Possibility of thermal analysis of different types of bonding of water in minerals

Various types of water bonding were studied. e.g. water bound by occlusion, by adsorption, by capillary condensation, by chemisorption and as a solid solution, zeolitic water, interlayer water, crystal water and structural water bound in form of hydroxil groups. The differentiation of these various types of bonding is rather difficult, for on heating water is evolved at various temperatures and in rather wide temperature domains which overlap to different extents. Efforts were made to improve the detection by applying the quasi-isothermal quasi-isobaric measuring technique.

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Zusammenfassung Es wurden verschiedene Bindungstypen von Wasser untersucht. Wasser kann unter anderem durch Einschlüsse, Adsorption. Kapillarkondensation, Chemisorption und in Form von Mischkristallen, zeolitisch, schichteingebettetem und Kristallwasser sowie als OH-Form gebunden sein. Die Untersuchung dieser zahlreichen Bindungstypen ist äußerst schwierig, da die Wasserabgabe bei verschiedenen Temperaturen geschieht und die ziemlich breiten Temperaturintervalle mehr oder weniger überlappen. Mittels quasiisothermen und quasiisobaren Meßtechniken wurde versucht, die Möglichkeit der Bestimmung zu verbessern.

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. , , , , , , , . , , . , .

     

Kinetics and mechanism of TI(III) oxidation of cellobiose in acidic medium

TI(III) oxidation of cellobiose in the presence of H₂SO₄ in aqueous acetic acid is first order in each reactant and is acid catalyzed. TI(OAc) ₂ ⁺ is the active species. Products identified are gluconic acid and glucose. A mechanism consistent with the temperature, solvent, acidity and salt effects is been proposed.

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TI(III) H₂SO₄ . TI(OAc) ₂ ⁺ . . , , , .

     

Effects of radioactivity on surfaces: I. Influence of Cr-51 on the catalytic activity of chromium catalysts

Chromium catalysts were prepared on monolith supports, some of them with radioactive Cr-51 in the surface. The dehydrogenation-hydrogenation reaction of cyclohexene was used to compare the catalytic activities of the radioactive and inactive catalysts. Differences were observed in the distribution of the main products at low temperatures and of the byproducts also at high temperatures.

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, Cr-51. - . , — , .

     

Compounds responsible for the deactivation of H-USY zeolite during the alkylation of phenol with methanol

H-USY deactivates very rapidly during the alkylation of phenol with methanol at 200°C. The retention in the pores of compounds resulting from successive O- and C-alkylation of phenol (such as polymethylphenols and polymethylanisoles) is responsible for this deactivation. The retention of these compounds in the pores is not due to their steric blockage but to their low volatility and their strong adsorption.

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H-USY 200°C. , - - , ( -). , .

     

Measurements and calculations of stresses in metal-ceramic systems

Deflection changes dependent on temperature and thickness of ceramics have been measured on ceramic-coated metal strips, using a modified commercial dilatometer.The deflections are not only dependent on the difference in the thermal expansion coefficients of the two materials, but are also influenced by the thickness ratio of the ceramic to the metal. The stresses existing in the ceramic have been calculated for the surface layer and for the layer in the transition zone ceramic/metal. The results have shown that there is no proportional relation between the value of deflection and the stresses in the ceramic; however, the maxima in the deflection curves coincide with the peaks shown in the stress curves. From a certain thickness ratio of ceramic to metal — determined by the Young's moduli of the materials — tensile stresses in the surface of the ceramic occur even at the higher expansion coefficient of the metal.

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Zusammenfassung An mit Keramik beschichteten Metallstreifen wurden in einem modifizierten, handelsüblichen Dilatometer Ausbiegungsänderungen in Abhängigkeit von der Temperatur und der Keramikdicke gemessen. Die Verformungen hängen nicht allein von der Differenz der thermischen Ausdehnungskoeffizienten der beiden Werkstoffe ab, sondern werden auch durch das Dickenverhältnis von Keramik zu Metall beeinflusst. Die in der Keramik vorhandenen Spannungen wurden für die Oberflächenschicht und für die Schicht in der Grenzzone Keramik/Metall berechnet. Die Ergebnisse haben gezeigt, daß kein proportionaler Zusammenhang zwischen der Grösse der Ausbiegung und den Spannungen in der Keramik vorhanden ist. Maxima in den Ausbiegungskurven fallen jedoch mit ausgezeichneten Punkten in den Spannungskurven zusammen. Ab einem durch die Elastizitäts-Moduln der Werkstoffe bestimmten Dickenverhältnis von Keramik zu Metall treten auch bei einem grösseren Ausdehnungskoeffizienten des Metalls Zugspannungen in der Oberfläche der Keramik auf.

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Résumé On a mesuré, sur des bandes de métal recouvertes de céramique et en se servant d'un dilatomètre commercial modifié, les changements de déflection qui dépendent de la température et de l'épaisseur des céramiques.Les déflections dépendent non seulement de la différence des coefficients de dilatation thermique des deux matériaux, mais aussi du rapport des épaisseurs respectives de la céramique et du métal. Les contraintes existant dans la céramique ont été calculées pour la couche superficielle et pour la couche de la zone de transition céramique/métal. Les résultats ont montré qu'il n'y a pas de relation de proportionnalité entre la valeur de la déflection et les contraintes dans la céramique; cependant, les maximums des courbes de déflection coïncident avec les pics des courbes de contrainte. A partir d'un certain rapport d'épaisseur de la céramique au métal — déterminé par les modules d'Young des matériaux — les contraintes d'allongement à la surface de la céramique se produisent même si le métal possède un coefficient de dilatation plus élevé.

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. , . /. , . , . , , , .

     

Photoinduced oxygen adsorption of AgBr crystals at 77 K

Photoinduced adsorption (PIA) of oxygen molecules on AgBr films at 77 K has been experimentally observed and investigated. Lifetimes of PIA centers and desorption activation energies of O₂ molecules have been determined. The process is suggested to compete with the ionic step of AgBr photolysis.

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- () - AgBr 77 K. - O₂. , , - AgBr.

     

Study of the combustion of a fire retardant coating by thermal analysis and different complementary techniques

An intumescent fire retardant coating can effectively control fire spread and damage. Its dual purpose is to confine the surface spread of flame to the boundaries of an already established fire, and to retard the penetration of heat and flame to and through the coated surface. Our composition expanded and provided an insulation layer between the flame source and the combustion substrate, and liberated a quantity of primarily non-flammable decomposition products which tended to extinguish the flame. The main ingredients of the coating were cellulose acetate butyrate and HMDI (Desmodur N) for Polyurethane, and Chlorowax-70 (chlorinated paraffins) as fire retardant component. This fire retardant coating was applied to wood panels, and tested in a 2-foot tunnel, its flame spread rating being measured. The effects of three parameters of interest were investigated: the type of wood used, the percentage of Chlorowax, and the coating thickness. It was found of interest to study the oxidation of the coating using different techniques, e.g. flash pyrolysis under oxygen and GC/MS for analysis of the decomposed products. Combustion studies of the coating were also conducted using DSC and thermogravimetry, either with the scanning mode or under isothermal conditions. Comparisons were made between the results obtained from pyrolysis and combustion.

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Zusammenfassung Ein schwellender feuerhemmender Überzug kann Ausbreitung und Schäden von Feuer wirksam einschränken und wird zwei Zwecken gerecht: Verhinderung der Ausbreitung von ausgebrochenem Feuer und Schutz der überzogenen Oberfläche vor Hitze- und direkter Flammeneinwirkung. Die beschriebene Komposition quillt und bildet eine Isolationsschicht zwischen der Flammenquelle und dem brennbaren Material, liefert zugleich aber auch eine gewisse Menge von nichtbrennbaren, die Flamme erstickenden primären Zersetzungsprodukten. Die Hauptbestandteile des Überzugs sind Celluloseacetat und -butyrat und HMDI (Desmodur N) für Polyurethan sowie Chlorowax-70 (chlorierte Paraffine) als feuerhemmende Komponente. Dieser feuerhemmende Überzug wurde auf Holzplatten aufgebracht und in einem 2ft-Tunnel getestet, wobei die Flammenausbreitungsgeschwindigkeit gemessen wurde. Der Einfluß von drei interessierenden Parametern wurde untersucht: Typ des benutzten Holzes, Anteil von Chlorowax und Überzugsschichtdicke. Es erwies sich als interessant, die Oxydation des Überzugmaterials mit verschiedenen Techniken zu untersuchen, z.B. durch Schnellpyrolyse und Analyse der Zersetzungsprodukte mittels GC/MS. Verbrennungsuntersuchungen des Überzugmaterials wurden auch mittels DSC und Thermogravimetrie entweder nach der scanning-Arbeitsweise oder unter isothermen Bedingungen ausgeführt. Die bei Pyrolyse und Verbrennung erhaltenen Ergebnisse werden miteinander verglichen.

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. -, , — . , . - ( ) ( ) . , . : , . , , , - . . , .

     

Correlation between oxygen binding energy and catalytic activity of oxides

Oxygen binding energy is suggested as a measure for the ability of oxide cations to enter into weak chemical interactions with reactant molecules, which is a necessary prorequisite for the adsorbability and catalytic activity of oxides.

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, . .

     

Influence of the thermal treatment of platinum alumina catalysts with exhaust gases on their activity in cyclopropane hydrogenation

The activity of platinum/alumina catalysts in cyclopropane hydrogenation has been investigated. Catalysts heated in exhaust gases are considerably less active in cyclopropane hydrogenation as compared to samples calcined in air. A relatively stable modification of the metallic surface is formed, probably as a result of coke or poison deposition.

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- . , , , , , . , , .

     

Formation and thermal decomposition of silicon oxynitride compounds II

In studies on the reactions of silicon oxynitride, Si₂N₂O, with lithium oxide and of lithium metasilicate with lithium nitride, the formation of a previously unknown compound with stoichiometry Li₅SiNO₃ has been observed.

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Zusammenfassung Eine bisher unbekannte Verbindung der Zusammensetzung Li₅SiNO₃ wurde bei Reaktionen von Siliciumoxynitrid (Si₂N₂O) mit Lithiumoxid und von Lithiummetasilikat mit Lithiumnitrid erhalten.

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(Si₂N₂O) , Li₅SiNO₃.

     

Catalytic decomposition of isopropyl alcohol on iron(II) sulfide

The decomposition of isopropyl alcohol on troilite (FeS) which was thermally activated at 873, 973 and 1073 K, is described in this paper. The catalyst subjected to thermal activation exhibits improved activity, which increases with temperature of activation. It has been observed that the apparent activation energy E and the preexponential factor A have a compensating effect. The experiments involving the preadsorption of pyridine have shown that this substance is preferentially and irreversibly adsorbed on hydrogenation active centers.

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(FeS), 873, 973 1073 . , , , . . , .

     

Bauxites as hydrotreatment catalysts

The effects of calcination temperature on structural and textural characteristics of two Greek bauxites were examined by different physicochemical techniques. Although the above minerals exhibited lower activity than a commercial CoMo/Al₂O₃ catalyst, they were evaluated as possible hydrotreating catalysts.

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. , CoMo/Al₂O₃, , .

     

Comparison of the acid strength of solid catalysts

The catalytic activity of some solid acidic catalysts was tested in the depolymerization of paraldehyde. It was found that the activities of sulfonated ion exchange resin and mounted phosphotungstic acid strongly exceed the activity of silica-alumina and other oxide catalysts. By means of Brönsted relationship, the differences in H_O of the surfaces were estimated.

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. , - - . H_O .

     

M?ssbauer spectroscopic studies of passivated layers of iron-containing catalysts for ammonia synthesis

Combined conversion electron (CEMS) and transmission -ray (MS) Mössbauer spectroscopy was used to study the structure of passivated layers of promoted and unpromoted iron-containing catalysts. In both catalysts the oxide-coated films were found to consist of small paramagnetic (at 300 K) clusters of ferric oxide.

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. , ( 300 ) .

     

Measurement of thermal constants of calcium chromite by Laser Flash method

Calcium chromite, CaCr₂O₄, was prepared and its purity and stoichiometry were ascertained by chemical analysis and X-ray diffraction methods. The thermal diffusivity, specific heat capacity and thermal conductivity of calcium chromite were measured by Laser Flash method using an Ulvac-Sinku Riko TC-3000 series instrument in the temperature range of 298 to 1100 K. The heat capacity data were utilised to calculate the thermodynamic parametersenthalpy increments, entropy increments and free energy increments—in the above temperature range.

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Zusammenfassung Kalziumchromit, CaCr₂O₄, wurde hergestellt und seine Reinheit und stöchiometrische Zusammensetzung mit Hilfe chemischer Analyse und Röntgendiffraktionsmethoden ermittelt. Anhand eines Ulyac-Sinku Riko TC-3000 Gerätes wurde mit Laser Flash Verfahren die Temperaturleitfähigkeit, die spezifische Wärmekapazität und die Wärmeleitfähigkeit von Kalziumchromit im Temperaturbereich 298–1100 K bestimmt. Die Wärmekapazitätsdaten wurden zur Berechnung der thermodynamischen Größen (Enthalpie-, Entropie-, Freie Energieänderung) in obigem Temperaturbereich benutzt.

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CaCr₂O₄, . , - TC-3000, 298–1100K , . , , .

     

Kinetics of ammonia decomposition of polycrystalline rhodium at pressures between 0.013 and 103 kPa

The rates of ammonia decomposition on polycrystalline Rh wires between 600 and 1800 K and at pressures between 13.3 Pa and 103 kPa were measured and fitted with a Langmuir-Hinshelwood unimolecular reaction rate expression. At high temperatures and pressures the reaction seems to be mass transfer controlled.

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Rh 600–1800 K 13,3 –103 . , -. .

     

Recombination mechanism of hydrogen atoms on ZnS surface

It has been established that physically adsorbed and chemisorbed atoms take part in the recombination of H-atoms on ZnS surface.

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- ZnS .