Rhodium (Rhodium in English) is a silvery hard metal with high reflectivity. Rhodium metal usually does not form oxides. Even when heated, oxygen in the atmosphere is absorbed only when rhodium is heated to the melting point, but is released during solidification.
Chemical elements are divided into four categories.
1 belongs to gaseous simple materials and can be considered as elements: light, heat, oxygen, nitrogen and hydrogen.
2. Simple nonmetallic substances that can be oxidized into acids: sulfur, phosphorus, carbon, hydrochloric acid group, hydrofluoric acid group and boric acid group.
3. Simple metal substances that can be oxidized into salts: antimony, arsenic, silver, cobalt, copper and tin. Iron, manganese, mercury, molybdenum, gold, platinum,
Lead, tungsten and zinc.
4. Simple soil capable of forming salt: lime, bitter soil, heavy soil, bauxite and silica.
Rhodium is a blue-white metal similar to aluminum, which is hard and brittle, has strong reflective ability and is particularly soft when heated. Rhodium has good chemical stability. Rhodium has good oxidation resistance and can keep luster in the air for a long time. At high temperature, rhodium reacts with oxygen to generate volatile oxides, increasing its evaporation rate.
When rhodium is heated, it will be covered by a black oxide film, and when the temperature exceeds 1200℃, the oxide film disappears. Rhodium has high corrosion resistance to acids (except concentrated sulfuric acid), aqua regia and sulfur, chlorine and fluorine.
Rhodium has good high temperature strength, but poor cold plasticity. 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.
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.