Compositional diversity of vitrified silicate ceramics: Delimiting the chemical perimeter of industrial bodies

The compositional diversity of vitrified silicate ceramics has been quantified through multivariate statistical analysis and by means of specific chemical parameters of bodies. Distinct compositional spaces can be drawn for porcelains, porcelain stoneware, red stoneware, and silicate glass-ceramics. Porcelain and vitreous china bodies are strongly peraluminous with commonly a potassic character. A sharp boundary at ~79 % alumosity separates them from porcelain stoneware bodies, which are peraluminous with a predominantly sodic character. The comparison of glazed versus unglazed porcelain stoneware revealed essential differences in iron content, but a deeper analysis is needed at the manufacturing district scale. Glass-ceramic bodies are peralkaline and low in silica. Red stoneware is characterized by Fe2O3 content about 3–9 wt% and variable Na/K and alkali-to-alkali￾earths ratios. The compositional gap between red stoneware and porcelain stoneware bodies (1.5 % < Fe2O3 < 3 %), still unexploited by industry, is crucial to enable many resource efficiency and waste recycling actions. The formulation of waste-based silicate ceramics usually implies a shift of the chemical composition towards higher Fe2O3/Al2O3 ratio and lower alkali-to-alkali earth ratio. This can lead to batches that fall outside the compositional space of porcelain or porcelain stoneware, opening to technological behaviour and technical performance that require further research.