2003 Volume 89 Issue 9 Pages 988-993
The trace oxygen analysis in steel is usually measured by infrared method after fusion under inert gas. For the high accuracy analysis of the trace oxygen, it is necessary to remove completely the oxide of the sample surface ahead of the determination. Also it is important to decrease the carbon monoxide gas evolved from the graphite crucible. The sample after the surface oxide is removed is oxidized easily or adsorbs moisture. Therefore, it is necessary to analyze without exposing the sample to atmosphere after the oxide film is removed. Then, to take out the sample in the graphite crucible in the closed system, the mechanism of impulse furnace has been improved. To remove the oxide film of the sample surface, the sample was heated for 60 sec by the inert gas fused furnace of 1000°C. The sample was cooled down to the room temperature in the impulse furnace. The sample was taken out of the graphite crucible with a magnet stick after granule Sn was dropped in the closed system. The sample and the magnet were kept above the upper electrode in the closed system. Afterwards, oxygen in Sn was reduced to carbon monoxide gas and removed by heating at 2400°C of the temperature in which the sample was analyzed. When the base line became a constant, the output signal was initialized. The sample kept with the magnet was dropped and melted. Oxygen was reduced to the carbon monoxide, and measured with the non-dispersion infrared detector. The analytical result of the oxygen of steel sample JSS GS-6b (oxygen concentration 3.4 μg·g-1) that removed the surface oxygen was 2.9μg·g-1, and the standard deviation was 0.05 μg·g-1. This standard deviation has been improved to past 1/4.