JP4637485B2 - Capacitive pressure transducer and process for adjusting relaxor material for the capacitive pressure transducer - Google Patents

Description

  The present invention relates to a lead iron tungstate capacitive transducer. More particularly, the present invention relates to a lead iron tungstate capacitive pressure transducer having a low temperature coefficient, a large pressure coefficient, and low hysteresis.

  Pressure measurement is extremely important in industrial manufacturing and processing. In particular, accurate pressure measurement over a wide range is necessary for industries such as automobiles, aircraft, steel, and for the synthesis of high strength materials. In all these industrial fields, the accuracy of measurement is very important not only for quality considerations but also for safety requirements. A single instrument cannot measure the entire pressure range with the same accuracy and repeatability. Also, the device is sensitive enough to small pressure changes and cannot be stable over a wide operating temperature (range 10-50 ° C.). Therefore, there is a need for a system that has the characteristics of a large pressure coefficient that can detect small changes even at high absolute pressures and that has minimal drift over a wide temperature range, ie, a small temperature coefficient. Pressure measurement has been conventionally performed using a liquid column manometer. This serves as an absolute device, but its use is limited to lower pressures of 0.1 Pa to 200 kPa. Another drawback of this device is that it cannot move from one location to another. Non-Patent Document 1 and Non-Patent Document 2 disclose that a pressure up to 300 MPa can be easily measured by a piston gauge, and that these piston gauges can be moved with a certain care. However, these piston gauges cannot be used for pressures above 300 MPa without increasing the overall size of the assembly, thereby making them cumbersome to use by trained workers. As a result, this device is useless in the field.

  Non-Patent Document 3 discloses the use of a manganin resistance wire that detects a wide range of pressures. The main drawback of manganin resistance wires is that they typically have an accuracy of ± 0.1% when an accuracy of at least ± 0.05% is usually required. Furthermore, this sensor has the undesirable property that the zero point shifts with time, leading to erroneous measurements and requiring strict temperature control during the measurement. While this device is useful for high pressure operation, it has limitations in the low pressure range such as 58 MPa. Other devices must be used to cover the lower range. Another pressure measuring device is disclosed in Non-Patent Document 4. This disclosure describes the device as a strain gauge. However, this device also has the same disadvantages as Manganin wire, and the pressure measurement accuracy of this device is low due to large hysteresis and zero shift.

  Still another type of pressure measuring device based on resistance measurement is disclosed in Patent Document 1. The disclosure of the patent teaches that pressure due to a force applied on a transducer array consisting essentially of resistive elements results in a change in resistance when the applied force changes. The dependence on pressure is related to the gradual contact of the two arrays, thereby reducing the resistance of the system. The inventors have disclosed a curve relationship between measured resistance and applied pressure. At high pressure, the resistance drops to a very low value. This low resistance value cannot be measured accurately, thereby creating a risk of error in the pressure measurement. Another disadvantage is that the device of this patent requires a threshold pressure to act as a pressure sensor. As a result, the use of this device is constrained for pressures below the required threshold. G.F.Molinar, et al attempted to use ceramic rods in 1998 to improve existing pressure sensors (Non-Patent Document 5). This pressure transducer had improved resolution and sensitivity, but lacked reproducibility and high hysteresis. The presence of the last characteristic is undesirable because it increases the error in the measured pressure.

  Patent Document 2 discloses a capacitive transducer capable of measuring pressures from as low as 100 PSI to 22,000 PSI. However, the structure used is rather complex and the metal diaphragm is separated from the dielectric alumina by a distance of 0.00005 inches and 0.020 inches. This small distance between the metal diaphragm and the insulator disk is difficult to maintain. Furthermore, the transducer is not robust to withstand transport movements when field experiments are required. Also, the disclosed device has a large hysteresis due to its structure itself. Non-Patent Document 6 discloses that an ionic crystal is formed in a capacitor having a sandwich structure and used as a pressure sensing element. Pressure measurement is based on the principle that the capacitance of a capacitor structure comprising a material as a dielectric medium between two electrodes changes with applied pressure. However, the reported material has a large capacity change due to temperature change (temperature coefficient = 250 ppm / ° C.) and a small pressure coefficient (−38 ppm / MPa). As a result, the disclosed material acts as a temperature sensor rather than as a pressure sensor.

Non-patent document 7 discloses the use of germanium bismuth oxide. It is disclosed that the pressure and temperature coefficients of the capacity are 100 ppm / MPa and 60 ppm / ° C., respectively. This suggests that capacity fluctuation due to pressure is useful as a means for measuring pressure. Reliability is guaranteed to some extent by a small temperature coefficient, but it is not a level as a pressure gauge. Still other materials are disclosed in Non-Patent Document 8. The disclosed material is a relaxor material with the following composition: 44% lead iron niobate, 44% lead zirconium niobate, 12% barium titanate. Although the pressure coefficient of this composite was observed to improve, the temperature coefficient did not decrease significantly, so again the material was not worth using as a pressure transducer with capacitive parameters. A typical sintering process temperature parameter is 900 ° C. The pressure coefficient was 430 ppm / MPa and the temperature coefficient was + 0.002 / ° C. Therefore, the relaxor material has no great application as a pressure transducer.

Thus, the common drawbacks in all prior art disclosures are inaccuracy, constraints on the usable pressure range, the need to maintain the transducer temperature accurately, and hysteresis.
PLMHeydemann and BEWelch, et al in 'Experimental Thermodynamics', (Vol.II, B.LeNiendre and B.Vodar (eds), Butterworth (1975)) RSDadson, et al in 'The Pressure Balance: Theory and Practice', National Physical Laboratory, Teddington, England and JKNSharma and Kamlesh K. Jain, Pramana, J Phys Vol 27 pp 417 (1986) GFMolinar and L. Bianchi and JKNSharma, et al AWBirks (Report No. 1566 of Queen's University of Belfast) US Pat. No. 5,578,765 GFMolinar, et al, (Measurement, Vol.24, pp 161 (1998)) PCT application PCT / WO US9405313 Andeen, et al, in Rev. of Sci. Instruments, Vol. 42, pp 495, (1971) Kamlesh K. Jain and Subhash C. Kashyap in 'High Temperature and High Pressures' Vol. 27/28 pp 371 (1995) MVRadhika Rao, et al in J Material Science Letter Vol. 12, pp 122 (1997)

  The main object of the present invention is to provide a lead iron tungstate capacitive transducer.

  Another object of the present invention is to provide a process for preparing a lead iron tungstate material having a small thermal coefficient, a large pressure coefficient, and a small hysteresis.

Yet another object of the present invention is to provide a solid state calcination process for preparing doped lead iron tungstate relaxor materials.

Yet another object of the present invention is to provide a two-step calcination process for preparing a lead iron tungstate relaxor material that does not require any doping.

  Another object of the present invention is to provide a capacitive pressure transducer for measuring a wide pressure range from a low pressure of 0.5 MPa to a high pressure of 415 MPa.

  Accordingly, the present invention provides a lead iron tungstate capacitive pressure transducer comprising a disk having a polished smooth first flat surface and a polished smooth second flat surface, wherein the polishing The smoothed first flat surface is completely covered with the metal electrode, and the polished smooth second flat surface is also covered with the metal electrode, and the polished smooth second surface including the circular portion formed and coated is formed. The metal electrode on a flat surface includes a central portion and a coated concentric annular portion separated from the central portion by a concentric annular void region, the conductive metal wire being polished smooth A metal electrode on the first flat surface, a metal electrode on the coated central portion of the polished smooth second flat surface, and a coated concentric annular portion of the polished smooth second flat surface Fixed to the metal electrode.

  In one embodiment of the invention, the metal electrode is selected from the group consisting of silver, aluminum, and gold.

  In another embodiment of the invention, the thickness of the metal electrode is in the range of 1000 to 2000 mm.

In another embodiment of the invention, the width of the concentric annular region is 10-50 inches .

  In other embodiments of the invention, the metal wire is gold or silver.

  In other embodiments of the invention, the purity of the metal wire is at least 99.99%.

  In yet another embodiment of the present invention, the metal electrode is deposited by a known vacuum evaporation method such as thermal evaporation.

  In yet another embodiment of the invention, the capacitive pressure transducer is useful for pressure measurements in the range of 0.5 MPa to 415 MPa.

  In another embodiment of the present invention, the accuracy of the pressure transducer is ± 0.05% over the entire range from 0.5 MPa to 415 MPa.

  In yet another embodiment of the present invention, the absolute value of the transducer pressure coefficient ranges from 497 ppm / MPa to 622 ppm / MPa.

  In other embodiments of the present invention, the temperature coefficient of the transducer is in the range of -0.006 / ° C to 0.008 / ° C.

  In other embodiments of the invention, the transducer can ignore the hysteresis.

The present invention also relates to a lead iron tungstate relaxor material comprising an undoped form of stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ used in the manufacture of capacitive transducers.

In one embodiment of the invention, the relaxor material is doped with 1 wt% or 5 wt% lead.

The present invention also provides wet-milled iron oxide, tungsten oxide, oxidized, weighed to produce the final material as _{unstoichiometric} Pb (Fe _2/3 W _1/3 ) O ₃ It also relates to a process for preparing a relaxor material useful for producing lead iron tungstate capacitive transducers by sintering a suitable mixture of lead in the solid state.

  In one embodiment of the process, the purity of the starting material is at least 99.9%.

In another embodiment of the present invention, excess PbO is used to obtain a self-doped stoichiometric relaxor material with a doping level on the order of 1-5% by weight.

  In other embodiments of the process, doping is performed by adding an excess amount of PbO salt to the initial mixture and wet milling the resulting mixture.

  In another embodiment of the invention, the wet milled material is calcined at a temperature of at least 800 ° C. for 2 hours.

  In another embodiment of the invention, the calcined material is further ground for about 10 hours to ensure complete homogenization of the mixed and reacted components.

  In another embodiment of the invention, a binder, preferably polyvinyl alcohol, is added to the homogenized powder.

The present invention also includes subjecting a suitable mixture of wet pulverized iron oxide and tungsten oxide to a calcining temperature of about 1000 ° C. for 2 hours, mixing the calcined material with lead oxide, It relates to a two-step calcination process by grinding for about 10 hours to produce the final product stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ .

The relaxor material of the present invention is prepared by solid state sintering. All sintered materials are pure and preferably have a purity of 99.9%. The material is weighed to the weight at which the final material is produced as undoped stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ (PFW). The same material can also be prepared by using an excess of PbO salt so as to obtain a self-doped stoichiometric PFW. Doping is performed by adding an excess amount of PbO salt into the initial mixture for wet milling for material homogenization. Excess lead oxide is added to compensate for the loss of lead components due to high vapor pressure during high temperature processing. Another advantage of adding an excess of lead oxide is to obtain lead self-doping that affects properties in the final material. The weighed and wet milled material is then calcined to fully react with the oxide and form the PFW. Calcination is generally performed at least 800 ° C. for 2 hours. The calcined material is further ground for about 10 hours. This long grinding is necessary to ensure complete homogenization of the mixed and reacted components. A binder, preferably polyvinyl alcohol, is added to the powder. This mixture is then placed in a pelletizing machine to make a sample.

In a preferred embodiment, a two-step calcination process is used to prepare the lead iron tungstate relaxor material. In this process, called the Colombite process, all starting materials are preferably pure and the purity is at least 99.9%. The material is weighed such that the final material is produced as stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ (hereinafter referred to as PFW). A suitably weighed weight of wet ground iron oxide and tungsten oxide is mixed and preferably calcined at about 1000 ° C. for 2 hours. After mixing the calcined material with lead oxide, it is pulverized for about another 10 hours. This long grinding is necessary to ensure complete homogenization of the mixed and reacted components. The mixed and calcined powder is again calcined at a temperature in the range of 750 ° C. to 830 ° C., preferably at a temperature of 810 ° C. A binder, preferably polyvinyl alcohol, is added to the powder. This mixture is then placed in a pelletizing machine to produce a disk-shaped sample.

The typical size of the sample in both preferred embodiments for preparing the relaxor material was 18 mm in diameter and 1.5 mm in thickness, but is not limited. The prepared PFW sample was then used to determine pressure measurement parameters. These samples were coated with silver film on both sides by vacuum evaporation to complete the capacitive structure. The electrode structure was such that one flat surface of the disk was preferably coated with a thin film of silver. The other flat surface opposite the first surface of the pellet is also covered with a silver film by a thin wire ring mask so that the central circular portion of the coating film is formed together with the peripheral concentric annular film at the edge. did.

All depositions were performed by a standard vacuum thermal evaporation system. The two parts were separated by a concentric annular space with a narrow gap. The annular space of this void was typically 50 mm . This concentric annular ring was used to eliminate errors due to stray capacitance during AC measurements. A thin silver wire of 99.99% purity was deposited on the metal electrode. The capacitive structure thus formed was then used to measure the thermal and pressure coefficients of doped and undoped PFW materials prepared by two preferred embodiments for preparing the relaxor material of the present invention. Capacitive structures were placed in standard specimen holders for temperature and pressure measurements. This holder was placed in a conventional high pressure vessel. The temperature of the vessel was maintained within ± 0.05 ° C. using a temperature bath (Model No. RTE 8DD, NESLAB, USA). Pressure was transmitted through a diethylhexyl sebacate fluid.

At a preset constant temperature, the pressure is gradually changed from the atmospheric pressure (0.1 MPa to 415 MPa), and the change in the capacity of the test piece is fixed at 1 kHz by an automatic capacity bridge (Andene Hagerling, model 2500 A, USA). Measured with frequency. During the measurement of the pressure characteristics of the relaxor material, data were taken of the change in capacity when the magnitude of the pressure was increased and the change in capacity when the pressure was reduced from the applied maximum pressure. This was done to determine the hysteresis of the material.

FIG. 1 shows the change in the K / K ₀ ratio with applied pressure at a sample temperature of 30 ° C. The K / K ₀ ratio was determined by calculating the dielectric constants K and K ₀ from the measured capacitance using the following equation.
Pellet thickness x capacitance dielectric constant =
Dielectric constant of vacuum x parallel plate area
K and K ₀ are dielectric constants when a pressure is applied and when no pressure is applied, respectively.

In FIG. 1, plot (A) is a change in K / K ₀ with respect to the pressure of the undoped relaxor material, and shows almost a straight line without hysteresis. Plot (B) in the same figure is for a material doped with 1% by weight of Pb. The slope of this line appears to be larger than the slope of (A), suggesting a role for doping in improving pressure characteristics. This is due to the fact that small pressure changes result in large dielectric constant changes. Curve (C) is for a material doped with 5% lead by weight, further increasing the slope of the curve between power and pressure. Thus, increased doping results in better properties of the material. The pressure coefficient is calculated using the following formula:
Dielectric constant change pressure coefficient =
Initial dielectric constant x pressure change

Next, the temperature was changed from 10 ° C. to 50 ° C. while maintaining the fixed pressure at 0.1 MPa, and the temperature coefficient of the capacity was measured. During the measurement of the temperature characteristics of the relaxor material, in order to determine the hysteresis of the material, data were taken of the change in capacity when the temperature was raised and the change in capacity when the temperature was lowered from the maximum temperature reached.

From the capacitance data and the dielectric constant, the temperature coefficient and pressure coefficient of the test piece were calculated using the following equations.
Dielectric constant change temperature coefficient =
Initial dielectric constant x temperature change

  The dielectric constant was determined using the capacitance value and other material parameters and constants from the above equation.

FIG. 2 shows the change in K / K ₀ as a function of temperature at a given fixed pressure of 0.1 MPa. Curve (A) is for the undoped material and (B) and (C) are for the 1 wt% and 5 wt% doped materials, respectively. The plot (A) in the figure gives a greater slope of change than plots (B) and (C). This clearly suggests that doping with lead improves the temperature behavior of lead iron tungstate, and that the material can be readily used as a pressure transducer with the desirable properties of a large pressure coefficient and a small temperature coefficient.

FIG. 3 shows the change in K / K ₀ ratio with the applied pressure of a lead iron tungstate relaxor material sample prepared by two-step calcination (Columbite process) while maintaining the sample temperature within 30 ° C. within ± 0.05 ° C. Is shown. The K / K ₀ ratio is obtained by calculating the dielectric constants K and K ₀ from the measured capacitance using the following formula.
Pellet thickness x capacitance dielectric constant =
Dielectric constant of vacuum x parallel plate area

K is the dielectric constant when applying a pressure, K ₀ is the dielectric constant in the case of not applying pressure.

In FIG. 3, plot (A) is a change in K / K ₀ due to the pressure of the relaxor material, showing no straight line and almost a straight line. The plot is for a sample that was calcined a second time at 750 ° C. after mixing the required amount of lead oxide in the stoichiometric material. Plot (B) in the same figure is for a sample that was calcined a second time at 810 ° C. The slope of this line appears to be slightly smaller than the slope of (A), suggesting a role that increasing sintering temperature plays in the pressure characteristics. Curve (C) is for a sample with a second calcination temperature of 830 ° C. and shows somewhat similar behavior, but the slope of the curve between K / K ₀ and pressure tends to increase. . This indicates that an increase in the calcination temperature can affect the pressure characteristics. The pressure coefficient is calculated using the following formula:
Dielectric constant change pressure coefficient =
Initial dielectric constant x pressure change

Next, the temperature of the sample was changed from 10 ° C. to 50 ° C. while maintaining the fixed pressure at 0.1 MPa, and the temperature coefficient of the capacity was measured. While measuring the temperature characteristics of the relaxor material, to determine the hysteresis of the material, we took the data of the capacity change when the temperature is increased and the capacity change when the temperature is decreased from the maximum temperature reached. It was. This was done to determine the hysteresis of the material. From the capacitance data, the dielectric constant and the temperature coefficient of the test piece were calculated using the following equations.
Dielectric constant change temperature coefficient =
Initial dielectric constant x temperature change

  The dielectric constant was determined using the capacitance value and other material parameters and constants from the above equation.

FIG. 4 shows the change in K / K ₀ as a function of temperature at a given fixed pressure of 0.1 MPa. Here, K ₀ is a dielectric constant at 10 ° C. Plot (A) shows the change in K / K ₀ with the temperature of the relaxor material and no hysteresis. The plot is for a sample that was lead calcined at 750 ° C. for the second time after mixing the amount of lead oxide required by the stoichiometric material. The curve shows a negative slope and becomes smaller with increasing temperature. This means that the material has better temperature characteristics when operating at slightly higher temperatures. Plot (B) in the same figure is for a material having a second calcination temperature of 810 ° C. (B) in the figure has a greater slope of change than the slope of plot (A), but is still negative in the temperature range under consideration. Curve (C) is for a sample with a second calcination temperature of 830 ° C. This curve behaves similarly to (A) and (B), but can still be used as a pressure transducer.

This clearly suggests that the present process without any doping material can be easily used as a pressure transducer with the desirable characteristics of a large pressure coefficient and a small temperature coefficient. The above behavior in pressure and temperature characteristics may be due to the increase in grain size of the polycrystalline material formed as the perovskite phase. The scientific principle of using lead iron tungstate relaxor materials for pressure measurements is based on the fact that these materials have large capacity changes per unit change in applied pressure. In other words, these materials have a large capacity pressure coefficient. Another feature of the material is that it has a small temperature coefficient. This property is highly desirable and important because the material acts as a pressure sensor that can be used in environments where temperature fluctuations are unavoidable. Also, a material useful as a pressure sensor should not have a memory effect, i.e. no hysteresis.

The novelty of the relaxor material of the present invention is that the relaxor material has a small temperature coefficient, a large pressure coefficient, and a low hysteresis due to the inventive step of doping the lead iron tungstate parent material with 1% excess lead. is there. To prepare lead iron tungstate (Pb, abbreviated PFW (Fe _2/3 W _1/3 ) O ₃ ), the starting oxides were PbO, Fe ₂ O ₃ , WO ₃ . The test piece was prepared using the following formula.
PbO + 1 / 3Fe ₂ O ₃ +1/3 WO ₃ + X
Where X is excess (0%, 1%, 5%) wt% PbO. The PFW took 4.4171 grams of PbO, 1.0535 grams of Fe ₂ O ₃ , 1.5294 grams of WO ₃ and was prepared as a 7 gram sample. X was zero in the two-step Columbyte process.

  The following examples are given by way of illustration only and are not intended to limit the scope of the invention.

[Example 1]
Weighed lead oxide, tungsten trioxide and ferric oxide were taken, mixed and wet-ground in acetone for 10 hours. The mixture was then calcined at 810 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. Polyvinyl alcohol was added as a binder to the pulverized powder to produce circular pellets having a diameter of 18 mm and a thickness of 1.5 mm. The pellet was later sintered at a temperature of 870 ° C. for 2 hours. After sintering, the test piece was cooled and the surface was polished, and then a silver electrode was formed on the flat surface by vacuum deposition.

[Example 2]
The pressure characteristics were measured using the material of Example 1. The material was kept in a constant temperature bath to keep the temperature of the material constant at 30 ° C. ± 0.05 ° C. The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.1 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. The pressure coefficient calculated from the slope of the change in dielectric constant with pressure was found to be -500 ppm / MPa.

[Example 3]
The temperature characteristics were measured using the material of Example 1. The pressure applied to the material was kept constant at 100 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. It was found that the temperature coefficient calculated from the slope of the change in dielectric constant with temperature was -0.0063 / ° C.

[Example 4]
Weighed lead oxide, tungsten trioxide and ferric oxide were taken and mixed with 1 wt% additional PbO and wet milled in acetone for 10 hours. The mixture was then calcined at 810 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. Polyvinyl alcohol was added as a binder to the pulverized powder to produce circular pellets having a diameter of 18 mm and a thickness of 1.5 mm. The pellet was then sintered at a temperature of 870 ° C. for 2 hours. After sintering, the specimen was cooled, the surface was polished, and a silver electrode was formed by vacuum deposition.

[Example 5]
The pressure characteristics were measured using the material of Example 4. The temperature of the material was kept constant at 30 ° C. ± 0.05 ° C. by keeping the material in a constant temperature bath. The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.1 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. It was found that the pressure coefficient calculated from the slope of the change in dielectric constant with pressure was 515 ppm / MPa.

[Example 6]
The temperature characteristics were measured using the material of Example 4. The pressure applied to the material was kept constant at 100 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. The temperature coefficient calculated from the slope of the change in dielectric constant with temperature was found to be -0.0005 / ° C.

[Example 7]
Weighed lead oxide, tungsten trioxide and ferric oxide were taken and mixed with 5 wt% additional PbO and wet milled in acetone for 10 hours. The mixture was then calcined at 810 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. Polyvinyl alcohol was added as a binder to the pulverized powder to produce circular pellets having a diameter of 18 mm and a thickness of 1.5 mm. The pellet was then sintered at a temperature of 870 ° C. for 2 hours. After sintering, the specimen was cooled, the surface was polished, and a silver electrode was formed by vacuum deposition.

[Example 8]
The pressure characteristics were measured using the material of Example 7. By keeping the material in a constant temperature bath, the temperature of the material was kept constant at 30 ° C. (± 0.05 ° C.). The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.1 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. It was found that the pressure coefficient calculated from the slope of the change in dielectric constant with pressure was 556 ppm / MPa.

[Example 9]
The temperature characteristics were measured using the material of Example 7. The pressure applied to the material was kept constant at 0.1 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. The temperature coefficient calculated from the slope of the change in dielectric constant with temperature was found to be -0.007 / ° C.

[Example 10]
Wet crushed iron oxide and tungsten oxide were weighed and calcined at a temperature of 1000 ° C. for 2 hours. The calcined material was mixed with lead oxide and then ground for about 10 hours. The mixture was then calcined at 750 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. To this pulverized powder, polyvinyl alcohol was added as a binder to produce a cylindrical specimen, and then sintered at a temperature of 870 ° C. for 2 hours. After sintering, the test piece was cooled and the surface was polished, and then a silver electrode was formed by vacuum deposition.

[Example 11]
The pressure characteristics were measured using the material of Example 10. The temperature of the material was kept constant at 30 ° C. ± 0.05 ° C. by keeping the material in a constant temperature bath. The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.5 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. The pressure coefficient calculated from the slope of the change in dielectric constant with pressure was found to be -497 ppm / MPa.

[Example 12]
The temperature characteristics were measured using the material of Example 11. The pressure applied to the material was kept constant at 0.1 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. It was found that the temperature coefficient calculated from the slope of the change in dielectric constant with temperature was -0.0033 / ° C.

[Example 13]
Wet crushed iron oxide and tungsten oxide were weighed and calcined at a temperature of 1000 ° C. for 2 hours. The calcined material was mixed with lead oxide and then ground for about 10 hours. The mixture was then calcined at 810 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. To this pulverized powder, polyvinyl alcohol was added as a binder to produce a cylindrical specimen, and then sintered at a temperature of 870 ° C. for 2 hours. After sintering, the test piece was cooled and the surface was polished, and then a silver electrode was formed by vacuum deposition.

[Example 14]
The pressure characteristics were measured using the material of Example 13. By keeping the material in a constant temperature bath, the temperature of the material was kept constant at 30 ° C. (± 0.05 ° C.). The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.5 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. The pressure coefficient calculated from the slope of the change in dielectric constant with pressure was found to be -534 ppm / MPa.

[Example 15]
The temperature characteristics were measured using the material of Example 13. The pressure applied to the material was kept constant at 0.1 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. The temperature coefficient calculated from the slope of the change in dielectric constant with temperature was found to be -0.008 / ° C.

[Example 16]
Wet crushed iron oxide and tungsten oxide were weighed and calcined at a temperature of 1000 ° C. for 2 hours. The calcined material was mixed with lead oxide and then ground for about 10 hours. The mixture was then calcined at 830 ° C. for 2 hours. The calcined powder was further pulverized for 10 hours. To this pulverized powder, polyvinyl alcohol was added as a binder to produce a cylindrical specimen, and then sintered at a temperature of 870 ° C. for 2 hours. After sintering, the test piece was cooled and the surface was polished, and then a silver electrode was formed by vacuum deposition.

[Example 17]
The pressure characteristics were measured using the material of Example 16. The temperature of the material was kept constant at 30 ° C. ± 0.05 ° C. by keeping the material in a constant temperature bath. The capacitance of the capacitor structure incorporating the lead iron tungstate material was measured as a function of applied pressure from 0.1 MPa to 415 MPa. The dielectric constant of the material was then calculated and plotted as a function of pressure. The pressure coefficient calculated from the slope of the change in dielectric constant with pressure was found to be -622 ppm / MPa.

[Example 18]
The temperature characteristics were measured using the material of Example 16. The pressure applied to the material was kept constant at 0.1 MPa. By holding the material in a constant temperature bath, the temperature is kept constant at ± 0.05 ° C., and the capacitance of the capacitor structure incorporating the lead iron tungstate material is changed as a function of the material temperature (10-50 ° C. Measured). The dielectric constant of the material was then calculated and plotted as a function of temperature. The temperature coefficient calculated from the slope of the change in dielectric constant with temperature was found to be 0.007 / ° C.

The main advantages of the present invention are:
1) Relaxor material can be used in a wide pressure range.
2) The relaxor material can be used in an environment where the temperature changes, thereby avoiding the use of additional means for temperature control.
3) The material can be used in a wide temperature range of 10 ° C to 50 ° C.
4) Capacitive transducers can use a wide range from 0.5 MPa to 415 MPa for pressure measurements with an accuracy of ± 0.05% over the entire range.

Represents the change in relative permittivity with pressure, plot (A) is for pure lead iron tungstate material, plot (B) is for material doped with 1 wt% lead, plot (C) is It is a graph showing the thing of the material which doped 5 weight% of lead. It shows the change in relative permittivity with the temperature of the sample. Plot (A) is for a pure lead iron tungstate material, Plot (B) is for a material doped with 1% lead by weight, and plot (C ) Is a graph showing a material doped with 5% by weight of lead. Represents the change in relative dielectric constant due to pressure, the sample temperature during the capacitance measurement is the same temperature of 30 ° C, curve (A) is for the second calcination temperature 750 ° C, curve (B) is the second time The calcination temperature is 810 ° C, and the curve (C) is a graph showing the second calcination temperature of 830 ° C. It represents the change in relative permittivity with the temperature of the sample. The applied pressure during all measurements is 0.1 MPa. Curve (A) is for the second calcination temperature of 750 ° C. Curve (B) is 2 The second calcination temperature is 810 ° C., and the curve (C) is a graph showing the second calcination temperature of 830 ° C.

Claims (11)

A capacitive pressure transducer comprising a disk of lead iron tungstate relaxor material having a polished smooth first flat surface and a polished smooth second flat surface,
The polished smooth first flat surface is completely covered with a metal electrode,
The polished smooth second flat surface is also covered with a metal electrode,
The metal electrode on a polished smooth second flat surface including a formed and coated circular portion is coated with a concentric annular shape separated from the central portion by a concentric annular void region. Including, and
A conductive metal wire has a metal electrode on the polished smooth first flat surface, a metal electrode on the coated central portion of the polished smooth second flat surface, and a polished smooth second flat surface. Fixed to the metal electrode on the concentric annular part of the coated surface,
Capacitive pressure transducer, wherein the lead iron tungstate relaxor material is a material obtained by doping stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ with excess PbO .   The capacitive pressure transducer of claim 1, wherein the metal electrode is selected from the group consisting of silver, aluminum, and gold.   The capacitive pressure transducer according to claim 1, wherein a thickness of the metal electrode is in a range of 1000 to 2000 mm.   The capacitive pressure transducer of claim 1, wherein the metal wire is selected from a gold wire and a silver wire.   The capacitive pressure transducer of claim 1, wherein the purity of the metal wire is at least 99.99%.   The capacitive pressure transducer of claim 1, wherein the metal electrode is deposited by a vacuum deposition method. The capacitive pressure transducer of claim 6 , wherein the metal electrode is deposited by thermal evaporation.   The capacitive pressure transducer according to claim 1, wherein the capacitive pressure transducer is useful for pressure measurement in a range of 0.5 MPa to 415 MPa. A process for preparing a relaxor material for a capacitive pressure transducer comprising a disk made of lead iron tungstate relaxor material, comprising:
The process is at least pure, wet-ground, weighed so that the final material is produced as a material doped with excess PbO in stoichiometric Pb (Fe _2/3 W _1/3 ) O ₃ Sintering a suitable mixture of 99.9% iron oxide, tungsten oxide, lead oxide in the solid state;
Doping is performed by adding an excess amount of PbO salt to the initial mixture and wet grinding the resulting mixture to homogenize the material;
Calcining the wet milled material at least 800 ° C. for 2 hours;
A process characterized in that the calcined material is further ground for about 10 hours to ensure complete homogenization of the mixed and reacted components. The process according to claim 9 , wherein a binder is added to the homogenized powder. The process of claim 10 wherein the binder comprises polyvinyl alcohol.

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