KR0166390B1 - Production method of lithium ion conductive powder carbon dioxide detect material and carbon dioxide sensor - Google Patents

Abstract

The present invention relates to a method for producing a lithium ion conductor powder carbon dioxide gas monitoring material and a solid electrolyte carbon dioxide gas sensor using the sensing material, the conventional sodium ion conductor powder carbon dioxide gas sensor according to the concentration at a concentration of around 5,000ppm In order to solve the problem that the high temperature process of 1,200 ° C. or higher is required when producing the material, the process of preparing an alkoxide gel containing Li ions by the wet method, removing water from the prepared metal alkoxide gel Process, calcination process at 600 ~ 800 ℃ to remove contained organic matter, grinding process to obtain fine powder, shaping process of pulverized powder, and sintering process at 900 ~ 1,100 ℃ for densification and crystallization A carbon dioxide gas sensing material, which is a Li ion conductor powder, was prepared, and a carbon dioxide was detected by attaching a working electrode and a reference electrode to the sensing material. , To produce a scan sensor.

Description

Lithium ion conductor powder carbon dioxide gas sensing material manufacturing method and solid electrolyte carbon dioxide gas sensor using the sensing material

1 is a cross-sectional structure of a solid electrolyte carbon dioxide gas sensor using the monitoring material of Example 1 of the present invention.

2 is a cross-sectional structure of a solid electrolyte carbon dioxide gas sensor using the monitoring material of Example 2 of the present invention.

3 is a sensitivity of the carbon dioxide gas sensor using the monitoring material of the present invention heat-treated at 900 ℃.

4 is a sensitivity of the carbon dioxide gas sensor using the sensing material of the present invention heat-treated at 1,000 ℃.

5 is a sensitivity of the carbon dioxide gas sensor using the sensing material of the present invention heat-treated at 1,100 ℃.

6 is a sensitivity of the carbon dioxide gas sensor is inserted Ni / NiO between the sensing material and the substrate of the present invention.

7 is a view showing a time response characteristic of the carbon dioxide gas sensor of the present invention.

8 is a diagram showing the long-term stability characteristics of the carbon dioxide gas sensor of the present invention.

The present invention relates to a method for producing a lithium ion conductor powder carbon dioxide sensing material capable of reliably detecting and quantifying carbon dioxide (CO ₂ ) in the air with high sensitivity and to a solid electrolyte carbon dioxide gas sensor using the sensing material. will be.

Carbon dioxide (CO ₂ ) is contained in clean air at about 0.03% (300ppm), but the concentration is more than 350ppm due to the recent increase in fossil fuel usage. Increasing the amount of carbon dioxide contained in the atmosphere increases the absorption of infrared radiation from the Earth into the atmosphere, which is known to cause climate change represented by global warming. Therefore, continuously detecting and coping with the amount of carbon dioxide gas has emerged as a major problem in the field of environmental measurement and environmental control.

Until now, non-dispersive infrared method (NDIR method) and photo-acoustic measurement method are mainly used to measure the concentration of carbon dioxide, but the devices using these methods are expensive and simple to use. It is evaluated as unsuitable for the popular type.

In order to overcome such a problem, a great deal of attention has recently been focused on the development of small and easy-to-use semiconductor or solid electrolyte carbon dioxide gas sensing devices.

Recently introduced carbon dioxide gas sensors include sensors using materials such as SnO ₂ + La ₂ O ₃ and Sm ₂ O ₃ -BaCO ₃ -Na ₂ CO ₃ and PbO-BaTiO ₃ . The problem is that temperature is high temperature of 600 degreeC or more. As the solid electrolyte carbon dioxide gas sensing device, ion conductor devices such as NASICON and Li ₂ Ti ₂ (PO ₄ ) + Li ₃ PO ₄ have been introduced (Japanese Patent 4-230842, 4-174354, 4-344456, 5-107220, 4-110649 and Papers Sensor and Actuators B, 13-14, 1993. 476-479, etc.)

NASICON sensor, which occupies most of these sensors, has problems such as lack of linearity according to concentration at low concentration of around 5,000ppm, low stability of characteristics, and high temperature process of more than 1,200 ℃ for device manufacturing. have.

The present invention solves the above problems of the prior art by using the Li ion conductor powder synthesized by the sol-gel method as a carbon dioxide gas sensing material and has a small and lightweight new material composition (CO ₂ ) It is an object to provide a detection sensor.

The present invention is also characterized in that the carbon dioxide gas concentration is high with respect to the carbon dioxide gas in the heat treatment process of 900 ℃ lower than the heat treatment temperature (1,200 ℃ or more) required for the production of a sensor device having a good linearity at 300 ~ 5,000ppm It is an object to provide a material having sensing characteristics.

According to the above object, unlike the conventional method of forming the parent material of the bulk carbon dioxide sensing material by the dry mixing method, by forming a parent material having Li ion conductivity by the wet mixing method and molding the heat treatment process and the operation electrode and the reference electrode Through the process for forming a high sensitivity and good linear solid electrolyte carbon dioxide gas sensor is provided, a process for producing an alkoxide gel (gel) containing Li ions by a wet method, to remove the water of the metal alkoxide gel Process, calcination process to remove contained organic matter, pulverization process to obtain fine powder, shaping process of pulverized powder, sintering (heat treatment) process for densification and crystallization of molded body, sensitivity to carbon dioxide gas And electrodeposition process, reference electrode formation process and substrate or quartz using carbonate and gold The solid electrolyte carbon dioxide gas sensor of the present invention is manufactured by a method including an adhesion process with a tube.

The sensor of the present invention as described above has a high sensitivity and stability in the range of carbon dioxide gas concentration of 300 ~ 5,000ppm by using the ionic conductor of the fine powder by the sol-gel method of electromotive force The value changes linearly to make it easy to measure and to manufacture carbon dioxide sensing material with high sensitivity even at relatively low heat treatment process (900 ℃).

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Example 1

The present invention synthesized the raw material of the carbon dioxide gas sensor according to the wet process described below and manufactured a high sensitivity carbon dioxide gas sensing material using the same. First, Lithium ion conductor (LISICON), which is a base material, was synthesized as follows.

(1) 20 ml of TEOS was added to a well mixed solution at a ratio of 5 ml of ethyl alcohol, 20 µl of nitric acid and 2 ml of water.

(2) 30 ml of zirconium was added to the solution of (1) and mixed well with a magnetic stirrer.

(3) To the mixed solution of step (2), 5 ml and 20 ml of ethyl alcohol and water were added and mixed.

(4) 14 ml of tributyl phosphate (PO [OC ₄ H ₉ ] ₃ ) was added to the finished solution of ( ₃ ) and mixed well.

(5) To the finished solution of (4), 3 ml and 1 ml of ethyl alcohol and water were added, respectively.

(6) 6 g of lithium methoxide was added to the finished solution of (5) and mixed well. Lithium ethoxide may be used instead of lithium methoxide.

(7) Ethyl alcohol and acetic acid were weighed out to 8 ml and 860 µl, respectively, and the mixture was stirred well.

(8) The solution obtained from the process of (1)-(7) was dried at 100 degreeC for 48 hours, and the dark brown substance was obtained.

(9) After pulverizing the mass of the material, it was calcined (heat treatment) at 600 ~ 800 ℃ for 2 hours to obtain a LISICON powder.

The mixing amount of the above raw materials is presented as an example and the present invention is not limited thereto, and the mixing ratio is not important.

The powder obtained by the above method was molded into a disk shape having a diameter of 10 mm and a thickness of 1 mm at a pressure of 5 ton / cm ² , and then a sensor having the structure of FIG. 1 was manufactured by the following procedure.

(1) Sintering (heat treatment) for 10 to 30 hours at a temperature of 900 ~ 1,100 ℃ to obtain a LISICON specimen.

(2) A platinum or gold mesh 4 was placed on one surface of the sintered test piece 3 as shown in FIG. 1, and an carbonate of an alkali metal was fused thereon to form an operation electrode 5.

(3) Platinum black (Pt-black) was applied to the other side of the sintered specimen and the platinum wire was attached to form a reference electrode (2).

(4) Using the inorganic adhesive (6) was bonded to the specimen and the alumina substrate (1) through the process of (1) ~ (3).

In FIG. 1, the size of the solid electrolyte carbon dioxide gas sensor thus manufactured is 15 × 15 × 4 mm ^{3. In} FIG. 1, 7 is a heater and 8 is a heater protection plate.

Example 2

Synthesis of Raw Material [0085] A carbon dioxide gas sensor was manufactured from LISICON powder prepared in the same procedure as in Example 1 according to the following process.

From (1) to (2), LISICON specimens were made as in Example 1, and the operation electrode 6 was formed.

(3) Platinum black (2 ') was applied to one surface of the sintered specimen and Ni / NiO or PdO powder (2' ') was attached thereon to form a reference electrode (2).

(4) It produced similarly to the process (4) of Example 1.

2 is a cross-sectional view of a carbon dioxide gas sensor of a Li ion conductor manufactured by the method of Example 2. FIG.

Although the method for producing the carbon dioxide gas sensing element material of the present invention has been described above by way of example, the present invention is not limited thereto, and a metal alcohol side gel including Li ions is manufactured by a wet method, followed by drying, pulverizing, and heat treatment. All methods for producing a carbon dioxide gas detecting and holding material by forming and sintering are all within the scope of the present invention.

The structure of the solid electrolyte carbon dioxide gas sensor shown in FIGS. 1 and 2 can be expressed as follows.

(+) Pt, CO ₂ ′, O ₂ ｜ LISICON ｜ M (CO ₃ ) | CO ₂ '', O ₂ '', Au (-) ――― (1)

M (CO ₃ ) is an alkali metal carbonate and used as a material for the working electrode. CO ₂ 'and O _2' is a carbon dioxide and oxygen in the reference electrode, CO ₂ '', and O ₂ '' denotes a carbon dioxide gas and oxygen at the operating electrodes.

At the interface between LISICON and Li ₂ CO ₃ (one of MCO ₃ ) the reaction with CO ₂ is

2Li + ½O ₂ + CO ₂ + 2e- → Li ₂ CO ₃ ――― (2)

2Li ⁺ + Li ₂ CO ₃ → 2Li ⁺ + Li ₂ O + CO ₂ ――― (3)

And the Nernst equation for the above reaction is

here,

E: Generator electromotive force R: Gas constant

T: Absolute temperature F: Faraday constant

n: number of reaction electrons Pco ₂ : partial pressure of carbon dioxide

Po ₂ : partial pressure of oxygen

If the oxygen partial pressures at both ends of the device are the same, Equation (4) is as follows. In other words,

Thus, the value of the electromotive force is proportional to the difference in the carbon dioxide concentration across the device.

3 is a result of measuring the value of the electromotive force according to the carbon dioxide gas concentration of the LISICON device of the present invention, which shows the characteristics of the sensor manufactured according to Example 1. The characteristic of FIG. 3 is a case where the heat treatment temperature for forming the Li ion conductor is 900 ° C., and it can be seen that the Nernst equation is well followed. The temperature shown in FIG. 3 is the operating temperature of the sensor. The higher the operating temperature of the sensor, the higher the value of the electromotive force represented by the same concentration of carbon dioxide gas, and good linearity at the concentration of 300 to 5,000 ppm of carbon dioxide gas. As shown in FIG. 3, the carbon dioxide sensing material heat-treated at 900 ° C. exhibits good sensitivity even at 350 ° C. and the carbon dioxide gas concentration increases from 300 to 3,000 ppm at 400 ° C. The change in output voltage (electromotive force) is about 60mV.

4 shows the sensitivity to carbon dioxide gas when the heat treatment temperature for forming the ion conductor is 1,000 ° C., and the absolute value of the output voltage is higher than that of the carbon dioxide gas sensing material heat-treated at 900 ° C. FIG. As shown in this figure, the change in output voltage (electromotive force) is about 70 mV when the carbon dioxide concentration changes from 300 to 3,000 ppm at an operating temperature of 400 ° C, which is calculated by the Nernst equation in Eq. (5). It shows good detection characteristics such as The change in electromotive force of the same carbon dioxide gas concentration change (300 → 3,000 ppm) is about 60mV even at a low operating temperature of about 350 ° C.

5 is a sensitivity characteristic of carbon dioxide gas of a sensor fabricated as a Li ion conductor obtained at a heat treatment temperature of 1,100 ° C. The sensor is characterized by a lower absolute value of electromotive force at the same carbon dioxide concentration and a relatively gentle slope of the straight line than heat treatment at 900 ° C (Sensor A) and 1,000 ° C (Sensor B). Sensor (Sensor C) made of a sensing material heat-treated at 1,100 ℃ has a change of electromotive force of about 50mV when carbon dioxide concentration is changed from 300 → 3,000ppm. The value is lower than that of the element (sensor B) in degrees Celsius. However, this is also believed to be a change in electromotive force sufficient to be used as an element for measuring carbon dioxide concentration.

6 is a sensitivity characteristic of the sensor (sensor D) to the carbon dioxide gas produced by inserting Ni / NiO or PdO between the substrate and the monitoring material when forming the reference electrode. This shows similar characteristics to the sensor C, but the response time is faster than that of the sensor A or the sensor B as shown in FIG. However, there seems to be room for improvement in terms of stability.

7 shows the response time for 1,000 ppm of carbon dioxide gas when the operating temperature of the sensor is 400 ° C. The electromotive force reaches 90% of the saturation value. The sensor D is about 10 seconds, and the sensors A and B are about 20 seconds. It takes about.

8 shows the long-term stability characteristics of the sensor fabricated according to the present invention, which is the result of measuring the output voltage after 120 hours after the sensor was operated (400 DEG C operating temperature). In this result, the sensor A and the sensor C showed a slight variation in the output voltage value of about 2%, but the sensor B showed a constant value with almost no change in the output voltage value.

Carbon dioxide gas sensor of the present invention as described above is a compact and lightweight sensor manufactured at a relatively low heat treatment temperature (900 ~ 1,000 ℃) using Li ion conductor powder synthesized by the wet method in the region of 300 ~ 3,000 ppm concentration of carbon dioxide gas The detection output voltage has very good linearity and high sensitivity to carbon dioxide gas (approximately 60mV electromotive force change for 300 ~ 3,000ppm carbon dioxide gas change) and good long-term stability and time response at low operating temperature of 350 ℃. These characteristics are the result of the formation of highly efficient sensing electrode by synthesizing Li ion conductor of fine powder and optimizing the sensor structure.

Claims (5)

A process for producing a metal alkoxide gel containing a lithium ion by a wet method by mixing and stirring nitric acid, zirconium, tributyl phosphate, lithium methoxide (or lithium ethoxide) and acetic acid, drying the metal alkoxide gel. A method for producing a Li ion conductor powder carbon dioxide gas sensing material comprising a grinding and heat treatment step, a shaping and heat treatment step of a pulverized metal alkoxide. The method of manufacturing a Li ion conductor powder carbon dioxide gas sensing material according to claim 1, wherein ethyl alcohol and water are added to the metal alcohol gel containing the lithium ions. The method according to claim 1 or 2, wherein the heat treatment of the metal alcohol side powder is carried out over a period of 10 to 30 hours at a temperature of 900 ~ 1,100 ℃. Carbon dioxide gas sensing material, reference electrode attached to one side of carbon dioxide gas sensing material, working electrode attached to the other side of carbon dioxide gas sensing material, insulation board equipped with heater and carbon dioxide gas sensing material and combination of reference electrode and working electrode In the solid electrolyte carbon dioxide gas sensor comprising a, carbon dioxide gas sensing material is a lithium ion prepared by mixing and stirring nitric acid, zirconium, tributyl phosphate, lithium methoxide (or lithium ethoxide) and acetic acid And a powder obtained by drying, decomposing and heat-treating the metal alkoxide gel comprising a disk into a disk shape and sintering the solid electrolyte carbon dioxide gas sensor. The solid electrolyte carbon dioxide gas sensor of claim 4, wherein the reference electrode is platinum wire, Ni / NiO, or PdO attached on a platinum black applied to the carbon dioxide sensing material.