Investigation of Influencing Parameters on Zone Melting Refining of Aluminium, Part One Impurities:

M.Sc. Xiaoxin Zhang, Dr.-Ing. Semiramis Friedrich, Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich

Zone melting is one of the most important techniques to produce electronic grade materials. It is of good reliability, easy operation, less polluting aspects and has the possibility to produce ultra-pure materials in a considerably higher efficiency than the other refining techniques. However, the refining yield and the final purity depend significantly on the process parameters and properties of the individual material. Using an industrial sized zone melter and starting material of 2N8-Al made from 4N7-Al doped with the deliberate impurities of Fe (0.09 wt.-%) and Si (0.09 wt.-%), the influences of movement velocity of the induction coil as well as heating induction power on the purification of the above mentioned impurities have been investigated. The results were divided into two parts; first the comparison of removal efficiency for each impurity in relation with their distribution coefficients, and second the effect of process parameters on the refining yield. They showed that after three coil passes, the concentration of both Fe and Si in the first half of the Al-bar was reduced by around 50 %, where the refining efficiency of Si is slightly higher than that of Fe under the same experimental conditions. Compared to published equilibrium distribution coefficients (the “effective distribution coefficient” (keff) of silicon was lower in comparison with iron. Experiments with the lowest movement velocity of 0.8 mm/min, or moderate power of 9 or 9.5 kW represent higher refining efficiency. This zone refining efficiency is defined by the term of zone length, which itself is influenced by an optimum combination of coil movement velocity and electrical power.

Investigation of Influencing Parameters on Zone Melting Refining of Aluminium, Part One Impurities: Iron and Silicon