Volcanic ash as flux in clay based triaxial ceramic materials, effect of the firing temperature in phases and mechanical properties

The study of possible incorporation of nontraditional starting powders is a contribution to the rational utilization of raw materials in the ceramic industry. The technological properties of solid waste problems (both urban and industrial) in many cases are not correctly studied and reported. The main objective of the present work is to study and demonstrate the applicability of the volcanic ash for the fabrication of clay based ceramic materials as the flux fraction for replacing feldspar. This paper deals with a particular raw material (volcanic ash) but the results can be extended to materials resulting from similar sources and properties. The milled volcanic ash was characterized and employed as a flux agent replacing feldspar in a model triaxial ceramic material (clay–quartz–flux) formulation. Previously, the volcanic ash was characterized. Differential Thermal Analysis and termogravimetry (DTA–TG) in order to establish the firing conditions were also carried out. Afterwards, the thermal treatments (900–1300 °C) conditions were studied: the firing temperatures were correlated with the shrinkage–porosity–density evolution.The crystalline phase thermal evolution was also established and compared to the one observed in the model feldspar based material. Finally the mechanical properties of the obtained materials (flexural strength and dynamic elastic modulus) were evaluated. The results permitted to corroborate the applicability and establish some of the technological properties of ash based ceramic material.