Preparation of Tungsten Hexafluoride from Waste Tungsten Cutting Head

In tungsten fluoride, tungsten hexafluoride (WF6) is the only stable and industrialized production of varieties. It is an important raw material in modern electronics industry. It can be used to produce high-purity tungsten powder as raw material for metal tungsten chemical vapor deposition (CVD) process, especially the WSi₂ made from it can be used as wiring material for large-scale integrated circuit (LSI).

In industrial production, the purification of tungsten hexafluoride generally requires two processes, namely, primary purification and re-purification. Tungsten hexafluoride tungsten purity requirements are very high, our scholar innovation more than 10 kinds of purification of tungsten hexafluoride purification method, but with the recovery of waste tungsten hexafluoride technology is rare. Recently, some scholars have proposed a method of recycling waste tungsten hexafluoride production methods and described below:

1)The waste tungsten cut head, the entire production line of tungsten hexafluoride pipe equipment used by the nitrogen after the cold nitrogen storage tank and then heated by the heater after the hot nitrogen purge drying (preheating temperature of 150 ~ 200 ℃). After the purging is completed, the vacuum pump is used for vacuuming to remove residual air and moisture.

2)Introducing hydrogen fluoride into the electrolytic cell to electrolyze fluorine, purifying the generated low-purity fluorine gas through the purification tower 1, the first cryogenic tank 41 and the second cryogenic tank 42 in sequence, and purifying fluorine gas. The reaction system is reacted, the raw material tungsten is made of waste tungsten cutting head; the diameter of the waste tungsten cutting head can be 4 to 10 mm and the length can be 5 to 20 mm; the purity of the waste tungsten cutting head is more than 99.9%, which is favorable for preparing High purity tungsten hexafluoride gas;

3)The cleaned fluorine gas is re-introduced into a first horizontal fixed bed reactor equipped with a waste tungsten cutting head and a second horizontal fixed bed reactor, and the prepared tungsten hexafluoride gas is passed through primary condensation collectors, intermediate condensers and advanced condensers, 150kg when thawed separately flows to the first accumulator, the second accumulator and the third collection tank, the impurity gas is not condensed or by reaction of the tail pipe to discharge rinsing alkali absorption tower, the crude tungsten hexafluoride collected by the first storage tank, the second storage tank, and the third storage tank is raised in temperature and is then subjected to rectification and purification using a filter to a rectifying tower.

Through this process, tungsten hexafluoride is prepared, the utilization rate of waste tungsten cutting head is 99% and the utilization rate of fluorine gas is up to 90%. The impurity indexes of crude tungsten hexafluoride are detected and analyzed, the purity is more than 99.99%. This indicator is conducive to the next chemical purification and further distillation purification. In order to reduce corrosion, the material of the pipe connecting the cryogenic tank, the horizontal fixed-bed reactor and the condenser is nickel, or Monel.

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