Study On The Preparation Of High Purity Tin By Vacuum Distillation-regional Melting Combined Method

High purity tin has been widely used in aerospace manufacturing,electronic information,semiconductor materials,etc.,It has become a key material to support the development of human science and technology.This paper introduces the properties,application and production of high-purity metal and high-purity tin in china.The theoretical analysis of the process of preparing high purity metal by vacuum distillation and zone melting was carried out.In the vacuum distillation process,the boiling point and saturated vapor pressure were studied which explained the volatilization law of impurities from thermodynamics and the relationship between the conditions of evaporation and the evaporation rate in the evaporation process was obtained.The relationship between the distribution of impurities and the conditions were obtained in zone melting.In the vacuum distillation process of experiment,experimental material composed of Sn97.4185%,it can be reach Pb0.012%,Sb0.045%,Sn99.8752%,Bi0.0005%,As0.0005%by vacuum distillation under the pressure is less than 15Pa,1400 degrees Celsius temperature,holding time 60min.However,the Fe and Cu elements in the crude tin did not change,the final product was Sn99.8752%,the direct yield of tin was 99.89%.A regional smelting experiment was carried out using 4N tin as the raw material by single factor analysis,the number of Sn increased from 99.99731%to 99.9977%when the melting times increased from 5 to 20 which indicated that the melting times were not the most important factors.When the melting rate of the alloy is reduced from 1.4mm/min to 0.6mm/min,the purity of the metal in the ingot increases from 99.99727%to 99.99906%in the raw material,which indicates that the slower the melting rate,the better the purification effect.The experimental results show that the equilibrium partition coefficient of Ag,Al,Bi,Ca,Cu,As,Ni,Pb,Au,Co,Zn is less than 1,and the equilibrium distribution coefficient of Sb is close to 1,and the effect of impurity redistribution is not obvious.In the process of preparing high purity tin by vacuum distillation and zone melting,the vacuum distillation method can be used to purify the crude tin from 97.4185%to under the condition of distillation temperature of 1600℃,pressure below 20Pa and holding time of 60min.After the 10 zone melting and zone melting of speed of 0.6mm/min,99.95857%can be purified to tin 99.99312%,including Pb,Bi,As,Cu,Fe,Ag,Ni and other major impurities are significantly reduced,and the distribution trend.If we can increase the melting time and reduce the melting rate,we can get more than 5N pure tin by vacuum distillation and zone melting method.