A study of the temperature variation effect in a steel sample for rapid analysis using LIBS
Introduction
The advent and development of alloy materials are inseparable from the needs of machinery manufacturing, transportation and the military-industrial complex. The on-line detection of the sample components is of great significance for the quality assurance, process control and end-point control of the metal smelting process. The need to increase productivity in many industrial fields has promoted the development of real-time measurement. Due to the requirement for accuracy and stability, many measurements are still performed off-line. At present, standard techniques, such as spark source atomic emission spectrometry and inductively coupled plasma optic emission spectrometry, are usually used for high precision multi-element analysis of samples [1], [2], [3]. The above techniques need to transport the molten samples to another laboratory for analysis; and the samples need preparation, which takes more time. Laser-induced breakdown spectroscopy (LIBS) has the potential for rapid analyses of samples due to its features such as no sample preparation and online analysis [4], [5], [6], [7], [8], [9], [10]. As a valuable and promising spectral analysis method, LIBS has been applied to many fields to realize rapid monitoring and on-line analysis of samples [11], [12], [13], [14], [15]. It can realize various kinds of material analysis, such as liquid, gas, solid, solid liquid mixture and so on.
Today, real-time measurement of the experimental process is a hot topic. There are many challenges for online monitoring in some complex environments. This requires us to dig deeper into the data and provide more sufficient research methods for the problems encountered in the experimental process. C. Carlhoff et al. [16] applied LIBS for the first time to carry out in-situ analysis of molten steel in a converter used in steelmaking. Aragón et al. [17] also used LIBS to analyze molten steel. The accuracy of carbon content increased to 10% in the concentration range of 150–1100 ppm. Gruber et al. [18] added admixtures inducer containing chromium (Cr), copper (Cu), manganese (Mn) and nickel (Ni) in the laboratory induction furnace to detect the LIBS signal of molten steel. Hubmer et al. [19] proposed a method to analyze the elements including Cr, Ni, molybdenum (Mo), Cu and cobalt (Co) in high alloy steel. The error of the liquid steel was less than 0.2%. Sun et al. [20], [21], [22], [23] realized monitoring of the composition change of Cr, Mn, silicon (Si), and Ni in a 30 kg induction furnace. It was proved that the ability to detect trace elements in molten steel is greater than in solid steel [24], [25], [26], [27]. However, the studies described above were mainly focused on the two states in metal measurement, solid and melt, which did not involve the spectral line variation regularity between the states of solid and melt in steelmaking.
In this study, our main aim was to study the temperature variation effect in a steel sample by on-line analysis of the steelmaking process using LIBS. The atomic and ionic signals of the steel samples obtained from 20 °C to 1432 °C were comprehensively compared to find the sensitivity and accuracy variation regularity along with the increasing temperature. Both the qualitative and quantitative analysis of the elements at different temperatures was also carried out and the detection limits were calculated.
Section snippets
Experimental setup and materials
A schematic diagram of the experimental setup used in this work is shown in Fig. 1. The sample was placed in a cylindrical crucible with a diameter of 40 mm. The cylindrical crucible was heated by a medium frequency furnace. The medium frequency furnace voltage was adjusted to increase the sample’s temperature. The experiments were conducted in a vacuum tank. The air in the vacuum tank was pumped out by a vacuum pump, while argon was added to the vacuum tank at the same time. The pressure in
Analytical lines selection
The difference in the concentration of the elements is reflected in the spectral intensity of the spectra, which is the basis for discriminating the steel species effectively. The spectral intensity of liquid steel samples is significantly higher than that of normal solid steel samples. Moreover, the continuous background spectral intensity is also higher than that of solid steel samples. Combining spectral peak identification software and concentration difference of sample element content, the
Conclusions
In this work, the spectral intensity of ions and atoms increased with the increase in the temperature. To analyze the reasons for the enhancement of spectral lines, the plasma temperature of Fe at different temperatures was calculated by Boltzmann plane method. The plasma temperature at 1432 °C and 20 °C was 14,709 K and 14,227 K, respectively. The results showed that sample temperature had little effect on plasma temperature. Finally, the quantitative analysis of the elements at different
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This paper was supported by National Natural Science Foundation of China (NSFC, No. 51374040), National Key Scientific Instrument and Equipment Development Project (No.2014YQ120351) and Education Department of Jilin Province of China (grant No.JJKH20210737KJ).
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