CN102788772B - Method for measuring content of powdery substantial elements based on dual pluses - Google Patents
Method for measuring content of powdery substantial elements based on dual pluses Download PDFInfo
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- CN102788772B CN102788772B CN201210244861.5A CN201210244861A CN102788772B CN 102788772 B CN102788772 B CN 102788772B CN 201210244861 A CN201210244861 A CN 201210244861A CN 102788772 B CN102788772 B CN 102788772B
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Abstract
The invention discloses a method for measuring the content of powdery substantial elements based on dual pluses, characterized in that: a powdery sample is put on a transparent glass pallet, the two pulses are focused onto the bottom of the powder through the glass pallet, the first pulse generates plasmas at the bottom of the powder, the second pulse carries out subsequent heating on the generated plasmas, radiant light signals emitted by the plasmas pass through the glass pallet and are collected by a collecting lens arranged below the glass pallet, and the collected radiant light signals are transmitted to a spectrometer through optical fibers for analyzing. According to the invention, there in no need of further treatment of the powdery sample, thus the speed of on-line detection is raised; the measuring signal fluctuation caused by the unevenness of the powder layer surface is overcome, and the repeatability of the measurement is raised; in addition, the application of the dual pluses allows the plasmas to be more close to a local thermal equilibrium state, thus the raising of the measurement precision is benefited.
Description
Technical field
The present invention relates to a kind of measuring method of material element content, specifically, this method is to adopt Laser-induced Breakdown Spectroscopy technology (being called for short LIBS) to measure constituent content, belongs to atomic emission spectrum field of measuring technique.
Background technology
LIBS is a kind of brand-new material element analytical technology growing up in the twentieth century later stage.The principle of work of LIBS is: under intense laser pulse effect, the material of sample surfaces is provoked into as plasma decay rapidly, in attenuation process, give off the photon of characteristic frequency, produce characteristic spectral line, element kind and concentration information that its frequency and strength information have comprised analytic target.LIBS technical operation cost is low, and measuring speed is fast, have high sensitivity, without or need sample pretreatment seldom and realize the advantages such as multielement measurement, and radiationless harm has great development potentiality in commercial production.
But because the laser action point of LIBS is very little, seldom, for inhomogeneous, anisotropic material matrix effect is very obvious for ablation amount of substance; Meanwhile, the fluctuation of laser energy, the repeatable accuracy that the difference of the physical parameters such as plasma temperature, electron density causes LIBS to measure is lower; In addition, the electronic noise of the impact of environmental parameter and instrument internal components and parts itself etc. all easily produces and disturbs LIBS; Therefore the measuring accuracy of utilizing LIBS directly to measure sample can not be guaranteed, and has limited the application of LIBS in production reality.Through research, find, single laser pulse impacts in sample surfaces, plasma region in laser pulse incident direction, electron density is larger, thereby laser energy has been played to the effect shielding, make follow-up laser energy cannot arrive sample surfaces, stoped the continuation ablation of sample, and double-pulse laser technology can weaken this shielding action, reach the object that increases ablation quality, when having increased signal intensity, make plasma more approach local thermal equilibrium, be conducive to improve the measuring accuracy of LIBS.
Directly powdered sample is carried out to LIBS measurement poor aspect repeated, this is because on the one hand powdered sample is subject to can splashing after the effect of laser pulse, sample surfaces is no longer smooth, be difficult to guarantee that condenser lens, to the constant distance of sample surfaces, can cause larger uncertainty to laser ablation like this; On the other hand, the powdered sample gasoloid producing that splashes can absorb follow-up laser pulse, affect the ratio that laser energy arrives sample surfaces, can impact the repeatability of measurement equally.
At the disclosed patent documentation (application number: 201110040537.7 based on Laser-induced Breakdown Spectroscopy measuring technique; 201110210361.5) in, by the compressing effective precision that LIBS measures that improved of powdered sample.But powder is pressed and makes system comparatively complicated, reduced the travelling speed of measuring system, be difficult to realize on-line measurement, become the bottleneck that restriction LIBS technology further develops.Therefore for powdered sample, directly carrying out LIBS measurement is a very potential application direction.
Summary of the invention
Technical scheme of the present invention is:
Flour constituent content measuring method based on double-pulse laser, is characterized in that the method has comprised following steps:
1) element of wish in sample being measured is decided to be object element; The known one group of powdered sample of the object element mass concentration of usining is as calibration sample; The object element concentration of each calibration sample is designated as respectively C
1, C
2, C
3
2) in one group of calibration sample from step 1), choose any one kind of them and be laid on transparent glass tray;
3) utilize Laser-induced Breakdown Spectroscopy system to detect: to adopt two pulsed lasers, the first pulsed laser and the second pulsed laser are placed in to the below of glass tray, the position of two pulsed lasers and calibration sample conllinear or not conllinear, take pulsed laser as excitation source, from first pulsed laser emitting laser, after focusing on, passes by condenser lens glass tray, adjust the position of condenser lens, make the laser after focusing on produce plasma in the calibration sample inside at the surface of contact place of calibration sample and glass tray; After the time interval of 5 μ s～10 μ s, from second pulsed laser emitting laser, focus on plasma, plasma heats;
4) the collection lens that the radiant light signal of plasma generation is arranged on glass tray bottom through glass tray are collected, by optical fiber lead-in light spectrometer, after spectrometer, change into electric signal by computer acquisition, obtain step 2) in the characteristic light spectrogram of selected calibration sample, from this characteristic light spectrogram, obtain the characteristic spectral line intensity I of object element;
5) to each calibration sample repeating step 2) to step 4), obtain successively the object element characteristic spectral line intensity I that each calibration sample is corresponding
1, I
2, I
3
6) with object element concentration C
1, C
2, C
3for independent variable, characteristic spectral line intensity I
1, I
2, I
3for dependent variable is set up calibration curve by approximating method, the equation of calibration curve is y=f (x), and wherein, x is independent variable, and y is dependent variable;
7) when the testing sample of object element mass concentration the unknown is detected, first according to step 1) to step 4), testing sample is processed, obtained line strength I of object element in testing sample
c, then on calibration curve, find I
ccorresponding concentration value is the concentration of object element in testing sample.
The present invention has the following advantages and high-lighting effect:
The present invention utilizes the laser after focusing to see through glass tray from glass tray below and impacts powdered sample, the inner plasma that produces of powdered sample at the surface of contact place of powdered sample and glass tray, prevent that powder is subject to splashing after laser pulse effect, not only cause the distance of condenser lens and sample surfaces to change, and the powdered sample splashing can absorb laser pulse next time, cause the energy that arrives sample surfaces to reduce, the final uncertainty of measuring that reduces.Compare with disclosed other measuring methods based on Laser-induced Breakdown Spectroscopy, the present invention does not need the operation that powdered sample is pressed, and the method can be applied on fast on-line measurement better.And owing to producing plasma in powdered sample inside, be subject to the impact of the gravity of powdered sample own, powder bed can produce space constraint effect by plasma, can strengthen to a certain extent line strength of plasma emission spectroscopy like this, increase the signal to noise ratio (S/N ratio) of characteristic spectral line, reduce the detectability of object element.In addition, the application of double-pulse laser, the volume of plasma producing than single-pulse laser is larger, more approach the state of local thermodynamic equilibrium, the light signal of collecting is stronger, can effectively further reduce the detectability of object element, significant to the detection of trace element in sample.
Accompanying drawing explanation
Fig. 1 is Laser-induced Breakdown Spectroscopy system architecture diagram of the present invention.
In figure: the 1-the first pulsed laser; The 2-the second pulsed laser; 3-condenser lens; 4-glass tray; 5-sample; 6-plasma; 7-collection lens; 8-optical fiber; 9-spectrometer; 10-computing machine.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further illustrated.
Flour constituent content measuring method based on double-pulse laser, is characterized in that the method has comprised following steps:
1) element of wish in sample being measured is decided to be object element; The known one group of powdered sample of the object element mass concentration of usining is as calibration sample; The object element concentration of each calibration sample is designated as respectively C
1, C
2, C
3
2) in one group of calibration sample from step 1), choose any one kind of them and be laid on transparent glass tray 4;
3) utilize Laser-induced Breakdown Spectroscopy system to detect: to adopt two pulsed lasers, the first pulsed laser 1 and the second pulsed laser 2 are placed in to the below of glass tray, the position of two pulsed lasers and calibration sample conllinear or not conllinear, take pulsed laser as excitation source, from first pulsed laser emitting laser, after focusing on, passes by condenser lens 3 glass tray (in conllinear situation, two pulsed lasers share condenser lenses), adjust the position of condenser lens, make the laser after focusing on produce plasma 6 in calibration sample 5 and the calibration sample inside at the surface of contact place of glass tray, after the time interval of 5 μ s～10 μ s, from second pulsed laser emitting laser, focus on plasma 6, plasma heats,
4) the collection lens 7 that the radiant light signal of plasma generation is arranged on glass tray bottom through glass tray are collected, by optical fiber 8 lead-in light spectrometers 9, after spectrometer, changing into electric signal is gathered by computing machine 10, obtain step 2) in the characteristic light spectrogram of selected calibration sample, from this characteristic light spectrogram, select object element characteristic spectral line, by the method for integration, obtain the peak area of spectral line, peak area is the characteristic spectral line intensity I of object element;
5) to each calibration sample repeating step 2) to step 4), obtain successively the object element characteristic spectral line intensity I that each calibration sample is corresponding
1, I
2, I
3
6) with object element concentration C
1, C
2, C
3for independent variable, characteristic spectral line intensity I
1, I
2, I
3for dependent variable is set up calibration curve by approximating method, the equation of calibration curve is y=f (x), and wherein, x is independent variable, and y is dependent variable;
7) when the testing sample of object element mass concentration the unknown is detected, first according to step 1) to step 4), testing sample is processed, obtained line strength I of object element in testing sample
c, then on calibration curve, find I
ccorresponding concentration value is the concentration of object element in testing sample.
Embodiment:
Take and utilize LIBS to measure carbon content in coal element to be example, the flour constituent content measuring method based on double-pulse laser is set forth.
1) carbon of wish in coal sample being measured is decided to be object element, first uses 11 kinds of coal samples that each elemental mass concentration is known as calibration sample, and the mass concentration of the essential element of each coal sample is as shown in table 1; The carbon concentration of each calibration sample is designated as C successively
1, C
2, C
3
Table 1. mark coal sample composition
2) in one group of calibration sample from step 1), select the first to be laid on transparent glass tray 4;
3) utilize Laser-induced Breakdown Spectroscopy system to detect: to adopt two pulsed lasers, the first pulsed laser 1 and the second pulsed laser 2 are placed in to the below of glass tray, the position of two pulsed lasers and calibration sample conllinear or not conllinear, take pulsed laser as excitation source, from first pulsed laser emitting laser, after focusing on, condenser lens 3 passes glass tray, adjust the position of condenser lens, make the laser after focusing on produce plasma 6 in calibration sample 5 and the calibration sample inside at the surface of contact place of glass tray; After the time interval of 5 μ s, from second pulsed laser emitting laser, focus on plasma 6, plasma heats;
4) the collection lens 7 that the radiant light signal of plasma generation is arranged on glass tray bottom through glass tray are collected, by optical fiber 8 lead-in light spectrometers 9, after spectrometer, changing into electric signal is gathered by computing machine 10, obtain step 2) in the characteristic light spectrogram of selected calibration sample, from this characteristic light spectrogram, select carbon 193.09nm as the characteristic spectral line of carbon, integration obtains the characteristic spectral line intensity I of carbon;
5) to each calibration sample repeating step 2) to step 4), obtain successively the carbon characteristic spectral line intensity I that each calibration sample is corresponding
1, I
2, I
3
6) with carbon concentration C
1, C
2, C
3for independent variable, characteristic spectral line intensity I
1, I
2, I
3for dependent variable is set up calibration curve by the method for matching, in this example, adopting the simplest single argument linear fit method to obtain calibration curve equation is y=0.0081x-0.0076, and wherein x is independent variable, and y is dependent variable;
7) when the testing sample of carbon mass concentration the unknown is detected, first according to step 1) to step 4), testing sample is processed, obtained line strength I of object element in testing sample
c, then on calibration curve, find I
ccorresponding concentration value is the concentration of object element in testing sample.
Accuracy for verification method, when using each elemental mass concentration to be respectively carbon: 60.26%, hydrogen: 2.75%, nitrogen: 1.06% coal sample is as testing sample, the mass concentration that obtains after tested its carbon is 61.46%, measuring relative error is 2.0%, and visible this method precision is higher, can meet need of production.
Principle of work of the present invention is:
Laser-induced Breakdown Spectroscopy technology refers to that sample can be gasificated into high temperature, highdensity plasma in moment when intense pulse laser is irradiated on sample through focusing on, and the plasma cognition in excited state externally discharges different rays.The wavelength that plasma emission spectroscopy spectral line is corresponding and intensity reflect respectively component and its concentration in surveyed object.This technology has high detection sensitivity, and cost is lower, can be simultaneously multiple element be analyzed etc. to advantage.
The present invention utilizes the laser after focusing to see through glass tray from glass tray below and impacts powdered sample, the inner plasma that produces of powdered sample at the surface of contact place of powdered sample and glass tray, prevent that powder is subject to splashing after laser pulse effect, not only cause the distance of condenser lens and sample surfaces to change, and the powdered sample splashing can absorb laser pulse next time, cause the energy that arrives sample surfaces to reduce, the final uncertainty of measuring that reduces.Compare with disclosed other measuring methods based on Laser-induced Breakdown Spectroscopy, the present invention does not need the operation that powdered sample is pressed, and the method can be applied on fast on-line measurement better.
In addition, at the inner plasma that produces of powdered sample, impact due to the gravity of powdered sample own, powder bed can produce space constraint effect by plasma, can strengthen to a certain extent line strength of plasma emission spectroscopy like this, increase the signal to noise ratio (S/N ratio) of characteristic spectral line, reduce the detectability of object element.The good effect that space constraint effect is measured Laser-induced Breakdown Spectroscopy is at patent documentation (application number: illustrate 201110040537.7), by the space constraint effect of cavity, plasma shape changes and reduces, ablation quality is also more stable, can reduce the uncertainty of experiment like this, thereby make calibration curve have the better goodness of fit.
Utilize double-pulse laser to produce plasma, than single-pulse laser, have the following advantages.First, the plasma that first pulse produces thins out gas around, shielding action to follow-up laser energy weakens to some extent, second pulse has more laser energy for ablation sample, therefore in plasma, total population increases to some extent, is conducive to reduce the uncertainty that LIBS measures; The second, due to increasing of absorbing laser energy, the radiant light signal of plasma is strengthened greatly, is conducive to detecting of element that mass concentration is lower.The 3rd, through the heat effect of second pulse, in plasma, electron density is higher, and distribution of particles is more even, more approaches local thermal equilibrium, is conducive to improve the goodness of fit and the precision of prediction of calibration model.
Claims (1)
1. the flour constituent content measuring method based on double-pulse laser, is characterized in that the method has comprised following steps:
1) element of wish in sample being measured is decided to be object element; The known one group of powdered sample of the object element mass concentration of usining is as calibration sample; The object element concentration of each calibration sample is designated as respectively C
1, C
2, C
3
2) in one group of calibration sample from step 1), choose any one kind of them and be laid on transparent glass tray (4);
3) utilize Laser-induced Breakdown Spectroscopy system to detect: to adopt two pulsed lasers, the first pulsed laser (1) and the second pulsed laser (2) are placed in to the below of glass tray, the position of two pulsed lasers and calibration sample conllinear or not conllinear, take pulsed laser as excitation source, from first pulsed laser emitting laser, after focusing on, passes by condenser lens (3) glass tray, adjust the position of condenser lens, make the laser after focusing on produce plasma (6) in calibration sample (5) and the calibration sample inside at the surface of contact place of glass tray, after the time interval of 5 μ s～10 μ s, from second pulsed laser emitting laser, focus on plasma (6), plasma heats,
4) the collection lens (7) that the radiant light signal of plasma generation is arranged on glass tray bottom through glass tray are collected, by optical fiber (8) lead-in light spectrometer (9), after spectrometer, changing into electric signal is gathered by computing machine (10), obtain step 2) in the characteristic light spectrogram of selected calibration sample, from this characteristic light spectrogram, obtain the characteristic spectral line intensity I of object element;
5) to each calibration sample repeating step 2) to step 4), obtain successively the object element characteristic spectral line intensity I that each calibration sample is corresponding
1, I
2, I
3
6) with object element concentration C
1, C
2, C
3for independent variable, characteristic spectral line intensity I
1, I
2, I
3for dependent variable is set up calibration curve by approximating method, the equation of calibration curve is y=f (x), and wherein, x is independent variable, and y is dependent variable;
7) when the testing sample of object element mass concentration the unknown is detected, first according to step 1) to step 4), testing sample is processed, obtained line strength I of object element in testing sample
c, then on calibration curve, find I
ccorresponding concentration value is the concentration of object element in testing sample.
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| CN103063623A (en) * | 2012-12-26 | 2013-04-24 | 清华大学 | Method for increasing measurement accuracy of laser induced breakdown spectroscopy |
| CN104374778A (en) * | 2014-11-27 | 2015-02-25 | 南京大学 | Optical system of low-temperature scanning laser microscope |
| CN114486772A (en) * | 2021-12-29 | 2022-05-13 | 中国烟草总公司郑州烟草研究院 | Heavy metal detection equipment and detection method for cigarette products |
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| CN102262075A (en) * | 2011-07-26 | 2011-11-30 | 清华大学 | Method for measuring elemental concentration through laser-induced breakdown spectroscopy based on spectrophotometry |
| CN102507512A (en) * | 2011-11-07 | 2012-06-20 | 大连理工大学 | On-line in situ detecting method for infrared-ultraviolet double pulse laser induced breakdown spectroscopy |
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| CN102262075A (en) * | 2011-07-26 | 2011-11-30 | 清华大学 | Method for measuring elemental concentration through laser-induced breakdown spectroscopy based on spectrophotometry |
| CN102507512A (en) * | 2011-11-07 | 2012-06-20 | 大连理工大学 | On-line in situ detecting method for infrared-ultraviolet double pulse laser induced breakdown spectroscopy |
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