Low Vanadium Content Research Articles

Magnetic and electrical study of amorphous metallic alloys CoBV and CoBTi

Investigations on the temperature dependences of the magnetization of the rapidly quenched alloys (Co 85B 15) 100− x V x ( x = 5, 10, 15, 20, 25) and (Co 85B 15) 100− x Ti x ( x = 10, 15, 20) reveal that vanadium suppresses the magnetization more strongly than titanium. The values of the Curie temperature ranging up to 900 K for x = 5 are at least 150 K lower for the V- than for the Ti-containing alloys. The magnetic moments decrease monotonically with the V and Ti content and are lower in V-based alloys. The threshold crystallization temperatures of the alloys studied are relatively high, exceeding 580 K. At low vanadium and titanium content, the electrical resistivity and thermoelectric power vary proportionally to T 2, whereas for higher values of x they become a linear function of temperature. Changes in the temperature dependence of the resistivity and the thermoelectric power are observed at the Curie temperature. Correlations between the thermoelectric power and electrical resistivity are discussed.

Oxidative dehydrogenation of propane on vanadium supported on magnesium silicates

Sepiolite supported vanadium catalysts have been studied in the oxidative dehydrogenation of propane. Different vanadium species are present on the catalysts and the proportion changes with the preparation methods, support modifications, and vanadium content. At low vanadium content, isolated tetrahedral species are formed and both activity and selectivity to propene increase when increasing the vanadium content. At medium or high vanadium content the appearance of associated vanadium species can be observed and, while the activity still increases when increasing total vanadium, the selectivity to propene remains constant. MgV 2O 6 and V 2O 5 crystallites are formed at vanadium content higher than 30 wt.% of V 2O 5, and, depending on the propane conversion level, the selectivity to propene remains constant or decreases when increasing the vanadium content. On a comparative basis, the oxidative dehydrogenation of propane has also been carried out on a V 2O 5/MgO catalyst. From the comparison between catalytic properties in the oxidative dehydrogenation of propane on V/sepiolite and V/MgO catalysts a reaction network has been established and both type of catalysts show the same conversion-selectivity behaviour. The nature of the sites responsible for selective and non-selective oxidation on V/sepiolite catalysts has been proposed.

Vanadium site in VAPO-5: Characterization and catalytic properties in liquid-phase alkene epoxidation and benzylic oxidation

Solid state NMR ( 51V, 27Al, 31P) and ESR were used to characterize the vanadium site in VAPO-5, as obtained by a fluoride-assisted synthesis. It was found that the main species at low vanadium content is a monomeric vanadyl unit in square pyramidal or distorted octahedral coordination, both in oxidation state (IV) for the as-synthesized material and in oxidation state (V) for the calcined material. Chemical compositions of the samples and site geometries strongly suggest a phosphate environment, and vanadyl ions are thought to occupy aluminium sites. At higher vanadium contents (1.3% V/(V+Al+P) atomic ratio) tetrahedral vanadium (V) is also formed upon calcination. At 3.0% V/(V+Al+P), the material is not entirely stable towards calcination. The vanadium species readily interacts with water, tert-butanol and tert-butyl hydroperoxide (TBHP). VAPO-5 was found to be an active and very selective catalyst for the epoxidation of allylic alcohols with TBHP. It also catalyses the epoxidation of simple alkenes and the side chain oxygenation of aromatics using the same oxidant. The epoxidation reactions involve a heterolytic oxygen transfer from what is probably a vanadium alkylperoxo surface complex.

Surface pecularities of vanadium oxides grown in the field of laser light

Peculiarities of O/V atomic and weight ratios of vanadium oxides grown on the surface of metallic vanadium plates under influence of CW YAG laser radiation have been investigated. The dependence of the normalized weight ratio on the oxygen content showed that the area of the surface to be illuminated consists of nonstoichiometric oxides (oxygen content of 30%–35%). otherwise in the vicinity of the laser spot almost stoichiometric vanadium pentoxide polycrystals have grown: the oxygen content varied between 35% and 50%. Far from the laser spot the oxygen content decreased drastically to 4%–8%. There were some very specific zones with sizes of a few micronmeters showing particularly high or low vanadium contents (saturated V 2O 5 and /or VO 4 with x ≤ 2 or some Magneli phases V n O 2 n−1 ) randomly distributed on the surface. Special microhardness measurements have been carried out in order to follow the surface structures among the commonly used SEM, BSE and EDS methods.

51V NMR study of strongly bound vanadia in V 2O 5/Al 2O 3 catalysts

By using 51V NMR spectroscopy the process of partial dissolution of the V 2O 5 of vanadia-alumina catalysts by 0.3 N NH 4OH was studied and samples prepared by impregnation and partial dissolution were compared. The relative participation of three vanadia species identified on both types of samples with low and medium vanadium concentrations (NMR lines at −350, −550 and −750 ppm) and the catalytic activity for the NONH 3 reaction were found to be controlled mainly by vanadium concentration and less by the method of preparation. Formation of AlVO 4 at high concentrations and the complex behavior of this species during subsequent calcination and catalytic testing indicated a fundamental restructure of the catalyst surface and precluded any viable comparison of samples at the highest concentration levels prepared by both methods. VO 2+ content in oxidized samples was found to be ≈4–5 times higher in catalysts prepared by partial dissolution, compared with impregnated samples.

Characterization of surface species of supported V 2O 5Al 2O 3 catalysts by 51V NMR

51VNMR spectra were used for the study of the interaction between vanadium oxocomplexes in solution and the Al 2O 3 surface, and for the identification of surface vanadium species formed over Al 2O 3 surface for different preparation conditions (pH, concentration of supported V, treatment temperature). At low vanadium concentration, mainly isolated tetrahedral surface complexes are formed over the Al 2O 3 surface, bound with one or two bonds. The increase in vanadium concentration results in the formation of surface clusters with a part of the V in a distorted octahedral environment. After treatment at 500 °C and at a V concentration of ∼ 10 wt.%, the formation of AlVO 4 and V 2O 5 crystals over the Al 2O 3 surface takes place.

The Chemical Composition and Characteristics of Residues of Chinese Crude Oil

Abstract The residues of six Chinese crude oils have been separated into eight fractions, i.e., saturated, light, middle, and heavy aromatics, light, middle, and heavy resins, and asphaltenes, by solvent treatment and liquid-solid chromatography. The elemental composition and the structural parameters based on NMR spectra of the fractions were obtained. The data show that most of these residues have high nitrogen, nickel, wax, and resin contents, and low sulfur, vanadium, and asphaltene contents. This is convincing evidence that indicates the continental origin of the Chinese crude oils.

Catalytic oxidation of toluene over V2O5-WO3 catalysts

The catalytic performance of V2O5-WO3 catalysts in the oxidation of toluene was investigated and correlated with features shown by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and chemical analysis of vanadium valence states. At low vanadium concentrations high selectivity and activity was obtained and these catalysts consisted of highly dispersed V2O5 supported on WO3. V4+ formation upon use was highest in this region. Increased vanadium concentrations resulted in decreased dispersion with formation of less active and less reducible crystallites, and both activity and selectivity decreased towards values for V2O5. Dissolution of W6+, increasing with WO3 concentration, affects crystallization of V2O5. The (010) to (101) ratio, from XRD data, increases at the lowest addition levels, but decreases strongly at higher levels. Activity and selectivity are not simply correlated with this ratio, but overall are inversely correlated with it. Activity and selectivity correlate with the increase in the V4+-to-ΣV ratio with use in the reaction, indicating the importance of reduced phases and surface defects.

Optimization of sodium orthovanadate to treat streptozotocin-induced diabetic rats

Oral administration of sodium orthovanadate restored blood glucose to normal levels in streptozotocin-induced diabetic rats. To establish the safety dose and to evaluate the side effects of over dose, if any, different doses of vanadium were used in the present study. Low concentrations of vanadium (0.1 and 0.3 mg/ml in drinking water) restored blood glucose, urea, cholesterol and the status of liver pathophysiological enzymes to normal levels in experimental rats. High vanadate treatment proved to be toxic not only to diabetic but also to normal rats as evidenced from the observations on the blood urea, plasma and liver glutamate oxaloacetate transaminase and glutamate pyruvate transaminase. Low vanadate treatment restored body homeostasis of diabetic rats and was found to be nontoxic to normals.

Measurement of vanadium impurity in oxygen-implanted silicon by isotope dilution and resonance ionization mass spectrometry

The combined analytical capabilities of isotope dilution, laser-induced resonance ionization spectroscopy, and mass spectrometry, integrated in the resonance ionization mass spectrometry technique (RIMS), have been evaluated as a tool for quantitative elemental impurity analysis of SIMOX (separation by implanted oxygen), a new silicon-based material prepared by oxygen implants. The vanadium impurity content was measured in the top crystalline SIMOX film and the oxygen-synthesized buried oxide layer in commercial wafers, resulting in 0.14 {mu}g/g {plus minus} 20%, or 1.7 {times} 10{sup 15} atoms/cm{sup 3}. A similar analysis on the substrate bulk shows about 30 times lower vanadium impurity levels. The origin of this contamination may be linked to the oxygen implant, although no modeling for it is offered here. The sensitivity of RIMS to vanadium is in the pg/g range. The accuracy of results is limited by the uncertainty in the blank, in view of the low total vanadium content in the specimen.

Effect of alloying on the features of crystallization and on the structure of cast vanadium-containing steels

1. On account of considerable dendritic liquation the crystallization of vanadium-containing steels even with low vanadium content (approximately 0.12%) may be accompanied by the formation of eutectic vanadium carbonitrides with variegated morphology: coarse boundary segregations and point-type "carbide rust spots." 2. When steel contains 0.25% C, the lower concentration limit of formation of carbide eutectic in regard to vanadium in castings with section 50 mm amounts to 0.33%. When the carbon content increases to 0.85%, this threshold drops to 0.12%. 3. The amount of carbide eutectic depends largely on the speed of crystallization which is determined chiefly by the section of the casting. By its effect on the amount of eutectic carbides, an increase of the diameter of the casting by 50 mm is equivalent to an increase of the vanadium content of the steel on an average by 0.20%. 4. In the complexly alloyed steels 150KhNMF and 150KhNMFT the process of crystallization may be accompanied by the segregation of carbides with eutectic morphology, with complex composition, type (V, M)C. In dependence on the alloying, complex carbides contain, in addition to vanadium, also chromium, molybdenum, and titanium.

Characterization of vanadium oxide catalysts supported on γ-Al2O3by51V solid state n.m.r. spectroscopy

51 V Solid state n.m.r. of V2O5/Al2O3 catalysts reveals two types of vanadia species on the surface: one due to a dispersed vanadia phase at lower vanadium contents and the other due to crystalline vanadia phase at higher vanadium content.

Optical absorption of vanadium in sodium diborate glasses

The optical absorption in blown films and bulk specimens of sodium diborate glasses containing vanadium oxide based on the system [Na2O-2B2O3]1−x [V2O5]x, wherex = 0, 0.05, 0.10, 0.15 and 0.20, has been studied in the wavelength range 200 to 900 nm. The fundamental absorption edge has been analysed in the light of the existing models. It is found that glasses containing a higher content of vanadium have fewer defects when compared with those containing a low vanadium content. The absorption spectra are interpreted as due solely to pentavalent vanadium.

Analysis of Burmese and Thai Rubies by PIXE

Trace element analysis of 60 Burmese and Thai rubies by using the technique of proton-induced x-ray emission was carried out. It was found that the Burmese rubies contained higher concentrations of all impurities except iron. Our results also reveal that vanadium and iron are useful indicators for Burmese and Thai ruby attribution. The Thai rubies have high contents of iron and very low concentrations of vanadium. On the other hand, all the Burmese rubies examined contain significant amounts of vanadium, and their iron contents are, on the average, four times lower than those in the Thai rubies.

Activity measurements and spectroscopic studies of the catalytic oxidation of toluene over silica-supported vanadium oxides

Vanadium oxides on silica gel (Davison 952) with varying vanadium concentrations have been investigated for the activities and selectivities in the oxidation of toluene. These results were correlated with the features shown by X.r.d., ESCA, u.v.–visible and i.r. studies of adsorbed CO. The catalysts show a low activity in comparison with V/alumina. The support alone shows 60% selectivity for benzaldehyde formation. From i.r. data it is suggested that this benzaldehyde is formed on sites in association with sodium impurities. Introduction of vanadium increases the rate of reaction but the selectivity is shifted towards carbon oxides. The increased activity at low vanadium content is due to isolated four-coordinated vanadium species. U.v.–visible data show that the isolated species agglomerate at further loading to polyvanadium chains. These polymers possess an increased activity as a further route of reduction of VV to VIV is present. Five-coordinated vanadium of the same activity as the chains and producing selective oxidation products other than benzaldehyde is found with a loading of 2% V. Larger agglomerates and V2O5 crystallites are present on the 10% V catalyst. These species only give a somewhat increased activity, but with a product pattern different from crystalline V2O5 and 10% V/alumina.

Low-alloy tungsten-free high-speed steels 11M5F and 11M5FYu and their heat treatment

The development and heat treatment of two tungsten-free low-alloy high-speed steels 11M5F and 11M5FYu are discussed. The steels are characterized by the absence of eutectic molybdenum carbide, a heating temperature for hardening about 60/degree/: No. 11, (Nov 1987)C lower than for steel R6M5, and a low vanadium concentration. The steels contain about 1% C, 5% Mo, 4% Cr, and 1.5 % UV-14-1-2678-79. Tests were conducted to ascertain pertinent tool steel properties such as grindability, impact strength, and wear. Numerous industrial tests of cutting tools made of steel 11M5F have shown that their resistance is not lower, and those made of steel 11M5FYuS are markedly higher, than tools made of steel R6M5.

A study of rapid redox initiation by reaction calorimetry

The rate of radical formation, ϱ i , obtained by using a rapid redox system based on t-butyl hydroperoxide, vanadium(IV) and ascorbic acid was studied under emulsion polymerization conditions using a calorimetric reactor. The rate of radical formation was found to follow the expression: ϱ = k[VO 2+][(CH 3) 3COOH] with k =139 1 mol −1 s −1 i at 50 °C and an activation energy of 94 kJ mol −1. Under weakly acidic conditions (pH 3–5) and in the presence of an excess of ascorbic acid, the five-valent vanadium formed in the redox reaction was immediately reduced back to VO 2+. Under these conditions, a rapid pseudo first order reduction of the hydroperoxide could be maintained at low vanadium concentrations. Using redox systems of this kind, emulsion polymerizations can be carried out at closely controlled rates of initiation.

ChemInform Abstract: Multicomponent Polyanions. Part 36. Hydrolysis and Redox Equilibria of the H+ ‐ HVO42‐ System in 0.6M Na(Cl).

AbstractComplementary Potentiometric and 51V NMR Study at Low Vanadium Concentrations in Acid Solution.

The use of TiO2 contaminated with phosphorus and potassium as a support for V2O5 catalysts in the selective oxidation of toluene

The structure of V2O5–TiO2 catalysts, both of the supported type and the fused mixed oxide type, has been investigated by a variety of physicochemical techniques and correlated with their activity and selectivity in the oxidation of toluene. Special emphasis is put on the influence of phosphorus and potassium contaminants of commercial TiO2 preparations. These contaminants are mainly present in the TiO2 surface and prevent the formation of ideal monolayer catalysts. There are no results indicating V–P–O phase formation, but unselective potassium vanadate crystallites could be observed at a combination of high potassium and Iow vanadium concentrations. For fused catalysts of high vanadium contents, no such compound formation appears to occur. All preparations of low vanadium concentrations have a much lower activity in toluene oxidation than those of higher concentration containing bulk vanadium oxide crystallites. The selectivity for benzaldehyde could, however, be as high as for the most active catalyst prepared by the decomposition of NH4VO3. Selectivity for oxidative coupling products appears with the presence of vanadium oxide crystallites in catalysts with higher vanadium concentrations. Activity and selectivity data for the bulk V2O5–TiO2 catalysts emphasizes the importance of defects and reduced phases.

Electron spin resonance of vanadium oxide monolayer catalysts

The structural conversion in the course of synthesis and thermal activation of silica-supported vanadium oxide catalysts has been investigated by means of ESR, O 2 chemisorption and XPS techniques over wide temperature ranges and low vanadium concentrations. Three ESR signals (A, assigned to the reduction V 2O 3 phases; B, due to the V 4+ ions surrounded by an axial distorted ligand field in amorphous V 2O 3; and C, assigned to VO 2+ ions in some static disordered states), their relative appearance as a function of pretreatments, concentration of vanadium, and chemical route of preparation, are discussed. Moreover, the O 2 chemisorption data show that the number of V 4+ centres able to adsorb oxygen varied with the vanadium content and the preparation method, XPS and ESR results have also shown that the chemical species in the surface, and their structure, are more affected by the pretreatment in highly dispersed vanadium oxide than in silica-supported vanadium oxide catalysts.