Research On The Preparation Of 5N High-purity Aluminum By Zone Smelting

High purity Al is an important basic material.Materials based on high purity aluminum are widely used in cathode sputtering target,special alloy,i ntegrated circuit,photoelectric media storage equipment,aerospace,precision instruments and other high-tech fields.And with the continuous upgrading of China's manufacturing industry,the demand for purity and output of high-purity Al is also increasing.At present,the main methods to prepare 5N high purity Al are three-layer liquid electrolytic refining and segregation.There are some problems in the three-layer liquid electrolytic refining process,such as high energy consumption,fluoride electrolyte(NaF-AlF₃-Ba Cl₃-Na Cl and NaF-AlF₃-Ba F₂-Ca F₂)has great impact on the environment,and some countries have begun to use segregation method to prepare high purity Al from the three-layer liquid electrolytic refining process.Zone refining is a method of purifying metals by segregation,which is an important method to prepare high purity metals.The zone refining method is used to purify metal Al and the distribution of various impurity elements in Al between the solid and the liquid phase is studied.The main conclusions obtained are as follows:1.Theoretical analysis shows that the impurity elements of Cu,Si and Fe with balanced distribution coefficient k₀<1 migrate in the same direction as the movement of the induction coil under the ac tion of crystallization,and gather at the tail of the aluminum ingot;V and Ti with k₀>1 The impurity elements migrate to the head end of the aluminum ingot to be enriched in the direction opposite to the movement of the induction coil.2.Zone refining is carried out under argon atmosphere and vacuum conditions.The results show that under these two environments,as the number of purification increases,the enrichment of impurity elements at both ends increases.In vacuum,the refining speed is 1.5 mm/min,after 15 refining,the migration effect of impurities is significant,and high-purity Al with a purity of 5N5 can be obtained.The Al content can reach up to 99.99973%,the removal effect of impurity elements Cu,Si,Fe is the best;the migration of impu rity elements V and Ti is not obvious when the number of refining times is 5 and 10,and there is not a large amount of aggregation at the head end.When the number of refining times is increased to 15,the migration of Titanium element appears regularity,the content at the head end is greater than the content at the tail and middle;when the number of refining is increased to 20 times,the downward trend of impurities slows down,and the content of impurity elements tends to stabilize,indicating that the impurities are close to the distribution balance.Continue to increase the purification frequency,purification effect has little effect.3.In vacuum,the same purification times and zone refining results at different zone refining speeds show that the i mpurity migration phenomenon is not obvious under the condition of the refining zone moving speed of 4.6 mm/min.When the speed is reduced to 1.5 mm/min,two impurity elements agglomeration degree of the first and the second ends of the Al ingot is significant.When it continues to decrease to 0.7 mm/min,the content of Cu,Si,and Fe at the end of the Al ingot changes very little;the removal rate of the impurity element Ti with k₀>1 is reduced from 79.6%to77.09%,Which shows that when the speed is 1.5 mm/min,the removal effect of various impurities is the best.4.The microscopic morphology analysis of the product after refining under vacuum and normal pressure revealed that the size of the crystal particles is directly related to the purity of Al.Refining speed is 1.5 mm/min.Increase the number of refining will cause the Al crystals at the middle end(NO.4,NO.5)to grow and gather,which is quite different from the Al crystals at the head end(NO.1);refining 15 times,the results of changing the zone refining speed show that as the speed drops from4.6mm/min to 0.7mm/min,the crystals in the middle region show a tendency to gradually grow,and change from the layered structure in the raw material to full spherical type.