Discussion on the accuracy of direct reading spectrometer analysis - Database & Sql Blog Articles

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Discussion on the accuracy of direct reading spectrometer

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Direct Reading Spectrometer

Both are applied to the pre-furnace analysis of the smelting or casting process. In order to obtain an accurate analysis result, in addition to the performance of the spectrometer itself, the correct use, operation, maintenance and management

instrument

In order to fully play its role and get accurate analysis results.

It is inevitable that errors will occur during the analysis. There are many sources of error. In terms of photoelectric spectrum analysis, in addition to the uneven composition of the standard sample and the analyzed sample, the inconsistent state of the structure, the unstable performance of the spectrum and the improper surface treatment of the sample, and the insufficient purity of the argon gas may cause errors. So for each analyst, it is important to understand the cause of the error and to further study the method of eliminating the error.

The excitation source is an extremely important component of an optoelectronic spectrometer. Its function is to provide evaporation, atomization or excitation energy to the analytical sample. There is no clear boundary between evaporation, atomization or excitation of the sample during spectral analysis, and these processes are performed almost simultaneously. This series of processes directly affects the results of the analysis. Evaporation, dissociation, excitation, ionization, emission of spectral lines and intensity of spectral lines in the sample, except for the melting point, boiling point, atomic weight, chemical reaction, dissociation energy of the compound, ionization energy of the element, excitation energy In addition to the physical and chemical properties of the atomic (ion) energy level, it is also closely related to the characteristics of the light source used. Different excitation sources have different evaporation behaviors and excitation energies for various samples and various elements, so it is necessary to select excitation sources with corresponding characteristics according to different analysis objects.

At present, there are two commonly used light sources: one is a classic light source including an arc and a spark light source, among which a high-voltage wave-control light source, a low-pressure spark high-speed light source, and a high-energy pre-spark source are widely used in metallurgical analysis, and one type is a plasma light source. Most of them are widely used in different fields.

Spectroscopic analysis commonly used light sources have the following types of discharge:

1. High-energy pre-spark discharge with a maximum current of 150 amps and a burning time of 150 microseconds, which makes the structure of the burning spots in the sample more uniform, thereby eliminating the effects of interference between elements and bonding between elements.

2. Spark-type discharge is good for reproducibility of most elements.

3. The reproducibility of arc-type discharge is 2-3 times worse than that of spark discharge, but the detection limit for trace elements is much lower.

Therefore, the following requirements should be met when selecting a light source:

1. High sensitivity, as the concentration of the element in the sample changes slightly, the detected signal has a large change;

2. Low detection limit, which can test trace and trace components;

3. Good stability, stable evaporation, atomization and excitation of the sample, so that the result has high precision:

4. The ratio of line intensity to background intensity is large (signal to noise ratio is large);

5. The analysis speed is fast and the pre-ignition time is short;

6. Simple construction, easy to operate and safe;

7. The self-absorption effect is small, and the linear range of the calibration curve is wide.

The selection of the excitation condition of the light source is determined according to the test object. The pre-combustion time is different for different samples under different light sources, which mainly depends on the evaporation process of the sample during spark discharge. It is not only closely related to the energy and discharge atmosphere of the light source, but also related to the sample. Composition, structural state, inclusion type, size, etc. are closely related.

Spark discharge in an argon atmosphere can generally be divided into two extreme states: concentrated discharge and diffusion discharge. The concentrated discharge is called when the discharge is performed on the metal phase, and the diffusion discharge is called when the discharge is performed on the non-metal phase. When discharging in argon, the main causes of diffusion discharge are as follows: 1. Purity of argon; 2. Leakage of argon inlet and outlet pipes or discharge cells is the second source of oxygen introduced during discharge. : 3. The sample itself is the third source (such as inclusions, bubbles and cracks) that introduces oxygen during discharge. When discharging in argon, argon pressure, argon flow rate and rinsing time also affect the photoelectric spectrum. Results of the analysis.

The matrix effect, also known as the coexistence element, the third element or the concomitant effect, mainly refers to the influence of all other components present in the sample except the analyte, which is the main cause of the variation of the spectral line intensity in the spectral analysis. This effect, also known as the interference effect, is the most complex problem in spectral analysis.

In actual work, due to the difference between the smelting process and the physical state of the analysis sample and the standard sample, the calibration curve is often changed. Usually, the standard samples are mostly forged and rolled, and the analysis samples are mostly cast, in order to avoid trial. The influence of the metallurgical state change on the analysis is usually a control sample that is consistent with the metallurgical process and physical state of the analysis sample, and is used to control the analysis result of the sample.

In spectral analysis, the sampling method and its handling of the sample are critical, which directly affects the accuracy and accuracy of the analysis. In the pre-furnace analysis, a rapid red cut was taken on the as-cast steel sample in the furnace, and it was found that the sample had cracks, inclusions and pores to be resampled. In the case of low carbon steel, the red material is quenched in flowing water to promote the formation of martensite and austenite in the sample structure to ensure the accuracy of the carbon analysis results. In case of high carbon sample cutting, it should be warm and cold to avoid cracks. For the analysis of cast iron and ductile iron, the analysis sample must be fully whitened, and sampling should be standardized, such as sampling temperature, demolding time, and cooling rate. It is also important to analyze different materials and use abrasive tools of different properties. Generally, alumina grinding wheels are used, the particles are medium, not too thin. The surface of the sample should be removed by 0.5 to 1.5 mm, because the oxide layer on the surface of the sample often leads to erroneous analysis results, especially for the analysis of carbon.

In short, detection and analysis errors always exist, the important thing is to treat it correctly and eliminate it. For photoelectric spectroscopy, the error is mainly caused by the following five factors:

Person: The operator's quality awareness, skill level, proficiency and physical fitness.

Equipment: Equipment maintenance is critical, the performance and reproducibility of the light source, the stability of the argon system, the sample processing equipment and its maintenance.

Sample: uniformity, representativeness, heat treatment state and structural state of the components to be tested. The uniformity of the standard sample and the control sample composition, the reliability of the standard content of the component content, and the identity of the structure. The method of grinding the sample and its effect are key.

Analytical method: the production of the calibration curve and its fitting degree, the standardization process and its effect, the selection of the control sample and the fixed value must be strictly operated.

Environment: Control the temperature, humidity, electromagnetic interference and cleaning conditions of the analysis room. With a stable operating environment, the stability of the instrument will be good.