JP2005321215A - Catalytic combustion type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalytic combustion type gas sensor having a wide detecting concentration range and high sensitivity. <P>SOLUTION: Since the catalytic combustion type gas sensor has a thin-film carrier with in a catalyst mixed and a plurality of pores enabling a combustible gas to be brought into contact with the catalyst in the carrier are formed to the surface of the carrier, a region, where catalytic combustion is performed, is sharply increased and a detection range on a high-concentration side is drastically expanded. Further, since the carrier adheres to a conductor in a thin-film form, the heat capacity of the carrier is largely lowered and the sensitivity in a low-concentration region is enhanced. Accordingly, the detection range on the low-concentration side is also widened. Furthermore, the irregularity of the surface temperature of the carrier is not caused by the lowering of the heat capacity of the carrier and good gas selectivity can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalytic combustion type gas sensor that detects the concentration of a flammable gas by catalytic combustion of a flammable gas, and particularly relates to a highly sensitive catalytic combustion type gas sensor having a wide detectable concentration range and a manufacturing method thereof.

  The catalytic combustion type gas sensor is a sensor of a type that uses catalytic combustion of combustible gas by a catalyst and detects a change in temperature of the sensor as a change in sensor resistance value. Since the sensitivity of the sensor has a good proportional relationship with the concentration of combustible gas, a catalytic combustion type gas sensor is used for equipment for measuring and monitoring the gas concentration (for example, a safety device for a gas water heater). Has been.

  FIG. 1 is a view for explaining the structure of a conventional catalytic combustion type gas sensor. FIG. 1A is a diagram showing the structure of a catalytic combustion type gas sensor as a sensing element. The sensing element has a structure in which, for example, a platinum wire coil having a diameter of about 20 μm is wrapped spherically with alumina as a carrier. There is a catalyst (for example, a noble metal such as platinum or palladium) supported on the surface of the carrier.

  Such a contact combustion type gas sensor is manufactured by dropping a carrier on a coil and attaching it to the coil. After firing, the catalyst is further applied to the surface of the carrier and then fired.

  FIG.1 (b) is a figure which shows the basic circuit of the measuring apparatus using a contact combustion type sensor. In addition to serving as a heater for heating the sensor, the platinum coil also serves as a thermometer that captures changes in temperature due to contact combustion of combustible gas. For this reason, the resistance value of the detection element E1 also changes with respect to temperature changes other than gas catalytic combustion, for example, ambient temperature and wind changes. A temperature compensation element E2 is used to compensate for this. The temperature compensation element E2 is preferably the same in temperature characteristics as the sensing element E1, and therefore, the same platinum coil as the sensing element E1 is obtained by sintering alumina that does not carry a catalyst. The measurement principle by the circuit of FIG. 1 (b) is as follows.

  As shown in FIG. 1 (a), the air containing flammable gas is brought into contact with the sensing element E1 in which the platinum coil is wrapped with alumina having platinum or palladium having high catalytic activity for the oxidation reaction of the flammable gas. Then, the combustible gas and oxygen in the air react (catalytic combustion reaction) on the catalyst, and reaction heat (combustion heat) is generated. This reaction heat is proportional to the concentration of the combustible gas, and the resistance value of the platinum coil increases accordingly. For this reason, the resistance value of the platinum coil increases in proportion to the concentration of the combustible gas in the air. In order to convert this into an electric quantity, as shown in FIG. 1B, a bridge circuit having two sides of the detection element E1 and the temperature compensation element E2 (the other sides are fixed resistors R1 and R2) is used. The detection element E1 and the compensation element E2 are constantly supplied with a current of about 100 mA, and are maintained at a temperature necessary for the combustible gas to cause a catalytic combustion reaction. Since the electric resistances of the detection element E1 and the temperature compensation element E2 are set to be equal, the bridge circuit is kept in balance in air containing no flammable gas, and no potential difference is generated between A and B. . On the other hand, when there is a flammable gas in the air, the temperature of the sensing element E1 rises due to the contact combustion, and the electrical resistance increases, so that a potential difference occurs between A and B. Since this potential difference changes in proportion to the combustible gas concentration, the concentration of the combustible gas in the air can be known from this potential difference.

  However, the conventional catalytic combustion type gas sensor has the following problems.

  First, since the carrier covers the cylindrical coil in a spherical shape, the distance between the coil and the surface of the sphere varies depending on the position of the carrier, so that when the coil is energized to burn the combustible gas, the surface temperature Vary considerably. Therefore, not all surface temperatures can be maintained at the combustion temperature of the combustible gas to be detected, and gases other than the combustible gas to be detected are combusted, and good combustible gas selectivity cannot be obtained.

  For example, in the case of a catalytic combustion type gas sensor that detects carbon monoxide using a platinum catalyst, the platinum catalyst causes catalytic combustion with the carbon monoxide gas at a coil temperature of about 160 ° C. On the other hand, the platinum catalyst causes catalytic combustion with hydrogen gas at about 200 ° C. Therefore, if temperature unevenness occurs on the surface of the carrier and a part of the temperature rises too much, contact combustion may occur with hydrogen gas that is not a combustible gas to be detected, leading to deterioration in gas selectivity.

  Second, since the carrier is made spherical, there is a problem that the mass with respect to the surface area of the carrier is increased, and the heat capacity of the sensor is increased. When the heat capacity is large, when the combustible gas comes into contact with the catalyst and burns, the temperature of the entire sensor is increased, the detection response is deteriorated, and the detection sensitivity of the gas particularly in the low concentration region is deteriorated. The detection range on the low density side is narrowed. For example, conventionally, the measurement of the concentration of carbon monoxide gas on the low concentration side is limited to the measurement up to about 0.03% (300 ppm). Further, due to the aging of the sensor, hydrocarbons other than the combustible gas to be detected remain attached to the surface of the carrier without burning, and the carrier surface may be covered to deteriorate the sensitivity. In order to prevent such a situation, it is necessary to raise the surface temperature of the carrier to a temperature higher than the detection temperature of the detected combustible gas concentration, and to perform heat cleaning that burns hydrocarbons other than the detected combustible gas adhering to the carrier surface. However, when the heat capacity is large, there is a problem that it takes a considerable time to raise the temperature of the surface of the carrier and to lower the temperature to the detection temperature after the temperature rise.

  Thirdly, although the surface area supporting the catalyst can be increased to some extent by making fine pores on the alumina surface of the support, for high concentration gas exceeding the combustion capacity of the catalyst supported on the surface Combustion is saturated, and the detection range on the high concentration side is limited. For example, conventionally, in the measurement of the concentration of carbon monoxide gas, only measurement up to about 0.3% (3000 ppm) was possible.

  Further, Patent Document 1 (Japanese Patent Laid-Open No. 2003-121402) described below has a high gas selectivity by making the winding pitch at both ends of the coil denser than the winding pitch at the center. A sensitive catalytic combustion type gas sensor is disclosed, and a catalytic combustion type gas sensor in which a carrier is attached to a coil in a cylindrical shape by electrodeposition is also disclosed.

According to this sensor, the configuration in which the cylindrical carrier is attached to the coil can secure a surface area on the inner surface of the hollow area of the cylinder, and the contact area between the combustible gas and the catalyst is improved. Sensitivity is improved. Further, since the distance between the coil and the carrier surface can be made substantially constant, an improvement in gas selectivity can be expected. The following Patent Document 1 describes a method for producing a catalytic combustion type gas sensor by electrodeposition as follows. That is, the carrier is electrodeposited on the coil wire by immersing the coil in an electrodeposition liquid in which an appropriate amount of the electrodeposition resin and the carrier is mixed and energizing for a predetermined time. At this time, in order to form a surface on which the catalyst is applied later, the electrode is electrodeposited to a sufficient thickness until the carrier has a cylindrical shape. After the carrier is attached to the coil in a cylindrical shape, it is fired, and then the catalyst is applied to the surface of the carrier and further fired to produce a catalytic combustion type gas sensor.
JP 2003-121402 A

  However, the catalytic combustion gas sensor manufactured by the manufacturing method of Patent Document 1 also has the same problems as the spherical catalytic combustion gas sensor described above. That is, since the mass with respect to the surface area of the carrier is still large, the heat capacity is also large, and there is a limit in improving the sensitivity and the detection concentration range in the low concentration region. Further, since the heat capacity is still large, it takes a long time to raise the temperature, and temperature unevenness is likely to occur on the surface of the carrier, making it difficult to obtain good gas selectivity. Also, in the high concentration region, the contact area increases by the area of the inner surface of the cylindrical carrier, so that the detectable concentration range is slightly expanded compared to the spherical contact combustion type gas sensor, but in practical use. The conventional spherical contact combustion type gas sensor is not so different.

  Therefore, an object of the present invention is to provide a highly sensitive catalytic combustion gas sensor having a wider detection concentration range and a manufacturing method thereof.

  In order to achieve the above object, a catalytic combustion type gas sensor according to the present invention has a carrier carrying a catalyst attached to a conducting wire, and the combustible gas is obtained by catalytic combustion of the combustible gas by the catalyst. In the contact combustion type gas sensor for detecting the concentration of the catalyst, the catalyst is supported in a state of being mixed with the carrier, and a plurality of catalysts that make the catalyst inside the carrier come into contact with the combustible gas on the surface of the carrier. A hole is formed, and the thickness of the carrier is 0.1 mm to 0.5 mm.

  The catalytic combustion type gas sensor according to claim 2 is the catalytic combustion type gas sensor according to claim 1, wherein the plurality of holes pass from the first part of the surface of the carrier through the inside of the carrier. And a through hole penetrating the second portion of the surface of the carrier.

  Moreover, the catalytic combustion type gas sensor according to claim 3 is the catalytic combustion type gas sensor according to claim 1 or 2, wherein the conducting wire is formed in a coil shape, the carrier is attached to the conducting wire in a cylindrical shape, The thickness of the carrier is a thickness between the outer surface and the inner surface of the carrier.

  According to a fourth aspect of the present invention, there is provided the catalytic combustion type gas sensor according to the first or second aspect, wherein the conducting wire is configured as a flat wavy line, and the carrier adheres to the conducting wire in a thin plate shape. The thickness of the carrier is a thickness between one surface and the other surface of the carrier.

  In order to achieve the above object, the catalytic combustion type gas sensor of the present invention has a carrier supporting a catalyst attached to a conducting wire, and the combustible gas by catalytic combustion of the combustible gas by the catalyst. In the catalytic combustion type gas sensor for detecting the concentration of the volatile gas, the catalyst is supported in a state of being mixed with the carrier, and the catalyst inside the carrier can be brought into contact with the flammable gas on the surface of the carrier. A plurality of holes are formed, the plurality of holes having a through-hole penetrating from a first portion of the surface of the carrier through the inside of the carrier to a second portion of the surface of the carrier. Features.

  The catalytic combustion type gas sensor according to claim 6 is the catalytic combustion type gas sensor according to claim 5, wherein the conducting wire is configured in a coil shape, the carrier is attached to the conducting wire in a cylindrical shape, and the through hole Is characterized by penetrating between the outer surface and the inner surface of the carrier.

  The catalytic combustion type gas sensor according to claim 7 is the catalytic combustion type gas sensor according to claim 5, wherein the conducting wire is formed in a flat wavy shape, the carrier adheres to the conducting wire in a thin plate shape, 6. The catalytic combustion type gas sensor according to claim 5, wherein the through hole penetrates between one surface and the other surface of the carrier.

  Moreover, the catalytic combustion type gas sensor according to claim 8 is the catalytic combustion type gas sensor according to any one of claims 1 to 7, wherein the catalytic combustion type gas sensor is selected from the combustible gas in which hydrogen gas and carbon monoxide gas are mixed. The concentration of either the hydrogen gas or the carbon monoxide gas is detected.

  In order to achieve the above object, a method for producing a catalytic combustion type gas sensor according to the present invention provides a method for producing a catalytic combustion type gas sensor that detects the concentration of the combustible gas by the catalytic combustion of the combustible gas. In the method, an electrodeposition step of immersing a conducting wire in an electrodeposition solution containing an electrodeposition resin, a catalyst and a carrier, and attaching the carrier mixed with the electrodeposition resin and the catalyst to the conducting wire by electrodeposition; The support is baked so that the electrodeposition resin is separated from the support attached to the conductor, the catalyst is mixed with the support, and a plurality of holes are provided on the surface to allow the catalyst inside to be in contact with the combustible gas. And a firing step in which the thickness of the carrier is 0.1 mm to 0.5 mm.

  Further, the manufacturing method of the catalytic combustion type gas sensor according to claim 10 is the manufacturing method according to claim 9, wherein the plurality of holes pass from the first part through the inside of the carrier. It has a through-hole penetrating the second part.

  Moreover, the manufacturing method of the catalytic combustion type gas sensor of Claim 11 WHEREIN: The manufacturing method of Claim 9 or 10 WHEREIN: The said conducting wire is comprised by coil shape, the said carrier adheres to the said conducting wire in the shape of a cylinder, The thickness of the carrier is a thickness between an outer surface and an inner surface of the carrier.

  A method for manufacturing a catalytic combustion type gas sensor according to claim 12 is the method according to claim 9 or 10, wherein the conducting wire is formed in a flat wavy shape, and the carrier is attached to the conducting wire in a thin plate shape. The thickness of the carrier is a thickness between one side and the other side of the carrier.

  Moreover, the manufacturing method of the contact combustion type gas sensor combustion type gas sensor of the present invention for achieving the above object is a contact method for detecting the concentration of the combustible gas by the contact combustion of the combustible gas as described in claim 13. In the method for manufacturing a combustion type gas sensor, an electric wire is immersed in an electrodeposition liquid containing an electrodeposition resin, a catalyst and a carrier, and the carrier mixed with the electrodeposition resin and the catalyst is attached to the electric wire by electrodeposition. And firing the carrier so that the electrodeposition resin is separated from the carrier adhered to the conductor, and the catalyst is mixed with the carrier so that the catalyst inside can be contacted with the combustible gas. A plurality of holes are formed on the surface, the plurality of holes having through holes penetrating from the first portion of the surface of the carrier through the inside of the carrier to the second portion of the surface of the carrier. Having a firing step It is characterized in.

  Further, the manufacturing method of the catalytic combustion type gas sensor according to claim 14 is the manufacturing method according to claim 13, wherein the conducting wire is configured in a coil shape, the carrier is attached to the conducting wire in a cylindrical shape, and the penetration is made. A hole is formed between the outer surface and the inner surface of the carrier.

  Moreover, the manufacturing method of the catalytic combustion type gas sensor according to claim 15 is the manufacturing method according to claim 13, wherein the conducting wire is configured in a flat wavy shape, and the carrier adheres to the conducting wire in a thin plate shape, The through hole penetrates between one surface and the other surface of the carrier.

  The method for producing a catalytic combustion type gas sensor according to claim 16 is the method according to any one of claims 9 to 15, wherein the ratio of the weight of the electrodeposition resin to the total weight of the catalyst and the carrier is used. Is 60:40 to 85:15.

  Moreover, the manufacturing method of the contact combustion type gas sensor combustion type gas sensor according to claim 17 is the manufacturing method according to any one of claims 9 to 15, wherein the electrodeposition step is performed by immersing the electrodeposition liquid in the electrodeposition step. A voltage is intermittently applied to the conducting wire.

  In the catalytic combustion type gas sensor of the present invention, the carrier is supported in the form of a thin film with the catalyst mixed therein, and a plurality of holes are formed on the surface of the carrier so that the combustible gas can contact the catalyst inside the carrier. The area where combustion is performed is greatly increased, and the detection range on the high concentration side is dramatically expanded. Further, since the carrier is attached to the conductive wire in a thin film and made porous, the heat capacity of the carrier is greatly reduced, the sensitivity in the low concentration region is improved, and the detection range on the low concentration side is widened. Further, due to the decrease in the heat capacity, the temperature unevenness of the surface temperature of the carrier does not occur and good gas selectivity can be obtained.

  In particular, when used for the detection of carbon monoxide gas, the catalytic combustion type gas sensor of the present invention has a wide concentration measurement range of approximately 0.005% (50 ppm) to 7% (70000 ppm), and is a small and simple sensor. Nevertheless, it is possible to measure a concentration range equivalent to that of a fixed concentration measuring device of infrared type or gas chromatography type that requires a large-scale and large power source.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to the scope of the present embodiment.

  The catalytic combustion type gas sensor according to the embodiment of the present invention is supported in a state where a catalyst is mixed with a carrier adhering to a conducting wire, and further, a plurality of catalysts capable of contacting the catalyst inside the carrier with a combustible gas on the surface of the carrier. These holes are formed. Preferably, the support is made porous so as to have through holes.

  That is, compared with the case where the catalyst is supported only on the surface of the carrier, the catalyst is also supported inside the carrier, and the catalyst inside the carrier can come into contact with the combustible gas entering from a plurality of holes. As a result, the area of the carrier where the catalyst can be contact-combusted increases dramatically. In addition, compared to the fine pores derived from the crystal structure of the carrier, pores with a relatively large diameter are formed so that the catalyst inside the carrier can come into contact with the combustible gas. Sufficient breathability is also ensured for supplying the catalyst to the catalyst inside the carrier. Since the air permeability inside the hole is ensured, the inflow of combustible gas and oxygen into the inside of the hole, and further the discharge of carbon dioxide from the inside of the hole by catalytic combustion is performed efficiently. For this reason, the measurable range is greatly expanded even in a high concentration range that could not be measured due to combustion saturation. For example, in the detection of carbon monoxide gas, conventionally, the upper limit of the measurable concentration is about 0.5% (5000 ppm), but it can be measured up to about 7% (70000 ppm).

  Also, by attaching the carrier to the conductor in a thin film and making the carrier porous and reducing the mass of the carrier attached to the conductor, the heat capacity of the carrier can be reduced and the sensitivity in the low concentration region can be improved. It becomes possible. In particular, as described above, in addition to dramatically increasing the surface area at which the catalyst can be catalytically combusted, by reducing the mass of the carrier adhering to the conductor, a significant sensitivity improvement effect in a low concentration region is obtained. be able to. For example, in the detection of carbon monoxide gas, conventionally, the lower limit of the measurable concentration is about 0.03% (300 ppm), but it can be measured to about 0.005% (50 ppm). .

  Hereinafter, the structure and manufacturing method of the catalytic combustion type gas sensor in the embodiment of the present invention will be described in detail.

  FIG. 2 is an external perspective view showing an example of the structure of the catalytic combustion type gas sensor in the embodiment of the present invention. As shown in FIG. 2A, in the catalytic combustion type gas sensor 10 according to the embodiment of the present invention, a carrier 14 supporting a catalyst is attached to a coil wire (for example, platinum wire or nickel wire) 12 in a thin film shape. It has a structure. That is, the carrier 14 adheres like a garment to the coil wire 12 like a thin film, and the central portion of the coil becomes hollow. Further, when the winding pitch of the coil wire is narrower than the thickness of the thin film, the carriers adhering to the adjacent coil wire 12 come into contact with each other, and the coil wire 12 is formed like a contact combustion gas sensor 10 shown in FIG. The hollow cylindrical shape covered with the thin film carrier 14 is formed. Note that the catalyst and the plurality of holes formed in the surface of the carrier 14 not shown in FIGS. 2 and 3 will be described with reference to FIG.

  FIG. 3 is a schematic diagram showing another example of the structure of the catalytic combustion type gas sensor in the embodiment of the present invention. As shown in FIG. 3A, the catalytic combustion type gas sensor 10 may have a configuration in which a carrier 14 is attached to a flat triangular wave conductor 13 in a thin film shape instead of the coil wire 12. FIG. 3B is a view as seen from the direction of the arrow A in FIG. 3A, and shows the thickness of the carrier 14 of the catalytic combustion type gas sensor 10. Similarly to the case of the coil wire 12 of FIG. 2B, when the pitch of the triangular wave-like conductor 13 is narrow, it adheres to the adjacent conductor as in the contact combustion type gas sensor 10 shown in FIG. The carriers to be brought into contact with each other form a thin plate shape. FIG. 3D is a view seen from the direction of arrow B in FIG. 3C, and the thickness of the carrier 14 of the catalytic combustion type gas sensor 10 is shown as in FIG. 3B. The catalytic combustion type gas sensor 10 configured in such a thin plate shape is suitable for application to a portion where the thickness is limited, such as application to a printed circuit board. Moreover, as long as it is a flat thin plate shape, the shape is not limited to a triangular wave shape, and may be a rectangular wave shape, for example.

  FIG. 4 is a view for explaining the characteristics of the catalytic combustion type gas sensor according to the embodiment of the present invention. Fig.4 (a) is sectional drawing of the contact combustion type gas sensor sensor manufactured by the conventional electrodeposition manufacturing method, and the enlarged view of a dotted-line part is also shown. FIG. 4B is a cross-sectional view of a catalytic combustion type gas sensor manufactured by the electrodeposition method in the embodiment of the present invention, and an enlarged view of a dotted line portion is also shown. FIG. 4 illustrates a contact combustion type gas sensor configured by attaching a carrier 14 to a coil wire 12 in a cylindrical shape.

  In FIG. 4 (a), as described above, the catalytic combustion type gas sensor by the conventional electrodeposition manufacturing method attaches the carrier 14 to the coil wire 12 by electrodeposition and bakes it, and then applies the catalyst 16 to the surface. It is formed. Conventionally, since the catalyst 16 is intended to be supported on the surface of the carrier, it has not been considered whether or not the electrodeposition resin adhering to the conductor together with the carrier is separated during firing. For this reason, some electrodeposition resin is separated by firing, and a plurality of pores are formed on the surface of the carrier, but most of them are small and shallow that remain near the surface of the carrier. Therefore, the catalyst 16 is supported only on the surface of the carrier 14 and the shallow portion (near the surface) of the formed hole 18.

  Further, when the catalyst 16 is supported only in the vicinity of the surface of the carrier 14, in order to increase the surface area for supporting the catalyst, the carrier needs to have a certain thickness. Therefore, the thickness d1 of the carrier adhering to the coil is Relatively thick. The thickness is, for example, 1 mm or more. The relatively thick film thickness is also a factor that the holes formed by firing are not deeply formed inside the carrier. Furthermore, since most of the catalyst is attached to the surface of the carrier, combustion occurs on the surface, and carbon dioxide is generated near the surface, so that the combustible gas and oxygen are difficult to enter the pores. As a result, even if the catalyst adheres to the inside of the hole, an environment in which catalytic combustion does not easily occur inside.

  On the other hand, in FIG. 4B, in the catalytic combustion type gas sensor according to the electrodeposition method of the present invention, the catalyst 16 is supported in a state of being mixed with the carrier 14. Therefore, the catalyst 16 is present not only on the surface of the carrier 14 but also substantially uniformly inside the carrier 14. A large number of holes 18 are formed on the surface of the carrier 14 having such a size and depth as to have air permeability necessary for allowing the internal catalyst to come into contact with the combustible gas. In particular, it is preferable that a through hole 19 penetrating the outer surface and the inner surface of the cylindrical carrier is formed. Further, as illustrated in FIG. 3C, when the carrier adheres to the conducting wire in a thin plate shape, the through hole penetrates from one surface of the thin plate of the carrier to the other surface. The through-hole 19 is particularly excellent in air permeability because both ends thereof are open. In this way, by forming a large number of holes with air permeability, the supply of combustible gas and oxygen for combustion inside the carrier, and the discharge of carbon dioxide after combustion can be performed smoothly. Is called. For this reason, not only the surface of a support | carrier but the catalytic combustion by the catalyst inside a support | carrier can be performed efficiently, and the area | region where a contact combustion is performed increases dramatically. Therefore, the detectable range in the high density region is greatly expanded.

  In addition, by reducing the film thickness d2, a large number of holes formed by separation of the electrodeposition resin are formed at a relatively deep position inside the carrier during firing, and the through holes are also formed. Is easily formed. Further, by reducing the film thickness d2, the mass of the carrier itself can be reduced and the heat capacity of the carrier can be lowered, so that the sensitivity in the low concentration region can be improved. According to the experiments by the inventors of the present invention, the preferred film thickness d2 is 0.1 mm to 0.5 mm. Further, in order to make the combustible gas in the gas to be measured in contact combustion with the catalyst inside the carrier and to obtain a wide detection concentration range, the hole formed on the surface of the carrier by separation of the electrodeposition resin is approximately 10 μm to It is desired to have a diameter of 60 μm.

  As described above, the contact combustion type gas sensor according to the embodiment of the present invention has a concentration detection range on both the low concentration side and the high concentration side compared to the contact combustion type gas sensor manufactured by the conventional electrodeposition method. However, the catalytic combustion type gas sensor according to the embodiment of the present invention including this point has a very excellent effect in the following points.

  (1) A region where catalytic combustion is performed because a plurality of air-permeable holes are formed on the surface of the carrier so that the catalyst inside the carrier can come into contact with the combustible gas. Dramatically increases the detectable range even in a high concentration region.

  (2) The mass of the carrier is greatly reduced and the heat capacity is greatly reduced while sufficiently securing a region where catalytic combustion is performed, so that the detectable range on the low concentration side is expanded, and the sensitivity in that region is further increased. Maintained stably.

  (3) Since the carrier is attached to the conductive wire in a thin film and is made porous, the heat capacity of the carrier is reduced, so that there is no variation in the temperature of the surface of the carrier and the selectivity to the type of combustible gas is improved.

  (4) Since the heat capacity of the carrier is small, the time until the temperature falls to the appropriate measurement temperature (set temperature) for heat-up and detection after heat-up in the area where catalytic combustion is performed is greatly reduced. Is done.

  (5) Since the time required for heat cleaning is shortened, the load on the conducting wire is reduced and the life of the conducting wire is extended.

  FIG. 5 is a diagram for explaining a method of manufacturing the catalytic combustion type gas sensor in the present embodiment. The catalytic combustion type gas sensor of the present invention is manufactured as follows using an electrodeposition coating method.

  First, as shown to Fig.5 (a), a coil wire is created from the nickel (Ni) wire and platinum (Pt) wire of a thin wire | line of about 15 micrometers-30 micrometers. In addition, an Fe—Pd alloy wire may be used as the wire of the coil wire. A coil wire prepared in advance may be prepared.

  Subsequently, as shown in FIG. 5B, the coil wire is immersed in an electrodeposition solution in which a carrier, a catalyst, and an electrodeposition resin are mixed. A coil wire is used as a cathode, a predetermined voltage is applied for a predetermined time, and a carrier in which a catalyst and an electrodeposition resin are mixed is electrodeposited on the coil wire. At this time, it is preferable to apply the voltage intermittently. The voltage is intermittently applied because it is possible to provide a diffusion time for maintaining a constant concentration of the components of the electrodeposition liquid during electrodeposition, compared with the case where a constant voltage is applied continuously. This is because the concentration unevenness of the liquid component can be suppressed.

  FIG. 6 is a diagram illustrating a waveform example of the voltage applied intermittently. In the experiments by the inventors, the electrodeposition state is good if the frequency is 10 Hz or more, but if the frequency is smaller than that, adhesion at both ends of the coil wire occurs preferentially, and the amount of adhesion of the carrier varies. Resulting in loss of uniformity.

  The electrodeposition time is determined based on the integrated power amount and adjusted so that the integrated power amount becomes a predetermined amount. This is because the film thickness changes according to the integrated power amount. The inventor of the present invention has found that the above-described remarkable characteristics are obtained when the film thickness is 0.1 mm to 0.5 mm (more preferably, 0.15 to 0.35 mm). For this reason, the integrated electric energy that is within the range of the film thickness is obtained, and the electrodeposition time that becomes the integrated electric energy is determined for the set current value and voltage value. In the embodiment described below, the integrated power amount for making the film thickness about 0.15 to 0.35 mm is about 0.6 to 2.0 mW. If the electrodeposition time is too long, the film thickness becomes thicker than that range, so the amount of adhesion increases, the mass of the sensor increases, and the heat capacity increases, resulting in a decrease in sensitivity. On the other hand, when the electrodeposition time is too short, the amount of adhesion is not constant, and an exposed portion where the electrodeposition liquid does not adhere to the coil is generated.

  The electrodeposition liquid is an aqueous solution containing a catalyst, a carrier, and an electrodeposition resin, and the respective components are mixed at a predetermined ratio. About the component ratio (weight ratio) of each component, it is preferable that electrodeposition resin: (catalyst + support | carrier) is 60: 40-85: 15. By relatively increasing the ratio of the electrodeposition resin that is oxidized during baking to become pores (up to about 85%), a large number of through-holes and relatively large and deep holes can be formed. The catalyst can be used effectively.

  When the electrodeposition conditions (time, voltage, etc.) are the same, if the amount of electrodeposition resin is small (less than 60%), the mass after firing does not decrease sufficiently, and the heat capacity increases, causing a decrease in sensitivity. Further, when the amount of the electrodeposition resin is too much (over 85%), the mass is reduced and the heat capacity is also reduced, so that the sensitivity is improved. However, when the ratio of the pore portion to the volume of the carrier is too large, for example, Problems arise. That is, if the ratio of the pore portion to the volume of the carrier becomes too large, the amount of oxygen (air layer) on the surface of the carrier increases, and the temperature of the surface of the carrier becomes too high when a relatively high concentration of combustible gas is burned. . For example, when a carbon monoxide gas concentration is detected from a gas in which hydrogen gas and carbon monoxide gas are mixed using a platinum (Pt) catalyst, the coil temperature for burning the carbon monoxide gas in the platinum catalyst is: The coil temperature for burning hydrogen is 200 ° C., which is relatively close to about 160 ° C. Therefore, when a contact combustion type gas sensor is used for detecting the concentration of carbon monoxide gas, if the temperature of the support surface rises too much, there is a risk of reaching the combustion temperature of hydrogen, and a gas in which carbon monoxide gas and hydrogen are mixed. (In general, when gas using hydrocarbons as fuel, such as city gas, is incompletely burned), hydrogen is also burned near the surface, leading to poor carbon monoxide gas detection selectivity. .

The carrier is usually alumina (Al ₂ O ₃ ), but silica (SiO ₂ ), zinc oxide (ZnO), or the like may be used. The electrodeposition resin is, for example, a mixture of vinyl acetate and an acrylic acid alkyl ester (acrylic resin).

  The catalyst is selected from platinum (Pt), palladium (Pd), rhodium (Rd), and the like according to the type of combustible gas to be detected. For example, platinum (Pt) is used for detecting the concentration of carbon monoxide gas. The coil temperature for burning carbon monoxide gas in the platinum (Pt) catalyst is about 160 ° C. In the platinum catalyst, the coil temperature for burning hydrogen gas is 200 ° C., which is relatively close to the temperature of carbon monoxide gas. In the catalytic combustion type gas sensor of the present embodiment using a platinum catalyst, since the carrier is attached to the coil wire in a thin film form, the distance between the coil wire and the surface of the carrier becomes closer and becomes almost constant. There is no variation in temperature on the surface of the carrier, and good carbon monoxide gas selectivity can be obtained. Therefore, the concentration of the carbon monoxide gas can be accurately detected without burning the hydrogen gas even in a gas mixture of the carbon monoxide gas and the hydrogen gas.

  Further, palladium (Pd) is used for detecting the concentration of hydrogen gas. In the palladium catalyst, the coil temperature for burning hydrogen gas is about 150 ° C., whereas the coil temperature for burning carbon monoxide gas is about 180 ° C. Also in this case, the coil temperatures of hydrogen gas and carbon monoxide gas are relatively close. In the catalytic combustion type gas sensor of the embodiment of the present invention using palladium, good hydrogen gas selectivity can be obtained. That is, the concentration of the hydrogen gas can be accurately detected without burning the carbon monoxide gas even in a gas mixture of carbon monoxide gas and hydrogen gas.

  As shown in FIG. 5 (c), the mixture of the catalyst, the electrodeposition resin and the carrier adheres to the coil wire in a thin film shape by electrodeposition, and the coil wire as shown in FIG. 2 (b) and FIG. 3 (b). When the pitch is narrow, the mixtures adhering to the adjacent coil wires come into contact with each other and form a hollow thin-film cylindrical shape in appearance.

  Then, as shown in FIG. 5 (d), when the coil in which the mixture of the catalyst, the electrodeposition resin and the carrier is attached in a thin film is fired, the electrodeposition resin component mixed in the attached carrier is oxidized and separated. Therefore, the deposit becomes a foamed carrier having a plurality of pores mixed with the catalyst. In the firing, heat is applied from the outside in an air (oxygen) atmosphere, and at the same time, the coil is energized to heat the coil, thereby heating from the inside. Firing is performed under conditions necessary for separating the electrodeposition resin. Preferable firing conditions are an atmospheric temperature: 500 to 700 ° C., a coil applied voltage: 3 to 5 V, and a firing time: 10 minutes or more. If the ambient temperature and the applied voltage are increased more than this, the coil wire (in the case of Ni wire) will oxidize and will no longer serve as a coil. Moreover, when the above conditions are satisfied, the electrodeposition resin is not sufficiently combusted and the characteristics of the catalytic combustion type gas sensor of the present invention cannot be exhibited.

  Examples of the catalytic combustion type gas sensor of the present invention will be described below.

  As the coil wire, a nickel (Ni) wire having a diameter of 18 μm and a winding pitch of 0.1 mm with 21 turns was used.

The electrodeposition liquid is an aqueous solution containing a catalyst, a carrier, and an electrodeposition resin. The constituent ratio of each component is catalyst: 8.5%, carrier (alumina): 6.0%, electrodeposition resin: 55.7. %, Water: 29.8% was used. The electrodeposition resin is a mixture of vinyl acetate and alkyl acrylate (acrylic resin), and the composition ratio is (Please tell me the composition ratio), and the catalyst is platinum (Pt), chromium oxide ( Cr ₂ O ₃ ) and copper oxide (CuO) are mixed at a molar ratio of 1: 0.5: 0.5.

  Electrodeposition was performed by intermittently applying a voltage. An AC voltage with a maximum voltage of 20 V and a frequency of 50 Hz was applied, the current value was 20 mA, and three sample sensors with different application times were created. As described above, the difference in application time, that is, the difference in accumulated electric energy (mW), and the film thickness of the carrier attached to the coil is substantially proportional to the accumulated electric energy.

  Table 1 shows the electrodeposition conditions of the prepared sample sensor.

コイルに電着液が付着したセンサの焼成条件は、以下の通りである。

The firing conditions of the sensor with the electrodeposition liquid attached to the coil are as follows.

Atmospheric temperature: 500 ° C
Coil applied voltage: 3V (coil temperature 300 ° C)
Baking time: 10 minutes FIG. 7 is a graph showing sensitivity characteristics of the prepared sample sensor with respect to carbon monoxide gas (CO), and FIG. 7A shows sensitivity characteristics on the low concentration side, and FIG. (B) shows sensitivity characteristics on the high density side. As is apparent from FIG. 7A, regarding the sensitivity characteristics on the low concentration side, the sensor 1 with a smaller film thickness is more sensitive to the density change on the lower concentration side than the sensors 2 and 3 with a relatively thick film thickness. Sensitivity is greatly improved even in the region of 0.03% (300ppm) or less, which was not able to be measured in the past, because the gradient of the sensor output is large. It was.

  On the other hand, in the high concentration region, as is apparent from FIG. 7B, the sensor 1 with the thinnest film thickness saturates the sensor output with respect to the concentration change even if the concentration exceeds 3% (30000 ppm). However, although it has a good correlation and is not shown in the figure, it was revealed that the concentration can be measured up to 7% (70000 ppm). Regarding the sensor 2 and the sensor 3, the sensor output was saturated before the concentrations of 2% and 3%, respectively, and a good sensor output in the high concentration region was not obtained. These sensors have a relatively large film thickness and a large heat capacity, so the sensitivity is not improved, and no through-holes are formed. Therefore, catalytic combustion is not efficiently performed inside the carrier, and catalytic combustion is performed. This is probably because the surface area expansion effect was not obtained.

It is a figure for demonstrating the structure of the conventional catalytic combustion type gas sensor. It is an external appearance perspective view which shows the structure of the contact combustion type gas sensor in embodiment of this invention. It is a schematic diagram which shows another structure of the contact combustion type gas sensor in embodiment of this invention. It is a figure for demonstrating the characteristic of the contact combustion type gas sensor of this invention. It is a figure for demonstrating the manufacturing method of the contact combustion type gas sensor in this Embodiment. It is a figure which shows the waveform example of the voltage applied intermittently. It is a graph which shows the sensitivity characteristic with respect to the carbon monoxide gas of the produced sample sensor.

Explanation of symbols

  10: catalytic combustion type gas sensor, 12: coil wire, 14: support, 16: catalyst, 18: hole, 19: through hole

Claims (17)

In a catalytic combustion type gas sensor in which a carrier carrying a catalyst is attached to a conductive wire, and the concentration of the combustible gas is detected by catalytic combustion of the combustible gas by the catalyst,
The catalyst is supported in a state of being mixed with the carrier, and a plurality of holes are formed on the surface of the carrier to allow the catalyst inside the carrier to contact the combustible gas.
The contact combustion type gas sensor according to claim 1, wherein the carrier has a thickness of 0.1 mm to 0.5 mm.   The plurality of holes have through-holes that penetrate from the first part of the surface of the carrier to the second part of the surface of the carrier through the inside of the carrier. The contact combustion type gas sensor as described. The conducting wire is configured in a coil shape,
The carrier adheres to the conducting wire in a cylindrical shape,
The catalytic combustion type gas sensor according to claim 1, wherein the thickness of the carrier is a thickness between an outer surface and an inner surface of the carrier. The conducting wire is configured in a planar wavy shape,
The carrier adheres to the conducting wire in a thin plate shape,
The catalytic combustion type gas sensor according to claim 1 or 2, wherein the thickness of the carrier is a thickness between one surface and the other surface of the carrier. In a contact combustion type gas sensor in which a carrier carrying a catalyst is attached to a conductive wire, and the concentration of the combustible gas is detected by contact combustion of the combustible gas by the catalyst,
The catalyst is supported in a state of being mixed with the carrier, and a plurality of holes are formed on the surface of the carrier to allow the catalyst inside the carrier to come into contact with the combustible gas.
The contact combustion type gas sensor, wherein the plurality of holes have through-holes that penetrate from the first part on the surface of the carrier to the second part on the surface of the carrier through the inside of the carrier. . The conducting wire is configured in a coil shape,
The carrier adheres to the conducting wire in a cylindrical shape,
6. The catalytic combustion gas sensor according to claim 5, wherein the through hole penetrates between an outer surface and an inner surface of the carrier. The conducting wire is configured in a planar wavy shape,
The carrier adheres to the conducting wire in a thin plate shape,
6. The catalytic combustion gas sensor according to claim 5, wherein the through hole penetrates between one surface and the other surface of the carrier.   The concentration of either the hydrogen gas or the carbon monoxide gas is detected from a combustible gas in which hydrogen gas and carbon monoxide gas are mixed. A contact combustion gas sensor according to claim 1. In the method of manufacturing a contact combustion type gas sensor that detects the concentration of the combustible gas by contact combustion of the combustible gas,
An electrodeposition step of immersing a conducting wire in an electrodeposition solution containing an electrodeposition resin, a catalyst and a carrier, and attaching the carrier mixed with the electrodeposition resin and the catalyst to the conducting wire by electrodeposition;
The carrier is baked so that the electrodeposition resin is separated from the carrier attached to the conductive wire, the catalyst is mixed with the carrier, and a plurality of holes are provided on the surface to allow the catalyst inside to be in contact with the combustible gas. And a firing step in which the carrier has a thickness of 0.1 mm to 0.5 mm.   10. The catalytic combustion type gas sensor according to claim 9, wherein the plurality of holes have through holes penetrating from the first part through the inside of the carrier to the second part. Method. The conducting wire is configured in a coil shape,
The carrier adheres to the conducting wire in a cylindrical shape,
The catalytic combustion type gas sensor according to claim 9 or 10, wherein the thickness of the carrier is a thickness between an outer surface and an inner surface of the carrier. The conducting wire is configured in a planar wavy shape,
The carrier adheres to the conducting wire in a thin plate shape,
The catalytic combustion type gas sensor according to claim 9 or 10, wherein the thickness of the carrier is a thickness between one surface and the other surface of the carrier. In the method of manufacturing a contact combustion type gas sensor that detects the concentration of the combustible gas by contact combustion of the combustible gas,
An electrodeposition step of immersing a conducting wire in an electrodeposition solution containing an electrodeposition resin, a catalyst and a carrier, and attaching the carrier mixed with the electrodeposition resin and the catalyst to the conducting wire by electrodeposition;
The carrier is baked so that the electrodeposition resin is separated from the carrier attached to the conductor, and the catalyst is mixed with the carrier, so that the catalyst inside can be contacted with the combustible gas. Formed in the surface, and the plurality of holes have a through-hole penetrating from the first part of the surface of the carrier through the inside of the carrier to the second part of the surface of the carrier; A method for producing a contact combustion type gas sensor, comprising: The conducting wire is configured in a coil shape,
The carrier adheres to the conducting wire in a cylindrical shape,
The catalytic combustion gas sensor according to claim 13, wherein the through hole penetrates between an outer surface and an inner surface of the carrier. The conducting wire is configured in a planar wavy shape,
The carrier adheres to the conducting wire in a thin plate shape,
The catalytic combustion gas sensor according to claim 13, wherein the through hole penetrates between one surface and the other surface of the carrier.   16. The method for producing a catalytic combustion type gas sensor according to claim 9, wherein the ratio of the weight of the electrodeposition resin to the total weight of the catalyst and the carrier is 60:40 to 85:15.   16. The method for manufacturing a catalytic combustion gas sensor according to claim 9, wherein, in the electrodeposition step, a voltage is intermittently applied to the conducting wire immersed in the electrodeposition liquid.

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