and a synthetic jennite were characterized by ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy and their cation exchange properties were measured. ²⁷Al MASNMR spectroscopy revealed that both the 1.4 nm tobermorite and synthetic jennite contained trace quantities of Al in tetrahedral coordination. The 1.4 nm tobermorite also contained octahedrally coordinated Al probably due to the presence of an aluminum compound as a trace impurity. The ²⁹Si MASNMR spectrum of 1.4 nm tobermorite exhibited a strong resonance at −85.2 ppm and a small shoulder at −80 ppm which are attributed to chain middle groups (Q²) and end groups (disilicates) respectively. ²⁹Si MASNMR spectroscopy of the synthetic jennite showed a strong resonance at −85.7 ppm and a moderately strong resonance at −81.4 ppm which correspond to single chains and end groups respectively. Jennite showed a considerably larger quantity of end groups than the 1.4 nm tobermorite. The unsubstituted 1.4 nm tobermorite and synthetic jennite exhibited only small cation exchange capacities.     

Mechanism of the cathode process in the electrolytic boriding in molten salts

The mechanism of the cathode process in the electrolytic deposition of boron on a platinum electrode has been investigated in the systems LiF---KF---KBF₄ and LiF---KF---B₂O₃ by means of the voltametric and chronopotentiometric methods. It was found that in the system LiF---KF---KBF₄ boron is reduced directly from the tetrafluoroborate complex anion by a simple 3-electron process. In the system LiF---KF---B₂O₃ boron oxide reacts with the basic fluoride electrolyte under formation of the BF⁻₄ anion and of unspecified oxofluoro complex(es) with a mean oxygen to boron ratio of 1.66. The ratio of boron concentrations in the BF⁻₄ anion and in the oxofluoro complex(es) is about 0.1. The difference between the deposition potential of boron from those two electrochemically active species is about 0.47 V in favour of BF⁻₄. The value of the diffusion coefficient of the BF⁻₄ anion was found to be 4.4 × 10⁻⁹ m² s⁻¹ (700°C).     

The electrochemistry of tellurium in methylene chloride

It was found that TeCl₄ in methylene chloride (containing tetrabutylammonium perchlorate as a supporting electrolyte) is reduced to TeCl₂, Te⁰ and Te⁻² in potential applied. Two reduction waves are observed during the reduction of TeCl₄ at a platinum rde (Ep₁ = 0.08 ± 0.02 V, Ep₂ = −1.10 ± 0.02 V) due to the reduction of TeCl₄ to Te and Te⁻² respectively. A cathodic deposition of tellurium from TeCl₄ is followed by anodic stripping wave (Ep₁ = 0.42 ± 0.02 V), corresponding to the oxidation of Te to TeCl₂. It has been shown that reduction of TeCl₄, or TeCl⁻²₆ to Te causes coating of the electrode with metallic tellurium, on whose surface chloride ions are strongly bonded. It was found that when the electrolysis solution contains excess of chloride ion with respect to Te^IV the peak potentials of the cathodic waves shift to more cathodic values (Ep₁ = 0.30 ± 0.02 V, Ep₂ = −1.25 ± 0.02 V). After cathodic deposition of at least a monolayer of tellurium from such a solution two anodic waves appear (Ep₁ = 0.12 ± 0.03 V, Ep₂ = 0.24 ± 0.03 V) which are both due to the oxidation of Te to Te^II.     

Anodic reactions of several reducing agents on illuminated cadmium sulfide electrode

Anodic reactions of several reducing agents occurring in competition with the electrode dissolution at an illuminated CdS electrode were studied under the potentiostatic condition. S²⁻, SO²⁻₃, and S₂O²⁻₃ ions, which can effectively suppress the photoanodic dissolution of CdS, shift the flatband potential of this electrode to the cathodic direction, leading to the shift of the onset potential for the anodic photocurrent. This shift is attributed to the adsorption of these ions on the electrode surface. Two- or three-step wave appeared in the photoanodic polarization curves in the electrolytes containing low concentration of these ions. The mechanism for these electrodic reactions was discussed in detail in terms of the energy band structure. It can be concluded that the reducing agents which interact so strongly with the CdS electrode surface that the energy band structure at the electrode/electrolyte interface is changed can suppress effectively the photoanodic dissolution of the electrode. The tendency of this interaction was S²⁻ > SO²⁻₃ > S₂O²⁻₃.     

Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays

Supported vanadium-containing catalysts were prepared by impregnation of Al-pillared clays with NaVO₃ precursor aqueous solutions. A montmorillonite and a saponite, both natural as well as previously pillared with Al₁₃-Keggin polycations, were used as supports, being impregnated with solutions of the precursor by means of the incipient wetness technique. The layered structure of the supports is maintained after impregnation, and even after calcination of the impregnated solids at 500 °C, although with a significant worsening of the textural properties of the solids, in particular, a loss of specific surface area. Three crystalline vanadium-containing phases were identified in the impregnated solids, namely, NaV₃O₈, AlVO₄ and V₂O₅ (shcherbinaite). The reduction of these phases to V³⁺ species was observed as wide processes in the 450–750 °C range, all of them centred at ca. 600 °C.     

Effect of temperature on the structure and density of ammonium chloride particles

The structure and density of individual ammonium chloride particles formed at 0 and −20°C by homogeneous nucleation were studied using electron microscopy and X-ray diffraction. The crystal size apparently increased at the lower temperature and many of the particles formed at −20°C were single crystals or had an oriented polycrystalline structure. These results differ from those reported previously for particles formed at room temperature (23–26°C), which showed an amorphous or randomly-oriented fine crystal structure. Coagulation was more frequently observed as the temperature decreased and the porosity present in the particles appeared to be much finer and more uniform. The density of these particles decreased from about 0.26 g cm⁻³ for particles of size 0.1–0.2 μm to approximately 0.1 g cm⁻³ for particles slightly smaller than 1 μ.     

On the possibility of the application of a radiotracer method for the in situ study of the accumulation of ions in corrosion products adhered to the surface of some steels

The sorption of ³⁶Cl labelled Cl⁻ ions into the layer of corrosion products adhered to the surface of corroding powdered steel samples has been studied as a function of the time at 1.8 × 10⁻² NaCl concentration. The effect of CrO²⁻₄ and SO₂₋₄ ions on the sorption process and the mobility of sorbed species was investigated.     

Estimation of particle size distribution parameters in animal lungs

A constant of specific solubility of 2·5 × 10⁻⁸ g cm⁻²day⁻¹ was determined for fused aluminosilicate particles, by observing in vivo retention kinetics after intravenous injection into rats. Studies over the past years in this laboratory, in which dogs and rats have inhaled labeled aerosols of these particles, have shown retention half-lives in the lung of 460 and 285 days, respectively. By applying these values for solubility and half-life to Mercer's theory of dissolution from the deep lung, the initial distribution of particles deposited in the pulmonary regions of dogs and rats following inhalation was calculated. From an inhaled aerosol with a mass median diameter, D_m, of 1·0 μm and σ_o = 1·7, a distribution described by D_m = 0·51 μm and σ_o's ranging from 1·16–1·48 was estimated to have been deposited in the Beagle dog lung. and a D_m =< 0·32 μm and σ_o's ranging from 1·18–1·29 was similarly calculated for rats.     

Comportement electrochimique d''oxocarbones et d''aci-reductones en relation avec le transport d''electrons dans les processus biologiques—I: tetrahydroxyquinone et acide rhodizonique

The oxidation products of inositol:rhodizonic acid 1, tetrahydroxyquinone 2 and hexahydroxybenzene 3 have been studied in aqueous solution, using polarographic and coulometric techniques,

The ionic 1/2 and 2/3 couples form reversible redox systems. The 1/3 couple exchanges four electrons. The intermediate species 2⁻ disproportionates up to 50%.

The ^′°_1/2 and ^′°_2/3 values approach those of the vitamin K₁/dihydrovitamin K₁ system. They explain the catalytic action of these systems in the oxidation, by oxygen, of thiols to disulphides.