Anodizing

There are many different types and purposes of anodization, but for titanium bicycles the primary use is decorative. The process creates an anode out of the titanium in a chemical bath and progressively builds an oxide film through electrolysis. As voltage is varied, the oxide thickens and a color spectrum is created. The final product is a dense adherent titanium oxide film.

There are three basic variations of this oxide, determined by voltage levels and electrical dispersion. The titanium oxides are composed chiefly of anatase and/or rutile crystals; anatase and rutile are the main ores from which pure titanium is separated.

Unfortunately, titanium oxide is extremely brittle (regardless of color), and the oxide film is not easily separated from the titanium substrate due to titanium dissolution into the oxide. The normal bending loads seen in a frame will cause slip lines in the brittle colored surface and ultimately create cracks in this anodized shell. The failed oxide film propagates the cracks through the dissoluted titanium oxide mixture and finally into the uncontaminated titanium below the oxide. Once the cracks have moved into the tube wall, they propagate further, ultimately causing frame failure.

Thus, it can be seen that an anodized titanium substrate acts in exactly the same way as an oxygen-contaminated weld zone. The outermost titanium fibers, which see the greatest stress and therefore need the best ductility, become the most brittle. The potential for stress failure is vastly increased.

For these reasons, Merlin strongly suggests avoiding the anodization of any structurally important titanium part. Merlin's lifetime frame warranty is voided if the frame has been anodized.