bluuebunny/crossref_metadata_2025 huggingface dataset:
A Proton Spin‐Lattice Relaxation Study of the Water‐Dioxane System
Authors: Czubryt J. J. , Chatterjee N. , Bock E. , Tomchuk E. , Hutton H. M. , Kydon D. W.
Published: March 2014

A proton spin‐lattice relaxation study of the water‐dioxane system has been carried out. It was found that contrary to earlier literature reports the intramolecular proton spin‐lattice relaxation rate of the dioxane molecule in dilute aqueous solutions is strongly concentration dependent and in general shows a similar behaviour as the solution viscosity, density, free energy of mixing, and other physical properties. The motions of the dioxane and water molecules in solution appear to become correlated at ∼0.143 mol fraction dioxane; i.e. at a mol ratio of dioxane/water = 1/6. It is suggested that a weak complex, C4H8O2·6H2O, is formed in solution.
Streulichtuntersuchungen an exotherm‐pseudoidealen Lösungen in Abhängigkeit von Druck und Temperatur
Authors: Wolf B. A.
Published: March 2014

Fraktionierte Proben von Polyisobutylen (PIB) (Mw = 73 500 und 690 000) wurden in n‐Pentan (70–85°C) und in i‐Octan (15–45°C) bei Drucken bis zu 1000 atm untersucht.

An beiden Systemen beobachtet man eine ausgeprägte Zunahme des zweiten osmotischen Virialkoeffizienten A2 mit steigendem Druck und eine wesentlich schwächere Abnahme mit steigender Temperatur. Eine genauere Analyse ergibt folgendes Bild:

Der bei verschiedenen konstanten Drucken aus der Temperaturabhängigkeit von A2 ermittelte A2,H‐Wert nimmt mit steigender Temperatur zu und mit steigendem Druck ab; dieser Befund steht im Einklang mit den Ergebnissen der früheren Untersuchungen [1 – 3]. Im vorliegenden Fall bedeutet er, daß die Verdünnungswärme bei Temperaturerhöhung exothermer und bei Druckerhöhung weniger exotherm wird.

Aus der bei verschiedenen konstanten Temperaturen gemessenen Druckabhängigkeit erhält man A2,v den durch die Nichtadditivität der Komponentenvolumina hervorgerufenen Anteil an A2.

Berechnet man daraus das partielle molare Exzeßvolumen des Lösungsmittels, so zeigt sich, daß diese Größe für die hier untersuchten Fälle negativ ist, mit steigendem Druck zu weniger negativen und mit steigender Temperatur zu noch negativeren Werten hin verschoben wird. Die theoretische Erklärung des thermodynamischen Verhaltens von exotherm‐pseudoidealen Lösungen (A2 = 0; δh1, δs1E < 0), sowie des Auftretens von δ s1E < 0 überhaupt, liegt außerhalb der Möglichkeiten von Theorien, denen die Annahme eines starren Gitters zugrundeliegt. Für das theoretisch besonders einfach zu behandelnde System PIB/i‐Octan (Polymeres/“Dimeres“) wurde daher die Prigoginesche Theorie überprüft und qualitative übereinstimmung gefunden.

Eine aus dieser Theorie folgende Ungleichung zur Abschätzung des oberen θ‐Punktes aus Messungen bei niedrigeren Temperaturen liefert gute Resultate.

Die Knäueldimensionen von PIB in i‐Octan nehmen mit steigendem Druck zu. Berechnet man daraus und aus den gemessenen A2‐Werten mit Hilfe theoretischer Beziehungen die ungestörten Dimensionen, so läßt sich kein signifikanter Druckeinfluß erkennen.
Doppelschicht und Gleichstrompolarisation von AgBr
Authors: Weiss K.
Published: March 2014

Messungen des Polarisationsstroms, des Ladungsumsatzes bei der Gleichstrompolarisation und örtlicher Differenzen des elektrochemischen Potentials der Elektronen in der Zelle Ag/AgBr/Pt wurden bei 377 °C und 391 °C ausgeführt. Die Meßergebnisse wurden für den Fall analysiert, da β wohl an den Phasengrenzen Ag/AgBr und AgBr/Pt, nicht aber im Probeninneren Raumladungen auftreten. Die Differenz der chemischen Potentiale der Silberionen in Ag und AgBr wird <0,6eV geschätzt. Grimley und Mott berechnen hierfür mit einem Kreisprozeß 1,4eV.
Photoelektrochemische Prozesse und Photokatalyse an Zinkoxid‐Suspensionen und Zinkoxid‐Deckschichten
Authors: Gerischer H. , Cammann K.
Published: March 2014

Es wurden Photospannungen und Photoströme an ZnO‐Suspensionen im Kontakt mit Edelmetallelektroden sowie an ZnO‐Deckschichten auf metallischen Unterlagen untersucht. Die Deckschichten wurden durch Sinterung von ZnO‐Pulver oder durch anodische Oxidation von Zinkmetall hergestellt. Bei Bestrahlung mit UV‐Licht treten Photoströme und Photospannungen auf, die sich in Analogie zu Prozessen an ZnO‐Einkristallen deuten lassen. Die spektrale Abhängigkeit der Photoeffekte zeigt, daβ sich solche Schichten ähnlich wie amorphe Halbleiter verhalten. Entscheidend für das Reaktionsvermögen ist, wie bei den Einkristallen, die Erzeugung von Defektelektronen.
Mößbauer‐Effekt‐Untersuchungen bei Änderung des Grundzustandes: 5 T2‐1 A1‐„Spin‐Gleichgewichte”︁ in Tris(2‐methyl‐1,10‐phenanthrolin)Eisen(II)‐Komplexen
Authors: König E. , Ritter G. , Braunecker B. , Madeja K. , Goodwin H. A. , Smith F. E.
Published: March 2014

Der 5 7Fe‐Mößbauer‐Effekt wurde in [Fe(mephen)3](BPh4)2(I) und [Fe(mephen)3]I2(II) zwischen 298 und 4,2°K untersucht (mephen = 2‐Methyl‐1,10‐phenanthrolin). Verbindung I zeigt bei 298°K ein für einen 5 T2‐Grundzustand charakteristisches Dublett mit Δ EQ(2 T2) = 0,96mm sec‐1 und δIS (5 T2) = +0,96mm sec‐1 . Ab 223°K beobachtet man das Auftreten eines zweiten, für einen 1 A1‐Grundzustand charakteristischen Dubletts, dessen Intensität mit fallender Temperatur zunimmt. Bei 4,2°K hat 1A1 eine Intensität von 75,2% und es ist Δ EQ(1 A1) = 0,61 mm sec‐1, δIS 1A1) = +0,42mm sec‐1 . Das Verhalten der Verbindung II ist ähnlich, 1 A1 hat bei 4,2°K eine Intensität entsprechend 37,3%. Aus der Temperaturabhängigkeit von ΔEQ(5 T2) läβt sich die axiale Ligandenfeldaufspaltung zu δ = ‐440cm‐1 für I sowie II abschätzen. Die Analyse magnetischer Daten zeigt, daβ der 5 T2−1A1‐Termabstand ϵ stark von der Temperatur abhängt, ϵ = 98 cm−1 bei 303°K und ϵ = 890 cm−1 bei 83°K für I mit ähnlichen Werten für II. In einem äußeren Magnetfeld von 40 kG ergibt sich Vzz > 0 für den 1A1‐Grundzustand von I und II. Für die Natur des beobachteten Überganges können drei Vorstellungen diskutiert werden: 1. reine Boltzmann‐Verteilung; 2. „Spin‐Gleichgewichte”︁ mit permanent paramagnetischem Anteil; 3. „Umklapp”︁‐Mechanismus. Ein direkter Einfluß des Anions auf den 5T2‐1A1‐Übergang ist nicht festzustellen.
Untersuchungen von Ionenreaktionen mittels Photoionisations‐Massenspektrometrie V. Reaktionen von N+2 und CO+
Authors: Warneck Peter
Published: March 2014

Die Reaktionen der Ionen von molekularem Stickstoff und Kohlenmonoxyd mit neun neutralen Reaktionspartnern (H2, CO2. CH4, N2O. SO2. O2, C2H2, COS und NO) wurden hinsichtlich ihrer Geschwindigkeitskonstanten und der Produktverteilungen untersucht und mit‐einander verglichen. Zum Vergleich wurden außerdem nach der Theorie von Gioumousis und Stevenson berechnete Geschwindigkeitskonstanten herangezogen; die Theorie sagt für beide Ionen mit demselben Neutralreaktanten gleiche Geschwindigkeitskonstanten voraus. sofern die Reaktionswahrscheinlichkeit eins ist. In der Tat ergaben die Experimente (mit wenigen Ausnahmen) gleiche Werte, selbst wenn die Reaktionswahrscheinlichkeit kleiner war als eins. Der vorherrschende Mechanismus ist Ladungsaustausch, aber bei den Reaktionen von CO+ werden vergleichsweise häufig auch Umlagerungen beobachtet. Die Ergebnisse legen nahe, daβ der Reaktionsmechanismus durch die Stärke der chemischen Wechselwirkung beim Nahkontakt der Reaktionspartner bedingt ist. Dieser Gesichtspunkt wird anhand eines Potentialmodells diskutiert, wobei die Reaktion von N2+ mit Sauerstoff zur Veranschaulichung herangezogen wird.
Eine Untersuchung der Elektroneneinfangreaktion durch einfache Cyanide im thermischen Energiebereich
Authors: Mothes K. G. , Schultes E. , Schindler R. N.
Published: March 2014

Die folgenden absoluten Geschwindigkeitskonstanten k[cm3 ‐ Molekül‐1 sec‐1] für den Einfang thermischer Elektronen in der Gasphase wurden mit Hilfe der ECR‐Technik erhalten:

magnified image

Aus der Änderung der relativen Signalgröße bei Erhöhung der Elektronenenergie im Resonator werden neue Informationen über den Verlauf des Wirkungsquerschnittes im Energiebereich 0,03 eV bis ca. 0,3 eV erhalten.
Kristallisationsvorgänge bei der elektrolytischen Kupferabscheidung auf polykristalline Kupferunterlagen. II. Einfluß eines primären Grenzflächeninhibitors auf die Kristallisation, Keimbildungsprozesse
Authors: Eichkorn G. , Fischer H. , Mache H.‐R.
Published: March 2014

Das in Teil I dieser Arbeit abgeleitete Verfahren zum Abtrennen der Kristallisations‐ von der Gesamtüberspannung wird auf die Kupferabscheidung mit primärem Grenzflächeninhibitor (β‐Naphthochinolin) angewendet. Für den untersuchten Gefügeübergang: feinkristalline, hochaktive Kupferunterlage/relativ gröber kristalliner Kupferniederschlag wurde eine Zunahme der Kristallisationsüberspannungsänderung mit der Stromdichte und der Inhibitorkonzentration gefunden.

Durch röntgenographische Linienbreitenmessung wurde die Teilchengröße der Niederschläge bestimmt. Durch Kombination der Teilchengrößemessungen mit den elektrochemischen Messungen konnte mit Hilfe einer modifizierten Volmer‐Gleichung nachgewiesen werden, daβ bei der Abscheidung des arteigenen, den Elektrolysebedingungen angepaßten Niederschlags die Bildung zweidimensionaler Keime die wesentliche Kristallisationshemmung darstellt. Außerdem wurden Werte für die kritische Bildungsenthalpie von (220)‐Netzebenenkeimen ermittelt.
Die Pt‐Netzelektrode als Bezugselektrode bei polarographischen Untersuchungen an Merocyaninen in aprotonischen Lösungsmitteln
Authors: Jacobs Erwin P. , Dörr Friedrich
Published: March 2014

Bei polarographischen Untersuchungen an Polymethinfarbstoffen wurde eine Pt‐Netzelektrode als Bezugselektrode erprobt. Die Messungen wurden in Propylencarbonat und Hexamethylphosphorsäuretriamid durchgeführt; als Vergleichselektrode diente eine gesättigte Kalomel‐elektrode. Unter Verwendung der Leitsalze Tetraäthylammoniumjodid und Tetrabutylammoniumjodid wurden die Halbstufenpotentiale der Merocyanine vom Typ (CH3)2N‐(CH = CH‐)nCHC(CN)2, n = 0,1,2,3,4 bestimmt.

Es zeigte sich, daβ die Pt‐Netzelektrode unter den angegebenen Bedingungen sehr gut reproduzierbare Ergebnisse liefert und somit als Bezugselektrode verwendet werden kann.
Feldionenmikroskopische Untersuchungen an Gold. Beobachtung und Deutung von Spotstrukturen
Authors: Schmidt W. , Krautz E.
Published: March 2014

Strukturierte Bildpunkte, die auch als direkte Molekülabbildungen gedeutet wurden, sind bereits 1950 mit dem Feldelektronenmikroskop (FEM) beobachtet worden. Ähnliche Spotstrukturen konnten auch bei Abbildungen im Feldionenmikroskop (FIM), u. a. bei Wolfram mit Methan als Abbildungsgas, nachgewiesen werden. Mit Argon als Abbildungsgas konnten nun höher symmetrische Spotkonfigurationen auf Goldspitzen gefunden werden, die ihre Form nur bei Veränderung der Spitzenspannung verschiedentlich ändern.

Die Elektronen‐Hohlrohrwellen‐Theorie, die von A. P. Komar und A. A. Komar zur Erklärung der „Molekülabbildungen”︁ im FEM verwendet wurde, kann auch zur Deutung der im FIM gefundenen Spots herangezogen werden. Damit werden die verschiedenen Spotstrukturen bestimmten Schwingungsmoden der Elektronen in whiskerartigen Erhöhungen auf der FIM bzw. FEM‐Spitze zugeordnet. Die berechneten Moden für elliptische Querschnitte stimmen mit den beobachteten Formen gut überein.
Analysis of the Thermodynamic Behavior of Hydrogen in Body‐Centered‐Cubic Metals with Application to Niobium‐Hydrogen
Authors: O'keeffe M. , Steward S. A.
Published: March 2014

A critical analysis of experimental data for the Nb‐H system shows that the partial molar entropy data are best interpreted by assuming a random solution of hydrogen in the metal on one site per metal atom even in concentrated solutions. A possible geometrical interpretation of this result is suggested.
A Mass‐Spectrometric Study of the Thermal Dissociation of Thorium Iodides
Authors: Knacke O. , Münstermann E. , Probst H.
Published: March 2014

Solid ThJ4 dissociates thermally below 500°C to form ThJ4‐gas, molecular iodine vapour and, successively, the solid sub‐iodides ThJ3, ThJ2, ThJ and, eventually, the metal. By sublimating and dissociating solid ThJ4 from a Knudsen cell, the partial pressures of ThJ4 and J2 are both determined simultaneously by means of a mass‐spectrometer and calibrated partly gravimetrically. The measurements reported here and complementary earlier DTA measurements allow to calculate the heats of formation and standard entropies of the various iodides as well as the phase diagrams of the system Th — J. The main results of the mass‐spectrometric effusion experiments are the stepwise dissociation of ThJ4, its unexpected high dissociation pressure as compared with published estimates and the probable existence of a stable lower iodide with composition near ThJ.
Polarized Emission Studies and Crystal Data of KLi[Pt(CN)4] · 2H2O
Authors: Holzapfel W. , Yersin H. , Gliemann G. , Otto H. H.
Published: March 2014

Polarized emission of KLi[Pt(CN)4] · 2H2O (KLiCP) single crystals was monitored in the temperature range from 295 to 5 K and compared with the polarized emission of several other tetracyanoplatinates(II) with columnar structures of in‐chain Pt‐Pt‐distances between R = 3.15 and R = 3.67 Å. A correlation between the energetic position of the emission maxima and the Pt‐Pt‐distance of adjacent molecules in the column is used to predict R for KLiCP by use of spectroscopic data. The in‐chain Pt‐Pt‐distance found by this method is (3.20 ± 0.01) Å. — X‐ray diffraction measurements yield, that KLi[Pt(CN)4] · 2H2O crystals are orthorhombic with lattice constants a = 10.296(2) Å, b = 14.390(3) Å, c = 6.399(2) Å. The probable space group is C92v — P21 cn. The observed density is D0 = 2.64(3) g/cm3 and the calculated one Dx = 2.671(2) g/cm3 for 4 formula units per unit cell. X‐ray powder data are given. The [Pt(CN)4]2−‐complexes lie in columns along [001]. The groups are separated by c/2 ≡ R = (3.200 ± 0.002) Å, which agrees with the spectroscopic prediction and confirms the former correlation.
The Role of Phase Boundaries in Phase Transformations in Metals
Authors: Hillert Mats
Published: March 2014

The diffusion of solute atoms inside and in front of migrating phase boundaries is considered for various types of phase transformations in alloys. A model is developed which evaluates the Gibbs energy loss due to this diffusion. This model can be used to describe cases where there is a deviation from local equilibrium at the migrating phase boundary. In particular, massive transformation, diffusionless solidification and discontinuous precipitation are considered.
The Influence of Grain Boundaries on the Thermal Stability of Lamellar Microstructures
Authors: Frebel Manfred , Duddek Gerd , Graf Wolfram , Faridani Mohammed Nuhi , Otte Bernhard
Published: March 2014

Lamellar alloys consist of lamellar grains which are separated from one another by grain boundaries. The normal components of the forces exerted on the grain boundaries by the lamellar interfaces depend on the angle between the lamellae and the grain boundaries. Generally the net force resulting from the forces of the lamellae of two neighbouring grains is different from zero thus giving rise to migration of the grain boundary. As the lamellae of the growing grain tend to grow normal to the moving boundary an enlargement of the interlamellar spacing is observed which leads to a discontinuous coarsening reaction. The morphology and the kinetics of this reaction are presented in three examples: a lamellar microstructure created by a discontinuous precipitation reaction (α‐Ni ‐ In solid solutions), a unidirectionally transformed eutectoid (β‐Cu‐In) and a unidirectionally solidified eutectic (Pb ‐ Sn).
The Role of Phase Boundaries in Heterogeneous Solid State Reactions (I) Classification and the Dynamic Equilibrium at Interfaces
Authors: Schmalzried Hermann
Published: March 2014

For a discussion of mobile phase boundaries between two phases a classification is given into coherent, semicoherent and incoherent boundaries. In case of coherent and semicoherent boundaries the interface mobility is defined and discussed for the example α/β‐Ag2S and NiO/NiAl2O4/Al2O3.
On the Kinetics of the Formation of Micelles in Aqueous Solutions III
Authors: Chan S.‐K. , Herrmann U. , Ostner W. , Kahlweit M.
Published: March 2014

As a supplement to our previously published analyses of the amplitudes and the time constants of the relaxation processes in aqueous solutions of ionic surfactants, this paper presents the results of experiments with some cationic and anionic surfactants together with a more detailed discussion of the concentration dependence of the time constant of the slow relaxation process.
Influence of Excess Energy on the Low Temperature Fluorescence from Inhomogenously Broadened Lines in Anthracene
Authors: Friedrich J. , Flatscher G. , Dörr F.
Published: March 2014

The shape of the low temperature fluorescence of anthracene dissolved in a 2 methyl‐tetrahydrofuran glass is investigated as a function of increasing excess energy. The excitation energy was scanned up to 2000 cm−1 above the origin. The change in the bandshape is attributed to three different mechanisms: an increasing coupling between the impurity molecules and the lattice with increasing site energy, a population of a few discrete sites via vibrational transitions, the inhomogenous widths of which are strongly overlapping, and a phonon assisted population of lower sites which is very efficient at certain positions of excitation.
A Combined Flash Photolysis/Shock‐Tube Study of the Absolute Rate Constants for Reactions of the Hydroxyl Radical with CH4 and CF3H around 1300 K
Authors: Ernst J. , Wagner H. Gg. , Zellner R.
Published: March 2014

A combined flash photolysis/shock‐tube technique for the direct investigation of the rates of bimolecular reactions of the OH radical at temperatures between 1000‐1500 K is described. In this technique shock heated mixtures of approximately 0.5% of H2O in Ar and containing small amounts of a selected reactant, are subjected to flash photolysis as an instantaneous source of OH. The shock wave only serves to heat the gas mixture; thermal decomposition does not occur. Formation and subsequent decay of OH are monitored by time resolved UV resonance absorption. – First results with this technique have been obtained for the reactions (1) OH + CH4 r̊ CH3 + H2O and (2) OH + CF3H r̊ CF3 + H2O. Rate constants were found to be k1 (1300 K) = (2.5 ± 0.8) 1012 and k2 (1350 K) = (4.0 ± 1.0) 1011 cm3/mol · s. The result for reaction (1) is shown to confirm previously suggested non‐Arrhenius behaviour for this reaction, and in combination with low temperature data yields k1(T) = 106.19 (T/K)2.13 exp(‐1234 K/T) cm3/mol · s. The dependence of k1, on temperature is described in terms of transition state theory.
Instability of CdSe and CdS Photoanodes in Sulfide‐Polysulfide Electrolyte
Authors: Gerischer H. , Gobrecht J.
Published: March 2014

A transformation of the surface of CdSe and CdS single crystal photoanodes under illumination in sulfide/polysulfide redox electrolytes to polycrystalline or amorphous CdS has been found. A reaction mechanism is proposed and its thermodynamics are discussed. The discovered transformation could cause problems for the application of these systems for electrochemical solar cells.
Zur Ion‐Lösungsmittel‐Wechselwirkung beim Transport in wäßrigen Elektrolytlösungen
Authors: Schönert H.
Published: March 2014

Die Reibungskoeffizienten Rik, die in den phänomenologischen Gleichungen der irreversiblen Thermodynamik auftreten und die das isotherme Transportverhalten in Mischphasen beschreiben, können einerseits aus konventionellen Transportexperimenten (Äquivalentleitfähigkeit, Überführungszahlen, Diffusionskoeffizient) bestimmt und andererseits nach Debye‐Hückel‐Onsager berechnet werden. Zwischen den experimentellen und theoretischen Werten der Rii besteht eine in der Konzentration lineare Differenz, die ionenspezifisch ist und die sich mit dem ionenspezifischen B‐Term der Viskosität korrelieren läßt.
Equation of State for the Vapour of Concentrated and Diluted Hydrochloric Acid
Authors: Kindler Wolfgang , Wüster Günter , Ran Hans
Published: March 2014

Pressure‐volume‐temperature relations have been measured for hydrochloric acid with mole fractions of HCl up to 0.23 at temperatures up to 780 K and pressures up to 150 bar. A simplified Redlich‐Kwong equation was fitted to the results and is able to describe the behaviour in the single‐ (vapour‐) phase region fairly well (mostly ± 1%). The saturation line is also given as a function of temperature and mole fraction of HCl.
13C Relaxation Rates in the System Pyridine‐Methanol
Authors: Kratochwill A.
Published: March 2014

The13C‐relaxation rates and the NOE have been determined at 30°C for the o‐, m‐, and p‐carbons of pyridine in mixtures with methanol. The intramolecular dipolar part is analyzed with Woessner's symmetric rotator model. Pyridine reorients anisotropically with the fastest motion around the C4–N–OH axis,D∥/D⟂∼ 4.
On the Pressure Dependence of the Reaction of HO with CO
Authors: Biermann H. W. , Zetzsch C. , Stuhl F.
Published: March 2014

The reaction of HO with CO was studied at 300 K using pulsed vacuum uv photolysis of H2O to generate HO. Resonance absorption was used to monitor HO in the presence of large amounts of N2 or He. The rate constant of this reaction was found to be independent of pressure in the range from 25 to 750 Torr. However traces of impurities in the reaction system and also small amounts of added O2 cause the rate constant to increase at high pressures. A mechanism is proposed to explain this effect.
Calculation of the Structure of Laminar Flat Flames II: Flame Velocity and Structure of Freely Propagating Hydrogen‐Oxygen and Hydrogen‐Air‐Flames
Authors: Warnatz J.
Published: March 2014

The solution of the conservation equations governing a freely propagating laminar flat flame has been performed for the hydrogen‐oxygen‐nitrogen system. A reaction mechanism with rate constants from recent reviews is given which reproduces within the limits of experimental errors flame velocities in hydrogen‐oxygen and hydrogen‐oxygen‐nitrogen mixtures between 10 cm/s and 1000 cm/s.
Infrared Chemiluminescence Studies of the Reactions H + S2Cl2, H + SOCl2 and H + SCl2
Authors: Bardorff W. , Heydtmann H.
Published: March 2014

Infrared chemiluminescence studies of the bimolecular reactions H + S2Cl2, H + SOCl2, and H + SCl2 were carried out in order to explore the primary vibrational‐rotational distributions of the excited product molecule HCl. Assuming no formation of HCl(v′ = 0) in the case of the reactions H + SOCl2 and S2Cl2 at least 38%, respectively 32% of the available energy enter vibration and rotation of the newly formed HCl molecule. In contrast for the reaction H + SCl2 more than 56% of the available energy are transferred to the internal degrees of freedom of HCl. The bimodal rotational distribution of the HCl formed by H + SCl2 reported previously [4] was confirmed.
Struktur und Eigenschaften silikatischer Schmelzen als Faktoren der magmatischen Gesteinsbildung
Authors: Seifert F.
Published: March 2014

Natural silicate melts (magmas) are highly polymerized and their structure can essentially be described by the anionic species three‐dimensional network (3D), sheet‐ and chain‐like unit. The concentration of these species depends on the ratio of nonbridging oxygens to tetrahedrally coordinated cations (NBO/T), temperature and electronegativity of the network modifier. Their concentration controls e.g. viscosity, density, solubility of fluids and crystallization of the melts. Melts with a high proportion of 3D units with six‐membered rings (e.g. NaAlSi3O8) exhibit a decrease of viscosity with increasing pressure.
ApVT‐Apparatus for Measurements on Gas/Oil Solutions up to 2000 Bar and 440K
Authors: Killesreiter H. , Wiese P. , Kuss E.
Published: March 2014

A high pressure piezometer is described with which pVT‐measurements on solutions of gases in liquids like oils can be performed at pressures and temperatures up to 2000 bar and 440 K, respectively. The present investigations deal mainly with the system squalane/CO2 at different mole fractions, but also with squalane/N2. – The high accuracy of the measurements reveals a pronounced structure of the pV‐curves in dependence on temperature and mole fraction. At larger mole fractions is the unequivocal assignment of the phases ambiguous, and the representation of the experimental data in terms of an equation of state not possible for the whole pressure and temperature range. However, for solutions with lower mole fractions could be determined the saturation pressures and the isothermal compressibility in the unsaturated region. Furthermore, the molar excess volumes of the mixtures have been calculated and the phase behaviour has been discussed briefly.
Solubility Constants and Free Enthalpies of Metal Sulphides and Carbonates
Authors: Gamsjäger H. , Reiterer F. , Heindl R.
Published: March 2014

Solubility constants, *Kpso = [Fe2+]P [H+]−2, of iron(II) sulphide phases such as troilite, FeS, hexagonal pyrrhotite, FeS1,11, and natural monoclinic pyrrhotite, FeS1,14, have been determined at 323.15 K and total anionic molality, I = 1.0 mol kg−1 (Na)ClO4. At the same conditions the equilibrium constant for the reaction Fe2+ + 2Tl(s) ≈ Fe(s) + 2Tl+ was measured and used for the evaluation of the standard electrode potential of Fe2+/Fe. The respective solubility constants combined with the standard electrode potential of Fe2+/Fe and the well known thermodynamic data of hydrogen sulphide led to the free enthalpies of formation, ΔfG⊖ of the above mentioned iron(II) sulphide phases. Nickel(II) carbonate, NiCO3, was synthesized and its solubility constant determined at 348.15, 358.15 and 363.15 K and at I = 1.00 and 0.20 mol kg−1 (Na)ClO4. From the results obtained the ΔfG⊖ of NiCO3 was calculated and turned out to be considerably more negative (> 30 kJ mol−1) than the value previously accepted.
Partikelmeßtechnik
Authors: Leschonski K.
Published: March 2014

Particle characterization comprises the measurement and the quantitative description of physical properties of dispersed particulate systems such as geometrical size, settling rate, optical properties but also of concentration, velocity, flowability. It deals on the one hand with single stationary or moving particles and on the other hand with the properties of a bulk material. — After describing the main areas of particle characterization this paper concentrates on optical methods such as image analysis, and light scattering techniques. A new instrument for diffraction pattern analysis and its theoretical background and an on‐line photometric surface area analyzer finally is described.
Electrical Double Layer and London — van der Waals Forces in Soap Films Studied by Laser Light Scattering
Authors: Joosten J. G. H.
Published: March 2014

Electrical double layer and London — van der Waals forces in soap films are studied as a function of thickness by means of time‐averaged light scattering and Photon Correlation Spectroscopy. The free films are drawn from a solution containing 10−2 mol/dm3 of the cationic surfactant dodecyltrimethylammonium bromide. Thermally excited surface waves on the interfaces of a film give rise to a measurable diffuse reflection, being a combination of squeezing mode and bending mode scattering. Because of the large difference in the characteristic time scales the dynamics of the squeezing and bending modes can be studied separately. The relaxation of the bending mode was measured using Photon Correlation Spectroscopy yielding the surface tension of the soap film. Up to frequencies of about 4 MHz this tension appears to be equal to the bulk value of the surface tension. From thickness and angle dependent time‐averaged light scattering experiments we obtained V″, being the second derivative of the free energy of film formation with respect to film thickness. The experimental data are interpreted by the DLVO theory using the Lifshitz theory for the London — van der Waals part of V″. We found an exponential thickness dependence of the electrical double layer contribution to V″. The experimental decay length of the latter contribution agrees very good with the theoretical value of the Debye length. For the surface potential a value of 95 mV was found.
Rate Constants and Vinoxy Product Yield in the Reaction OH + Ethylene Oxide
Authors: Lorenz K. , Zellner R.
Published: March 2014

Absolute rate constants and the vinoxy (CH2CHO) product yield for the reaction of OH radicals with ethylene oxide (C2H4O) have been determined using a combined laser photolysis/resonance fluorescence (laser induced fluorescence) technique. The rate constant for OH decay is k1 = (1.1 ± 0.4)‐ 10−11 exp[‐(1460 ± 150) K/T] cm3/s over the temperature range T = 298–435 K. The branching ratio for vinoxy (VO) formation at 298 K is found to be ϕvo = 0.08 and 0.23 at 13 and 80 mbar, respectively. A potential energy scheme accounting for reagent ring opening and the formation of vinoxy is presented.
Diffusion and Thermal Diffusion in Some Binary Mixtures of the Major Components of Air
Authors: Robjohns H. L. , Dunlop Peter J.
Published: March 2014

Diffusion coefficients are reported for the systems N2‐CO2, O2‐CO2, N2‐O2and Ar‐CO2. Thermal diffusion factors have also been measured for the first two systems and used, together with the above diffusion coefficients and second virial coefficients from the literature, to derive approximate spherical potentials to describe the unlike interactions in these two systems.
Microscopic Observation of Crystallites in the Deionized Suspensions of Monodispersed Polystyrene Spheres
Authors: Okubo T.
Published: March 2014

Photographs are taken for the crystallites and grain boundaries in the ordered colloidal crystals of monodispersed polystyrene spheres by four methods, (1) using a metallurgical microscope with a standard illumination device, (2) a metallurgical microscope with diagonal illumination, (3) a polarized metallurgical microscope, and (4) close‐up photographing. The size of the crystallites is 100–200 urn and increases as the concentration of spheres decreases, which is consistent with the results from the reflection spectrum measurements.
Renormalization Group from a Center Manifold Reduction in Dynamic Critical Phenomena
Authors: Fernández Ariel
Published: March 2014

We prove that a coarse‐graining procedure is obtained by performing a center‐manifold reduction of fast‐relaxing short wavelength modes in dissipative spin systems. The probability distribution width about the center manifold is only dependent on static spin autocorrelations. Agreement with renormalization group derivations is found.
A structural interpretation of impedance spectra and radioisotope diffusion in dental enamel
Authors: Scholberg H. P. F. , Borggreven J. M. P. M. , Driessens F. C. M.
Published: March 2014

In this study complex impedance measurements and radioisotope diffusion experiments are used to estimate physical parameters for enamel such as pore‐diameter, membrane‐porosity and membrane‐charge. The assumptions implied in deriving a model and in estimating the membrane‐parameters and ionic radii were Verified by comparing the experimental observations with values calculated with the proposed model. A good congruence was found between the measured and calculated values. The membrane‐porosity appeared to be the main determinant for the experimentally observed wide ranges in permeability and conductance. The dependence of conductance on the electrolyte‐concentration (2 to 100 mmol/1) and ionic species (RbCl, KCl, KNO3 and Mg(NO3)2) are shown to be explained by the model in a satisfactory way.
Diffusion coefficients and thermal diffusion factors for the systems He‐CF4 and Ne‐CF4
Authors: Dunlop Peter J. , Robjohns H. L. , Bignell C. M.
Published: March 2014

Diffusion coefficients and thermal diffusion factors are reported for the systems He‐CF4 and Ne‐CF4 between 200–400 K. The results are used to generate and test approximate potential functions for the unlike interactions.
Dynamics of proton transfer in solution by NMR relaxation
Authors: Latanowicz L.
Published: March 2014

The expression has been derived for the rate of intramolecular part of the relaxation induced by the motion of nuclei transferred between the two sites of unequal energy and by isotropic reorientation of nuclear pairs. This expression should be useful in analizing T1 data for hydrogen bonded liquids. — The relaxation time T1 of protons in H2O—D2O mixtures has been measured and analysed on the basis of the presented theory.
Structure determination of adsorbates on single crystal electrodes with X‐ray standing waves
Authors: Materlik G. , Schmäh M. , Zegenhagen J. , Uelhoff W.
Published: March 2014

Tl submonolayers were deposited from an aqueous electrolyte on a Cu(lll) surface. The electrodes were studied inside and outside the electrolyte with standing X‐ray wave fields. These measurements allow to determine the fraction and the position of Tl atoms which occupy adsorption sites coherently relative to the bulk diffraction planes. The results show that the method can be applied to ex‐situ as well as in‐situ structure studies of the solid/liquid interface. The influence of oxygen on immersed and emersed Cu electrodes is discussed in detail.
In situ microweighing at the junction metal/electrolyte
Authors: Stöckel Wolfgang , Schumacher Rolf
Published: March 2014

We report on in situ measurements of frequency shifts and charge fluxes registered simultaneously with the Electrochemical Quartz Microbalance (EQMB) on 5 MHz, 6 MHz and 10 MHz crystals, oscillating in a liquid environment. The investigations on gold electrodes reveal an influence of pH on the interfacial processes forming oxidic overlayers. This result is in agreement with a recent XPS investigation on emersed samples. It is further demonstrated, that in contrast to a single potential excursion the metallic gold surface becomes rough upon multiple potential excursions. This becomes evident from a frequency gap, that persists upon reduction. Anodic and cathodic processes on platinum electrodes lead to strong frequency changes, which are not related to weight changes. In agreement with an IR study performed recently on emersed Platinum electrodes, We attribute these frequency changes upon cycling to a transition from the hydrophilic to the hydrophobic surface state and vice versa.
The time‐resolved response of semiconductor‐electrolyte interfaces to short pulses of illumination
Authors: Gottesfeld Shimshon
Published: March 2014

The kinetics of elementary steps in the overall process of photoelectrochemical current generation at an illuminated semiconductor‐electrolyte interface can be investigated using relaxation techniques based on perturbations by pulses of illumination. This article reviews theoretical predictions for the form of transients expected under various experimental conditions, and compares these predictions with experimental results. Photopotential, photocurrent, and photoluminescence transient measurements following such perturbations of the semiconductor/electrolyte interface are described.
Photocapacitance study of n‐GaAs/electrolyte interfaces
Authors: Allongue P. , Cachet H.
Published: March 2014

The electrochemical photocapacitance spectroscopy (EPS) is used to determine the interface state distribution at n‐GaAs/aqueous electrolyte junctions. Two states (Ec — 1.30eV and Ec — 1.05 eV) are found to be related to corrosion of GaAs. It is also shown that ruthenium induces additional states 0.2 eV above the valence band. A new insight of its effect on the stabilization of GaAs is given.
Electrochemical reactivity of ordered and disordered n‐GaAs(110) surfaces. A combined XPS, LEED and electrochemical study
Authors: Solomun T. , Richtering W. , Gerischer H.
Published: March 2014

Initial stages of electrochemical oxidation of UHV‐prepared n‐GaAs(110) surfaces, possessing either a long‐range order or an extensively damaged surface layer, were compared using an apparatus coupling ultra‐high vacuum and electrochemical practices. Not only the sputtered but also the annealed, stoichiometric surface is initially significantly more active than a surface prepared by Br2/Me etching. Anodic treatment results in a rapid loss of surface order and reactivity. A subsequent XPS analysis reveals that, irrespective of the extent of the initial surface order, an overlayer with a great enrichment of As is produced in acidic solution but not in an alkaline environment. A model is derived explaining the influence of the pH on the reactivity.
Computer supported pulse measurements of current and capacity during fast oxide formation on iron
Authors: König U. , Lohrengel M. M. , Schultze J. W.
Published: March 2014

Computer supported potentiostatic pulse measurements are described which allow the determination of current density i in a wide range of / orders of magnitude of i and t. Pulse measurements of capacity in the same time scale reveal the electronic properties of the interface. Oxide film formation on iron is investigated as an example. Common models of high field mechanism of oxide growth and an n‐type semiconducting film are confirmed qualitatively, but in detail they have to be corrected. The n‐type semiconducting film represents only a part of the oxide, and the dielectric constant D and the donor concentration N decrease with time. The properties of a stable semiconductor develop slowly, parallel to the decrease of ionic currents in the film. That is also shown by the slow stabilization of the transpassivity.
Electroluminescence at p‐type semiconductor/electrolyte interfaces
Authors: Uosaki Kohei , Kita Hideaki
Published: March 2014

Electroluminescence (EL) was observed at p‐InP/1 M NaOH—0.15 M S2O2−8 and p‐GaAs/0.5 M H2SO4—0.15 M S2O2−8 interfaces. Although in the former case EL was observed only when potential was kept at very negative potential as at p‐GaAs/1 M NaOH—0.15 M S2O2−8 interface, in the latter case EL was observed not only during cathodic pulse but also just after the potential was pulsed to the anodic limit. The EL observed during cathodic pulse is caused by the recombination of hole in the valence band injected by S2O2−8 and/or SO*−4, which is the one electron reduction product of S2O2−8, and electron in the conduction band. The comparison of the result at p‐GaAs in 0.5 M H2SO4—0.15 M S2O2−8 interface with that in 1 M NaOH—0.15 M S2O2−8 suggests that S2O2−8 and/or SO*−4 adsorb more strongly in 1 M NaOH than in 0.5 M H2SO4.
Some nontraditional approaches for examining strong‐ and weak‐overlap electron‐transfer processes at electrodes
Authors: Weaver Michael J.
Published: March 2014

Some nontraditional approaches for gaining molecular‐level information on the roles of surface‐reactant interactions in electrode kinetics and mechanisms are described with the aid of recent results from our laboratory. The virtues of evaluating unimolecular rate constants, ket (s−1), for one‐electron transfer reactions for both inner‐ and outer‐sphere pathways are pointed out. Illustrative data are presented for the reduction of pentaamminecobalt(lll) anchored to metal surfaces via systematic series of organic and inorganic bridges, X, with the objective of probing the sensitivity of the electronic transmission coefficient, Kel, and the intrinsic electron‐transfer barrier, ΔG*int to the geometry and electronic structure of the bridging ligand. Evidence is presented that most of the ca. 106 fold rate variations are due to variations in Kel, the reactions being of the “weak‐overlap” type, although the especially large ka values seen for the small inorganic bridges may be due in part to diminutions in ΔG*int, caused by the onset of “strong‐overlap” behavior. Several applications of surface‐enhanced Raman spectroscopy for examining the vibrational properties of adsorbed reactants and reaction intermediates are also described. These include experiments aimed at elucidating the structural perturbations induced by surface‐reactant binding, and for obtaining a molecular identification of adsorbed reaction intermediates in multistep electrode processes.
The kinetics of the polycrystalline Ag/Ag+‐electrode studied by high‐frequency impedance spectroscopy
Authors: Schöne G. , Wiesbeck W. , Stoll M. , Lorenz W. J.
Published: March 2014

The fast charge‐transfer reaction of the polycrystalline Ag/Ag+‐electrode was studied using a new technique of high‐impedance spectroscopy working in the frequency range between 1 kHz and 5 MHz. The method is characterized by a special electrochemical cell with two working electrodes, a new designed de‐control being completely ac‐decoupled, a highly precise impedance measurement technique (ICEP = Impedance Conversion and Error Processing) and the quantitative calculation of the electrodynamic field distribution. The accuracy of the measurements is better than 0.05%. The results obtained in the Ag/Ag+‐system are in a quantitative agreement with a theoretical transfer function based on a 2‐D inhomogeneous surface model. The exchange current densities were found to be about half an order of magnitude higher than the literature data.
Research on chemically modified electrodes: Electrocatalytic reduction of dioxygen by iron tetraphenylporphyrin modified glassy carbon electrode with heat treatment
Authors: Dong Shaojun , Jiang Rongzhon
Published: March 2014

The heat treatment of iron tetraphenylporphyrin chemically modified glassy carbon electrode is described. This electrode shows high catalytic activity and good stability for dioxygen reduction. Its catalytic activity is still maintained through 1000 cycles of potential scans (100 mv/s) in an air saturated solution of 0.05 M H2SO4 after a heat treatment to 500°C. Using XPS, Mössbauer, UV‐VIS spectroscopy and mass spectroscopy the microstructure of the electrode surface has been analyzed. The electrocatalytic and dynamic behavior for dioxygen reduction has been studied by cyclic voltammetry and rotating disk electrode respectively. The rate constants for dioxygen reduction at the electrode in a variety of pH solutions have been measured.
Electrochemical Photocapacitance of ZnSe: Effect of Photoelectrochemical Etching
Authors: Tenne R. , Haak R. , Triboulet R.
Published: March 2014

Measurements of electrochemical photocapacitance spectroscopy (EPS) of ZnSe were carried out with the aim of studying the effect of photoelectrochemical etching. A new transition is observed that can be assigned to a shallow acceptor state. The observation of that transition is explained by the etching‐out of shallow donor states which are associated with acceptor states. Thus acceptor states which were “dormant” before the process become observable after photoelectrochemical etching.
Thermochemical Study of the Gaseous Molecules EuNbO3, EuNbO2, EuNb2O6 and of the Niobium Oxides NbO and NbO2
Authors: Balducci G. , Gigli G. , Guido M.
Published: March 2014

The gaseous ternary oxide molecules EuNbO3, EuNbO2 and EuNb2O6 have been identified by high temperature mass spectrometry in the vapours in equilibrium over a mixture of europium sesquioxide and niobium monoxide in a molybdenum Knudsen cell over the temperature interval 1996–2382 K. From the study of various all‐gas equilibria, the atomization energies and the standard heats of formation for these molecules were derived. In addition, from the study of a gaseous exchange reaction involving EuO, NbO, and NbO2, new results for the niobium oxides were obtained and compared with literature data. — The proposed values are: ΔH0o,at(EuNbO3 = 2396 ± 29 kJ/mol; ΔH0o,at(EuNbO3 ∼ 1675 kJ/mol; ΔH0o,at(EuNbO3 = 5070 ± 39 kJ/mol; D0o(NbO) = 774 ± 18 kj/mol; ΔH0o,at(NbO2) = 1405 ± 14 kJ/mol. — The corresponding standard heats of formation are: ΔH0f,298(EuNbO3,g) = −756 ± 33 kJ/mol; ΔH0f,298(EuNbO2,g ∼ −279 kJ/mol; ΔH0f,298(EuNbO2O6,g = −1972 ± 51 kJ/mol; ΔH0f,298(NbO,g) = 202 ± 25 kJ/mol; ΔH0f,298(NbO2,g) = −185 ± 22kJ/mol.
The Interaction of CFCl3 and CF2Cl2 with Solid Surfaces Studied by Thermal Desorption Mass Spectroscopy
Authors: Buchmann Lutz‐Martin , Illenberger Eugen
Published: March 2014

Adsorption and desorption of CFCl3 and CF2Cl2 on Fe and pyrex glass surfaces has been studied in the temperature range 90–400 K. In contrast to a previous study of the interaction of CFCl3 with a clean Fe(100) surface, for the samples presently used no extra cleaning procedure has been applied in the UHV. Under these conditions adsorption only occurs at temperatures not far from conditions for condensation. From the desorption spectra, the activation energy of desorption for CFCl3 on a Fe surface is 36.8 ± 2 kJ mol−1 (at 148 K) and the heat of vaporization 34.7 kJ mol−1 (at 128 K). No evidence for dissociative adsorption of CF2Cl2 or CFCl3 (as was the case for CFCl3 on a clean Fe surface) has been found. In addition, no evidence for a photon stimulated decomposition of these molecules when adsorbed on these surfaces has been found when visible laser light is used. The results are discussed with respect to the problem whether surfaces may operate as sinks for halocarbons released into the atmosphere.
Scavenging of Radicals from the Gas Phase by Freezing with Dimethyl Disulfide
Authors: Schottler M. , Homann K. H.
Published: March 2014

H and O atoms and methyl radicals produced in microwave discharges of H2/He, O2/He and CH4/He mixtures, respectively, were scavenged by supersonic nozzle probing with subsequent freezing and reaction with dimethyl disulfide on a liquid nitrogen cooled wall. The main reaction products for the three kinds of radicals were CH3SH, CH3S(O)SCH3 and CH3SCH3, respectively. Side products were CH3SCH2SSCH3 and CH3SSSCH3 for H atoms and CH3S(O)2SCH3 for O atoms. – The scavenging efficiencies for the different radicals were determined and measured as a function of the gas phase radical concentration, the flow of scavenger molecules, the pressure in the vacuum chamber, and the conditions of the discharge and the flow through the sampling nozzle. It is concluded that this method is suitable for light radicals with reservations in the case of H atoms and can probably be used with still better success for heavier radicals.
Scavenging of Radicals from the Gas Phase by Freezing with Dimethyl Disulfide. 2. Radicals from Discharges and a Flame of Acetylene
Authors: Kubitza Ch. , Schottler M. , Homann K. H.
Published: March 2014

The method of detecting radicals from low‐pressure gas‐phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C2H2/He mixtures and to a C2H2/O2 flame. It was accomplished by condensing a supersonic nozzle beam from the reaction system together with a beam of DMD on a liquid‐N2 cooled surface. The scavenging products were measured by GC/MS after warming‐up. Radicals measured in the discharge were C2H, C4H, C6H, C3H2, C2 besides H atoms. Preliminary measurements on the flame showed that C6H5 (phenyl), CH2, C3H2, besides H and O atoms were prominent radicals at the end of the oxidation zone. The concentration of phenyl is of the same order as that of e.g. naphthalene. The method provides a means to distinguish condensible flame products from those that are formed during the sampling process when no scavenger is added.
Kinetics, Energetics and OH Product Yield of the Reaction CH3O + O(3P) → CH3O*2 → Products
Authors: Ewig F. , Rhäsa D. , Zellner R.
Published: March 2014

The rate constant for the reaction (1) CH3O + O → products at 298 K has been determined using 248 nm laser co‐photolysis of CH3ONO/O3 mixtures for the generation of CH3O radicals and O atoms combined with LTF for time resolved detection of CH3O and product OH. k1 is found to be (2.5±0.7) 10−11 cm3/s with a relative yield of OH of Φ = ‐Δ[OH]/Δ[CH3O] = 0.12+0.08−0.04. The results are shown to be consistent with a primary capture mechanism on an electronically adiabatic surface forming highly vibrationally excited CH3O and followed by rapid subsequent decomposition or isomerization, viz. magnified image.

From modelling of the OH yield using RRKM theory the isomerization barrier between CH3O2 and CH2OOH is placed near 160 kJ/mol in good agreement with recent ab initio calculations. As a consequence the CH3 + O2 combustion reaction is predicted to proceed primarily via the low energy CH2O + OH channel, in contrast to most previous suggestions.