Evaluation of Pure Substances as Oxygen Reference Materials for Inert Gas Fusion Infrared Absorption Method

With the growing demand for less uncertainty in the determination of oxygen in steel, an alternative reference material has been investigated. Among the several pure substances we experimented on using an infrared method after fusion under an inert gas, potassium dichromate, when being dropped into a tin bath of 1 g at a temperature of 2300 degrees C, was completely decomposed and showed an oxygen analysis value that conformed with the theoretical value with a good repeatability standard deviation (sigma < 2 mu g/g) and good linearity (R(2) = 0.9997) to 500 mu g/g in the calibration curve. A suitable amount of tin bath is needed when using potassium dichromate, because the oxygen that it contains cannot be completely extracted without a tin bath. These results show that potassium dichromate is applicable for calibration. The oxygen analysis results of other pure substances didn't conform with the theoretical values. To identify the causes of the discrepancy, we further analyzed, using FT-IR, the composition of evolved gases generated at the impulse furnace. Carbon dioxide and hydrocarbon gases were detected in addition to carbon monoxide. We also found from the infrared absorption spectrum that potassium hydrogen phthalate contained water of crystallization when being dried. These are considered to be the causes that make the oxygen analysis results higher than the theoretical values.