Rhodium is a silver-white metallic element that is highly reflective and resistant to corrosion. It is considered the rarest and most valuable precious metal in the world — well above gold or silver.
- Density: 12.41 grams per cubic centimeter
- Phase at room temperature: Solid
- Melting point: 3,567 degrees F (1,964 degrees C)
- Boiling point: 6,683 degrees F (3,695 degrees C)
The main use for rhodium is in catalytic converters designed to clean vehicle emissions. Rhodium — often together with palladium and/or platinum — accomplishes this by reducing nitrogen oxide in exhaust gas. Without rhodium catalysts, the air in our cities would be much worse due to vehicle exhausts.
Since rhodium is quite brilliant and resistant to tarnishing, it is used as a finish for jewelry, searchlights and mirrors. It is also alloyed with platinum for aircraft turbine engines. In the chemical industry, rhodium is used as a catalyst in the making of nitric acid, acetic acid and hydrogenation reactions, according to the Royal Society of Chemistry (RSC).Other uses for rhodium are coating optic fibers, crucibles, thermocouple elements and headlight reflectors. Since it has a low electrical resistance and is highly resistant to corrosion, it is used as an electrical contact material as well.
Rhodium is often alloyed with platinum and iridium to make an oxidation-resistant metal that can stand against high temperatures. These alloys are used in furnace windings, pen nibs, phonograph needles, high-temperature thermocouple and resistance wires, electrodes for aircraft spark plugs, bearings and electrical contacts.
Rhodium has no known biological use and no known use for life processes. While some compounds of rhodium are carcinogenic, there are almost no reported cases of humans being affected by this element in any way. This may be because rhodium compounds are encountered so rarely. Test on plants have shown that it is the least toxic member of the platinum group of metals.
Although rhodium is generally considered non-toxic, some of its compounds are toxic and carcinogenic