Fast drying for the manufacturing of clay ceramics using natural clays

Abstract

In this work, the feasibility of using natural clays for the manufacture of clay ceramics processed by fast drying was studied using mixture design (DoE). Three clays were selected and their chemical (XRF), mineralogical (XRD) and particle size characteristics (laser diffraction) were determined. A plastic clay, a sandy clay and a claystone were used in a simplex centroid mixture design resulting in 10 compositions that were processed by extrusion. The extruded samples were subjected to forced drying in fast cycles of 180 min. The performance of the process, content of coarser particles, moisture loss and drying shrinkage were evaluated by response surfaces. As a result, the plastic clay was the most significant factor for the properties under analysis, since mixtures using above 33% of this clay resulted in losses of moisture by drying greater than 50%. The plastic clay showed low content of coarser particles (>45 μm), therefore hindering the diffusion of water between capillaries, resulting in high shrinkage and causing cracks during drying. The use of claystone could stabilize the shrinkage in the neutral zone of drying, minimizing the number of defective samples during drying caused by cracking.