Effect of air adsorption in discharge chamber on the determination precision of oxygen content in automobile steel sheet by spark discharge atomic emission spectrometry
SHEN Ke
Quality Inspection Center of WISCO, Wuhan 430083, China
Abstract：During the determination of oxygen by spark discharge atomic emission spectrometry (SDOES), it was found that the detection limit was high. Aiming at this problem, the effect of air adsorption in discharge chamber on the determination precision of oxygen content in automobile steel sheet by SDOES was discussed. The results showed that the air was sucked into discharge chamber due to Bernoulli′s effect, leading to air adsorption. The oxygen and water vapor could not be fully removed by pre-flush argon before discharge, resulting in the worse precision for the analysis of oxygen. Some measures were adopted in experiments: the excitation hole was covered with sealing block for use when the sample was not analyzed; the sample was processed to flat and smooth to make sure that there was no gap between sample and excitation platform, which could reduce the intake of air. The background fluctuation of O 130.1nm line could be effectively controlled. The relative standard deviation (RSD) decreased from 14.2% before sealing to 5.5% after sealing. The calibration curve of oxygen was prepared using standard sample of low alloy steel. The correlation coefficient (r) was 0.9902, and the low limit of determination was 0.00096%. The samples with oxygen mass fraction of 0.0037% and 0.0011% were used for precision test. The RSD of results was 7.5% and 9.8%, respectively. The analysis results of automobile steel sheet sample by the experimental method were compared with the national standard (i.e., pulse heating inert gas fusion-infrared absorption method). The difference was less than the critical difference (CD0.95) specified in GB/T 11261-2006. Under experimental conditions, the working efficiency of proposed method was higher than the infrared absorption method for batch analysis of oxygen samples.
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