JP2013239636A - Method for manufacturing ultrasonic thickness sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin and flexible ultrasonic thickness measurement sensor which can follow up even a curved surface to be measured, can eliminate various works before and after thickness measurement, while reducing the effort and time required for the thickness measurement, by always pasting a sheet to a part to be measured, can measure the thickness of a large number of parts simultaneously or measure the thickness continuously, and can be used even at a relatively high temperature of 300°C or higher.SOLUTION: The method for manufacturing an ultrasonic thickness sensor comprises: a process including the steps of mixing bismuth titanate powder with low-melting point glass powder of bismuth-based glass or the like, applying paste of the mixture to a surface of a thin-plate-like support member to make one of electrodes with at least its surface having conductivity, and heating and sintering the support member, thereby forming a relatively-porous and flexible thin bismuth titanate sintered compact layer over the surface of the thin-plate-like support member; and a subsequent process including the steps of attaching the other electrode, and performing a polarization process, thereby arranging the sensor to have flexibility generally.

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, the formed body is sintered, and a ceramic is obtained. 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 and having a particle size of about several μm to several tens of μm. 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.

By the way, in piping of factories and plants, there are many that flow a high-temperature fluid of about 300 ° C. or more, and various containers also contain a high-temperature medium of about 300 ° C. or more. An ultrasonic thickness measurement sensor used for piping and containers needs to be able to operate reliably and measure thickness even at a relatively high temperature of 300 ° C. or higher.
Here, as described above, lead zirconate titanate (Pb (Zr, Ti) O ₃ ) called PZT is generally used as an oxide-based piezoelectric material used for piezoelectric elements for various applications. However, PZT has a Curie temperature of about 350 ° C. or less. Therefore, if PZT is used in a high temperature range of about 300 ° C. or more, polarization is lost and piezoelectric properties are not exhibited, and thickness measurement can be performed. There is a risk of disappearing. Therefore, a thickness sensor using PZT is inappropriate in a relatively high temperature environment of about 300 ° C. or higher. Therefore, an ultrasonic thickness sensor that can reliably measure the thickness even at a relatively high temperature of about 300 ° C. or higher has been developed. It is desired.
In addition, a thickness sensor installed in a location where there is a risk that the ambient temperature may rise to 300 ° C. or higher due to a fire or an accident although it is not normally used in a usage environment of 300 ° C. or higher is similarly 300 ° C. An ultrasonic thickness sensor that operates even at relatively high temperatures of the order or more is desired.

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. Provided is a method for manufacturing an ultrasonic thickness measurement sensor that can measure an ultrasonic thickness without loss of piezoelectric properties even when exposed to a high temperature of about 300 ° C. or higher.

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 a 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. Newly found.

  Here, in order to form a 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 particle size as described above is formed on the thin metal plate. However, it is conceivable to apply a paste of sintered raw material powder of about several μm to several tens of μm, heat the whole support (metal thin plate), and fire the paste. 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.

By the way, among various oxide-based piezoelectric materials, bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) called BIT has a Curie temperature of about 410 ° C., which is higher than the Curie temperature of PZT. Therefore, if BIT is used as a piezoelectric element material for an ultrasonic thickness sensor, it can be used at a higher temperature than when PZT is used. Therefore, the present inventors considered using BIT as an oxide-based piezoelectric material of an ultrasonic sensor that can be used up to about 400 ° C.

  And as a result of repeated experiments and researches on the method of manufacturing an ultrasonic thickness sensor using bismuth titanate as a piezoelectric material, the present inventor has obtained bismuth titanate as a powder to be used for sintering. (Bi) If low melting glass powder represented by (Bi) glass is added and mixed, and the mixture is fired, the low melting glass powder particles existing between the bismuth titanate powder particles even at a relatively low firing temperature. At least partly melts or softens and functions as a binder between the bismuth titanate particles, so that even if the density of the bismuth titanate powder is relatively low, the bismuth titanate particles are physically bonded to some extent. I found out that it was in a state of being. In that case, it was found that sintering was possible at about 450 to 550 ° C., and after the polarization treatment, piezoelectric properties and flexibility required for an ultrasonic thickness sensor were obtained.

  That is, in the manufacture of a piezoelectric element made of BIT, conventionally, BIT powder having a particle diameter of about 1 to 10 μm pulverized by a ball mill has been usually formed and fired. If a low-melting glass powder such as the above is added, mixed and fired, the piezoelectric material powder of the piezoelectric material powder can be fired at a temperature of about 450 to 550 ° C., which is much lower than the conventional firing temperature (about 1200 to 1300 ° C.). It is possible to obtain a sintered body layer in which the particles are physically bonded to each other, and such a sintered body layer has a polarization treatment with a piezoelectric property of a necessary degree as a thickness sensor even at a low density of 70 to 80%. A sintered body layer that can be shown later can be formed. In this case, the sintered body layer has a certain degree of strength and can exhibit flexibility while being supported by a support that also serves as an electrode. It was found. 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, It has been found that it is effective in reducing material costs. As a result, it has been found that an ultrasonic thickness sensor having flexibility that can be used even in a relatively high temperature range of about 300 ° C. or more (usually about 400 ° C. or less) can be manufactured at low cost. Invented the invention.

Therefore, in the method of manufacturing an ultrasonic thickness sensor of the present invention, basically, BIT powder as a raw material for BIT ceramic is not fired alone, but powder of low melting point glass such as bismuth glass is added as a binder. , Mix to make a raw material, and paste the mixed raw material,
It is applied to the surface of a thin plate support to be one electrode, heated and fired while supporting the paste layer or ultrafine powder layer by the thin plate support, and can be relatively porous and flexible. A bonded layer was formed on the surface of the thin plate-like support, and then the other electrode was formed and polarized so that the entire sensor could exhibit flexibility.

Specifically, the manufacturing method of the ultrasonic thickness sensor of the basic aspect (first aspect) of the present invention is:
A sintering raw material paste preparation step of preparing a paste-like sintering raw material by mixing a powder made of bismuth titanate with a low melting glass powder,
The paste of the sintering raw material is applied on the plate surface of the first electrode made of a thin plate-like support having at least one plate surface having conductivity, dried, and then on the plate surface of the first electrode. A sintering material layer forming step for forming a sintering material layer;
The sintering raw material layer is heated and fired at a temperature within a range of 450 to 550 ° C., and a firing step of forming a bismuth titanate sintered body layer,
A second electrode forming step of forming a second electrode on a surface opposite to the first electrode in the bismuth titanate sintered body layer after or after the firing step;
A polarization treatment step of applying a potential difference in the thickness direction of the sintered body layer to perform polarization treatment;
It is characterized by having.

In the method of manufacturing the ultrasonic thickness sensor according to the basic aspect of the present invention, the low melting point glass powder mixed with the powder of bismuth titanate (BIT) is obtained by using the first paste of the sintered raw material mixed as the first. In the sintered raw material layer applied and dried on a thin plate-like support as an electrode, it is present between the BIT powder particles, and in firing the sintered raw material layer, the low melting point glass powder particles At least a part is melted or softened to function as a binder between the BIT powder particles, whereby the BIT powder particles are in a state of being bonded while the density of the BIT powder remains relatively low. That is, since the low melting point glass starts to melt or soften even at a relatively low temperature, the BIT powder particles are physically bonded even at a firing temperature of 450 to 550 ° C. As a result, a relatively low density (for example, 70 to 80%) However, it is possible to obtain a sintered body layer in which BIT particles are firmly bonded to some extent. Such a sintered body layer can exhibit, after the polarization treatment, piezoelectric characteristics that do not hinder the ultrasonic thickness sensor.
Here, in the sintering material paste preparation step to the firing step, the sintering material paste layer or the sintering material layer obtained by drying the paste layer is supported by a thin plate-like support as the first electrode. Therefore, even if the thickness of the paste layer or the sintered raw material layer after drying is thinned, it can be fired without any trouble. In addition, the thin plate-like support not only functions as an electrode when used as a thickness sensor, but also functions as a support for a sintered body layer (BIT ceramic layer), and the sintered body layer peels off. Can be prevented.
If the thin plate-like support 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. Thus, it can be flexible.

  Moreover, BIT has a Curie temperature of about 410 ° C., which is higher than the Curie temperature of PZT, so that even if a sintered body layer (piezoelectric ceramic layer) made of BIT after polarization treatment is exposed to a high temperature close to 400 ° C. Polarization is not lost, and therefore it can be used as an ultrasonic thickness sensor up to about 400 ° C.

  Moreover, the manufacturing method of the ultrasonic thickness sensor of the 2nd aspect of this invention is the manufacturing method of the ultrasonic thickness sensor of the said 1st aspect, The average particle diameter is 1.0-20 as the said low melting glass powder. The thing within the range of 0.0 micrometer is used.

  Thus, by using the low melting point glass powder having an average particle size in the range of 1.0 to 20.0 μm, the final firing is achieved without causing an increase in cost for making the glass powder into a fine powder. It is possible to prevent the glass phase intervening between the piezoelectric material particles from becoming excessive in the binder layer, thereby preventing the piezoelectric characteristics from being impaired.

  The ultrasonic thickness sensor manufacturing method according to the third aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first and second aspects, wherein the bismuth titanate powder in the sintering raw material paste preparation step is used. And the low melting point glass powder are adjusted so that the total of the bismuth titanate powder and the low melting point glass powder is 100 parts by weight, and the low melting point glass powder occupies 15 to 25 parts by weight. Is.

  By adjusting the blending ratio of the piezoelectric material powder and the low-melting glass powder in this way, the effect of physically bonding the particles of the piezoelectric material powder with the melt or softened material of the low-melting glass powder in the subsequent firing step is achieved. At the same time, it is ensured that the amount of the glass phase intervening between the piezoelectric material particles in the finally obtained sintered body layer is excessive, and the piezoelectric properties after the polarization treatment are impaired. Can be avoided.

  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, wherein the low melting point glass powder is a bismuth glass powder. It is characterized by using.

  Since the bismuth-based glass powder used in the method of manufacturing the ultrasonic thickness sensor of the fourth aspect is reliably and sufficiently melted at a firing temperature of 450 to 550 ° C., it is reliable as a binder between the particles of the piezoelectric material powder. Can function.

  The ultrasonic thickness sensor manufacturing method of the fifth aspect of the present invention is the ultrasonic thickness sensor manufacturing method of any one of the first to fourth aspects, wherein the density is 70 to 80 by the baking step. % Bismuth titanate sintered body layer is obtained.

In the manufacturing method of the ultrasonic thickness sensor of the fifth aspect, the density of the BIT sintered body layer (piezoelectric ceramic layer) is set to 80% or less, which is lower than that of a conventional general piezoelectric ceramic, so that the sintering is performed. Flexibility can be exhibited in a state in which the body layer is supported on the thin plate-like support of the first electrode. At the same time, by setting the density of the BIT sintered body layer to 70% or more, it is possible to ensure the necessary piezoelectric performance as an ultrasonic thickness sensor, and the BIT sintered body layer has an excessively low density. By becoming brittle, it can prevent that a sintered compact layer peels from a 1st electrode.
In addition, in this specification, the density of a sintered compact layer shall mean the reciprocal number of a porosity, ie, a relative density.

  Furthermore, the manufacturing method of the ultrasonic thickness sensor according to the sixth aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first to fifth aspects, wherein the thickness is 30 to 150 μm by the baking step. The bismuth titanate sintered body layer within the range is formed.

  In such an ultrasonic thickness sensor manufacturing method of the sixth aspect, a thin BIT sintered body layer having a thickness in the range of 30 to 150 μm is obtained. Flexibility can be exhibited in a state of being supported by an electrode (thin plate-like support).

  Furthermore, the manufacturing method of the ultrasonic thickness sensor according to the seventh aspect of the present invention is the method of manufacturing the ultrasonic thickness sensor according to the sixth aspect, wherein the thickness of the thin plate-like support constituting the first electrode is 10 to 10. A thin metal plate having a thickness of 150 μm is used, and the second electrode is formed to have a thickness of 10 to 100 μm.

  In the manufacturing method of the ultrasonic thickness sensor of the seventh aspect, in addition to the thickness of the sintered body layer being as thin as 30 to 150 μm, the metal thin plate (first electrode) and the second electrode are also provided. Since it is thin, it is possible to easily obtain a flexible thickness sensor that is finally obtained.

  On the other hand, the ultrasonic thickness sensor manufacturing method according to the eighth aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to the sixth aspect, wherein the thickness is 30 as the thin plate-like support constituting the first electrode. Using a metallized plate in which a metallized layer having an average film thickness of 5 to 20 μm made of a high-temperature oxidation-resistant metal having good conductivity is formed on the surface of a ceramic substrate made of partially stabilized zirconia within a range of ˜100 μm, and The second electrode is formed so as to have a thickness in the range of 10 to 100 μm.

  As in the eighth embodiment, a metalized layer having an average film thickness of 5 to 20 μm made of a highly conductive high-temperature oxidation resistant metal is formed on the surface of a ceramic substrate made of partially stabilized zirconia having a thickness of 30 to 100 μm. Even when a metallized plate is used, a final ultrasonic thickness sensor can be easily obtained that exhibits flexibility.

  Further, the ultrasonic thickness sensor manufacturing method according to the ninth aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first to eighth aspects, wherein the ultrasonic electrode thickness sensor is formed before or after the second electrode forming step. In the polarization treatment step, the polarization treatment electrode is arranged so that the polarization electrode is in direct contact with the surface of the sintered body layer or the surface of the second electrode. In the method, the sintered body layer is polarized by applying a voltage between the polarization electrode and the surface of the thin plate-like support.

  By subjecting the sintered body layer to polarization treatment in this manner, the sintered body layer made of BIT exhibits the piezoelectric characteristics required for the ultrasonic thickness sensor and can actually be used as the ultrasonic thickness sensor.

  On the other hand, the ultrasonic thickness sensor manufacturing method according to the tenth aspect of the present invention is the ultrasonic thickness sensor manufacturing method according to any one of the first to eighth aspects, before or after the second electrode forming step. The polarization treatment step is performed, and in the polarization treatment step, a corona discharge electrode is disposed at a position away from the surface of the sintered body layer or the second electrode surface, and the corona discharge electrode and the support surface in the gas. And applying a voltage between them to cause a corona discharge therebetween, and exposing the sintered body layer to an electric field region caused by the corona discharge to polarize the sintered body layer. .

  As described above, in the tenth aspect, instead of the conventional general polarization treatment method applied in the ninth aspect, the polarization treatment by corona discharge is applied, but such polarization treatment by corona discharge is applied. By applying, the BIT sintered body layer can be polarized to the extent necessary for an ultrasonic thickness sensor. Further, here, the corona discharge is performed in any state in which the second electrode is not yet formed on the surface of the sintered body layer and in which the second electrode is already formed on the sintered body layer. The sintered body layer can be polarized even if the polarization treatment is performed.

  According to the method for manufacturing an ultrasonic thickness sensor of the present invention, it is possible to easily manufacture an ultrasonic thickness sensor that is thin and flexible as a whole sensor. Particularly in the method of the present invention, a powder made of bismuth titanate (BIT) as an oxide-based piezoelectric material is mixed with a low-melting glass powder to prepare a paste-like sintered raw material, and in the state of the mixed sintered material For firing, the melting or softening material of the low-melting glass functions as a binder for the bismuth titanate powder particles when firing at a low temperature of 450 to 550 ° C. They can be physically connected to each other. Since the firing temperature can be lowered as described above, it is not necessary to use an expensive material such as platinum which is remarkably excellent in high-temperature oxidation resistance as an electrode material, so that the material cost can be suppressed. 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.

  Furthermore, the ultrasonic thickness sensor obtained by the manufacturing method of the present invention is a bismuth titanate (BIT) having a Curie temperature higher than that of lead zirconate titanate (PZT) as an oxide-based piezoelectric material for ultrasonic transmission / reception. Therefore, it can be used up to a higher temperature than when using PZT and operates reliably up to about 400 ° C. Optimum for thickness measurement in various containers that contain medium of high temperature above about 300 degree C. When used for thickness measurement in other places where there is a risk of exposure to high temperature of about 300 degree C. or higher The thickness measurement can be continued even after being exposed to a high temperature.

It is a flowchart which shows 1st Embodiment of the manufacturing method of the ultrasonic thickness sensor of this invention. 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. It is a rough front view which shows an example of the condition which is implementing the polarization process by the corona discharge applied in the manufacturing method of the ultrasonic thickness sensor of this invention. FIG. 5 is a schematic longitudinal side view taken along line VV in FIG. 4. FIG. 6 is a schematic plan view taken along line VI-VI in FIG. 4.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 shows an ultrasonic thickness sensor manufacturing method according to an embodiment of the present invention.
In this embodiment, basically, a thin metal plate such as stainless steel is used as a thin plate-like support to be the first electrode, and an ultrafine powder (average particle size of 0.15) made of bismuth titanate (BIT) is used. ˜0.25 μm) is used as a sintering raw material and fired on a thin metal plate also serving as the first electrode.

Specifically, as shown in FIG.
P1: A preparation step (BIT powder preparation step) of preparing a powder made of bismuth titanate (BIT) as an oxide-based piezoelectric material,
P2: Sintering raw material paste preparation step in which the above-mentioned BIT powder is mixed with powder of low melting point glass (for example, bismuth glass) and dispersed in an appropriate dispersion medium to prepare a paste-like sintering raw material,
P3: The sintered raw material paste is applied to one plate surface of the first electrode made of a thin metal plate with a predetermined thickness, the paste layer is dried, and the sintered raw material is formed on one plate surface of the first electrode. Termination raw material layer forming step of forming a layer,
P4: After the sintering raw material layer forming step is completed, the sintering raw material layer is heated and fired to form a bismuth titanate (BIT) sintered body layer on one plate surface of the first electrode,
P5A, P5B: second electrode formation for forming a second electrode on the surface opposite to the first electrode in the sintered body layer after the end of the firing step P4 and before the next polarization treatment step Step (Note: This second electrode formation step is performed after the firing step P4 and before the next polarization treatment step (indicated as P5A in FIG. 1), and prior to the polarization treatment step (FIG. 1). And P5B))),
P6A, P6B: Polarization treatment step in which a potential difference is applied in the thickness direction of the sintered body layer to polarize the sintered body layer (note: the case where this polarization treatment is performed after the second electrode formation step P5A is denoted by P6A in FIG. And the case of performing before the second electrode forming step P5B is indicated as P6B in FIG. 1),
An ultrasonic thickness sensor using BIT as an oxide-based piezoelectric material is manufactured by a process including the above steps.
Each of these steps will be specifically described below.

[Preparation process (BIT powder preparation process) P1]
First, as a preparation step, BIT powder having an average particle size of about 1 to 10 μm is prepared.
Here, BIT powder is commercially available as a raw material powder for a piezoelectric element from a manufacturer of ceramic powder. Therefore, when implementing the method of manufacturing an ultrasonic thickness sensor of the present invention, this type of commercially available BIT powder is used. And may be used as it is or after being pulverized to an average particle size of about 1 to 10 μm. However, as a matter of course, the process for preparing the BIT powder may be started, and the process for preparing the BIT powder will be briefly described as a preparation process prior to the sintering raw material paste preparation process.

That is, an oxide powder as a raw material of BIT, for example, each powder of titanium oxide (TiO ₂ ) and bismuth oxide (Bi ₂ O ₃ ) is blended so as to have a target BIT composition, and a solvent such as ethanol, A surfactant such as polyethyleneimine is appropriately added and kneaded by a ball mill or the like, and the obtained kneaded product (slurry) is dried to obtain a mixed powder. Further, the mixed powder is temporarily fired in a powder state. This pre-baking may be normally performed in an air atmosphere at a temperature of about 700 to 1000 ° C. for about 1 to 20 hours. By such preliminary calcination, the components of the mixed oxide powder are dissolved in each other, and bismuth titanate (BIT; Bi ₄ Ti ₃ O ₁₂ ) having a bismuth layered perovskite crystal structure is generated. BIT powder (raw material powder) can be obtained by pulverizing the obtained product (usually a lump in the state after calcination) with a ball mill or the like. The particle size of the BIT powder in this state is not particularly limited, but generally the average particle size may be about 0.5 μm to 10 μm.

  In the present invention, based on the BIT composition, one or more of Mn, Mg, Ca, Sr, Ba, V, Nb, Ta, La, Nd, Sc, Gd and the like are added as trace elements. In addition, about 10% by weight or less of each may be added. In short, all materials referred to as BIT (bismuth titanate) piezoelectric ceramic materials are targeted.

[Sintering raw material paste preparation process P2]
This sintering raw material paste preparation step uses a powder of low melting point glass such as bismuth (Bi) glass, mixes the BIT powder prepared as described above with the low melting point glass powder, and uses a suitable dispersion medium. This is a step of preparing a paste-like sintered raw material by dispersing.
Here, as the low melting point glass, a glass having a softening point (softening start temperature) lower than 450 ° C. may be selected. In addition to the above bismuth glass, phosphate glass, borophosphate glass, vanadium borate system. Although glass such as alkali silicate glass and lead glass such as PbO—SiO ₂ —B ₂ O ₃ can be used, bismuth glass is most desirable.

Here, Bi ₂ O _3, which is an oxide of bismuth, does not vitrify alone, but other oxides (glass-forming oxides) such as SiO ₂ , B ₂ O ₃ , P ₂ O ₅ , Li ₂ O It is known that a glass having a low melting point can be formed by vitrification by combining with one or more selected from among these. Specific examples of the bismuth glass include Bi ₂ O ₃ —SiO ₂ glass, Bi ₂ O ₃ —Li ₂ O glass, and Bi ₂ O ₃ —B ₂ O ₃ glass.
The above Bi ₂ O ₃ —SiO ₂ glass is
_{xBi 2 O 3 · (100-} x) SiO 2
However, x = 35-65 mol%,
And Bi ₂ O ₃ —Li ₂ O glass is
_{xLi 2 O · (100-x} ) Bi 2 O 3
However, x = 20-40 mol% or 70-80 mol%,
Furthermore, Bi ₂ O ₃ —B ₂ O ₃ -based glass is
_{xBi 2 O 3 · (100-} x) B 2 O 3
However, x = 30-80 mol%,
It can be expressed. Any of these bismuth-based glasses has a softening point lower than 450 ° C., and can be suitably used as a low-melting glass to be mixed with BIT powder in the present invention.
In any of the bismuth-based glasses, if necessary, as another oxide, one of PbO, ZnO, SrO, BaO, CuO, Al ₂ O ₃ , Fe ₂ O ₃ , MgO, CeO or You may contain 2 or more types.

The average particle size of the low melting point glass powder such as bismuth glass used here is 1.0.
Within the range of ˜20.0 μm is preferable. If the average particle size of the low-melting glass powder is less than 1 μm, the cost for making the powder fine will increase. On the other hand, if the average particle size exceeds 20.0 μm, it will be between the BIT powder particles in the finally obtained sintered body layer. There is a possibility that the intervening glass phase is too large and the piezoelectric properties after the polarization treatment are impaired.
The blending ratio of the BIT powder and the low melting point glass powder such as bismuth glass is 15 to 25 parts by weight if the total amount of the BIT powder and the low melting point glass powder is 100 parts by weight. It is desirable to blend in. If the low-melting glass powder is less than 15 parts by weight, the effect of physically bonding the particles of the BIT powder by the melt or softened material of the low-melting glass powder in the subsequent firing step cannot be sufficiently obtained. May become fragile and peel from the metal thin plate that also serves as the first electrode. On the other hand, if the low melting point glass powder exceeds 25 parts by weight, the amount of the glass phase intervening between the BIT particles in the finally obtained sintered body layer is too much, which may impair the piezoelectric properties after the polarization treatment. There is.

Further, the dispersion medium for dispersing the BIT powder and the low melting point glass powder is not particularly limited, and an appropriate solvent or water such as butyl carbitol, ethanol, ethyl acetate may be used. Further, the ratio of the dispersion medium to the BIT powder and the low melting point glass powder is not particularly limited, but the ratio of the dispersion medium is determined so that the viscosity of the paste obtained by dispersion and kneading becomes 1000 to 20000 mPa · s. Is desirable. If the viscosity of the paste is less than 1000 mPa · s, it becomes difficult to form the paste with a uniform thickness on the metal thin plate in the subsequent sintering raw material layer forming step, whereas if it exceeds 20000 mPa · s, the viscosity is too high and leveling is required. There is a risk of problems in smoothing.
Thus, the paste formed by mixing the BIT powder with the low melting point glass powder such as bismuth glass and dispersing and mixing it in the dispersion medium is used as the sintering raw material paste in the subsequent sintering raw material layer forming step.

[Sintering raw material layer forming step P3]
In this sintering raw material layer forming step, the sintering raw material paste is applied to the surface of the metal thin plate as the first electrode with a predetermined thickness by coating or printing, and the surface of the metal thin plate is sintered with a predetermined thickness. In this step, a sintered raw material paste layer is formed, and the sintered raw material paste layer is further dried to form a sintered raw material layer on a thin metal plate.
The metal thin plate not only functions as an electrode, but also functions as a support in a firing step after drying or when used as a thickness sensor. Although the material of the metal thin plate is not particularly limited, in the present invention, a low melting point glass powder such as bismuth glass is used as a sintering raw material and fired at a low temperature of 450 to 550 ° C. It is not necessary to use an expensive metal that can withstand up to 1200 ° C. or more, such as platinum, as a metal thin plate as an electrode, and use stainless steel or other general heat-resistant steel as a metal thin plate that also serves as the first electrode. Can do. 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 10 μm to 150 μm. If the thickness is less than 10 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 150 μm, the flexibility of the metal thin plate is lost, and the flexibility of the thickness sensor as a whole is inferior. May be difficult to do.

A typical method for attaching the paste as the sintering material on the metal thin plate is to apply the paste to the surface of the metal thin plate. Further, as the application means in that case, a roll coater, a dock blade, a squeegee, and other application / printing means applied in general printing technology can be arbitrarily applied. After coating in this way, it is dried to form a sintered raw material layer. The drying means is not particularly limited, but usually it may be naturally dried, and in some cases, it may be heated to about 60 ° C. or less to promote drying.
Here, when the coating layer is dried, it shrinks from the state before drying to a thickness of about 1/2 to 1/4 before drying, but the ultrafine powder layer (sintered raw material layer after drying) ) (Thus, the thickness at the stage immediately before the start of the firing process described later) is preferably in the range of 70 to 200 μm. If the thickness of the ultrafine powder layer in 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, the sintered body layer becomes the first electrode. There is a risk of peeling from the metal sheet. 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.
When the paste is dried on the surface of the thin metal plate in this manner, the low melting point glass powder particles are interposed between the adjacent BIT powder particles as the dispersion medium disappears.
In addition, you may perform the drying after apply | coating a paste on the metal thin plate which serves as a 1st electrode in the initial stage of the heating for sintering in the following baking process.

[Baking step P4]
Subsequently, the sintered material layer is heated and fired in the state where the sintered material layer is formed on the plate surface of the metal thin plate as the first electrode as described above. In this firing step, the heating temperature is set within a range of 450 to 550 ° C. In the case of the method of the present invention, powder particles of a low melting glass such as bismuth glass are interposed between the particles of the BIT powder in the sintering raw material layer, and the powder particles of the low melting glass have a temperature of 450 to 550 ° C. When heating in the zone, melting or softening is started, which functions as a binder between the BIT powder particles, and can physically bond the BIT powder particles to each other. Therefore, by firing in the temperature range of 450 to 550 ° C., it is possible to obtain a sintered body layer in which the BIT powder particles are firmly bonded to each other without increasing the density so much.
Here, when the firing temperature is less than 450 ° C., the melting or softening of the low-melting glass powder particles during firing may be insufficient even when the low-melting glass powder is mixed. It may be difficult to sufficiently bond the. On the other hand, if the firing temperature exceeds 550 ° C., a direct sintering reaction between BIT powder particles proceeds during firing, and it becomes difficult to obtain a sintered body layer having a density of 80% or less. In addition, if the firing temperature exceeds 550 ° C. in this way, it is necessary to use a metal sheet having high heat resistance as the first electrode, and the material selection range of the metal sheet is narrowed, and the material cost is increased. May be incurred. The firing temperature is particularly preferably within the range of 480 to 530 ° C, even within the range of 450 to 550 ° C.

Moreover, the density of the sintered body layer in the state after firing is desirably in the range of 70 to 80%.
If the density of the BIT sintered body layer after firing becomes a high density exceeding 80%, the rigidity of the sintered body layer becomes high and the flexibility becomes inferior. As a result, when used as a thickness sensor, If the sensor 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 should be applied to curved parts such as pipes for thickness measurement. It becomes difficult. At the same time, when fired to a high density exceeding 80%, shrinkage during firing is increased, and there is a strong possibility of peeling from the metal thin plate as the first electrode. It becomes difficult to obtain a sintered body layer in close contact with a thin metal plate as an electrode.
On the other hand, when the density of the sintered body layer 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.

The atmosphere during firing is preferably air (air). Further, although the firing time varies depending on the firing temperature, it is usually preferably 1 to 10 hours.
By such a firing process, a sintered body layer made of bismuth titanate (BIT) having a predetermined thickness and a predetermined density is formed on one surface of the metal thin plate as the first electrode that also serves as a support. The

[Second electrode forming step P5A, P5B]
In the second electrode forming step, a second electrode 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 BIT sintered body layer. It is a process and is performed as a process (P5A) before performing the next polarization treatment process P6A or as a process (P5B) after performing the polarization treatment process P6B.
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 BIT as a piezoelectric material is formed on one plate surface of the first electrode (metal thin plate) that also serves as a support, and the first layer is formed on the surface of the sintered body layer. A laminate in which two electrodes are formed is obtained.

[Polarization process P6A, P6B]
This polarization treatment step is a laminate in which the second electrode is formed on the upper surface of the BIT sintered body layer on the first electrode (metal thin plate) through the second electrode formation step P5A, or the second electrode formation step. Before the implementation of P5B, the thickness of the BIT sintered body layer in the laminated body is intended for a laminated body in which the second electrode is not yet formed on the upper surface of the BIT sintered body layer on the first electrode (metal thin plate). This is a step of applying a potential difference in the direction to polarize the BIT sintered body.
As this polarization treatment,
A: A conventional general polarization treatment method, that is, a laminate is directly sandwiched between a pair of polarization electrodes, immersed in a discharge preventing liquid such as silicon oil, and a high voltage is applied between the polarization electrodes in that state. A method of polarizing the sintered body (conventional polarization method),
B: Unlike the conventional general polarization treatment method, the sintered body is exposed to an electric field region by corona discharge generated in gas (usually air) to polarize the sintered body (corona discharge polarization). Law),
Either A or B above is applied.

  When the conventional polarization method of A is applied, for example, for preventing discharge of silicon oil or the like for sandwiching the laminate by polarization electrodes from both sides and preventing the occurrence of spark discharge (all-path discharge) due to dielectric breakdown What is necessary is just to apply the high voltage DC voltage or pulse voltage about 2000-3000V / mm of thickness of a sintered compact layer to the thickness direction of a sintered compact layer in the state immersed in the medium (liquid). In order to promote polarization, a high voltage may be applied in silicone oil heated to about 80 to 200 ° C. as appropriate. Since the polarization method A itself may be the same as the conventional one, its details are omitted.

On the other hand, the corona discharge polarization method of B has been conventionally applied to polarization for surface modification of organic materials, but has been conventionally applied to polarization of inorganic materials (oxide-based inorganic piezoelectric materials). There wasn't. However, the present inventors are required to polarize so that the piezoelectric characteristics of a degree necessary for an ultrasonic thickness sensor can be obtained if it is a 70 to 80% low density BIT sintered body used as an ultrasonic thickness sensor. Found that it was possible.
That is, in a gas (usually the atmosphere), a high voltage photoelectric is applied between a corona discharge electrode composed of a linear electrode or a needle electrode and a base electrode on a flat plate facing the corona discharge electrode. If a corona discharge is caused by gas ionization from the base electrode to the base electrode, and the sintered body layer of the laminate is exposed in an electric field region (discharge region) by the corona discharge, a potential difference occurs in the thickness direction of the sintered body layer. Can be polarized. The polarization treatment by corona discharge is performed when the second electrode is formed in advance on the surface of the sintered body layer in the previous second electrode forming step, and when the second electrode is still on the surface of the sintered body layer. It has been confirmed that it can be carried out in any case where no is formed (that is, when the second electrode forming step is carried out after the polarization treatment step).

  A specific example of an apparatus for performing such polarization processing by corona discharge and details of polarization processing using the device will be described later with reference to FIGS.

By applying the polarization treatment by the conventional polarization method A or the corona discharge polarization method B as described above, the sintered body layer exhibits piezoelectric characteristics, and can be used for an ultrasonic thickness sensor.
In addition, when the 2nd electrode formation process is not performed before the polarization treatment process, the 2nd electrode formation process P5B is implemented as a post process of the polarization treatment process P6b, and the sintered body layer already polarized is performed. A second electrode is formed on the surface in the same manner as described above.

  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.

The ultrasonic thickness sensor manufactured by the method of the above embodiment and the situation at the time of use are shown in FIGS.
2 and 3, reference numeral 1 denotes a first electrode (a thin metal plate also serving as a support) of the ultrasonic thickness sensor 9, and one of the plate surfaces of the first electrode 1 is formed of a BIT made of BIT. A consolidated layer (piezoelectric ceramic layer) 3 is formed, and a second electrode 5 is formed on the surface of the sintered body layer 3. Each of the first electrode 1 and the second electrode 5 is formed. Lead wires 7A and 7B are drawn out. The thickness sensor 9 configured in this way has an adhesive 13 or the like so that one surface of the first electrode 1 is in contact with the surface of a thickness measurement object 11 (such as a metal tube wall or a container outer wall). By using and sticking, the thickness of the measurement object can be measured at any time. As the adhesive 13 at this time, a silver paste, a glass paste, a platinum paste, a gold paste, or the like may be used.

Here, the ultrasonic thickness sensor manufactured according to the embodiment of the present invention is a very thin sensor composed of a three-layer structure of a first electrode (metal thin plate), a sintered body layer, and a second electrode as a whole. Even if a jacket is provided outside the pipe for protection or heat insulation, the pipe is bonded to the outer surface of the pipe in advance when assembling the pipe, and the jacket for protection or heat insulation from the outside of the thickness sensor is used. In this state, the piping equipment can be used as it is, and the thickness can be measured 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 measuring object 11 is curved as shown in FIG. An ultrasonic thickness sensor can be bonded along the surface to measure the thickness at the curved portion.

  Furthermore, since the ultrasonic thickness sensor manufactured according to the embodiment of the present invention uses bismuth titanate (BIT) having a Curie temperature of about 410 ° C. as the piezoelectric material, it is a piezoelectric material up to about 400 ° C. The BIT sintered body layer does not lose its polarization, so that the thickness can be reliably measured even in a relatively high temperature range up to about 400 ° C.

  Next, in the case where the corona discharge polarization method is applied to the polarization treatment step, an example of a corona discharge polarization treatment apparatus for performing the polarization treatment is shown in FIGS. 4 to 6, and the polarization treatment using the apparatus is further performed. The desirable mode of will be described.

4 to 6, an electrode table 23 is located above a fixed table 21 installed on a fixed horizontal surface such as a floor surface. The electrode table 23 is connected to the fixed table 21 via an elevation adjustment mechanism 25. And is supported for vertical position adjustment. For example, the electrode base 32 is supported by a guide shaft 27 extending vertically upward from the fixed base 1 and can be moved up and down, and can be automatically or manually operated by a fluid pressure cylinder such as a hydraulic cylinder, a rotary screw mechanism, or other various link mechanisms. It is configured to be lifted and lowered by a lifting adjustment mechanism 5 having an arbitrary configuration.
The electrode table 23 has a flat surface 23A whose upper surface is horizontal, and the electrode table 23 basically has only to have a configuration in which at least its upper surface (flat surface) 23A has conductivity. However, in the case of the present embodiment, the entire electrode base 23 is made of a conductive material such as aluminum, aluminum alloy, copper or copper alloy. The electrode base 23 is electrically grounded through a ground wire 29 so as to maintain a ground potential. It should be noted that heating means (not shown) such as an electric heater, a hot water heater, and an oil heater may be incorporated in the electrode table 23 as necessary.

  Further, above the electrode base 23, as the corona discharge electrode 31, one or more (three in the illustrated example) linear electrodes 31A to 31C made of a linear conductive wire have their lengths. They are arranged so that the directions are horizontal (thus parallel to the upper surface 23A of the electrode table 23) and at equal intervals S in parallel in the same horizontal plane. These linear electrodes 31A to 31C are made of a high melting point conductive material such as tungsten (W) into a wire having an outer diameter of about 50 to 100 μm. The linear electrodes 31 </ b> A to 31 </ b> C are stretched between a pair of support portions 33 </ b> A and 33 </ b> B that protrude downward with an interval from the arm-shaped electrode support member 33, for example, so as to maintain a horizontal state. The linear electrodes 31 </ b> A to 31 </ b> C are electrically connected to one side (positive electrode or negative electrode side) of a polarization voltage marking power source 35 including a DC high voltage power source via a lead wire 36.

As described above, the polarization processing apparatus in which the linear electrodes 31A to 31C for corona discharge parallel to the upper surface 23A of the electrode table 23 are disposed at a position separated by a predetermined distance G above the electrode table 23. It is configured. The distance G between the upper surface 23 </ b> A of the electrode table 23 and the linear electrodes 31 </ b> A to 31 </ b> C can be adjusted as appropriate by changing the vertical position of the electrode table 23 by the elevation adjustment mechanism 25.
However, in some cases, while the vertical position of the electrode base 23 is fixed, the electrode support member 33 can be moved up and down, and a lift adjustment mechanism is provided in the electrode support member 33, and the electrode support member is provided as necessary. It is also possible to adjust the distance G between the upper surface 23A of the electrode base 23 and the linear electrodes 31A to 31C by moving up and down 33 to move the linear electrodes 31A to 31C up and down. Therefore, in essence, as an interval adjusting means for adjusting the distance G between the upper surface 23A of the electrode table 23 and the linear electrodes 31A to 31C, an elevation adjustment mechanism is provided on either the electrode table 23 or the electrode support member 33. Just do it.

Next, a method for applying a polarization treatment to the sintered body layer made of BIT in the laminate using the corona discharge polarization treatment apparatus shown in FIGS. 4 to 6 will be described.
Here, as described above, the laminated body 40 uses the thin metal thin plate (first electrode) 1 having a conductivity of about 10 to 150 μm such as stainless steel or platinum as a support, and the metal thin plate 1 One plate surface (upper surface) in which a sintered body layer 3 made of BIT is formed in a thin layer of about 30 to 150 μm (when the second electrode forming step is not performed before the polarization treatment step), or Similarly to the above, a sintered body layer 3 made of BIT is formed on the plate surface of a thin metal plate (first electrode) 1 as a support, and a second electrode 5 is formed on the surface of the sintered body layer 3. It has been done. However, in the examples of FIGS. 4 to 6, the stacked body 40 in which the second electrode 5 is not formed is illustrated. Here, the metal thin plate 3 functions also as a plate-like base electrode as a counter electrode of the corona discharge electrodes (linear electrodes 31; 31A to 31C) when a voltage for corona discharge is applied.

In performing polarization treatment on the sintered body layer 3 in the laminated body 40 as described above, the laminated body 40 is placed so that the plate surface (lower surface) of the thin metal plate 1 is in contact with the upper surface 23 </ b> A of the electrode base 23. In this state, the electrode base 23 and the metal thin plate 1 are electrically connected, the metal thin plate 1 becomes the same potential as the electrode base 23 (usually ground potential), and the metal thin plate 1 itself is subjected to corona discharge. It can function as a flat base electrode. In this state, the upper surface of the layered sintered body 3 is horizontal, and there is a predetermined interval between the linear electrodes 31 </ b> A to 31 </ b> C that are also horizontally stretched.
When the polarization voltage marking power source 35 is driven in this state, a high voltage is applied between the linear electrodes 31A to 31C and the thin metal plate 1, and thereby the linear electrodes 31A to 31C are directed toward the thin metal plate 1. Corona discharge occurs, and an electric field region (discharge region; potential difference region) is formed. Since the layered sintered body 3 is formed on the side of the linear electrodes 31A to 31C with respect to the metal thin plate 1, the sintered body layer 3 is exposed to an electric field by corona discharge, and as a result, the sintered body Layer 3 will be polarized.
According to the experiments by the present inventors, if the sintered body layer is made of a thin BIT having a low density of 70 to 80% and a thickness of several hundreds μm or less, the ultrasonic thickness is reduced by corona discharge. It has been found that polarization characteristics and piezoelectric characteristics required for a sensor can be obtained.

  In some cases, as already described, a configuration in which heating means is incorporated in the electrode base 23 in advance as a polarization processing apparatus is applied, and the heating means is operated during the polarization processing to connect the electrode base 23 and the thin metal plate 1. The layered sintered body 3 may be heated to, for example, about 80 to 200 ° C., and corona discharge may be caused in that state to promote polarization.

  In the case of this example, as the corona discharge electrode, a linear electrode is used instead of a general needle electrode in conventional corona discharge. When viewed in a vertical cross section of the linear electrode extending in the direction of the point, the shape is a point, and therefore, corona discharge can be generated toward the flat base electrode (metal thin plate 1). Moreover, from each of the linear electrodes 31A to 31C, an electric field (discharge region) is formed in a strip shape along the length direction of the linear electrode, so that the layered sintered body 3 having a certain surface area spreads on the surface. By simultaneously exposing the region having to an electric field, it is possible to simultaneously polarize a certain area of the layered sintered body.

Here, if a plurality of parallel electrodes (31A to 31C) are provided as the linear electrode 31, the layered sintered body 3 can be exposed to an electric field by corona discharge over a wide area at the same time.
For example, in the example shown in FIGS. 4 to 6, between each of the three linear electrodes 31 </ b> A, 31 </ b> B, 31 </ b> C arranged in parallel at intervals and the thin metal plate 1 corresponding to the flat base electrode, Electric field regions (discharge regions) 41A, 41B, and 41C are formed by corona discharge, respectively. These electric field regions 41A, 41B, and 41C are each formed as a band-like region along the length direction of the linear electrodes 31A, 31B, and 31C with a maximum width (width in the vicinity of the surface of the thin metal plate) W. And the space | interval S between linear electrode 31A, 31B, 31C and linear electrode 31A, 31B, 31C and electrode stand 23 so that the edge part vicinity of each width direction of each electric field area | region 41A, 41B, 41C may mutually overlap. If the distance G between the two is set, the entire sintered body layer 3 formed on the metal thin plate 1 is exposed to the electric field region, and the entire layered sintered body 3 is exposed. It becomes possible to polarize at the same time.

Note that the gap G ₀ between the linear electrode 31 (31A to 31C) as a corona discharge electrode during corona discharge for polarization and the flat base electrode (metal thin plate 39) opposed thereto is 0. About 5 to 2 cm is preferable. The distance G ₀ is less than 0.5 cm, the distance between the opposing electrodes is too small, there is a possibility that a spark discharge due to insulation breakdown (total road discharge) occurs, whereas if the interval G ₀ is exceeds the 2 cm, corona discharge It becomes difficult to occur.
Further, the applied voltage applied at the time of corona discharge for polarization varies depending on the gap G ₀ , but is usually preferably about 5000 to 15000V. If it is less than 5000 V, corona discharge is less likely to occur, whereas if it exceeds 15000 V, the thin linear electrode may be burned out. According to the experiments by the present inventors, if the density of the sintered body layer is 70 to 80% and the thickness is as thin as about 30 to 150 μm, the range of the inter-electrode distance condition and the applied voltage condition described above. It has been confirmed that polarization characteristics (piezoelectric characteristics) of a degree necessary for an ultrasonic thickness sensor can be obtained by corona discharge inside.
Furthermore, the time for applying the high voltage, that is, the time for performing the polarization treatment by corona discharge is preferably about 1 to 5 minutes. If the polarization treatment time is less than 1 minute, there is a possibility that the sintered body having a low density of 70 to 80% cannot be polarized to the extent necessary as an ultrasonic thickness sensor, while it exceeds 5 minutes. Even if the polarization treatment is performed, in the sintered body having a low density of 70 to 80%, the polarization does not proceed any more and only the productivity is impaired. However, in the case of a piezoelectric material that is difficult to polarize, it is allowed to perform a polarization process for a long time exceeding 5 minutes.

  4 to 6 show an example in which the polarization treatment by corona discharge is performed when the second electrode 5 is not formed on the surface of the sintered body layer 3 in advance. It goes without saying that the sintered body layer 3 formed in advance may be subjected to polarization treatment by corona discharge, and even in this case, the second electrode 5 is formed in advance on the surface of the sintered body layer 3. It has been confirmed that polarization can be performed under the same conditions as the polarization treatment conditions in a state in which no polarization is performed.

  Furthermore, in the above description, a thin plate-like support for supporting the sintered body layer (also serving as the first electrode as the ultrasonic thickness sensor) is a metal thin plate such as stainless steel. Basically, the thin plate-like supporter may be any member as long as conductivity is imparted to at least the surface in order to function as the first electrode. Therefore, for example, platinum (Pt), gold (Au), silver (Ag), other materials such as palladium (Pd), rhodium (Rh), etc. on the surface of a thin substrate having an average thickness of about 30 to 100 μm made of zirconia ceramics. It is also acceptable to use a thin plate-like support formed by metallizing a metal having excellent properties and high-temperature oxidation resistance to form a metallized layer having an average film thickness of about 5 to 20 μm.

That is, zirconia-based ceramics are generally excellent in toughness and ductility among various ceramics, and can exhibit a certain degree of flexibility if they are thin. Therefore, the ultrasonic thickness targeted by the present invention. In the sensor, it can be used as a plate-like support instead of a thin metal plate. Particularly among zirconia-based ceramics, partially stabilized zirconia is excellent in toughness and ductility, and therefore can be used for an ultrasonic thickness sensor. Examples of the partially stabilized zirconia include rare earth element oxides represented by yttrium (Y) (for example, yttria: Y ₂ O ₃ ), magnesium oxide (magnesia: MgO), calcium oxide (calcia: CaO), and the like. Among these, it is most desirable to use yttria partially-stabilized zirconia (3YSZ) added with yttria as a stabilizer in terms of characteristics (flexibility) and cost.

  Examples of the present invention will be described below.

  This Example 1 uses a bismuth-based glass powder as the low melting point glass powder, and applies a method in silicon oil sandwiched between a pair of polarization electrodes as a polarization treatment, It is the manufactured Example.

That is, first, powders of bismuth oxide (Bi ₂ O ₃ ) and titanium oxide (TiO ₂ ) were prepared as raw material powders for generating BIT, and these were in a ratio of Bi ₂ O ₃ : 2 mol and TiO ₂ : 3 mol. And the solvent was ethanol, the dispersant was polyethyleneimine, and wet kneaded with a ball mill for 24 hours to form a slurry. The slurry is dried to form a mixed powder lump, then placed in an alumina crucible, covered with alumina, heat-treated (pre-baked) at 850 ° C. for 10 hours, and BIT, that is, Bi ₄ Ti ₃ O ₁₂ powder. A lump was obtained. The BIT 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 BIT powder having an average particle size of 2.2 μm. Dried.

Next, the BIT powder having an average particle size of 2.2 μm is mixed with a bismuth-based glass powder having an average particle size of 2.5 μm, and a butyl carbitol solvent is added as a dispersion medium, kneaded by a roll mill, and baked. A raw material paste was prepared. Here, as the bismuth-based glass powder, Bi ₂ O ₃ —SiO ₂ -based glass, that is, xBi ₂ O _3. (100-x) SiO ₂ with x = 50 mol% was used. The blending ratio of BIT powder and bismuth glass powder was 20 parts by weight of bismuth glass powder with respect to 80 parts by weight of BIT powder. The obtained paste had a viscosity of 2000 mPa · s.

Next, the sintered raw material paste was applied to the center of a thin metal plate (thickness 50 μm, 1 cm × 2 cm square) made of SUS304 as a first electrode in a square shape of 8 mm square with a thickness of 100 μm. As a specific coating method, masking was performed with a tape having a thickness of 100 μm so that an opening of 8 mm square was formed on the surface of the metal thin plate, and a paste was applied to the opening with a thickness of 100 μm using a roll coater.
After coating, the paste was dried, put in an electric furnace, heated to 500 ° C. at a heating rate of 500 ° C./hr in an air atmosphere, held at 500 ° C. for 1 hour, and then furnace-aged. As a result, a BIT sintered body layer having a thickness of 60 μm made of fired BIT was baked onto a metal thin plate made of SUS304 having a thickness of 50 μm as the first electrode.
Furthermore, a silver paste for the second electrode is applied in a 4 mm circle to the center of the sintered body layer (8 mm square) made of BIT, and baked at 300 ° C., so that the second electrode (silver electrode) having an average thickness of 20 μm Formed.

In this way, a laminated body in which a sintered body layer (ceramic layer) made of BIT is formed on the first electrode (SUS304) and a second electrode (silver) is formed on the sintered body layer is obtained. It was. The density of the sintered body layer was about 75%.
Then, the laminated body was immersed in 150 degreeC silicon oil, and the polarization process which gives the electric potential difference of 3000 V / mm between the 1st electrode in the laminated body and the 2nd electrode was implemented 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. In addition, as an ultrasonic thickness sensor, when the thickness of the tube wall was measured at room temperature by attaching it to a tube wall of a stainless steel 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 well and the thickness was measured correctly. Furthermore, when the above-mentioned thickness measurement target tube wall is heated to 350 ° C. and the thickness is measured in the same manner as described above, it operates as well as at room temperature and the thickness is measured correctly. Was confirmed.

  In this Example 2, a bismuth glass powder was used as the low melting point glass powder in the same manner as in Example 1, and as the polarization treatment, a polarization treatment by corona discharge was applied instead of the above-mentioned Example 1, and ultrasonic waves were applied. It is the Example which manufactured the thickness sensor.

That is, in the same manner as in Example 1, BIT powder having an average particle size of 2.2 μm and bismuth glass powder having an average particle size of 2.5 μm were mixed at a weight ratio of 8: 2, and the dispersion medium was mixed. A butyl carbitol solvent was added and kneaded to prepare a sintered raw material paste having a viscosity of 2000 mPa · s. The paste was applied to a metal thin plate (SUS304) as a first electrode in the same manner as in Example 1, dried and fired, and a second electrode was formed on the obtained sintered body layer made of BIT, and laminated. The body.
Next, polarization treatment by corona discharge was performed as follows. That is, the apparatus shown in FIGS. 4-6 was used as a corona discharge polarization processing apparatus, the laminated body 40 was mounted on the electrode stand 23, and the polarization process by a corona discharge was performed. Here, as the corona discharge electrode 31, three linear electrodes 31 </ b> A to 31 </ b> C made of tungsten (W) having an outer diameter of 100 μm and a length of 150 mm are arranged in parallel at intervals of 30 mm. The interval between the electrode electrodes 31A to 31C was 1 cm, and a voltage of 9000 V was applied between the linear electrodes 31A to 31C and the electrode base 23, and the treatment 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 by corona discharge was examined using a d33 meter, it was confirmed that the sample was favorably polarized as in Example 1. Further, as an ultrasonic thickness sensor, it was attached to a tube wall of a stainless steel tube having an outer diameter of 10 cm and a wall thickness of 8 mm by using a gold paste as an adhesive. When the thickness of the tube wall was measured in the heated state, it was confirmed that it worked well and the thickness was measured correctly in both the room temperature and 350 ° C. heated states.

  This Example 3 uses a bismuth-based glass powder as the low melting point glass powder in the same manner as in Example 1. Also, as a polarization treatment, the polarization treatment by corona discharge is changed from that in Example 2 and is made of BIT. This is an example in which an ultrasonic thickness sensor was manufactured by carrying out in a state where the second electrode was not yet formed on the body layer, and then forming the second electrode on the sintered body layer after the polarization treatment. .

That is, it is exactly the same as Example 2 until the sintered body layer made of BIT is formed on the thin metal plate (SUS304), and the laminated body in which the second electrode is not formed on the sintered body layer. Was placed on the electrode stage 23 of the corona discharge polarization treatment apparatus shown in FIGS. 4 to 6 and subjected to polarization treatment by corona discharge under the same conditions as in Example 2.
After the polarization treatment, a silver paste for the second electrode having a 4 mm round size is applied to the center of the sintered body layer (8 mm square) made of BIT, and baked at 300 ° C., and the second electrode having an average thickness of 20 μm. (Silver electrode) was formed. 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 by corona discharge was examined using a d33 meter, it was confirmed that the sample was well polarized as in Example 2. Further, as an ultrasonic thickness sensor, it was attached to a tube wall of a stainless steel tube having an outer diameter of 10 cm and a wall thickness of 8 mm by using a gold paste as an adhesive. When the thickness of the tube wall was measured in the heated state, it was confirmed that it worked well and the thickness was measured correctly in both the room temperature and 350 ° C. heated states.

  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; thin plate support)
3 Sintered body layer (BIT piezoelectric ceramic layer)
5 Second electrode 9 Ultrasonic thickness sensor 11 Thickness measurement object 31, 31A to 31C Linear electrode (corona discharge electrode)
40 Laminated bodies 41A to 41C Electric field region (discharge region)

Claims (10)

A sintering raw material paste preparation step of preparing a paste-like sintering raw material by mixing a powder made of bismuth titanate with a low melting glass powder,
The paste of the sintering raw material is applied on the plate surface of the first electrode made of a thin plate-like support having at least one plate surface having conductivity, dried, and then on the plate surface of the first electrode. A sintering material layer forming step for forming a sintering material layer;
The sintering raw material layer is heated and fired at a temperature within a range of 450 to 550 ° C., and a firing step of forming a bismuth titanate sintered body layer,
A second electrode forming step of forming a second electrode on a surface opposite to the first electrode in the bismuth titanate sintered body layer after or after the firing step;
A polarization treatment step of applying a potential difference in the thickness direction of the sintered body layer to perform polarization treatment;
The manufacturing method of the ultrasonic thickness sensor characterized by having.   2. The method of manufacturing an ultrasonic thickness sensor according to claim 1, wherein the low melting point glass powder has an average particle diameter in the range of 1.0 to 20.0 μm.   The compounding ratio of the bismuth titanate powder and the low melting glass powder in the sintering raw material paste preparation step is 100 parts by weight of the total of the bismuth titanate powder and the low melting glass powder, and the low melting glass powder is 15 to 25 parts by weight. The method for manufacturing an ultrasonic thickness sensor according to claim 1, wherein the ultrasonic thickness sensor is adjusted so as to occupy the frequency.   The ultrasonic thickness sensor manufacturing method according to any one of claims 1 to 3, wherein a bismuth-based glass powder is used as the low melting point glass powder.   The ultrasonic thickness sensor according to any one of claims 1 to 4, wherein a bismuth titanate sintered body layer having a density in the range of 70 to 80% is obtained by the firing step. Manufacturing method.   The ultrasonic thickness sensor according to any one of claims 1 to 5, wherein a bismuth titanate sintered body layer having a thickness in a range of 30 to 150 µm is obtained by the firing step. Production method.   As the thin plate-like support constituting the first electrode, a metal thin plate having a thickness in the range of 10 to 150 μm is used, and the second electrode has a thickness in the range of 10 to 100 μm. It forms, The manufacturing method of the ultrasonic thickness sensor of Claim 6 characterized by the above-mentioned.   As the thin plate-like support constituting the first electrode, an average film thickness made of a high-temperature oxidation-resistant metal having good conductivity on the surface of a ceramic substrate made of partially stabilized zirconia having a thickness in the range of 30 to 100 μm. A metallized plate having a metallized layer having a thickness of 5 to 20 μm is used, and the second electrode is formed to have a thickness in the range of 10 to 100 μm. Item 7. A method for manufacturing an ultrasonic thickness sensor according to Item 6.   The polarization treatment step is performed before or after the second electrode forming step, and in the polarization treatment step, the polarization electrode is used so that the polarization electrode is in direct contact with the surface of the sintered body layer or the surface of the second electrode. The electrode is arranged, and the sintered body layer is polarized by applying a voltage between the electrode for polarization and the surface of the thin plate-like support in the spark discharge prevention medium. The method for manufacturing an ultrasonic thickness sensor according to claim 8.   The polarization treatment step is performed before or after the second electrode formation step, and in the polarization treatment step, a corona discharge electrode is arranged at a position away from the sintered body layer surface or the second electrode surface, A voltage is applied between the corona discharge electrode and the support surface to cause a corona discharge therebetween, and the sintered body layer is exposed by exposing the sintered body layer to an electric field region by the corona discharge. The method for manufacturing an ultrasonic thickness sensor according to any one of claims 1 to 8, wherein polarization is performed.

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