JPS6152935B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, by providing a coil-shaped heater to which an inorganic insulating adhesive is used as a carrier and a precious metal catalyst is provided around a gas sensitive body, gas having a low ignition point is combusted to some extent on the surface of the heater, thereby substantially reducing the The present invention relates to a combustible gas detection element that can distinguish and detect to some extent from other gases with relatively high ignition points by lowering the concentration of the gas that reaches the sensitive body. In recent years, as propane gas and city gas have become widely used as fuel gas in general households,
Various combustible gas detection elements have been developed and put into practical use in order to detect trace amounts of flammable gas before they occur without leaving a trace of explosion accidents caused by these flammable gases. Especially as city gas becomes more and more natural gas,
The number of households using natural gas, whose main component is methane gas, is increasing, and the range of gases that can be detected is also expanding. Also, compared to other gases such as propane, methane gas is lighter than air, so the detection and alarm device must be installed at a high place. Therefore, during cooking, gases such as alcohol may be detected and cause false alarms, so gas selectivity has become more important. Conventionally, methods for controlling gas selectivity in combustible gas detection elements include material technology measures such as improving the composition of the sensitive material, adding noble metal catalysts to the sensitive material, or improving the behavior of the sensitive material. Efforts have been made to control the temperature. However, it was technically quite difficult, and the reliability was not always satisfactory. The present invention provides a combustible gas detection element that can have a certain degree of gas selectivity by focusing on the structure of the element. The present invention is characterized by the fact that the ignition temperature of each combustible gas differs depending on the type of combustible gas, and by using a noble metal catalyst as the ignition heat source, the gas has a property that it is easy to burn even at a temperature lower than the ignition temperature of the gas. This is a positive application of certain points. Specifically, a coil-shaped heater in which a noble metal catalyst is provided around a gas sensitive body is maintained at a temperature lower than the ignition temperature of the gas. If flammable gas comes into contact with this heater in this state, part of the gas will burn, so the concentration of the gas that reaches the sensitive body surrounded by the heater will be lower than the original concentration. Therefore, the sensitive body comes into contact with a gas having a concentration lower than the actual concentration of the surrounding material, and the amount of change in resistance value decreases accordingly. By using this method, if the temperature of the heater provided with the noble metal catalyst is set so that only gases with low ignition temperatures (e.g., alcohol, isobutane, etc.) are combusted, the sensitivity to these gases will be apparently reduced. It shows its original sensitivity to gases with high ignition points, such as hydrogen gas and methane gas, and can selectively detect them. The details of the embodiment will be explained below. FIG. 1 is a schematic diagram of a combustible gas detection element according to the present invention. A general-purpose sintered type is used for the sensitive body 1.
Only the sensitive part of the SnO ₂ semiconductor sensor was used. A pair of platinum (Pt) electrodes 2 for detecting resistance were attached to both ends of this sensitive body using conductive paste 3.
Around the sensitive body, an inorganic cement paste mainly composed of Al ₂ O ₃ is used as a carrier, and a precious metal catalyst is used.
5 wt % of Pt powder was added and kneaded and applied to a metal wire coil to provide a heater 4 with mechanical reinforcement of the coil and insulation between the wires. At this time, the heater coil was made large enough to sufficiently cover the sensitive body so that the effect could be fully exhibited. Note that the addition of 5 wt% of Pt did not impair the insulation between the lines. Using the combustible gas detection element of the present invention constructed as described above, specific gas sensitivity characteristics were investigated. Methane, hydrogen, and alcohol were used as the gases to be detected at this time. The table below shows the operating temperature of the sensitive body.
These are the characteristics at 350°C, and are comparison values between when a noble metal catalyst (Pt) is applied to the heater as described above (this example) and when it is not applied. Electrical resistance value at 1000ppm.

[Table] As you can see from this table, clean air, methane,
In each hydrogen atmosphere, there is no difference in characteristics between the presence and absence of a catalyst, but in an alcohol atmosphere, when a catalyst is present (this example), the sensitivity is clearly lower. In the examples, the case where the gas detection method was a semiconductor type was described, but a similar study was conducted on a catalytic combustion type, and results similar to those obtained in the case of the semiconductor type were obtained. Therefore, the present invention is effective regardless of the detection method, whether it is a semiconductor type or a catalytic combustion type. A gas detection element can be provided. As described above, the flammable gas detection element of the present invention has
To reduce the sensitivity to gases having a low ignition temperature without impairing the sensitivity to gases having a high ignition temperature by applying a noble metal catalyst to a coil-shaped heater provided around the sensitive body. This makes it possible to practically realize a combustible gas detection element with gas selectivity that produces fewer false alarms for alcohol and the like.

[Brief explanation of the drawing]

The drawing is a partially cutaway perspective view showing an embodiment of the combustible gas detection element of the present invention. 1... Sintered sensitive body of SnO ₂ , 2... Electrode for resistance detection, 3... Conductive paste, 4... Heater for heating.

Claims (1)

[Scope of Claims] 1. A heater is provided at a predetermined interval around a gas sensitive body that detects combustible gas, and the heater includes a coiled heating wire and an inorganic insulating adhesive on the heating wire. A combustible gas detection element comprising a carrier and a filling part provided with a noble metal catalyst. 2. A so-called semiconductor type gas sensitive body that uses a metal oxide and detects the presence of flammable gas as a change in the resistance value of the metal oxide, or a noble metal catalyst that detects the temperature at which the combustible gas burns. The combustible gas detection element according to claim 1, characterized in that it is constructed of a so-called catalytic combustion type element that detects the rise as an increase in the resistance value of a platinum wire or the like.