Effect of presynthesis of Ta precursor on the formation of Ta nitrides
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Jae-Hwan Pee Ceramicware Technology Center, Korea Institute of Ceramic Engineering and Technology, Icheon, Korea
Hyung-Ho Parka) Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea (Received 11 October 2009; accepted 19 January 2010)
We synthesized Ta3N5 by ammonolysis of Ta(OH)5. Ta(OH)5 was prepared by titration using TaCl5. The stirring speed and the amount of NH4OH to be added were important factors for controlling the particle size and formation of Ta(OH)5 during titration. During transformation of Ta(OH)5 to Ta3N5, the color changed from white to red. A small particle size and high level of formation of Ta(OH)5 improved nitridation, which was related to the color value. An x-ray diffractometer was used for phase identification. A scanning electron microscope was used to determine the microstructure, particle shape, and size. A colorimeter was used to obtain CIELab values. Ultraviolet–visible (UV–VIS) spectroscopy was carried out to determine the absorbance of colored powders. Thermogravimetry and a differential scanning calorimeter were used in air with a heating rate of 5 C/min for thermal stability and behavior. An ON detector was used for detecting oxygen and nitrogen contents in Ta3N5. I. INTRODUCTION
Among the inorganic pigments that are currently widely used, red and yellow pigments contain large amounts of heavy metals and transition metals, which can have negative effects on the environment and the human body if their amounts exceed tolerance limits. Red and yellow cadmium-based pigments are hazardous substances; they are harmful to human health and raise other environmental issues upon disposal and incineration.1,2 Furthermore, the restriction of hazardous substances (RoHS), enforced in 2006 by the European Union, strongly limits the use of heavy metals. Therefore, it is necessary to develop alternatives to special pigments that are nontoxic and inherently stable. Nanosized a-Fe2O3 (red), frit capsulated CdSe/CdS (red and yellow), TaON (yellow), and Ta3N5 (red) are being actively studied as Cd-free alternatives. a-Fe2O3 is synthesized by hydrothermal synthesis and other methods, and the shape and size of its particles are adjusted to control color expression.3 To ensure the continued use of CdSe pigments that exhibit reddish colors well, Ferro, a performance materials company, has also experimented with the idea of Cd-based substances encapsulated with frit to prevent the extraction of hazardous materials.4 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0114 J. Mater. Res., Vol. 25, No. 5, May 2010
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Among various alternative Cd-based pigments that have been studied, TaON and Ta3N5 have drawn the most attention.1,5–9 TaON and Ta3N5 are semiconducting compounds that can freely exhibit a wide range of colors from white through yellow, orange, red, and brown to black because of the electronic interband transition between the valence band and the vacant conduc
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