Heating chamber, heating furnace, analysis device, and method for analyzing foreign matter contents in samples

Abstract

A heating chamber (1) for a heating furnace is proposed, with which electrothermal vaporization of impurities from samples can be effected in order to be able to then analyze them spectrometrically. The heating chamber has a wall (3), a sample reception area (5), a nozzle area (7) and two electrical connection areas (9, 11). The heating chamber (1) is specially configured such that an electric current flows through the wall (3) in such a way that a heating capacity caused by it is higher in the nozzle area (7) than in the sample reception area (5). For example, the electrical connection areas (9, 11) may be arranged in a radial direction remoter from the longitudinal axis (8) than a part of the wall (3) surrounding the nozzle area (7), and the heating chamber (1) may be configured, for example by means of a locally constricted area (13), in such a way that the current between the two electrical connection areas (9, 11) is predominantly conducted radially inwards towards the part of the wall (3) surrounding the nozzle area (7). Advantageous heat distribution in the heating chamber (1) achievable thereby may have a positive effect on the analysis of sample impurities.

Claims

1. A heating chamber for a heating furnace, comprising: an electrically conductive wall; a sample reception area; a nozzle area; a first electrical connection area; and a second electrical connection area, wherein the sample reception area and the nozzle area are each surrounded by the wall, wherein the sample reception area and the nozzle are arranged one after the other along a central longitudinal axis and are configured in fluid communication with each other, and the sample reception area has a larger cross-sectional area than the nozzle area, wherein the first and second electrical connection areas are arranged adjacent to opposite ends of the heating chamber relative to the longitudinal axis of the heating chamber and are electrically connected to the wall, wherein the heating chamber is configured in such a way that an electric current produced by applying an electric voltage to the first and second electrical connection areas flows through the wall in such a way that a heating capacity caused by it is one of equal and higher in the nozzle area compared to the sample reception area, wherein the first and second electrical connection areas are in a radial direction arranged further from the longitudinal axis than a part of the wall surrounding the nozzle area, wherein the heating chamber is configured in such a way that the current produced between the first and second electrical connection areas is directed predominantly radially inwards towards the part of the wall surrounding the nozzle area, and wherein the wall has a narrowed cross-section geometry in a constricted section in which the wall surrounds the nozzle area compared to areas of non-constricted sections in which the wall surrounds the sample reception area, such that, in the constricted section, a radially outward facing surface of the wall is on average less remote from the central longitudinal axis than in the non-constricted sections in which the wall surrounds the sample reception area, such that an electric current fed at the first electrical connection area must, in the constricted section, first of all flow towards the radially inner nozzle area and there flow through a small cross-section so that a high electric current density is reached locally and thus a high heating capacity is achieved.

2. The heating chamber according to claim 1, wherein the first and second electrical connection areas are formed by end faces of the wall at the opposite ends of the heating chamber, and wherein the first and second electrical connection areas have a substantially identical cross-section geometry.

3. The heating chamber according to claim 1, wherein at least one of the sample reception area and the nozzle area are configured axially symmetrical relative to the longitudinal axis.

4. The heating chamber according to claim 3, wherein at least one of the sample reception area and the nozzle area are configured rotationally symmetrical relative to the longitudinal axis.

5. The heating chamber according to claim 1, wherein the wall, adjacent to at least one of the sample reception area and the nozzle area, is configured axially symmetrical relative to the longitudinal axis.

6. The heating chamber according to claim 5, wherein the wall, adjacent to at least one of the sample reception area and the nozzle area, is configured rotationally symmetrical relative to the longitudinal axis.

7. The heating chamber according to claim 1, wherein the nozzle area with a nozzle outlet located radially far inside protrudes in an axial direction beyond end faces of the wall located radially further outside.

8. The heating chamber according to claim 1, wherein the wall is made of graphite.

9. The heating chamber according to claim 1, wherein the entire heating chamber is made of graphite.

10. The heating chamber according to claim 1, wherein the entire heating chamber is integrally formed.

11. A heating chamber for a heating furnace, comprising: an electrically conductive wall; a sample reception area; a nozzle area; a first electrical connection area; and a second electrical connection area, wherein the sample reception area and the nozzle area are each surrounded by the wall, wherein the sample reception area and the nozzle are arranged one after the other along a central longitudinal axis and are configured in fluid communication with each other, and the sample reception area has a larger cross-sectional area than the nozzle area, wherein the first and second electrical connection areas are arranged adjacent to opposite ends of the heating chamber relative to the longitudinal axis of the heating chamber and are electrically connected to the wall, and wherein the heating chamber is configured in such a way that an electric current produced by applying an electric voltage to the first and second electrical connection areas flows through the wall in such a way that a heating capacity caused by it is one of equal and higher in the nozzle area compared to the sample reception area, wherein the wall has a narrowed cross-section geometry in a constricted section in which the wall surrounds the nozzle area compared to areas in which the wall surrounds the sample reception area, and wherein the heating chamber, in the constricted section, has web areas which bridge the constricted section in order to form a mechanically loadable linear connection between the opposite ends of the heating chamber.

12. A heating chamber for a heating furnace, comprising: an electrically conductive wall; a sample reception area; a nozzle area; a first electrical connection area; and a second electrical connection area, wherein the sample reception area and the nozzle area are each surrounded by the wall, wherein the sample reception area and the nozzle are arranged one after the other along a central longitudinal axis and are configured in fluid communication with each other, and the sample reception area has a larger cross-sectional area than the nozzle area, wherein the first and second electrical connection areas are arranged adjacent to opposite ends of the heating chamber relative to the longitudinal axis of the heating chamber and are electrically connected to the wall, and wherein the heating chamber is configured in such a way that an electric current produced by applying an electric voltage to the first and second electrical connection areas flows through the wall in such a way that a heating capacity caused by it is one of equal and higher in the nozzle area compared to the sample reception area, wherein the wall has a narrowed cross-section geometry in a constricted section in which the wall surrounds the nozzle area compared to areas in which the wall surrounds the sample reception area, and wherein the heating chamber has a plurality of web regions distributed equidistantly along a circumference of the constricted section.

13. A heating furnace, comprising: a mechanical mount; first and second electrical contacts; and a heating chamber according to claim 1, wherein the heating chamber is held in the mount and the first electrical connection area is contacted with the first electrical contact and the second electrical connection area is contacted with the second electrical contact.

14. An analysis device for analyzing foreign matter contents in samples, comprising: a heating furnace according to claim 13; a connecting tube; and a spectrometer, wherein the nozzle area of the heating chamber of the heating furnace opens into the connecting tube in such a way and the connecting tube opens into the spectrometer in such a way that gas formed in the sample reception area of the heating chamber may be conducted into the spectrometer via the nozzle area and the connecting tube.

15. A method of analyzing foreign matter contents in samples, wherein the samples are heated in a sample reception area of a heating chamber according to claim 1 in order to release foreign matter contents contained therein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, advantageous embodiments of the invention are further explained with reference to the attached drawings, wherein neither the drawings nor the explanations are to be interpreted as restricting the invention in any way.

(2) FIG. 1 shows a cross-section of an analysis device with a conventional heating chamber.

(3) FIG. 2 shows a perspective view of a heating chamber according to an embodiment of the present invention.

(4) FIG. 3 shows a front view of the heating chamber of FIG. 2.

(5) FIG. 4 shows a side view of the heating chamber of FIG. 2.

(6) FIG. 5 shows a sectional view along the line A-A of FIG. 3 of the heating chamber of FIG. 2.

(7) FIG. 6 shows a sectional view along the line B-B of FIG. 4 of the heating chamber of FIG. 2.

(8) FIGS. 7 to 9 show side views of heating chambers according to alternative embodiments of the present invention.

(9) The figures are only schematic and not to scale. In the different drawings, identical reference signs designate identical feature or features having identical effects.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

(10) FIG. 1 shows an analysis device 100 which can be used to analyze foreign matter contents in a sample 102. The analysis device 100 comprises a heating furnace 104, a connecting tube 106 and a spectrometer 108.

(11) In the example shown in FIG. 1, a conventional heating chamber 101 is accommodated in the heating furnace 104. The heating chamber 101 has a hollow-cylinder-shaped wall 103. In a front half, the wall 103 surrounds a sample reception area 105. In the sample reception area 105, a sample carrier 112 containing the sample 102 can be received. In a rear half, the wall 103 surrounds a nozzle 110 with a nozzle area 107 accommodated therein. Furthermore, the heating chamber 101 also has electrical connection areas 109, 111 each at its rear end and at its front end. The two electrical connection areas 109, 111 are formed by end faces of the tubular wall 103, which is thickened at its ends.

(12) The heating chamber 101 is accommodated and held in the heating furnace 104 in such a way that the wall 103 is clamped between two electrical contacts 114, 116, each of which has a circular ring shape, and by them is held mechanically as well as is electrically connected at the electrical connection areas 109, 111. The electrical contacts 114, 116 are in turn held by a mechanical mount 118 which thus indirectly also holds the heating chamber 101. Furthermore, the electrical contacts 114, 116 are connected to a current source 120 which can be used to produce an electric current through the electrically conductive wall 103 of the heating chamber 101.

(13) In order to analyze foreign matter contents in a sample 102, such as a graphite sample, the sample 102 is introduced into the sample reception area 105 of the heating chamber 101 on the carrier 112. The heating chamber 101 is then heated by conducting an electric current through its electrically conductive wall 103, where it generates heat due to electrical resistance losses, which, among other things, heats up the sample reception area 105 and the sample 102 accommodated therein to temperatures of up to 3000° C. or even 3200° C.

(14) At such high temperatures, impurities are released from the sample 102. At the same time, a carrier gas 122, e. g. argon, is passed through the sample reception area 105 together with reaction gases, which can react with the impurities to form volatile substances. The hot carrier gas 122 together with the impurity vapors absorbed therein, e. g. foreign atomic halide vapors, then flows through the nozzle area 107 of the nozzle 110. An outlet 124 of this nozzle 110 protrudes in the longitudinal direction of the heating chamber 101 beyond the end faces radially located further outside at the front electrical connection area 109 of the heating chamber 101 and also beyond the annular electrical contact 114 of the heating furnace 104 and opens into the connection tube 106. Together with the hot gas from the heating chamber 101, a cooler sheathing gas 126 is introduced into the connecting tube 106 so that an aerosol 128 forms there which may then be introduced into an analysis chamber 130 of the spectrometer 108. There, the constituents of this aerosol, including the impurities contained therein originating from the sample 102, may be analyzed.

(15) When using an analysis device 100 with a conventional heating chamber 101 as exemplarily shown in FIG. 1, some deficits or problems have been observed.

(16) For example, it has been observed that in the case of special elements, in particular some elements from the group of carbide formers such as boron, silicon, vanadium, etc., a recovery rate during an analysis procedure carried out with the analysis device 100 may be significantly lower than with other elements. This may lead to a non-linear and only limitedly reproducible calibration behavior of these elements, in particular boron and silicon, and consequently to major fluctuations in the analysis results.

(17) Furthermore, a significant tendency to carry over analytes from one analysis run to another has been observed, especially with regard to the above-mentioned elements of the group of carbide formers.

(18) The effects mentioned above may lead to an analytical precision of a sample analysis based on electrothermal vaporization being significantly lower in the statistical sense compared to other analysis methods, i. e. the values for relative standard deviations (RSD) may be considerably higher than the values known, for example, from liquid sample injection methods.

(19) Furthermore, it has been observed that the endurance or service life of conventional heating chambers is sometimes significantly limited. For example, a failure of the heating chamber and in particular of its tubular wall was often observed in the same places, i. e. approximately in the second front quarter of the wall, circa in the area of a position of the sample carrier 112. A significant reduction of a wall cross-section in this area with the consequence of a mechanically caused component fracture was predominantly recognized as the reason for the failure.

(20) There has therefore been a need to solve the aforementioned deficits and problems. To this end, the causes of, for example, the reduced analysis sensitivity in particular to elements from the group of carbide formers, for the carryover of analytes into subsequent analysis runs and for a lack of analytical precision when using the ETV method had to be investigated.

(21) Microscopic examinations of the nozzle 110, especially in the rear area of the heating chamber 101, revealed deposits dependent on a type and concentration of analytes used. These deposits consisted mainly of the above-mentioned elements of the group of carbide formers, for which a significantly reduced recovery rate and a risk of carryover to subsequent analysis runs were observed.

(22) A subsequent measurement of a temperature profile of the heating chamber 101 showed significant temperature inhomogeneities along the longitudinal extension of the component. In particular, where mechanical failure of the wall 103 of the heating chamber 101 was frequently observed, some considerable temperature increases were found, which could be regarded as the reason for the assumed material removal and thus for a reduction of the wall thickness of the heating chamber 101 in this section.

(23) In addition, it was observed that in the rear area of the heating chamber 101 and especially at the outlet 124 of the nozzle 110, often much lower temperatures prevailed compared to the rest of the heating chamber 101. It is assumed that these cooler places lead to analyte condensation or to chemical reactions, which under these temperature conditions are reversible only to a limited extent, with the material of the nozzle wall, i. e. in particular to carbide formation between the analytes and the carbon of the nozzle 110, which usually consists of graphite. This can also be seen as a cause for the observed low recovery rates, material carryovers and increased values of the relative standard deviations.

(24) As a result of such investigations, it could be deduced that it is highly likely that a temperature profile prevailing in the heating chamber 101 would be largely responsible for the observed deficits and problems in carrying out analyses of foreign matter content using conventional analysis devices.

(25) In order to eliminate these problems and deficits, it is therefore proposed to make the temperature distribution within the heating chamber used for electrothermal vaporization more homogeneous or even shift a temperature maximum to an area of an outlet from the heating chamber, i. e. to the nozzle area, preferably without negatively influencing other important properties of the heating chamber, such as its mechanical stability.

(26) For this purpose, it is proposed to modify the heating chamber in such a manner that an electric current produced by applying a voltage to the first and second electrical connection areas flows through the wall in such a way that a heating capacity generated by it is higher in the nozzle area than in the sample reception area.

(27) While in the conventional heating chamber 101, which is illustrated in FIG. 1 as an example, the nozzle 110 is heated only indirectly, i. e. for example by heat radiation of the surrounding, actively heated wall 103, the nozzle area of the further developed heating chamber proposed herein is to be heated specifically actively and directly by directing an electric current produced in the heating chamber precisely in such a way that an increased heating capacity is achieved in this nozzle area.

(28) In contrast to the conventional heating chamber 101, in which the nozzle 110 was only indirectly heated and thus generally became hot later than, for example, the sample reception area 105 and also only experienced lower maximum temperatures, this increased heating capacity specifically achieved in the nozzle area may lead to the fact that in the modified heating chamber proposed herein, the nozzle area is preferably heated faster than the sample reception area and is preferably also heated up to higher temperatures compared to this sample reception area.

(29) This helps to prevent, among other things, that at the beginning of an analysis process, the sample reception area 105 and the sample 102 taken up in it are first heated to high temperatures and impurities start to be released from the sample 102 before the nozzle 110 has been heated to sufficiently high temperatures, so that analytes may in part deposit on the still too cold wall of the nozzle 110.

(30) Instead, at the beginning of the analysis process, first the nozzle area is brought to sufficiently high temperatures before the sample 102 taken up in the sample reception area 105 reaches sufficient temperatures to release impurities to a significant degree. This may significantly reduce the risk of deposits of impurity vapors on the wall of the nozzle.

(31) Among other things, this may lead to the fact that, for example, the above-mentioned elements from the group of carbide formers, coming from the heating chamber, to a greater extent reach the spectrometer 108, where they can be analyzed quantitatively with high sensitivity.

(32) With reference to the heating chamber 1 according to an embodiment of the present invention, which is represented in different ways in FIGS. 2 to 6, possible features and modifications of the heating chamber 1 presented here are to be explained in more detail below in comparison with conventional heating chambers 101.

(33) Essentially, the heating chamber 1, like the conventional heating chamber 101, has a cylindrical shape and is therefore sometimes referred to as a furnace pipe. In the example shown, the entire heating chamber 1 is integrally made of graphite. The heating chamber 1 has an electrically conductive wall 3 which surrounds a sample reception area 5 in a front part of the heating chamber 1 and which surrounds a nozzle area 7 in a rear part of the heating chamber 1. The sample reception area 5 and the nozzle area 7 are therefore preferably cylindrical cavities, which are accommodated within the wall 3 of the heating chamber 1 and are bounded by it in the radial direction, merge into each other and are open towards the outside at their end faces in the form of an inlet or an outlet. The sample reception area 5, via a conical, funnel-shaped intermediate area 6, opens into the nozzle area 7 and is thus connected therewith in fluid communication, so that gases arising or flowing in the sample reception area 5 can flow into the nozzle area 7. The sample reception area 5 and the nozzle area 7 are thus arranged one after the other along a central longitudinal axis 8. The nozzle area 7 has a substantially smaller cross-sectional area than the sample reception area 5.

(34) In the example shown, both the sample reception area 5 and the nozzle area 7 are designed rotationally symmetrical with respect to the longitudinal axis 8, i. e. they have an essentially cylindrical geometry, in which a cylindrically shaped barrel inner surface 4 of the wall 3 laterally surrounds the volumes of the sample reception area 5 and the nozzle area 7, respectively. The funnel-shaped intermediate area 6 is also configured to be rotationally symmetrical. The sample reception area 5 is open towards a front end face 14 so that a sample 2 together with a sample carrier 12 holding it may be introduced into the sample reception area 5. The nozzle area 7 is at one end face 10 open to the rear, so that gas can escape from it.

(35) In addition, the nozzle area 7 projects backwards beyond areas of the rear end face 10 of the heating chamber 1 which are located further outside in the axial direction, so that a nozzle outlet 24 may for example extend into a connecting tube 106 which is disposed adjacent to it in the longitudinal extension. Gas escaping from the nozzle outlet 24 may thus be entrained by a stream of sheathing gas flowing in the connecting tube 106.

(36) At opposite ends of the heating chamber 1, a first and a second electrical connection area 9, 11, respectively, are provided. These electrical connection areas are formed by local thickenings near areas of the end faces of the wall 3 which are located radially outside. The electrical connection areas 9, 11 are thus electrically connected to the remaining areas of the wall 3, so that when a voltage is applied to these two electrical connection areas 9, 11, an electric current is produced within the wall 3. Due to electrical resistances in the wall 3 and resulting electric conduction losses, the wall 3 heats up considerably.

(37) In order to achieve a preferably higher heating capacity in the nozzle area 7 than in the sample reception area 5, the heating chamber 1 is preferably designed in such a way that the first and second electrical connection areas 9, 11 are arranged further apart from the longitudinal axis 8 in the radial direction than a part of the wall 3 surrounding the nozzle area 7. The heating chamber 1 is preferably designed in such a way that the current between the first and second electrical connection areas 9, 11 produced in the wall 3 is preferably directed predominantly radially inwards towards the part of the wall 3 surrounding the nozzle area 7, where it develops an increased heating capacity concentrated on the nozzle area 7.

(38) In addition, a cross-sectional area of the wall 3 may optionally be smaller in sections surrounding the nozzle area 7 than in other sections, in particular than in the sections surrounding the sample reception area 5, so that a higher electric current density and thus a higher heating capacity may be achieved locally adjacent to the nozzle area.

(39) In order to be able to achieve such a specific diversion of the electrical current used for heating towards the nozzle area 7 located radially further inside, a constricted section 13 is provided at the heating chamber 1, in which the wall 3 surrounds the nozzle area 7 and which has a narrowed cross-section geometry compared to areas 15 in which the wall 3 surrounds the sample reception area 5. In other words, the otherwise tubular, cylindrical structure of the heating chamber 1 exhibits a local “necking” in the rear area adjacent to the nozzle area 7, i. e. is reduced to a smaller cross-section. Therefore, an electric current fed at the front electrical connection area 9 must, in this constricted section 13, first of all flow towards the radially inner nozzle area 7 and there flow through a small cross-section so that a high electric current density is reached locally and thus a high heating capacity is achieved. Only after that can the electric current again move radially further outwards and there flow through the wall 3 in the section 15, whereby a current density is lower and thus a heating capacity is reduced in this area 15 adjacent to the sample reception area 5.

(40) In order to provide sufficient mechanical stability for the heating chamber 1 in spite of the local constriction in the constricted section 13 proposed here, several web areas 17 are provided in the constricted section 13. These web areas 17 run parallel to the longitudinal axis 8 and bridge the constricted section 13 locally to form a mechanically loadable linear connection between the opposite ends of the heating chamber 1.

(41) If the heating chamber 1 is mechanically clamped between the electrical contacts 114, 116, as exemplarily shown in FIG. 1, and is therefore mechanically loaded in a direction parallel to the longitudinal axis 8, these web areas 17 are able to transmit the mechanical forces acting between the electrical connection areas 9, 11 in the process so that these forces do not endanger a mechanical integrity of the heating chamber 1, especially in the constricted section 13.

(42) In the embodiment described in FIGS. 2 to 6, four web areas 17 are shown which are distributed equidistantly along the circumference of the constricted section 13. In addition, recesses 19 are provided in the web areas 17, which are designed in such a way that on the one hand an electrical current is to the greatest possible extent conducted towards the nozzle area 7 located radially inwards and on the other hand a mechanical stability of the web areas 17 is maintained.

(43) Of course, in order to achieve the desired functionality, i. e. to direct the heating current in a rear area of the heating chamber 1 specifically radially inwards towards the nozzle area 7, a geometric design of the heating chamber 1 may also be carried out in another way. For example, the geometric design of the constricted section 13, a number of web areas 17 provided in the constricted section 13 and/or a geometric design of these web areas 17 and any recesses 19 formed therein may be varied.

(44) FIG. 7, for example, shows a heating chamber 1 with webs 17 in the form of simple ribs without recesses. FIG. 8 shows a heating chamber 1 with tapered webs 17 or additionally inserted constrictions where a web width increases or decreases towards the outside. FIG. 9 shows a heating chamber 1 with webs 17 arranged at an angle in the axial direction. Non-linear webs, e. g. in the form of arches, are also conceivable. In principle, a heating chamber 1 can be provided without any web areas, given that sufficient mechanical stability is ensured in another suitable way especially in the constricted section.

(45) A heating furnace or analysis device fitted with the modified heating chamber 1 proposed herein may in principle have the same or analogous design as the conventional analysis device shown in FIG. 1.

(46) Finally, it should be noted that terms such as “having”, “comprising”, etc. do not exclude any other elements or steps and terms such as “a” or “an” do not exclude a plurality. It should also be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be regarded as a limitation.

LIST OF REFERENCE SIGNS

(47) 1 heating chamber 2 sample 3 wall 4 barrel inner surface 5 sample reception area 6 funnel-shaped intermediate area 7 nozzle area 8 longitudinal axis 9 first electrical connection area 10 rear end face 11 second electrical connection area 12 sample carrier 13 constricted section 14 front end face 15 non-constricted section 17 web area 19 recess 24 nozzle outlet 100 analysis device 101 heating chamber 102 sample 103 wall 104 heating furnace 105 sample reception area 106 connecting tube 107 nozzle area 108 spectrometer 109 first electrical connection area 110 nozzle 111 second electrical connection area 112 sample carrier 114 first electrical contact 116 second electrical contact 118 mechanical mount 120 current source 122 carrier gas 124 nozzle outlet 126 sheathing gas 128 aerosol