A method of laser-induced breakdown spectroscopy measurement with enhanced emission line intensity

Abstract

The application discloses a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, and has the following characteristics: firstly, an epoxy resin curing film is prepared on the surface of a sample to be measured; then, a laser beam is used to pre-ablate the surface of the sample covered with the epoxy resin curing film, and the sample surface in the pre-ablation area is powdered while the epoxy resin curing film in the pre-ablation area is removed; finally, the sample surface in the pre-ablation area is ablated again by using the laser beam, and a spectrometer is used to collect plasma emission spectrum to obtain the content of each element in the sample. The application can effectively improve the emission line intensity of the element to be measured and the detection repeatability, has the advantages of simple operation, low cost, wide application, etc., and has greater advantages than other enhancement methods, especially when large-area area detection is required, such as sample surface imaging.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of atomic emission spectrum detection, and relates to a laser-induced breakdown spectrum measurement method, in particular to a laser-induced breakdown spectrum measurement method with enhanced emission line intensity. BACKGROUND

[0002] In order to improve the detection sensitivity of the laser-induced breakdown spectrum analysis technology on a solid sample and realize quantitative analysis of low-content elements, under the premise of not damaging the solid sample, enhancing the emission line intensity of the low-content elements is an effective method.

[0003] Double-pulse enhancement, microwave-assisted enhancement, micro-torch-assisted enhancement, spark discharge-assisted enhancement and plasma magnetic confinement are enhancement methods for re-heating or restraining the plasma by adding additional equipment, so as to improve the plasma intensity or lifetime. Although these methods can effectively improve the emission line intensity of the elements to be detected, the additional equipment makes the detection device more complex and the operation more cumbersome, and also increases the instrument cost and maintenance cost.

[0004] The sample pretreatment method is another method for enhancing the emission line intensity of elements without adding additional equipment, which only needs to perform simple pretreatment on the sample to be detected. Among them, depositing nanoparticles on the surface of the sample to be detected is a common sample pretreatment method. However, since the nanoparticles used are mostly noble metals such as gold or silver, when a large area needs to be detected, such as sample surface imaging, the cost is high, and if other metal nanoparticles are used, the detection results of the same elements will be affected. Therefore, a simple, convenient, economical and widely applicable method for enhancing the emission line intensity of elements is needed. SUMMARY

[0005] The application provides a laser-induced breakdown spectrum measurement method with enhanced emission line intensity to overcome the defects of the prior art.

[0006] To achieve the above-mentioned purpose, the application provides a laser-induced breakdown spectrum measurement method with enhanced emission line intensity, which has the following characteristics: first, an epoxy resin curing film is made on the surface of the sample to be detected; then, a laser beam is used to pre-ablate the surface of the sample covered with the epoxy resin curing film, and the surface of the pre-ablation area of the sample is powdered while the epoxy resin curing film in the pre-ablation area is removed; finally, the area of the sample after pre-ablation is ablated again using a laser beam, and the plasma emission spectrum is collected using a spectrometer to obtain the content of each element in the sample.

[0007] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: wherein the method comprises the following steps: S1, performing smoothing treatment on the surface of the sample to be measured; S2, pouring epoxy resin and a curing agent (an epoxy resin curing agent) into a mold, uniformly mixing until no filament is present, and placing until bubbles disappear; S3, placing at least one piece of polyvinyl chloride plastic sheet into the mold to control the thickness of the epoxy resin cured film on the surface of the sample to be measured; S4, placing the surface of the sample after the smoothing treatment into the mold, and then moving the plastic sheet to between the surface of the sample and the bottom of the mold; S5, pressing the sample to extrude the mixture of the epoxy resin and the curing agent between the surface of the sample to be measured, the plastic sheet, and the bottom of the mold, and then placing until the epoxy resin is completely cured; S6, taking the sample out of the mold, removing the epoxy resin cured material around the sample, and obtaining the sample with the epoxy resin cured film on the surface; S7, performing pre-ablation on different regions of the surface of the sample with the epoxy resin cured film using a laser beam, powdering the surface of the sample in the pre-ablation region, and removing the epoxy resin cured film in the pre-ablation region; S8, performing ablation again on the region of the sample after the pre-ablation using the laser beam, collecting the plasma emission spectrum of the region after the ablation again using a spectrometer, processing the spectrum data, obtaining the characteristic spectrum lines of each element in the sample, and obtaining the content of each element in the sample according to the characteristic spectrum lines of the elements.

[0008] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: wherein in S3, multiple plastic sheets are placed; and in S4, when the plastic sheets are moved to between the surface of the sample and the bottom of the mold, the plastic sheets are arranged at the edges of the surface of the sample, and the multiple plastic sheets are arranged in a closed shape, such as a triangle, a rectangle, a circle, or the like.

[0009] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: wherein in S3, three plastic sheets are placed; and in S4, when the plastic sheets are moved to between the surface of the sample and the bottom of the mold, the plastic sheets are arranged at the edges of the surface of the sample, and the three plastic sheets are arranged in an equilateral triangle shape.

[0010] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: wherein in S7, the sample is fixedly placed on a displacement table, an S-shaped scanning mode is adopted to perform pre-ablation on different regions of the surface of the sample with the epoxy resin cured film, and the displacement table is reset after the pre-ablation process is completed; and in S8, ablation again is performed on the region of the sample after the pre-ablation according to the same step length and number of steps.

[0011] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: in S8, the spectrometer detects the spectrum in the range of 300-900 nm on the sample surface, and each pre-ablation area is measured only once, and the element characteristic spectrum is obtained by calculating the average value of the characteristic spectrum at the same peak position in the multiple spectra obtained by detecting different pre-ablation areas of the same sample.

[0012] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: the repeatability of the measurement result is obtained by calculating the relative standard deviation of the characteristic spectrum at the same peak position in the multiple spectra obtained by detecting different pre-ablation areas of the same sample.

[0013] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: the thickness of the epoxy resin curing film is 0.1-0.4 mm, and the thickness of the plastic sheet is 0.1-0.4 mm.

[0014] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: the laser beam energy of the pre-ablation is 85-100 mJ, and the laser beam energy of the re-ablation is 100 mJ.

[0015] Further, the application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can further have the following features: the mold is a silica gel mold.

[0016] The beneficial effects of the application are as follows:

[0017] The present application realizes the powdering treatment of the pre-ablation area instead of directly vaporizing the sample in the pre-ablation area by preparing an epoxy resin cured product film on the surface of the sample, so that only part of the laser beam energy in the pre-ablation process is used for interaction with the surface of the sample, the sample after powdering is easier to be vaporized by the laser beam than the sample before powdering, the ablation efficiency is improved, the purpose of enhancing the intensity of the emission line of the element is achieved, in addition, the RSD of the emission line intensity of the same element at the same peak position obtained at different positions is smaller, which indicates that the detection repeatability is higher, because the high ablation rate makes the laser beam almost completely vaporize the sample in the powdering area, reduces the difference in ablation effect of different areas, the ablation pit morphology obtained after detection at different positions is similar, and the ablation efficiency of the laser beam on the surface of the sample without pretreatment is low, the ablation effect of different areas is different, and the ablation pit morphology obtained is greatly different, resulting in a large difference in the emission line intensity obtained by detecting different areas and a large RSD, and low repeatability. The present application can effectively improve the emission line intensity of the element to be detected and the detection repeatability, has the advantages of simple operation, low cost, wide application, etc., and has greater advantages than other enhancement methods, especially when large-area area detection is required, such as sample surface imaging. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a flowchart of a laser-induced breakdown spectroscopy measurement method for enhancing the intensity of an emission line according to the present application;

[0019] Figure 2 is a sample image after pre-ablation in the example;

[0020] Figure 3 is a sample image after re-ablation of one area in the example;

[0021] Figure 4 is a sample image after re-ablation of multiple areas in the example;

[0022] Figure 5 is a sample image after ablation of one area in the comparative example;

[0023] Figure 6 is a sample image after ablation of multiple areas in the comparative example;

[0024] Figure 7 is a comparison diagram of the characteristic spectral line intensity and RSD of Cr, Fe, Ni, W and Mn in the stainless steel of the example and the comparative example. DETAILED DESCRIPTION

[0025] The embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0026] As shown in Figure 1 , the present embodiment provides a laser-induced breakdown spectroscopy measurement method for enhancing the intensity of an emission line, comprising the following steps:

[0027] S1, smooth the surface of the stainless steel sample to be tested for standby.

[0028] S2, pour the curing agent and epoxy resin into the silica gel mold according to a certain proportion, uniformly mix until there is no filament, and place for a period of time to wait for the bubbles to disappear.

[0029] S3, put three pieces of polyvinyl chloride plastic sheet with a thickness of 0.2 mm into the bottom of the silica gel mold for controlling the thickness of the sample surface film.

[0030] S4, put the sample after the smooth treatment into the silica gel mold, then move the plastic sheet previously put into the sample surface between the mold bottom, and make the plastic sheet at the edge of the sample surface, and the three plastic sheets are distributed in an equilateral triangle.

[0031] S5, gently press the sample, extrude and discharge the excess mixture of curing agent and epoxy resin between the sample to be tested, the plastic sheet and the mold bottom, and then place for a period of time to wait for the epoxy resin to completely cure.

[0032] S6, take out the treated sample from the mold, remove the epoxy resin cured product that is not covered on the sample surface part, and get the sample with a thickness of 0.2 mm epoxy resin cured film on the surface.

[0033] S7, use a laser beam to pre-ablate different areas of the treated sample surface, which plays a dual role of powdering the sample surface of these areas and removing the film in these areas, as shown in Figure 2 .

[0034] Specifically, the sample is fixedly placed on the displacement table, and pre-ablation is performed on different areas of the sample surface according to the set step size and number of steps in an "S" type scanning mode. After the pre-ablation process is completed, the displacement table is reset.

[0035] S8, use a laser beam to ablate the areas of the sample after pre-ablation, as shown in Figure 3 and 4 , use a spectrometer to collect the plasma emission spectrum of the ablated area, then process the spectral data to obtain the characteristic spectrum of each element in the sample, and then obtain the content of each element in the sample according to the characteristic spectrum of each element.

[0036] Specifically, the sample surface after pre-ablation is detected again according to the step size and number of steps set during pre-ablation using a laser beam with the same energy as that used during pre-ablation.

[0037] The spectrometer detects the spectrum of the sample surface in the range of 300-900 nm, each pre-ablation area is measured only once, and the element characteristic spectrum is obtained by calculating the average value of the characteristic spectrum at the same peak position in the multiple spectra detected from different pre-ablation areas of the same sample.

[0038] The repeatability of the measurement results is obtained by calculating the relative standard deviation (RSD) of the characteristic spectrum at the same peak position in the multiple spectra detected from different pre-ablation areas of the same sample.

[0039] In this embodiment, the characteristic spectrum lines of the selected metal elements Cr, Fe, Ni, W and Mn are 482.38 nm, 404.16 nm, 354.81 nm, 478.37 nm and 405.93 nm respectively, the laser used is a Nd:YAG solid laser, the laser beam energy is always 100 mJ, the output wavelength is 1064 nm, the pulse width is 6.6 ns, the repetition frequency is 3 Hz, the spectrometer is a echelle grating spectrometer Me5000, the gate width is 20 μs, the delay time is 1.5 μs, the gain level is 1000, the focal length of the focusing lens is 10 cm, and the moving speed of the X and Y axes of the displacement table is 2.7 cm / s.

[0040] The stainless steel sample without coating and pre-ablation (i.e. without S2-S7) is used as a comparative example for detection, and the sample images after ablation of one area and multiple areas are shown in Figure 5 and 6 .

[0041] The characteristic spectrum line intensity and RSD of Cr, Fe, Ni, W and Mn in the stainless steel of the embodiment (pre-treatment) and the comparative example (no pre-treatment) are shown in Figure 7 . It can be seen from Figure 7 that after the method of pre-treatment, the characteristic spectrum line intensity detected is significantly improved, and the RSD is significantly reduced.

[0042] In summary, the present application provides a laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, which can effectively enhance the emission line intensity of the element to be detected and improve the detection repeatability. Specifically, the present method needs to prepare an epoxy resin cured product film on the surface of the sample first, and then use a laser beam for pre-ablation. Due to the presence of the film, the laser beam in the pre-ablation process will powder the pre-ablation area of the sample surface instead of directly vaporizing it. At the same time, the film in the pre-ablation area will be peeled off to form a circular hole so that the sample surface can be detected next. Since the sample surface after powdering is more easily ablated and vaporized by the laser beam, a higher emission intensity is obtained. Higher ablation efficiency makes the ablation of the pre-ablation area of the sample surface more thorough, reduces the difference in ablation effect between different areas, and makes the ablation craters formed after ablation at different positions more similar, thus obtaining higher repeatability. Compared with other emission line intensity enhancement methods, the present application does not need to increase additional equipment for plasma reheating. In addition, compared with other methods for enhancing the emission line intensity by pretreatment, the pretreatment process of the present application is simpler, the reagent used for pretreatment is cheap and easy to obtain, the pretreatment cost is reduced, and the applicability of the present application is improved.

[0043] It should be understood that the above is a preferred embodiment of the present application, but the present application is not limited to the embodiment and the disclosure of the drawings. Various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

[0044] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity, characterized in that: Includes the following steps: S1. Smooth the surface of the sample to be tested; S2. Pour the epoxy resin and curing agent into the mold, mix evenly until there are no fibrous materials, and let it stand until the air bubbles disappear. S3. Place at least one polyvinyl chloride plastic sheet into the mold; S4. Place the smoothed side of the sample into the mold, and then move the plastic sheet between the sample surface and the bottom of the mold. S5. Press the sample to squeeze out the excess mixture of epoxy resin and curing agent between the sample surface to be tested, the plastic sheet and the bottom of the mold, and then let it sit until the epoxy resin is completely cured. S6. Remove the sample from the mold and remove the epoxy resin cured material around the sample to obtain a sample with an epoxy resin cured film on the surface. S7. Use a laser beam to pre-ablate different areas of the sample surface covered with epoxy resin cured film, pulverize the sample surface of the pre-ablated area and remove the epoxy resin cured film in the pre-ablated area. S8. Use a laser beam to ablate the area of ​​the sample after pre-ablation, and use a spectrometer to collect the plasma emission spectrum of the ablated area. Then process the spectral data to obtain the characteristic spectral lines of each element in the sample, and obtain the content of each element in the sample based on the characteristic spectral lines.

2. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, Multiple plastic sheets are placed in S3; In S4, when the plastic sheet is moved between the sample surface and the bottom of the mold, the plastic sheet is positioned at the edge of the sample surface, and multiple plastic sheets are arranged into a closed pattern.

3. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 2, characterized in that: in, Place three plastic sheets into S3; In S4, when the plastic sheet is moved between the sample surface and the bottom of the mold, the plastic sheet is positioned at the edge of the sample surface, and the three plastic sheets are distributed in an equilateral triangle.

4. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, In S7, the sample is fixed on the displacement stage and pre-electrode in different areas of the sample surface covered with epoxy resin curing film using an "S" scanning method. After the pre-electrode process is completed, the displacement stage is reset. In S8, the area of ​​the sample after pre-ablation is ablated again and detected according to the same step size and number of steps as the pre-ablation.

5. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, In S8, the spectrometer detects the spectrum in the range of 300~900nm on the sample surface. Each pre-ablation region is measured only once. The elemental characteristic spectral lines are obtained by calculating the average value of the characteristic spectral lines with the same peak position in multiple spectra obtained from different pre-ablation regions of the same sample.

6. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, The repeatability of the measurement results is obtained by calculating the relative standard deviation of the characteristic spectral lines with the same peak position in multiple spectra obtained from different pre-ablation regions of the same sample.

7. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, The thickness of the epoxy resin cured film is 0.1~0.4mm.

8. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, The laser beam energy for the pre-ablation is 85-100 mJ, and the laser beam energy for the second ablation is 100 mJ.

9. The laser-induced breakdown spectroscopy measurement method with enhanced emission line intensity according to claim 1, characterized in that: in, The mold is a silicone mold.

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