RECORDER WITH A MEMBRANE FOR USE WITH HYDROGEN-CONTAINING FLUID MEDIA

Description

Technical field

[0001] The invention relates to a sensor with a membrane for use with hydrogen-containing fluid media. State of the art

[0002] A membrane separates a fluid medium in a first chamber from a second chamber. In pressure measurement technology, sensors often incorporate a membrane that separates a measuring device, such as a sensor element, from the fluid medium, for example, a gaseous and / or liquid medium whose pressure is to be determined. A membrane typically has a surface with a first dimension and a second dimension, both of which are largely perpendicular to a longitudinal axis. In a third dimension, parallel to the longitudinal axis, the membrane has a thickness, also called wall thickness.

[0003] In the following, a fluid medium is understood to be a hydrogen-containing fluid medium that has at least 1 vol% (volume percent) of hydrogen.

[0004] The membrane surface typically includes an area in contact with the fluid medium in a primary chamber. In the case of a pressure sensor, the pressure of the fluid medium acting on the membrane is transmitted to a pressure sensor element, or simply sensor element, with minimal loss. To prevent the sensitivity of a measuring arrangement with a pressure sensor element from being excessively affected by the membrane, the area of ​​the membrane directly exposed to the fluid medium must exhibit the highest possible compliance or the lowest possible stiffness. However, the material in this low-stiffness area must not be irreversibly deformed by the measuring pressure. If materials with a yield strength of approximately 400 MPa (megapascals) are used, the membrane must be correspondingly thick to prevent irreversible deformation.The diaphragm can also have thicker sections, which connect it to, for example, a sensor housing. These thicker sections can also contribute to the diaphragm's stability. They do not, however, transmit pressure from the fluid medium to the pressure sensor element.

[0005] The yield strength of a metallic material is determined according to the standard DIN EN ISO 6892-1. It corresponds to the RP 0.2 value.

[0006] The surface of a membrane can extend largely along the first extension and the second extension, but may be partially curved in the direction of the longitudinal axis.

[0007] Membranes can also separate a fluid medium from other types of sensor elements, for example, temperature sensors, in which a temperature sensor element is separated from the fluid medium by a membrane. In this case, the temperature of the fluid medium is transmitted through the membrane to a temperature sensor element. Again, the membrane should be as thin-walled as possible to maximize the heat transfer coefficient.

[0008] If the fluid medium contains hydrogen, the membrane must be both hydrogen-tight and hydrogen-resistant. Therefore, for membranes that are also heat-resistant above 200°C, commercially available, hydrogen-resistant polycrystalline metals are often used, such as the austenitic steel 1.4404 (also known as 316L) with a yield strength of approximately 400 MPa at room temperature, or the nickel-based alloy 2.4819 (also known as C-276) with a yield strength of approximately 400 MPa at room temperature. These materials are characterized by a mean grain size greater than 20 µm. These coarse-grained, polycrystalline metals are unsuitable as materials for thin membranes with a thickness of less than 500 µm because their low yield strength prevents the design of thin-walled membranes. A thin membrane would quickly become irreversibly deformed.Due to the small number of crystal grains in the thin-walled region of the membranes, the material is not isotropic. Furthermore, the diffusion path for molecular and / or atomic hydrogen along the grain boundaries between the crystal grains through coarse-grained regions is relatively short. This is disadvantageous, as hydrogen can thus diffuse readily through the membrane via a short path.

[0009] In metals and alloys, the term microstructure refers to the microstructure of the material. Martensite is an example of a microstructure.

[0010] The designation 1.4404, as well as other material numbers mentioned below, comply with DIN EN 10027-2.

[0011] When molecular and / or atomic hydrogen penetrates a metallic material, a process called hydrogen embrittlement occurs. This results in a risk of brittle fracture under stress.

[0012] Hydrogen embrittlement refers to a change in the ductility and strength of a metal or metal alloy due to the penetration and subsequent incorporation of hydrogen into the metal's or alloy's lattice structure. This can lead to hydrogen-induced cracking, thus limiting the use of susceptible materials in applications involving hydrogen contact.

[0013] It is well known that a metal or metal alloy with high strength is more prone to hydrogen embrittlement than a metal with lower strength.

[0014] The materials steel 1.4404 (also known as 316L) and alloy 2.4819 (also known as C-276) are generally considered corrosion-resistant. They have a low yield strength and are therefore more easily deformed under lower forces than materials with a higher yield strength. To compensate for this disadvantage, membranes are often manufactured with a thickness greater than 500 µm. However, this is disadvantageous due to the high inertial mass of a thick membrane. A thick membrane also exhibits higher stiffness.

[0015] In a known embodiment, pressure sensors have a space behind the diaphragm filled with a fluid pressure transmission medium. In this embodiment, the risk of irreversible plastic deformation of the diaphragm is reduced because the fluid pressure transmission medium counteracts any deformation. The fluid pressure transmission medium, for example, a slightly compressible oil, transmits the pressure acting on the diaphragm to a measuring element located at a distance from the diaphragm. The diaphragm must also transmit the pressure with minimal loss; that is, the diaphragm should advantageously be thin. If the fluid medium to be measured contains hydrogen, hydrogen accumulates in the fluid pressure transmission medium over time, causing the volume to increase and consequently the diaphragm to bulge outwards. The diaphragm is inflated by the hydrogen diffusing through it.This can damage the membrane and also alter the pressure conditions around the measuring element. The long-term stability of the sensor is negatively affected by the diffusion of molecular and / or atomic hydrogen through the membrane.

[0016] Document US20050109114A1 describes a sensor with a diaphragm made of alloy 2.4819 (also known as C-276). While the material itself is considered corrosion-resistant, it is not hydrogen-tight due to the thinness of the diaphragm. US20050109114A1 proposes addressing this insufficient hydrogen resistance by coating the diaphragm.

[0017] From DE102014104113A1 a pressure sensor for measuring the pressure of hydrogen or a hydrogen-containing fluid is known, wherein both the pressure connection and the pressure transmitter are made of an austenitic chromium-nickel-molybdenum steel.

[0018] A strain sensor for corrosive media is known from EP1619487A1, wherein a body which generates a strain in response to an external stress is formed from austenitic, precipitation-hardening Fe-Ni heat-resistant steel.

[0019] From EP3327417A1 a metallic membrane with a plate is known which is subjected to a pressure of a medium, wherein the metal structure of the plate has grown parallel to the flat plate surface.

[0020] The object of the invention is to improve a membrane in such a way as to reduce the aforementioned disadvantages. A further object of the invention is to achieve improved corrosion resistance of the membrane against atomic and / or molecular hydrogen. Description of the invention

[0021] The problem is solved by the features of an independent claim.

[0022] The invention relates to a sensor for determining the pressure of a hydrogen-containing fluid medium. The hydrogen-containing fluid medium is arranged in a first chamber. The sensor has a pressure-side end facing the fluid medium. The sensor has a housing which includes a second chamber. The sensor includes a measuring arrangement. The measuring arrangement is arranged in the second chamber. At its pressure-side end, the sensor has a membrane for hermetically separating the first chamber containing the hydrogen-containing fluid medium from the second chamber. The membrane is made of a metallic material. The metallic material has a martensitic microstructure. According to the invention, the metallic material of the membrane is made of a high-alloy martensite.

[0023] The membrane is designed to separate a chamber containing a hydrogen-containing fluid medium from another chamber. A hydrogen-containing fluid medium has at least 1% hydrogen by volume and is hereinafter also referred to as a corrosive fluid medium.

[0024] Corrosion is generally understood to be a measurable change in a material. Corrosion can occur through the action of a variety of substances. For example, corrosion of metallic materials in connection with various alkalis or acids, gases such as hydrogen or oxygen, salt water, and many other substances is known. For the purposes of this description, however, unless otherwise specified, corrosion is understood to mean corrosion caused by atomic or molecular hydrogen. The membrane according to the invention must exhibit a low tendency to be corroded by hydrogen.

[0025] The fine-grained steel with a martensitic microstructure, or simply martensite, surprisingly exhibits a low tendency towards hydrogen embrittlement and therefore a certain degree of hydrogen resistance. The metallic material of the membrane is thus corrosion-resistant to hydrogen.

[0026] The structure of martensite is characterized by a mean grain diameter of less than 20 µm and is therefore suitable for the production of thin-walled membranes with thicknesses of less than 500 µm. Due to the mean grain diameter of less than 20 µm, the component exhibits isotropic physical properties, which is advantageous when used in membrane applications. Otherwise, adverse effects such as direction-dependent loading of the membrane can occur. Furthermore, the diffusion of hydrogen through the membrane is reduced by the numerous grain boundaries of the fine-grained material, in contrast to coarse-grained materials. The use of martensite in connection with hydrogen-containing fluids is surprising, as martensite is generally considered unsuitable for contact with hydrogen-containing fluids due to its relatively high strength.In VYTVYTS'KYI VI: "Strength of Alloys Based on Iron, Nickel, and Titanium in High-Pressure Hydrogen", MATERIALS SCIENCE, KLUWER ACADEMIC PUBLISHERS-CONSULTANTS BUREAU, NE, Vol. 40, No. 6, November 1, 2004 (2004-11-01), pages 717-730, ISSN: 1573-885X, DOI: 1 0.1 007 / S1 1003-005-0108-8, a "catastrophic degradation in hydrogen" is described.

[0027] It goes without saying that the diaphragm does not need to be entirely less than 500 µm thick. The diaphragm can also have thicker sections, for example, where it is connected to a sensor housing. These thicker sections can also contribute to the diaphragm's stability. However, it is important that the diaphragm also has thin-walled sections with lower stiffness.

[0028] The metallic material of the membrane is advantageously a highly alloyed martensite with partially coherent or incoherent precipitates.

[0029] The term "high-alloyed" is used in accordance with Dubbel - Taschenbuch für den Maschinenbau (Handbook of Mechanical Engineering), 14th edition, Springer-Verlag 1981, Chapter 3.1.4, to refer to martensite with an alloy content > 5 wt.% (weight percent). The alloy content is the mass fraction of an alloying element. This results in increased overall corrosion resistance. In this context, the alloying elements are exclusively Cr (chromium), Mo (molybdenum), or Ni (nickel). These alloying elements increase the overall corrosion resistance, including increased resistance to hydrogen corrosion.

[0030] A martensite with partially coherent precipitates or a martensite with incoherent precipitates is defined as a martensite in which precipitates form during heat treatment (precipitation hardening, also known as quenching or aging, or in English as "precipitation hardening," "age hardening," or "particle hardening"). Partially coherent or incoherent precipitates, as defined here, are described in *Materials Science - Steel - Volume 1*, published by the Association of German Iron and Steel Engineers (Verein Deutscher Eisenhüttenleute), Springer Verlag 1984, or in Pirlog, Madalina, and P.K. Pranzas, "Characterization of Copper Precipitates in Fe-Cu Alloys with Small-Angle Neutron Scattering."

[0031] In precipitates, atoms of an alloying element form aggregates. This is accompanied by a change in the material's hardness. The relationship between a material's hardness and its thermal aging time is well-known. This is often illustrated in a diagram showing the hardness of a material over a period of time. The hardness increases with increasing aging time until it reaches a global maximum of maximum hardness and then decreases again. The thermal aging time is a measure of the duration of the thermal treatment at a specific temperature. The maximum hardness Hmax of a material is reached at an aging time t (maximum hardness). At this maximum hardness Hmax, so-called partially coherent precipitates are present. At longer aging times, incoherent precipitates are present.The precipitates form preferentially at grain boundaries within the material, as described in Metallkunde, E. Hornbogen and H. Warlimont, 4th edition, Springer Verlag 2001.

[0032] Incoherent and partially coherent precipitates act as hydrogen sinks. Hydrogen accumulates at these sinks, preventing it from penetrating further into the material. The mobility of hydrogen is reduced compared to a material with coherent precipitates because coherent precipitates are located within a grain, while hydrogen is preferentially mobile along grain boundaries within the material.

[0033] The membrane material is preferably a high-alloy lancet martensite with partially coherent and / or incoherent precipitates. Lancet martensite is defined as a material described in *Materials Science - Steel - Volume 1*, *Verein Deutscher Eisenhüttenleute* (ed.), Springer Verlag 1984, Chapter B6.4.4, or in *Metallkunde*, E. Hornbogen and H. Warlimont, 4th edition, Springer Verlag 2001, Chapter 15.2. Lancet martensite exhibits flattened lancets in its microstructure, arranged in layers. Lancet martensite is also known as block martensite or massive martensite. It has been shown that the mobility of hydrogen in lancet martensite is further reduced compared to martensite without lancets.

[0034] Advantageously, the metallic material of the membrane has a chromium content of at least 10 wt.% and a nickel content of at least 4 wt.%. Metallic materials with lower proportions of these elements are less resistant to general corrosion. The weight fraction of non-metals is advantageously less than 0.20 wt.%. This is beneficial because a higher weight fraction of non-metals leads to material defects and a more brittle material, which is disadvantageous for membrane manufacturing. Brittle materials have lower resistance to unstable crack propagation.

[0035] Advantageously, the metallic material of the diaphragm has a yield strength of at least 600 MPa and at most 1500 MPa. The high yield strength above 600 MPa prevents irreversible plastic deformation of the metallic material. To keep the diaphragm's stiffness low, the yield strength of the metallic material, for a given diaphragm geometry with a thickness of less than 500 µm, must not exceed 1500 MPa. A typical diameter of a pressure sensor diaphragm is usually between 2.0 mm and 20 mm.

[0036] Advantageously, the metallic material of the membrane has a Rockwell C hardness between 38 and 50 HRC. At lower hardness levels, the material exhibits coherent precipitates. At excessively high hardness levels, the tendency towards hydrogen embrittlement increases again.

[0037] All values ​​such as yield strength, stiffness, tensile strength, hardness, etc. are given at room temperature unless explicitly stated otherwise. Room temperature is defined as a temperature of 20°C.

[0038] The metallic material of the membrane advantageously has a mean grain size of less than 20 µm. This ensures that the material exhibits isotropic physical properties, even in delicate structures. Furthermore, the diffusion path along the grain boundaries is significantly longer than in a material with a coarse-grained structure and a mean grain size greater than 20 µm. As a result, hydrogen has difficulty penetrating or diffusing into the material along the grain boundaries due to the longer diffusion path. The small grain size makes the material suitable for the production of thin-walled membranes. Because even thin structures with a thickness of less than 500 µm have multiple layers of grains, the metallic material is also hermetically sealed against hydrogen. For the same reason, thin structures exhibit isotropic physical properties.

[0039] Hermetically sealed is defined as a leakage rate with respect to helium of less than 10⁻⁶ < mbar l / s (millibar liters per second).

[0040] It has been shown that the metallic material of the membrane may have a retained austenite content of less than 30 vol.% (volume percent) and still retain the advantages of a membrane made of the metallic material described above. A retained austenite content between 0 vol.% and 10 vol.% of the metallic material is preferred. The retained austenite content is determined according to the standard ASTM E 975.

[0041] The membrane is particularly advantageous due to its metallic material with a retained austenite content greater than 1 vol.%. It has been shown that hydrogen diffusing through the metallic material at grain boundaries preferentially accumulates in the retained austenite. The retained austenite thus acts as a hydrogen sink, trapping hydrogen and preventing it from escaping. The hydrogen trapped in the retained austenite cannot diffuse deeper into the metallic material. A retained austenite content greater than 1 vol.% reduces the mobility of hydrogen, thereby increasing the membrane's resistance to corrosion. The reduced mobility of hydrogen within the metallic membrane also lowers the leakage rate of atomic or molecular hydrogen.

[0042] The membrane is made of a material that is impermeable to atomic or molecular hydrogen. For the purposes of this description, a material is considered impermeable if a 500 µm thick membrane made of this material exhibits a leakage rate of less than 10⁻⁶ mbar l / s for atomic or molecular hydrogen, with a maximum membrane thickness of 500 µm. The membrane has a minimum area of ​​1 mm². This is advantageous because it prevents hydrogen from accumulating in the second chamber. Hydrogen accumulation in the second chamber could cause the membrane to bulge, potentially damaging it. Furthermore, hydrogen accumulation could lead to a pressure increase in the second chamber, altering the pressure conditions around the measuring element and thus distorting the pressure measurement.

[0043] Particularly advantageous as a metallic material is the quenched and tempered steel grade 1.4418 with a yield strength of 900 MPa or less at room temperature. Also particularly advantageous as a metallic material is the precipitation-hardened steel grade 1.4534 with a yield strength of 1500 MPa or less. Furthermore, the precipitation-hardened steel grade 1.4614 with a yield strength of 1500 MPa or less is particularly advantageous as a metallic material. Also advantageous is the steel grade 1.4548 with a yield strength of 1500 MPa or less.

[0044] Typically, the metallic material has a coefficient of thermal expansion between 10·10 -6< K -1< and 12·10 -6< K -1< in the temperature range between 20°C and 100°C.

[0045] Advantageously, the metallic material has a surface facing the fluid medium that is free of depressions, indentations, holes, or grooves, in order to minimize the adsorption tendency of the fluid medium. This results in poorer adsorption of the fluid medium onto the membrane, since surface defects promote adsorption. The advantage lies in increased resistance to surface corrosion by the fluid medium.

[0046] Particularly advantageous is the waviness of the surface of the metallic material facing the fluid medium, whereby the notch stress caused by this waviness is less than 1500 MPa.

[0047] Waviness refers to a deviation in a sub-region of the surface from the plane of an adjacent sub-region. For membranes with a round surface in the area in direct contact with the fluid medium, concentric circular waves are commonly used to increase the membrane's compliance. However, these waves induce notch stress in the material, depending on the chosen radius. Notches, in the sense of notch stress, do not necessarily have to be pointed; they can also result from rounded surfaces, changes in cross-section, holes, and similar features. The notch stress therefore depends on the geometric dimensions of the membrane or the notch and on the metallic material of the membrane. The notch stress is determined using finite element analysis with the geometric dimensions and material parameters such as tensile strength, elasticity, modulus of elasticity, yield strength (Rp0.2), etc.The determination is described, for example, in "Computational Strength Verification for Machine Components - FKM Guideline", published by VDMA-Verlag, 7th edition 2020, or in "Fatigue Strength with FEM: Quickly Understand & Apply" by Stefan Einbock and Florian Mailänder, 2018. High notch stress in the metallic material promotes crack formation. A notch or crack negatively affects the corrosion resistance of a surface. Through the crack, adversely corrosive elements from a fluid medium can penetrate the material structure and damage the material along the crack. This is also known as stress corrosion cracking.

[0048] Alternatively, for a round membrane with a thickness of less than 500 µm, the surface of the membrane, at least in the area in contact with the fluid medium, can advantageously be designed with a corrugation such that transitions between two non-parallel planes have radii of at least 100 µm and / or facets of at least 30 µm. This reduces stress corrosion cracking compared to membranes with transitions between two non-parallel planes of smaller dimensions.

[0049] Advantageously, the membrane, at least in the area in contact with the fluid medium, has a surface finish with a mean roughness (Ra) of less than 0.8 µm. The mean roughness (Ra) is defined by DIN EN ISO 1302. A surface with a higher mean roughness offers the fluid medium a larger area on which atoms or molecules of the fluid medium can adsorb compared to a surface with a lower mean roughness. Furthermore, a surface with a mean roughness below 0.8 µm exhibits fewer surface defects in the crystal lattice of the metallic material compared to a surface with a higher mean roughness. Defects promote adsorption and chemical reactions at the surface and lead to faster surface corrosion. A low mean roughness of less than 0.8 µm thus increases the corrosion resistance of the surface.

[0050] Preferably, the metallic material of the membrane is produced from an austenite by a diffusion-free transformation.

[0051] The membrane can have a coating on the side facing the fluid medium. The preceding description of the properties and characteristics of the membrane in its various embodiments, in particular the metallic material and the surface, is explicitly compatible with the coating. A coating can further increase the corrosion resistance of the membrane.

[0052] The membrane is suitable for having an internal coating. Since the internal coating is not in contact with the fluid medium, its physical and chemical parameters may differ from any coating present on the side of the membrane facing the fluid medium. For example, the internal coating or the coating itself may be electrically insulating. Furthermore, the coating on the side of the membrane facing the fluid medium may exhibit resistance to other substances that the internal coating does not necessarily possess.

[0053] A measuring arrangement for determining the pressure of a fluid medium comprises, for example, at least one piezoelectric crystal which generates piezoelectric charges depending on the pressure applied to the membrane. In one embodiment, the piezoelectric crystal is arranged in a preload sleeve, which exerts a preload on the piezoelectric crystal. This allows both negative and positive pressure changes to be detected. Alternatively, a measuring arrangement can also include capacitive measuring elements that detect mechanical deformation as a change in capacitance.

[0054] Alternatively, a measuring arrangement can also include piezoresistive measuring elements or strain gauges, also known as strain gauges or DMS, which detect mechanical deformation as a change in electrical resistance. Further measuring arrangements are known to those skilled in the art, which are used in sensors to determine the pressure of a fluid medium.

[0055] The diaphragm is located at the pressure-side end of the housing and hermetically separates the measuring arrangement from the fluid medium. The housing and the diaphragm are joined by a material-bonded connection. A material-bonded connection could be, for example, a welded or soldered joint. A material-bonded connection using an adhesive is also conceivable.

[0056] The membrane has a first area that is in contact with the fluid medium during use. The membrane has a second area that is not in contact with the fluid medium during use. The bonded connection is located in the second area. Bonded connections made by soldering or welding typically exhibit a higher number of cracks or pores. Even in the case of a bonded connection using adhesive, the adhesive can be damaged by the fluid medium. Therefore, it is advantageous to have the bonded connection located in the second area, which is not exposed to the fluid medium.

[0057] If the membrane has a coating, it is arranged at least in the entire first area, but can also extend at least partially over the second area.

[0058] A second area is not in contact with the fluid medium within the meaning of this description if the concentration of corrosive components of the fluid medium in the second area is at most 1% of the concentration of corrosive components in the first area.

[0059] The first and second sections can be separated, for example, by a sealing element. Depending on the sensor's application with regard to temperature and pressure ranges, a metal seal such as a copper seal, a seal made of steel 1.4404 or 1.4301, a sealing element made of a metal alloy, or metal-coated seals made of a metal alloy can be used. Plastic seals are also known for certain temperature and pressure ranges, for example, those made of polytetrafluoroethylene, fluoroelastomers, or nitrile compounds. Other materials are also suitable as sealing elements.

[0060] The sensor is preferably used to determine the pressure of a fluid medium when the fluid medium is corrosive and conventional sensors cannot be used.

[0061] The sensor is particularly well-suited for determining the pressure of a fluid medium containing at least some molecular or atomic hydrogen. Hydrogen is known to cause hydrogen embrittlement in a variety of metallic materials, which, under thermal and / or mechanical stress, leads to hydrogen embrittlement and a reduction in the yield strength. The sensor described above significantly reduces these disadvantages.

[0062] All described embodiments of a sensor are possible as embodiments with a pressure transmission medium arranged in the second chamber. However, all described embodiments can also be implemented without a pressure transmission medium arranged in the second chamber.

[0063] The invention also includes a sensor for determining the temperature of a fluid medium. The sensor has a pressure-side end facing the fluid medium. The sensor has a housing. The sensor has a measuring arrangement for determining the temperature of a fluid medium. The measuring arrangement is located inside the housing. The sensor has a diaphragm in one of the embodiments described above. Brief description of the drawings

[0064] The invention will be explained in more detail below using the figures as an example. Fig. 1 shows a schematic sectional view of an embodiment of a sensor with an embodiment of a membrane according to the invention, Fig. 2 shows a schematic partial view of a sectional view of a sensor with a membrane according to Fig. 1 , which is arranged in a wall; Fig. 3 shows a schematic representation of a diagram of hardness versus thermal aging time of a material at a specific temperature. Ways to implement the invention

[0065] Fig. 1 and Fig. 2 Each figure shows a schematic sectional view of an embodiment of a sensor 1 with a diaphragm 2. The sensor 1 is suitable for determining the pressure of a fluid medium 13. The sensor 1 has a pressure-side end 11 facing the fluid medium. The sensor 1 has a housing 7. A measuring arrangement 16 is arranged in the housing 7.

[0066] The membrane 2 is arranged at the pressure-side end 11 of the sensor 1 and hermetically separates the measuring arrangement 16 from the fluid medium 13.

[0067] In the non-scale representation of the Fig. 1 An optional coating of the metallic material 3 is shown as a dashed line.

[0068] The Fig. 2 This shows another embodiment of a membrane. The thickness of membrane 2 is not shown proportionally for clarity.

[0069] Membrane 2 of the Fig. 1 and 2 The device comprises a metallic material 3 and hermetically separates a first chamber 14 from a second chamber 15. A fluid medium 13 is arranged in the first chamber 14, and at least one physical quantity of this medium can be determined. A physical quantity could be, for example, pressure and / or temperature.

[0070] Membrane 2 has a first area 9, which is in contact with the fluid medium 13 when membrane 2 is in use. Membrane 2 has a second area 10, which is not in contact with the fluid medium 13 when used, as shown in Fig. 1 and 2 depicted.

[0071] The surface 6 of the membrane 2, which is in direct contact with the fluid medium 13 when used, advantageously has a waviness, wherein the notch stress caused by this waviness is less than 1500 MPa. The surface of the membrane is in the Fig. 1 and 2 shown. Transitions between two non-parallel planes have radii 18 of at least 100 µm and / or facets 18 of at least 30 µm.

[0072] The housing 7 and the diaphragm 2 of the sensor 1 are connected by a material-bonded connection 8. The diaphragm 2 has a first region 9, which is in contact with the fluid medium 13 when in use. The diaphragm 2 has a second region 10, which is not in contact with the fluid medium 13 when in use. The first region 9 and the second region 10 are separated from each other by a sealing element 12 when the sensor 1 is in use. The material-bonded connection 8 is located in the second region 10 in every illustrated embodiment.

[0073] However, it is also conceivable to arrange the metallurgical bond 8 in an area which, when the membrane 2 is used, is in contact with the fluid medium 13. Advantageously, the metallurgical bond 8 is completely covered by the coating 4 (not shown).

[0074] Fig. 2Figure 1 shows the sensor 1 for determining the pressure of a fluid medium 13 inserted into a wall 17. The wall 17 can be, for example, a wall 17 of a tank for a fluid medium 13, a compressor, a heat pump, a refrigeration unit, a pipe for a fluid medium 13, a combustion chamber of an internal combustion engine, or a gas turbine.

[0075] Figure 3 schematically shows the dependence of a metallic material, for example a precipitation-hardening martensite, on the thermal aging period t at a specific aging temperature.

[0076] The embodiments of the sensor 1 or the membrane 2 disclosed in this document are, of course, combinable with one another. This document explicitly includes embodiments that exhibit a combination of the features of the embodiments described herein. Reference symbol list

[0077] 1 Sensor 2 Membrane 3 Metallic material 6 Surface 7 Housing 8 Bonded connection 9 First area 10 Second area 11 Pressure-side end 12 Sealing element 13 Fluid medium 14 First chamber 15 Second chamber 16 Measuring arrangement 17 Wall 18 Chamfer / Facet / Curvature 21 Thin-walled area

Claims

1. System comprising a transducer (1), a hydrogen-containing fluid medium (13) and a first space (14); which transducer (1) determines the pressure of the hydrogen-containing fluid medium (13); wherein the hydrogen-containing fluid medium (13) is arranged in the first space (14); wherein the transducer (1) comprises a pressure side end (11) facing the fluid medium (13); wherein the transducer (1) comprises a housing (7) which comprises a second space (15); wherein the transducer (1) comprises a measuring arrangement (16); wherein the measuring arrangement (16) is arranged in the second space (15); wherein at the pressure side end (11) the transducer (1) comprises a diaphragm (2) for hermetically separating the first space (14) containing the hydrogen-containing fluid medium (13) from the second space (15); wherein the diaphragm (2) comprises a metallic material (3); characterized in that the metallic material (3) is made of a high-alloy martensite; wherein a high-alloy martensite is a martensite with an alloy content > 5 wt.%; wherein the alloy content is the content by mass of an alloying element; wherein alloying elements are understood to mean exclusively chromium, molybdenum or nickel.

2. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm (2) is made of a high-alloy martensite with partially coherent or incoherent precipitates.

3. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm (2) is made of a high-alloy lancet martensite with partially coherent or incoherent precipitates.

4. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims; characterized in that the metallic material (3) is resistant to hydrogen corrosion; and in that the metallic material (3) is not permeable to atomic hydrogen with a leakage rate of the diaphragm for hydrogen of less than 10-6 mbar l / s, wherein the diaphragm thickness is at most 500 µm.

5. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the content by mass of at least one of the elements chromium or molybdenum or nickel in the metallic material (3) exceeds 5% by weight.

6. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims 1 to 4, characterized in that the metallic material (3) of the diaphragm (2) has a chromium content of at least 10% by weight.

7. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm (2) has an average grain size of less than 20 µm, which renders the metallic material (3) suitable for the production of thin-walled diaphragms (2) with geometric dimensions of less than 500 µm.

8. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm has a residual austenite content of less than 30% by volume, preferably a residual austenite content of between 0% and 10% by volume.

9. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to the preceding claim, characterized in that the metallic material (3) of the diaphragm has a residual austenite content greater than 1% by volume.

10. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm (2) has a yield strength of at least 600 MPa and at most 1500 MPa.

11. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material (3) of the diaphragm (2) has a chromium content of at least 10% by weight and a nickel content of at least 4% by weight; and in that the proportion by weight of non-metals is less than 0.20% by weight or in that the metallic material (3) of the diaphragm (2) is of quenched and tempered grade 1.4418 steel having a yield strength of less than or equal to 900 MPa at room temperature or of precipitation-hardened grade 1.4534 steel having a yield strength of less than or equal to 1500 MPa or of precipitation-hardened grade 1.4614 steel having a yield strength of less than or equal to 1500 MPa or of grade 1.4548 steel having a yield strength of less than or equal to 1500 MPa; and in that the material has a coefficient of thermal expansion between 10·10-6 K-1 and 12·10-6 K-1, preferably 11.3·10-6 K-1, in the temperature range between 20°C and 100°C.

12. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that a surface (6) of the metallic material (3) which faces the fluid medium (13) has a corrugation; wherein the notch stress caused by this corrugation is less than 1500 MPa, or in that the surface (6) has a corrugation at least in the region which is in contact with the fluid medium during use, wherein transitions between two non-parallel planes have radii of at least 100 µm and / or facets of at least 30 µm.

13. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the diaphragm (2) has a surface quality at least in the region which is in contact with the fluid medium (13) during use with a mean roughness index Ra of less than 0.8 µm.

14. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims, characterized in that the metallic material of the diaphragm (2) has a hardness according to Rockwell C between 38 and 50 HRC.

15. System comprising a transducer (1) and a hydrogen-containing fluid medium (13) according to any of the preceding claims; characterized in that the housing (7) and the diaphragm (2) are connected by a material bonding connection (8); in that the diaphragm (2) has a first region (9) which is in contact with the fluid medium (13) during use; in that the diaphragm (2) has a second region which is not in contact with the fluid medium (13) during use; and in that the material bonding connection (8) is positioned in the second region.