Hexavalent to Trivalent (and Back Again)

As the demand for non-chromium protection of zinc and zinc alloy plating has increased, trivalent chromium passivation systems have appeared. Early on, an interesting phenomenon was observed: Hexavalent chrome was found on coatings that were not supposed to contain hexavalent chrome. It was thought that the processor must be cheating and using hexavalent chrome in the working solution in order to achieve increased corrosion resistance. While all of the questions have not been answered, there are some conclusions. Before explaining the various parts of this mystery, it's important to … [Read more...]