The mechanism for the nucleation and crystallization of glass-ceramics fabricated from coal bottom ash discharged at a thermal power plant was studied by examining the activation energy and Avrami constant using a non-isothermal analysis, and the effect of TiO2 additions on the surface crystallization behavior was investigated. The glass of the coal bottom ash-Li2OCaO system had three exothermic peaks in the differential thermal analysis(DTA), and the crystals formed at 946.3 K corresponding to the lowest temperature peak(Tp1) had an Avrami constant of 0.94 showing a surface-dominant crystallizing behavior consisting of β-spodumene and magnetite phases identified by X-ray diffraction analysis. Additions of TiO2 suppressed the surface crystallization, which was observed by SEM, resulting predominantly in bulk crystallization. By altering the crystallizing behavior from a surface to bulk mechanism, the physical properties of the glass-ceramics could be changed, the surface color yellow to silver and the hardness increased.

Keywords: surface crystallization, Avrami constant, glass-ceramics, nucleation agent, hardness, coal bottom ash.