JP2015045544A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor using a carbon nano-tube specifically having excellent heat resistance, enabling its use in a severe measurement environment.SOLUTION: A pressure sensor comprises: a sensor element body 7 composed of a plurality of coated carbon nano-tubes 5 in which a coating film 5b oriented vertically to a conductive member 6 and having heat resistance on the surface; an accommodation member 8 in which the sensor element body 7 is accommodated; and a diaphragm 9 provided in an opening of the accommodation member 8 and having flexibility and conductivity, the diaphragm 9 being a pressure-receiving part covering the tip of the plurality of coated carbon nano-tubes 5. The pressure sensor is arranged so that when in a non-loaded state, the diaphragm 9 and the tip of the coated carbon nano-tubes 5 come in contact, and, when in a load-acting state, pressure is measured by detecting a change in resistance value due to that the coated carbon nano-tubes 5 are distorted via the diaphragm 9.

Description

  The present invention relates to a pressure sensor using carbon nanotubes.

  An example of a conventional pressure sensor includes a sensor element body (sensing element) including a plurality of carbon nanotubes and an electrical probe in contact with the sensor element body, and measures a mechanical state of stress and strain (for example, Patent Document 1).

JP 2006-521212 Gazette

  However, since such a conventional pressure sensor uses carbon nanotubes for the sensor element body, it is a sensor element body for the purpose of use in a harsh measurement environment such as a high temperature or an oxidizing atmosphere. Carbon nanotubes are also corroded and may not be used as pressure sensors.

  An object of the present invention is to solve the above-mentioned problems and to provide a pressure sensor using carbon nanotubes that are particularly excellent in heat resistance and can be used in a severe measurement environment.

The pressure sensor according to the first embodiment of the present invention includes a sensor element body composed of a plurality of coated carbon nanotubes that are oriented perpendicularly to a conductive member and on which a heat-resistant coating film is formed, and the sensor element body includes: A housing member to be housed, and a flexible and conductive diaphragm that is a pressure receiving portion that is provided in an opening of the housing member and covers the tips of the plurality of coated carbon nanotubes;
In a state where there is no load, the diaphragm and the tip of the coated carbon nanotube are disposed so as to abut,
In addition, the pressure can be measured by detecting a change in resistance value due to distortion of the coated carbon nanotube through the diaphragm in a state where a load is applied.

In addition, the pressure sensor according to the second embodiment of the present invention includes a sensor element body including a plurality of coated carbon nanotubes that are vertically aligned with a conductive member and have a heat-resistant coating film formed on a surface thereof, and the sensor element. A housing member in which the body is housed, and a flexible and conductive diaphragm that is a pressure receiving portion that is provided at an opening of the housing member and covers the tips of the plurality of coated carbon nanotubes,
In a state where there is no load, the diaphragm and the tip of the coated carbon nanotube are arranged so as to be separated from each other,
In addition, in a state where a load is applied, the pressure can be measured by detecting a change in resistance value due to an increase or decrease in the contact area between the coated carbon nanotube and the diaphragm.

  In the pressure sensor according to the first embodiment, the coating film is formed of silicon, germanium, gallium arsenide, indium phosphide, gallium nitride, zinc sulfide, zinc selenide, silicon carbide, silicon germanium, or two. It is preferably made of a composite material containing more than seeds.

  Furthermore, in the pressure sensor according to Example 2, the coating film is made of aluminum, titanium, copper, chromium, iron, cobalt, nickel, magnesium, zinc, gold, silver, or an alloy containing two or more kinds, Alternatively, it is preferably made of at least one oxide.

  According to the pressure sensor of the present invention, since the coated carbon nanotube in which a coating film having heat resistance is formed is used as a sensor element body, for example, use in a harsh measurement environment such as a high temperature or an oxidizing atmosphere, It is particularly excellent for use at high temperatures.

It is a block diagram which shows schematic structure of the pressure measuring device using the pressure sensor which concerns on Example 1 of this invention. It is sectional drawing which shows the state without the load of the same pressure sensor. It is sectional drawing which shows the state by which the load of the same pressure sensor was acted. It is a block diagram which shows schematic structure of the pressure measuring device using the pressure sensor which concerns on Example 2 of this invention. It is sectional drawing which shows the state without the load of the same pressure sensor. It is sectional drawing which shows the state by which the load of the same pressure sensor was acted.

[Example 1]
A pressure sensor 1 according to Embodiment 1 of the present invention and a pressure measuring instrument 10 using the pressure sensor 1 will be described with reference to FIGS.

  As shown in FIG. 1, the pressure measuring instrument 10 generally includes a sensor unit 10a and a calculation output unit 10b. The pressure sensor 1 according to the first embodiment is provided in the sensor unit 10a, and the calculation output unit 10b. 1 includes a resistance meter 2 that measures and outputs a resistance value of the pressure sensor 1, a resistance / pressure conversion unit 3 that converts the resistance value input from the resistance meter 2 into a pressure value, and outputs the resistance value. And a pressure display unit 4 for displaying the converted pressure value input from the unit 3.

Hereinafter, a pressure sensor 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.
The pressure sensor 1 according to the first embodiment of the present invention is a strain gauge type pressure sensor 1 and uses a coated carbon nanotube 5 as a sensor element as shown in FIG. As shown in FIG. 1, the pressure sensor 1 is provided in the sensor unit 10 a, and the pressure sensor 1 is connected to the resistance meter 2 of the calculation output unit 10 b and changes in resistivity due to distortion (bending) of the coated carbon nanotube 5. Is measured. That is, a received load (pressure) is detected using a piezoresistance effect (described later) due to distortion (bending) of the coated carbon nanotube 5.

  Specifically, as shown in FIG. 2, the pressure sensor 1 has a vertical orientation with respect to the conductive member 6 and is provided with a coating material having a heat resistance on the surface. A sensor element body 7 composed of a plurality of coated carbon nanotubes 5 on which a covering film 5a is formed (coated), a housing member 8 in which the sensor element body 7 is housed, and a plurality of coatings provided in the opening of the housing member 8 A diaphragm 9 having flexibility and conductivity, which is a pressure receiving portion that covers the tip of the carbon nanotube 5, is provided. The pressure sensor 1, specifically, the conductive member 6 and the diaphragm 9 are connected to the ohmmeter 2. In a state where there is no load (pressure) (hereinafter referred to as a reference state), as shown in FIG. 2, the coated carbon nanotubes 5 are not bent and have a vertical orientation. The tip is in contact with the tip. Here, as the vertically aligned coated carbon nanotubes 5, those in which the carbon nanotubes 5 a are formed within a range of approximately 90 ° ± 10 ° with respect to the conductive member 6 are used.

Multi-walled carbon nanotubes are used as the carbon nanotubes 5 a in the coated carbon nanotubes 5. The multi-walled carbon nanotube is a carbon nanotube having two or more layers. In the present invention, the multi-walled carbon nanotube to be used is desirably three or more layers. The length is 30 μm to 500 μm. The sensor element body 7 has a brush-like structure formed by aligning a plurality of carbon nanotubes 5a perpendicularly to the conductive member 6 with a number density of 10 ⁸ to 10 ¹¹ / cm ² . Further, as shown in FIG. 2, the surface of the carbon nanotubes 5a is covered with a semiconductor material having heat resistance, specifically, a silicon carbide (SiC) coating film 5b. In addition to silicon carbide, semiconductor materials include silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), and zinc sulfide. (ZnS), zinc selenide (ZnSe), silicon carbide (SiC), silicon germanium (SiGe), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ) Is applicable. At this time, if the thickness of the coating film 5b is too thin, the change in resistivity due to strain is small and the sensitivity of the sensor element body 7 is low, and if it is too thick, the coated carbon nanotube 5 is difficult to be distorted. The range of is preferable.

  As shown in FIG. 2, the conductive member 6 is a plate-like material or a film-like material made of a conductive material, and includes aluminum (Al), titanium (Ti), copper (Cu), chromium (Cr), iron. (Fe), cobalt (Co), nickel (Ni), magnesium (Mg), zinc (Zn), gold (Au), silver (Ag), tantalum (Ta), zirconium (Zr), molybdenum (Mo) One kind, an alloy containing two or more kinds, or at least one kind of oxide, or an alloy containing two or more kinds of oxides can be applied. Of these, copper (Cu), aluminum (Al), titanium (Ti), zirconium (Zr), tantalum (Ta), chromium (Cr) and molybdenum (Mo) are particularly effective.

As shown in FIG. 2, the diaphragm 9 has a two-layer structure in which a highly corrosion-resistant ceramic layer (film) 9a is overlapped on the front surface side and a conductive metal layer (film) 9b is stacked on the back surface side. . The metal layer 9b of the diaphragm 9 is a plate or film made of a material having heat resistance, oxidation resistance and conductivity. The metal layer 9b of the diaphragm 9 includes aluminum (Al), titanium (Ti), copper (Cu), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), magnesium (Mg), zinc (Zn), gold (Au), silver (Ag), tantalum (Ta), zirconium (Zr), tungsten (W), molybdenum (Mo), or an alloy containing two or more, or at least one Oxides can be applied. Of these, tungsten (W), tantalum (Ta), molybdenum (Mo), and titanium (Ti) are particularly effective, and copper (Cu), gold (Au), and the like are particularly effective in terms of conductivity. Further, aluminum oxide (Al ₂ O ₃ ) or silicon carbide (SiC) can be applied to the ceramic layer 9a.

  The housing member 8 in which the sensor element body 7 is housed is made of an insulator such as glass having heat resistance and oxidation resistance. The shape is not particularly limited, but a square container is used in this embodiment.

  Hereinafter, a pressure measuring instrument 10 using the pressure sensor 1 according to the first embodiment will be described with reference to FIG. The pressure measuring instrument 10 includes a pressure sensor 1 according to the first embodiment, an ohmmeter 2 for measuring the resistance value of the coated carbon nanotube 5 of the pressure sensor 1, and a resistance value output from the ohmmeter 2 into a pressure value. And a resistance / pressure conversion unit 3 having a conversion table for outputting a pressure value. For the conversion table, for example, resistance-pressure characteristics obtained in advance by experiments are used.

Hereinafter, a pressure measuring method using the pressure sensor 1 according to the first embodiment of the present invention will be described with reference to FIGS.
The basic principle will be described. Since the diaphragm 9 and the coated carbon nanotube 5 are arranged in contact with each other in the reference state, the coated carbon nanotube 5 is deformed by the deformation of the diaphragm 9 during pressure reception. The carbon nanotube 5 is distorted. The resistance value of the sensor element changes as the resistivity of the coated carbon nanotube 5 changes due to this strain. A so-called piezoresistance effect is obtained. The piezoresistive effect is generally said to be that when the force is applied to a semiconductor or the like, the crystal lattice is distorted and the number and mobility of carriers in the semiconductor change, so that the resistivity changes. . Specifically, in the first embodiment, the resistivity increases in proportion to the pressure F1 received by the diaphragm 9. In this embodiment, the change in resistivity, that is, the resistance value of the coated carbon nanotube 5 is measured by the ohmmeter 2 having a Wheatstone bridge circuit.

  Explaining the measurement method together with the state of the pressure sensor 1, as shown in FIG. 2, in the reference state, the diaphragm 9 and the conductive member 6 are connected to the resistance meter 2, and the diaphragm 9, the conductive member 6, and the coated carbon nanotube are connected. A voltage is applied to 5 to make it energized. As shown in FIG. 3, when the diaphragm 9 receives the pressure F <b> 1, the coated carbon nanotube 5 together with the diaphragm 9 is deformed (bent) and deformed into a concave cross section as a whole. The resistance value of the coated carbon nanotube 5 deformed in this way is measured by the resistance meter 2, and this resistance value is input to the resistance / pressure conversion unit 3, and the pressure value is determined based on the resistance-pressure characteristics obtained in advance through experiments. A value is obtained. This pressure value is displayed on the pressure display unit 4.

  In the pressure sensor 1 according to the first embodiment and the pressure measuring instrument 10 using the pressure sensor 1, the coated carbon nanotube 5 on which the heat-resistant coating film 5b is formed is used as the sensor element body. Use in a harsh measurement environment such as in an oxidizing atmosphere, particularly at a high temperature of 400 ° C. or higher (however, it is preferably below the melting point of the coating material, and about 1400 ° C. in the case of silicon carbide (SiC)). Excellent use.

  Further, in the pressure sensor 1 according to the first embodiment and the pressure measuring instrument 10 using the pressure sensor 1, since the coating film 5b is a semiconductor material, the resistivity change due to strain is larger than that of the metal, and therefore the coated carbon nanotube 5 can be detected accurately, and the sensitivity of the pressure sensor 1 can be increased.

  In the pressure sensor 1 according to the first embodiment and the pressure measuring instrument 10 using the pressure sensor 1, the carbon nanotubes having no vertical alignment are obtained by using the coated carbon nanotubes 5 having the vertical alignment for the sensor element body 7. Since the number of carbon nanotubes 5a contributing to resistance value (strain) detection is increased as compared with the case of using, the sensitivity of the pressure sensor 1 can be increased.

In the pressure measuring instrument 10 using the pressure sensor 1 according to the first embodiment, the coated carbon nanotube 5 that is a main part of the sensor element is housed in a glass housing member 8 having heat resistance and oxidation resistance. Since it is covered with the diaphragm 9 having heat resistance and oxidation resistance, the coated carbon nanotube 5 is shielded from the measurement environment and is not affected by the measurement atmosphere. Therefore, the pressure measuring instrument 10 using the pressure sensor 1 enables accurate measurement regardless of the measurement atmosphere.
[Example 2]
A pressure sensor 20 according to a second embodiment of the present invention and a pressure measuring instrument 30 using the pressure sensor 20 will be described with reference to FIGS. The pressure sensor 20 according to the second embodiment has a configuration in which the tip of the coated carbon nanotube 21 and the diaphragm 9 are spaced apart from the pressure sensor 20 according to the first embodiment. Are the same. Therefore, about the same structure as Example 1, the same code | symbol may be attached | subjected and description may be abbreviate | omitted. As shown in FIG. 4, as in the first embodiment, the pressure sensor 20 according to the second embodiment is used in the sensor unit 30 a of the pressure measuring instrument 30 including the sensor unit 30 a and the calculation output unit 30 b.

  As shown in FIG. 5, the pressure sensor 20 is vertically aligned with the conductive member 6 and has a vertical alignment property, and has a coating material, a coating film of the metal material 21 b in Example 2 formed on the surface. A sensor element body 7 composed of a plurality of coated carbon nanotubes 21, a housing member 8 in which the sensor element body 7 is housed, and a pressure receiving portion that is provided in an opening of the housing member 8 and covers the tips of the plurality of coated carbon nanotubes 21. And a diaphragm 9 having flexibility and conductivity. The pressure sensor 20, specifically, the conductive member (metal plate or metal film) 6 and the diaphragm 9 are connected to the resistance meter 2. Further, in the reference state, the diaphragm 9 and the tip of the coated carbon nanotube 21 are arranged apart from each other. About the magnitude | size of separation, it designs suitably by various conditions, such as a desired measurement range, the length of the carbon nanotube 21a, and the characteristic (deflection amount) of the diaphragm 9.

  Similar to Example 1, the carbon nanotubes 21a in the coated carbon nanotubes 21 are multi-walled carbon nanotubes (preferably three or more layers). The surface of the carbon nanotube 21a is covered with a heat-resistant metal material, specifically, a titanium (Ti) coating film 21b. In addition to titanium, heat-resistant metal materials include aluminum (Al), titanium (Ti), copper (Cu), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), magnesium Any one of (Mg), zinc (Zn), gold (Au), silver (Ag), an alloy containing two or more, or at least one oxide can be used. At this time, the thickness of the coating film 21a of the metal material coated on the surface of the coated carbon nanotube 21 is preferably 5 nm or more.

  A measurement method using the pressure sensor 20 according to the second embodiment will be described with reference to FIGS. In the reference state, as shown in FIG. 5, the diaphragm 9 and the tip of the carbon nanotube 21a are spaced apart from each other. Therefore, in a state where a load (pressure) is applied, as shown in FIG. When 9 is deformed, the diaphragm 9 and the tip side of the coated carbon nanotube 21 come into contact with each other, the contact area changes according to the number of carbon nanotubes 21a in contact with the diaphragm 9, and the contact resistance changes. Therefore, the resistance value is measured by the resistance meter 2 at the time of receiving pressure in the pressure sensor 20, and the resistance / pressure conversion unit 3 obtains the pressure value from the resistance-pressure characteristic obtained in advance by an experiment, and this is used as the measured value. .

  Explaining the measurement method together with the state of the pressure sensor 20, in the reference state, as shown in FIG. 5, the diaphragm 9 and the conductive member 6 are connected to the ohmmeter 2, and a voltage is applied to the diaphragm 9 and the conductive member 6. To turn it on. As shown in FIG. 6, when the diaphragm 9 receives the pressure F2, the number of the coated carbon nanotubes 21 that are deformed into a concave shape in cross section and come into contact gradually increases. A contact resistance value between the diaphragm 9 and the coated carbon nanotube 21 is measured by an ohmmeter 2, and this resistance value is input to the resistance / pressure conversion unit 3 and is based on a resistance-pressure characteristic obtained in advance through experiments. A pressure value is obtained. This pressure value is displayed on the pressure display unit 4.

  In the pressure sensor 20 according to the second embodiment and the pressure measuring instrument 30 using the pressure sensor 20, since the coating film 21b is made of a metal material, the conductivity is improved as compared with the semiconductor material (the coating material illustrated in the first embodiment). In addition, it is easy to detect changes in contact resistance, and since the amount of change in resistance value due to strain is small with respect to change in resistance value due to change in contact area, the relationship between the contact area and resistance value is almost proportional, Changes in contact resistance can be detected with high accuracy.

  Further, in the pressure sensor 20 according to the second embodiment and the pressure measuring instrument 30 using the pressure sensor 20, the coated carbon nanotube 21 on which the heat-resistant coating film 21 b is formed is used as the sensor element body. It can be used under the above high temperature (however, it is preferably below the melting point of the coating material, and in the case of titanium (Ti), it is about 1600 ° C.).

And the pressure measuring instrument 30 using the pressure sensor 20 according to the second embodiment includes the coated carbon nanotubes 21 that are the main part of the sensor element housed in a glass housing member 8 having heat resistance and oxidation resistance. Since it is covered with the diaphragm 9 having heat resistance and oxidation resistance, the coated carbon nanotube 21 is shielded from the measurement environment and is not affected by the measurement atmosphere. Therefore, the pressure measuring instrument 30 using the pressure sensor 20 enables accurate measurement regardless of the measurement atmosphere.
[Modification]
In the pressure sensor 1 according to the first embodiment, a semiconductor material is used as the coating material of the coating film 5b in the coated carbon nanotube 5, and in the pressure sensor 20 according to the second embodiment, the coating film 21b in the coated carbon nanotube 21 is formed. Although a metal material is used as the coating material, the present invention is not limited to this. For example, in the pressure sensor 1 according to the first embodiment, the metal material exemplified in the second embodiment is used as the coating material for the coating film 5b. In the pressure sensor 2 according to the second embodiment, the coating material for the coating film 21b is used. The semiconductor material exemplified in Example 1 may be used.

  In the pressure sensors 1 and 20 according to the first and second embodiments, the multi-walled carbon nanotubes 5a and 21a in the coated carbon nanotubes 5 and 21 are used, but the invention is not limited to this. For example, single-walled carbon nanotubes may be used. Single-walled carbon nanotubes are classified into a metal type and a semiconductor type depending on the chirality that is a way of connecting six-membered rings of carbon atoms. In Example 1, a semiconductor type having higher strain sensitivity is used in Example 2. It is preferable to use metal types having higher conductivity. As described above, the semiconductor type and the metal type can be selected based on this chirality. However, in order to use the metal type and the semiconductor type without distinction, as in Example 1 or Example 2, single-layer carbon is used. What is necessary is just to coat | cover the coating films 5b and 21b of a semiconductor material or a metal material on the surface of a nanotube, respectively. At this time, it is desirable that the coating films 5b and 21b are formed by applying a semiconductor material or a metal material to a plurality of single-walled carbon nanotubes and then drying them. In Example 1 and Example 2, when the single-walled carbon nanotube is used without being covered, the inside of the housing member 8 is an inert gas atmosphere or vacuum filled with an inert gas (for example, nitrogen or argon). It is good to make it.

  In the first embodiment, the tip of the coated carbon nanotube 5 and the diaphragm 9 are arranged in contact with each other. However, in order to more reliably contact each other, for example, both may be fixed by fusion or adhesion.

  In Example 1 and Example 2, the carbon nanotubes 5a and 21a are fixed to the conductive member 6 side. However, in order to maintain the vertical orientation of the coated carbon nanotubes 5 and 21, the base end portions of the coated carbon nanotubes 5 and 21 are formed. You may fix with resin etc.

  In the first and second embodiments, the diaphragm 9 has a two-layer structure, but a single-layer structure may naturally be used. In this case, the material used for the diaphragm 9 is the same as that of the first and second embodiments and the metal layer 9b of the diaphragm 9.

DESCRIPTION OF SYMBOLS 1 Pressure sensor 2 Resistance meter 3 Resistance / pressure conversion part 4 Pressure display part 5 Coated carbon nanotube 5a Carbon nanotube 5b Cover film 6 Conductive member 7 Sensor element body 8 Housing member 9 Diaphragm 9a Ceramic layer 9b Metal layer 10 Pressure measuring instrument 10a Sensor unit 10b Calculation output unit 20 Pressure sensor 21 Coated carbon nanotube 21a Carbon nanotube 21b Coating film 30 Pressure measuring device 30a Sensor unit 30b Calculation output unit

Claims (4)

A sensor element body composed of a plurality of coated carbon nanotubes that are oriented perpendicular to the conductive member and have a heat-resistant coating film formed on the surface, a housing member that houses the sensor element body, and an opening of the housing member A diaphragm having flexibility and conductivity, which is a pressure receiving portion that is provided in a portion and covers the tips of the plurality of coated carbon nanotubes,
In a state where there is no load, the diaphragm and the tip of the coated carbon nanotube are disposed so as to abut,
A pressure sensor characterized in that a pressure can be measured by detecting a change in resistance value due to distortion of the coated carbon nanotube through the diaphragm in a state where a load is applied. A sensor element body composed of a plurality of coated carbon nanotubes that are oriented perpendicular to the conductive member and have a heat-resistant coating film formed on the surface, a housing member that houses the sensor element body, and an opening of the housing member A diaphragm having flexibility and conductivity, which is a pressure receiving portion that is provided in a portion and covers the tips of the plurality of coated carbon nanotubes,
In a state where there is no load, the diaphragm and the tip of the coated carbon nanotube are arranged so as to be separated from each other,
In addition, the pressure sensor can measure the pressure by detecting a change in the resistance value due to an increase or decrease in the contact area between the coated carbon nanotube and the diaphragm in a state where a load is applied.   The coating film is composed of any one of silicon, germanium, gallium arsenide, indium phosphide, gallium nitride, zinc sulfide, zinc selenide, silicon carbide, silicon germanium, or a composite material including two or more kinds. The pressure sensor according to claim 1.   The coating film is made of any one of aluminum, titanium, copper, chromium, iron, cobalt, nickel, magnesium, zinc, gold, silver, an alloy containing two or more, or at least one oxide. The pressure sensor according to claim 2.

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