JP5959101B2 - Hydrogen selective gas sensor - Google Patents

Description

  The present invention relates to a gas sensor that can selectively detect hydrogen.

Hydrogen gas is detected by a catalytic combustion gas sensor in which a Joule heating element is covered with a sensitive element including an oxidation catalyst.
However, there is a problem that measurement errors occur because the alcohol vapor used for cleaning or the like has high sensitivity.
For this reason, as seen in Non-Patent Document 1, a method of forming a filter on the surface with silicone has also been proposed.

H2 selective gas sensor based on SnO2 Original Research Article Sensors and Actuators B: Chemical, Volume 52, Issues 1-2, 15 September 1998, Pages 30-37

However, there is a problem that complicated man-hours such as vapor deposition work are required.
The present invention has been made in view of such problems, and an object thereof is to provide a hydrogen-selective gas sensor that can be manufactured by a relatively simple process.

  In order to achieve such a problem, the sensor of the present invention is formed on the surface of a coiled heater that generates heat by Joule heat, and fixes a wire ring forming the heater, and a surface of the fixed layer. It consists of an oxidation catalyst layer containing phosphoric acid formed.

  The sensitivity to alcohol is suppressed by phosphoric acid, and hydrogen in an environment where alcohol is mixed can be accurately detected while suppressing the influence of alcohol as much as possible.

Drawing (a)-(d) is an explanatory view showing a manufacturing process of a sensor of the present invention. It is a diagram which shows the change of the sensitivity of the mixing ratio of phosphoric acid and an oxidation catalyst, and isopropyl alcohol.

  A wire material having a large temperature resistance coefficient such as a platinum wire is wound in a coil shape to constitute the heater 1 (FIG. 1 (a)), water glass is applied to the outer periphery of the wire, dried, and then fired at about 1000 ° C. to form the heater 1. The fixing layer 2 for fixing the wire ring that constitutes is formed. (FIG. 1 (b)). Thus, the heating element 3 whose outer periphery is solidified by the glass fixing layer 2 is completed. By thus forming the glass layer 2 on the outer periphery of the heater 1, the heater 1 can be reinforced and electrically insulated.

At this time, if necessary, a phosphoric acid solution is applied to the fixing layer 2 and fired again to form the fixing layer 2 containing phosphoric acid (FIG. 1C).
This intermediate body 4 can be used as a so-called compensation element, which is usually combined with a gas detection element to compensate for output fluctuations due to outside air temperature.

  For reference, when the output of the heating element 3 not coated with the phosphoric acid solution and the intermediate 4 with respect to the isopropyl alcohol was measured, it was 1000: 1. From this, it was found that the heating element 3 carrying phosphoric acid can reduce the sensitivity to isopropyl alcohol.

An oxidation catalyst layer 5 is formed on the surface of the intermediate body 4 thus configured (FIG. 1D).
That is, γ-alumina fine particles are suspended in a solution in which an oxidation catalyst material, in this example, palladium is dissolved, and the oxidation catalyst material is sufficiently adsorbed on γ-alumina to remove moisture and powderize. A preferable weight ratio of palladium to γ-alumina fine particles is, for example, about 3 to 7.

Next, γ-alumina adsorbing the oxidation catalyst substance and phosphoric acid are kneaded with water to form a mud, which is applied to the surface of the intermediate 4 to form an oxidation catalyst preparation layer.
As soon as the heater 1 is energized, it is housed in a heating furnace and the oxidation catalyst preparation layer is heated and fired at a temperature of 500 ° C. to form the oxidation catalyst layer 5. Thereby, the oxidation catalyst layer 5 containing phosphoric acid is formed.

  FIG. 2 shows the sensitivity (output) of isopropyl alcohol (10000 ppm) and hydrogen (2000 ppm) with respect to the mixing ratio (weight ratio) of phosphoric acid and the oxidation catalyst material (γ alumina adsorbing the oxidation catalyst material). The result was as follows.

In other words, if the weight ratio of phosphoric acid to γ-alumina adsorbing the oxidation catalyst substance is 3 or more and the weight ratio with the oxidation catalyst substance itself is 5 to 95 or more, hydrogen is sufficiently detected while suppressing sensitivity to isopropyl alcohol. It turns out that you can. It should be noted that the upper limit of the weight ratio of phosphoric acid to γ-alumina adsorbing the oxidation catalyst substance was 15 to the extent that hydrogen could be detected with practical sensitivity, according to experiments.

  In order to suppress sufficient performance of the intermediate as a compensation element, that is, to suppress sensitivity to not only isopropyl alcohol but also a gas to be detected, gold chloride is applied to the surface and then fired to form a gold layer. desirable.

1 Heater 2 Fixed Layer 3 Heating Element 4 Intermediate 5 Oxidation Catalyst Layer

Claims (4)

Hydrogen selection comprising: a fixing layer formed on the surface of a coiled heater that generates heat by Joule heat and fixing a wire ring forming the heater; and an oxidation catalyst layer containing phosphoric acid formed on the surface of the fixing layer Gas sensor. The hydrogen selective gas sensor according to claim 1, wherein the oxidation catalyst is palladium. The hydrogen selective gas sensor according to claim 1, wherein the fixed layer also contains phosphoric acid. The hydrogen selective gas sensor according to claim 2, wherein a weight ratio of phosphoric acid to palladium is 5 to 95 or more.

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