Determination of water content by means of the Derivatograph

The determination of water content by means of the Derivatograph is treated in the paper. The determination of water in analytical precipitates, various pharmaceutical products, biological substances, the products of food industry is treated on the basis of some practical examples. The applicability of the Derivatograph for determining the adsorption capacity of industrial adsorbents, the hydration conditions of cement, the system Ca₃A-CaSO₄ · H₂O and the rehydrability of clay minerals is demonstrated. The aluminium oxide barrier layers were investigated on the basis of the water content of the aluminium hydroxide. For the characterization of the different strengths by which water is bound in strontium chloride hydrates the apparent activation energies are also presented.

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Zusammenfassung Die Bestimmung von Wasser mit Hilfe des Derivatographen wurde besprochen. Es wurden die verschiedenen Anwendungsmöglichkeiten der Methode, wie die Bestimmung des Wassers in analytischen Niederschlägen, Arzeneimitteln, Lebensmittel, biologischen Substanzen an Beispielen besprochen. Die Anwendbarkeit des Derivatographen zur Bestimmung der Adsorptionskapazität von industriellen Adsorbenten, der Hydrationsverhältnisse von Zement, des Systems Ca₃A-CaSO₄ · H₂O und der Rehydration von Tonmineralien wurde erörtert. Aluminiumoxydgrenzschichten konnten auf Grund des Wassergehalts des Aluminiumhydroxyds geprüft werden. Zur Charakterisierung der verschiedenen wasserbindenden Kräfte werden die Werte der scheinbaren Aktivierungsenergien der Alkalierdchlorid-hydrate vorgelegt.

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Résumé L'article traite de la détermination de la teneur en eau à l'aide du Derivatograph. La méthode est exposée en se servant d'exemples pratiques comme les précipités analytiques, divers produits pharmaceutiques, alimentaires, des substances biologiques. On montre que le Derivatograph peut être utilisé pour déterminer la capacité d'adsorption des adsorbants industriels, pour examiner l'hydration du ciment, du' système Ca₃A-CaSO₄ · H₂O et la rehydration des minéraux argileux. Examination des couches interfaces d'oxyde d'aluminium sur Ja base de la teneur en eau du hydroxide d'aluminium. L'énergie d'activation apparente a été déterminée et utilisée pour caractériser les différentes forces de liaison de l'eau dans les chlorures alcalino-terreux hydratés.

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, .

     

Isomerization of unsaturated compounds on Pd/Al2O3 in the presence of additives

Studies of the effect of zinc chloride and aluminium additives on the activity of a Pd/Al₂O₃ catalyst (5 wt.%Pd) in the isomerization of heptene-1, allylbenzene,p-allylphenol and 4-allyl-2-methoxyphenol (eugenol) indicate that the rate and selectivity of isomerization depend on the sequence of addition of salts and reagent to the catalytic system. The simultaneous addition of ZnCl₂ or AlCl₃ with olefin, produces a 2–3 fold increase in the isomer yield compared to ethanol.

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Pd/Al₂O₃- (5 .% Pd) -1, , -, 4--2- (). , . ZnCl₂ AlCl₃ 2–3 .

     

Theory of differential thermal analysis taking into account heat exchange between the specimen and reference cells

A basic formula of differential thermal analysis is evolved for the case when the heat transfer coefficient between the specimen cell and the reference cell is not zero. The more general formula obtained differs from the classical formula by including the parameters of the reference cell and the heat transfer coefficient between the cells. It indicates that utilization of the classical formula is not correct if heat exchange occurs between the cells. To utilize the generalized formula, additional measurements of the temperature changes of the reference material are required. However, if the time constants of the two cells are identical, the formula can be changed to assume the form of the classical formula for DTA if a correction factor is introduced which takes into account the effect of heat exchange between the cells.

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Zusammenfassung Für den Fall, dass der Übertragungskoeffizient zwischen der Proben- und der Referenzzelle nicht Zero ist, wurde eine Grundformel der Differentialthermoanalyse entwickelt. Die entstandene Formel, die vielmehr allgemein ist, weicht von der klassischen dadurch ab, dass sie auch die Parameter der Referenzzelle, und den Wärmeübertragungskoeffizient zwischen den Zellen enthält. Sie deutet darauf hin, dass die Anwendung der klassischen Formel in dem Fall nicht einwandfrei ist, wenn ein Wärmeaustausch zwischen den Zellen zustande kommt. Zur Anwendung der verallgemeinerten Formel sind weitere Messungen des Temperaturaustausches vom Referenzmaterial erforderlich. Sind aber die Zeitkonstanten der zwei Zellen identisch, kann die Formel so geändert werden, dass sie die Gestalt der klassischen DTA-Formel annimt, wenn ein, mit der Wirkung des Wärmeaustausches zwischen den Zellen rechnender Korrektionsfaktor eingeführt wird.

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, . , , . . , , , , .

     

Kinetics of tritium isotope exchange between H2S and CH3OH vapor in glass vessels

Two different mechanisms of tritium exchange between and CH₃OH vapor in glass vessels have been found: (i) bimolecular exchange in the gas phase, (ii) pseudomonomolecular exchange between gaseous and CH₃OH adsorbed on the surface. The total and partial orders, rate constants and activation energies are given.

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, CH₃OH , : 1) 2) CH₃OH, . , .

     

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO₄·1/2H₂O(VO)₂P₂O₇+2 H₂O for VOHPO₄·1/2H₂O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different PV atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different PV ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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Zusammenfassung Der Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO₄.1/2H₂O(VO)₂P₂O₇+2H₂O für auf verschiedene Weise dargestelltes VOHPO₄.1/2H₂O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.

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- . , VOHPO₄ · 1/2H₂O, VOHPO₄ · 1/2H₂O(VO)₂P₂O₇ + 2H₂O, - PV 0,91,3. - 1-.

     

Studies on transition-metal picoline complexes

A large number of transition-metal picoline halides were prepared, and their thermal decompositions were investigated by TG, DTG, DTA and thermomicroscopy. The compounds were classified on the basis of their thermal properties and two possible mechanisms of thermal decomposition were established.

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Zusammenfassung Zahlreiche übergangsmetall-Picolin-Halide wurden dargestellt und deren thermische Zersetzung mittels TG, DTG, DTA und Thermomikroskopie untersucht. Die Verbindungen wurden nach ihren thermischen Eigenschaften klassifiziert, und zwei mögliche Mechanismen der thermischen Zersetzung sind angegeben.

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, , , . .

     

Kinetics and mechanism of homogeneous catalytic oxidation of pyrocatechol in aqueous solutions containing Cu(II) and histidine

Kinetic studies of pyrocatechol oxidation by oxygen in weakly acidic aqueous solutions containing pyrocatechol, Cu(II) ions and histidine, indicate that the reaction involves mixed copper-pyrocatechol histidine complexes. The proposed mechanism of the process agrees with the kinetic relationships obtained.

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, , Cu(II) . , . , -.

     

Effect of preparation conditions on the properties of carbon-supported nickel catalysts

Carbon-supported Ni catalysts were prepared from nickel nitrate or chloride. Characterization was carried out by H₂ and CO chemisorption, XRD and TEM. Catalysts were further tested in the hydrogenolysis of n-butane.

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, , . H₂ CO, ., -.

     

Steady-state rate of complex reactions under limitation and near equilibrium (one-route mechanism of catalytic reactions)

Explicit equations for the steady-state rate in case when one of the steps is rate-limiting, and in the neighborhood of equilibrium have been derived for a one-route mechanism of a catalytic reaction. Equations have been obtained for a dependence of the observed reaction order and activation energy on the thermodynamic characteristics of the overall reaction.

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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.

     

DSC and vapour pressure investigation of some β-diketonates

DSC and vapour pressure measurements are presented on some Be, Al and Cr complexes with 2,4-pentanedione tetramethyl-3,5-heptanedione, 1,1,1-trifluoro-2,4-pentanedione and hexafluoro-2,4-pentanedione. Thermodynamic functions are given for the sublimation, vaporization and melting processes of the substances.

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Zusammenfassung Die Ergebnisse von DSC- und Dampfdruckmessungen einiger Komplexe von Beryllium, Aluminium und Chrom mit 2,4-Pentandion (HAA), Tetramethyl-3,5-heptandion (HTHD), 1,1,1-Trifluoro-2,4-pentandion (HATA) und Hexafluoro-2,4-pentandion (HHFA) werden beschrieben. Die berechneten thermodynamischen Funktionen für Sublimation, Verdampfung und Schmelzen der Komplexverbindungen sind tabelliert.

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, 2,4- , 1,1,1-- -2,4- -3,5- . , .

     

Kinetics of ion-exchange of transition metals on tin(IV) arseno-silicate cation exchanger

Exchange kinetics of some transition metal ions on tin(IV) arsenosilicate has been studied at various temperatures under particle diffusion controlled conditions. Various useful kinetic parameters such as self-diffusion coefficient (D_o), energy of activation (E_a) and entropy of activation (S^*) have been calculated and compared with other similar materials.

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(IV) . , (D_O), (E_a) (S^*), .

     

Poly(vinylpyridine) complexes of palladium as hydrogenation catalysts. Effect of polymeric ligand structure

The title complexes exhibit high catalytic activity, selectivity and stability in hydrogenation of allyl alcohol. The structure of a polymeric ligand (i.e. the position of the nitrogen atom in the pyridine ring) affects catalyst activity. According to the hydrogenation rates of allyl alcohol, the complexes studied are arranged in the sequence: P4VP-Pd>P2VP-Pd>P2M5VP-Pd.

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, - - . ( ) . : 4->2-Pd>25-.

     

Hydrogenation of CO2

The hydrogenation of CO₂ has been studied on three different series of catalysts: Fe/MgO, Ni/Ti, Cr/Zn doped with potassium. Reaction was carried out in a conventional flow microreactor system at 15 bar at 250–350°C. Three independent competing reactions: Reverse gas-water shift (RGWS), Fischer-Tropsch (FT) and methanol synthesis were observed.

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CO₂ : Fe/MgO, Ni/Ti, Cr/Zn . 15 250–350°C. : RGWS, F.T. .

     

Tiegelkonstruktionen für die Differenzthermoanalytische Untersuchung ternärer intermetallischer Verbindungen mit leichtflüchtigen Komponenten

Zusammenfassung Zur differenzthermoanalytischen Untersuchung von ternären intermetallischen Verbindungen wie Li₂ZnGe, Li₂ZnSi, LiMgAs, TlZnSb und TlCdSb wurden gasdicht verschraubbare Tiegel aus Tantal, Molybdän und Titan konstruiert, die den besonderen Eigenschaften dieser Verbindungen, insbesondere der leichten Flüchtigkeit von Lithium, Magnesium, Zink und Cadmium sowie der großen Korrosivität der Schmelzen Rechnung tragen mußten. Außer diesen »Metallautoklaven« wurden geschlossene, in einer Metallhülse gelagerte Quarzampullen eingesetzt. Die kalorimetrischen Eigenschaften dieser Tiegel wurden in verschiedenen Temperaturbereichen untersucht und miteinander verglichen.

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For DTA measurements on ternary intermetallic compounds such as Li₂ZnGe, Li₂ZnSi, LiMgAs, TlZnSb and TlCdSb, gastight screwable crucibles were constructed from tantalum, molybdenum and titanium. They had to be suited to the special properties of these compounds, particularly the high volatility of lithium, magnesium, zinc and cadmium and the corroding characteristic of their melts. Besides these metallic autoclaves, closed quartz glass ampules were used, which were supported in a metallic hull. The calorimetric properties of these crucibles were investigated in different regions of temperature and compared with one another.

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Li₂ZnGe, Li₂ZnSi, LiMgAs, TlZnSb TlCdSb , , . , , , , , . « », , . .

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Teilweise vorgetragen auf dem TA-Symposium der GEFTA, Aachen, Deutschland, Oktober 1981.

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Der Deutschen Forschungsgemeinschaft und dem Verband der Chemischen Industrie danken wir für die Förderung unserer Arbeiten.     

Effect of acid treatment on the properties of an activated carbon

The enhancement of the activity of a carbon treated with HF is due to the drastic diminution of its inorganic impurities, which produces an increase of the surface area of the carbon, a stronger Pt-C interaction and a higher Pt dispersity.

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, HF, , , Pt-C Pt.

     

Catalytic reaction of methane with carbon dioxide

High activities and selectivities of Ni on SiO₂ catalysts producing CO in the reaction of CH₄ with CO₂, have been obtained at relatively low temperatures. These aspects are considerably different from the activities or selectivities of other catalysts, and have been explained by assuming that the Ni on SiO₂ catalyst markedly suppresses carbon deposition.

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CO Ni SiO₂ CH₄ CO₂. , Ni SiO₂.

     

Temperature-programmed reduction and oxidation of bimetallic Pd?Ni/Al2O3 catalysts

Temperature-programmed reduction and oxidation of bimetallic catalysts Pd–Ni/Al₂O₃ seem to indicate phase segregation of palladium and nickel oxides and alloying of palladium and nickel in the process of reduction of oxidized catalysts.

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- Pd–Ni/Al₂O₃ , .

     

Influence of Zr, Ge, B and Co additives on the activity of Pt/Al2O3 catalysts for dehydrocyclization

IR studies of the effect of Zr, Ge, B and Co additives on the activity of the Pt/Al₂O₃ catalyst for dehydrocyclization have revealed their promoting action on both oxidation and reduction of platinum. Benzene yield depends on the degree of platinum reduction promoted by boron, whereas with increasing platinum oxidation, the cracking product yield decreases.

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, , . , . . . .

     

Mechanism of thermal decomposition of lead thiosulphate

The thermal decomposition of lead thiosulfate (LTS) was studied by various methods: X-ray phase analysis, IR and ESR spectroscopy, etc. A mechanism of thermal decomposition is suggested, including rupture of the S-S bond and the formation of radicals. According to the mechanism, the reaction rate can be enhanced in the presence of the PbS phase. The formation of PbS is the cause of the topochemical character of the reaction. The composition of the thermolysis products of LTS containing a radioactive isotope of sulfur is predicted.

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Zusammenfassung Die thermische Zersetzung von Bleithiosulfat PbS₂O₃ wurde durch Röntgenphasenanalyse, IR- und ESR-Spektroskopie und Thermogravimetrie untersucht. Ein Mechanismus der thermischen Zersetzung wird angegeben, der über die Trennung von S-S-Bindungen und die Bildung von Radikalen verläuft. Nach diesem Mechanismus wird die Reaktionsgeschwindigkeit in Gegenwart der PbS-Phase beschleunigt, was den topochemischen Charakter der Reaktion bedingt.Für die Verteilung radioaktiven Schwefels auf die Zersetzungsprodukte unterschiedlich markierten (PbS^*SO₃ bzw. PbSS^*O₃) Bleithiosulfats wird eine Vorhersage gemacht.

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, - . , S—S . , . . , .