Synthetic Conditions and Color Characteristics of Tantalum Oxynitride Prepared via Liquid-NH3Process
Tantalum oxynitrides, such as TaON, exhibit promising color properties and can be employed as nontoxic yellow pigments containing no heavy metals. We have developed a process for preparing nitrides or oxynitrides involving the vacuum-calcination of a precursor material obtained via reaction between a metal halide and liquidNH3. Herein, we describe the synthetic conditions of the liquid-NH3process that affect the color, and thus the color characteristics, of the resulting pigments. Reaction and postreaction treatment conditions were adjusted to obtain the desired yellow color. The liquid-NH3process was performed using 1.0 eq ofH2O(relative toTaCl5) as the oxygen source and 30.0 eq of KCl (relative toTaCl5) as flux. Calcination of the precursor at 1073 K under vacuum was followed by recalcination from room temperature to 973 K at rate of 10 Kmin−1under air. A powder with a color index ofL∗=84.20,a∗=−2.71, andb∗=44.07was obtained.