## 4 Results and Discussion
### Thermal Behavior and XRD Mineralogical Evolution in Fixed Samples  
The thermal analyses (TGA-DTG) measurements are reported in Figure 5. The thermal analyses show three mass losses: the first loss occurs around 60-66 \({}^{\circ}\)C and corresponds to the loss of adsorbed water [25; 26; 27]. The second mass loss at 241-252 \({}^{\circ}\)C is associated with the conversion of goethite into hematite, and the last one at 489-492 \({}^{\circ}\)C is related to the dehydroxylation of kaolinite [28]. The goethite to hematite conversions confirm that iron is mainly present in form of goethite and that this will probably lead to a reddish color in the fired sample. The variation in the temperature of the last mass loss (489-492 \({}^{\circ}\)C) is associated with the crystallinity difference of the kaolinite [25]. As previously reported, FTIR revealed that kaolinite has a high degree of disorder, characteristic of several alluvial environments [18; 29]. The intensity of the dehydroxylation peaks (489-492 \({}^{\circ}\)C) is coherent with kaolinite-rich materials and the associated mass loss varied between 14% and 18%; these values are consistent with the theoretical weight loss from the kaolinite ideal formula of 14%.  
The color of the specimens is variable as a function of the initial color of the raw materials, as well as their mineral compositions. The pale brown sample becomes light red; the light gray becomes dark red or white; and brownish gray becomes pink (Table 3, Figure 6). This is associated with the fact that, during the sintering process, goethite is  
Figure 4: Empirical diagram defining suitable domains for different types of tiles: (**a**) white stoneware tiles; (**b**) red stoneware tiles; (**c**) and (**d**) porous tiles.  
Figure 3: Plotting of the Lokoundje alluvial clays in Al\({}_{2}\)O\({}_{3}\)-CaO-(Na\({}_{2}\)O + K\({}_{2}\)O) (**a**) and Al\({}_{2}\)O\({}_{3}\)-CaO-Fe\({}_{2}\)O\({}_{3}\) (**b**).  
converted into hematite, which justifies the reddish and brownish colors, as suggested by the thermal analyses. The whitish color is mainly the mark of a sample with low iron content [30]. The sound of the fired products is metallic (Table 3), which is indicative of vitrification that accounts for improved sintering. The cohesion of the fired products is good to very good (Table 3). The weak cohesion of sample BR9 may be related to the proportion of coarse particles. The mineral assemblage of the fired products, from XRD analyses (Figure 7), is made of quartz, mullite, rutile and hematite. Mullite is developed from the spinel phase, which is formed from the demision of metakaolin that is formed after kaolinite dehydroxylation [31; 32]. The illite peak, although low, is still observable in the products fired at 800 \({}^{\circ}\)C and 900 \({}^{\circ}\)C. Illite dehydroxylation evolved from 300 \({}^{\circ}\)C to 700 \({}^{\circ}\)C. The relic illite structure breaks down between 700 \({}^{\circ}\)C and 850 \({}^{\circ}\)C, leading to a liquid phase formation, which crystallizes to form a spinel which crystalizes until it changes to mullite above 1100 \({}^{\circ}\)C [33]. In the particular case of these materials, the mullitization peaks, observed from 800 \({}^{\circ}\)C, are associated with the structural disorder of the clay minerals present in the raw samples.