Concentrations Of V2O5 Research Articles

Photocatalytic destruction of Escherichia coli in water by V2O5/TiO2

Vanadia modified titania (V2O5/TiO2) photo-catalysts are prepared by incipient wet impregnation method using aqueous ammonium metavanadate and anatase (Aldrich) titania. Titania with various loading concentrations of vanadia from 0 to 10wt.% have been prepared and characterized by X-ray diffraction (XRD), Thermogravimetry (TGA), Laser Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), UV–Visible Spectrophotometry and Transmission Electron Microscopy (TEM). XRD study reveals that vanadia loading on titania does not bring any phase change of titania, however, diffuse (UV–Vis) reflectance spectra show that absorption edge of titania shifted from UV to visible region. TEM confirms that titania and vanadia modified titania have the particle size below 50nm. XPS shows alteration of 2p3/2 peak of V(V) in the V2O5/TiO2 samples whereas no such change is noticed in pure V2O5 indicating the interaction between vanadia and titania support. Antibacterial activity of each sample has been investigated against Escherichia coli present in the water under both UV–Visible irradiation and UV alone. V2O5/TiO2 catalysts exhibit better photocatalytic effect than the unmodified titania and pure V2O5. It is observed that with increasing loading concentrations of V2O5 from 0 to 10wt.% on titania support, the photocatalytic annihilation of E.coli is also increased and found to be little higher under UV alone than the UV–Visible irradiation.

Vanadium pentoxide prevents NK-92MI cell proliferation and IFNγ secretion through sustained JAK3 phosphorylation

Vanadium is a major air pollutant with toxic and carcinogenic effects; it also exercises immunosuppressive effects on the adaptive immune response. Its effect on the innate immune response is poorly explored. The aim of this study was to identify if vanadium pentoxide (V2O5) impairs the function of immunoregulatory NK cells and to determine possible mechanisms associated with this effect. Interleukin-2-independent NK-92MI cells were exposed to different V2O5 concentrations for 6, 12, or 24 h periods. Cell proliferation was then evaluated using CFSE staining, apoptosis by Annexin V binding, and necrosis by 7-AAD staining. The release of IL-2, -4, -6, -10, -17A, IFNγ, and TNFα by the cells were assessed using a human CBA kit. Expression of CD45, SOCS1, JAK3, pJAK3, STAT5, pSTAT5, IL-2R, IL-15R, Fas, and FasL in/on the cells was determined by flow cytometry; JAK3 and pJAK3 expression were also evaluated via confocal microscopy. The results indicated that V2O5 could inhibit NK-92MI cell proliferation and induce cell apoptosis in a dose- and time-related manner. V2O5 also inhibited IL-2, IL-10, and IFNγ secretion but mostly only after 24 h of exposure and with primarily the higher doses tested. V2O5 had no effect on expression of JAK3 and STAT5, but did cause an increase in pJAK3 and appeared to lead (trend) to reductions in levels of phosphorylated STAT5. V2O5 increased the expression of IL-2R, IL-15R, Fas, and FasL at concentrations above the 50–100 µM range. V2O5 had no effect on expression of the CD45 membrane phosphatase, but it did cause an increase in the expression of SOCS1. These results indicate that a key toxic effect of V2O5 on NK cells is a dysregulation of signaling pathways mediated by IL-2. These effects could help to explain the previously-reported deleterious effects on innate immune responses of hosts exposed to inhaled V2O5.

Composition dependence of the crystalline-to-amorphous phase transformation of vanadate compounds in the CdO–V2O5 binary system

By mixing different molar concentrations of V2O5 and CdO as reactants, and using the melt-quenching method, an evolution from crystalline vanadate compounds to amorphous materials was produced. For chemical compositions with high mol% of V2O5, crystalline phases with the sequence V2O5, CdV2O6, and Cd2V2O7 were synthesized. On the other hand, high mol% of CdO led to the formation of amorphous materials. The identification of the crystalline and amorphous phases was carried out by X-ray diffraction and Raman scattering experiments. From optical absorption data, the optical band gap was determined with values between 1.97 and 2.83eV. Dark conductivity measurements from room temperature to 450K were made for the whole set of samples. In all cases thermally activated transport was observed. By scanning electron microscopy, depending on the mol% of the reactants, different morphological structures for each crystalline and amorphous material were recorded.

Impact of vanadium ions in barium borate glass

Combined optical and infrared spectral measurements of prepared barium borate glasses containing different concentrations of V2O5 were carried out. Vanadium containing glasses exhibit extended UV–visible (UV/Vis.) bands when compared with base binary borate glass. UV/Vis. spectrum shows the presence of an unsymmetrical strong UV broad band centered at 214nm attributed to the presence of unavoidable trace iron impurities within the raw materials used for the preparation of such glass.The calculated direct and indirect optical band gaps are found to decrease with increasing the vanadium content (2.9:137 for indirect and 3.99:2.01 for direct transition). This change was discussed in terms of structural changes in the glass network. Infrared absorption spectra of the glasses reveal the appearance of both triangular and tetrahedral borate units. Electron spin resonance analyses indicate the presence of unpaired species in sufficient quantity to be identified and to confirm the spectral data.

Structural investigation of vanadium ions doped Li2O[sbnd]PbO[sbnd]B2O3[sbnd]P2O5 glasses by means of spectroscopic and dielectric studies

In the present investigation we report the synthesis of a series of transparent glasses of composition 20Li2O20PbO45B2O3(15−x) P2O5: xV2O5 with eight values of x ranging from 0 to 2.5mol%, and their characterization. X-ray diffraction (XRD) spectra reflected the amorphous nature of the glasses. Optical absorption, electron paramagnetic resonance (EPR) spectra and FTIR study of vanadyl ions in the present glass network have been analyzed. The optical absorption and EPR investigations have revealed that vanadium ions do exist in both V4+ and V5+ states and the redox ratio (V4+/V5+) is observed to increase with the increase in concentration of V2O5. Dielectric properties viz., dielectric constant ε′(ω), loss tanδ, electrical moduli M′(ω), M″(ω), a.c. conductivity σac over an extensive scale of frequency and temperature have been investigated as a function of V2O5 concentration. The dispersion of dielectric constant ε′(ω) with temperature has been interpreted by space charge polarization model. The dielectric loss and electrical moduli variation with frequency and temperature exhibited relaxation effects. These effects are ascribed to V4+ ions. The a.c. conductivity of the prepared glasses is perceived to escalate with the hike in V2O5 concentration whereas the activation energy for conduction exhibits a reverse trend. The conductivity mechanism is explained on the basis of polaronic transfer between V4+ and V5+ ions. The low temperature a.c. conductivity mechanism is elucidated by the quantum mechanical tunneling model. The growth in the values of dielectric parameters with raise in the concentration of V2O5 is due to V4+ ions which act as modifiers. The investigation of these results has indicated that at higher concentrations of V2O5, the VO2+ ions in the glasses were present in octahedral sites with tetragonal compression and belong to C4v symmetry.

Photoluminescence in Er-doped V2O5 and Er-doped CdV2O6

A group of samples from the CdO–V2O5 binary system, particularly with high V2O5 content, doped with Er3+ were prepared. The set of samples was fabricated using the conventional melt-quenching method. Depending on the proportion of the used reactants, the existence of V2O5 and of CdV2O6 was identified from X-ray diffraction measurements and Raman spectroscopy. Depending on the relative concentrations of CdO and V2O5, different types of morphologies for each sample were found in a scanning electron microscope. Their chemical composition was measured from energy dispersive spectroscopy in the same instrument. An effective Er-doping of the order of 1.0±0.35at% was found for each sample. From optical absorption data, the composition dependent optical band gap was determined with values between 1.94 and 2.29eV. Finally, photoluminescence experiments showed, in the samples with the highest V2O5 content, wide bands associated to oxygen vacancies. For the rest of the samples emissions from electronic transitions of Er3+ ions were detected.

Vanadium pentoxide: Risk assessment implications of a treatment- but not dose-related tumorigenic response in B6C3F1 mice

The US Environmental Protection Agency (USEPA) is currently conducting a toxicological review of vanadium pentoxide (V2O5). As part of that effort, the Agency will need to address the fact that while a National Toxicology Program (NTP) chronic inhalation bioassay of V2O5 produced clear evidence of treatment-related lung tumors in both male and female B6C3F1 mice, neither of these responses were dose-related across the groups exposed to 1, 2, and 4mg/m3. While lung tumor incidence was significantly elevated in all three exposed groups relative to that in the control groups, it was essentially flat across them. Herein we report results from computing poly-3-adjusted Cochran–Armitage trend test statistics with and without inclusion of the lung tumor incidence data from control group mice. These results confirm the absence of any significant dose-related effect on mouse lung tumor incidence in the study groups exposed to V2O5. We also considered two estimates of area under the vanadium lung burden versus time curve as plausible alternative dose metrics to the V2O5 chamber concentration. However, these alternative dose metrics were so highly correlated with the V2O5 chamber concentration (r=0.998) that nothing is to be gained from their use in place of the V2O5 chamber concentration in attempts to perform dose–response modeling of the tumor incidence or unit cancer risk computations. At the present time, there is no scientific basis to support linear (or nonlinear) extrapolations of estimated cancer risks to V2O5 exposure levels below 1mg/m3. Additional tumor data at multiple V2O5 concentrations lower than 1mg/m3 are required to support such extrapolations.

Conductivity and dielectric behavior of NaPO3–ZnO–V2O5 glasses

A series of zinc-phosphate glass containing different concentrations of V2O5 ((80−x) NaPO3+20 ZnO+x V2O5 (x=0–25mol%)) was prepared by melt quenching method and analyzed by differential scanning caloremetry (DSC) and impredance spectroscopy. The electrical properties of these samples were measured using ac impedance spectroscopy technique over a frequency range of 10Hz to 13MHz at several temperatures in the range of 323–673K.The ac conductivity, dc conductivity, dielectric constant and loss factors were obtained from these measurements. Constant-phase elements (CPE) are used in equivalent electrical circuits for the fitting of experimental impedance data.The impedance spectra have also indicated that the conduction is predominantly polaronic in nature. The frequency and temperature dependence of the electrical modulis as well as dielectric loss parameters have exhibited a relaxation character attributed to the vanadyl complexes.The relaxation effects have been analyzed by the graphical method. From this analysis, it has been established that there is a spread of relaxation times. The results have been further discussed quantitatively in the light of different valance states of vanadium ions with the aid of the data on spectroscopic properties.The frequency dependence of the electric conductivity was found to follow a simple power law behavior, in accordance with the relation σac(ω)=σ(0)+A1.ω1s+A2.ω2s, where s1 and s2 are smaller than 1. The thermal activation energies for the electronic conduction were estimated on the basis of the Arrhenius plots.

Expression of caspase-3, Bcl-2, and Bax in pentavalent vanadium-induced neuronal apoptosis

To investigate the expression of caspase-3, Bcl-2, and Bax in pentavalent vanadium-induced neuronal apoptosis and the neurotoxicity of pentavalent vanadium to in vitro cultured rat neurons. Neurons from rats were cultured in vitro and treated with different concentrations of V2O5. Neuronal apoptosis was evaluated by TdT-mediated dUTP-biotin nick end labeling (TUNEL). The expression of caspase-3, Bcl-2, and Bax in neurons was measured by Western blot. The images collected by gel imaging system and scanner were analyzed. The TUNEL showed that compared with the control group, the middle- and high-dose exposure groups had significantly increased apoptosis index (AI) of neurons (P < 0.05 or P < 0.01). The Western blot showed that compared with the control group, the middle- and high-dose exposure groups had significantly increased expression of caspase-3 and Bax and significantly decreased expression of Bcl-2 (P <0.05 or P < 0.01). The AI of neurons was positively correlated with the expression of caspase-3 and Bax (r = 0.943, P < 0.01; r = 0.937, P < 0.01) and negatively correlated with the expression of Bcl-2 (r = -0.908, P < 0.01). Pentavalent vanadium may induce neuronal apoptosis, and the expression of caspase-3, Bcl-2, and Bax, which regulate apoptosis, plays an important role in the neuronal apoptosis induced by pentavalent vanadium.

V2O5–polyimide hybrid material: synthesis, characterization, and sulfur removal properties in fuels

We describe the synthesis of a new sorbent material for desulfurization of gasoline, which is composed of polyimide (PI) and vanadium pentoxide via the solution direct-dispersing method. The highly porous PI–V2O5 hybrid materials, containing different concentrations of V2O5 ranging from 1 to 10 wt%, were prepared from pyromellitic dianhydride, 2,4,6-triaminopyrimidine, and vanadium pentoxide. The produced PI–V2O5 composites were investigated by X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscope, and thermal analysis techniques. The effect of V2O5 on the sulfur removal properties as well as the thermal stability and porous structure of composites were investigated. Then the obtained material was investigated to determine their sorption characteristics for sulfur compounds from fuels. By use of this material, 91 wt% of the sulfur content was removed from sulfur-containing standard oil. An economic sensitive and simple method for the removal and separation of sulfur in fuel samples, using an PI–V2O5 packed mini chromatographic column, was established.

Effect of V2O5 loading of V2O5/TiO2 catalysts prepared via CVC and impregnation methods on NOx removal

In this study, V2O5/CVC-TiO2 materials with different concentrations of V2O5 were prepared via chemical vapor condensation (CVC) and impregnation. The catalytic activities of these materials were tested and the physicochemical characteristics were analyzed using XRD, BET, FT-IR spectroscopy, XPS, HR-TEM, EDX mapping, H2-TPR, and NH3-TPD. The NOx removal efficiency of the V2O5/CVC-TiO2 catalysts was higher than that of the V2O5/P25-TiO2 catalysts and increased with increasing V2O5 concentration. At 200°C, the highest NOx conversion was observed using 7 and 10wt.% V2O5/CVC-TiO2 catalysts. The NOx conversion curve reached a plateau corresponding to the maximum conversion when the V2O5 content was greater than 7wt.%. The V2O5/CVC-TiO2 catalyst comprised mainly anatase-phase TiO2 and well-dispersed V2O5. A greater concentration of V (well-balanced V4+/V5+) species existed on the V2O5/CVC-TiO2 catalyst surface. H2-TPR and NH3-TPD testing confirmed that the V2O5/CVC-TiO2 catalyst is highly reducible and has many acidic sites.

THE UPPER ZONE OF THE BUSHVELD COMPLEX AT ROOSSENEKAL, SOUTH AFRICA: GEOCHEMICAL STRATIGRAPHY AND EVIDENCE OF MULTIPLE EPISODES OF MAGMA REPLENISHMENT

Drill core from a fence of five boreholes located in the vicinity of Roossenekal, in the eastern limb of the Bushveld Complex, South Africa, provides complete coverage of what is probably one of the thickest and most well-developed sections of the Upper Zone. The lowermost portions of the Rooiberg Group felsites that overlie the Upper Zone, and the uppermost portion of the Upper Main Zone, which forms the footwall, were also intersected. Field relationships from floor-attached domes (eastern limb) and gap areas (western limb) reveal a marked angular unconformity at the base of the Upper Zone. The Upper Zone represents a discrete intrusive event and should not be interpreted as a continuum, or the fractionated residue of the underlying components of the Rustenburg Layered Suite (RLS). A new subdivision of the Upper Zone into five subunits (A through E) is proposed on the basis of the cumulus mineralogy and whole-rock geochemistry, the latter based on samples at an average vertical spacing of 20 m throughout the column at Roossenekal. The separation of subzones A and B is based on our geochemical data, as is the identification of subzone E, but recognition of subzones C (olivine) and D (apatite) is broadly consistent with the detailed mapping and stratigraphic column presented by Von Gruenewaldt (1973). Subunits A through D reveal macro-layering for which the intrusion is so well known. More than 40 individual Ti-magnetite layers were identified in the drill-core, which together with the numerous anorthosite layers, are the most prominent feature of this part of the column. The principal lithology is a somewhat monotonous sequence of ferrogabbro or magnetite-olivine gabbro. The absence of Ti-magnetite layers and anorthosite from subzone E, which is dominated by diorite with <5 modal % Ti-magnetite is significant. The whole-rock geochemical data presented here is not consistent with a closed system fractionation hypothesis for subunits A through D, despite this being widely accepted in recent contributions. An upward differentiation trend is preserved only in subunit E. The incremental build up of cumulates from successive pulse of magma is not only consistent with our views on the underlying layered cumulates (periods of closed system differentiation are rare) but is also consistent with field relationships, including each of the principal limbs representing individual sill-like features. The Upper Zone crystallized from batches of iron-rich tholeiitic magma derived from a deep staging chamber. Magma was injected as near-lateral flows, probably in a southward direction in the eastern limb. The introduction of evolved magma into a shallow crustal environment resulted in the early crystallization of Fe-Ti oxides. Ti-magnetite layers crystallized from oxide-rich slurries intruded near the floor of the chamber. Fe-Ti oxide pipes formed from slurries forced downward in areas of structural weakness. The regular, albeit step-like, upward change in composition of the Ti-magnetite layers identified by Molyneux (1974) and others is ascribed to mixing of crystal-rich magma slurries with increasingly differentiated resident magma: the lowermost layers (and pipes) contain the highest concentrations of V2O5. The spatial association of Ti-magnetite layers and anorthosite is emphasized and we suggest the latter formed as a consequence of disequilibrium partial melting of earlier formed silicate cumulates due to heat associated with new pulses of magma.

Effect of Er‐doping on the structural and optical properties of Cd2V2O7

AbstractThe melt‐quenching method was used to prepare two groups of samples using CdO and V2O5 as starting materials. Taking into account that a crystalline‐amorphous phase transition would be expected for the CdO–V2O5 system, a first batch was prepared varying the proportions of CdO and V2O5 in the intervals 60–95 and 40–5 wt%, respectively. With the aim of investigating the effect of erbium in the phase transition and crystalline quality of the first group of samples, a second batch was fabricated with the same proportions of CdO and V2O5, with the addition of 5 wt% of Er(NO3)5H2O as source of Er3+ ions. It was found that crystalline or amorphous samples could be obtained depending on the relative concentrations of CdO and V2O5, and that the borderline between amorphous and crystalline samples was affected by the incorporation of Er. From X‐ray diffraction, it was possible to identify the formation of the ternary compound Cd2V2O7 in the crystalline cases. The Raman and infrared bands in these samples were in agreement with the lattice modes of Cd2V2O7. Additionally, an improvement in the crystalline quality of Cd2V2O7 was obtained for the Er‐doped samples. The effect of the local environment around the Er3+ ions on the room temperature photoluminescence was also investigated for the amorphous and crystalline samples.

The influence of vanadium pentoxide on the structure and dielectric properties of poly(vinyl alcohol)

AbstractPolymers containing metal oxides of nanoscale dimensions have attracted attention because of their unique properties and new findings concerning technological applications. Polymers containing vanadium pentoxide (V2O5) have attracted our interest in respect of their potential applications in memory and switching devices. Poly(vinyl alcohol) (PVA) containing different concentrations of V2O5 ranging from 0 to 0.5 wt% were prepared. The synthesized PVA/V2O5 composites were cast as self‐standing flexible films. The composites were characterized using X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. An attempt was made to study the relaxation characteristics of PVA/V2O5 samples. The permittivity and dielectric loss were determined as a function of V2O5 concentration. The results show that the optimum concentration is 0.3 wt%. The electrical conductivity and dielectric modulus in the temperature range 303–433 K at various frequencies (10–100 kHz) for the optimum concentration were investigated. XRD and FTIR results show that the addition of V2O5 reduces the crystallinity of PVA due to the interaction of vanadium ions with the OH groups of PVA. The application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of the electrical conductivity follows the Jonscher universal dynamic law. The conductivity in the direct regime is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt's model is well adapted to PVA/V2O5 films. Copyright © 2010 Society of Chemical Industry

Spectroscopic and dielectric properties of ZnF2–As2O3–TeO2 glass system doped with V2O5

ZnF2–As2O3–TeO2 glasses mixed with different concentrations of V2O5 (ranging from 0 to 0.6 mol%) were synthesized. The amorphous nature of these glasses was checked by X-ray diffraction and scanning electron microscopy techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra and dielectric properties (constant ε′, loss tan δ, ac conductivity σac over a wide range of frequency and temperature) of these glasses have been explored. The optical absorption, electron spin resonance studies together indicated vanadium ions coexist in V4+ with V5+state in these samples. The IR spectra of these samples have exhibited bands due to νs-TeO2ax and AsO3 structural groups; these results indicated the most structural disorder in the network as the concentration of V2O5 is increased. Luminescent emission spectra recorded at room temperature of these glasses excited at 640 nm have exhibited a broad emission band in the spectral wavelength range of 750–850 nm. The luminescence efficiency is found to be the highest for the sample doped with 0.6 mol%. The dielectric parameters viz., ε′, tan δ and σa.c are found to increase and the activation energy for ac conduction is found to decrease with the increase in the concentration of V2O5 up to 0.6 mol%, reflecting an increase in the concentration of V4+ ions that take part modifying positions in the glass network. The ac conduction in these glasses could satisfactorily be explained by both classical activation energy and the tunneling phenomena.

Effects of V and Mn Colorants on the Crystallization Behavior and Optical Properties of Ce‐Doped Li‐Disilicate Glass–Ceramics

The critical cooling rate and fluorescence properties of lithium (Li) disilicate glasses and glass–ceramics, doped with 2.0 wt% CeO2 and with up to 0.7 wt% V2O5 and 0.3 wt% MnO2 added as colorants, were investigated. The critical cooling rates, Rc, of glass melts were determined using differential thermal analysis and were found to be dependent on the relative concentrations of V2O5 and MnO2, decreasing from 25±3° to 16±3°C/min. Annealed glasses were heat treated first to 670°C, and then to 850°C to form Li metasilicate and Li disilicate glass–ceramics, respectively. The fluorescence intensities of the Ce‐doped glasses and glass–ceramics decrease by a factor of 100 with the addition of the transition metal oxides. This optical quenching effect is explained by the association of the Ce3+ ions with the transition metal ions in the residual glassy phase of the glass–ceramics.

Dielectric and spectroscopic properties of PbO–Nb2O5–P2O5:V2O5 glass system

AbstractPbO–Nb2O5–P2O5 glasses containing different concentrations of V2O5 ranging from 0 to 1.0 mol% were prepared. A number of studies, viz. differential thermal analysis, infrared, optical absorption, Raman and ESR spectra and dielectric properties (dielectric constant ϵ′, loss tan δ, a.c. conductivity σac over a range of frequency and temperature), of these glasses have been carried out. The results have been analysed in the light of different oxidation states of vanadium ions. The analysis indicates that when the concentration of V2O5 is increased gradually, vanadium ions are observed to exist mostly in the V4+ state, occupy network‐modifying positions and decrease the rigidity of the glass network. A transformation of NbO4 to NbO6 structural units and a decrease in the concentration of PO4 structural units have also been observed with an increase in the concentration of V2O5 in the glass network. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structure of vanadium tellurite glasses studied by neutron and X-ray diffraction

Details of the Te–O first-neighbor distances in V2O5–TeO2 glasses were obtained by neutron diffraction experiments with a measuring range up to Qmax=400nm−1 (Q is the magnitude of scattering vector). A sharp Te–O peak at 0.191nm and a second broad component at about 0.21nm were resolved. Quantitative analyses of the areas of both peak components for a compositional series of four samples support the model of a change of TeO4 trigonal bipyramids to TeO3 trigonal pyramids upon V2O5 additions. In glasses of up to ∼10mol% V2O5 each VOn polyhedron introduced is accompanied by the formation of a TeO3 unit. The number of TeO3 units increases further for glasses of higher V2O5 concentrations but the increase is less than that of the number of V sites.

Investigation of the magnetic properties in strontium–borate vanadate glasses

To further elucidate the nature of the valence state of V ions in vanadate glasses, magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independent paramagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a weak antiferromagnetic interaction between the V4+ ions. These results are consistent with a glass network structure consisting of VO5 polyhedra in which the V4+ would be predominantly isolated species, and any interactions between the V4+ ions would result from superexchange interactions through V–O–V bonds.

X-ray Absorption Studies of Vanadium Valence and Local Environment in Borosilicate Waste Glasses

ABSTRACTXANES and EXAFS data were collected and analyzed to characterize vanadium in borosilicate glasses used for immobilization of sulfur-containing nuclear wastes. Earlier studies suggested that adding vanadium to the melt improves sulfur solubility. Data are presented for a variety of borosilicate glasses, some containing sulfur and some sulfur-free, that have V2O5 concentrations as high as 12 wt%, and for crystalline vanadium sulfide, silicate, and oxide standards. The data for all glasses investigated indicate that most or all vanadium has a +5 valence and is tetrahedrally coordinated by oxygen atoms. Both XANES and EXAFS also show that glasses synthesized under reducing conditions can have pentacoordinated V+4 populations up to approximately 20 to 25% of all vanadium present with the remainder being V+5O4. There is no evidence from XANES or EXAFS of V-S bonds in any of the glasses investigated.