Precipitation synthesis of Zn2-xCoxSiO4 blue ceramic pigments: Color performance and application

Abstract

A simplified precipitation route based on using silica hydrogel derived from serpentine minerals as a source of silica SiO2 has been first applied for producing blue cobalt-doped willemite pigments. The relevant variations of cobalt ions concentrations in SiO2–NaOH–ZnCl2–CoCl2–H2O system adequate with Zn2-xCoxSiO4 compositions where 0<x ≤ 0.92 and heat-treatment at 900 °C have yielded the pigments demonstrating a wide spectrum of blue tints. The optical characteristics of these pigments have revealed that Zn1·5Co0·5SiO4 pigment is distinguished by the highest absorption responsible for deepest blue hue similar to ultramarine. The comparison of their chromatic parameters with those of the identical ones produced by sol-gel routes has shown that the synthesized pigments with the compositions where x = 0.2 ÷ 0.5 manifest competitive color performances. The synthesis optimization has reduced calcination temperature up to 800 °C and stirring time up to 60 min. The homogeneity achieved in the intermediates by the suggested synthesis has yielded the pigments having uniform crystalline structure with controlled particle size. 120-minutes stirring has reduced the pigment particle size to dimensions less than 66 nm. Zn1.5Co0.5SiO4 pigment exhibits excellent color performances and tinting on heating up to 1200 °C and in wall tile glaze.