Editing Chrome plating (section)

==Trivalent chromium==
''Trivalent chromium plating'', also known as ''tri-chrome'', ''Cr<sup>3+</sup>'', and ''chrome(III)'' plating, uses [[Chromium(III) sulfate|chromium sulfate]] or [[chromium chloride]] as the main ingredient. Trivalent chromium plating is an alternative to hexavalent chromium in certain applications and thicknesses (e.g. decorative plating).<ref name="newmoa"/>

A trivalent chromium plating process is similar to the hexavalent chromium plating process, except for the bath chemistry and anode composition. There are three main types of trivalent chromium bath configurations:<ref name="newmoa"/>

*A chloride- or sulfate-based electrolyte bath using [[graphite]] or composite anodes, plus additives to prevent the [[oxidation]] of trivalent chromium to the anodes.
*A sulfate-based bath that uses lead anodes surrounded by boxes filled with sulfuric acid (known as shielded anodes), which keeps the trivalent chromium from oxidizing at the anodes.
*A sulfate-based bath that uses insoluble catalytic anodes, which maintains an [[electrode potential]] that prevents oxidation.

The trivalent chromium-plating process can plate the workpieces at a similar temperature, rate and hardness, as compared to hexavalent chromium. Plating thickness ranges from {{convert|5|to|50|μin|μm|abbr=on}}.<ref name="newmoa"/>

=== Advantages and disadvantages ===
The functional advantages of trivalent chromium are higher cathode efficiency and better throwing power. Better throwing power means better production rates. Less energy is required because of the lower current densities required. The process is more robust than hexavalent chromium because it can withstand current interruptions.<ref name="newmoa"/>

One of the disadvantages when the process was first introduced was that decorative customers disapproved of the color differences. Companies now use additives to adjust the color. In hard coating applications, the corrosion resistance of thicker coatings is not quite as good as it is with hexavalent chromium. The cost of the chemicals is greater, but this is usually offset by greater production rates and lower overhead costs. In general, the process must be controlled more closely than in hexavalent chromium plating, especially with respect to metallic impurities. This means processes that are hard to control, such as barrel plating, are much more difficult using a trivalent chromium bath.<ref name="newmoa"/>