DETERMINATION OF MICRO TRACE OXYGEN IN HIGH-PURITY IRON WITH THE INERT-GAS FUSION METHOD

Method of the determination of micro trace oxygen (ppm level) in the high purity iron has been studied cooperatively by 14 member laboratories in the Chemical Characterization Sub-committee, 19th Committee (steel making), Japan Society for Promotion of Science. The purposes of this study were set in the following focuses, 1) Improvement of analytical precision. 2) Clarification of detectable limit for oxygen determination with inert gas fusion method. 3) Establishment of sample pretreatment technique. Two types of high purity iron samples (oxygen content: < 3 ppm and 5 ppm approximately 10 ppm) were prepared at the Institute for Material Research, Tohoku University. Purities of these samples were respectively 99.995% except of carbon used to killing agent. The oxygen contents in the surface layer of the sample gave an considerable increase to the analytical values for ppm-level analysis. So, pretreatment method of the samples were mainly studied in details. As the results, the pickling method with H2O2 + HF aq. solution was established. The results obtained by the recommended procedure were compared with He3+ particles activation analytical values and the precisions of the both oxygen values in each sample were satisfactory. The detectable limit of oxygen by the inert gas fusion method was about 1.5 ppm.