Here are the differences that we summarize between Trivalent and hexavalent chromes.
Difference Between Trivalent and Hexavalent Chromium
Hexavalent chromium plating is the traditional method of chromium plating (most commonly known as chrome plating) and can be used for decorative and functional finishes. Hexavalent chromium plating is achieved by submerging substrates into a bath of chromium trioxide (CrO3) and sulfuric acid (SO4). This type of chromium plating provides corrosion and wear resistance, as well as aesthetic appeal.
Automotive steering wheel component in a hexavalent chrome finish
Hexavalent chromium plating has its disadvantages, however. This type of plating produces several byproducts which are considered hazardous waste, including lead chromates and barium sulfate. Hexavalent chromium itself is a hazardous substance and carcinogen and is heavily regulated by the EPA. In recent years, automotive OEMs such as Chrysler have made efforts to replace hexavalent chromium finishes with more eco-friendly finishes.
Trivalent chromium is another method of decorative chrome plating, and is considered the environmentally friendly alternative to hexavalent chromium, with many of the same characteristics; just like hexavalent chrome finishes, trivalent chrome finishes provide scratch and corrosion resistance and are available in a variety of color options. Trivalent chromium plating uses chromium sulfate or chromium chloride as its main ingredient, instead of chromium trioxide; making trivalent chromium less toxic than hexavalent chromium.
Assembled grill in black trivalent chrome over bright nickel
While the trivalent chromium plating process is more difficult to control, and the necessary chemicals more expensive than that used for hexavalent chromium, the advantages of this method make it cost-competitive with other methods of finishing. The trivalent process requires less energy than the hexavalent process and can withstand current interruptions, making it more robust. Trivalent chromium’s lower toxicity means that it is regulated less stringently, reducing hazardous waste and other compliance costs.
With regulations on hazardous substances tightening in the U.S. and EU, the need for environmentally friendly finishes like trivalent chrome is on the rise.
Hexavalent Chromium Plating Solution
Hard chromium plated deposits, which are usually thicker plating, are widely used in the mining and aircraft industries and for hydraulics and metal forming equipment. They are also used in the finishing of medical and surgical equipment.
Hexavalent chromium electrolytes require a source of chromium ions and one or more catalysts in order to plate. The formulation of the traditional process, called the conventional bath, contains hexavalent chromium and sulfate as the only catalyst.
Proprietary additives that can be added to the conventional hexavalent chromium plating bath formulation to enhance the process are called mixed-catalyst baths since the additives contain at least one additional catalyst in addition to sulfate.
Trivalent Chromium Plating Solution
The electrolytes for trivalent chromium plating solutions differ in chemistry, but they all contain a source of trivalent chromium, which is typically added as the sulfate or chloride salt. They also contain a solubilizing material that combines with the chromium to permit it to plate in the desire to increase conductivity in the solution.
Wetting agents are used to help in the deposition reaction and to reduce the surface tension of the solution. The reduced surface tension essentially eliminates the formation of mist at the anode or cathode. The plating process operates more like Nickel bath chemistry than a Hex chrome bath. It has a much narrower process window than hexavalent Chrome plating. That means that most of the process parameters must be controlled well, and much more precisely. The efficiency of Trivalent Chrome is higher than that for Hex. The deposit is good and can be very attractive.
Hexavalent chromium plating has its disadvantages, however. It is known as human carcinogen and can lead to serious health problems. Remember what made Erin Brockovich a household name? This type of plating produces several byproducts which are considered hazardous.
Trivalent chromium plating is more environmentally friendly than hexavalent chromium; the electrodeposition process is generally accepted to be more than 500 times less toxic than hexavalent Chromium. The major benefit of trivalent chromium processes is that it is more versatile. Plating distribution is more uniform, barrel plating is possible for trivalent chrome, which is not possible with hexavalent chrome.
Hexavalent Vs Trivalent Chromium
| Items | Hexavalent Chromium | Trivalent Chromium |
| Waste Treatment | Expensive | Easy |
| Throwing Power | Poor | Good |
| Safety | Very Unsafe | Relatively safe; similar to Nickel |
| Tolerance to Contamination | Fairly Good | Not as Good |
| NSS and CASS | Similar | Similar |
| Resistance to burning | Not good | Very good |
Table comparing some properties of Hexavalent and Trivalent Chromium
About CheeYuen
Established in Hong Kong in 1969, CheeYuen is a solution provider for plastic part manufacturing and surface treatment. Equipped with advanced machines and production lines (1 tooling and injection molding center, 2 electroplating lines, 2 painting lines, 2 PVD line and others) and led by a committed team of experts and technicians, CheeYuen Surface Treatment provides a turnkey solution for chromed, painting & PVD parts, from tool design for manufacturing (DFM) to PPAP and eventually to finished part delivery across the globe.
Certified by IATF16949, ISO9001 and ISO14001 and audited with VDA 6.3 and CSR, CheeYuen Surface Treatment has become a widely-acclaimed supplier and strategic partner of a great number of well-known brands and manufacturers in automotive, appliance, and bath product industries, including Continental, ALPS, ITW, Whirlpool, De’Longhi and Grohe, etc.
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Post time: Nov-11-2023