JP4571665B2 - Hydrogen gas sensor - Google Patents

Description

  The present invention relates to a hydrogen gas sensor that detects hydrogen gas.

  Conventionally, a combustible gas can be detected by dispersing a catalyst such as platinum or palladium in a bead-shaped porous combustor and detecting the reaction heat generated when the combustible gas is burned using the catalyst. A contact combustion type gas sensor is provided. FIG. 12 shows a conventional gas sensor disclosed in Japanese Laid-Open Patent Publication No. 90210 (hereinafter referred to as “gazette”). The gas sensor 20 includes a combustor 21 that combusts combustible gas, and a heating resistor 22 that heats the combustor 21 with Joule heat generated in response to energization.

  The combustor 21 is formed of an insulator such as alumina in a bead shape and contains a catalyst such as palladium or platinum. The heating resistor 22 is mainly made of a platinum wire having a high temperature resistance coefficient. The heating resistor 22 is wound in a coil shape, and a portion wound in the coil shape is embedded in the combustion body 21.

  In this type of gas sensor 20, a substantially constant current is passed through the heating resistor 22, and the combustor 21 is heated to a constant temperature by Joule heat generated in the heating resistor 22. When the combustible gas burns on the surface of the combustor 21, the temperature of the heating resistor 22 rises due to the combustion heat, and the resistance value of the heating resistor 22 changes. Therefore, the combustible gas is detected from this resistance value change. can do. That is, as shown in FIG. 13, the gas sensor 20, the compensation element 23, and the fixed resistors 24 and 25 form a bridge circuit, and the voltage Vc between the output terminals c and d of the bridge circuit is measured. A change in resistance value is obtained, and combustible gas is detected from the change in resistance value.

  The compensation element 23 is composed of a heating resistor and a bead-like insulator as in the gas sensor 20, and the temperature characteristics and humidity characteristics are substantially the same as those of the gas sensor 20, but a catalyst for burning a combustible gas in the insulator is used. Since it is not contained, it does not react with combustible gas. In the bridge circuit shown in FIG. 13, a series circuit of the gas sensor 20 and the compensation element 23 and a series circuit of the fixed resistors 24 and 25 are connected between the terminals a and b, respectively. A variable resistor 26 for balance adjustment is connected between the terminals a and b, and an intermediate tap of the variable resistor 26 is connected to an intermediate point between the fixed resistors 24 and 25. A DC power source E1 is connected between the terminals a and b via the variable resistor 27 and the switch SW, and the voltage applied between the terminals a and b is adjusted by adjusting the resistance value of the variable resistor 27. is doing.

Thus, in this measurement circuit, by adjusting the resistance value of the variable resistor 27, the current flowing through the heating resistor 22 is changed and the amount of generated heat is adjusted, so that no flammable gas exists in the atmosphere. Then, the resistance value of the variable resistor 27 is adjusted to heat the combustor 21 to about 300 ° C. to 500 ° C., and the variable resistor 26 is adjusted in this state to maintain the equilibrium state of the bridge circuit. Thereafter, when the combustible gas comes into contact with the surface of the combustor 21, the combustible gas is combusted by the action of the catalyst contained in the combustor 21, and the electric resistance of the heating resistor 22 is increased by the combustion heat. On the other hand, since the compensation element 23 does not contain a catalyst, the combustible gas does not burn on the surface of the compensation element 23 and the electrical resistance of the heating resistor does not change. Therefore, a resistance difference occurs in the electric resistance of the metal wire between the gas sensor 20 and the compensation element 23, and a bridge voltage is generated between the output terminals c and d. Since the bridge voltage is output in proportion to the gas concentration of the combustible gas, the gas concentration of the combustible gas can be detected by detecting the bridge voltage. FIG. 14 shows examples of output characteristics for various combustible gases. In the figure, a is methane (CH ₄ ), b is carbon monoxide (CO), and c is hydrogen ( H ₂ ) and d in the figure indicate output characteristics for isobutane (i-C ₄ H ₁₀ ), respectively.

  In a general manufacturing method of this type of gas sensor 20, first, a heating wire 22 is formed by winding a platinum wire having a wire diameter of about 20 to 50 μm in a coil shape. Next, a ceramic carrier mainly composed of an inorganic insulator such as alumina is made into a sol or paste form, applied to the coil portion of the heating resistor 22 so as to have an elliptical shape, and subjected to a heat treatment to thereby form a bead-shaped combustion body. 21. Next, the gas sensor 20 in which the catalyst is supported on the alumina carrier in a highly dispersed manner is formed by impregnating the combustion body 21 with a catalyst such as platinum or palladium and performing heat treatment.

  By the way, in recent years, hydrogen has been attracting attention as an energy source to replace petroleum, and the development of automobiles equipped with fuel cells has been promoted. However, in such fuel cell vehicles, hydrogen leakage from fuel cells and hydrogen tanks has occurred. In order to detect, it is necessary to install one or a plurality of hydrogen gas sensors, and it has been studied to use a catalytic combustion type gas sensor as the hydrogen gas sensor.

  However, when a gas sensor is used in an automobile, durability against physical conditions such as vibration is required, and detection characteristics are affected even in harsh atmospheres such as high temperature and high humidity conditions and miscellaneous gases. It is difficult to be affected, and durability that does not deteriorate the characteristics over a long period of time in such an atmosphere is required. In the conventional gas sensor 20 described above, the combustion body 21 provided so as to cover the coil portion of the heating resistor 22 is formed in a bead shape. Therefore, the inertia of the combustion body 21 is relatively large, and vibration occurs when mounted on an automobile. There is a possibility that the heating resistor 22 may be deformed or disconnected by an impact. Further, when the combustor 21 is heated to a high temperature in order to detect low-concentration hydrogen gas, the rate of loss caused by radiating the generated heat into the air (so-called gas heat conduction rate) increases. There has been a problem that the humidity dependency in the atmosphere is increased and the reactivity with poisoning substances is increased to deteriorate long-term reliability. In addition, the catalytic activity deteriorates in a high-humidity atmosphere, and the agglomeration phenomenon of the catalyst component supported on the combustor 21 in a highly dispersed state occurs. Further, the combustible gas is combusted by the catalyst carried on the combustor 21, the temperature of the combustor 21 having a large heat capacity is increased by the combustion heat, and the temperature rise is not transmitted to the heat generating resistor 22 until the heat generating resistor 22 is heated. As the electrical resistance of the gas changes, there is a limit to improving the sensitivity and response speed of the combustible gas.

  Furthermore, in the method for manufacturing the gas sensor 20 described above, the sol or paste such as alumina manufactured to form the combustor 21 is attached to the coil portion of the heating resistor 22 and dried, and then fired. Since the formation is performed by hand work or work close to hand work, it is difficult to finely control the outer dimensions of the combustor 21, and it is necessary to select a thermally equivalent compensation element 23 to be combined. Therefore, there is a problem that complicated work is required and the number of work steps increases, resulting in an increase in cost.

  Further, in the above-mentioned publication, a catalytic combustion type in which a porous insulator thin film is formed on the surface of the heating resistor 22 wound in a coil shape, and a catalyst such as platinum or palladium is dispersed on the surface of the thin film. Gas sensors have also been proposed, but the porous insulating thin film with the catalyst dispersed and supported by the coiled heating element is weak, so when mounted on an automobile, the catalyst is dispersed and supported by vibration or impact. There is a possibility that the insulating material is peeled off from the coiled heating element and the sensitivity is deteriorated.

The present invention was made to solve the above problems and is excellent in vibration resistance and impact resistance, the detection performance is to provide a long-term stable hydrogen gas sensor.

The hydrogen gas sensor according to the present invention detects hydrogen gas. This hydrogen gas sensor includes a heating resistor. The surface composition of this heating resistor is an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt. The heating resistor is heated to a temperature at which hydrogen gas can be combusted by Joule heat by energization, hydrogen gas burns on the alloyed surface of the heating resistor, and the electrical resistance changes as the temperature rises due to the combustion heat. The change in electrical resistance is output as a hydrogen gas concentration detection signal.

  According to this invention, hydrogen gas is burned on the surface of the heating resistor, and the electrical resistance of the heating resistor changes according to the temperature rise due to the heat of combustion, and the change in electrical resistance is output as a hydrogen gas concentration detection signal. Thus, the heating resistor can have a function of heating the catalyst, a function of burning hydrogen gas, and a function of generating a change in electrical resistance due to combustion heat. Therefore, unlike the conventional gas sensor, it is not necessary to form a bead-shaped combustion body on the heating resistor, and the possibility that the heating resistor is deformed by vibration or impact can be reduced, and the heating resistor itself has a catalytic action. Since it is formed of the metal material having, there is no reduction in the aggregation or peeling of the catalyst, and the effect that the detection performance is stable over the long term is obtained. Furthermore, the surface composition of the heating resistor is formed of an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt, and the catalyst and platinum are alloyed. Thus, the catalyst supported on the combustor is not peeled off, the stability of the platinum catalyst is increased, the sensitivity deterioration is reduced, and the detection performance can be stabilized for a long time.

  It is also preferable to provide a compensation resistor that is made of the same material as the heating resistor and eliminates the combustion activity against hydrogen gas, because hydrogen gas does not burn on the surface of the compensation resistor, and resistance value change due to combustion heat does not occur. The output signal of the heating resistor can be compensated using the output value of the compensation resistor.

  In addition, a case that houses the heating resistor and compensation resistor is formed, and a vent hole that communicates with the outside is formed in this case, and poisonous substances are adsorbed in the gas flow path between the vent hole, the heating resistor, and the compensation resistor. It is also preferable to provide a filter that absorbs the poisoning substance, so that a decrease in sensitivity due to the poisoning substance can be reduced.

FIG. 3 is a partially omitted front view illustrating the hydrogen gas sensor according to the first embodiment. It is an external appearance perspective view of a hydrogen gas sensor same as the above. It is sectional drawing of a hydrogen gas sensor same as the above. It is a front view which can omit a part which shows the other structure of a hydrogen gas sensor same as the above. It is a front view which can omit a part which shows another structure of a hydrogen gas sensor same as the above. 6 is an external perspective view showing a hydrogen gas sensor according to Embodiment 2. FIG. 6 is an external perspective view showing a hydrogen gas sensor of Embodiment 3. FIG. It is sectional drawing of a hydrogen gas sensor same as the above. It is an output characteristic figure of a hydrogen gas sensor same as the above. It is an output characteristic figure of a hydrogen gas sensor same as the above. It is an output characteristic figure of a hydrogen gas sensor same as the above. It is an external appearance perspective view in which a conventional catalytic combustion type gas sensor is partially broken. It is a circuit diagram of the measurement circuit using the gas sensor same as the above. It is an output characteristic figure of a gas sensor same as the above.

  In order to describe the present invention in detail, it will be described with reference to the accompanying drawings.

(First embodiment)
A first embodiment according to the present invention will be described with reference to the accompanying drawings. In the following description, the vertical and horizontal directions are defined in the direction shown in FIG. 1 unless otherwise specified.

  FIG. 1 is a diagram schematically showing the structure of a hydrogen gas sensor 1 of the present embodiment, FIG. 2 is an external perspective view, and FIG. 3 is a sectional view. The hydrogen gas sensor 1 includes a heating resistor 2, stems 3a, 3b, A base 4 and a protective cap 5 are provided.

  The heating resistor 2 has the functions of both the combustion body 21 and the heating resistor 22 in the conventional gas sensor, and the surface composition is composed of at least one of palladium, ruthenium, rhodium, nickel, cobalt and platinum. An alloy platinum wire is wound in a coil shape, and both ends thereof are electrically and mechanically connected to the stems 3a and 3b. In the present embodiment, the heating resistor 2 having, for example, a wire diameter of about 20 μm is used, the coil diameter is about 210 μm, the space between the wires is about 20 μm, and the coil is wound for 10 turns. In the present embodiment, a platinum wire is used as the heating resistor 2, but a material other than pure platinum may be used as long as it is a platinum-based resistance wire. For example, zirconia stabilized platinum may be used. In the present embodiment, the surface of the platinum resistance wire is alloyed with at least one of palladium, ruthenium, rhodium, nickel, and cobalt to form the heating resistor 2. Platinum-based resistance may be used.

  The base 4 is formed in a disc shape from a synthetic resin, and the three stems 3a, 3b, 3c are insert-molded in the base 4 so as to penetrate the base 4 in the vertical direction. Of the three stems 3a to 3c, the central stem 3c has a shorter protruding amount from the upper surface than the other two stems 3a and 3b, and the two stems 3a and 3b at the both ends are the same. Both ends 2a and 2b of the heating resistor 2 are fixed to a portion protruding from the upper surface of the case 4 by a method such as welding. The central stem 3c is used when both the heating resistor 2 and the compensation resistor 8 are attached as will be described in the second embodiment, and the stem 3c is used when only the heating resistor 2 is used. do not do.

  The protective cap 5 has a substantially cylindrical shape with an opening on the lower surface side, and the base 4 is press-fitted and fixed so that the heating resistor 2 can be accommodated in the opening. A circular hole 6 is provided in the center of the ceiling surface of the protective cap 5, and a 100 mesh stainless steel wire mesh 7 is attached to the hole 6 for explosion protection. The protective cap 5 may be made of metal or resin.

  Here, when measuring hydrogen gas, a substantially constant voltage is applied between the stems 3a and 3b by a measurement circuit (not shown) to heat the heating resistor 2 to a predetermined temperature (for example, about 100 ° C.). When the hydrogen gas that has entered inside through the vent hole 6 of the protective cap 5 comes into contact with the heating resistor 2, the hydrogen gas burns on the surface of the heating resistor 2 by the catalytic action of platinum on the surface of the heating resistor 2. At this time, the temperature of the heating resistor 2 rises due to the combustion heat of hydrogen gas, and the electrical resistance increases as the temperature rises. Therefore, the measurement circuit measures the amount of change in the electrical resistance value of the heating resistor 2. It becomes possible to measure the gas concentration of hydrogen gas.

  In the present embodiment, the heating resistor 2 is formed in a coil shape and is attached to the stems 3a and 3b so that the axial direction of the coil is substantially parallel to the vertical direction. However, as shown in FIG. You may attach to stem 3a, 3b so that it may be substantially parallel to the left-right direction. Further, although the heating resistor 2 is formed in a coil shape, the surface area is increased, but as shown in FIG. 5, it may be formed in a linear shape, and the work of winding the coil shape can be eliminated.

  Next, a method for manufacturing the heating resistor 2 will be described below. First, a resistance wire (base material) made of platinum (for example, platinum or zirconia stabilized platinum) is wound in a coil shape, and the surface of the resistance wire is alloyed with at least one of palladium, ruthenium, rhodium, nickel, and cobalt. For example, an aqueous solution containing a predetermined concentration of at least one of palladium nitrate, ruthenium nitrate, rhodium nitrate, nickel nitrate, and cobalt nitrate is applied to the resistance wire, and then air-dried at room temperature for about 1 hour. Remove. Thereafter, a voltage of about 1.1 V is applied between both ends of the resistance wire for about 10 minutes, and the surface temperature of the resistance wire is heated to about 900 ° C., so that the surface of the resistance wire is made of palladium, ruthenium, rhodium, nickel, cobalt. Alloy with at least one of them. Thus, since the heating resistor 2 is formed into an alloy by applying a predetermined voltage after applying a solution containing a desired catalyst on the surface of the resistance wire after forming the resistance wire in a desired shape, Unlike the conventional gas sensor, the process of forming the bead-shaped combustion body on the coil-shaped heating resistor becomes unnecessary, and the manufacturing process can be simplified. In the case of forming a bead-shaped combustion body, there is a large variation in the shape and dimensions of the combustion body. However, in this embodiment, since the resistance wire is wound in a coil shape and the surface thereof is alloyed, Variations in shape and dimensions can be reduced, and variations in sensitivity can be reduced. In addition, since the heating resistor 2 is composed of a platinum-based resistance wire having a catalyst-platinum alloy formed on the surface thereof, the catalyst carried on the combustor is not peeled off unlike conventional gas sensors. The performance can be stabilized in the long term.

  The output characteristics of the gas sensor 1 formed as described above will be described with reference to FIGS. Note that there was no significant difference in characteristics between the case where the heating resistor 2 was wound in a coil shape and the case where the heating resistor 2 was formed in a linear shape. Therefore, in the following, reference is made to measurement data when the heating resistor 2 is wound in a coil shape. To explain.

In the measurement circuit shown in FIG. 13, the gas sensor 1 of this embodiment is connected instead of the gas sensor 20, and a fixed resistance of 10Ω, for example, is used instead of the compensation element 23, and the applied voltage to the gas sensor 1 is about 0 in a clean atmosphere. Adjustment was performed using the variable resistor 27 so as to be 2 V. Here, when a voltage of about 0.2 V is applied to the gas sensor 1, the temperature of the heating resistor 2 is heated to about 100 ° C. When hydrogen gas passes through the metal mesh 7 from the vent hole 6 and enters the protective cap 6, the hydrogen gas burns on the surface of the heating resistor 2, and the resistance value of the heating resistor 2 changes due to the combustion heat. At this time, since the voltage between the output terminals c and d of the bridge circuit changes, the hydrogen gas concentration can be measured from the change in the output voltage. FIG. 9 shows measurement results of gas sensitivity with respect to various combustible gases. The horizontal axis represents the gas concentration (ppm), and the vertical axis represents the output voltage (mV) of the bridge circuit. In the figure, a represents hydrogen, b represents carbon monoxide, c represents methane, d represents isobutane, and e represents ethanol. From the measurement result of FIG. 9, in the temperature range of about 100 ° C., combustible gases other than hydrogen gas (CO, CH ₄ , IB, ethanol) do not burn, and only hydrogen gas burns, so the selectivity of hydrogen gas is very high It was found that hydrogen gas can be detected with high accuracy. In this case, the power consumption of the gas sensor 1 is about 10 mW, and the measurement can be performed with a very small power consumption. The reason why it is possible to operate with such low power consumption is that it does not have the combustor 21 having a large heat capacity unlike the conventional catalytic combustion type gas sensor, and efficiently transfers the combustion heat generated by the combustion of hydrogen gas to the platinum wire. This is because a change in the resistance value of the heating resistor 2 can be detected without heating the heating resistor 2 to a high temperature.

  Here, the composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the one whose surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum-nickel alloy, When the gas sensitivity to hydrogen gas was measured for each of the platinum-cobalt alloys, the gas sensitivity at the initial stage of use was almost the same in any case. However, when a voltage of about 0.2 V is applied to each resistance platinum resistance wire and the operation is continued in a clean atmosphere, the surface composition is pure platinum or zirconia stabilized platinum (that is, the surface of the platinum resistance wire is alloyed). It was found that the sensitivity was slightly reduced at the time when more than ten days had passed. The cause of the decrease in sensitivity is unknown, but it is thought that the combustion active site of platinum on the surface is deactivated for some reason. On the other hand, in the case of the alloyed surface, the deactivation does not occur for 60 days or more, so it is considered that the durability of the active sites is increased by alloying.

  In addition, since there is a demand to use the gas sensor 1 of the present embodiment in a fuel cell vehicle to detect leakage of hydrogen gas, it is assumed that the gas sensor 1 is attached to a device that generates severe vibration such as an automobile. A drop test was conducted. In the drop test, the gas sensor 1 is dropped 50 times on the concrete from a height of 1 m and the shape of the coil portion of the heating resistor 2 is observed before and after the test. The shape of the coil portion is changed before and after the test. It was confirmed that there were no functional problems. FIG. 10 shows the result of sensitivity measurement with respect to hydrogen gas before and after the drop test. In the figure, a indicates measurement data before the test, and b in the figure indicates measurement data after the test. From this measurement result, there was no particular change in sensitivity to hydrogen gas. In addition, although the heating resistor 2 of the gas sensor 1 used in the experiment was formed with a platinum-palladium alloy on the surface, the same test results were obtained even when a platinum alloy having another composition was formed on the surface. .

  In a conventional gas sensor in which a resistance wire is wound in a coil shape and a bead-shaped alumina carrier (combustion body) is formed so as to cover the coil portion, the resistance wire is dropped several times because the weight of the combustion body is large. Although deformation or disconnection occurs, in the present embodiment, the heating resistor 2 has the three functions of the heating element, the combustion body, and the catalyst, so there is no need to form an alumina carrier on the heating resistor 2. Since the inertia of the heating resistor 2 itself is reduced, it has been found that it is very resistant to impact. In addition, with respect to vibration, the vibration resistance can be improved by reducing the inertia of the heating resistor 2.

  Next, humidity characteristics of the gas sensor 1 will be described with reference to FIG. FIG. 11 shows the results of measuring hydrogen gas sensitivity when the atmospheric temperature is substantially constant (21 ° C. or 22 ° C.) and the humidity in the atmosphere is changed from about 30% to about 80%. Here, a in the figure is measurement data when the temperature is 22 ° C. and the humidity is 31%, b in the figure is measurement data when the temperature is 21 ° C. and the humidity is 52%, and c in the figure is the temperature. Measurement data when the temperature is 21 ° C. and the humidity is 78%. From this test result, it was confirmed that there was almost no change in the output characteristics of the gas sensor 1 in the humidity range from about 30% to about 80%. The heating resistor 2 of the gas sensor 1 used in the experiment has a platinum-palladium alloy formed on the surface thereof, but the same test results were obtained even when a platinum alloy having another composition was formed on the surface. . The gas sensor 1 according to the present embodiment is operated at a relatively low temperature, and most of the heat generated by the heating resistor 2 is released through the stems 3a and 3b, and is radiated into the air (ratio of gas heat conduction). Therefore, it is considered that the influence on the output characteristics is small even if the humidity in the atmosphere (that is, the gas thermal conductivity) changes. That is, it is considered that the gas sensor 1 of the present embodiment has a property that is not easily affected by a change (humidity change) in the gas thermal conductivity of the atmosphere, and as a result, the output fluctuation due to the humidity change can be reduced.

  Moreover, the result of having measured the gas characteristic in the high humidity atmosphere about the gas sensor 1 of this embodiment is demonstrated. The composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum-nickel alloy, platinum-cobalt. For each alloy, when a voltage of about 0.2 V is applied to the heating resistor 2 in an atmosphere at a temperature of 60 ° C. and a humidity of 80% Rh for a long time, the composition of the surface of the heating resistor 2 However, in the case of pure platinum or zirconia stabilized platinum (that is, the one in which the surface of the platinum resistance wire is not alloyed), the sensitivity to hydrogen gas disappeared within 24 hours. On the other hand, when the composition of the surface of the heating resistor 2 is platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, or platinum-nickel alloy, there is almost no deterioration in sensitivity within 24 hours. The sensitivity gradually decreased, and when about 20 days passed, the sensitivity was about half, but after that, the sensitivity at this time was maintained even after about one month. Further, when the composition of the surface of the heating resistor 2 was a platinum-cobalt alloy, the sensitivity was not lowered for about one month. From the above results, a platinum alloy with the composition of the surface of the heating resistor 2 has improved durability in a high-humidity atmosphere. I was able to improve.

  Furthermore, the result of having performed the durability test in high concentration gas about the gas sensor 1 of this embodiment is demonstrated. The composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum-nickel alloy, platinum-cobalt. When the alloy was operated continuously for 24 hours by applying a voltage of about 0.2 V to the heating resistor 2 in an atmosphere containing 10000 ppm of hydrogen gas, methane, isobutane, and ethanol, all the gas sensors 1 were Sensitivity deterioration was not seen. The reason why the sensitivity does not deteriorate in methane, isobutane, and ethanol is that the gas sensor 1 of the present embodiment operates at a relatively low temperature, so that a combustible gas other than hydrogen gas (methane) is generated on the surface of the heating resistor 2. , Isobutane, ethanol, etc.) does not burn and is therefore less susceptible to the heat of combustion. On the other hand, hydrogen gas burns in the hydrogen gas, and the surface temperature of the heating resistor 2 rises due to the heat of combustion. Here, in the conventional catalytic combustion sensor, there is a case where a sensitivity reduction phenomenon is observed because the catalyst supported in a highly dispersed state is sintered. However, the gas sensor 1 of the present embodiment uses platinum or the Since active sites exist on the zirconia-stabilized platinum or platinum alloy, the aggregation phenomenon of the catalyst hardly occurs, and it is considered that the sensitivity is not lowered.

  The results of examining the influence of poisoning by sulfurous acid gas and silicon gas, which are known as poisoning components of the catalyst, in the gas sensor 1 of the present embodiment will be described below. Here, the composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the one whose surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum-nickel alloy, When the platinum-cobalt alloy was continuously operated for 24 hours by applying a voltage of about 0.2 V to the heating resistor 2 in an atmosphere of 300 ppm sulfurous acid gas and 150 ppm hexamethyldisiloxane, When the surface composition of the body 2 was pure platinum or zirconia stabilized platinum (that is, the surface of the platinum resistance wire was not alloyed), the sensitivity to hydrogen gas disappeared after about 10 minutes. On the other hand, when the composition of the surface of the heating resistor 2 is a platinum-ruthenium alloy, a platinum-rhodium alloy, or a platinum-nickel alloy, the sensitivity starts to decrease after 5 minutes. It was. Further, when the composition of the surface of the heating resistor 2 was a platinum-palladium alloy, the sensitivity was hardly deteriorated even after 15 minutes, and about half the sensitivity was maintained even after 24 hours. From the above results, it was found that the durability against poisoning gas was greatly improved when the composition of the surface of the heating resistor 2 was a platinum alloy.

(Second Embodiment)
A second embodiment according to the present invention will be described with reference to FIG. In this embodiment, the gas sensor 1 described in the first embodiment is provided with a compensation resistor 8 that is made of the same material as the heating resistor 2 and has no activity against hydrogen gas. Since the configuration other than the compensation resistor 8 is the same as that of the first embodiment, common components are denoted by the same reference numerals, and description thereof is omitted.

  The compensation resistor 8 is formed by winding a platinum wire in a coil shape like the heating resistor 2 described in the first embodiment, and is formed in substantially the same shape and size as the heating resistor 2. The treatment for eliminating the combustion activity against hydrogen gas is performed. The material of the compensation resistor 8 is not limited to the platinum wire, but may be formed of the same platinum resistance wire as that of the heating resistor 2.

  Since the compensation resistor 8 has no combustion activity with respect to hydrogen gas, even if the compensation resistor 8 is heated to the same temperature as the heating resistor 2, hydrogen gas does not burn on the surface of the compensation resistor 8. No temperature rise occurs. Since the compensation resistor 8 is made of the same material as that of the heating resistor 2, it has the same temperature-resistance characteristics as the heating resistor 2. By correcting the atmospheric conditions such as the above, the resistance value change of the heating resistor 2 due to the heat of combustion can be measured more accurately, and the detection accuracy for hydrogen gas is improved.

  The base 4 is formed in a disc shape from a synthetic resin, and is insert-molded so that the three stems 3a, 3b, 3c penetrate the base 4 in the vertical direction. The three stems 3a, 3b, 3c are provided so as to be arranged in a line in the same plane, and the central stem 3c has a shorter protruding amount from the upper surface than the other two stems 3a, 3b. Then, both ends of the heating resistor 2 are fixed to the left two stems 3a and 3c by a method such as welding to a portion protruding from the upper surface of the base 4, and the right two stems 3b and 3c are fixed to the two stems 3b and 3c on the right side. Both ends of the compensation resistor 8 are fixed to a portion protruding from the upper surface of the base 4 by a method such as welding. Here, since the three stems 3a to 3c are arranged in the same plane, when the heating resistor 2 and the compensation resistor 8 are laser welded to the stems 3a to 3c, the welding work can be performed at one time. There is an advantage that the performance is improved.

  In manufacturing the gas sensor of the present embodiment, first, a resistance wire (base material) of platinum (for example, platinum, zirconia stabilized platinum, etc.) is wound into a coil shape, and two coils having the same shape and dimensions are wound. After the formation, both ends of one coil are fixed to the stems 3a and 3c insert-molded on the base 4, and both ends of the other coil are fixed to the stems 3b and 3c, respectively. Next, in order to alloy the surface of each coil with at least one of palladium, ruthenium, rhodium, nickel and cobalt, for example, at least one of palladium nitrate, ruthenium nitrate, rhodium nitrate, nickel nitrate and cobalt nitrate. After applying an aqueous solution containing a predetermined concentration to both coils, the solvent is removed by air drying at room temperature for about 1 hour. Thereafter, a voltage of about 1.1 V is applied between the stems 3a and 3c and between the stems 3b and 3c for about 10 minutes, and the surface temperature of the coil is heated to about 900 ° C., so that the surface of the coil is palladium, ruthenium, rhodium. Alloy with at least one of nickel, cobalt. Thereafter, in order to heat the coil serving as the compensation resistor 8, a voltage of about 0.8 V is applied between the stems 3b and 3c to heat the coil to about 700 ° C., and about 10,000 ppm of sulfurous acid gas or about 1000 ppm of the atmosphere is heated. Hexamethyldisiloxane vapor is introduced and held for about 1 minute to poison the catalyst and deactivate the catalytic activity of the platinum alloy to form the compensation resistor 8. The compensation resistor 8 whose catalytic activity has been deactivated by this method has the same size and shape as the heating resistor 2, and the surface of the compensating resistor 8 is not different from the surface of the heating resistor 2 in appearance. Further, the compensation resistor 8 is formed by winding the same platinum resistance wire as that of the heating resistor 2 in a coil shape with a winding machine, alloying the surface, and further deactivating the catalytic activity of the surface. The same shape and the same size as the resistor 2 can be easily manufactured, and the heating resistor 2 and the compensation resistor 8 having the same temperature-resistance characteristics can be easily combined.

  In this embodiment, since the heating resistor 2 and the compensation resistor 8 are housed in the same case, the atmospheric conditions of the heating resistor 2 and the compensation resistor 8 can be made substantially the same, and the resistance value of the compensation resistor 8 can be changed. It is possible to correct the output of the heating resistor 2 accurately, but if the atmospheric conditions of the heating resistor 2 and the compensation resistor 8 can be made substantially the same, they may be housed in separate cases. .

(Third embodiment)
A third embodiment according to the present invention will be described with reference to FIGS. In this embodiment, in the gas sensor 1 described in the second embodiment, a filter cap 9 holding a filter 12 is put on the upper side of the protective cap 5. Since the configuration other than the filter cap 9 and the filter 12 is the same as that of the second embodiment, common components are denoted by the same reference numerals and description thereof is omitted.

  The filter cap 9 is made of a synthetic resin, and is formed in a substantially cylindrical shape whose end on the upper surface side is closed. A round hole-shaped air hole 10 is provided in the upper surface of the filter cap 9, and a 100-mesh stainless steel wire mesh 11 is attached to the air hole 10 for explosion prevention. Further, a filter 12 that adsorbs poisonous substances in the gas entering the inside through the vent hole 10 is mounted in the tube of the filter cap 9. The filter 12 is made of an adsorbent porous material such as activated carbon, silica gel, or zeolite, or an adsorbent obtained by impregnating an organic or inorganic porous material with a chemical substance-capturing liquid component. It has a function of adsorbing a substance (for example, silicon). Examples of the chemical substance-capturing liquid component include KOH, ammonia, and phosphoric acid, which are carried to remove oxidizing gas, to adsorb specific poisonous substances. What is necessary is just to use the liquid of an appropriate component by impregnating the organic-inorganic porous material.

  Here, the base 4, the protective cap 5, and the filter cap 9 constitute a case for housing the heating resistor 2 and the compensation resistor 8 therein. The vent hole 10 provided in the case (filter cap 9) and the heating resistor 2 Since the filter 12 for adsorbing the poisonous substance is provided in the gas flow path between the compensation resistor 8 and the compensation resistor 8, the poisonous substance in the gas entering the inside through the vent hole 10 can be adsorbed. The poisoning of the heating resistor 2 and the compensation resistor 8 is suppressed, and deterioration in sensitivity can be reduced.

  Here, with respect to the gas sensor 1 of the present embodiment, the results of examining the influence of poisoning by sulfurous acid gas and silicon gas known as poisoning components of the catalyst will be described below. Here, the composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the one whose surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum-nickel alloy, When the platinum-cobalt alloy was operated continuously for 24 hours by applying a voltage of about 0.2 V to the heating resistor 2 in an atmosphere of 300 ppm sulfurous acid gas and 150 ppm hexamethyldisiloxane, The gas sensor 1 also had the same gas sensitivity as before the test after 24 hours. Thus, the provision of the filter 12 can greatly improve the poisoning durability, and it is possible to maintain stable performance for a long time even when the atmospheric conditions are poor. In the gas sensor 1 described in the first embodiment, it goes without saying that the filter cap 9 holding the filter 12 may be placed on the upper side of the protective cap 5 as in the present embodiment. It is possible to suppress poisoning and reduce deterioration of sensitivity.

Since it is apparent that a wide variety of different embodiments can be constructed without departing from the spirit and scope of the present invention as described above, the invention is not limited to the specific embodiments except as defined in the appended claims. It is not restricted.

Claims (3)

A hydrogen gas sensor for detecting hydrogen gas,
With a heating resistor ,
This heating resistor consists of a platinum wire alloyed only on the surface so as to leave a non-alloyed part in the center,
The surface composition of the heating resistor is an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt,
The heating resistor is heated to a temperature at which hydrogen gas can be combusted by Joule heat by energization, and hydrogen gas is burned on the alloyed surface of the heating resistor, and the electric resistance changes according to the temperature rise due to the combustion heat The change in electrical resistance is output as a hydrogen gas concentration detection signal.
A hydrogen gas sensor characterized by that . It is formed of the same material as before Symbol heating resistor, hydrogen gas sensor according to claim 1, characterized in that it comprises a compensation resistor eliminated combustion activity for hydrogen gas. E Bei a case accommodating the said compensation resistance before and Symbol heating resistor, this case is formed vent hole communicating with the outside, the gas flow between the vent hole and the heat-generating resistor and the compensating resistor The hydrogen gas sensor according to claim 2, wherein a filter for adsorbing a poisonous substance is provided on the path.

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