Difference between revisions of "Rhenium"
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Heating must be done slowly because ammonium perrhenate decomposes to volatile [[Rhenium(VII) oxide|Re<sub>2</sub>O<sub>7</sub>]] starting at 250 °C. When heated in a sealed tube at 500 °C, APR decomposes to [[rhenium dioxide]]: | Heating must be done slowly because ammonium perrhenate decomposes to volatile [[Rhenium(VII) oxide|Re<sub>2</sub>O<sub>7</sub>]] starting at 250 °C. When heated in a sealed tube at 500 °C, APR decomposes to [[rhenium dioxide]]: | ||
| − | : | + | :2 NH<sub>4</sub>ReO<sub>4</sub> → 2 ReO<sub>2</sub> + N<sub>2</sub> + 4 H<sub>2</sub>O |
Melting the powder can only be done using an electric arc furnace, in an inert atmosphere. | Melting the powder can only be done using an electric arc furnace, in an inert atmosphere. | ||
Revision as of 20:12, 20 February 2020
| General properties | |||||
|---|---|---|---|---|---|
| Name, symbol | Rhenium, Re | ||||
| Appearance | Silvery-gray metal | ||||
| Rhenium in the periodic table | |||||
| |||||
| Atomic number | 75 | ||||
| Standard atomic weight (Ar) | 186.207(1) | ||||
| Group, block | VII; d-block | ||||
| Period | period 6 | ||||
| Electron configuration | [Xe] 4f14 5d5 6s2 | ||||
per shell | 2, 8, 18, 32, 13, 2 | ||||
| Physical properties | |||||
| Silvery-gray | |||||
| Phase | Solid | ||||
| Melting point | 3459 K (3186 °C, 5767 °F) | ||||
| Boiling point | 5869 K (5596 °C, 10,105 °F) | ||||
| Density near r.t. | 21.02 g/cm3 | ||||
| when liquid, at | 18.9 g/cm3 | ||||
| Heat of fusion | 60.43 kJ/mol | ||||
| Heat of | 704 kJ/mol | ||||
| Molar heat capacity | 25.48 J/(mol·K) | ||||
| pressure | |||||
| Atomic properties | |||||
| Oxidation states | 7, 6, 5, 4, 3, 2, 1, 0, −1, −3 (a mildly acidic oxide) | ||||
| Electronegativity | Pauling scale: 1.9 | ||||
| energies |
1st: 760 kJ/mol 2nd: 1260 kJ/mol 3rd: 2510 kJ/mol (more) | ||||
| Atomic radius | empirical: 137 pm | ||||
| Covalent radius | 151±7 pm | ||||
| Miscellanea | |||||
| Crystal structure | hexagonal close-packed (hcp) | ||||
| Speed of sound thin rod | 4700 m/s (at 20 °C) | ||||
| Thermal expansion | 6.2 µm/(m·K) | ||||
| Thermal conductivity | 48.0 W/(m·K) | ||||
| Electrical resistivity | 193 Ω·m (at 20 °C) | ||||
| Magnetic ordering | Paramagnetic | ||||
| Young's modulus | 463 GPa | ||||
| Shear modulus | 178 GPa | ||||
| Bulk modulus | 370 GPa | ||||
| Poisson ratio | 0.30 | ||||
| Mohs hardness | 7.0 | ||||
| Vickers hardness | 1350–7850 MPa | ||||
| Brinell hardness | 1320–2500 MPa | ||||
| CAS Registry Number | 7440-15-5 | ||||
| History | |||||
| Naming | after the river Rhine (German: Rhein) | ||||
| Discovery and first isolation | Masataka Ogawa (1908) | ||||
| Named by | Walter Noddack, Ida Noddack, Otto Berg (1922) | ||||
Rhenium is a chemical element with symbol Re and atomic number 75. It is a silvery-gray or silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust.
Contents
Properties
Chemical
Rhenium resembles manganese and technetium chemically. Rhenium has good chemical resistance to acids, such as sulfuric acid, hydrochloric acid, aqua regia, as well as alkalis, but it dissolves in concentrated nitric acid. It also reacts with halogens at high temperatures, such as fluorine at 400 °C.
Physical
Rhenium is a silvery-white (or gray) hard metal. Rhenium has with one of the highest melting points of all elements (3186 °C), third after tungsten and carbon (though carbon is not a metal and does not melt under standard pressure). It also has the highest boiling point of all elements (5596 °C). Rhenium's density (21.02 g/cm3) is only exceeded by platinum, iridium and osmium. These properties make rhenium a valuable metal in the manufacturing of superalloys.
Availability
Rhenium is sold by various chemical suppliers and other metal companies, though it's not cheap.
Isolation
Rhenium can be obtained by reducing ammonium perrhenate at high temperatures with a reducing agent, such as hydrogen.
- 2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3
Heating must be done slowly because ammonium perrhenate decomposes to volatile Re2O7 starting at 250 °C. When heated in a sealed tube at 500 °C, APR decomposes to rhenium dioxide:
- 2 NH4ReO4 → 2 ReO2 + N2 + 4 H2O
Melting the powder can only be done using an electric arc furnace, in an inert atmosphere.
Projects
- Make ammonium perrhenate
- Metal coatings
- Catalysts
- Make rhenium(VII) oxide
Handling
Safety
Little is known about rhenium's biological effects. Medical studies performed on animals indicate that both the metal and its salts show little toxicity, though only potassium perrhenate and rhenium trichloride have been tested.
Storage
Rhenium can be stored in any container, though it should be kept away from nitric acid.
Disposal
Due to its rarity, it's best to recycle rhenium and its compounds as much as possible, instead of throwing it away.
