Certified Reference Materials for Micro-Analysis of Carbon and Nitrogen

Abstract.

Quantitative analysis by electron probe micro analysis (EPMA) is usually carried out by reference to materials of known composition (standards) but because of the low X-ray yield arising from electron bombardment of low atomic number elements there is a particular problem when analysing these elements. This paper addresses the problem by describing briefly the production and certification of reference materials for two elements, carbon and nitrogen. Cementite (Fe₃C), a line compound, was chosen as a suitable material for carbon and γ′-Fe₄N for nitrogen. The compounds were produced by, respectively, carburising or nitriding pure iron under carefully controlled conditions. Particular emphasis is placed on a homogeneity study, background correction methods and methodology validation using these reference materials. A linear relationship was established between the certified content of the material and zero. Certified values (6.69±k 0.13 wt% C and 5.77±k 0.094 wt% N) were assigned for the composition, where k is the coverage factor.