## 3 Results
### Characterization of Porous Ceramics  
In the first series (grain size <1000 micron), three compositions were created using different percentages of char mixed with clay: 5% (PC 5%), 10% (PC 10%) and 15% (PC 15%). Table 6 summarizes the characterization of these samples, which showed acceptable consistency for 5 wt% of char, slightly crumbly consistency for 10 wt% and extremely crumbly consistency for 15 wt%. The data were compared to the reference sample containing only clay (PC 0%). \begin{table}
\begin{tabular}{l l l l l l} \hline \hline Sample & **Water Absorption (\%)** & **Weight Loss (\%)** & **Shrinkage after Firing (\%)** & **Apparent Density (kg/m\({}^{\dagger}\))** & **Total Porosity (\%)** \\ \hline PC 0\% & 15.60 & 12.00 & 1.15 & 1550.0 & 40.80 \\ PC 5\% & 19.26 & 12.92 & 2.42 & 1576.8 & 42.15 \\ PC 10\% & 29.01 & 17.88 & 2.96 & 1134.5 & 58.35 \\ PC 15\% & - & 18.25 & 3.88 & 918.6 & 66.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Physical properties of porous ceramics (<1000 \(\mu\)m). Figure 9: SEM micrographs (backscattered electrons) of a cross-section of the LWA Char 15% sample with magnification of 600\(\times\) (**a**) and 2400\(\times\) (**b**), as well as the relative EDS spectrum (**c**). The total porosity was calculated, as in the case of the LWAs, using the apparent density and the real density (Equation (3)). Furthermore, as the percentage of char in the compound increased, an increase in the final porosity and water absorption was noted, even if, as previously mentioned, the 10% and 15% samples could not be considered reliable given their high fragility and tendency to deteriorate. As can be observed in Figure 10, the samples containing 15 wt% (the last ones on the right) exhibited flaking and were not perfectly sintered. The weight loss increased with the increase in the amount of char used in the composition due to its thermal decomposition, which also corresponded to a reduction in the weight of the materials obtained. As a result of the fragility of the samples containing more than 10 wt% of char, a second series of specimens was realized by using sieved char smaller than 250 \(\upmu\)m up to the level of 10 wt% of char due to the high corresponding volume. These samples showed better results (Table 7) as regards the compactness of the porous ceramics created. By comparing the results for the porous ceramics of the first series, below 1000 \(\upmu\)m, and those of the second, below 250 \(\upmu\)m, it is possible to note that the latter, despite having similar shrinkage and weight loss values, had a slightly higher apparent density, thus resulting in specimens with a lower total porosity due to the higher degree of sintering. Considering that only 8% of the total char obtained by pyrolysis resulted in <250 microns, it is possible to conclude that this operation would not be environmentally viable. As regards the mineralogical composition of the porous ceramics produced, they were mainly composed of quartz (SiO\({}_{2}\)), and hematite (Fe\({}_{2}\)O\({}_{3}\)) and sanidine ((Na, K) (Si\({}_{3}\) Al) O\({}_{8}\)) were also present. Comparing the mineralogical results for the porous ceramic containing 5% char (Figure 11) with the LWA containing 7.5% char (Figure 5), it can be seen that, in the samples pressed and fired in a slow-firing cycle, there was a more pronounced crystallinity (demonstrated by the flattening of the baseline). Furthermore, the disappearance of the calcite occurred, which was certainly decomposed during the thermal treatment. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Water Absorption (\%)**} & \multirow{2}{*}{**Weight Loss**} & \multirow{2}{*}{**Shrinkage after Firing (\%)**} & \multirow{2}{*}{**Apparent Density (kg/m\({}^{3}\))**} & **Porosity** \\  & & & & & **(\%)** \\ \hline
**PC 5\%** & 18.07 & 12.67 & 2.73 & 1653.2 & 39.3 \\
**PC 10\%** & 31.36 & 17.11 & 2.68 & 1266.4 & 53.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Porous ceramics (<250 \(\upmu\)m) characterization results.