CERAMIC SENSOR

Abstract

Sensor intended for monitoring a target part at a temperature above 400°C, the sensor comprising: - an array of electrically conductive particles (6), at least a portion of the conductive particles constituting a conductive network (7) whose electrical property is a function of an arrangement of the conductive particles constituting the conductive network, said arrangement being modifiable, more than 90% of the conductive particles, referred to as "elongated conductive particles", by number percentage, having a form factor greater than 2 and a thickness less than 1000 nanometers, - a ceramic phase (4) for protecting the conductive network, the ceramic phase being made up of ceramic particles, the ceramic phase comprising more than 90% of ceramic particles having a length between 0.1 and 100 µm, referred to as "fine ceramic particles", by number percentage,The shape ratio of a particle is equal to the ratio of the length of said particle divided by the thickness of said particle. Figure for the abbreviation: Fig 1.

Description

Title of the invention: CERAMIC SENSOR technical field

[0001] The invention relates to a sensor intended for monitoring the physical state of a target part in an environment with a temperature above 400°C. Previous technique

[0002] Acoustic sensors, piezoelectric sensors and resistive sensors, in particular sensors incorporating a Wheatstone bridge or of the type described in WO2017 / 009256A1, are used to precisely control the deformation of a part.

[0003] These strain sensors, however, cannot withstand temperatures exceeding 400°C, particularly for monitoring ceramic or glass parts commonly used at such temperatures. Cooling them is possible, but this significantly complicates the measurement process.

[0004] Furthermore, these strain sensors do not allow for the physical recording of the occurrence of an abnormally high strain. To detect such an occurrence, it is therefore necessary to perform measurements and analyze them continuously. However, continuous monitoring is not always possible.

[0005] In addition, these strain sensors can be difficult to integrate into confined spaces.

[0006] These strain sensors also do not allow measurement of the fatigue of the part if this fatigue has not changed the external shape of the part.

[0007] Finally, the properties of these strain sensors, and in particular their dilatometric behavior, may be incompatible with the part to be controlled.

[0008] There is therefore a need for a suitable sensor for monitoring the physical state of a target part placed in an environment at a temperature above 400°C, and which does not have the disadvantages mentioned above.

[0009] One object of the invention is to meet, at least partially, this need. Summary of the invention

[0010] The invention proposes a sensor comprising: - a set of electrically conductive particles, at least a part of the conductive particles constituting a conductive network whose electrical property is a function of an arrangement of the conductive particles constituting the conductive network, said arrangement being modifiable, more than 90% of the conductive particles, called "elongated conductive particles", as a percentage by number, exhibiting a form factor greater than 2 and a thickness less than 1000 nanometers, - a ceramic phase for the protection of the conductive network, the ceramic phase being made up of ceramic particles, the ceramic phase comprising more than 90% of ceramic particles having a length between 0.1 and 100 pm, called "fine ceramic particles", as a percentage by number, the conductive particles being in a material having an electrical resistivity, measured at 20°C, of ​​less than 1 mQ.m and the ceramic particles being in a material having an electrical resistivity, measured at 20°C, greater than 1 mQ.m.

[0011] As will be seen in more detail later in the description, the arrangement of the conductive particles of the conductive network can be modified in particular under the effect of a stress exerted on a target part on which the sensor is fixed, or in which the sensor is integrated.

[0012] Measuring this electrical property makes it possible to assess the effect of this stress, and in particular any deformation or fatigue of the target part. The sensor allows, in particular, the evaluation of damage to the target part, and specifically the detection of microcracks before failure of the target part, or the measurement of the target part's usage.

[0013] Remarkably, the ceramic phase, capable of withstanding high temperatures, protects the conductive network from high temperatures, particularly those exceeding 400°C. The sensor can therefore be used in high-temperature environments. The ceramic phase also protects the conductive network from abrasion and chemical attack.

[0014] Furthermore, the plasticity of the sensor can be exploited to trace the occurrence of high stresses exerted on the target part.

[0015] In addition, the sensor is inexpensive to manufacture and compact.

[0016] Finally, the ceramic phase improves compatibility with target parts made of a ceramic or glass-ceramic material generally used in high-temperature applications.

[0017] A sensor on the invention may further include one or more of the following optional and preferred features: • more than 90%, more than 95%, more than 99%, preferably substantially 100% of the elongated conductive particles, as a percentage by number, have a form factor greater than 5, preferably greater than 10, or even greater than 1000 or greater than 1000, and / or less than 10,000; • more than 90%, more than 95%, more than 99%, preferably substantially 100% of said conductive particles, preferably more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conductive particles elongated, in percentage by number, each have a thickness of less than 500 nanometers, preferably less than 100 nanometers, or even less than 50 nanometers, and / or greater than 1 nm, or 10 nm; at least the elongated conducting particles, preferably all conducting particles, are - particles, preferably fibers, of a metal or metalloid, preferably platinum, and / or - carbon nanotubes and / or - composite particles comprising a non-conductive core, preferably made of ceramic, glass-ceramic or glass, coated with a coating, at least partial, of a metal or a metalloid, and / or - composite particles comprising a ceramic core functionalized in the mass so as to be electrically conductive; the ceramic phase comprises, preferably is made up of, more than 80%, more than 90%, more than 95%, more than 99%, preferably substantially 100% of its mass, of one or more compound(s) selected from the group formed by Al2O3, ZrO2, Cr2O3; MgO, CaO, SiO2, SiC a or [3, BN, B4C; C, in particular in the form of diamond, Si3N4, AIN and Silicon oxynitrides including SiAlON; preferably, in particular if the elongated conducting particles are oxidizable at 20°C, and in particular if the elongated conducting particles are oxidizable at any temperature up to 1200°C, the ceramic phase is in a non-oxide material, preferably in diamond, and / or in a carbide, preferably comprising, by mass percentage, more than 90%, preferably substantially 100% of SiC a or [3 , and / or BN and / or B4C, and / or in a nitride, in particular comprising, by mass percentage, more than 90%, preferably substantially 100% of Si3N4 and / or AIN and / or one or more Silicon oxynitrides including SiAlON; elongated conducting particles, preferably all conducting particles, comprise, preferably are made up of, more than 80%, more than 90%, more than 95%, more than 99%, preferably substantially 100% of their mass, of one or more constituent(s) chosen from the group formed by Ag, Al, Au, Cu, Fe, Ge, Mo, Ni, Pd, Pt, Rh, Si, Ta, Ti, W, graphite, graphene, TiB2, TiC, TiN, ZrB2, ZrC, ZrN, VB2, VC, VN, CrB2, CrBN and WC; The elongated conducting particles, preferably all the conducting particles, are made of a material exhibiting electrical resistivity less than 0.5 mQ.m and, preferably less than 10 4 Qm, preferably less than 1 pQ.m; the fine ceramic particles, preferably all ceramic particles, are in a material having an electrical resistivity greater than 10 mQ.m, preferably greater than 1 Qm, preferably greater than 10 Qm, preferably greater than 100 Qm, preferably greater than 1000 Qm; the elongated conductive particles, preferably all the conductive particles, are made of a material having an electrical resistivity of less than 1 pQ.m and, preferably, the fine ceramic particles, preferably all the ceramic particles, are made of a material having an electrical resistivity greater than 1000 Qm; The elongated conducting particles, preferably all the conducting particles, are distributed, preferably homogeneously, in the ceramic phase, the ceramic phase being preferably continuous, preferably in the form of a layer, or the elongated conducting particles, preferably all the conducting particles, are distributed in at least one layer, called the "conducting layer", and, preferably, the ceramic particles of the ceramic phase are distributed in at least one layer, called the "ceramic layer"; said conductive and ceramic layers are superimposed one on top of the other, and preferably partially interpenetrate; elongated conducting particles, preferably all conducting particles have a preferred orientation; fine ceramic particles, preferably all ceramic particles, have a preferred orientation which, where appropriate, may be identical or different from the preferred orientation of elongated conducting particles or of all conducting particles; the conducting network has a preferred orientation, preferably extends along a preferred direction or a preferred plane; the conductive network has two connection terminals intended for measuring the electrical property between said terminals, or forms a closed circuit on itself; the ceramic phase forms a continuous layer, preferably in contact with the conductive network, preferably interposed between the conductive network and the external environment of the sensor; • the sensor comprises a fibrous ceramic phase in which the conductive particles of the conductive network, preferably metallic fibers, are dispersed; • the ceramic phase is sintered, that is to say it has a microstructure obtained by sintering.

[0018] The invention also relates to a method for manufacturing a sensor according to the invention, intended for monitoring the physical state of a target part, the method comprising the following steps: a) preparation of a starting load - in a form (al) of a slip comprising - ceramic particles and / or ceramic particle precursors, and - conductive particles and / or precursors of conductive particles; or - in a form (a2) of a first slip comprising ceramic particles and / or precursors of ceramic particles, and a second slip, different from the first slip, comprising conductive particles and / or precursors of conductive particles; or - in a form (a3) ​​of a powder comprising - ceramic particles and / or ceramic particle precursors, and - conductive particles and / or precursors of conductive particles; or - in a form (a4) of a first powder comprising ceramic particles and / or precursors of ceramic particles, and a second powder, different from the first powder, comprising conductive particles and / or precursors of conductive particles; or - in a form (a5) of a slip comprising conductive particles and / or precursors of conductive particles; or - in a form (a6) of a powder comprising conductive particles and / or precursors of conductive particles; or - in a form (a7) of a slip comprising ceramic particles and / or ceramic particle precursors, onto which conductive particles and / or conductive particle precursors are fixed; or - in a form (a8) of a powder comprising ceramic particles and / or precursors of ceramic particles, on which conductive particles and / or precursors of conductive particles are fixed; b) shaping the initial charge so as to obtain a preform, said shaping being (bl) by depositing the starting charge, preferably in the form of one or more layers, preferably, when the starting charge is in the form (al1), (a2), (a5) or (a7), by strip casting or spraying, preferably by strip casting, of preferably on a thickness between 0.05 and 3 mm, on a substrate, temporary or permanent, preferably on a raw piece of the target part or on the target part, or (b2) by integrating the initial charge into the mass of a substrate, preferably in a raw piece of the target part or in the target part, or preferably, when the starting charge is in the form (a1), (a2) or (a5), by impregnation of the substrate, or (b3) where the starting charge is in the form (al1), (a3), (a7) or (a8), by shaping the starting charge into the form of the target part or a raw part of the target part, then, if the initial shaped charge contains a liquid phase, drying of the initial shaped charge; c) thermal consolidation of the preform, preferably by sintering, so as to obtain a measuring mass; d) Optionally, fixing the measuring mass to a support and / or fixing an interface layer to the measuring mass and / or to the support, ceramic particles, ceramic particle precursors, conductive particles and conductive particle precursors being chosen so as to obtain, at the end of step c) or step d), a sensor according to the invention, the substrate can optionally be separated from the preform after drying or separated from the measuring mass after consolidation.

[0019] A method for manufacturing a sensor according to the invention may further include one or more of the following optional and preferred features: • the shaping of step b) involves an operation of orienting the conductive particles along a preferred plane or along a preferred direction, preferably by means of an electric or magnetic field; • the shaping of step b) includes an operation of orienting the ceramic particles according to a preferred plane or according to a preferred direction, preferably by freeze casting, the orientation of the ceramic particles being identical or different to the possible preferred orientation of the conductive particles; • the substrate is a porous body with an open porosity preferably greater than 30% by volume, preferably greater than 40%, and / or preferably less than 70%, or even less than 60%, by volume; • the substrate is a porous body with oriented pores preferably having a thickness greater than 50 nm and less than 1 pm, and a width less than or equal to 10 pm; • the substrate is fibrous; • in step b), - metallic particle precursors or conductive particle precursors in a ceramic material are deposited onto pores within the porous body, and then these precursors are thermally or chemically reduced to form the conductive particles, or - A slip made up of metallic particles or conductive particles in a ceramic material, suspended in a solvent, is deposited onto pores inside the porous body, and then the solvent is evaporated. so as to constitute a conductive network; • after deposition of the conductive particles, a layer of a ceramic material is deposited on the conductive network, and preferably said layer is sintered, preferably at a temperature below 1600°C, preferably below 1500°C, preferably under a non-oxidizing atmosphere, preferably by SPS.

[0020] The invention also relates to a device comprising a target piece and a sensor according to the invention fixed on the target piece or integrated into the target piece, so that the arrangement of the conductive particles of the conductive network is modified under the effect of a stress applied to the target piece.

[0021] A device on the invention may further include one or more of the following optional and preferred features: • the conductive particles and the ceramic phase have the form of different and superimposed layers; • the target part has an open porosity, by volume, greater than 1%, greater than 3%, 5% or 10%, and the conductive particles of the conductive network are fixed to the surface of open pores on the surface and / or in the mass of the target part; • the conductive network is covered, at least partially, preferably completely, with a ceramic phase in the form of a layer; • the target part has an open porosity oriented preferentially parallel to a preferred plane or direction; • the target part is a fragile part; • the target part is made of a ceramic material and / or glass and / or a glass-ceramic and / or in a "Ceramic Matrix Composite", or "CMC"; • The target piece is chosen from a group consisting of a refractory tile, a ceramic piece from a solar absorber, a cooking support, a block furnace refractory, an abrasion protection piece, a bonded abrasive, a ceramic cutting tool, a ceramic pump or hydraulic circuit element, a ceramic electrical insulating support or tube, a ceramic tile or a ceramic or glass-ceramic facing piece, a plate, a tube comprising a glass-ceramic material, a brake pad or disc or a ceramic object of a braking device, glazing, a filter for liquid or gaseous filtration, a radome; • the conductive network extends into a bonding phase which binds grains of the target part, preferably grains in a refractory material, preferably in a ceramic material, for example abrasive grains, the bonding phase being able in particular to result from a sintering of a raw part of the target part, for example from a reactive sintering.

[0022] The invention further relates to a method of manufacturing a device according to the invention intended for monitoring the physical state of a target part, the method comprising fixing the sensor according to the invention on the target part or integrating the sensor into the target part.

[0023] Furthermore, the invention relates to a method for monitoring the physical state of a target part, said method comprising the following steps: 1) at an initial instant, fixing a sensor according to the invention on the target part or integrating a sensor according to the invention into the target part, so as to constitute a device according to the invention; 2) calibration of the device so as to determine a relationship between said physical state and an electrical property of the sensor's conductive network; 3) commissioning of the device in an environment at a service temperature, then, at a time-stamped date, measurement of said property at said service temperature and, from said relationship, determination of said physical state at the time-stamped date.

[0024] A monitoring method according to the invention may further include one or more of the following optional and preferred features: • the service temperature is above 400°C, 500°C, 600°C, or 700°C, and / or below 1500°C; • calibration is performed from measurements of electrical properties taken at said service temperature; • the determination of said physical state includes the detection of microcracking and / or the detection or measurement of fatigue of the target part; • step 3) is repeated, with two successive updated moments being separated, for example, by more than 1 minute, 1 hour, a day, or a week; • in step 3), said property is measured without contact with the conductive network of the sensor; • at step 3), depending on said measurement of said property: a mechanical shock suffered, before step 3), by the target part is detected, for example during transport of said target part, and / or an amplitude of said mechanical shock is measured; a thermomechanical stress is detected, before step 3), by the target part and / or an amplitude of said thermomechanical stress is measured; we detect and / or measure a set of stresses experienced by the target part and which have led to fatigue of the target part without microcracking; • said property is an impedance, preferably an electrical resistance.

[0025] The invention further relates to a kit, in particular for implementing a monitoring method according to the invention, said kit comprising a device according to the invention and a measuring apparatus adapted to measure, preferably without contact, said elastic property in step 3). Definitions

[0026] The term "ceramic" means a product that is neither metallic nor organic. For the purposes of this invention, diamond, graphite, graphene, carbides, and cermets are considered ceramic materials. A non-metallic, amorphous mineral material, for example, silica glass, is considered a ceramic.

[0027] Unless otherwise specified, "ceramic particles" means ceramic particles of the ceramic phase. In particular, conductive particles may be made of a ceramic material but are not referred to in this description as "ceramic particles".

[0028] The “particles” are elements which do not form a continuous film or a continuous mass, but can be distinguished from one another.

[0029] The dimensions of a particle are its length, its width and its thickness.

[0030] The “length” L or “size” of a particle is its largest observable dimension on a photograph taken along a direction perpendicular to the plane on which said particle rests.

[0031] The "width" W1 and "thickness" W2 of a particle are the lengths of the major and minor axes, respectively, of the smallest possible ellipse in which the median cross-section (section at mid-length and taken perpendicular to the direction of length) of said particle can be inscribed.

[0032] A particle has a "stick-like" shape when it meets the following three conditions: 1. 4 < L / W < 10 and W = (Wl+W2) / 2, 2.4 < L / Wl, and 3. W2<1.5.W1.

[0033] A particle has a "platelet" shape when it meets the following two conditions: 1.4 < L / Wl, and 2. W2 > 1.5 W1, preferably W2 > 2 W1.

[0034] Preferably, the cross-section of a plate is substantially constant over the entire length of the plate, is substantially polygonal and has at least 4 sides.

[0035] The "shape factor" of a particle is the ratio of its length to its thickness.

[0036] The arrangement of the conductive particles is "modifiable" when, in the intended use, said conductive particles can, at least for a part of them, move closer together or further apart, which modifies an electrical property of the conductive network, in particular its resistance.

[0037] A distinction is made between the "particles" of the sensor and the "grains" of the target part. This distinction is made solely for the sake of clarity. In particular, in one embodiment, the grains of the target part may constitute the ceramic particles of the sensor.

[0038] A particle whose length is greater than five times its thickness and greater than five times its width is called a "fiber".

[0039] A particle is considered "multi-faceted" when it has at least two facets, a facet being a surface bounded by an edge. A "nut-shaped" form is an example of a two-faceted form.

[0040] “Ceramic particle precursors” and “conductive particle precursors” are constituents of the starting charge which, during the manufacture of a sensor according to the invention, lead to ceramic particles and conductive particles, respectively.

[0041] A set of particles or pores exhibits a "preferred orientation" when the orientation of these particles or pores is not random. In particular, the particles or pores may be oriented along a preferred plane, for example, by being stacked in layers, or along a preferred direction, for example, when their longitudinal axes are oriented substantially parallel to each other.

[0042] A liquid or gel medium containing dispersed particles and / or particle precursors, for example in ionic form, is called a "slip".

[0043] The conducting network exhibits a "preferred orientation" when it does not extend randomly. In particular, the conducting network can extend in a preferred plane or along a preferred direction.

[0044] The measurement of open porosity, or apparent porosity, can be determined by the Archimedes method, for example according to the ISO 18754 method.

[0045] The total porosity, expressed as a percentage, is conventionally equal to 100 * (1 - the ratio of the geometric density divided by the absolute density). The absolute density value, expressed in g / cm³, is conventionally measured by dividing the mass of a sample by the volume of that sample ground in such a way as to substantially reduce the porosity. In this case, the grinding is adapted to reduce the sample to a powder with particles smaller than 40 micrometers. The absolute density can be measured by helium pycnometry using an Accupyc II 1340 instrument from Micromeritics. The standard used by the manufacturer is ASTM C604-02(2012).

[0046] A "tubular pore" is a pore that has the general shape of a tube opening at one of its two ends ("blind pore") or at both ends ("through pore"). The direction of a frustoconical tubular pore is referred to as the "longitudinal direction" of the pore.

[0047] The "tubular" character of a pore can be determined by observation of photographs of the pores, in particular in perspective or in longitudinal section.

[0048] A truncated conical tubular pore is said to be "macroscopic", or called "macropore" if it has a median cross-section (at mid-length) having an equivalent diameter greater than 0.15 pm and less than 450 pm.

[0049] The "equivalent diameter" of the opening or of a section of a pore is called the diameter of a disk with the same surface area as said opening or said section.

[0050] A "raw part" of the target part is a part which substantially has the shape of the raw part and which, during sintering, leads to said target part.

[0051] By "brittle part" is meant a part made of a material whose plastic deformation range under load before failure represents less than 1% of the elastic deformation range, preferably being substantially zero. In other words, the width of the stress range leading to plastic deformation without failure represents less than 1% of the width of the stress range leading to elastic deformation.

[0052] A material can be composite or monolithic depending on whether or not it contains fibers. In particular, it can be a "Ceramic Matrix Composite", or "CMC", that is to say, a product composed of fibers bonded together by a ceramic matrix.

[0053] A person skilled in the art knows how to measure the deformation of a part. In particular, they know that the load is applied in compression for a monolithic material and in tension for a fibrous ceramic composite, especially a CMC, the elongation being classically measured in the direction of the fibers.

[0054] “Integration” of the sensor into the target part consists of physically incorporating This sensor is embedded in this part, for example by using a binding phase from this part as a ceramic phase, or by forming the sensor within the porosity of the target part. Therefore, the sensor cannot be isolated without affecting the integrity of the target part.

[0055] A "block" is defined as a piece having a mass greater than 20 g, preferably greater than 50 g, or even greater than 100 g. A "plate" is defined as a piece whose width is more than five times its thickness.

[0056] By "stress," we mean a stimulus exerted on a target part, for example, a mechanical stimulus such as a shock or a thermal (for example, a shock or a thermal gradient) or thermomechanical stimulus, a chemical or corrosion stimulus, a force, or a moment of force. The stress may be of both thermal and mechanical origin when thermal stresses are combined with mechanical stresses, for example, in the case of temperature finishing under load.

[0057] A stress can have a temporary or permanent effect on the target part. By extension, the intensity of this stress relative to the surface of the part in question is called a "stress." The stresses Ca, Ce, and Cemin, or the stresses Cr and Cs', defined later, are applied in the same way to the target part. For example, if the stress is a mechanical action, this action is applied at the same location on the target part, along the same direction; only the intensity of this action may differ for Ca, Ce, and Cemin.

[0058] The invention is of particular interest for fragile parts made of a very rigid and very mechanically resistant material, in particular whose MOE / MOR ratio is greater than 100, where MOE is Young's modulus and MOR is the modulus of rupture, expressed in MPa under the load conditions described above, depending on whether the material is monolithic or fibrous composite in particular.

[0059] The "physical state" of a part can be, for example, "damaged state" or "state "Integral state." It can also be more precise. For example, it can be "slightly damaged state," "moderately damaged state," or "severely damaged state."

[0060] The "damage" to a target part is an irreversible consequence of the application of stress on the target part. Damage can in particular result in microcracks or fatigue.

[0061] Microcracks lead to a change in the volume of the target part, which itself can produce a deformation of a sensor according to the invention.

[0062] Fatigue, or "aging," of the target part results from its previous use and / or the passage of time. It does not necessarily lead to deformation of the target part. However, it results in a modification of the conductive network, particularly because "bridges" between conductive particles can break down through aging, which alters the electrical properties of the conductive network.

[0063] Any stress that produces damage is called a "damage stress".

[0064] The damage stress that has the lowest intensity is called the "minimum damage stress".

[0065] By "electrical property" of a conductive network, and by extension, of a sensor, we mean a characteristic of that sensor that is a function of the impedance of the conductive network. Conventionally, the property of the sensor, for example its resistance (or equivalently its resistivity), can be measured electrically.

[0066] Unless otherwise specified, "resistance" is electrical resistance, measured in Ohms.

[0067] Electrical resistivity is measured according to ASTM F76. Unless otherwise specified, resistivities are measured at a temperature of 20°C.

[0068] “Contain”, “present” or “include” must be interpreted in such a way broad, not exhaustive. Brief description of the drawings

[0069] Other features and advantages of the invention will become apparent upon reading the detailed description that follows and upon examination of the accompanying drawing in which • Fig. 1 [Fig. 1] schematically illustrates a kit according to the invention comprising a device according to the invention; • Fig. 2 schematically illustrates a first example of a sensor according to the invention; • Fig. 3 schematically illustrates a second example of a sensor according to the invention; • Fig. 4 [Fig. 4] schematically illustrates the operation of a device according to the invention.

[0070] In the various figures, identical references are used to designate identical or analogous parts. Detailed description Sensor

[0071] A sensor 2 according to the invention comprises a set of electrically conductive particles 4, at least a portion of the conductive particles being in contact electrical so as to constitute a three-dimensional conducting network 7 whose electrical property is a function of an arrangement of the conducting particles constituting the conducting network.

[0072] The sensor 2 also includes a ceramic phase 4 which protects the conductive network 7 from the external environment.

[0073] Preferably, the volume ratio of the "conductive network / ceramic phase" is greater than or equal to 1% and / or less than 30%, preferably less than 25%, more preferably less than 20%, or even less than 15% or even less than 10%. Advantageously, the electrically conductive network is then sensitive to micro-deformations while remaining protected by the ceramic phase.

[0074] The conductive network 7 consists of a set of conductive particles that is not rigid, but allows for the displacement of conductive particles relative to adjacent conductive particles, and / or a change in the orientation of the conductive particles. "Conductive bridges" between conductive particles can thus be created or destroyed depending on whether conductive particles come into contact with other conductive particles or whether such contacts are broken.

[0075] Under the effect of a stress, the arrangement of the conductive particles of the conductive network, and therefore the number and / or quality of the contacts between the conductive particles of the conductive network, are modified. This results in a modification of the impedance, and in particular of the electrical resistance of the conductive network 7.

[0076] The modification of the geometry of the sensor, and more specifically of the arrangement of the conductive particles of the conductive network, can in particular result from its crushing, stretching, bending or rotation.

[0077] The conductive network 7 is said to be "percolating", that is to say, it permanently allows a passage of current between two predetermined end points or in a closed loop.

[0078] Thus, in one embodiment, the conductive network 7 forms an electrically conductive circuit, closed upon itself. The sensor can then provide information without being physically connected to an electrical power source. In particular, the flow of current can be achieved by means of a magnetic field. A measuring device can then measure the electrical impedance of the circuit and its variations.

[0079] Not all conductive particles 4 are necessarily part of the conductive network 7. Conductive particles may indeed be isolated from the conductive network. The particles that are part of the conductive network are modified according to the stresses experienced by the sensor. In particular, under the effect of fatigue, particles may detach from the conductive network.

[0080] Preferably, at least the elongated conducting particles, preferably all the conducting particles, have a preferred orientation.

[0081] Preferably, at least the fine ceramic particles, preferably all the ceramic particles have a preferred orientation, identical or different from that of the conducting particles or the elongated conducting particles.

[0082] A preferred orientation advantageously allows for anisotropic behavior. In particular, the sensor's response to a deformation can depend on how that deformation occurs. For example, the property measured by the sensor can be significantly modified when the deformation occurs along an axis, for example perpendicular to the preferred direction, and only slightly modified when the deformation occurs along the preferred direction.

[0083] According to a first main embodiment, the sensor 2 comprises a ceramic phase 4 in which electrically conductive particles 6 are dispersed, as illustrated in [Fig.2]. Preferably, the conductive particles are uniformly distributed in the ceramic phase, which forms a “ceramic matrix”.

[0084] In the first main embodiment, the sensor 2 may include a layer in which the ceramic particles and the conductive particles are uniformly distributed. The thickness of the layer is preferably between 0.05 mm and 3 mm, preferably between 0.1 mm and 1 mm.

[0085] According to a second principal embodiment, illustrated in [Fig. 3], the sensor 2 comprises a ceramic layer forming a ceramic phase 4, preferably electrically insulating, and a conductive layer in which electrically conductive particles 6 (not shown) are dispersed so as to form the conductive network 7. The ceramic and conductive layers are superimposed on one another, as illustrated in [Fig. 3]. Preferably, the ceramic layer covers the conductive layer, thereby effectively protecting it from temperature and abrasion.

[0086] The second main embodiment is particularly advantageous for controlling a target part that is porous or fibrous. In particular, it allows for the precise perception of the stresses experienced by the target part.

[0087] The number of said layers is not limiting.

[0088] In the second main embodiment, the sensor therefore comprises a plurality of superimposed ceramic and conductive layers, each layer comprising ceramic particles or conductive particles, preferably distributed uniformly.

[0089] In a third main embodiment, the sensor is integrated into the target part. In other words, the sensor is inseparable from the target part.

[0090] In one embodiment, the sensor is passive, that is to say, it does not include any source of electrical energy.

[0091] The conductive network can form an electrically conductive circuit closed on itself, preferably shaped to be readable by magnetic induction.

[0092] According to one embodiment, the sensor requires connection to an electrical power source. Preferably, and preferably at the end points of the conductive network, it comprises connection terminals 18 provided to facilitate the connection of this electrical power source, in particular a measuring device 16. Conductive particles

[0093] The conductive network 7 is made up of conductive particles 6.

[0094] A conductive particle 6, and in particular an elongated conductive particle, can be made of a single conductive material, for example copper or platinum.

[0095] A conductive particle 6, and in particular an elongated conductive particle, can alternatively be a "functionalized" particle, thus made conductive.

[0096] In particular, it may consist of a non-conductive central core, preferably made of a ceramic material, in particular a crystalline material, a glass-ceramic or a glass, preferably in the form of a fiber, the central core being coated with an electrically conductive coating, for example an inorganic coating, in particular a copper, platinum, silver, or titanium carbide or boride-based coating. All functionalization processes may be considered.

[0097] In particular, it is possible to deposit a metal precursor, for example, by depositing an inorganic metal salt or an organometallic compound, or by using a sol-gel route starting from an alkoxide, and then proceeding with a reduction to the elemental state of the metal, for example by heat treatment or chemical reaction with a reducing agent. Preferably, a water-soluble organic salt that dissociates to form a free cation is deposited. The deposition can be carried out, in particular, by spraying, dipping, impregnation, or in the gas phase.

[0098] It is also possible to deposit conductive nanoparticles on the central core, for example by chemisorption after silanization of the central core, by physisorption or by electrostatic attraction.

[0099] The presence of a central nucleus advantageously allows modification of the properties, and in particular the dilatometric behavior of the conducting particle.

[0100] A conductive particle 6 may also consist of a non-conductive nucleus in which conductive nanoparticles are dispersed, conferring the property of electrical conductivity.

[0101] The thickness and / or width of said conducting particles is preferably less than 500 nanometers, preferably less than 100 nanometers, or even less than 50 nanometers.

[0102] The length of said conducting particles is preferably greater than 20 nanometers, preferably greater than 50 nanometers, or even greater than 100 nanometers, and / or less than 1000 nanometers, or even less than 500 nanometers

[0103] Preferably, for more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conductive particles, as a percentage by number, the form factor is greater than 5, preferably greater than 10, or even greater than 1000.

[0104] In a preferred embodiment, the conductive particles are acicular in shape, preferably are fibers, preferably fibers whose length is more than ten times the thickness and more than ten times the width.

[0105] Such conductive particles are particularly advantageous for limiting their aggregation during consolidation while ensuring a modifiable conductive network.

[0106] Preferably, more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conductive particles, as a percentage by number, are made up, for more than 90%, more than 95%, more than 99%, preferably substantially 100% of their mass, of one or more constituents chosen from the group consisting of conducting metals and metalloids, preferably from the group consisting of Ag, Al, Au, Cu, Fe, Ge, Mo, Ni, Pd, Pt, Rh, Si, Ta, Ti, W, graphite, graphene, TiB2, TiC, TiN, ZrB2, ZrC, ZrN, VB2, VC, VN, CrB2, CrBN and WC.

[0107] In one embodiment, more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conducting particles, as a percentage by number, are carbon nanotubes such as for example described by WO2004 / 065926.

[0108] In one embodiment, more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conductive particles, as a percentage by number, are conductive particles described in WO2017 / 009256.

[0109] Preferably, more than 90%, more than 95%, more than 99%, preferably substantially 100% of the conductive particles, as a percentage by number, are fibers of a refractory metal, preferably Platinum, for example Platinum (Pt) fibers as described in WO2010003389A2.

[0110] The electrical resistivity of the material constituting the conductive particles is less than 1 mΩ·m, preferably less than 100 microohm·m (pΩ·m), preferably less than 10⁶ ohm·m at the service temperature, preferably at any temperature between 20°C and 1000°C, preferably between 20°C and 1200°C. Ceramic particles

[0111] The ceramic phase 4 consists of ceramic particles.

[0112] Preferably, more than 90%, more than 95%, more than 99%, preferably 100% by number of said ceramic particles have a length between 0.1 and 100 pm. These particles are referred to as "fine ceramic particles".

[0113] Preferably, more than 90%, more than 95%, more than 99%, or more preferably 100% by number of said ceramic particles have a width greater than 0.5 pm and / or less than 50 pm, preferably less than 5 pm. Preferably, more than 90%, more than 95%, more than 99%, or more preferably 100% by number of said ceramic particles have a length greater than 10 pm, preferably greater than 50 pm and / or less than 500 pm.

[0114] The function of the ceramic particles is to prevent the agglomeration of the conductive particles and to protect them from the temperature and / or potentially aggressive atmosphere in the environment in which the sensor is used.

[0115] The ceramic particles are made of an electrically insulating ceramic material, which has an electrical resistivity greater than 1 Ohm.m, preferably greater than or equal to 103 Ohm.m, preferably greater than 106 Ohm.m and / or less than 1012 Ohm.m, at 20°C, preferably at any temperature between 20°C and 1000°C, preferably between 20°C and 1200°C.

[0116] In one embodiment, the ceramic particles are acicular in shape, preferably fibers, preferably fibers whose length is more than ten times their thickness and more than ten times their width. This embodiment is particularly suitable when conductive particles are deposited in a fibrous or porous substrate.

[0117] Preferably, the fine ceramic particles, preferably all the ceramic particles are made up of more than 90%, more than 95%, more than 99%, preferably substantially 100%, of a compound selected from the following compounds: Al2O3, ZrO2, Cr2O3, MgO, CaO, SiO2, SiC a or [3, BN, B4C, C, preferably in diamond form, AIN, Si3N4 and Silicon oxynitrides including SiAlON. Preferably, especially if the conductive particles are metallic particles or carbon nanoparticles, the particles consist of more than 90%, more than 95%, preferably more than 99%, preferably substantially 100%, of a compound selected from the following compounds: SiC a or [3, BN, B4C, C in diamond form, AIN, Si3N4 and Silicon oxynitrides including SiAlON.

[0118] Preferably, all the fine ceramic particles, preferably all the ceramic particles have substantially the same composition.

[0119] In the ceramic phase 4, the ceramic particles are preferably bonded to each other by sintering.

[0120] Preferably, the ceramic phase consists of more than 90%, more than 95%, preferably more than 99%, preferably substantially 100%, of one or more of the following compound(s): Al2O3, ZrO2, MgO, CaO, SiO2, SiC, BN, and Silicon oxynitrides including SiAlON and Si3N4.

[0121] The "measuring mass" consisting of the conductive particles 6 and the ceramic phase 4 can by itself constitute a sensor according to the invention.

[0122] It can also be fixed to a support 8. In particular, the support 8 can be a strip or a tablecloth, so as to constitute a patch.

[0123] The assembly 4-6-8 then forms a sensor 2 in the form of a patch.

[0124] The support 8 may for example have a surface area of ​​0.5 to 1000 mm2, preferably of 1 to 100 mm2, preferably greater than 10 mm by 10 mm, and / or a thickness of less than 1 mm, or even less than 500 micrometers.

[0125] In a preferred embodiment, the sensor 2 includes an interface layer 9 fixed to the support, in particular on a face of the support opposite to the face that supports the measuring mass, and / or, in particular in the absence of a support, fixed to the measuring mass.

[0126] The interface layer 9 can be, particularly if the service temperature is less than or equal to 400°C, an adhesive comprising a thermosetting, thermoplastic, or crosslinkable elastomer polymer. Preferably, when the polymer is thermosetting, its degree of crosslinking is greater than 75%, or even greater than 90%. Preferably, when the polymer is thermoplastic, its degree of crystallinity varies from 0% to 80%. Even more preferably, the adhesive comprises more than 50% by mass of polymer(s), for example, polyurethane or epoxy. If the service temperature is greater than or equal to 400°C, the interface layer is preferably an inorganic adhesive, for example a geopolymer-based adhesive, for example including sodium silicate, or for example a platinum- or copper-based adhesive, or for example a refractory adhesive described in the article by R. Luhn, E. Zimmermann and G.Kôhler, Jena “Anorganische Hochtemperaturklebstoffe -Anwendungsmôglichkeiten und Grenzen” published in “Schweifien und Schneiden 2000 Vortrage der gleichnamigen Grofien Schweifitechnischen Tagung in Nümberg vom 27. bis 29. September 2000”, pages 249 to 252, for example a Pyro-Putty #653 or 2400 ceramic adhesive supplied by Aremco, .

[0127] The thickness of the interface layer 9 is preferably constant, preferably greater than 0.1 mm and / or less than 2 mm, preferably less than 1 mm. The interface layer preferably extends so as to cover the entire surface of the substrate intended to be placed on the target part.

[0128] Preferably, the nature of the interface layer 9 is adapted to the behavior of the target part. Advantageously, the same patch can thus be used for different target parts or for different applications, by modifying only the interface layer 9.

[0129] To choose an interface layer, said patches can be glued onto parts with different glues, to create identical test devices, and then the one that allows the sensor to behave as desired can be chosen, for example to maintain elastic behavior up to stresses as close as possible to the minimum damage stress, and then to adopt plastic behavior beyond the minimum damage stress.

[0130] A person skilled in the art knows how to modify the elastic limit of an adhesive. Generally, the behavior of an adhesive can be modified by adjusting its composition, for example by changing the amount of organic materials (thermosetting polymers, thermoplastics, or crosslinking elastomers), accelerators, retarders, or fluidizers. It is also possible to add fillers, in particular with an elastomer filler or one made of polymer or mineral fibers.

[0131] Preferably, the deformation of the sensor 2 is guided by the deformation of the measuring mass and / or by the deformation of the interface layer 9. In other words, the sensor deforms elastically or plastically depending on whether the measuring mass and / or the interface layer deforms elastically or plastically, respectively. Device

[0132] A device according to the invention of the type shown in [Fig.1] comprises a sensor 2 and a target piece 10, on which the sensor 2 is fixed.

[0133] The target part 10 may in particular be a fragile part.

[0134] The target part 10 can be made of ceramic and / or glass and / or a glass-ceramic and / or a ceramic-phase composite (CMC), preferably with a melting temperature above 1000°C, or even above 1200°C. In the case of a ceramic target part, the target part may be made of one or more of the following materials: alumina, zirconia, silica, silicon or boron carbide, and silicon nitride.

[0135] The target part 10 can be made of a molten or sintered material. In one embodiment, the target part consists of more than 80%, more than 90%, or even substantially 100% of its mass, of ceramic grains, preferably agglomerated by sintering.

[0136] The target part 10 may have a mass greater than 500 g, preferably greater than 1 kg and / or less than 100 kg, less than 50 kg, less than 10 kg, or even less than 5 kg.

[0137] The target part 10 can have any shape, determined according to the intended application. In particular, the target part 10 can have the shape of a rectangular parallelepiped brick. It can be in the form of a cylinder, a roll or a rod, a hollow part or one having a closed or open internal cavity, for example, a crucible, a tube open on one or both ends, a disc or a flat cylinder with a hole, especially with a central opening. In particular, it can be in the form of a plate or a disc with a thickness greater than 5 mm, preferably greater than 10 mm and / or less than 20 mm.

[0138] In use as a furnace lining in particular, the target piece preferably has a length greater than 20 cm and / or less than 50 cm, and / or a width greater than 10 cm and / or less than 30 cm, and / or a thickness greater than 1 cm and / or less than 5 cm.

[0139] In use as a WRT protective coating in particular, the target part preferably has a length greater than 50 cm and / or less than 200 cm, a width greater than 30 cm and / or less than 50 cm and a thickness greater than 3 mm and / or less than 10 cm.

[0140] In use as a cooking support in particular, the target piece preferably has a length greater than 20 cm and / or less than 200 cm, and / or a width greater than 20 cm and / or less than 70 cm, and / or a thickness greater than 3, preferably greater than 5 mm and / or less than 5 cm.

[0141] In the case of an abrasive tool, the target part may have a diameter greater than 20 cm and a width greater than 1 mm or more (abrasive disc), or even greater than 10 mm, or even greater than 100 mm (abrasive grinding wheel).

[0142] Preferably, the sensor is arranged so as not to be directly subjected to the stresses applied to the target part. For example, if the target part is a cooking plate, the sensor is preferably not in direct contact with the food to be cooked that is placed on the cooking plate.

[0143] However, the sensor must be positioned so as to experience, at least indirectly, stresses applied to the target part. Positioning it on the most vulnerable parts of the target part, for example the corners and edges, may be satisfactory.

[0144] The sensor can be disposed on the surface and / or in the mass of the target part.

[0145] The surface of the target part on which the sensor 2 is fixed can be a surface any surface of the target part 10. Preferably, this surface is one which, in service, is likely to be subjected to mechanical or thermomechanical stresses capable of degrading the target part. In particular, these stresses may result from high temperatures, temperature variations, or mechanical shocks.

[0146] The shape of the surface on which the sensor is fixed is not limiting. It can be smooth or rough, have through holes or be continuous, optionally have cavities or bosses, be developable or not, be flat or not.

[0147] In one embodiment, the ceramic particles and / or conductive particles forming the conductive network are distributed in the target part, preferably in the form of one or more ceramic layers, on the surface and / or within the target part, preferably in a binding phase binding grains of the target part or on the surface of open pores of the target part.

[0148] Preferably, the target part is chosen from: • a component of a heat exchanger, in particular a refractory tile, in particular a boiler lining tile and / or a heater tube protective shell of an incinerator, a ceramic component of a solar absorber • a kiln furniture, especially for firing ceramic objects, in English • a tile or protective part of a combustion turbine chamber, in particular a gas turbine chamber, • a refractory furnace block, in particular from a metallurgical furnace or a glass melting furnace, in particular a wall block, a hearth block or a vaulting piece, • an abrasion-resistant part, known as "anti-abrasion", particularly for a conveyor, especially a conveyor intended for the transport of ores (in English "Wear Resistant Technology", WRT), • an abrasive, in particular a bonded abrasive comprising ceramic particles in a binding matrix, in particular a grinding wheel or abrasive disc intended especially for grinding or surface treatment including sharpening, polishing, deburring • a ceramic cutting tool, • a ceramic pump or hydraulic circuit element, • a ceramic electrical insulating support or tube • a ceramic tile or a ceramic or glass-ceramic facing piece, • a plate, a tube comprising a glass-ceramic material, • a brake pad or disc or a ceramic object from a device braking, • glazing, and in particular a sheet of glass or a windshield, • a filter for liquid or gaseous filtration, • a radome or a room protecting a radio or radar antenna. Kit

[0149] A kit according to the invention comprises a device according to the invention and a measuring apparatus 16 adapted to measure said electrical property, in particular in step 3).

[0150] The measuring device 16 can be connected to the conductive network 7 by means of cables, for example by connecting it to the connection terminals 18 ([Fig. 1]). Preferably, the cables and the connection terminals are made of a refractory metal resistant to temperatures exceeding 400°C, for example, platinum. A refractory and conductive platinum-based adhesive can be used to improve electrical contact.

[0151] In a preferred embodiment, the measuring device 16 is not connected to the conductive network 7. The latter, however, forms a loop allowing for contactless measurement by induction.

[0152] The measuring device 16 is connected to an analysis device 22, that is to say a device classically comprising a processor, computer memory and software configured to determine, from the measured electrical property, a state of the part.

[0153] The measuring device 16 can alternatively be physically integrated into the analysis device.

[0154] Any conventional measuring and analysis device can be used. In particular, the processing, analysis and recording of the measured electrical property and its variations can employ amplification, filtering, multiplexing and digitization methods known to those skilled in the art in the field of resistive sensors, in particular resistive composite sensors.

[0155] Communication between the sensor and the measuring device and / or between the measuring device and the analysis device can be carried out wired or wirelessly, for example by wifi or Bluetooth®.

[0156] Preferably, the measuring device is programmed to record the sensor impedance at regular time intervals.

[0157] Methods for manufacturing the sensor of the device and the kit

[0158] In one embodiment, a sensor according to the invention, intended to constitute, with a target part, a device according to the invention, is manufactured according to a process comprising steps a) to d).

[0159] In step a), a starting load is prepared.

[0160] The starting charge may take the form (al) of a slip comprising: - ceramic particles, and / or precursors of ceramic particles, - electrically conductive particles and / or precursors of electrically conductive particles, and - a solvent.

[0161] The quantities of ceramic particles and / or precursors of ceramic particles and of conductive particles and / or precursors of conductive particles in the slip are determined so that the slip leads, after step c), to a microstructure consisting of conductive particles dispersed in a ceramic phase.

[0162] Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles dispersed in the solvent, as a percentage by number, are ceramic particles and / or precursors of ceramic particles, and / or conductive particles and / or precursors of conductive particles.

[0163] The starting charge can take the form (a2) of a “ceramic” slip comprising ceramic particles and / or precursors of ceramic particles and a first solvent, and a “conductive” slip comprising electrically conductive particles and a second solvent, preferably identical to the first solvent.

[0164] Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles dispersed in the first solvent, as a percentage by number, are ceramic particles and / or precursors of ceramic particles.

[0165] Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles dispersed in the second solvent, as a percentage by number, are conductive particles and / or precursors of conductive particles.

[0166] For shapes (al1) and (a2), the quantities of particles and precursors and their nature are chosen to obtain, at the end of step c) or step d), a sensor according to the invention. This choice does not pose any particular difficulty for those skilled in the art.

[0167] The precursors of ceramic particles can in particular be chosen from preceramic polymers which during heat treatment decompose into ceramic particles, for example be a Polysiloxane, a polysilaxane, a polycarboxylane, a TetraEthylOrthoSilicate, a silicone-based polymer, or a Poly vinylpyrolidone-based polymer.

[0168] The precursors of conductive particles can in particular be chosen from organometallic compounds or the precursors of conductive ceramic particles chosen for example from Dimethyl[tris(dimethylamino)titanio]amine, a Zirconium borohydride, a tungsten polymer called bis(tert-butylimido)bis(dimethylamido)tungsten, a dinitrile polymer of formula (— BioHi2N=C-(CH2)aC=N—) where a is between 5 and 8, a polymer of general formula (—Bi0Hi2N=C(CH2)5C=N—) to which is added a fine powder, for example submicron, of MO2 where M is Ti or Zr in order to obtain after step c) a Boron and Zirconium or Titanium nitride, or borazine (B3N3H6).

[0169] The quantity of conductive particles is preferably between 0.1 and 30%, preferably between 0.1% and 10% by volume, based on the volume of the slip.

[0170] The solvent may be aqueous or non-aqueous. It is preferably organic, particularly for dispersing metallic particles. Preferably, the solvent is isopropanol.

[0171] Particularly in the specific case of ceramic conductive particles, the solvent may be a carboxylic acid, for example oleic acid, a propionic acid or a coprylic acid, water with a tetraethyl ammonium, a PolylminoEthylene (PEI), 2-butanone / ethanol or C57H105O12P or "Castor oil phosphate".

[0172] The dry matter content in a slip is preferably greater than 20%, preferably greater than 30%, preferably greater than 50%.

[0173] The mixing of particles in a solvent can be carried out by any means, preferably with a mechanical agitator, an ultrasonic-assisted mechanical agitator, an ultra turrax®, or by acoustic resonance.

[0174] Optionally, the dispersion of particles can be controlled by ultrasound and / or by acoustic resonance.

[0175] The starting load may also optionally include:

[0176] - a dispersant, for example a lipopeptide or phosphate ester, preferably between 0.01% and 5% by mass based on the initial charge, and / or

[0177] - a binder, for example a maleic anhydride-isobutylene copolymer, of PVB (PolyVivylButyral), a soluble copolymer of isobutylene and maleic anhydride, a high molecular weight PEG (PolyEthyleneGlycol), i.e. greater than 800 g / mol, or even 1000 g / mol, preferably between 0.01% and 5% by mass based on the starting charge, and / or

[0178] - a plasticizer, preferably selected from phthalates, in particular BBP (ButylBenzylPhthalate), preferably between 0.01% and 5% by mass based on the starting charge.

[0179] The starting charge may take the form (a3) ​​of a powder comprising a mixture of ceramic particles and / or precursors of ceramic particles, and conductive particles.

[0180] Preferably, more than 90%, preferably more than 95%, preferably 100% of the powder particles, as a percentage by number, are ceramic particles and / or precursors of ceramic particles, and / or conductive particles and / or precursors of conductive particles.

[0181] The starting charge may take the form (a4) of at least two different powders, a first powder preferably comprising particles ceramics and / or ceramic particle precursors, a second powder comprising, preferably consisting of conductive particles.

[0182] Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles in the first powder, as a percentage by number, are ceramic particles and / or precursors of ceramic particles.

[0183] Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles of the second powder, as a percentage by number, are conductive particles and / or precursors of conductive particles.

[0184] When step b) involves the deposition of several superimposed layers, the starting charge can be a first powder made up of ceramic particles and / or precursors of ceramic particles to constitute certain layers, called "ceramic layers", and a second powder made up of conductive particles to constitute other layers, called "conductive layers".

[0185] In one embodiment, the substrate onto which the starting feedstock is deposited or integrated in step b) constitutes the ceramic phase or is a precursor of the ceramic phase, i.e., it is transformed into the ceramic phase in step c), preferably by sintering. It is then not necessary for the starting feedstock to contain ceramic particles or precursors of ceramic particles.

[0186] The starting charge can thus take the form (a5) of a "conductive" slip comprising conductive particles, preferably metallic, and / or precursors of conductive particles, or the form (a6) of a "conductive" powder comprising conductive particles and / or precursors of conductive particles. Preferably, more than 90%, preferably more than 95%, preferably 100% of the particles in the conductive slip or the conductive powder, by number percentage, are conductive particles and / or precursors of conductive particles.

[0187] In one embodiment, the starting charge takes the form (a7) of a "functionalized" slip or the form (a8) of a "functionalized" powder comprising ceramic particles and / or ceramic particle precursors on which conductive particles and / or conductive particle precursors are fixed.

[0188] The ceramic particles may in particular be platelets, for example in alumina, alpha-SiC or AIN.

[0189] Preferably, more than 90%, preferably more than 95%, preferably more than 98%, preferably more than 99%, by volume, of platelets have a length of less than 150 pm, preferably less than 100 pm, and / or preferably more than 5 pm, preferably more than 10 pm.

[0190] Preferably, more than 90%, preferably more than 95%, preferably more than 98%, preferably more than 99%, by volume, of platelets have an aspect ratio (length-to-thickness ratio of the plate) less than 70, preferably less than 50, and / or preferably greater than 10, preferably greater than 15, preferably greater than 20.

[0191] Shapes (a7) and (a8) advantageously allow the manufacture of a target part in which the sensor is integrated, for example as described in PCT / IB2013 / 060700.

[0192] The conductive particles may in particular be made of a metal chosen from Ag, Cu, Pt and Fe.

[0193] In step b), the starting charge is put into the form of a preform.

[0194] A first variant (bl) consists of depositing the starting charge on a substrate.

[0195] The substrate can be: • the target part for which the sensor is intended, or • a raw piece which, during step c), is transformed into the target piece at which sensor is intended for, or • a substrate independent of the target part, which can be temporary when separated from the measurement mass before use of the sensor, or permanent in the opposite situation.

[0196] When the substrate is the target part or a raw part of the target part, and is porous or fibrous, for example when the substrate is a woven, knitted, or braided textile, it is preferable to form the sensor by depositing one or more layers directly into the porosity of the target part.

[0197] If the substrate is a raw part of the target part, the sintering temperature of the raw part is preferably lower than the consolidation temperature of the preform.

[0198] The substrate is preferably the target part. Advantageously, the manufacture of the latter, and in particular the sintering operation of the possible raw part, does not risk damaging the sensor.

[0199] The target part is preferably a porous body with an open porosity greater than 1%, 3%, 5%, or 10%, preferably with open porosity oriented along a plane or preferred direction. The sensor's accuracy is advantageously improved along one or more deformation directions.

[0200] Preferably, the dimensions and / or orientation of the pores are determined according to the desired deformation behavior for the sensor.

[0201] In a preferred embodiment, the target part is a product, preferably sintered, comprising a plurality of frustoconical tubular pores, preferably macroscopic, preferably oriented along a preferred direction.

[0202] Preferably, the target piece conforms to the teaching of PCT / IB2013 / 060700.

[0203] In one embodiment, the substrate is a flexible, hand-flexible substrate, by example of the Flexiramics type manufactured by the company Eurekite, or a Nextel fabric.

[0204] The starting charge is preferably deposited on the substrate in any form, provided that it is suitable for the intended application.

[0205] In particular, with a starting charge in the form (al), the shaped starting charge can be massive. It can have a thickness greater than 1 mm, 5 mm or 10 mm and / or less than 20 mm.

[0206] Regardless of the shape of the starting charge (a1), (a2), (a3) ​​or (a4), the starting charge is preferably deposited on the substrate in the form of one, two or more layers. The successive layers may be identical or different.

[0207] In particular, with a starting charge in the form (a2) or (a4), layers of different natures can be fabricated. Preferably, a ceramic layer, i.e. a layer which comprises ceramic particles and / or precursors of ceramic particles but not conductive particles or precursors of conductive particles, follows a conductive layer, i.e. a layer which comprises conductive particles but not ceramic particles or precursors of ceramic particles, and / or a conductive layer follows a ceramic layer.

[0208] All deposition techniques adapted to the shape of the starting charge are possible.

[0209] When the target part is porous, the layer(s) can be deposited by impregnation of the target part.

[0210] The coating can be applied by tape pouring or spraying, preferably by tape pouring. The coating thickness is preferably between 0.05 mm and 3 mm, preferably between 0.1 mm and 1 mm.

[0211] Optionally, an electric or magnetic field is applied to orient and / or disperse the conductive particles. Advantageously, the electrical property can thus be different depending on the stress experienced by the sensor.

[0212] Tape casting is particularly suitable, preferably using electrophoresis or chemophoresis techniques to control the structure and orientation of the conductive particles during shaping. Spraying the starting charge, preferably at room temperature, typically around 20°C, is also effective.

[0213] The second variant (b2) consists of incorporating the starting charge into the mass of the substrate. Preferably, the starting charge is incorporated within the raw part of the target part or within the target part itself. Step c) then leads directly to a device according to the invention.

[0214] In the third variant (b3), the starting charge is shaped so as to constitute a raw part of the target part. In other words, the device according to the invention is identical with the sensor according to the invention, the target part constituting the sensor.

[0215] The starting charge can be configured in particular for the manufacture of a porous body, for example such as that described in PCT / IB2013 / 060700. It can include colloidal silica to facilitate eventual sintering.

[0216] The starting charge may in particular be in the form (al), (a3), (a7) or (a8).

[0217] Preferably, the elongated conducting particles and / or fine ceramic particles are oriented along a preferred direction or plane, preferably a preferred direction. The orientation of the particles can, for example, be modified magnetically or by a freeze-casting process, as described, for example, in PCT / IB2013 / 060700. The anisotropic (non-spherical) shape of a particle, for example, a platelet, rod, or grain-of-rice shape, or a multi-faceted shape, can promote its preferred orientation. A simple test can be performed to verify whether a particle is orientable.

[0218] Regardless of embodiment (bl), (b2) or (b3), if the starting charge after shaping includes a liquid phase, it is then dried, preferably at a temperature below 100°C, preferably below 80°C, preferably for a period of more than 2 hours, preferably more than 4 hours.

[0219] To manufacture a multilayer measuring mass, each deposited layer can be dried before depositing the next layer.

[0220] Drying leads to a preform.

[0221] In step c), the preform obtained in step b) is consolidated by heat treatment.

[0222] Optionally, prior to heat treatment, the preform may undergo a treatment to transform the ceramic particle precursors and / or the conductive particle precursors into ceramic particles and conductive particles, respectively. For example, a reduction treatment of conductive particle precursors, for example deposited as salts or gels, may be applied to transform these precursors into conductive metallic nanoparticles, preferably by: • thermal route, under controlled inert or reducing atmosphere, at a temperature below 1500°C; • chemical route.

[0223] For example, after an "electroless" deposition of a mixture of metal ions and a chemical reducer, the metal ions can be chemically reduced at less than 100°C, as described for example in US5681617A.

[0224] In one embodiment (bl), the starting charge is deposited on a substrate intended to be consolidated. In another embodiment (b2), the starting charge is incorporated into the mass of a substrate intended to be consolidated.

[0225] When the substrate is intended to be consolidated, the heat treatment is preferably adapted to simultaneously consolidate the preform and the substrate. This embodiment is particularly advantageous when the substrate is a raw part intended to be sintered to form the target part, and especially when the difference between the sintering temperature of the raw part and the sintering temperature of the preform is less than 50°C.

[0226] To manufacture a multilayer ceramic phase, consolidation can be carried out after each layer deposition or for all layers simultaneously.

[0227] Consolidation is preferably carried out in a conventional manner under a controlled oxidizing, neutral or reducing atmosphere, depending on the desired ceramic phase, preferably under a non-oxidizing atmosphere if the ceramic particles are in a non-oxide material.

[0228] Consolidation can be sintering.

[0229] Sintering can be carried out in air, particularly if the preform is made of a material with oriented porosity of the oxide type. Sintering can be carried out in a non-oxidizing atmosphere, particularly if the preform is made of a non-oxide material.

[0230] Sintering can preferably be carried out without pressure, in particular if the preform is made of a material with oriented porosity.

[0231] Sintering can be carried out under pressure, preferably by SPS (“Spark Plasma Sintering” in English).

[0232] Preferably, the SPS is carried out: • at a maximum temperature between 1300°C and 1700°C, preferably between 1450°C and 1550°C, and / or • at a pressure greater than 30 MPa, preferably greater than 40 MPa.

[0233] Sintering can also be carried out using a hot pressing process.

[0234] Sintering can be carried out at a temperature below 1600°C, below 1500°C, below 1400°C, below 1200°C, or even below 1000°C.

[0235] The sintering time is preferably less than one hour, which limits the migration and agglomeration of conductive particles, and thus improves the sensitivity of the sensor.

[0236] Sintering can be hydrothermal or solvothermal sintering, of the type introduced in 1972 by DM Roy et al.

[0237] Preferably, particularly if the filler is in the form of a slip (al1) or (a2) comprising ceramic particles, the thermal consolidation by sintering is carried out under a controlled inert or reducing atmosphere, at a temperature below 1600°C, preferably below 1500°C, preferably below 1400°C, with a sintering temperature plateau of less than 4 hours, preferably less than 2 hours, or even less than one hour.

[0238] The cooking process can be, for example, an rHLPD (“reactive Hydrothermal Liquid Phase densification”), developed by Riman of Rutgers University, or a CSP (“cold sintering process”), developed at Pennsylvania State University in Professor Clive A. Randall’s group.

[0239] Step c) leads to a measuring mass comprising a conductive network of conductive particles and a ceramic phase, preferably electrically insulating, preferably covering or encasing the conductive network.

[0240] At step d), the measuring mass resulting from the consolidation of the preform can be fixed on a support.

[0241] This step is optional. In particular, in some embodiments, the substrate can serve as a support.

[0242] In the embodiment where the measuring mass is not integrated into the target part or into a raw part of the target part, step c) does not lead to a device according to the invention, but to a sensor independent of the target part. The support can facilitate handling of the sensor, but also serve to modify its deformation behavior, in particular to adapt it to the deformations of the target part.

[0243] In embodiment (b2) where, in step b), the starting load is put in the form of the target part (third main embodiment), step c) leads to the fabrication of the sensor and the target part, which become one. No support is therefore required.

[0244] If the substrate is provisional, it can be separated from the preform after drying or separated from the measuring mass after consolidation.

[0245] An interface layer 9 can be added to the sensor so as to be interposed between the target part and the other elements of the sensor. In particular, it can be interposed between the support 8 and the target part 10, or, in the absence of a support, between the measuring mass and the target part 10.

[0246] To manufacture a device according to the invention, the following step is carried out after step c) or, where applicable, after step d):

[0247] e) fixing the sensor on the target part 10, so as to constitute a device according to the invention, for example of the type shown in [Fig.2].

[0248] The interface layer 9 can be an adhesive enabling this fixation.

[0249] Preferably, this glue is dried before use of the target part. It is preferably subjected to cooking in order to consolidate, preferably at a temperature lower than the consolidation temperature of the measuring mass in step c).

[0250] Step e) is particularly well suited when the target part is a fabric or part having a porous or fibrous texture, for example a fabric of glass fibers and / or fibers in a non-metallic inorganic material and at least partially crystallized. Use

[0251] The use of the sensor and device follows directly from the preceding description.

[0252] In step 1), a device according to the invention is manufactured, for example by fixing a sensor 2 on a target part 10 as shown in [Fig.1].

[0253] In step 2), the device is calibrated, that is to say a calibration curve 24 or 24' is determined providing, for each possible response M of the sensor 2, information on the physical state of the part, and in particular on the damage E, and preferably information on the amplitude of the damage.

[0254] The determination of the calibration curve (or “calibration”) is preferably carried out at a reference time prior to the first commissioning of the device according to the invention.

[0255] The M response measurements are preferably carried out at a temperature substantially equal to the service temperature at which the target part is intended to be used.

[0256] Preferably, calibration is performed on test devices identical to the device according to the invention, each of which is subjected to a specific stress. Any damage to the part is then observed. Preferably, any damage is measured, preferably without contact, preferably using X-rays, ultrasound, or a resonance method.

[0257] By applying increasing intensity constraints, it is thus possible to detect the minimum damage stress beyond which any stress leads to microcracking of the part, as well as the corresponding response of the sensor.

[0258] Increased damage, for example, the multiplication of microcracks, leads to increasing deformation of the sensor, and therefore causes the response M to change accordingly. In the region of the calibration curve corresponding to plastic deformation of the sensor, it is therefore advantageously possible to establish a relationship between a response M, i.e., a measure of said electrical property of the conductive network 7, and the magnitude of the damage.

[0259] Fatigue of the target part leads to fatigue of the conductive network, which can be measured by the evolution of the measured electrical property. The calibration curve thus makes it possible to establish a relationship between a response M and the amplitude of fatigue, even in the absence of perceptible deformation of the target part or the sensor.

[0260] In step 3), the sensor 2 is interrogated at the updated time and with the measuring device 16, to measure said electrical property and information on the state of the target part is deduced.

[0261] The time interval between the calibration time and the updated time can be, for example, greater than one week, two weeks, one month, two months and / or less than one year, or six months.

[0262] If said electrical property is an electrical resistance of the conductive network, the two cables of the measuring device 16, classically an ohmmeter, are conventionally connected to the connection terminals 18 ([Fig.l]).

[0263] The connection of the measuring device to the connection terminals can be deactivated, which is particularly useful when the inspection of the target part is carried out on an ad hoc basis. It can be non-deactivatable, i.e., permanent, particularly when the inspection is substantially continuous.

[0264] In a preferred embodiment, the measurement of said electrical property is carried out without contact with the sensor. In particular, the electrical property may be an inductance, which can conventionally be measured remotely.

[0265] The response M provided by the sensor may depend on its level of deformation or its state of fatigue.

[0266] Unlike strain gauges, the shape and length of the conductive particles in the sensor according to the invention make it possible to detect very small tensile and compressive deformations that appear on the target part during the damage phase, as well as to measure the fatigue state. The ceramic phase, which protects the conductive network, also allows the sensor to operate at high temperatures, preferably without additional cooling.

[0267] The sensor response M, i.e., the measured electrical property, is then analyzed by the analysis device 22, connected to the measuring device 16, preferably to provide information on possible damage to the part. More specifically, the analysis device uses the calibration curve 24 or 24' to determine damage information E on the target part.

[0268] In one embodiment, the condition of the target part is considered different depending on whether the measured value is above or below a threshold value that corresponds to a predetermined stress for the target part, or "threshold stress." For example, the threshold value may be determined such that beyond the threshold value, there is a risk of breakage or damage becomes unacceptable. In this case, the condition of the target part is considered "unsatisfactory." Otherwise, it is considered "satisfactory."

[0269] The threshold value depends on the target part, in particular its geometry and the material it is made of, but also on the applications and conditions of use The threshold stress can be determined by setting up a test assembly consisting of a target part with a sensor and measuring the effect of different stresses applied to the target part under similar operating conditions, particularly temperature, to those in the intended application. This allows the threshold value corresponding to the threshold stress to be determined.

[0270] In an embodiment where the sensor is used as a "strain sensor," the threshold value can be the measure at which the stress applied to the target part leads to the initiation of cracking or results in damage such that its use becomes dangerous or risky. The threshold stress can, in particular, be the stress applied to the target part beyond which the deformation of the target part is no longer elastic and becomes plastic.

[0271] The threshold value, i.e. the electrical property measured when the threshold stress is applied, is preferably greater than 100 times, or even 1000 times, the electrical property measured without the application of stress, at the same temperature.

[0272] When the measured electrical property exceeds the threshold value, the calibration curve advantageously allows for the assessment of the level of damage. The condition of the part can, for example, be described as "slightly cracked", "moderately cracked" or "severely cracked", depending on the value of the measured electrical property.

[0273] Depending on the condition of the target part thus determined, it is possible to identify the type of defect in the target part and / or to decide whether the target part remains usable or whether it must be replaced and / or to plan maintenance operations.

[0274] In an embodiment where the sensor is used as a "fatigue sensor," the threshold value can also be the electrical property beyond which the use of the target part becomes dangerous or risky. In this embodiment, the calibration curve 24' can also be used to provide an assessment at any given time of the fatigue state of the target part.

[0275] In one embodiment, the physical states determined according to the invention are processed statistically, for example by means of artificial intelligence algorithms, so as to improve decision-making. Examples of non-limiting applications: Microcrack detection

[0276] Figure 4 illustrates the deformation e of the target part (solid line) and the sensor conductive network (dashed line) of a device according to the invention, as a function of the stress Ca applied to the target part. Cr denotes the breaking stress of the target part and erM denotes the maximum deformation, corresponding to the breaking of the target part.

[0277] This min, or "minimum damage stress," of the target part is the smallest stress leading to damage of the target part by microcracking. The end of the elastic deformation range and the beginning of the plastic deformation range of the target part are considered to be defined by Cemin; stresses greater than or equal to Cemin lead to damage of the target part in the form of microcracking.

[0278] The sensor 2 exhibits elastic behavior as long as the applied stress Ca on the target part is less than the threshold stress Cs. Above the threshold stress, it deforms plastically. The portions of the curves corresponding to plastic deformations are shown in thick lines.

[0279] After the application of a stress Ca lower than the threshold stress Cs and the return to rest (absence of applied stress), the sensor therefore recovers its initial geometry as long as the threshold stress has not been reached or exceeded.

[0280] Preferably, the threshold stress, which corresponds to the plasticity limit of the sensor, is less than or equal to the minimum damage stress Ce min, i.e., Cs < Ce min. Any stress Ca applied to the target part that constitutes a damage stress producing microcracking, i.e., greater than the minimum damage stress Ce min, therefore produces plastic deformation of the sensor. In other words, plastic deformation of the target part only occurs when the sensor itself undergoes plastic deformation.

[0281] When a stress Ca greater than or equal to the minimum damage stress is applied, the sensor, and more specifically the conductive network, deforms plastically, thus retaining a "physical memory" of this application. The electrical properties of the conductive network, in particular its electrical resistance, vary depending on the geometry and / or structure of the network. The plastic deformation of the conductive network permanently alters its resistance. The sensor thus makes it possible to detect, by means of the calibration curve, that a damage stress has been applied, and therefore that the target part is microcracked.

[0282] In addition, the measurement of plastic deformation makes it advantageous to evaluate the extent of the damage stress, and therefore of the microcracking of the target part.

[0283] The arrow illustrates how the sensor reacts under the application of a damage stress on the target part, greater than Ce min: It first deforms elastically, until a threshold stress C s is applied to the target part, then plastically until the stress reaches Ce min. This plastic deformation allows, if the stress ceases, for a trace to be retained that stresses close to The stresses leading to damage to the target part through microcracking have been reached. If the stress continues to increase, it causes plastic deformation of the target part, in addition to the plastic deformation of the sensor. For example, it reaches stress C2, corresponding to deformation e2. When the stress then decreases until it reaches zero, this plastic deformation results in a residual deformation e3, which thus records the application of the maximum stress C2 applied to the target part.

[0284] In one embodiment, the plastic deformation range of the sensor begins while the ceramic part is still undergoing elastic deformation. The deformation sensor can thus memorize a high stress that did not lead to damage of the target part.

[0285] Preferably, the threshold stress is such that (Ce min - Cs)ICs < 20%. The sensor therefore deforms elastically when the stress applied to the target part is not close to the minimum damage stress, i.e. typically during normal operation of the target part.

[0286] To prevent the sensor from plastically deforming when the device has not been subjected to any microcracking damage stress, it is preferable that the threshold stress be as close as possible to the minimum damage stress. Preferably, (Ce min - Cs)ICs < 10%, preferably (Ce min - Cs)!Cs < 5%, preferably (Ce min - Cs)!Cs < 1%. The tolerance (Ce min - Cs)ICs depends on the intended application.

[0287] Preferably, the sensor is configured so that it is not destroyed by the application of any stress on the target part that does not lead to its breakage. In other words, the sensor remains operational as long as the stress applied to the target part does not cause it to break. In [Fig. 4], it can be seen in particular that the plastic deformation range of the sensor ends after the ceramic part has broken. The deformation sensor can thus memorize any stress that has led to damage to the target part.

[0288] The above example requires choosing a material for the ceramic phase which has a more limited elastic deformation range than the target part material and which preferably has a plastic range that extends beyond that of the target part material. Breakdown alert

[0289] In one embodiment, the sensor is chosen so as to break under the effect of a stress Cs' applied on the target part less than the stress Cr leading to the breakage of the target part, preferably less than Ce min.

[0290] Preferably, (Cr - CsyCs' < 20%, preferably (Cr - CsyCs' < 10%, preferably (Cr - Cs')!Cs' < 5%, preferably (Cr - CsyCs' < 1%.

[0291] Sensor failure thus leads to an alert, in an "all or nothing" mode, and triggers, for example, a shutdown alarm for the target part. Fatigue measurement

[0292] A sensor in the form of a patch is fixed to a SiC ceramic plate by means of a layer of thermosetting epoxy-based adhesive. The thickness of the adhesive layer is substantially constant and less than 0.5 mm.

[0293] The device thus manufactured is calibrated, as described above, by applying repeated stresses that do not lead to microcracking. This establishes a calibration curve that allows the fatigue state of the part to be evaluated, of the type of curve 24'.

[0294] The evolution of the electrical property, in this case the electrical resistance of the conductive network, is more gradual than during the detection of microcracks, which quickly lead to the destruction of the target part.

[0295] Of course, it is possible, with the same sensor or with different sensors, to assess both the level of fatigue and the risk of the appearance or occurrence of microcracks. The resistance value also allows, by means of the calibration curve, the assessment of the extent of fatigue and / or microcracking. Gas turbine

[0296] No device currently exists that allows for rapid, at any time and at low cost control of the integrity of ceramic parts used in applications where the temperature exceeds 350°C.

[0297] In the case of land-based turbines, ceramic tiles are conventionally positioned on the walls of the combustion chamber. These tiles are subjected to a strong thermal gradient (approximately 1500°C on the hot side and approximately 600°C on the opposite cold side, facing the combustion chamber). The sudden deterioration of a tile can have serious consequences, particularly if a tile fragment damages one of the turbine blades.

[0298] A starting charge is prepared in the form of a slip in which alumina particles approximately 1 micron in length and conductive particles, in the form of 100-nanometer platinum (Pt) fibers of the type described in WO2010003389A2, are mixed in isopropanol. The composition of the slip, in volume percentages, is preferably as follows: 15% platinum fibers, 30% alumina particles, and 55% solvent and shaping additives.

[0299] In one embodiment, the alumina particles are replaced by SiC or BN particles.

[0300] In one embodiment, the Platinum (Pt) fibers are replaced by carbon nanotubes.

[0301] A film of the slip is deposited by pouring onto a tile manufactured for example according to the teaching of WO2015011623A1, then dried at 110°C to obtain a film of average thickness of about 500pm.

[0302] In the sensor according to the invention obtained, the conductive particles are coated in the ceramic phase.

[0303] Platinum wires are connected to each end of the conductive network, so as to allow an electrical connection to an ohmmeter.

[0304] The sensor is then fixed to the cold side of a ceramic tile of a gas turbine, preferably by ceramic bonding or mechanical adhesion. In particular, the sensor can be fixed using Pyro-Putty #653 high-temperature ceramic adhesive supplied by Aremco.

[0305] It is observed that the precision of the sensor makes it possible to detect small variations in the electrical resistance of the conductive network, and therefore to anticipate the occurrence of harmful phenomena. Cooking support

[0306] A sensor according to the invention, in the form of a patch, is glued to the surface of a cooking support.

[0307] After each use of the cooking support, the electrical resistance of the conductive network is measured between two connection points. It is observed that the electrical resistance increases, presumably due to the progressive breaking of "bridges" between the conductive particles. Measuring the resistance thus allows for the advantageous estimation of fatigue in the target part. Abrasive grinding wheel

[0308] Measuring the electrical property of the sensor, preferably the electrical resistance of the conductive network, is also useful for evaluating the wear of an abrasive grinding wheel.

[0309] A sensor can be disposed on the surface of an abrasive grinding wheel, preferably in the form of a patch glued to the side of the grinding wheel, preferably perpendicular to the working surface of the grinding wheel.

[0310] The sensor is preferably "integrated" into the target workpiece. In particular, the ceramic particles of the sensor may be abrasive grains from the grinding wheel or, preferably, be dispersed in all or part of the matrix that binds the abrasive grains. of the grinding wheel, particularly when the abrasive grains are too large to form fine ceramic particles.

[0311] The sensor can thus be used to measure the progressive reduction in the volume of the grinding wheel during its use, and to assess its integrity. This information advantageously allows for optimal management of the use and replacement of the grinding wheel. Sensor in the form of a CMC

[0312] Conductive particles are incorporated into a ceramic nonwoven or into a ceramic woven made of ceramic fibers, preferably oriented along a preferred plane, preferably along a preferred direction.

[0313] The conductive particles are preferably manufactured by functionalizing ceramic fibers, identical or different from the ceramic fibers that constitute the ceramic nonwoven. The functionalization methods described above can be implemented for this purpose.

[0314] The incorporation of conductive particles can be carried out by tape casting, by pressing or by layer deposition.

[0315] The structure made up of the ceramic nonwoven in which the conductive particles have been incorporated is then sintered, preferably until an open porosity of less than 10%, preferably less than 5%, and preferably greater than 1% is obtained. Sensor in the form of a thin plate

[0316] Alumina platelets having a length between 10 and 100 pm and an aspect ratio between 20 and 50, and conductive particles of a metal selected from Ag, Cu, Pt and Fe are dispersed in isopropanol to constitute a slip.

[0317] Precursors of conductive particles can be used to replace, at least in part, the conductive particles. They are then reduced to be transformed into said conductive particles.

[0318] The slip is cast in strips (“tape casting”), in the conventional manner. The thickness of the strip is preferably between 100 and 600 micrometers in order to orient the plates.

[0319] The strip is then preferably sintered until an open porosity of less than 10%, preferably less than 5%, and preferably greater than 1% is obtained.

[0320] A thin plate is obtained, whose behavior is anisotropic due to the orientation of the platelets. The conductive particles create a conductive network oriented preferentially parallel to the platelets. porous sensor

[0321] A sintered porous body is manufactured following the teaching of PCT / IB2013 / 060700.

[0322] The porous body preferably has a volume porosity of between 30% and 70%, preferably between 40% and 60%.

[0323] The porous body has substantially parallel tubular pores. The platelets used may be, in particular, alumina, alpha-SiC, or AlN platelets. They preferably have a length between 10 and 100 pm and an aspect ratio between 20 and 50.

[0324] The porous body is then impregnated with a slip consisting of conductive particles, preferably metallic, suspended in a solvent (form (a5)). The quantity of conductive particles is adapted to obtain, after drying, a conductive network whose electrical resistance can be modified by deformation and / or fatigue.

[0325] The length of the conducting particles is less than 1 pm, preferably less than or equal to 100 nm.

[0326] Impregnation can be carried out under vacuum or, more generally, by creating a pressure gradient that promotes the penetration of the slip into the tubular pores.

[0327] The deposition of conductive particles can also be carried out by spraying the slip, preferably at room temperature.

[0328] The deposition of conductive particles can also be carried out by infiltration of the slip, preferably under a residual pressure of 0.1 bar or less, and preferably at ambient temperature. In this embodiment, the viscosity of the slip, measured at ambient temperature, is preferably between 0.5 and 20 centipoise. The infiltration time is preferably from 5 minutes to several hours, depending on the thickness of the porous body. The slip is preferably a colloidal solution.

[0329] In particular in this latter embodiment, the porous body can be replaced by the raw body which, by sintering, leads to the porous body.

[0330] Conductive particles can be replaced by conductive particle precursors, which are then reduced to metallic conductive particles. In particular, a mixture of metal ions and a chemical reducing agent can be deposited electroless, the metal ion, as described, for example, in US 5681617A, preferably below 100°C, preferably at room temperature. A catalyst, in particular a catalytic metal, can be added to the mixture to accelerate the transformation of the conductive particle precursors into conductive particles.

[0331] To improve the fixation of metallic particles or precursors of conductive particles, the porous body can be functionalized with a thiol or a silane. In particular, silane may have a polar group such as an amine, phosphonate, sulfonate or carboxylate group.

[0332] After drying at a temperature between 50°C and 150°C, and optional treatment to transform the precursors of conductive particles into conductive particles, a conductive network is obtained that extends over the surface of the pores. This conductive network is advantageously protected by the porous body. It is also advantageously preferentially oriented because it rests on preferentially oriented pores.

[0333] Impregnation or percolation can be total or, preferably partial, so as to size the conductive network as desired.

[0334] Preferably, after deposition of the conductive particles or precursors of the conductive particles, a layer of ceramic particles forming a ceramic phase is preferably deposited above said conductive particles or precursors of the conductive particles. Advantageously, this layer provides electrical insulation and physical protection.

[0335] Preferably, the process is adapted so that the residual open porosity of the porous body thus obtained, which constitutes a sensor according to the invention, is between 1 and 10% by volume. Advantageously, this sensor exhibits a range of plastic deformability.

[0336] To ensure the connection between the connecting terminals and the conductive network formed in the open porosity, a metallic film, preferably in a metal chosen from Cu, Au, Pt, Pd, Ag, Sn, Al, Ni, Pb, Zn and their alloys, can be made by metallization / spraying onto the surface of the porous body and in contact with the conductive network.

[0337] In one embodiment, the conductive particles are mixed with the alumina platelets before the formation of the porous body. Preferably, they represent more than 10% by mass of the particles, the remainder to 100% being made up of alumina platelets.

[0338] As is now clear, the invention thus provides a sensor in which the ceramic phase provides thermal and / or abrasion protection to the conductive network. It allows, in a simple manner, to • detect past application of a damage stress on a target part, for example thermal or mechanical shock, at a temperature above 400°C, • evaluate said stress and / or said damage, in particular microcracking and / or fatigue of the target part.

[0339] The invention is advantageously applicable to target parts of any geometry. Furthermore, the invention does not substantially alter the overall size of these parts.

[0340] Finally, the invention makes it possible to detect small amplitude deformations, the sensor being very sensitive. It therefore allows the detection of weak signals, and thus the anticipation of catastrophic degradation of the target part.

[0341] Of course, the invention is not limited to the embodiments described and represented, which are provided for illustrative purposes only.

[0342] In particular, the position of the sensor on the part and the number of strain sensors are not limiting.

Claims

Demands

1. A sensor for monitoring a target part at a temperature above 400°C, the sensor comprising: - an array of electrically conductive particles (6), at least a portion of the conductive particles constituting a conductive network (7) whose electrical property is a function of an arrangement of the conductive particles constituting the conductive network, said arrangement being modifiable, more than 90% of the conductive particles, referred to as "elongated conductive particles", by number percentage, having a form factor greater than 2 and a thickness less than 1000 nanometers, - a ceramic phase (4) for protecting the conductive network, the ceramic phase being composed of ceramic particles, the ceramic phase comprising more than 90% of ceramic particles having a length between 0.1 and 100 pm, referred to as "fine ceramic particles", by number percentage,the shape ratio of a particle being equal to the ratio of the length of said particle divided by the thickness of said particle, the conductive particles being made of a material having an electrical resistivity, measured at 20°C, of ​​less than 1 mQ.m and the ceramic particles being made of a material having an electrical resistivity, measured at 20°C, greater than 1 Qm, the arrangement of the conductive particles being "modifiable" in that, under the effect of a stress, the arrangement of the conductive particles of the conductive network is modified so that there results in a modification of the impedance of the conductive network.

2. Sensor according to the preceding claim, wherein more than 90% of the elongated conductive particles, by number percentage, have a form factor greater than 5.

3. Sensor according to the immediately preceding claim, wherein more than 90% of the elongated conductive particles, as a percentage by number, have a form factor greater than 100.

4. Sensor according to the immediately preceding claim, wherein more than 90% of the elongated conductive particles, as a percentage by number, have a form factor greater than 1000.

5. Sensor according to any one of the preceding claims, wherein the elongated conducting particles have a thickness of less than 500 nanometers.

6. Sensor according to any one of the preceding claims, wherein at least the elongated conducting particles are - fibers of a metal or metalloid, preferably Platinum, and / or - carbon nanotubes and / or composite particles having a non-conducting core coated with a coating, at least partial, of a metal or metalloid, and / or - composite particles having a ceramic core functionalized throughout so as to be electrically conductive, and / or wherein the ceramic phase consists, for more than 80% of its mass, of one or more compound(s) selected from the group formed by Al2O3, ZrO2, Cr2O3; MgO, CaO, SiO2, SiC a or [3, BN, B4C, C in the form of diamond, Si3N4, AIN, and Silicon oxynitrides including SiAlON.

7. Sensor according to the immediately preceding claim, wherein the elongated conductive particles are made up, for more than 80% of their mass, of one or more constituents chosen from the group formed by Ag, Al, Au, Cu, Fe, Ge, Mo, Ni, Pd, Pt, Rh, Si, Ta, Ti, W, graphite, graphene, TiB2, TiC, TiN, ZrB2, ZrC, ZrN, VB2, VC, VN, CrB2, CrBN and WC.

8. A sensor according to any one of the preceding claims, wherein the elongated conductive particles are made of a material having an electrical resistivity of less than 10 pQ.m and the fine ceramic particles are made of a material having an electrical resistivity greater than 1 Qm

9. A sensor according to the immediately preceding claim, wherein the elongated conductive particles are made of a material having an electrical resistivity of less than 1 pQ.m and the fine ceramic particles are made of a material having an electrical resistivity greater than 1000 Ωm

10. Sensor according to any one of the preceding claims, in which - the elongated conductive particles of the conductive network are distributed homogeneously in the ceramic phase, or - the elongated conductive particles of the conductive network are distributed in at least one layer, called the "conductive layer", and the ceramic particles of the ceramic phase are distributed in at least one layer, called the "ceramic layer", said conductive and ceramic layers being superimposed on each other.

11. Sensor according to any one of the preceding claims, wherein the elongated conducting particles and / or the fine ceramic particles and / or the conducting network (7) have a preferred orientation.

12. Sensor according to any one of the preceding claims, wherein the conductive network forms a closed circuit on itself.

13. Sensor according to any one of the preceding claims, wherein the ceramic phase forms a continuous layer interposed between the conductive network and the external environment of the sensor.

14. Sensor according to any one of the preceding claims, in which comprising a fibrous ceramic phase in which the conductive particles of the conductive network are dispersed.

15. Sensor according to any one of the preceding claims, wherein the ceramic phase is sintered.

16. A method for manufacturing a sensor according to any one of the preceding claims, intended for monitoring the physical state of a target part, the method comprising the following steps: a) preparing a starting charge - in a form (a1) of a slurry comprising - ceramic particles and / or ceramic particle precursors, and - conductive particles and / or conductive particle precursors; or - in a form (a2) of a first slurry comprising ceramic particles and / or ceramic particle precursors, and a second slurry, different from the first slurry, comprising conductive particles and / or conductive particle precursors; or - in a form (a3) ​​of a powder comprising - ceramic particles and / or ceramic particle precursors, and - conductive particles and / or precursors of conductive particles; or - in a form (a4) of a first powder comprising ceramic particles and / or precursors of ceramic particles, and a second powder, different from the first powder, comprising conductive particles and / or precursors of conductive particles or - in the form (a5) of a slip comprising conductive particles and / or precursors of conductive particles; or - in the form (a6) of a powder comprising conductive particles and / or precursors of conductive particles; or - in the form (a7) of a slip comprising ceramic particles and / or precursors of ceramic particles, to which conductive particles and / or precursors of conductive particles are fixed; or - in a form (a8) of a powder comprising ceramic particles and / or precursors of ceramic particles, on which conductive particles and / or precursors of conductive particles are fixed; b) shaping the initial charge so as to obtain a preform, said shaping being (bl) by depositing the starting charge, preferably in the form of one or more layers, preferably, when the starting charge is in the form (al1), (a2), (a5) or (a7), by strip casting or spraying, preferably by strip casting, preferably to a thickness of between 0.05 and 3 mm, onto a substrate, temporary or permanent, preferably onto a raw piece of the target part or onto the target part, or (b2) by integrating the starting charge into the mass of a substrate, preferably in a raw piece of the target piece or in the target piece, preferably, when the starting charge is in the form (a1a), (a2) or (a5), by impregnation of the substrate, or (b3) where the starting charge is in the form (al1), (a3), (a7) or (a8), by shaping the starting charge into the form of the target part or a raw part of the target part, then, if the initial shaped charge includes a liquid phase, drying of the initial shaped charge; c) thermal consolidation of the preform so as to obtain a measuring mass consisting of a conductive network made up of conductive particles and a ceramic phase; d) optionally, fixing the measuring mass on a support and / or fixing an interface layer on the measuring mass and / or on the support, the ceramic particles, ceramic particle precursors, conductive particles and conductive particle precursors being chosen so as to obtain, at the end of step c) or step d), a sensor according to any one of the preceding claims.

17. A manufacturing method according to the immediately preceding claim, wherein the shaping in step b) comprises an operation of orienting the conductive particles along a preferred plane or direction.

18. A manufacturing method according to any one of the two immediately preceding claims, wherein the substrate is a porous body having an open porosity greater than 30% by volume and / or is fibrous.

19. A manufacturing method according to the immediately preceding claim, wherein the porous body has an oriented open porosity.

20. A manufacturing method according to any one of the two immediately preceding claims, wherein, in step b), - metallic particle precursors or conductive particle precursors in a ceramic material are deposited on pores inside the porous body, and then said precursors are thermally or chemically reduced to constitute the conductive particles, or - a slurry consisting of metallic particles or conductive particles in a ceramic material, suspended in a solvent, is deposited on pores inside the porous body, and then the solvent is evaporated, so as to constitute a conductive network.

21. A manufacturing method according to the immediately preceding claim, wherein after deposition of the conductive particles, a layer of ceramic material is deposited on the conductive network, and, preferably, said layer is sintered.

22. Device comprising a target part and a sensor according to any one of claims 1 to 15, the sensor being fixed to or integrated into the target part, so that the conductive network deforms under the effect of a stress applied to the target part.

23. Device according to the immediately preceding claim, wherein the conductive particles and the ceramic phase have the form of different and superimposed layers.

24. Device according to any one of the two immediately preceding claims, wherein the target part has - an open porosity greater than 5% by volume and the conductive particles of the conductive network are fixed to the surface of the open pores, or - the conductive network extends into a binding phase which binds grains of the target part.

25. Device according to the immediately preceding claim, wherein the target part has an open porosity oriented preferentially parallel to a preferred plane or preferred direction.

26. Device according to any one of the two immediately preceding claims, wherein the conductive network is covered, at least partially, with a ceramic phase in the form of a layer.

27. ​​Device according to any one of the five immediately preceding claims, wherein the target part is made of a ceramic material and / or of a glass and / or of a glass-ceramic and / or of a ceramic-phase composite.

28. Device according to any one of the six immediately preceding claims, wherein the target part is a fragile part.

29. A device according to any one of the seven immediately preceding claims, wherein the target part is selected from a group consisting of a refractory tile, a ceramic part of a solar absorber, a baking support, a refractory kiln block, an abrasion protection part, a bonded abrasive, a ceramic cutting tool, an element of ceramic pump or hydraulic circuit, ceramic electrical insulating support or tube, ceramic tile or ceramic or glass-ceramic facing piece, plate, tube comprising a glass-ceramic material, brake pad or disc or ceramic object of a braking device, glazing, filter for liquid or gaseous filtration, radome.

30. Kit comprising - a device according to any one of the eight immediately preceding claims, and - a measuring apparatus adapted to measure, after connection between two connection terminals of the conductive or non-contact network, an electrical property of the conductive network.

31. A method for monitoring the physical state of a target part, said method comprising the following steps: 1) at an initial time, fixing a sensor according to any one of claims 1 to 15 on the target part or integrating a sensor according to any one of claims 1 to 15 into the target part, so as to constitute a device according to any one of claims 22 to 29; 2) calibrating the device so as to determine a relationship between said physical state and an electrical property of the sensor's conductive network; 3) putting the device into service in an environment at a service temperature, then, at a current time, measuring said property at said service temperature and, from said relationship, determining said physical state at the current time.

32. A monitoring method according to the immediately preceding claim, wherein the operating temperature is greater than 400°C.

33. A monitoring method according to the immediately preceding claim, wherein the operating temperature is greater than 700°C.

34. A monitoring method according to any one of the three immediately preceding claims, wherein the calibration is carried out from electrical property measurements taken at said service temperature.

35. A monitoring method according to any one of the four immediately preceding claims, wherein the Determination of said physical state includes detection of microcracking and / or detection or measurement of fatigue of the target part.

Images