JPS6313146B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a humidity sensor used in food cooking equipment such as microwave ovens, air conditioning equipment such as air conditioners, humidity control systems, and the like. Conventional structure and its problems The electric moisture sensing element that has been used in the past has
Those using electrolyte materials such as lithium chloride (LiCl), those with an oxide film formed on the surface of a single crystal, those with carbon dispersed in a hydrophilic organic polymer, those with surface oxidation of metal, and those with colloidal films. What I used,
Alternatively, there is an element using a metal oxide porous material. All of these detect changes in humidity as changes in the amount of electricity, but each has major problems. For example, electrolyte materials dissolve into water under condensation and are unstable;
There is a problem with reliability. Furthermore, those using single crystals are expensive and susceptible to dirt. Those using organic polymers have poor responsiveness, and those using vapor-deposited films have poor compatibility.
It takes a long time to stabilize the film, and its properties are unstable. Porous metal oxide materials using Al ₂ O ₃ , Cr ₂ O ₃ , or Ni ₂ O ₃ do not have the above-mentioned drawbacks, but on the other hand, they generally have high resistance;
Not only are they difficult to use in practice, but they also have the problem of being susceptible to dirt, and a common problem with each of them is deterioration of characteristics due to dirt. To solve these problems, metal oxide porous ceramics are heated from the outside or from the surface to remove dirt.
However, under extremely harsh conditions, it shows some changes over time. In addition, if the average pore diameter of the electrode, the porosity of the ceramic element, and the average pore diameter are reduced,
Although the life expectancy is improving, a problem arises in that the response becomes slow. OBJECTS OF THE INVENTION The present invention solves the above-mentioned problems, is responsive,
The present invention aims to provide a humidity sensor with a long life and little change over time. Structure of the Invention The present invention prevents inorganic and organic substances harmful to humidity characteristics from entering the ceramic body by controlling the average pore diameter and porosity of the electrode material and ceramic body of a porous ceramic humidity sensor. The above objective was achieved by preventing That is, in the present invention, by providing small diameter pores on the surface of the ruthenium oxide electrode, deterioration of characteristics due to contamination is reduced, and by providing the electrode on a ceramic body, the life characteristics are further improved.
Furthermore, by reducing the grain size of the ceramic body, the grain boundary area increases, making it possible to lower the sensor resistance value and making the circuit easier to use. Description of Examples Using a MgCr ₂ O ₄ -TiO ₂ -based P-type semiconductor ceramic humidity sensor material, compounding, mixing, pre-combustion, and pulverization were performed sequentially according to ordinary ceramic methods, and then a binder was added. and granulated. This granulated powder was molded into a plate shape with dimensions of 4 mm x 4 mm x 0.25 mm under a pressure of 750 kg/ ^cm2 , and heated from 1100°C to 1300°C in air.
The ceramic body was fired for 2 hours at a temperature within a range of up to °C. Approx.
An electrode paste containing ruthenium oxide powder with a particle size of 0.01 μm to 1 μm and glass frit is applied to a thickness of 10 to 30 μm by screen printing, and heated at 750°C.
The ruthenium oxide electrode was formed by baking at a temperature in the range from 900°C to 900°C. The porosity, average pore diameter, and rate of change over time of these ceramic bodies and ruthenium oxide electrodes are shown in Tables 1 and 2, respectively. Furthermore, Table 3 shows the synergistic effect of the ceramic body and the ruthenium oxide electrode in terms of average pore diameter and rate of change over time. In addition, humidity responsiveness is measured at a temperature of 20°C and a relative humidity of 10% to 50%.
It shows the time taken to reach equilibrium when changing from 90% to 50%, as well as when changing from 90% to 50%. In addition, the life test was performed by adding a temperature cycle (cleaning cycle) in which the element temperature was held at 540°C for 10 seconds to incinerate contaminants, and then held at room temperature for the next 10 seconds. The rate of change in resistance was defined as the rate of change in life.

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[Table] As is clear from the results in the above table, the average pore diameter of the ceramic body and the ruthenium oxide electrode is 0.01 to 1μ.
A humidity sensor in which the porosity of the ceramic body is within the range of 20 to 40% has good humidity responsiveness and change over time. Effects of the Invention As is clear from the above explanation, the humidity sensor of the present invention has stable changes over time and humidity response in an atmosphere with severe humidity resistance characteristics.
The humidity characteristics are highly reliable, and the humidity measuring device can be easily used in devices such as a humidity meter.

Claims (1)

[Claims] 1 P with a porosity in the range of 20% to 40% and an average pore diameter in the range of 0.01 μm to 1 μm
1. A humidity sensor comprising a ruthenium oxide porous electrode having an average porosity in the range of 0.01 μm to 1 μm adhered to the surface of a semiconductor metal oxide ceramic body.