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在中真空条件(18~50 Pa)下,从原子碰撞与碰撞凝聚的角度分析系统温度、铝分压及冷凝区温度梯度对铝蒸气相变形核及冷凝的影响。采用真空蒸发冷凝法(不充入惰性气体)制备出铝珠及铝粉,并利用扫描电镜与能谱进行表征。结果表明:在中真空条件(18~50 Pa)下,蒸气过饱和度增大,利于液相形核,这与温度对单位时间铝原子碰撞次数的影响一致,但当系统温度降到液气转变最低温度后,铝蒸气将冷凝成固态。中真空下,其影响蒸气冷凝方式的重要因素之一是系统中冷凝区的温度梯度。通过真空蒸发冷凝法,在冷凝区温度梯度约1.4 K/mm时制得金属铝珠,温度梯度约19.5 K/mm时制得金属铝粉。
The effect of system temperature, aluminum partial pressure and temperature gradient of condensation zone on nucleation and condensation of phase transformation of aluminum vapor was analyzed under the conditions of atomic vacuum and collision at 18 ~ 50 Pa. Aluminum beads and aluminum powder were prepared by vacuum evaporation and condensation method (not filled with inert gas) and characterized by scanning electron microscopy and energy dispersive spectroscopy. The results show that the vapor supersaturation increases under medium vacuum (18-50 Pa), which is favorable for liquid nucleation. This is consistent with the effect of temperature on the number of collisions of aluminum atoms per unit time. However, when the temperature of the system drops to that of liquid gas After changing the minimum temperature, the aluminum vapor will condense into a solid state. Under vacuum, one of the important factors that influence the way of vapor condensation is the temperature gradient in the condensing zone of the system. Aluminum vacuum evaporation condensation method, the temperature gradient in the condensation zone of about 1.4 K / mm obtained when the aluminum metal beads, the temperature gradient of about 19.5 K / mm prepared aluminum powder.