Differential scanning calorimetric studies of several compounds showing order-disorder transition

Differential scanning calorimetric measurements have been carried out for Cul, CuBr, Agl, Ag₂S, NaNO₂, NaNO₃ and KSCN. First-order phase transformations occur with the compounds Cul, CuBr, Agl and Ag₂S; NaNO₂, NaNO₃ and KSCN exhibit -type transformations. The enthalpy changes due to phase transitions have been determined. Thermal hysteresis exhibited by these compounds have been examined in the light of their change in unit cell volumes.

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Zusammenfassung Es wurden DSC-Untersuchungen von Cul, CuBr, Agl, Ag₂S, NaNO₂, NaNO₃ und KSCN ausgeführt. Phasenübergänge erster Ordnung verlaufen bei den Verbindungen Cul, CuBr, Agl und Ag₂S, während NaNO₂, NaNO₃ und KSCN Übergänge des -Typs zeigen. Die Phasenübergängen zuzuschreibenden Enthalpieveränderungen wurden bestimmt. Die bei diesen Verbindungen auftretende thermische Hysterese wurde im Zusammenhang mit den Veränderungen des Elementarzellenvolumens untersucht.

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- Cul, CuBr, Agl, Ag₂S, NaNO₂, NaNO₃ KSCN. , Cul, CuBr, Agl Ag₂S -, a NaNO₂, NaNO₃ KSCN- -. . , , .

     

Exchange kinetics of amino acid anions in solutions of ternary copper(II) complexes with diethylenetriamine

Rate constants for the chemical exchange of some amino acid anions in solutions of copper(II) ternary complexes with diethylenetriamine have been determined by the NMR method. The coordination of amino acid anions in ternary and binary species is different and ligand substitution in the Cu(II) complexes follows an associative mechanism.

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- (II) . - (II).

     

Thermal decomposition of alkylcyclohexane mixtures

Thermal decomposition of model alkylcyclohexane mixtures with different ratios of components has been investigated. The possibility to estimate the yield of reaction products by calculating the relative activities of a group of hydrocarbons is shown.

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. .

     

Studies on the thermal decomposition of N-2,4,6 tetranitro-N-methyl aniline

The kinetics of the initial stage of thermal decomposition of N-2,4,6 tetranitro-N-methyl aniline (tetryl) in condensed state has been investigated by high temperature infrared spectroscopy (IR) in conjunction with pyrolysis gas analysis and thermogravimetry (TG). The decomposition in KBr matrix in the temperature range of 131 to 145 °C shows rapid decrease in the N-NO₂ band intensity as compared to the C-NO₂ band. Decomposition products in the initial stage show mainly NO₂ gas and picric acid. The studies show that the initial stage of decomposition of tetryl occurs by the rupture of the N-NO₂ bond and the energy of activation for this process is 177 kJ/mol.

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Zusammenfassung Mittels Hochtemperatur-IR-Spektroskopie wurde in Verbindung mit Pyrolysengasanalyse und Thermogravimetrie (TG) die Kinetik des einleitenden Schrittes der thermischen Zersetzung von N-2,4,6-Tetranitro-N-Methylanilin (Tetryl) im kondensierten Zustand untersucht. Die Zersetzung in einer KBr-Matrix im Temperaturbereich von 131–145 °C äußert sich in einem schnellen Abnehmen der Intensität der N-NO₂ Bande bezogen auf die der C-NO₂ Bande. Zersetzungsprodukte des einleitenden Schrittes sind hauptsächlich NO₂ Gas und Pikrinsäure. Die Untersuchungen zeigten, daß der einleitende Schritt der Zersetzung von Tetryl die Spaltung der N-NO₂ Bindung ist. Die Aktivierungsenergie für diesen Prozess beträgt 177 kJ/mol.

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N-2,4,6-N- () , . 131–145 °C N-NO₂ C-NO₂. . , N-NO₂, 177 /.

     

Reactivity of photoinduced hole centers on anatase and activation of molecular oxygen

The centers (g₁=1,999; g₂=1.984 and g₃=1.979) assigned to the stabilization of photoinduced O^– holes on coordinatively unsaturated Ti⁴⁺ ions, not interacting with CO up to 250 K, are shown to be the activation centers of the molecular oxygen as an complex (g₁=2.046; g₂=2.008) for CO oxidation even at 87 K with the formation of CO ₃ ^– (g=2.0285, g=2.005).

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, (g₁=1,999; g₂=1,984; g₃=1,979), O^– Ti⁴⁺, CO 250° K (g₁=2,046; g₂=2,008) CO 87°K CO ₃ ^– (g=2,0285) g=2,0055).

     

The influence of long additional thermal treatment of controlled porous glasses on the structuralization of their silica network

The materials used as sorbents in gas and liquid chromatography include controlled porosity glasses (CPG). The heating of CPG in the temperature range 400–800 °C leads not only to dehydroxylation of their surface, but also to a diffusion of the boron atoms (and a smaller amount of sodium atoms) remaining in the silica network of the CPG towards the glass surface. Simultaneously, crystallization of the silica network of the CPG takes place.The present paper deals with the changes of the crystallographic structures in thermally treated glasses which differ in their mean pore diameters. The results show not only the existence of cristobalite in the siliceous lattice of the heated glasses, but also the presence of -quartz, the very symmetrical structure of SiO₂.

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Zusammenfassung Gläser kontrollierter Porosität (CPG) gehören zu den in der Gas- und Flüssigkeitschromatographie verwendeten Sorbenten. Erhitzen von CPG auf 400–800 °C führt nicht nur zur Dehydroxylierung ihrer Oberflächen, sondern auch zur Diffusion der im Siliciumdioxidgitter des CPG verbleibenden Boratome (und in geringerem Maße auch von Natriumatomen) zur Glasoberfläche. Gleichzeitig erfolgt die Kristallisation des Siliciumdioxidgitters der CPG. Im vorliegenden Artikel werden die Veränderungen der kristallographischen Strukturen in thermisch behandelten, sich im mittleren Porendurchmesser unterscheidenden Gläsern untersucht. Es wird gezeigt, daß im Siliciumdioxidgitter der hitzebehandelten Gläser nicht nur Cristobalit, sondern auch die hochsymmetrische SiO₂-Struktur des -Quarzes vorliegt.

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, , . 400–800 °C , ( ) . . , . , - .

     

Study of oxygen adsorption on Pt(110) surface with EELS

The forms of oxygen adsorbed on Pt(110) are characterized using Electron Energy loss Spectroscopy (EELS).

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Pt(110).

     

n-Butane oxidation over a vanadium-phosphorus catalyst

The activity of vanadium-phosphorus oxide catalysts with respect to maleic anhydride formation in n-butane oxidation has been found to correlate with the concentration of V⁴⁺ ions in the catalysts. The steady catalytic activitv of the samples examined is achieved more rapidly upon prereduction.

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, - - . , .

     

Thermal decomposition of calcium sulphate in carbon monoxide

Simultaneous TG and DTA studies were performed on analytical grade calcium sulfate and on samples of natural gypsum and phosphogypsum in carbon monoxide atmosphere. The decomposition temperatures and mechanism are influenced by the mineral impurities of the sample and the heating rate as well as the CO content of the gas atmosphere.

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Zusammenfassung Simultane TG- und DTA-Untersuchungen von analytisch reinem Calciumsulfat und Proben von natürlichem Gips und Phosphogips wurden in Kohlenmonoxidatmosphäre ausgeführt. Temperatur und Mechanismus der Zersetzung werden durch mineralische Verunreinigungen der Probe, durch die Aufheizgeschwindigkeit und durch den CO-Gehalt der Gasatmosphäre beeinflußt.

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. - , , .

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The authors are indebted to Professor M. Veiderma for fruitful discussions and continuous support. The scholarship from Finnish Government to one of us (R. K.) is gratefully acknowledged.     

Establishment of chemical equilibrium: A mathematical characteristic

The time derivative of mean value of the state position indicator and the probability density of the first passage times for the state of exact equilibrium, both in the form of a function approximating the -distribution, characterize the establishment of macroscopic chemical equilibrium. The time parameter of this function has the meaning of the time required for chemical equilibrium to be established.

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, , -, . , .

     

m-Xylene isomerization/disproportionation selectivity over dealuminated Y zeolite

The conversion of m-xylene over dealuminated zeolite Y with different sodium exchange level has been studied. It has been established that m-xylene isomerization/disproportination selectivity depends on the concentration of the acid centers in the aluminium-deficient faujasite.

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- Y - . - /qd .

     

Reactivity of the carbonaceous surface overlayer on supported platinum catalysts studied by high temperature pyrolysis gas chromatography

The reactivity of the carbonaceous surface overlayer formed on Pt/Al₂O₃ catalysts in n-hexane dehydrocyclization has been studied by high temperature Pyrolysis Gas Chromatography. This method can be used to characterize surface carbon overlayers formed on different catalysts in the course of hydrocarbon reactions.

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, Pt/Al₂O₃ -, . , .

     

Hydrocarbon cool flame-induced transformations of alkali metal chlorides

Studies of the effect of stabilized cool flame propane oxidation on alkali metal chlorides have revealed the partial removal of surface chlorine and the formation of alkali and formiate. Formiate formation was tentatively detected by IR spectroscopy. Excess heating (up to 23°C) established on such surfaces in the zone of cool flame compared to untreated ones, can be due to the recombination of surface radicals.

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. , . . , . , 23°C, .

     

Kinetics of amine-inhibited naphthalene hydroxylation by rat liver microsomal cytochrome P-450

Inhibition constants for amine-inhibited naphthalene hydroxylation by rat liver microsomal cytochrome P-450 have been determined. Irrespective of the nature of the amine added, inhibition has a competitive character. The inhibition mechanism of cytochrome P-450 dependent hydroxylation is discussed.

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P-450 . , . - P-450- .

     

Thermal desorption analysis:

Experiments on water desorption from silicate glass powders of different chemical compositions were carried out by means of DSC. In order to establish the desorption energy distributions, a model of the heterogeneous surface was applied to the thermoanalytical desorption curves, and the results are discussed together with contact angle measurements on flat polished glass samples.The maxima in the desorption curves shift to lower temperature with increasing hydrophobic character; this is caused by divalent cations such as Pb²⁺, Ca²⁺ and Zn²⁺, while alkali metal ions are responsible for an increase in the hydrophilic behaviour.

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Zusammenfassung Wasserdesorptionsexperimente an Silikatglaspulvern unterschiedlicher Zusammensetzung wurden mittels DSC ausgeführt. Für die Berechnung von Desorptionsenergieverteilungen wurde ein Modell der heterogenen Oberfläche genutzt und zusammen mit Randwinkelmessungen an glatten, polierten Glasoberflächen diskutiert. Das Maximum der Desorptionskurven verschiebt sich mit wachsendem hydrophoben Verhalten nach tieferen Temperaturen, wofür divalente Kationen wie Pb²⁺ Ca²⁺ Zn²⁺ verantwortlich sind, während Alkaliionen das hydrophile Verhalten begünstigen.

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. . , , , .

     

Reactions of isoflavone and 2-hydroxyisoflavanone with sodium ethoxide in anhydrous ethanol

Recent observation /1,4/ on the existence and unreactivity of IV under basic conditions, as well as its part in the inhibitory effect on the decomposition into deoxybenzoin is unequivocally proved by comparing the decompositions of I and VI. It is also shown that the decomposition of I is detemined neither by the character of the solvent nor by the nucleophilic character of the reactant, but by the possibility of the formation of IV.

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IV , I VI. , I . , , IV.

     

Differential scanning calorimetry study of reactions of phenyl glycidyl ether with phosphoric acid

The reactions of phenyl glycidyl ether (PGE) with phosphoric acid in three molar ratios have been studied by means of DSC alone. The results obtained from isothermal measurements are as follows:H=–91.0 kJ/mole PGE(1:1 molar ratio);H=–100.5 kj/mole PGE (1:2/3 molar ratio).The DSC curves obtained from dynamic experiments are multipeaked and giveHvalues higher than those obtained from isothermal measurements. These results can be explained by taking into account the acid concentration, the different reactivities of the hydrogens of the phosphoric acid and the possibility that secondary reactions occur.

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Zusammenfassung Die Reaktion von Phenylglycidyläther (PGE) mit Phosphorsäure wurde bei drei verschiedenen molaren Verhältnissen allein mittels DSC untersucht. Isotherme Messungen ergaben folgende Werte:H=–91.0kJ/mol PGE (molares Verhältnis 1:1);H=–100.5 kJ/mol PGE (molares Verhältnis 3:2). Die bei dynamischen Experimenten erhaltenen DSC-Kurven weisen viele Peaks auf und ergebenH-Werte, die größer als die durch isotherme Messungen erhaltenen sind. Diese Ergebnisse können erklärt werden, wenn die Säurekonzentration, die unterschiedliche Reaktivität der Wasserstoffatome der Phosphorsäure und die Möglichkeit des Verlaufs sekundärer Reaktionen in Rechnung gestellt werden.

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() () . 11 12/3, H, –91.0 –100.5 ·^–1. , , H . , , .

     

Thermal analysis of phenolic resin based pyropolymers

The formation and thermal behaviour of pyropolymers based on novolak resin synthesized under carefully controlled processing conditions have been studied by various thermoanalytical techniques. A suitable reaction scheme has been proposed for the formation of these pyropolymers. Only a small (3–8%) weight loss has been observed up to 800 °C in static air. DTA curves confirmed multistage exothermic processes predominantly due to two different linkages which control their thermo/thermo-oxidative stability. Hot metal filtration (700 °C) in an inert atmosphere exhibited only negligible weight loss.

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Zusammenfassung Mittels verschiedener thermoanalytischer Verfahren wurde Bildung und thermisches Verhalten von Pyropolymeren auf Novolackbasis unter streng geregelten Reaktionsbedingungen untersucht. Zur Bildung dieser Pyropolymere wurde ein geeignetes Reaktionsschema entwickelt. In unbewegter Luftatmosphäre kann bis 800 °C nur ein geringer (3–8%) Gewichtsverluft beobachtet werden. Die DTA-Kurven zeigen einen exothermen Mehrstufenprozeß, der hauptsächlich auf zwei verschiedene Verkettungen zurückzuführen ist, welche die thermische/thermisch-oxidative Stabilität bestimmen.

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. . 800° (3–8%) . , , / - . (700° .

     

Temperature-programmed desorption of hydrogen from Rh/C catalysts

A strong temperature-activated character of hydrogen adsorption on the surface of Rh/C catalyst has been found, especially in relation to high-temperature form. The unreactivity of this form toward oxygen at room temperature suggests that its source is the carbon surface.

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- Rh/C, . .

     

Shape-selective ester hydrolysis by octadecyl immobilized H-ZSM-5 catalyst in liquid phase

The shape-selective property of octadecyltrichlorosilane treated H-ZSM-5, keeping the original acid strength (–5.6<Ho–3.0) in liquid phase in the hydrolysis of straight chain esters has been observed by comparing the reaction rates with those over octadecyltrichlorosilane treated SiO₂-Al₂O₃. The most pronounced effect was found in the case of ethyl decanoate, viz. ca. 6 times.

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H-ZSM-5, (–5.6<–3.0) , - . SiO₂–Al₂O₃, . , 6.