Sulfur is a harmful impurity, and its content must be strictly limited in steel. Sulfur, as a non-metal element for routine analysis, has a long characteristic wavelength due to excitation, low energy, and is greatly affected by the light path, so it is a more sensitive element in the analysis of spectrometers. In daily analysis, the effects of instrument drift, such as abnormal power supply, equipment vibration, aging of photomultiplier tubes, etc. For sulfur, the excitation intensity generally deviates to the low end, which is prone to data inaccuracies.
Analyze the reasons
Influence of argon
Argon can prevent the surface of the sample from being oxidized, increase the ratio of the background to the intensity of the spectral lines, and stabilize the quality of the excitation. The stability of sulfur analysis is related to the flow and pressure of argon, and it is also affected by the purity of argon.
The influence of argon is divided into three aspects: (1) impure argon; (2) the argon flow is too small; (3) the static flow of argon.
(1) The intensity of sulfur fluctuates to some extent when the argon is impure, which generally appears as irregularly low, and standardization cannot eliminate the effect. This effect is easy to find. Once the argon is impure, the excitation appears as an abnormal sound. It sounds sharp, and the excitation point is not normal. When the argon gas is severely impure, there are white spots on the edges, and there are white flowers on the edges of the points when it is slightly impure, because the presence of oxygen in argon will re-excite the initial stage to combine with metal atoms to form an oxide layer, which will disturb or even destroy the entire excitation process. , So that the strength of sulfur is affected to varying degrees. The key to eliminating this effect is to ensure that the purity of argon is not less than 99.995% and that the airtightness of the pipeline is good.
(2) The effect of argon flow and pressure is too small. The flow rate and pressure of argon gas determine the impact force of argon gas on the discharge surface of the sample. If the flow rate and pressure of argon gas are too small, the impact force is low, which is not enough to flush out the oxygen and oxides generated during the sample excitation. The oxide will condense on the surface of the sample and the electrode, which prevents the sample from continuing to evaporate, causing the sulfur element to not evaporate completely and the final analysis result to be low (this phenomenon is also applicable to other elements). The flow rate and pressure of argon make the argon gas in the excitation chamber insufficient, make the excitation quality poor or incomplete, and the intensity of sulfur appears to be severely low or not. As long as the argon flow rate is increased, it can be solved. Check the argon first before normal analysis. Gas flow pressure gauge, the output pressure is controlled between 2.2Mpa-2.5Mpa, and the flow rate is 3.5L / min.
(3) Influence of static flow of argon. The spectrometer must ensure a certain static flow rate when it is not in analysis or for a period of time. The flow rate of static argon is controlled about 0.2 ~ 0.5L / min. There is no static argon or insufficient static argon in the optical path, which will affect the light intensity of elements below 200nm. The light intensity value of S is low and accompanied by instability, and the light intensity value increases continuously over time. The solution to this phenomenon is simple. Excite a few times and wait for more than 30 minutes. (This phenomenon also applies to C and P elements)
2.Effect of displacement of the entrance slit due to vibration
The entrance slit is very important in the photoelectric direct-reading spectrometer
. From the perspective of imaging relationship, the spectrometer is a monochrome image of the entrance slit. The quality and position of the entrance slit directly affect the quality of the spectral line. The situation that the incident slit is displaced due to vibration does not manifest itself in a short time, and it is generally not easy to detect. At this time, the internal standard line can be scanned. In addition, analyzing the indoor temperature and humidity fluctuations too large can also make the element spectral lines deviate from the exit slit.
3. Impact of lens contamination
Metal dust and gas are generated during the excitation of the sample. Most of these dust gases will enter the filtering system with argon, and a small amount of dust S vapor will reach the lens through the optical path and be adsorbed on the surface of the lens due to the high temperature of the lens. After a long time, a yellow adhesion layer will be formed on the surface of the lens, causing a decrease in light transmittance and affecting the absolute strength of the measurement.
As long as it is not deep contamination in the case of lens anomalies, drift correction can eliminate this effect. To maintain the best condition of the instrument, clean the lens once a month.