Discussion on the influence factors of flux on determination of highcontent carbon in iron and steel by sodium carbonate calibration-highfrequency combustion infrared absorption method
ZHONG Hua
Pangang Group Research Institute Co., Ltd., State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization, Panzhihua 617000, China
Abstract：The determination of carbon by high frequency combustion infrared absorption method belonged to relative measurement. The instrument should be calibrated with certified reference material containing carbon such as sodium carbonate. The key of this calibration method was to select appropriate flux conditions to make sure that the combustion release rate of carbon in chemical reagent and the sample of iron and steel was the same. The influence factors of flux on determination of high-content carbon in iron and steel (mass fraction of 1.0%-5.0%) by sodium carbonate calibration-high frequency combustion infrared absorption method was inveatigated in experiments. According to GB/T 223.86-2009, the calibration sample of sodium carbonate was placed in tin capsule. The tin-iron-tungsten ternary flux was adopted for determination. The results showed that the determination results of carbon in sodium carbonate were lower than that in certified reference material of iron and steel. Moreover, this phenomenon was more significant with the increase of carbon content. It was indicated that if the tin-iron-tungsten ternary flux was used, the determination results of carbon in iron and steel sample would be higher than the certified value when sodium carbonate was used for calibration. The orthogonal test (three factors and three levels including the amounts of tin, pure iron scrap and tungsten particle) showed that the flux of tin had most significant influence on the determination. The addition of tin flux was disadvantageous to the determination of sodium carbonate calibration sample. Moreover, the influence of tin flux on the determination of carbon in carbonate calibration sample was more obvious than that in certified reference material of pig iron. Therefore, the binary flux of iron and tungsten was used for determination and the flux conditions were optimized. The results indicated that the flux conditions in sodium carbonate calibration were listed as follows: 1.00g of pure iron powder and 2.0g of tungsten particle were added successively on the sample; the conditions for iron and steel sample were listed as follows: 2.0g of tungsten particle and 0.50g of pure iron powder were added successively on the sample. The calibration sample of sodium carbonate was determined under the above optimal flux conditions to plot the calibration curve. The calibration range for the mass fraction of carbon was 1.00%-5.00%, and the linear correlation coefficient of calibration curve was up to 0.9999. The content of carbon in eight certified reference materials of high-carbon iron and steel was determined under the optimal flux conditions. The results were consistent with the certified values, indicating that the combustion release rate of carbon in sodium carbonate calibration sample and the sample of iron and steel was consistent. The experimental method was applied for the determination of carbon in five production samples of iron and steel. The relative standard deviations (RSDs, n=5) were between 0.21% and 0.33%. The determination results were basically consistent with those obtained by tube furnace combustion-gravimetric method.
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