JP2013175993A - Process of manufacturing ultrasonic thickness sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process of manufacturing an ultrasonic thickness measurement sensor, thin and exhibiting flexibility, and particularly, to prevent a liquid reservoir from being generated during slurry coating in a method of coating a mixture slurry of a comparatively coarse powder of an oxide-based piezoelectric material having an average particle diameter of 1 to 10 μm and alkoxide sol of a metal composition of an oxide-based piezoelectric material onto a metal thin plate which is to be one of electrodes, drying, and baking to form a piezoelectric layer.SOLUTION: In coating the mixture slurry onto the metal thin plate, a coating layer is coated while being heated from the metal thin plate side, a sintering raw material layer is formed by coating and drying at the same time, then the sintering raw material layer is baked to form a thin sintered body layer, comparatively porous and capable of exhibiting flexibility, on a surface of the metal thin plate, and the other electrode is mounted and polarization treatment is performed.

Description

  The present invention uses a piezoelectric element made of an oxide-based piezoelectric material to detect various thicknesses such as the thickness of metal pipes of various pipes, the wall thickness of other pipes, or the thickness of the outer wall of various metal containers by ultrasonic waves. The present invention relates to a method for manufacturing an ultrasonic thickness sensor.

2. Description of the Related Art As is well known, apparatuses that perform transmission / reception of ultrasonic waves using a piezoelectric element to detect various objects and target parts, perform various measurements, and diagnoses have been widely used. For example, sonar for underwater exploration, ultrasonic flaw detectors, and ultrasonic diagnostic apparatuses have been widely known. In addition, ultrasonic sensors are also used for thickness sensors that detect the thickness of metal plates and metal tubes. (For example, Patent Documents 1 and 2).
As a material of such a piezoelectric element for ultrasonic transmission / reception, an oxide-based piezoelectric material having a perovskite crystal structure represented by lead zirconate titanate (Pb (Zr, Ti) O ₃ ) called PZT ( Piezoelectric ceramics) is the most representative.

By the way, as a method of manufacturing a piezoelectric element made of this type of oxide-based piezoelectric material, a raw material powder such as PZT is formed into a predetermined bulk shape such as a disk shape or a cubic shape, and the formed body is sintered, and ceramic In general, a sintered body is formed, and then an electrode is attached to the sintered body, and then a polarization treatment is performed to form a piezoelectric element (see, for example, Patent Document 3).
Specifically, for example, in the case of a PZT piezoelectric element, first, raw material powder for PZT such as PbO, ZrO ₂ , TiO ₂ is blended at a predetermined ratio, and pure water is added to the blended powder and mixed and pulverized by a ball mill, It is dried and calcined, pulverized again to obtain a powder, further calcined and then pulverized again to obtain a PZT powder having a perovskite crystal structure. Then, a binder such as PVA (polyvinyl alcohol) is added to the PZT powder and mixed to obtain a granulated powder having an appropriate size. Thereafter, the granulated powder is molded by applying pressure to obtain a molded body having a predetermined bulk shape such as a thick disk shape or a cubic shape. Further, the molded body is heated to remove the binder, then heated to a high temperature and fired (sintered) to form a ceramic sintered body, and then processed into a predetermined product shape (piezoelectric element shape). Usually, an electrode such as a silver electrode is attached by baking or the like, and subjected to polarization treatment to impart piezoelectric characteristics.

  In the conventional method for manufacturing an oxide-based piezoelectric element as described above, it is known that the density of the sintered body is rapidly increased by raising the heating temperature at the time of sintering the molded body to about 1200 ° C. or higher. Therefore, sintering is generally performed at about 1200 to 1300 ° C. And it is known that the sintered body is densified to a density of 90% or more by firing at a high temperature of 1200 ° C. or higher, and a dense sintered body is obtained.

  As described above, the reason for increasing the density of the sintered body in the conventional manufacturing method is that the higher the density of the sensor element made of the sintered body, the higher the piezoelectric characteristics after the polarization treatment, and the more efficiently. It is possible to oscillate ultrasonic waves and easily increase the output of ultrasonic waves. Therefore, in the past, when manufacturing a piezoelectric element made of an oxide-based piezoelectric material, the sintering temperature is set to a high temperature of 1200 ° C. or higher so that the sintered body is densified to increase the piezoelectric characteristics as much as possible and to increase the output. Was common sense.

For example, in the case of ultrasonic sonar, the distance from the sensor to the detection target is remarkably large, and therefore a large output is required to reliably capture the target. In the case of ultrasonic flaw detectors, even if the distance to the site to be detected is short, the shape of the scratch or defect to be detected is not uniform, and the reflected wave from the scratch or defect is more It is necessary to discriminate between the received signals of the two kinds of reflected waves, that is, the reflected waves from the interface between the outer surface of the tube / external space existing at a distant position, and therefore, it is necessary to increase the output to some extent. Furthermore, in the case of an ultrasonic diagnostic apparatus, the shape of the region to be inspected is not uniform, and the attenuation of ultrasonic waves when passing through human tissue is large. Therefore, in these applications, the ceramic piezoelectric element is required to be as dense as possible. As for thickness sensors, it has been common knowledge to increase the density as in other applications.
If the output of the piezoelectric element is increased, the energy of the reflected wave increases accordingly. If the energy of the reflected wave is excessive, noise in the received signal of the reflected wave becomes large. Therefore, conventionally, when an excessive reflected wave is expected, a damper for attenuating the reflected wave is also incorporated.

By the way, in the conventional ultrasonic thickness sensor, every time it is necessary to measure the thickness, an ultrasonic medium such as water is applied to the front surface of the probe of the sensor and the outer surface of an object to be measured such as piping of various facilities. Usually, the thickness is measured by pressing and transmitting / receiving ultrasonic waves.
However, as for piping of various facilities, the outer surface of the metal pipe is often covered with a jacket such as a protective material or a heat insulating material. In such a case, when measuring the thickness of the pipe with the ultrasonic thickness sensor, it is necessary to prepare for removing the outer coating of the measurement location and applying or supplying the medium to the outer surface of the metal tube. Later, it is necessary to carry out a repairing work for wiping off the medium and further repairing the jacket. Therefore, the actual situation is that much work and time are required for one thickness measurement operation.

Further, in the conventional ultrasonic thickness sensor, whenever the thickness measurement is required as described above, the front surface of the sensor probe is placed on the outer surface of the measurement object via an ultrasonic medium such as water. Since it is usually pressed, it is difficult to measure the thickness of many places on the pipe and the outer wall of the container at the same time. Therefore, if you want to obtain thickness measurement data at many places, it takes a lot of time and effort. It was necessary to.
For the same reason, it has been difficult to continuously obtain measurement data of thickness over time.

On the other hand, since a piezoelectric element using an oxide-based piezoelectric material (ceramic piezoelectric material) obtained by a conventional manufacturing method has a dense sintered body and a thick bulk shape as a whole, it is flexible. Usually, it has no property (flexibility; flexibility). For this reason, when such a piezoelectric element is used in an ultrasonic thickness sensor for pipes, container outer walls, and the like, there are the following problems.
That is, among pipes, pipes having a small diameter, that is, pipe walls of pipes having a small radius of curvature on the outer surface, L-shaped bent portions or L-shaped welded portions of the piping, that is, elbow portions, When trying to measure the thickness of a curved part (convex or concave curved part) such as a corner of a T-shaped welded part, the front surface of the probe should be uniformly applied to the curved part. As a result, there is a problem that measurement error becomes large and thickness measurement becomes difficult.

JP-A-1-202609 JP 2002-228431 A JP-A-7-45124

  The present invention has been made against the background of the above circumstances, and as an ultrasonic thickness sensor using an oxide-based piezoelectric material, it can be thin and flexible as a whole. By following the curved surface even if it is curved, it is possible to reliably measure the thickness on the curved surface, and by always sticking the thickness sensor to the measurement target part such as the pipe or the outer wall of the container This eliminates the need for preparatory work before thickness measurement and repair work after measurement, which can greatly reduce the time and effort involved in thickness measurement, as well as simultaneous thickness measurement at multiple locations and continuous measurement. It is an object of the present invention to provide a method capable of efficiently manufacturing an ultrasonic thickness measurement sensor that can also perform accurate thickness measurement at low cost.

As described above, a piezoelectric element made of a conventional oxide piezoelectric material used for ultrasonic transmission / reception for various object detection, inspection, measurement, diagnosis and the like has a density of 90 in order to obtain high piezoelectric efficiency. It has been common knowledge to be dense so as to be equal to or higher than 50%, and an ultrasonic thickness sensor similarly uses a high-density piezoelectric element of 90% or higher.
However, the present inventors have found that high piezoelectric efficiency and high output as in other applications are not necessarily required for measuring the thickness of pipe walls and outer walls of containers in various facilities.

That is, as already described, in the case of an ultrasonic sonar for underwater exploration, an ultrasonic flaw detector, an ultrasonic diagnostic device, etc., the distance to the object is long, or the shape of the object is indefinite. High output is desired from the point that the attenuation until the ultrasonic wave reaches the target site is large, but in the case of thickness measurement of pipes and containers,
The thickness of the target tube wall and the outer wall of the container (distance to transmit / reflect the ultrasonic wave) is as small as several hundreds μm to a few dozen mm at the most, and the reflecting surface is a uniform fixed surface. It has been found that the thickness can be reliably measured even if the ultrasonic output is smaller than other applications because it is not necessary to distinguish the received signals of two or more kinds of reflected waves as in the case of ultrasonic flaw detection. . In other words, in the case of a thickness sensor, it has been found that even if the piezoelectric efficiency is lower than other applications, it can function sufficiently as a thickness sensor.

On the other hand, in a piezoelectric element made of an oxide-based piezoelectric material, if the density of the sintered body becomes low and becomes relatively porous, the piezoelectric efficiency decreases, but the thin flexible on the support body. If the sintered body layer is formed thin and porous, flexibility can be imparted. In that case, the support is also used as one of the pair of electrodes necessary for the piezoelectric element, and the support is allowed to function as one electrode even after the sintered body layer is formed on the support. Thus, it has been found that a thickness sensor can be manufactured by a simple process.
As described above, the thickness sensor can be made to have flexibility as a thickness sensor while reducing the density of the sintered body to some extent and simultaneously measuring thinning to slightly reduce the piezoelectric efficiency. I found it.

Here, in order to form a thin sintered body layer thinly on a thin support that also serves as an electrode as described above, a thin metal plate is used as the support, and the sintered raw material powder paste or It is considered that the slurry is applied and dried, and the whole support (metal thin plate) is heated and fired. In this case, following the above-described conventional method, if heated to a high temperature of about 1200 to 1300 ° C., excellent high temperature oxidation resistance that does not oxidize at a high temperature of 1200 to 1300 ° C. as a metal thin plate of an electrode and support. Platinum (Pt) or the like having a hydrogen content must be used. However, such a material having excellent high-temperature oxidation resistance such as platinum is usually extremely expensive, and in this case, the material cost of the thickness sensor becomes remarkably high.
However, when the present inventor repeated experiments and researches, as a sintering raw material, a powder of an oxide-based piezoelectric material (for example, PZT) and an alkoxide sol of a metal constituting the piezoelectric material (for example, an alkoxide of Pb, Zr, Ti) If the mixture slurry is applied onto a thin metal plate, dried and fired, it is fired at a temperature much lower than the conventional temperature of about 600 to 800 ° C. or lower. I found it possible to conclude. And if it is such a relatively low firing temperature, it becomes unnecessary to use expensive platinum or the like as the support that also serves as an electrode, and it is possible to use an inexpensive material such as stainless steel, The inventors have already found out that this is effective in reducing the material cost, and the present inventors have already proposed this technology in another patent application.

  Specifically, in the method of manufacturing an ultrasonic thickness sensor according to the above proposal, a powder (raw material powder) having an average particle diameter of 1 to 10 μm of an oxide-based piezoelectric material (for example, PZT) such as PZT, which is a raw material of the piezoelectric ceramic, The raw material powder is mixed with a alkoxide sol of a metal component (for example, Pb, Zr, Ti) to form a slurry, and the mixture slurry is a thin metal plate such as thin stainless steel to serve as one electrode (first electrode). Then, the slurry coating layer is dried and then heated and fired to form a relatively porous and flexible sintered body layer on the surface of the metal thin plate. The other electrode (second electrode) was attached and further subjected to polarization so that the entire sensor could exhibit flexibility.

In the proposed method, at the time of firing, the metal thin plate as the first electrode functions as a support for supporting the coating layer at the time of drying and subsequent firing. Therefore, even if the coating layer is thin, it can be fired without any trouble. The metal thin plate not only functions as the first electrode even when used as a thickness sensor, but also functions as a support for the sintered body layer (piezoelectric ceramic layer), and the sintered body layer peels off. Can be prevented.
And if the metal thin plate used as the first electrode is thin enough to show flexibility, and the second electrode is also sufficiently thin, the thickness of the thickness sensor is reduced, It can have flexibility.

  Further, as a sintering raw material, a relatively coarse powder (average particle diameter of 1 to 10 μm) made of an oxide-based piezoelectric material and an alkoxide sol having the same metal component as that of the oxide-based piezoelectric material are mixed. In the firing step, a sintered body layer having a certain density (for example, about 70 to 80%) even at a relatively low firing temperature (for example, 600 to 800 ° C.) It is possible to form a sintered body layer that can obtain a piezoelectric characteristic that does not hinder the sound wave thickness sensor after the polarization treatment. That is, at the stage where the slurry coating layer is dried (the stage just before the start of firing), the coating layer on the metal thin plate (sintering raw material layer) is in the gaps between the particles of the relatively coarse oxide-based piezoelectric material powder. The same metal component alkoxide (or decomposition product thereof) is present in the form of fine particles, and the alkoxide (or decomposition product thereof) is baked during firing to form an oxide-based piezoelectric material (ceramic). . Therefore, the alkoxide and its decomposition products function as fine bonding substances (sintering aids) that bond the particles of the relatively coarse oxide piezoelectric material powder. At the same time, the decomposition product of the alkoxide itself becomes an oxide-based piezoelectric material such as PZT, so the entire sintered layer is necessary for the thickness sensor even at a relatively low density (70 to 80%) as a whole. Thus, it is possible to show such good piezoelectric characteristics.

By the way, as a result of further experiments for practical application of the above proposed method, it has been found that the following problems occur in the course of drying and firing from the application of the mixture slurry.
That is, the slurry applied on the metal thin plate is a mixture of relatively coarse powder particles having an average particle diameter of 1 to 10 μm and a liquid sol (colloid solution). If left as it is, the powder and the sol are separated from each other, and a liquid portion (liquid reservoir) in which a liquid sol or a solvent component is locally accumulated is likely to be generated.
That is, if the slurry after coating is left as it is in a horizontal state, in an ideal state, the relatively coarse oxide-based piezoelectric material powder in the slurry should be uniformly separated and settled in the coating layer. In practice, however, mechanical micro-vibration is applied, or vibration is applied due to handling and transfer between processes. Therefore, the oxide piezoelectric material powder particles settle unevenly in the coating layer, and a portion where the powder is unevenly distributed and accumulated is likely to occur. Conversely, a liquid portion mainly composed of a sol component that does not substantially contain a relatively coarse oxide-based piezoelectric material powder, that is, a liquid pool tends to be locally formed.

If the slurry coating layer is dried in the state where the liquid pool has occurred as described above, the liquid pool portion is substantially free of the relatively coarse oxide-based piezoelectric material powder. Compared with the part, it becomes much larger, and the part tends to crack. If the heating for firing is further performed in a state where the crack is generated, the crack is further enlarged and is easily peeled off from the metal thin plate. In addition, the liquid reservoir portion does not include a relatively coarse oxide-based piezoelectric material powder, and after drying, there is substantially only an alkoxide derived from the sol or a decomposition product thereof. The portion becomes a dense and high-density layer (a dense oxide-based piezoelectric material layer obtained by alkoxide decomposition) after firing, and such a dense portion is inferior in flexibility, so that it is a metal when used as an ultrasonic thickness sensor. The sintered body layer easily peels from the thin plate. In particular, when the sensor is bent to measure the thickness of the curved portion, cracks occur from the dense portion that was the liquid pool, and the sintered body layer peels off from the metal thin plate (first electrode). Therefore, it cannot be applied to the thickness measurement of the curved portion.
Furthermore, as described above, if the liquid pool part shrinks greatly during drying, the part becomes a recess, so that the surface unevenness becomes remarkably large, and the recess remains after firing, and the sintered body layer The thickness becomes non-uniform, which may adversely affect the polarization characteristics after the polarization treatment.

  In this way, a slurry in which the relatively coarse powder of the oxide-based piezoelectric material and the alkoxide sol of the metal component of the piezoelectric material are mixed on the surface of the metal thin plate serving as the first electrode is used as the metal serving as the first electrode. When it is applied to the surface of a thin plate, and then the coating layer is dried again and then subjected to firing, defective products (those with the sintered body layer peeled off, flexible due to the occurrence of liquid pool during coating) Inferior to those having poor polarization characteristics), and it was found that the yield of non-defective products was inevitably lowered.

  Therefore, the present inventors based on the above proposal, and as a result of repeated investigations on measures for preventing the occurrence of liquid pool during slurry application, in order to improve the yield of good products, while applying the slurry to the surface of the metal thin plate, By heating the coating layer from the side of the thin metal plate, the oxide piezoelectric material powder is uniformly mixed with the metal alkoxide (or its decomposition product) while preventing the occurrence of liquid accumulation as described above. It was found that the film can be dried with a water vapor, and the present invention has been made.

Specifically, the manufacturing method of the ultrasonic thickness sensor according to the basic aspect (first aspect) of the present invention includes a powder having an average particle diameter of 1 to 10 μm made of an oxide piezoelectric material, and the oxide piezoelectric. Sintering raw material slurry preparation step of mixing the alkoxide sol of the metal component of the material and preparing a sintering raw material slurry comprising the mixture,
In forming the coating layer of the sintering raw material slurry on one plate surface of the metal thin plate to be the first electrode, the coating layer is formed on the metal thin plate while applying the sintering raw material slurry to the plate surface of the metal thin plate. A heating and drying process from the side, a coating / drying process for forming a sintered raw material layer on one plate surface of the metal thin plate; and
The sintering raw material layer is heated and fired, and a firing step of forming a piezoelectric material sintered body layer on one plate surface of the metal thin plate,
A second electrode forming step of forming a second electrode on the surface opposite to the metal thin plate in the piezoelectric material sintered body layer after the firing step;
A polarization treatment step of performing polarization treatment by applying a potential difference between the first electrode and the second electrode made of the metal thin plate;
It is characterized by having.

  In the method of manufacturing the ultrasonic thickness sensor according to the basic aspect of the present invention, a relatively coarse powder (average particle diameter of 1 to 10 μm) made of an oxide piezoelectric material and the oxide piezoelectric material When applying the sintering raw material slurry consisting of a mixture of the metal component alkoxide sol on the metal thin plate to be the first electrode, the coating layer is heated from the side of the metal thin plate while applying the slurry. Drying of the slurry of the layer is started from the side of the metal sheet on the metal sheet immediately after the start of application. That is, evaporation of liquid components (mainly alkoxide sol dispersion medium and further slurry solvent) is started from the side of the metal sheet while being applied, and drying is started from the side of the metal sheet. The entire layer is dried. As described above, since the coating layer starts drying from the side of the thin metal plate immediately after the start of coating, the oxide-based piezoelectric material powder in the slurry is released unevenly due to the influence of mechanical vibration or the like. Without being settled and accumulated (that is, without forming a liquid pool), and dried uniformly. In the drying process, the slurry coating layer shrinks, but in the case of the present invention, the liquid shrinkage does not occur, and the oxide-based piezoelectric material powder shrinks while being uniformly dispersed in the sol. Therefore, it is possible to avoid the occurrence of cracks due to the large local shrinkage of the liquid pool portion. Furthermore, it is possible to prevent a large concave portion from being locally generated in the sintered body layer after firing due to a large local shrinkage of the liquid pool portion, and thus the thickness of the sintered body layer becomes uniform.

  In the firing step, the sintered raw material layer (layer obtained by drying the slurry coating layer) on the metal thin plate as the first electrode is a relatively coarse particle of oxide piezoelectric material powder in a state before firing is started. An alkoxide of the same metal component or a decomposition product thereof is present in an ultrafine state in the space between them, and at the time of firing, the alkoxide or decomposition product is also fired to form an oxide-based piezoelectric material (ceramic). Therefore, since the alkoxide or the decomposition product functions as a bonding substance (sintering aid) for bonding particles of relatively coarse oxide piezoelectric material powder, the density is 70% or more even at a relatively low firing temperature. At the same time, since the decomposition product of the alkoxide itself becomes an oxide piezoelectric material, even with a relatively low density (70 to 80%), the piezoelectric layer has good piezoelectric characteristics as necessary for the thickness sensor as a whole. Can be shown.

Here, the decomposition product of the alkoxide is extremely fine. Therefore, when a liquid pool as described above occurs, the liquid pool portion (portion not including a relatively coarse oxide-based piezoelectric material powder) is fired. However, in the case of the present invention, since the liquid does not accumulate at the time of slurry application, it originates from the liquid pool. A local dense layer portion is not formed. That is, the sintered body layer as a whole has a relatively low density and can exhibit flexibility as a whole.
In this way, the combination of the prevention of local cracking due to the liquid pool and the prevention of local densification of the liquid pool portion, the ultrasonic thickness sensor is applied to the curved portion. Even if it sticks, it can prevent effectively that a sintered compact layer cracks or peels.

In addition, in the coating / drying process, when heated from the surface side of the slurry coating layer, the coating layer is preferentially heated to form a dense film (metal alkoxide which is a dispersoid component of the alkoxide sol) on the surface. Alternatively, a dense solid layer made of the decomposition product thereof is thinly formed. In this state, the inside of the coating layer is undried, so the dense film becomes a barrier when bubbles generated in the undried slurry inside the coating layer escape to the outside. Therefore, gas bubbles generated inside the coating layer gather and expand (expand) under the dense film, eventually break through the dense film on the surface and are released as gas to the outside. In this case, the inner undried slurry is scattered, resulting in large irregularities on the surface, which remains after drying and the thickness of the sintered raw material layer is also non-uniform, and the thickness after firing is also non-uniform There is a strong risk of becoming.
However, by heating the slurry application layer from the side of the metal thin plate while applying the slurry on the metal thin plate, it is possible to prevent a dense film from being preferentially generated on the surface of the application layer. The occurrence of problems can be avoided.

  The ultrasonic thickness sensor manufacturing method according to the second aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to the first aspect, wherein the sintering raw material slurry is made of the metal thin plate in the coating and drying step. The coating layer is heated and dried from the side of the metal sheet while being applied to the surface, and then the coating layer is heated and dried from the side of the sheet metal while applying the sintering raw material slurry again to the surface of the dried layer. The process is repeated one or more times to obtain a sintered raw material layer having a predetermined thickness.

  As already described, if the sintered raw material slurry is applied and dried, shrinkage occurs, and the thickness after drying becomes significantly smaller than the initial thickness of the coating layer. Therefore, as in the second aspect, if the sintering raw material slurry is repeatedly applied and dried a plurality of times, a sintered body layer that is thick to some extent can be formed. In this case, by continuing to heat the coating layer from the side of the thin metal plate even during the repetition period, a uniform, healthy and relatively thick sintered body layer without cracking can be obtained uniformly It can be formed with an appropriate thickness.

  And the manufacturing method of the ultrasonic thickness sensor of the 3rd aspect of this invention WHEREIN: The manufacturing method of the ultrasonic thickness sensor of the said 1st or 2nd aspect WHEREIN: In the said application | coating and drying process, the said metal thin plate is made good heat. It is placed on a heat transfer plate made of a conductive material, and the heat transfer plate is heated by a heating means from the time before starting the application of the sintering raw material slurry, and the coating layer is made of metal through the heat transfer plate and the metal thin plate. Heating is performed from the thin plate side.

  In the manufacturing method of the ultrasonic thickness sensor of the third aspect as described above, since the sintering raw material slurry applied on the metal thin plate is heated by heat conduction from the heat transfer plate through the metal thin plate, The temperature can be increased from the side of the thin metal plate, and drying can be started from that side.

  The ultrasonic thickness sensor manufacturing method according to the fourth aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first to third aspects, in the coating and drying step, the metal thin plate. On the plate surface, a mask member on a thin plate having an opening penetrating in the thickness direction is preliminarily stacked, and when applying the sintering material slurry, the sintering material slurry is accommodated in the opening. The sintering raw material slurry is applied from above the mask member.

  In such a 4th aspect, since slurry is apply | coated using a mask member, the coating layer of uniform thickness can be easily formed with the predetermined | prescribed dimension and shape decided by the dimension and shape of an opening part.

  And the manufacturing method of the ultrasonic thickness sensor of the 5th mode of the present invention is the manufacturing method of the ultrasonic thickness sensor of any one of the 1st-4th modes. The temperature is set to 50 ° C. or higher and lower than the boiling point of the liquid component of the sintering raw material slurry.

  Thus, the heating temperature in the coating / drying step is 50 ° C. or higher and lower than the boiling point of the liquid component of the sintering raw material slurry, so that the liquid component in the slurry is boiled on the metal thin plate. It is possible to dry the coating layer and form the sintered raw material layer with a uniform thickness without causing the slurry of the coating layer to scatter or cause large irregularities.

  The ultrasonic thickness sensor manufacturing method of the sixth aspect of the present invention is the ultrasonic thickness sensor manufacturing method of the fifth aspect, wherein the heating temperature in the coating / drying step is 50 ° C. or higher and 80 ° C. Within the following range.

  In this way, when the heating temperature in the coating / drying step is within the range of 50 ° C. or higher and 80 ° C. or lower, the generation of bubbles from the slurry is minimized, and the bubbles escape to the outside as a gas. The coating layer can be dried while suppressing the scattering of the slurry and the generation of irregularities.

The ultrasonic thickness sensor manufacturing method according to the seventh aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first to sixth aspects, wherein the heating temperature in the baking step is 600. A piezoelectric material sintered body layer having a density in a range of 70 to 80% within a range of ˜800 ° C. is obtained.
In addition, in this specification, the density of a sintered compact layer shall mean the reciprocal number of a porosity, ie, a relative density.

  In the manufacturing method of the ultrasonic thickness sensor of the seventh aspect, the heating temperature in the firing step is set in the range of 600 to 800 ° C., which is much lower than the firing temperature in the conventional general piezoelectric ceramic production. Since the alkoxide of the same metal component is interposed in the voids between the relatively coarse oxide-based piezoelectric material powders (average particle diameter of 1 to 10 μm) and functions as a sintering aid, Sintering also proceeds by sintering, so that a sintered body layer having a density (70 to 80% lower than that in the prior art) that can exhibit the piezoelectric characteristics required for an ultrasonic thickness sensor can be formed. In addition, by setting the sintered body layer to be 80% or less of a density lower than that of a conventional general piezoelectric ceramic, the sintered body layer can be supported in the state of being supported by the metal thin plate of the first electrode. Flexibility can be shown. At the same time, by setting the density of the piezoelectric material sintered body layer to 70% or more, it is possible to ensure the necessary piezoelectric performance as an ultrasonic thickness sensor, and the piezoelectric material sintered body layer has an excessively low density. As a result, the sintered body layer can be prevented from peeling off from the first electrode.

  And the manufacturing method of the ultrasonic thickness sensor of the 8th aspect of this invention is the manufacturing method of the ultrasonic thickness sensor of the said any one of the 1st-7th aspect. The piezoelectric material sintered body layer is formed so as to have a thickness in the range of 30 to 150 μm, and the second electrode has a thickness of 10 to 100 μm. It is formed so that it may become in the range.

  In the manufacturing method of the ultrasonic thickness sensor of the eighth aspect as described above, since the thickness of the sintered body layer is as thin as 30 to 150 μm, the sintered body layer is supported by the first electrode, Flexibility can be exhibited, and since the metal thin plate and the second electrode of the first electrode are also thin, the finally obtained thickness sensor can easily exhibit flexibility.

  The ultrasonic thickness sensor manufacturing method of the ninth aspect of the present invention is the raw material made of the oxide piezoelectric material in the ultrasonic thickness sensor manufacturing method of any one of the first to eighth aspects. As the powder, a lead zirconate titanate piezoelectric material powder is used.

  A method for manufacturing an ultrasonic thickness sensor according to a tenth aspect of the present invention is the method for manufacturing an ultrasonic thickness sensor according to any one of the first to ninth aspects, wherein a thin plate of stainless steel is used as the first electrode. It is characterized by using.

According to the method for manufacturing an ultrasonic thickness sensor of the present invention, a mixture slurry comprising a powder of an oxide piezoelectric material having an average particle diameter of 1 to 10 μm and an alkoxide sol of the metal component of the oxide piezoelectric material is fired. Since it is used as a raw material, the firing temperature can be made relatively low, and therefore it is not necessary to use an expensive material such as platinum that is remarkably excellent in high-temperature oxidation resistance as an electrode material. An ultrasonic thickness sensor that is thin and flexible as the entire sensor can be easily manufactured.
In particular, in the case of the production method of the present invention, when the mixture slurry is applied to one surface of the metal thin plate to be the first electrode, the application layer is heated and dried while the mixture slurry is applied to the metal thin plate. Therefore, it is possible to prevent the occurrence of a part (liquid pool) in which the liquid components (sol and solvent) of the slurry are unevenly distributed. Therefore, inconveniences resulting from the liquid pool (local shrinkage and local densification during drying) (Breakage of cracks, deterioration of flexibility) can be avoided. Furthermore, in the coating / drying step, heating while coating is performed from the side of the thin metal plate, so that a dense film can be prevented from being generated on the surface of the coating layer, and as a result, the above-described dense film is generated. Inconveniences (slurry scattering and unevenness due to breakage of the surface dense film due to expansion of bubbles from the undried slurry inside) can be avoided.
If the ultrasonic thickness sensor is thin and flexible as described above, even if the measurement target site is a curved surface, it can be deformed following the curved surface. Thickness measurement can be performed reliably. In addition, such a thickness sensor can be pasted on a measurement object such as a pipe in advance, and piping equipment etc. can be operated as it is, and the thickness can be measured whenever necessary. Pre- and post-operations, such as outer cover removal and medium coating before measurement, and medium wiping and outer cover repair after measurement, can be made unnecessary. In addition, thickness sensors can be attached to a number of locations to facilitate simultaneous measurement of thicknesses at a number of locations, as well as continuous and continuous thickness measurement. A remarkable effect can be obtained.

It is a flowchart which shows embodiment of the manufacturing method of the ultrasonic thickness sensor of this invention. It is typical sectional drawing which shows an example of the implementation condition of the application | coating and drying process in the manufacturing method of the ultrasonic thickness sensor of this invention. It is typical sectional drawing which shows gradually the other example of the implementation condition of the application | coating and drying process in the manufacturing method of the ultrasonic thickness sensor of this invention in steps. It is a rough longitudinal cross-sectional view which shows an example of the ultrasonic thickness sensor obtained by the manufacturing method of this invention as the condition at the time of the use. It is a rough longitudinal cross-sectional view which shows the other example of the condition at the time of use of an example of the ultrasonic thickness sensor obtained by the manufacturing method of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 schematically shows an ultrasonic thickness sensor manufacturing method according to an embodiment of the present invention.
In this embodiment, basically,
P1: An oxide piezoelectric material, for example, a raw material powder having an average particle diameter of 1 to 100 μm, such as PZT, and an alkoxide sol of a metal component of an oxide piezoelectric material, such as PZT, are prepared and mixed. A sintering raw material slurry preparation step for preparing a slurry (sintering raw material slurry),
P2: While applying the sintering raw material slurry to one plate surface of the metal thin plate to be the first electrode, the coating layer is heated and dried from the side of the metal thin plate, on one plate surface of the metal thin plate Coating / drying process to form a sintering raw material layer on
P3: A firing step of heating and firing the sintering raw material layer on the metal thin plate, and forming a piezoelectric material sintered body layer on one plate surface of the first electrode,
P4: a second electrode forming step of forming a second electrode on the surface of the piezoelectric material sintered body layer opposite to the metal thin plate after the firing step P3,
P5: a polarization treatment step of applying a potential difference between the first electrode made of the metal thin plate and the second electrode to polarize the piezoelectric material sintered body layer,
An ultrasonic thickness sensor made of a ceramic piezoelectric material is manufactured by the process consisting of the above steps P1 to P5.
These steps P1 to P5 will be specifically described below.

[Sintering raw material slurry preparation process P1]
As a preparation step, an oxide piezoelectric material made of a ferroelectric material having a perovskite crystal structure, for example, a powder having an average particle diameter of 1 to 10 μm made of PZT or the like is prepared in advance.
Here, as the raw material powder for the oxide-based piezoelectric element, a powder composed of particles having a predetermined component composition having a perovskite type crystal structure, for example, PZT powder is commercially available from a ceramic powder manufacturer or the like. In carrying out the method for manufacturing an ultrasonic thickness sensor, a commercially available powder for a ceramic piezoelectric element of this kind may be purchased and mixed with an alkoxide sol using it as a starting material. However, it is of course possible to start from the preparation of the oxide-based piezoelectric material powder, and the process for preparing the oxide-based piezoelectric material powder will be briefly described as a preparation process.
That is, an oxide powder as a raw material such as PZT, for example, each powder of PbO, ZrO ₂ and TiO ₂ is blended so as to have a target PZT composition, and a solvent such as ethanol and a dispersion medium such as polyethyleneimine are mixed. Add appropriately and knead by a ball mill or the like, and dry the kneaded product (slurry) to obtain a mixed powder. Further, the mixed powder is temporarily fired in a powder state. This pre-baking may be usually performed in an air atmosphere at a temperature of about 700 to 900 ° C. for about 1 to 20 hours. By such preliminary calcination, each component of the mixed powder (for example, PbO, ZrO ₂ , TiO ₂ ) is solid-solved with each other, and a perovskite crystal structure is obtained. If the obtained powder (however in the state after temporary firing) is pulverized by a ball mill or the like, an oxide-based piezoelectric material powder such as PZT having an average particle diameter of 1 to 10 μm can be obtained.

In the present invention, the type and composition of the target oxide-based piezoelectric material (ceramic piezoelectric material) are not basically limited, but are oxide-based piezoelectric materials made of a ferroelectric having a perovskite crystal structure. Among them, among them, lead zirconate titanate (Pb (Zr, Ti) O ₃ ) called PZT, more specifically, Pb (Zr _x Ti _1-x ) O ₃ [however, 0. 5 ≦ x ≦ 0.7], and more preferably PZT having a composition in which the value of x is about 0.52. In addition, on the basis of the PZT composition described above, one or more of Mn, Mg, Ca, Sr, Ba, V, Nb, Ta, La, Nd, Sc, Gd, and the like are added as trace elements. Each of them may be added in an amount of about 10% by weight or less. In short, all materials called PZT-based (lead zirconate titanate) piezoelectric ceramic materials are targeted. Furthermore, the piezoelectric ceramic material is not limited to the PZT-based piezoelectric ceramic material, and other piezoelectric ceramic materials having a perovskite crystal structure, such as LiNbO _3, and other piezoelectric ceramic materials having no perovskite crystal structure, such as Bi ₃ Ti ₄ O _12, etc. Can also be applied.

  The particle diameter of the oxide-based piezoelectric material powder is set to an average particle diameter of 1 to 10 μm. This is a conventional general method, that is, the oxide powder of the metal component constituting the oxide-based piezoelectric material. This is because the powder obtained by mixing and firing and mechanically pulverizing the powder usually has an average particle size of about 1 to 10 μm. Here, setting the average particle size of the oxide-based piezoelectric material powder to less than 1 μm is problematic from the viewpoint of pulverization efficiency, while setting the average particle size of the oxide-based piezoelectric material powder to more than 10 μm is a result. It becomes a problem from the viewpoint of sex.

On the other hand, along with the preparation of the above-described oxide-based piezoelectric material powder, an alkoxide sol of a metal component of an oxide-based piezoelectric material such as PZT is prepared. The alkoxide sol prepared here is an alkoxide of each metal component of the oxide used as a raw material of the above-described oxide-based piezoelectric material, that is, the metal component is M and the alkyl group is R, and is represented by the general formula M (OR) _X. A mixed sol of each metal alkoxide. For example, in the case of PZT, since the metal component M is mainly composed of lead (Pb), zirconium (Zr), and titanium (Ti), a sol in which lead alkoxide, zirconium alkoxide, and titanium alkoxide are mixed is prepared. On the other hand, the alkyl group R is not particularly limited, but methyl group, ethyl group, propyl group, isopropyl group, amyl group, hexyl group, cyclohexyl group, butyl group, isobutyl group, t-butyl group, s-butyl group, etc. are applied. can do. More specifically, in the case of PZT, as lead alkoxide, lead diisoproxide, lead dibutoxide, etc., as zirconium alkoxide, zirconium tetrabutoxide, zirconium tetrapropoxide, etc., as titanium alkoxide, titanium tetraisopropoxide, titanium, etc. Tetrapropoxide or the like is preferably used.
In this case, it is desirable that the composition of each metal alkoxide is determined so that the proportion of the metal component is equivalent to the proportion of the metal component in the target oxide-based piezoelectric material. That is, in the case of PZT represented by the general formula Pb (Zr _x Ti _1-x ) O ₃ , the molar ratio of the metal components of each alkoxide is Pb: Zr: Ti = 1: x: 1-x. It is desirable to blend as such.
However, based on the PZT composition of Pb (Zr _x Ti _1-x ) O ₃ [where 0.5 ≦ x ≦ 0.7], and as a trace amount of added elements, Mn, Mg, Ca, Sr, Ba, V, When a PZT-based piezoelectric ceramic material to which one or more of Nb, Ta, La, Nd, Sc, Gd and the like are added is targeted, the alkoxide sol does not necessarily include even the alkoxides of these trace element metals. It is not necessary, and it is sufficient if it contains alkoxides of Pb, Zr and Ti which are the main components. Of course, depending on the case, a sol containing a metal alkoxide of these trace addition elements may be used.

Depending on the type of oxide-based piezoelectric material (composition of composite oxide), among the constituent metals of the composite oxide, an alkoxide is used for a certain metal, and an organic metal salt other than an alkoxide is used for another metal. (For example, in the case of Bi ₃ Ti ₄ O ₁₂ (bismuth titanate: BIT), LiNbO ₃ (lithium niobate), etc.) In this specification, even in such a case, the mixed sol is included in the alkoxide sol.

  The method for obtaining the alkoxide sol as described above is not particularly limited, and may follow a conventional method. For example, as a solvent (dispersion medium), alcohols such as butanol, acid solutions such as acetic acid, ethyl acetate, An organic acid ester such as butyl acetate, an organic imine such as polyethyleneimine, or an aromatic compound such as xylene may be used, and the alkoxide of each metal component may be dissolved (dispersed) in these solvents. In general, when preparing an alkoxide sol, an appropriate stabilizer such as acetic acid or methanol is often added together with a solvent to stabilize the sol. In the present invention, these stabilizers are also added. May be.

If a relatively coarse powder (average particle diameter of 1 to 10 μm) made of an oxide piezoelectric material having a perovskite crystal structure as described above is mixed with an alkoxide sol having a metal component of the same oxide piezoelectric material. A mixture slurry as a sintering raw material is obtained. Of course, in addition to the alkoxide sol, an appropriate solvent such as butanol, ethyl acetate, xylene, acetic acid and methanol may be added and kneaded.
The mixing ratio of the above oxide-based piezoelectric material powder and the alkoxide sol is not particularly limited, but usually the metal component in the alkoxide sol with respect to the metal component in the oxide-based piezoelectric material powder as compared with the same metal component. It is desirable to mix so that the molar ratio may be in the range of 0.2 to 1.0. When the above molar ratio is less than 0.2, the alkoxide sol is too little, and the decomposition product of the sol does not function sufficiently as a sintering aid in the firing step, and therefore, sintering at low temperature becomes difficult, If the molar ratio exceeds 1.0, the alkoxide sol is too much and the particles of the relatively coarse oxide-based piezoelectric material powder are sufficiently bonded when fired on a thin metal plate also serving as the first electrode. Therefore, the sintered body layer becomes powdery and increases the risk of scattering or peeling off.

[Coating / drying process P2]
In this coating / drying process, the coating layer is heated from the side of the thin metal plate while applying the raw material slurry (mixture slurry) to the surface of the thin metal plate that will be the first electrode in the final ultrasonic thickness sensor. And drying to form a sintered raw material layer on the surface of the thin metal plate.

Specifically, as shown in FIG. 2, for example, aluminum, aluminum alloy, copper or copper is formed on the upper surface (heating surface) of a heating table 9 provided with appropriate heating means 9A such as an electric heater, a hot water heater, and an oil heater. A heat transfer plate 7 made of a good heat conductive material such as an alloy is disposed, and a thin metal plate 1 serving as a first electrode is placed on the upper surface of the heat transfer plate 7. On the other hand, a thin plate-like or sheet-like mask member 3 formed so as to penetrate through the opening 3A for partitioning the slurry coating layer in the thickness direction is prepared in advance, and the mask member 3 is attached to the metal thin plate 1. Overlay on top side. Then, the heating means 9A is operated to heat the metal thin plate 1 from the heating table 9 via the heat transfer plate 7. In this state, the slurry is applied from the upper surface side of the mask member 3 by an appropriate application means such as spray, and the slurry is filled into the opening 3 </ b> A of the mask member 3. As a result, the slurry coating layer 5 is formed with a predetermined thickness in a predetermined region on the plate surface of the thin metal plate 1 (region in the opening 3A). The slurry of the coating layer 5 is heated from the side of the thin metal plate 1 from the start of coating layer formation (at the start of coating by spraying or the like). Therefore, the slurry is dried from the side in contact with the thin metal plate 1 immediately after the start of coating. Be started.
In FIG. 2, the heating means 9A is provided on the heating table 9 that supports the heat transfer plate 7. However, in some cases, the heating means 9A may be provided on the heat transfer plate 7 itself. .

  Here, in the drying process of the mixture slurry, first, the evaporation of the liquid component (sol dispersion medium, slurry solvent) in the slurry is started, and then the process proceeds to hydrolysis of the alkoxide sol component in the slurry. In the slurry application, these processes proceed from the side in contact with the metal thin plate 1 immediately after the start of application, and in the stage after the application / drying process, particles of relatively coarse oxide-based piezoelectric material powder (average particles) An alkoxide or a decomposition product thereof (ultrafine particles) is interposed between 1 to 10 μm in diameter, and PZT (oxide-based piezoelectric material) is newly formed therefrom.

  In the coating / drying process, the slurry on the metal thin plate starts drying immediately after the slurry coating starts, so that the oxide-based piezoelectric material powder in the slurry is liberated due to the influence of mechanical vibration, etc. Without being settled and accumulated in an unevenly distributed state (that is, without generating a liquid pool), it is dried while maintaining a uniform dispersed state. Further, during the drying process, the slurry coating layer contracts, but as described above, the liquid shrinkage does not occur and the oxide piezoelectric material powder shrinks while being uniformly dispersed throughout the slurry coating layer. Therefore, it is possible to avoid the occurrence of cracks due to the large local shrinkage of the liquid pool portion. Furthermore, since the liquid is dried in a state where no liquid pool is generated, it is possible to prevent a large concave portion from being formed in the sintered body layer after firing due to a large local shrinkage of the liquid pool portion. The layer thickness is also uniform.

  Furthermore, since the heating for drying the slurry on the metal thin plate is performed from the side of the metal thin plate, the surface of the coating layer is preferentially dried and applied to the surface as in the case where the coating layer is heated from the surface side. It is avoided that a dense thin film is formed preferentially. Therefore, the bubbles generated from the slurry inside the coating layer can be rapidly and gently released as a gas without causing aggregation and enlargement. As a result, it is possible to obtain a sintered raw material layer having a uniform thickness with few surface irregularities as a layer after drying.

Here, the heating temperature in the coating / drying step is preferably 50 ° C. or higher and lower than the boiling point of the liquid component of the sintered raw material mixed slurry.
When the heating temperature is less than 50 ° C., there is little difference from the ambient room temperature, and the effect of promoting drying by heating cannot be sufficiently obtained. On the other hand, when the heating temperature is equal to or higher than the boiling point, the liquid component in the slurry is boiled, and the slurry is scattered due to a sudden boiling phenomenon, or the surface unevenness becomes intense and a uniform film cannot be obtained.
Here, the temperature lower than the boiling point of the liquid component of the slurry means a temperature lower than the boiling point of the single liquid when the liquid component consists of only one type of liquid, and a mixture of two or more types of liquids. Is the temperature lower than the lowest temperature among the boiling points of each liquid in the state of the mixed liquid. When the mixed liquid is a coprecipitation solution, it means a temperature lower than the coprecipitation boiling temperature.
In practice, in order to reliably and stably prevent the occurrence of boiling, the upper limit of the heating temperature is preferably 10 ° C. lower than the boiling point of the liquid component in the slurry.

Furthermore, the above heating temperature is 50 ° C. or higher and less than the boiling point of the liquid component of the sintering raw material mixed slurry (or 10 ° C. or lower), particularly within the range of 50 ° C. to 80 ° C. It is desirable that the temperature be in the range of 50 to 70 ° C.
That is, if the heating temperature is too high, even when the boiling point has not been reached, gas components such as air adsorbed on the oxide piezoelectric material powder and gas components such as air dissolved in the slurry are vaporized, Generation of bubbles from the inside of the coating layer increases. As a result, the unevenness of the surface after drying becomes large, the film thickness becomes non-uniform, the surface properties are deteriorated, and the polarization characteristics after the polarization treatment are deteriorated. Moreover, the sintered body layer after firing is not uniform and is easily peeled off from the metal thin plate. On the other hand, if the heating temperature is in the range of 50 ° C. to 80 ° C., particularly 50 to 70 ° C., the above-described problems can be avoided by minimizing the generation of bubbles in the inner shell of the slurry coating layer. Can do.

  Here, as a dispersion medium for alkoxide sol or a solvent for slurry, butanol, butyl acetate, acetic acid, xylene, methanol, isopropanol, etc. are used, butanol has a boiling point of about 117 ° C. and butyl acetate has a boiling point of about 126 ° C. Acetic acid has a boiling point of about 117 ° C., xylene has a boiling point of around 140 ° C., methanol has a boiling point of about 65 ° C., and isopropanol has a boiling point of about 83 ° C. Therefore, when these are used as a sol dispersion medium or slurry solvent, The heating temperature within the above range of 50 to 80 ° C. or 50 to 70 ° C. is sufficiently lower than the boiling points of each except for methanol, and therefore boiling does not occur and generation of gas bubbles is minimized. Can be suppressed. In the case of methanol, it may be heated to a temperature lower than its boiling point and 50 ° C. or higher.

  The above-described thin metal plate not only functions as an electrode but also functions as a support during the firing process after coating and drying or when used as a thickness sensor. The material of the metal thin plate is not particularly limited, but in the case of the present invention, a slurry of a relatively coarse mixture of oxide-based piezoelectric material powder and alkoxide sol is used as a sintering raw material, and therefore, about 600 to 800 ° C. Therefore, a general-purpose refractory metal having oxidation resistance up to about 800 ° C. can be used. That is, it is not necessary to use an expensive metal that can withstand up to 1200 ° C. or more, such as platinum, and stainless steel or other general-purpose heat-resistant steel can be used as a metal thin plate that also serves as the first electrode. Specifically, SUS304 series austenitic stainless steel known as 18Cr-8Ni, 18Cr-12Ni-2.5Mo SUS316 series austenitic stainless steel, and 22Ni-12Cr SUH309 series austenitic heat resistant steel. Can be used. All of these can be obtained at a much lower price than platinum.

  The thickness of the metal thin plate as the first electrode is preferably 15 μm to 100 μm. If the thickness is less than 15 μm, the strength is insufficient, which may hinder handling during the sensor manufacturing process, and may be deformed or damaged during use as a thickness sensor. On the other hand, if the thickness exceeds 100 μm, the flexibility of the thin metal plate is lost, and the flexibility of the thickness sensor as a whole is inferior. May be difficult to do.

  As a means for applying the mixture slurry, in addition to spray application by spraying, application using a roll coater, squeegee, or brush, or any other application / printing means applied in general application / printing is arbitrarily applied. However, the method of the present invention is most effective in drying the slurry on the metal thin plate while increasing the coating thickness of the slurry on the thin plate substrate by spraying.

  In addition, the material of the mask member 3 in this embodiment is not specifically limited, The stainless steel (SUS) similar to the metal thin plate 1 or resin can be used arbitrarily. Moreover, since the thickness of the mask member 3 corresponds to the thickness of the slurry filled in each opening 3A, that is, the thickness of the sintering raw material layer, 70 to 200 μm can be secured as the thickness after drying as described below. What is necessary is just to set to a proper thickness.

  The thickness after application and drying of the slurry (thus, the thickness of the sintered raw material layer) is preferably in the range of 70 to 200 μm. If the thickness at the stage immediately before the start of the firing process is less than 70 μm, the thickness of the sintered body layer after firing is too thin, and when the sensor is bent, it may be peeled off from the metal thin plate as the first electrode. On the other hand, if the thickness in the stage immediately before the firing process exceeds 200 μm, the thickness of the sintered body layer after firing becomes too thick, and as a result, sufficient flexibility is given to the sintered body layer as will be described later. May be difficult.

  In order to sufficiently secure the thickness of the sintered body layer, the application / drying of the slurry may be repeated a plurality of times in the application / drying step. That is, the coating layer is heated from the side of the metal thin plate while being dried while the sintering raw material slurry is being applied to the plate surface of the metal thin plate, and then the coating layer is again applied to the surface of the dried layer. The process of drying by heating from the side of the thin metal plate may be repeated one or more times to obtain a sintered raw material layer having a predetermined thickness. An example of the coating / drying process in that case is shown in FIG.

  In the example of FIG. 3, the slurry is applied by spraying using the mask member 3 having the opening 3A, as in the example shown in FIG. In this case, as shown in FIGS. 3A to 3C, the first slurry 5 is applied while being heated from the side of the thin metal plate 1, and the first layer (sintered raw material) contracted by drying. The first layer 61 is formed, and then the slurry 5 is again heated and heated on the coated first layer (sintered raw material first layer) 61 as shown in FIGS. 3D and 3E. Is applied and dried to form a coating second layer (sintered raw material second layer) 62. Further, if necessary, such a process is repeated to finally obtain a sintered raw material layer 6 having a predetermined thickness as shown in FIG.

[Baking step P3]
After completion of the coating / drying step, the sintering material layer formed on the plate surface of the metal thin plate as the first electrode is heated and fired.
In this firing step, the alkoxide or the decomposition products (ultrafine particles) present between the relatively coarse raw material powder particles (average particle size of 1 to 10 μm) burn the relatively coarse raw material powder particles. It functions as a binder, that is, as a sintering aid. In addition, since the alkoxide and decomposition product itself have a target oxide ceramic piezoelectric material composition such as PZT, the alkoxide and decomposition product also have a function of improving piezoelectric characteristics. Therefore, by mixing and baking the alkoxide sol with the relatively coarse raw material powder in this way, sintering proceeds at a relatively low temperature and the piezoelectric characteristics are improved.

Here, in the firing step, it is desirable to perform firing so that the heating temperature is in the range of 600 to 800 ° C., and the density of the state after firing (piezoelectric material sintered body layer) is in the range of 70 to 80%. .
If the density of the sintered ceramic body after firing reaches a high density exceeding 80%, the rigidity of the sintered body layer becomes high and the flexibility becomes inferior. As a result, the sensor is used when used as a thickness sensor. If it is curved, the sintered body layer may be peeled off from the metal thin plate as the first electrode or cracks may be generated. Therefore, it can be applied to a curved portion such as a pipe whose thickness is to be measured. It becomes difficult. At the same time, when fired to a high density exceeding 80%, the shrinkage during firing is large, and there is a strong risk of peeling from the metal thin plate (support) as the first electrode. It becomes difficult to obtain a sintered body layer that is in close contact with the metal thin plate as the first electrode.
On the other hand, if the density of the sintered ceramic body after firing is less than 70%, the porosity of the sintered body layer is too high, and the particles inside the sintered body layer are not sufficiently bonded. In addition, the sintered body layer may be peeled off during handling in subsequent processes or when used as a sensor, and at the same time, the porosity inside the sintered body layer is increased, resulting in a thickness measurement. Therefore, there is a possibility that sufficient piezoelectric characteristics as an ultrasonic sensor cannot be obtained.

Therefore, the density of the sintered ceramic body after firing is desirably in the range of 70 to 80%, but in order to form a sintered body layer having such a density, the firing temperature is 600 to 800 ° C. It is preferable to be within the range. Thus, even at a firing temperature of 600 to 800 ° C., which is lower than the firing temperature of a conventional general oxide-based piezoelectric material (ceramic piezoelectric material), the decomposition product of the alkoxide blended in the sintering raw material serves as a sintering aid. In order to function, the sintered compact density which shows the piezoelectric characteristic required as an ultrasonic thickness sensor can fully be obtained.
If the firing temperature is higher than 800 ° C., the sintering reaction between the powder particles proceeds rapidly during firing, making it difficult to obtain a sintered body layer having a density of 80% or less. On the other hand, if the firing temperature is lower than 600 ° C., the sintering reaction between the powder particles does not proceed sufficiently, and it becomes difficult to increase the density of the sintered body layer to 70% or more. The baking temperature is particularly preferably in the range of 650 to 750 ° C. even in the range of 600 to 800 ° C.
The atmosphere during firing is preferably air. Further, although the firing time varies depending on the firing temperature, it is usually preferably 1 to 10 hours.
By such a firing step, a piezoelectric material sintered body layer having a predetermined thickness and a predetermined density is formed on one surface of the thin metal plate serving as the first electrode that also serves as the support.

[Second electrode formation step P4]
In the second electrode forming step, a second electrode serving as a counter electrode of the first electrode (thin metal plate) is formed on the upper surface (surface opposite to the first electrode) of the piezoelectric material sintered body layer. It is a process.
The specific means for forming the second electrode is not particularly limited. For example, a conductive metal powder for electrodes such as silver (Ag) is made into a paste, and the paste is applied to the surface of the sintered body layer. It may be baked, or a conductive metal thin film for electrodes may be placed on or pasted on the surface of the sintered body layer and baked. In addition, it is preferable that the thickness of this 2nd electrode shall be 10-100 micrometers. If the thickness of the second electrode exceeds 100 μm, the flexibility of the thickness sensor may be impaired. On the other hand, when the second electrode is thinly formed to be less than 10 μm, the second electrode is locally formed by unevenness on the surface of the sintered body layer. There is a possibility that the two electrodes become discontinuous.

  In this way, a sintered body layer made of a ceramic piezoelectric material is formed on one plate surface of the first electrode (metal thin plate) that also serves as a support, and the second electrode is formed on the surface of the sintered body layer. A laminated body in which is formed is obtained. Here, the first and second electrodes function as electrodes for applying a polarization voltage in the next polarization process, and at the same time function as electrodes for transmitting and receiving ultrasonic waves when used as a thickness sensor. It is.

[Polarization process P5]
Thereafter, a polarization process is performed by applying a direct current or pulsed potential difference between the first and second electrodes in the laminate. This polarization treatment may be performed in the same manner as in the case of manufacturing a conventional general piezoelectric element.
By applying the polarization treatment in this way, the sintered body layer becomes piezoelectric and can be used in an ultrasonic thickness sensor.

  In an actual ultrasonic sensor, it is necessary to attach lead wires to the first electrode and the second electrode in order to input and output voltage signals for ultrasonic measurement. Therefore, it is usual to attach a lead wire to each electrode using a conductive paste or the like after the polarization treatment or before the polarization treatment.

FIG. 4 shows an ultrasonic thickness sensor manufactured by the method of the embodiment as described above and a situation at the time of use.
In FIG. 4, a piezoelectric material sintered body layer (for example, PZT piezoelectric ceramic layer) 21 is formed on one plate surface of the first electrode (metal thin plate) 1 in the ultrasonic thickness sensor 25, and further the piezoelectric material. A second electrode 23 is formed on the surface of the sintered body layer 21. Lead wires 27A and 27B are drawn out from the first electrode 1 and the second electrode 23, respectively. The thickness sensor 25 configured as described above has an adhesive 31 or the like so that one surface of the first electrode 1 is in contact with the surface of a thickness measurement object 29 (such as a tube wall of a metal tube or an outer wall of a container). By using and sticking, the thickness of the measurement object can be measured at any time. As the adhesive 31 at this time, a silver paste, a glass paste, a platinum paste, a gold paste, or the like may be used.

The ultrasonic thickness sensor manufactured according to each embodiment of the present invention as described above is an extremely thin one having a three-layer structure of a first electrode, a sintered body layer, and a second electrode as a whole. Even when a jacket is provided on the outside of the pipe for protection or heat insulation, the pipe is bonded to the outer surface in advance during pipe assembly, and a jacket for protection or heat insulation of the pipe is provided from the outside of the thickness sensor. In this state, the piping equipment can be used as it is, and the thickness can be measured appropriately in the state as it is. In that case, it is not necessary to remove the outer covering before the thickness measurement or to repair the outer covering after the measurement, and to apply the ultrasonic medium to the surface of the object before the thickness measurement, and the ultrasonic wave after the measurement. The work of wiping off the medium is also unnecessary.
Further, since this ultrasonic thickness sensor is thin and flexible as a whole, even if the surface of the measurement object 29 is curved as shown in FIG. The ultrasonic thickness sensor 25 can be adhered along the curved surface to measure the thickness at the curved portion.

  Examples of the present invention will be described below.

Example 1 includes a sintered body layer (ceramic piezoelectric layer) made of PZT using a slurry mixture of ZT powder and an alkoxide sol of a metal component of PZT (using butyl acetate as a solvent for the sol). 2 is an example of manufacturing an ultrasonic thickness sensor.
First, as raw material powders for PZT, lead oxide (PbO), titanium oxide (TiO ₂ ), and zirconium oxide (ZrO ₂ ) powders are prepared. These are PbO: 1 mol, ZrO ₂ : 0.5 mol, TiO _{2. 2} : It mix | blended in the ratio of 0.5 mol, the solvent was ethanol, the dispersing agent was polyethyleneimine, and it wet-kneaded with the ball mill for 24 hours, and was set as the slurry. The slurry is dried to form a mixed powder lump, which is then placed in an alumina crucible, covered with alumina, and subjected to heat treatment (temporary firing) at 850 ° C. for 10 hours to obtain a PZT powder lump having a perovskite crystal structure. It was. The PZT powder mass is pulverized, put through a 300 micron sieve into a ball mill, and pulverized in ethanol using zirconia balls as a pulverization medium for 24 hours to obtain a PZT powder having an average particle size of 2 μm and dried. It was.

  On the other hand, lead diisoproxide is prepared as lead alkoxide, zirconium tetrabutoxide is prepared as zirconium alkoxide, and titanium tetraisopropoxide is prepared as titanium alkoxide, and these have a molar ratio of Pb: Zr: Ti = 1: 0.5: 0.5. And dissolved (dispersed) in butyl acetate as a dispersion medium to obtain an alkoxide sol. The concentration of this alkoxide sol was determined so that the total amount of each alkoxide component was 10% by weight. The alkoxide sol and the PZT powder having an average particle diameter of 2 μm were mixed at a weight ratio of 2: 1 to obtain an alkoxide sol-PZT mixed slurry. At this time, the molar ratio of the metal component in the PZT powder and the metal component in the alkoxide sol is about 2: 1.

On the other hand, it is made of 100 μm thick glued paper with a 10 mmφ round hole (opening) formed as a mask member in the center of a thin metal plate (thickness 25 μm, 2 cm × 2 cm square) made of SUS304 as the first electrode. A masking tape was pasted and placed on an aluminum plate having a thickness of 3 mm as a heat transfer plate. Then, the aluminum plate is heated to 60 ° C. in advance with an electric heater, and while the heating state is maintained, the alkoxide sol-PZT mixed slurry is applied by spraying and at the same time, the drying of the slurry application layer is advanced. Drying was repeated 5 times to form a PZT sintering raw material layer having a thickness of 100 μm.
Thereafter, as a firing step, the temperature was increased to 450 ° C. over 15 hours at a temperature increase rate of 30 ° C./hr, then heated to 650 ° C. at a temperature increase rate of 200 ° C./hr and held at 650 ° C. for 10 minutes. After that, the furnace was cooled. As a result, a sintered material of a sintered piezoelectric material made of PZT having a thickness of 100 μm was baked on a thin metal plate made of SUS304 having a thickness of 25 μm as the first electrode.
Next, a silver paste for a second electrode having a 5 mm round size is applied to the center of the piezoelectric material sintered body layer (10 mm round) made of PZT, and baked at 450 ° C., and a second electrode having an average thickness of 20 μm. Electrode (silver electrode) was formed.

In this way, a piezoelectric material sintered body layer (piezoelectric ceramic layer) made of PZT is formed on the first electrode (SUS304), and a second electrode (silver) is formed on the piezoelectric material sintered body layer. A laminate was obtained. The density of the piezoelectric material sintered body layer was about 75%.
Thereafter, the laminate was immersed in silicon oil at 150 ° C., and a polarization treatment for applying a potential difference of 4500 V / mm between the first electrode and the second electrode in the laminate was performed for 5 minutes. Thereafter, a lead wire was bonded to each of the first electrode (SUS304) and the second electrode (silver) with a conductive paste to form a thickness sensor.

  When the polarization state (piezoelectric constant d33) of the sample after the polarization treatment was examined using a d33 meter, it was confirmed that the sample was well polarized. Moreover, as an ultrasonic thickness sensor, when the thickness of the tube wall was measured by attaching it to a tube wall of a stainless steel tube having an outer diameter of 10 cm and a wall thickness of 8 mm using a silver paste as an adhesive, It was confirmed that it worked and the thickness was measured correctly.

  In addition, at the time of application | coating and drying of a slurry, it was confirmed that a liquid pool does not arise in the application layer of the slurry apply | coated by spray. At the same time, it was confirmed that the slurry does not scatter or large irregularities are generated on the surface due to boiling of liquid components (sudden boiling) of the slurry or generation of abrupt bubbles in the inner shell of the coating layer.

In Example 2, an ultrasonic sensor having a sintered body layer (ceramic piezoelectric layer) made of PZT was manufactured by using N-butanol as a solvent for the alkoxide sol instead of butyl acetate in Example 1. This is an example.
That is, in the same manner as in Example 1, a PZT powder having an average particle size of 2 μm was prepared. On the other hand, lead diisoproxide is prepared as lead alkoxide, zirconium tetrabutoxide is prepared as zirconium alkoxide, and titanium tetraisopropoxide is prepared as titanium alkoxide, and these have a molar ratio of Pb: Zr: Ti = 1: 0.5: 0.5. And dissolved (dispersed) in N-butanol as a dispersion medium to obtain an alkoxide sol. The concentration of this alkoxide sol was determined so that the total amount of each alkoxide component was 10% by weight. The alkoxide sol and the above-mentioned PZT powder having an average particle diameter of 2 μm were mixed so that the weight ratio of sol: PZT powder was 1: 2, and an alkoxide sol-PZT mixed slurry was obtained. At this time, the molar ratio of the metal component in the PZT powder to the metal component in the alkoxide sol is about 1: 2.

On the other hand, it is made of 100 μm thick glued paper with a 10 mmφ round hole (opening) formed as a mask member in the center of a thin metal plate (thickness 25 μm, 2 cm × 2 cm square) made of SUS304 as the first electrode. A masking tape was pasted and placed on an aluminum plate having a thickness of 3 mm as a heat transfer plate. Then, the aluminum plate is heated to 60 ° C. in advance with an electric heater, and while the heating state is maintained, the alkoxide sol-PZT mixed slurry is applied by spraying and at the same time, the drying of the slurry application layer is advanced. Drying was repeated 5 times to form a PZT sintering raw material layer having a thickness of 100 μm.
Thereafter, as a firing step, the temperature was increased to 450 ° C. over 15 hours at a temperature increase rate of 30 ° C./hr as in Example 1, and subsequently heated to 650 ° C. at a temperature increase rate of 200 ° C./hr. After holding at 10 ° C. for 10 minutes, the furnace was cooled. As a result, a sintered material of a sintered piezoelectric material made of PZT having a thickness of 100 μm was baked on a thin metal plate made of SUS304 having a thickness of 25 μm as the first electrode.
The density of the piezoelectric material sintered body layer was about 75%.

  Thereafter, in the same manner as in Example 1, the formation of the second electrode, the polarization treatment, and the attachment of the lead wire were performed to obtain an ultrasonic thickness sensor. When the polarization state (piezoelectric constant d33) of the sample after the polarization treatment was examined using a d33 meter, it was confirmed that the sample was well polarized. Moreover, as an ultrasonic thickness sensor, when the thickness of the tube wall was measured by attaching it to a tube wall of a stainless steel tube having an outer diameter of 10 cm and a wall thickness of 8 mm using a silver paste as an adhesive, It was confirmed that it worked and the thickness was measured correctly.

  Also in the case of Example 2, it was confirmed that no liquid pool was generated in the sprayed slurry coating layer during the slurry coating and drying, and at the same time, the liquid component in the slurry boiled (sudden boiling) and the coating layer. It was also confirmed that the slurry does not scatter due to the rapid generation of bubbles in the inner shell, or that large irregularities are not generated on the surface.

  The preferred embodiments and examples of the present invention have been described above. However, these embodiments and examples are merely examples within the scope of the present invention, and do not depart from the spirit of the present invention. Thus, addition, omission, replacement, and other changes of the configuration are possible. That is, the present invention is not limited by the above description, is limited only by the scope of the appended claims, and can be appropriately changed within the scope.

1 Metal thin plate (first electrode)
3 Mask member 3A Opening 5 Slurry coating layer 7 Heat transfer plate 9A Heating means 21 Sintered body layer 23 Second electrode 25 Ultrasonic thickness sensor 29 Thickness measurement object

Claims (10)

A sintering raw material slurry for preparing a sintering raw material slurry comprising a mixture of a powder having an average particle diameter of 1 to 10 μm made of an oxide piezoelectric material and an alkoxide sol of the metal component of the oxide piezoelectric material A preparation process;
In forming the coating layer of the sintering raw material slurry on one plate surface of the metal thin plate to be the first electrode, the coating layer is formed on the metal thin plate while applying the sintering raw material slurry to the plate surface of the metal thin plate. A heating and drying process from the side, a coating / drying process for forming a sintered raw material layer on one plate surface of the metal thin plate; and
The sintering raw material layer is heated and fired, and a firing step of forming a piezoelectric material sintered body layer on one plate surface of the metal thin plate,
A second electrode forming step of forming a second electrode on the surface opposite to the metal thin plate in the piezoelectric material sintered body layer after the firing step;
A polarization treatment step of performing polarization treatment by applying a potential difference between the first electrode and the second electrode made of the metal thin plate;
The manufacturing method of the ultrasonic thickness sensor characterized by having.   In the coating / drying step, the coating layer is heated and dried from the side of the metal thin plate while applying the sintering raw material slurry to the plate surface of the metal thin plate, and then the sintering raw material slurry is applied to the surface of the dried layer. The ultrasonic wave according to claim 1, wherein a process of heating and drying the coating layer from the side of the thin metal plate while being applied again is repeated one or more times to obtain a sintered raw material layer having a predetermined thickness. Manufacturing method of thickness sensor.   In the coating / drying step, the metal thin plate is placed on a heat transfer plate made of a good heat conductive material, and the heat transfer plate is heated by a heating means from the time before the application of the sintering raw material slurry, 3. The method of manufacturing an ultrasonic thickness sensor according to claim 1, wherein the coating layer is heated from the side of the thin metal plate via the heat transfer plate and the thin metal plate.   In the coating / drying step, a thin plate-like mask member having an opening penetrating in the thickness direction is preliminarily stacked on the plate surface of the metal thin plate, and when applying the sintering raw material slurry, The manufacturing of the ultrasonic thickness sensor according to any one of claims 1 to 3, wherein the sintering raw material slurry is applied from above the mask member so that the sintering raw material slurry is accommodated. Method.   The heating temperature in the coating / drying step is set to 50 ° C or higher and lower than the boiling point of the liquid component of the sintering raw material slurry. The manufacturing method of the ultrasonic thickness sensor of description.   6. The method of manufacturing an ultrasonic thickness sensor according to claim 5, wherein a heating temperature in the coating / drying step is set in a range of 50 ° C. or higher and 80 ° C. or lower.   The heating temperature in the said baking process shall be in the range of 600-800 degreeC, and the density of a piezoelectric material sintered compact layer in the range of 70-80% will be obtained, The any one of Claims 1-6 characterized by the above-mentioned. The manufacturing method of the ultrasonic thickness sensor of the said claim.   A thin metal plate having a thickness in the range of 10 to 150 μm is used, and the piezoelectric material sintered body layer is formed to have a thickness in the range of 30 to 150 μm. The method of manufacturing an ultrasonic thickness sensor according to any one of claims 1 to 7, wherein the electrode is formed so that the thickness thereof is within a range of 10 to 100 µm.   9. The ultrasonic thickness sensor according to claim 1, wherein a lead zirconate titanate piezoelectric material powder is used as the raw material powder made of the oxide piezoelectric material. Manufacturing method.   The method for manufacturing an ultrasonic thickness sensor according to any one of claims 1 to 9, wherein a thin plate of stainless steel is used as the first electrode.

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