AlPO4?ZrO2 catalysts, II. Synthesis, textural properties and crystal structure of systems obtained in ethylene oxide

The effects of surface dehydration on textural properties, crystallinity and the structure of AlPO₄–ZrO₂ (weight ratio AlPO₄/ZrO₂=3) systems precipitated with ethylene oxide have been studied by N₂ adsorption and XRD measurements. The increase in calcination temperature in the range 773–1273 K decreases the textural parameters as a consequence of AlPO₄ crystallization to the tridymite form.

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, AlPO₄–ZrO₂ ( AlPO₄/ZrO₂=3), , N₂ - . 773 1273 , AlPO₄ .

     

Thermal treatment and analysis involved in the preparation and investigation of different types of inorganic glasses

The importance of the thermal behaviour of glasses is illustrated. Some procedural characteristics for glass preparation upon quenching are discussed to distinguish the positive effects of increasing cooling rate. The basic thermodynamic quantities, kinetic data and procedural parameters are listed. The glass-transformation interval is treated in detail to demonstrate the temperature-dependences of heat capacity, enthalpy an Gibbs energy for as-quenched and annealed glasses, exemplifying processes of thermally stimulated reordering. Particular attention is paid to DTA measurements, which are of use for the determination of characteristic temperatures and to for the distinction of possible types of processes which occur upon reheating. Most common cases are illustrated by a series of hypothetical H vs. T and T _dta vs. T plots. Different glass formation coefficients based on the onset temperatures are discussed to confirm the general knowledge that their maxima match with concentration regions close to that of invariant melting of the system.

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Zusammenfassung Es wird die Bedeutung des thermischen Verhaltens von Glas verdeutlicht. Einige technologische Kenngrößen der Gasherstellung beim Abschrecken sowie grundlegende thermodynamische Größen, kinetische Daten und technologische Parameter, wurden beschrieben, um bei steigender Abkühlgeschwindigkeit positive Einflüsse erkennen zu können. Zur Unterstreichung thermisch stimulierter Umordnungsprozesse und zur Verdeutlichung der Temperaturabhängigkeit von Wärmekapazität, Enthalpie und freier Enthalpie von abgeschrecktem und kühlgeglühtem Glas wird das Intervall der Glasumformung ausführlich behandelt. Erhöhte Aufmerksamkeit wurde DTA-Messungen geschenkt, um charakteristische Temperaturwerte festzustellen und um eventuelle Typen der Prozesse, die beim Nachhitzen ablaufen, zu erkennen. Die häufigsten Fälle werden durch hypothetische H-T und T _dta -T Diagramme illustriert. Verschiedene Glasformationskoeffizienten für die Anfangstemperatur wurden diskutiert, um den allgemeinen Fakt zu bekräftigen, daß deren Maximum mit den Konzentrationsbereichen nonvariant schmelzender Systeme übereinstimmt.

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. , . , . , , , . , , . H- _a-. , , , .

     

Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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, . : > > > . .

     

Conversion of hydrocarbons on supported catalysts prepared via decomposition of surface complexes. Preparation and properties of (Ga+Pt)/SiO2 and (Ga+Pt)/Al2O3 catalysts

The addition of gallium is shown to increase Pt dispersity and its stability to deactivation in n-hexane dehydrocyclization, to decrease the rate of n-hexane hydrogenolysis and to increase the selectivity to benzene, apparently, due to the interaction of Pt clusters with surface Ga ions.

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, -, - . .

     

Epoxy polymers: Glass transition/cure degree correlation

The correlation between the glass transition temperature,T _g , and the cure degree, , of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses.A physical meaning has been given to the coefficients of the series expansion of the functionT _g=T _g ().This analysis allows one to verify that the experimental (T _g ,) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,T _o, appearing in the VTF equation, is larger thanT _g .This conclusion may be supported by the thermodynamic interpretation ofT ₀ as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T ₀ would represent the minimum temperature at which the system becomes able to enhance its cure degree.

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Zusammenfassung Die Korrelation zwischen der Glasumwandlungs-temperaturT _g und dem Aushärtungsgrad von Epoxidpolymeren wurde analysiert, und zwar basierend auf einer Erweiterung der Vogel-Tamman-Fulcher-Gleichung für die Viskosität von Polymeren und Gläsern. Den bei der Reihenentwicklung der FunktionT _g =T _g () auftretenden Koeffizienten wurde eine physikalische Bedeutung zugeschrieben. Diese Analyse ermöglicht nachzuweisen, daß die experimentellen Daten (T _g ), die Schlußfolgerung stützen, daß im Falle von hitzehärtbaren Polymeren die in der VTF-Gleichung auftretende sogenannte ideale GlasumwandlungstemperaturT ₀ höher alsT _g ist. Diese Konklusion wird auch durch die thermodynamische Interpretation vonT ₀ gestützt, nämlich als die Temperatur, bei der die Überschußentropie des Systems gegen Null geht: im Falle von teilweise ausgehärteten hitzehärtbaren Polymeren würdeT ₀ die minimale Temperatur darstellen, bei der eine Erhöhung des Aushärtungsgrades des Systems einsetzt.

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T _g () - - . qT _g =T _g (). T _g , T ₀, -- , T _g . T ₀, , . ,T ₀ , .

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Work supported by the Progetto Finalizzato Chimica Fine e Secondaria of the Italian C.N.R., grant No. 84.01304.95     

Activity of γ-Al2O3 modified by NaOH in disproportionation of methanethiol

Na⁺/Al₂O₃ catalysts in disproportionation of methanethiol are highly selective towards dimethyl sulfide but less active compared to -Al₂O₃. Their activity falls with increasing Na⁺ in the sample. This decrease is due to the neutralization of Brönsted acid centers on the catalyst.

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Na⁺/Al₂O₃ , , -Al₂O₃. Na⁺ . .

     

X-ray study of palladium catalysts. Influence of thermal treatment in hydrogen on the phase composition

The thermal treatment of Pd catalysts in a reducing atmosphere of hydrogen leads to interaction of supported metal and support to form solid solutions.

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, .

     

Low temperature adsorption of oxygen on Ni(100)

LEED, AES and data indicate the nonreconstructive character of oxygen adsorption on Ni(100) at 170 K and reconstructive chemisorption at T>270 K with the formation of a c(2×2)0 structure.

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, , Ni (100) 170 >270 (2×2)0.

     

Reactive silica, XIV. Sorption and polymerization of ethylene oxide on reactive silica

Ethylene oxide vapor was exposed to reactive silica (RS). It chemisorbed immediately on a pair of silicon radicals as –O–CH₂–CH₂–, and the adsorbed species polymerized. It is assumed that polymerization is not an ionic but a radical type reaction.

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. –O–CH₂–CH₂– . , , .

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Part XIII: Ref. 15     

Thermal analysis of the direct nitridation of silicon to Si3N4

The coefficients of the virial expansion of the excess enthalpies of ternary aqueous solutions containing D-glucose and an alcohol (ethanol,n-propanol,n-butanol andtert-butanol) were determined at 25 °C. The trend of the cross coefficients versus the self coefficients of the alcohols exhibits a maximum in accordance with the system containingtert-butanol. This behaviour is similar to that found for the interaction of the same alcohols with any other hydrophilic solute examined up to now. The results are interpreted in terms of a prevailing release of water from the structured cospheres of the alcohols.

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Zusammenfassung Die Koeffizienten der Virialentwicklung der Überschußenthalpien von ternären, D-Glucose und einen Alkohol (Ethanol,n-Propanol,n-Butanol,tert-Butanol) enthaltenden wässrigen Lösungen wurden bei 25 °C bestimmt. Bei dem tert-Butanol enthaltenden System wird ein Maximum erhalten, wenn die Koeffizienten der Wechselwirkung zwischen verschiedenartigen Molekülen gegen die Wechselwirkung zwischen den Alkoholmolekülen aufgetragen werden. Dieses Verhalten ist identisch mit dem, das für die Wechselwirkung der gleichen Alkohole mit anderen bis jetzt untersuchten hydrophilen gelösten Stoffen gefunden wurde. Die Ergebnisse werden interpretiert, indem ein bevorzugter Austritt von Wasser aus der strukturierten Koordinationssphäre des Alkohols angenommen wird.

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25° , - (, - , -). . - . .

     

Potential for coal calorific value corrections,dependent on the carbonate mineral type present

In addition to calcite, other carbonate minerals in coal all undergo endothermic reactions on heating, i.e. dolomite, ankerite, siderite, aragonite, magnesite, rhodochrosite, witherite and strontianite. Of these, when determined in air, siderite and rhodochrosite give small exothermic resultants, while the amount of Fe in ankerites affects the actual endothermic values obtained. The magnitude of these carbonate decomposition reactions can be shown by DTA to be different and will need to be allowed for individually in calorific value corrections of coals containing them.

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Zusammenfassung Nicht nur Kalkspat, sondern auch andere in Kohle vorkommende Karbonatmineralien wie z. B. Dolomit, Ankerit, Spateisenstein, Aragonit, Magnesit, roter Braunstein, Witherit und Strontionit gehen bei Erhitzen endothermische Reaktionen ein. Von diesen zeigen Spateisenstein und roter Braunstein exotherme Ergebnisse kleinen Wertes, während der Betrag an Eisengehalt in Ankeriten den jeweils gemessenen endothermischen Wert beeinflußt. Das Ausmaß dieser Karbonatzersetzungsreaktionen kann durch DTA-Messungen als unterschiedlich nachgewiesen werden und muß bei den Kaloriewertkorrektionen für Kohlen, die diese Mineralien enthalten, berücksichtigt werden.

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

     

Study of distribution of elements in the depth of V?P?Co catalyst grain

It has been shown that addition of cobalt to a vanadium-phosphorus oxide catalyst increases the P/V molar ratio on the surface, the surface acidity and the selectivity of butane oxidation. It has been established that in the V–P–Co–O catalyst the probability of the removal of phosphorus from the surface is markedly reduced.

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, , . , V–P–Co–O .

     

High temperature thermal decomposition of propane

The thermal decomposition of propane has been studied by pulse chromatographic method within the temperature range of 975–1083 K. The kinetic parameters of the reaction have been determined.

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- 975–1083 . .

     

Calculation of the energy spectrum of surface oxygen on CuO by the interacting bonds method

Using the interacting bonds model a calculation has been made for the energy spectrum of oxygen on the CuO surface. Dissociative adsorption of oxygen can be realized in one and two-center forms with 9.2 and 60.4 kcal/mol, respectively. Intermediate values of the adsorption heats are attributed to oxygen adsorption on induced and biographic defects. The theoretically calculated energy spectrum of adsorbed oxygen is in reasonable agreement with that obtained experimentally from the dependence of isosteric heats of oxygen adsorption on the surface coverage.

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CuO. - 9,2 60,4 / . . .

     

Hysteresis of thermogravimetric curves of nickel catalysts for methane conversion in CH4+CO2 mixture

Characteristic peculiarities of the supercarbonization peak, i. e. the effect of carbon accumulation on the catalyst surface and its subsequent removal under heating in the CH₄+CO₂ mixture have been studied. Hysteresis of thermogravimetric curves in the heating/cooling cycle has been established.

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— . -.

     

Thermal behaviour of melamine

Melamine undergoes condensation on heating with elimination of ammonia and formation of insoluble products. Thermogravimetry and infrared characterisation show that two products of successive condensation can be reproducibly obtained upon heating atT}<500 °C and then at 600 °C. Above 620 °C, the melamine condensate undergoes thermal degradation with quantitative formation of volatile products.

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Zusammenfassung Melanin geht beim Erhitzen eine Kondensation unter Abgabe von Ammoniak und Bildung unlöslicher Produkte ein. Durch Thermogravimetrie und Infrarotspektroskopie wird gezeigt, daß beim Erhitzen zwei Produkte von aufeinanderfolgenden Kondensationsreaktionen beiT}<500 °C undT= 600 °C reproduzierbar erhalten werden. Oberhalb 620 °C wird das Melaminkondensat vollständig unter Bildung flüchtiger Produkte thermisch zersetzt.

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. , . , 500°, — 600°. 620° .

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The authors wish to thank Dr. N. Del Fanti of Mantefluos, Italy for most helpful discussion.

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This work has been supported by the Consiglio Nazionale delle Ricerche through the Progetto Finalizzato Chimica Fine e Secondaria.     

Thermoanalytical investigations of some industrial wastes produced in steel works

The experiments involves three types of industrial wastes produced by iron works, which create serious hazards to the natural environment: (1) paint-shop sludge, (2) oil-polluted diatomite, and (3) oil-polluted scale. The choice of an appropriate and safe storage method should be based on extensive physicochemical examination.DTA, in combination with other data, allows characterization of the combustible properties of wastes. Thermoanalytical measurements were carried out in a dynamic air atmosphere. Enthalpy values were calculated from peak areas of DTA curves. Thermoanalytical data were compared with calorimetric results obtained with an oxygen bomb.

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Zusammenfassung Drei Arten industrieller Abtälle eines Stahlwerks, die schwere Umweltbelastungen darstellen, wurden untersucht: (1) Lackiererei-Schlamm, (2) ölhaltiger Diatomit, (3) ölhaltiger Kesselstein. Geeignete sichere Deponien setzen ausführliche physikalisch-chemische Untersuchungen voraus. DTA in Kombination mit anderen Untersuchungen erlaubt die Charakterisierung der Verbrennungseigenschaften der Abfälle. Die thermoanalytischen Untersuchungen erfolgten im Luftstrom, die Verbrennungswärmen wurden aus den DTA-peak-Flächen berechnet. Die Ergebnisse werden mit denen kalorimetrischer Messungen in einer Sauerstoffbombe verglichen.

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- , . , . , - . . . . , .

     

Methanol conversion to hydrocarbons and dimethyl ether on decationized zeolite T

Methanol transformations over the hydrogen forms of zeolite T (32%–76% decationization and 13%–32% dealumination) during contact with methanol vapor was studied at 200°–400°C. The catalysts used show a high activity in methanol conversion into light hydrocarbons and dimethyl ether but over a short period.

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T (32–16% 13–32% ) 200–400°C. , .

     

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.