Influence of valence and concentration of electrolytes on the ζ-potential of polyacrylic lattices

The -potential of copolymer particles of acrylic amide, acrylic acid, acrylic butyl ester, and styrene were measured in different electrolyte solutions. In an isotonic solution of sodium chloride, they vary with the content of acrylic acid between –36 mV and –49 mV. In the presence of 21-electrolytes, the -potential could be correlated with the logarithm of the electrolyte concentration. The 21-electrolytes predominantly determine the -potential of the particles not only in the solutions of these electrolytes, but also in mixed electrolyte solutions. In the presence of human serum, the electrophoretic mobility increases with increasing acrylic acid content of the polymer.     

The Effect of Water Addition on the Electrosurface Properties of Quartz in Solutions of Alkali Metal Bromides in Ethanol

Electrosurface properties (the -potential and surface conductivity) of quartz particles in water–ethanol solutions of CsBr, NaBr, and LiBr with concentrations C = 10^–5–10^–2 M are studied. The (log C) dependences plotted from the results of electrophoretic measurements with allowance made for the particle surface conductivity demonstrate that, when water content in the aforementioned solutions increases from 4 to 40 vol %, the -potential of quartz becomes more negative and the isoelectric point shifts toward higher electrolyte concentrations, which increase in the following series: CsBr < NaBr < LiBr. This shift of the isoelectric point is explained by a decrease in the specific interaction of the alkali metal cations with the quartz surface because of a rise in the degree of their hydration (supersolvation).     

Conductivity and Electrokinetic Potential of Microcrystalline Cellulose Particles in Aqueous HCl and NaOH Solutions

The conductivity of microcrystalline cellulose (MCC) dispersions in aqueous 10^–5–10^–2 M HCl and NaOH solutions was measured as a function of the particle volume fraction by the conductometry. The dependence of the relative conductivity of MCC particles on pH of equilibrium solutions was determined using the Wagner equation. The electrophoretic mobility of MCC particles in the aforementioned solutions was measured by the microelectrophoresis, and corresponding dependences of the particle potentials on pH of aqueous HCl and NaOH solutions (pH 2–11) were calculated using the Smoluchowski and Henry equations of the electrophoresis theory. It was shown that, in the case of MCC, the Henry equation, which allows for the significant conductivity of the dispersed particles, as compared with the dispersion medium, makes it possible to calculate more accurate potential values and, consequently, to derive the (pH) dependence, which is satisfactorily consistent with the effect of the surface charge and solution ionic strength on the potential in a wide pH range.     

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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Demulsification rate and zeta potential of O/W emulsions

Dilute oil-in-water (O/W) emulsions have been used to study the correlation between demulsification rate and-potential as a function of surfactant concentration. The demulsification rate of octane and isooctane emulsions stabilized by sodium dodecyl sulfate (SDS) or cetyldimethylbenzylammonium chloride (CDBACl) are evaluated by counting the particle number. Flocculation is considered the main factor of instability. The-potential of the droplets is also calculated from microelectrophoretic measurements by a new demountable microelectrophoretic apparatus. The stability of the emulsions is attributed mainly to electrostatic repulsion. Small differences between straight and branched-chain hydrocarbons are observed.     

Hexadiene formation during decomposition of 2-propanol over Ca?P?O catalysts

Hexadiene formation from 2-propanol was investigated in view of acid-base properties of Ca–P–O catalysts with the Ca/P atomic ratio varying from 1.5 to 5.0. The catalytic activity in hexadiene formation increased up to a maximum at Ca/P=2.0, having almost the same amount of weak acidic sites as weak basic sites, and decreased with futher increase in Ca/P ratio.

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2- - Ca–P–O Ca/P, 1,5 5,0. , Ca/P=2, , Ca/P.

     

Investigation of protein foams obtained by bubbling

Summary The foaminesses of bovine serum albumin solutions, (BSA) with and without buffer, salt and alcohol additives were measured by bubbling and their surface tensions were obtained as function of the timet. The timet _DG , which is necessary to attain the equilibrium surface tension is long (15 h). The area requirement of a single surface adsorbed moleculeA _j0 was obtained fromd/dc, wherec the surfactant concentration, by the Gibbs relation. By assuming the existence of a hydration complex, which consists of the surfactant andX water molecules, the,coordination numbers were estimated toX=12±1 fromA _j0 and the surface requirement of the hydrophilic group of the surfactant. The dependences of CMC andX on the additives are discussed. A good relation prevails between andt _DG . By applying the phase change model of Avrami for the adsorption and surface denaturation of theBS A, simple relation was found between the dimensionless surface tensionV = (₀ - _s) (_st-_s) and the timet:log (2.3 logV) =n logt + logb The good relations between andn as well as between andnb indicate the applicability of this model.

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Zusammenfassung Das Schaumbildungsvermögen von Rinderserumalbumin-Lösungen (BSA), mit und ohne Zusätze wurde gemessen und ihre Oberflächenspannung als Funktion der Meßzeit ermittelt. Die Einstellzeitt _DG der Gleichgewichtsoberflächenspannung _eq ist lang. Zwischen undt _DG läßt sich eine einfache Beziehung aufstellen. Aus der Änderung von _eq mit der bedarf des adsorbierten Molekel ermitteln. Durch die Anwendung des Modells von Steinbach kann gezeigt werden, daß sich der Flächenbedarf durch die Bildung eines Assoziates erklären läßt, bei dem das Wasser komplexartig um das Protein-Molekül lagert. Für die Koordinationszahl der WassermoleküleX ergab sichX=12±1.Durch das Kristallwachstumsmodell von Avrami, das von überreiter auf Polymeradsorption angewendet wurde, läßt sich die Zeitabhängigkeit der Oberflächenspannung beschreiben. Das Schaumbildungsvermögen kann man als einfache Funktion der Konstanten dieser Avrami-Gleichung darstellen.

     

Electrokinetic study on concentrated suspensions using colloid vibration potential measurements

-potentials of a silica suspension and three types of polystyrene latex suspensions with different surface charge groups were measured, as a function of the particle concentration () in the suspension over a wide range, using the colloid vibration potential (CVP) technique. The concentration dependence of the-potential in silica suspension is explained well by Levine et al.s [1] cell model theory, verifying the applicability of the cell model to the CVP in silica suspension. However, the-potential of latex suspensions ordinarily decreases as the particle concentration increases, even after being corrected by the term of (1-). This tendency is especially noticeable in the systems that have particles with high surface charge densities. Furthermore, the conductivity measurements of these suspensions reveal that the conductivity of these systems, especially in their highly charged state, increases as the particle concentration is increased; opposite in tendency to silica suspensions. These new findings can be explained as follows: on the highly charged surface of a latex particle, a polyelectrolyte-like (hairy) layer is present, which overlaps at some point. This permits interparticle surface conduction and results in the abnormal behavior of CVP in these systems.     

Thermochemical studies on the systems ACl/CeCl3 (A=Na-Cs)

The pseudobinary systems ACl/CeCl₃ (A=Na-Cs) were reinvestigated by means of DTA. The following compounds were found and identified through their X-ray patterns (primarily detected compounds in italics):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. The compounds A₂CeCl₅ crystallize with the K₂PrCl₅ structure. The high-temperature modifications of the compounds A₃CeCl₆ have the cubic elpasolite structure. The hexagonal unit cell of KCe_1.67Cl₆ is related to the CeCl₃ structure: 0.33 Ce³⁺ are substituted by one K^s+. The structure of CsCe₂Cl₇ can be described with a hexagonal subcellZ=4,a=9.72 andc=14.94 Å; however, small superstructure reflexions reduce the symmetry.The thermodynamic functions for the reactionsnACl+CeCl₃=A _n CeCl _n+3(A=K, Rb) were determined by means of e.m.f. measurements.Measurements of the e.m.f.E vs. T yielded the Gibbs enthalpiesG ^r . The temperature-dependence was found to be linear.The most important result is the formation of the elpasolites (A₃CeCl₆) and ACe₂Cl₇.

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Zusammenfassung Die pseudobinären Systeme ACl/CeCl₃ (A=Na-Cs) wurden mittels Differenzthermoanalyse (DTA) neu untersucht. Folgende Verbindungen wurden gefunden und durch ihre Röntgenbeugungsmuster charakterisiert (erstmalig nachgewiesene Verbindungen sind kursiv):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. Die Verbindungen A₂CeCl₅ kristallisieren im K₂PrCl₅-Typ. Die Hochtemperaturmodifikationen der Verbindungen A₃CeCl₆ liegen in der kubischen Elpasolith-Struktur vor. Die hexagonale Elementarzelle des KCe_1.67Cl₆ ist mit der CeCl₃-Struktur verwandt: 0,33 Ce³⁺ sind durch ein K⁺ ersetzt. Die Struktur des CsCe₂Cl₇ kann mit einer hexagonalen Pseudozelle beschrieben werden:a=9,72;c=14,94Å;Z=4; schwache Überstrukturreflexe reduzieren jedoch die Symmetrie. Die thermodynamischen Funktionen für die Reaktionen:n ACl + CeCl₃=A _n CeCl _n+3 (A=K, Rb) wurden durch EMK-Messungen bestimmt. Messungen der Abhängigkeit von e. m. f.E gegenT ergaben die Gibbs-EnthalpienG ^r . Es wurde eine lineare Temperaturabhängigkeit gefunden. Als wichtigstes Resultat ist die Bildung von Elpasoliten (A₃CeCl₆) und von Verbindungen (ACe₂Cl₇) anzusehen.

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ACl/CeCl₃, A . - ( ):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅ CsCe ₂Cl₇. A₂CeCl₅ K₂PrCl₅. A₃CeCl₆ . KCe_1.67Cl₆ CeCl₃, 0,33 Ce³⁺ . CsCe₂Cl₇ a=9,72 Å,c=14,94 Å Z=4. , . n ACl + CeCl₃=A _n CeCl _n+3(A=K, Rb) . . . . . .E , G ^r . ACe₂Cl₇.

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Presented as a poster at the 8th ICTA, Bratislava, 1985.

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Conductance of Cs+ ion in water: Molecular dynamics simulation

The continuum theory of Hubbard-Onsager predicts for the friction coefficients the following behavior: >0 and /P<0. In contrast to Hubbard-Onsager theory, experimental observations on Cs⁺ ion in water show that at low temperatures <0 and /P>0. To explain the observed behavior of Nakahara et al. proposed the passage through cavities (PTC) mechanism. We performed a molecular dynamics computer simulation to determine if the PTC mechanism is responsible for the observed behavior of . No passage through cavities was observed. Molecular dynamics computer simulations were performed on Cs⁺ ion in water at temperature of 268 K and densities of 1.00 and 1.083 g-cm^–3. Our results indicate that the observed behavior of for Cs⁺ ion is related to the difference in the reorientation times of water molecules in the solvation shell and in the bulk.     

Thermal decomposition of [Co(NH3)6]Cl3

The thermal decomposition reactions of [Co(NH₃)₆]Cl₃ were determined in dynamic argon and air atmospheres. The investigations were carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions, thermogravimetry under quasi-isothermal conditions, reflectance spectroscopy, absorption spectroscopy, X-ray diffraction and chemical analysis. The data show that the thermal decomposition of [Co(NH₃)₆]Cl₃ occurs in three and four stages in argon and air atmospheres, respectively. The determined sequences are in agreement with that proposed by Simons and Wendlandt [2, 5].The changes in the morphology of the studied complex crystalline powder in the course of thermal decomposition in air were followed by scanning electron microscopy.

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Zusammenfassung In bewegter Argon- und Luftatmosphäre wurden die Zersetzungsreaktionen für [Co(NH₃)₆]Cl₃ bestimmt. Zu den Untersuchungen wurden folgende Methoden zu Hilfe gezogen: simultane TG-DTG-DTA-Messungen unter nichtisothermen Bedingungen, Thermogravimetrie unter quasi-isothermen Bedingungen, Remissionsspektroskopie, Absorptionsspektroskopie, Röntgendiffraktion und chemische Analyse. Die Ergebnisse zeigen, daß sich [Co(NH₃)₆]Cl₃ in Argon in drei und in Luft in vier Schritten thermisch zersetzt. Die festgestellten Sequenzen stehen in Übereinstimmung mit den von Simon und Wendlandt [2, 5] vorgeschlagenen. Veränderungen in der Morphologie des untersuchten Komplexkristallpulvers wurden über die thermische Zersetzung in Luft mittels Scanning-Elektronen-Mikroskopie beobachtet.

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[Co(NH₃)₆]Cl₃. , , - , , , . , , , , , , .

     

The complete multi-ζ electric dipole moment matrix of π-(C6H6) Cr(CO)3 and tests of semi-empirical MO models

First, we evaluated the complete electric dipole moment matrixeZ using a multi- AO basis on Cr, C, and O centers fortheimportant, parent organometallic molecule -C₆H₆Cr(CO)₃. Second, we generated ground state LCAO-MO eigenvectors employing five commonly used semi-empirical procedures for molecules of this size which contain transition metals. Transformation of operator matrixeZ into the MO space of each of the five methods then leads us to conclude that the empirical input of Basch, Viste and Gray is most suitable. Finally, we compare the merits of several single- basis orbitals with the multi- metal orbitals.[/p]     

Basicity and catalytic properties of multicomponent catalysts for oxidative ammonolysis of propane

Studies of the effect of phosphorus and tungsten on the basicity and catalytic properties of catalysts for oxidative ammonolysis of propane indicate that, besides the common decrease in the number of active centers on the catalyst surface, the sharply decrease the concentration of strong basis centers.

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. , , , .

     

Thermal decomposition of 5-Nitro-2-Furaldehyde Semicarbazone

Nitrofurazone, 5-nitro-2-furaldehydesemicarbazone, pharmaceutical compound, has been synthesized and its thermal behaviour studied by DTA, DSC and TG. The resulting thermoanalytical curves, showing that the maximum change in mass occurred at 516.5 K, with a 67% weight loss, are in good correlation with the enthalpy of the decomposition reaction, 326.93 kJ mol^–1. On the basis of the results, it is possible to establish the mechanism of the thermal decomposition and to acquire information on the stability of the analyzed organic compound, 5-nitro-2-furaldehydesemicarbazone.

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Zusammenfassung Das Arzneimittel Nitrofurazon (5-Nitro-2-furaldehyd-Semicarbazon) wurde synthetisiert und dessen thermisches Verhalten mittels DTA, DSC und TG untersucht. Die erhaltenen thermoanalytischen Kurven, die einen Gewichtsverlust von 67 Gew.-% mit maximaler Geschwindigkeit der Gewichtsabnahme bei 516,5 K zeigen, sind in guter Übereinstimmung mit der Enthalpie der Zersetzungsreaktion von 326,93 kJ·mol^–1. Aus den Versuchsergebnissen können der Mechanismus der thermischen Zersetzung abgeleitet und Informationen über die Stabilität von 5-Nitro-2-furaldehyd-Semicarbazon erhalten werden.

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, — 5-. , (67%) 516,5 , , 326,93 ·^–1. .

     

Influence of chemical non-steady-state on SO2 conversion in fluidized catalyst bed

The effect of the influence of catalyst non-steady-state on SO₂ conversion ion a fluidized catalyst bed has been studied depending on the ratio of relaxation time for the catalytic reaction step to the characteristic time of particles diffusion.

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On the relationship between thermal stability and catalytic properties of supported molyboo-vanado-phosphoric heteropoly acids

Catalytic properties of four heteropoly acids of the molybdophosphoric type were studied in the selective oxidation of isobutene to methacrolein. Results show that the highest selectivities for methacrolein were achieved with samples in which the original structure of the heteropoly anion is least affected by thermal destruction.

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. , .

     

Reaction mechanism and principles of choosing catalysts for selective oxidation at C?H bonds

Reaction mechanism for selective oxidation of organic compounds at C–H bonds is discussed. The criteria of selecting catalysts for these reactions have been formulated; 1) fast heterolytic activation of C–H bonds; 2) relatively slow primary activation of oxygen; 3) fast diffusion of oxygen vacancies; 4) fast electron transfer from the adsorbed substrate to catalyst.

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C–H . : 1) C–H ; 2) ; 3) ; 4) .

     

Stability and intermediate phase formation

A close relation between thermal data and the thermodynamic stability of intermetallic compounds is pointed out. Several series of intermediate phases formed by metals of theA and transition groups with elements of groups IB to IVB have been considered. The dependence of the thermal and thermodynamic stabilities on the atomic size, the electronic configuration, the electronegativity and the melting temperature of the component is discussed.

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Zusammenfassung Es wird auf eine enge Beziehung zwischen thermischen Daten und der thermischen Stabilität von intermetallischen Verbindungen hingewiesen. Verschiedene Serien von intermediären Phasen der Metalle der A- oder Übergangsgruppen mit den Elementen der Gruppen IB bis IVB werden in Betracht genommen. Die Abhängigkeit der thermischen und thermodynamischen Stabilität von der Atomgröße, der Elektronenkonfiguration, der Elektronegativität und dem Schmelzpunkt der Metallkomponenten wird diskutiert.

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. , IB–IVB. , , .

     

A gradientless flow microreactor

A simple flow microreactor can perform as a gradientless microreactor under suitable conditions so that, thanks to molecular diffusion, the reactant concentration is leveled out considerably. This was demonstrated on the basis of a mathematical analysis of the reactant concentration distribution in a flow reactor and the observation was confirmed experimentally. A simple flow microreactor was designed and its gradientless property was verified using carbon dioxide hydrogenation as a test reaction.

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. . , . , .

     

Thermodynamics and thermochemistry of kinetic (real) phase diagrams involving solids

A theoretical analysis of the formation of materials with metastable microstructures under non-ideal and highly non-equilibrium conditions is presented.

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Zusammenfassung Es wird eine theoretische Untersuchung der Bildung von Stoffen mit metastabilen MikroStrukturen unter nichtidealen Bedingungen weitab vom Gleichgewicht dargelegt.

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