1997 Volume 83 Issue 7 Pages 419-424
In our previous paper concerning the analysis of low carbon steel by atomic emission spectrometry, carbon intensity was found to increase considerably with the rise of sample temperature before discharge and with the time intervals between analyses. However, the mechanism of this intensity rise has not been known. Therefore, we tried to establish a model for this mechanism.
The results were as follows:
(1) The analytical value of carbon increased 0.2ppm with 1°C rise in sample temperature before discharge. It is explained from the additional atomic emission; (1)an oxide layer produced on the sample surface was thicker as the sample temperature rose.; (2)carbon monoxide gas (CO gas) was formed through the oxidation of carbon in the sample by the oxide layer (C+O_??_CO).;(3)the formed CO gas was introduced in a discharge column and decomposed to C and O to give rise to the carbon intensity.
Therefore, to analyze carbon in low carbon steels accurately, the sample temperature before discharge should be adjusted to room temperature. If the sample temperature is higher than room temperature, we must grind the sample again after cooling the sample to lower temperature than room temperature and adjust the sample to room temperature.
(2) Carbon intensity increased when the time intervals between analyses were prolonged. It is considered that this increase results from water adhesion to W-electrode; (1)in the time intervals, the dust as by-product of discharge adhered to W-electrode.; (2)as being discharged under this condition, CO2 in water adsorbed to the dust was introduced in discharge column and decomposed to C and O to give rise to carbon intensity. Therefore, to analyze carbon in low carbon steels accurately, we needed to remove the dust adhered to W-electrode by discharge of cleaning or heating of Ar gas as an atmosphere.
