Purification of copper foils driven by single crystallization

Abstract

High-purity copper (Cu) with excellent thermal and electrical conductivity, is crucial in modern technological applications, including heat exchangers, integrated circuits, and superconducting magnets. The current purification process is mainly based on the zone/electrolytic refining or anion exchange, however, which excessively relies on specific integrated equipment with ultra-high vacuum or chemical solution environment, and is also bothered by external contaminants and energy consumption. Here we report a simple approach to purify the Cu foils from 99.9% (3N) to 99.99% (4N) by a temperature-gradient thermal annealing technique, accompanied by the kinetic evolution of single crystallization of Cu. The success of purification mainly relies on (i) the segregation of elements with low effective distribution coefficient driven by grain-boundary movements and (ii) the high-temperature evaporation of elements with high saturated vapor pressure. The purified Cu foils display higher flexibility (elongation of 70%) and electrical conductivity (104% IACS) than that of the original commercial rolled Cu foils (elongation of 10%, electrical conductivity of ∼100% IACS). Our results provide an effective strategy to optimize the as-produced metal medium, and therefore will facilitate the potential applications of Cu foils in precision electronic products and high-frequency printed circuit boards.