DE102016115183A1 - Porous material, powder for producing a porous material, process for producing a porous material and component - Google Patents

Abstract

The invention relates to a porous material, in particular a potting compound for a sensor, wherein the porous material, in particular the potting compound according to the invention, a specific electrical resistance of at least 105 Ω · cm, in particular of at least 106 Ω · cm, at a temperature of 1000 ° C. having.

Description

The invention relates to a porous material, in particular to a potting compound for a sensor. The invention further relates to a powder for producing a porous material comprising metal oxide particles, in particular aluminum oxide particles (Al ₂ O ₃ ) and / or magnesium oxide particles (MgO) and / or beryllium oxide particles (BeO). Moreover, the invention relates to a method for producing a porous material, in particular a porous material according to the invention. Furthermore, the invention relates to a component with a coating and / or embedded in a potting compound, wherein the coating and / or the potting compound is a porous material according to the invention or a porous material produced according to the invention.

Sensors must be protected against chemically aggressive environments. For example, sensors in the exhaust line of an automobile must be protected from a chemically aggressive environment. A sensor embedded in a housing must also meet requirements for corrosion resistance and / or thermal shock resistance and / or vibration resistance.

Casting compounds based on phosphate cement are known from the prior art. However, such potting compounds have an increasing electrical conductivity at high temperatures. In addition, phosphate cement is chemically reactive.

Furthermore, it is known to ausuberulvern the housing in which the sensor is located. Disadvantage of such an embodiment of a sensor is the insufficient thermal shock and vibration resistance.

The invention is based on the object of specifying a further developed porous material, in particular a potting compound for a sensor. The porous material, in particular the potting compound is to be developed such that the porous material, in particular the potting compound at high temperatures acts electrically insulating. Furthermore, the porous material, in particular the potting compound, should be resistant to thermal shock and vibration. Preferably, the porous material, in particular the potting compound, should be suitable for use within a sensor housing, wherein the sensor is preferably a platinum thin-film sensor.

Furthermore, it is an object of the present invention to provide a powder for producing a porous material, in particular for producing a potting compound. Another object of the invention is to provide a further developed method for producing a porous material, in particular a potting compound for a sensor. It is another object of the present invention to provide a further developed component with a coating and / or embedded in a potting compound, wherein the coating and / or the potting compound is further developed according to the invention.

According to the invention this object is achieved with regard to a porous material by the features of claim 1. With regard to a powder for producing a porous material, the object is achieved by the features of claim 7. With regard to a method for producing a porous material, the object is achieved by the features of claim 11. With regard to a component with a coating and / or embedded in a potting compound, the object is achieved by the features of claim 18.

The invention is based on the idea of a porous material, particularly a sealing compound for a sensor to indicate the electrical resistivity of the porous material, in particular of the sealing compound for a sensor, at least 10 ⁵ Ω · cm, especially at least 10 ⁶ Ω · cm at a temperature of 1000 ° C.

The determination of the specific electrical resistance (RS) of the porous material, in particular the potting compound for a sensor, is preferably carried out with a 4-point measurement or a 2-point measurement according to the Standard ASTM D257-07 , For this purpose, a substrate, for example glass with the size of, for example, 20 mm × 60 mm is provided. The porous material to be examined, in particular the potting compound for a sensor, is applied to the substrate. The respective ends are provided with flat metal strips. The metal strips are arranged parallel to each other at a distance of eg 10 mm. A power source (Keithley 2000) is connected to the two contacts and set a current value.

In the case of the 4-point measurement, the potential drop between the metal strips is measured with two pressed test probes and a potentiometer (Hewlett-Packard 4355A) and the surface resistance (SR) is determined. The layer thickness (d) is determined on a layer produced in parallel. For the specific electrical resistance: RS = SR · d.

The high electrical resistivity of the potting compound at a temperature of 1000 ° C causes a sensor even when supplied for example in the exhaust system high temperatures provides accurate readings.

The porous material may comprise metal oxide, in particular aluminum oxide (Al ₂ O ₃ ) and / or magnesium oxide (MgO) and / or beryllium oxide (BeO).

Preferably, the porous material is characterized in that the pores are interconnected and form a perculatory system. Such metal oxides or mixtures of such metal oxides are, for example, chemically neutral to platinum, so that the porous material according to the invention can serve in particular as a potting compound for a platinum sensor.

The porous material may comprise high purity alumina, with the purity of the alumina (Al ₂ O ₃ ) being at least 99.99%. Particularly preferably, the porous material consists only of highly pure aluminum oxide (Al ₂ O ₃ ), wherein the degree of purity of the aluminum oxide (Al ₂ O ₃ ) is at least 99.99%. Such a pure alumina ensures extremely good electrical insulation.

Preferably, the carbon content (C) of the porous material is less than 1,000 ppm, in particular less than 500 ppm, in particular less than 250 ppm, in particular less than 100 ppm, based on the total mass of the porous material.

Furthermore, the proportion of an element selected from the group consisting of:
Lithium (Li), sodium (Na), potassium (K), boron (B), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), indium (In), thallium (Tl), Phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), zinc (Zn), cadmium (Cd), silver (Ag) and Mercury (Hg)

less than 100 ppm based on the total mass of the porous material. Several elements of said group preferably have a total content of less than 1000 ppm based on the total mass of the porous material. In other words, the proportion of individual elements selected from the above group is less than 100 ppm. If there are several elements selected from the above-mentioned group, the proportion of the sum of all elements is less than 1,000 ppm based on the total mass of the porous material.

The porosity of the D of the material is preferably 25% to 50%. The pore volume of the porous material is preferably 0.05 cm ³ / g to 0.5 cm ³ / g. Particularly preferably, the porosity is 35%, the pore volume is in a particularly preferred embodiment 0.14 cm ³ / g.

The porosity and / or the pore volume are preferably determined by means of mercury porosimetry. To carry out a mercury porosimetry, it is preferable to use devices from Porotec (Pascal 140 in the low-pressure range, Pascal 440 in the high-pressure range). According to the Standard DIN 66133 The pore volume distribution and the specific surface area of solids are determined by mercury intrusion. Preferably, the relevant layer of the porous material is baked at 200 ° C for about 1 h before the measurement.

The porous material may further have a pore size d50 of 50 to 150 nm. In other words, the pore size may have a d50 value (median) of 50 to 150 nm. In a particularly preferred embodiment, a d50 value for the pore size is 88 nm.

The pore size, in particular the determination of the d 50 value (median), is preferably determined by means of mercury porosimetry, as has already been described. Furthermore, it is possible that this value is determined by microscopy.

The thermal expansion coefficient of the porous material may be in a range of 6 × 10 ^-6 / K to 15 × 10 ^-6 / K. In other words, the thermal expansion coefficient of the porous material is preferably 6 × 10 ⁶ / K to 15 × 10 ⁶ / K. In a further embodiment of the invention, the thermal Extension 6.5 · 10 ⁶ / K to 8.5 · 10 ⁶ / K amount. The thermal expansion is determined, for example, by means of dilatometry.

Furthermore, the 3-point bending strength of the porous material is preferably at least 20 N / mm ² . In a particularly preferred embodiment of the invention, the 3-point bending strength is 46 N / mm ² .

The porous material, which is designed in particular as potting compound for a sensor, combines several advantages. Accordingly, the porous material has an extremely good electrical insulation. In addition, the porous material has a high strength. The porous microstructure of the porous material further allows for oxygen delivery to the sensor. Furthermore, the porous material is chemically neutral to platinum and absorbs metal and metal oxide vapors emanating, for example, from a protective sleeve.

Due to the purity of the material used, in particular the alumina used, a lower poisoning of a sensor, in particular a platinum sensor is achieved. Due to the porosity of the material, a filter function can be achieved.

The porous material, in particular the potting compound for a sensor, is in particular a fired or sintered material.

Another aspect of the invention relates to a powder for producing a porous material. In particular, this aspect of the invention relates to a powder for producing a porous material according to the invention. The powder comprises metal oxide particles, in particular aluminum oxide particles (Al ₂ O ₃ ) and / or magnesium oxide particles (MgO) and / or beryllium oxide particles (BeO).

According to the invention, the powder comprises at least two particle fractions, in particular at least three particle fractions, the particle sizes d50 of the respective particle fractions having different values.

The grain size d50 is a median value.

In a particularly preferred embodiment, the powder has high-purity aluminum oxide (Al ₂ O ₃ ), wherein the degree of purity of the aluminum oxide (Al ₂ O ₃ ) is at least 99.99%. In yet another highly preferred embodiment of the invention, the powder consists only of high-purity alumina (Al ₂ O ₃ ), wherein the degree of purity of the alumina Al ₂ O _{3 is} at least 99.99%.

The carbon content of the powder is preferably less than 1,000 ppm, preferably less than 500 ppm, in particular less than 250 ppm, in particular less than 100 ppm, based on the total mass of the powder.

The powder may have further elements, wherein the proportion of an element selected from the group consisting of:
Lithium (Li), sodium (Na), potassium (K), boron (B), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), indium (In), thallium (Tl), Phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), zinc (Zn), cadmium (Cd), silver (Ag) and Mercury (Hg)

less than 100 ppm based on the total mass of the powder. Several elements of said group preferably have a total content of less than 1000 ppm based on the total mass of the powder. In other words, the proportion of individual elements selected from the above group is less than 100 ppm. If there are several elements selected from the above group, the proportion of the sum of all elements is less than 1,000 ppm.

The purity of the powder, in particular of the Al ₂ O ₃ powder, is determined by means of emission spectrometry. For measurement, ICP spectrometers of the type iCAP 6500 duo or iCAP 7400 duo from the manufacturer ThermoFisher Scientific are used.

The measurements are made according to the Standard DIN EN ISO 11885 carried out. In the case of aluminum oxide (Al ₂ O ₃ ) powder, 100 mg of the sample are mixed with 8 ml of hydrogen chloride (HCl), 2 ml of nitric acid (HNO ₃ ) and 1.5 ml of hydrogen fluoride (HF) and digested using a microwave pressure digestion. Subsequently, the dissolved sample is transferred to a sample tube and filled with ultrapure water. The Measuring solution is pumped into the measuring device where it is atomized and the aerosol is introduced into an argon plasma. There, the components of the sample are vaporized, atomized, excited and partially ionized. The light emitted when the atoms / ions return to the ground state is subsequently detected. The wavelengths of the emitted light are characteristic of the respective elements contained in the sample. The intensity of the wavelengths is proportional to the concentration of each element.

The first particle fraction of the powder according to the invention preferably has a particle size d50 of 10 nm to 1000 nm. The second particle fraction preferably has a particle size d50 of 0.5 μm to 50 μm. The particle sizes are preferably determined by means of laser diffraction.

In a particularly preferred embodiment, the powder comprises a third particle fraction with a particle size d50 of 30 μm to 120 μm.

The metal oxide particles of the powder according to the invention for producing a porous material can thus have a particle size d50 of 0.001 μm to 120 μm.

The particle fractions can be present in a specific mixing ratio: First particle fraction: 5-20% by weight Second particle fraction: 40-70% by weight Third particle fraction: 10-40% by weight.

Due to such a mixing ratio, in particular due to the use of particle fractions with nanoscale particles, a good sintering result in the production of the porous material can be achieved even at low temperatures with the aid of the powder according to the invention. With regard to the particle size distribution is based on a measurement method according to Standard DIN EN 725-5 proceed. For the measurement of particles in the size range 1 μm to 100 μm, a laser diffraction device from Sympatec (Helos 0724) is used. For the measurement of particles in the size range smaller than 1 .mu.m, a laser diffraction device from Horiba (LA-950) is used.

The powder according to the invention for producing a porous material can also be used for producing a mineral-insulated conductor, or for producing a mineral-insulated pipe.

Another subsidiary aspect of the invention relates to a method for producing a porous material, in particular a method for producing a porous material according to the invention.

• a) Herstellen einer Dispersion aus einem Pulver, das Metalloxidpartikel umfasst, insbesondere aus einem erfindungsgemäßen Pulver, und aus einem Lösungsmittel, insbesondere einem anorganischen Lösungsmittel, besonderes bevorzugt Wasser;
• b) Bereitstellen einer Form oder eines Trägers;
• c) Befüllen der Form mit der Dispersion oder Beschichten des Trägers mit der Dispersion.

The process according to the invention is characterized by the following process steps:

• a) producing a dispersion from a powder comprising metal oxide particles, in particular from a powder according to the invention, and from a solvent, in particular an inorganic solvent, particularly preferably water;
• b) providing a mold or a carrier;
• c) filling the mold with the dispersion or coating the support with the dispersion.

It is possible that the dispersion may contain other components, e.g. Additives and / or defoamers and / or flow aids and / or stabilizers.

• d) Erwärmen der befüllten Form/des beschichteten Trägers und anschließendes
• e) Abkühlen der befüllten Form/des beschichteten Trägers sowie optional
• f) Entfernen der Form/des Trägers.

The method according to the invention may further comprise the following steps:

• d) heating the filled form / carrier and then
• e) cooling the filled form / carrier and optional
• f) removing the mold / carrier.

The step c), in particular the filling of the mold, can be carried out under reduced pressure.

If a component is to be provided with a coating and / or embedded in a potting compound, this component should be at least temporarily fixed in the mold. The fixing of a component takes place in step b).

In particular, after step f), ie after the mold and / or the carrier has been removed, the porous material can be ground and / or polished and / or drilled and / or milled and / or welded and / or soldered in a further processing step.

The solids content of the dispersion is preferably 70% by weight -90% by weight. The solids content of the dispersion is particularly preferably 85% by weight. The solids content can be determined in a simple weighing process.

Furthermore, it is possible that the viscosity of the dispersion is 5 Pa · s-15 Pa · s. The viscosity of the dispersion is preferably in accordance with Standard DIN 53019 determined with a Brookfield rheometer DV3T.

In step d), the mold / coated support is preferably heated to a temperature of 100 ° C.-1,400 ° C., in particular from 400 ° C.-1,100 ° C., in particular from 600 ° C.-900 ° C.

The volume shrinkage between steps c) and e) is preferably less than 5%. In a particularly preferred embodiment of the invention, the volume shrinkage between steps c) and e) is less than 4%.

• 1. Ein Reagenzglas wird mit der Dispersion gefüllt.
• 2. Die Füllhöhe der Dispersion nach dem Befüllen (h1) wird bestimmt.
• 3. Die Dispersion wird im Reagenzglas bei Raumtemperatur mindestens 48 h getrocknet und danach aus dem Reagenzglas entnommen.
• 4. Der Grünkörper wird bei Temperaturen von 600 °C - 900 °C ausgeheizt.
• 5. Die Höhe (h2) des Festkörpers nach dem Ausheizen wird bestimmt.

The measurement of the volume shrinkage of the porous material, in particular the casting compound, between steps c) and e), in particular during heating, is carried out as follows:

• 1. A test tube is filled with the dispersion.
• 2. The filling level of the dispersion after filling (h1) is determined.
• 3. The dispersion is dried in the test tube at room temperature for at least 48 h and then removed from the test tube.
• 4. The green body is baked at temperatures of 600 ° C - 900 ° C.
• 5. The height (h2) of the solid after annealing is determined.

For volume shrinkage during heating (DV) the following applies: DV = (h1 - h2) / h1 · 100%.

The mold and / or the support may be made, for example, of metal and / or a metal alloy and / or a ceramic and / or of glass ceramic and / or of wood and / or paper and / or polymer and / or plastic. The shape may further be formed as a tube or as a sleeve or as a box or as a ball or as a hemisphere.

On the other hand, the carrier may be formed as a film or plate or substrate or as a layer.

In one embodiment of the invention, the mold may be a lost mold. Furthermore, it is possible that the mold after step c), in particular after a drying process, but which is not associated with a heating step according to step d) is removed.

In the context of the method according to the invention, it is possible that in step b) in the form or on the support to be coated and / or embedded component, in particular an electrical component and / or an electronic component and / or a wire and / or a pipe and / or a sensor, in particular a platinum sensor, and / or a connector and / or a sleeve and / or a single-core or multi-core coaxial cable, is / are arranged.

In connection with the method according to the invention for the production of a porous material, there are similar advantages to those already mentioned in connection with the porous material and / or the powder according to the invention for producing a porous material.

A further subsidiary aspect of the invention relates to a component with a coating and / or a component which is embedded in a potting compound, wherein the coating and / or the potting compound is a porous material according to the invention and / or a porous material produced according to the invention.

The component may be a sensor, in particular a temperature sensor. The component is preferably installed in the exhaust gas flow and / or engine system of a vehicle. The component can also be a wire and / or a tube and / or a connector and / or a sleeve and / or a single core coaxial cable and / or a multi-core coaxial cable.

• a) mindestens 30.000 Thermoschock-Zyklen zwischen 25 °C und 1.100 °C, Temperaturgradient mindestens 1.000 K/s;
• b) mindestens 1.000 h Auslagerung bei 1.100 °C;
• c) mindestens 150 h Hot-Shaker-Test mit einem Gleitsinus von maximal 5 kHz Vibrationsfrequenz;
• d) Pendelschlag-Test bei Raumtemperatur 10 mal mit einer Beschleunigung von mindestens 8.000 g;

The component according to the invention, in particular the sensor according to the invention, holds at least one, preferably several, of the following loads:

• a) at least 30,000 thermal shock cycles between 25 ° C and 1,100 ° C, temperature gradient at least 1,000 K / s;
• b) at least 1,000 h aging at 1,100 ° C;
• c) at least 150 h hot shaker test with a maximum sliding frequency of 5 kHz vibration frequency;
• d) Pendulum impact test at room temperature 10 times with an acceleration of at least 8,000 g;

The invention will be explained in more detail with reference to an embodiment.

By means of the method according to the invention, a platinum sensor is produced, which is embedded in a potting compound.

For this purpose, a dispersion of a high-purity alumina (Al ₂ O ₃ ) powder and water is first prepared. The alumina powder has a purity of at least 99.99%. The aluminum oxide powder has three particle fractions, the particle size d50 of the first particle fraction being 100 nm, the particle size d50 of the second particle fraction being 1 μm and the particle size d50 of the third particle fraction being 70 μm.

In a protective sleeve, the platinum sensor is first positioned and fixed. In a next step, the described powder is filled into the protective sleeve.

There is a heating of the filled protective sleeve. The solids content of the dispersion is 85%. The heating of the protective sleeve with the platinum sensor therein and the dispersion takes place at a temperature of 600 ° C-900 ° C.

After heating, the protective sleeve is cooled down with the sensor located therein and the potting compound or a porous material now present. The volume shrinkage between the filling of the protective sleeve with the dispersion and the finally produced porous material or potting compound is 4%.

After the manufacture of the sensor, which is embedded in a potting compound, there is a potting compound with a specific electrical resistance of 2.0 · 10 ⁶ Ω · cm at a temperature of 1000 ° C. The specific electrical resistance can be determined by means of voltammetry.

The porosity of the porous material or potting compound is 35%. The pore volume of the potting compound is 0.14 cm ³ / g. The pore size d50 is between 78 and 98 nm. The porosity, the pore volume and the pore size d50 are determined by means of a mercury porosimetry.

The thermal expansion coefficient of the potting compound is 6.5-8.5 · 10 ^-6 / K. The thermal expansion is determined by dilatometry. The 3-point bending strength, however, is 46 N / mm ² . Thus, there is a potting compound that meets all requirements of corrosion, thermal shock and vibration resistance.

In addition, the potting compound acts electrically insulating even at high temperatures up to 1100 ° C. The platinum sensor is subject to less poisoning due to the selected alumina powder.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Standard ASTM D257-07 [0009]
• Standard DIN 66133 [0019]
• Standard DIN EN ISO 11885 [0035]
• Standard DIN EN 725-5 [0040]
• Standard DIN 53019 [0050]

Claims (19)

Porous material, in particular potting compound for a sensor, characterized by a specific electrical resistance of at least 10 ⁵ Ω · cm, in particular of at least 10 ⁶ Ω · cm, at a temperature of 1000 ° C. Porous material according to claim 1, characterized in that this metal oxide, in particular aluminum oxide (Al ₂ O ₃ ) and / or magnesium oxide (MgO) and / or beryllium oxide (BeO), having. Porous material according to claim 1 or 2, characterized in that this high-purity alumina (Al ₂ O ₃ ), in particular consists of high-purity alumina (Al ₂ O ₃ ), wherein the degree of purity of the aluminum oxide (Al ₂ O ₃ ) at least 99.99 % is. Porous material according to one of claims 1 to 3, characterized in that the carbon content (C) of the porous material less than 1,000 ppm, in particular less than 500 ppm, in particular less than 250 ppm, in particular less than 100 ppm, based on the total mass of porous material. Porous material according to one of the preceding claims, characterized in that the porosity D of the material is 25% -50% and / or the pore volume is 0.05 cm ³ / g-0.5 cm ³ / g, wherein the porosity and / or the pore volume is determined by mercury porosimetry. Porous material according to one of the preceding claims, characterized by a pore size d50 of 50-150 nm. Powder for producing a porous material, in particular a porous material according to one of claims 1 to 6, comprising metal oxide particles, in particular aluminum oxide particles (Al ₂ O ₃ ) and / or magnesium oxide particles (MgO) and / or beryllium oxide particles (BeO), characterized in that Powder at least two particle fractions, in particular at least three particle fractions, wherein the particle sizes d50 of the respective particle fractions have different values. Powder according to claim 7, characterized by a first particle fraction with a particle size d50 of 10 nm-1000 nm and a second particle fraction with a particle size d50 of 0.5 μm-50 μm. Powder according to claim 8, characterized by a third particle fraction with a particle size d50 of 30 μm-120 μm. Powder according to one of claims 7 to 9, characterized in that the metal oxide particles have a particle size d50 of 0.001 μm-120 μm. Process for producing a porous material, in particular a porous material according to one of Claims 1 to 6, characterized by the following process steps: a) preparing a dispersion of a powder comprising metal oxide particles, in particular of a powder according to any one of claims 7 to 10, and of a solvent, in particular an inorganic solvent, particularly preferably water; b) providing a mold or a carrier; c) filling the mold with the dispersion or coating the support with the dispersion. Method according to claim 11, marked by the further steps: d) heating the filled form / carrier and then e) cooling the filled form / carrier as well as optional f) removing the mold / carrier. A method according to claim 11 or 12, characterized in that the step c), in particular the filling of the mold, is carried out at reduced pressure. Process according to one of Claims 11 to 13, characterized in that the solids content of the dispersion is 70% by weight -90% by weight and / or the viscosity of the dispersion is 5 Pa · s-15 Pa · s. Method according to one of claims 12 to 14, characterized in that in step d) heating of the mold / the coated carrier to a temperature of 100 ° C-1400 ° C, in particular from 400 ° C-1100 ° C, in particular from 600 ° C-900 ° C. Method according to one of claims 12 to 15, characterized in that the volume shrinkage between steps c) and e) is less than 5%. Method according to one of claims 11 to 15, characterized in that in step b) in the form or on the carrier to be encased and / or embedded component, in particular an electrical component and / or an electronic component and / or a wire and / or or a pipe and / or a sensor and / or a connector and / or a sleeve and / or a single or multi-core coaxial cable, is / are arranged. Component with a coating and / or embedded in a casting compound, wherein the coating and / or the casting compound is a porous material according to one of claims 1 to 6 and / or a porous material, which is produced according to one of claims 11 to 17. Component according to claim 18, characterized in that this is a sensor, in particular a temperature sensor, and is preferably installed in the exhaust stream and / or engine system of a vehicle.