# Glass Ceramic with Improved Structure and Properties Made with Wastes from FeNi Production
## 3 Materials and Methods  
The results of chemical analyses elucidate that the main residue EFS and the dust D contain relatively high amounts of glass formers, while the leaching results demonstrated that the most problematic waste was CS. In order to use the wastes simultaneously, they were mixed in ratio D/CS/EFS = 1/1/10 (comparable to the production rate) and homogenized. The chemical composition of the resulting mix (labelled WM) is also reported in Table 1. Due to high amounts of iron oxides and MgO and elevate Cr\({}_{2}\)O\({}_{3}\) percentage, the direct (as it is) vitrifications of WM will be problematic, because spontaneous and uncontrolled crystallization during the melt-cooling is possible. In order to decrease the crystallization tendency, 30% container glass cullet CG (crushed to particles below 5 mm) was mixed with 70% WM. The chemical compositions of the CG and of the resulting composition, WG, are also shown in Table 1. The usage of cheap waste-glass is a common technique in the synthesis of similar glass-ceramics [1; 2; 3; 4]; it favors the glass melting, decreases the crystallization trends and improves the chemical durability. A batch of approximately 400 g was melted in a corundum crucible (99% Al\({}_{2}\)O\({}_{3}\)) using an electric furnace. A portion of the mix was placed in the crucible at room temperature. The remaining batch was added during an additional step at \(\sim\)1200 \({}^{\circ}\)C, and then the temperature was raised up to 1400 \({}^{\circ}\)C. After 1-1.5 h melting, although there were high amounts of wastes in the batch, the melt formed a clean surface free of bubbles, which is an indication of quick refining and homogenization processes. After another 0.5 h holding, the melt was poured out in copper casting molds to manufacture 15-20 cm glass bars. The obtained glass was characterized by glossy black surfaces, similar to that of natural basalt slabs. The main part of the glass was annealed for 30 min at 600 \(\pm\) 5 \({}^{\circ}\)C and then the glass bars obtained were cut into samples appropriate for the planned studies. A quantum of 4-5 g of non-annealed glass was crushed into small bulk samples suitable for DTA analysis. The heat treatment for nucleation was studied by DTA technique in an air atmosphere (PerkinElmer Diamond apparatus). The optimal temperature for nucleation was evaluated by means of small bulk samples weighing 10-15 mg, held for 1 h at various temperatures and then heated at 20 \({}^{\circ}\)C/min to 1000 \({}^{\circ}\)C. The efficiency of the nucleation was related to the temperature shift (\(\Delta\)T) between the peak temperatures (T\({}_{P}\)) of the crystallization exo-effects of the nucleated samples and a non-nucleated sample. Then, the optimal nucleation time was estimated by calculating the variation of \(\Delta\)T vs. the duration of the holding time at the optimal nucleation temperature. The proper temperatures and times of the crystallization temperature were estimated by use of the increase of density due to crystallization [5]. Both nucleated and non-nucleated samples weighing 3-4 g were subjected to heat treatments at diverse temperatures for different times. The density of each sample was measured twice: before and after the crystallization step. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **D** & **EFS** & **CS** & **WG** & **GC** & **Applied Limits [23]** \\ \hline Fe & 1 & 202 & 1155 & 0.416 & 0.26 & \\ Ni & 6.1 & 2.7 & 19.2 & 0.311 & 0.1 & 1 \\ Co & 0.4 & 0.14 & 1.1 & \(<\)0.005 & \(<\)0.005 & 2 \\ Cd & \(<\)0.005 & \(<\)0.005 & \(<\)0.005 & \(<\)0.005 & 0.02 \\ Cu & 0.15 & 0.093 & 0.07 & 0.011 & 0.042 & 5 \\ Mn & 4.7 & 14.6 & 1.5 & \(<\)0.005 & \(<\)0.005 & \\ Pb & 0.026 & 0.031 & 0.086 & 0.017 & \(<\)0.005 & 1 \\ Zn & 3.6 & 0.29 & 0.42 & \(<\)0.005 & 0.006 & 5 \\ Cr & 0.22 & 1.1 & 2.9 & \(<\)0.005 & \(<\)0.005 & 1.0 \\ As & 1.2 & 0.011 & 0.18 & 0.009 & 0.003 & 0.2 \\ \hline \end{tabular}
\end{table} 
Table 2: Concentration of the heavy metals in the solution after TCLP test (mg L\({}^{-1}\)).