Rhodium Plating Services

ProPlate® provides rhodium plating services for electrical contacts, connectors, aerospace components, and high-wear precision applications requiring exceptional hardness, corrosion resistance, and stable electrical performance.

ProPlate® provides rhodium plating services for a wide range of industrial, aerospace, electronics, and semiconductor applications. Rhodium is one of the hardest and most corrosion-resistant precious metals available, making it the preferred finish for sliding electrical contacts, high-wear connectors, and components requiring exceptional surface stability over long service lives. ProPlate plates rhodium on small and large parts using barrel and rack methods to ASTM B634, MIL-R-46085, and AMS 2413E specifications.

Rhodium (Rh): Properties and Applications

Rhodium is a silvery-white, hard, and chemically inert precious metal that does not oxidize. It is one of the platinum group metals, which also includes Ruthenium, Iridium, Platinum, Osmium, and Palladium. These six metals share common physical properties: very high density, high melting points, and exceptional corrosion resistance. Rhodium is extremely durable with a Vickers Hardness of 1246 MPa, resistant to corrosion, tarnish, and scratches, with a boiling point of 3727°C and a melting point of 1966°C.

Rhodium’s inertness against corrosion and aggressive chemicals makes it ideal for protecting sliding electrical contacts from wear and galling. It is also useful in high voltage and high amperage electrical contacts to prevent oxide formations on the contact surface. Rhodium has a much whiter appearance than palladium and platinum.

For rhodium plating requirements, ProPlate® has capabilities for rhodium electroplating both small and large parts using barrel and rack plating methods, along with custom and prototype metal finishing.

Rhodium Plating Applications

Rhodium’s exceptional hardness, stable contact resistance, and corrosion resistance make it one of the most specified precious metal finishes for high-reliability electrical and mechanical applications.

Electrical Contacts and Connectors

Rhodium plating is widely specified for sliding electrical contacts, relay contacts, connector pins, and switches in telecommunications, aerospace, defense, semiconductor, and electronics applications. Rhodium’s low and stable contact resistance, high hardness (800-1000 HV), and excellent resistance to wear and galling make it the preferred finish for contacts subject to repeated mating cycles and mechanical stress. Typical coating thickness ranges from 0.5 to 2.5 microns for electronics applications and 2.5 to 10 microns for high-reliability aerospace and military applications.

Aerospace and Defense

Rhodium plating is specified for high-wear electrical connectors, switches, and contacts in avionics and aerospace systems that must perform reliably under vibration, temperature extremes, and chemically aggressive environments. Its high melting point, resistance to oxidation, and exceptional hardness make it well suited for aerospace components including electrical contacts, bearing surfaces, and sensor housings subjected to severe environmental stress.

Semiconductor and Electronics

Rhodium’s reflectivity and stability under ion bombardment make it suitable for niche sputtering targets and specialized electronic applications. It is widely used in electrical contacts, relays, and PCB connectors that must maintain conductivity and corrosion resistance over long operating cycles. ProPlate provides rhodium plating for electrical contacts, PCBs, and semiconductor components through our Semiconductors & Electronics plating capabilities.

Optical and Reflective Components

Rhodium provides one of the highest optical reflectivity levels of any metal in the visible spectrum while maintaining that reflectivity over time without tarnishing. It is specified for mirrors, optical instruments, reflective coatings, and precision scientific equipment where long-term surface stability is critical.

High-Temperature Applications

Rhodium alloyed with platinum is used in specialized thermocouples for high-temperature measurement in industrial furnaces and aerospace systems. Its exceptional thermal stability and resistance to oxidation at elevated temperatures make it well suited for components operating in extreme thermal environments.

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Rhodium Properties

Rhodium provides exceptionally uniform coverage over complex geometries and fine features, forming a dense, continuous plated surface. Its strong throwing power allows rhodium to effectively coat recessed areas and intricate details, helping to minimize porosity and reduce the formation of pinholes that could compromise performance.

Because rhodium deposits are extremely hard, highly reflective, and resistant to corrosion and wear, rhodium is well suited as a high-performance finish layer. Rhodium maintains its surface integrity in aggressive environments and under repeated use, offering long-term durability, tarnish resistance, and a bright, lustrous finish for applications requiring exceptional surface stability and reliability.

Rhodium - Rh
Atomic Number	45	Thermal Conductivity - W/(m*K)	150
Atomic Weight - g/mole	102.91	Electrical Resistivity - (Ohm*m)	4.30E-08
Density - g/cm³	12.4	Electrical Conductivity - (S/m)	2.30E-07
Melting Point - C°	1964	Hardness - Hv	1246
Melting Point - F°	3567	Specific Heat Capacity - J/(kg*K)	240

Rhodium Plating Specifications

ProPlate provides services per the certified ASTM B634, MIL-R-46085, and AMS 2413E plating specifications. Company specific specifications can also be provided if requested.

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.

Rhodium Plating to ASTM B634

3.1: Classification – Electrodeposited coatings of rhodium on the basis of thickness are classified as follows

Class 0.05 – 0.05µ minimum thickness
Class 0.25 – 0.25µ minimum thickness
Class 0.5 – 0.5µ minimum thickness
Class 1 – 1µ minimum thickness
Class 2.5 – 2.5µ minimum thickness
Class 6.25 – 6.25µ minimum thickness

5.2.2: Stress Relief Treatment – All steel parts having an ultimate tensile strength of 1050 MPa (approximately 35 HRC) and above and that have been machined, ground, cold formed, or cold straightened shall have heat treatment to 190°C +/- 15°C for a minimum of 8 hours within 4 hours after electroplating.

5.3.1: Embrittlement Relief – Steel parts having an ultimate tensile strength of 1200 MPa (approximately 38 HRC) or greater shall be baked at 190°C +/- 15°C for a minimum of 8 hours within 4 hours after electroplating.
Steel parts having an ultimate tensile strength greater than 1300 MPa (approximately 40 HRC) shall be baked at 190°C +/- 15°C for a minimum of 23 hours within 4 hours after electroplating.

6.2: Thickness – The rhodium coating thickness on all significant surfaces shall conform to the requirements of the specified class as defined in Section 3.

S14: Undercoats – Surfaces other than gold, platinum, or silver shall be electroplated with nickel or with copper followed by nickel in accordance with B456 except for the thickness requirements.
Corrosion or heat resistant steels shall have a minimum of 2.5µ of nickel or as otherwise specified by the purchaser.

Rhodium Plating to MIL-R-46085

1.2: Classification – Rhodium plating shall be of the following classes:

Class 1 – 0.000002 inch thick, minimum
Class 2 – 0.00001 inch thick, minimum
Class 3 – 0.00002 inch thick, minimum
Class 4 – 0.00010 inch thick, minimum
Class 5 – 0.00025 inch thick, minimum

3.3.1: Plating Application – Unless otherwise specified in the contract or order, the plating shall be applied after all machining, brazing, welding, forming, and perforating of the article have been completed.

3.3.2: Embrittlement relief – All ferrous parts having hardness of Rockwell C40 and higher shall be baked at a minimum of 190°C (375°F) for 3 hours or more within 4 hours after plating to provide hydrogen embrittlement relief.

3.5: Underplating – Surfaces other than gold, silver, platinum, or nickel shall be plated with nickel or copper plated as applicable in accordance with QQ-N-290.
An underplating of nickel shall be used on parts of corrosion or heat resistant steels.
The nickel plating shall be of such thickness that after under plating the rhodium thickness meets the thickness requirements.

3.6: Thickness – Thickness of the plating shall be in accordance with the requirements of the class specified by procurement agency.

6.1: Intended Use – Rhodium plating of metallic parts is intended to protect electrical connectors, prevent galling of sliding electrical contacts, furnish a highly decorative finish and provide mirror surface which is highly reflective and non-tarnishing.

Rhodium Plating to AMS 2413E

3.2.2: Copper Flash or Copper Strike – Except as specified in 3.2.2.1., a copper flash or copper strike shall be electrodeposited from a suitable copper plating solution.

3.2.2.1: Nickel Flash or Nickel Strike – When parts to be plated are made of a corrosion-resistant alloy, a nickel flash or nickel strike shall be electrodeposited instead of the copper flash or copper strike.

3.2.3: Silver Plating – Parts shall be plated by electrodeposition of silver from a suitable silver plating solution directly onto the flash or strike surfaces of 3.2.2 or 3.2.2.1.

3.2.4: Rhodium Plating – Parts shall be plated by electrodeposition of rhodium from a rhodium sulfate, rhodium phosphate, or other suitable rhodium plating solution onto the silver plating surfaces.

3.3: Hydrogen Embrittlement Relief – After plating, rinsing and drying, ferrous parts shall be treated in accordance with AMS 2759/9 using the parameters specified for cadmium.

3.4.1: Thickness – Shall be as follows unless otherwise specified

3.4.1.1: Copper or Nickel Flash or Strike – Not less than 0.0001 inch (2.5µ)
3.4.1.2: Silver Plate – Not less than 0.0005 inch (12.7µ)
3.4.1.3: Rhodium Flash – Not less than 0.000002 inch (0.5µ)
3.4.1.4: The plate shall be uniform in thickness on significant surfaces except that slight build-up on exterior corners or edges will be permitted provided drawing dimensions are met.

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Recommendations for Specifying Rhodium Plating

As Rhodium is a very dense metal, when it is used for electroplating, the thickness of the Rhodium coating should be as thin 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.

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.

Related Resources

Semiconductors & Electronics — Rhodium plating for electrical contacts, PCBs, and semiconductor components
Aerospace & Defense — Rhodium plating for high-wear aerospace electrical contacts and connectors
Rhodium Plating for Enhanced Durability in Aerospace Applications — ProPlate blog post
Rhodium Electroplating: Meeting Stringent Standards for Performance and Reliability — ProPlate blog post
Plating Methods — Barrel and rack plating capabilities

Frequently Asked Questions About Rhodium Plating Services

What is rhodium plating used for?

Rhodium plating is used for applications requiring exceptional hardness, corrosion resistance, and stable electrical contact performance. Common applications include sliding electrical contacts, relay contacts, connector pins, switches, optical reflective coatings, aerospace components, and precision scientific instruments. Rhodium is specified where wear resistance, tarnish resistance, and long-term surface stability are critical requirements.

What rhodium plating specifications does ProPlate plate to?

ProPlate provides rhodium plating services to ASTM B634, MIL-R-46085, and AMS 2413E specifications. Available thickness classes range from Class 0.05 (0.05µ minimum) through Class 6.25 (6.25µ minimum) per ASTM B634. Company-specific specifications can also be accommodated upon request.

What thickness of rhodium plating does ProPlate recommend?

Because rhodium deposits develop a very dense, highly fractured crystal structure that contributes to hardness and durability, the coating should be as thin as possible for the application. Thicker deposits are more likely to crack or flake. Good manufacturing practice dictates a rhodium electrodeposit of up to 100 microinches (2.5 microns) as a standard maximum. Typical thickness is 0.5 to 2.5 microns for electronics applications and 2.5 to 10 microns for high-reliability aerospace and military applications.

What underplate is recommended for rhodium plating?

Per ASTM B634, surfaces other than gold, platinum, or silver shall be electroplated with nickel or with copper followed by nickel before rhodium plating. Corrosion or heat resistant steels require a minimum of 2.5 microns of nickel. ProPlate also recommends a thin layer of gold under all rhodium plating where feasible, as this results in a dependable, stress-free electrodeposit even though typical specifications require a nickel undercoat.

What industries use rhodium plating services?

Rhodium plating is used in aerospace and defense, semiconductor and electronics, telecommunications, energy technology, and optical and scientific instrument manufacturing. ProPlate’s largest rhodium plating applications include electrical contacts, connector pins, relay contacts, PCB components, and aerospace connectors requiring high wear resistance and corrosion protection.

Is rhodium biocompatible for medical device applications?

Rhodium has good corrosion resistance and is generally considered inert, which gives it some biocompatibility characteristics. However rhodium is not as widely specified for implantable medical device applications as gold or platinum. ASTM B634 notes that rhodium plating is applicable to commercial, industrial, and medical device applications. If rhodium is being considered for a specific medical device application, ProPlate recommends evaluating biocompatibility requirements against the specific application and regulatory pathway.

What plating methods does ProPlate use for rhodium plating?

ProPlate plates rhodium using both barrel and rack methods. Barrel plating is suited for high volumes of small, robust parts. Rack plating is used for larger components, delicate parts, or applications requiring more precise thickness control and part handling. Custom engineered fixtures are available for components with selective coverage requirements or complex geometries.