- Aug 10, 2018 -
Trivalent chromium plating, also known as trichrome, Cr+3 and chromium (III) plating, uses chromium sulfate or chromium chloride as a main component. In some applications and thicknesses (eg, decorative plating), trivalent chromium plating is a replacement for hexavalent chromium. In addition to the bath chemistry and anode composition, the trivalent chromium plating process is similar to the hexavalent chromium plating process. There are three main types of trivalent chromium bath configurations:
1. A chloride or sulfate based electrolyte bath using graphite or a composite anode plus an additive to prevent oxidation of trivalent chromium to the anode.
2. A sulfate-based bath that uses a lead anode surrounded by a box containing sulfuric acid (called a shielded anode) to prevent trivalent chromium from being anodized.
3. Sulfate-based bath, using an insoluble catalytic anode, can maintain the electrode potential and prevent oxidation.
Compared to hexavalent chromium, the trivalent chrome process can plate workpieces at similar temperatures, rates and hardnesses. The plating thickness ranges from 0.005 to 0.05 mils (0.13 to 1.27 μm).
Advantages and Disadvantages: The functional advantage of trivalent chromium is higher cathode efficiency and better polishing ability. Better throwing power means better productivity. Less energy is required due to the lower current density required. This process is more durable than hexavalent chromium because it can withstand current interruptions.
From a health point of view, trivalent chromium is inherently less toxic than hexavalent chromium. Due to its low toxicity, it is not strictly regulated, which reduces management costs. Other health benefits include higher cathode efficiency, which reduces chromium air emissions; lower concentration levels result in less chromium waste and non-decomposed anodes.
One of the shortcomings of this method when it was first introduced is that decorative customers disapprove of color differences. The company now uses additives to adjust the color. In hardcoat applications, thicker coatings are not as corrosion resistant as hexavalent chromium. The cost of chemicals is higher, but this is usually offset by higher productivity and lower management costs. Generally, this method must be controlled more strictly than hexavalent chromium plating, especially for metallic impurities. This means that processes that are difficult to control with a trivalent chromium bath, such as barrel plating, are much more difficult.