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J Geis-Gerstorfer

Publications and source records attributed to J Geis-Gerstorfer.

54 records · Page 3Linked to original sources
PubMed1987

Scanning electron microscope studies on the breakdown of passivity of a nickel-chromium-molybdenum dental alloy.

The breakdown of passivity and localized corrosion of a Ni-20Cr-10Mo alloy was investigated. The methods employed were potentiodynamic polarization and SEM, and AES and EDX after potentiostatic polarization over a period of 20 hours in the passive and transpassive regions. The 1 micron finished as-cast specimens were polarized in aerated 0.1 M NaCl. The cyclic polarization curves revealed a critical pitting potential of 470 mV (SCE), while the protection potential was 300 mV (SCE). Using the potentiostatic polarization technique, nearly constant corrosion currents appeared, indicating that the whole surface was corroded uniformly. SEM pictures of samples, corroded at 650 mV, showed little pits under the oxide layer and a thinning down of the outer oxide layer. This lead to the opinion that the penetration as well as the adsorption mechanism determine the breakdown of passivity. EDX analysis and AES depth profiles showed an enrichment of Cr and Mo in the oxide. In contrast to oxidized samples, no second layer of Ni was found in the outer oxide region. In the transpassive region the relative amount of Cr and Mo in the oxide layer was higher than the one found in corresponding samples polarized in the passive region. The oxide thickness found was about 5 nm in the passive region (300 mV SCE) and about 250 nm in the transpassive region (650 mV SCE).

Chromium↗
PubMedDate not supplied

Roughness induced dynamic changes of wettability of acid etched titanium implant modifications.

Dynamic contact angle analysis (DCA) was used to investigate time-dependent wettability changes of sandblasted and acid-etched commercially pure (cp) titanium (Ti) implant modifications during their initial contact with aqueous systems compared to a macrostructured reference surface. Surface topography was analyzed by scanning electron microscopy and by contact stylus profilometry. The microstructured Ti surfaces were found to be initially extremely hydrophobic. This hydrophobic configuration can shift to a completely wettable surface behavior with water contact angles of 0 degrees after the first emersion loop during DCA experiments. It is suggested that a hierarchically structured surface topography could be responsible for this unexpected wetting phenomenon. Roughness spatial and hybrid parameters could describe topographical features interfering with dynamic wettability significantly better than roughness height parameters. The Ti modifications which shift very sudden from a hydrophobic to a hydrophilic state adsorbed the highest amount of immunologically assayed fibronectin. The results suggest that microstructuring greatly influences both the dynamic wettability of Ti implant surfaces during the initial host contact and the initial biological response of plasma protein adsorption. The microstructured surfaces, once in the totally wettable configuration, may improve the initial contact with host tissue after implantation, due to the drastically increased hydrophilicity.

Acids↗
PubMedDate not supplied

Ion release from Ni-Cr-Mo and Co-Cr-Mo casting alloys.

The substance loss from four commercially available Ni-Cr-Mo and four Co-Cr-Mo alloys was examined using a solution of 0.1 mol/L lactic acid and 0.1 mol/L sodium chloride. Dissolved ions were analyzed over a 5-week period using atomic absorption spectroscopy. The results revealed a considerable range of corrosion rates among the Ni-Cr-Mo alloys, with average values after 35 days between 0.54 and 3,261 micrograms/cm2, while the distribution of values for the Co-Cr-Mo alloys was not as wide--between 0.43 and 34.9 micrograms/cm2.

Biocompatible Materials↗