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Preparation of fine particles of tungsten disulfide

wallpapers News 2021-11-01
Tungsten disulfide is a new kind of tungsten fine chemical product. At present, tungsten disulfide is mainly used as a petroleum catalyst in China. Because of its characteristics of good cracking performance, stable and reliable catalytic activity, and long service life, it is very popular in petroleum refineries. Another important use of tungsten disulfide is as a lubricant. Its physical and chemical properties and known as the "king of lubrication" calcium disulfide similar. It is not only used in normal lubrication conditions but also can be used in certain high temperatures, high pressure, high vacuum, high load, radiation, and corrosive media, etc. With the development of science and technology, the application of tungsten disulfide has a broad prospect.
There are many preparation methods of tungsten disulfide, including ammonium tetrathiotungstate method, sulfur method, and preparation method of tungsten trioxide, tungsten powder as raw materials, through hydrogen sulfide gas or sulfur steam. At present, the most commonly used method in industry is ammonium tetrathiotungstate, which is heated to generate ammonium tungstate after mixing tungstate acid and ammonia water, and then through hydrogen sulfide gas to generate ammonium tetrathiotungstate, and then precipitate ammonium tetrathiotungstate crystals in high-temperature furnace for high-temperature roasting and tungsten disulfide. The process is long, the process control is complex, the production cycle is long, the product recovery rate is low, the product quality is difficult to meet the increasing requirements of users, especially the requirements of lubricants. Although there are units to improve the process, under the condition of air isolation, heating decomposition of ammonium tetrathiotungstate, with harsh temperature, the quality of stable, FSSS2~ 20μm crystal structure of hexagonal tungsten disulfide system. But other shortcomings remain. So it is necessary to study a new preparation method. We chose a relatively simple preparation method in the case of air isolation, so that tungsten powder and excess sulfur powder in the appropriate temperature vulcanization, and then at high-temperature evaporation of excess sulfur, and tungsten disulfide recrystallization, to meet the requirements of tungsten disulfide.
The basic principle
The objective reaction of this method is: W+2S=WS2
The reaction may be solid-solid, gas-solid, or liquid-solid, depending on the reaction temperature. To make the reaction easy to achieve and sufficient, we choose a liquid-solid reaction. Then, the reaction temperature should be above the melting point of sulfur, below the boiling point, namely: 112.8C~444.6C. According to the formation heat of WS2 △H°= -50kcal /mol[C2], it can be determined that the reaction is exothermic and the reaction temperature should not be too high.
According to the data, W+S2(g)= WS2(s) The applicable temperature range of the reaction is 298~ 1400K. As the reaction temperature decreases, the equilibrium constant Kp increases and the reaction progresses more thoroughly. However, when choosing a lower temperature, it should be considered that the vulcanization reaction requires certain activation energy (when the temperature is not higher than 460C). In addition, according to Arrhenius equation, the reaction velocity constant K increases significantly with the increase of temperature.
Therefore, considering the above factors, we choose the vulcanization temperature in a moderate range: 200~300C. To complete the sulfurization, the free sulfur must be evaporated at high temperature, so the reaction process must be divided into two stages: low-temperature sulfurization stage and high-temperature evaporation stage. We choose evaporation temperatures much higher than the boiling point of sulfur: 600~900C, during which free sulfur is evaporated and WS2 recrystallizes.

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