Volcanic ash as alternative raw materials for traditional vitrified ceramic products

Investigation on the use of volcanic ash as 100% raw materials for traditional vitrified ceramic products is reported. X-ray diffraction (XRD), thermogravimetric-thermal differential analyses (DTA-TGA) and chemical analysis were used to characterise raw samples. Fired specimens were used to evaluate their ceramic properties. Volcanic ash contains essentially classical traditional ceramic oxides, plagioclase, pyroxene and olivine as principal minerals. In the temperature range 1100-1150 degrees C, they present dense structure, low open porosity, without isolated quartz grains. The fired materials properties were found to be in agreement with those of stoneware class BI referring to standard ISO 13006 (i.e. the water absorption values were <1.5%). The presence of a sufficiently extended glassy phase capable of embedding crystalline phases developed during sintering allows comparison of the microstructure of fired volcanic ash with that of traditional porcelain or stoneware.