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Paper des Monats
- ja (75)
27Al nuclear magnetic resonance spectra of polycrystalline aluminium borate 9Al2O3 · 2B2O3 have been measured in double rotation at 11.7 and 7.0 T and high-speed magic-angle spinning at 7.0, 9.4, 11.7, 14.1 and 17.6 T. Spinning sidebands from the satellite transitions were observed at 7.0 and 14.1 T. Each of the four structural aluminium sites [Al(IV), Al(V)(1), Al(V)(2) and Al(VI)] are observed, characterised and assigned in the spectra. The obtained parameter set gives a fully consistent interpretation in agreement with the crystal structure of the compound.
Barrier properties of plasma and chemically fluorinated polypropylene and polyethyleneterephthalate
(1995)
The functionalization, perfluorination or an coating of polypropylene (PP) and polyethyleneterephthalate (PET) surfaces in different plasma atmospheres and in an F[2] + N[2] gas mixture were investigated. The aim of this work was to form a barrier layer against solvent and fuel permeation. Typical test solvents were n-pentane, toluene, tetrachloroethylene and mixtures of n-pentane and methanol. The permeation was gravimetrically measured. The permeation of the solvent mixtures was analyzed by mass spectrometry and Fourier transform IR spectroscopy. The permeation of the solvent mixtures through the plasma-modified polymer samples was associated with increased absorption of polar solvent components in the polymer film. The thickness of the plasma-fluorinated PP surface layer was 10-100 nm and that of chemically fluorinated PP about 5000 nm. Nearly the same barrier efficiency was measured for both plasma- and chemically fluorinated samples.
TiN hard coatings have been prepared by unbalanced magnetron (UBM) sputtering and cathodic arc deposition using uni- and bipolar pulsed bias voltages. For UBM sputtering using a unipolar pulsed bias voltage the average substrate bulk temperature Ts was reduced to 220 °C without considerable loss of microhardness and adhesion by variation of the pulse parameters. Determination of the average energy Ep delivered to the growing film per deposited particle leads to values lower than the critical transition energy (150 eV atom-1) between open porous and dense coatings. Using a bipolar pulsed bias voltage Ts decreased with increasing duration ton+ of the positive bias pulse. It was found that Ep increased with increasing ton+ up to values found for d.c. bias voltage. The coatings prepared using a bipolar pulsed bias voltage at low Ts are dense and in compressive stress with acceptable microhardness and adhesion. First results of the investigation of TiN coatings prepared by cathodic arc deposition using unipolar pulsed bias are given.
Template Electrodeposition of Nanowire Arrays on Gold Foils Fabricated by Pulsed-Laser Deposition
(1995)
Rapid resorbable, glassy crystalline materials on the basis of calcium alkali orthophosphates
(1995)
Neben Hydroxylapatit (HAp) findet verstärkt auch Tricalciumphosphat (TCP) Anwendung als Knochenersatzmaterial. In der Literatur finden sich widersprüchliche Angaben zur Löslichkeit von TCP. Bedingt durch unterschiedliche Darstellungsverfahren ergeben sich verschiedenartige Materialbeschaffenheiten, die sich erst nach der Implantation durch ein differenziertes Resorptions-verhalten dokumentieren (partikulärer Abbau, chemischer Lösungsprozeß). Zur Klärung derartiger Zusammenhänge in vitro wurden 2 Methoden zur Bestimmung des Lösungsverhaltens untersucht. Dafür wurden TCP-Proben aus verschiedenen Rohstoffen dargestellt, nach unterschiedlichen Temperaturregimen behandelt und/oder einer Nachbehandlung mit Phosphorsäure unterzogen.
Diese Materialien wurden vor allem mittels Röntgenpulverdiffraktometrie und Rasterelektronenmikroskopie charakterisiert. In anschließenden Löslichkeitsuntersuchungen wurden die optimalen Versuchsparameter (Lösungsmittel, Konzentration, Verhältnis Lösungsmittelmenge zur Lösungsoberfläche usw.) sowie geeignete Meßgrößen (Masseverlust, Ionenkonzentration) ermittelt. Die In-vitro-Löslichkeit erwies sich bei sorgfältiger Auswahl der Versuchsbedingungen als sehr wirkungsvolle Charakterisierungsmöglichkeit, die auf synthesebedingte chemische und morphologische Unterschiede sehr empfindlich reagiert.
Translated Abstract
Resorbable bone substitution on the basis of calcium phosphates
Besides hydroxyapatite (HAp), tricalcium phosphate is increasingly being used as bone substitution material. In literature there are contradictory claims of the TCP solubility. As a result of are contradictory claims of the TCP solubility. As a result of different manufacturing processes there are altered material properties, which are documented by different resorption behaviour especielly after implantation (particle separation, chemical solvatation). To clarify of such in vitro connections two methods for determining the solubility were investigated. Especially for this case, TCP samples prepared from different raw materials were synthesized. These samples were given different heat treatments and/or posttreatments with phosphoric acid.
The materials were characterized above all by using X-ray powder diffraction method and scanning electron microscopy. Following investigations of the solubility lead to optimized testing parameters (solvent, concentration, ratio of solvent's quantity to sample surface, etc.) as well as qualified test parameters (lost of weight, ion concentration). When the test conditions were carefully selected, the in vitro solubillity was proved to be a very effective possibility of materials characterisation which is also very sensitive regarding chemical differences caused by synthesizing or morphological differences.