Preventing Wetting Between Liquid Copper and Solid Steel: A Simple Extraction Technique

Abstract

Copper contamination of end-of-life steel scrap is the main barrier to high-quality recycling. Preferential melting of copper from solid steel scrap is a potential extraction technique, which could be integrated into conventional scrap re-melting with little additional energy. However, previous investigations show removal of liquid copper is limited by its adherence to solid scrap. Preventing wetting between liquid copper and steel is essential to enable separation. The carbon content of steel, initial surface oxidation, and applied coatings effect wetting behavior, but have not been systematically studied. In this study, the individual and combined effects of these parameters on wetting behavior in an inert gaseous environment are observed with a heating microscope. Carbon content appears to be the most significant factor: blistering of the oxide scale on medium-carbon steels causes liquid copper to flow rapidly between the oxide and steel substrate. Liquid copper exhibited a stable droplet on low-carbon steel, regardless of the initial level of oxidation. The tested coatings did not consistently improve nonwetting behavior, but impaired the connection between the scale and steel substrate. This study confirms the potential of the preferential melting technique, but further investigation is needed to determine the most robust process conditions to handle diverse, fragmented scrap at an industrial scale.

Wettability and microstructural evolution of copper filler in W and EUROFER brazed joints

“…Once the copper has melted and formed the droplet, in the case of the copper-EUROFER system, it tends to expand over the EUROFER substrate, covering a large surface area. This behavior is a result of the excellent wettability of copper in steel, a phenomenon that has been extensively studied in plain steel by several authors [21][22][23]. During the initial moments of the melting process, the expansion reaches up to 400% of the initial area.…”

Copper Surface Treatment Method with Antibacterial Performance Using “Super-Spread Wetting” Properties

“…In this study, for copper surface coating, the super-spread wettability properties of liquid copper are exploited. The literature reports that liquid copper is not able to wet a solid oxide [ 33 , 34 ]. However, our previous works have shown that liquid copper unusually penetrates and spreads on a surface with fine crevice structures formed by capillary action [ 35 ].…”