Chemical Fact Sheet
Rhodium
| Chemical Abstract Number (CAS #) | 7440-16-6 |
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| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Rh |
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Synopsis
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Rhodium - (Gr. rhodon, rose), Rh; at. wt. 102.90550(3); at. no. 45; m.p. 1964 +/- 3 deg C; b.p. 3695 +/- 100 deg C; sp. gr. 12.41 (20 deg C); valence 2, 3, 4, 5, and 6. Wollaston discovered rhodium in 1803-4 in crude platinum ore he presumably obtained from South America. Rhodium occurs native with other platinum metals in river sands of the Urals and in North and South America. It is also found with other platinum metals in the copper-nickel sulfide ores of the Sudbury, Ontario region. Although the quantity occurring here is very small, the large tonnages of nickel processed make the recovery commercially feasible. The annual world production of rhodium is only 7 or 8 tons. The metal is silvery white and at red heat slowly changes in air to the sesquioxide. At higher temperatures it converts back to the element. Rhodium has a higher melting point and lower density than platinum. Its major use is as an alloying agent to harden platinum and palladium. Such alloys are used for furnace windings, thermocouple elements, bushings for glass fiber production, electrodes for aircraft spark plugs, and laboratory crucibles. It is useful 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. It has a high reflectance and is hard and durable. Rhodium is also used for jewelry, for decoration, and as a catalyst. Forty four isotopes and isomers are now known. Soluble salts should not exceed 0.01 mg/cu. m. Rhodium metal (powder) costs about $300/g (99.9% pure). |
| Use | In alloy with platinum for catalysts & thermocouples; for spinnerets in rayon prodn; for glass-fiber bushings; for furnace winding; component of dental alloys; electroplating agent for bright or reflective surfaces; for electrical contacts; ingredient in gold decorations on glass & porcelain As a corrosion-resistant electroplate for protecting silverware from tarnishing; for making high-reflectivity mirrors for cinema projectors & searchlights; spongy or black form as catalyst in organic hydrogenation or organic oxidation reactions Plating optical instruments; for jewlery & decoration Strong, complexing agent |
| Consumption Patterns | 44% as a catalyst; 22% in electrical applications; 13% for electroplating jewelry; 12% for decorating glass & porcelain; 9% in misc applications (1975) |
| Apparent Color | white, hard, ductile, malleable metal; bluish-gray luster; gray-white, cubic crystals |
| Boiling Point | 3727 deg C |
| Melting Point | 1966 deg C |
| Molecular Weight | 102.905 |
| Density | 12.41 @ 20 deg C |
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Chemical and Physical Properties |
Electrical resistivity: 4.51 ohms at 0 deg C; brinnell hardness: 100; natural isotope: 103 Solid phase-temperature of transition (deg k): 2240; liquid phase-temperature of transition (deg k) 4150; heat of transition (kcal/g mole): solid phase 5.2; liquid phase 127; entropy of transition (eu): solid phase 2.3; liquid phase 30.7; entropy at 298 deg k (eu): solid phase 7.6 magnetic susceptibility (temp k= 298 deg) 111.0X10-6 cgs; (temp k= 723 deg) 123.0X10-6 cgs |
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Environmental Impact |
Risks arising in production of the metal are those associated with corrosive & oxidizing substances like nitric acid & sodium peroxide. |
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Environmental Fate |
Belongs to the platinum group of metals. One of the rarest elements; constitutes about 1X10-7% of the crust of the earth; found in small quantities associated with all native platinum; in minerals rhodite, sperryline & iridosmine; discovered in 1803 by Wollaston In some nickel-copper ores. Obtained from South America. In river sands of the Urals & in North America & South America. With other platinum metals in copper-nickel sulfide ores of the Sudbury, Ontatio, region. |
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