KR101694845B1 - Porous material for gas sensor, method for manufacturing thereof, and gas sensor comprising the porous material - Google Patents

Abstract

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

Description

TECHNICAL FIELD [0001] The present invention relates to a porous protective layer for a gas sensor, a method of manufacturing the porous protective layer, and a gas sensor including the porous protective layer.

The present invention relates to a gas sensor, and more particularly, to a porous protective layer for a gas sensor formed on the surface of a gas sensor, a method for manufacturing the same, and a gas sensor including the same.

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. And CO is the gas contained in exhaust gas of gasoline automobile and soot discharged from industrial site. It controls the emission amount of running vehicle on the road, prevents environmental pollution by controlling CO gas inflow in the following automobile interior, Measurement is necessary to maintain the environment.

In particular, gas sensors capable of measuring oxygen, hydrogen, carbon monoxide, carbon dioxide, nitrogen oxides (NOx) and the like for detecting a specific gas component in an exhaust gas or measuring the concentration thereof in an internal combustion engine or the like are widely used.

Generally, the gas sensor includes a sensing electrode portion for measuring a difference in electromotive force due to a difference in concentration of a specific gas component, a reference electrode portion for collecting specific gas component ions, a heater portion for heating the electrode of the sensing electrode portion to a temperature at which ion conductivity is imparted And are stacked in this order.

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 thereof. The exhaust gas contains liquid substances such as water and / or oil, The materials may be in contact with a sensing electrode or heater part of a gas sensor, in particular 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. 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.

Japanese Patent No. 4691095 discloses a sensor element for measuring a physical property of a measurement gas.

However, since the porous protective layer formed on the conventional gas sensor can not completely block the liquid material, 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 substances other than the target gas to be inspected due to peeling, cracking, pore collapse, and the like are directly brought to the gas sensor, poisonous substances are easily deposited on the porous protective layer, There is a problem that it is impossible to more accurately measure the measured gas concentration.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is a first object of the present invention to provide a gas sensor capable of protecting a gas sensor from an external impact and a liquid material, A porous protective layer for a gas sensor which can protect against a physical / chemical external factor such as a liquid substance and a poisonous substance, prevent the deterioration of the output of the gas sensor due to an external factor, And a method for producing the same.

A second problem to be solved by the present invention is to provide a gas sensor including a porous protective layer capable of measuring a target gas concentration more quickly and with a remarkably high durability.

SUMMARY OF THE INVENTION In order to solve the above-mentioned first problem, the present invention provides a method for producing a porous protective layer, comprising the steps of: (1) introducing a porous protective layer forming composition comprising a ceramic powder and a pore former onto a gas sensor; And (2) sintering the porous protective layer-forming composition applied on the gas sensor to produce a porous protective layer for a gas sensor, wherein the ceramic powder comprises particles having a degree of variability of 1.5 or more expressed by the following relational formula 1 And a porous protective layer for a gas sensor.

[Relation 1]

According to a preferred embodiment of the present invention, the ceramic powder is selected from the group consisting of 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 .

In the step (1), the degree of deformation of the ceramic powder may be 1.8 to 4.2.

In the ceramic powder of the step (1), the ceramic powder satisfying the above-mentioned separation-type condition may be 50% by weight or more of the total ceramic powder.

The cross-sectional shape of the ceramic powder satisfying the above-described dissimilarity condition may be at least one of polygonal, star, horn, alphabet, ellipse, dumbbell,

The ceramic powder of step (1) comprises a first ceramic powder having a degree of deformation of 1.5 to 2.0 and a second ceramic powder having a degree of deformation of 3.0 to 4.2. The weight ratio of the first ceramic powder to the second ceramic powder is 1: 1.6 To 3.0.

Wherein the pore former is selected from the group consisting of a polymer of monomers selected from the group consisting of radically polymerizable monomers, multifunctional crosslinking monomers, and combinations thereof, radical polymerizable monomers, multifunctional crosslinking monomers, and combinations thereof microemulsion polymer beads of the monomer; silicon dioxide (SiO _2), titanium dioxide (TiO ₂₎ and an oxide selected from the group consisting of;, carbon water is selected from carbon, carbohydrates and combinations thereof; And a mixture thereof.

The sintering temperature in the step (2) may be 800 to 1700 ° C.

In order to solve the above first problem, the present invention provides a porous protective layer for a gas sensor covering an outer surface of a gas sensor, wherein the porous protective layer for a gas sensor has a degree of variability represented by the following relational expression 1 of not less than 1.5 And at least a part of the ceramic powder particles including ceramic powder are fused to each other to form a porous protective layer for a gas sensor.

[Relation 1]

According to a preferred embodiment of the present invention, the ceramic powder includes at least one particle selected from the group consisting of alumina, spinel, titanium dioxide, zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite can do.

The degree of deformation of the ceramic powder may be 1.8 to 4.2.

The cross-sectional shape of the ceramic powder satisfying the dissimilarity condition may be at least one of elliptical shape, dumbbell shape, polygonal shape, star shape, horn shape, cross shape, cross shape, star shape, alphabet shape, groove shape and dumbbell shape.

Wherein the porous protective layer comprises a first surface facing a first surface of the gas sensor outer electrode and a second surface opposite to the first surface and a diameter gradient increasing from the second surface to the first surface Lt; / RTI >

The average diameter of the pores included in the second surface of the porous protective layer is 5.5 to 8 占 퐉 and the pores having the pore diameter of the average diameter of 占 占 퐉 may be 80% or more of the total pores included in the second surface .

The average diameter ratio of the pores included in the second surface of the porous protective layer and the pores included in the first surface may be 1: 1.8 to 6.

In order to solve the second problem, the present invention provides an electrode for a gas sensor including a porous protective layer for a gas sensor according to the present invention.

According to a preferred embodiment of the present invention, the thickness of the porous protective layer may be 20 to 200 mu m.

In order to solve the second problem, the present invention provides a gas sensor including an electrode for a gas sensor according to the present invention as an external sensing electrode.

In order to solve the above-mentioned second problem, the present invention provides a gas sensor including a porous protective layer for a gas sensor according to the present invention.

In the description of the preferred embodiment of the present invention, the layer and layer stacked shapes include 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 "

INDUSTRIAL APPLICABILITY The present invention not only protects the gas sensor from external physical impacts, physical / chemical external factors such as liquid substances and poisonous substances in the gas under test, but also prevents the output of the gas sensor from deteriorating due to external factors.

 In addition, pore formation and pore arrangement significantly improve the diffusion rate of the gas to be inspected, so that the response speed to the target gas can be made very fast and the influence of external factors such as poisonous substances on the gas sensor is prevented, The sensitivity is very high and the target gas concentration can be accurately measured.

Furthermore, the mechanical properties are remarkably excellent, and collapse and cracks of the pores do not occur in various impacts, which is remarkably superior in performance maintenance and durability improvement of the gas sensor.

FIG. 1 is a flow chart of a process for manufacturing a porous protective layer according to a preferred embodiment of the present invention.
2 is a cross-sectional view of a ceramic powder included in a preferred embodiment of the present invention.
3 is a cross-sectional view of a ceramic powder having a cross-section of a circular cross section according to a preferred embodiment of the present invention.
4 is a cross-sectional view of a ceramic powder having a dumbbell-shaped cross section according to a preferred embodiment of the present invention.
5 is a cross-sectional view of a ceramic powder having a haze-shaped cross section according to a preferred embodiment of the present invention.
6 is a cross-sectional view of a ceramic powder having a star-shaped cross section according to a preferred embodiment of the present invention.
7 is a cross-sectional view of a ceramic powder having a triangular cross section according to a preferred embodiment of the present invention.
8 is a cross-sectional view of a ceramic powder having a rectangular cross section according to a preferred embodiment of the present invention.
9 is a cross-sectional view of a ceramic powder having a pentagonal cross section according to a preferred embodiment of the present invention.
10 is a cross-sectional view of a ceramic powder having a hexagonal cross section according to a preferred embodiment of the present invention.
11 is a cross-sectional view of a ceramic powder having a cross-sectional shape according to a preferred embodiment of the present invention.
12 is a cross-sectional view of a ceramic powder having a cross-section according to a preferred embodiment of the present invention.
13 is a cross-sectional view of a ceramic powder having a hollow elliptical cross section according to a preferred embodiment of the present invention.
14 is a cross-sectional view of a ceramic powder having a groove-shaped cross section according to a preferred embodiment of the present invention.
15 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention.
16 is a cross-sectional schematic diagram of a porous protective layer according to a preferred embodiment of the present invention.
17 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention.
18 is an exploded perspective view of a stacked type gas sensor according to a preferred embodiment of the present invention.

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

(1) introducing a porous protective layer-forming composition including a ceramic powder and a pore-forming agent onto a gas sensor; And (2) sintering the porous protective layer-forming composition charged on the gas sensor to produce a porous protective layer for a gas sensor, wherein the ceramic powder comprises particles having a degree of variability of 1.5 or more represented by the following relational formula 1 And a porous protective layer for a gas sensor.

[Relation 1]

More specifically, FIG. 1 is a flow chart illustrating a process of manufacturing a porous protective layer according to a preferred embodiment of the present invention. In step (1), a porous protective layer forming composition including a ceramic powder and a pore- (S1), and then (S2) sintering the porous protective layer-forming composition applied on the gas sensor in step (2).

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

The composition for forming a porous protective layer includes a ceramic powder serving as a base material of the porous protective layer and a pore forming agent forming pores of the porous protective layer.

The ceramic powder may be a material that becomes a base material of a conventional porous protective layer for a gas sensor and may be used without limitation as long as it can protect the gas sensor from external physical / chemical factors and can easily 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 more preferably at least one of yttrium Stabilized zirconia.

The ceramic powder can more easily realize pores having desired diameters and desired pore distribution, and the produced porous protective layer does not collapse pores even under a strong physical impact, and the junction points or the bonding surfaces of the ceramic powders increase Cracks are not generated in the porous protective layer and the surface roughness of the porous protective layer facing the external sensor electrode of the gas sensor, preferably the gas sensor is increased to further improve the adhesive force of the porous protective layer, 1 is 1.5 or more.

Specifically, FIG. 2 is a sectional view of a ceramic powder included in a preferred embodiment of the present invention, wherein the dissimilarity diagram of the relational expression 1 means a ratio of a circumscribed circle diameter D and an inscribed circle diameter d in the section of the ceramic powder of FIG. 2 do. If the deviation degree is less than 1.5, it is difficult to realize the pore diameter and the pore diameter that the test gas can reach and reach the surface of the gas sensor quickly, and the pores may collapse in the external physical stimulus or cracks may occur in the porous protective layer itself And it may be difficult to realize the desired properties such as the presence of the catalyst.

According to a preferred embodiment of the present invention, at least 50% by weight, more preferably at least 70% by weight, more preferably at least 70% by weight of the ceramic powder contained in the composition for forming a porous protective layer, Preferably at least 85% by weight, more preferably at least 95% by weight is a ceramic powder which satisfies the variance condition of the above-mentioned formula (1).

If the ceramic powder satisfying the conditions of the dissimilarity of the above-mentioned formula 1 is less than 50% by weight of the total ceramic powder, it is difficult to realize the desired porosity and pore diameter through the ceramic powder having the differentiability, There is a problem that physical properties such as cracks may be generated in the porous protective layer itself.

Further, in order to realize higher physical properties, the degree of deformation of the ceramic powder may be 1.8 to 4.2. If the degree of deformation of the ceramic powder exceeds 4.2, the roughness of one surface of the gas sensor, preferably one surface of the porous protective layer facing the one surface of the gas sensor external sensing electrode, becomes too large to contact with the target gas, There is a possibility that the outer surface portion of the gas sensor to be measured may suffer physical damage, which may cause deterioration of the performance of the gas sensor, and that the roughness is too large to separate the porous protective layer from the gas sensor.

Although the cross-sectional shape of the ceramic powder satisfying the heterogeneity condition of the relational expression 1 is not limited as far as the degree of deformation is not less than 1.5, the cross-sectional shape of the ceramic powder satisfying the above-described dissimilarity condition is preferably polygonal, May have any one or more of a horn shape, an alphabet type, an elliptical shape, a dumbbell shape, a grasshopper shape, a cross shape, and a groove shape. The alphabetic type may be C-shaped, E-shaped, F-shaped, H-shaped, L-shaped, S-shaped, T-shaped, U-shaped or W-shaped.

3 to 20 are sectional views of a ceramic powder included in a preferred embodiment of the present invention. 3 is a cross-sectional view of a metal powder having a cross-section of a circular cross-section, in which two circles have a cross-sectional shape cross-linked. In this case, the major axis length a of the intersecting circle is the diameter of the circumscribed circle, and the minor axis length b is the diameter length of the inscribed circle. Fig. 4 is a dumbbell shape, in which the long axis length a of the dumbbell is the diameter of the circumscribed circle, and the short axis length b is the diameter length of the inscribed circle. Fig. 5 is a pentagonal shape, where d is the diameter of the inscribed circle and D is the diameter of the circumscribed circle. 6 is a star shape, where r is the diameter of the inscribed circle and R is the diameter of the circumscribed circle. Fig. 7 is a sectional view of the metal powder in a triangle, Fig. 8 is a quadrangle, Fig. 9 is a pentagon, and Fig. 10 is a hexagon. Fig. 11 is a cross sectional shape, and Fig. 12 is a cross sectional shape. Fig. 13 has a recessed elliptical shape, and Fig. 14 has a groove-shaped cross section.

The modified cross sections of the ceramic powders shown in Figs. 2 to 13 are all examples that can be applied to the present invention, and ceramic powders having a shape appropriately modified in a range satisfying the above-described dissimilarity condition can be used. The ceramic powder having various cross-sectional shapes according to the present invention may be manufactured by a mechanical method such as a ball mill using a bead-shaped ceramic powder having a particle size of 1 to 200 mu m. The ball mill may be made of zirconia ZrO ₂ , steel, or tungsten may be used. The specific method of the ball mill, the time conditions, and the like may be designed differently depending on the desired mold releasability. Thus, the present invention is not particularly limited thereto, For 1 minute to 10 hours.

According to a preferred embodiment of the present invention, two kinds of ceramic powders having different dissimilarity degrees are mixed and mixed in order to control the pore diameter easily, ensure uniformity of the pore diameter, minimize the pore collapse while realizing the desired pore distribution Preferably, a ceramic powder obtained by mixing a first ceramic powder having a degree of modification of 1.5 to 2.0 and a second ceramic powder having a degree of deformation of 3.0 to 4.2 in a weight ratio of 1: 1.6 to 3.0 may be used. When the ceramic powders having different dissimilarity values are mixed as described above, the bonding area between the particles can be further increased and the physical properties such as mechanical strength can be remarkably improved. If the first ceramic powder and the second ceramic powder satisfying the above-mentioned releasability degree range and the weight ratio condition of each particle are not satisfied, uniform pore diameters can not be realized and pore collapse frequently occurs, It can easily be damaged.

Next, the pore forming agent contained in the composition for forming a porous protective layer of step (1) according to the present invention will be described.

The pore-forming agent may be a pore-forming agent used for producing a porous protective layer for a gas sensor, which is easy to form pores, can be easily removed by physical and / or chemical dissolution, Can be used without limitation in the case of a pore-forming agent which does not give a sufficient effect. However, it is preferably selected from the group consisting of a polymer of a monomer selected from the group consisting of a radically polymerizable monomer, a polyfunctional crosslinking monomer, and a combination thereof, a radically polymerizable monomer, a polyfunctional crosslinking monomer, and combinations thereof microemulsion polymer beads of the monomer; silicon dioxide (SiO _2), titanium dioxide (TiO- ₂₎ and an oxide selected from the group consisting of;, carbon water is selected from carbon, carbohydrates and combinations thereof ; And a mixture thereof.

Specific examples of the radically polymerizable monomers include styrene, p-methylstyrene, m-methylstyrene, p-ethylstyrene, m-ethylstyrene, p-chlorostyrene, m-chlorostyrene, Aromatic vinyl monomers such as chloromethylstyrene, styrenesulfonic acid, pt-butoxystyrene, mt-butoxystyrene, fluorostyrene, alphamethylstyrene, vinyltoluene and chlorostyrene; Acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, stearyl Fluoroethyl acrylate, trifluoroethyl methacrylate, pentafluoropropyl methacrylate, fluoroethyl methacrylate, hexafluoroethane,

(Meth) acrylate monomers such as butyl (meth) acrylate, hexafluoroisopropyl methacrylate, perfluoroalkyl acrylate and octafluorophenyl methacrylate; And unsaturated carboxylic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl ether, allyl butyl ether, allyl glycidyl ether, (meth) acrylic acid, maleic acid; Alkyl (meth) acrylamides; A vinyl cyanide monomer of (meth) acrylonitrile; Or a mixture thereof. Representative examples of the polymer of the radical polymerizable monomers include polystyrene and polymethyl (meth) acrylate.

Examples of the multifunctional crosslinking monomer include allyl compounds such as divinylbenzene, 1,4-divinyloxybutane, divinyl sulfone, diallyl phthalate, diallyl acrylamide, triallyl (iso) cyanurate and triallyl trimellitate , Hexanediol diacrylate, ethylene glycol dimethacrylate, diethylene glycol methacrylate, triethylene glycol dimethacrylate, trimethylene propane trimethacrylate, 1,3-butanediol methacrylate, 1,6- Tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylol propane, tri (meth) Acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) acrylate, glycerol tri (meth) acrylate, allyl (meth) It may include water

Specific examples of the carbon material may be monosaccharides such as graphite, glucose, and galactose, disaccharides such as sucrose or polysaccharides such as starch and starch, and the properties may be particles of powder.

The pore-forming agent is preferably in the form of a particle. The particle size of the pore-forming agent is in the range of from 100 nm to 50 μm. The average particle diameter of the pore-forming agent is preferably at least 2 Or more, and 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 diameter gradient can be induced.

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

Next, a method of putting the porous protective layer-forming composition on the gas sensor 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.

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.

There is no particular limitation on the method of putting the porous electrode protective layer forming composition on the sensing electrode, and the porous electrode protective layer forming composition may be applied in a specific thickness or may be 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.

As a specific example thereof, if the vacuum protective layer forming method is applied to the composition for forming a porous protective layer, a method known in the art can be used. As a non-limiting method, the composition for forming a porous protective layer is first applied to a powder container And a gas sensor having an external sensing electrode or an external sensing electrode attached thereto is installed in the deposition chamber, and then a carrier gas is supplied from the carrier gas container located in the powder container. The carrier gas may be air, oxygen, nitrogen, helium, argon, or the like, but is not limited thereto. The flow rate of the carrier gas may be controlled within a range of 1 L / min or more so that the powder of the composition in the powder can flow into the carrier gas to be scattered. The carrier gas into which the composition powder flows may be introduced into the deposition chamber. After the introduction of the carrier gas into the deposition chamber, the degree of vacuum of the deposition chamber is suitably adjusted to facilitate the deposition. More specifically, May be more preferable.

As another specific example, when the composition for forming a porous protective layer is applied as a liquid to a gas sensor, the composition for forming a porous protective layer may further include a binder component and a solvent. The binder component serves to further improve the adhesion between the ceramic powders and the adhesion of the gas sensor surface, preferably the external sensing electrode, to the porous protective layer produced through step (2) described later. The binder component may be a binder component commonly used in the art, preferably a polyvinyl butyral such as a polyvinyl butyral, an ethyl cellulose, a polyester, an epoxy, a terpineol, And fluorine-based compounds such as polyvinylidene fluoride.

The solvent may be used without limitation as long as it can facilitate the dispersion of the porous protective layer-forming composition and the dissolution of the binder component. Non-limiting examples of the solvent include water, ethanol, isopropyl alcohol, n-propyl alcohol, But not limited thereto.

The binder component may include 8 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 8 parts by weight, the adhesion between the gas sensor and the prepared porous protective layer is weakened, so that the porous protective layer is separated from the gas sensor or the bonding force between the ceramic powders is weakened. And if it is contained in an amount exceeding 26 parts by weight, the pore of the porous 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 above-mentioned solvent, if the viscosity of the composition for forming the porous protective layer can be maintained to a desired thickness, the content of the solvent may be changed and used.

After the above step (1), the step (2) according to the present invention may be carried out by sintering the porous protective layer-forming composition put on the gas sensor.

In the step (2), the sintering may be performed at a temperature of 800 to 1700 ° C, more preferably 1000 to 1600 ° C, and even more preferably 1300 to 1550 ° C under an atmosphere of air and / or nitrogen. If the temperature is lower than 800 ° C., it is difficult to remove the pore-forming agent by heat. Therefore, it may be difficult to realize a porous protective layer having a desired porosity and pore diameter. When the temperature exceeds 1700 ° C., There may be a problem that can be received. The sintering may be performed for 20 minutes to 5 hours, but the sintering time is not limited thereto.

On the other hand, if a specific kind of pore-former is used, it may not be removed by thermal sintering after the step (2). In this case, it may be chemically dissolved and removed. In this case, a solution of strong acid or strong base may be used. As a representative example of the strong acid, hydrofluoric acid may be used. As a representative example of strong base, sodium hydroxide and potassium hydroxide may be used. It is not.

In addition, it is possible to carry out the step of eliminating the pore-forming agent between the steps (1) and (2) for the purpose of achieving the desired pore through more smooth removal of the pore-forming agent. The pore former may be desorbed preferably at 200 to 600 ° C, more preferably at 300 to 500 ° C for 20 minutes to 5 hours.

Meanwhile, according to a preferred embodiment of the present invention, in order to form a gradient of the difference in pore diameters between one surface of the porous protective layer and the other surface opposite to the one surface after the step (2) The porosity adjusting agent may be coated on the surface of the pores included in the other surface portion facing the one surface of the porous protective layer facing the external sensing electrode of the gas sensor. The other surface portion refers to a portion including 20% or less from the other surface in relation to the thickness of the porous protective layer, including the pores included in the surface of the other surface.

Specifically, the coating of the pore-controlling agent may be performed by applying a mixed solution containing a pore-controlling agent, a binder and a solvent on one surface of the prepared porous protective layer or by immersing the porous protective layer in the mixed solution, Can be performed through penetration into the pores and heat treatment. More specifically, the mixed solution may be applied to a part of the porous protective layer, or the porous protective layer may be immersed in the mixed solution, followed by applying a pressure of 1.5 to 5 atm for 1 minute to 2 hours, followed by heat treatment at a temperature of 800 to 1700 ° C . If the heat treatment temperature is less than 800 ° C, sufficient coating of the porosity regulator may not occur in the pores of the porous protective layer, and if it exceeds 1700 ° C, the gas sensor may malfunction due to high temperature.

When the viscosity of the mixed solution of the pore-controlling agent, the binder and the solvent can be maintained to the extent that they can penetrate into the pores of the porous protective layer, the mixing ratio thereof is not limited, and the content of the pore- The particle diameter, and the pore diameter of the other surface of the desired porous protective layer.

The porosity regulator may include at least one ceramic powder selected from the group consisting of alumina, spinel, titanium dioxide, zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite. It may be desirable to select and use the same kind of particles as the porous protective layer for implementation.

In addition, it is preferable that the pore regulator has a particle size smaller than the pore diameter formed at the other surface of the porous protective layer, and the diameter of the pore regulator can be selected in consideration of the pore diameter realized in the porous protective layer, Although not particularly limited, it is preferable to use a porosity regulator having a particle diameter of 35% or less, more preferably 25% or less, and even more preferably 10% or less of the pore diameter included in the other side of the porous protective layer.

The binder can be used without limitation as long as it is a binder that easily binds the selected pore-controlling agent to the pore surface. As a non-limiting example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, Vinyl acetate, cellulose acetate, etc. may be used alone or in combination of two or more.

The solvent may be any solvent which is suitable for the dispersion of the pore-controlling agent and the dissolution of the binder. For example, ethanol, isopropyl alcohol, n-propyl alcohol and butyl alcohol may be used. Can be used.

On the other hand, in the porous protective layer for a gas sensor included in a gas sensor,

The porous protective layer for a gas sensor includes a porous protective layer for a gas sensor, which includes ceramic powder having a degree of variance of 1.5 or more, expressed by the following relational formula 1, and at least some regions of the respective ceramic powder particles are fused together.

[Relation 1]

15 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention. FIG. 15 includes an external sensing electrode 22, a reference electrode portion 40, a heater portion 60, and a tunnel electrode 70 (P) facing the outer surface of the gas sensor and a second surface (P) facing the first surface (P), covering the entire exposed outer surface of the outer sensing electrode (22) (Q). ≪ / RTI >

First, a porous protective layer 200 for a gas sensor according to the present invention includes a ceramic powder having a degree of variance of 1.5 or more as represented by the above-mentioned relational expression 1, and at least some regions of the ceramic powder particles are formed by welding to each other.

16 is a cross-sectional schematic diagram of a porous protective layer according to a preferred embodiment of the present invention, wherein at least a part of the ceramic powder particles including the ceramic powder having a deviation degree of 1.5 or more are melted and bonded to each other. At least some regions of the particles may vary depending on the shape of the particles, the size of the particles, and the positional relationship between the surrounding particles. For example, when the shape of the particle cross-section is hexagonal as shown in FIG. 10, The boundary region or the surface portion of the particle, and the volume of the partial region may be varied depending on sintering conditions such as temperature.

The porous protective layer 200 includes a ceramic powder that satisfies the conditions of the present invention, and a part of the ceramic powder particles are melted and bonded to each other. Thus, the desired pore size and pore distribution can be easily And the porous protective layer produced by increasing the bonding point or the bonding surface of the ceramic powder particles does not collapse or crack in the pores even in strong physical impact and increases the surface roughness of the porous protective layer facing the gas sensor The adhesion of the porous protective layer can be further improved and separation of the porous protective layer can be prevented.

According to a preferred embodiment of the present invention, the degree of deformation of the ceramic powder may be 1.8 to 4.2 in order to realize higher physical properties. Further, in order to realize a porous protective layer that exhibits superior physical properties, it may be a porous protective layer containing at least 50% of ceramic particles satisfying the heterogeneity condition according to the present invention. Critical significance of the content of particles satisfying the heterogeneity condition according to the present invention among the ceramic powders is the same as that described in the above-mentioned manufacturing method and is omitted.

The ceramic powder may be a particle made of a material serving as a base material of a porous protective layer for a gas sensor and can be used without limitation as long as it can protect the gas sensor from external physical / .

The specific shape of the ceramic powder is not particularly limited as long as the specific shape of the ceramic powder satisfies the relativity formula 1, but it is preferably an ellipse, a dumbbell, a polygon, a star, a horn, a grasshopper, a cross, And a dumbbell shape.

According to a preferred embodiment of the present invention, the porous protective layer may include two types of ceramic powders having different degrees of differentiation, preferably a first ceramic powder having a degree of deformation of 1.5 to 2.0 and a second ceramic powder having a degree of deformation of 3.0 to 4.2 And the second ceramic powder may be contained in a weight ratio of 1: 0.8 to 2.5. Accordingly, a porous protective layer having a uniform pore diameter, achieving a desired pore distribution, being advantageous in realizing a dense porous protective layer, and significantly improving mechanical strength such as pore collapse can be realized.

According to a preferred embodiment of the present invention, since pores having a uniform pore diameter can be included in one side of the porous protective layer (the second surface of the porous protective layer in contact with the atmosphere containing the gas to be inspected) 2, the average diameter of the pores included in the surface is 5.5 to 8 占 퐉, and the pores having the pore diameter of the average diameter of 占 2 占 퐉 may be 80% or more of the total pores included in the second surface. Accordingly, the ability of blocking the porous protective layer against poisoning substances, liquids, and the like can be improved, and deterioration of the performance of the gas sensor can be prevented.

Meanwhile, according to a preferred embodiment of the present invention, the average diameter ratio of the pores included in the second surface of the porous protective layer may be 1.8: 6, more preferably, Can be 1: 2.0-4. When the average diameter of the pores included in the first surface and the second surface has such a diameter ratio, the porous protective layer can sufficiently block the penetration of the liquid material into the gas sensor, The damage caused by the liquid material of the gas sensor can be effectively suppressed and the measurement gas can be smoothly supplied to the gas sensor. Therefore, the measurement gas concentration can be more accurately measured.

According to a preferred embodiment of the present invention, the porous protective layer may have an average porosity per unit volume of 20 to 60%, preferably 30 to 50%.

Also, according to a preferred embodiment of the present invention, the porous protective layer may have an average pore diameter of 5.95 to 42 탆, preferably 16 to 32 탆.

Meanwhile, the present invention includes an electrode for a gas sensor including a porous protective layer for a gas sensor according to the present invention.

The electrode is included in a conventional gas sensor and may be an external sensing electrode of a gas sensor in contact with the gas to be inspected. The shape, thickness, size, and material of the electrode are not particularly limited in the present invention.

The porous protective layer may be formed to cover the entire one surface of the electrode, and the thickness may be 20 to 200 mu m. According to a preferred embodiment of the present invention, the thickness of the porous protective layer 200 formed on at least one surface of the gas sensor 100 may be 20 탆 to 200 탆, preferably 50 탆 to 100 탆. That is, liquid materials such as water and / or oil that can cause cracks of the gas sensor may penetrate into the pores of the porous protective layer 200. In the surface of the gas sensor of the present invention, (200) is formed to a thickness of 20 mu m or more, so that the liquid materials can be dispersed before being contacted with the gas sensor. In other words, the porous protective layer 200 can not sufficiently protect the gas sensor from external impact and liquid matter if it is formed on the surface of the gas sensor with a thickness of less than 20 mu m. 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 also includes a gas sensor including an electrode for a gas sensor according to the present invention.

17 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention. In FIG. 17, a porous protective layer (not shown) is formed so as to cover the entire upper surface of one surface including the external sensing electrode 22 'included in the gas sensor 100' 200 'are formed. In general, the gas sensor can be used without limitation in the case of a gas detecting sensor, and the present invention is not particularly limited in the specific detection method and structure.

The present invention also includes a gas sensor comprising a porous protective layer according to the present invention.

The gas sensor can be normally used without limitation in the case of a sensor for detecting a gas, and there is no particular limitation on the gas detection method, but it is preferably an electrochemical method (solution conduction method, electrostatic potential method, diaphragm electrode method) (Hydrogen ionization method, thermal conduction method, contact combustion method, semiconductor method). There is no limitation on the gas to be detected and the number of gas sensors used for detecting a gas composed of any one or more of C, H, O and N such as H ₂ , CO, NO _x , SO _x , NH ₃ and VOCs have. Hereinafter, the stacked type gas sensor will be specifically described, but the type of the gas sensor is not limited thereto.

18 is an exploded perspective view of a stacked type gas sensor according to a preferred embodiment of the present invention. The gas sensor 100 includes an electrode sensing unit 20, a reference electrode unit 40, and a heater unit 60, And the lower layer may be stacked in order.

The electrode sensing unit 20 may include an external sensing electrode 22 and a sensor sheet 24 as a part capable of measuring an electromotive force difference due to a concentration difference of a measurement gas.

The external sensing electrode 22 is stacked on top of the gas sensor 100, and can oxidize and / or reduce a specific measurement gas. The outer sensing electrode 22 may be made of various electrode materials having electrical conductivity, and preferably platinum, zirconia, and / or a platinum / zirconia mixture may be used as the material.

The sensor sheet 24 may be laminated under the external sensing electrode 22 to move a specific measurement gas oxidized and / or reduced in the external sensing electrode 22. The sensor sheet 24 may be made of various materials having high temperature ionic conductivity and high temperature durability, and preferably zirconia can be used as a material.

The reference electrode portion 40 may include insulating layers 42 and 46, an internal reference electrode 44, and a reference sheet 48 as portions capable of collecting specific measurement gas ions, The insulating layer 42, the internal reference electrode 44, the insulating layer 46, and the reference sheet 48 may be stacked in order from the top to the bottom.

The insulating layers 42 and 46 serve to isolate a heater electrode 64 and an electrode sensing unit 20, which will be described later. The insulating layer 42, 46 may be made of various materials having insulating properties, and alumina may preferably be used.

The internal reference electrode 44 serves to collect specific measurement gas ions. The internal reference electrode 44 may be made of various electrode materials having electrical conductivity, and preferably platinum, zirconia, and / or a platinum / zirconia mixture may be used as the material.

The reference sheet 48 can move heat generated in the heater unit 60. The reference sheet 48 may be made of various materials having thermal conductivity and high temperature durability, and preferably zirconia can be used as a material.

The heater 60 heats the external sensing electrode 22 of the electrode sensing unit 20 to a temperature at which ion conductivity is imparted to the heater unit 60. The heater unit 60 includes insulating layers 62 and 66, The heater electrode 64, the insulating layer 66, the tunnel sheet 68, and the tunnel electrode 70 may be formed on the upper side To the lower portion in order.

The insulating layers 62 and 66 of the heater unit 60 may be the same as or different from the insulating layers 42 and 46 of the reference electrode unit 40.

The heater electrode 64 generates heat to heat the external sensing electrode 22 to a temperature at which ion conductivity is imparted. The heater electrode 64 may be made of a variety of materials having exothermic properties by supplying electric resistive power and preferably platinum, alumina, lead, a platinum / lead mixture and / or a platinum / have.

The tunnel sheet 68 serves to insulate the stacked type gas sensor 100 excluding the tunnel electrode 70 and the tunnel electrode 70. The tunnel sheet 68 may be made of various materials having insulating properties, and preferably alumina can be used.

The tunnel electrode 70 connects the gas sensor 100 and an external terminal for supplying power to the gas sensor 100. The tunnel electrode 70 may be made of various materials having conductivity, and preferably platinum, alumina, and / or a platinum / alumina mixture may be used.

The gas sensor including the porous protective layer according to the present invention covers at least one surface of the gas sensor 100, preferably one surface including the external sensing electrode, according to the above-described porous protective layer according to the present invention. The porous protective layer 200 covers the upper, lower, left, and right slopes of the gas sensor 100 and the porous protective layer 200 'covers the external sensing electrode 22' May be formed so as to cover only the upper portion of one surface of the gas sensor 100 'and the portion covering the outer surface of the gas sensor other than the one surface including the external sensing electrode may be selected differently depending on the purpose.

According to a preferred embodiment of the present invention, the thickness of the porous protective layer 200 formed on at least one surface of the gas sensor 100 may be 20 탆 to 200 탆, preferably 50 탆 to 100 탆.

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 >

10 g of zirconia powder having a hexagonal cross section as shown in Fig. 10, 12 g of polyvinyl butyral as a binder component, 12 g of butyl alcohol as a solvent And 30 g of graphite having a diameter of 5 탆 as a pore forming agent were coated on four sides of a stacked type oxygen gas sensor including a platinum outer sensing electrode having the structure shown in Fig. 18 so that the average thickness after sintering became 70 탆 , The temperature was raised to 800 ° C., and the pore-forming agent was removed by oxidation at 800 ° C. for 1 hour. Thereafter, the temperature was raised to 1450 ° C. and maintained for 3 hours to prepare a gas sensor including the porous protective layer as shown in Table 1 .

≪ Examples 2 to 9 &

A gas sensor including a porous protective layer as shown in Tables 1 and 2 was fabricated in the same manner as in Example 1 except that the degree of deformation of the ceramic powder was changed as shown in Table 1 below.

≪ Examples 10 to 12 >

A gas sensor having the porous protective layer formed in Example 1 was produced in the same manner as in Example 1 except that a mixed solution of zirconia, butyl alcohol and polyvinylidene fluoride having a particle size of 0.8 μm (100 parts by weight of butyl alcohol 20 parts by weight of polyvinylidene fluoride and 50 parts by weight of zirconia powder, respectively, and 150 parts by weight of zirconia powder, respectively), followed by pressurization at 4 atm for 20 minutes, followed by heat treatment at 1300 ° C for 3 hours, A gas sensor including a porous protective layer was prepared.

≪ Comparative Examples 1 and 2 &

A gas sensor including a porous protective layer as shown in Table 2 below was prepared by changing the deformation degree of the ceramic powder as shown in Table 1 below.

≪ Comparative Example 3 &

A gas sensor including the porous protective layer as shown in Table 2 below was prepared without conducting the preparation of the binder component.

<Experimental Example 1>

The following physical properties of the gas sensor including the porous protective 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 protective 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% After photographing, the average diameter and porosity of the pores contained 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 temperature of the gas sensor was set at 800 DEG C, and 10 mu g of water drops were applied to the porous protective layer 20 times. After the dropwise addition, the porous protective layer was peeled off and the presence or absence of cracks in the gas sensor was observed with an optical microscope by red check (a method of applying a red permeation liquid to the surface) The results are shown as 1 ~ 5.

3. Evaluation of gas sensor output

The gas sensor output was measured under the condition that the temperature of the gas sensor was set to 700 DEG C, and the rate of change of the gas sensor output was calculated by the following equation (1). The closer the rate of change of the gas sensor output is to zero, the smaller the gas diffusion resistance of the porous protective layer and the more smooth gas can be supplied to the gas sensor. As the base gas sensor, a stacked type oxygen gas sensor not including a porous protective layer was used.

4. Evaluation of strength of porous protective layer

For the strength of the porous protective layer, it was evaluated whether or not the porous protective layer was adhered to the blue tape when the blue tape was detached after attaching the blue tape (Duct tape 3015, 3M) to the top of the porous protective layer. The case where the porous protective layer was not observed at all was denoted as 0, and the more dense the protective layer was denoted as 1 to 5.

5. Assessment of gas sensor surface damage

After separating the porous protective layer from the gas sensor, the surface of the gas sensor was observed under an optical microscope to evaluate whether the gas sensor was damaged due to the porous protective layer. As a result of observing, when there is no damage such as pressing or scratching of the surface of the gas sensor, it is represented as 0, and as the degree is greater, 1 to 5 is shown.

Specifically, as can be seen from Tables 1 and 2,

It can be seen that Examples 1 to 9 including a ceramic powder having a mold release degree of 1.5 or more produced less cracks in the gas sensor than Comparative Examples 1 and 2, and the gas sensor output was excellent and the strength of the porous protective layer was remarkably good.

In addition, it can be seen that the gas sensor of Comparative Example 3 including the porous protective layer produced without the pore-forming agent is not significantly improved in terms of cracking, performance, and strength of the sensor.

In Examples 1 to 5, the performance of the gas sensor was improved as the degree of degeneration of the ceramic powder was increased. However, in Example 4 using the ceramic powder having a mold release ratio of 4.2, Powder according to Example 5, conversely, it is confirmed that the high degree of dissociation damages the electrode on the surface of the gas sensor, and thus the performance of the gas sensor is somewhat deteriorated.

In Examples 6 to 8 using ceramic powders having different degrees of dissimilarity, Example 6, in which the first ceramic powder and the second ceramic powder were included in the weight ratio range according to the present invention, It can be confirmed that the performance of the sensor is good and the occurrence of cracks in the gas sensor is reduced.

In addition, in the case of the gas sensor of Example 9 in which the ceramic powder having a mold release degree of 1.5 or more contained 40% by weight of the total ceramic powder, the occurrence of cracks was remarkably increased, the output of the gas sensor was remarkably increased and the strength of the porous protective layer was also lowered can confirm.

Also, as can be seen from Table 3,

In Examples 10 to 12, in which the pore diameter of the first surface of the porous protective layer and the pore diameter of the second surface were adjusted, the gas sensor of Example 11 had a diameter gradient increasing in diameter toward the first surface side , The output of the gas sensor is excellent, the second surface portion contacting the atmosphere is dense, the strength is improved, and the surface of the gas sensor is not damaged. On the other hand, in the gas sensor of the tenth embodiment, it is confirmed that the diameter of the pore becomes weaker toward the first surface side, so that a crack is generated. In the gas sensor of the twelfth embodiment, the output of the gas sensor is remarkably decreased.

Claims (20)

(1) introducing a porous protective layer-forming composition comprising a ceramic powder and a pore-forming agent onto a gas sensor; And
(2) sintering the porous protective layer-forming composition charged on the gas sensor,
Wherein the ceramic powder comprises particles having a degree of variability of 1.5 to 4.2 represented by the following relational expression (1).
[Relation 1]

The method according to claim 1,
The ceramic powder is _{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. The} method of manufacturing a porous protective layer for a gas sensor according to claim 1, The method according to claim 1,
The method of manufacturing a porous protective layer for a gas sensor according to claim 1, wherein the degree of deformation of the ceramic powder in the step (1) is 1.8 to 4.2. The method according to claim 1,
The method for producing a porous protective layer for a gas sensor according to any one of claims 1 to 3, wherein the ceramic powder satisfying the above-mentioned separation-type condition is at least 50% by weight of the total ceramic powder. The method according to claim 1,
Wherein the cross-sectional shape of the ceramic powder satisfying the above-described dissimilarity condition is at least one of elliptical shape, dumbbell shape, polygonal shape, star shape, horn shape, otter shape, cruciform shape, star shape, alphabet shape, groove shape and dumbbell shape. Gt; The method according to claim 1,
The ceramic powder of the step (1) comprises a first ceramic powder having a degree of deformation of 1.5 to 2.0 and a second ceramic powder having a degree of deformation of 3.0 to 4.2,
Wherein the weight ratio of the first ceramic powder to the second ceramic powder is 1: 1.6 to 3.0. The method according to claim 1,
Wherein the pore former is selected from the group consisting of a polymer of monomers selected from the group consisting of radically polymerizable monomers, multifunctional crosslinking monomers, and combinations thereof, radical polymerizable monomers, multifunctional crosslinking monomers, and combinations thereof microemulsion polymer beads of the monomer; silicon dioxide (SiO _2), titanium dioxide (TiO- ₂₎ and an oxide selected from the group consisting of;, carbon water is selected from carbon, carbohydrates and combinations thereof ; And a mixture thereof. The method of manufacturing a porous protective layer for a gas sensor according to claim 1, The method according to claim 1,
Wherein the sintering temperature in the step (2) is 800 to 1700 占 폚. In the porous protective layer for a gas sensor contained in a gas sensor,
Wherein the porous protective layer for a gas sensor comprises a ceramic powder having a degree of variance of 1.5 to 4.2 represented by the following relational formula 1 and at least some regions of the ceramic powder particles are fused to each other to form a porous protective layer for a gas sensor .
[Relation 1]

10. The method of claim 9,
Wherein the ceramic powder comprises at least one particle selected from the group consisting of alumina, spinel, titanium dioxide, zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite. layer. 10. The method of claim 9,
Wherein the ceramic powder has a degree of deformation of 1.8 to 4.2. 10. The method of claim 9,
Wherein the porosity of the porous protective layer is 20 to 60%. 10. The method of claim 9,
Wherein the average pore diameter of the porous protective layer is 5.5 to 42 占 퐉. 10. The method of claim 9,
Wherein the porous protective layer comprises a first surface facing a first surface of the gas sensor outer electrode and a second surface opposite to the first surface and a diameter gradient increasing from the second surface to the first surface And a porous protective layer for a gas sensor. 15. The method of claim 14,
Wherein the average pore diameter of the pores contained in the second surface of the porous protective layer is 5.5 to 8 占 퐉 and the pores having the pore diameter of the average diameter of 占 퐉 are not less than 80% And a porous protective layer for a gas sensor. 15. The method of claim 14,
Wherein the average diameter ratio of the pores included in the second surface of the porous protective layer and the pores included in the first surface is 1: 1.8 to 6. An electrode for a gas sensor comprising a porous protective layer for a gas sensor according to any one of claims 9 to 16. 18. The method of claim 17,
Wherein the porous protective layer has a thickness of 20 to 200 占 퐉. A gas sensor comprising an electrode for a gas sensor according to claim 17 as an external sensing electrode. A gas sensor comprising a porous protective layer for a gas sensor according to any one of claims 9 to 16.

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