Rhodium Plating Services
For your Rhodium Plating (Rodium) requirements, ProPlate® has facilities for rhodium electroplating both small and large parts in various sized barrels and racks, along with custom and prototype metal finishing.
Rhodium is a silvery-white, hard, and chemically inert precious metal, which means that it does not oxidize. It is one of the platinum group of metals which includes rhodium, ruthenium, iridium, platinum, osmium and palladium, which all share some common physical properties. These six metals all are very dense, have high melting points, are very resistant to corrosion and are very hard.
As rhodium is much whiter than palladium and platinum, it is often used in rhodium plating services such as in plating white gold with a thin layer of rhodium to improve its appearance and plating sterling silver to increase its resistance to tarnishing. Because rhodium metal is inert against corrosion and most aggressive chemicals, other applications include sliding electrical contacts to protect them from galling or sliding contact wear and high voltage/high amperage electrical contacts where there is a potential for oxide formations on the contact surface.
MIL-R-46085, ASTM B634, AMS 2413
ASTM B634 – 88 (Reapproved 1999) Standard Specification for Electrodeposited Coatings of Rhodium for Engineering Use and MIL-R-46085 Rhodium Plating, Electrodeposited are relevant specifications for covering the requirements of the electrodeposition of rhodium over metallic surfaces.
There are two recommendations for specifying the use of rhodium for rhodium electroplating:
1. As rhodium is a very dense metal, when it is used for electroplating, the thickness of the rhodium coating should be as thing as possible. Coatings of electroplated rhodium develop a very dense crystal structure which is also highly fractured, contributing to the hardness and durability of the rhodium coating. However, the thicker the coating, the more likely that the rhodium might break and flake away from the surface which it is coating. Good manufacturing practices dictate that a rhodium electrodeposit of up to 100 micro inches or 2.5 micros which is also 0.000100 inches is regularly maintained. In addition, during the electroplating process, there should be no impurities in the rhodium bath and it should be monitored for maintaining the right amount of organic compounds for stress reduction.
2. Good manufacturing practices also dictate that a thin layer of gold be applied under all rhodium plating and be included in the plating specification, even though typical specifications for rhodium plating require an undercoat of nickel for performance purposes. However, by using gold under the rhodium electroplating in a proper bath, the result will be a dependable, stress free electrodeposit.
Call Us regarding your specific requirements.
Atomic symbol: Rh
Atomic weight: 102.9055
Atomic number: 45
Density: 12.41 grams/cc (@ 20C)
Melting point: 1966C
Boiling point: 4500C
Thermal conductivity: 150 J/(m-sec-K)
Electrical conductivity: 221.729 1/mohm-cm
Rhodium is the hardest of the PGM’s. Its’ knoop hardness is about 800. Compare that to cobalt hardened gold at 200 knoop, 14k ElectricGold at 400 knoop and palladium at 400 knoop. Rhodium is the hardest, most wear resistant metal that we plate at Professional Plating. In addition to its’ hardness, rhodium is extremely resistant to corrosion. Rhodium is an excellent choice where contact with corrosive gases or other high corrosion environments will be encountered. Remember also that as the operating environment temperature increases, the corrosion rate will also increase. So in high temperature applications, rhodium will provide a longer life cycle, than, for example, gold will. Rhodium will reliably operate beyond 1000F.
Alternative Finish Consideration
If your application is primarily considering rhodium for its’ hardness and wear-ability, we suggest that you consider our ElectriGold™ 14K gold product. ElectriGold™ is a 58/42 alloy of gold and cobalt. This is the same alloy that makes up a mil-spec 24k hard gold: gold and cobalt. The difference is the relative proportions of the two elements. 24K hard gold is 99.7% gold (minimum) and 0.03% cobalt (maximum), the remaining .27% is an allowance for impurities. The ElectriGold™ product is 58% gold and 42% cobalt. The result is a product which has a knoop hardness of 400. That is twice as hard as mil-spec hard gold and one half as hard as rhodium: It falls right in the middle. Further, because the alloy is only 58% gold, the material cost is proportionately lower than pure gold and a small fraction of the cost of rhodium plating. The color is yellow, like pure gold, although a more white-ish metallic look. This product is not nearly as hard as rhodium plating; it is not bright white like rhodium plating; and does not have as high a temperature rating as rhodium; however, when appropriately specified, it can be a extremely cost-effective alternative to rhodium plating. Call us for further information about your rhodium plating application. It could be possible that our ElectriGold™ product, or another of our products, will provide a less expensive and equally appropriate alternative. Our business is to provide you with the most consistent, highest quality and cost-efficient solution.