Conductivity measuring device suitable for operation at high temperatures.

Abstract

Conductivity Measurement Device Suitable for High-Temperature Operation. The invention relates to a conductivity measurement device 100 suitable for measuring conductivity at a temperature of 1500°C or higher, the device comprising: - a refractory and electrically insulating substrate 120; - four conductive tracks 110a, 110b, 110c, 110d arranged on the same surface of the substrate, each track extending in the same direction and each separated from neighboring tracks by a non-conductive portion of the substrate, each track comprising tantalum nitride or doped tantalum nitride; - a measuring element 130, the measuring element being electrically connected to each of the tracks of the measuring device. Figure for the abstract: Fig. 1.

Description

Title of the invention: Conductivity measuring device suitable for operation at high temperature. technical field

[0001] The present description relates to a conductivity measurement device capable of operating at high temperature. Previous technique

[0002] Increasing the operating temperature of aeronautical turbomachinery allows for an increase in their efficiency and therefore fuel savings.

[0003] However, the increase in operating temperatures subjects the constituent materials of the turbomachines to more aggressive conditions.

[0004] The aeronautical field therefore requires that candidate parts be certified for temperature increase before they can actually be used for commercial applications.

[0005] Such certifications require measuring and qualifying the behavior of the parts to be certified at high temperature.

[0006] This requires the development of new devices which themselves can withstand the operating temperature of the parts, and which allow the measurement of their behavior at these temperatures.

[0007] This last point poses a major problem in the case of electrical conductivity measurement devices.

[0008] In a conventional manner, for measurements carried out at temperatures up to 500°C, it has been proposed to use copper alloys, in particular alloys of copper and tin, copper and silver, copper and magnesium or even copper and chromium.

[0009] However, at higher temperatures, it becomes necessary to use noble metals, in particular platinum, gold or silver, but their ranges of use are inevitably limited by the melting temperature of the alloys.

[0010] In addition to this complexity, there is the particularity of the chemical environment of a turbomachine in which the measuring devices operate, which can be a source of oxides, detrimental to the proper functioning of the measuring tools.

[0011] It is therefore essential to develop new operating devices capable of measuring conductivity at a temperature greater than or equal to 1500°C. Description of the invention

[0012] The invention aims precisely to provide a device for measuring conductivity capable of performing the measurement at a temperature above 1500°C.

[0013] For this purpose, it relates, according to a first aspect, to a conductivity measurement device capable of performing a conductivity measurement at a temperature greater than or equal to 1500°C, the device comprising: - a refractory and electrically insulating substrate; - four conductive tracks arranged on the same surface of the substrate, the tracks each extending in the same direction and each being separated from neighboring tracks by a non-conductive portion of the substrate, each of the tracks comprising tantalum nitride or doped tantalum nitride; - a measuring device, the measuring device being electrically connected to each of the tracks of the measuring device.

[0014] It is to the credit of the inventors that they determined that tantalum nitride and doped tantalum nitride make it possible to combine on the one hand an excellent measurement of conductivity and on the other hand excellent temperature resistance, and that they were able to use these properties advantageously in the proposed device.

[0015] In the device, the four conductive tracks comprising tantalum nitride or doped tantalum nitride allow current to be conducted even at temperatures exceeding 1500°C. Furthermore, it should be noted that tantalum nitride or doped tantalum nitride is neither oxidized nor does it liquefy at such temperatures, nor in the chemical environment encountered by aeronautical turbomachinery components.

[0016] Finally, for the measurement of conductivity as such, it is sufficient to place a sample whose conductivity we want to know so that it intercepts the four conductive tracks of the device.

[0017] When a sample is arranged in this way, and since tantalum nitride is conductive even at temperatures greater than or equal to 1500°C, the device and in particular the measuring element electrically connected to the four conductive tracks, makes it possible to carry out a known conductivity measurement protocol, called the 4 probes method (also called in the literature by the English name "4 probes measurements method").

[0018] These measurements then make it possible to determine the conductivity of the sample.

[0019] The device is all the more remarkable as it allows the conductivity of the sample to be measured without the measuring element itself having to be placed at the temperature at which the measurement is carried out.

[0020] Indeed, the measuring device is electrically connected to the conductive tracks and the latter are in contact with the sample at the desired temperature, which is sufficient to implement the four-point measurement protocol.

[0021] The measuring elements of a device can then be relocated to a zone at more low temperature, but the device as a whole nevertheless allows the conductivity of a sample to be measured at a temperature greater than or equal to 1500°C.

[0022] In one embodiment, the conductive tracks may have a thickness less than or equal to 20 pm.

[0023] The inventors have indeed found that the conductivity of tantalum nitride was even better when it was formulated in the form of layers whose thickness conforms to that indicated.

[0024] In one embodiment, the spacing between two side-by-side conductive tracks is between 10 pm and 5 mm.

[0025] Such spacing allows optimal determination of the conductivity of the sample in particular in the range of interest between 0.01 and 104 S / cm.

[0026] In one embodiment, the conductive tracks comprise tantalum nitride with a hexagonal crystallographic structure or doped tantalum nitride with a hexagonal crystallographic structure.

[0027] The inventors have indeed determined that the conductivity of tantalum nitride with a hexagonal crystallographic structure was even better than that of tantalum nitride with a cubic crystallographic structure.

[0028] This determination was made under air (N2 / O2 mixture), but also under other atmospheres such as an atmosphere of argon (Ar), dihydrogen (H2) or their mixtures (Ar / H2), or gaseous mixtures of the type: CO / CO2, CH4, humid gases (presence of water vapor H2O).

[0029] This results in a device which can be used under different atmospheres representative of the actual operating conditions of the sample whose conductivity one wishes to measure.

[0030] In one embodiment, the conductive tracks comprise more than 95% atomic, or even more than 99% atomic, or are made of tantalum nitride.

[0031] In one embodiment, the conductive tracks comprise only tantalum nitride for more than 95% atomic content, the remainder consisting only of dopants, for example chosen from elements selected from alkali metals, alkaline earth metals and / or transition metals.

[0032] In one embodiment, the conductive tracks are made of undoped tantalum nitride with a hexagonal crystallographic structure.

[0033] In one embodiment, the conductive tracks are made of doped tantalum nitride with a hexagonal crystallographic structure.

[0034] Regardless of the dopant and the dopant content, it is preferable that the doped tantalum nitride remains of hexagonal crystallographic structure.

[0035] On the other hand, the invention is not limited either by the nature of the doping agent, or by the quantity of the latter.

[0036] In one embodiment, the conductive tracks are made of doped tantalum nitride with a hexagonal crystallographic structure, the tracks comprising a total dopant content less than or equal to 5 atomic % and the dopant being selected from alkali metals, alkaline earth metals and / or transition metals or a mixture of two or more of these elements.

[0037] In other words, the conductive tracks are made of TabxAxN doped tantalum nitride of hexagonal crystallographic structure with A designating a dopant corresponding to one or more elements chosen from alkali metals, alkaline earth metals and / or transition metals with x strictly positive and less than 0.05.

[0038] The specification that x is strictly positive in the preceding definition is not intended to exclude from the invention undoped tantalum nitride (TaN) conductive tracks, but rather aims to avoid redundancy with this embodiment described separately.

[0039] In one embodiment, the dopant may be one or more elements selected from alkali metals, alkaline earth metals and / or transition metals.

[0040] Such a dopant can be chosen to further functionalize the conductive tracks, for example by increasing conductivity, corrosion resistance or by improving the stability of the hexagonal crystalline phase.

[0041] In one embodiment, the dopant is a single dopant selected from alkali metals, alkaline earth metals and / or transition metals.

[0042] In one embodiment, the dopant may be chosen from potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), yttrium (Y), vanadium (V), titanium (Ti) and a mixture of one or more of these elements.

[0043] In one embodiment, the dopant is unique and chosen from potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), yttrium (Y), vanadium (V) and titanium (Ti).

[0044] In one embodiment, the dopant content is less than or equal to 5 atomic % or less than or equal to 1.0%.

[0045] In one embodiment, the dopant content is greater than or equal to 0.01 atomic % or even greater than or equal to 0.05 atomic %.

[0046] For example, the dopant content may be between 0.01% and 5.0% atomic, or even between 0.05% and 5.0% atomic, or even between 0.1% and 1.0% atomic.

[0047] Indeed, this dopant content is a sufficient, but not necessary, condition to ensure that the structure of tantalum nitride remains hexagonal despite the presence of a dopant.

[0048] In one embodiment, the tantalum nitride coating can be written as Ta[xAxN with A chosen from potassium (K), sodium (Na), calcium (Ca), the magnesium (Mg), yttrium (Y), vanadium (V), and titanium (Ti), and x between 0 excluded and 0.05 inclusive.

[0049] In one embodiment, the substrate consists of aluminum oxide, aluminum nitride, or a mixture of these compounds.

[0050] In one embodiment, the conductive tracks have a length greater than or equal to 20 mm.

[0051] In one embodiment, the conductive tracks are aligned and parallel to each other.

[0052] This embodiment facilitates the determination of conductivity because the distance separating two conductive tracks is then easily determinable.

[0053] According to another aspect, the invention relates to a method for determining the conductivity of a sample at a temperature greater than or equal to 1500°C, the method comprising at least the following steps: - the arrangement of the sample so that it intercepts the four conductive tracks of a device that has just been described; - heating the sample thus arranged to a temperature greater than or equal to 1500°C; - the determination of the conductivity of the sample by the four-point method, through the determination of at least one intensity between two of the four conductive tracks and of a voltage by the measuring device between the other two conductive tracks. Brief description of the drawings

[0054] [Fig-1] Fig. 1 is a schematic representation of a measuring device in an embodiment of the invention. Description of the implementation methods

[0055] The invention is described via a figure presented for descriptive purposes to illustrate one embodiment of the invention and which shall not be construed as limiting the invention.

[0056] Fig. 1 represents a conductivity measuring device 100 in an embodiment of the invention, the device being here arranged in a furnace 200.

[0057] The device 100 comprises four conductive tracks 110a, 110b, 110c and 110d, which are here rectangular, and parallel to each other.

[0058] In one embodiment, the length L of the conductive tracks 110a, 110b, 110c and 110d can be between 5 mm and 20 mm

[0059] In one embodiment, the width 1 of the conductive tracks 110a, 110b, 110c and 1 lOd, can be between 2 mm and 5 mm.

[0060] In one embodiment, the thickness e of the conductive tracks 110a, 110b, 110c and 1 lOd, may be less than or equal to 50 pm.

[0061] It should be noted that the thickness on [Fig. 1] is shown to be much greater than it actually is, and this is to aid understanding.

[0062] Indeed, the conductivity of tantalum nitride TaN or doped tantalum nitride is better when the latter is in the form of a thin film, which is ensured by a thickness e such as described.

[0063] In one embodiment, the spacing e between two conductive tracks 110a, 110b, 110c and 110d can be between 10 pm and 5 mm.

[0064] This spacing allows for optimal measurement of conductivity, ensuring a compromise between the minimum values ​​that can be measured and the intensity or voltage that must be applied to the conductive tracks 110a, 110b, 110c and 110d to perform the measurement.

[0065] As described, the device comprises a substrate 120, on which are arranged the four conductive tracks 110a, 110b, 110c and HOd.

[0066] The four conductive tracks 110a, 110b, 110c and 110d are not electrically connected to each other in the sense that the voltage and / or current of one of them does not affect the others in any way. Of course, in an operating mode of the device 100, each of them will be connected to the measuring element 130 for the purposes of determining conductivity.

[0067] For example, in one embodiment, the external conductive layers 110a and 110d allow a measurement of the current, while a voltage is measured between the internal conductive tracks 110b and 110c.

[0068] The substrate 120 is refractory, in the usual sense of the word refractory, namely that it does not have a behavior affected by the measurement temperature which is greater than or equal to 1500°C.

[0069] In one embodiment, the substrate 120 can be made of aluminium oxide A12O3 also called alumina, or of aluminium nitride AIN.

[0070] Such species have the advantage of being electrically insulating and of not exhibiting dimensional variations detrimental to the described device when exposed to temperatures greater than or equal to 1500°C.

[0071] As shown in [Fig.1], the sample 500 is placed so that it intercepts the four conductive tracks 110a, 110b, 110c and HOd.

[0072] As shown in [Fig.1], the sample 500, the substrate 120 and the conductive tracks 110a, 110b, 110c and 110d of the device 100 can be placed in a furnace 200, which allows, for example by lighting its heating means 201a, 201b, the sample as well as the substrate 120 and the conductive tracks 110a, 110b, 110c and 110d of the device 100 to be brought to a temperature greater than or equal to 1500°C.

[0073] Here, the heating means 201a and 201b shown are resistive but this is in no way limiting of the invention.

[0074] The device 100 further includes a measuring element 130, which is electrically connected to the conductive tracks 110a, 110b, 110c and 110d of the device 200.

[0075] For example, the conductive tracks 110a, 110b, 110c and 110d can be electrically connected to the measuring element 130 via wires 131.

[0076] Having a measuring element 130 electrically connected to the conductive tracks 110a, 110b, 110c and 110d of the substrate 120 allows, as shown in [Fig.1], the measuring element 130 to be moved away from the hot zone, here of the oven 200.

[0077] This particular organization allows the use of a measuring element 130 which does not have particular resistance to high temperatures, and requires high temperature resistance characteristics only for the conductive tracks 110a, 110b, 110c and 110d, this resistance being ensured by the composition of the conductive tracks in tantalum nitride or doped tantalum nitride.

[0078] This reduces the complexity and cost associated with the measuring element 130 and therefore with the device 100.

[0079] In one embodiment, the conductive tracks 110a, 110b, 110c and 110d of the device 100 can be deposited by any method allowing a deposit of tantalum nitride optionally doped.

[0080] Preferably, the method of depositing the conductive tracks 110a, 110b, 110c and 110d on the substrate 120 can be a high-power pulsed magnetron sputtering method (designated by the acronym "HiPIMS" in the English-language literature for "High-Power Impulse Magnetron Sputtering").

[0081] By precisely controlling the deposition parameters of such a method it is indeed possible to guarantee that the tantalum nitride deposit has a hexagonal crystallographic structure.

[0082] Examples of parameters ensuring the obtaining of such a hexagonal crystallographic structure are described in US document 2022 / 0349042.

[0083] This further increases the conductivity properties of the conductive tracks.

[0084] In one embodiment, the determination of the conductivity of the sample by the measuring member 130, electrically connected to the conductive tracks 110a, 110b, 110c and 110d can be carried out using the so-called four-point method.

[0085] For such a method, the measuring element 130 delivers a known voltage between the central conductive tracks 110b, 110c and a current of known intensity between the conductive tracks of the ends 110a and HOd.

[0086] The ratio of the measured voltage to the current flowing through sample 500 allows to determine the resistance between the center tracks 110b and 110c.

[0087] By then applying reasonable approximations or by performing numerical integral calculation taking into account the nature of the sample 400 and its geometry, the method then makes it possible to access the resistivity of the sample 400. For example, a method of determination is described in the article entitled "Automatic device for measuring resistivity between 4 and 1100K" by Dordor et al., Revue de Physique appliquée, 1985.

Claims

Demands

1. Conductivity measuring device (100) capable of performing a conductivity measurement at a temperature greater than or equal to 1500°C, the device comprising: - a refractory and electrically insulating substrate; - four conductive tracks (110a, 110b, 110c, HOd) arranged on the same surface of the substrate, the tracks each extending in the same direction and each being separated from the neighboring tracks by a non-conductive portion of the substrate, each of the tracks comprising tantalum nitride or doped tantalum nitride; - a measuring element (130), the measuring element being electrically connected to each of the tracks of the measuring device.

2. Measuring device (100) according to claim 1, wherein the conductive tracks (110a, 110b, 110c, HOd) have a thickness less than or equal to 20 pm.

3. Measuring device (100) according to claim 1 or 2, wherein the conductive tracks (110a, 110b, 110c, HOd) comprise tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride of hexagonal crystallographic structure.

4. Measuring device (100) according to claim 3, wherein the conductive tracks (110a, 110b, 110c, HOd) are made of doped tantalum nitride of hexagonal crystallographic structure, the conductive tracks comprising a total dopant content less than or equal to 5.0 atomic % and the dopant being selected from alkali metals, alkaline earth metals and / or transition metals or a mixture of two or more of these elements.

5. Measuring device (100) according to claim 4, wherein the dopant is selected from potassium K, sodium Na, calcium Ca, magnesium Mg, yttrium Y, vanadium V, titanium Ti and a mixture of one or more of these elements.

6. Measuring device (100) according to claim 4 or 5, wherein the dopant content is between 0.01% and 5.0% atomic.

7. Measuring device (100) according to any one of claims 1 to 6, wherein the substrate (120) is made of aluminium oxide Al2O3, aluminium nitride AIN or a mixture of these compounds.

8. Measuring device (100) according to any one of claims 1 to 7 wherein the spacing (e) between two conductive tracks (110a, 110b, 110c, 1 lOd) side-by-side is between 10 pm and 5 mm.

9. Measuring device (100) according to any one of claims 1 to 8, wherein the conductive tracks (110a, 110b, 110c, HOd) have a length greater than or equal to 20 mm.

10. A method for determining the conductivity of a sample at a temperature of 1500°C or higher, the method comprising at least the following steps: - arranging the sample (500) so that it intercepts the four conductive tracks (110a, 110b, 110c, HOd) of a device according to any one of claims 1 to 9; - heating the sample thus arranged to a temperature of 1500°C or higher; - determining the conductivity of the sample by the four-point method, by determining at least one current between two of the four conductive tracks and a voltage by the measuring element between the other two conductive tracks.

Images