ABSTRACT
X-ray photoelectron spectroscopy (XPS) has been used to investigate the correlation between composition of 316L stainless steel (SS316L) surface films formed by different surface treatments and their catalytic effects on surface activated anaerobic cure. The four surface treatments studied were: (1) machined only, (2) machined and buffed, (3) machined and passivated, and (4) machined, buffed and passivated. The passivation was performed by immersion of SS in HNO3 and EDTA solutions. It was found that the surface activity for anaerobic cure using Loctite 642 adhesive was significantly affected by the various treatments. The completely processed passivated 316L substrate, which includes machining, buffing and nitric acid/EDTA treatments, provided the greatest surface reactivity over the other treatments. The reason for this increase in surface activity for anaerobic cure appears to be due to alteration of surface composition. The results of XPS analysis indicate that layers of iron or chromium hydroxide with an overlayer of oxides were formed after machining. This metal hydroxide formation was due to metal contact with the cutting fluid, which contains the strong base ethanolamine. These iron/chromium hydroxide top layers were then partially converted to iron/chromium oxides after air exposure. The buffing apparently roughened the surface and removed minute iron particles and scale, but did not remove the oxide/hydroxide layers. The passivation process by HNO3/EDTA, however, causes the surface metal to form a well-defined new phase by reducing the thickness of the topmost oxide layers and enriching the top layer with metal hydroxide and/or oxyhydroxide. The new phases are more active in catalyzing the anaerobic cure than the original existing metal oxides. Surface reactivity is interpreted on the basis of the catalytic activity of metal hydroxides or oxyhydroxides for anaerobic polymerization. The correlation between the composition and chemical state of the passive film and cure mechanism is discussed.
