Molybdenum solutions

Discussion. Molybdates [Mo(VI)] are quantitatively reduced in 2M hydrochloric acid solution at 60-80 °C by the silver reductor to Mo(V). The reduced molybdenum solution is sufficiently stable over short periods of time in air to be titrated with standard cerium(IV) sulphate solution using ferroin or /V-phenylanthranilic acid as indicator. Nitric acid must be completely absent the presence of a little phosphoric(V) acid during the reduction of the molybdenum(VI) is not harmful and, indeed, appears to increase the rapidity of the subsequent oxidation with cerium(IV) sulphate. Elements such as iron, copper, and vanadium interfere nitrate interferes, since its reduction is catalysed by the presence of molybdates. 

Fig. 21. Amount of molybdenum and phosphorus adsorbed onto y-alumina from the injection of pulses of molybdate and phosphate solutions. 1, Pulses of molybdenum solution 2, pulses of phosphorus solution 3, pulses of Mo + P solution [reprinted with permission from Gishti et al. 59) copyright 1984 Elsevier Science].

Measurement. Flame Atomic Absorption. To obtain sufficient sensitivity for the measurement of molybdenum by flame atomic absorption, it is necessary to use a nitrous oxide-acetylene flame. Optimum conditions were established empirically by using standard aqueous molybdenum solutions. With the instrument used, the response of the flame AA measurement was linear up to a concentration of 100 /xg/ml, with a detection limit (S/N = 2) of 0.1 /xg/ml. With the ash from an original 100 g of sample and a final solution volume of 10 ml, a detection limit of 5-10 ng Mo/g was obtained. 

Figure 3 shows typical spectra taken shortly after the K3M0CI6 added had dissolved. The spectra obtained at high molybdenum concentration exhibited maxima at 425,552 and 685 nra. They resembled that reported by Scheffler [12] in chloroaluminate room temperatme melts. The spectrum obtained at low molybdenum concentration has similar peak maxima but also a fourth additional peak absorbance potential at 340 nm. The peak position steadily shifts with time to lower wave lengths, until the band maximum can no longer be resolved. This peak has not previously been reported in molybdenum solutions. 

The same traid may clearly be seen as was noticed for the electrochemical studies. The above electrochemical results indicate disproportionation of Mo(III) species solutions at concentrations below 0.05 moW. The complemoitary results got with UV-Visible spectroscopy is the presence of the absorption band initially at 340 nm in low molybdenum solution concentration. 

The aim of this work was to deposit molybdenum on a steel substrate at temperatures sufficiently low (< 650°C) in order to avoid structural modifications of the substrate. This is why the LiCl-KCl eutectic was selected as the solvent. A literature survey shows that molybdenum deposits have already been obtained from molten chlorides, fluorides, oxides, and mixed fluoride-oxide media, and that many questions concerning the chemistry of the molybdenum solutions and the reduction mechanism remain unanswered. In this paper, we will talk about the preparation of the molybdenum salt used as a solute, then describe the electrochemical kinetic investigation performed, and finally briefly outline a practical application of the knowledge gained during this work. 

Molybdenum solution prepared by dissolution of 50 g ammonium molybdate in water, 115 ml sulphuric acid (d = 1.84) and filled up to 1 liter Isobutanol... 

After addition of 10 ml molybdenum solution (I), the phosphoric molybdic acid is extracted with 10 ml isobutanol (J) (duration of shaking ca.30 sec). When the phases are separated, the aqueous phase (lower) is drained into a second separatory funnel and extracted again with 10 ml isobutanol. The extraction is once more repeated as described above, and the aqueous phase is discarded. 

Literature shows that phosphorus increases the solubility and stability of molybdenum solutions (ref. 1,4). Adsorption studies proposed that when alumina is coimpregnated with solutions containing molybdate and phosphate, there is a competition between both ions for the same adsorption sites (basic hydroxyl groups of alumina), thus, the adsorbed phosphate inhibits the adsorption of molybdates (3,6-9). However, most of these studies deal with molybdate and phosphate adsorption separately without considering the formation of phosphomolybdate compounds in the impregnating solution. 

It is used in certain nickel-based alloys, such as the "Hastelloys(R)" which are heat-resistant and corrosion-resistant to chemical solutions. Molybdenum oxidizes at elevated temperatures. The metal has found recent application as electrodes for electrically heated glass furnaces and foreheaths. The metal is also used in nuclear energy applications and for missile and aircraft parts. Molybdenum is valuable as a catalyst in the refining of petroleum. It has found applications as a filament material in electronic and electrical applications. Molybdenum is an... 

E. Vedejs (1978) developed a general method for the sterically controlled electrophilic or-hydroxylation of enolates. This uses a bulky molybdenum(VI) peroxide complex, MoO(02)2(HMPTA)(Py), which is rather stable and can be stored below 0 °C. If this peroxide is added to the enolate in THF solution (base e.g. LDA) at low temperatures, oneO—O bond is broken, and a molybdyl ester is formed. Excess peroxide is quenched with sodium sulfite after the reaction has occurred, and the molybdyl ester is cleaved to give the a-hydroxy car-... 

Moissanite, see Silicon carbide Molybdenite, see Molybdenum disulfide Molybdite, see Molybdenum(VI) oxide Molysite, see Iron(III) chloride Montroydite, see Mercury(II) oxide Morenosite, see Nickel sulfate 7-water Mosaic gold, see Tin disulfide Muriatic acid, see Hydrogen chloride, aqueous solutions... 

For nickel, cobalt, and hon-base alloys the amount of solute, particularly tungsten or molybdenum, intentionally added for strengthening by lattice or modulus misfit is generally limited by the instability of the alloy to unwanted CJ-phase formation. However, the Group 5(VB) bcc metals rely on additions of the Group 6(VIB) metals Mo and W for sohd-solution strengthening. 

United States included Waspaloy and M-252, which utilized molybdenum for s ohd-solution strengthening and carbide formation in addition to the y ... 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

Chemical products are produced from technical-grade oxide in two very different ways. Molybdenum trioxide can be purified by a sublimation process because molybdenum trioxide has an appreciable vapor pressure above 650°C, a temperature at which most impurities have very low volatiUty. The alternative process uses wet chemical methods in which the molybdenum oxide is dissolved in ammonium hydroxide, leaving the gangue impurities behind. An ammonium molybdate is crystallized from the resulting solution. The ammonium molybdate can be used either directly or thermally decomposed to produce the pure oxide, MoO. ... 

AMMONIUM compounds). Diammonium dimolybdate [27546-07-2] (NH 2 2 7 " ble commercially as the tetrahydrate and prepared from MoO and excess NH in aqueous solution at 100°C, has an infinite chain stmcture based on MoO octahedra. In aqueous solution the behavior of Mo(VI) is extremely pH-dependent (4). Above pH 7 molybdenum(VI) occurs as the tetrahedral oxyanion MoO , but below pH 7 a complex series of concentration-, temperature-, and pH-dependent equiUbria exist. The best known of these equiUbria lead to the formation of the heptamolybdate,... 

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

Molybdenum(V) compounds generally occur as mononuclear or dinuclear species. Molybdenum pentachloride [10241-05-1] MoCl, formed by combination of the elements, serves as a usebil and reactive starting material (Fig. 1). MoCl has a dinuclear stmcture (Fig. 3) in the soHd state but is mononuclear in the gas phase. In solution or in the soHd state the compound, actually Mo2C1 q (Fig- 3a), is readily hydroly2ed in air to form MoOCl ... 

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