JP2017096946A - Catalyst conversion type sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst conversion type sensor capable of improving a conversion rate and achieving miniaturization.SOLUTION: A catalyst conversion type sensor X comprises: a gas flow path 10 for passing a gas to be detected in order to detect the gas to be detected by detecting converted gas formed by oxidation; and a conversion part 30 including a heated catalyst part 30A connected with the gas flow path 10 and for oxidizing the gas to be detected by contacting a heated catalyst 31 to form the converted gas and a sensor element part 30B capable of detecting the converted gas formed by oxidation on a side separated by diffusion means 20 for naturally diffusing the gas to be detected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a catalytic conversion sensor that detects a detection target gas by detecting a conversion gas generated by oxidation.

Fluorine special gases such as nitrogen trifluoride (NF ₃ ), C ₄ F ₆ , C ₄ F ₈ , and carbon tetrafluoride, which are used as etching gas or cleaning gas in semiconductor manufacturing, are usually burdens on the surrounding environment There are thought to be. Therefore, by detecting the leakage of a fluorine-based special gas such as nitrogen trifluoride, measures can be taken so that these fluorine-based special gases are not released to the surrounding environment.

Since nitrogen trifluoride cannot be detected directly by an electrochemical reaction, it is known that the sensitivity of a gas sensor is low, and it can be detected by converting it into nitrogen dioxide (NO ₂ ) by thermal decomposition in advance.

  In addition, since the above-described “detecting the gas to be detected by detecting the converted gas generated by thermal decomposition” technology as a conventional technology in the present invention is a general technology, the prior art documents such as patent documents are Not shown.

  However, since the ratio (conversion rate) at which nitrogen trifluoride can be converted to nitrogen dioxide is as low as several percent (about 3%), it was difficult to efficiently detect nitrogen trifluoride. Further, since the conversion rate depends on the flow rate, if the flow rate per unit time increases due to the deterioration of the flow rate sensor, the conversion rate may further decrease. Furthermore, if nitrogen trifluoride is to be detected, there is a tendency to increase the size because it is necessary to add a thermal decomposition unit.

  Accordingly, it is an object of the present invention to provide a catalyst conversion type sensor that can improve the conversion rate and achieve downsizing.

  In order to achieve the above object, the first characteristic configuration of the catalytic conversion type sensor according to the present invention is a gas flow for flowing down the detection target gas in order to detect the detection target gas by detecting the conversion gas generated by oxidation. A heating means for generating a conversion gas by oxidizing the detection target gas by contacting with a heated catalyst on a side connected to a gas passage and a diffusion means for naturally diffusing the detection target gas The catalyst part and the conversion part which has the sensor element part which can detect the conversion gas produced | generated by oxidation exist in the point provided.

  In the catalyst conversion type sensor of this configuration, the gas to be detected flowing down the gas flow path by the diffusing means can be naturally diffused to the conversion part side, so that the gas amount of the detection target gas transferred to the conversion part is the gas flow path. It is possible to configure so as not to depend on the flow rate flowing down. For this reason, even if the flow rate of the detection target gas flowing down the gas flow passage with time changes due to deterioration of the flow sensor, it is difficult to influence the gas amount of the detection target gas that immediately moves to the conversion unit. The amount of gas to be detected that moves to the section is less likely to fluctuate. Therefore, in the catalyst conversion type sensor of the present invention, the conversion rate at which the detection target gas is converted into the conversion gas is not easily affected by the flow rate of the detection target gas, and therefore the conversion rate is less likely to decrease with time.

  Moreover, if it is a diffusion means of this structure, since the detection object gas which naturally diffuses and stays in the inside of a conversion part can be made to contact a heating catalyst part efficiently, a conversion rate can be improved. At this time, since the gas to be detected can generate the converted gas not by thermal decomposition but by oxidation by the catalyst, the heating temperature of the heating catalyst portion can be suppressed.

  In addition, the catalyst conversion type sensor of the present invention has a heating catalyst part and a sensor element part in the conversion part, so that it is not necessary to add a thermal decomposition unit, so that the downsizing can be achieved.

The second characteristic configuration of the catalyst conversion type sensor according to the present invention is that the air permeation resistance of the diffusing means is 800 mm · Pa ⁻¹ · s ⁻¹ or less.

  According to this configuration, at least a part of the detection target gas flowing down the gas flow path passes through the hole of the diffusing unit and is transmitted to the inside of the conversion unit in a state where the detection target gas is hardly affected by the flow pressure of the detection target gas. It can be constituted as follows.

  The third characteristic configuration of the catalyst conversion type sensor according to the present invention is that the diffusing means includes a resin film having a hole having a predetermined hole diameter and a gas permeable porous film disposed adjacent to each other.

  According to this configuration, by forming the hole in the resin film, it is possible to adjust the gas amount of the detection target gas that permeates the diffusion means and naturally diffuses into the conversion portion. In addition, the gas permeable porous membrane can define the degree to which the detection target gas naturally diffuses into the conversion portion to a desired degree.

  The diffusion means is configured to transmit the detection target gas so that the detection target gas flowing down the gas flow path can be naturally diffused to the conversion section side. On the other hand, the conversion gas generated in the conversion section is diffused. It is desirable to configure so that it does not easily pass through the gas flow path side. That is, if it becomes difficult for the converted gas to move to the gas flow path side, the converted gas can be efficiently detected by the sensor element unit. Therefore, if the diffusing means is configured such that the resin film and the porous film are arranged adjacent to each other as in this configuration, the pore diameter of the pores can be set variously, and the air permeability of the porous membrane can be changed variously. The gas permeation resistance of the diffusing means is configured so that the detection target gas to be applied can be naturally diffused to the conversion portion side, and the conversion gas does not easily move from the conversion portion to the gas flow path side. Can do.

  A fourth characteristic configuration of the catalyst conversion sensor according to the present invention is that the diffusion means is a resin film in which a hole having a predetermined hole diameter is formed.

  According to this configuration, it is possible to adjust the gas amount of the detection target gas that permeates the diffusion means and naturally diffuses into the conversion unit with a simple configuration.

  A fifth characteristic configuration of the catalyst conversion type sensor according to the present invention is that the detection target gas is nitrogen trifluoride and the conversion gas is nitrogen dioxide.

  According to this configuration, nitrogen trifluoride, which has low sensitivity by the gas sensor and cannot be detected by direct electrochemical reaction, can be converted into nitrogen dioxide and efficiently detected.

  A sixth feature of the catalyst conversion type sensor according to the present invention is that the catalyst in the heating catalyst part is a noble metal catalyst containing Pd and Pt, and the sensor element part has noble metal-supporting carbon and can detect nitrogen dioxide. The chemical nitrogen oxide sensor element is used.

  According to this configuration, an electrochemical nitrogen oxide sensor element having noble metal-supporting carbon and capable of detecting nitrogen dioxide has high sensitivity to nitrogen dioxide and can be miniaturized. Therefore, if the catalyst conversion type sensor of this configuration is used, further downsizing of the catalyst conversion type sensor can be achieved.

  A seventh characteristic configuration of the catalyst conversion type sensor according to the present invention is that the heating catalyst unit is a catalytic combustion type sensor, and the catalytic combustion type sensor has the catalyst and is sensitive to the detection target gas. The diameter is in the range of 0.76 to 1.08 mm.

  According to this structure, it is excellent in the efficiency which produces | generates inversion gas by oxidizing detection object gas, and it can be set as the range which satisfy | fills a preferable response speed (within 60 seconds).

  The eighth characteristic configuration of the catalyst conversion type sensor according to the present invention is that the heating catalyst section is heated to 300 to 700 ° C.

  According to this configuration, it is possible to achieve both a preferable response speed (within 60 seconds) and a detectable sensitivity.

  A ninth characteristic configuration of the catalyst conversion type sensor according to the present invention is that an applied voltage of the heating catalyst unit is set to 0.68 to 1.85V.

  According to this configuration, the temperature of the sensing element can be set to an appropriate temperature, and both a preferable response speed (within 60 seconds) and a detectable sensitivity can be achieved.

It is a section schematic diagram of the catalyst conversion type sensor of the present invention. It is the schematic of a spreading | diffusion means. It is the graph which showed the result of having investigated about the fluctuation | variation of the conversion rate at the time of changing various hole diameters of the hole part formed in the resin film of a spreading | diffusion means. It is the graph which showed the result of having detected nitrogen trifluoride in the catalyst conversion type sensor of this invention, and the conventional sensor. It is the graph which showed the result investigated about the air permeation resistance of a diffusion means. It is the graph which showed the result of having investigated about the relationship between each gas sensitivity at the time of using the spreading | diffusion means of a different aspect, and response time. It is the graph which showed the result of having investigated whether the indication value obtained in the case of gas detection depends on the flow volume of detection object gas. It is the graph which investigated the relationship between the applied voltage (about 220-1820mV) at the time of changing various the spherical diameters of the detection element of a contact combustion type sensor, and element temperature. It is the graph which investigated the relationship between the applied voltage (900-1300mV) at the time of changing various the spherical diameters of the detection element of a contact combustion type sensor, and element temperature. It is the schematic of the cap which does not have a spreading | diffusion restriction | limiting (cap | cover without a diffusion restriction | limiting). It is the schematic of the cap which does not have a spreading | diffusion restriction | limiting (cap | cover without a diffusion restriction | limiting). It is the schematic of the cap (diffusion-limited cap) which has a spreading | diffusion restriction | limiting. It is the schematic of the cap (diffusion-limited cap) which has a spreading | diffusion restriction | limiting. It is the graph which showed the result of the gas sensitivity at the time of changing the density | concentration of methane gas to 0-100% LEL in the case of using a cap without a diffusion restriction. It is the graph which showed the result of the gas sensitivity at the time of changing the density | concentration of methane gas to 0-100% LEL in the case of using a cap with a diffusion restriction. Against sphere diameter of the sensing element of the catalytic combustion type sensor is a graph showing a result of changes in NO ₂ sensitivity in electrochemical nitrogen oxide sensor element. It is the graph which showed the result of the change of the response speed in an electrochemical nitrogen oxide sensor element with respect to the spherical diameter of the detection element of a contact combustion type sensor. With respect to the temperature of the sensing element of the catalytic combustion type sensor is a graph showing a result of changes in NO ₂ sensitivity in electrochemical nitrogen oxide sensor element. It is the graph which showed the result of the change of the response speed in an electrochemical nitrogen oxide sensor element with respect to the temperature of the detection element of a contact combustion type sensor. It is the graph which showed the result of having investigated about temporal stability of the detection element of a contact combustion type sensor in the case of using two kinds of caps. It is the schematic (top view) of the 1st sensor case which comprises a heating catalyst part. It is the schematic (side view) of the 1st sensor case which comprises a heating catalyst part. It is the schematic (cross section) of the 1st sensor case which comprises a heating catalyst part. It is the schematic (top view) of the 2nd sensor case which comprises a sensor element part. It is the schematic (cross section) of the 2nd sensor case which comprises a sensor element part. It is the schematic when a 1st sensor case and a 2nd sensor case are integrated.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the catalytic conversion sensor X of the present invention includes a gas flow path 10 for flowing down a detection target gas in order to detect the detection target gas by detecting a conversion gas generated by oxidation, and a gas A heated catalyst unit 30A that is connected to the flow channel 10 and separated from the diffusion means 20 for naturally diffusing the detection target gas, contacts the heated catalyst 31 to oxidize the detection target gas to generate a converted gas, And the conversion part 30 which has the sensor element part 30B which can detect the conversion gas produced | generated by oxidation is provided.

  In the present embodiment, the case where the detection target gas is nitrogen trifluoride, the conversion gas is nitrogen dioxide, and the sensor element unit 30B is an electrochemical nitrogen oxide sensor element capable of detecting nitrogen dioxide will be described. It is not limited to. For example, if the sensor element unit 30B is an electrochemical nitrogen oxide sensor element, the detection target gas can be ammonia. In addition, if the sensor element unit 30B is a sensor element that can detect carbon monoxide or carbon dioxide as the conversion gas, other gases can be detected.

  The diffusing means 20 divides the gas flow path 10 and the conversion unit 30, as long as they are configured to be spatially distinguishable, and the detection target gas flowing down the gas flow path 10 is converted into the conversion unit 30. It is comprised so that it may become the aspect which permeate | transmits detection object gas so that it can diffuse naturally. That is, a part of the detection target gas flowing down the gas flow path 10 flows down to the downstream side of the gas flow path 10 as it is, and the remaining part permeates the diffusion means 20 and diffuses naturally into the conversion unit 30. It becomes an aspect. “Natural diffusion” in this specification means that the gas to be detected is not forced to pass through the holes of the diffusing means 20 by, for example, pressurizing the detection target gas and permeate into the conversion unit 30. It is assumed that at least a part of the detection target gas flowing down the gas passes through the hole of the diffusing means 20 and permeates into the conversion unit 30 in a state where it is difficult to be affected by the flow pressure.

Such diffusion means 20 may be configured to air resistance is a 800mm ^{· Pa -1 · s} -1 or less, preferably, that the 50~800mm ^{· Pa -1 · s} -1 Good.

  The diffusion means 20 may be configured by combining different materials, or may be configured by a single material. In the present embodiment, a case where different materials are combined will be described.

  When the diffusing means 20 is configured by combining different materials, as shown in FIG. 2, the resin film 21 having the hole 21a having a predetermined hole diameter and the gas permeable porous film 22 are arranged adjacent to each other. However, this is not a limitation. When these layers are stacked, the resin film 21 may be disposed on the gas flow path 10 side and the porous film 22 may be disposed on the conversion unit 30 side.

  The resin film 21 may be formed by molding a polymer component such as a plastic synthetic resin into a thin film shape, but is not limited thereto. One or a plurality of hole portions 21 a having a predetermined hole diameter are formed in the resin film 21. By setting the hole diameter and the number of holes of the hole 21a, the amount of the detection target gas that permeates the diffusion means 20 and naturally diffuses into the conversion unit 30 can be adjusted. The gas amount may be adjusted by setting the hole diameter and the number of holes of the hole 21a so as to obtain a desired gas amount.

  The porous membrane 22 may be a gas permeable porous membrane or the like, but is not limited to this. As such a porous membrane, for example, a PTFE (polytetrafluoroethylene) membrane or the like can be used. The porous film 22 can define the degree of natural diffusion of the detection target gas into the conversion unit 30 to a desired degree.

  As described above, the diffusing unit 20 is configured to transmit the detection target gas so that the detection target gas flowing down the gas flow path 10 can naturally diffuse to the conversion unit 30 side. It is desirable that the converted gas generated at 30 is difficult to pass through the diffusing means 20 and move to the gas flow path 10 side. That is, if it becomes difficult for the converted gas to move toward the gas flow path 10, the sensor element 30B can efficiently detect the converted gas. Therefore, in the case of the diffusion means 20 described above, various arrangement positions of the hole 21a in addition to the hole diameter and the number of holes 21a are set, and the air permeability of the porous film 22 is changed variously. The gas permeation resistance of the diffusing means 20 is such that the detection target gas to be applied can naturally diffuse to the conversion unit 30 side, and the conversion gas does not easily move from the conversion unit 30 to the gas flow path 10 side. Can be configured.

  For example, when the diffusion means 20 has an aspect in which a resin film 21 and a gas permeable porous film 22 are stacked, one hole 21a is formed at the center of the resin film 21 and the hole diameter is 1 to 4 mm. The conversion rate can be about 35 to 90%.

  When the diffusing means 20 is composed of a single material, for example, either a resin film having a hole having a predetermined hole diameter or a gas permeable porous film may be used. It is not limited.

  The resin film may be formed by molding a polymer component such as the above-described plastic synthetic resin into a thin film shape, but is not limited thereto. Also in this case, one or a plurality of holes having a predetermined hole diameter are formed in the resin film. By setting the hole diameter and the number of holes of the hole 2, it is possible to adjust the gas amount of the detection target gas that permeates the diffusion means 20 and naturally diffuses into the conversion unit 30. Therefore, what is necessary is just to set the hole diameter and the number of holes of a hole so that it may become a desired gas amount. For example, when the outer diameter of the resin film is 14 mm, the hole diameter is preferably 1 to 4 mm.

  As the porous membrane, for example, the above-mentioned PTFE membrane or the like can be used. When the diffusing means 20 is composed of a single material, it is possible to combine a plurality of porous PTFE membranes having different air permeability even if they are the same material (porous PTFE membrane). is there.

  With this configuration, it is possible to adjust the gas amount of the detection target gas that permeates the diffusion means 20 and naturally diffuses into the conversion unit 30 with a simple configuration. The gas amount may be adjusted by setting the hole diameter and the number of holes so that the desired gas amount is obtained.

  The conversion unit 30 includes a heating catalyst unit 30A and a sensor element unit 30B in order to detect the conversion gas generated by oxidizing the detection target gas. The conversion unit 30 of the present embodiment is configured as a part of the internal space of the casing 1. That is, the inside of the casing 1 is partitioned by the diffusing means 20, and one of the partitioned spaces is the conversion unit 30 and the other is part of the gas flow path 10. The casing 1 may have any shape such as a columnar shape or a cubic shape. In the present embodiment, the direction in which the detection target gas flows down the gas flow path 10 is different from the direction in which a part of the detection target gas permeates the diffusion means 20 and naturally diffuses into the conversion unit 30 (substantially orthogonal). ) Will be described. In this case, at least a part of the detection target gas flowing down the gas flow path 10 easily passes through the holes of the diffusion means 20 and is naturally diffused into the conversion unit 30 in a state that is less susceptible to the flow pressure. .

  30 A of heating catalyst parts permeate | transmit the spreading | diffusion means 20, and contact the detection target gas naturally diffused in the inside of the conversion part 30 with the heated catalyst 31, and oxidize detection target gas and produce | generate conversion gas. Although the case where the catalyst 31 in the present embodiment is a noble metal catalyst containing Pd and Pt will be described, the present invention is not limited thereto, and Ru, Rh, and Ir can also be used. The heating catalyst portion 30A may be configured to be heated to, for example, 300 to 700 ° C, preferably 350 to 600 ° C, and more preferably about 400 to 600 ° C. In this case, the applied voltage is preferably about 0.68 to 1.85V. When the detection target gas comes into contact with the heated catalyst 31, the detection target gas is oxidized, and a conversion gas can be generated by the oxidizing action of the catalyst. If there is only one heating catalyst unit, power consumption can be suppressed, but the number of installation is not limited to one, and a plurality of heating catalyst units may be provided. In the case where a plurality of heating catalyst units are provided, for example, two heating catalyst units may be juxtaposed at a predetermined interval, and the sensor element unit 30B may be disposed on the downstream side thereof. May be arranged so as to face each other inside the casing 1. When a plurality of heating catalyst units are provided, the temperature for heating each heating catalyst unit may be set to the same temperature, or may be changed to an appropriate temperature according to the installation position. The said temperature is good to set to the temperature which can exhibit the performance of the spreading | diffusion means 20 appropriately.

  In the present embodiment, a case where an element of a catalytic combustion type sensor is used as the heating catalyst unit 30A will be described. In this case, a heating catalyst part can be comprised in a simple and small aspect.

  The contact combustion type sensor includes a detection element that is sensitive to a predetermined gas. The detection element is a catalytic combustion type element, and the surface of the coil of a metal wire containing platinum or the like having a high temperature coefficient with respect to electrical resistance is made of alumina or the like that carries a noble metal catalyst active against the detection target gas. It is formed by covering with a carrier. As the noble metal catalyst, fine particles of at least one of Pt, Pd, Ru, Rh and Ir, which are the platinum group described above, can be used.

  The spherical diameter of the sensing element is preferably 0.76 to 1.08 mm, and preferably 0.84 to 1.00 mm. Within this range, the efficiency of generating the converted gas by oxidizing the detection target gas is excellent.

  As described above, in the present embodiment, the detection target gas is nitrogen trifluoride and the conversion gas is nitrogen dioxide. It is considered that the conversion proceeds according to the following reaction formulas 1 to 3.

  As the sensor element unit 30B, an electrochemical sensor, an optical sensor, a semiconductor gas sensor, a contact combustion sensor, or the like can be applied. In the present embodiment, a description will be given of a case of an electrochemical nitrogen oxide sensor element having noble metal-supported carbon and capable of detecting nitrogen dioxide which is a generated conversion gas.

  The electrochemical nitrogen oxide sensor element has a sensing electrode composed of a gas diffusion electrode, an auxiliary phase integrally joined to the sensing electrode, an electrolytic solution that is a room temperature molten salt, and a counter electrode that has the same configuration as the sensing electrode. It can comprise by accommodating in a case. The detection electrode is formed from a mixture of carbon powder carrying a gold catalyst (gold-carrying carbon) and polytetrafluoroethylene as a binder. The auxiliary phase is formed by filling lithium nitrate, which is an auxiliary phase material, in the pores of the porous nickel sheet. Such an electrochemical nitrogen oxide sensor element is highly sensitive to nitrogen dioxide.

This gold-supported carbon can be made fine to about 10 nm, so that the electrochemical nitrogen oxide sensor element can be miniaturized. Further, by making the gold-supporting carbon fine particles, the surface area can be increased and the sensitivity to nitrogen dioxide can be improved.
Since nitrogen trifluoride, which is a detection target gas used in the present invention, has low sensitivity by a gas sensor and cannot be directly detected by an electrochemical reaction, it can be detected by converting it into nitrogen dioxide (NO ₂ ) by oxidation in advance.

  The catalyst conversion type sensor X of the present invention includes a pump that sucks and flows down the detection target gas, a flow rate sensor, a calculation means that determines leakage of the detection target gas based on a result detected by the sensor element unit 30B, an alarm level or higher It can be used as a member of an alarm device or a gas detector together with alarm means (both not shown) for controlling to issue an alarm when the concentration of the detection target gas is continuously detected.

  In the catalyst conversion type sensor X of the present invention, the detection target gas flowing down the gas flow path 10 by the diffusion means 20 can be naturally diffused toward the conversion unit 30, and therefore the gas of the detection target gas that moves to the conversion unit 30. The amount can be configured not to depend on the flow rate flowing down the gas flow path 10. For this reason, even if the flow rate sensor deteriorates and the flow rate of the detection target gas flowing down the gas flow path 10 fluctuates over time, the amount of the detection target gas that immediately moves to the conversion unit 30 is hardly affected. Therefore, the gas amount of the detection target gas that moves to the conversion unit 30 is less likely to fluctuate. Therefore, in the catalyst conversion type sensor X of the present invention, the conversion rate at which the detection target gas is converted into the conversion gas is less affected by the flow rate of the detection target gas, and therefore the conversion rate is less likely to decrease with time.

  In the case of the diffusion means 20 described above, the detection target gas that naturally diffuses and stays inside the conversion unit 30 can be efficiently brought into contact with the heating catalyst unit 30A. Therefore, the conversion rate is about 35 to 90%, preferably It can be improved to about 45 to 90%. At this time, the gas to be detected is oxidized by the heating catalyst unit 30A, and a conversion gas can be generated by the oxidizing action of the catalyst. Therefore, the heating temperature of the heating catalyst unit 30A is 300 to 700 ° C, preferably 350 to 600 ° C. More preferably, it can be suppressed to 400 to 600 ° C., more preferably about 450 ° C. Within this temperature range, both response speed and detectable sensitivity can be achieved.

  If it is the diffusion means 20 mentioned above, since it can comprise so that conversion gas may become difficult to transfer outside (gas flow path 10) from the conversion part 30, the conversion gas which retains inside the conversion part 30 is efficiently obtained. It can be stably detected by the sensor element unit 30B.

  Further, the catalytic conversion type sensor X of the present invention can achieve downsizing because the conversion unit 30 includes the heating catalyst unit 30A and the sensor element unit 30B, so that it is not necessary to add a thermal decomposition unit.

[Example 1]
Examples of the present invention will be described.
Using the catalyst conversion sensor X of the present invention, the change in the conversion rate was examined.
The detection target gas was nitrogen trifluoride, the conversion gas was nitrogen dioxide, and the sensor element 30B was an electrochemical nitrogen oxide sensor element. Further, the diffusion means 20 has a mode in which a resin film (plastic synthetic resin) 21 formed in a circle and a gas permeable porous film (PTFE film) 22 are stacked, and one hole 21 a is formed at the center of the resin film 21. Formed. The change of the conversion rate when the hole diameter of the hole 21a was variously changed from φ1 to 14 mm was examined. φ14 mm is a size corresponding to the diameter of the cylindrical conversion portion 30.

  The gas to flow down was nitrogen trifluoride and nitrogen dioxide, and each was allowed to flow down separately. The reason why nitrogen dioxide is allowed to flow is to confirm how nitrogen dioxide behaves depending on the hole diameter of the hole 21a. The results are shown in FIG. When nitrogen trifluoride was caused to flow down, the sensor output of nitrogen dioxide, which is the conversion gas generated in the conversion unit 30, was measured. When nitrogen dioxide was allowed to flow down, the sensor output of nitrogen dioxide naturally diffused into the conversion unit 30 was measured.

  As a result, when nitrogen dioxide was allowed to flow down, when the pore diameter was large (φ8 to 14), it was recognized that the sensor output was high, so that natural diffusion was likely to occur in the conversion unit 30. However, in this case, it becomes easy to shift from the conversion unit 30 to the outside (the gas flow path 10).

  When nitrogen trifluoride was allowed to flow down, when the pore size was large (φ8 to 14), the conversion was about 10 to 20% because the sensor output was low. This is considered to be because nitrogen dioxide, which is a conversion gas generated from nitrogen trifluoride, easily moves from the conversion unit 30 to the outside (the gas flow path 10) because the pore diameter is large. Moreover, when the hole diameter was small (φ1 to 4), the conversion rate was about 35 to 90% because the sensor output was high. This is because nitrogen dioxide, which is a conversion gas generated from nitrogen trifluoride, is difficult to transfer from the conversion unit 30 to the outside (gas flow path 10) because the pore diameter is small, and thus can be detected efficiently. it was thought.

  From this, when one hole 21a is formed at the center of the resin film 21, it is recognized that a good conversion rate (about 35 to 90%) can be obtained when the hole diameter is 1 to 4 mm. It was recognized that a good conversion rate (about 45 to 90%) was obtained when the thickness was set to 1 to 3 mm.

[Example 2]
The sensitivity when detecting nitrogen trifluoride using the catalytic conversion sensor X of the present invention and the conventional sensor was compared. In order to detect the conventional sensor by converting nitrogen trifluoride into nitrogen dioxide by thermal decomposition, a sensor having a structure in which the detection target gas is thermally decomposed in advance by an additional thermal decomposition unit and introduced into the sensor portion is used. The thermal decomposition unit used was a unit having a known configuration.

The air resistance of the diffusing means 20 is 50 mm · Pa ⁻¹ · s ^−1, and one hole 21 a (hole diameter 6 mm) is formed at the center of the resin film 21 (resin film diameter 16 mm, PP film thickness 0.2 mm). What was formed was used as a porous PTFE membrane (manufactured by Yodogawa Paper Mill). The volume of the conversion unit 30 was 0.001 m ³ and the heating temperature of the heating catalyst unit 30A was 450 ° C. Further, the concentration of nitrogen trifluoride was 16 ppm, and the flow rate for flowing down the gas flow path in the catalytic conversion sensor X of the present invention and the conventional sensor was 0.5 L / min. The result of detecting nitrogen trifluoride by each sensor is shown in FIG.

  As a result, the sensitivity of nitrogen trifluoride in the catalytic conversion type sensor X of the present invention was as high as about 0.30 μA after 50 seconds, but the sensitivity of nitrogen trifluoride in the conventional sensor was 100 Even after a lapse of seconds, it remained at a low value around 0.15 μA. Therefore, it was recognized that the catalyst conversion type sensor X of the present invention is a highly sensitive sensor that can achieve a high conversion rate.

Example 3
The air permeation resistance of the diffusion means 20 in the catalyst conversion type sensor X used in Example 2 was examined. By changing the structure of the diffusing means 20 in various ways, the air resistance can be changed in various ways, and sufficient gas sensitivity can be obtained in consideration of the response speed within 60 seconds, more preferably within 30 seconds. The range of resistance was determined. The structure of the diffusing means 20 was PP film only (no porous PTFE sheet), and the hole diameters of the holes 21a were 1 mm, 2 mm, 3 mm, 4 mm, 6 mm, 8 mm and fully open (14 mm), respectively. The air permeability resistances were 50, 100, 150, 300, 800, 1000, and 1200, respectively, from the smallest pore diameter. The results are shown in FIG.

As a result, when the air resistance of the diffusing means was 800 mm · Pa ⁻¹ · s ⁻¹ or less, it was recognized that it was in a range satisfying a preferable response speed (within 60 seconds). Furthermore, when the air permeability resistance of the diffusing means was in the range of 50 to 800 mm · Pa ⁻¹ · s ⁻¹ , it was recognized as a range satisfying sufficient gas sensitivity (25 mV or more).

Example 4
In the catalyst conversion type sensor X of the present invention, when the diffusing means 20 is a resin film composed of a single material (Example 4-1), or the resin film 21 and the porous film 22 are disposed adjacent to each other. In the case of the overlapped mode (Example 4-2), the relationship between each gas sensitivity and response time was examined.

  In the sensor of Example 4-1, the diffusing means 20 in which a hole having a hole diameter of 2 mm was formed in a resin film having a film diameter of 14 mm was used. In the sensor of Example 4-2, the resin film 21 having a hole diameter of 14 mm and a hole having a hole diameter of 4 mm and the diffusion means 20 including a porous PTFE film having a film diameter of 14 mm were used. The concentration of nitrogen trifluoride was 16 ppm. The results are shown in FIG.

  As a result, it was recognized that high gas sensitivity of about 160 to 210 mV was obtained in about 100 to 200 seconds in any of the examples.

Example 5
Using the catalyst conversion sensor X of the present invention and the conventional sensor, it was examined whether or not the indicated value obtained at the time of gas detection depends on the flow rate of the detection target gas. The conventional sensor 1 used in Example 2 was used as the conventional sensor.
The detection target gas was 15 ppm nitrogen trifluoride, and the flow rate was variously changed between 0.2 and 0.8 L / min. The results are shown in FIG.

  As a result, the sensor 1 has a lower conversion value because the conversion rate decreases as the flow rate increases. However, the catalytic conversion sensor X of the present invention hardly changes even if the flow rate increases. There wasn't. Therefore, it was recognized that the catalyst conversion type sensor X of the present invention hardly depends on the flow rate of the detection target gas.

Example 6
When a catalytic combustion type sensor was used as the heating catalyst unit 30A, the relationship between the applied voltage and the element temperature when the spherical diameter of the detection element of the catalytic combustion type sensor was variously changed was examined.

  As the sensing element, a platinum coil coated with alumina supporting a noble metal catalyst containing Pd and Pt is used, and the spherical diameter of the sensing element is 0.76 mm (Invention Example 1), 0.84 mm (Invention). Example 2), 0.92 mm (Invention Example 3), 1.00 mm (Invention Example 4), 1.08 mm (Invention Example 5), and the applied voltage was about 220 to 1820 mV, and the element temperature was measured. . The results are shown in FIGS. FIG. 9 is an enlarged view of the graph of FIG. 8 when the applied voltage is between 900 and 1300 mV.

  As a result, it was recognized that the element temperature increased as the applied voltage was increased, and that the element temperature decreased at the same voltage as the spherical diameter of the sensing element was increased.

Example 7
When a catalytic combustion type sensor is used as the heating catalyst unit 30A, a cap that covers the detection element 32 of the catalytic combustion type sensor is a cap 33 that does not have diffusion restriction (FIGS. 10 and 11: hereinafter referred to as a diffusion restriction non-cap). When the cap 34 having diffusion limitation (FIGS. 12 and 13: hereinafter referred to as a diffusion limited cap) is used, it was examined how the spherical diameter of the sensing element 32 is related.

  The unrestricted cap 33 is constituted by a body portion 33a and a wire mesh portion 33b. The body part 33a is a seamless tube made of SUS304 with a 5.8-5.9 mm diameter hem-opening process, and the wire mesh part 33b has a semicircular shape with a maximum diameter of 5.2 mm, and has a wire diameter of 0 A metal mesh made of SUS316, which is 0.1 mm, 100 mesh, is configured to have a double structure. The metal mesh part 33b is fitted into the body part 33a by spot welding at four locations so that the long dimension when assembled is 11.5 mm. The diffusion restriction-free cap 33 is configured so as not to restrict, for example, the gas inside the diffusion restriction-free cap 33 from diffusing through the wire mesh portion 33 b of the diffusion restriction-free cap 33.

  On the other hand, the diffusion-restricted cap 34 has a cylindrical body part 34a made of SUS305-2D having a diameter of 5.9 mm and a length of 11.6 mm, and has a hole part 34b having a diameter of 3.6 mm. The cap 34 with diffusion restriction has a hole diameter that is narrower than the diameter of the body part 34a, so that, for example, gas inside the cap 34 with diffusion restriction diffuses through the hole 34b of the cap 34 with diffusion restriction. It is configured so as to limit the above to some extent.

  Note that the cap 34 with diffusion limitation has a diffusion limit of about 50% compared to the cap 33 without diffusion limitation.

  The gas used was methane gas as a test gas. FIG. 14 (diffusion-limited cap 33) and FIG. 15 (diffusion-limited cap 34) show the results of gas sensitivity when the concentration of methane gas was changed from 0 to 100% LEL.

  As a result, when the cap 33 without diffusion restriction is used from FIG. 14, the sensitivity increases as the sphere diameter of the detection element 32 increases, and when the cap 34 with diffusion restriction is used from FIG. It was found that the sensitivity hardly changed. It is considered that this is because the difference in sensitivity due to the spherical diameter of the sensing element 32 is less likely to occur due to the diffusion limiting action of the diffusion limited cap 34. As a result, when the cap 34 with diffusion restriction was used, for example, when the reactivity was lowered due to deterioration of the catalyst, the output value hardly changed and it was recognized that the decrease in sensitivity was small.

  In this way, when the cap 34 with diffusion restriction is used, there is almost no dependence on the spherical diameter of the sensitivity. Therefore, if a cap with diffusion restriction is used, the gas diffusion state is diffusion-controlled in the heating catalyst unit 30A. Conceivable. That is, the diffusion limited cap 34 is considered to be a cap that does not change in sensitivity even if the spherical diameter is intentionally changed. Furthermore, although methane gas is used in the present embodiment, it is considered that the cap is diffusion-controlled even when the cap 34 with diffusion limitation is used for a gas whose molecules are more difficult to diffuse than methane gas.

Example 8
When a catalytic combustion type sensor is used as the heating catalyst unit 30A, a change in NO ₂ sensitivity in the electrochemical nitrogen oxide sensor element (sensor element unit 30B) with respect to the spherical diameter of the detection element of the catalytic combustion type sensor, And the response speed was investigated. The spherical diameter of the sensing element was 0.76 to 1.08 mm set in Example 6, and the caps used in the contact combustion type sensor were the two types of caps used in Example 7. The detection target gas was 16 ppm nitrogen trifluoride, and the applied voltage was 1.1V. The results are shown in FIGS.

As a result, regardless of which cap is used, the sensitivity increases as the sphere diameter of the sensing element increases from FIG. 16, and the response speed decreases as the sphere diameter increases from FIG. . From these results, it was recognized that there is an optimum range for practical use in the ball diameter of the sensing element from the balance between sensitivity and response speed. Thus, for example NO ₂ sensitivity in e.g. 50mV above case (FIG. 16) is required, the sphere diameter of the sensing element if the size of 0.76～1.08Mm, the response speed of about 15 to 34 seconds (Fig. 17 It was recognized that the efficiency of generating the converted gas by oxidizing the detection target gas was excellent, and the range satisfying the preferable response speed (within 60 seconds).

In particular, when the spherical diameter of the sensing element is 0.84 to 1.00 mm, the NO ₂ sensitivity is 50 mV or more (FIG. 16) and the response speed is within a range of 30 seconds (FIG. 17). It was recognized.

Example 9
In Example 8, the change in NO ₂ sensitivity and the response speed in the electrochemical nitrogen oxide sensor element (sensor element part 30B) were examined with respect to the temperature of the sensing element (heating catalyst part 30A). The spherical diameter of the detection element 32 was 1.00 mm. The results are shown in FIGS.

From FIG. 18, it is recognized that the sensor output reaches a peak in the vicinity of 400 to 420 ° C., and the sensor output decreases as the temperature of the detection element increases after the top temperature of the detection element is different between the two types of caps. It was. Thus, for example if it is necessary more than 50mV in NO ₂ sensitivity, good to the 300 to 700 ° C. The temperature of the sensing element when using diffuse unlimited cap 33, when using a diffusion restricted cap 34 It has been found that the temperature of the sensing element should be 300-600 ° C.

  Further, from FIG. 19, it was recognized that in two types of caps, the higher the temperature of the sensing element, the faster the response speed. That is, when the cap 33 without diffusion restriction is used, a preferable response speed (within 60 seconds) is satisfied when the temperature is 300 ° C. or higher, and the response speed hardly changes from around 700 ° C. It has been found that the temperature is preferably 300 to 700 ° C. In addition, when the cap 34 with diffusion restriction is used, a preferable response speed (within 60 seconds) is satisfied when the temperature is about 350 ° C. or higher, and the response speed hardly changes from around 600 ° C. Has been found to be 350-600 ° C.

  When the temperature of the sensing element is set to 300 to 700 ° C., the applied voltage is preferably set to 0.68 V (the sensing element spherical diameter 0.76 mm) to 1.85 V (the sensing element spherical diameter 1.08 mm), for example. FIG. 8).

When the cap 34 with diffusion restriction was used, the top temperature shifted to a low temperature and the response speed was slow because the gas was trapped in the cap. Further, from the results of FIGS. 18 and 19, if the temperature of the detection element is 300 ° C. or lower, the conversion of the gas to be detected hardly proceeds, and if it is 700 ° C. or higher, the reaction from NO to N ₂ O ₂ occurs. Is thought to be difficult to progress.

Example 10
When a catalytic combustion type sensor is used as the heating catalyst unit 30A, the cap used for the catalytic combustion type sensor is a diffusion-limited cap 33 (FIGS. 10 and 11) and a diffusion-limited cap 34 (FIGS. 12 and 13). ) Was used to investigate the stability over time of the sensing element. The gas used was 15 ppm nitrogen trifluoride. The results are shown in FIG.

  As a result, when used for about two months or more, it was found that the person using the cap 33 without diffusion restriction gradually deteriorated, and the person using the cap 34 with diffusion restriction showed almost no deterioration. .

  Incidentally, it is considered that the use of the cap 33 having no diffusion restriction can be used sufficiently in a place where it can be used for a short time because the deterioration gradually proceeds with time but the sensor output is high. On the other hand, the use of the cap 34 with diffusion restriction has a low sensor output, but the sensor output is stable over time, so it is considered suitable for use in a place where it can be installed over a long period of time, such as a factory.

Example 11
In the above-described embodiment, the heating catalyst unit 30A and the sensor element unit 30B have been described as being disposed in the conversion unit 30 in a state of being separated from each other. However, the present invention is not limited to such an embodiment. You may arrange | position to the conversion part 30 in the aspect which integrated the element part 30B.

  For example, as shown in FIGS. 21 to 26, the first sensor case 40 constituting the heating catalyst unit 30 </ b> A and the second sensor case 50 constituting the sensor element unit 30 </ b> B may be integrated with a bolt or the like. Is possible.

  The first sensor case 40 is formed with a first gas inlet 41 through which gas flows, an insertion hole 42 into which a catalytic combustion sensor is inserted, and a gas outlet 43 through which gas flows out (FIGS. 21 to 21). 23). The gas to be detected flows from the gas inlet 41 and the converted gas flows out from the gas outlet 43.

  The second sensor case 50 is formed with a sensor housing portion 51 for housing an electrochemical sensor and the like, and a placement portion 52 for placing the first sensor case 40 (FIGS. 24 and 25). Further, the second sensor case 50 is formed with a second gas inlet 53 connected to the gas outlet 43 in the mounting portion 52, and communication for connecting the second gas inlet 53 and the sensor housing portion 51 is made. A portion 54 is formed. As a result, the converted gas flowing out from the gas outlet 43 flows into the sensor housing portion 51 via the second gas inlet 53 and the communication portion 54, and the converted gas can be detected by an electrochemical sensor or the like.

  Thus, the capacity | capacitance of the conversion part 30 can be made small by setting it as the aspect which integrated heating catalyst part 30A (1st sensor case 40) and sensor element part 30B (2nd sensor case 50).

  Moreover, by setting it as the aspect which does not mount the 1st sensor case 40 in the 2nd sensor case 50, it is set as the structure only of the sensor element part 30B (2nd sensor case 50), ie, the structure only of an electrochemical sensor. it can. Thereby, the structure provided with 30 A of heating catalyst parts and the sensor element part 30B, and the structure provided only with the sensor element part 30B can be selected easily.

  INDUSTRIAL APPLICABILITY The present invention can be used for a catalyst conversion type sensor that detects a detection target gas by detecting a conversion gas generated by oxidation.

X catalyst conversion type sensor 10 gas flow path 20 diffusion means 30 conversion part 30A heating catalyst part 30B sensor element part 31 catalyst

Claims (9)

In order to detect the gas to be detected by detecting the converted gas generated by oxidation,
A gas flow path for flowing down the detection target gas;
A heating catalyst unit that is connected to the gas flow path and that is separated by a diffusing unit that naturally diffuses the detection target gas, contacts the heated catalyst to oxidize the detection target gas to generate a converted gas, And a conversion unit having a sensor element unit capable of detecting a conversion gas generated by oxidation. The catalyst conversion type sensor according to claim 1, wherein the diffusion resistance of the diffusion means is 800 mm · Pa ⁻¹ · s ⁻¹ or less.   The catalyst conversion type sensor according to claim 1 or 2, wherein the diffusion means comprises a resin film having a hole having a predetermined hole diameter and a gas permeable porous film disposed adjacent to each other.   The catalyst conversion type sensor according to claim 1, wherein the diffusion means is a resin film in which a hole having a predetermined hole diameter is formed.   The catalytic conversion sensor according to any one of claims 1 to 4, wherein the detection target gas is nitrogen trifluoride, and the conversion gas is nitrogen dioxide.   The catalyst in the heating catalyst part is a noble metal catalyst containing Pd and Pt, and the sensor element part is an electrochemical nitrogen oxide sensor element having noble metal-supporting carbon and capable of detecting nitrogen dioxide. Catalyst conversion sensor.   The heating catalyst section is a catalytic combustion type sensor, and the spherical diameter of a detection element having the catalyst in the catalytic combustion type sensor and sensitive to the detection target gas is 0.76 to 1.08 mm. The catalyst conversion type sensor according to any one of 6.   The catalyst conversion type sensor according to any one of claims 1 to 7, wherein the heating catalyst part is heated to 300 to 700 ° C.   The catalyst conversion type sensor according to claim 8, wherein an applied voltage of the heating catalyst section is 0.68 to 1.85V.

Images