To investigate the formation mechanism of secondary amorphous silica inclusion in iron and copper, silicon-deoxidation experiment of copper at 1423 K was performed.
In the copper quenched into water after deoxidation, three types of secondary amorphous silica inclusions (pinecone-like inclusion, gourd-shaped inclusion and network-like inclusion) were observed. In the copper cooled ultra-rapidly, fine spherical inclusion and coral-like inclusion, which were secondary and amorphous, were observed.
The experimental temperature of 1423K is not only 573 K lower than the melting point of silica9) but also 20 K lower than the glass transition temperature of silica (1443K10)). Therefore, the presence of secondary amorphous silica inclusion should be strong evidence of the formation of liquid silica during cooling of the copper without temperature rise. It would also support the formation of secondary liquid silica inclusion in the iron alloy.
Consideration based on Ostwald's Step Rule indicated that liquid silica inclusion could be formed from the supersaturated state of copper.