University of Siegen

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End date: 1999Subject: search.filters.subject.540 Chemie

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    Bestimmung der Löslichkeit von Metallchelaten in überkritischem Kohlendioxid
    (1999)
    Wolf, André
    In the present work the bases for a direct reactive extraction of the metals palladium and rhodium were determined. The metals were converted thereby by addition of suitable ligands into chelates. Enormous differences in solubility of the chelates formed with the ligands DPDC and THD could be determined which is a basis for the selective extraction of metals. The most important basis for a selective extraction of a mixture of metal chelates is the knowledge of the solubility of the individual chelates in the extracting agent. For the investigation of this basis a dynamic-spectroscopic method was developed for the solubility determination of metal-organic compounds in supercritical carbon dioxide. The equipment used consisted in its core of a modified MPS 225 of the company Suprex, which was connected to a scanning UV detector. The calibration took place via an off-line quantification. With this equipment the solubility of chelates was determined as a function of the temperature and the density of the supercritical fluid. The temperatures, at which the isotherms were measured, were 50, 60 and 70 °C. The examined area of the reduced density extended from 1,1 to 1,9. The used model substances were chelates of the heavy metals palladium, rhodium and lead. As ligands 2.2.6.6 Tetramethylheptandione (THD), Diisopropyldithiocarbamate (DPDC) and the Methylthioglykolate (MTG) were selected.
    Source Type:Doctoral Thesis
      1  5
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    Chrom, Nickel und Zink in Klinker und Zement : Einbau, Eigenschaftsänderung und Auslaugung
    (1999)
    Stephan, Dietmar
    The aim of the work in the field of building chemistry was the investigation of the influence of higher concentrations of trace elements (e.g. Cr, Ni and Zn) on the production and the use of cement. The pure clinker phases C3S, C3A and C4AF as well as different industrial raw meals were doped with heavy metal oxides in different concentrations and burned. Different analyses were done on the unhydrated samples, e.g. determination of free lime, X-ray diffraction (XRD), scanning electron microscopy (SEM) in combination with energy disperse analysis of X-ray (EDAX). In order to examine the hydration, the samples were ground to the same fineness (clinker together with sulphate). The hydration was measured by differential scanning calorimetry and XRD and the hydration products were investigated with SEM and EDAX. Besides, the initial setting and the development of the strength of cement pastes were determined. For the leaching tests, again, doped cements were produced. On these cements and mortars produced from them, three different leaching tests were performed (leaching of cements, tank leaching test and DEV-S4 procedure). The investigations showed, that low concentrations of Cr, Ni and Zn neither have influence on the production of pure clinker phases and cements nor on the hydration of binders made from these. For changes at higher concentrations the composition of the cements is very important (main and minor elements).
    Source Type:Doctoral Thesis
      1  5
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    Präparative, röntgenographische und schwingungsspektroskopische Untersuchungen an Iodaten zweiwertiger Übergangsmetalle : DRIFT-Experimente
    (1998)
    Pracht, Gerhard
    The aim of this doctoral thesis, which was made in the inorganic solid state chemistry, was the preparation and characterization by x-ray diffraction and vibrational spectroscopy of some hydrate iodates of cobalt, nickel and zinc with following compositions: Ni(IO 3 ) 2 ⋅10H 2 O; M (IO 3 ) 2 ⋅4H 2 O with M =Co, Ni; M (IO 3 ) 2 ⋅2H 2 O with M = Co, Ni, Zn; 3 Co(IO 3 ) 2 ⋅2H 2 O; Co(IO 3 ) 2 ⋅H 2 O and M (IO 3 ) 2 with M =Co, Ni, Zn. The structures of three novel hydrate iodates with the compositions Ni(IO 3 ) 2 ⋅10H 2 O, Co(IO 3 ) 2 ⋅H 2 O and 2Co(IO 3 ) 2 ⋅3H 2 O was examined. In addition the structure of Zn(IO 3 ) 2 ⋅2H 2 O was solved by using single crystal data and the refinement of the structure of Co(IO 3 ) 2 ⋅H 2 O and β- Ni(IO 3 ) 2 by using powder data was presented. The structural relationship of some transition metal iodates were intensively discussed. For most of them the distances of the intra- and intermolecular hydrogen bonds were calculated. The results showed the exceptionally strong hydrogen bonds in Co(IO 3 ) 2 ⋅H 2 O. The influence of the solid state is discussed on vibrational spectra of halogenates with undisturbed C 3v symmetry. Furthermore experiments with a diffusive infrared-reflection unity (DRIFT) were presented. The DRIFT spectroscopy is an interesting alternative for vibrational spectroscopic measurements. The advantages of these technique compared with common transmission infrared spectroscopy were explained. As a result of the experiments some new embedding materials were introduced.
    Source Type:Doctoral Thesis
      4  18
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    Fallstudien zum Lehren und Lernen chemischer Sachverhalte mit Hilfe "Neuer Medien" : zur Konzeption, Entwicklung und Überprüfung interaktiv gestalteter Lernumgebungen für Studierende
    (1999)
    Pees, Günter
    Trotz einer mittlerweile weiten Verbreitung steckt die Entwicklung didaktisch sinnvoll aufbereiteter, interaktiv gestalteter Lernprogramme nach wie vor in ihren Anfängen. Die heutzutage auf dem Markt verfügbaren CBT-Anwendungen bieten aus lerntheoretischer Perspektive wenig Neues. Herkömmliche Lerninhalte werden mit Bildern, Ton und Videofilmen versehen, ins Internet gestellt oder auf eine CD-ROM gebrannt. Im großen und ganzen handelt es sich dabei also um "neuen Wein in alten Schläuchen"; eine unbedingt notwendige, auf pädagogischen Ansätzen fundierte Anpassung verschiedener medialer Komponenten findet meist nicht statt. Ausgangspunkt der vorliegenden Dissertation ist die These, dass der gezielte Einsatz von „Neuen Medien“ in der Lehre im Vergleich zu herkömmlichen Lehr- und Lernformen eine fachdidaktisch fundierte Sichtweise und Konzeption erfordert. Bei der Entwicklung der Lernumgebungen wurde durch Äußerungen der Studierenden sehr schnell deutlich, dass ein Lernweg nach dem Vorbild einer programmierten Instruktion (beispielsweise nach Skinner) nicht zu dem gewünschten Lernerfolg führt. Vielmehr wird deutlich, dass Lernumgebungen, die aus lerntheoretischer Sicht auf dem Behaviorismus basieren, sehr schnell ermüden. Motivation und Interesse lassen schnell nach: Das sture "Abarbeiten" des Lernweges wird als äußerst demotivierend und langweilig empfunden. Auf der Basis dieser Befunde wurde für die vorliegende Dissertation ein anderes lerntheoretisches Konzept zu Grunde gelegt, welches an Leitlinien von Foerster angelehnt wird. Die Ausrichtung der Lernumgebungen auf diese konstruktivistische Sichtweise legt eine sehr offene Struktur der Programme nahe. In diesen Umgebungen kann der Studierende entsprechend seinem Lernertyp und seinen Lernvorlieben navigieren. Sämtliche Optionen sind direkt aus dem Programm heraus verfügbar. Die offene Struktur dieser beiden entwickelten Programme wurde in Befragungen von den Studierenden nahezu uneingeschränkt positiv beurteilt. Gleichzeitg wurde ein weiterer wichtiger Aspekt rein computergestützter Lernumgebungen aufgedeckt: Beim Arbeiten mit CBT-Programmen ist ein pädagogischer Begleiter eher mehr denn weniger gefragt. Diesem kommt dabei zum einen die Rolle als Ansprechpartner bei fachlichen Problemen, zum anderen die Funktion eines Tutors zu, der den Lernenden auf seinem Lernweg berät und ihn an "langer Leine" auf seinem Lernweg führt. Im Laufe dieser Untersuchungen haben sich weitere Anforderungen an ein Lernmedium (CD-ROM) herauskristallisiert, die für diese neue Form des Lernens von fundamentaler Bedeutung zu sein scheinen: * Eine vollständige Substitution vorhandener Lernumgebungen durch solche auf multimedialer Basis erscheint nicht sinnvoll. * Zur Förderung individueller Lernprozesse sollte die Gestaltung der Lernumgebung von Beginn an auf eine möglichst offene Struktur hin ausgerichtet sein. * Dem Lernenden sollte ein Ansprechpartner (Tutor) über einen beliebigen Kommunikationskanal zur Verfügung gestellt werden. Seine Aufgabe liegt in der fachlichen Unterstützung wie auch in einer evtl. notwendigen Korrektur seines Lernweges. * Gezielt eingesetzte und auf konkrete Probleme hin optimierte Visualisierungen in Form von Videofilmen, Fotos oder Bildern können beim Lernen komplexer Sachverhalte hilfreich sein. Sie bedürfen jedoch einer strengen Auswahl, von der vorrangig die Kriterien: Vorverständnis, Einfachheit und Anschaulichkeit berücksichtigt werden sollten.
    Source Type:Doctoral Thesis
      438  279
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    Strukturuntersuchungen an Amminkomplexen und Hydroxiden von Übergangsmetallen
    (1999)
    Mockenhaupt, Christoph
    The crystal structures and IR-spectra of some ammoniakates, Co(OD) 2 , and Mn 2 (OH) 3 Cl have been determined with a view to study hydrogen bonding in these compounds. [Ni(NH 3 ) 6 ]SO 4 , [Cu(NH 3 ) 5 ]SO 4 and Mn 2 (OH) 3 Cl crystallize in the monoclinic space group P2 1 /c with a = 705.0(1), b = 1195.2(2), c = 1180.0(2) pm, β = 96.14(3)°, Z = 4, in the orthorhombic space group Pnma with a = 707.1(1), b = 1065.5(2), c = 1199.0(2) pm, Z = 4, and a = 650.02(2), b = 712.39(3), c = 953.10(3) pm, Z = 4, respectively. IR-spectra of microcrystalline Zn(NH 3 ) 2 Br 2 and Ni(NH 3 ) 2 X 2 (X = Cl, Br) and their isotopically diluted derivatives indicate that hydrogen bonds in these compounds are stronger than in the respective octahedral complexes. The broad range of N⋅⋅⋅O distances and OD stretching vibrations in [Ni(NH 3 ) 6 ]SO 4 and [Cu(NH 3 ) 5 ]SO 4 gives evidence for hydrogen bonds of very different strength. The predicted brucite type of Co(OD) 2 was confirmed (P-3m1, a = 317.79(4), c = 464.2(1) pm and Z = 1. In spectra of isotopically diluted samples two OD-stretching vibrations instead of the one expected were observed. The reason is found in the slow H/D exchange in these brucites with very low solubility, which leads to mixtures of fully and partially deuterated species. In Mn 2 (OH) 3 Cl both hydrogen atoms in positions directly between O and Cl take part in hydrogen bonding. A histogram of the O-H distances in brucite type hydroxides shows that the average distances are in the range 94-96 pm. Contrary to the lattice constants c the lattice constants a correlate well with the average O-H distances. The mean metal-oxygen distances of the first coordination sphere do not correlate withe the frequencies of the OH-stretching modes. Together with the red-shift of the OH valency modes with increasing pressures and the short O-H distances this is an indication for weak trifurcated hydrogen bridges in these compounds.
    Source Type:Doctoral Thesis
      1  6
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    Untersuchung des Cotton-Mouton-Effektes in der isotropen Phase flüssigkristalliner Substanzen
    (1999)
    Blachnik, Hasan-Nuri
    In the first part of the thesis a short description of the theory of liquid crystaline phases, of the Cotton-Mouton effect, critical laws and the Landau-de Gennes theory is given. In the second part a device is described, which allows the very exact determination of the magnetically induced birefringence (Cotton-Mouton (CM) constant) in the isotropic phase. Measurements of the CM constants of a larger number of liquid crystaline substances are presented. These values are used to discuss existing theories on pretransition effects in liquid crystals. In this work the conclusion is drawn that at the moment no theory exists which describes the pretransition phenomena at the phase transition isotropic-liquid crystalline correctly.
    Source Type:Doctoral Thesis
      3  4
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    Zur Berechnung relativistischer Effekte und zum Verständnis ihrer Trends bei Atomen und Molekülen
    (1999)
    Autschbach, Jochen
    After a brief discussion of quantum chemical standard methods (chapter 1) and relativistic quantum chemistry (chapter 2), in chapter 3 the relativistic effects of properties of atomic shells are investigated. A detailed analysis of the fractional relativistic corrections of atomic orbital energies and radii of the atoms no. 1 to 118 shows new relativistic periodic trends. An explanation of several anomalies of relativistic effects, among them the well known "gold-maximum", is given on the basis of the periodic trends and the appearently unsystematic atomic ground state configurations. Forces in molecules, especially by means of the Hellmann-Feynman theorem, are discussed in chapter 4, where also several formulae are derived, which are used in chapters 5 and 6. Chapter 5 contains a density-functional study of the binding forces in N2 and HCl. By analyzing the spatial origin of the Hellmann-Feynman forces it is concluded that both the topology of the molecular deformation density as well as the sharp core polarizations are approximately equally important to determine the forces. Relativistic bonding energies and forces of several diatomic gold compounds are analyzed in chapter 6. The relativistic energy corrections are computed with the help of an implementation of the nonsingular relativistic perturbation theory DPT into the Amsterdam density functional program. Several paradox interpretation schemes are applied to explain the spatial origin of relativistic bond energies and binding forces. Different mathematical formulations create different physical pictures. A "chemical" interpretation is preferrable and possible.
    Source Type:Doctoral Thesis
      2  13