EP2135061A1

EP2135061A1 - Device and method for analyzing a heterogeneous material by means of laser-induced plasma spectroscopy

Info

Publication number: EP2135061A1
Application number: EP08749520A
Authority: EP
Inventors: Gerd Wilsch; Dieter Schaurich; Friederike Weritz; Alexander Taffe
Original assignee: Bundesanstalt fuer Materialforschung und Pruefung BAM
Current assignee: Bundesanstalt fuer Materialforschung und Pruefung BAM
Priority date: 2007-04-05
Filing date: 2008-04-04
Publication date: 2009-12-23
Also published as: WO2008122622A1; DE102007016612A1

Abstract

The invention relates to a device (10) for analyzing a heterogeneous material (1) by means of laser-induced plasma spectroscopy, said device comprising a laser (100) for generating a plasma from the heterogeneous material (1), a broadband detector (200) that is configured to detect a continuous spectrum of a plasma emission radiation, and a narrow-band detector (250) that is configured to detect a prescribed spectral line within the same plasma emission radiation.

Description

Apparatus and method for assaying a heterogeneous material by laser-induced plasma spectroscopy

The present invention relates to a device for the examination of a heterogeneous material by means of laser-induced plasma spectroscopy as well as an associated analysis method for a heterogeneous material which includes several classes of materials.

The determination of harmful salts is done today by standard wet-chemical analysis in the laboratory. For this purpose, a sample, usually a drill core, is taken from the building or component to be examined. This is then divided into individual slices of about 10 to 20 mm thickness. The thickness of the slices determines the depth resolution of the chemical analysis. The minimum thickness is limited by the aggregate and is about 10 mm.

According to another method, a drill dust can be removed via a suction drill from different depths of the building material. The sample material must be crushed to a particle size smaller than 0.09 mm, homogenized and finally dried at 105 ⁰ C to constant mass in a drying oven. By a suitable exclusion process, the harmful salts are brought into solution. Potentiometric titration, direct potentiometry or photometry are typically used to determine the chloride content of concrete. For the determination of the sulphate content of concrete, gravimetric precipitation from barium sulphate is often used. The determined salt contents are then given in relation to the total mass or the cement mass, the latter roughly being estimated from the ratio of cement to aggregate (eg 1: 6). A concrete analysis to determine the existing cement content means a considerable extra effort. The results of the chemical analysis thus represent an average over the entire sample volume. Therefore, locally limited increased salt concentrations, such as may occur in cracks, can not be detected. The local salt concentration is therefore systematically underestimated in such a process. Especially with chlorides, which catalytically promote the pitting corrosion of reinforcing steel, the associated underestimation is critical. Furthermore, in the wet-chemical method for determining the content of various building salts, z. As chlorides, sulfates and nitrates, to determine the concrete composition each individual separate samples for each of the salts necessary. A direct correlation of element contents, which is crucial for the clarification of a cause of the damage, can not be made.

Furthermore, suction drilling machines are typically used in construction practice, which grind the concrete directly into drilling dust during drilling. However, their function is only guaranteed on dry components, as increased concrete moisture adheres the drill dust in the drill and hardens quickly together with the heat due to the friction in the drill hole. Since the exposure of a component with destructive salts is typically associated with the moisture penetration of the building material, the sampling by means of suction drill is therefore often used only limited.

Furthermore, the selection of the measuring point also has a major influence on the salt contents to be determined, since in the wet-chemical analysis only the total salt content of a discrete sample quantity is determined. In the case of an inhomogeneous building material such as concrete, which consists of a cement matrix and an embedded aggregate, this discrete quantity of sample contains a more or less large proportion of aggregate, depending on the extraction point. Since the aggregate usually contains no damaging salts, when taking the sample is precisely underestimated on a rock grain, the really existing salinity. This can lead to a misjudgment of the examined building substance. In practice, this problem is addressed by taking several samples of chips directly next to each other, so that depending on the diameter of the drill and the largest grain of the aggregate up to five individual samples per site must be removed. This significantly increases the overall examination effort.

Furthermore, the accuracy in the determination of the salt content by the presence of interfering ions, z. As iron or aluminum, influenced. Iron ions, which result from the unnoticed drilling of reinforcing steel ("iron hit") with the suction drill, can be built in practice only with increased measurement effort, eg. B. by non-destructive localization of the reinforcement, avoid. This effort is typically not operated.

DE 198 39 705 describes a method and a device for quantitative chemical rapid analysis, which provides a low-cost form of a rapid test for performing micro-Chromatografϊe and micro-titration for on-site analysis. DE 36 05 275 describes a spray method for the chemical determination of free halogen and pseudohalogen ions, in particular of chloride ions on surfaces of surfaces and fractures of materials. In this case, halogen and pseudohalogen ions can be determined by spraying various indicator liquids on surfaces or fracture surfaces on site.

DD 29 41 04 describes a method and an apparatus for determining the SaIz- and water content in mineral building materials, the chloride content of concrete by elution of drilling dust and measurement of the conductivity or the electrolyte resistance is determined.

A comparable method for the determination of the sodium chloride content in concrete components is described in DE 38 35 597.

DE 196 34 533 describes a method and a device for determining physical and chemical parameters in mineral solid media. The mineral solid medium is drilled continuously and without impact, whereby the borehole is rinsed with a measuring liquid. The measuring liquid is then analyzed by means of ion-selective sensors.

DE 3108924 describes a method and a device for the chromatographic separation and quantitative analysis of ions, in which the chromatographic separation and the quantitative analysis of anions and cations can be carried out in a single system.

In all the methods described above, the accuracy of the analysis is influenced by the type and duration of the elution and by the grain size of the drill dust. Furthermore, no spatially resolved measurement is possible, so that the heterogeneity of the building material is taken into account only to a limited extent.

The spectroscopic method of laser-induced emission spectroscopy, also known as LIBS for short, allows the quasi-destructive examination of material samples in the LIBS method is a small Part of the sample material evaporated by laser bombardment and excited by the same laser beam to a plasma. Subsequently, the spectrum of the radiation emitted by the plasma can be analyzed in order to obtain conclusions about the elements contained in the plasma by the lines found.

Furthermore, JP 2002-257729 describes a LIBS apparatus for continuously detecting the composition of a powder stream in a cement plant.

US 5,757,484 describes a LIBS soil survey device.

US 5,379,103 describes a mobile LIBS apparatus for testing groundwater and soil samples for heavy metals.

US 6,762,836 describes a portable LIBS device for detecting impurities on machine parts.

US 6,762,835 describes a fiber optic LIBS sensor for the investigation of molten metals.

EP 1416265 describes a scrap sorting system in which irregularly positioned parts are analyzed by means of a LIBS device and a scanner. Similar scrap sorting systems are also described in US2003 / 0132142, US 6,545,240 and US2003 / 0034281.

Also known from US 6,147,754 is a LIBS probe for measuring soil contamination.

DE 199 32 069 describes a device for laser-induced emission spectrometry, in which a sample surface is scanned by movement of a laser beam and measuring beam optics. In this procedure, the optics are moved and the sample to be examined is at rest. However, the aspheric optics to be used lead to aberrations that affect a spatial resolution. In addition, the scan area is limited, since with a rotation of the optics carrier, the focus position changes relative to the sample surface. US 6,466,309 describes a method and apparatus for chemical and topographical microanalysis in which a scanning near-field optical probe is combined with a LIBS device.

In view of the above-mentioned disadvantages of the prior art, it is therefore an object of the present invention to provide a LIBS device for on-site analysis of building materials.

This object is achieved by a device for the investigation of a heterogeneous material by means of laser-induced plasma spectroscopy according to claim 1 and by a method for analyzing a heterogeneous material which includes several classes of materials according to claim 41. Further aspects, details, advantages and features of the present invention will become apparent From the dependent claims, the description and the accompanying drawings.

In particular, the present invention relates to the determination of the material composition of a heterogeneous material, for example a concrete surface. However, it is also transferable to other heterogeneous material surfaces or heterogeneous materials. Concrete is characterized by a special degree of heterogeneity, whereby both the element distribution and the grain size distribution of the aggregate are heterogeneous. In addition, in the case of samples taken at a construction site or in the case of material surfaces to be tested, surface roughnesses on the order of a few millimeters to even in the centimeter range can be present. In the investigation of building materials by the present invention, in particular the content of harmful salts, in particular of chlorides and sulfates (trace elements), the determination of depth profiles, the determination of element distributions z. B. on cracks and the detection of other important elements (Na, K, Ca, Fe, Mg, etc.) and their distribution can be determined. In this case, such an investigation can be carried out directly and on site on the surface of the building substance, without a sampling and / or sample preparation is necessary. It is also possible to investigate smaller samples taken. The process is essentially non-destructive. Furthermore, the results are available on-site in order to be able to assess the degree of damage to a structure quickly and to make a decision on further measures as quickly as possible. The accuracy of the quantitative determination is at least 15%, wherein the resolution of depth profiles and element distributions is at least 5 mm. Furthermore, the device according to the invention is insensitive to the conditions prevailing on the construction site. In particular, the device is insensitive to dust, water, vibration and shock.

According to a first embodiment of the present invention, there is provided an apparatus for inspecting a heterogeneous material by laser-induced plasma spectroscopy (LIBS). The apparatus includes a laser for generating a plasma of the heterogeneous material, a broadband detector configured to detect a continuous spectrum of plasma emission radiation, and a narrow band detector configured to detect a predetermined spectral line within the same plasma emission radiation capture. A broadband detector is to be understood as a detector which can detect a continuous spectrum in a larger wavelength range, typically a few nanometers. In particular, the broadband detector can detect a wavelength range between 25 nm and 150 μm. In contrast, a narrow-band detector is understood to mean a detector which allows the exact recording of a single line. In particular, the narrow-band detector can detect a wavelength range between 1 nm and 10 nm, typically 5 nm.

In the above-described apparatus according to the embodiment of the present invention, the broadband detector is for detecting the intense spectral lines, e.g. As the main elements, and for detecting the entire relevant wavelength range in the form of a continuous spectrum. It is precisely in building materials and other heterogeneous and intermittent composite materials necessary to measure a continuous spectrum in order to have a quality control in the evaluation, in particular in an automated evaluation. In the continuous spectrum, additional occurring elements are detected and identified, and overlays of spectral lines are detected. The narrowband detector is specifically designed to detect weak spectral lines. Such weak spectral lines can be derived, for example, from trace substances or elements which give an indication of harmful compounds (Cl, S). Since the exposure of both detectors takes place simultaneously, the same sample volume can be used at the same time be measured exactly the same location. In this way, a correlation of the measured data of the wideband detector and the narrowband detector is possible. From the correlation of the measurement data from the wideband detector and the narrow band detector, different classes of materials present in the heterogeneous material can be identified. For example, in concrete z. B. the cement and the aggregate are distinguished from each other. The determined by the narrow-band detector content of trace elements can be assigned in this way a certain class of material, in concrete typically the cement. By employing the above-described apparatus according to the embodiment of the present invention, on-site analysis of the heterogeneous material which does not require a laborious sample preparation such as acid digestion can be performed. Instead, the LIBS measurement can be made directly on the surface of a component. Furthermore, a measurement with the apparatus described above according to the embodiment of the present invention is independent of the degree of component light, which may otherwise be problematic in sampling with a suction drill. In addition, it is not necessary to know the concrete composition before the measurement. Furthermore, the content of trace elements, in particular destructive salts, based on the cement content can be measured directly, and must not be determined by calculation based on empirical values. In addition, the accuracy of the determined contents is not dependent on the sampling point (the sample volume), that is, on the unknown proportion of the aggregate. Also, the accuracy of the determined salinity does not depend on whether a reinforcing steel was hit. The measurement effort is also significantly reduced since the content of different salts and the concrete composition can be determined simultaneously with a single measurement by the targeted evaluation of the line spectra. Finally, it is also possible with the device described above, locally narrow enrichments of harmful substances, eg. As in cracks or at interfaces (cement matrix / steel, cement matrix / aggregate) to determine and derive a realistic estimate of the existing damage potential. Due to the quasi-non-destructive determination of element distributions on component surfaces on site, a complex sampling and subsequent laboratory examination can be omitted. In particular, the analysis result is available on site within a short time. According to a further embodiment of the present invention, the wideband detector and the narrow-band detector are adapted to detect radiation in the red to near-infrared range. Typically, the two detectors are adapted to detect radiation in the wavelength range from 600 nm to 950 nm. In particular, the narrow-band detector can be set up to detect a spectral line of one of the following elements: sulfur, chlorine, titanium, lithium, sodium, potassium, magnesium, carbon. In particular, the narrow band detector may be aligned with a sulfur spectral line at 921.3 nm. In another embodiment, the narrow band detector may be aligned to a chlorine spectral line at 837.6 nm. Optionally, it is possible to use the narrow band detector between different specific wavelengths, e.g. As a sulfur line and a chlorine line switch. Alternatively, two or more narrow-band detectors may be provided, which are each aligned with a particular spectral line of a trace element. Typically, the broadband detector is designed as a CCD detector. The narrow-band detector can also be designed as a CCD detector or alternatively as a photomultiplier.

The acquisition of the spectra or spectral lines in the red or near-infrared range allows a good detection and identification of destructive substances. In particular, the non-metals sulfur and chlorine have spectral lines in the UV and near-infrared range. However, as the UV lines are strongly absorbed, an analysis of the weaker near-infrared lines is useful. In particular, the sulfur line at 921.3 nm and the chlorine spectral line at 837.6 nm provide sufficient intensity to perform a quantitative analysis. With regard to the type of detector, it should be noted here that a Paschen-Runge spectrometer is not suitable for building material analysis, since with such a spectrometer one can not resolve between pure spectral lines and superimpositions of spectral lines.

According to a further embodiment, the device has a pan-tilt head on which the laser is arranged. The pan-tilt head is designed as a scanning device. In this way, the pan-tilt head allows the scanning of a sample surface with the laser beam. The scanning should be done in the form of a scan or raster. By providing a pan-tilt head is on the one hand from DE 199 32 069 recognized as disadvantageous aspherical optics superfluous. Furthermore, the use of a pan-tilt head as a scanning device allows the laser beam is passed over the sample surface without having to move the sample itself. Finally, the pan-tilt head is also less sensitive to influences on the construction site, such as shocks and dust, as a deflection optics.

The apparatus may further include a focusing unit adapted to focus the laser beam onto the surface of the heterogeneous material. Typically, such a focusing unit has an autofocus device. Since the heterogeneous materials often have a high surface roughness down to the centimeter range, the focussing unit, in particular an autofocus device, can ensure that the laser is focused on the sample surface. In this way it is ensured, among other things, that in each case an equally large sample volume is measured.

According to another embodiment of the present invention, the device further comprises a laser-tight shield, for. As a laser-tight bellows, which can be arranged between the laser and a surface of the heterogeneous material. In this way, the laser safety of the device is guaranteed, in particular laser protection class 1 can be maintained. Thus, on-site use without laser safety goggles is possible. Typically, the laser-dense shield is flexibly connected to the laser such that the relative position of the shield relative to the surface of the heterogeneous material is fixed while the laser performs a scanning motion. In other words, the flexible connection allows the laser beam to be scanned across the sample surface while the laser-dense shield remains fixed relative to the surface.

According to a further embodiment, the device has a seal for contacting the sample surface, wherein the seal is arranged on an end face of the shield facing away from the laser. In this case, the seal is typically adapted to compensate for surface roughness of up to 2 cm. It should be understood that the seal does not necessarily provide complete gas tightness or liquid tightness. According to a development, a contact switch can be arranged on the front side of the shield, which is triggered only at a sufficiently high contact pressure of the laser-tight shielding to the sample surface. The purpose of this switch is the laser operation only when concerns the seal on the To allow sample surface. In this way, sufficient laser safety of the device can be ensured.

In yet another embodiment of the present invention, the apparatus may include means for supplying a purge gas to the sample surface. In particular, such a device may comprise a front-mounted on the seal flange with multiple gas inlet openings. In this case, the flange may have more and / or larger gas inlet opening in one area than in another area. Alternatively or additionally, the flange may be formed so that the gas flow of the purge gas is separately adjustable for individual regions of the flange. By supplying the purge gas, sample material ablated by the laser can be expelled from the measurement point. Furthermore, by using a suitable purge gas, the intensity of weak spectral lines can be less damped than in air. Also, by using a suitable purge gas, the interfering oxygen and nitrogen lines of the air in the spectrum can be avoided. Typically, helium is used as purge gas, since helium allows a particularly good measurement of the weak spectral lines of sulfur and chlorine. The argon usually used as purge gas, however, is disadvantageous because it has strong spectral lines in the near-infrared region.

According to a further embodiment, the device comprises a sample holder. The sample holder may typically be connected to the seal attached to the shield. The sample holder is particularly suitable for holding a core or part of a core. In this way, a core or a split surface of a core can be investigated on site with LIBS. In this case, the sample holder is typically formed so that it closes the front end of the shield together with the seal in order to ensure laser-tightness of the entire device.

According to a further embodiment of the present invention, the device is transportable and arranged in particular on a chassis. This allows easy transport to and on a construction site. According to a development, the device is pivotable on the chassis, in particular horizontally and / or vertically pivotable, arranged. In this way, the measuring head can be easily brought to a surface to be measured. According to another exemplary embodiment of the present invention, a method is provided for analyzing a heterogeneous material that includes multiple classes of materials. The method comprises the steps of generating a plasma from the heterogeneous material by means of a laser beam, detecting a continuous spectrum of plasma emission radiation by means of a broad band detector, detecting a predetermined spectral line within the same plasma emission radiation by means of a narrow band detector, the assignment of the continuous spectrum to a material class of the heterogeneous material and assigning the predetermined spectral line to the material class.

By the method described above, in which at the same time a continuous spectrum and a certain spectral line, typically a spectral line of weak intensity, are detected at the same measuring location, a correlation of the measured data with respect to measuring location and material classes can take place. In this way, as already described above, a spatially resolved determination of the quantitative contents of trace elements in the heterogeneous material is possible. According to a development, the measurement of the plasma emission radiation is repeated one or more times, the laser beam being directed at each repetition to another point on the surface of the heterogeneous material. Typically, the measuring points to which the laser beam is directed are arranged in a straight line one behind the other, whereby the distance between two points can be from 0.5 mm to 10 mm inclusive. In this way, a spatially resolving determination of the trace element contents in the sample is possible, which goes well beyond the state of the art in their spatial resolution. According to yet another embodiment, a plurality of lines of measuring points are arranged parallel to one another in order to ensure surface coverage of the surface.

Typical heterogeneous materials which can be tested by the method described above are concrete, geological samples, mineral samples, glasses or glass melts. The method described is particularly suitable for determining the depth profile of an element in a heterogeneous material. Here, a core is first removed from the heterogeneous material and then split. Then, the analysis method described above is performed on a split surface of the core, wherein a plurality of measurement points are arranged one behind the other in the depth direction of the core. Typically, the measuring points on lines aligned parallel to each other arranged. These lines are formed as level lines, that is, they are substantially parallel to the sample surface, that is, at the same depth. These level lines are then arranged at different depths one behind the other in the depth direction of the drill core. From the thus determined depth profile of the element, a penetration coefficient can be determined. Depending on the application, the state of a surface seal, a coating and / or a progressive damage to the building material, for example due to chlorine-induced corrosion due to thawing agents, can be determined on the basis of the penetration profile. The method just described can also be used in the context of quality assurance in the repair of concrete structures, first the damaged areas are determined, then removed and finally checked whether really the contaminated material was completely removed.

Reference to the accompanying drawings, embodiments of the present invention will now be explained. Showing:

Fig. 1 shows a device according to an embodiment of the present invention

Invention;

Fig. 2 shows a device according to an embodiment of the present invention

Invention in a first pivoted state;

Fig. 3 shows a device according to an embodiment of the present invention

Invention in a second pivoted state;

4 shows a focusing unit according to an embodiment of the present invention

Invention;

Fig. 5 is a continuous spectrum;

FIG. 6 is a narrow band image of a chlorine line at 837.6 nm; FIG.

7 shows a broadband spectrum; Fig. 8 shows two broadband spectra, measured on aggregate and cement;

9 shows a broadband spectrum;

10 shows a broadband spectrum, measured on aggregate and cement;

11 shows a measuring section on the gap surface of a drill core together with the respective spatially resolved measured values for main components of the sample material;

Fig. 12 is a diagram for classifying various heterogeneous materials;

13 shows the comparison between measurements with and without helium as purge gas;

14 shows a comparison between prior art analysis methods and the analysis method according to an exemplary embodiment of the present invention;

FIG. 15 shows a measurement of a depth profile on the gap surface of a drill core; FIG.

Fig. 16 is a comparison between a photographic representation of

Sample surface, the determined ratio of calcium and oxygen and the chloride contamination of the sample;

FIG. 17 shows a comparison of the determined depth profiles for chlorine in concrete according to the method according to the invention and the standard method; FIG.

FIG. 18 shows a comparison between the depth profiles for chlorine in concrete between a wet-chemical analysis and the method according to the invention; FIG.

19 shows a calibration curve for a method according to one exemplary embodiment of the present invention. Fig. 1 shows an apparatus according to an embodiment of the present invention. The apparatus 10 includes a laser 100 disposed on a pan-tilt head 160. The pan / tilt head 160 is designed as a scanning device, so that the laser beam 110 generated by the laser 100 can be scanned over a surface 1 of a wall to be examined. Typically, the laser 100 is a NdY AG laser. At a front end of the laser, a focusing unit 120 is arranged. The focusing unit 120 has an auto focus unit that can focus the laser beam on the surface 1.

The structure of the focusing unit 120 will be explained below with reference to FIG. 4. The focusing unit 120 shown in FIG. 4 has an inlet opening 122, through which the laser beam enters the focusing unit 120. The laser beam then passes through a semitransparent mirror 128 and a first lens 126 and exits the focusing unit 120 again through an outlet opening 124. The outlet opening 124 also serves as an inlet opening for the plasma emission radiation which is emitted from the sample surface. This plasma emission radiation enters the focusing unit 120 through the exit opening 124, where it is coupled via the semitransparent mirror 128 and a second lens 132 into a connection 130 for an optical waveguide. The second lens 132 is adapted to focus the plasma emission radiation on the input of the waveguide 130. Before the plasma emission radiation enters the optical waveguide, the radiation can be filtered by means of a filter 134, which is adjustable via a filter slide 136. Typically, the filter 134 is designed as an edge filter and serves to avoid spectral lines of higher order. In this way, the number of spectral lines occurring in the observation area is reduced, which facilitates the assignment of the observed spectral lines and in particular avoids overlays of spectral lines. Thus, on the one hand, the laser beam is focused onto the surface of the sample material by the focusing unit described above and, on the other hand, the plasma emission radiation emitted by the sample is coupled out into an optical waveguide. An autofocus function of the focusing unit 120 is particularly helpful when performing direct measurements on component surfaces, since in the case of heterogeneous materials, such as concrete, surface roughnesses occur in the centimeter range. The focusing device 120, however, ensures that measurements are always carried out for the same laser energy and the same impact volume. After the focusing unit 120 has now been explained with reference to FIG. 4, the description of the device 10 according to the invention will be continued with reference to FIG. The device 10 further has a laser-tight shield 300, which is formed in the present Ausftihrungsbeispiel as a laser-tight bellows. The design as a bellows, the length of the shield can be variably adjusted. The bellows 300 is coupled to the focusing unit 120 via a flexible connection 320. For example, the flexible connection 320 may be made of rubber. Due to the flexible connection 320 between the focusing unit 120 and the bellows 300, a relative movement of the focusing unit 120 with respect to the bellows 300 is made possible. In this way, the focusing device 120, typically rigidly coupled to the laser 100, may follow a scanning motion of the pan-tilt head 160 while the bellows 300 remains fixed in position. This allows the sample surface 1 to be scanned by the pan / tilt head 160 without having to change the position of the bellows 300 relative to the sample surface 10.

At the end facing away from the laser 100 front end of the bellows 300, a seal 340 is attached. This seal 340 serves on the one hand to ensure the laser-tightness of the device, and on the other hand to prevent or at least reduce the escape of a purge gas from the interior of the bellows 300. In this regard, it is noted that the seal 340 typically can not produce complete gas tightness between the surface 1 and the bellows 300. This is due, in particular, to the surface roughness of the sample material, which may typically be in the centimeter range for heterogeneous materials.

The apparatus 10 furthermore has a flushing gas system with which a flushing gas such as helium can be conducted to the sample surface 1. The purge gas system includes a purge gas tank 400, a purge gas conduit 420, and a gas inlet flange 440 disposed between the gasket 340 and the bellows 300. The purge gas may be introduced into the gas inlet flange 440 from the purge gas tank 400 through the purge gas line 420. The introduced gas quantity is controlled by a flow regulator 460. The gas inlet flange typically has more and / or larger gas inlet openings in one area than in another area. In the arrangement shown in Fig. 1, for example, in the lower region of the flange, in which the purge gas 420 to the flange 440 is connected, more and / or larger Gaseinlassöffhungen be provided. In this case, the sample surface 1 or the measuring point located on the sample surface is flowed through from below through the purge gas. In this way, sample material that has been lurked by the laser bombardment can be expelled from the ablation site. Furthermore, the introduction of purge gas serves to reduce the attenuation of the weak spectral lines, in particular the spectral lines of trace elements. In addition, when the inner volume of the bellows 300 is filled with the purge gas, disturbing oxygen and nitrogen lines from the air are suppressed. The overall assembly of flexible connection 320, bellows 300, gas inlet flange 440 and seal 340 is held by a bracket 500.

At the optical fiber connector 130 shown in Fig. 4, a Y-shaped glass fiber 140, hereinafter referred to as a Y fiber, is connected. The Y fiber leads from the port 130 of the focusing device 120 to the input of a broadband detector 200 which is arranged to detect a continuous spectrum of the plasma emission radiation. Another branch of the Y fiber leads from the port 130 of the focusing device 120 to an input of a narrow band detector 250 which is arranged to detect a predetermined spectral line within the same plasma emission radiation. The use of the Y-shaped optical waveguide 140 or the Y-fiber makes it possible to provide the same radiation both to the broadband detector 200 and to the narrowband detector 250. In this way, it is possible to detect plasma emission radiation from exactly the same measurement location both broadband by detector 200 and narrowband by detector 250. This allows a spatial correlation of the two spectra. Typically, the wideband detector 200 and the narrow band detector 250 are adapted to detect red to near infrared radiation, that is, in a wavelength range of 600 nm to 950 nm. In this case, a CCD detector is typically used for the broadband detector 200. Such a CCD detector may also be used for the narrow band detector 250. It is also possible to use a photomultiplier for the narrow-band detector 250.

The narrowband detector 250 is typically configured to detect a spectral line of one of the following elements: sulfur, chlorine, titanium, lithium, sodium, potassium, magnesium, or carbon. The detection of lithium, sodium or potassium can cause damage due to alkali-silica reactions (AKR). be determined. These AKRs lead to the formation of silica gel from mineral silicon, thus weakening the structural integrity of the component. The detection of magnesium is interesting in that the presence of magnesium atoms leads to a disruption of the sulfur line. Furthermore, magnesium leads to certain structural damage. On the one hand, the detection of carbon can be used to detect damage by carbonation, and on the other hand, for example, the quality of a polymer coating on the component can be discovered. However, detection of chlorine and / or sulfur is considered to be the main application in the field of structural damage diagnosis. For example, sulfates can lead to the transformation of cement minerals, which is accompanied by a loss of strength and mass (concrete corrosion). In addition to sulfate damage, chlorides in particular attack the reinforcing steel and can destroy it locally (pitting corrosion). In this way, a chloride-induced corrosion occurs, which takes place only at locally narrow places. Therefore, a spatially resolved detection of the chloride content is important. In addition to the elements given above, other elements, in particular nonmetals such as phosphorus, fluorine or bromine, can also be detected if that is of interest. Such a detection can also be carried out in homogeneous materials, for example in polymers.

The apparatus 10 further comprises a controller 600, which controls the laser 100, the pan / tilt head 160, and the focusing unit 120, respectively, to scan the surface 1 of the sample. On the other hand, the controller 600 receives the data from the two detectors 200, 250 and records them during the measurement. In addition, the controller 600 is adapted to regulate the flow regulator 460 and thus the purge gas supply to the measuring point. The entire assembly is arranged on a chassis 700 so that it can be easily moved to or on a construction site. Thus, an on-site examination of the building materials can be done. Likewise, it is of course possible to investigate with the portable LIBS device, as shown in Fig. 1, on-site geological samples or, for example, glass melts. Optionally, the device 10 may comprise a contact switch 620, which is arranged at the front end of the measuring head, that is, in the vicinity of the seal 340. Typically, the contact switch 620 can only be triggered against the surface of the sample material 1 at a predetermined contact pressure. As long as the contact switch is not triggered, the controller 600 prevents the operation of the laser 100. In this way, the laser safety of the device 10 is increased. In particular, by providing the bellows 300, the seal 340 and the contact switch 620 laser class 1 for the device 10 can be ensured.

Furthermore, the device comprises a sample holder (not shown). The sample holder can be connected to the seal 340 attached to the bellows 300. The sample holder is particularly suitable for holding a core or part of a core. In this way, a core or a split surface of a core can be investigated on site with LIBS. In this case, the sample holder is typically formed so that it closes the front end of the bellows 300 together with the seal 340 in order to ensure laser-tightness of the entire device.

FIG. 2 shows the device 10 from FIG. 1 in a first pivoted state. Therein, the LIBS device is pivoted in the vertical direction. As shown, the pan-tilt head 160 supporting the laser 100 and the two detectors 200, 250 are mounted on a bottom plate 530. The bottom plate 530 is part of a pivoting device 520 and connected by means of hinged connections 550 both to the chassis 700 and to a telescopic arm 540. The telescopic arm 540 is also connected to the chassis 700 via a hinge joint 550 and serves to hold the floor panel 530 in a pivoted position. In addition, the pivoting device 520 may be designed so that not only a vertical but also a horizontal pivoting of the LIBS device can take place. During pivoting, the bellows 300, the gas inlet flange 440, and the gasket 340 are held by the bracket 500, which is also secured to the bottom plate 530. The holder 500 is thus pivoted together with the bottom plate 530. In this way, a relative movement of the pan-tilt head 160 to the bellows 300 can be ensured even in the pivoted state.

Fig. 3 shows the device 10 in a second pivoted state. In this case, the measuring head has been pivoted so far that the laser 100 scans the ground in front of the chassis 700. In this way, a measurement of a soil surface is possible without having to remove a sample. In this arrangement, the bellows 300 is compressed because there is only a short distance to travel between the focusing unit and the floor in front of the chassis. The path difference is compensated by the focusing unit 120, so that even in this state, the laser beam is focused on the surface. Now that the transportable LIB S unit has been described for the analysis of heterogeneous materials, the associated measuring procedure is explained below. In accordance with an exemplary embodiment of the present invention, a method is provided for analyzing a heterogeneous material that includes a plurality of material classes. In this method, a plasma is first generated by means of the laser beam focused on the surface. The plasma emission radiation emitted by the generated plasma is detected by the wideband detector 200 and the narrow band detector 250. In this case, the broadband detector detects a continuous spectrum of the plasma emission radiation, as shown for example in FIG. 5. It is a continuous spectrum in the near-infrared range between 810 nm and 870 nm. Different spectral lines for sodium, calcium and oxygen are evident in the continuous spectrum. Furthermore, a very weak spectral line of chlorine at 837.6 nm is shown. This weak spectral line of chlorine is detected separately by means of the narrow-band detector 250. Such a spectrum taken by the narrow band detector 250 is shown in FIG. The narrow band spectrum extends around the chlorine line at 837.6 nm between 835 nm and 839 nm. Because the narrowband detector is specifically aligned with this line, it can with better resolution than that shown in FIG continuous spectrum are recorded. Based on the normalized maximum intensity, the area under or the half-width of the chlorine line, the quantitative content of chloride in the concrete can be determined. FIG. 6 shows, by way of example, the chlorine lines for different chloride concentrations. Typically, using a photomultiplier, a reading is obtained that reflects the integral value of the intensity at the observed wavelength. Typically, this value is detected in the intensity maximum of the line.

Due to the continuous spectrum shown in Fig. 5, it is possible to determine the class of material into which the measuring point falls. For example, it can be determined from the relative concentration of sodium, calcium and oxygen whether the measurement was on the aggregate or in the cement. Based on the quantitative analysis of the chloride content shown in Fig. 6, it is now possible to assign the pollutant content directly to the class of material, that is to correlate. In addition, these two results can be assigned to a unique measuring point, since both the results shown in FIG. 5 shown continuous spectrum and the single line shown in Fig. 6 were determined from the plasma emission radiation of a single measuring point.

Fig. 7 also shows a continuous spectrum in the wavelength region as in Fig. 5. The associated Fig. 8 shows how the spectrum shown in Fig. 7 changes when the measurement is performed on different material classes of the heterogeneous material. It can clearly be seen from FIG. 8 that the calcium line present in the cement is completely absent at 850 μm in the aggregate. Likewise, the weakly expressed chlorine line at 837.6 is present only in the cement spectrum but not in the spectrum of the aggregate. In this way it can be concluded from the shape of the continuous spectrum on the respective class of material on which the measurement is carried out.

FIG. 9 shows a continuous spectrum in the range between 890 nm and 940 nm. In this respect, its bandwidth is comparable to the spectrum shown in FIG. Here, however, the narrow band detector detects the sulfur line at 921.3 nm, which is also marked in FIG. As in the case of the wavelength range shown in FIG. 8, FIG. 10 shows that even in the wavelength range from 890 nm to 940 nm, the continuous spectra in the various material classes differ significantly from one another. For example, in the measurement on the aggregate, the calcium double line at 891.2 nm and 892.7 nm, which is clearly pronounced in the cement spectrum, is completely absent. Similarly, the line triplet of sulfur occurs at 921.3 nm, 922.8 nm and 923.8 nm only in the cement spectrum. It follows that also in this wavelength range by analysis of the continuous spectrum the material class can be determined, on which the measurement was carried out.

Fig. 11 shows in its upper part the photograph of a sawn concrete sample with three visible traces of LIBS measurements. Underneath, the respectively determined oxide contents are plotted on the marked laser track as a function of the location of the measurement. These are each 127 individual measurements. It is clearly recognizable, as measured in the range between 40 and 60 mm on the aggregate, whereas the remainder of the measuring track is essentially on cement. The results of all individual measurements can then be transferred according to their determined oxide content in the ternary diagram shown in Fig. 12. The position of the measuring points in relation to the Si-axis becomes determined by the ratio between aggregate and cement in the vaporized material. The measurements with the lowest Si contents characterize the cement. The position of the center of gravity of the measured values with the lowest Si content allows conclusions to be drawn about the type of cement used so that, for example, it can be determined whether, for example, a blast-furnace cement or a Portland cement has been used to produce the concrete.

Fig. 13 shows a comparison of LIBS measurements on cement mortar samples, wherein one measurement was made under air and another measurement under a helium atmosphere. As can be seen from FIG. 13, the measurement under a helium atmosphere increases the sensitivity for the chlorine line at 837.6 nm. Furthermore, the spectral lines for nitrogen and oxygen disappear, as a result of which, in particular, the sodium lines below 820 nm become clear emerge.

Fig. 14 shows a comparison between an analysis method according to an embodiment of the present invention and analysis methods of the prior art. According to the two methods, a core is first removed (step 1400) which is split into two parts A, B. According to the method according to the invention, a quantitative quantitative analysis of contaminating trace substances can be carried out on the gap surface of the drill core A. This is done by line scans along level lines, which are offset from one another in the depth direction of the drill core. In this case, a spatial resolution between the measurement lines of about 1 mm can be achieved. Such a measuring grid on the gap surface of the drill core is shown in FIG. 15. The second part B of the core is now analyzed in a conventional way. For this purpose, the core is first cut into slices of about 10 mm thickness, which are arranged one behind the other in the depth direction (see arrow to the right of the core) (step 1420). Next, these slices are ground (step 1430) to produce a powder. This powder is then firstly processed into a crimp (step 1440), which is subsequently examined in the laboratory with a LIBS device. Another part of the powder is subjected to standard wet chemical analysis in the laboratory (step 1450).

A result of the analysis method according to the invention from step 1410 is shown in FIG. FIG. 16 shows on the left side the photograph of the examined split surface of the drill core divided along its longitudinal axis. The measuring tracks are visible at a vertical distance of 2 mm. The middle illustration shows the graphical representation of the Ratio of calcium and oxygen in grayscale. Black corresponds to the aggregate, whereas gray corresponds to increasing Ca contents with increasing brightness. Thus, gray values correspond essentially to the cement matrix. In the picture on the right, areas contaminated with chlorides are marked light gray. In the example shown, chlorides could be detected to a depth of 27 mm below the surface. Figure 17 shows a depth profile for chloride taken with the LIBS process of the present invention as compared to the values determined by the standard wet chemical process. Each point of the LIBS profile is formed by averaging from the 30 measured values per track. For comparison, the chloride contents determined at the same drill core by wet-chemical methods are shown in profile depths of 10 mm each. From Fig. 17 it can be seen that one obtains a much more accurate representation of the chloride penetration behavior by means of the LIBS method. From this representation, for example, the chloride diffusion coefficient can be derived, with the aid of which the future penetration behavior and thus future damage can be determined. Since the procedure for the determination of sulfur contents is in principle the same as for chlorine contents, a separate representation for sulfur is omitted here. From the sulfur content can then be concluded via stoichiometric conversion to the sulfate content. The described method is also transferable to the determination of other element contents.

Fig. 18 shows the comparison between the results of a wet chemical standard analysis in step 1450 compared to the LIBS method in step 1440 for two different compacts NL6 and NL7. It shows that only in the near-surface region between 0 and 20 mm there is a good correlation between the results. By contrast, no LIBS signal is available in the range between 20 and 40 mm, since the chloride content is below the detection limit. This is partly due to the fact that the grinding of the sample material is a homogenization and thus an averaging over the entire pressing. In contrast, the inventive method provides a spatially resolved measurement with high spatial resolution.

Figure 19 shows LIBS measured chloride levels over standard chemically determined chloride levels for both samples NL6 and NL7. The calibration of the LIBS method with the aid of wet-chemically analyzed samples thus results in a nearly linear Context. Reference samples may be provided for the quantitative determination of chlorine, sulfur and sodium levels.

The method described above can also be used for quality assurance in the repair of concrete structures. For this purpose, the pollutant content in the concrete structure is first determined by scanning a surface of the concrete according to one of the analysis methods described above. The narrow-band detector is set to a spectral line of the pollutant. Subsequently, the concrete layer recognized as contaminated is removed from the concrete structure. Then, the above-described LIB S process can again be performed on the new surface to determine if the pollutant-contaminated concrete has been completely removed.

The present invention has been explained with reference to exemplary embodiments. These embodiments should by no means be construed as limiting the present invention.

Claims

claims

1. Device (10) for examining a heterogeneous material (1) by means of laser-induced plasma spectroscopy, comprising

a laser (100) for generating a plasma from the heterogeneous material (1),

a broadband detector (200) arranged to detect a continuous spectrum of plasma emission radiation, and

a narrow band detector (250) configured to detect a predetermined spectral line within the same plasma emission radiation.

2. Apparatus according to claim 1, wherein the broadband detector (200) and the narrow band detector (250) are adapted to detect radiation in the red to near infrared range.

3. Apparatus according to claim 2, wherein the broadband detector (200) and the narrow band detector (250) for detecting radiation in the wavelength range of 600 nm to 950 nm are adapted.

Apparatus according to any one of the preceding claims, wherein the narrow band detector (250) is arranged to detect a spectral line of one of the following elements: sulfur, chlorine, titanium, lithium, sodium, potassium, magnesium, carbon, fluorine, bromine.

The apparatus of claim 4, wherein the predetermined spectral line is a sulfur spectral line at 921.3 nm.

The device of claim 4, wherein the predetermined spectral line is a chlorine spectral line at 837.6 nm.

7. Device according to one of claims 4 to 6, wherein the narrow-band detector (250) is switchable between the detection of a sulfur spectral line and the detection of a chlorine spectral line.

Apparatus according to any one of claims 4 to 6, wherein the apparatus comprises a first narrow band detector (250) for detecting a sulfur spectral line and a second narrow band detector for detecting a chlorine spectral line.

9. Device according to one of the preceding claims, wherein the broadband detector (200) and / or the narrow-band detector (250) is a CCD detector.

10. Device according to one of claims 1 to 9, wherein the narrow-band detector (250) is a photomultiplier.

11. Device according to one of the preceding claims, wherein the plasma emission radiation to be detected by means of a Y-shaped light guide (140) to the wideband detector (200) and to the narrow-band detector (250) is transmitted.

The apparatus of any one of the preceding claims, wherein the laser (100) is adapted to scan a surface of the heterogeneous material (1).

13. The apparatus of claim 12, wherein the laser (100) is arranged on a pan-tilt head (160) as a scanning device.

14. Device according to one of the preceding claims, wherein the laser (100) is a NdYAG laser.

A device according to any one of the preceding claims, further comprising a focusing unit (120) for focusing a laser beam (110) on a surface of the heterogeneous material (1).

16. The apparatus of claim 15, wherein the focusing unit (120) comprises an autofocus device.

17. The apparatus of claim 15 or 16, wherein the focusing unit (120) is further adapted to couple the plasma emission radiation to be detected in a light guide (140).

18. The apparatus of claim 17, wherein the light guide (140) is a Y-fiber, wherein a first end to the output of the focusing unit (120) has a second end with the broadband detector (200) and a third end with the narrow band Detector (250) is connected.

19. Device according to one of claims 15 to 18, wherein the focusing unit (120) is fixedly connected to the laser (100).

The apparatus of any one of the preceding claims, wherein the apparatus further comprises a laser-tight shield (300) that can be disposed between the laser (100) and a surface of the heterogeneous material (1).

21. The apparatus of claim 20, wherein the laser-dense shield (300) is a laser-tight bellows.

22. Device according to one of claims 20 or 21, wherein the laser-tight shield (300) is flexibly connected to the laser (100), so that the relative position of the shield (300) with respect to a surface of the heterogeneous material (1) is fixed, while the laser (100) performs a scanning movement.

The apparatus of any one of claims 20 to 22, further comprising a seal (340) for contacting a surface of the heterogeneous material (1), the seal (340) disposed on an end of the shield (300) remote from the laser (100) is.

24. Device according to one of claims 20 to 23, further comprising a contact switch (620) which is disposed on a side facing away from the laser (100) front side of the shield (300), wherein the contact switch (620) at a predetermined contact pressure against a surface of the heterogeneous material (1) is triggered.

25. The apparatus of claim 24, wherein the apparatus is arranged so that operation of the laser (100) is only possible when the contact switch (620) is triggered.

Apparatus according to any one of the preceding claims, further comprising means (400, 420, 440, 460) for supplying a purge gas to a surface of the heterogeneous material (1).

27. The apparatus of claim 26, wherein the means for supplying a purge gas comprises a purge gas tank (400) and a purge gas supply line (420, 440), wherein the purge gas supply line is adapted to purge gas from the purge gas tank (400) to the surface of the heterogeneous material (1).

28. The apparatus of claim 27, wherein the purge gas supply line comprises a flange (440) having one or more gas inlet openings, wherein the flange (440) on a side facing away from the laser (100) front side of a shield (300) is arranged.

29. The apparatus of claim 28, wherein the flange (440) between a front side of the shield (300) and a seal (340) is arranged.

30. Device according to one of claims 28 or 29, wherein the flange (440) in one area more and / or larger gas inlet openings than in another area.

31. Device according to one of claims 28 to 30, wherein the gas flow for individual areas of the flange (440) is separately adjustable.

32. Device according to one of claims 27 to 31, wherein the means for supplying a purge gas for the use of helium is adapted as purge gas.

33. Device according to one of the preceding claims, further comprising a sample holder.

34. The apparatus of claim 33, wherein the sample holder with a seal (340), which is arranged on a side facing away from the laser (100) front side of a shield (300) is formed connectable.

35. Device according to one of the preceding claims, wherein the device (10) is transportable.

36. Device according to one of the preceding claims, further comprising a chassis (700) on which the device is arranged.

37. The apparatus of claim 36, wherein at least the laser (100) together with a scanning device (160) horizontally and / or vertically with respect to the chassis (700) is pivotable.

38. The apparatus of claim 37, further comprising a broadband detector (200) and / or a narrow band detector (250) and / or a focusing unit (120) and / or a shield (300) and / or a purge gas supply line (420, 440) together with the laser (100) horizontally and / or vertically with respect to the chassis (700) is pivotable.

39. The apparatus of claim 37 or 38, further comprising a pivotable support (530) for holding the laser (100) and the scanning device (160) during pivoting.

40. The apparatus of claim 39, wherein the support (500, 530) is formed so that the relative position of a laser-tight shield (300) flexibly connected to the laser (100) is fixed with respect to a surface of the heterogeneous material (1) the laser (100) performs a scanning movement.

41. A method of analyzing a heterogeneous material that includes multiple classes of materials, comprising the steps of:

(a) generating a plasma from the heterogeneous material by means of a

Laser beam; (b) detecting a continuous spectrum of plasma emission radiation by means of a broadband detector;

(c) detecting a predetermined spectral line within the same plasma emission radiation by means of a narrow band detector;

(d) assigning the continuous spectrum to a group of heterogeneous material; and

(e) assigning the predetermined spectral line to the substance group.

42. The method of claim 41, wherein steps (a) to (e) are repeated one or more times, wherein the laser beam is directed at each repetition to another point on the surface of the heterogeneous material.

43. The method of claim 42, wherein the points to which the laser beam is directed are arranged in a straight line one behind the other.

44. Method according to claim 42 or 43, wherein the distance between two points is from 0.5 mm to 10 mm inclusive, in particular from 1 mm to 5 mm inclusive.

45. The method according to any one of claims 42 to 44, wherein a plurality of lines are arranged parallel to each other to allow a surface area detection of the surface.

46. The method according to any one of claims 41 to 45, wherein the continuous spectrum and the predetermined spectral line in the red to near-infrared region are detected.

47. The method of claim 46, wherein the plasma emission radiation in the wavelength range of 600 nm to 950 nm is detected.

48. The method of claim 41, wherein the predetermined spectral line is a spectral line of one of the following elements: sulfur, chlorine, titanium, lithium, sodium, potassium, magnesium, carbon, fluorine, bromine.

49. The method of claim 48, wherein the predetermined spectral line is a sulfur spectral line at 921.3 nm.

50. The method of claim 48, wherein the predetermined spectral line is a chlorine spectral line at 837.6 nm.

51. The method according to any one of claims 48 to 50, wherein the quantitative content of the element is determined from the predetermined spectral line.

52. The method of claim 41, wherein the laser beam is focused on a surface of the heterogeneous material.

53. The method of any of claims 41 to 52, disposing a laser-tight shield between a laser and a surface of the heterogeneous material.

54. The method of claim 53, wherein a seal disposed on a laser facing away from the end of the shield, is brought into contact with a surface of the heterogeneous material.

55. The method of claim 41, further comprising passing a purge gas to the surface of the heterogeneous material.

56. The method of claim 55, wherein helium is used as purge gas.

57. The method of any one of claims 41 to 56, wherein the heterogeneous material is concrete.

58. The method according to any one of claims 41 to 56, wherein the heterogeneous material is a geological sample and / or a mineral sample and / or a glass and / or a molten glass.

59. A method for determining the depth profile of an element in a heterogeneous material, comprising the steps of:

Removing a core of the heterogeneous material;

Columns of the core; and

multiple exporting the analysis method according to any one of claims 40 to 58 on a split surface of the core, wherein

a spectral line of the element is selected as the predetermined spectral line and a plurality of measurements are carried out at different points, wherein the points are arranged one behind the other in the depth direction of the drill core.

60. The method of claim 59, wherein the measurement points are disposed on a first and a second line, wherein the first and second lines on the gap surface of the drill core are substantially parallel to a surface of the heterogeneous material, and wherein the first line and the second line in the depth direction of the core are arranged one behind the other.

61. The method of claim 59 or 60, further comprising determining a penetration coefficient of the element from detected elemental contents.

62. Quality assurance procedure for the repair of concrete structures, comprising the steps of:

(1) determining a pollutant content in the concrete structure by scanning a surface of the concrete with a method according to any one of claims 40 to 58, wherein the predetermined spectral line is a spectral line of a pollutant; (2) removing a concrete layer contaminated with the pollutant from the concrete structure;

(3) re-performing step (1) to determine if the pollutant-contaminated concrete has been completely removed.