颗粒多晶硅气泡强化脱氢机理与方法

Mechanism and method of enhanced dehydrogenation by bubble from granular silicon

针对颗粒硅中氢含量高、难去除、危害大的问题,采用水模型与高温熔炼实验,开展了吹气熔炼过程气泡强化脱氢机理研究。通过硅熔体高温熔炼脱氢实验对硅熔体脱氢动力学进行了分析,发现无吹气脱氢过程符合1.5级动力学模型,证实了脱氢受限于液相中的传质与气液界面处的反应速率,这可为气泡强化脱氢提供理论基础。通过水模型实验开展了气泡行为对强化除气机制的研究。结果表明:气泡直径和容量传质系数随着通气流量的增加而上升,随着通气量从0.25 L/min增加到1.25 L/min,气泡直径从1.75 cm上升到1.93 cm,容量传质系数从0.135上升到0.337;气泡直径随着吹气管孔径的增加而上升,而容量传质系数则随着吹气管孔径的增加而下降,随着吹气管孔径从3 mm增加到5 mm,气泡直径从1.92 cm上升到2.21 cm,容量传质系数从0.337下降到0.302;随着吹气管通气管根数的上升,单根吹气管产生的气泡直径和容量传质系数则随之下降,随着吹气管根数从1根增加到5根,气泡直径从1.46 cm下降到1.23 cm,容量传质系数从0.135增加到0.169,而吹气管孔距小于气泡直径时,气泡会发生合并,导致容量传质系数下降。基于水模型气泡行为调控方法,开展了硅熔体高温气泡强化脱氢研究。结果表明:随着通气流量的上升,除氢率也随之上升,随着通气量从0.25 L/min上升到1 L/min,除氢率从61.41%上升到71.41%;随着吹气管孔径的上升,除氢率则随之下降,随着吹气管孔径从3 mm增加到5 mm,除氢率从71.15%下降到68.97%;随着吹气管根数的上升,除氢率随之上升,随着吹气管根数从1根增加到5根,除氢率从71.15%上升到76.35%;当吹气管孔距大于4 cm时,除氢率保持在76.35%左右,孔距小于4 cm时,除氢率保持在72.94%左右,最终能够将氢含量去除到4.5×10^(-6)左右,这证明了气泡强化脱氢方法可以实现颗粒多晶硅中痕量氢的深度去除,从而满足太阳能级多晶硅的要求。

In order to solve the problem of high hydrogen content which is difficult to remove and harmful in granular silicon,the mechanism of bubble enhanced dehydrogenation in blowing refining process was studied by water model and high temperature refining experiment.The dehydrogenation kinetics of silicon melt was analyzed by high temperature refining dehydrogenation experiment of silicon melt without blowing.It was found that the dehydrogenation process was in accordance with the 1.5 order kinetics model,which confirmed that dehydrogenation was limited by mass transfer in liquid phase and reaction rate at gas-liquid interface,and provided a theoretical basis for bubble enhanced dehydrogenation.The bubble behavior was carried out through the water model experiment to study the mechanism of enhanced degassation.The results show that the bubble diameter and volumetric mass transfer coefficient increase with the increase of blowing rate.With the air blowing rate increasing from 0.25 L/min to 1.25 L/min,the bubble diameter increases from 1.75 cm to 1.93 cm,and the mass transfer coefficient increases from 0.135 to 0.337.The bubble diameter increases with the increase of blowing tube diameter,while the mass transfer coefficient decreases with the increase of blowing tube diameter.As the aperture of blowing tube increased from 3 mm to 5 mm,the diameter of bubble increased from 1.92 cm to 2.21 cm,and the mass transfer coefficient decreased from 0.337 to 0.302.With the increase of the number of blowing tubes,the diameter of bubbles produced by single tube decreases and the mass transfer coefficient decreases.As the number of blowing tubes increased from 1 to 5,the diameter of bubble decreased from 1.46 cm to 1.23 cm and the volumetric mass transfer coefficient increased from 0.135 to 0.169.And the bubbles merge when the hole distance of blowing tube is smaller than the bubble diameter,resulting in the decrease of volumetric mass transfer coefficient.Based on the bubble behavior regulation method of water model,the experiment of bubbles enhanced dehydrogenation in silicon melt under high temperature was studied.The results show that with the increase of blowing rate,hydrogen removal rate also increases.With the increase of blowing rate from 0.25 L/min to 1 L/min,the hydrogen removal rate increases from 61.41%to 71.41%.The hydrogen removal rate decreases with the increase of blowing tube diameter.With the increase of blowing tube diameter from 3 mm to 5 mm,hydrogen removal rate decreased from 71.15%to 68.97%.The hydrogen removal rate increases with the increase of blowing tubes number.As the number of blowing tubes increases from 1 to 5,the hydrogen removal rate increases from 71.15%to 76.35%.When the hole distance of blowing tube is larger than 4cm,the hydrogen removal rate remains about 76.35%,and when the hole distance is smaller than 4 cm,the hydrogen removal rate remains about 72.94%.Finally,the hydrogen content can be removed to around 4.5×10^(-6).These results indicated that the method of bubble enhanced dehydrogenation can achieve the depth removal of trace hydrogen in granular polysilicon,so as to meet the requirements of solar level polysilicon.