Structural characterization of Na2O–CaO–SiO2 glass ceramics reinforced with electric arc furnace dust

Crystallization process of thermally treated vitrified EAFD waste

“…14 This explains why the size of the crystals does not exhibit any observable change in the time interval of 2-60 h. The crystals of diopside do not appear from the beginning of crystallization during the nucleation process and thus, their crystallization is not observed in the DTA thermographs. According to previous observations, 8 the elements of EAFD in the glass-ceramics act as nucleating agents, which favour the formation of wollastonite. During the crystallization process, the EAFD elements are diffused in the neighbouring glass matrix.…”

“…E1 and E2 samples with crystallization time t = 15 and 30 min, respectively, exhibited wollastonite as the only phase crystallized, verifying previous observations. 8,10 Furthermore, in samples E3 and E4, the appearance a small peak at θ = 27.5 • and the broadening of the main reflection of wollastonite at θ = 30 • can be attributed to the emergence of the new crystal phase, which was observed by optical microscopy and SEM images. Taking the EDXS analysis into account, the new phase was identified as a diopside-like structure (CaMgSi 2 O 6 ).…”

“…In the glass-ceramics with 15 and 30 min crystallization times, wollastonite was the only crystal phase separated from the vitreous matrix, having a stoichiometry that revealed the incorporation of a significant amount of the metallic elements present in the EAFD. 8,10,11 Conversely, in the glass-ceramics with 2 and 60 h crystallization times, except wollastonite a new crystalline phase was observed to separate from the matrix (Fig. 1).…”

“…In particular, the composition chosen for the formation of vitreous products was the one found to demonstrate the best crystallization state (bulk crystallization), namely 15% EAFD, 55% SiO 2 , 5% Na 2 O, 25% CaO (wt%). 8 The mixture was placed in a Pt crucible and heated in an electric furnace at 1400 • C for 2 h, in ambient atmosphere. The melt was poured on a stainless steel plate and was rapidly cooled down at room temperature.…”

“…4 Wollastonite (pyroxenoid) and diopside (pyroxene) are two crystalline phases that are frequently encountered in the glass-ceramics systems, containing industrial wastes, depending on the initial composition. [5][6][7] In a previous experiment, 8 the incorporation of EAFD waste in the SiO 2 -CaO-Na 2 O system to produce glass-ceramics, resulted in the formation of a pyroxenoid (wollastonite) as the only crystalline phase. Small divalent cations such as Mg, Fe, Mn, contained in EAFD, were found to be incorporated in the crystalline structure of wollastonite.…”