Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
  • G01N27/16—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by burning or catalytic oxidation of surrounding material to be tested, e.g. of gas
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
  • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
  • G01N33/005—H2

Definitions

• the present invention relates to a detection element and a compensation element for a catalytic combustion type gas sensor that detects various gas leaks, and a catalytic combustion type gas sensor including them.
• a contact combustion type gas sensor is known as a sensor for detecting a combustible gas such as hydrogen gas or methane gas.
• a contact combustion type gas sensor embeds a heater coil 23 in a heat conduction layer (catalyst carrier) 22 that covers or carries a combustion catalyst layer 21 that burns a gas to be detected by contact.
• a heat conduction layer catalyst carrier 22 that covers or carries a combustion catalyst layer 21 that burns a gas to be detected by contact.
• the resistance value of the heater coil 23 changes, and the presence of the combustion gas is detected by detecting this as a voltage (see, for example, Patent Document 1).
• the compensation element 26 (resistance value R) is connected in series with the sensing element 20 (resistance value R) inside the sensor body 25.
• a Wheatstone bridge circuit is formed by connecting two fixed resistance elements 27 (resistance value R1) and 28 (resistance value R2) in series with a series circuit connected in series.
• a gas detection device that detects the output voltage Vout between the connection point a of the detection element 20 and the compensation element 26 and the connection point b of the two resistance elements 27 and 28 by applying a DC voltage using the The same patent document 1 describes.
• the compensation element 26 in this case, a heater coil having the same electrical characteristics as that of the sensing element 20 is embedded in a heat conductive layer covered with a compensation material layer instead of the combustion catalyst layer.
• the output voltage Vout of the Wheatstone bridge circuit described above indicates a voltage according to the balance of the energization resistances (R and R) of the detection element 20 and the compensation element 26. In a clean atmosphere
• the resistance value R and resistance value R are determined by the balance between the heating value of the heater coil built in each of the intelligent element 20 and the compensation element 26 and the amount of heat released to the atmosphere, and the output voltage Vout is zero. Generate point values. When the gas to be detected comes into contact with the sensing element 20, the temperature of the sensing element 20 rises due to contact combustion and only its resistance value R rises, so the output voltage Vout increases.
• the target gas is detected based on the amount of the rise.
• FCV fuel cell vehicles
• the catalytic combustion type gas sensor has high overall adaptability as a hydrogen sensor for FCV, and is considered to be one of the sensors that have an operating principle. It has a structurally high water resistance. Therefore, the reason will be briefly described.
• the sensing element and the compensating element in the conventional catalytic combustion type gas sensor have a cross-sectional structure as shown in FIG. 13, and the sensing element 20 has a hydrogen combustion activity even in the thickness direction of the combustion catalyst layer 21. It has a sponge-like cross-sectional structure that allows the penetration of hydrogen, and it is easy for water vapor or fine water droplets to enter the combustion catalyst layer 21.
• the constituent material of the combustion catalyst layer 21 is "tin oxide + iron oxide + platinum fine powder + palladium fine powder + other", and the retention property of water droplets and the like is also high due to the hydrophilic properties of these materials. Show the characteristics.
• the compensation material layer of the compensation element does not have a sponge-like cross-sectional structure, but its constituent material is “tin oxide + copper oxide + others”, and the hydrophilic property itself is the same as that of the sensing element.
• the heat conduction layer located inside the combustion catalyst layer and compensation material layer of the sensing element and compensation element is structurally dense, and the constituent material is ⁇ alumina + titer + boron nitride + bismuth oxide glass. + Other ”, etc., and these factors indicate hydrophobicity.
• FCV manufacturers take measures including high-cost factors such as setting up a dedicated environment so that water is not applied to the hydrogen sensor, and the future of FCV will improve the water resistance performance of the hydrogen sensor itself. Is required.
• Patent Document 1 JP-A-3-162658
• Patent Document 2 JP-A-2004-69436
• a detection element for a contact combustion type gas sensor embeds a heater coil in a heat conduction layer, and covers or carries a combustion catalyst layer for burning the detection target gas by contact on the surface of the heat conduction layer.
• the combustion catalyst It is characterized in that the layer and the heat conductive layer are made of a fired material whose main component is tin oxide.
• the heat conduction layer may be formed of fine powder of a firing material mainly composed of tin oxide fired at a higher temperature than the firing material of the combustion catalyst layer.
• a compensation element for a contact combustion gas sensor is a compensation element in which a heater coil is embedded in a heat conduction layer, and a surface of the heat conduction layer is covered with or supported by a compensation material layer.
• the compensation material layer and the heat conduction layer are both made of a fired material mainly composed of tin oxide.
• the heat conductive layer may be formed of fine powder of a fired material mainly composed of tin oxide fired at a higher temperature than the fired material of the compensation material layer.
• a catalytic combustion type gas sensor comprises the above-described catalytic combustion type gas sensor detection element and compensation element according to the present invention, and includes a heater coil and a compensation element of the detection element.
• a Wheatstone bridge circuit is configured by connecting in parallel a first series circuit in which a heater coil is connected in series and a second series circuit in which a first resistance element and a second resistance element are connected in series. .
• a DC voltage is applied between the connection points of the first series circuit and the second series circuit, and the connection point between the detection element and the compensation element, the first resistance element, and the second resistance element
• the voltage between the connection points is output as a detection signal for the detection target gas.
• Various combustible gases can be used as the detection target gas, but they are particularly effective for detecting hydrogen gas. It is.
• the contact combustion type gas sensor according to the present invention can improve the durability and water resistance of the sensing element and the compensation element, the durability and water resistance of the sensor itself can be improved, and a special environment can be set. Even without taking the above measures, it can be installed in FCV.
• FIG. 1 is a cross-sectional view along the longitudinal direction showing one embodiment of a detection element for a catalytic combustion gas sensor according to the present invention.
• FIG. 2 is a cross-sectional view along the longitudinal direction showing one embodiment of a compensation element for a catalytic combustion gas sensor according to the present invention.
• FIG. 3 is an enlarged cross-sectional view of the sensing element along the line AA in FIG.
• FIG. 4 is a diagram showing the sintering activity by enlarging the part surrounded by the broken line B in FIG.
• FIG. 5 is a view similar to FIG. 5 of another embodiment of the present invention.
• FIG. 6 is a flowchart for explaining a process for producing a material for a heat conductive layer used in the present invention.
• Fig. 7 is a front view of the sensor main body showing the attachment state of the sensing element in the catalytic combustion gas sensor according to the present invention.
• FIG. 8 is a diagram showing a basic circuit configuration of a catalytic combustion type gas sensor according to the present invention.
• FIG. 9 is a diagram showing the results of a freezing test of a catalytic combustion type gas sensor using a detection element and a compensation element having a heat conductive layer specification according to the present invention.
• FIG. 10 is a diagram showing the results of a freezing test of a catalytic combustion type gas sensor using a detection element and a compensation element of a conventional heat conduction layer specification.
• FIG. 11 is a diagram showing the results of a power ON-OFF test during condensation of a contact combustion type gas sensor using a detection element and a compensation element having a heat conduction layer specification according to the present invention.
• FIG. 12 A diagram showing the results of a power ON-OFF test during condensation of a catalytic combustion type gas sensor using a conventional heat conducting layer specification sensing element and compensation element.
• FIG. 13 is a cross-sectional view along the longitudinal direction showing an example of a conventional catalytic combustion type gas sensor sensing element.
• FIG. 14 is a diagram showing a basic circuit configuration of a conventional catalytic combustion type gas sensor.
• Electrode pin 7 First resistance element 8: Second resistance element
• Fig. 1 is a cross-sectional view along the longitudinal direction of the sensing element
• Fig. 3 is a cross-sectional view along the line AA.
• the detection element 10 includes a combustion catalyst layer (oxidation catalyst layer) that is a catalyst layer in which the bead portion of the heater coil 13 is embedded in the heat conduction layer 12 and the gas to be detected is oxidized and burned by contact on the surface of the heat conduction layer 12. (Also called) 11 is covered.
• oxidation catalyst layer a catalyst layer in which the bead portion of the heater coil 13 is embedded in the heat conduction layer 12 and the gas to be detected is oxidized and burned by contact on the surface of the heat conduction layer 12.
• the heater coil 13 is made of a platinum alloy wire such as a platinum wire or a platinum rhodium alloy.
• a single wound coil is created by winding an original wire having a wire diameter of 10 ⁇ m to 50 ⁇ m, more preferably 20 ⁇ m to 30 ⁇ m around a cored bar, and then winding it around the cored bar again. Double the bead part. In this way, the contact area of the heater coil 13 with the heat conductive layer 12 is increased and the resistance value is increased, so that high gas sensitivity can be obtained.
• the lead portions 13a and 13b are also single wound coils, they can absorb the impact of external force and become a sensor resistant to impact.
• the present invention is not limited to this, and a conventional general heater coil, that is, a bead portion that is a single winding coil and a lead portion that is linear may be used.
• the heat conduction layer 12 and the combustion catalyst layer 11 can improve water resistance in a high humidity environment by reducing the difference in water content and achieving physical affinity.
• the combustion catalyst layer 11 was not changed from the viewpoint of gas sensitivity characteristics, and the heat conductive layer 12 was changed by changing the material of the combustion catalyst layer 11 to realize it. Therefore, both the heat conduction layer 12 and the combustion catalyst layer 11 of the sensing element 10 are made of a fired material mainly composed of tin oxide.
• the combustion catalyst layer 11 is composed of tin oxide (SnO) as a main component and, if necessary, iron oxide, and finely powdered platinum (Pt) as a catalyst, as in the case of a conventional sensing element. )
• the surface of the heat conductive layer 12 is coated with a fired material obtained by dispersing palladium (Pd) and firing in the atmosphere at a temperature of about 600 ° C.
• the heat conductive layer 12 uses tin oxide instead of the conventional alumina and titanium.
• the tin oxide for the heat conduction layer is different from the one for the combustion catalyst layer, which is fired at a high temperature in the atmosphere of 1100 to 1200 ° C, compared with that of 600 ° C for the combustion catalyst layer. It is preferable to form by using a fine powder of the fired material.
• At least one of platinum and palladium may be added to the tin oxide for the heat conductive layer.
• this intermediate layer is set by applying a platinum-palladium solution to the surface of an alumina-titer heat conduction layer in the manufacturing process of the sensing element, and then forming it on the surface of the heat conduction layer by heat treatment.
• this intermediate layer forming step can be omitted.
• the oxide-based low melting point glass is mixed and bound to the above-described tin oxide-based fired material powder for the heat conductive layer. As a result, fine pores are distributed inside, allowing the detection target gas to enter the heat conduction layer 12.
• a tin salt and an iron salt are mixed with an aqueous solution and fired.
• the heat-conducting layer is mixed with the acid-bismuth-based low melting point glass. Material for use.
• the reason why the heat conductive layer material is made into a fine powder is to prevent the formation of void layers in the heat conductive layer and prevent the heat conduction performance from slowing down.
• FIG. 2 is a cross-sectional view along the longitudinal direction showing one embodiment of a compensation element for a catalytic combustion gas sensor according to the present invention.
• the bead portion of the heater coil 33 is embedded in the heat conduction layer 32, and the compensation material layer 31 is covered on the surface of the heat conduction layer 32.
• the heater coil 33 and the heat conduction layer 32 of the compensation element 30 are configured to have the same heat capacity with the same material as the heater coil 13 and the heat conduction layer 12 of the sensing element 10. Therefore, the heater coil 33 is made of a platinum wire such as a platinum-rhodium alloy.
• the heat conductive layer 32 is formed of a fired material mainly composed of tin oxide instead of the conventional alumina and titaure.
• the compensation material layer 31 is also formed to have the same heat capacity as that of the combustion catalyst layer 11 by adding copper oxide or the like to the sintering material mainly composed of tin oxide, similarly to the combustion catalyst layer 11 of the sensing element 10. . However, no platinum or palladium as an acid catalyst is added.
• the fired material mainly composed of tin oxide of the heat conductive layer 32 is preferably formed from fine powder of a fired material mainly composed of tin oxide fired at a higher temperature than the fired material of the compensation material layer 31. Furthermore, fine powder of the fired material forming the heat conductive layer may be bound with bismuth oxide low melting glass. Since these are the same as those in the case of the heat conductive layer 12 of the sensing element 10 described above, detailed description thereof will be omitted.
• the compensation element 30 also has a physical affinity with the compensation material layer by changing the material of the heat conduction layer, even if condensation occurs on the compensation element 30 and freezing occurs, The material layer is no longer missing from the surface of the heat conduction layer, and the durability and water resistance of the compensation device for catalytic combustion gas sensors is greatly improved.
• FIG. 7 is a front view of the sensor body.
• the sensor body 1 shown in FIG. 7 has a plate-like mount base 3 made of ceramic resin, and contacts the external connection electrode pins 4 and 5 penetrating the mount base 3 according to the present invention.
• the detection element 10 for the combustion type gas sensor is fixed by engaging the lead portions 13a and 13b of the heater coil 13 that also exerts force at both ends thereof.
• the above-described contact combustion type gas sensor compensation element 30 according to the present invention is similarly provided with leads at both ends of the heater coil 33.
• the part is fixed to another pair of electrode pins.
• the detection element 10 and the compensation element 30 are surrounded by a mount base 3 and an explosion-proof structure (not shown) having a gas-permeable wire mesh, or a sintered body force of metal powder or ceramic powder.
• FIG. 8 shows a basic circuit configuration of the catalytic combustion type gas sensor according to the present invention, and is a circuit diagram of a Wheatstone bridge circuit and a power source for applying a DC voltage thereto.
• a Wheatstone bridge circuit is configured by connecting a second series circuit connected in series in parallel. Then, a DC voltage is applied by the power source 9 between the connection points of the first series circuit and the second series circuit, and the connection point a between the detection element 10 and the compensation element 30 and the first resistance element 7 The voltage Vout between the connection point b and the second resistance element 8 is output as a detection signal of the detection target gas.
• the output voltage Vout of the wheatstone bridge circuit is zero volts (OmV).
• the first resistance element 7 and the second resistance element 8 should have the same resistance value and the same temperature characteristics. desirable.
• the operating temperature is generated in the sensing element 10 and the compensation element 30.
• the output voltage Vout depending on the resistance values R and R can be obtained in an equilibrium state between the heat supply component from the heater coil built into each element and the heat dissipation component emitted into the atmosphere. .
• the output voltage at this time is set to ⁇ Zero point
• the output voltage Vout rises to the plus (+) side according to the gas sensitivity and can be detected.
• Examples of the detection target gas include methane gas, hydrogen gas, LP gas (liquid petroleum gas), open pan gas, butane gas, ethylene gas, carbon monoxide gas, or organic component gases such as ethanol and acetone. Can be mentioned.
• this catalytic combustion gas sensor is installed in a fuel cell vehicle (FCV), leakage of hydrogen gas can be detected with high sensitivity.
• this contact combustion type gas sensor uses the sensing element 10 and the compensation element 30 according to the present invention, the durability and water resistance performance are remarkably improved, and therefore, it passes a severe test on automobile parts. can do.
• Table 1 and Fig. 9 are data showing the results of a freezing test of a contact combustion type gas sensor using a sensing element and a compensating element having a heat conduction layer specification according to the present invention, and the number of refrigerations is 600 times.
• the sensor output fluctuation is ⁇ 500 [H
• Table 2 and Fig. 10 are data showing the results of freezing tests of conventional combustion gas sensors using sensing elements and compensating elements with conventional thermal conduction layer specifications.
• the sensor output fluctuation increases rapidly and exceeds ⁇ 500 [H Zppm].
• Table 3 and Fig. 11 are data showing the power ON-OFF test results of the contact combustion gas sensor using the detection element and the compensation element of the thermal conduction layer specification according to the present invention. Even if the number is 6000, the sensor output fluctuation is ⁇ 50
• Table 4 and Figure 12 are data showing the power ON-OFF test results during the condensation of the contact combustion gas sensor using the sensing element and compensation element of the conventional thermal conduction layer specification. If it exceeds, the sensor output fluctuation will increase rapidly and exceed 500 [H 2 ppm], and it will be understood that one or both of the sensing element and the compensating element started to break.
• the detection element, the compensation element, and the contact combustion type gas sensor according to the present invention can be widely applied as a device or system using various combustible gases, or a gas leak detection device in a room where they are installed.
• fuel cells which are expected to be put to practical use in the future, use combustible hydrogen gas as a fuel. Therefore, it is essential to equip sensors that detect hydrogen leakage. It was obliged to install hydrogen sensors in each compartment.
• it is essential to provide a hydrogen gas sensor in a fuel cell system used as an auxiliary power source for industrial use or household use, and it is extremely effective to apply the present invention to such a hydrogen sensor. .

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• 2006
  • 2006-03-31 JP JP2006100258A patent/JP4833717B2/ja not_active Expired - Fee Related
• 2007
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