Crystallization behavior of glasses in the system of Na2O–CaO–MgO–Fe2O3–Al2O3–SiO2 with high contents of nickel oxide

The structural behavior of nickel oxide in glassy and glass-ceramic materials, obtained in the system of Na2O–CaO–MgO–Fe2O3–Al2O3–SiO2, was investigated. The influence of the NiO content on the vitrification, crystallization, structure and exploitation properties of two model compositions, with different ratios [CaO]/[MgO] was analyzed. On the basis of DSC and XRD data, it is shown that NiO promoted the formation of bunsenite crystals, as nuclei for crystallization. On the other hand, NiO promoted formation of pyroxenes even for compositions with low MgO contents, which formed gehlenite without NiO admixtures. It is shown that in the composition with relatively high MgO contents, NiO could participate in the formation of two types of pyroxenes with the structure and chemical composition similar to (MgO0.4NiO0.6)(CaO0.9NiO0.1)Si2O6 and diopside–hedenbergite solid solutions. The optimal contents of NiO in both model compositions was about of 7 wt%, since higher contents reduced the exploitation properties. The glass-ceramics with optimal contents of NiO were also produced using Ni bearing galvanic slurry and coal ash; the resulting materials showed similar exploitation properties to those mentioned above.