Abstract
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 liquid NH3. Herein, we describe the synthetic conditions of the liquid‐NH3 process 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‐NH3 process was performed using 1.0 eq of H2O (relative to TaCl5) as the oxygen source and 30.0 eq of KCl (relative to TaCl5) 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 K min−1 under air. A powder with a color index of L∗ = 84.20, a∗ = −2.71, and b∗ = 44.07 was obtained.
Highlights
The development of green chemical processes is desirable but expected for creating a sustainable society in harmony with nature. Tantalum oxynitrides, such as TaON, have shown promise as nontoxic yellow pigments containing no heavy metals, which are similar to praseodymium yellow and cerium zirconium bismuth based oxide [1]. These materials have been prepared via a gas nitriding process, in which tantalum oxide is transformed into the nitride under a flow of NH3 gas under high temperatures [1]
The color of the tantalum oxynitride prepared via the liquid-NH3 process was different from the color of TaON (Yellow TaON) prepared via the gas nitriding process using a flow of moist NH3 gas, but was similar to that of green TaON [5]
Using a liquid-NH3 process, we have prepared a TaON powder that can be employed as a nontoxic yellow pigment containing no heavy metals
Summary
The development of green chemical processes is desirable but expected for creating a sustainable society in harmony with nature. Tantalum oxynitrides, such as TaON, have shown promise as nontoxic yellow pigments containing no heavy metals, which are similar to praseodymium yellow and cerium zirconium bismuth based oxide [1]. To date, these materials have been prepared via a gas nitriding process, in which tantalum oxide is transformed into the nitride under a flow of NH3 gas under high temperatures [1]. An additional recalcination step in air was carried out after the vacuumcalcinations
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