## 3 Results
### Thermal Study of the Mixtures  
The results corresponding to the thermal analysis performed on the powdered mixtures by DTA and heating microscopy techniques are reported in Table 2. From DTA curves the glass transition temperature (Tg) is in the range 657-665 \({}^{\circ}\)C and two exothermic peaks, one small at 450-460 \({}^{\circ}\)C (probably due to organic compounds decomposition, derived from the ceramic sludge) and the other indicating a neo formation crystalline phase at 870 \({}^{\circ}\)C are present. Besides, from the heating microscopy measure, it is possible to obtain the characteristic temperatures for the two mixtures (V125 and V75). The results achieved (Table 2) plainly show for both mixtures the reduction of sintering temperature with respect to traditional ceramic materials, encouraging the possibility to employ these mixtures (\(<\)125 \(\upmu\)m and \(<\)75 \(\upmu\)m) to obtain ceramic supports at lower temperatures with respect to the commercial ones. The positive effect of the granulometry on the densification and softening temperatures is evident, lower values for V75 with respect to V125 were achieved. \begin{table}
\begin{tabular}{c c c} \hline
**Oxide** & **Ceramic Sludge** & **Glass Cullet** \\
**(wt\%)** & **Ceramic Sludge** & **Glass Cullet** \\ \hline SiO\({}_{2}\) & 52.36 & 71.16 \\ Al\({}_{2}\)O\({}_{3}\) & 19.37 & 2.39 \\ CaO & 5.73 & 9.98 \\ MgO & 2.43 & 2.03 \\ Na\({}_{2}\)O & 3.9 & 12.63 \\ K\({}_{2}\)O & 1.32 & 1.34 \\ Fe\({}_{2}\)O\({}_{3}\) & 0.84 & 0.10 \\ TiO\({}_{2}\) & 0.45 & 0.02 \\ BaO & 0.54 & 0.12 \\ ZnO & 0.99 & 0.04 \\ PbO & 0.49 & 0.02 \\ CuO & 0.10 & 0.04 \\ Cr\({}_{2}\)O\({}_{3}\) & 0.07 & - \\ ZrO\({}_{2}\) & 3.01 & 0.13 \\ Others & 0.50 & - \\ L.O.I & 8.00 & - \\ TOTAL & 100.4 & 100.00 \\ CaCO\({}_{3}\) & 6.17 & - \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical analysis (XRF) of raw materials used. In Figure 1 the dilatometric curves of the two mixtures (V125 and V75) are compared. This technique allows to estimate the temperatures corresponding to the beginning of sintering and the maximum sintering rate. No more differences are observed, the curves present a thermal expansion up to 700 \({}^{\circ}\)C and successively the starting of sintering 720 \({}^{\circ}\)C (V75) and 760 \({}^{\circ}\)C (V125) with a small shift (40 \({}^{\circ}\)C) to lower temperatures for the mixture <75 \(\upmu\)m; the temperature of maximum sintering rate (identified by the first derivate curve) are 858 and 861 \({}^{\circ}\)C, respectively. The data confirm that the particle size distributions chosen are suitable for the sintering process, because smaller particles with a high reactivity fill the holes created by the larger ones and thus the solid volume increases. The achieved results show for both mixtures the reduction of sintering temperatures with respect to traditional ceramic tiles. On the basis of the thermal analyses, the pieces were undergone to different heating cycles (800-1000 \({}^{\circ}\)C) with a soaking times of 30 and 60 min for optimizing the densification conditions. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**HEATING MICROSCOPY**} & \multicolumn{2}{c}{**DTA**} \\ \hline \multirow{2}{*}{**MIXES**} & **T (\({}^{\circ}\)C)** & **T (\({}^{\circ}\)C)** & **T (\({}^{\circ}\)C)** & **T (\({}^{\circ}\)C)** & **T (\({}^{\circ}\)C)** \\  & **Sintering** & **Softening** & **Melting** & **Tg (\({}^{\circ}\)C)** & **Crystalization** \\ \hline
**V125** & 858 & 1090 & 1222 & 665 & 870 \\
**V75** & 802 & 876 & 1216 & 657 & 870 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristic temperatures determined by DTA and Optical Hot stage microscopy for the two mixtures prepared V125 and V75. Figure 1: Dilatometric curves for V125 and V75 mixes. The sintering degree of the mixtures as a function of thermal treatments was checked by linear shrinkage (L.S%), water absorption (W.A%) and apparent density (\(D_{ap}\)).