Thermal reactions of inorganic hydroxy-compounds under applied electric fields

The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation to-Fe₂O₃ was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe₃O₄ and FeO at the expense of Fe₂O₃ is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

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Zusammenfassung Der Einfluß eines elektrischen Feldes auf die thermische Dehydratisierung des amorphen hydratisierten Eisen(III)oxids in oxidierenden, inerten und reduzierenden Atmosphären wurde durch Röntgendiffraktometrie untersucht. In oxidierenden und inerten Atmosphären wurde die Umwandlung zu -Fe₂O₃ durch elektrische Felder gefördert, besonders an der negativen Elektrode. Die Form der Kristallite des Produkts war ebenfalls an der negativen Elektrode am größten. Beide Ergebnisse werden durch die Proteinwanderung zur negativen Elektrode erklärt, wo diese Wasser bilden, das für die kristalline Phase als Keimbildner fungiert. In reduzierenden Atmosphären wird die Bildung von Fe₃O₄ und FeO auf Kosten von Fe₂O₃ durch elektrische Felder besonders an der negativen Elektrode erleichtert. Mögliche Reaktionsmechanismen werden erörtert und die Rolle der Protonen bei der Stabilisierung defekt-spineller Zwischenstufen und Produkte besprochen.

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Résumé L'effet d'un champ électrique sur la déshydratation thermique de l'oxyde de fer(III) hydraté amorphe a été étudié par diffractométrie des rayons X, dans des atmosphères oxydante, inerte et réductrice. En atmosphères oxydante et inerte, le champ électrique facilite la transformation en -Fe₂O₃, en particulier à l'électrode négative. La taille des cristaux formés est également plus élevée à l'électrode négative où il se forme de l'eau qui agit comme agent de nucléation de la phase cristalline. En atmosphère réductrice, le champ électrique facilite la formation de Fe₃O₄ et FeO, aux dépens de Fe₂O₃, en particulier à l'électrode négative. On considère les mécanismes de réaction possibles et on discute le rôle des protons sur la stabilisation des produits et des intermédiaires défauts-spinelles.

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- (III) , . -Fe₂O₃ , , . , , . Fe₃O₄ FeO Fe₂O₃ . , .

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The author is indebted to P. J. Melling for assistance with the measurements in H₂/N₂ atmospheres.     

Historical Aspects of the Chemical Bond. Chemical Relationality versus Physical Objectivity

Chemists have always defined the properties of materials on the basis of the changes observed when they reacted with other substances. Whereas this approach led chemists to relational concepts such as affinity, acid, and oxidant, physicists made measurements of objects they considered unchanged, determining their mass, charge, dipole moment, etc. In the middle of the 18th century, the Jesuit Josip Ruder Bocovi started thinking about the way in which atoms might be present in crystals, introducing a new concept according to which atoms in condensed phases represented punctual centres of attracting and repelling forces. Josef Loschmidt became aware of these ideas through the philosopher J. F. Herbart, and it is to Loschmidt that we owe the first representation of bonds as atomic spheres penetrating one another. The term quantum chemistry was first used by the physicist Arthur Erich Haas, who was born in Brno. However, Hans Hellmann (1903–1938) was the true founder of quantum chemistry. Hellmann, who was shot in Moscow in 1938, was the first person to realize the quantum-physical effect that leads to the chemical bond. In the 1960s K. Ruedenberg and others took theory a stage further when – thanks to the concept of the localized electron pair – they realized that the different approaches to the phenomenon of the chemical bond taken by chemists and physicists were largely comparable. This made it possible to bring the differing standpoints largely into line with one another.     

Quantitative DTA of epoxy adhesives of technological interest

The glass transition temperatures,T _g, and thermal effects of polymerization,H, have been determined for five epoxy adhesives of unknown composition. From the trendsH vs./t _cure it has been possible to attain a phenomenological kinetic order of the polymerization rate at 100° through an iterative calculation procedure. For most of the investigated adhesives there are reasons (double peak of polymerization and doubleT _g signal) to assume that they are graft copolymers.

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Zusammenfassung Die Glas-Übergangstemperaturen (T _g) und dieH thermische Effekte der Polymerisation wurden für fünf Epoxy-Klebstoffe unbekannter Zusammensetzung bestimmt.Aus den TrendsH gegenübert _cure war es möglich eine phenomenologische kinetische Ordnung der Polymerisationsgeschwindigkeit bei 100° durch ein iteratives Berechnungsverfahren zu ermitteln.Für die meisten untersuchten Klebstoffe besteht der Grund — Doppelpeak der Polymerisation und doppeltesT _g-Signal — sie als Pfropfcopolymere zu betrachten.

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Résumé On a déterminé, pour cinq adhésifs époxy de composition inconnue, les températures de transition vitreuseT _g et les effets thermiques de polymérisationH.A partir de la variation deH en fonction du temps de recuit et par une méthode de calcul itératif, un ordre cinétique phénoménologique de la vitesse de polymérisation à 100° a pu être obtenu.Pour la plupart des adhésifs étudiés l'existence d'un pic double de polymérisation et d'une double transition vitreuseT _g permet de supposer qu'il s'agit de copolymères greffés.

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T _g H. H.-t. 100° . T _g , - .

     

High-temperature pyrolysis of polymers

The experimental results on the pyrolysis of thermoplastic polymers under high-temperature heating and burning conditions are discussed. The reaction of polymer degradation in this case proceeds in the same way as in a low-temperature region.

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Zusammenfassung Die experimentellen Ergebnisse der Pyrolyse von thermoplastischen Polymeren unter Erhitzungs- und Brehnbedingungen hoher Temperatur werden besprochen. Die Reaktion der Polymerzersetzung verläuft in diesem Falle genau so wie in der Niedrigtemperaturzone ab.

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. , .

     

Oxidation of hydrogen sulfide by oxygen in presence of PW11M(H2O)O395? (M=Fe, Co, Ni)

It has been found that at pH=3.5–5 and T=20°C PW₁₁Fe(H₂O)O ₃₉ ^5– is an active catalyst for H₂S oxidation by oxygen. Comparison of the catalytic reaction rate with the rate for PW₁₁Fe^II(H₂O)O ₃₉ ^5– oxidation by oxygen indicates that at least one of the reactants is activated by this heteropoly complex.

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, pH=3,5–5 20°C PW₁₁Fe(H₂O)O ₃₉ ^5– H₂S . PW₁₁Fe^II(H₂O)O ₃₉ ^5– .

     

Microstructure and Chemical Bonding in Silicon Carbonitride Films Synthesized by Plasma Enhanced Chemical Vapor Deposition

Silicon carbonitride films were synthesized by plasma enhanced chemical vapor deposition using silyl derivatives of asymmetric dimethylhydrazine, (CH₃)₂HSiNHN(CH₃)₂ and (CH₃)₂Si[NHN(CH₃)₂]₂, as molecular precursors. The film material consists of an amorphous matrix with nanocrystalline inclusions. Indexing of synchrotron radiation Xray diffraction patterns suggests that the structure of the nanocrystals is tetragonal with lattice parameters a = 9.6 and c = 6.4. Xray photoelectron spectra indicate that Si—N and C—N sp ³ hybrid bonds are predominant. The absence of G or Dmodes in Raman spectra, which are otherwise typical of structures possessing sp ² bonding, provides further support for the tetragonal structure of the nanocrystals.     

Preparation of some α,α-diaryl-substitutedβ-thiolactones andβ-lactones

Conclusions The general method of obtaining-propiothiolactones that we have proposed previously has been used for the synthesis of a series of new,-diaryl-substituted-propiothiolactones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2025–2027, November, 1966.     

Heterogeneous reactions of solid nickel(II) complexes, IV

The decomposition heats (H) for complexes of the type Ni(NCS)₂L₂ were studied by means of a differential scanning calorimeter. From the decreasing values ofH the following order has been established:a) for pseudooctahedral complexes: py >-pic > > Q; andb) for square-planar complexes: 2,6-lut > Q >-pic. The results obtained are compared with the data from the TG, DTG, and DTA curves.

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Zusammenfassung Es erfolgte die Bestimmung der Zersetzungswärmen (H) der Komplexe vom Typ Ni(NCS)₂L₂ durch die Differential Scanning Calorimetrie. Mit abnehmendenH Werten ergab sich die Reihenfolge:a) Pseudooktaedrische Komplexe: Py >ß-Pic > Q;b) Quadratische Komplexe: 2,6-Lut. > Q >-Pic. Ergebnisse mit aus den DTA, TG und DTG-Kurven gewonnenen Resultaten wurden verglichen.

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Résumé Détermination par analyse enthalpique différentielle des chaleurs de décomposition (H) des complexes de formule générale Ni(SCN)₂L₂. Le classement des valeurs deH par ordre décroissant montre que pour les complexes pseudo-octaédriques py >gb-pic > Q et que pour les complexes plans carrés lut-2,6 > Q >-pic. Comparaison de ces résultats avec les données des courbes TG, TGD et ATD.

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(H) Ni(NCS)₂L₂. H : ) >-pic > Q; ) 2,6 lut > Q >-Pic. , , .

     

Cluster and ligand effects in CO adsorption on high dispersity supported Ni?Cu alloys

IR spectroscopic studies of CO chemisorption on SiO₂-supported Ni and Ni–Cu microcrystals have revealed that the alloy composition affects the intensity and frequency of absorption bands of the linear form of chemisorbed CO. Chemisorbed hydrogen is shown to shift its absorption band to the high-frequency region on pure Ni and low-copper Ni–Cu alloys and does not affect it on high-copper ones. The presence of Cu in the alloy increases significantly the reactivity of chemisorbed oxygen in the reaction with CO. The results are treated in terms of the concepts of cluster and ligand effects.

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- CO SiO₂ Ni Ni–Cu. CO. CO Ni–Cu , Cu CO , Cu. Cu CO. .

     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

A method has been developed that allows the deconvolution of up to 15 overlapping solidstate reactions without previous assumptions. Both the kinetic parameters and the reaction mechanisms fitted by the unit reactions can be determined from a series of non-isothermal experiments carried out at different heating rates.

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Zusammenfassung Es wurde eine methode zur Dekonvolution von bis zu 15 einander überlappenden Festphasenreaktionen entwickelt, die keinerlei vorherige Annahmen notwendig macht. Mittels einer Reihe nichtisothermer Experimente mit unterschiedlichen Aufheizgeschwindigkeiten können sowohl die kinetischen Parameter als auch der Reaktionsmechanismus der Teilreaktionen bestimmt werden.

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, 15. .

     

Influence of sodium salt addition on the morphological and catalytic properties (ethane hydrogenolysis) of aluminasupported cobalt

NaNO₃ addition to Co/Al₂O₃ results in an increase in the reducibility, in a smaller dispersity of the metal and in a decrease in the ethane hydrogenolysis rate due to a decorative effect.

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NaNO₃ Co/Al₂O₃ ,

     

In situ laser thermal analysis of bulk materials

The application of thermal analysis techniques directly to the materials being processed could open up new opportunities in the fields of non-destructive testing and process monitoring on the industrial floor. In this paper, a convergent-thermal-wave technique is proposed for the measurement of thermal diffusivity when access to the material is restricted to one side only. Such a technique permits measurement of the thermal properties of samples of large or unknown thickness, as well as coated or stratified materials. A finite-difference numerical model is used to evaluate the possibilities and the accuracy offered by such a technique, and a laser-based experimental apparatus for the non-contact generation and monitoring of annular thermal waves is described.

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Zusammenfassung Die direkte Anwendung thermischer Analysenverfahren auf darzustellende Materialien könnte neue Möglichkeiten auf dem Gebiet der nichtzerstörenden Materialprüfung und der industriellen Prozeßüberwachung bieten. In diesem Artikel wird eine Konvergenzthermowellen-Technik zur Messung des thermischen Diffusionsvermögens vorgeschlagen, die auch dann anwendbar ist, wenn das Material nur von einer Seite her zugänglich ist. Diese Technik ermöglicht die Messung thermischer Eigenschaften von Porben unbekannter Größe oder Dicke sowie die von belegten oder beschichteten Materialien. Ein numerisches endliches Differenz-Modell wird zur Bewertung der durch solch eine Technik gebotenen Möglichkeiten und deren Genauigkeit herangezogen. Eine auf Laser basierende Versuchsapparatur zur Nicht-Kontakt-Erzeugung und Aufzeichnung von ringförmigen thermischen Wellen wird beschrieben.

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. , . , . . .

     

Infrared study of unsaturated surface compounds on supported bimetallic catalysts

Surface species of unsaturated hydrocarbons and their catalytic transformations on bimetallic systems have been studied by IR spectroscopy. The results obtained allow to estimate the role of individual components of the given systems in catalytic processes.

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- . .

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Reactivity of coordinated O2? towards. One-electron oxidants

Ion-radical complexes Ti(IV) (O ₂ ^– ) are unreactive towards most oxidants except Ce(IV) and Cr₂O ₇ ^2– . The one-electron redox potential for the O_{2 coord.}/O _{2 coord.} ^– couple lies between 1 and 1.6 V.

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- O ₂ ^– Ti(IV) , Ce(IV) Cr₂ O ₇ ^2– . - O_{2 .}/O ₂ ^– . 1 1,6 .

     

Catalytic properties of nickel phosphates. Isomerization of butenes

The effect of calcination temperature on the catalytic properties of nickel phosphate has been studied using the isomerization of butene-1 as a test reaction. A simple relationship was found between the catalyst activity in isomerization and the hydroxy content of the catalyst surface. Interrelations between the activity of the catalyst and its structure are discussed.

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, -1 . . .

     

Kinetics of cumene hydroperoxide-dependent aniline hydroxylation with hemoglobin participation

The kinetics of cumene hydroperoxide-dependent aniline hydroxylation to p-aminophenol with hemoglobin (Hb³⁺) participation has been studied in a phosphate buffer at pH 7.4 and 37°C. The data obtained point to hemoglobin complexing with aniline and cumene hydroperoxide (CHP). The character of aniline hydroxylation by the CHP-Hb³⁺ system is discussed.

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37°C pH 7,4 - (Ho³⁺). Hb³⁺ . -Hb³⁺.

     

Kinetic investigation on alcoholysis of triethylaluminium by differential thermal analysis

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from –150 to –170 kJ mole^–1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofS _E2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

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Zusammenfassung Die Reaktion zwischen einer Lösung von Alumimumtriethyl und einer Reihe von aliphatischen oder aromatischen Alkoholen kann mittels DTA quantitativ verfolgt werden. Die negative Reaktionsenthalpie der Alkoholyse mit primären Alkoholen beträgt 150 bis 170 kJ mol^–1, sofern ein Lösungsmittelgemisch aus Tetrahydrofuran/Toluen eingesetzt wird. Die Reaktionsgeschwindigkeit in unpolaren Kohlenwasserstoffen ist grösser als in Gegenwart von Lewis-Basen. Wahrscheinlich ist der Reaktionsmechanismus vom TypS _E2, wobei die Reaktivität in der Folge primäre, sekundäre, tertiäre Alkohole fällt. Der zweite Schritt der Alkoholyse, ausgehend vom Diethylaluminiumalkoxid, ist wegen der starken Selbstassoziation weniger reaktiv. Bei Umsatz von 2 Mol Alkohol treten entsprechend der Folgereaktion zwei DTA-Peaks auf.

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. –150 –170 ^–1 - . , . , S _E2 , , . , , . -, .