Gas detection element

Abstract

The object is to provide a gas detection element in which the decrease in sensitivity over a short period of time is suppressed. The gas sensing element of the present invention contains a solid solution of copper(I) bromide and copper(I) iodide.

Description

[Technical Field]

[0001] The present invention relates to a gas sensing element. [Background technology]

[0002] Conventionally, a gas sensor disclosed in Patent Document 1, for example, has been used to detect ammonia. The gas sensor in Patent Document 1 includes a gas-sensing element having a cuprous bromide film. When a predetermined voltage is applied to this cuprous bromide film, ionic conduction occurs with copper ions as carriers. However, when ammonia is present around the cuprous bromide film, the copper ions preferentially react with the ammonia to form a copper-ammine complex, inhibiting ionic conduction and increasing the resistance of the cuprous bromide film. There is a correlation between the concentration of ammonia around the cuprous bromide film and the rate of change in the resistance of the cuprous bromide film, and this correlation can be used to measure the concentration of ammonia. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-227514 Summary of the Invention [Problem to be solved by the invention]

[0004] Gas sensors with a copper(I) bromide film have the advantage of being able to detect very low ammonia concentrations (several ppb or more), and also of being highly selective, since they respond only to molecules that undergo complex formation reactions with copper ions.However, gas sensors with a copper(I) bromide film have the problem that their sensitivity to ammonia decreases in a short period of time when stored indoors without electricity.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a gas detection element in which the decrease in sensitivity over a short period of time is suppressed. [Means for solving the problem]

[0006] The gas sensing element of the present invention contains a solid solution of copper(I) bromide and copper(I) iodide. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a gas detection element in which the decrease in sensitivity over a short period of time is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the configuration of a gas sensor incorporating a gas detection element according to an embodiment of the present invention. [Figure 2A] 1 is a graph showing the change in the base resistance R0 of a gas detection element of an example (a solid solution of copper bromide and copper iodide: x=0.03) over the number of days that have passed since the element was left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2B] This is a graph showing the change in the base resistance R0 of the gas detection element of an example (solid solution of copper bromide and copper iodide: x=0.06) over the number of days when it is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2C] 1 is a graph showing the change in the base resistance R0 of a gas detection element of an example (a solid solution of copper bromide and copper iodide: x=0.20) over the number of days when the element is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2D] This is a graph showing the change in the base resistance R0 of the gas detection element of an example (solid solution of copper bromide and copper iodide: x=0.29) over the number of days when it is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2E]1 is a graph showing the change in the base resistance R0 of a gas detection element of an example (solid solution of copper bromide and copper iodide: x=0.48) over the number of days when the element is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2F] This is a graph showing the change in the base resistance R0 of the gas detection element of an example (solid solution of copper bromide and copper iodide: x=0.55) over the number of days when it is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2G] 1 is a graph showing the change in the base resistance R0 of a gas detection element of an example (a solid solution of copper bromide and copper iodide: x=0.70) over the number of days that have passed since the element was left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 2H] 1 is a graph showing the change in the base resistance R0 of a gas detection element of an example (a solid solution of copper bromide and copper iodide: x=0.97) over the number of days that have passed since the element was left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 3A] This is a graph showing the change in the base resistance R0 of a gas detection element (copper bromide alone) of a comparative example over the number of days when the element is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 3B] 1 is a graph showing the change in the base resistance R0 of a comparative example gas detection element (copper iodide alone) over the number of days that have passed since the element was left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 3C] This is a graph showing the change in the base resistance R0 of a gas detection element of a comparative example (a simple mixture of copper bromide and copper iodide: y=0.06) over the number of days when it is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 3D]This is a graph showing the change in the base resistance R0 of a gas detection element of a comparative example (a simple mixture of copper bromide and copper iodide: y=0.20) over the number of days when it is left indoors, and the change in the ratio RS / R0 of the base resistance R0 to the detection resistance RS. [Figure 4] FIG. 1 shows X-ray diffraction patterns obtained from copper bromide alone, copper iodide alone, and a solid solution of copper bromide and copper iodide (x=0.21, 0.48). DETAILED DESCRIPTION OF THE INVENTION

[0009] A gas detection element according to one embodiment of the present invention will be described below with reference to the drawings. The gas detection element 1 will be described below by taking an example in which the gas detection element 1 is incorporated into a gas sensor GS, as shown in FIG. 1. However, the embodiment shown below is merely an example, and the gas detection element of the present invention is not limited to the following example. Furthermore, the gas detection element of the present invention can also be incorporated into and used in gas sensors other than the gas sensor GS described below.

[0010] The gas sensor GS, into which the gas detection element 1 of this embodiment is illustratively incorporated, is a gas sensor that detects a target gas in a specific temperature range. An example of the target gas that the gas sensor GS detects is ammonia. However, the gas sensor GS can also be configured to detect gases other than ammonia. The "specific temperature range" refers to the operating temperature range of the gas sensor GS (particularly the gas detection element 1) that is suitable for detecting the target gas. When the target gas is ammonia, the specific temperature range is a temperature range near room temperature, such as -10 to 50°C, preferably 0 to 40°C, and more preferably 10 to 30°C. However, when the target gas is a gas other than ammonia, the specific temperature range may be another temperature range suitable for detecting that gas.

[0011] 1, the gas sensor GS includes a gas detection element 1 containing copper halide, a voltage supply unit V for applying a detection voltage to the gas detection element 1, a gas detection circuit DC in which the gas detection element 1 and the voltage supply unit V are incorporated, and a control unit C communicatively connected to the gas detection circuit DC. The gas sensor GS may also include a heating unit (not shown) for heating the gas detection element 1.

[0012] The gas detection element 1 operates within a specific temperature range and detects a target gas when a detection voltage is applied from a voltage supply unit V. When the detection voltage is applied to the gas detection element 1, it generates ionic conduction in the gas detection element 1, with the copper ions contained in the copper halide serving as carriers. Therefore, when the detection voltage is applied to the gas detection element 1, ionic conduction occurs with the copper ions contained in the copper halide serving as carriers. When a target gas is present around the gas detection element 1, the target gas reacts with the copper ions to form a reaction product (e.g., a complex), reducing the concentration of the copper ions that act as carriers and increasing the resistance of the gas detection element 1. The gas detection element 1 detects the target gas by utilizing the phenomenon of increased resistance when a target gas is present around it. For example, ammonia easily reacts with copper ions to form a complex, making it a suitable target gas. In this embodiment, the gas detection element 1 is configured to detect ammonia at a concentration of 10 ppb or less. However, the gas detection element 1 can detect gases other than ammonia that can react with copper ions as the detection target gas.

[0013] The gas detection element 1 is not particularly limited in structure as long as it contains copper halide and is configured to detect a target gas when a detection voltage is applied. In this embodiment, the gas detection element 1 is formed as a thin film on a substrate S (such as an alumina substrate) as shown in FIG. 1. The formation method is not particularly limited, and known film formation techniques can be used. The gas detection element 1 can be formed, for example, by mixing copper halide powder with a known dispersant (such as acetonitrile) to form a paste, which is then applied to the substrate S and dried. The gas detection element 1 can also be formed, for example, by depositing copper halide on the substrate S by vacuum deposition. Copper halide will be described in detail later.

[0014] The gas detection circuit DC supplies a detection voltage from a voltage supply unit V to the gas detection element 1 and measures the resistance of the gas detection element 1. As shown in FIG. 1, the gas detection circuit DC includes the gas detection element 1, a pair of electrodes EL, EL connected to the gas detection element 1 for applying a detection voltage to the gas detection element 1, a load resistor R electrically connected in series with the gas detection element 1, and a voltage supply unit V for supplying the detection voltage to be applied to the gas detection element 1. The voltage supply unit V supplies the detection voltage to the gas detection element 1 under the control of the control unit C. The gas detection circuit DC measures the resistance of the gas detection element 1 based on the terminal voltage of the load resistor R and transmits the measured resistance value to the control unit C.

[0015] The control unit C determines the presence or absence of the target gas in the ambient atmosphere and calculates the concentration of the target gas based on the resistance value of the gas detection element 1 received from the gas detection circuit DC. In this embodiment, the control unit C calculates the base resistance value R0 of the gas detection element 1 obtained when the target gas is not present and the detection resistance value R of the gas detection element 1 obtained during gas detection operation to detect the target gas. S Ratio to SThe control unit C determines the presence or absence of the target gas based on the resistance R / R0 and calculates the concentration of the target gas. For example, the control unit C uses the sensitivity characteristic (calibration curve) of the gas detection element 1 relative to the concentration of the target gas to calculate the base resistance R / R0 and the detection resistance R / R0. S Ratio to S / R0, the concentration of the target gas can be calculated. However, the control unit C only needs to be able to determine whether or not the target gas is present in the ambient atmosphere, and does not have to be configured to calculate the concentration of the target gas. In addition, the determination of the presence or absence of the target gas and the calculation of the concentration of the target gas are performed using the base resistance value R0 and the detection resistance value R S Ratio to S In addition to / R0, the base resistance R0 and the detection resistance R S The calculation can also be performed based on other values ​​related to the resistance value of the gas detection element 1, such as the difference between the resistance value of the gas detection element 1 and the resistance value of the gas detection element 1.

[0016] Next, the copper halide contained in the gas detection element 1 of this embodiment will be described in detail in the following examples, demonstrating the excellent effects of the gas detection element 1 of this embodiment. The gas detection element 1 of this embodiment contains a solid solution (or mixed crystal) of copper (I) bromide and copper (I) iodide (hereinafter simply referred to as "solid solution") as the copper halide. Conventional gas detection elements made of copper (I) bromide have had the problem of their sensitivity to target gases (e.g., ammonia) decreasing over a short period of time when left unpowered in an indoor environment. After extensive research, the inventors have found that gas detection element 1 containing a solid solution of copper (I) bromide and copper (I) iodide reduces the decrease in sensitivity over a short period of time when left unattended compared to a gas detection element made of copper (I) bromide. Furthermore, gas detection element 1 reduces the decrease in sensitivity over a short period of time when left unattended compared to a gas detection element made of a simple mixture of copper (I) bromide and copper (I) iodide. Furthermore, the gas detection element 1 is prevented from decreasing in sensitivity over a short period of time when left unused, and maintains excellent selectivity.

[0017] Copper(I) bromide is an ionic compound formed by the combination of monovalent copper ions and monovalent bromine ions. When it does not contain other ions, it is cuprous bromide represented by the chemical formula CuBr. Also, copper(I) iodide is an ionic compound formed by the combination of monovalent copper ions and monovalent iodine ions. When it does not contain other ions, it is cuprous iodide represented by the chemical formula CuI. The solid solution in this embodiment contains copper(I) bromide in which iodine ions are dissolved, and / or copper(I) iodide in which bromine ions are dissolved. More specifically, the solid solution contains copper(I) bromide in which bromine ions are partially substituted by iodine ions, and / or copper(I) iodide in which iodine ions are partially substituted by bromine ions. Note that copper(I) bromide and copper(I) iodide preferably have stoichiometric compositions, but may have compositions deviated from the stoichiometric compositions by containing other ions.

[0018] The solid solution in this embodiment has the chemical formula CuBr 1-x I x (0 < x < 1) or the chemical formula CuI 1-x Br x (0 < x < 1) and can be represented thereby. The solid solution contains copper ions, bromine ions, and iodine ions and forms a single phase, forming a complete solid solution that does not contain other phases. It is preferable that the solid solution contains only bromine ions and iodine ions as anions that bind to copper ions and forms a single phase, but other anions other than bromine ions and iodine ions may be dissolved.

[0019] The solid solution in this embodiment is a crystalline compound having the same zinc blende-type structure as copper(I) bromide and copper(I) iodide. The solid solution has a lattice constant greater than 0.5687 nm, which is the lattice constant of copper(I) bromide, and smaller than 0.6040 nm, which is the lattice constant of copper(I) iodide. However, the solid solution does not necessarily have to be crystallized and may be amorphous.

[0020] The solid solution may contain both bromide ions and iodide ions as anions, and the composition ratio is not particularly limited. However, from the viewpoint of further suppressing a decrease in sensitivity over a short period of time when left standing, the molar fraction of iodide ions relative to the total of bromide ions and iodide ions is preferably 0.03 or more, more preferably 0.06 or more, and even more preferably 0.20 or more. Furthermore, from the viewpoint of detecting a target gas (e.g., ammonia) at a concentration of 1 ppm or less with sufficient sensitivity, the molar fraction of iodide ions relative to the total of bromide ions and iodide ions is preferably 0.50 or less, more preferably 0.30 or less.

[0021] The solid solution can be prepared by known methods, and the preparation method is not particularly limited. For example, the solid solution can be obtained by mixing and stirring an aqueous solution containing copper(II) bromide, an aqueous solution containing ascorbic acid for reducing copper(II) bromide, and an aqueous solution containing potassium iodide, recovering the product by centrifugation, and drying at room temperature to 40°C. The molar ratio of copper(II) bromide, ascorbic acid, and potassium iodide can be appropriately set within a range that allows the solid solution to be obtained. For example, the molar ratio of copper(II) bromide and ascorbic acid is not particularly limited as long as it can reduce copper from divalent to monovalent, but it can be set so that the number of moles of copper(II) bromide is the same as the number of moles of ascorbic acid (e.g., copper(II) bromide: 10 mmol, ascorbic acid: 10 mmol) or so that the number of moles of ascorbic acid is greater than the number of moles of copper(II) bromide. The molar ratio of copper(II) bromide and potassium iodide can be set to correspond to the target composition ratio of bromide ions and iodide ions in the solid solution. For example, to achieve a 1:1 molar ratio of bromide ions to iodide ions in the solid solution, the copper(II) bromide and potassium iodide can be set to 10 mmol and 10 mmol, respectively. Other reducing agents for copper(II) bromide, such as sodium sulfite and oxalic acid, can also be used in addition to ascorbic acid. Other iodide compounds, such as sodium iodide and ammonium iodide, can also be used as sources of iodide ions.

[0022] The method for preparing the solid solution is not limited to the above method, and other preparation methods can also be used. For example, the solid solution can be prepared by dissolving copper(I) iodide powder and copper(I) bromide powder in 2-methoxyethanol and monoethanolamine, applying the solution to a substrate, and then heating and drying the solution at 170°C for 5 minutes in a nitrogen atmosphere. [Example]

[0023] The excellent effects of the gas detection element of this embodiment will be described below based on examples, but the gas detection element of the present invention is not limited to the following examples.

[0024] (gas detection element) The gas detection element of the embodiment is made of a solid solution of copper bromide (I) and copper iodide (I) (CuBr 1-x I x , x = 0.03, 0.06, 0.20, 0.21, 0.29, 0.48, 0.55, 0.70, 0.97) were prepared. The solid solution was prepared by mixing and stirring an aqueous solution containing copper(II) bromide, an aqueous solution containing ascorbic acid (for reducing copper(II) bromide), and an aqueous solution containing potassium iodide. The resulting solution was collected by centrifugation and dried at room temperature. The amount of copper(II) bromide and the amount of ascorbic acid were 10 mmol. The amount of potassium iodide relative to copper(II) bromide was adjusted to obtain the above-mentioned molar fraction of iodide ions in the solid solution. The gas detection element of the example was prepared by mixing the solid solution powder with a dispersant (acetonitrile) to form a paste, which was then applied to an alumina substrate and dried at room temperature.

[0025] The materials used to construct the gas detection element of the comparative example were copper(I) bromide, copper(I) iodide, and a simple mixture of copper(I) bromide and copper(I) iodide ((1-y)CuBr+yCuI, y = 0.06, 0.20). The term "simple mixture" refers to a mixture in which copper(I) bromide and copper(I) iodide are not solid solutions but are mixed while maintaining their respective phases. Commercially available powders of copper(I) bromide and copper(I) iodide were used. The gas detection element of the comparative example was prepared by mixing powders of copper(I) bromide, copper(I) iodide, and the simple mixture of copper(I) bromide and copper(I) iodide with a dispersant (acetonitrile) to form a paste, which was then applied to an alumina substrate S and dried at room temperature.

[0026] (gas sensor) The gas sensors used were the gas sensors shown in Figure 1, each incorporating a gas detection element of the example and comparative example. Using these gas sensors, the base resistance R0 of the gas detection element obtained when no target gas is present, and the detection resistance R of the gas detection element obtained during gas detection operation to detect the target gas were measured. S and were measured.

[0027] (Crystallinity evaluation) Using a powder X-ray diffractometer, copper(I) bromide, copper(I) iodide, and a solid solution of copper(I) bromide and copper(I) iodide (CuBr 1-x I x The X-ray diffraction patterns were measured using a MultiFlex (Rigaku Corporation) X-ray source: CuKα, 2 kW, tube voltage: 40 kV, tube current: 40 mA, 2θ scan range: 3 to 85°, step: 0.010°, and speed: 1,000° / min.

[0028] (Gas detection element life evaluation) The gas detection element is left indoors (22°C, 50% RH), and the change in the base resistance R0 of the gas detection element over the number of days that have passed is measured. S Ratio to SThe change in R0 was measured. The target gases used were ammonia (NH3) at concentrations of 100 ppb, 200 ppb, 500 ppb, 1 ppm, 5 ppm, 10 ppm, 25 ppm, 50 ppm, 100 ppm, and 500 ppm. Ammonia at low concentrations was used for gas detection elements with high sensitivity, and ammonia at high concentrations was used for gas detection elements with low sensitivity. In order to evaluate the selectivity of the gas detection elements, measurements were also performed using 1000 ppm acetone and 1000 ppm ethanol as the target gases.

[0029] (Results of crystallinity evaluation) Figure 4 shows the X-ray diffraction patterns obtained from copper(I) bromide, copper(I) iodide, and a solid solution of copper(I) bromide and copper(I) iodide (x = 0.21, 0.48). Referring to Figure 4, for copper bromide (x = 0) and copper iodide (x = 1.0), diffraction peaks corresponding to the lattice planes (111), (200), (220), (311), and (222) appear at different scattering angles. In contrast, for the copper bromide and copper iodide solid solution (x = 0.21, 0.48), diffraction peaks appear at scattering angles between those of copper bromide and copper iodide, with the scattering angle shifting depending on the iodide ion concentration. The diffraction peaks of copper bromide and copper iodide do not appear. This shows that the solid solution of copper(I) bromide and copper(I) iodide in the example is formed of a single phase with a lattice constant that is larger than the lattice constant of copper(I) bromide, 0.5687 nm, and smaller than the lattice constant of copper(I) iodide, 0.6040 nm.

[0030] (Gas detection element life evaluation results) 2A to 2H show the results of the life evaluation of the gas detection element of the example, and FIGS. 3A to 3D show the results of the life evaluation of the gas detection element of the comparative example. First, referring to the results of the comparative example in FIG. 3A, when the gas detection element is composed of copper(I) bromide alone, the base resistance value R0 and the detection resistance value R1 were 0.01 and 0.02, respectively, after 8 days, regardless of the ammonia concentration. S Ratio to S / R0 drops to almost 1. This shows that when the gas detection element is made of copper (I) bromide alone, its sensitivity to ammonia drops in a short period of time. Furthermore, referring to the results of the comparative example in Figure 3B, when the gas detection element is made of copper (I) iodide alone, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 was close to 1 even before the passage of time, and after 7 days had passed, it had dropped to almost 1. This shows that if the gas detection element is made up of copper (I) iodide alone, not only will it not be able to obtain sufficient sensitivity to ammonia, but its sensitivity to ammonia will also decrease in a short period of time.

[0031] Next, referring to the results of the example shown in FIG. 2A, in the gas detection element containing the solid solution of x=0.03, the base resistance value R0 and the detection resistance value R S Ratio to S Although / R0 decreases, at least when the ammonia concentration is 500 ppb or 1 ppm, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 is greater than 1. Furthermore, referring to the results of the example in FIG. 2H, the gas detection element containing the solid solution with x=0.97 has a lower sensitivity to ammonia compared to the other examples, but at least when the ammonia concentration is 50 ppm, the base resistance value R0 and the detection resistance value R S Ratio to S 2B and 2C, when x=0.06 (see FIG. 2B), the base resistance value R0 and the detection resistance value R0 are greater than 1, regardless of the ammonia concentration, even if the number of days elapsed exceeds 100 days, and when x=0.20 (see FIG. 2C), the base resistance value R0 and the detection resistance value R0 are greater than 1, regardless of the ammonia concentration, even if the number of days elapsed exceeds 180 days. S Ratio to S / R0 shows a value greater than 1 with almost no decrease. Also, referring to the results of the example in FIG. 2D, when x=0.29, at least when the ammonia concentration is 200 ppb, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 shows a value greater than 1 with almost no decrease. Also, referring to the results of the example in FIG. 2E, when x=0.48, the sensitivity to ammonia is lower than in the other examples, but higher than in the case where the electrode is composed of copper (I) iodide alone, and even after 140 days have passed, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 shows a value greater than 1. Furthermore, referring to the results of the example in Figures 2F and 2G, as the mole fraction of iodide ions increases, the sensitivity to ammonia decreases, but the value is higher than when composed of copper (I) iodide alone. Also, as the mole fraction of iodide ions increases, the base resistance value R0 and the detection resistance value R S Ratio to S Although the number of days until / R0 approaches 1 is getting shorter, even after 100 days have passed, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 is greater than 1.

[0032] From the above results, it can be seen that the gas detection element containing a solid solution of copper(I) bromide and copper(I) iodide suppresses the decrease in sensitivity over a short period of time when left unused, compared to when the gas detection element is composed of copper(I) bromide or copper(I) iodide alone. From the viewpoint of further suppressing the decrease in sensitivity over a short period of time when left unused, it can be seen that the molar fraction of iodide ions relative to the total of bromide ions and iodide ions is preferably 0.03 or more, more preferably 0.06 or more, and even more preferably 0.20 or more.

[0033] 2A to 2H, it can be seen that the gas detection element can detect ammonia at concentrations in the ppb range in the region where the molar fraction of iodine ions is low, and can detect ammonia at concentrations in the ppm range in the region where the molar fraction of iodine ions is high. For example, from the viewpoint of detecting ammonia at a concentration of 1 ppm or less with sufficient sensitivity, it can be seen that the molar fraction of iodine ions relative to the total of bromide ions and iodine ions is preferably 0.50 or less, and more preferably 0.30 or less. Furthermore, the detection signal strength (the ratio between the base resistance R0 and the detection resistance R S Ratio to S / R0), a gas detection element with a low molar fraction of iodide ions is suitable for highly accurate detection of ammonia concentrations in the ppb range, while a gas detection element with a high molar fraction of iodide ions is suitable for highly accurate detection of ammonia concentrations in the ppm range.

[0034] Referring again to the results of the comparative example in Figures 3A to 3D, as described above, when the gas detection element is composed of copper bromide (I) alone or copper iodide (I) alone (see Figures 3A and 3B), the base resistance value R0 and the detection resistance value R S Ratio to S In the gas sensing element made of the simple mixture of y = 0.06 and 0.20 (see Figures 3B and 3C), the base resistance R and the sensing resistance R were significantly lower than those made of copper (I) bromide or copper (I) iodide alone. S Ratio to S Although the time until / R0 becomes almost 1 is extended, the ratio decreases as time passes. In particular, in the case of the simple mixture with y=0.20, the base resistance value R0 and the detected resistance value R S Ratio to SIn contrast, in the gas sensing element containing the solid solutions of x = 0.06 and 0.20, which contain iodide ions in the same proportion as the simple mixture (see Figures 2B and 2C), the base resistance R and the sensing resistance R remained constant regardless of the ammonia concentration, even after 100 days, especially for x = 0.20, even after 180 days. S Ratio to S / R0 does not decrease, and the value is greater than 1. This shows that the gas detection element containing a solid solution of copper bromide (I) and copper iodide (I) suppresses the decrease in sensitivity over a short period of time when left unused, compared to when the gas detection element is composed of a simple mixture of copper bromide (I) and copper iodide (I) that contains iodide ions in the same proportion as the solid solution.

[0035] (Results of gas detection element selectivity evaluation) Referring to the results of the example shown in Figures 2A to 2H, although the concentrations of acetone and ethanol are overwhelmingly higher than the concentration of ammonia, the base resistance value R0 and the detection resistance value R S Ratio to S / R0 is overwhelmingly lower than that of ammonia, at almost 1. This shows that the gas detection element, which contains a solid solution of copper bromide (I) and copper iodide (I), suppresses the decrease in sensitivity over a short period of time when left unused, while maintaining excellent selectivity. [Explanation of symbols]

[0036] 1 Gas detection element C control section DC Gas Detection Circuit EL electrode GS gas sensor R Load resistor S board V Voltage supply

Claims

[Claim 1] A gas sensing element comprising a solid solution of copper(I) bromide and copper(I) iodide.

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