Rhodium was discovered by British chemist William Hyde wollaston in 1803. Shortly after the discovery of palladium, he discovered rhodium again. Firstly, the crude platinum is dissolved in aqua regia, then the excess acid is neutralized by caustic soda NaOH, and platinum containing ammonium chloride and palladium containing mercury cyanide are precipitated in the neutralized solution, and then the filter residue is treated with hydrochloric acid, which should be thoroughly dried to avoid excessive mercury cyanide. The residue after ethanol treatment is dark red rhodium salt and sodium salt powder. Rhodium can be produced without heating the powder in a hydrogen stream.
Rhodium is obtained from the by-product of nickel production. It also exists in platinum ores and is used as a catalyst in some platinum alloys.
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Rhodium is mainly used as wear-resistant coating and catalyst for high-quality scientific instruments, and rhodium-platinum alloy is used to produce thermocouples. It is also used for electroplating headlights, telephone repeaters, pen tips, etc.
Automobile manufacturing is the largest user of rhodium. At present, the main application of rhodium in automobile manufacturing industry is automobile exhaust catalyst. Other industrial sectors that consume rhodium are glass manufacturing, dental alloy manufacturing and jewelry products. With the continuous development of fuel cell technology and the gradual maturity of fuel cell vehicle technology, the usage of rhodium in automobile industry will continue to increase.
Platinum group metals and alloys have many important industrial uses. In the past, the production of distillation still mainly used concentrated lead chamber method to produce dilute sulfuric acid, and the standard scale and weight were also made of platinum-iridium alloy. /kloc-in the middle of the 0/9th century, Russia made platinum-iridium gold coins and circulated them in the market. At present, the main use of platinum group metals and their alloys is to manufacture catalysts. Platinum-rhodium alloy has special corrosion resistance to molten glass and can be used to manufacture crucibles for producing glass fibers. Platinum-iridium, platinum-rhodium and platinum-palladium alloys have high arc combustion resistance and are used as electrical contact alloys, which is one of the main uses of platinum. Because of the stable chemical properties of platinum, experimental utensils made of pure platinum, platinum-rhodium alloy or platinum-iridium alloy, such as crucibles, electrodes and resistance wires, are necessary for chemical laboratories. Platinum-cobalt alloy is a machinable hard magnetic material with high magnetic energy product. Platinum and platinum alloys are widely used to make all kinds of jewelry, especially diamond-encrusted rings, watchcases and brooches. Alloys of platinum or palladium can also be used as dental materials. Platinum, palladium and rhodium can be used as electroplating layers, which are often used in electronic industry and jewelry processing. In recent years, titanium anode coated with ruthenium and platinum has replaced graphite anode in electrolytic cell, which improves electrolytic efficiency and prolongs electrode life. This is an important technological progress in chlor-alkali industry, which opens up a new way for the industrial application of ruthenium. Osmium-iridium alloy can be used to make pen tips and iron pens. Palladium alloy is also used to make hydrogen purification materials and high temperature brazing materials. Platinum coating equipment is also used in chemical industry.