MoO3 Content Research Articles

Characterization and Physical Properties of PbO–As2O3 Glasses Containing Molybdenum Ions

PbO–As2O3 glasses containing different concentrations of MoO3 ranging from 0 to 1 mol% (in steps of 0.2) were prepared. The samples were characterized by X-ray diffraction, differential thermal analysis and scanning electron microscopy. A number of studies, viz., optical absorption, magnetic susceptibilities, ESR spectra, IR spectra, elastic properties (Young's modulus E, shear modulus G and microhardness H) and dielectric properties (constant ε, loss tan δ, a.c. conductivity σac over a range of frequency and temperature and breakdown strength), have been carried out on these glasses. Optical absorption, ESR and magnetic susceptibility measurements suggest that when MoO3 concentration is greater than 0.4 mol% in the glass matrix, molybdenum ions exist in Mo5+ state with Mo(V)O−3 complexes that act as modifiers in addition to Mo6+ state with MoO4 and MoO6 structural groups. The studies on elastic and dielectric properties indicate that the mechanical and insulating strengths of the glass are considerably high when the content of MoO3 is about 0.4 mol% in the glass matrix.

Non-isothermal crystallization kinetics of V2O5-MoO3-Bi2O3 glasses

Characteristic temperatures, such as T g (glass transition), T x (crystallization temperature) and T l (liquidus temperature) of glasses from the V2O5-MoO3-Bi2O3 system were determined by means of differential thermal analysis (DTA). The higher content of MoO3 improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was investigated and following energies of the crystal growth were obtained: glass #1 (80V2O5·20Bi2O3) E G=280 kJ mol-1, glass #2 (40V2O5·30MoO3·30Bi2O3) E G=422 kJ mol-1 and glass #3 (80MoO3·10V2O5·10Bi2O3) E G=305 kJ mol-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide acts as a nucleation agent and facilitates bulk crystallization.

Structural and electrical properties of MoO3-TeO2glasses

The dc conductivity of MoO3-TeO2 glasses prepared by meltquenching has been investigated in the temperature range 323-473 K. Seebeckcoefficient measurements indicate the glasses to be n-type. The conductivityincreases with increase of MoO3 content and at 418 K varies from about6×10-6 to 1×10-8 S cm-1. The conduction isattributed to non-adiabatic hopping of small polarons due to the differentvalence states, Mo5+ and Mo6+, the existence of which was confirmedfrom x-ray photoelectron spectroscopy analysis of the glasses. Fouriertransform infrared spectroscopic studies show the presence of MoO6,MoO4, TeO3 and TeO4 structural units in the glasses.

Electrical and Optical Properties of MoO3-TeO2 Amorphous Films Prepared by PVD Method

Electrical and optical properties of MoO3–TeO2 amorphous films prepared by vacuum deposition method were investigated. X-ray diffraction patterns show an amorphous structure. The dc conductivity of the films was measured in the temperature range 323–523 K and follows a non-adiabatic small polaron hopping conduction mechanism between Mo4+ and Mo5+, confirmed by X-ray photoelectron spectroscopy measurements. Conductivity of the films increases with increase of MoO3 content. The Seebeck coefficient indicates the films to be n-type semiconductor. Optical absorption edge analysis gave a band gap energy of 2.7–2.9 eV depending on composition. The Urbach tail analysis gave the width of localized states between 0.23 and 0.25 eV.

Activity and Structure of Hydrotreating Ni, Mo, and Ni–Mo Sulfide Catalysts Supported on γ-Al2O3–USY Zeolite

The catalytic hydrocracking (HC) of diphenylmethane (DPM) and hydrodesulfurization (HDS) of dibenzothiophene (DBT) over Ni, Mo, and Ni–Mo sulfide catalysts supported on a mixed ultrastable Y (USY) zeolite and γ-Al2O3 were studied. The catalysts were characterized using NH3 temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–Vis–NIR diffuse reflectance spectroscopy (DRS), high-resolution transmission electron microscopy (HRTEM), and chemical composition analysis. Because addition of zeolite to a conventional alumina support improves acidity, Ni, Mo, and Ni–Mo catalysts supported on the combined supports had much higher HC activity. Ni was found to be uniformly distributed throughout the catalysts; however, Mo preferentially entered the structure of γ-Al2O3 or was accommodated as oxide aggregates on γ-Al2O3, rather than associating with zeolite. Ni and Mo catalysts supported on γ-Al2O3–USY zeolite were good HDS catalysts and showed a shallow maximum in catalytic activity at a NiO and MoO3 content of 5 mol%. The higher activity at this content occurred because Ni or Mo species had higher surface concentrations, higher dispersion, and were more easily sulfided. Ni–Mo catalysts supported on γ-Al2O3–USY zeolite had high HDS activity, which showed a prominent maximum at a NiO/(NiO+MoO3) ratio of about 0.4, because at this ratio the surface species of Ni and Mo were well dispersed and more easily sulfided to form a Ni–Mo–S phase responsible for the high HDS activity. The Ni–Mo catalysts supported on γ-Al2O3–USY zeolite have slightly higher HDS activity than γ-Al2O3-supported Ni–Mo catalysts.

Structural and electrical properties of iron molybdenum phosphate glasses

Iron molybdenum phosphate glasses [xMoO3 · (0.6 -x)P2O5 · 0.4Li2O] :yFe2O3 with 0 ≤x ≤ 0.6 andy = 0.03 (mol%) prepared in ambient atmosphere using the melt quenching technique were studied by using DC electrical conductivity,57Fe Mossbauer and infrared spectroscopies. The DC conductivity depends on the MoO3 concentrationx. It was observed that, with increasingx, the ratio Fe2+ /(Fe3+ + Fe2+) and the DC conductivity increase. Infrared spectroscopy and X-ray powder diffraction indicate that a Li2 MoO4 crystalline phase is present for high MoO3 content samples (x = 0.5, 0.6).

Corrosion inhibition by molybdate/polymaliate mixtures

The inhibition of the corrosion of mild steel in continuously aerated potable water by the addition of sodium molybdate, Na 2MoO 4, was examined by two independent techniques. The first involved the measurement of open circuit potentials of coupons as a function of time till steady-state, constant potentials, E st, were established. The plot of E st as a function of the logarithm of [MoO 4 2−] disclosed consecutive domains of active corrosion, localized (pitting) corrosion and full passivation. The curve did not allow, however, the evaluation of corrosion rates. This information was ascertained from weight loss determination. The rate of corrosion/log [MoO 4 2−] was mirror image of the potential curve. BELGARD EV® (BELEV), a polymeric maleic anhydride preparation used as an anti-scalant, acted in the neutralized state as a moderate adsorption inhibitor affecting anodic sites. Complete surface coverage was ensured in the presence of ca 100 ppm inhibitor in solution. Mixtures of molybdate and BELEV exhibited inhibition synergism. The combined effect of the mixture exceeded the sum produced by the two individual agents. Differences in behaviour was noted between solutions containing low (30 ppm) and high (≥50 ppm) BELEV. The former solutions failed to inhibit corrosion completely whatever the concentration of MoO 4 2− was. With higher BELEV additions inhibition was achieved at definite [MoO 4 2−]/[BELEV] ratios. These were the compositions which raised the metal potential to or above that characterizing a pitting attack in MoO 4 2− solutions only. Visual observation of the metal coupons and test solutions confirmed the above conclusion. Successful mixtures of MoO 4 2− and BELEV could be worked out which ensured complete inhibition and substantial cost savings.

Kinetics of molybdenum loss from iron molybdate catalysts under nitrogen atmosphere

The loss rate of molybdenum in Fe−Mo/SiO2 catalyst has been measured. When the catalyst is composed of a Fe2(MoO4)3 crystalline phase and monolayer dispersed MoO3, the loss rate of MoO3 varies with the content of MoO3 in the catalyst. If a MoO3 crystalline phase arises in the catalyst, the loss rate will be accelerated.

ESR and FTIR spectroscopy study of Sb-Mo oxide catalysts

Abstract A kinetic study of MoO3-Sb2O4 catalysts, showed that conversion of methanol increased significantly as MoO3 content was increased. A relationship was found between the ESR signal's intensity and the catalysts' yield for formaldehyde. FTIR confirmed the appearance of cis-dioxo MoO+2 sites, which explains these high yields.

Surface state of molybdenum cations in MoO3/CeO2

1 The dispersion capacity of MoO3 supported on CeO2 is 0.81 rnmo1/100 m2. For samples with MoO3 content is below the dispersion capacity, Mo6+ ions exist in the surface vacancies to form the surface Mo species, and the highly dispersed Mo6+ cations are coordinated by 7 oxygen ions based on the assumption that the CeO2(111) plane is preferentially exposed. 2 The differences of the dispersions between MoO3 on CeO2 and MoO3on ZnO-modified CeO2 indicate that the surface vacancies play an important role in the dispersion of MoO3.

Dielectric properties and polarizability of molybdenum tellurite glasses

The dielectric behaviour of the [TeO2]1−x[MoO3]x, x=0.2, 0.3 and 0.45 mol%, glassy system is reported for the temperature range 300–573 K and the frequency range of 0.1–10 kHz. Both the static and high frequency dielectric constants for these binary tellurite glasses decrease with increasing MoO3 content. The temperature dependence of the dielectric constants of these glasses are positive. The frequency dependence of the dielectric constant identifies a frequency dependence which does not show a flattening at low frequency. The room temperature static dielectric polarizability is discussed in terms of the MoO3 concentration. The temperature dependence of the dielectric constant has been analysed in terms of the temperature changes of both volume and polarizability and also a volume change of the polarizability.

Experimental evidence for a relationship between liquid immiscibility and ore-formation in felsic magmas

Geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process. In order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma, we carried out a series of experiments at high temperature and atmospheric pressure. The experimental results show that the granite ∼ KBF 4∼Na 2MoO 4 system is a homogeneous melt at high temperature. With decrease in temperature, however, the melt decomposes into two immiscible melts: silicate melt and ore-forming melt. The ore-forming melt exists as globules in the silicate phase. Molybdenm, Ca, Na, Mg, P, Mn, F, B, and OH are concentrated in these globules. The ore forming melt is characterized with very low SiO 2 and Al 2O 3 concentrations but the concentration of MoO 3 and CaO is very high. In contrast, the silicate melts are significantly enriched in SiO 2 and Al 2O 3, and depleted in MoO 3 and CaO. In the silicate melt the concentrations of network modifying elements (e.g. Mo, Ca, Na, P, Mg) and volatiles (F, OH) are very low. The differences between the two immiscible melts exist not only in chemical composition but also in structure. The ore-forming melt structurally consists of [MoO 4], [MoOF 4], [B(OH) 4], and OH, while the silicate melt is [Si0 4]. Because of the difference in composition and structure the two immiscible melts possess different physical properties. Compared to silicate melt, the ore-forming melt has a lower density and viscosity, which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber. This process is probably responsible for the concentration of ore-forming elements in the upper part of granite bodies and their immediate aureoles. The present experimental results suggest that liquation in felsic magma can be the first step in the ore-forming process during granitoid evolution.

Experimental evidence for a relationship between liquid immiscibility and ore-formation in felsic magmas

Abstract Geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process. In order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma, we carried out a series of experiments at high temperature and atmospheric pressure. The experimental results show that the granite ∼ KBF 4 ∼Na 2 MoO 4 system is a homogeneous melt at high temperature. With decrease in temperature, however, the melt decomposes into two immiscible melts: silicate melt and ore-forming melt. The ore-forming melt exists as globules in the silicate phase. Molybdenm, Ca, Na, Mg, P, Mn, F, B, and OH are concentrated in these globules. The ore forming melt is characterized with very low SiO 2 and Al 2 O 3 concentrations but the concentration of MoO 3 and CaO is very high. In contrast, the silicate melts are significantly enriched in SiO 2 and Al 2 O 3 , and depleted in MoO 3 and CaO. In the silicate melt the concentrations of network modifying elements (e.g. Mo, Ca, Na, P, Mg) and volatiles (F, OH) are very low. The differences between the two immiscible melts exist not only in chemical composition but also in structure. The ore-forming melt structurally consists of [MoO 4 ], [MoOF 4 ], [B(OH) 4 ], and OH, while the silicate melt is [Si0 4 ]. Because of the difference in composition and structure the two immiscible melts possess different physical properties. Compared to silicate melt, the ore-forming melt has a lower density and viscosity, which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber. This process is probably responsible for the concentration of ore-forming elements in the upper part of granite bodies and their immediate aureoles. The present experimental results suggest that liquation in felsic magma can be the first step in the ore-forming process during granitoid evolution.

Growth of lithium triborate crystals. I. Mathematical model

A finite element mathematical model for the top seeded solution growth of Li 2O·3B 2O 3 (LBO) crystals, grown from a melt containing the flux MoO 3, is presented. The model is used to calculate the thermal fields and fluid flow in the melt during growth. The thermal boundary conditions used in the model are estimated from temperature measurements made in the melt. The phase diagram of the LBO MoO 3 system is determined experimentally using differential thermal analysis. The physical parameters required in the model are obtained from the literature, when available. Values of the melt viscosity, as a function of the MoO 3 concentration, are determined experimentally. The temperature fields and fluid flow in the melt, particularly below the growing crystal, are calculated for a range of crystal rotations, crucible rotations, crucible sizes, and melt viscosities. The results show that the most effective means of producing fluid flow in this system is by crucible rotation. Fluid flow immediately below the crystal interface determines the movement of the MoO 3 flux rejected by the crystal, away from the interface. This flow is primarily dependent on crucible rotation. If the concentration of MoO 3 at the interface reaches the eutectic composition, MoO 3-rich phases form, terminating the growth of a satisfactory quality LBO crystal.

Structural study of MoO3TeO2 glasses

MoO3TeO2 glasses were investigated by Raman spectroscopy and differential thermal analysis, and transition temperature, thermal expansion and density were measured. Mo  O bonds are present in the entire glass composition. The glasses contain TeO4 trigonal bipyramids, TeO3+1 polyhedra and MoO6 octahedra as basic structural units. Glasses having low MoO3 content contain MoO6 octahedra having two Mo  O bonds. As MoO3 content increases, the fraction of Mo  O bonds to Mo6+ decreases. When MoO3 content reaches 30–40 mol%, the structure of glasses shows close resemblance to that of MoTe2O7 crystal. On the basis of local structural difference around second-component atoms between MoO3-TeO2 and WO3-TeO2 glasses, differences in the properties of both glasses are discussed.

5405957 Wavelength-specific photosensitive compounds and expanded porphyrin-like compounds and methods of use

The infrared spectra of the entire glass-forming range of the vitreous system Mo-P-O are reported. The data are interpreted in the light of previous studies of other vitreous phosphates, and related crystalline phosphates. The spectra show that with increasing MoO3 content progressive rupture of P = O bonds takes place and there is little of the bond-type left in compositions exceeding 53 mol% MoO3. The P=88O stretching frequency is reduced by hydrogen bonding but increases with increasing Mo content. The P-O-P ring frequency is strong throughout most of the composition range, consistent with a three-dimensional network structure relatively free of chains. The spectra in midcomposition range are characterised by vibrations characteristic of PO3 and P2O7 groups with edge sharing MoO6 octahedra having relatively little effect. However, the spectra of Morich structures display unique features characteristic of edge sharing MoO6 octahedra as in pure MoO3 oxide. Generally, the data are also consistent with the proposition, used in a previous ultrasonic study, that these glasses consist of distorted versions of the crystal groups: PO4 tetrahedra, MoO3 octahedra, metaphosphate and pyrophosphate, in proportions that change systematically and distinctively with content. It is suggested that acoustic and optical Debye temperatures calculated from these spectra ought to correlate with (in respect of composition dependence) analogous quantities calculated from published data on acoustic wave velocities and the temperature dependence of electrical conductivity in this wide-ranging glass system.

Raman Spectra of Molybednum Phosphate Glasses and Some Crystalline Analogues

The Raman spectra of a series of glasses in the system MoO3‐P2O5 and the polyerystalline compounds molybdenum metaphosphate (MoO2(P03)2) and molybdenum pyrophosphate ((MoO2)2P2O2) are reported. The spectra indicate that traces of P=O and phosphate chains are present only in glasses having less than 50 mol% MoO3. Comparison of the glass spectra with spectra of crystalline molybdenum phosphates indicates the presence of metaphosphate and orthophosphate structural groups of MoO3 concentrations of about 50 mol% or less. As the MoO3 concentration is increased, the bands characteristic of pyrophosphate groups appear in the spectra and become the dominant feature at 76 mol% MoO3 concentration. Metaphosphate groups are present in the glass even at the highest MoO3 concentrations measured.

ChemInform Abstract: Partial Oxidation of Propene on Mo‐Pr‐O Catalysts.

AbstractMild propene oxidation over a new catalytic system, Mo‐Pr‐O, has been studied using catalysts with Mo/(Mo+Pr) atomic ratios ranging from 0 to 1. The catalytic activity first decreases with increasing MoO3 content and then increases to a maximum activity at an atomic ratio of 0.84‐0.88.

Influence of Mo Addition on the Electrical Properties of Y-Ba-Cu-O Compound

The effects of MoO3 addition on the electrical properties and the microstructures of Y-Ba-Cu-O system were investigated. The electrical resistivity at 300K grew along with the increasing addition of MoO3 content, and the specimen without MoO3 showed zero resistance but the specimens containing MoO3 did not. The grain diameter was maximum at 1wt% MoO3.

Synergetic effect of silver and molybdenum (VI) oxide additives in vanadia catalysts for the selective oxidation of benzene

It has been shown that the selectivity of V2O5−MoO3 catalysts for benzene oxidation to maleic anhydride can be enhanced by small amounts of silver introduced by impregnation with AgNO3 solution. The effect of Ag2O additive is synergetic and increases with increasing concentration of MoO3 up to 28.5 mol %. The best effect was obtained when about 7 Ag atoms were introduced for 1000 (V+Mo) atoms at the surface.