Design of Experiments with Mixture Variables as a Tool for the Formulation of Pigments: The Case of the Blue (V-ZrSiO{sub}4)

摘要

Pigments play a crucial role in the manufacture of ceramic tiles. Today, the process most commonly used in the industrial synthesis of these pigments is the solid state reaction of oxides and other raw materials. Although this process has long been utilized, the role of the several variables involved is as yet little understood, so most manufacturers still work with formulas without a real understanding of the process. Under such conditions, if any given raw material is unavailable or too costly and must therefore be replaced, or even if the characteristics of a raw material have changed, the formula may no longer work adequately, thus posing a serious problem for the manufacturer. In this context, the present work purported to apply the design of experiments (DOE) tool to mixtures in order to study the synthesis of turquoise blue ceramic pigment V-ZrSiO{sub}4. To this end, the variable to be studied was the proportion of ZrO{sub}2, SiO{sub}2, V{sub}2O{sub}5 precursors and mineralizers, for which the necessary combination was determined for a linear model with a central point, using statistical software. The control parameters were the colorimetric readings of the tile samples, which were prepared under standard conditions simulating the real setup and were fired simultaneously in an industrial kiln. The processing conditions were standardized to allow for a comparative evaluation of the results, which were treated with statistical software. A linear polynomial then was modeled with an inverse term that relates the measured property (△E) as a function of the contents of the three different raw materials used in the desired pigment. This simple procedure enhanced control over the manufacturing procedure, facilitating the evaluation of substitute raw materials and providing information regarding the consequences of changing the proportion of raw materials.