What to do if the stability of C, S, P measured by optical emission spectrometer is not good
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Author : Jerry He
Update time : 2020-09-28 09:00:28
C, S, Si, Mn, and P are the five conventional elements in steel, and we usually use spark optical emission spectrometer for detection. In daily use, we often encounter unstable analysis results and relatively large deviations, especially non-metallic elements such as C, S, and P. Below we will analyze the reasons for this situation.
1. The instrument didn't do standardization and CRM calibration for a long time. As a high-precision analytical instrument, calibration is essential. At the beginning of the working day, sample control calibration must be carried out first to ensure the accuracy of the instrument before the sample analysis can be started. In addition, every half a month or so, the curve will drift a bit. At this time, we need to do standardization.
2. Sample preparation is also critical. First of all, make sure that the surface of the sample is flat and there is no air leakage. If there is air leakage, the sound will be abnormal when activated. Secondly, the thickness and direction of the abrasive grains on the surface of the sample should be consistent, and there should be no cross grains. When selecting the sample, it must be representative, and there should be no defects such as segregation, cracks, and pores.
3. The tip of the electrode should have a certain angle so that the optical axis does not deviate from the center, and the discharge gap should remain unchanged, otherwise the intensity of the spectrum will change. After repeated discharges several times, the electrode will grow sharp, changing the discharge gap. The metal vapor generated by the excitation can contaminate the electrode. Therefore, it is necessary to clean the electrode with an electrode brush and replace the electrode regularly.
4. Daily maintenance is not in place. The inner surface of the lens is often contaminated by oil vapor from the vacuum pump, and the outer surface is adhered to the metal vapor generated during analysis, which significantly reduces the transmittance. Especially, the influence on the transmittance of C, S, and P spectral lines with a wavelength of less than 200nm is more obvious, so the lens should be cleaned regularly.
5. Check whether the vacuum is sufficient. A low vacuum will affect the analysis sensitivity.
6. Check the purity of argon. The direct reading spectrometer needs to be equipped with 99.999% high-purity argon. Impure argon will cause poor excitation quality, which will affect the detection results.
7. The instrument and parts have their own service life, which will cause aging after long-term use.