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 μm 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)

The Effects of Cleaning on the Kinetics of in vitro Metal Release from Dental Casting Alloys

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution us. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions. Auger analyses of alloy surfaces after exposure to medium showed the presence of organic films up to 50 nm thick. This study demonstrated the importance of consideration of the cleaning method and kinetic release pattern when in vitro tests which assess the cytotoxicities of these alloys are planned.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67010/2/10.1177_00220345920710071101.pd

Reaction of fibroblasts to various dental casting alloys

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72968/1/j.1600-0714.1988.tb01547.x.pd

Korrosion von NiCr20Mo Dentallegierungen Vergleichende elektrochemische und spektroskopische Untersuchungen

Available from TIB Hannover: DW 8736 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Influence of Sol-Gel coatings on the corrosion behaviour of MgZn1 foams with 30 % porosity

The aim of this study was to investigate the ion release behaviour of MgZn1 foam with 30 % porosity and three different sol-gel coatings by static immersion test. Compared to uncoated samples the corrosion could be reduced significantly with all three coatings. Under these test conditions Coating 1 revealed the best corrosion protection