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. Here we present a model study on the heat treatment of electrospun polyvinylpyrrolidone [PVP, (C 6 H 9 NO) n ] and ammonium metatungstate [AMT, (NH 4 ) 6 [H 2 W 12 O 40 ]· n H 2 O] nanofibers. It clearly demonstrates the importance of finding the
Abstract
The kinetics and mechanism of the dehydration and decomposition of heteropolyacids of molybdenum, tungsten and vanadium (H3+xYx+M12O40mH2O; Y=Si, P; M=Mo, W) were studied. The data obtained on the dehydration kinetic parameters correlate with the expected structures, of these crystal hydrates, the IR data and X-ray phase analysis.
Abstract
The use of XRD and DTA methods has allowed studies on the interaction of the SbVO5 and MoO3, taking place in the solid state and in the medium of ambient air. The experimental results of XRD and DTA for all the samples showed the presence of a novel phase, i.e. Sb3V2Mo3O21 apart from various amounts of MoO3 and V9Mo6O40 or SbVO5 and V2O5(s.s.). The SbVO5–MoO3 system is not a real two-component system over the entire range of component concentrations up to the solidus line.
Abstract
The extractability of99Mo-molybdophosphoric acid H3/PMo12O40/ and99mTc-pertechnetic acid /PTcO4/ in 20% (v/v) bis /2-ethylhexyl/ phosphoric acid /HDEHP/ in benzene has been investigated at different concentrations of HCl, HBr and HNO3 acids. The effect of extractant concentration and diluent on the extractability of molybdophosphoric and pertechnetic acids with 20% (v/v) HDEHP in benzene from different concentrations of HCl acid has also been studied.99Mo-molybdo-phosphoric acid was found to be selectively extracted and separated from99mTc-pertechnetic acid with 20% HDEHP in benzene at an acidity of about 0.49M HCl, HBr and HNO3. The extractability of H3/PMo12O40/ from these acids generally follows the decreasing order HBr>HCl>HNO3. The separation factors /Kd molybdophosphoric/Kd pertechnetic/ were found to be 12.9×105 and 7.6×105 for HBr and HCl, respectively. The extractability of pertechnetic acid follows the order HCl>HBr
HNO3. Benzene is the diluent due to its radiation stability. A new procedure for the separation of99mTc from99Mo was suggested.
New type of sorbents based on polyethers and some hydrophobic anions
II. Sorption of radium on polyethylene glycol — Metal(II) salts of heteropolyacids
Abstract
The preparation of sorbents composed of polyethylene glycol and metal(II) salts of heteropolyacids has been described. It has been found that the calcium salt of phosphomolybdic acid of the type Ca3(PMo12O40)2 is precipitated in the presence of polyethylene glycol (m.wt. 1000). In this precipitate one calcium cation combines approximately with 10.9 ethylene oxide units of polyethylene glycol. The solubility of the sorbents has been found to be several tenths of a gram per litre of water or 0.1M hydrochloric acid. The sorption of radium has been studied as a function of the composition of the sorbents. High distribution ratios (KD∼103∼104) have been reached using 0.1M hydrochloric acid solution.
Abstract
Thermal decomposition of BaC2O40.5H2O in air was studied by a combination of stepwise isothermal analysis (SIA) and non-isothermal thermogravimetry. The results from both techniques show that the crystal water is released in one step and that anhydrous barium oxalate is decomposed in one step, while BaCO3 decomposes in three steps to BaO, forming two intermediate compounds with the formulas of BaCO3(BaO)2 and (BaCO3)0.5(BaO)2.5. Reaction mechanism analyses using the data from SIA measurements show that the controlling mechanism for all the five decomposition steps in isothermal conditions is a two-dimensional phase-boundary controlled process. Kinetic parameters are obtained for the five decomposition steps from the non-isothermal thermogravimetric data.
Studies of the thermal behaviour of binary oxide mixtures containing vanadium(V) oxide (V2O5-TiO2, V2,O5- MoO3, V2,O5-ZrO2 and V2O5-ZnO) have shown that the evolution of gaseous oxygen at fairly low temperatures is characteristic of those systems which are eflective catalysts for the oxidation of hydrocarbons. No weight changes were observed with V2, O5-ZnO mixtures under these conditions and, in accordance with this, zinc(II) oxide does not enhance the catalytic activity of vanadium(V) oxide. In V2O5-containing systems, evolution of oxygen occurs during the reduction of V2O5 to V2O4. This process is accelerated in the presence of certain metal oxides and such acceleration may be caused by structural interactions at the interface of the oxides. Among the systems studied, the formation of compounds such as Mo6V9O40 is thought to be of little significance from the catalytic point of view.
Abstract
We studied the extraction of phosphomolybdic acid labelled with99Mo and32P and of other species extracted. From the influence of the acidity and of the concentration of excess molybdenum on the distribution coefficient of phosphorus, we propose the following equilibrium for the formation of phosphomolybdate in our experimental conditions
free
molybdenum has been shown. It can be eliminated by washing the organic phase with a 5M HNO3 solution. Subsequently we test a method using radioactive molybdenum, proposed by J. E. KENNEY and M. P. MENON1 for the titration of phosphorus in steels. Because of the presence of interfering elements (Nb, Zr, Ti, V, Si, etc.) specific conditions for the extraction of phosphomolybdic acid have to be found for the application of this method to steels.
(PW 12 O 40 ) as well as undecatungstophosphate (PW 11 O 39 ) for solvent free liquid phase oxidation of styrene using hydrogen peroxide as an oxidant. The oxidation reaction was studied by varying different parameters such as reaction time and amount
. Groups of Venturello [ 4 , 5 ] and Ishii [ 6 , 7 ] have contributed significantly to the developments of olefin epoxidation with H 2 O 2 based on [PW 12 O 40 ] 3− and {PO 4 [WO(O 2 ) 2 ] 4 } 3− . However, the Venturello–Ishii epoxidation system had
