Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decreased the current during anodic polarization by as much as two orders of magnitude. A potential scan reversal at + 700 mV for all specimens resulted in a hysteresis for passivated specimens (both smooth and porous) but not for nonpassivated specimens. The protection potential was + 296 ± 68 and + 345 ± 69 mV versus the saturated calomel electrode (SCE) for porous and smooth passivated specimens, respectively.
There were two objectives of this work. The first was to see if a simple anodic polarization test could detect any basic difference in corrosion behavior between porous and smooth Vitallium. The second was to see if a standard passivation treatment affected these two geometries differently, again as detected by anodic polarization. The authors found that this porous configuration responds to polarization in a manner similar to the smooth surface in either the passivated or nonpassivated condition. There is an increase in current associated with the increased surface area. However, the increase in current appeared to be less than one would predict, assuming a linear proportionality between the current and surface area.
All tests were performed on Vitallium in the form of modified patella buttons. The specimens were manufactured by Howmedica, Inc. The porous surface was identical to the P.C.A. configuration. All specimens, both smooth and porous-coated, underwent the same production heat cycle.