Abstract
The passive layer of a metal implant is responsible for its tolerance in a biological environment. A report is given on ESCA-investigations on the passive layer on Vitallium implants which consists largely of Cr-oxide and is only approx. 3-5 micrometer thick. This passive layer can easily be damaged with OP-instruments. The oxide layers rebuilt on exposure to air or on sterilization in boiling water were also investigated by ESCA. Oxide layers normally formed are very similar to the original passive layer. Accumulations of Co- and Mo-oxides are also observed, however. Some short implantation experiments show that the thin Cr-oxide layer is indeed effective as a passive layer. The analytical findings indicate that the formation or re-formation of the passive layer is due to a selective dissolution process. This accords with results obtained by the neutron activation analysis of the serum.

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