Speciation of chromium in solid materials with the aid of soft-X-ray spectrometry

Chromium compounds can be found in many different forms in steel and steel coatings. They are capable of strongly influencing the mechanical and technological properties of the material. Chromium occurs in steel mainly as a metal or in the carbide or nitride form. In the surface refinement of steel sheets, Cr(III) and Cr(VI) compounds are also used. With the development and optimisation of metallurgical processes, there is an increased demand for the determination of compounds in which chromium is present. X-Ray-spectra in the soft-X-ray area (2-15 nn) contain all the information necessary for characterisation and quantification of the chromium compounds. Generation and analysis of these X-ray spectra is in principle easily possible with a common wavelength-dispersive X-ray-fluorescence spectrometer. When an electron source for low-energy electrons (2-6 keV) is used instead of the usual X-ray tube, essentially better results are obtained, in comparison to the conventional X-ray-fluorescence spectrometer. The technical steps for changing an X-ray-fluorescence-spectrometer to a soft-X-ray-spectrometer are described. At the hand of the examination of galvanised steel sheets the analytical potential of this method was tested. The differentiation between Cr(III) and Cr(VI) is possible with sufficient precision. (C) 1999 Elsevier Science B.V. All rights reserved.