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结晶,就是从均匀液相中得到一定形状和大小的固体颗粒的过程。影响结晶大小的因素有哪些?

问答题
2022-03-04 11:18
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正确答案

a、过饱和度:
一般过饱和度增加,所得晶体较细,温度的影响比较复杂,当溶液快速冷却时,达到的过饱和程度较高,所得晶体也较细而且常常形成什状结晶,缓慢冷却常得到较粗大的颗粒。
b、温度
经验还表明,因为温度对晶比生长速度的影响要比成核速度显著,所以在低温下结品得到的晶体较细小。
c、搅拌速度
搅拌能促使成核相加速扩散,提高晶校长大速度,但超过一定范围后,效果就越显著,相反搅拌越烈,晶体越细。
总之,若要获得比较粗大和均匀的晶体,一般温度不宣太低,搅拌不宜太快,并要控制好晶核生成速度大大小于晶体成长速度,最好在较低的饱和度下将溶液控制在介稳区内结晶,那么在较长的时间里可以只有一定量的晶核生成,而使原有的晶核不断成长为晶体。
此外,加入晶种,能控制品体的形状、大小和均匀度。但首要的品种自身应有一定的形状、大小和比较均匀,不仅如此,加入晶种还可使品核的生成提前,世就是说所需的过饱和度可以比不加晶种时低很多。所以,在工业生产中如遇结晶液浓度太低而结晶发生因难时,可适当加入些晶种,能使结晶顺利进行


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