Fine-Grained Glass-Ceramics Obtained by Crystallisation of Vitrified Coal Ashes

Abstract

Coal fly ashes have been vitrified by melting with Na 2 O and CaO as fluxing additives.Adequate heat treatments on the fly ash derived glass produced attractive dark green glass-ceramics. These glass-ceramics exhibited fine-grained microstructures consisting of esseneite and nepheline crystals, with average size below 200 nm, homogeneously dispersed in a residual glassy matrix. Several properties, such as density, thermal expansion coefficient, bending strength, hardness and brittleness index were determined and the correlation microstructure-properties is discussed. The results suggest that these coal ash-based glass-ceramics have potential applications as structural materials or as cladding materials.

Glass-ceramics: Their production from wastes—A Review

“…The crystals were reported to be wollastonite, but the authors made no attempt to explain their fineness and morphology. The optimised glass-ceramics based on the high alumina fly ash had slightly better mechanical properties (Hv: 7.1 GPa; 4-point bending strength: 103 MPa) than those of the low alumina fly ash based glass-ceramic and the glass-ceramics reported by Ferro et al [100].…”

“…The Portuguese ashes investigated by Leroy et al [99] gave melts that were too viscous to pour at 1520°C and hence 10wt%Na 2 O and 10wt%CaO (by adding pure Na 2 CO 3 and CaCO 3 ) were added to the ash to lower the viscosity. Pourable melts were obtained which were successfully transformed into glass-ceramics with esseneite (CaFeAlSiO 6 ) as the main crystalline phase formed and nepheline (NaAlSiO 4 ), as secondary phase [99,100]. The microstructures were notable for their fineness;…”

Comparison of the properties of glass, glass–ceramic and ceramic materials produced from coal fly ash

“…From SEM observations, we can clearly see that the average crystal sizes of both TFA1448 and TFA1473 samples were smaller than the other samples and the hardness values were better. It was reported in the literature that the fine-grained ceramic materials possess better hardness property together with finer crystal size [9]. It is obvious that the TFA1473 sample had more dense microcrystalline structure with better physical and mechanical properties than those of the other TFA samples.…”

“…There has been considerable research on the production of glass [5], glass-ceramic [1,[6][7][8][9][10][11] and ceramic [12][13][14][15] materials from coal fly ash without or with the addition of natural raw materials and wastes such as glass cullet, dolomite slag and tincal ore waste in the last few decades. However, there has not been paid much attention to obtain glass, glass-ceramic and ceramic materials by using only one material source, coal fly ash.…”

Preparation and characterization of nucleated glass-ceramics based on basaltic rocks

“…In addition, the CTE of diopside and anorthite are reported by Rigby and Green [27] to be 8.3.0 × 10 −6°C−1 and 6.4 × 10 -6°C−1 , respectively. The present thermal expansion is relatively more or less the previous values; however, the difference is attributed to not only the ratios of the crystallinity to the residual glass but also to the developed crystalline phase [28][29][30][31].…”