Thermodynamic data on chalcogenide glasses

The temperature-dependence of the specific heat near to the glass temperature was investigated for several Te- and As-based chalcogenide glasses, the latent heats of melting and crystallization of the former alloys also being measured. No thermal change could be detected in the transformation of the As-based alloys from the solid to the liquid state.

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Zusammenfassung Die Temperaturabhängigkeit der spezifischen Wärme verschiedener Te- und As-Chalkogenid Gläser wurde in der Nähe der Glastemperatur untersucht, indem die latente Schmelzwärme und die Kristallisation gemessen wurden. Bei den Legierungen auf As-Basis konnte nach dem Übergang von dem festen in den flüssigen Zustand keine thermische Veränderung nachgewiesen werden.

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Résumé On a étudié au voisinage de la température de la transition vitreuse la variation de chaleur spécifique en fonction de la température pour différents verres à base de chalcogénures de Te et As, en mesurant la chaleur latente de fusion et de cristallisation. Pour les alliages à base d'arsenic on n'a pas détecté de changement thermique après la transformation de l'état solide à l'état liquide.

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Te As . . As .

     

Percolation Effects on the Surface of a Polyimide Film Modified with Aqueous Solutions of an Alkali and Acid

A cluster structure of the surface of a polypyromellitimide film was studied by the electron microscopy and ATR IR spectroscopy methods at different steps of consecutive treatment with aqueous solutions of an alkali and acid. The effective size and fractal dimension D of polyamidoacid clusters, as well as the degree _s of the filling of the surface with the latter were calculated from the data of the electron microscopy as a function of the degree of imide group conversion into amidoacid units on the film surface. The _s and D parameters were shown to increase with a rise in : _s = 0.1–0.3 and D = 1.3–1.4 at < _cr and _s 0.6 and D 1.7 at > _cr, where _cr is a critical degree of conversion, which corresponds to the formation of a continuous physical network of polyamidoacid macromolecules or a percolation cluster. In a region close to _cr (at < _cr), the correlation length land the concentration C of the clusters vary according to the laws of the percolation theory for two-dimensional lattices: l (_cr – )^– and C (_cr – ), where = 1.3 ± 0.1 and = 0.67 ± 0.05.     

Triterpene Glycosides of Tragacantha Stipulosa and Their Genins. Structures of Askendosides G and D and Cycloglobiceposide B from One- and Two-Dimensional 1H and 13C NMR Spectroscopy

Roots of Tragacantha stipulosa Boriss yielded three triterpene glycosides of the cycloartane series: askendoside G (1), askendoside D (2), and cycloglobiceposide B (3). Glycoside 1 is 3-O--L-arabinopyranosyl-(12)--D-xylopyranoside; 16-O--D-glucopyranoside-24R-cycloartan-3,6,16,24,25-pentaol; 2 - 3-O--L-arabinopyranosyl-(12)--D-xylopyranoside; 6-O--D-xylopyranoside-20R,24S-epoxycycloartan-3,6,16,25-tetraol; 3 - 3-O--D-xylopyranoside; 16-O--D-glucopyranoside; 25-O--D-glucopyranoside-24R-cycloartan-3,6,16,24,25-pentaol.     

Interaction of PM12?nVnO40?(3+n) (M=Mo, W) heteropoly complexes with nitrogen oxide

In aqueous solution, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) hetero-polyanions provide a much faster oxidation of NO than mononuclear VO ₂ ⁺ ions, yielding HNO₂, NO ₃ ^– and reduced HPA.

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, PM_12–nV_nO₄₀ ^–(3+n) (M=Mo,W) , VO ₂ ⁺ , NO HNO₂ NO ₃ ^– .

     

Molecular Recognition Based on Roof-shaped Diol Hosts. X-Ray Crystal Structures of Inclusion Compounds with Methanol, Pyridine and Toluene

Three crystalline inclusion compounds of roof-shapedtrans-11,12-bis(diaryl-hydroxymethyl)-9,10-dihydro-9,10-ethanoanthracene host molecules [where aryl is 4-methyl-phenyl (3) or4-t-butylphenyl (4)] have been studied by X-ray diffraction.The crystals of both the 3methanol (2 : 1) [a = 10.755(1),b = 11.571(1), c = 14.697(2) Å, = 75.12(1), = 89.67(1), = 87.13(1) °] and the 4-pyridine (2 : 3) compounds[a = 14.045(3), b = 14.366(3), c = 15.607(3) Å, = 91.62(1), = 103.65(1) and =116.05(1)°] are triclinic (P–1),while the 3toluene (1 : 1) complex has orthorhombic (Fddd) symmetry [a = 16.041(1), b = 25.008(1), c = 40.440(4) Å]. The host–guest interactions in both triclinic crystals are characterised by hydrogen bonds, with different patterns however. The determined crystal structures indicate a compromise between the requirement of hydrogen bonding on the one hand and close packing on the other. The highly symmetrical host framework in the toluene (1 : 1) complex of 3 seems to be the result of shape recognition, although atendency towards weak (C_methyl)H _arylinteractions [C_methyl = 3.533(7) and 3.674(6) Å] between the hosts was observed. The present roof-shaped diol hosts give excellent examples of molecular recognition by exhibiting two significantly different conformations, mostly depending on the proton donor/acceptor ability of the guest component. (O)H O intramolecular bonding between the two alcoholic groups characterises the so-called active form, whereas weaker (O)H and interactions stabilise the `inactive'conformation.     

Thermal and other studies on bivalent metal selenltes

BaSeO₃·2·5H₂O(I), PbSeO₃· 2H₂O(II) and CdSeO₃·3.5H₂O(III) were prepared and analysed. Their hygroscopicity and solubility was investigated. These compounds have high thermal Stability, as shown by their TG and DTA data. IR spectra show multi-dentate coordination of selenite to cations, due to considerable splitting of the asymmetric v₃ and v₄ bands of SeO ₃ ^{2 –} in the 780-730 cm^–1 and 420-325 cm^–1 region.Tentative structures have been proposed involving bridging oxygen atoms.

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Zusammenfassung BaSeO₃-2.5H₂O(I), PbSeO₃ · 2H₂O(II) und CdSeO₃· 3.5H₂O(III) wurden hergestellt, analysiert sowie deren Hygroskopizität und Löslichkeit untersucht. TG- und DTA-Untersuchungen erweisen die hohe thermische Stabilität dieser Verbindungen. Die IR-Spektren zeigen mehrzählige Koordination von Selenit zu Kationen, was aus einer beträchtlichen Aufspaltung der antisymmetrischenv ₃ undv ₄ Banden von SeO ₃ ^{2 –} im Bereich 780-730cm^–1 bzw. 420-325 cm^–1 hervorgeht. Es wurden versuchsweise Strukturen mit überbrückenden Sauerstoffatomen vorgeschlagen.

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BaSeO₃· 2,5H₂O, PbSeO₃ · 2H₂O CdSeO₃ · 3,5H₂O . . - , v ₃ v ₄ SeO ₃ ² }- 780-730 420-325 ^–1. , .

     

Preparation et proprietes physico-chimiques de l'hydrure d'aluminium AlH3γ

Résumé AlH₃ a été synthétisé. La décomposition thermique de cet hydrure ainsi que la désolvatation de Al(AlH₄)₃, (C₂H₅)₂O ont été étudiés par analyse thermogravimétrique. L'analyse thermique différentielle effectuée sur AlH₃ montre un effet exothermique dû au passage à la forme AlH₃ puis endothermique correspondant à la décomposition de la phase formée. Une structure type alanate est proposée pour AlH₃ .

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Aluminium hydride has been synthetised. Thermogravimetry has been used to investigate the thermal decomposition of this phase and the desolvation of A1(AlH₄)₃· (C₂H₅)₂O. Differential thermal analysis of-AlH₃ shows an exothermic effect due to transformation to -A1H₃, followed by the endotherm of -AlH₃ decomposition. A structure of alanate type is proposed for -AlH₃.

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Zusammenfassung -AlH₃ wurde synthetisiert. Die thermische Zersetzung dieses Hydrids sowie die Desolvatation von Al(AlH₄)₃·(C₂H₅)₂O wurden mittels Thermogravimetrie untersucht. Die Differentialthermoanalyse von-AlH₃ zeigt einen dem Übergang in die AlH₃ -Form entsprechenden exothermen und mit nachfolgenden endothermen Effekt, welcher der Zersetzung der gebildeten Phase entspricht. Eine Struktur von solvatfreien Alanat-Typ wird für-AlH₃ vorgeschlagen.

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- . l(l₄)₃. (C₂H₅)₂O . l₃ , l₃. lH₃ .

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Ce travail a été effectué dans le cadre d'un contrat de recherches passé par le Laboratoire de Chimie Minérale avec la Direction des Recherches et Moyen d'Essai. Nous remercions bien vivement cet organisme ainsi que le Centre de Recherches ELF ERAP de Solaize de l'aide qu'ils nous ont apportée.     

Thermodynamics of 2,2′,2′'-terpyridinecopper(II) complexes in aqueous solution

Summary The thermodynamic quantities relative to the protonation and the complexation of 2,2,2'-terpyridine with copper(II) ion have been determined at 25° and I=0.1 mol dm^–3 (NaNO₃). The G data was obtained by potentiometric measurements; a copper selective electrode was employed for the study of the complexation equilibria. The H values have been determined by direct calorimetry.The hydrolytic species, existing at pH>6 and their relative G and H values have also been obtained.From the thermodynamic data the importance of enthalpy and entropy terms in stabilizing the complexes is assessed.Moreover some considerations on the chelating effect are reported.Presented in part at 2 Congresso Nazionale di Chimica Analitica, Catania (1977).     

Mössbauer study of the thermal decompositions of alkaline earth tris(oxalato)ferrates(III)

The thermal decompositions of alkaline earth tris(oxalato)ferrates(III) (Mg, Ca, Sr and Ba) have been studied by Mössbauer spectroscopy and other techniques. During the thermal decomposition, dehydration occurs first, followed by reduction to iron(II) species, and oxides and ferrites (MFe^IIIO₄) are then formed at higher temperature. In the case of strontium tris(oxalato)ferrate(III), strontium ferrite (SrFe^IVO₄) is formed at 700°.

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Zusammenfassung Die thermische Zersetzung von Tris(oxalato)ferraten(III) der Erdalkalimetalle (Mg, Ca, Sr, Ba) wurde durch Mössbauer-Spektroskopie und andere Techniken untersucht. Im Verlaufe der thermischen Zersetzung verläuft zunächst die Dehydratisierung, gefolgt von der Reduktion zu Eisen(II)-Species. Oxide und Ferrite (MFe^IIIO₄) werden danach bei höheren Temperaturen gebildet. Strontium-tris(oxalato)-ferrat(III) geht bei 700 °C in Strontiumferrit (SrFe^IVO₄) über.

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() () , , ë . , , MFe^IIIO₄. 700° SrFe^IVO₄.

     

Study of the solid solution of MoO3 in Fe2V4O13

Differential thermal and phase X-ray analyses have shown that MoO₃ and Fe₂V₄O₁₃ form a solid substitution solution, in which Mo⁶⁺ ions are incorporate into the crystal lattice of Fe₂V₄O₁₃ in place of V⁵⁺ ions. The solubility limit of MoO₃ in Fe₂V₄O₁₃ at ambient temperature is 18 mole % of MoO₃. The phase equilibria in the system Fe₂V₄O₁₃-FeVMoO₇, were also studied. Results are presented in the form of a phase diagram.

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Zusammenfassung Durch DTA und Röntgenphasenanalyse wurde gezeigt, daß MoO₃ und Fe₂V₄O₁₃ Substitutionsmischkristalle bilden, in denen Mo⁶⁺-Ionen anstelle von V⁵⁺-Ionen in das Kristallgitter von Fe₂V₄O₁₃ eingebaut sind. Die Löslichkeitsgrenze von MoO₃ in Fe₂V₄O₁₃ beträgt bei Umgebungstemperatur 18 Mol-% MoO₃. Ebenfalls wurden die Phasengleichgewichte im System Fe₂V₄O₁₃-FeVMoO₇ untersucht. Die Ergebnisse sind in Form eines Phasendiagramms dargestellt.

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- , ₃ Fe₂V₄O₁₃ , o⁶⁺ V^5– Fe₂V₄O₁₃. ₃ Fe₂V₄O₁₃ 18 %. Fe₂V₄O₁₃-FeVMoO₇ .

     

Proton Magnetic Resonance and Molecular Simulation in Configurational and Conformational Analysis of Cyclohexanone Derivatives

Developing the previously tested approach to the configurational and conformational analysis of cyclic chiral compounds based on a complex use of NMR spectra and molecular simulation, we determined the configuration 1R, 2R, 4R, 1S and conformational state of 2[1hydroxy1(4carbomethoxyphenyl) methyl]pmenthane3one, a minor product of the directed aldol reaction of (–)menthone with 4carbomethoxybenzaldehyde. The configurations of the cyclic chiral centers were determined by analysis of the spin–spin coupling constants of the protons of the cyclohexanone ring for the most probable conformations of alternative stereoisomers. The S configuration of the C (1) exocyclic chiral center was established from the different orientation of the benzene ring relative to the cyclohexanone fragment in alternative stereoisomers, as shown by semiempirical quantumchemical simulations (AM1 and PM3 methods), and from the observed difference in proton chemical shift between the examined hydroxyketone and the model (+)isomenthone (1R, 4Rdiastereomer).     

Catalytic conversion of dimethylsulfide to methylmercaptan

The effect of reaction conditions on the methylmercaptan formation from dimethylsulfide in H₂S catalyzed by -Al₂O₃ has been studied. The reaction is first order with respect to dimethylsulfide. It has been revealed that the maximum activity in this reaction is observed for the catalysts whose surface contains a large number of aprotonic acid centers and moderate-strength basic sites.

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-Al₂O₃. , . . , , .

     

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH₂O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO₂), condensation (C₂H₄, C₂H₆) and methanation products through CH₃O^– formation and decomposition.

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(600–750°C) CH₂O - . , (CO, CO₂) (C₂H₄, C₂H₆), , CH₃O^–.

     

Effects of some admixtures on the decomposition of calcium sulphate

The by-product phosphogypsum contains CaHPO₄, H₃PO₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ etc. besides the main product CaSO₄. By means of TG-DTA the thermochemical decomposition of pure phosphogypsum and phosphogypsum containing CaO, Al₂O₃, Fe₂O₃ and SiO₂ in a reductive atmosphere was studied. The solid phase was examined by high-temperature thermomicroscopy, scanning electronmicroscopy, X-ray diffraction and other methods. It could be confirmed, that most of the admixtures undergo secondary reactions with CaO and CaS, modifying the decomposition rate of CaSO₄.

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Zusammenfassung Das Abfallprodukt Phosphatgips enthält neben dem Hauptbestandteil CaSO₄ noch CaHPO₄, H₃PO₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ und anderes. Die thermochemische Zersetzung von Phosphatgips bzw. Phosphatgips mit Zusätzen von CaO, Al₂O₃, Fe₂O₃ und SiO₂ wurde in reduzierender Atmosphäre mittels TG-DTA untersucht. Die feste Phase wurde durch Hochtemperatur-Thermomikroskopie, Rasterelektronenmikroskopie, Röntgenbeugung und andere Methoden untersucht. Dabei wurde bestätigt, dass die meisten Beimengungen mit dem Calciumoxid bzw. -sulfid Sekundärreaktionen eingehen, wodurch auch die Zersetzungsgeschwindigkeit des CaSO₄ beeinflusst wird.

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, , ₄, Ca₅(PO₄)₃F, Al₂O₃, Fe₂O₃, SiO₂ . - , , , . , , . , , .

     

Effect of preparation method of nickel-zeolite catalysts on their catalytic properties

The effect of the carrier-gas (H₂, N₂, CO₂ and air) and the influence of additives (H₂S and water vapors) in the activation of Ni- and Cr-containing zeolites on their catalytic activity have been studied in toluene disproportionation.

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- (H₂, N₂, CO₂ ) (H₂S ) , Ni Cr, .

     

Calorimetric measurement of structural relaxation in chalcogenide and metallic glasses

Some special characteristics of the structural relaxation (SR) in chalcogenide and metallic glasses are presented and the current theories dealing with the physical nature of the SR are recalled. The type of experiments used to measure SR by differential scanning calorimetry are reviewed and some rules to be taken into account when measuring calorimetrically the SR are stressed.

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Zusammenfassung Es werden einige spezielle Charakteristiken der Strukturrelaxation (SR) von Chalkogeniden und Metallgläsern vorgestellt und die gegenwärtigen Theorien über die physikalische Natur der SR zitiert. Die Art von Experimenten zur Messung von SR mittels DSC wurden kritisch besprochen und einige inbetrachtzuziehende Regeln für die kalorimetrische Bestimmung der SR hervorgehoben.

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. , . , . , .

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This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) project MAT88-0439.     

Thermal properties of thiocyanatocopperc(II) complexes with picolines and lutidines

The thermal properties of coordination compounds of the composition Cu(NCS)₂L₂ (whereL=pyridine, 2-, 3- and 4-picoline, and 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-lutidine) are dealt with. The thermal decomposition of these compounds begins with the release of the ligandL. The compounds with pyridine derivatives containing a methyl substituent at position 2 show a markedly decreased initial decomposition temperature. It was found that X-ray irradiation caused a reduction of the central atom Cu(II) in the coordination compounds under investigation. X-ray electron spectra data showed the stability of the compounds Cu(NCS)₂L₂ withL=picoline or lutidine having a methyl substituent at position 2 to be distinctly lower in the surface layers. From the given series, the compounds Cu(NCS)₂(pyridine)₂ and Cu(NCS)₂(3,5-lutidine)₂ exhibit an analogous course of thermal decomposition in nitrogen atmosphere up to 600°. The stoichiometries of thermal decomposition are discussed.

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Zusammenfassung Der Artikel befaßt sich mit den thermischen Eigenschaften von Koordi-nationsverbindungen der Zusammensetzung Cu(NCS)₂ L ₂ (L= Pyridin, 2-, 3-, 4-Pikolin, 2,3-, 2.4-, 2,5-, 2,6-, 3,4- und 3,5-Lutidin). Die thermische Zersetzung dieser Verbindungen beginnt mit der Abspaltung des LigandenL. Die Verbindungen mit Pyridinderivaten, welche einen Methylsubstituenten in Position 2 im Pyridinring enthalten, zeigen eine deutlich herabgesetzte anfängliche Zersetzungstemperatur. Es wurde gefunden, daß die Röntgenbestrahlung eine Reduktion des zentralen Cu(II)-Atoms bei den untersuchten Koordinationsverbindungen herbeiführte. Die Daten der Röntgen-Elektronenspektren zeigten, daß die Stabilität der Verbindungen Cu(NCS)₂L₂ mitL=Pikolin oder Lutidin, welche einen Methylsubstituenten in Position 2 enthalten, in den Oberflächenschichten wesentlich geringer ist. Von der gegebenen Reihe der Verbindungen zeigen Cu(NCS)₂(Pyridin)₂ und Cu(NCS)₂(3,5-Lutidin)₂ in Stickstoff-Atmosphäre bis zu 600° einen ähnlichen Verlauf der thermischen Zersetzung. Die Stöchiometrie ihrer thermischen Zersetzung wird beschrieben.

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Résumé L'article a trait aux propriétés thermiques des composés de coordination de composition Cu(SCN)₂L₂ (L=pyridine, 2-, 3-, 4-picoline, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-lutidine). La décomposition thermique de ces composés commence avec la libération du ligandL. Les composés avec des dérivés de la pyridine contenant un substituant méthyle en position 2 sur le cycle de la pyridine présentent une température initiale de décomposition qui se trouve abaissée de manière appréciable. On observe que le traitement aux rayons X provoque une réduction de l'atome central Cu(II) dans les composés de coordination étudiés. Les données fournies par les spectres électroniques des rayons X ont montré que la stabilité des composés Cu(SCN)₂L₂ avecL= picoline ou lutidine, ayant un substituant méthyle en position 2, est nettement plus faible dans les couches superficielles. Dans cette série de composés, Cu(SCN)₂ (pyridine)₂ et Cu(SCN)₂(3,5-lutidine)₂ montrent, en atmosphère d'azote, jusqu'à 600°, un processus analogue de décomposition thermique. La stoechiométrie de leur réaction de décomposition thermique est examinée.

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Cu(NCS)₂L₂ L=, 2-, 3-, 4- , 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-. L. 2- . , , Cu(II). , Cu(NCS)₂L₂ c L= , 2, . Cu(NCS)₂ ( )₂ Cu(NCS)₂ (3,5-)₂ 600°. .

     

Kinetics of partly diffusion controlled reactions, IX. Cage effect in the photolysis of benzyl chloride in the liquid phase. First results

The cage recombination of free benzyl and chloride radicals after their formation via photolysis of benzyl chloride is interpreted using a model for partly diffusion controlled reactions. A new kinetic model is presented which takes into account the noncontact of the interacting species at the moment of their formation. There is good agreement between the results observed and the model presented.

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, , , . , . .

     

Kinetic studies of hydrogen and carbon monoxide adsorption on Re2O7/Al2O3 catalysts

Kinetic studies of hydrogen and carbon monoxide adsorption on reduced Re₂O₇/Al₂O₃ catalysts have revealed that its activation energy decreases with increasing reduction degree of rhenium oxide. Adsorption of gases is suggested to take place on metallic rhenium atoms.

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- . , . , .

     

Determination of α and β parameters in approximate SCF MO theories

The formula proposed by Linderberg for the evaluation of the resonance integral is further investigated. Consistency requirements for the parameters lead to an explanation of the Wolfsberg-Helmholz form for. The simple assumption that is proportional to the overlap integral is improved. The dependency of a and values on the distance in a diatomic molecule in this approximation is presented and discussed.

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Zusammenfassung Linderbergs Formel zur Berechnung des Resonanzintegrals wird weiter untersucht. Konsistenzforderungen für die-Parameter führen zu einer Erklärung der Wolfsberg-Helmholz-Form für. Die einfache Annahme, daß dem Überlappungsintegral proportional ist, wird verbessert. Die Abhängigkeit von- und-Werten vom Atomabstand in einem zweiatomigen Molekül wird in dieser Näherung angegeben und diskutiert.

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Résumé Etude de la formule proposée par Linderberg pour le calcul de l'intégrale de résonance. Des nécessités de cohérence pour les paramètres conduisent à une explication de la formule de Wolfsberg-Helmholz pour. L'hypothèse simple selon laquelle est proportionnel à l'intégrale de recouvrement est améliorée. On présente en la discutant la dépendance à la distance des valeurs de et de dans une molécule diatomique dans cette approximation.