Phase equilibria in the V2O5-Cr2O3 system

The phase equilibria in the total range of component concentrations in the V₂O₅-Cr₂O₃ system up to 1000 °C were studied by means of phase powder diffraction and DTA. Two compounds exist in the system: CrVO₄, melting incongruently at 860±5 °C, and Cr₂V₄O₁₃, which decomposes in the solid state at 640±5 °C to CrVO_4(s) and V₂O_5(s). At 645±5 °C, CrVO₄ and V₂O₅ form a eutectic mixture with the CrVO₄ content not exceeding 2% mol.

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Zusammenfassung Mittels DTA und Pulverdiffraktionsaufnahmen wurde das Phasengleichgewicht des Systems V₂O₅-Cr₂O₃ bis 1000 °C im gesamten Konzentrationsbereich untersucht. Innerhalb des Systemes existieren zwei Verbindungen: CrVO₄ mit einem inkongruentem Schmelzpunkt bei 860±5 °C und Cr₂V₄O₁₃, das sich in festem Zustand bei 640±5 °C in CrVO_4(s) und V₂O_5(s) zersetzt. Bei 645±5 °C bilden CrVO₄ und V₂O₅ ein eutektisches Gemisch mit einem maximalen CrVO₄-Gehalt von 2 mol%.

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DTA V₂₅-Cr₂₃ 1000° . : CrVO₄, 860±5° Cr₂V₄O₁₃, 640±5° CrVO₄ V₂O₅, 645±5° CrVO₄, 2 %.

     

Steroids of the furostan and spirostan series from Nolina microcarpa II. structures of nolinospiroside D and nolinofurosides D, E, and F

Proofs are given of the structures of two new glycosides of the furostan series isolated from the leaves of the plantNolina microscarpa S. Wats. (family Dracaenaceae). Nolinofuroside D is (25S)-furost-5-ene-1,3,22,26-tetraol 1-O--D-galactopyranoside 26-O--D-glucopyranoside (I), and nolinofuroside F is (25S)-furost-5-ene-1,3,22,26-tetraol 1-O--D-fucopyranoside 26-O--D-glucopyranoside 3-O--L-rhamnopyranoside (VII). The latter was characterized as its 22-O-methyl ether (VIII). Nolinofuroside E (IV) has the structure of (25S)-furost-5-ene-1,3,22,26-tetraol 26-O--glucopyranoside 1-O-[O--L-rhamnopyranosyl-(12)--D-fucopyranoside], which followed from the structure of the fermentation product (VI). The products of the fermentation of the above-named compounds were present in the plant in only trace amounts. Only one of them — nolinospiroside D (III) — has not been described previously. This monoside of the spirostan series is (25S)-spirost-5-ene-1,3-diol 1-O--D-galactopyranoside.M. V. Frunze Simferopol' State University. Institute of Chemistry of Plant Substances, Uzbek Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 678–686, September–October, 1991.     

On the formation mechanism of hexafluoropropylene oxide in low-temperature liquid-phase oxidation of hexafluoropropylene by molecular oxygen

The effect of initiation rate (dose-rate of -radiation) on the formation rate of hexafluoropropylene oxide has been studied. Experimental data confirm that the epoxide forms in the reaction R–O–C₃F ₆ ^· R^·+C₃F₆O, as contrasted to the generally accepted fragmentation of -peroxyalkyl radicals R–O–O–C₃F ₆ ^· RO^·+C₃F₆O.

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( -) . , , R–O–C₃F₆R+C₃F₆O R–O–O–C₃F₆RO+C₃F₆O.

     

Thermal decomposition kinetics of sodium metaperiodate

Aged and fresh samples of sodium metaperiodate are subjected to thermal decomposition studies in air by TG, DTG and DTA techniques. The kinetic parameters for their decomposition have been evaluated by weighted least squares method using equations of Coats-Redfern, Horowitz-Metzger and Freeman-Carroll. The results indicate that, within the limits of experimental error, ageing did not change the E^* values considerably.

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, . , -, - -. , , , E^*.

     

Isoflavones of the roots of Lupinus luteus

Conclusions For the first time in the isoflavone series, a compound which has the structure of 5,7-dihydroxy-3,4-methylenedioxyisoflavone (3,4-methylenedioxyorobol) and two of its glucosides — 3,4-methylenedioxyorobol 7-O--D-glucoside and 3,4-methylenedioxyorobol 7-O--D-glucosylglucoside — and also a genistein C-monoglucoside, have been described. The isoflavones were isolated from the roots ofLupinus luteus L. by preparative chromatography on paper and on columns of polyamide. In addition, the previously known genistein, genistein 7-O--D-glucoside (genistin), and genistein 7-O--D-glucosylglucoside have been obtained.V. F. Kuprevich Institute of Experimental Botany, Academy of Sciences of the Belorussian SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 162–166, March–April, 1974.     

Effect of hydrogen sulfide on the catalytic hydrodenitrogenation of 1,2,3,4-tetrahydroquinoline. Comparison of NiMo/Al2O3 and CoMo/Al2O3

The hydrodenitrogenation of 1,2,3,4-tetrahydroquinoline was carried out in a flow reactor (350 °C, 35 atm) over CoMo/Al₂O₃ and NiMo/Al₂O₃. It is shown that in both cases the addition of hydrogen sulfide to the feed promotes denitrogenation and inhibits hydrogenation.

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1,2,3,4- (350°C, 35 ) CoMo/Al₂O₃ NiMo/Al₂O₃. , .

     

Platinum-palladium catalysts for hydrogen fuel cell electrodes

Five series of Pt–Pd/C catalysts were prepared with different total metal loading and different atomic composition in Pt and Pd. The activity in electrooxidation of hydrogen were measured for all these catalysts. Electrooxidation of hydrogen is a structure insensitive reaction on platinum and a structure sensitive reaction on palladium. For bimetallic catalysts, curves of activity as a function of the composition of the catalyst can exhibit a maximum. Yet, metal loading can alter the atomic composition at which activities are maxima.

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Pt–Pd/C Pt Pd. . - - . . , .

     

Generation of mechanisms of chemical reactions. Gas phase CO+H2 reaction in the absence of catalysts

An algorithm for the generation of chemical reaction mechanisms in the absence of catalysts tested for the reaction of CO hydrogenation is suggested.

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. .

     

Thermal analysis of an epoxide resin system

TG, DTG, DTA and DSC methods were used to study the curing reaction of diglycidyl ether of bisphenol A and nadic methyl anhydride in the presence of a reactive diluent. DTG plots were used to identify the various stages of weight loss arising from volatilization of components from the resin formulation and pyrolysis of cured resin. DTA and DSC results established the temperatures at which catalysed and thermally activated cure occurred.The results demonstrate the advantages of combining thermogravimetry and differential thermal techniques to study some factors that affect resin cure and to establish the correct choice of temperature regime and catalyst.

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Zusammenfassung Die Härtung des Diglycidäthers von Bisphenol A und nadic methyl anhydrid in Gegenwart eines reaktiven Verdünnungsmittels wurde durch TG, DTG, DTA und DSC untersucht. Die verschiedenen Stadien des durch die Verflüchtigung von Komponenten der Formulierung und bei der Pyrolyse von gehärtetem Harz eintretenden Gewichtsverlustes wurden an Hand von DTG-Kurven identifiziert. Die Temperaturen, bei denen die katalytische und thermisch aktivierte Härtung einsetzt, wurden durch DTA- und DSC-Messungen ermittelt. Die Ergebnisse zeigen die Vorteile auf, die kombinierte thermogravimetrische und thermometrische Techniken bei der Untersuchung einiger die Harzbildung beeinflussender Faktoren und bei der Wahl der richtigen Temperaturverhältnisse und des Katalysators aufweisen.

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, , . , . , . , , .

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We gratefully acknowledge Harold Woodward for his support and helpful discussion.     

Influence of chemical non-steady-state on SO2 conversion in fluidized catalyst bed

The effect of the influence of catalyst non-steady-state on SO₂ conversion ion a fluidized catalyst bed has been studied depending on the ratio of relaxation time for the catalytic reaction step to the characteristic time of particles diffusion.

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.

     

Temperature-programmed hydrogen desorption from water on bimetallic catalysts Ir?Fe/Al2O3

Desorption of hydrogen liberated in the process of water decomposition on bimetallic catalysts (3% Ir–Fe/Al₂O₃) at linear temperature growth was observed. In the case of iridium the amounts of desorbing hydrogen are relatively small, whereas for iron they are many times greater.

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, 3% Ir–Fe/Al₂O₃ . , , .

     

Kinetics of thermal decomposition of pyrite in an inert atmosphere

The thermal decomposition of pyrite in an inert atmosphere was studied in order to obtain a detailed knowledge of the kinetics and mechanism of the reaction 2 FeS₂=2FeS+S₂, which is one of the methods of producing elementary sulphur. The process was studied under isothermal conditions at temperatures of 600, 660, 700, 750, 800 and 850 °C in a nitrogen atmosphere, by means of a thermobalance. The rate-controlling processes were determined and their kinetic parameters were calculated. The optimum temperature for the process was found to be 800 °C.

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Zusammenfassung Es wurde die thermische Zersetzung von Pyrit in inerter Atmosphäre bestimmt, um detaillierte Informationen über Kinetik und Mechanismus der Reaktion 2 FeS₂=2FeS+S₂, einer der Darstellungsreaktionen von elementarem Schwefel zu erlangen. Der Vorgang wurde mittels einer Thermowaage unter isothermen Bedingungen bei Temperaturen von 600, 660, 700, 750, 800 und 850 °C untersucht. Es wurden die geschwindigkeitsbestimmenden Schritte bestimmt und deren kinetische Parameter errechnet. Als Optimumtemperatur für diesen Prozeß erwies sich 800 °C.

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- 2FeS₂=2FeS + S₂, . 600, 660, 700, 750, 800 850 ° . , 800°.

     

The autocatalytic character of the reaction methanol to hydrocarbons over amorphous silica-alumina catalysts

Conversion of methanol to hydrocarbons was studied on an amorphous silica-alumina over the 330–420°C temperature range and contact times up to 8 h. The reaction was confirmed as autocatalytic from the results of varying both contact time and temperature.

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330–420°C 8 . , , , .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Thermal conductivity measurements on samples with low cross-sections

A simple, low-cost apparatus has been designed and constructed for measurement of the thermal conductivities of samples with low cross-sections (10^–7 m²). This apparatus has been used to determine variations in the thermal conductivity of the metallic glass Fe₈₀B₂₀ (Metglas 2605) in the crystallization process induced by thermal treatment.In spite of the simplicity, the deviations from the real values of thermal conductivities measured have been lower than 8%, which has proved to be satisfactory for establishing the glass formation, temperature, T₈, from changes in thermal conductivity.

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Zusammenfassung Eine einfache, billige Apparatur zur Messung der Wärmeleitfähigkeit von Proben mit kleinen Querschnitten (10^–7 m²) wurde entworfen und gebaut. Die Apparatur wurde zur Bestimmung von Veränderungen der Wärmeleitfähigkeit des metallischen Glases Fe₈₀B₂₀ (Mctglass 2605) während des durch thermische Behandlung ausgelösten Kristallisationsprozesses benutzt. Trotz der Einfachkeit betrug die Abweichung von den gemessenen tatsächlichen Wärmeleitfähigkeitswerten weniger als 8%, was sich als ausreichend für die Ermittlung der Glasbildungstemperatur 7₉ aus Veränderungen der Wärmeleitfähigkeit erwiesen hat.

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( 10^–7 ₄). Fe₈₀B₂₀ 2605) , . , 8%, _g .

     

Effect of deuteration on the thermal dehydration of lithium sulfate monohydrate

Effects of deuteration on the thermal stability, enthalpy change and kinetic parameters for the thermal dehydration of Li₂SO₄·H₂O were examined by means of TG and DSC. The enthalpy change for the monohydrate was smaller by 1.63±0.75 kJ/mol than that for the monodeuterate. The rate constant for the monohydrate was a little larger than that for the monodeuterate. However, the thermal stability, activation energy and frequency factor were practically unaffected by deuteration of the hydrate. It is suggested that the activation entropy as well as the activation energy should be considered in explaining the kinetic deuterium isotope effect in the thermal dehydration of Li₂SO₄·H₂O.

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Zusammenfassung Die Wirkung der Deuterisierung auf die Thermostabilität, die Enthalpie-Änderungen und kinetischen Parameter der thermischen Dehydratisierung von Li₂SO₄·H₂O wurden durch TG und DSC untersucht. Die Enthalpie-Änderung für das Monohydrat wurde um 1.63±0.75 kJ/mol niedriger gefunden als für das Monodeuterat. Die Geschwindigkeitskonstante für das Monohydrat war etwas größer als für das Monodeuterat. Die Thermostabilität, die Aktivierungsenergie und der Frequenzfaktor wurden jedoch von der Deuterisierung des Hydrats praktisch nicht beeinflußt. Es wird vorgeschlagen, daß bei der Erklärung des kinetischen Deuterium-Isotop-Effekts bei der thermischen Dehydratisierung von Li₂SO₄·H₂O sowohl die Aktivierungsentropie als auch die Aktivierungsenergie berücksichtigt werden müssen.

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, Li₂SO₄·H₂O. 1.63+0.75 /. , . , , . , Li₂SO₄·H₂O.

     

Thermal analysis of conducting polymers part I

Thermogravimetry (TG) has been conducted on a series of electroconducting acid-doped polyanilines. The weight loss results suggest that the majority of dopants are eliminated between 230 °C to 350 °C leaving behind the skeletal non-conducting polyaniline. The doped polyaniline are thermally more stable than the pristine polyaniline in air at high temperatures. This suggests that despite the early elimination observed, the presence of dopant at the begining has a stabilizing effect on the skeletal polyaniline. By comparison the acid-doped polyanilines are more thermally stable than many other electroconductive polymers, such as polypyrroles and polyacetylenes.

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Zusammenfassung An einer Reihe von elektrisch leitenden säureversetzten Polyanilinen wurden thermogravimetrische (TG) Untersuchungen durchgeführt. Die Gewichtsverluste zeigen, daß die Mehrzahl der Zusätze bei einer Temperatur zwischen 230 °C und 350 °C eliminiert werden, wobei die nichtleitenden Polyaniline zurückbleiben. Bei hohen Temperaturen ist das versetzte Polyanilin in Luft thermisch stabiler als das ursprüngliche Polyanilin. Das bedeutet, daß eine anfängliche Gegenwart der Zusätze ungeachtet der frühen Eliminierung einen stabilisierenden Effekt auf das Polyanilingerüst ausübt. Im Vergleich erwiesen sich säureversetzte Polyaniline als thermisch stabiler als andere elektrisch leitende Polymere wie z. B. Polypyrrole oder Polyazethylene.

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, . , 230–350°, . , . , , . , - , , , .

     

Simultaneous TG,DTG, DTA and EGA examination of argillaceous rocks. Part I

The suggested new measuring technique is based on the fact that in the course of the decomposition of clays only three gaseous decomposition products, i.e. SO₃ (SO₂), CO₂ and H₂O are being formed. By thermogastitrimetry the liberation process of the two former products is traced, while by means of a water detector the water released is determined in a selective way. Thus the overlapping processes can be separated. Interpretation and evaluation of the curves can be further improved by performing the examinations in N₂ and O₂ atmospheres respectively, which offers a possibility to conduct the reactions into another direction.

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Zusammenfassung Das empfohlene neue Meßverfahren basiert auf der Tatsache, daß im Verlauf der Zersetzung von Tonerde nur drei verschiedene gasförmige Produkte gebildet Werden: SO₃ (SO₂), CO₂ und H₂O. Der Prozeß der Freisetzung der beiden ersteren Produkte wird durch Thermogastitrimetrie verfolgt, das freigesetzte Wasser wird selektiv über einen Wasserdetektor bestimmt. Die einander überlagerten Prozesse können somit separat betrachtet werden. Interpretation und Ausweitung der Kurven können weiter verbessert werden, indem die Untersuchung auch in Stickstoff- und Sauerstoffatmosphäre durchgeführt wird, was die Möglichkeit darbietet, den Verlauf der Reaktion in eine andere Richtung zu leiten.

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, , , , ( ), . , . . , , , - .

     

Computation in kinetics I. A general program KILET for simulation and evaluation of kinetic experimental data in multicomponent systems

A general regression program KILET written in FORTRAN IV for an IBM PC and other computers (MV 4000 Eclipse and EC 1033) enables (i) to model multicomponent kinetic data (ii) to load the smooth curves with random noise of required level (iii) to evaluate rate constants and/or simultaneously concentrations. Complete statistical analysis of residuals is performed. The program can be used for the discrimination of chemical kinetic models and for analytical purposes.

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KILET, FORTRAN IV IBM PC (MV 4000 Eclipce EC 1033), 1) , 2) , 3) / . . .