Influences of composition, melt viscosity and crystallization on the color strength and stability of multioxide glass frit/zircon-vanadium pigment systems for ceramic whitewares coatings applications

Color control is becoming increasingly important in the industrial processing of ceramics coatings. Multi-oxide glass frits are the predominant materials in ceramic whitewares coatings, and zircon doped pigments are the most commonly used colorants.;The primary objective of this research was to determine if glass frits could be formulated to improve the fired color strength and high-temperature stability of ceramic coatings colored with zircon-vanadium (Zr-V) blue pigments. The results would also be applicable to other ceramic pigments that utilize the same zircon structure to incorporate colorant metal ions. A secondary goal was to relate the frit oxide composition, pigment content, firing temperature, melt viscosity and microstructural development to the fired color. A ceramic tile process was applied to fabricate sample coatings for the study. A coating's color was quantified and related to human perception with CIE L*, a* and b* values and pigment absorption factors (K/S), calculated based on spectral reflectance data.;The research was successful in quantifying the influence of individual glass frit oxides on the fired color strength and high-temperature stability of the coatings. Opaque and transparent glossy frit compositions which yield excellent color strength and stability were formulated. Mathematical models for predicting a coating's color strength and stability given the frit oxide composition, Zr-V pigment loading and peak firing temperature were derived. Frit oxides of ZrO2, SrO, ZnO, Al2O3, Na 2O and K2O were found to have a significant influence on crystallization, pigment dissolution and color development. The properties, sizes, morphologies and quantities of crystalline phases that precipitated in the coatings during firing were related to the color. A technique for producing uniquely light yet high chroma colors through control of zircon precipitate particle size was demonstrated.;In addition, a statistical model was developed for calculating the coating melt viscosity as a function of the frit oxide composition and temperature. Melt viscosity versus temperature curves were applied to predict a frit's potential for producing strong and stable color.