Iron oxide and jadeite nucleation in high alumina glass-ceramics prepared from secondary aluminum dross

Abstract

Secondary aluminum dross (SAD) is a solid waste of aluminum dross after it is extracted aluminum. Soda-lime-aluminosilicate (SLAS) glass-ceramics with high alumina contents (over 30 wt%) were successfully manufactured from SAD using pyrometallurgy without additional nucleation agents. The nucleation process of SLAS glass was studied, and 670 °C was selected as the nucleation temperature according to differential scanning calorimetry and X-ray diffraction results. Field-emission transmission electron microscopy was applied to study the microstructure of the specimens thermally treated at 670 °C for 3 and 12 h. Nucleation consisted of two parts: iron oxide nucleation and jadeite nucleation. During iron oxide nucleation, when the thermal treatment time increased from 3 to 12 h, the iron oxides first congregated in an amorphous phase and a small amount of metastable crystal; then, the congregated iron oxides crystallized into hematite and magnetite, which acted as crystal nuclei. During jadeite nucleation, the jadeite spontaneously crystallized from the glass matrix after thermal treatment at 670 °C. When the thermal treatment time increased from 3 to 12 h, the size of the jadeite crystals increased from approximately 6 to 12 nm. Jadeite crystals with a diameter of 12 nm acted as crystal nuclei. For glass-ceramics with a high content of aluminum and sodium, jadeite crystals can act as crystal nuclei without additional nucleation agents.