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Properties of rhenium

Physical properties of rhenium
Rhenium is a very hard, silver-white metal, looks just like platinum, but pure rhenium powder is generally gray. The physical properties of rhenium are very similar to that of refractory metal molybdenum and tungsten in VII group of the periodic table, and sort of similar to platinum group metals, especially platinum, ruthenium and osmium. Rhenium is a refractory metal, with melting point of 3180°C, second only to tungsten, and same to molybdenum and tungsten that are good refractory metals. Rhenium has a big specific gravity, but the relative density is 21.03g/cm3, only lower than platinum, iridium and osmium. This property makes rhenium the densest metal other than platinum group metals, with great hardness, wear resistance and corrosion resistance. Rhenium has a very high mechanical strength. Rhenium alloy wire thinner than a human hair is able to withstand more than seven kilograms of gravity. In addition, rhenium has other electrical properties such as high resistance, with resistivity 3.84 times to tungsten. Its modulus of elasticity and mechanical properties are similar to iron. Natural rhenium consists of two isotopes Re187 and Re185. Re187 is radioisotope, accounting for 62.6% in natural rhenium; Re185 is non-radioactive isotope, accounting for 37.2%. The half-life of Re187 is 43 million a, emitting very weak radiation that can not wear through the skin or harm to the human body.

Chemical properties of rhenium
Rhenium is stable in chemical properties, highly corrosion-resistant, free of being oxidized in air, and strongly resistant to the corrosive effect of acids and bases. Rhenium is stable at room temperature, and begins to be oxidized from 300°C. At high temperature, rhenium can generate rhenium disulfide with sulfur vapor, and generate halides with fluorine, chlorine and bromine. Rhenium is insoluble in hydrochloric acid, and soluble in nitric acid and hot sulfuric acid to generate high rhenium acid (HReO4). Rhenium has a strong affinity to oxygen. Its oxidation state are + 1, + 2, + 3, + 4, + 5, + 6, + 7, and its oxides are Re2O, Re2O3, ReO2, ReO3, Re2O7. High valence oxide of rhenium (Re2O7) is soluble in water, usually processed into stable salts such as ammonium perrhenate (NH4ReO4) and rhenium potassium (KReO4). Rhenium does not react with carbon, and is the only refractory metal element that does not generate carbide with carbon. The most prominent chemical property of rhenium is the high volatility of Re2O7, and easy to dissolve in water and oxygenated solvents. These two properties are used extensively in rhenium recove. Rhenium aqueous solution is acidic, and its electromotive force is between copper and thallium, therefore, iron and zinc can precipitate rhenium in aqueous solution.