Valence Variation Research Articles

The mechanism for the colour change of iron chromium black pigments in glazes through transmission electron microscopy techniques

Black iron–chromium (Fe–Cr) bearing oxide pigments are generally utilised as effective colourants in a wide variety of applications. However, in the case of their use within ZnO-containing glazes, they yield an undesirable brown colour instead of expected black colour. In order to understand the colour change in this system, we report the use of focused ion beam (FIB) sample preparation technique followed by the use of analytical transmission electron microscopy (TEM) characterisation techniques. According to the results, the formation of a reaction layer between the pigment and glaze was identified with an average composition of Zn 0.48Fe 0.79Cr 1.32O 4. Additionally, the valance of Fe was determined as 3+ in the pigment grain, whereas 2+ in the reaction layer and the glaze, respectively. Therefore, it was concluded that the colour change is occurring as result of the valence variation of Fe, the formation of Zn 0.48Fe 0.79Cr 1.32O 4 compound and the outward diffusion of Fe into the glaze.

Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts

Research Article| January 01, 2011 Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts Clive Oppenheimer; Clive Oppenheimer 1Le Studium, Institute for Advanced Studies, Orléans and Tours, France2Centre National de la Recherche Scientifique-Institut National des Sciences de, l’Univers, Université d’Orléans, Université François Rabelais de Tours, Institut des Sciences de la Terre d’Orléans, 1a rue de la Férollerie, Orléans 45071, France3Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, United Kingdom Search for other works by this author on: GSW Google Scholar Bruno Scaillet; Bruno Scaillet 2Centre National de la Recherche Scientifique-Institut National des Sciences de, l’Univers, Université d’Orléans, Université François Rabelais de Tours, Institut des Sciences de la Terre d’Orléans, 1a rue de la Férollerie, Orléans 45071, France Search for other works by this author on: GSW Google Scholar Robert S. Martin Robert S. Martin 4School of Biological and Chemical Sciences, Queen Mary, University of London, United Kingdom, co200@cam.ac.uk Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2011) 73 (1): 363–421. https://doi.org/10.2138/rmg.2011.73.13 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Clive Oppenheimer, Bruno Scaillet, Robert S. Martin; Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts. Reviews in Mineralogy and Geochemistry 2011;; 73 (1): 363–421. doi: https://doi.org/10.2138/rmg.2011.73.13 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Despite its relatively minor abundance in magmas (compared with H2O and CO2), sulfur degassing from volcanoes is of tremendous significance. It can exert substantial influence on magmatic evolution (potentially capable of triggering eruptions); represents one of the most convenient opportunities for volcano monitoring and hazard assessment; and can result in major impacts on the atmosphere, climate and terrestrial ecosystems at a range of spatial and temporal scales. The complex behavior of sulfur in magmas owes much to its multiple valence states (−II, 0, IV, VI), speciation (e.g., S2, H2S, SO2,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Molecular Alloys: Experimental and Theoretical Investigations on the Substitution of Zinc by Cadmium and Mercury in the Homologous Series [Mo(M′R)12] and [M(M′R)8] (M=Pd, Pt; M′=Zn, Cd, Hg)

The synthesis and structural characterization of novel, metal-rich, highly coordinated compounds [Mo(M'R)(12)] and [M(M'R)(8)] (M: Pd, Pt, Mo; M': Zn, Cd; R: Me=CH(3), Cp*=pentamethylcyclopentadienyl) are reported. Additionally, a description of the bonding situation of the new compounds by means of quantum-chemical calculations is presented including the Hg analogues. Reaction of [Pt(GaCp*)(4)] with CdMe(2) results in the formation of the unprecedented all-Cd coordinated [Pt(CdMe)(4)(CdCp*)(4)] (1). Similarly, the treatment of the all-Zn coordinated [Pd(ZnMe)(4)(ZnCp*)(4)] with CdMe(2) affords the novel Zn/Cd mixed compound [Pd(CdMe)(4)(ZnCp*)(4)] (2). The related Zn/Cd mixed compound [Mo(ZnCp*)(3)(CdMe)(9)] (3) is prepared by reaction of [Mo(ZnCp*)(4)(GaMe)(4)] with an excess amount of CdMe(2). All compounds were analyzed by (1)H and (13)C NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The bonding situation of these highly coordinated, metal-rich molecules 1-3 were studied by quantum-chemical calculations using density functional theory (DFT) at the BP86/TZ2P+ level, atoms-in-molecules (AIM) analysis, and energy-decomposition analysis (EDA), as well as the its natural orbitals for chemical valence variation (EDA-NOCV) and including the hypothetically all-Hg-coordinated analogues. The results point out that the radial interactions M-M' in the icosahedral compounds that have twelve ligands are best described as classical electron-pair-sharing covalent bonds, whereas the dodecahedral species, which have eight ligands, exhibit metal-ligand donor-acceptor bonds. The attractive interactions between the metal-ligand fragments M'R by means of M'-M' bonds are weaker but not insignificant. All complexes fulfill the 18-electron rule. The analysis clarifies the electronic structures as being distinctly different from typical endohedral clusters M@(M''R)(n) that exhibit strong peripheral M''-M'' interactions: The M'-M' bonds are not strong enough to yield stable (M'R)(n) cages.

Influence of the tetravalent cation on the high-voltage electrochemical activity of LiNi 0.5M 1.5O 4 spinel cathode materials

The electrochemical properties of substituted LiNi 0.5Mn 1.5− x M x O 4 spinels at high potential (>4 V vs Li +/Li) have been investigated for M = Ti and Ru, in order to determine the role of the tetravalent cation in such systems where nickel is a priori the only electroactive species. These systems are found to form extended solid solutions (up to x = 1.3 and x = 1.0 for Ti and Ru, respectively) that were characterized by X-ray diffraction and Raman spectroscopy. Titanium substitution induces a drastic decrease in high potential electrochemical capacity, whereas the capacity is maintained and the kinetics are even improved in the presence of ruthenium. These results are completed by new results on the Li 4−2 x Ni 3 x Ti 5− x O 12 spinel system, which shows not any high potential activity in spite of the presence of up to 0.5 Ni 2+ per spinel formula unit on the octahedral site. Taking into account previous data on LiNi 0.5Ge 1.5O 4, we clearly show that even if the tetravalent cation does not participate in the overall redox reaction, electrochemical activity is only possible when nickel is surrounded by tetravalent cations able to accept a local variation of valence (Mn, Ru), whereas full-shell cations such as Ti 4+ and Ge 4+ block the necessary electron transfer pathways in the spinel oxide electrode.

Temperature and pressure-induced valence transitions inYbNi2Ge2andYbPd2Si2

We have measured the temperature and pressure-induced Yb valence transitions in tetragonal ${\text{YbNi}}_{2}{\text{Ge}}_{2}$ and ${\text{YbPd}}_{2}{\text{Si}}_{2}$ using x-ray absorption spectroscopy in the partial fluorescence yield mode and resonant x-ray emission spectroscopy. A temperature dependence of the Yb valence on the order of 0.1 has been measured, consistent with the magnetic-susceptibility study. The crossover from the low-temperature state having a stronger mixed valence to a high-temperature local moment behavior is analyzed within the Anderson impurity model. Pressure-induced second-order valence transitions are observed for both compounds with a more gradual transition in ${\text{YbPd}}_{2}{\text{Si}}_{2}$ than that of ${\text{YbNi}}_{2}{\text{Ge}}_{2}$. The mean valences are slightly less than $3+$ at ambient pressure but increase with applying pressure. Small variations in the Yb valence on the order of 0.03--0.05 can result in drastic change in the physical properties such as magnetic order and transport properties. Our results show that the Yb valence is noninteger around the quantum critical point.

Valence variation of arsenic in bioleaching process of arsenic-bearing gold ore

The concentration and variational trend of As 3+ and As 5+, the bacterial resistance for the As 3+ and As 5+ and converting conditions from As 3+ to As 5+ were analyzed. The additive was used to prompt the bacterial leaching efficiency by changing valence state of arsenic. The results show that the concentration of As 3+ is larger than that of As 5+ in the lag phase. The concentration of As 3+ decreases in the log phase, and is lower than that of As 5+. HQ-0211 typed bacteria express better resistance for As 3+ and As 5+ and remain growing when the concentrations of As 3+ and As 5+ are above 6.0 g/L and 12.0 g/L, respectively. It is found that Fe 3+ cannot oxidize As 3+ singly as strong oxidant in the leaching system, but can cooperate with pyrite or chalcopyrite to do that. The oxidation of As 3+ is prompted with addition of H 2O 2. The bacterial activity is improved in favor of bacterial leaching efficiency. NaClO restrains the bacterial growth to depress leaching efficiency because of the chloric compounds affecting bacterial activity.

Electrical properties changes induced by electron radiation at TiO2/Si interface

TiO2/Si structures were fabricated by electron beam evaporation, and exposed to electron beam irradiation to investigate their electrical properties using the high frequency capacitance–voltage measurements. It was found that samples annealed in oxygen became more radiation resistant than un-annealed samples, which can be explained by the Ti valence variations induced by radiation. The samples were characterized by X-ray diffraction to show the Ti2O3 crystalline phase transformed to anatase-crystalline phase after oxygen annealing.

The study of the oscillatory behavior during methane oxidation over Pd catalysts

The application of the thermogravimetric analysis (TGA) combined with on-line mass-spectrometry of the effluent gas mixture and temperature-programed oxidation (TPO) experiments allowed to demonstrate that significant variation of the carbon content in Pd catalysts occurred during the oscillatory methane oxidation. Together with the visual observation of the color changes due to the periodic variation of the Pd valence, these data indicate a very complicated mechanism associated with the oscillatory behavior, where both Pd oxidation–reduction processes and carbon deposition-removal play a crucial role. Depending on the phase of the oscillatory cycle, three states of metallic Pd with different reactivities were revealed: highly active, freshly reduced, metallic Pd; moderately active metallic Pd modified by carbon; and poorly active metallic Pd with adsorbed oxygen. It was found that hundreds of carbon monolayers could be periodically accumulated in the Pd powder catalyst during the oscillatory cycle. The accumulation of carbon on the Pd catalyst was the reason for the antiphase oscillations of the reaction products CO 2 and H 2O.

Annealing and oxidation study of Mo–Ru hard coatings on tungsten carbide

As a protective hard coating on glass molding dies, Mo–Ru coatings were fabricated on binderless tungsten carbide substrates by RF magnetron sputtering. The Mo–Ru deposits were deposited at 550 °C, which revealed a columnar structure with a major axis perpendicular to the substrate. To evaluate the performance of hard coating in a realistic glass molding environment, the annealing effect was studied by heating the samples at 600 °C under the atmosphere constructed with a steady flow of nitrogen and controlled oxygen content of 12 ppm. The oxygen was absorbed into the Mo–Ru deposits, which affected the phase stability and mechanical properties. The Auger electron spectroscopy depth profiles certified the difference of oxidation resistance between Mo-rich and Ru-rich deposits. The X-ray photoelectron spectroscopy proved the valence variation of Mo in the near surface, accompanied by the introduction of oxygen ions. A scale of MoO 3 and a Mo-depleted transition zone near the surface were pointed out by the transmission electron microscopy investigation on the Mo-rich deposit. On the other hand, the Ru-rich deposits absorbed oxygen in a less content and behaved higher hardness after annealing in the glass molding atmosphere, and became an appropriate protective coating for the die material.

Electrochemical characterizations on MnO2 supercapacitors with potassium polyacrylate and potassium polyacrylate-co-polyacrylamide gel polymer electrolytes

MnO2·nH2O supercapacitors with potassium polyacrylate (PAAK) and potassium polyacrylate-co-polyacrylamide (PAAK-co-PAAM) gel polymer electrolytes (GPEs) having the weight compositions of polymer:KCl:H2O = 9%:6.7%:84.3% have been characterized for their electrochemical performance. Compared with the liquid electrolyte (LE) counterpart, the GPE cells exhibit remarkable (∼50–130%) enhancement in specific capacitance of the oxide electrode, and the extent of the enhancement increases with increasing amount of the carboxylate groups in the polymers as well as with increasing oxide/electrolyte interfacial area. In situ X-ray absorption near-edge structure (XANES) analysis indicates that the oxide electrodes of the GPE cells possess higher Mn-ion valences and are subjected to greater extent of valence variation than that of the LE cell upon charging/discharging over the same potential range. Copolymerization of PAAK with PAAM greatly improves the cycling stability of the MnO2·nH2O electrode, and the improvement is attributable to the alkaline nature of the amino groups. Both GPEs exhibit ionic conductivities greater than 1.0 × 10−1 S cm−1 and are promising for high-rate applications.

Effects of the Counter Ion Valency on the Colloidal Interaction between Two Cylindrical Particles

In this study, the effects of counter ion valency of the electrolyte on the colloidal repulsion between two parallel cylindrical particles were investigated. Electrostatic interactions of the cylindrical particles were calculated with the variation of counter ion valency. To calculate the electrical repulsive energy working between these two cylindrical particles, Derjaguin approximation was applied. The electrostatic potential profiles were obtained numerically by solving nonlinear Poission-Boltzmann (P-B) equation and calculating middle point potential and repulsive energy working between interacting surfaces. The electrical potential and repulsive energy were influenced by counter ion valency, Debye length, and surface potential. The potential profile and middle point potential decayed with the counter ion valency due to the promoted shielding of electrical charge. On the while, the repulsive energy increased with the counter ion valency at a short separation distance. These behaviors of electrostatic interaction agreed with previous results on planar or spherical surfaces.

Effects of water intercalation in NaxCoO2·yH2O

Water intercalation is necessary for the occurrence of superconductivity in NaxCoO2 · yH2O. It is known that water insertion leads to the elongation of the c-axis. Beyond that, it remains controversial about the effects of water intercalation on the electronic structure of NaxCoO2 · yH2O. In this paper, we report the Co-K edge spectroscopy on y=0.7 and 1.4 samples, respectively. The spectra are compared with those of the reference samples. It is found that the variation of the Co valence can not be explained by the simple electron counting. These results are consistent with those of the previous chemical titration.

Thin Water Layers on CaCO3 Particles Dispersed in Oil with Added Salts

We report an investigation of the presence of thin water layers on calcium carbonate particles dispersed in cyclohexane using small-angle neutron scattering. We identify an adsorbed water layer and measure the thickness using contrast variation to optimize the sensitivity of the scattering to the water. We also report the variation in thickness of these water layers in the presence of salt solutions with the variation of salt concentration and valency. We conclude that thin water layers can be observed using SANS; however, the layers are thin and correspond to essentially the hydration of the particle surfaces.

Impact of disorder on ionic charge in spinel compounds

In order to obtain a correlation between the ionic charge and the local environment, the evolution of valence charges of cations in different 2–3 spinel compounds was investigated as a function of the temperature. The evolution of the structural parameters in normal (MgAl2O4), mixed (MgGa2O4) and inverse (MgIn2O4) spinels as a function of the temperature was extracted from X-ray diffraction patterns collected during different thermal annealings. The evolution of these structural parameters as a function of the disorder is analyzed within the bond valence shell model: large variations of the cation valence are observed in these three spinel compounds. From this analysis, a strong correlation between the change of the cation valence and the local disorder is pointed out. Including this dependence in the microscopic models may provide a better agreement between experimental observations and simulations.

Thermal variation of Ce valence in mixed valence–Kondo lattice systems CeT 2(Si 1−xGe x) 2 with T=Mn and Ni

The results on the thermal variation of Ce L 3-valence in CeT 2(Si 1− x Ge x ) 2 series with 0⩽ x⩽1 and T=Mn and Ni are reported. It is observed that for both series, the Ce valence increases with decreasing temperature and has little thermal variation for samples in the nearly trivalent regime. The magnitude of this thermal variation in the T=Mn series is much greater than in the T=Ni series. The results are explained by the degenerate Anderson model and correlated with the specific heat data.

Design and synthesis of novel multivalent mannosides targeting the mannose receptor

According to the characteristics of C-type lectin-like domains in the mannose receptor (MR), a novel design of multivalent mannosides targeting the MR was accomplished. Beginning with a divalent mannoside as the sugar unit, a series of multivalent mannosides with variations in both valence and space were synthesized in a convergent approach. The synthetic multivalent mannosides are to be explored to study MR–sugar binding events.

EELS Spectrum Imaging Studies of Boron K-edge and Ce Valence Variations in Alkali Borosilicate glasses

EELS Spectrum Imaging Studies of Boron K-edge and Ce Valence Variations in Alkali Borosilicate glasses

The role of pleasant music in servicescapes: A test of the dual model of environmental perception

This article explores the psychological processes by which background music in servicescapes influences service evaluation and purchase intention. Drawing on the dual model of environmental perception, it is hypothesized that: (1) servicescape is perceived in an ambient holistic manner and serves as the background for perceptions of the provider and thereby has direct and provider-mediated effects on outcomes; (2) the presence of music influences outcomes because it reinforces the holistic quality of the servicescape, makes the provider stand out, and moderates the contribution of provider-mediated servicescape effects; (3) when pleasant music is present, a double-mediating process fully accounts for the impact of variations in the music valence, such that music valence gets transferred into servicescape attitude, which then exercises direct and provider-mediated effects on service outcomes. Two experimental studies in real and online environments support the above research hypotheses.

Collapse of antiferromagnetism induced by Ni-substitution in Eu [formula omitted

To clarify anomalous behaviour under high pressure in the antiferromagnet EuPt 2 Si 2 ( T N = 15 K ) , effects of substitution of Ni for Pt in EuPt 2 Si 2 are investigated. Eu ( Pt 1 - x Ni x ) 2 Si 2 is of single phase in the concentration range of 0 ⩽ x ⩽ 0.25 with preserving the identical crystal structure. The Ni-substitution decreases the lattice volume and the Néel temperature T N . For x ⩾ 0.20 the antiferromagnetism is collapsed completely. These phenomena correspond well to the behaviour under high pressure in EuPt 2 Si 2 and are associated with Eu valence variation toward a nonmagnetic trivalent direction.

Physical origin of coloration and radiation hardness of lead tungstate scintillation crystals

The prevailing role of defect clusters, WO 3− x , of variable composition in the coloration of scintillation crystals PbWO 4 (PWO) and mechanisms underlying this process are revealed. Comparative studies of the influence of irradiation and reductive annealing on the optical properties of the material show that both treatments cause variation of tungsten valency in the WO 3− x clusters that results in a variation of the optical absorption spectrum and, consequently, in the color of the entire PWO crystal. Irradiation causes reversible redistribution of electrons inside the cluster, while the reductive annealing initiates migration of oxygen atoms out of the crystal which makes the coloration unrecoverable. The negative influence of intentionally introduced variable-valency element (niobium) on the radiation hardness as well as possibilities for improvement of the radiation hardness by growth optimization based on the model proposed are demonstrated.