Quantitative estimation of calcite in limestones by differential thermal analysis

A quantitative method is presented for the estimation of calcite in limestones by differential thermal analysis, using calcium hydroxide as an internal standard. The effects of variations due to particle size and impurities such as quartz, iron oxide, organic material, dolomite, magnesite, gypsum and phosphates are discussed.

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Zusammenfassung Es wurde eine quantitative Methode zur Ermittlung von Kalzit im Kalkstein durch Differentialthermoanalyse unter Anwendung von Kalziumhydroxyd als inneren Standard vorgestellt. Der Einfluß von durch unterschiedliche Teilchengröße und Verunreinigungen, wie Quarz, Eisenoxyd, organische Stoffe, Dolomit, Magnesit, Gips und Phosphat hervorgerufenen Veränderungen wurde erörtert.

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Résumé On propose une méthode de dosage par ATD de la calcite dans les roches calcaires en utilisant l'hydroxyde de calcium comme étalon interne. On discute l'influence de la taille des particles et de la nature des impuretés: quartz, oxyde de fer, corps organiques, gypse, dolomite, magnésite et phosphates.

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, . , , , , , , .

     

Cumene hydroperoxide decomposition in the presence of metal complex catalysts supported on amorphous SiO2

By the method of molecular deposition, ions of CrO ₂ ²⁺ VO³⁺ and MoO ₂ ²⁺ were supported on a matrix of amorphous SiO₂. Different types of organic ligands were supported subsequently on the surface compounds so formed. The catalytic activity of the samples was studied in the decomposition of comene hydroperoxide.

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SiO₂ CrO ₂ ²⁺ , VO³⁺, MoO ₂ ²⁺ . . .

     

Hydrolysis of ethyl acetate on cation-form sulfonic resins

Catalytic properties of metal cations on sulfonic resin have been studied in ester hydrolysis. The catalytic activities were related to the electronegativity of the metal cation, while the activation energies were close to that for H-form resin and not affected by the cation concentration, suggesting the variation of entropy factors in catalysis.

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. . - . , .

     

Meaningful activation energies for complex systems II

The validity of the Friedman method is assessed for systems of overlapping reactions. By means of mathematical analysis and numerical examples it is shown that, in the case of competitive reactions, the method gives the true value of the instantaneous mean activation energy. However, some error may be incurred if this method is applied to systems of independent reactions. The relative accuracy of the Friedman and Ozawa-Flynn-Wall methods is discussed in respect of complex systems of reactions.

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Zusammenfassung Die Gültigkeit der Friedman-Methode wird für Systeme von überlappenden Reaktionen einer Betrachtung unterzogen. Durch mathematische Analyse und numerische Beispiele wird gezeigt, daß im Falle kompetitiver Reaktionen die Methode den richtigen Wert der jeweiligen mittleren Aktivierungsenergie ergibt. Fehler können jedoch auftreten, wenn diese Methode auf Systeme voneinander unabhängiger Reaktionen angewandt wird. Die relative Genauigkeit der Methoden von Friedman und Ozawa-Flynn-Wall wird mit Hinsicht auf komplexe Reaktionssysteme diskutiert.

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. , . , , . -- .

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The author wishes to thank the British Gas Corporation for permission to publish this work.     

Barium sulphate reduction with carbon

The reduction of BaSO₄ by carbon was investigated by means of isothermal thermogravimetric measurements. In combination with a high-temperature thermobalance, solid electrolyte cells were used (i) to purify the N₂ flow gas, and (ii) to measure the partial pressure of oxygen (COCO₂ ratio, respectively) in the outlet gases.Mass loss curves and in the outlet gases were recorded at 743–955 °C. The activation energy of the process was calculated from the isothermal TG curves. X-ray diffraction and SEM showed that the solid product in the whole temperature interval comprised only cubic BaS.

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Zusammenfassung Die Reduktion von BaSO₄ mit Kohlenstoff wurde durch isotherme thermogravimetrische Messungen verfolgt. Mit einer Hochtemperatur-Thermowaage wurden Festelektrolyten kombiniert (1)zur Reinigung des Spülgases N₂ von Sauerstoff, (2) zur Messung des O₂-Partialdruckes (bzw. des Verhältnisses COCO₂) im entweichenden Gas. Die Gewichtsverlust- und Sauerstoffpartialdruck-Kurven bei 743–955 °C wurden aufgezeichnet. Aus den TG-Kurven wurde die Aktivierungsenergie des Prozesses berechnet. Im gesamten untersuchten Temperaturbereich entstand als festes Reaktionsprodukt nach Röntgenbeugungs- und SEM-Untersuchungen nur kubisches B₂S.

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. , -, ( :₂) . 743–955° — . . , .

     

Kinetics and mechanism of ketone-bisulfite addition reaction in aqueous solution

The kinetics of the addition of bisulfite to acetone has been studied by the polarographic technique. The specific rate increases with pH and hence the reaction is probably base catalyzed. Mechanisms have been suggested for the reaction in the presence and absence of added base.

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- . pH, , , . .

     

Kinetics and mechanism of the hydrogenation of substituted anthraquinones on Raney nickel catalysts

The rate and direction of the hydrogenation of anthraquinone has been established to depend considerably on the nature and position of the substituent as well as on the structure and phase composition of the catalyst. The selectivity of the process is increased by introducing electronaccepting substituents into the anthraquinone molecule or upon doping the Ni–Al alloy by additives increasing the M–H bond energy.

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, . Ni–Al , M–H, .

     

On the mechanism of alcohol insertion into the carbonyl group in the coordination sphere of Fe(III) tris-hexafluoroacetylacetonate

The kinetics of formation of hemiacetals in the Fe(III) coordination sphere resulting from the reaction of Fe(III) tris-hexafluoroacetylacetonate with methanol has been studied by the stopped-flow method. Two molecules of methanol and coordinated hexafluoroacetylacetonate anion (HFA^–) take part in the rate-determining step. The effect of the second molecule of alcohol can be attributed to catalysis of proton transfer from methanol to the HFA^– ligand through the chain of hydrogen bonds in 6-membered cyclic structures.

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stopped-flow Fe(III). , -. , , .

     

Transverse photothermal deflection spectroscopy (PDS) applied to thermal diffusiyity measurements

Transverse photothermal deflection spectroscopy(PDS) is applied for the determination of thermal diffusivities of solid surfaces. The theory of PDS is briefly recalled and some approximated analytical formulae concerning the transverse configuration are derived. In materials where the thermal diffusivity is smaller than that of the air, the dependence of the deflection angle on the displacement between pump and probe beams is shown to have a minimum that relates to the thermal diffusivity, thereby allowing its straightforward measurement. Measurements carried out on Al₂O₃ samples with different porosities at room temperature show a good agreement between experiment and theory.

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Zusammenfassung Die transverse photothermische Reflektionsspektroskopie (PDS) wird zur Bestimmung der thermischen Diffusivität von festen Oberflächen herangezogen. Die Theorie der PDS wird kurz dargelegt und einige sich auf die transverse Konfiguration beziehenden analytischen Näherungsgleichungen abgeleitet. Es wird gezeigt, daß bei Materialien mit kleinerer thermischer Diffusivität als Luft die Abhängigkeit des Deflektionswinkels von der Ablenkung zwischen Pumpen- und Probenstrahl ein Minimum aufweist, das mit der thermischen Diffusivität im Zusammenhang steht und somit deren zuverlässige Messung ermöglicht. An Al₂O₃-Proben unterschiedlicher Porosität bei Raumtemperatur ausgeführte Messungen zeigen gute Übereinstimmung von Experiment und Theorie.

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IR spectroscopic studies of surface acrolein and acrylic acid compounds in conditions of catalytic oxidation of acrolein on V?Mo?Si?O catalyst

Three surface complexes of acrolein have been identified by high-temperature IR spectroscopic method. Their extinction coefficients have been decermined. - .     

Formation of the active component of a vanadium complex catalyst for the oxidation of anthracene to anthraquinone

The phase composition in various stages of preparation of the active material coating the catalyst for the partial oxidation of anthracene to anthraquinone was studied. The presence of an active phase was evidenced in the final active material as well in a precursor.

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, . , .

     

Determination of sucrose content of cariogenic diets by thermal analysis

The sucrose content of cariogenic diets was determined by thermal analysis. The thermal characteristics of various cariogenic diets were examined up to 700 °C. A linear correlation was found between the sucrose content of the sample and the mass loss in the range 180–240 °C.The values determined by thermogravimetry were compared with those obtained by photometry as reference values.

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Zusammenfassung Mittels Thermoanalyse wurde der Saccharosegehalt von Karies verursachenden Diäten bestimmt. Die thermischen Eigenschaften verschiedener kariogener Diäten wurden bis 700 °C untersucht. Zwischen Saccharosegehalt der Probe und Massenverlust bei 180–240 °C konnte ein linearer Zusammenhang festgestellt werden. Die thermogravimetrisch erhaltenen Werte wurden mit den durch Fotometrie erhaltenen Werten als Referenzwerte vergliche.

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. 700°. 180–240°. , , , .

     

Hydrogenation of xylenes over supported Pt catalysts. Influence of different variables on their catalytic activity

In this work we studied and compared the catalytic activity of various supported Pt systems on the gas-phase hydrogenation of o-, m- and p-xylene. We analyzed the influence of different catalyst preparation variables (solvent, precursor, salt, support and catalyst reduction temperature used) on the catalytic activity and selectivity towards the corresponding cis-and trans-dimethylcyclohexanes.

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- o-, m- -. (, , ) - -.

     

Reduction of alkenes by hydrogen transfer over a Pd/sepiolite catalyst. Compensation effect

This paper shows the occurrence of a linear relationship between the activation energy (E_A) and the logarithm of the pre-exponential factor (ln A) in the Arrhenius equation, and between the enthalpy increment (H) and the entropy increment (S) in the Eyring equation for the reduction of olefinic double bonds by hydrogen transfer over a Pd/sepiolite catalyst. Such a relationship is known as the compensation effect or isokinetic relationship.

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Pd/ (E_a) (ln A) (H) (S) . .

     

Influence of Sn added to Pt catalysts on the adsorption heats of hydrogen

It has been established that supported Pt–Sn catalysts adsorb hydrogen at 330 K at least in two forms. They are weak and strong forms with the binding energies of about 50–70 and above 100 kJ/mol, respectively. On catalyst surface weak forms transform into strongly bound hydrogen.

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330 K, , : 50–70 / 100 /. .

     

Temperature programmed reduction and oxidation of Ir/Al2O3 catalysts

3 % Ir/Al₂O₃ catalysts have been studied by means of temperature programmed reduction and oxidation. With growing degree of metal oxidation (higher T_ox) reducibility of the catalysts at low temperatures decreases.

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3% Ir/Al₂O₃ . ( ) .

     

High resolution solid state1H NMR spectra of hydroxy groups in aluminas

Using magic angle spinning technique, the¹H NMR spectra of surface hydroxy groups of different alumina modifications (-, -, and -Al₂O₃) have been studied. Several types of hydroxy groups that differ in their chemical shifts are tentatively attributed to different types of coordination of OH groups to aluminium atoms.

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¹H (-, -, -Al₂O₃). , , , .

     

Temperature dependence of CO insertion on S-, Ag-, and Cu-promoted Rh/SiO2 catalysts

The addition of sulfur and silver to Rh/SiO₂ inhibits hydrogenation of C₂H₄, but promotes CO insertion and extends the linearity of Arrhenius curves for CO insertion above 543 K.

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Rh/SiO₂ C₂H₄, CO CO 543 .