Abstract
Aluminum and aluminum-based alloys have been used for many years. In view of the increase in material purity requirements of advanced technology products, research regarding high-purity aluminum has gained significant attention in recent years. In this review, we seek to describe the fundamental purification principles and the mechanisms of various segregation techniques used to produce high-purity aluminum. Moreover, we aim to provide an overview of high-purity aluminum production, with particular emphasis on: (a) principles on how to produce high-purity aluminum by layer- and suspension-based segregation methods; (b) discussion of various influencing process parameters for each technique, including three-layer electrolysis, vacuum distillation, organic electrolysis, suspension-based segregation, zone melting, Pechiney, Cooled Finger, and directional solidification; as well as (c) investigations of fundamental working principles of various segregation methods and corresponding reported end-purification for the production of HP-Al. Eventually, the end-reported product purity, and advantages and disadvantages of various purification methods and technologies are summarized. By analyzing and comparing the characteristics of different methods, we put forward suggestions for realizing efficient and environmentally friendly production of high-purity aluminum in the future.
Highlights
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We aim to provide an overview of high-purity aluminum production, with particular emphasis on: (a) principles on how to produce high-purity aluminum by layer- and suspension-based segregation methods; (b) discussion of various influencing process parameters for each technique, including three-layer electrolysis, vacuum distillation, organic electrolysis, suspension-based segregation, zone melting, Pechiney, Cooled Finger, and directional solidification; as well as (c) investigations of fundamental working principles of various segregation methods and corresponding reported end-purification for the production of HP-Al
Many efforts have been taken to realize simple and low-cost fabrication procedures, high production efficiency, flexible application, as well as the trade-off among these parameters for HP-Al. Both vacuum distillation and organic electrolysis achieve high levels of purity, their design and working principles suggest that they would lack the productivity required for high-volume industrial application
Summary
The primary form of aluminum—from the Hall–Héroult process—has a purity range of 99.7 to 99.9%, with major impurities of iron (Fe), silicon (Si), zinc (Zn), and gallium (Ga). While this purity range is sufficient for most industrial applications and alloying, the use of aluminum in high-technology fields, such as semiconductor, electronics, superconducting, and so forth requires higher purity levels exceeding the ones obtained via classical aluminum production processes [1,2]. To reach such purity, several technologies have been developed. A metal with 5 ppm of impurities would have 99.9995% purity and would be described as 5N5
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