Ohiko Kammori1, Naoharu Yamaguchi1 and Hideo Kanno1
1Tokyo Research Institute, Yawata Iron and Steel Co., Ltd., Kawasaki
The detection limits and the precision of vacuum fusion-mass spectrometric analysis of microamounts of gases in iron and steel are considerably affected by both the blank value of crucibles and thermal insulators and the variation of the blank. Therefore, some kind of crucibles and insulators were compared to reduce the blank value.
The insulating method in which the crucible was wrapped by graphite fiber felt and graphite fiber powder was packed between them showed a lower blank value and made it easy to exchange the crucible and to evacuate the furnace.
The blank value of the graphite crucible was reduced by heating the crucible to red and washing in the boiling solution of sulfuric acid or by making many holes in the crucible, but the blank value obtained varied by each treatment. The glassy carbon crucible was found to be suitable only for small amounts of sample. The porous graphite crucible was best suited to the analysis of microamounts of gases in iron and steel: The blank value of oxygen in this crucible was approximately 1.0 μg/5 min, and it was proved that 0.5 g of oxygen could be determined by measuring the blank value before each analysis.
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