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Because the liquid-N process involves the circulation of an inert gas within a glove box, the atmosphere is reductive and thus the oxidation number of Ta can be lower than expected. Our aim is to clarify the conditions of the liquid-N process that control the color of the products, and to understand the color characteristics of the resulting pigments. In one case, the color of the tantalum oxynitride prepared via the liquid-N process was different from the color of TaON (Yellow TaON) prepared via the gas nitriding process using a flow of moist N gas, but was similar to that of green TaON. Because the liquid-N process allows for the precise control of the elemental composition of the starting materials, the process is suitable for screening new pigment compositions. In contrast, the liquid-N process affords the nitride or oxynitride through vacuum-calcination of a precursor material obtained by the reaction between a metal halide and liquid-N. 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 NH 3 gas under high temperatures. 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. The development of green chemical processes is not only desirable but expected for creating a sustainable society in harmony with nature. A powder with a color index of, , and was obtained. Calcination of the precursor at 1073 K under vacuum was followed by recalcination from room temperature to 973 K at rate of 10 K under air. The liquid- process was performed using 1.0 eq of (relative to ) as the oxygen source and 30.0 eq of KCl (relative to ) as flux.

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Reaction and postreaction treatment conditions were adjusted to obtain the desired yellow color. Herein, we describe the synthetic conditions of the liquid- process that affect the color, and thus the color characteristics, of the resulting pigments. 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. Tantalum oxynitrides, such as TaON, exhibit promising color properties and can be employed as nontoxic yellow pigments containing no heavy metals.

$crystaldiffract download 1.4$

Crystaldiffract download 1.4