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Introduction to rare metals - rhenium

1 Chemical properties of rhenium

The color of rhenium is very similar to platinum. Its melting point is 3160℃, which is close to the melting point of tungsten, but its evaporation rate is very low. At 2200℃, the vapor pressure is 133.3x10-*Pa (1.0x10-°Torr). Among refractory metals, rhenium has a higher resistivity (19.8μΩ.cm at 20℃) and good mechanical properties. It can be seen that the properties of rhenium can meet most of the requirements of electric vacuum metals.

After annealing, the relative elongation of rhenium wire is 25%, and its plasticity is similar to that of molybdenum, and it remains unchanged after mechanical processing.

The chemical properties of rhenium are the most stable among refractory metals. In oxygen, rhenium can only be oxidized when the heating temperature reaches 100℃. Rhenium does not work with hydrogen and nitrogen, but it can form carbides with carbon. From the perspective of the effect of rhenium and gas, it is a metal with excellent vacuum properties.

Rhenium is stable to any acid except nitric acid. Rhenium can react with molten alkali.

2 Uses of Rhenium

Rhenium was discovered only in 1925. Not only was it discovered relatively late, but it is also a rare metal that is dispersed and mixed in the ores of certain metals. Therefore, it is not as widely used as other refractory metals.

Rhenium and tungsten are made into tungsten-rhenium alloy wire. Adding (3-5)% rhenium to pure tungsten can increase the recrystallization temperature of tungsten wire, improve mechanical strength and ductility, and improve corrosion resistance and resistivity. Due to the significant improvement in the performance of tungsten wire, the shock resistance, reliability and life of the lamp are improved.

Because the incandescent filament is required not to fall, an alloy with WA1: as the base and low rhenium content (WA1: powder containing silicon, aluminum and potassium as the base, the rhenium content is generally less than 5%) should be used.

Tungsten-rhenium alloy wire can be used to make spiral bulbs, shock-resistant bulb filaments, bent filaments and filaments with special requirements. If WA1-Re3% rhenium tungsten alloy wire is used to make high-power (100W) fluorescent lamp cathode filaments, the ignition life of the lamp tube can be increased to 5000~8000h.

The maximum diameter of tungsten-rhenium wire (WA1-Re) is 1800μm, and the minimum diameter is 12μm. The tungsten filament inner lead of halogen tungsten lamp is easily corroded by bromine. Using 1-3% rhenium tungsten-rhenium alloy wire as the inner lead can prevent bromine corrosion. If the inner lead is relatively thick, the bromine concentration is low when the lamp is working, and the rated life of the lamp is short, the inner lead content of 0.1% rhenium is sufficient. The inner lead can be made into a spiral or a straight line. In addition to tungsten-rhenium alloy, rhenium can also be plated on the tungsten inner lead by vapor phase spraying. The lamp can be filled with hydrogen bromide or dibromomethane. Tungsten-rhenium alloy can be used in spotlights, infrared radiation sources, photographic lights, etc.

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