Etude de la degradation thermique des oligomeres du polyacrylonitrile

To obtain more information on the reactions during the pyrolysis of polyacrylonitrile at 290° in air, we studied the thermal degradation of its trimers, tetramers and pentamers having the general formula: R  CH(CN)  CH₂  CH(CN)_n?1  R where R = H or CH₃ and n = 3,4,5. Study by gas chromatography of the volatile compounds produced during pyrolysis at 290° and 770° showed that the first step of the degradation is homolytic scission of the chain. There are then intra and intermolecular polymerisations of the nitrile groups and formation of a ladder polymer. This reaction is clearly exothermic only for pentamers. This increase of the reactivity with DP is borne out by a kinetic study by EPR of the pyrolysis in air at 290°, oxidation of the ladder polymer giving a paramagnetic solid. Its EPR characteristics (band width and number of spins per g) are very dependent of the DP and nature of the end-groups, H or CH₃, of the pyrolysed oligomer.     

Rearrangement thermique des α-ceto, α-cyano epoxydes en dioxoles : Etude du mecanisme de la reaction

The thermolysis of α-cyano α-keto epoxides to give dioxoles is a new rearrangement. The reactivity of the epoxides is dependent upon the nature of the substituents on the epoxide ring, and solvent polarity. When the reaction is carried in the presence of benzaldehyde, a 1,3 cycloadduct is obtained. These results are in good agreement with a carbonyl ylide intermediate.     

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl₂, H₂O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H₂O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl₂.     

Etude des transitions de phases du Stearate de lithium: Influence de l'histoire thermique

The phase transitions of lithium stearate have been studied by differential scanning calorimetry and the observation of thin foils under polarized light. A new phase has been demonstrated. The phase transition temperatures and enthalpies have been measured and the dependence of some of them on the earlier cycle characteristics (number, maximum temperature and temperature rate) is demonstrated.     

Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. I. Etude du comportement thermique des n-alcanes en programmation lineaire de temperature

Middle distillates contain various amounts of n-alkanes which are responsible for low temperature properties. The thermal behavior of 14 alkanes ranging from n-C₁₂H₂₆ to C₂₅H₅₂ has been studied by means of a Mettler TA 2000 B heat flow DSC. Different hydrocarbon matrices such as gas oil (diesel) where n-alkanes have previously been removed, kerosene and gas oil containing a known distribution of n-alkanes have been used. A comparative study of the values of the enthalpy of dissolution obtained for each n-alkane in a gas oil with or without a distribution of n-alkanes has been carried out.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—I: Degradation thermique du chloro-4-hexene-2

This paper describes an extensive kinetic study of thermal dehydrochlorination for 4-chloro-2-hexene (model of an allylic unstable structure in polyvinylchloride) in solution in dichloroethane. di-ethyl-2-hexyl phthalate and other solvents. The reaction, which is reversible, has an ionic mechanism. It is catalysed by a charge transfer complex between hexadiene and hydrochloric acid. It is inhibited by complexing agents for hydrochloric acid, such as tetrahydrofuran. The addition of hydrochloric acid to conjugated dienes has been shown to occur also in the case of β-carotene.     

Variations des proprietes d'adsorption d'eau de la montmorillonite-lithium en fonction du traitement thermique

Journal of Thermal Analysis and Calorimetry - L'adsorption de vapeur d'eau sur montmorillonite lithique en provenance de Marnia et Camp Berteaux a été analysée après...     

Decomposition thermique du trichlorure de ruthenium hexammine

The thermal decomposition of [Ru(NH₃)₆]Cl₃ leads between 200 and 400° in inert gas to metallic ruthenium through the intermediates [Ru(NH₃)₅Cl]Cl₂, [Ru(NH₃)₄Cl₂]Cl and [Ru(NH₃)₃Cl₃]. In the total decomposition $$[Ru(NH_3 )_6 ]Cl_3 \to Ru + 1/2N_2 + 3NH_3 + HCl + 2NH_4 Cl$$ finely divided ruthenium is obtained above 240°. In oxygen the same intermediates are formed, the final product, however, being the metal and its dioxide.     

Le calcul des parametres cinetiques des Reactions de Decomposition thermique a l'aide des donnees de l'analyse thermique differentielle

Résumé On a modifié la méthode différentielle pour le calcul des paramètres cinétiques des réactions de décomposition thermique du type: A_(s) B_(s) + C_(g), en utilisant les données de l'analyse thermodifférentielle. En effectuant le calcul des paramètres cinétiques des réactions de déshydratation de l'oxalate de calcium monohydraté et de décomposition du carbonate de calcium on obtient des résultats qui concordent d'une manière satisfaisante avec ceux obtenus par d'autres méthodes.

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A modification of the differential method is presented in order to evaluate the kinetic parameters of thermal decomposition reactions of the type A _s B _s + +C_g, using differential thermal analysis (DTA) data. The kinetic parameters calculated for the dehydration and decomposition of calcium oxalate and carbonate agree satisfactorily with those mentioned in the literature.

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Zusammenfassung Es wird über eine Abänderung der Differentialmethode zur Errechnung der kinetischen Parameter von thermischen Zersetzungsreaktionen des Typs A_(s) B_(s) + C_(g) mit Hilfe von differentialthermoanalytischen Daten berichtet. Die am Beispiel der Dehydratation des Calciumoxalat-Monohydrats und der Zersetzung des Calciumcarbonats erhaltenen Ergebnisse der auf angegebene Weise durchgeführten kinetischen Berechnungen stimmen gut mit den nach anderen Methoden erhaltenen Resultaten überein.

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A_{(s) (s)} + C_(g), (). , , , .

     

Structure et stabilité thermique des deux formes du formiate de magnesium dihydraté

We have prepared and studied a new form of dehydrated magnesium formate. This form is orthorhomic (a = 8.710(2), Å, b = 8.427(2), Å, c = 7.477(2)Å, Z = 4, Pbca). The structure (R = 0.060, R_w = 0.049) shows that the Mg are bonded together by formate bridges, thus forming sheets parallel to the x0y plane. Tridimensional cohesion is secured by water molecules inserted between sheets; these water molecules are bonded to the Mg of one sheet and, by hydrogen bonds, to two formate groups of the next neighbor sheet. From the structural comparison of the two forms (monoclinic and orthorhomic), a lower stability of the orthorhombic variety was predicted. This was confirmed by study of the thermal decomposition under argon atmosphere as observed by thermogravimetric and thermodifferential analysis, powder X-ray diffraction and infrared spectra.     

Comportement thermique complexe du propionate de magnesium dihydrate

Résumé Un sel nouveau, le propionate de magnésium dihydraté, est préparé. Il cristallise dans le système monoclinique. Son étude par TG et ATD montre un comportement thermique assez complexe en trois étapes: déshydratation conduisant au sel anhydre amorphe aux rayons X, cristallisation du sel anhydre dont 25 % environ se transforment simultanément en sel basique [4Mg(C₂H₅CO₂)₂,MgO], enfin fusion et décomposition du mélange sel neutresel basique avec formation d'oxyde MgO bien cristallisé. Au cours de la décomposition, il y a dégagement de diéthylcétone, mis en évidence par chromatographie.

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A new salt, magnesium propionate dihydrate, has been prepared. It crystallizes in the monoclinic system. TG and DTA study shows rather complex thermal behaviour in three stages: dehydration leading to an anhydrous salt amorphous to X-rays; crystallization of the anhydrous salt, about 25% of which simultaneously transforms into the basic salt [4Mg(C₂H₅CO₂)₂,MgO]; fusion and decomposition of the neutral salt + basic salt mixture to a well-crystalline MgO residue. During the decomposition, gas-chromatography reveals evolution of diethyl ketone.

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Zusammenfassung Ein neues Salz, das Magnesiumpropionat-Dihydrat, wurde hergestellt. Es kristallisiert im monoklinen System. Seine Untersuchung durch TG und DTA ergibt ein ziemlich komplexes thermisches Verhalten in drei Stufen: eine Dehydratierung, welche — wie durch Röntgenbeugung nachweisbar — zum amorphen Anhydro-Salz führt, die Kristallisation des Anhydro-Salzes, wovon etwa 25% gleichzeitig in das basische Salz übergehen [4Mg(C₂H-,CO₂)₂,MgO] und schließlich das Schmelzen und die Zersetzung des Gemisches aus neutralem Salz und basischem Salz unter Bildung von gut kristallisiertem MgO. Das im Verlauf der Zersetzung freigesetzte Diäthylketon wurde chromatographisch nachgewiesen.

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, . , : , , , 25% [4Mg(C₂H₅CO₂)₂, MgO] , . , .

     

Etude sur le comportement thermique de quelques polymeres ignifugeants contenant du phosphore et des halogenes

The thermal behaviour a series of polyphosphonates was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The obtained data permitted the calculation of activation energies and reaction orders on decomposition zones by the Coats — Redfern method.     

Etude de la decomposition thermique des polyheteroarylenes

An investigation was made of the thermal and thermooxidative decompositions of polybenzimidazopyrrolones and polybenzimidazobenzoquinolines, as well as a number of heterocyclic compounds modelling the linkages and individual fragments of these polymers. It was established that in the pyrolyses of the polyheteroarylenes and the corresponding model compounds the destruction of cycles occurs either simultaneously with cleveage of the C_ar-H bond or at a higher temperature. It was shown that the completely aromatic compounds and the heterocyclic compounds condensed with the benzene nucleus are the most thermostable of the investigated compounds. A comparative study revealed a correlation between the structures and thermal stabilities of the studied compounds.

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Zusammenfassung Die thermische und thermooxydative Zersetzung von Polybenzimidazopyrrolonen und Polybenzimidazobenzochinolinen und einige der die Bindungen und individuellen Fragmente modellierenden heterozyklischen Verbindungen dieser Polymere wurden untersucht. Es wurde festgestellt, daß bei der Pyrolyse von Polyheteroarylenen und der entsprechenden Modellverbindungen das Aufsprengen der Ringe entweder gleichzeitig mit der Spaltung der C_ar-H-Bindung oder bei höheren Temperaturen erfolgt. Von den untersuchten Verbindungen sind die vollständig aromatischen und die mit Benzolringen kondensierten heterozyklischen Verbindungen am thermostabilsten. Eine vergleichende Untersuchung der Struktur und Thermostabilität der untersuchten Verbindungen ergab eine Korrelation.

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, , , , , . , , C _ap -H, . , , , . .

     

Contribution a l'etude de la decomposition thermique du carbonate de cadmium

The thermal decomposition of CdCO₃ has been studied by DTA on samples of different origins. A classical experimental device enables work at different pressures up to 12 bar for any gas used. Evaluation of the data measured by the author and their comparison with those given by others show that the carbonates obtained by the chemical method are different from those prepared by hydrothermal crystallization. As the latter exhibit higher thermal stability, they may permit a further, real thermodynamic study on the decomposition of cadmium carbonate.     

Degradation thermique des copolymeres methacrylate de methyle-chlorure de vinylidene

The thermal degradation, under inert atmosphere, of a set of methyl-methacrylate-vinylidene chloride copolymers prepared by free radical copolymerization with constant composition conditions, is studied by thermogravimetry coupled with titration of HCl evolved and with gas chromatographic analysis of volatile products (monomers, methyl chloride). Only the formation of methyl methacrylate can be related to the sequence distribution.     

La formation du ferrite spinelle de magnesium pendant la decomposition thermique des systèmes contenant des oxalates

Résumé Quoique pendant la décomposition thermique de la solution solide MgFe₂(C₂O₄)₃ ·6H₂O et celle du complexe H₄Mg[Fe(C₂O₄)₃]₂·nH₂O, la formation du spinelle MgFe₂O₄ commence à des températures basses (inférieures à 500°), en même temps que la décarboxylation, les rendements de la réaction ne dépassent pas 60%, même à 600°.

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Although during the thermal decompositon of the solid solution MgFe₂(C₂O₄)₃·6H₂O and that of the complex H₄Mg[Fe(C₂O₄)₃]₂·nH₂O, the formation of the spinel MgFe₂O₄ begins at lower temperatures (under 500°), at the same time withthe decarboxylation, the yields of the reactions are not higher than 60% even at 600°.

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Zusammenfassung Obwohl während der thermischen Zersetzung der festen Lösung MgFe₂(C₂O₄)₃·6H₂O und der des Komplexes H₄Mg[Fe(C₂O₄)₃]₂·nH₂O die Bildung des Spinells MgFe₂O₄ bei niedrigen Temperaturen (unterhalb von 500°) zu gleicher Zeit mit der Decarboxylierung beginnt, liegen die Ausbeuten selbst bei 600°C nicht höher als 60%.

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, MgFe₂(C₂O₄)₃·6H₂O H₄Mg[Fe(C₂O₄)₃]₂·nH₂O MgFeO₄ ( 500°). . 60% 600°.

     

Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. II. Determination du taux de n-alcanes contenu dans un gazole. Determination du point de trouble

The study of the thermal behavior of n-alkanes in a hydrocarbon matrix has been carried out by means of a Mettler TA 2000 B heat flow differential scanning calorimeter. A quantitative method to determine the composition in n-alkanes contained in a gas oil is described. It is assumed that the determination of the cloud point by means of DSC measurements can be obtained with a good precision.     

Analyse du comportement thermique d'une serie de derives camphoriques

Thermal analysis of a series of camphor derivatives has been studied by differential scanning calorimetry. Different behaviors with the appearance of glassy, amorphous, crystalline, polymorphous compounds and tautomeric mixture were detected.These results have been confirmed by infrared spectroscopy and by X-ray diffraction.

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Zusammenfassung Mittels DSC wurde eine Reihe von Kampferderivaten untersucht. Dabei konnte verschiedenes Verhalten mit dem Auftreten von glasartigen, amorphen, kristallinen und polymorphen Verbindungen und tautomeren Gemischen beobachtet werden.Die erhaltenen Resultate wurden durch IR-Spektroskopie und Röntgendiffraktion bestätigt.