Gas detection element

Abstract

A gas detection element according to the present disclosure contains a solid solution of copper (I) bromide and copper (I) iodide.

Description

Gas detection element

[0001] The present invention relates to a gas detection element.

[0002] Conventionally, for detecting ammonia, for example, the gas sensor disclosed in Patent Document 1 has been used. The gas sensor of Patent Document 1 includes a gas-sensitive element having a cuprous bromide film. When a predetermined voltage is applied to this cuprous bromide film, ionic conduction using copper ions as carriers occurs. If ammonia is present around the cuprous bromide film, copper ions preferentially react with ammonia to form a copper-ammine complex, thereby 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 resistance of the cuprous bromide film, and the concentration of ammonia can be measured by utilizing this correlation.

[0003] Japanese Unexamined Patent Application Publication No. 2017-227514

[0004] A gas-sensitive element having a cuprous bromide film not only has a very detectable ammonia concentration (several ppb or higher), but also exhibits a response only to molecules that undergo a complex formation reaction with copper ions, and thus has the feature of extremely high selectivity. On the other hand, when a gas-sensitive element having a cuprous bromide film is stored in an indoor environment without power supply, there is a problem that the sensitivity to ammonia decreases in a short period of time.

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

[0006] The gas detection element of the present invention includes a solid solution of copper(I) bromide and copper(I) iodide.

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

[0008] It is a schematic diagram showing the configuration of a gas sensor incorporating a gas detection element according to an embodiment of the present invention. When the gas detection element of the example (solid solution of copper bromide and copper iodide: x=0.03) is left indoors, the change in the base resistance value R0 of the gas detection element with respect to the number of elapsed days, the base resistance value R0 and the detection resistance RS ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.06) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.20) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.29) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.48) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.55) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.70) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to S / R0. It is a graph showing changes in the base resistance value R0 of the gas detection element with respect to the number of elapsed days when the gas detection element of the example (solid solution of copper bromide and copper iodide: x = 0.97) is left indoors, and the detection resistance R and the base resistance value R0 S ratio R to SThis graph shows the change in R0. It compares the change in the base resistance R0 of a gas detection element (copper bromide only) as the number of days elapsed when left indoors, and the relationship between the base resistance R0 and the detection resistance R S R S This graph shows the change in R0. It compares the change in the base resistance R0 of a gas detection element (copper iodide only) as it is left indoors, and the relationship between the base resistance R0 and the detection resistance R S R S This graph shows the change in R0. It shows the change in the base resistance R0 of a gas detection element (a simple mixture of copper bromide and copper iodide: y = 0.06) as the number of days elapsed when left indoors, and the relationship between the base resistance R0 and the detection resistance R S R S This graph shows the change in R0. It compares the change in the base resistance R0 of a gas detection element (a simple mixture of copper bromide and copper iodide: y = 0.20) left indoors over time, and the relationship between the base resistance R0 and the detection resistance R S R S This graph shows the change in R0. It also shows the X-ray diffraction patterns obtained from elemental copper bromide, elemental copper iodide, and solid solutions of copper bromide and copper iodide (x = 0.21, 0.48).

[0009] A gas detection element according to one embodiment of the present invention will be described below with reference to the drawings. In the following description, the gas detection element 1 will be described using an example in which the gas detection element 1 is incorporated into a gas sensor GS, as shown in Figure 1. However, the embodiments shown below are merely examples, and the gas detection element of the present invention is not limited to the following examples. 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 in which the gas detection element 1 of the present embodiment is exemplarily incorporated is a gas sensor that detects a detection target gas in a specific temperature range. Ammonia is exemplified as the detection target gas to be detected by the gas sensor GS. However, the gas sensor GS can also be configured to detect gases other than ammonia. Further, the specific temperature range means an operating temperature range of the gas sensor GS (particularly the gas detection element 1) suitable for detecting the detection target gas. When the detection target gas is ammonia, the specific temperature range is a temperature range around room temperature, for example, -10 to 50°C, preferably 0 to 40°C, and more preferably 10 to 30°C is exemplified. However, when the detection target gas is a gas other than ammonia, the specific temperature range may be another temperature range suitable for detecting that gas.

[0011] As shown in FIG. 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 communicably connected to the gas detection circuit DC. The gas sensor GS may include a heating unit (not shown) for heating the gas detection element 1.

[0012] The gas detection element 1 operates in a specific temperature range and detects the target gas when a detection voltage is applied by the voltage supply unit V. The detection voltage is a voltage that, when applied to the gas detection element 1, can cause ionic conduction using copper ions contained in copper halide as carriers. Therefore, when a detection voltage is applied to the gas detection element 1, ionic conduction using copper ions contained in copper halide as carriers occurs. When the target gas is present around the gas detection element 1, the target gas and copper ions react to form a reaction product (for example, a complex), which lowers the concentration of copper ions as carriers and increases the resistance of the gas detection element 1. The gas detection element 1 detects the target gas by utilizing the phenomenon that the resistance increases when the target gas is present in the surroundings. For example, ammonia readily 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 as the target gas. However, the gas detection element 1 can detect gases other than ammonia that can react with copper ions.

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

[0014] The gas detection circuit DC supplies a detection voltage from the voltage supply unit V to the gas detection element 1 and measures the resistance value of the gas detection element 1. As shown in Figure 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 that supplies 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 value 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 based on the resistance value of the gas detection element 1 received from the gas detection circuit DC, and calculates the concentration of the target gas. In this embodiment, the control unit C uses the base resistance value R0 of the gas detection element 1 obtained when the target gas is not present, and the detection resistance value R0 of the gas detection element 1 obtained during the gas detection operation to detect the target gas. S R S Based on R0, the presence or absence of the target gas is determined, and the concentration of the target gas is calculated. The control unit C, for example, uses the sensitivity characteristics (calibration curve) of the gas detection element 1 with respect to the concentration of the target gas to determine the base resistance value R0 and the detection resistance value R S R S The concentration of the target gas can be calculated from R0. 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 need to be configured to calculate the concentration of the target gas. Furthermore, 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 R S In addition to R0, there are also the base resistance value R0 and the sensing resistance value R S This can also be done based on other values ​​related to the resistance value of the gas detection element 1, such as the difference between the two values.

[0016] Next, the excellent effects of the gas detection element 1 of this embodiment will be demonstrated in the following examples, and the copper halide contained in the gas detection element 1 will be explained in detail. The gas detection element 1 of this embodiment contains a solid solution (or mixed crystal) of copper(I) bromide and copper(I) iodide (hereinafter also simply referred to as "solid solution") as the copper halide. Until now, gas detection elements composed of copper(I) bromide have had the problem that their sensitivity to the target gas (for example, ammonia) decreases in a short period of time when left unattended in an indoor environment without power. As a result of diligent research, the inventors have found that by including a solid solution of copper(I) bromide and copper(I) iodide in the gas detection element 1, the decrease in sensitivity in a short period of time when left unattended is suppressed compared to the case where it is composed of copper(I) bromide alone. Furthermore, the decrease in sensitivity in a short period of time when left unattended is suppressed even when the gas detection element 1 is composed of a simple mixture of copper(I) bromide and copper(I) iodide. Furthermore, the gas detection element 1 is designed to suppress a decrease in sensitivity over a short period of time when left unattended, while maintaining excellent selectivity.

[0017] Copper(I) bromide is an ionic compound formed by the bonding of a monovalent copper ion and a monovalent bromide ion, and if it does not contain other ions, it is cuprous bromide represented by the chemical formula CuBr. Similarly, copper(I) iodide is an ionic compound formed by the bonding of a monovalent copper ion and a monovalent iodide ion, and if it does not contain other ions, it is cuprous iodide represented by the chemical formula CuI. The solid solution in this embodiment includes copper(I) bromide in which iodide ions are dissolved, and / or copper(I) iodide in which bromide ions are dissolved. More specifically, the solid solution includes copper(I) bromide in which bromide ions are partially replaced by iodide ions, and / or copper(I) iodide in which iodide ions are partially replaced by bromide ions. It is preferable that copper(I) bromide and copper(I) iodide each have a stoichiometric composition, but they may have a composition that deviates from the stoichiometric composition by containing other ions.

[0018] The solid solution in this embodiment has the chemical formula CuBr 1-x I x (0 < x < 1) or chemical formula CuI 1-xBr x It can be expressed as (0 < x < 1). The solid solution contains copper ions, bromide ions, and iodide ions to form a single phase, forming a complete solid solution that does not contain other phases. Preferably, the solid solution contains only bromide ions and iodide ions as anions that bind to copper ions to form a single phase, but other anions other than bromide ions and iodide ions may also be in solid solution.

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

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

[0021] Solid solutions can be prepared by known methods, and the method of preparation is not particularly limited. For example, a solid solution can be obtained by mixing and stirring an aqueous solution in which copper(II) bromide is dissolved, an aqueous solution in which ascorbic acid is dissolved to reduce copper(II) bromide, and an aqueous solution in which potassium iodide is dissolved, recovering the product by centrifugation, and drying it at room temperature to 40°C. The molar ratios of copper(II) bromide, ascorbic acid, and potassium iodide can be appropriately set within the range in which a solid solution can 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 the number of moles of copper(II) bromide can be the same as the number of moles of ascorbic acid (for example, copper(II) bromide: 10 mmol, ascorbic acid: 10 mmol), or the number of moles of ascorbic acid can be greater than the number of moles of copper(II) bromide. Furthermore, the molar ratio of copper(II) bromide and potassium iodide can be set to correspond to the target composition ratio of bromide and iodide ions in the solid solution. For example, to achieve a 1:1 molar ratio of bromide and iodide ions in the solid solution, the amounts of copper(II) bromide and potassium iodide can be set to 10 mmol and 10 mmol respectively. In addition to ascorbic acid, other reducing agents such as sodium sulfite and oxalic acid can be used as reducing agents for copper(II) bromide. Also, in addition to potassium iodide, other iodide compounds such as sodium iodide and ammonium iodide can be used as sources of iodide ions.

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

[0023] The following describes the excellent effects of the gas detection element of this embodiment based on examples. However, the gas detection element of the present invention is not limited to the following examples.

[0024] (Gas detection element) The constituent material of the gas detection element in the embodiment is a solid solution of copper(I) bromide and copper(I) iodide (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 an aqueous solution in which copper(II) bromide was dissolved, an aqueous solution in which ascorbic acid was dissolved to reduce copper(II) bromide, and an aqueous solution in which potassium iodide was dissolved, stirring the mixture, recovering the product by centrifugation, and drying it at room temperature. At this time, 10 mmol of copper(II) bromide and 10 mmol of ascorbic acid were used. The amount of potassium iodide relative to copper(II) bromide was adjusted so that the above mole fractions of iodide ions were obtained in the solid solution. The gas detection element of the example was obtained by mixing the solid solution powder with a dispersant (acetonitrile) to form a paste, coating it onto an alumina substrate, and drying it at room temperature.

[0025] As constituent materials for the comparative example gas detection element, pure copper(I) bromide, pure copper(I) iodide, and a simple mixture of copper(I) bromide and copper(I) iodide ((1-y)CuBr + yCuI, y = 0.06, 0.20) were prepared. A simple mixture means a mixture in which copper(I) bromide and copper(I) iodide are not solid-solved with each other and are mixed while maintaining their respective phases. Commercially available powders of copper(I) bromide and copper(I) iodide were used. The comparative example gas detection element was obtained by mixing the powders of pure copper(I) bromide, pure copper(I) iodide, and the simple mixture of copper(I) bromide and copper(I) iodide with a dispersant (acetonitrile) to form a paste, coating it onto an alumina substrate S, and drying it at room temperature.

[0026] (Gas Sensor) As the gas sensor, the gas sensor shown in Figure 1 was used, with the gas detection elements of the example and comparative example incorporated into it. Using this gas sensor, the base resistance value R0 of the gas detection element obtained when the target gas is not present and the detection resistance value R of the gas detection element obtained during the gas detection operation to detect the target gas were obtained. S and were measured.

[0027] (Evaluation of crystallinity) Using a powder X-ray diffractometer, copper(I) bromide, copper(I) iodide, and solid solutions of copper(I) bromide and copper(I) iodide (CuBr) were evaluated. 1-x I x The X-ray diffraction patterns were measured at x = 0.21 and x = 0.48. The measurement conditions for the X-ray diffraction patterns were as follows: Instrument name: MultiFlex (manufactured by Rigaku Corporation), X-ray source: CuKα, 2kW, tube voltage: 40kV, tube current: 40mA, scan range of 2θ: 3 to 85°, step: 0.010°, speed: 1.000° / min.

[0028] (Evaluation of the lifespan of the gas detection element) The gas detection element was left indoors (22°C, 50% RH), and the change in the base resistance R0 of the gas detection element over the number of days elapsed was compared with the base resistance R0 and the detection resistance R S R S The 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. Lower concentrations of ammonia were used for highly sensitive gas detection elements, and higher concentrations were used for less sensitive gas detection elements. In addition, 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 elemental copper(I) bromide, elemental copper(I) iodide, and solid solutions of copper(I) bromide and copper(I) iodide (x = 0.21, 0.48). Referring to Figure 4, for elemental copper bromide (x = 0) and elemental copper iodide (x = 1.0), diffraction peaks corresponding to the respective lattice planes (111), (200), (220), (311), and (222) appear at different scattering angle positions. In contrast, for the solid solution of copper bromide and copper iodide (x = 0.21, 0.48), diffraction peaks appear at scattering angle positions between the diffraction peaks of elemental copper bromide and elemental copper iodide, with the scattering angle shifting according to the iodine ion concentration, and the diffraction peaks of elemental copper bromide and elemental copper iodide are not present. From this, it can be seen that the solid solution of copper(I) bromide and copper(I) iodide in the example is formed as a single phase having a lattice constant greater than the lattice constant of copper(I) bromide (0.5687 nm) and less than the lattice constant of copper(I) iodide (0.6040 nm).

[0030] (Results of Life Evaluation of Gas Detection Element) Figures 2A to 2H show the results of the life evaluation of the gas detection element in the example, and Figures 3A to 3D show the results of the life evaluation of the gas detection element in the comparative example. First, referring to the results of the comparative example in Figure 3A, when the gas detection element is composed of copper(I) bromide alone, regardless of the ammonia concentration, the base resistance value R0 and the detection resistance value R0 were determined after 8 days. S R S The R0 value has decreased to almost 1. This indicates that when the gas detection element is composed solely of copper(I) bromide, its sensitivity to ammonia decreases rapidly. Furthermore, referring to the results of the comparative example in Figure 3B, when the gas detection element is composed solely of copper(I) iodide, even at a high ammonia concentration of 50 ppm, the base resistance R0 and the detection resistance R S R S The R0 value was close to 1 even before the passage of time, and decreased to almost 1 after 7 days. This indicates that when the gas detection element is composed solely of copper(I) iodide, not only is sufficient sensitivity to ammonia not obtained, but the sensitivity to ammonia decreases rapidly.

[0031] Next, referring to the results of the embodiment in Figure 2A, in the gas detection element containing a solid solution of x = 0.03, the base resistance value R0 and the detection resistance value R in the initial stages of the process S R S Although R0 decreases, at least when the ammonia concentration is 500 ppb or 1 ppm, the base resistance R0 and the detection resistance R remain constant even after more than 50 days have passed. S R S / R0 shows a value greater than 1. Also, referring to the results of the example in Figure 2H, the gas detection element containing the solid solution x = 0.97 has 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 R S / R0 shows a value greater than 1. Also, referring to the results of the examples in Figures 2B and 2C, at x = 0.06 (see Figure 2B), regardless of the ammonia concentration, even if the number of elapsed days exceeds 100 days, and at x = 0.20 (see Figure 2C), regardless of the ammonia concentration, even if the number of elapsed days exceeds 180 days, the base resistance value R0 and the detection resistance value R S R S R0 shows a value greater than 1 without decreasing significantly. Also, referring to the results of the example in Figure 2D, at x = 0.29, at least when the ammonia concentration is 200 ppb, the base resistance R0 and the detection resistance R remain constant even after more than 180 days. S R S R0 shows a value greater than 1 without decreasing significantly. Also, referring to the results of the example in Figure 2E, at x = 0.48, the sensitivity to ammonia is lower compared to other examples, but higher than when composed of copper(I) iodide alone, and even after more than 140 days, the base resistance value R0 and the detection resistance value R S R SThe value of R0 is greater than 1. Furthermore, referring to the results of the examples in Figures 2F and 2G, although the sensitivity to ammonia decreases with increasing mole fraction of iodide ions, it is still higher than when composed of copper(I) iodide alone. Also, with increasing mole fraction of iodide ions, the base resistance value R0 and the detection resistance value R S R S Although the number of days until R0 approaches 1 is getting shorter, even after more than 100 days have passed, the base resistance value R0 and the detection resistance value R S R S The value of / R0 is greater than 1.

[0032] From the above results, it can be seen that by including a solid solution of copper(I) bromide and copper(I) iodide in the gas detection element, the decrease in sensitivity over a short period of time when left standing is suppressed compared to cases where it is composed of copper(I) bromide alone or copper(I) iodide alone. Furthermore, from the viewpoint of further suppressing the decrease in sensitivity over a short period of time when left standing, it can be seen that the mole fraction of iodide ions to the total of bromide ions is preferably 0.03 or higher, more preferably 0.06 or higher, and even more preferably 0.20 or higher.

[0033] Furthermore, from the results of the embodiments shown in Figures 2A to H, it can be seen that the gas detection element can detect ammonia at concentrations in the ppb range in the region where the mole fraction of iodide ions is low, and can detect ammonia at concentrations in the ppm range in the region where the mole fraction of iodide ions is high. For example, from the viewpoint of detecting ammonia at concentrations of 1 ppm or less with sufficient sensitivity, it can be seen that the mole fraction of iodide ions relative to the sum of bromide ions and iodide ions is preferably 0.50 or less, and more preferably 0.30 or less. Also, the detection signal intensity (base resistance R0 and detection resistance R0) relative to the ammonia concentration is... S R SConsidering the range in which a linear relationship is maintained in the relationship (R0), it can be said that a gas detection element with a low mole fraction of iodide ions is suitable for detecting ammonia concentrations in the ppb range with high accuracy, while a gas detection element with a high mole fraction of iodide ions is suitable for detecting ammonia concentrations in the ppm range with high accuracy.

[0034] Referring again to the results of the comparative examples in Figures 3A to D, as mentioned above, when the gas detection element is composed of copper(I) bromide alone or copper(I) iodide alone (see Figures 3A and 3B), the base resistance value R0 and the detection resistance value R S R S R0 has decreased to almost 1. Also, in the gas detection element composed of a simple mixture of y = 0.06 and 0.20 (see Figures 3B and 3C), the base resistance R0 and detection resistance R S R S Although the time it takes for R0 to become approximately 1 is increasing, the ratio is decreasing over time. In particular, in the case of a simple mixture with y = 0.20, when the number of days elapsed exceeds 40, the base resistance value R0 and the detection resistance value R S R S R0 has decreased to almost 1. In contrast, in gas detection elements containing solid solutions with x = 0.06 and 0.20, which contain iodide ions in the same proportion as in a simple mixture (see Figures 2B and 2C), regardless of the ammonia concentration, even after more than 100 days have passed, and especially after more than 180 days at x = 0.20, the base resistance R0 and the detection resistance R S R S The R0 value remains greater than 1 without decreasing. This indicates that the gas detection element, by 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 standing, compared to the case where the element is composed of a simple mixture of copper(I) bromide and copper(I) iodide containing iodide ions in the same proportion as the solid solution.

[0035] (Results of gas detection element selectivity evaluation) Referring to the results of the examples in Figures 2A to H, even though the concentrations of acetone and ethanol are overwhelmingly higher than the concentration of ammonia, the base resistance value R0 and detection resistance value R0 of acetone and ethanol are different. S R S The R0 value is overwhelmingly lower than that of ammonia, almost 1. This indicates that the gas detection element, by containing a solid solution of copper(I) bromide and copper(I) iodide, suppresses the decrease in sensitivity over a short period when left standing, while maintaining excellent selectivity.

[0036] 1. Gas detection element C. Control unit DC. Gas detection circuit EL. Electrode GS. Gas sensor R. Load resistor S. Substrate V. Voltage supply unit

Claims

1. A gas detection element containing a solid solution of copper(I) bromide and copper(I) iodide.

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