Reduction of maturation point in crystalline glaze through frit addition

Abstract

This study aims to systematically investigate the effect of frit addition into crystalline glaze on the maturation point decrease. The samples were based on a general formula: (x)[Frit] + (1 − x)[Base glaze]; x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 (by weight fraction). In depth, melting behavior coupled with microstructural alterations was examined by various characterization techniques to gain sufficient technical knowledge and bring about the science behind crystalline glazes. Between 1125 and 1200 °C, crystallographic changes took place, resulting in an amorphous or non-crystalline structure as evident by a small XRD halo in the 20–35° 2θ range which is typical for silicate glass structure as further confirmed by infrared spectroscopy. Raman broad peaks could be deconvoluted to extract information on the mean number of non-bridging oxygen. Increasing frit amount resulted in an increase in the degree of non-oxygen bridging which could be associated with the pivotal role of the frit as a network modifier in the glass structure. The non-fritted glaze started to sinter at approximately 1091 °C and finally reached its half-sphere point at 1200 °C. Increasing the frit to 20 wt % resulted in a drastic decrease in the sintering point down to 994 °C with a half-sphere point lying in the 1175 °C range. If considering the half-sphere point as a crude estimation of the onset of maturation, adding frit by 20 wt % could effectively lower the melting point by 25 °C whereas a higher amount of frit (40 wt %) suggested the glaze to be matured at as low as 1005 °C. Although the lowest maturation starting point could be lowered to 900 °C for the sample with 100 wt % frit amount, such composition might not be appropriate for the current study on crystalline glaze as the fraction of ZnO to the total glaze body might not be sufficient enough for crystallization of willemite (Zn2SiO4) phase.