Phase transition during nucleation process in calcium aluminate glass-ceramics manufactured from secondary aluminum dross

Abstract

Secondary aluminum dross is a solid waste discharged during aluminum processing and melting. Calcium aluminate glass-ceramics was manufactured from secondary aluminum dross without adding nucleating agent. Phase transition of glass-ceramics was studied. Nucleation temperature was set at 846 ℃ according to differential scanning calorimetry and X-ray diffraction results. Field-emission transmission electron microscopy was applied to observe microstructure of the thermally treated parent glass. During nucleation process, omphacite grew from glass network. Omphacite growth consisted of two steps: migration of silicon group and cation; growth of omphacite. After parent glass was thermally treated at 846 ℃ for 3 h, silicon group and cation migrated and formed silicon enrichment field. A little of omphacite crystal formed in silicon enrichment field. When thermal treatment time was increased to 12 h, more independent omphacite crystals grew in silicon enrichment field. The independent omphacite crystals grew larger and contacted with each other to form a large omphacite crystal. The large omphacite crystal became nucleus of glass-ceramics. Omphacite nucleation had two effects on crystallization of glass-ceramics. First, omphacite crystal became nucleus, which provided surface for growing crystals. Second, omphacite growth consumed silicon group in glass network, which decreased polymerization degree of glass network and promoted crystallization. In calcium aluminate glass-ceramics with silicon, omphacite crystal could act as the nucleus without additional nucleation agents. • Calcium aluminate glass ceramics was made from the secondary aluminum dross. • Nucleation was attributed to omphacite growth. • Nucleation consisted of silicon groups migrating and omphacite growing. • Omphacite nucleation consumed silicon groups and promoted crystallization. • Omphacite acted as a novel nucleus in calcium aluminate glass ceramics with silicon.