温度和速率对磷酸区域熔融过程的影响

区域熔融法是一种有效的制取高纯物质的方法,可被应用于高纯磷酸制备过程中。为了获得最佳的磷酸净化效果,考察了区域熔融过程中冷凝、加热温度和熔区移动速率对于区熔过程的影响。结果表明:在冷凝温度为5℃,加热温度为65℃时,可以得到合适的熔区大小,且此时形成稳定熔区的时间为33 min。冷凝或加热温度过高,熔区明显变大,凝固界面不稳定;冷凝或加热温度过低,熔区变小甚至无法形成熔区,凝固界面晶体生长呈针状。在考察范围内,随着熔区移动速率的增加,Cr,Ca,Mg,Zn,Al和Fe 6种杂质在区域熔融后的脱除效果有不同程度的降低。当移动速率小于25 mm/h时,6种杂质均具有较好的脱除效果,但是实验需要较长的时间,不利于实际应用;当移动速率高于25 mm/h时,Cr,Ca,Zn脱除效果明显下降。移动速率为25 mm/h是最佳移动速率。

Effect of temperature and moving rate on purification of phosphoric acid by zone melting

Zone melting is an effective method for the preparation of high-purity material and can be used to prepare high-purity phosphoric acid.The effects of condensing and heating temperature,and the moving rate of melting zone on the zone melting process were studied.The results show that when the condensing temperature is 5 ℃ and the heating temperature is 65 ℃,the size of melting zone is suitable and the time of forming stable melting zone is 33 min.When the condensing temperature or heating temperature is too high,the zone gets larger apparently and the solidification interface is unsteady;when the condensing temperature or heating temperature is too low,the zone gets smaller or even disappears,and the crystal is acicular at the solidification interface.With the increase of moving rate,the removal efficiency of Cr,Ca,Mg,Zn,Al,Fe reduces in different degrees after zone melting.When the moving rate of melting zone v< 25 mm/h,the purification of the six impurities is effective,but it needs a long time in practice;when v> 25 mm/h,the removal efficiency of Cr,Ca,Zn reduces obviously.25 mm/h is the optimal moving rate of melting zone.