Elemental analysis device for a sample to be studied by optical emission spectrometry on laser-produced plasma, comprising a sample holder

Abstract

Title: Elemental analysis device for a sample to be studied by laser-generated plasma optical emission spectrometry, comprising a sample holder. The invention relates to an elemental analysis device for a sample to be studied, the device comprising: a base (1) having a flat surface (10) and intended to support a sample (2) to be studied; a system (3) for generating a laser beam (30) intended to impact the sample (2) to be studied in a direction perpendicular to the flat surface (10) of the base (31), to generate a plasma (P) producing optical emission (40); means for collecting the optical emission (40); a sample holder (5) intended to rest on the base (1). Figure for the abstract: Fig. 1

Description

Title of the invention: Elemental analysis device for a sample to be studied by optical emission spectrometry on laser-produced plasma, comprising a sample holder

[0001] The present invention relates to the field of high-resolution mapping and analysis of elements in solids.

[0002] More particularly, the invention relates, in particular but not exclusively, to a device for qualitative and quantitative analysis of the elemental chemical composition of a solid sample.

[0003] The invention can in particular be applied to the elemental analysis of hydrogen and oxygen by optical emission spectrometry on laser-produced plasma, in the field of the nuclear industry, or even the aeronautical or space industry.

[0004] In applications such as the characterization of devices subjected to radioactive sources, or the characterization of the aging ability of devices used in particularly severe environments, for example in aircraft or spacecraft, it may prove essential to carry out the elemental analysis of metallic samples.

[0005] More specifically, it may be necessary to be able to map these elements within the analyzed sample. By mapping, we mean an identification of the elements composing the analyzed sample and, possibly, the distribution and the relationship between the different elements.

[0006] Such an analysis can prove particularly useful in studies of hydrogen embrittlement of metals, or in studies of aging of fuel cladding in the presence of oxygen, or in studies of embrittlement of fuel cladding caused by the formation of hydrides, the latter promoting the propagation of cracks.

[0007] There are various known methods of mapping elements present in samples.

[0008] One of these methods is elemental analysis by optical emission spectrometry on laser-produced plasma, designated by the acronym "SEOPPL", a technique which is carried out in a natural atmosphere, also designated by the English acronym "LIBS" corresponding to the English expression "laser induced breakdown spectroscopy".

[0009] This method is particularly applicable to the control and in situ characterization of samples of parts to be analyzed.

[0010] A method and device for elemental analysis by laser-produced plasma optical emission spectrometry is described, for example, in the patent document published under number WO 01 / 33202.

[0011] Such an analysis device comprises: - a base intended to support a sample to be studied; - a laser beam generation system intended to impact the sample to be studied in a direction perpendicular to the base, to generate a plasma producing optical emission; - means of collecting optical emission.

[0012] The laser beam generated by the generation system, after shaping by a shaping module, is applied to a sample to be studied via optical focusing means.

[0013] A plasma is then created at the point of impact of the laser beam on the sample to be studied, the plasma generating an optical emission to be analyzed in order to map the elements composing the sample studied.

[0014] The collection of the optical emission from the plasma is then carried out by the collection means.

[0015] The displacement of the sample to be studied relative to the laser beam allows access to the distributions of the concentrations of the constituent elements of the surface of the sample, which makes it possible to establish elemental maps.

[0016] The device described in the aforementioned document includes means for moving the sample to be analyzed.

[0017] The sample is positioned more precisely to the micrometer on a stage. This stage, for example motorized, allows for micro-displacements along two axes of direction.

[0018] The focusing produced by the optical focusing means is a critical parameter. Indeed, this focusing must be maintained throughout the analysis of the surface of the sample to be studied.

[0019] In the case where the surface to be analyzed of the sample is sufficiently flat (a surface being considered sufficiently flat if its relief does not present differences in height greater than the depth of field of the optical focusing means), and where the perfect perpendicularity of this surface is ensured with respect to the laser beam, then there is no focusing problem.

[0020] In the case where the surface of the sample is not flat, and / or where this surface is not perfectly perpendicular to the laser beam, then an adjustment of the focus must be made as the analysis progresses.

[0021] A similar device is also known, described in patent document published under number WO 2016203163.

[0022] The device includes an autofocus system for compensating for such defects in flatness and perpendicularity relative to the laser beam of the surface of the sample to be studied. For this, the device uses a sensor that measures any flatness defects of the sample, as well as a motorization of the sample holder capable of orienting the sample holder according to the flatness defect measured.

[0023] This design solves the problem relating to the need for focusing the laser beam, but inherently leads to a more complex device.

[0024] The invention aims in particular to overcome this drawback of the prior art.

[0025] More specifically, the invention aims to provide an elemental analysis device for a sample to be studied, of the type described above, which makes it possible to overcome defects in flatness and perpendicularity with respect to the laser beam of the surface of the sample to be studied in a less complex way than that proposed by the prior art.

[0026] This objective, as well as others that will appear subsequently, is achieved thanks to the invention, which relates to a device for the elemental analysis of a sample to be studied, the device comprising: - a base with a flat surface designed to support a sample to be studied; - a laser beam generation system intended to impact the sample to be studied in a direction perpendicular to the flat surface of the base, to generate a plasma producing optical emission; - means of collecting optical emission; characterized in that it comprises a sample holder including: - a flat lower face intended to rest on a flat surface of the base; - a cavity designed to hold the sample; - at least one shoulder forming a bearing surface oriented towards the cavity, the bearing surface being inscribed in a plane parallel to the flat lower face of the sample holder; - elastic return means configured to press the sample against the support surface.

[0027] Thanks to the device according to the invention, the defects of flatness and perpendicularity as described above are overcome in a way that is less complex than that proposed by the prior art (autofocus).

[0028] Indeed, the design of the device according to the invention makes it possible to guarantee that the surface of the sample to be studied extends perpendicularly to the laser beam generated by the generation system of the device.

[0029] Thanks to the sample holder, the sample is pressed against the support surface, and the sample surface then extends in the plane parallel to the flat lower face of the sample holder. In this way, and because the flat lower face of the The sample holder rests on the flat surface of the base; the plane in which the face to be studied of the sample extends parallel to the flat surface of the base and thus perpendicular to the laser beam which, during the operation of the device, extends perpendicularly to the flat surface of the base.

[0030] By ensuring that the surface of the sample to be analyzed is pressed against the shoulder, there is no focusing problem when studying the surface of the sample. The sample holder of the device according to the invention provides a simple mechanical solution, and in particular a simpler one than that using autofocus.

[0031] Advantageously, the sample holder comprises a cylindrical block, in particular a cylindrical block of revolution, having the cavity and the shoulder(s).

[0032] Such a cylindrical block is obtained for example by precision machining.

[0033] This cylindrical block allows for the presentation of faces extending, when the sample holder is integrated into the device, parallel or perpendicular to the flat lower face of the sample holder, and to the flat surface of the base.

[0034] More precisely, the radially external surface of the block and more precisely the generatrices of this surface then extend perpendicularly to the flat surface of the base while the bases of the cylinder extend parallel to the flat surface of the base.

[0035] Advantageously, the shoulder takes an annular shape.

[0036] Such a shoulder makes it possible to form a continuous bearing surface on which the sample can be pressed.

[0037] According to a preferred design, the sample holder comprises a base having a flat lower face, and means for retaining the block on the base, the retaining means comprising two clamping jaws for the block each having a clamping surface whose generatrices extend perpendicularly to the flat lower face.

[0038] Thanks to the two clamping jaws of the block, each of which has a clamping surface whose generatrices extend perpendicularly to the flat lower face, it is ensured that these clamping jaws come into flat contact against the radially external surface of the block during clamping, thus guaranteeing that the clamping does not cause an angular tilting of the central axis of the cylindrical block of revolution relative to the flat surface of the base.

[0039] Conversely, tightening by means of a screw which would exert a point load, perpendicular to the central axis of the cylindrical block of revolution, on the radially external surface of the cylindrical block, could cause such a shift distorting the measurement.

[0040] According to an advantageous feature, the sample holder includes a stop coupling with the block and forming a support for the elastic retrieval means.

[0041] Thanks to such a stop separate from the block, then the positioning of the sample in the block, then the elastic return means, and finally of the stop are carried out in a simple manner, while contributing to ensuring the correct positioning of the sample with respect to the axis of the laser beam.

[0042] Preferably, the elastic return means have at least two upper contact points intended to be in contact with the sample, and at least two lower contact points intended to be in contact with the stop.

[0043] In this way, it is ensured that the support taken by the elastic return means against the stop, and the forces applied by the elastic return means are exerted in a regularly distributed manner to properly press the sample against the support surface formed by the shoulder.

[0044] According to an advantageous embodiment, the elastic return means take the form of a corrugated spring washer.

[0045] Such a corrugated spring washer is suitable for achieving the elastic return ensuring proper contact of the sample against the support surface.

[0046] Even more preferably, the spring washer has, according to a side view, an S-shaped profile.

[0047] Such a spring washer perfectly ensures the correct pressing of the sample against the bearing surface.

[0048] The invention also relates to a method for elemental analysis of a sample to be studied by laser-produced plasma optical emission spectrometry, comprising a sample preparation step and a sample positioning step on a base for analysis, characterized in that the sample preparation step includes a substep of forming a flat surface to be studied by polishing on the sample, and in that the positioning step includes the use of a sample holder, and comprises: - a sub-step of inserting the sample into the sample holder and positioning the flat face to be studied against a support surface of the sample holder in a plane parallel to a flat lower face of the sample holder intended to rest on a flat surface of the base; - a sub-step of adding elastic restoring means to press the flat face to be studied of the prepared sample against the support surface.

[0049] The analysis process can be implemented by the device according to the aforementioned invention.

[0050] This analysis method guarantees the correct positioning of the sample relative to the axis of the laser beam.

[0051] Other features and advantages of the invention will become more apparent upon reading the following description of various preferred embodiments of the invention, given by way of illustrative and non-limiting examples, and the accompanying drawings, among which: • [Fig.1] [Fig.1] is a schematic side view representation of an elemental analysis device for a sample to be studied according to the invention, including in particular a sample holder resting on a base; • [Fig. 2] [Fig. 2] is a schematic representation in cross-section. transverse of the sample holder of a device according to the invention, the sample holder comprising a block receiving the sample, elastic return means and a stop allowing the sample to be pressed into the block, as well as a base and means for holding the block on the base; • [Fig. 3] [Fig. 3] is a schematic representation in cross-section transverse of the block accommodating the sample and housing within it the elastic return means and the stop; • [Fig.4] [Fig.4] is a schematic cross-sectional representation of the single block; • [Fig. 5] [Fig. 5] is a schematic cross-sectional representation of the stop; • [Fig.6] [Fig.6] is a schematic representation from a side view elastic return means, in particular taking the form of a corrugated washer; • [Fig.7] [Fig.7] is a schematic representation viewed from above of the door- sample illustrating in particular the means of securing the block to the base.

[0052] With reference to [Fig.1], an elemental analysis device for a sample to be studied is shown.

[0053] The analysis device is of the type projecting a laser beam 30 onto a sample 2 to be studied to generate a plasma P producing an optical emission 40 intended to be collected and analyzed.

[0054] Still referring to [Fig. 1], the device comprises: - a base 1 intended to support the sample 2 to be studied, the base 1 having a flat surface 10; - a system 3 for generating a laser beam 30 intended to impact the sample 2 to be studied, to generate a plasma P producing optical emission 40; - means of collecting 4 of the optical emission 40; - a sample holder 5 intended to hold the sample 2 to be studied above the base 1, the sample holder 5 resting on the base 1, and more precisely on the flat surface 10 of base 1.

[0055] The laser beam generation system 30 is configured to emit the laser beam 30 in a direction perpendicular to the flat surface 10 of the base 1.

[0056] The laser beam generation system 30 includes a laser beam generation source, laser beam shaping means, and optical laser beam focusing means.

[0057] The generation system 3 is configured so that the focusing of the laser beam 30 is adapted to the sample 2 to be studied.

[0058] This focusing is defined in part by a depth of field within which the surface of the sample 2 to be studied impacted by the laser beam 30 must be located.

[0059] The means for collecting 4 of the optical emission 40, meanwhile, include for example an optical fiber 41 oriented towards the plasma P, and positioned as close as possible to the plasma P to collect the optical emission 40.

[0060] The sample holder 5 is described in more detail below.

[0061] With reference to Figures 2, 3 and 7, the sample holder 5 comprises: - a block 54; - a 55 base; - means of holding block 54 on base 55.

[0062] In a simplified design, the sample holder 5 comprises: - a flat lower face 50 intended to rest on the flat surface 10 of the base 1; - a cavity 51 intended to receive sample 2; - a support surface 520 oriented towards the cavity, this support surface 520 being inscribed in a plane parallel to the flat lower face 50 of the sample holder 5; - elastic return means 53 configured to press the sample 2 against the support surface 520.

[0063] According to the present embodiments, the flat lower face 50 is presented by the base 55.

[0064] When the sample holder 5 is placed on the base 1, then the flat lower face 50 of the base 55 is in flat contact with the flat surface 10 of the base 1.

[0065] The cavity 51, intended to receive the sample 2, is presented by the block 54.

[0066] The sample holder 5 also includes at least one shoulder 52 which forms the bearing surface 520.

[0067] The bearing surface 520 is in this case formed by a single shoulder 52.

[0068] This shoulder 52 is presented by the block 54 which is intended to receive the sample 2 in its cavity 51.

[0069] In this case, the shoulder 52 takes on an annular shape. This shoulder 52 thus corresponds to an internal shoulder of the block 54 which is, according to the present method of cylindrical realization, and more specifically cylindrical of revolution around a central axis.

[0070] The bearing surface 520 thus extends from a peripheral wall of the block 54 in the direction of the central axis of the cylindrical block 54 of revolution.

[0071] The cylindrical block 54 of revolution has: - a radially external surface 541; - a lower surface 540 fitting within one of the two bases corresponding to the cylindrical shape of revolution; - a top surface 542 fitting into the other of the two bases of the cylindrical shape of revolution.

[0072] The cavity 51 opens onto the lower face 540.

[0073] Indeed, the block 54 has a light 543 centered on the upper surface 542, and opening into the cavity 51 to allow the laser beam 30 to impact the sample 2.

[0074] Being cylindrical, the generatrices of the radially external surface 541 all extend perpendicularly to the lower face 540 and to the upper face 542.

[0075] Similarly, these generatrices extend perpendicularly to a plane in which the support surface 520 is inscribed.

[0076] As detailed functionally thereafter, block 54 includes an internal thread 544.

[0077] With reference to figures 2, 3 and 5, the sample holder 5 includes a stop 57.

[0078] This stop 57 couples to the cylindrical block 54 and forms a support for the elastic return means 53. This stop 57 notably takes an annular shape.

[0079] The stop 57 is coupled to the cylindrical block 54 by being screwed inside the cavity 51.

[0080] For this purpose, the stop 57 has an external thread 571 complementary to the internal thread 544.

[0081] The stop 57 and the block 54 are configured so that screwing the stop 57 into the cavity 51 brings an upper surface 570 of the stop 57 into a plane that is parallel to the plane in which the bearing surface 520 is inscribed.

[0082] In order for the block 54 and the stop 57 to have rigorously geometric shapes, and in particular to have faces and sides that fall in parallel or perpendicular planes, then these two parts are manufactured by high-precision machining, or even by 3D printing.

[0083] With reference to figures 2, 3 and 6, the elastic return means 53 take the form of a corrugated spring washer.

[0084] More specifically, the spring washer has, according to a side view, an S-shaped profile.

[0085] Such a wavy spring washer allows the elastic return means 53 to have at least two upper contact points 531, and in this case three upper contact points 531 intended to be in contact with the sample 2, and at least two lower contact points 532, and in this case three lower contact points 532 intended to bear against the stop 57, and more specifically against the upper surface 570 of the stop 57.

[0086] Due to the profile view of [Fig.6], only two upper contact points 531 and two lower contact points 532 are visible; however, it can easily be understood that the washer has a third upper point 531 behind the upper point 531 located on the right side of the figure, and a third lower contact point 532 behind the lower contact point 532 located on the left side of the figure.

[0087] Now, with reference to Figures 2 and 7, the retaining means 56 are described in more detail below.

[0088] These retaining means 56 are fixed on the base 55. The retaining means 56 comprise two jaws 561 for clamping the block 54.

[0089] Each jaw 561 has a clamping surface 562 whose generatrix(ies) extend perpendicularly to the flat lower face 50 presented by the base 55.

[0090] More specifically, the retaining means 56 are configured so that the two clamping jaws 561 can be moved towards each other while maintaining the perpendicularity of the generatrices of the clamping surfaces 562 with respect to the flat lower face 50.

[0091] To this end, and with reference more specifically to the embodiment of [Fig. 7], the retaining means 56 comprise a hinge 563 defining a pivot axis of one of the jaws relative to the other jaw 561 extending perpendicularly to the flat lower face 50. This pivot axis extends perpendicularly to the flat lower face 50. According to another preferred embodiment, not shown, the retaining means 56 are made of a material that is at least partially elastically deformable and comprise a thickness reduction in place of the hinge 563. In this way, the two jaws can be separated from each other to allow the insertion of the block 54.

[0092] In addition, the retaining means 56 include a bolt 564 coupled to the two clamping jaws 561 to allow the two clamping jaws 561 to be brought closer together.

[0093] Such clamping means ensure that the block 54 is clamped in a position in which the central axis of the block 54 extends perpendicularly to the flat lower face 50.

[0094] The invention also includes a method for elemental analysis of sample 2 to be studied by optical emission spectrometry on laser-produced plasma.

[0095] This process includes a step of preparing a sample 2, then a step of positioning the sample 2 on the base 1 for its analysis.

[0096] The step of preparing a sample 2 includes in particular the formation of the sample 2.

[0097] As schematically illustrated in Figures 2 and 3, sample 2 takes an essentially cylindrical shape of revolution.

[0098] For the purposes of the analysis, the material to be analyzed corresponds, for example, to a metal strip embedded in a resin block designed so that the strip to be analyzed is flush with one of the bases of the resin block. This block forms the sample 2 to be studied.

[0099] During the sample preparation step 2, a sub-step of forming a flat face to be studied is carried out by polishing on the sample 2.

[0100] For this purpose, the resin block is polished by bringing its base, on which the slide of material to be analyzed is flush, into contact with an abrasive surface.

[0101] Subsequently, the step of positioning the sample 2 on the base 1 for its analysis includes the use of the sample holder 5 described previously.

[0102] This positioning step thus comprises: - a sub-step of inserting the sample 2 into the sample holder 5, and in particular of inserting the sample 2 into the cavity 31 of the block 54, and of positioning the flat face to be studied against the support surface 520 of the sample holder 5; - a sub-step of adding elastic return means 53 to press the flat face to be studied the sample 2 against the support surface 520.

[0103] Subsequently, of course, the stop 57 is screwed in so as to allow the elastic return means to bear against this stop 57 and to exert an elastic return force on the sample 2 to keep it pressed down.

[0104] The block 54 is then positioned on the base 55 and tightened by the retaining means 56.

[0105] Subsequently, the analysis by optical emission spectrometry on laser-produced plasma can be carried out, the sample holder 5 ensuring that the surface of the sample 2 to be analyzed is well positioned perpendicular to the laser beam 30, and the polishing ensuring that the surface condition of the sample 2 to be analyzed does not have height differences located outside the depth of the field of focus of the generation system 3.

Claims

Demands

1. Device for elemental analysis of a sample to be studied, the device comprising: - a base (1) having a flat surface (10) and intended to support a sample (2) to be studied; - a system (3) for generating a laser beam (30) intended to impact the sample (2) to be studied in a direction perpendicular to the flat surface (10) of the base (31), to generate a plasma (P) producing an optical emission (40); - means of collecting (4) optical emission (40); characterized in that it comprises a sample holder (5) comprising: - a flat lower face (50) intended to rest on the flat surface (10) of the base (1); - a cavity (51) intended to receive the sample (2); - at least one shoulder (52) forming a bearing surface (520) oriented towards the cavity (51), the bearing surface (520) being inscribed in a plane parallel to the flat lower face (50) of the sample holder (5); - elastic return means (53) configured to press the sample (2) against the support surface (520), - a cylindrical block (54) having the cavity (51) and the shoulder(s) (52), - a base (55) having the lower flat face (50), and means for retaining (56) the block (54) on the base (55), the means for retaining (56) comprising two jaws (561) for clamping the block (54) each having a clamping surface (562) whose generatrices extend perpendicularly to the lower flat face (50).

2.

3.

4. Device according to the preceding claim, characterized in that the cylindrical block (54) is cylindrical of revolution. Device according to the preceding claim, characterized in that the shoulder (52) takes an annular shape. Device according to any one of the preceding claims, characterized in that the sample holder (5) comprises a stop (57) coupling to the block (54) and forming a support for the elastic retrieval means (53).

5. Device according to any one of the preceding claims, characterized in that the elastic return means (53) have at least two upper contact points (531) intended to be in contact with the sample (2), and at least two lower contact points (532) intended to be in contact with the stop (57).

6. Device according to any one of the preceding claims, characterized in that the elastic return means (53) take the form of a corrugated spring washer.

7. Device according to claims 5 and 6, characterized in that the spring washer has, according to a side view, an S-shaped profile.

8. Method for elemental analysis of a sample (2) to be studied by laser-produced plasma optical emission spectrometry, comprising a step of preparing a sample (2) and a step of positioning the sample (2) on a base (1) for its analysis, characterized in that the step of preparing a sample (2) includes a substep of forming by polishing on the sample (2) a flat face to be studied, and in that the positioning step includes the use of a sample holder (5) comprising: - a flat lower face (50) intended to rest on the flat surface (10) of the base (1); - a cavity (51) intended to receive the sample (2); - at least one shoulder (52) forming a bearing surface (520) oriented towards the cavity (51), the bearing surface (520) being in a plane parallel to the flat lower face (50) of the sample holder (5);- elastic return means (53) configured to press the sample (2) against the support surface (520), - a cylindrical block (54) having the cavity (51) and the shoulder(s) (52), - a base (55) having the flat lower face (50), and means for retaining (56) the block (54) on the base (55), the retaining means (56) comprising two jaws (561) for clamping the block (54) each having a clamping surface (562) whose generatrices extend perpendicularly to the; flat underside (50), and in that the positioning stage includes: - a sub-step of inserting the sample (2) into the sample holder (5) and positioning the flat face to be studied against a support surface (520) of the sample holder (5) which is in a plane parallel to a flat lower face (50) of the sample holder (5) intended to rest on a flat surface (10) of the base (1); - a substep of adding elastic restoring means (53) to press the flat face to be studied of the sample (2) against the support surface (520).

Images