Development of analytical methods for the determination of trace impurities in non-oxide advanced ceramics by ICP-AES

New uses of non-oxide advanced ceramics have been expected because of their attractive properties, such as high melting point, hardness and high electric conductivity. Because their properties are markedly affected by impurities (some metals, carbon), the determination of metal impurities is important in their characterizations. In the present thesis, the determination of metal impurities in TaC, TaN, TiB2, TiSi2, VC, ZrB2 and ZrSi2 powder samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) is presented. For ICP-AES, the powder samples must be digested into solution. Considering the contamination from reagents, decomposition vessels and the decomposition procedure, itself, sample-decomposition procedures with inorganic acids were carried out under high pressure in a PTFE pressure vessel. In a series of decomposition studies, several new findings concerning the acid-resistance of the ceramics mentioned above were obtained. Although it has been reported that, for instance, TaN was insoluble in all acids, TaN could he dissolved in a mixture of hydrofluoric acid and hydrogen peroxide solution. The matrix effects on the background levels and the emission intensities of the impurity elements in the ICP-AES measurement were compensated by matrix-matched standard solutions for a calibration. For most elements, the values obtained by the proposed method were in good agreement with those obtained by atomic-absorption spectrometry. These results indicate that the proposed methods discussed here are useful to determine metal impurities in ceramic powders and that they will contribute to the development of new applications of non-oxide advanced ceramics.