JPH0473544B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a hydrogen gas detection element and a manufacturing method thereof. [Prior Art] As a hydrogen gas detection element using a metal oxide, a hydrogen selectivity sensor is known in which a membrane selectively permeable to hydrogen molecules, such as a combustion-inactive thin film, is formed on a gas-sensitive element. In such sensors, hydrogen gas must pass through a thin film filter;
It takes time to adsorb to metal oxides, resulting in delayed response. Furthermore, since this sensor detects gas at a relatively high temperature, in elements containing a catalyst such as Pd in a metal oxide, the catalyst deteriorates quickly and loses its function. [Problems to be Solved by the Invention] Therefore, there is a demand for a hydrogen detection element with lower temperature and/or shorter response time. [Means for Solving the Problems] Conventionally, a carbon monoxide gas detection device for selectively detecting carbon monoxide gas in exhaust gas discharged from various devices and a method for manufacturing the same have been disclosed, for example, in Japanese Patent Laid-Open No. 1986-
It is known from Publication No. 119249. In the method described in this patent publication, a mixture of stannic oxide and an aqueous solution of chloroplatinic acid containing platinum in an amount of 2 to 10 mol % relative to the stannic oxide is freeze-dried, and the resulting mixture is A mixture containing ~8 mol% antimony oxychloride is added to an organic solvent to form a paste, and this paste is applied to an insulator with electrodes and baked in air, allowing the device to remain at room temperature without heating. The company manufactures carbon monoxide gas detection equipment that can detect carbon monoxide. However, it has been found that when this carbon monoxide gas detection element is treated in an atmosphere containing dilute silane-based gas, an element can be obtained that can selectively detect hydrogen at a temperature in the 300°C range with a high signal-to-noise ratio. However, in the case of this element, the response time to hydrogen is 200℃~400℃.
It took 100 to 150 seconds at the device operating temperature of ℃, but by also adding palladium chloride to this device,
It has been found that an element with high hydrogen gas selectivity and a response time that can be shortened to within 50 seconds can be obtained. Therefore, in this invention, Pd/Sn=0.1 to 8 mol%,
Pt/Sn - 0.5-8 mol%, metal Pd and metal Pt with Sb/Sn ratio 0-8 mol%, or metal Pd and metal Pt
and a device in which Sb oxide is dispersed on SnO ₂ .
The present invention relates to a hydrogen gas detection element which is processed in a 500 to 5000 ppm silane gas atmosphere to disperse Si oxide on the element. Furthermore, this invention uses palladium chloride (PdCl ₂ )
An aqueous solution is prepared, and a chloroplatinic acid (H ₂ PtCl ₆ ) aqueous solution is prepared, and the palladium chloride is added to the stannic oxide in an amount such that Pd/Sn is 0.1 to 8 mol% and Pt/Sn is 0.5 to 8 mol%. The aqueous solution and the chloroplatinic acid aqueous solution are added in any order, and the SnO ₂ in the resulting mixture is preferably well dispersed by ultrasonication, and then dried, and the dried product has an Sb/Sn ratio of 0 to 8. amount of mole%
Add SbOCl and mix thoroughly in a mortar, etc., for example, approximately
After mixing for about 30 minutes, this is made into a paste in an organic solvent such as isopropyl alcohol, applied to an alumina porcelain tube equipped with electrodes, dried, and coated on the surface.
SnO ₂ and PdCl ₂ and H ₂ PtCl ₆ or SnO ₂
A device comprising a layer containing PdCl ₂ , H ₂ PtCl ₆ and SbOCl is fired at 600°C to 850°C in an air atmosphere or an antimony oxidation gas atmosphere to oxidize metal Pd and metal Pt or metal Pd, metal Pt and Sb. A heater is attached to the fired _element , heated to 300°C ± 50°C and aged in air for a predetermined period of time.
Heating to 350℃ increases the concentration of silane gas to 500~
Processed in a 5000ppm atmosphere to further coat the device.
It also relates to a method for manufacturing a hydrogen gas detection element, which comprises dispersing SiO ₂ . [Effect] Since PdCl ₂ is difficult to dissolve in water, 0.2% hydrochloric acid is used to create an aqueous PdCl ₂ solution. The concentration of hydrochloric acid may be any concentration that simply dissolves PdCl ₂ . Chloroplatinic acid dissolves in pure water. Pd/Sn or Pt/
The amount of Sn is less than 0.1 mol% or 0.5 mol%, respectively
If the amount of Pd/Sn or Pt/Sn is less than 8 mol %, hydrogen detection ability will decrease, which is not preferable. The PdCl ₂ thus obtained and
After the SnO ₂ in the PtCl ₆ mixture is well dispersed using ultrasonic waves or the like, the product yield is improved by rapid freeze-drying at -40°C or lower in a vacuum freeze dryer.
Devices can be manufactured without vacuum freeze-drying.
In this case, the yield of the product decreases. In addition to isopropyl alcohol, the organic solvent used to make a paste from the mixture of the dried product and antimony oxychloride is a mixed solvent of 25% by weight of β-terpineol, 72% by weight of butyl carbitol acetate, and 3% by weight of ethyl cellulose. In addition to a porcelain tube, a tube or plate-shaped insulator that can withstand firing may be used as the paste to be applied. The paste can be dried naturally, even if it only takes a few minutes.
It may also be carried out in a constant temperature bath. Antimony oxidation gas atmosphere is SbOCl or
Sb ₂ O ₃ 0.5 to 7.5 mg, converted to ₃ moles of Sb ₂ O 2×
It is prepared by firing 10 ^-9 to 3×10 ^-8 mol/cm ³ at 600 to 850°C for about 5 to 30 minutes. If more than 7.5mg of SbOCl is used, it will be coated with Pd and Pt and Pd and Pt
activity decreases. The element is fired in the air or in an atmosphere of antimony oxidation gas at a temperature of 600 to 850°C for 5 to 60 minutes. Antimony cannot be doped at temperatures below 600°C and times below 5 minutes. At temperatures above 850°C, the activity of Pd and Pt becomes low and hydrogen cannot be selectively detected. Aging of the device is performed by heating the device to 300±50° C. with a heater attached to the device and heating it in an air atmosphere for 12 hours or more, thereby stabilizing the semiconductor layer. The device is treated in an air atmosphere containing silane gas at a concentration of 500 to 5000 ppm by heating the device in an air atmosphere containing dichlorosilane (SiH ₂ Cl ₂ ) gas or monosilane (SiH ₄ ) gas at a concentration of 300 to 350 ppm. This is done by heating for 5 to 45 minutes at . The sensitivity of hydrogen detection decreases outside this range of silane gas concentration and processing time. The device is then heated to 300±50°C in air for 12 hours or more to produce a product. Selectivity to hydrogen gas can be further improved by performing the treatment in an air atmosphere containing a silane gas and the subsequent heat treatment in air in the same procedure. In this invention, Si is dispersed on the surface of the element by treating the element with a small amount of silane gas. Further, as is clear from the examples described later, the operating temperature is in the 300° C. range, and the response speed is within 50 seconds. The present invention will be explained in more detail with reference to Examples below. Hereinafter, unless otherwise specified, the examples will be simply described as examples. Examples 1 to 13 PdCl ₂ -0.2% hydrochloric acid solution and an aqueous solution of H ₂ PtCl ₆ in pure water were added sequentially to SnO ₂ in the amounts shown in Table 1,
The SnO ₂ in this mixture is well dispersed by ultrasonic waves,
After this dispersion is rapidly freeze-dried at -40°C, it is placed in a vacuum freeze dryer and dried. Next, this dried material was mixed with SbOCl in an amount to give the indicated Sb/Sn mol%, mixed in a mortar for about 30 minutes, and isopropyl alcohol was added to this mixture to make a paste. Apply to porcelain tube and let dry naturally. Next, add 2.5 mg of this element to
It was fired at 700°C for 15 minutes in a quartz tube in an antimony oxidation gas atmosphere created by firing SbOCl. After attaching a heater to the fired element, electricity is applied to the heater to heat the element to 300℃, and then it is left in the air.
After aging for 12 hours, the devices were heated to 325°C and treated with dichlorosilane, except for example 1 (comparative example).
Treated once for 10 minutes in an air atmosphere containing 100 ppm,
Thereafter, it was aged for 12 hours in air while being heated to 300°C. The electrical resistance value (kΩ) and SN ratio (resistance value of the element in clean air / Table 1 shows the resistance value (resistance value) and response time (seconds) of the element in the test gas. In the table, Example 1 is a comparative example showing a device without silane treatment, and Examples 2 to 13 are examples. The response time for each example 2 to example 13 is within 30 seconds, and example 2 shows that the amount of Pd and Pt added is the lower limit, and example 13 shows that the amount of added Pd, Pt, and Sb is the upper limit. . The data shown in Table 1 are the average values of data from all eight samples prepared for each example. The response characteristics of one element in the group of Example 6 to each sample gas are shown in FIG.

【table】

[Table] Example 14 The procedure was as in Examples 2 to 13, except that the first treatment with SiH ₂ Cl ₂ was carried out at 1000 ppm for 10 minutes, and the second treatment was carried out at 1000 ppm for 10 minutes. Table 2 below shows the performance of the obtained device in comparison with the devices of Examples 1 and 3. In Table 2, Example 4 compared to Example 3.
The S/N ratio of hydrogen gas was greatly improved, while the S/N ratio of other gases decreased, indicating that hydrogen selectivity was significantly improved. The element temperature during measurement was 325°C ± 10°C. Example 15 Example 15 shows an example of the production of a device that was operated in the same manner as Examples 2 to 13, except that antimony oxychloride was not added and the treatment was not carried out in an oxidizing atmosphere of antimony oxychloride. The response time of the element in Example 15 is 37 seconds and Example 2
Although it is slightly slower than the device of Example 13, it is still much faster than the case where Pt is added alone, and the hydrogen selectivity is also good. The manufacturing conditions and performance of the devices of Examples 14 and 15 are shown in Table 2.

[Table] Note that when the amount of Si dispersed in the elements of the group of Example 4 was calculated, it was estimated to be 0.5% by weight. Also, regarding the dispersion state of Pt, Pd, and Si on the element surface for one element in the group of Example 14,
Measured with an Electron Probe Microanalyzer at 3000x magnification. As a result, Pt and Pd were dispersed on SnO ₂ (the dispersion was slight because Pt was a trace amount of 0.5 mol% relative to Sn), and Si
was confirmed to be dispersed in a manner that almost corresponds to the dispersion state of Pd and Pt. Therefore,
It is presumed that a considerable portion of Si is dispersed on the surfaces of Pd and Pt, as shown in the model diagram of Figure 2. As a result, it becomes extremely difficult for gases other than hydrogen to exchange electrons with the element surface, resulting in a decrease in the SN ratio.On the other hand, hydrogen gas is adsorbed onto the element surface and exchanges electrons smoothly, so the SN ratio is reduced. It is thought that the ratio will be improved and the response will be faster.

[Brief explanation of drawings]

Figure 1 shows one of the hydrogen gas detection elements according to the present invention.
The response characteristic diagram of the example, FIG. 2, is a model diagram showing the dispersion state of Si.

Claims (1)

[Claims] 1. Pd/Sn = 0.1 to 8 mol% in raw material compound ratio,
Pt/Sn=0.5-8 mol%, Sb/Sn=0-8 mol%
amount of metal Pt and metal Pd or metal Pt, metal
A device in which Pd and Sb oxides are dispersed on SnO ₂
A hydrogen gas detection element formed by further dispersing Si oxide on the element processed in a 500 to 5000 ppm silane gas atmosphere. 2. Prepare a palladium chloride (PdCl ₂ ) aqueous solution and a chloroplatinic acid (H ₂ PtCl ₆ ) aqueous solution, respectively, and add 0.1 to 8 mol% of Pd/Sn to stannic oxide (SnO ₂ ).
The palladium chloride aqueous solution and the chloroplatinic acid aqueous solution in an amount such that Pt/Sn is 0.5 to 8 mol% are added in any order, the SnO ₂ in the resulting mixture is well dispersed, and then dried. Antimony oxychloride (SbOCl) in an amount such that Sb/Sn is 0 to 8 mol%.
After addition and mixing, this is applied as a paste in an organic solvent to an alumina porcelain tube equipped with electrodes, dried, and the surface is coated with SnO ₂ and PdCl ₂ and H ₂ PtCl ₆ or
A device comprising a layer containing SnO ₂ and PdCl ₂ and H ₂ PtCl ₆ and SbOCl is fired in the air or in an antimony oxidation gas atmosphere to form metal Pd and metal Pt or metal Pd and metal Pt and Sb on SnO ₂ . A heater is attached to the fired element, heated to 300°C ± 50°C and aged in air for a predetermined period of time, and the resulting element is heated to 300-350°C and treated with silane gas. A method for manufacturing a hydrogen gas detection element, which comprises further dispersing Si oxide on the element by processing in an atmosphere with a concentration of 500 to 5000 ppm. 3. The method for manufacturing a hydrogen gas detection element according to claim 2, wherein the drying after well dispersing SnO ₂ is rapid freeze drying.