Advantages and Disadvantages of Trivalent Chromium Plating

Advantages and Disadvantages of Trivalent Chromium Plating

The advantages of the trivalent chromium processes over the hexavalent chromium process are fewer environmental concerns due to the lower toxicity of trivalent chromium, higher productivity, and lower operating costs. In the trivalent chromium process, hexavalent chromium is a plating bath contaminant. Therefore, the bath does not contain any appreciable amount of hexavalent chromium. The total chromium concentration of trivalent chromium solutions is approximately one-fifth that of hexavalent chromium solutions. As a result of the chemistry of the trivalent chromium electrolyte, misting does not occur during plating as it does during hexavalent chromium plating. The use of trivalent chromium also reduces waste disposal problems and costs.

The disadvantages of the trivalent chromium process are that the process is more sensitive to contamination than the hexavalent chromium process, and the trivalent chromium process cannot plate the full range of plate thicknesses that the hexavalent chromium process can. Because it is sensitive to contamination, the trivalent chromium process requires more thorough rinsing and tighter laboratory control than does the hexavalent chromium process. Trivalent chromium baths can plate thicknesses ranging up to 0.13 to 25 µm. It cannot be used for most hard chromium plating applications.  

Trivalent chromium electroplating baths have been developed primarily to replace decorative hexavalent chromium plating baths. The development of a trivalent bath has proven to be difficult because trivalent chromium solvates in water to form complex stable ions that do not readily release chromium. Currently, there are two types of trivalent chromium processes on the market: single-cell and double-cell. The major differences in the two processes are that the double-cell process solution contains minimal-to-no chlorides, whereas the single-cell process solution contains a high concentration of chlorides. In addition, the double-cell process utilizes lead anodes that are placed in anode boxes that contain a dilute sulfuric acid solution and are lined with a permeable membrane, whereas the single-cell process utilizes carbon or graphite anodes that are placed in direct contact with the plating solution. Details on these processes are not available because the trivalent chromium baths currently on the market are proprietary.