H. Cross Company - Precision Metal Ribbons and Strips
H. Cross Company - Precision Metal Wire

Rhodium
Rhodium Periodic Table

Table of Contents
 

Standard Dimensions and Tolerances

History
Properties
Fabrication and Forms
Sources
Uses
Packaging


History

William Hyde Wollaston discovered rhodium in 1803-4 in crude platinum ore from South America rather soon after his discovery of another element, palladium. He dissolved the ore in aqua regia (a mixture of hydrochloric and nitric acids), neutralized the acid with sodium hydroxide (NaOH), and precipitated the platinum by treatment with ammonium chloride, NH4Cl, as ammonium chloroplatinate. Palladium was then removed as palladium cyanide by treatment with mercuric cyanide. The remaining material was a red material containing rhodium chloride salts from which rhodium metal was obtained by reduction with hydrogen gas.

Properties

Rhodium metal is silvery white. Rhodium has a higher melting point and lower density than platinum. It has a high reflectance and is hard and durable. Upon heating it turns to the oxide when red and at higher temperatures turns back to the element. It is a major component of industrial catalytic systems.

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Sources

The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. Sometimes extraction of the precious metals such as rhodium, platinum and palladium is the main focus of a particular industrial operation while in other cases it is a byproduct. The extraction is complex because of the other metals present and only worthwhile since rhodium is the basis of very important catalysts in industry.

Preliminary treatment of the ore or base metal byproduct is required to remove silver, gold, palladium, and platinum. The resulting residue is melted with sodium bisulphate (NaHSO4) and the resulting mixture extracted water to give a solution containing rhodium sulphate, Rh2(SO4)3. The rhodium is precipitated out as the hydroxide by addition of sodium hydroxide, NaOH, and redissolved in hydrochloric acid, HCl, to give H3RhCl6. This is treated with NaNO2 and NH4Cl to form a precipitate of the rhodium complex (NH4)3[Rh(NO2)6]. Dissolution of the precipitate in HCl gives a solution of pure (NH4)3RhCl6. Evaporation to dryness and burning under hydrogen gas gives pure rhodium.

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Uses

The following uses of rhodium are gathered from a variety of sources.

  • Alloying agent to harden platinum and palladium. Such alloys are used for furnace windings, thermocouple elements, bushings for glass fibre production, electrodes for aircraft spark plugs, and laboratory crucibles
  • Used as an electrical contact material as it has a low electrical resistance, a low and stable contact resistance, and is highly resistant to corrosion
  • Plated rhodium produced by electroplating or evaporation is exceptionally hard and is used for optical instruments
  • Used for jewelry
  • Industrial catalyst
  • Rhodium is used as part of the catalytic system in car catalytic converters, used to clean up exhaust gases to some extent
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Fabrication and Forms

H Cross Company can provide Rhodium in commercially pure grade in wire sizes from .005" diameter up to .100" diameter, strips and ribbons from .0005" thick to .020" thick and from .020" to .100" wide and in sheet or foil form from .0005" thick to .020" thick and up to 2" wide. Please email us if you have needs outside of these ranges, as we will always try to be of assistance for your specific requests.

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Packaging

Each H. Cross Company product is delivered in packaging specifically designed for the product's application. As an example, wire is furnished on returnable plastic reels, each containing a single length of wire. Strips, Ribbons, Sheets and foils are flat packed to prevent damage during shipping. If required, H. Cross Company can adapt standard packaging methods or develop new ones for your special needs.