KR101694849B1 - Method for manufacturing Porous material for gas sensor - Google Patents

Abstract

The present invention relates to a porous electrode protection layer for a gas sensor, a method of manufacturing the same, and a gas sensor including the porous electrode protection layer. More particularly, A porous electrode protection layer for a gas sensor which can protect against chemical external factors and prevent the output of the gas sensor from deteriorating from an external factor and enable measurement of the target gas concentration more quickly and accurately, To a gas sensor.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a porous electrode protective layer for a gas sensor,

The present invention relates to a method of manufacturing a porous electrode protection layer for a gas sensor, and more particularly, to a method for manufacturing a porous electrode protection layer for a gas sensor, To a method for manufacturing a porous electrode protection layer for a gas sensor capable of minimizing the generation of byproducts during the pore formation process and capable of compressing and sintering the porous electrode protection layer to realize a protective layer having a sufficient density.

H ₂ S, H ₂ , CO, NO _x , SO _x , NH ₃ , VOC _s, etc.) due to air pollution, environmental pollution, There is an increasing need for a gas sensor. Among them, H ₂ S is a gas contained in bad smell such as bad smell and bad breath, and it must be measured in order to purify the environment and establish a pleasant living environment. In addition, CO is a gas contained in exhaust gas of gasoline automobile and soot discharged from industrial site. It controls the emission amount of the running vehicle on the road, prevents environmental pollution by controlling the inflow of CO gas into the automobile interior, Measurement is required to maintain the indoor environment.

In particular, a gas sensor capable of measuring oxygen, hydrogen, carbon monoxide, carbon dioxide, nitrogen oxide (NOx), and the like is widely used for detecting a specific gas component in an exhaust gas or measuring the concentration thereof in an internal combustion engine, 2012-0070252 discloses a gas sensor capable of sensing hydrogen.

In general, a gas sensor includes an external sensing electrode unit and a reference sensing electrode unit sensing unit for measuring a difference in electromotive force between a specific gas component contained in the gas under test and a specific gas component contained in the atmosphere, And a heater portion for heating the substrate to a temperature at which ion conductivity is achieved.

The gas sensor can be installed in an exhaust gas exhausting engine of an internal combustion engine to detect a gas component to be measured or to measure the concentration of the gas component. The exhaust gas contains liquid substances such as water and / or oil, The liquid materials may be in contact with a gas sensor, in particular a sensing electrode or a heater portion of a gas sensor, which may be hotter than room temperature. The liquid material in contact with the gas sensor provides stress and thermal shock to the gas sensor, which can cause cracking in the gas sensor, particularly the sensing electrode. In addition, the exhaust gas includes poisoning substances such as silicon and phosphorus, and the gas sensor is exposed to the poisoning substance, which may hinder accurate sensing of the gas to be measured.

In order to solve such a problem, a porous protective layer is generally formed on the surface of the gas sensor. The porous protective layer protects the gas sensor from an external impact and is made of a porous material so that the gas sensor can sense the measurement gas, as well as being able to protect from the aforementioned liquid and poisonous substances.

However, the porous electrode protection layer formed by the method of manufacturing the porous electrode protection layer formed on the conventional gas sensor can not completely block the liquid material contained in the gas under test, Cracks are generated in the external sensing electrode due to thermal shock or the porous electrode protection layer is directly brought to the gas sensor up to substances other than the target gas to be inspected due to peeling, cracking, pore collapse and the like of the gas sensor. The formation of pores in the protective layer may not be achieved at a desired level, or by-products may remain in the pores, which may degrade the gas sensing speed of the gas sensor or affect sensing, thereby providing false information.

Further, in the conventional method of manufacturing the porous electrode protection layer formed on the gas sensor, the pore-forming agent is not properly removed, and it is very difficult to realize the desired porosity and pore diameter. In the process of manufacturing the porous protection layer, Cracks frequently occurred in the separating porous protective layer at the interface between the protective layer and the protective layer, and the conventional production method causes an increase in the production time and an increase in the consumption of various resources to be supplied to each process, there was.

Disclosure of the Invention The present invention has been devised to solve the above-mentioned problems, and it is an object of the present invention to provide a porous electrode protection layer having a desired porosity and pore diameter while maximizing productivity such as shortening of manufacturing time, And a method of manufacturing a porous electrode protection layer for a gas sensor, which can realize a protective layer having a sufficient density by being able to press and sinter the porous electrode protection layer.

In order to solve the above-described problems, the present invention provides a method of manufacturing a porous electrode protection layer for a gas sensor that protects a sensing electrode of a gas sensor by heat-treating a composition for forming a porous electrode protection layer, A first oxidation step performed in a temperature range lower than the first oxidation temperature; And a sintering process performed at 1300-1700 deg. C after the first oxidation process. The method of manufacturing a porous electrode protection layer for a gas sensor according to claim 1,

According to a preferred embodiment of the present invention, a second oxidation process is further included between the first oxidation process and the sintering process, wherein the second oxidation process is performed at a temperature higher than the first oxidation temperature, Temperature can be performed at a temperature lower than the temperature.

The composition for forming a porous electrode protection layer may include a ceramic powder, a binder component, a solvent, and a pore-forming agent.

The ceramic powder may include at least one selected from the group consisting of alumina, spinel, titanium dioxide, zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite.

The pore-forming agent may be selected from the group consisting of carbonaceous materials including at least one of graphite, carbon black and carbohydrate; And low-melting-point fibers comprising at least one of a low-melting-point polyester and a low-melting-point polyamide fiber; Or the like.

Further, the pore-forming agent may include at least one of graphite and carbon black.

Also, the rate of temperature rise between 150 ° C and the first oxidation temperature is 0.1 to 2 ° C / min in the temperature range in which the first oxidation step is performed, and the rate of temperature increase is 1 to 5 Lt; 0 > C / min.

In addition, the second oxidation process may include a maintenance interval maintained at a second oxidation temperature for 40 minutes to 5 hours.

In the first oxidation step and the second oxidation step, the value of the following formula (1) may be 100 to 350 minutes.

[Equation 1]

In this case, ΔT ₁ is the temperature (° C.) between 150 ° C. and the first oxidation temperature (° C.), v ₁ is the rate of temperature rise (° C./min) from 150 ° C. to the first oxidation temperature, ΔT ₂ is the first oxidation (° C.) between a temperature (° C.) and a second oxidation temperature (° C.), and v ₂ is a rate of temperature increase (° C./min) from the first oxidation temperature to the second oxidation temperature.

Also, the rate of temperature increase in the temperature range from 150 ° C to the first oxidation temperature is 0.3 to 1 ° C / min in the temperature range in which the first oxidation process is performed, and the rate of temperature increase is 1 to 3.0 Lt; 0 > C / min.

According to another preferred embodiment of the present invention, the sintering process may be performed for 1 to 5 hours.

In order to solve the above problems, the present invention provides a porous electrode protection layer for a gas sensor manufactured by the manufacturing method according to the present invention.

Hereinafter, terms used in the present invention will be described.

The term " first oxidation temperature " used in the present invention means the upper limit temperature of the temperature section in the temperature interval during which the first oxidation process is performed, And is not meant to be performed at the first oxidation temperature.

The term " second oxidation temperature " used in the present invention means the upper limit temperature of the temperature section in the temperature section in which the second oxidation process is performed, and the second oxidation process is performed at the second oxidation temperature Is performed over the following temperature range and does not mean that it is carried out at the second oxidation temperature.

In the description of a preferred embodiment of the present invention, the layered and laminated shape includes both " direct " and " indirect ". For example, the shape in which the first layer and the second layer are laminated is a " direct " in which a third layer is not interposed between the first and second layers or a "Quot; indirect "

The present invention provides a porous electrode protection layer having a desired porosity and pore diameter while maximizing productivity such as shortening of production time and the like, minimizing the generation of by-products during the pore formation process, The porous electrode protection layer can be squeezed and sintered so that the gas sensor can be protected from external physical impact and physical / chemical external factors such as liquid substances and poisonous substances in the test gas And the output of the gas sensor can be prevented from deteriorating from an external factor.

 Also, since the influence of the gas sensor due to external factors such as poisonous substances or by-products remaining in the pores in the process of manufacturing the porous electrode protective layer is prevented, the sensitivity to the target gas is excellent and the target gas concentration can be measured accurately Do.

FIG. 1 is a flowchart illustrating a manufacturing process of a porous electrode protection layer according to a preferred embodiment of the present invention.

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

As described above, in the conventional method of manufacturing the porous electrode protection layer formed on the gas sensor, the pore-forming agent is not properly removed, and it is very difficult to realize the desired porosity and pore diameter. In the manufacturing process, And the prolongation of the production time and the prolonged production time increase the consumption of various resources to be supplied to the process, resulting in poor productivity and economical efficiency. In addition, the porous electrode protection layer manufactured through such a conventional method can not completely block the liquid material contained in the gas under test, but also cracks may occur in the external sensing electrode due to the thermal shock due to the temperature difference between the liquid material and the gas sensor, There is a problem in that the electrode protection layer directly reaches the gas sensor to a substance other than the target gas to be inspected due to peeling, cracking, pore collapse and the resulting gas sensor, and the formation of pores in the porous electrode protection layer is not achieved Or the by-products remain in the pores, thereby degrading the gas sensing speed of the gas sensor or affecting the sensing, thereby providing false information.

Accordingly, the present invention provides a method of manufacturing a porous electrode protection layer for a gas sensor that protects a sensing electrode of a gas sensor by heat-treating a composition for forming a porous electrode protection layer, wherein the heat treatment is performed at a temperature A first oxidation step carried out in the section; And a sintering process performed at 1300 to 1700 ° C after the first oxidation process. The present invention has been made to solve the above-described problems by a method for manufacturing a porous electrode protection layer for a gas sensor.

As a result, it is possible to improve the productivity as much as possible by shortening the manufacturing time and to realize a porous electrode protection layer having a desired porosity and pore diameter, to minimize the occurrence of by-products during the pore formation process, It is possible to protect the gas sensor from external physical impact and physical / chemical external factors such as liquid substances and poisonous substances in the gas to be inspected by implementing a protective layer having a sufficient density capable of squeezing and sintering the porous electrode protection layer In addition, it is possible to prevent the output of the gas sensor from deteriorating from an external factor.

Specifically, FIG. 1 is a flow chart illustrating a process of manufacturing a porous electrode protection layer according to a preferred embodiment of the present invention. In step (1), a step (S1) of applying a composition for forming a porous electrode protection layer onto a sensing electrode In step (2), a step (S2) of performing a first oxidation process on the porous electrode protective layer-forming composition put on the sensing electrode is performed, a sintering process (S4) is performed after the first oxidation process, A second oxidation step (S3) may be further performed between the first oxidation step (S2) and the sintering step (S4).

Before the heat treatment for the composition for forming a porous electrode protective layer according to the present invention is described, step (S1) of putting the composition for forming a porous electrode protective layer onto the sensing electrode in step (1) will be described.

First, the composition for forming a porous electrode protection layer of the step (1) according to the present invention will be described.

The composition for forming the porous electrode protection layer may be used without limitation for a composition used for preparing a conventional porous electrode protection layer for a gas sensor. Specifically, the composition for forming a porous electrode protection layer may include a ceramic powder, a binder component, a solvent, and a pore-forming agent.

The ceramic powder may be in the form of a particle and may protect the gas sensor from external physical / chemical factors and may be used without limitation if it is easy to form pores. . Preferably, _{Al 2 O 3, SiO 2,} TiO 2, ZrO 2, AlN, Si 3 N 4, Ti 3 N 4, Zr 3 N 4, Al 4 C 3, SiC, TiC, ZrC, AlB, Si 3 B _{4, Ti 3 B 4, Zr} 3 B 4, 3Al 2 O 3 · 2SiO 2 And MgAl ₂ O ₄ , and more preferably at least one of alumina, zirconia, and yttrium oxide, and still more preferably, yttrium stabilized zirconia. The ceramic powder particle size may be designed differently considering the pore size of the porous electrode protection layer to be realized, and the present invention is not particularly limited, but may be preferably 0.1 to 500 μm.

The pore-forming agent may be a pore-forming agent used in the production of a porous electrode protective layer for a gas sensor, which is easy to form pores, can be easily removed by physical and / or chemical dissolution, Pore formers which do not affect can be used without limitation. However, in order to produce a porous electrode protection layer in which intended physical properties such as formation of pores and prevention of residual by-products are remarkably improved in the first oxidation step and / or the second oxidation step described later, at least one of graphite, carbon black and carbohydrates Carbon; And low-melting-point fibers comprising at least one of a low-melting-point polyester and a low-melting-point polyamide fiber; Or the like.

Specific examples of carbohydrates in the above-mentioned carbohydrates include monosaccharides such as glucose and galactose, disaccharides such as sucrose and the like, and polysaccharides such as starch and starch.

The low melting point fibers may be very suitable for forming pores formed in the porous electrode protection layer to be perpendicular to the sensing electrode, thereby enabling a more sensitive sensing speed of the gas to be detected to be developed, When a short fiber having both ends difference in fineness is used, a diameter gradient can be realized according to the position of the through pores (height based on the sensing electrode), thereby preventing thermal shock due to moisture and the like, The durability can be remarkably increased.

However, ordinary fibers have a high melting point of 250 ° C or higher and are difficult to easily remove even at a high temperature exceeding the melting point, and even if they are removed, the first pore diameter can not be realized due to carbonization of a part thereof, And / or the desired properties can not be realized through the second oxidation process. Accordingly, the low-melting-point fiber may be a fiber having a melting point of 80 to 200 ° C, preferably 80 to 150 ° C, and preferably a polyester or polyolefin having a melting point of 80 to 200 ° C, Amide fibers may be included singly or in combination.

As a non-limiting example of the low melting point polyester fiber, a fiber obtained by polycondensing an esterification reaction product of a diol such as ethylene glycol with isophthalic acid in addition to terephthalic acid as a polyvalent carboxylic acid. Further, in the case of the low melting point polyamide fiber, it may be a fiber spun through a polyamide resin in which nylon 6 and / or nylon 6,6 and nylon 6,10 nylon 11 and / or nylon 12 are copolymerized.

On the other hand, the pore-forming agent has an average particle diameter of 100 nm to 50 탆 when the pore-forming agent is in the form of particles, and includes at least two kinds of average particle diameters in order to form a diameter gradient of pores , More preferably 2 to 4 kinds. When a pore-forming agent having two kinds of average particle sizes is used, a pore-forming agent having a large average particle size forms pores having a large diameter, and a pore-forming agent having a small average particle size forms pores having a small diameter, A star diameter gradient can be derived.

When the pore-forming agent is a fiber, the fineness may be 0.5 to 3 D (denier), preferably 1.3 to 2.1 D, and the fiber length may be changed depending on the thickness of the porous electrode protection layer.

The binder component serves to further improve the adhesion between the ceramic powder and the adhesion between the porous electrode protection layer formed on the surface of the gas sensor, preferably the external sensing electrode and the step (2) described later. The binder component may be a component commonly used in the art, but is preferably a polyvinyl butyral such as polyvinyl butyral, ethyl cellulose, polyester, epoxy, terpineol and polyvinyl And fluorine-based compounds such as lithium fluoride and the like.

The solvent may be used without limitation as long as it can facilitate the dispersion of the porous electrode protective layer forming composition and the dissolution of the binder component. Examples of the solvent include water, ethanol, isopropyl alcohol, n-propyl alcohol and butyl Alcohols may be included, but not limited thereto.

The above-described composition for forming a porous electrode protection layer may contain 20 to 60 parts of a pore-forming agent per 100 parts of ceramic powder. If the pore forming agent is contained in less than 20 parts skin, it may be difficult to realize the desired porosity. If the pore forming agent exceeds 60 parts skin, pores of the porous electrode protective layer may be collapsed or the mechanical properties may be significantly deteriorated have.

The binder component may include 5 to 26 parts by weight based on 100 parts by weight of the ceramic powder, and the solvent may include 20 to 50 parts by weight. When the binder component is contained in an amount of less than 5 parts by weight, the adhesion between the gas sensor and the porous electrode protective layer to be produced is weakened so that the porous electrode protecting layer is separated from the gas sensor or the bonding force between ceramic powders is weakened, And if it exceeds 26 parts by weight, the pore of the porous electrode protective layer may be blocked by the binder component, so that it may be difficult to realize the desired porosity and pore diameter. In the case of the solvent, if the viscosity of the composition for forming the porous electrode protective layer can be maintained to a desired thickness, the content of the solvent may be changed and used.

As described above, the composition for forming a porous electrode protection layer may further include known dispersants, plasticizers, and the like to improve the dispersion of the pore-forming agent.

On the other hand, a method of putting the above-mentioned composition for forming a porous electrode protective layer onto a sensing electrode will be described.

First, the sensing electrode generally refers to an electrode for detecting a specific gas to be detected by a gas sensor that detects a gas. The sensing electrode may be a gas sensing type (for example, a sensor for oxygen detection, a sensor for nitrogen detection, etc.), a gas detection system (for example, an electrochemical system (solution electroconductive system, electrostatic electrolytic system, Irrespective of the kind of gas sensor classified by the method (hydrogen ionization method, thermal conduction method, contact combustion method, semiconductor method)). As the sensing electrode, various electrode materials having electrical conductivity may be used, and preferably platinum, zirconia, and / or a platinum / zirconia mixture may be used.

There is no particular limitation on the method of putting the composition for forming a porous electrode protective layer onto the sensing electrode. The composition can be applied in a specific thickness or printed by a printing method known in the art. In addition, the amount of the composition to be applied or printed may be changed depending on the thickness of the desired porous electrode protection layer, and is not particularly limited.

The sensing electrode may include at least one of the sensing electrodes directly facing at least one surface of the sensing electrode, and at least one surface of the sensing electrode may include another layer to face the composition.

Next, a method of heat-treating the porous forming composition put on the sensing electrode will be described.

Wherein the heat treatment is performed in a temperature range of 350 to 500 DEG C at a first oxidation temperature or lower; And a sintering process performed at 1300 to 1700 ° C after the first oxidation process.

First, the first oxidation step will be described.

The first oxidation process according to the present invention is performed over a temperature range of 350 to 500 DEG C and below the first oxidation temperature. Preferably in a temperature range of from 150 ° C to a first oxidation temperature or lower. This is related to the melting point and boiling point of a pore forming agent such as a binder component, a solvent, a resin ball and the like contained in the porous forming composition to be removed through the first oxidation step, a dispersant, a plasticizer, When the first oxidation process is performed in this temperature range, it is easy to remove the target material, thereby imparting strength to the elementary body and suppressing cracking. If the first oxidation temperature is less than 350 ° C, the solvent and the binder component can not be sufficiently removed because the first oxidation process can not be performed at a temperature sufficient to perform the first oxidation process, and thus it may be unsuitable for the production of a porous electrode protection layer having desired physical properties . In addition, when entering the sintering process in this state, the solvent, the binder component, and the like may be volumetically expanded at a rapid rate upon vaporization, resulting in cracks in the porous protective layer or separation of the interface between the sensing electrode and the porous protective layer . Further, in order to prevent rapid expansion of the solvent, binder component and the like during the vaporization, it is necessary to adjust the heating rate. If the first oxidation temperature exceeds 500 ° C, the operation time required for the first oxidation process The productivity and the production cost may increase, the process time may be significantly prolonged, and the removal rate of the material removed through the first oxidation process may be insignificant.

In the temperature range during which the first oxidation process is performed, the heating rate is preferably 0.1 to 2.0 ° C / min, more preferably 0.3 to 1 ° C / min. If the temperature raising rate is less than 0.1 캜 / minute, the temperature of the target material can be smoothly increased when the temperature is raised to the first oxidation temperature as the temperature is raised very slowly, but the manufacturing process is significantly extended, There is a problem. If the rate of temperature increase exceeds 2 DEG C / min, the temperature rise time may be shortened to the first oxidation temperature, but the material to be removed may not be oxidized and carbonized or remains as impurities and may not be removed properly. Unless the content of the binder component and other components in the composition is minimized, the physical properties of the desired gas sensor may be difficult to manifest.

Also, according to a preferred embodiment of the present invention, the first oxidation step may be performed for 40 to 2000 minutes, preferably 200 to 1500 minutes, and more preferably 400 to 1200 minutes. If the process is performed in 40 minutes, the desired oxidation effect may not be exhibited. If the process is performed for more than 2000 minutes, the production time may be extended and the production cost may increase. The execution time includes both the time required for raising the temperature in the temperature range lower than the first oxidation temperature, preferably the temperature range from 150 캜 to the first oxidation temperature, and the time that can be maintained at the first oxidation temperature.

On the other hand, the temperature raising rate up to 150 DEG C, which is a preferable temperature at which the first oxidation process is started at room temperature, does not significantly affect the oxidation of the material to be removed in the first oxidation process, so that the present invention is not particularly limited.

The first oxidation step may be performed in an atmospheric environment, but is not limited thereto. Depending on the purpose, the first oxidation step may be performed by compressing air, pure air, or the like to shorten the oxidation process time and / May be performed by using a damper / dust collecting system for forcibly drawing the gas into the chamber and discharging the generated gas.

Next, the second oxidation step (S3) which can be further performed between the first oxidation step (S2) and the sintering step (S4) described below will be described.

A conventional process for preparing a porous electrode protection layer for a gas sensor is manufactured by raising the sintering temperature at a constant rate at room temperature. In such a process, removal of the pore forming agent may not be removed to a desired level. Particularly, carbon materials containing at least one of graphite, carbon black and carbohydrate which are disclosed in a preferred embodiment of the present invention; And / or a low melting point fiber comprising at least one of a low melting point polyester and a low melting point polyamide fiber, may not be particularly smoothly removed by a conventional sintering process.

 If residual impurities are present such as incomplete combustion or pyrolysis reaction and carbonization to form amorphous carbon, the performance of the gas sensor is deteriorated, the sinterability is lowered, the strength of the sintered body is lowered, and the crack is generated. ≪ / RTI >

It may be desirable to further perform a second oxidation step between the first oxidation step and the sintering step described below, which may be performed at a temperature interval between the first oxidation temperature and the second oxidation temperature. This allows the porous electrode protection layer to achieve desired porosity, pore diameter, etc., and to remove residual impurities completely, thereby imparting strength to the porous body.

More specifically, the second oxidation process may be performed at a first oxidation temperature to a second oxidation temperature, and the second oxidation temperature may be more preferably 700 to 850 ° C. This is related to the pore forming agent contained in the porous forming composition for removing through the second oxidation step. When the second oxidizing step is performed in this temperature range, the removal of the pore forming agent is facilitated, It is possible to produce a porous body having a strength and impart strength to the body to suppress cracking.

If the second oxidation process is performed after the second oxidation process is performed at a second oxidation temperature of less than 700 < 0 > C, the pore forming agent can not be removed smoothly upon entering the sintering process, and incomplete burning or pyrolysis reaction occurs to carbonize to form amorphous carbon, There may be a problem to make. In addition, if the second oxidation process is performed at a second oxidation temperature exceeding 850 DEG C, the removal rate of the pore forming agent may be insignificant, and there may be problems such as prolonged production time.

The temperature raising rate is preferably 1 to 5 占 폚 / min, more preferably 1 to 3 占 폚 / min in the temperature range during which the second oxidation process is performed. If the heating rate is less than 1 ° C / min, the pore-forming agent can be oxidized smoothly when the temperature is raised to the second oxidation temperature as the temperature is raised very slowly, but on the contrary, the production process is remarkably prolonged, There is a problem. If the rate of temperature increase exceeds 5 DEG C / min, the temperature rise time can be shortened to the second oxidation temperature, but the pore-forming agent is not oxidized, is carbonized or remains as impurities and is not removed properly, Cracks may be generated at the interface, and the unevenness of the pore shape may increase, which may make it difficult to manifest the physical properties of the desired gas sensor.

Meanwhile, according to a preferred embodiment of the present invention, the second oxidation step may include a maintenance period for maintaining the second oxidation temperature for 40 minutes to 5 hours, more preferably 40 minutes to 2 hours. The second oxidation process includes a maintenance period at a certain temperature, thereby more effectively removing the pore-forming agent, which is advantageous in realizing the desired physical properties. If the retention time is less than 40 minutes, it may not be possible to produce a porous electrode protective layer having a desired pore structure such that removal of the pore forming agent is not smooth. In addition, if the holding time exceeds 5 hours, improvement in the effect obtained through the maintenance section may be insignificant, which may lead to an increase in manufacturing time and an increase in manufacturing cost.

Further, according to a preferred embodiment of the present invention, the second oxidation process may be performed for 80 to 800 minutes, preferably 300 to 600 minutes. If the treatment is carried out for less than 80 minutes, the desired oxidizing effect may not be sufficiently exhibited. If the treatment is performed for more than 800 minutes, the increase of the oxidizing effect is insignificant, . The execution time includes both the time required to raise the temperature in the temperature range from the first oxidation temperature to the second oxidation temperature, and the time to be maintained at the second oxidation temperature.

The second oxidation process may be performed in an atmospheric environment, but the present invention is not limited thereto. Depending on the purpose, compressed air, pure air, or the like may be used for shortening the time of the oxidation process and / May be performed by using a damper / dust collecting system for forcibly drawing the gas into the chamber and discharging the generated gas.

According to a preferred embodiment of the present invention, the first oxidation process and the second oxidation process described above can satisfy the following Equation 1 for 100 to 350 minutes, and the ceramic powder It is possible to effectively remove substances other than the porous electrode protection layer and to prevent impurities such as residual substances and / or carbonized substances from being removed, and to prevent separation of the porous electrode protection layer from cracks or an interface between the porous electrode and the sensing electrode It is advantageous to realize the physical properties of the intended porous electrode protection layer.

[Equation 1]

In this case, ΔT ₁ is the temperature (° C.) between 150 ° C. and the first oxidation temperature (° C.), v ₁ is the rate of temperature rise (° C./min) from 150 ° C. to the first oxidation temperature, ΔT ₂ is the first oxidation (° C.) between a temperature (° C.) and a second oxidation temperature (° C.), and v ₂ is a rate of temperature increase (° C./min) from the first oxidation temperature to the second oxidation temperature.

If the value of Equation (1) exceeds 350 minutes, the production time is significantly prolonged. If the value of Equation (1) is less than 100, the binder component, solvent, dispersant , The plasticizer and the like may not be completely removed and the second oxidation process may be performed. In this case, the remaining material may be carbonized and converted into new impurities, and the remaining materials and / There is a possibility that the desired mechanical strength of the intended porous electrode protection layer can not be achieved by interfering with the sintering of the body in the sintering process. In addition, such residual materials and / or impurities may interfere with the formation of pores, which may make it difficult to realize a porous body having a desired pore structure. In addition, or even if the first step does not proceed rapidly, there is a problem that pyrolysis of the pore-forming agent may be promoted and / or incomplete combustion may occur as the second oxidation step proceeds rapidly, There is a problem that the increase in the mechanical strength or the implementation of the desired pore structure may be difficult.

By satisfying the range of the formula (1) according to a preferred embodiment of the present invention, the binder component, the solvent, the dispersant, the plasticizer and the pore-forming agent contained in the composition for forming a porous electrode protection layer are completely removed, And the mechanical strength of the resin. Particularly, among the above-described porous electrode protective layer compositions, polyvinyl compounds such as polyvinyl butyral, fluorine compounds such as ethyl cellulose, polyester, epoxy, polyvinylidene fluoride, and terpineol Binder component; And pore-forming agents such as carbon fibers and low melting point fibers.

Next, the sintering process performed after the oxidation process will be described.

The sintering process is performed at a temperature of 1300 to 1700 ° C, preferably at 1400 to 1500 ° C. By satisfying the above-mentioned temperature range, the sintering of the ceramic powder contained in the composition for forming a porous electrode protective layer is smooth, and desired physical properties such as desired mechanical strength, suppression of cracking, and suppression of pore collapse can be achieved. The sintering temperature may vary depending on the type of the ceramic powder to be selected. However, when the sintering temperature is lower than 1300 ° C, sintering is not performed properly and the mechanical strength of the sintered body may be lowered. , Pores may collapse due to thermal shock due to moisture, or cracks may be generated in the porous electrode protection layer, and the porous electrode protection layer may peel off from the sensing electrode. In addition, if the sintering temperature exceeds 1700 ° C, cracks may occur in the protective layer due to a difference in shrinkage percentage or the like.

The sintering process may include a maintenance period in which the temperature is raised to a predetermined sintering temperature in the sintering temperature range of 1300 to 1700 ° C, and then maintained at the predetermined sintering temperature for 30 minutes to 3 hours. By including such a holding period, there is an advantage that the strength of the body can be further improved. If the maintenance time of the maintenance section is less than 30 minutes, the effect through the maintenance section may be insignificant. If the maintenance section exceeds 3 hours, the improvement effect achieved through the maintenance section may be insignificant. Can be increased.

According to one preferred embodiment of the present invention, the sintering process may be performed for 1 to 5 hours. If it is carried out for less than 1 hour, the desired sintering effect may not be exhibited, and if it is carried out for more than 5 hours, the manufacturing time may be extended and the production cost may increase.

Meanwhile, the present invention may include a porous electrode protection layer for a gas sensor manufactured through the above-described manufacturing method.

The porous electrode protection layer may have an average porosity of 20 to 60%, preferably 30 to 50%, per unit volume. If the average porosity per unit volume of the porous electrode protection layer is less than 20%, the gas permeability is lowered and the supply and / or discharge of the measurement gas to the gas sensor is difficult to smoothly proceed, If it exceeds 60%, the mechanical strength may be considerably lowered, and the pores may be collapsed, cracks, thin films, and the like.

Also, according to a preferred embodiment of the present invention, the porous electrode protection layer may have an average pore diameter of 5.95 mu m to 42 mu m, preferably 16 mu m to 32 mu m. If the average diameter of the pores is less than 5.95 mu m, the gas permeability to the porous electrode protection layer is lowered, and the supply and / or discharge of the measurement gas to the gas sensor is difficult to smoothly proceed, And when it is more than 42 탆, the liquid substance, poisoning substance in the exhaust gas which can permeate into the pores may penetrate into the porous electrode protection layer and reach the gas sensor, so that it may be difficult to protect the gas sensor from such material , It is difficult to supply an appropriate amount of the measurement gas to the gas sensor, which may make it difficult to more accurately measure the measurement gas concentration.

The porous electrode protection layer may be formed to cover at least a part of one surface of the sensing electrode, and the thickness may be 20 to 200 탆, and preferably 50 to 100 탆. In the gas sensor including the porous electrode protection layer, liquid substances such as water and / or oil, which can cause cracks of the sensing electrode during use, may penetrate into the pores of the porous electrode protection layer. The liquid materials may be dispersed before being contacted with the gas sensor. If the porous electrode protection layer is formed on the surface of the gas sensor to a thickness of less than 20 mu m, it may not be possible to sufficiently protect the gas sensor from external impact and liquid matter. In addition, if it is formed with a thickness exceeding 200 mu m, it is not only inefficient in terms of manufacturing cost of the gas sensor, but also slows down the response speed, and it may become difficult to measure the measurement gas concentration more accurately.

The present invention will now be described more specifically with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

≪ Example 1 >

70 g of yttrium-stabilized zirconia having a particle size of 3 탆 (95.5 mol% of zirconia, 4.5 mol% of yttrium), 12 g of polyvinyl butyral as a binder component, 25 g of butyl alcohol as a solvent and 30 g of graphite having a diameter of 5 탆 as a pore- The composition for forming the electrode protecting layer was screen-printed on the upper surface of the platinum serving as the sensing substrate so that the average thickness after sintering was 70 mu m.

After that, the temperature was raised from room temperature to 150 ° C at a rate of 2.5 ° C / min in an atmospheric environment for heat treatment, and then the temperature was raised to 400 ° C at a rate of 1 ° C / min to perform a first oxidation process. Thereafter, the temperature was raised to a second oxidation temperature of 800 ° C at a rate of 2.5 ° C / minute, and then maintained at 800 ° C for 1 hour to perform a second oxidation process. Thereafter, the temperature was raised to 1470 ° C so as to fall within a range of 1 ° C / minute, and the sintering process was terminated by maintaining the temperature at 1470 ° C for 2 hours to prepare a porous electrode protective layer as shown in Table 1 below.

≪ Examples 2 to 12 >

The conditions of the first oxidation step and the second oxidation step were changed as in the following Tables 1 to 3 to prepare a porous electrode protective layer as shown in Tables 1 to 3 below.

≪ Example 13 >

The procedure of Example 1 was repeated except that the second oxidation step was not performed and the temperature was raised to the sintering temperature at the rate of temperature rise of the first oxidation step to prepare a porous electrode protection layer as shown in Table 4.

≪ Comparative Examples 1 and 2 &

The first oxidation temperature was changed as shown in Table 4 below. After passing through the first oxidation temperature, the temperature was raised to 1470 ° C at a rate of 2.5 ° C / min and then maintained at 1470 ° C for 2 hours And the sintering process was terminated to prepare a porous electrode protective layer as shown in Table 4 below.

<Experimental Example 1>

The following physical properties of the gas sensor including the porous electrode protection layer prepared through the above Examples and Comparative Examples were measured and shown in Tables 1 to 3 below.

1. Measurement of pore diameter and porosity

The prepared porous electrode protection layer was cut in a direction perpendicular to the surface of the gas sensor, and a four-part SEM photograph of 20% thick, 40% thick, 60% thick and 80% The average diameter and porosity of the pores included in the area of 100 mu m x 100 mu m were measured.

Further, an SEM photograph of a first surface contacting a surface of the gas sensor and a second surface facing the first surface was taken, and then an average diameter of pores included in a region of 100 m x 100 m was measured, The ratio of the pores included in the range of the average diameter of the second surface of 占 2 占 퐉 among the pore diameters included in the second surface was calculated.

2. Whether the gas sensor is cracked or not

The presence or absence of cracks in the prepared porous electrode protective layer was observed with an optical microscope, and the degree of occurrence of no cracking was expressed as 0, and the degree of occurrence of cracking was expressed as 1 to 5 as the degree of occurrence increased.

3. Evaluation of Strength of Porous Electrode Protection Layer

For the strength of the porous electrode protection layer, it was evaluated whether or not the porous electrode protection layer adhered to the blue tape upon detachment of the blue tape after the blue tape (Duct tape 3015, 3M) was attached to the top of the porous electrode protection layer. 0 &quot;, &quot; 0 &quot;, &quot; 5 &quot;, &quot; 5 &quot;

Example 1 Example 2 Example 3 Example 4 Oxidation
fair The first oxidation step Temperature section (℃) 150 ~ 400 150 ~ 400 150 ~ 400 150 ~ 400 The rate of temperature rise (v1, DEG C / min) One 0.2 One 0.4 Holding time (minutes) 0 0 0 0 Execution time (t1, min) 250 1250 250 625 Second oxidation step Temperature section (℃) 400 to 800 400 to 800 400 to 800 400 to 800 The rate of temperature rise (v1, DEG C / min) 2.5 2.5 0.7 2.5 Holding time (minutes) 60 60 60 60 Execution time (t2, min) 220 220 631.4 220 Oxidation process execution time 470 1470 881.4 845 Equation 1 126.5 632.5 451.8 316.2 The porous electrode
Protective layer Porosity (%) 55 54 58 55 Pore average diameter (탆) 12.3 11.9 13.1 12.0 Crack occurrence 0 0 0 0 Strength evaluation 0 0 0 0

Example 5 Example 6 Example 7 Example 8 Oxidation process The first oxidation step Temperature section (℃) 150 ~ 400 150 ~ 400 150 ~ 400 150 ~ 400 The rate of temperature rise (v1, DEG C / min) One 1.3 1.8 2.2 Holding time (minutes) 0 0 0 0 Execution time (t1, min) 250 192.3 138.9 113.6 Second oxidation step Temperature section (℃) 400 to 800 400 to 800 400 to 800 400 to 800 The rate of temperature rise (v1, DEG C / min) 3 2.5 2.5 2.5 Holding time (minutes) 60 60 60 60 Execution time (t2, min) 193.3 220 220 220 Oxidation process execution time 443.3 412.3 358.9 333.6 Equation 1 105.4 97.3 70.3 57.5 The porous electrode protective layer Porosity (%) 55 54 58 55 Pore average diameter (탆) 12.3 11.9 13.1 12.0 Crack occurrence 0 One 2 4 Strength evaluation 0 One 3 4

Example 9 Example 10 Example 11 Example 12 Oxidation process The first oxidation step Temperature section (℃) 150 ~ 400 150 ~ 400 150 ~ 400 150 ~ 400 The rate of temperature rise (v1, DEG C / min) One One One One Holding time (minutes) 0 0 0 0 Execution time (t1, min) 250 250 250 250 Second oxidation step Temperature section (℃) 400 to 800 400 to 800 400 to 800 400 to 800 The rate of temperature rise (v1, DEG C / min) 3.3 4.8 6 2.5 Holding time (minutes) 60 60 60 0 Execution time (t2, min) 181.2 143.3 126.7 160 Oxidation process execution time 431.2 393.3 376.7 410 Equation 1 95.8 65.9 52.7 126.5 The porous electrode protective layer Porosity (%) 53 55 48 47 Pore average diameter (탆) 11.1 10.9 9.4 12.0 Crack occurrence 0 One 2 0 Strength evaluation 2 3 4 2

Example 13 Comparative Example 1 Comparative Example 2 Oxidation process The first oxidation step Temperature section (℃) 150 ~ 400 150-300 150 ~ 600 The rate of temperature rise (v1, DEG C / min) One One One Holding time (minutes) 0 0 0 Execution time (t1, min) 250 150 250 Second oxidation step Temperature section (℃) - 300 to 800 600 to 800 The rate of temperature rise (v1, DEG C / min) - 2.5 2.5 Holding time (minutes) - 60 60 Execution time (t2, min) - 260 140 Oxidation process execution time 250 410 590 Equation 1 - 109.5 120 The porous electrode protective layer Porosity (%) 51 51 45 Pore average diameter (탆) 12.2 15.6 9.7 Crack occurrence 0 5 0 Strength evaluation 2 5 3

Specifically, as shown in Tables 1 to 4 above,

It can be confirmed that the time for performing the oxidation process increased more than three times in the case of Example 2 in which the rate of temperature rise in the first oxidation process was lower than that in Example 1. In Example 3, It is confirmed that the execution time of the oxidation process is extended to about 2 times.

In addition, it was confirmed that the properties similar to those of Example 2 were maintained and the production time was significantly reduced in Example 4, while the properties similar to those of Example 1 were maintained and the production time was reduced in Example 5 .

However, in the case of Example 6, the reduction of the production time was achieved more than that of Example 1, but it was confirmed that the first oxidation process was not sufficiently performed due to the increase in the rate of the first oxidation process, so that cracks were generated in the porous electrode protection layer. In Examples 7 to 8 in which the rate of the first oxidation process was further increased, it was confirmed that although the production time was shortened, cracks occurred or the strength decreased. Particularly, in the case of Example 8, it can be confirmed that the crack occurrence evaluation and the strength evaluation were not very good as compared with Example 7.

On the other hand, in Examples 9 to 11 in which the temperature for raising the temperature of the second oxidation step exceeds 3 캜 / minute, the production time could be shortened as the raising rate of temperature was increased, but the second oxidation step was not sufficiently performed, And the pore-forming agent could not be oxidized properly, so that the average pore diameter was reduced.

Also, in the case of Example 12 in which the holding time was not set at 800 占 폚 in the second oxidation step, the development of pores was poor, and the remaining pore formers affected the sintering process and the strength was lowered.

In addition, in the case where the second oxidation step is not carried out, it can be confirmed that the oxidation of the pore-forming agent is not properly performed and the strength is lowered.

In the case of Examples 6 to 11 in which the value of Equation 1 is less than 100 as compared with Example 1 which satisfies Equation 1 according to a preferred embodiment of the present invention, instead of shortening the manufacturing time, It can be seen that the production time is remarkably extended in Examples 2 and 3 in which the value of Equation 1 exceeds 350.

On the other hand, in the case of Comparative Example 1 in which the first oxidation temperature was lower than 350 ° C, it was confirmed that cracks occurred due to rapid expansion of the components due to the oxidation of the binder component, solvent, etc., I could, and the strength was not very good.

Also, in the case of Comparative Example 2 in which the first oxidation temperature was higher than 500 ° C, the time for performing the second oxidation process was not sufficient, and the strength was remarkably lowered, and the development of pores was remarkably insufficient.

Claims (12)

A method for manufacturing a porous electrode protection layer for a gas sensor, which protects a sensing electrode of a gas sensor by heat-treating a composition for forming a porous electrode protection layer,
Wherein the heat treatment is performed in a temperature range of 350 to 500 DEG C at a first oxidation temperature or lower;
A second oxidation step performed at a temperature range exceeding the first oxidation temperature, lower than the second oxidation temperature of 700 to 850 ° C, and maintained at the second oxidation temperature for 40 minutes to 5 hours; And
And performing a sintering process performed at 1300 to 1700 ° C after the second oxidation process.
delete The method according to claim 1,
Wherein the composition for forming a porous electrode protection layer comprises a ceramic powder, a binder component, a solvent, and a pore-forming agent.
The method of claim 3,
Wherein the ceramic powder comprises at least one selected from the group consisting of alumina, spinel, titanium dioxide, zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite. Lt; / RTI &gt;
4. The method of claim 3, wherein the pore-
Graphite, carbon black, and carbohydrates; And
Low melting point fibers comprising at least one of a low melting point polyester and a low melting point polyamide fiber; Wherein the porous electrode layer is formed on the surface of the porous electrode layer.
6. The method of claim 5,
Wherein the pore-forming agent comprises at least one of graphite and carbon black.
The method according to claim 1,
The rate of temperature rise between 150 ° C and the first oxidation temperature is 0.1 to 2 ° C / min in a temperature section in which the first oxidation process is performed, and the rate of temperature increase is 1 to 5 ° C / min Wherein the porous electrode is formed of a porous material.
delete The method of claim 7, wherein
Wherein the first oxidation process and the second oxidation process each have a value of the following formula (1): 100 to 350 minutes;
[Equation 1]

In this case, ΔT ₁ is the temperature (° C.) between 150 ° C. and the first oxidation temperature (° C.), v ₁ is the rate of temperature rise (° C./min) from 150 ° C. to the first oxidation temperature, ΔT ₂ is the first oxidation (° C.) between the temperature (° C.) and the second oxidation temperature (° C.), and v ₂ is the rate of temperature rise (° C./min) from the first oxidation temperature to the second oxidation temperature.
8. The method of claim 7,
The rate of temperature rise in the temperature range from 150 ° C. to the first oxidation temperature is 0.3 to 1 ° C./min in the temperature range during which the first oxidation process is performed. Min. &Lt; / RTI &gt;
The method according to claim 1,
Wherein the sintering process is performed for 1 to 5 hours.
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