Rhodium Plating Qualities, Specifications, and Uses

Rhodium Plating Qualities, Specifications, and Uses

Rhodium Plating has a variety of qualities and uses. Rhodium is white in color and is a precious metal, meaning non-oxidizing.  The Platinum group of metals includes Rhodium. The Platinum group of metals is a group of six metals. Specifically, These include Platinum, Rhodium, Palladium, Ruthenium, Osmium, and Iridium. Likewise, these six metals all share some common physical properties. For example, they have high melting points; they are very dense, hard, and resistant to corrosion.

  • Excellent corrosion resistance. Rhodium is an excellent choice where contact with corrosive gases and chemicals or other high corrosion environments will be encountered. 
  • Excellent electrical conductivity. Rhodium-plated product is well suited for such applications as moving electrical contacts that require protection from rubbing contact wear or galling. Because of its’ high-temperature tolerance to oxidation, rhodium is a great choice for high voltage/high amperage electrical contacts where contact arcing would otherwise cause the formation of highly electrically resistive oxide formations on the contact surface.
  • Excellent in high-temperature applications. Rhodium will provide a longer life cycle, than, for example, gold.  High melting point. Rhodium will reliably operate beyond 1000F.
  • Excellent solderability
  • Excellent wear resistance. Electroplated rhodium has a hardness ranging from 400-550 Vickers which makes it very resistant to abrasion.
  • Excellent reflectivity relatively high reflecting power. Rhodium is an extremely bright white metal. It is much whiter than palladium and platinum. 
  • Rhodium is the hardest of the platinum group metals.  Its’ Knoop hardness is about 800. For example, compare that to cobalt hardened gold at 200 Knoop, and palladium at 400 Knoop.

Plating Specifications

MIL-R-46085 Rhodium Plating, Electrodeposited, and ASTM B 634 – 88 (Reapproved 1999) Standard Specification for Electrodeposited Coatings of Rhodium for Engineering Use.

We have two suggestions for specifying the plating of Rhodium:

1. Thickness of the deposit should be minimized. Electroplated Rhodium deposits tend to develop a highly fractured crystal structure. Likewise, this high fracture crystal structure contributes directly to the hardness and durability of the Rhodium surface. However, as the thickness of the deposit increases the possibility of the electrodeposit fracturing and delaminating from the substrate increases. When appropriately maintained, a Rhodium electrodeposit of up to 100 micro inches (2.5 microns, 0.000100 inches) is often attained.

A general Rhodium thickness would be 20 -30 micro inches. Please call us regarding your specific requirement.

2. Finally, it is our standard practice to undercoat all Rhodium plating with a thin layer of Gold and electroless Nickel. Furthermore, we suggest that a thin Gold under-layer be included in the plating specification. Generally, plating specifications require only a nickel underplate for performance. However, in conjunction with a Nickel layer and proper bath maintenance, the Gold under-layer will provide the most stress-free, dependable electrodeposit. 

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