• Uncategorized 28.10.2016

    Reaction Fahrenheit was greatly affecting the generation of the trichlorosilane, if the temperature is too low, the reaction will slowly, too high (greater than 450°C), the SiHCl3 generated in the reaction was reduced and SiCl4 increased, this is because the SiCl4 structure having a high degree symmetry, silicon atom and chlorine atom is combined with covalent bone, so the generated SiCl4 at up to 600°C reaction temperatures would not cause thermal decomposition, while the molecular classified of SiHCl3 is asymmetric, silicon speck and hydrogen atom combined is else near than electrovalent bond, so it is instability, becoming to the heat stable of SiHCl3 is poor, germinate to decompose at 400°C, vigorous decomposition at 550°C, therefore, with the appropriate reaction isothermal (280 to 320°C ) in the production process is an effective drive to improve the contentment of SiHCl3.
    Free oxygen and moisture, is extremely harmful to the synthesis reaction, because the Si-Cl bond is more stable than Si-O bond, reaction products easily oxidized and hydrolyzed, make the SiHCl3 yield decreased, the silica generated by hydrolysis was clogging pipes, make the operation become difficult, the hydrochloric acid generated by hydrolysis has strong corrosive effect on equipment. Free oxygen or vapor also can gradually form a layer of dense oxide deposit in silicon surface, affecting the normal progress of the reaction, the greater the moisture content of the silicon sprinkle and HCl, then the product will contain lower SiHCl3, when the HCl containing 0.1% water, the SiHCl3 content less than 80%, when the HCl containing 0.05% water, SiHCl3 content increased to nearly 90%, because that Si powder and HCl must be pre-dehydration.
    Using a catalyst cup reduced the reaction temperature of silicon and HCl when preparing SiHCl3, improve the reaction rate and yield of SiHCl3; also can avoid the harmful effects of a small amount of oxygen and moisture. Add Cu5% silicon alloy jug reduce 240 ~ 250℃ of the reaction temperature, and receptacle improve SiHCl3 content, as well since add cuprous chloride (Cu2Cl2) powder, the proportion is Si:Cu2Cl2 = 100:0.4-1, when the temperature control at 280℃, the SiHCl3 content can up to 85 ~ 95%.

    According to metal powder supplier, silicon powder react with HCl mustard is carried out on the silicon surface, so that the big silicon powder surface area (small particle size) is good for the reaction. But the particle size too big, strike against each other in the process of “boiling”, easy friction electrification, gathered into a group under the influence of an electric field, make the boiling occur channeling phenomenon, affect the normal reaction, but the particles are too small, the possibility of taken out synthesis furnace by the air becomes larger, not only waste of raw materials, but also easy to cause obstruction. The practice indicates that 80 to 120 interlock silicon powder to get the high content SiHCl3 and maintain the normal operation is appropriated.
    Silicon powder bed height et alii HCl flow were also the important factors to impress the render and quality of SiHCl3, it often based on the amount of the area and height of the fluidized bed. Practice to determine that if the material film is too high, in order to maintain the boiling state, requires excessive HCl pressure, but it will result in that the silicon powder in synthesis furnace is easily flow out, also caused the back system blocking, bring hardships to the production; if the material layer is too low, boiling unevenness increases, the reaction temperature is difficult to control. HCl flow is too small, the boiling situation deteriorates, the reaction is inadequate, the SiHCl3 yield decreased.
    As can be seen from the above analysis, the factors affecting the yield and quality of SiHCl3 are various, when applied to the production, should be combined the theory and practice, in order to select and determine the quality and soaring yield operation conditions, in addition, it should also try to reform the method machinery and process piping, make the production normally, and reduce the consumption of raw materials, reduce the degree of the environment contamination.
    Source:http://www.mhcmp.com

    Posted by kid @ 12:13 pm

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