Limiting temperatures of the thermal decomposition of polymers and their determination by rapid thermal analysis

Experimental and theoretical foundations are established for the limiting temperatures of thermal decomposition of thermoplastic polymers. The correlation between the limiting temperatures and the intermolecular interactions of the polymers investigated is reported.

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Zusammenfassung Experimentelle und theoretische Grundlagen der Grenztemperaturen der thermischen Zersetzung von thermoplastischen Polymeren werden behandelt. Es besteht eine Korrelation zwischen den Grenztemperaturen und den intermolekularen Wechselwirkungen der untersuchten Polymere.

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. .

     

Decomposition of benzenediazonium fluoborate in esters of α,β-unsaturated acids

Summary It was shown that In contrast to the Meerwein-Koelsch reaction, the decomposition of benzenediazonlum fluoborate In esters of ,-unsaturated acids proceeds by a heterolytlc mechanism with the phenyl attacking the -carbon and the carbalkoxyl group of these esters. The reaction with ethyl crotonate gave -methylatropic acid (after hydrolysis) and a small amount of a dibasic acid, C₁₄H₁₆O₄ (or C₁₄H₁₄O₄). With methyl acrylate it gave atropic acid, phenyl acrylate, and a smaller amount of -methyl--phenylglutaric acid. With methyl methacrylate It formed benzylacrylic acid and the product of further conversions of phenyl methacrylate, namely the keto phenol 2-methyl-5-hydroxyindan-1-one.     

Effect of the central metal ion on the inhibiting properties of metal dithiocarbamates in oxidation processes

The dependence of inhibiting properties of M(dtc) on M for the complexes of M(II) and n M(III) has been studied. Inhibition is due to the interaction of M(dtc)_n with RO₂.

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M(dtc)_n M M(II) M(III). M(dtc)_n RO₂.

     

Synthesis and properties of composite catalysts containing Pd and Ho2O3 particles in pores of carbon carrier

Specific activity (TOF) of the catalysts prepared through the interaction of C₃H₅PdC₅H₅ with the surface of evacuated Ho₂O₃/C is two orders of magnitude higher compared to that of Pd/C in the synthesis of both CH₃OH and CH₄. Deactivation data suggest that CH₃OH and CH₄ are formed on different active sites.

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, C₃H₅PdC₅H₅ Ho₂O₃/C, Pd/C CH₃OH, CH₄. CH₃OH CH₄ .

     

Active coke formation in oxydehydrogenation of ethylbenzene to styrene

In oxydehydrogenation of ethylbenzene to styrene catalytic active centers are created by coke formed during the reaction. Formation of active coke can be made evident by product analysis in the first minutes of operation and by analysis of the carbonaceous resisdues by temperature programmed oxidation (TPO) and EPR.

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. , , , .

     

Chemical conversion of various celluloses to glucose and its derivatives in supercritical water

The supercritical water biomass conversion system was designed and developed in our laboratory. The reaction vessel with cellulose sample was treated with this system at supercritical state of water for a designated period (3–105s) under the conditions of a tin bath temperature of 500°C and pressure of 35MPa. The recovered products of hydrolysates were then analyzed by high performance liquid chromatography. The obtained results indicated that a high amount of glucose and levoglucosan can be achieved from both celluloses I and II for 5–10s supercritical treatment, while that from starch for 3–5s treatment. Although this difference could be due to a difference in the molecular structure between cellulose and starch, a difference between celluloses I and II was not significant. Instead, an accessibility of the water towards cellulose molecules seemed to be significant for their chemical conversion. With the longer treatment, amounts of these compounds observed were decreased due to decomposition. Therefore, it may be concluded that, compared with acid hydrolysis or enzymatic saccharification, cellulose may be hydrolyzed to glucose and its derivatives more or less to the same degree as in corn starch under supercritical state. This finding suggests that the supercritical treatment can overcome the difficulties in hydrolyzing cellulose to glucose, found in the acid hydrolysis or enzymatic saccharification techniques.     

On the structure and activity of a Pt/C catalyst subjected to repeated deactivation and regeneration cycles

Electron microscopic studies reveal that repeated air/hydrogen regeneration cycles cause irreversible structural changes of a Pt/C catalyst involving sintering and migration of the platinum over the support. This is reflected by a serious decrease of the catalytic activity. With hydrogen treatment only, these effects are less significant.

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, / Pt/C, . . .

     

Pyrolysis of propane in the presence of acetylene

Pyrolysis of propane in the presence of acetylene and acetylene labeled with C-14 has been studied in the temperature range of 833–1019 K. The inhibition effect of acetylene on the thermal decomposition of propane is turning into an accelerating effect at higher temperature.

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C¹⁴ 833–1019 . .

     

ESR studies of the state of Ti3+ and Ti2+ in Ti?Mg catalysts for olefin polymerization

ESR studies have revealed that in Ti–Mg catalysts after interaction with organoaluminium compounds, the Ti³⁺ ions formed are present mainly as TiCl₃ associates. Isolated Ti³⁺ ions of various types are also detected. Part of titanium ions is in the divalent state and provides an ESR signal after oxidation by water to the trivalent state in the form of Ti³⁺ ordered by cooperative Jahn-Teller interaction.

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, - , Ti³⁺ TiCl₃. Ti³⁺ . Ti³⁺ - -.

     

Theoretical considerations on the oxidation of propylene on transition metal molybdates

Molecular orbital calculations of charge distributions for the -allyl complex with transition metal ions in molybdates show that the activated -allyl species is formed by transfer of charge density to the metal ion. The relative charge distributions on the three carbon atoms of the adsorbed allyl species govern the course of oxidation reaction.

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- , - . .

     

Kinetic analysis of thermogravimetric data,V

The statistical analysis of activation energy and of logZ values derived from thermogravimetric data for 134 decomposition reactions of bisdioximatocobalt(III) complexes shows the validity of a linear compensation law, i.e. both the effects of heating rate and of the nature of the ligand manifest themselves in the kinetic compensation effect. The parametera of the compensation law is sensitive to ligand effects and its value is influenced both by the nature of the coordinated dione-dioxime and by the nature of the outer sphere anion X, which replaces an ammonia molecule in the thermal decomposition reaction.

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Zusammenfassung Die statistische Analyse der aus den thermogravimetrischen Resultaten erhaltenen Aktivierungsenergiewerte und log Z-Werte von 134 Zersetzungsreaktionen der verschiedenen bisdioxamato Kobalt(III) Komplexen zeigte die Gültigkeit eines Gesetzes der linearen Kompensation, d.h. der Effekt der Heizungsgeschwindigkeit und der Natur des Liganden verursachten in erster Näherung den kinetischen Kompensationseffekt. Parametera des Kompensationsgesetzes (1) repräsentiert den Ligandeffekt. Sein Wert wird durch die Natur des koordinierten Dion-dioxims und des Anions X in der äußeren Sphäre beeinflußt, das ein Aminmolekül während der thermischen Zersetzungsreaktion ersetzt.

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Résumé L'analyse statistique des valeurs des énergies d'activation et de celles de logZ obtenues à partir des résultats thermogravimétriques de 134 réactions de décomposition des complexes différent de bisdioximato-cobalt(III) montre la validité d'une loi de compensation linéaire du type (1); ceci signifie que l'effet de la vitesse de chauffage et celui de la nature du ligand sont responsables en première approximation de l'effet de compensation cinétique. Le paramètrea de la loi de compensation est sensible aux effets du ligand et la nature de la bis-dioxime coordonnée ainsi que la nature de l'anion X dans la sphère externe remplaÇant une molécule d'aminé durant la réaction de décomposition thermique influencent sa valeur.

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logZ, 134 - (III), . a - X, .

     

Kinetics of solid polypropylene oxidation inhibited by aromatic nitrons

C-phenylcarbamoyl-N-phenylnitron and C(2,4-di-tert-butyl-3-hydroxyphenylcarbamoyl)-N-(p-di-methylaminophenyl) nitron inhibit the oxidation of solid polypropylene. In this case the nitrons studied demonstrate properties of polyfunctional inhibitors: they interrupt oxidation chains by chains by reactions with alkyl and peroxyl radicals.

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C--N- C-(2,4----3-)-N-(-) . , .

     

Heterogeneous reactions of solid nickel(II) complexes,XII

The possibilities of correlating the structures and the stepwise thermal decomposition reactions of solid coordination compounds are discussed. The starting compounds were Ni(NCS)₂(py)₄, (py=pyridine), CuSO₄ · 5 H₂O and NiSO₄ · 7 H₂O, for which correlations of the above type were studied. It was found that the structural data on the initial compound alone are not sufficient to predict the stepwise course of the thermal decompositions of coordination compounds.

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Zusammenfassung Die Möglichkeiten der Korrelierung der Struktur und der stufenweisen thermischen Zersetzungsreaktionen fester Koordinationsverbindungen werden erörtert. Die Ausgangssubstanzen waren Ni(NCS)₂(py)₄, (py=Pyridin), CuSO₄·5 H₂O und NiSO₄·7 H₂O, für welche Korrelationsberechnungen des untersuchten Typs durchgeführt wurden. Es wurde festgestellt, daß die Strukturangaben der Ausgangsverbindung allein nicht ausreichen, um den stufenweisen Verlauf der thermischen Zersetzung von Koordinationsverbindungen zu beschreiben.

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Résumé On discute les possibilités d'établir une corrélation entre la structure et les réactions de décomposition thermique graduelle de composés de coordination solides. Les composés de départ étaient les suivants: Ni(SCN)₂(py)₄, (py=pyridine), CuSO₄·5 H₂O et NiSO₄·7 H₂O pour lesquels on a effectué le calcul des corrélations du type étudié. On a trouvé que les données relatives à la structure du composé de départ ne suffisaient pas pour prédire les étapes de la décomposition thermique des composés de coordination.

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, . Ni(NH₃)₂Pt(CN)₄ · 2₆₅ Ni(en)₂Pt(CN)₂· 0,14₆₅. , . : —Ni(NH₃)₂Pt(CN)₄·2₆₅, «» — Ni(en)₂Pt(CN)₄·0.14₆₅. . -« »-NiPt(CN)₄ · 6₂ Ni(en)₃Pt(CN)₄·₂. Ni(NH₃)₂Pt(CN)₄·2₆₅ 55–244°, Ni(en)₂Pt(CN)₄·0.14₆₅ - 139– 284°.

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Thermochemical studies on organic eutectics and molecular complexes

The phase diagrams of the binary systems of picric acid with naphthalene, anthracene and phenanthrene, and of -naphthol withp-toluidine, determined by the thaw-melt method, show the formation of a molecular complex and two eutectics in each system. The heats of the pure components, eutectics and molecular complexes were determined by differential scanning calorimetry. Comparison of the experimental heats of fusion with the theoretical values calculated via the mixture law suggests cluster formation in the melts. The entropy of fusion, enthalpy of mixing and excess thermodynamic functions were also calculated from the heat of fusion data.

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Zusammenfassung Die Phasendiagramme der binären Systeme von Pikrinsäure mit Naphthalin, Anthrazen und Phenanthren sowie von -Naphthol mit p-Aminotoluol wurden bestimmt. In jedem System zeigt sich die Bildung eines Molekülkomplexes sowie je zwei Eutektika. Mittels DSC wurden die Schmelzwärmen der reinen Komponenten, der eutektischen Mischungen und der Molekülkomplexe ermitteis. Der Vergleich der experimentell ermittelten Schmelzwärmen mit den mittels der Mischungsregel errechneten Werten läßt auf eine Clusterbildung in der Schmelze schließen. Weiterhin wurden aus den Schmelzwärmen auch Werte für Schmelzentropie und Mischungsenthalpie errechnet.

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— , , - . , . , . , .

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Thanks are due to Prof. I. S. Ahuja, Head, Chemistry Department, Banaras Hindu University, for providing research facilities. Thanks are also due to CSIR, New Delhi, for financial assistance.     

Surface hydration of crystalline and amorphous silicas

The surface properties of three SiO₂ samples, one crystalline (quartz) and two amorphous, with a large difference in particle size, have been investigated by thermal analysis, adsorption calorimetry and infrared spectroscopy. The variation in the silanol group population upon thermal treatment has been followed via the evolution of the i.r. bands at 3745–3750 cm^–1 (free hydroxyl groups) and 3650-3550 cm^–1 (adjacent pairs of SiOH) and the evolution of the heat of adsorption of water with coverage on the outgassed samples.The adsorption capacities increase in the sequence high surface area amorphous sample T=673 K) brings about dehydroxylation leaving only isolated silanols on the high surface area amorphous silica, and partial dehydroxylation of the low surface area material. Quartz is totally hydrophilic, as its regular structure probably stabilizes the hydroxyl layers at the surface.

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Zusammenfassung Die Oberflächeneigenschaften von einer kristallinen (Quarz) und zwei amorphen SiO₂-Proben mit großen Unterschieden in der Partikelgröße wurden durch thermische Analyse, Adsorptionskalorimetrie und Infrarotspektroskopie untersucht. Bei thermischer Behandlung eintretende Veränderungen in der Silanolgruppenpopulation wurden durch Messung der IR-Banden bei 3745–3750 cm^–1 (freie Hydroxylgruppen) und 3650–3550 cm^–1 (benachbarte SiOH-Paare) und der Adsorptionswärme von Wasser an ausgeheitzten Proben untersucht. Die Adsorptionskapazitäten nehmen in folgender Reihenfolge ab: amorphe Probe mit großer Oberfläche > amorphe Probe mit geringer Oberfläche > Quarz. Dehydroxylierung der Oberfläche hat zunehmenden hydrophoben Charakter (Gestalt der Isothermen, Adsorptionswärme kleiner als Kondensationswärme von Wasser) zur Folge. Bei der gleichen thermischen Behandlung (673 K) werden bei amorphen Siliciumdioxid mit großer Oberfläche eine nur isolierte Hydroxylgruppen zurücklassende Dehydroxylierung und bei Material mit kleiner Oberfläche eine teilweise Dehydroxylierung beobachtet. Quarz ist vollkommen hydrophyl, da die reguläre Struktur wahrscheinlich die Hydroxylschichten an der Oberfläche stabilisiert.

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, , (), — . 3745–3750 ^–1 ( ) 3650–3550 ^–1 ( SiOH), . < < . ( , ). (T=673 K) . , , , .

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This research was supported by the Ministry of Public Education within a national programme relating to the structure and reactivity of surfaces.     

Development towards a single-run DSC for heat capacity measurements

It is shown that it should be possible to construct a single-run heat conduction type DSC that records heat capacity directly, eliminating the present need for three separate runs. A simplified mathematical derivation of the needed computation is given and some suggestions about improved DSC construction are presented.

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Zusammenfassung Es wird gezeigt, daß es möglich sein müßte, ein single-run DSC vom Wärmeleittyp zu konstruieren, mit dessen Hilfe man anstelle der bisherigen drei separaten Durchgänge die Wärmekapazität direkt registrieren kann. Es werden für die notwendigen Berechnungen eine vereinfachte mathematische Ableitung und für den Bau des verbesserten DSC einige Anregungen gegeben.

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, , , , . .

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The work has been supported by a Grant from the Hercules Co. to ATHAS.     

Thermal decompositions of zinc(II) benzenedicarboxylates

The thermal decompositions of zinc(II)benzenedicarboxylates were studied in air atmosphere at a heating-rate of 10 deg min^–1. Zinc phthalate and isophthalate were dehydrated in one step and next decomposed directly to ZnO. Zinc terephthalate was dehydrated in two steps and then decomposed directly to ZnO.

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Zusammenfassung Bei einer Aufheizgeschwindigkeit von 10°-min^–1 wurde die thermische Zersetzung von Zink(II)benzoldikarboxylat in Luft untersucht. Zinkphtalat und -isophtalat wird zunächst in einem Schritt dehydratisiert und anschließend zu ZnO zersetzt. Zinkterephtalat wird vor der endgültigen Zersetzung zu ZnO in zwei Schritten dehydratisiert.

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10 / . - . , .

     

X-ray and thermal studies on uranyl acetates of zinc,magnesium and nickel

Thermal decomposition of metal uranyl acetates is one of the best ways of preparation of uranates in crystalline form at low temperatures. Acetates of the type M(UO₂)₂(OAc)₆·7H₂O (M=Zn(II), Mg(II) and Ni(II) were prepared and characterised. Their X-ray powder diffraction analysis showed that they all belong to the orthorhombic crystal class.The thermal decomposition of acetates in air goes through the reduction of uranium(VI) to uranium(IV) during acetate decomposition followed by reoxidation by oxygen. Zinc uranylacetate gave on thermal decomposition ZnU₃O₁₀, the nickel salt gave NiU₃O₁₀ and the magnesium salt gave a mixture of MgUO₄ and MgU₃O₁₀. The thermal decomposition of acetates in helium led to reduction of uranium(VI) to uranium(IV) with the formation of UO₂. No lower valent uranates could be identified.

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Zusammenfassung Thermische Zersetzung von Metalluranylazetaten ist eine der geeignetsten Methoden zur Darstellung kristalliner Uranate bei niedrigen Temperaturen. Azetate des Types M(UO₂)₂(OAc)₆·7H₂O mitM=Zn(II), Mg(II) und Ni(II) wurden hergestellt und beschrieben. Eine Pulverdiffraktionsanalyse zeigte, daß alle der orthorhombischen Kristallklasse angehören. Der thermische Zerfall der Azetate in Luft vollzieht sich während des Azetatzerfalls über die Reduktion von Uran(VI) zu Uran(IV) bis zu einer anschließenden Reoxydation durch Sauerstoff. Bei der thermischen Zersetzung liefert Zinkuranylazetat ZnU₃O₁₀, das Nickelsalz liefert NiU₃O₁₀ und das Magnesiumsalz ein Gemisch aus MgUO₄ und MgU₃O₁₀. Der thermische Zerfall der Azetate in Helium führt zur Reduktion von Uran(VI) zu Uran(IV) unter Bildung von UO₃. Uranate mit niedrigerer Wertigkeit konnten nicht identifiziert werden.

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. M(UO₂)₂(OAc)₆ · 7H₂O, M = , . , . , . ZnU₃O₁₀, — NiU₃O₁₀, MgUO₄ MgU₃O₁₀. . .

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The authors thank Dr. D. D. Sood, Head, Fuel Chemistry Division, for his encouragement during the course of this work.