2001 Volume 87 Issue 12 Pages 756-761
Removing the oxide from sample surface is important in analyzing clean steel by infrared method after fusion under inert gas. Generally electropolishing or chemical polishing methods are used as sample pretreatment. No method without grow-discharge method could be perfectly eliminated surface oxide. It is because of exposing sample to air, re-oxidation caused easily. The oxide is not negligible to analyze trace oxygen in the bulk. In order to control surface oxide, sample was preheated two times at 1050°C in graphite crusible. After sample was preheated at 1050°C, clean surface was obtained. To transfer the sample from graphite crusible to throw position, first oxide caused easily by exposing to air but it controlled. After the first oxide was analyzed at 1050°C, the same procedure to transfer the sample to throw position was done. Second oxide also caused easily. The oxide and bulk oxygen were together analyzed at 2400°C for total oxygen. Both first and second oxides were same volume and character. So we could calculate bulk oxygen to eliminate second oxide from total oxygen. Analytical curve was made from potassium nitrate method. This development method can be a quantitative analysis. The analytical results obtained from the certified materials are low about 1 ppm from certified value, but the precision is satisfactory. It estimated that surface oxide was included in the certified value.
