JP7352461B2 - Semiconductor gas detection element - Google Patents

Description

The present invention relates to a semiconductor gas sensing element.

A semiconductor type gas sensing element used in a gas detector includes a gas sensitive part having a metal oxide semiconductor, as disclosed in Patent Document 1, for example. When the gas sensing part comes into contact with the gas to be detected (hereinafter referred to as "the gas to be detected"), electrons are exchanged with the gas to be detected through an oxidation-reduction reaction, and the electrical resistance value changes. . A gas detector can detect a gas to be detected by directly or indirectly detecting this change in electrical resistance value in a semiconductor gas detection element.

As disclosed in Patent Document 1, tin oxide is often used as the main component of the metal oxide semiconductor constituting the gas sensitive section. However, when detecting ammonia gas as a detection target gas using a gas sensitive part whose main component is tin oxide, although a certain degree of detection sensitivity for ammonia gas can be obtained, long-term stability after long-term use etc. Inferior. On the other hand, by using indium oxide as the main component of the metal oxide semiconductor, problems such as long-term stability are alleviated.

Japanese Patent Application Publication No. 2012-112701

However, a gas sensitive section formed of indium oxide alone has a higher detection sensitivity for interfering gases such as hydrogen gas than for ammonia gas, and it is difficult to obtain sufficient selectivity for ammonia gas relative to interfering gases. For example, it is desirable to keep the detection sensitivity for interference gas lower than at least the detection sensitivity for ammonia gas. However, the reality is that no study has been made to date to improve the selectivity of ammonia gas with respect to the gas sensing section whose main component is indium oxide.

The present invention was made in view of the above problems, and an object of the present invention is to provide a semiconductor gas detection element with improved selectivity for ammonia gas.

The semiconductor type gas detection element of the present invention is a semiconductor type gas detection element for detecting ammonia gas, wherein the semiconductor type gas detection element includes a gas sensitive part containing a metal oxide semiconductor containing indium oxide as a main component. , characterized in that vanadium is added to the gas sensitive section.

Further, it is preferable that antimony is further added to the gas sensitive portion.

Further, it is preferable that the amount of antimony added is 0.05 to 2.50 parts by weight based on 100 parts by weight of the indium oxide.

Further, the amount of vanadium added is preferably 0.015 to 0.20 parts by weight based on 100 parts by weight of the indium oxide.

Further, it is preferable that the metal oxide semiconductor further contains tungsten oxide, and the content of the tungsten oxide is 0.5 to 5.0 parts by weight based on 100 parts by weight of the indium oxide.

Further, it is preferable that the gas sensitive part is covered with a catalytically active protective layer, and the catalytically active protective layer contains a metal oxide semiconductor.

According to the present invention, it is possible to provide a semiconductor type gas detection element with improved selectivity for ammonia gas.

1 is a schematic diagram of a semiconductor gas sensing element according to an embodiment of the present invention. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensing part is 0 parts by weight, the sensor output obtained from hydrogen gas relative to the sensor output obtained from ammonia gas depends on the amount of vanadium added to the gas sensing part. It is a graph showing how the ratio of output changes. For a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensing part is 3.0 parts by weight, the amount of vanadium added to the gas sensing part varies depending on the sensor output obtained from hydrogen gas relative to the sensor output obtained from ammonia gas. 12 is a graph showing how the ratio of sensor outputs changes. For a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 5.0 parts by weight, the amount of vanadium added to the gas sensitive part varies depending on the sensor output obtained from hydrogen gas relative to the sensor output obtained from ammonia gas. 12 is a graph showing how the ratio of sensor outputs changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensing part is 0 parts by weight, the sensor output of the semiconductor type gas sensing element obtained from ammonia gas depends on the amount of antimony added to the gas sensing part. It is a graph showing how it changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 3.0 parts by weight, the sensor of the semiconductor type gas sensing element obtained from ammonia gas is determined according to the amount of antimony added to the gas sensitive part. It is a graph showing how the output changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 5.0 parts by weight, the sensor of the semiconductor type gas sensing element obtained from ammonia gas is determined according to the amount of antimony added to the gas sensitive part. It is a graph showing how the output changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 0 parts by weight, the sensor output of the semiconductor type gas sensing element obtained from ammonia gas depends on the amount of vanadium added to the gas sensitive part. It is a graph showing how it changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 3.0 parts by weight, the sensor of the semiconductor type gas sensing element obtained from ammonia gas is determined according to the amount of vanadium added to the gas sensitive part. It is a graph showing how the output changes. Regarding a semiconductor type gas sensing element in which the amount of tungsten oxide added in the sensitive part is 5.0 parts by weight, the sensor of the semiconductor type gas sensing element obtained from ammonia gas is determined according to the amount of vanadium added to the gas sensitive part. It is a graph showing how the output changes. It is a graph showing a change in sensor output over time under a predetermined environment for a semiconductor type gas detection element. 3 is a graph showing the difference in sensor output of a semiconductor gas detection element for ammonia gas and hydrogen gas, depending on the presence or absence of a catalytically active protective layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor gas detection element according to an embodiment of the present invention will be described below with reference to the accompanying drawings. However, the embodiment shown below is an example, and the semiconductor gas sensing element of the present invention is not limited to the following example.

The semiconductor type gas detection element of this embodiment is used, for example, in an environment such as the atmosphere, for detecting ammonia gas contained in the environment. As shown in FIG. 1, the semiconductor gas sensing element 1 includes a gas sensing portion 2 containing a metal oxide semiconductor. The semiconductor type gas sensing element 1 detects that the resistance value (or electrical conductivity) of the gas sensitive part 2 changes due to a chemical reaction between oxygen adsorbed on the surface of the gas sensitive part 2 and ammonia gas in the environment. It is used to detect ammonia gas. As shown in FIG. 1, the semiconductor gas sensing element 1 may optionally include a catalytically active protective layer 3 covering the gas sensitive part 2.

In this embodiment, the semiconductor gas detection element 1 is configured as a coil type (or hot wire type, two terminal type) in which a coil 4 made of a noble metal is further provided, and a gas sensing section 2 is provided around the coil 4. . In this embodiment, the coil 4 is used to heat the gas sensitive section 2 (and the catalytically active protective layer 3) to a temperature suitable for detecting ammonia gas, and to detect changes in the resistance value of the gas sensitive section 2. It will be done. The coil 4 is not particularly limited, and may be made of a material, wire diameter, coil diameter, and number of coil turns that are commonly used in semiconductor gas sensing elements. The semiconductor type gas detection element 1 is of a coil type, so that it is easy to manufacture and can detect ammonia gas in a wide concentration range. However, the semiconductor type gas sensing element may be of a substrate type or the like, and is not limited to a coil type, as long as it is provided with a gas sensitive section (and optionally a catalytically active protective layer).

The semiconductor gas sensing element 1 is incorporated into, for example, a known bridge circuit (not shown), and changes in resistance due to a chemical reaction between adsorbed oxygen on the surface of the gas sensing part 2 and ammonia gas in the environment. is detected. The semiconductor type gas detection element 1 is incorporated into a bridge circuit via a coil 4 in order to detect a change in the resistance value of the gas sensing section 2. The bridge circuit uses a potentiometer to measure a change in potential difference within the circuit caused by a change in resistance value in the semiconductor gas sensing element 1, and outputs the change in potential difference as an ammonia gas detection signal. However, the semiconductor type gas detection element 1 is not limited to the bridge circuit as long as it can detect the change in resistance value that occurs due to the chemical reaction between the adsorbed oxygen on the surface of the gas sensing part 2 and the ammonia gas. , and may be used by being incorporated into a circuit different from the bridge circuit.

The gas sensitive portion 2 includes a metal oxide semiconductor and is a portion whose electrical resistance changes due to a chemical reaction between oxygen adsorbed on the surface and ammonia gas. The metal oxide semiconductor of the gas sensitive section 2 is not particularly limited as long as it has an electrical resistance that changes due to the chemical reaction between adsorbed oxygen and ammonia gas. In this embodiment, the metal oxide semiconductor of the gas sensitive section 2 has indium oxide as a main component. By including a metal oxide semiconductor containing indium oxide as a main component, the gas sensitive section 2 can improve the long-term stability of detection sensitivity to ammonia gas.

A metal element may be added as a donor to the metal oxide semiconductor of the gas sensitive part 2 in order to adjust the electrical resistance. The metal element to be added is not particularly limited as long as it can be added to the metal oxide semiconductor as a donor and can adjust the electrical resistance of the metal oxide semiconductor, and any known donor metal element can be used. metal is used. The donor metal element concentration in the metal oxide semiconductor can be appropriately set depending on the required electrical resistance.

Indium oxide contained in the metal oxide semiconductor of the gas sensitive part 2 only needs to be contained at least in the gas sensitive part 2, and the form of its content in the gas sensitive part 2 is not particularly limited. The gas sensitive section 2 can be formed, for example, as an aggregate of fine powder of indium oxide. The gas sensitive portion 2 can be formed, for example, by mixing fine powder of indium oxide produced by a known method with a solvent to form a paste, applying it around the coil 4, and drying it.

The metal oxide semiconductor of the gas sensitive part 2 may further contain tungsten oxide. In the gas sensitive section 2, the metal oxide semiconductor further contains tungsten oxide, so that the long-term stability of detection sensitivity to ammonia gas can be improved. Tungsten oxide only needs to be contained in the gas sensitive section 2 together with indium oxide, and the form in which it is contained in the gas sensitive section 2 is not particularly limited. For example, indium oxide and tungsten oxide are each formed in the form of fine powder, and are provided throughout the gas sensitive section 2 so as to mix with each other. The gas sensitive portion 2 can be formed, for example, by mixing fine powder of indium oxide and fine powder of tungsten oxide in a solvent to form a paste, applying it around the coil 4, and drying it.

The blending ratio of indium oxide and tungsten oxide contained in the metal oxide semiconductor of the gas sensitive part 2 is not particularly limited, but from the viewpoint of improving the long-term stability of detection sensitivity to ammonia gas, it is preferable to The content is preferably 0.5 parts by weight or more, more preferably 1.0 parts by weight or more, even more preferably 1.5 parts by weight or more based on 100 parts by weight of indium oxide. , most preferably 2.0 parts by weight or more. In addition, from the viewpoint of suppressing the deterioration in coating properties when the fine powder of indium oxide and the fine powder of tungsten oxide are mixed in a solvent and made into a paste and applied around the coil 4, the content of tungsten oxide is set as follows. It is preferably at most 5.0 parts by weight, more preferably at most 4.5 parts by weight, even more preferably at most 4.0 parts by weight, and even more preferably at most 3.5 parts by weight, based on 100 parts by weight of indium oxide. Most preferably, it is less than parts by weight.

Vanadium is added to the gas sensitive part 2. By adding vanadium, the gas sensitive part 2 relatively reduces the detection sensitivity to interference gas (hydrogen gas, etc.) when detecting ammonia gas, and improves the selectivity of ammonia gas to interference gas. be able to. As long as vanadium is added to the gas sensitive section 2, its arrangement in the gas sensitive section 2 is not particularly limited, and vanadium may be added to the surface of the gas sensitive section 2, or vanadium may be added to the gas sensitive section 2. may be added inside.

The amount of vanadium added is not particularly limited, but from the viewpoint of further improving the selectivity of ammonia gas to interference gas, it is preferably 0.015 parts by weight or more based on 100 parts by weight of indium oxide. , more preferably 0.03 parts by weight or more, even more preferably 0.045 parts by weight or more, and most preferably 0.06 parts by weight or more. Further, the amount of vanadium added is preferably 0.20 parts by weight or less, and 0.16 parts by weight or less, based on 100 parts by weight of indium oxide, from the viewpoint of suppressing a decrease in detection sensitivity to ammonia gas. It is even more preferable that the amount is 0.12 parts by weight or less, even more preferably 0.080 parts by weight or less.

The method for adding vanadium to the gas sensitive section 2 is not particularly limited as long as vanadium can be added to the surface and/or inside of the gas sensitive section 2. For example, vanadium may be added to the gas sensitive part 2 by dropping a solution containing vanadium onto the gas sensitive part 2 that has already been formed, or indium oxide may be added to the gas sensitive part 2 before forming the gas sensitive part 2. Vanadium may be added to the gas sensitive part 2 by immersing a fine powder of (and optionally tungsten oxide) in a solution containing vanadium. Vanadium is added to the gas sensitive part 2 in the form of a simple substance and/or a compound containing vanadium.

The solution containing vanadium is not particularly limited as long as vanadium can be added to the gas sensing part 2, and examples include ammonium vanadate solution and vanadium organic acid aqueous solution (vanadium complex solution) such as vanadium citrate aqueous solution. Examples include.

Antimony may be further added to the gas sensitive portion 2. By further adding antimony to the gas sensitive section 2, the detection sensitivity to ammonia gas can be improved, and the long-term stability of the detection sensitivity to ammonia gas can be improved. As long as antimony is added to the gas sensitive section 2, its placement in the gas sensitive section 2 is not particularly limited, and antimony may be added to the surface of the gas sensitive section 2, or antimony may be added to the gas sensitive section 2. may be added inside.

The amount of antimony added is not particularly limited, but from the viewpoint of further improving the detection sensitivity to ammonia gas and further improving the long-term stability of the detection sensitivity to ammonia gas, 100 parts by weight of indium oxide is added. It is preferably 0.05 part by weight or more, more preferably 0.50 part by weight or more, even more preferably 0.80 part by weight or more, and even more preferably 1.00 part by weight. is most preferable. Further, the amount of antimony added is not particularly limited, but from the viewpoint of stabilizing the surface properties of the gas sensitive part 2, it is preferably 2.50 parts by weight or less based on 100 parts by weight of indium oxide. , more preferably 2.00 parts by weight or less, even more preferably 1.50 parts by weight or less, and most preferably 1.30 parts by weight or less.

The method for adding antimony to the gas sensitive section 2 is not particularly limited as long as antimony can be added to the surface and/or inside of the gas sensitive section 2. For example, antimony may be added to the gas sensitive section 2 by dropping a solution containing antimony onto the gas sensitive section 2 that has already been formed, or indium oxide (and Antimony may optionally be added to the gas sensitive part 2 by immersing a fine powder of tungsten oxide (tungsten oxide) in a solution containing antimony. Antimony is added to the gas sensitive part 2 in the form of a simple substance and/or a compound containing antimony.

The solution containing antimony is not particularly limited as long as antimony can be added to the gas sensitive part 2, and examples thereof include an antimony tartrate solution and an antimony organic acid aqueous solution (antimony complex solution) such as an antimony citrate aqueous solution. is exemplified.

Referring again to FIG. 1, in the semiconductor type gas sensing element 1 of this embodiment, the gas sensing portion 2 is covered with the catalytically active protective layer 3, as described above. The catalytically active protective layer 3 relatively lowers the detection sensitivity of interfering gases other than ammonia gas, such as hydrogen gas, and improves the selectivity of ammonia gas with respect to the interfering gases. In this embodiment, the catalytically active protective layer 3 contains a metal oxide semiconductor. The reason why the selectivity of ammonia gas is improved by at least partially covering the gas sensitive part 2 with the catalytically active protective layer 3 containing a metal oxide semiconductor is that interference gases such as hydrogen gas are selected by the metal oxide semiconductor. This is thought to be because the interfering gas is inhibited from reaching the gas sensing section 2 due to combustion, etc., and the detection sensitivity of the interfering gas is relatively reduced.

In the catalytically active protective layer 3, the metal oxide semiconductor may be formed into a fine powder and may be contained as a single substance, or may be contained as a composite together with other metal oxide fine powder. . The catalytically active protective layer 3 can be formed, for example, by mixing fine powder of a metal oxide semiconductor produced by a known method with a solvent to form a paste, and applying it around the gas sensitive part 2 and drying it, or It can be formed by mixing a fine powder of a metal oxide semiconductor and a fine powder of another metal oxide in a solvent to form a paste, which is then applied around the gas sensitive section 2 and dried.

The metal oxide semiconductor contained in the catalytically active protective layer 3 may be any metal oxide semiconductor that can improve the selectivity of ammonia gas, and is not particularly limited, such as tin oxide, indium oxide, etc. , zinc oxide, tungsten oxide, etc. Among these, tin oxide is preferably employed from the viewpoint of further improving the selectivity of ammonia gas. Further, examples of metal oxides that can be included in the catalytically active protective layer 3 include alumina-based oxides and silica-based oxides, but from the viewpoint of improving the long-term stability of detection sensitivity to ammonia gas, alumina is Suitably adopted.

From the viewpoint of further improving the selectivity of ammonia gas, it is preferable that at least one of ruthenium, rhodium, palladium, osmium, iridium, and platinum is added to the metal oxide semiconductor, and among these, ammonia gas Rhodium is preferably used from the viewpoint of suppressing gas combustion. Addition of the above-mentioned metal to the metal oxide semiconductor is not particularly limited, and can be added by a known method. For example, when tin oxide and rhodium are used as metal oxide semiconductors and additive metals, tin hydroxide and rhodium chloride are reacted and fired to form fine powder of tin oxide to which rhodium is added. be able to.

When adding rhodium to tin oxide, the amount of rhodium added to the tin oxide is not particularly limited, but from the viewpoint of further improving the selectivity of ammonia gas, the amount of rhodium added in the tin oxide is 0.01 to 0. It is preferably .4 mol%, more preferably 0.1 to 0.3 mol%, even more preferably 0.15 to 0.25 mol%, and even more preferably 0.18 to 0.22 mol%. is most preferable.

Other metal oxides contained in the catalytically active protective layer 3 are not particularly limited, but examples include alumina, silica, and silica-alumina, with alumina being preferably employed. For example, when adding alumina to tin oxide containing rhodium, the amount of alumina added is selected such that tin oxide containing rhodium: alumina is 90 wt %: 10 wt % to 99 wt %: 1 wt %. Among these, the amount of alumina added is preferably 1.5 to 8 wt%, more preferably 2 to 6 wt%, even more preferably 2.5 to 4 wt%, and most preferably 2.7 to 3.5 wt%.

The thickness of the catalytically active protective layer 3 is not particularly limited, but is appropriately selected within the range of 20 to 100 μm, preferably 30 to 90 μm, more preferably 35 to 80 μm, and even more preferably 40 to 70 μm. More preferably, 45 to 65 μm is most preferred.

In the following, the excellent effects of the semiconductor gas sensing element of this embodiment will be explained based on Examples. However, the semiconductor gas sensing element of the present invention is not limited to the following examples.

(Semiconductor type gas detection element)
As a semiconductor type gas sensing element, two types of semiconductor type gas sensing element 1 shown in FIG. Each component of the semiconductor gas sensing element 1 was manufactured in the following manner.

The gas sensing part 2 is made by mixing indium oxide fine powder prepared by a known method, or indium oxide fine powder and tungsten oxide fine powder prepared by a known method, in a known solvent to form a paste. was applied around the coil 4, dried, and then fired at about 650° C. to form a substantially spherical shape. The amount of tungsten oxide added was 2.0 parts by weight, 3.0 parts by weight, and 5.0 parts by weight with respect to 100 parts by weight of indium oxide. The particle size of the gas sensitive part 2 was approximately 480 μm.

The gas sensitive section 2 was prepared without adding vanadium and/or antimony, and with the addition of vanadium and/or antimony. The amount of vanadium added was 0.018 parts by weight, 0.071 parts by weight, and 0.141 parts by weight based on 100 parts by weight of indium oxide. The amount of antimony added was 0.08 parts by weight, 0.40 parts by weight, 0.81 parts by weight, 1.17 parts by weight, and 2.43 parts by weight with respect to 100 parts by weight of indium oxide. Vanadium and antimony are added to the gas sensitive part 2 by dropping an ammonium vanadate solution and an antimony tartrate solution into the gas sensitive part 2 prepared by the method described above, drying them, and then firing them at about 650°C. This was done by

The catalytically active protective layer 3 is made by reacting tin hydroxide and rhodium chloride and firing to create rhodium-containing tin oxide fine powder, mixing it with alumina fine powder, and mixing it with a known solvent to form a paste. The film was formed by coating the film on the gas sensitive part 2, drying it, and then firing it at about 650°C. The amount of rhodium added to the tin oxide was 0.2 mol %, and the amount of alumina added to the tin oxide containing rhodium was 3 wt %. The thickness of the catalytically active protective layer 3 was approximately 60 μm.

(Measurement of sensor output of semiconductor gas detection element)
By incorporating the fabricated semiconductor gas detection element into a known bridge circuit, semiconductor gas detection can be performed in an atmospheric environment that does not contain ammonia gas or hydrogen gas, or in an atmospheric environment that contains ammonia gas or hydrogen gas at a predetermined concentration. The sensor output (potential difference generated within the bridge circuit) output from the element was measured. The gas concentrations of ammonia gas were 10 ppm, 25 ppm, 50 ppm, and 100 ppm, and the gas concentrations of hydrogen gas were 50 ppm and 100 ppm. The temperature of the semiconductor gas sensing element during measurement was approximately 500°C.

(Selectivity of ammonia gas)
FIGS. 2A to 2C show sensor outputs obtained from ammonia gas (25 ppm, 100 ppm) depending on the amount of vanadium added to the gas sensitive part for a semiconductor gas sensing element that is not provided with a catalytically active protective layer. It shows how the ratio of sensor output obtained from hydrogen gas (100 ppm) to hydrogen gas (hydrogen gas/ammonia gas) changes. 2A, FIG. 2B, and FIG. 2C show cases where the amount of tungsten oxide added to 100 parts by weight of indium oxide is 0 parts by weight, 3.0 parts by weight, and 5.0 parts by weight, respectively. , cases in which the amount of antimony added to 100 parts by weight of indium oxide are 0 parts by weight, 0.08 parts by weight, 1.17 parts by weight, and 2.43 parts by weight are shown.

Referring to FIGS. 2A to 2C, no matter what amount of antimony or tungsten oxide is added, by adding vanadium to the sensitive part, the ratio of the sensor output obtained from hydrogen gas to the sensor output obtained from ammonia gas is is decreasing. From this, it can be seen that by adding vanadium to the gas sensitive part, the selectivity of ammonia gas with respect to hydrogen gas is improved.

(Detection sensitivity for ammonia gas)
FIGS. 3A to 3C show semiconductor gas detection elements obtained from ammonia gas (25 ppm, 100 ppm) depending on the amount of antimony added to the gas sensitive part for semiconductor gas sensing elements that are not provided with a catalytically active protective layer. It shows how the sensor output of the gas detection element changes. 3A, FIG. 3B, and FIG. 3C show cases where the amount of tungsten oxide added to 100 parts by weight of indium oxide is 0 parts by weight, 3.0 parts by weight, and 5.0 parts by weight, respectively. , cases in which the amount of vanadium added to 100 parts by weight of indium oxide are 0 parts by weight, 0.018 parts by weight, 0.071 parts by weight, and 0.141 parts by weight are shown.

Referring to FIGS. 3A to 3C, regardless of the amount of vanadium or tungsten oxide added, adding antimony to the sensitive portion increases the sensor output obtained from ammonia gas. From this, it can be seen that the detection sensitivity to ammonia gas is improved by adding antimony to the gas sensitive part. At least when vanadium is added to the gas sensitive part, the sensor output obtained from ammonia gas increases as the amount of antimony increases, regardless of the amount of vanadium or tungsten oxide added. ing. From this, it can be seen that from the viewpoint of further improving the detection sensitivity to ammonia gas, it is preferable to add a large amount of antimony.

FIGS. 4A to 4C show semiconductor gas sensing elements obtained from ammonia gas (25 ppm, 100 ppm) depending on the amount of vanadium added to the gas sensitive part for semiconductor gas sensing elements that are not provided with a catalytically active protective layer. It shows how the sensor output of the gas detection element changes. 4A, FIG. 4B, and FIG. 4C respectively show cases where the amount of tungsten oxide is 0 parts by weight, 3.0 parts by weight, and 5.0 parts by weight with respect to 100 parts by weight of indium oxide, and in order from the left in each figure, The cases in which the amounts of antimony added to 100 parts by weight of indium oxide are 0 parts by weight, 0.08 parts by weight, 1.17 parts by weight, and 2.43 parts by weight are shown.

Referring to FIG. 4A, when tungsten oxide is not added to the sensitive part, the addition of vanadium increases the sensor output obtained from ammonia gas, regardless of the amount of antimony added. The smaller the amount added, the higher the sensor output obtained from ammonia gas. A similar tendency was observed in the results when the amount of antimony added was 1.17 parts by weight and 2.43 parts by weight in Figure 4B (tungsten oxide: 3.0 parts by weight) and Figure 4C (tungsten oxide: 5.0 parts by weight). It has been seen. On the other hand, referring to the results when the amount of antimony added is 0 part by weight and 0.08 part by weight in FIG. 4B (tungsten oxide: 3.0 parts by weight) and FIG. 4C (tungsten oxide: 5.0 parts by weight), vanadium Over the entire range of the amount of vanadium added, the smaller the amount of vanadium added, the higher the sensor output obtained from the ammonia gas. From this, it can be seen that from the viewpoint of suppressing a decrease in detection sensitivity to ammonia gas, it is preferable to add a small amount of vanadium.

(Long-term stability of detection sensitivity for ammonia gas)
FIG. 5 shows the results of examining changes in sensor output over time under a predetermined environment for a semiconductor gas sensing element that is not provided with a catalytically active protective layer. The temporal environments at this time include an atmospheric environment that does not contain ammonia gas and hydrogen gas, an atmospheric environment that contains ammonia gas at concentrations of 25 ppm, 50 ppm, and 100 ppm, and an atmospheric environment that contains hydrogen gas at a concentration of 100 ppm. did. Further, the semiconductor type gas detector was left in an energized state (approximately 500° C.) under each environment. The upper and lower rows of FIG. 5 show cases where the amount of tungsten oxide added to 100 parts by weight of indium oxide is 0 parts by weight and 2.0 parts by weight, respectively, and the left and right columns of FIG. The case where the amount of antimony added per part is 0.40 part by weight and 0.81 part by weight. The amount of vanadium added was 0.071 parts by weight based on 100 parts by weight of indium oxide.

Referring to the graph on the left side of the upper row of Figure 5 (tungsten oxide: 0 parts by weight, antimony: 0.40 parts by weight), the sensor output decreases slightly as the number of days passes under any environment. . On the other hand, in the upper right graph of FIG. 5 (tungsten oxide: 0 part by weight, antimony: 0.81 part by weight), the slope of the change in sensor output with respect to the number of days that has passed is small. From this, it can be seen that by increasing the amount of antimony added to the gas sensitive part, the change over time in the sensor output is reduced, and the long-term stability of the detection sensitivity to ammonia gas is improved. This tendency is also seen in the lower row of FIG. 5 (tungsten oxide: 2.0 parts by weight).

Furthermore, when comparing the upper graph (tungsten oxide: 0 parts by weight) and the lower graph (tungsten oxide: 2.0 parts by weight) in Figure 5, the lower graph shows a better relationship to the number of elapsed days than the upper graph. The slope of the change in sensor output has become smaller. From this, it can be seen that by adding tungsten oxide to the gas sensitive part, the change in sensor output over time is reduced, and the long-term stability of detection sensitivity to ammonia gas is improved.

(Covering effect of catalytically active protective layer on gas sensitive part)
FIG. 6 shows the difference in sensor output of the semiconductor gas detection element for ammonia gas and hydrogen gas, depending on the presence or absence of the catalytically active protective layer. In the gas sensitive part of the semiconductor gas detector used at this time, the amount of tungsten oxide added was 3.0 parts by weight per 100 parts by weight of indium oxide, and the amount of antimony added was 3.0 parts by weight per 100 parts by weight of indium oxide. The amount of vanadium added was 1.17 parts by weight, and the amount of vanadium added was 0.071 parts by weight based on 100 parts by weight of indium oxide. Referring to FIG. 6, the sensor output for ammonia gas is almost the same when there is a catalytically active protective layer (FIG. 6(b)) compared to when there is no catalytically active protective layer (FIG. 6(a)). On the other hand, the sensor output for hydrogen gas has decreased significantly. This shows that by covering the gas sensitive portion with the catalytically active protective layer, the detection sensitivity to hydrogen gas, which is an interfering gas, is reduced, and the selectivity of ammonia gas to the interfering gas is improved.

1 Semiconductor type gas detection element 2 Gas sensitive section 3 Catalyst active protective layer 4 Coil

Claims (7)

A semiconductor gas detection element for detecting ammonia gas,
The semiconductor type gas sensing element includes a gas sensitive part containing a metal oxide semiconductor containing indium oxide as a main component,
Vanadium and antimony are added to the gas sensitive portion in addition to the donor metal that may be added to the metal oxide semiconductor .
Semiconductor type gas detection element. A semiconductor gas detection element for detecting ammonia gas,
The semiconductor type gas sensing element includes a gas sensitive part containing a metal oxide semiconductor containing indium oxide as a main component,
Vanadium is added to the gas sensitive part,
The gas sensitive portion includes tungsten oxide in addition to indium oxide as the metal oxide semiconductor.
Semiconductor type gas detection element. Antimony is further added to the gas sensitive part.
The semiconductor gas sensing element according to claim 2 . The amount of antimony added is 0.05 to 2.50 parts by weight based on 100 parts by weight of the indium oxide.
The semiconductor gas sensing element according to claim 1 or 3 . The amount of vanadium added is 0.015 to 0.20 parts by weight based on 100 parts by weight of the indium oxide.
The semiconductor gas sensing element according to any one of claims 1 to 4 . the metal oxide semiconductor further includes tungsten oxide,
The content of the tungsten oxide is 0.5 to 5.0 parts by weight based on 100 parts by weight of the indium oxide.
The semiconductor gas sensing element according to claim 1 . the gas sensitive part is covered with a catalytically active protective layer,
the catalytically active protective layer comprises a metal oxide semiconductor;
The semiconductor gas sensing element according to any one of claims 1 to 6 .

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