MULTIELEMENT CHARACTERIZATION OF SILICON-NITRIDE POWDERS BY INSTRUMENTAL AND RADIOCHEMICAL NEUTRON-ACTIVATION ANALYSIS

An optimized instrumental neutron activation analysis method was applied to the comprehensive trace characterization of good- and high-purity silicon nitride powders of different origins. Experimental modes are given for 55 elements leading to limits of detection below 1 ng g-1 for 28 elements, between 1 and 100 ng g-1 for 19 elements and higher than 100 ng g-1 for 8 elements. For the removal of the radionuclides La-138, Ta-182 and W-187, which cause the major activity in certain types of materials, radiochemical procedures based on cation exchange from 2 M HCl and anion exchange from 2 M HF were developed. Cu-64 was selectively extracted with dithizone from 10 M HF for counting the 511-keV line. By radiochemical neutron activation analysis, the limits of detection were improved by up to three orders of magnitude. Comparison with results obtained by inductively coupled plasma (ICP) atomic emission spectrometry and ICP mass spectrometry shows satisfactory agreement and demonstrates the advantages of neutron activation analysis especially when low elements contents are to be determined.