This content has been provided by Hydro Aluminium High Purity GmbH.
High-purity aluminium is solid aluminium with a purity of 99.99 % or above. It is most commonly used in the electronics and other high-tech industries where good electrical conductivity and corrosion resistance are important.
This is achieved using the 3-layer electrolysis or a combination of 3-layer electrolysis and fractional crystallisation .
In 3-layer electrolysis, high-purity aluminium is achieved through the reduction of aluminium ions in an electrolytic cell containing three different separated liquid layers.
The anode, being the bottom layer, consists of a molten alloy of copper and primary aluminium.
The electrolyte, or middle layer, is a molten mixture of elements in defined proportions.
The cathode, the upper layer, consists of molten high purity aluminium .
In the second process, fractional crystallisation, the aluminium is refined by taking advantage of differences in solubility.
The purity of Hydro's final product is precisely analysed using multiple techniques including glow discharge mass spectroscopy (GDMS), optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), and various techniques for the analysis of hydrogen content and diffusion .
High-purity aluminium is used in a wide range of applications in the electronics industry. Hydro's 99.99 % pure (4N) aluminium is sought after in the manufacturing of capacitor foils and for producing high-purity alumina. It can also be used for decorative applications.
The super-high-purity grades of 99.999 % (5N) and higher from Hydro are used in applications with even higher requirements for purity. Sputtering of aluminium thin films in the semiconductor industry requires extremely pure sputter targets – high purity aluminium is one of the major components.
Similarly, the metallization in the manufacturing of flat panel and liquid crystal displays (LCD) is very important. These high grades can also be used to produce high-purity alumina – the starting material for single crystal sapphire substrates for LEDs, separators for Li-ion batteries as well as for medical and cosmetic applications.
High-purity aluminium is available made to measure from Hydro in the form of slabs, billets, ingots, pigs and small shapes such as pyramids.
 Norsk Hydro, High Purity Aluminium High Performance Solutions. [Online]. Available: www.hydro.com/globalassets/1-english/products/casthouse-products/high-purity-aluminium---brochure.pdf [Accessed Sept. 12, 2018].
 W. Hoopes, F. C. Frary, J. D. Edwards, “Electrolytic refining of aluminum,” U.S. Patent 1534318, Dec. 21, 1922.
Hydro plants in Norway and Germany cover the complete range of production processes: