Use of soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix

The study was directed towards determining the feasibility of using soda-lime scrap-glass as a fluxing agent in a porcelain stoneware tile mix. Both laboratory and industrial scale tests were carried out. Starting from a reference mix composition, different amounts (5–20 wt.%) of sodium feldspar were replaced with the same amounts of soda-lime scrap-glass. The soda-lime scrap-glass was added in the form of powder, prepared by wet grinding in a centrifugal ball mill. The rheological study of the resulting slips showed that increasing the amount of glass in the mix composition increased the viscosity but decreased the yield stress. Both the laboratory experiments and results of industrial trials showed that the only mix in which the soda-lime glass acted as a good fluxing agent, i.e. lowered the firing temperature, was the mix in which the scrap-glass replaced 10 wt.% of the sodium feldspar. This mix also showed better mechanical characteristics, attributed to enhanced microstructural homogeneity.