## 4 Results and Discussion
### Physicochemical Properties  
#### 4.3.1 Particle Size Fractions  
Knowledge of the particle size distribution of clay materials is an important factor to determine its suitability for various applications [1]. Table 3 presents the physicochemical characteristics of the different samples. Generally, the different granulometric proportions of the analyzed samples showed that the clay fraction (<2 \(\upmu\)m) ranged from 26% (N1C3) to 99% (N1C2), silt (2 < \(\O\) > 20 \(\upmu\)m) and sand (20 < \(\O\) > 200 \(\upmu\)m) varied from 1% (N1C2) to 70% (N1C3) and 0 (Y1C3, N1C2) to 4% (N1C3), respectively. The proportions of the clay fraction (<2 \(\upmu\)m) varied from 30.5% to 39.5% for Yansoki, 59.2-68% for Japoma and 34-99% for Ndogpassi. The clay fraction had the most quantities in all the studied samples (50.9%, average amount). The proportions of the silt fraction (2 < \(\O\) > 20 \(\upmu\)m) ranged between 68.1% to 71.5% for Yansoki, 30.5% to 41.5% for Japoma and 1% to 70% for Ndogpassi. Except for the N1C1 sample, the studied samples from Yansoki and Ndogpassi had higher quantities of the silt fraction. Silt was the second most important fraction of the studied samples. However, the quantities of the sand fraction were 0% to 1% in Yansoki, 0.8-1.5% in Japoma and 0-4% in Ndogpassi. The sand fraction had the lowest quantities in the selected samples from different sites of the study area. These samples were therefore richer in clay fractions (<2 \(\upmu\)m) than the clay materials of the Lake Chad basin, which ranged from 16.54 to 21.54% [1]. The higher content of fine fraction (clay and silt) observed in the clay materials is favored by morphoclimatic and hydrological conditions in the Littoral region of Cameroon. The hot and humid tropical climate of the Littoral region favors the intense alteration of the materials compared to the clay materials of the Lake Chad basin, which are subjected to the sahelo-sudanian and sahelo-saharan climates. The particle size distribution of clay plays an essential role in defining the properties of suspensions (plasticity and viscosity) and green pastes during drying and firing [19; 61]. The particle size analysis of the studied samples was plotted in the Belgian diagram of textural classifications of clayey materials [36]. This diagram indicates that the clay materials are very heavy clays and silty clays (Figure 10). This is in perfect correlation with the most amount of fine particle sizes found in the areas corresponding to very heavy clays and silty clays. Figure 9: Composition of clay materials of the eastern part of the Douala sub-basin in the diagram of [PERSON] et al. [35]. The ternary diagram of [PERSON] [37] was used to classify clay materials according to their porosity and permeability. According to this diagram [37], all the studied samples may be classified as weakly porous and permeable with the exception of the NIC2 sample from Ndogpassi, which was found in the range of high porosity and very low permeability (Figure 11). The permeability therefore depends largely on the shape, size and sorting of the particles. This observation agrees with the distribution of the constitutive particles of the studied clayery materials. Figure 11: Porosity and permeability of clay materials of the eastern part of Doulaa sub-basin in the triangular diagram after [37]. Figure 10: Classification of the clay materials of the eastern part of the Doulaa sub-basin according to the Belgian triangle of textures [36]. The particle size was projected in the Winkler diagram [38] (Figure 12). The use of the Winkler diagram made it possible to predict the ceramic suitability of clay materials. However, neither the firing conditions nor the properties of ceramic magnitudes can be known. The particle size distribution of the eastern part of the Douala sub-basin showed that they are made up of fine particles.