Das System KNbO3-Nb2O5

Zusammenfassung Das System KNbO₃–Nb₂O₅ wurde mit thermoanalytischen, dilatometrischen und röntgenographischen Methoden neu untersucht. Acht ternäre Verbindungen werden im Bereich von 0–50 Mol-% K₂O gefunden. Nur K₄Nb₆O₁₇ schmilzt kongruent, alle anderen zersetzen sich peritektisch. Bei den beiden niobreichaten ternären Verbindungen handelt es sich um Hochtemperaturphasen, die sich erst oberhalb 1273 bzw. 1551 K bilden. Drei der acht Verbindungen wandeln sich mit steigender Temperatur in ihre Hochtemperaturmodifikation um.

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The KNbO₃-Nb₂O₅ system was studied by thermal analysis, dilatometry and X-ray techniques. Eight ternary compounds were found in the range from 0 to 50 mol% K₂O. Only K₄Nb₆O₇ was found to melt congruently, the other compounds decomposed peritectically. For the two ternary compounds with the highest percentage of niobium high-temperature phases were observed which were formed only above 1273 and 1551°, respectively. Three of the compounds studied transformed into their high temperature modifications on heating.

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, $ KN₃-Nb₂O₅. 0 50 % . , K₄Nb₆O₇ , $ . $ $ 1273 1551°. $ $ .

     

A method for preliminary estimation of solid oxidation kinetics and mechanism

The possibility of preliminary estimation of the oxidation kinetics and mechanism using the quantity t_o from the exponential kinetic rate equation is discussed.

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, t_o .

     

Activity of γ-Al2O3 modified by NaOH in disproportionation of methanethiol

Na⁺/Al₂O₃ catalysts in disproportionation of methanethiol are highly selective towards dimethyl sulfide but less active compared to -Al₂O₃. Their activity falls with increasing Na⁺ in the sample. This decrease is due to the neutralization of Brönsted acid centers on the catalyst.

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Na⁺/Al₂O₃ , , -Al₂O₃. Na⁺ . .

     

Hysteresis of thermogravimetric curves of nickel catalysts for methane conversion in CH4+CO2 mixture

Characteristic peculiarities of the supercarbonization peak, i. e. the effect of carbon accumulation on the catalyst surface and its subsequent removal under heating in the CH₄+CO₂ mixture have been studied. Hysteresis of thermogravimetric curves in the heating/cooling cycle has been established.

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Chain transfer mechanism and kinetics in radical telomerization of ethylene with bromalkanes

Rate constants for chain transfer via bromoalkanes of various structure are estimated for primary, secondary and tertiary alkyl radicals and isokinetic dependences are shown to exist for their activation parameters. Isokinetic temperatures are calculated.

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Ausbrennen von Kohlenstoffhaltigen,in den Ziegelrohstoff Eingepressten Stoffen

Zusammenfassung Die Kinetik der Ausbrennung organischer Stoffe im Ziegelscherben wird verfolgt und erläutert. Die Möglichkeiten der Beeinflussung des energetischen Aufwandes unter Nutzung moderner analytischer Methoden sind festzustellen. Bei einem diffusen Ausbrennen ist die Dichte und Durchlässigkeit des Scherbens massgebend. Praktische Anwendungsmöglichkeiten verschiedener auszubrennender Stoffe in unterschiedlichen Rohstoffen der Ziegelindustrie.

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The kinetics of burn-out of organic materials in bricks has been followed and explained. It is to establish that using new analytical methods the energy consumption can be influenced. The diffuse burn-out is determined by the density and permeability of bricks. There is a possibility for practical use of the results in the brick-industry with the different compounds to be burnt out from various raw materials.

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Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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, . : > > > . .

     

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.

     

Comparison of properties of supported organozirconium catalysts containing zirconium ions in different valence states

A comparison of the properties of supported zirconium catalysts containing zirconium ions in different valence states in ethylene polymerization shows that an increase in the proportion of active centers involving Zr(III) ions results in a decreasing molecular weight of the polymer. The catalyst activity is practically unchanged.

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, , . , , Zr(III) . .

     

Activity in CO oxidation of manganese dioxide for batteries

The low temperature oxidation of CO over MnO₂ containing samples for batteries has been investigated. It is found that the samples contain compositional and hydrate water and Mn⁴⁺, Mn³⁺, Mn²⁺ ions. The high efficiency is due to Mn⁴⁺ content.

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CO MnO₂, . , Mn⁴⁺, Mn³⁺, Mn²⁺. Mn⁴⁺.

     

Solid aluminiumalkyl-based isomerization catalysts. Surface acidity and catalytic activity

Isomerization catalysts with high activity and selectivity were prepared by chemical anchoring of aluminiumethyldichloride on the surface of inorganic oxides. Surface acidity was studied by calorimetric and IR spectroscopy methods, and was found to correspond well with catalytic activity for m-xylene isomerization.

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. . , -.

     

On the relationship between thermal stability and catalytic properties of supported molyboo-vanado-phosphoric heteropoly acids

Catalytic properties of four heteropoly acids of the molybdophosphoric type were studied in the selective oxidation of isobutene to methacrolein. Results show that the highest selectivities for methacrolein were achieved with samples in which the original structure of the heteropoly anion is least affected by thermal destruction.

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. , .

     

Kinetics of reaction between 1,3-butadiene and p-benzoquinone

Kinetics of Diels-Alder reaction between 1,3-butadiene and p-benzoquinone in benzene and glacial acetic acid as a catalyst has been studied. Influence of reactant and catalyst concentrations on the rate has been established. Kinetic equation has been derived to describe experimental data.

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- 1,3- 1,4- - . , .

     

Reactive silica, XIV. Sorption and polymerization of ethylene oxide on reactive silica

Ethylene oxide vapor was exposed to reactive silica (RS). It chemisorbed immediately on a pair of silicon radicals as –O–CH₂–CH₂–, and the adsorbed species polymerized. It is assumed that polymerization is not an ionic but a radical type reaction.

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. –O–CH₂–CH₂– . , , .

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Part XIII: Ref. 15     

Possibilities of applying the piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and their derivatives

Piloyan activation energiesE as well as initals of exothermT _D of sevenN-monoalkyl and fiveN,N-dialkyl-2,4-dinitroanilines were determined. Relationships were found between the T_D values and R_f factors as well asE values and those R_M functions and also theET _D ^–1 term and R_M functions.

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Zusammenfassung Die AktivierungsenergienE nach Piloyan sowie die Anfangswerte der ExothermenT _D wurden für siebenN-Monoalkyl- und fünfN,N-Dialkyl-2,4-dinitroaniline bestimmt. Die Zusammenhänge zwischen denT _D-Werten und den papierchromatographischenR _f-Faktoren der gemessenen Dinitroaniline wurden abgeleitet und erörtert. Desgleichen wurden auch die Zusammenhänge zwischen denE-Werten und denR _M-Funktionen der Papierchromatographie abgeleitet und erörtert. Auch zwischen dem AusdruckE ·T _D ^–1 und denR _M-Funktionen wurde ein Zusammenhang gefunden.

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Résumé On a déterminé les températures initialesT _D de l'effet exothermique ainsi que les énergies d'activationE d'après la méthode de Piloyan, de sept N-mono alcoyl et cinqN,N-dialcoyl-2, 4-dinitroanilines. Une corrélation entre les valeursT _D et les facteursR _f de la Chromatographie sur papier des dinitroanilines étudiées a été trouvée et discutée, ainsi qu'entre les valeursE et les fonctionsR _M de la Chromatographie sur papier. Une relation entre le termeE ·T _D ^–1 et les fonctionsR _M a également été trouvée.

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E T _D N- N,N- -2,4- . _D R _f , E R _M. E. _D ^–1 R _M.

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The authors would like to thank Mrs. Anna Collàkovà for careful DTA measurements, and Dr. Ladislav Smolka for help in treatment of the measured results with the Wang 600 computer.     

The thermal analysis of “argentic oxynitrate” and silver oxides

The precise stoichiometry of argentic oxynitrate has been elucidated by analytical and thermal analytical techniques. A decomposition path of the oxynitrate has been proposed and values of the enthalpy changes obtained. TG has been used as the criterion of purity of silver(II) oxide and new values for the heat of formation of silver(I) and silver(II) oxide are reported.

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Zusammenfassung Die genaue Stöchiometrie des Silberoxynitrats wurde durch analytische und thermoanalytische Prüfung geklärt. Der Zersetzungsvorgang des Oxynitrats wurde verfolgt und die Enthalpieänderungen beobachtet. Die Reinheit von Silber(II)oxyd läßt sich thermogravimetrisch kontrollieren. Es wurden neue Werte für die Bildungswärmen des Silber(II)oxyds und Silber(I)oxyds gefunden.

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Résumé Etude de la stoechiométrie précise de l'oxynitrate argentique par les techniques analytiques et thermoanalytiques. On propose un schéma de décomposition de l'oxynitrate et l'on évalue les variations d'enthalpie. Emploi de la TG comme critère de pureté de l'oxyde d'argent(II). Communication de nouvelles valeurs pour les chaleurs de formation des oxydes d'argent (I) et d'argent (II).

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. . (II) . (I) (II).

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The authors wish to thank Mr. J. McEwan and Mrs. I. M. Walker for valuable practical assistance and the United Kingdom Atomic Energy Authority for financial support.     

Reaction mechanism and principles of choosing catalysts for selective oxidation at C?H bonds

Reaction mechanism for selective oxidation of organic compounds at C–H bonds is discussed. The criteria of selecting catalysts for these reactions have been formulated; 1) fast heterolytic activation of C–H bonds; 2) relatively slow primary activation of oxygen; 3) fast diffusion of oxygen vacancies; 4) fast electron transfer from the adsorbed substrate to catalyst.

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C–H . : 1) C–H ; 2) ; 3) ; 4) .

     

Kinetics of ion exchange sorption of phosphate

The kinetics of phosphate sorption on Amberlite IRA-400 has been studied as a function of temperature, nature of counterions, at two different concentrations. The film and particle diffusion coefficients and the activation parameters of the process are calculated.

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IRA-400 , . .

     

Effect of methanol dilution on H-ZSM-5 zeolite deactivation in the process of light olefin formation

Conversion of methanol in the presence of H₂O, O₂, H₂, CO, CO₂ and He was studied at 733 K on H-ZSM-5 zeolite. The effect of diluent on the selectivity to light olefins and resistance to coking of H-ZSM-5 were observed. Among the diluents studied only water exerts a promoting effect on prolonged activity of the catalyst. Some explanations of the deactivation process are given.

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H₂O, O₂, H₂, CO, CO₂ He H-ZSM-5 733K. H-ZSM-5. . .

     

Thermal characterization of bismaleimide blends

4,4-bismaleimidophenyl methane (BM) and 3,3-bismaleimidophenyl sulfone (BS) were blended in solution using weight ratios 31 (MS31), 21 (MS21), 11 (MS11), 12 (MS12) and 13 (MS13). Chain extended bismaleimide resins were also prepared by treating BS/BM with 4,4-diaminodiphenyl ether in molar ratios of 10.3 (BM-E and BS-E resins). These resins were also blended with bismaleimides and the curing characteristics were evaluated by differential scanning calorimetry. Increase in BM content in BMBS blends or increase in chain extended bismaleimide content in BM-EBS or BS-E BM blends resulted in a reduction of melting and curing temperatures. Indication about the extent of cross-linking was obtained from solubility measurements (in DMF) of isothermally cured resins (180 °C, lh and 220 °C, lh in an air oven). Thermogravimetric analysis of samples isothermally cured at 180 °C and 220 °C (lh each) was carried out in nitrogen atmosphere. Improvement in thermal stability of chain extended bismaleimides was observed on blending.

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Zusammenfassung 4,4-Bismalimidophenyl-methan (BM) und 3,3-Bismalimidophenyl-sulfon (BS) wurden in Lösung in den Gewichtsverhältnissen 31 (MS31), 21 (MS21), 11 (MS11), 12 (MS12) und 13 (MS13) gemischt. Auch kettenpolymerisierten Bismalimid-Harze wurden durch Behandlung von BS/BM mit Diaminodiphenylether im Molverhältnis 10,3 dargestellt (BM-E- und BS-E-Harze). Die Kennwerte der Aushärtung von Mischungen dieser Harze mit den Bismalimiden wurden mittels DSC ermittelt. Eine Erhöhung des BM-Gehaltes in den BM BS-Mischungen oder des Gehaltes der BM-E BS oder BS-E-Mischungen an kettenpolymerisierten Bismalimiden führt zu einer Erniedrigung der Schmelz- und Aushärtetemperaturen. Hinweise über den Vernetzungsgrad wurden aus Löslichkeitsmessungen (in DMF) von Isotherm (je 1 Stunde bei 180 und 220 °C in Luft) gehärteten Harzen erhalten. Die thermogravimetrische Analyse der Isotherm bei 180 bzw. 220 °C 1 Stunde ausgehärteten Proben wurde in Stickstoffatmosphäre ausgeführt. Die thermische Stabilität der Bismalimide wird durch Verschneiden verbessert.

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4,4-- () 3,3-- () 31 (MC 31), 21 (MC 21), 11 (MC 11), 12 (MC 12) 13 (MC13). - / 4,4- 10,3 ( - C-). - . - - - - , . ( 1 180 220°) . . - .

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The financial assistance provided by Department of Science and Technology is gratefully acknowledged.