- Filling of the reaction tube Many pure tungsten oxyhalides (WO2Cl2, WOCl4, WOCl3, WOCl2, WO2Br2, WOBr4, WOBr3, WOBr2 and WO2I2) have been prepared by chemical transport technology.
- In a hard glass tube with a length of 15cm and a diameter of 2.4cm, 9.274g (40mmol) tungsten oxide (Ⅵ) and 7.931g (20mmol) tungsten chloride (Ⅵ) (made from tungsten and chlorine) mixtures. To this material was added a slight excess of 1 mg of WCl6 per ml of tube volume. Freeze one end of this tube in liquid nitrogen, connect the other end to a vacuum system, and evacuate to 10-2×133.22Pa (as shown in Figure 1).
The tube is sealed at A and placed in a furnace with a temperature gradient of 350/275°C. The reactant is placed on the hotter part of the tube. The two-temperature zone furnace used to generate the temperature gradient T2/T1 is composed of two hollow aluminum cylinders (outer diameter 8cm, inner diameter 4cm, length 35cm). Made of copper-nickel alloy Kanthal wire, the two aluminum cylinders were housed in an iron cabinet filled with asbestos wool and covered with asbestos sheets. The furnace is placed at a slight inclination (approximately 10°) to prevent the liquid product from flowing back into the hotter part of the tube and causing a possible explosion. After about 20 hours, the reaction is completed, and the growth area is filled with yellow flaky tungsten dichloride (Ⅵ) crystals. Then place the tube in a reverse temperature gradient (200°C/room temperature) while it is hot, so that more volatile impurities (such as WCl6 and WOCl4) condense into the empty end of the reaction tube. The yield of tungsten(VI) dichloride is about 17g (98% based on the amount of tungsten oxide). If further purification or better crystallization is required, sublimation of the crystals can be carried out at any time in the presence of a slight excess of tungsten(VI) chloride [e.g. 1 mg of tungsten(VI) chloride per ml tube volume]
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