# Glass Ceramic with Improved Structure and Properties Made with Wastes from FeNi Production
###### Abstract  
Hazardous residues from ferronickel production are vitrified. The optimum thermal regime for the conversion of the resulting glass into glass-ceramics is estimated by rapid alternative methods: the nucleation step is valued by DTA, and the crystallization step by density measurements. The results show that a short and inexpensive thermal treatment can be used. The evolution of phase formation is highlighted by XRD, SEM-EDS, FESEM and TEM. Due to the presence of 1.5 wt % chromium oxides and high amounts of iron and magnesium oxides, the crystallization process is peculiar. It starts during the melt's cooling with the precipitation of preliminary Fe-Mg-Cr spinel crystals, which then act as centers for growth of pyroxenes. Simultaneously, due to liquid-liquid immiscibility, the main amorphous phase forms a nonhomogeneous binodal structure, which becomes finer after the nucleation treatment. Subsequently, thus formed iron-rich drops are transformed into tiny secondary magnetite spinel, acting as nuclei for the main crystallization process. As a result, new pyroxenes with sizes of about 200 nm are formed and the total crystallinity reaches about 60%. Regardless of the large amounts of problematic wastes in the batch, the resulting glass shows good chemical durability, while the glass-ceramic is characterized by optimal mechanical characteristics. waste vitrification; glass-ceramics; nano structure +
Footnote †: journal:  
began its expansion in the first decades of the twentieth century in the former Soviet Union and Germany, must be considered to be a forerunner of glass-ceramic production, because partially controlled crystallization takes place during the forming, cooling and annealing of the basalt melts used. Typical petrurgical products are tiles, tubes and bends, as well as basalt fiber or sintered materials. Due to the high chemical resistance and the very good mechanical properties of the obtained materials this industry is still viable. As an example, in Figure 1a is presented the application of paving tiles from a modern re-fused rock company [10]. It is also very interesting to remember that basaltic natural blocks were applied as pavements in the Roman Empire more than two millennia ago (as is shown in Figure 1b). Many medieval squares and streets in Naples, Rome and other sites in Italy are covered with large natural basaltic tiles or cobblestone. Even today, different companies continue successfully to produce similar natural materials. The silicate melts, rich with iron oxides, are characterized by intriguing peculiarities, which reduce the costs of the glass melting and the crystallization treatment. Firstly, their viscosity curves simultaneously show high glass transition temperatures and low melting temperature range. Practically, the glass transition is similar to the ones of common container and windows glasses, while the melting temperatures are lower by 150-200 \({}^{\circ}\)C. The relatively high temperature of glass-transition indicates the good chemical durability of the glasses, whereas the low melting temperature leads to a decreased melting cost. The crystallization process of these glasses is also specific. Since the iron oxides have low solubility in silicate melts, a tendency for liquid-liquid separation at higher temperatures is typically observed. As a result, an enrichment of iron oxide occurs in the liquid phase during the cooling, which provokes the subsequent quick crystallization of tiny magnetite spinel crystals. Then, this spinel phase provides centers for the main crystallization process. In many cases, the quantity of thereby-formed spinel crystals does not change expressively with the nucleation heat-treatment, so the iron-rich glass-ceramics can be manufactured by one-step crystallization heat-treatment.