KR100900092B1 - Manufacturing method of oxygen sensor - Google Patents

Abstract

The present invention comprises the steps of preparing a solid electrolyte powder in the form of an ink and ball mill; Applying the prepared solid electrolyte to one surface of a substrate; And applying a Pt ink on the solid electrolyte coating layer, and connecting a platinum wire to the method of manufacturing an oxygen sensor, wherein the electrolyte has excellent sensitivity in a wide range of oxygen concentration using a solid electrolyte. In addition, it is possible to manufacture a semiconductor resistance type oxygen sensor that can be used in mixed combustion gas atmosphere.

Solid electrolyte, ball mill, oxygen sensor

Description

Preparation method of oxygen sensor {Preparation method of oxygen sensor}

1 is a flow chart for the production of La ₂ CuO ₄ using the auto-ignition method,

2 is an overall process diagram for manufacturing an oxygen sensor according to the present invention,

3 is a schematic diagram of an oxygen sensor according to the present invention,

Figure 4 is a photograph of the equipment for measuring the performance of the oxygen sensor according to the present invention,

5 is a graph showing a resistance change value and a time change due to an oxygen concentration change when measuring an oxygen concentration against a temperature change using an oxygen sensor manufactured according to an embodiment of the present invention.

Figure 6 shows the repeated response time by the change in oxygen concentration when measuring the oxygen concentration with respect to the temperature change using an oxygen sensor prepared according to an embodiment of the present invention.

The present invention relates to a method for producing a semiconductor resistance type oxygen sensor having a high sensitivity in a wide range of oxygen concentration range using a solid electrolyte, which can be used in a mixed combustion gas atmosphere.

Semiconductor oxygen sensor mainly includes semiconductor gas sensor using gas adsorption and desorption and contact combustion gas sensor using gas reactivity.

When gas molecules are adsorbed on the surface of the semiconductor, the electrical conductivity of the semiconductor changes depending on the type of semiconductor and the type of gas molecules. This is to detect the type and amount of gas by using the resistance change when the gas sensor is contacted by connecting the gas sensor to an appropriate circuit.

Such a semiconductor oxygen sensor is a non-stoichiometric semiconductor, and the dual layer formed on the surface is a surface defect and an adsorption layer, and uses the principle that a deficiency layer or an accumulation layer is formed.

Accordingly, it is an object of the present invention to provide a method for producing a semiconductor resistance type oxygen sensor which has excellent sensitivity in a wide range of oxygen concentration range using a solid electrolyte and can be used in a mixed combustion gas atmosphere.

In order to achieve the above object,

The present invention comprises the steps of preparing a solid electrolyte powder in the form of an ink and ball mill; Applying the prepared solid electrolyte to one surface of a substrate; And applying Pt ink on the solid electrolyte coating layer, and connecting the platinum wire.

Hereinafter, the present invention will be described in more detail.

One material selected usable solid electrolyte powder in the present invention are from the group consisting of ZnO, _{talc, SiO 2, Al 2 O 3} , Nb 2 O 5, TiO 2, CeO 2, SrTiO 3, LaCoO 3 , and La ₂ CuO ₄ It is prepared in the form of an ink by adding a solvent and a thickener to the solid electrolyte powder.

In this case, the method of synthesizing the solid electrolyte powder, which is the semiconductor oxygen sensor material used, may be a melting method, a freeze-drying method, a precipitation method, an auto-ignition method, a sol-gel method, etc., but each has characteristics.

Melting by the solid phase reaction requires a temperature as high as 1100 ° C., which is uneconomical and difficult to obtain nano-sized particles, and also has various types of structures depending on the high temperature and the oxidation-reduction atmosphere.

The sol-gel method is widely used as a method for preparing nano-sized particles, but has a disadvantage in that it is difficult to manufacture due to instability of precursors. On the other hand, the auto-ignition method is a method in which precursors are sintered using amorphous binuclear complexes. Thus, it is easy to prepare a material having a very small particle size and a relatively large surface area.

Accordingly, in the present invention, a semiconductor oxygen sensor material is prepared by using an auto-ignition method which can be easily prepared at low temperatures.

In addition, the solvent is used one or more mixed solvents selected from the group consisting of ethanol, isopropanol, acetone, benzene, ammonia water, distilled water, carbon tetrachloride, acetic acid and toluene, preferably at least one selected from water or ethanol do.

At this time, the solvent is used in 10-50 parts by weight with respect to 1 part by weight of the solid electrolyte powder, when using an excess or a small amount of solvent outside the above range, the resistance value is low or high can not accurately detect the concentration of oxygen Problems may arise.

In addition, the thickener is one selected from the group consisting of polyethylene glycol, carboxymethyl cellulose, xanthan gum, carrageenan, starch and sodium alginate, preferably polyethylene glycol or sodium alginate.

In this case, the thickener is used in an amount of 100-200 parts by weight based on 100 parts by weight of the solid electrolyte powder, and when the excess or small amount of the thickener is used out of the range, the viscosity may be low or high, causing screen printing not to be efficiently performed. Can be.

The ball mill treatment according to the present invention uses a two-roll mill, and the rotation ratio is 2: 1, and it is preferable to operate for 15-25 hours by fixing at 120 rpm and 60 rpm, respectively.

Outside the range of rotation speed may cause a problem that the particles are too multiplied or coarse, and when outside the time range it may not be sufficiently mixed, or may cause a problem of thinning of the viscosity.

The solid electrolyte prepared as described above is an ink particle having a particle diameter of about 1-10 μm. At this time, if the particle diameter is larger or smaller than the above range, the oxygen concentration may not be accurately measured due to the variation of the resistance value.

The solid electrolyte prepared as described above is applied to one surface of the substrate.

As a substrate usable in the present invention, Al ₂ O ₃ or YSZ (Yttrium Stabilized Zirconia) is used, and a solid electrolyte is coated on the substrate by screen printing.

At this time, the thickness of the coating layer is preferably 0.01-0.05 mm, the outside of the range may cause a problem that the reaction time is delayed or the change in the resistance value is dull.

In addition, Pt ink (Pt paste) is applied to the solid electrolyte coating layer by the screen printing method, and a platinum wire is connected thereto.

Referring to Figure 2 in more detail, the present invention is a step of preparing a solid electrolyte powder (S100), the step of adding a thickener and a solvent to the solid electrolyte powder and mixing (S110), ball mill the mixture to a solid electrolyte ink Oxygen through the manufacturing step (S120 and S130), screen printing the solid electrolyte ink on the substrate (S140), sintering (S150), screen printing the Pt ink (S160) and sintering (S170) Sensors can be manufactured.

Oxygen sensor according to the present invention can be applied to both home and industrial boilers equipped with a chimney, which can optimize the combustion-fuel ratio to induce a second energy saving and prevent air pollution due to complete combustion. have.

In addition, industrially, it can be applied to control of chemical reaction process, to prevent suffocation when working in storage tanks such as chemical plants or oil tankers, to prevent air pollution in the environment and instrument fields, and to analyze gas pollution. It can play a role as a sensor to prevent the accident of life due to lack of oxygen during work or manhole work.

In addition, in the medical field, it can be used as a preventive measure for human accidents such as prevention of deficiency of oxygen concentration during anesthesia during surgery and blindness of infants caused by high oxygen concentration in incubator.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

< Reference Example  1> materials and appliances

The YSZ (Yttria Stabilized Zirconium, 8M% Yttria) of the zirconia support used as the oxygen sensor substrate in the present invention is Marketch International Inc. having a standard of 20 mm x 10 mm x 100 μm. The product was purchased and used, and Pt ink used in the screen printer was used by Heraeus.

Oxygen sensor solid electrolyte was used to synthesize La ₂ CuO ₄ . La (NO ₃ ) ₃ , Cu (NO ₃ ) ₂ and citric acid, the reagents used to synthesize La ₂ CuO ₄ , were purchased from Aldrich Co.

< Reference Example  2> La ₂ CuO ₄ Manufacture

La ₂ CuO ₄ was prepared using an auto-ignition process as shown in FIG. 1 by adding citric acid to a mixture of La (NO ₃ ) ₃ and Cu (NO ₃ ) ₂ .

At this time, the molar ratio of citric acid used as the reducing agent and nitrates (La (NO ₃ ) ₃ , Cu (NO ₃ ) ₂ ) used as the oxidizing agent was prepared as citric acid / nitrate = 0.90. At this time, when the molar ratio of citric acid / nitrate is less than 0.3, auto-ignition does not occur after gelling formation, and when it is 1.0 or more, it starts to expand while releasing a large amount of gas and has a cascading explosive reaction.

Citric acid solution was added to the mixture of La (NO ₃ ) ₃ and Cu (NO ₃ ) _{2, and} the mixture was continuously stirred while maintaining a temperature of 85 ° C. to 90 ° C. When gelled, autoignition was carried out on a heating plate, and the material thus prepared was sintered at 500 ° C. and 600 ° C. and left for 10 hours to obtain a solid electrolyte of La ₂ CuO ₄ .

< Example  1> Manufacture of Oxygen Sensor

The manufacturing process of the oxygen sensor is shown in FIG.

More specifically, 2 parts by weight of starch and 10 parts by weight of distilled water are mixed with 1 part by weight of the prepared La ₂ CuO ₄ powder, and the rotation ratio of the 2-roll mill is fixed at 120 rpm and 60 rpm, and treated for 20 hours. A solid electrolyte in the form was prepared.

The prepared solid electrolyte ink was screen printed on an YSZ substrate, and then sintered at 700 ° C. for 2 hours and then cooled.

After screen printing Pt ink again, Pt wire was attached and sintered at 800 ° C. for 2 hours to complete an oxygen sensor as shown in FIG. 3.

As shown in the oxygen sensor schematic of FIG. 3, La ₂ CuO ₄ , an oxygen sensor material, manufactured on one side of an YSZ (20 mm x 10 mm x 100 μm) substrate was coated to a thickness of 0.01-0.05 mm by using a screen printing method, and the coating layer was coated on the coating layer. Pt ink was applied at 0.01-0.05 mm thickness using screen printing method to connect platinum wire to it, and oxygen sensor was fabricated. Oxygen concentration was measured by measuring resistance value by oxygen partial pressure difference between two electrodes. .

The manufactured oxygen sensor is capable of controlling gas flow and temperature as shown in FIG. 4, and is manufactured by attaching an apparatus capable of automatically detecting a change in resistance value according to a change in concentration of various gases. Was measured.

< Experimental Example  1> Oxygen concentration measurement

Oxygen concentration was measured using the oxygen sensor produced in Example 1. At this time, nitrogen gas was used as the carrier gas. The gas flow rate was 300 mL / min. And the oxygen concentration was analyzed by measuring the resistance value generated between the two electrodes according to the oxygen concentration change in the range of 0%-100% oxygen concentration.

As a result, the resistance value and the response time due to the oxygen concentration change when measuring the oxygen concentration with respect to the temperature change are shown in FIGS. 5 and 6. It is reported that the resistance type oxygen sensor decreases the response time as the particle size decreases at a certain temperature.

Therefore, in this experiment, the effects of solid electrolyte materials with the same particle size on the reaction rate and oxygen concentration according to the temperature change were investigated. As a result, the oxygen resistance and the typical oxygen response according to the temperature change were shown. Indicated.

At the same temperature, the resistance tends to increase as the oxygen concentration increases, which is believed to be due to the increase in resistance because the YSZ substrate cannot pump a large amount of oxygen.

Regardless of the oxygen concentration, the resistance tends to decrease as the temperature increases. This is because the oxygen diffusion rate increases as the oxygen concentration increases, and as a result, the inflow of oxygen increases.

In addition, as indicated by the gradient of sensitivity according to the change of oxygen concentration at various temperatures, the linear results were shown as the oxygen temperature was increased at 500 ℃, 600 ℃, and 700 ℃, but the linear results according to the change of oxygen concentration at 400 ℃. Not shown. This is because at low temperatures, the YSZ substrate's self-resistance is so large that it does not properly pump oxygen into the diffusion barrier.

The resistance value of the oxygen sensor is shown to be lower as the temperature is increased, because the resistance value of the YSZ substrate with the temperature rise is relatively low, it is determined that a large amount of oxygen can be pumped at the low resistance value.

On the other hand, in FIG. 5 illustrates the response time of the temperature change of the oxygen sensor, the electrochemical reaction in each electrode from the reference electrode surface _{^{O 2 + 4e - → 2O 2}} -, 2O 2 in the indicator electrode surface ^- → O ₂ Reactions of + 4e ^- occur respectively.

This reaction is governed by the diffusion rate on the electrode surface, and the reaction time is very slow (approximately 140 seconds) due to the slow diffusion rate of oxygen on the electrode surface at around 400 ° C, and the chemical equilibrium rate is very fast on the electrode surface above 500 ° C. Wake up response time is also very fast (about 5 seconds) has a very good oxygen sensor performance at high temperature.

Figure 6 shows the sensitivity of the oxygen sensor according to the change in concentration of 0-100% O ₂ , showed a stable resistance value without drifting according to the change in oxygen concentration, the combustion measurement of one time, two times to obtain a reproducible results The results showed a rapid response time from 0% to 100% oxygen concentration and a linear result proportional to oxygen concentration.

As described above, the oxygen sensor manufactured according to the present invention not only shows a very good sensitivity and response time under various environmental conditions but also has a very good reproducibility, and can prevent accidents due to low indoor oxygen concentration and other gas pollution when applied to a fan. have.

Claims (5)

Preparation of ZnO, _{talc, SiO 2, Al 2 O 3} , Nb 2 O 5, TiO 2, CeO 2, SrTiO 3, LaCoO 3 , and a material of the solid electrolyte powders selected from the group consisting of La ₂ CuO ₄ in ink form And ball milling; Applying a solid electrolyte prepared in the form of ink and prepared by ball milling to one surface of the substrate; And And applying a Pt ink on the substrate to which the solid electrolyte is applied, and connecting platinum wires. delete The method of claim 1, wherein a solvent and a thickener are added to the solid electrolyte powder to prepare the ink in the form of an ink. The method of claim 3, wherein the solvent is one or more mixed solvents selected from the group consisting of ethanol, isopropanol, acetone, benzene, ammonia water, water, carbon tetrachloride, acetic acid and toluene. The method of claim 1, wherein the ball mill uses a two-roll mill and the rotation ratio is fixed at 120 rpm and 60 rpm to operate for 15-25 hours.

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