Molybdenum thread has unique properties. It is resistant to aggressive environments, withstands vacuum high temperature up to 1800 °C. Molybdenum filament compared with tungsten easier almost doubled, so molybdenum products have high specific strength (at a temperature of not more than 1370 °C).
Practically the only disadvantage is the high cost of such yarns, since molybdenum is a metal belonging to rare earth elements and in its pure form is quite difficult to identify. Besides, he is refractory and hard to work.
Molybdenum reacts with hydrochloric, sulfuric acids only at the temperature. 80−100°C. Nitric acid, Aqua Regia dissolved molybdenum only when температуре100°C. In cold alkaline solutions it is stable, but in hot alkaline solutions the molybdenum slowly being destroyed. Impurities of carbon, oxygen, silicon, aluminum, nitrogen, iron, sulfur and calcium, phosphorus, contained in the technical molybdenum in hundredths or thousandth fractions of a percent, significantly affect the properties of molybdenum. The bulk of these impurities makes molybdenum more fragile. Most harmful of all impurities is oxygen. If it is contained in a volume 0,0008−0,004%, the low-melting oxides can lead to a sharp increase in its brittleness and a decrease in properties to plastic deformation, especially in the simultaneous presence of carbon with nitrogen. With increasing percentage of oxygen than 0.015% molybdenum is not handled the pressure and becomes brittle.
|The temperature at which the obtained data the features of t°C||20°C|
|The linear thermal expansion coefficient α [1/°C]||Of 4.9x10-6|
|The melting temperature t°C||2620°C|
|Specific heat at 20 °C [kJ/(kg·deg)]||0,256|
|The thermal conductivity K [W/(m·K)]||142|
|Electrical resistivity R, Mhmm2/m||0,054|
First, rolling in a rotary swaging machine hot billet, are made of molybdenum wire of diameter from 1 to 10 mm. After that, with the help of drawing wire is pulled into a thin thread. It is sometimes produced from pure molybdenum MCH, MCIT, or with the addition of chromium, cobalt. In this case, the workability, the strength of the fiber increases. From one kilogram of molybdenum rolled thread length of about 3 km.
|True annealing temperature, ° C||Diameter molybdenum filament|
|1500−1550||200 — 800 µm|
|1450−1500||801 — 1000 µm|
|1400−1450||1001 — 1250 µm|
|1300−1350||1251 — 2500 µm|
Molybdenum filament, and tungsten is used in lighting devices. Depending on the condition and diameter of the surface is made respiratoorse and spiral cathodes, springs, nets, springs of semiconductor devices, loop heaters electronic devices. Also made traverses, glands and parts of the instrument, without the use of doped molybdenum.
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