Volumen II - SAM

plasticity of both clays. The incorporation of EAFD is beneficial to the Bclay, displacing its position to the
acceptable extrusion region. By contrast, the influence of the EAFD in the plasticity of the Aclay is
practically insignificant. In practice, the incorporation of up to 20 wt.% of EAFD did not change
significantly the workability of the Aclay.
Figure 1. Extrusion prognostic through the Atterberg Limits. [14]
Figures 2 to 4 show the water absorption, diametral compression and diametral shrinkage of the fired
ceramic body compositions as a function of the amount EAFD, respectively. One should observe that the
water absorption, Fig. 2, of all compositions with Bclay are higher than the Aclay. This is associated with
the general refractory behavior of kaolinitic clays [15,16], like the Bclay investigated in this work. With
respect to the effect of the EAFD incorporation, it is observed that in the Bclay, within the error bars, the
water absorption practically does not change. On the other hand, with the Aclay, the water absorption tends
to decrease with EAFD incorporation, mainly, for 20 wt.% incorporation. Probably the presence Na2O in the
EAFD formed eutectics easily with the Aclay due to the higher amount of SiO2 and lower amount of Al2O3.
Consequently, the liquid phase was generated in higher amount with the Aclay, which helps to make
possible a more efficient closing of open pores.
According to Figure 3, it is observed that the compositions with Bclay have higher mechanical strength than
that with Aclay composition. In principle, one would expect the opposite due to the lower values of water
absorption, i.e., open porosity, of the compositions with the Aclay. This apparent contraditory result may be
attributed to the higher amount of free SiO2 present in the Aclay. It is well-known that coarse quartz particles
decreases the mechanical strength of the ceramic due to its allotropic transformation around 573 o C,
generating cracks [17]. Fig. 3 also shows that, statistically, there is no change in the mechanical strength of
the Bclay with EAFD incorporations. By contrary, the Aclay displays significant improvement on the
mechanical strength with the amount of incorporated EAFD. This may also be due to the larger amount of
formed liquid phase, which proves that the mechanical strength of the ceramic materials is not dependent
only of the open porosity. Cracks, close porosity and flaw size, among others, are also important factors that
influence the mechanical performance of brittle materials.
Finally, Figure 4 shows that the EAFD incorporation did not change the shrinkage of the ceramic
compositions incorporated with both clays. It is also observed that the Bclay compositions display higher
shrinkage that can be attributed to the higher amount of loss on ignition.
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