KR101727078B1 - 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 forming the same, and a gas sensor including the porous protective layer. 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 from an external factor, and enable measurement of the target gas concentration more quickly and accurately, a method for forming the same, .

Description

TECHNICAL FIELD [0001] The present invention relates to a porous protective layer for a gas sensor, a method of forming 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 formed on the surface of a gas sensor, a method of forming 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 not only protects the gas sensor from the above-mentioned liquid and poisoned substances, but also protects the gas sensor from external impact and is made of a porous material so that the gas sensor can sense the measuring gas.

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 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 forming the same.

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

In order to solve the above-described first problem, the present invention provides a porous protective layer for a gas sensor, comprising a through-hole penetrating a first surface facing a sensing electrode and a second surface facing the first surface, .

According to a preferred embodiment of the present invention, the average diameter of the through pores may be 5.5 to 42 탆.

According to another preferred embodiment of the present invention, the average porosity per unit volume of the porous protective layer may be 20 to 60%.

According to another preferred embodiment of the present invention, the penetrating pores may be larger in diameter from the second surface to the first surface of the porous protective layer.

According to another preferred embodiment of the present invention, the ratio of the diameter of the second surface to the diameter of the first surface of the porous protective layer may be 1: 1.8-6.

In order to solve the above-described first problem, the present invention provides a method of manufacturing a sensing electrode, comprising the steps of: (1) heating a composition comprising a porous formed body and a low melting point short fiber provided on a sensing electrode to dissolve low melting point staple fibers to form pores And (2) firing the composition in which the low melting point staple fiber is removed to form a porous protective layer.

According to a preferred embodiment of the present invention, the low melting point staple fibers may pass through a first surface facing the sensing electrode of the porous protective layer and a second surface facing the first surface.

According to another preferred embodiment of the present invention, the low melting point staple fiber is disappeared to form through pores passing through the first surface and the second surface of the porous protective layer, and the average diameter of the through pores is 5.5 to 42 Lt; / RTI >

According to another preferred embodiment of the present invention, the low melting point staple fiber may have a fineness of 0.5 to 5 denier.

According to another preferred embodiment of the present invention, the fineness of the low melting point staple fibers can be reduced from one end to the other end.

According to another preferred embodiment of the present invention, the low melting point staple fiber is disappeared to form through pores having a larger diameter from the second surface to the first surface of the porous protective layer.

According to another preferred embodiment of the present invention, the ratio of the diameter of the second surface to the diameter of the first surface of the porous protective layer may be 1: 1.8-6.

According to another preferred embodiment of the present invention, the low-melting-point staple fiber may be a polyester-based fiber having a melting point of 70 to 150 ° C.

According to another preferred embodiment of the present invention, the firing temperature in the step (1) may be 200 to 400 ° C, and the firing temperature in the step (2) may be 1100 to 1800 ° C.

According to another preferred embodiment of the present invention, the porous formed body is composed of alumina, spinel, titanium dioxide, zirconia, yttrium stabilized zirconia, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cerium oxide and mullite And the like.

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.

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.

1 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention.
2 is a cross-sectional view of a porous protective layer for a gas sensor according to a preferred embodiment of the present invention.
3 is an exploded perspective view of a gas sensor according to a preferred embodiment of the present invention.

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

FIG. 1 is a cross-sectional view of a gas sensor according to a preferred embodiment of the present invention. Referring to FIG. 1, a gas sensor 100 includes a sensing unit including an external sensing electrode 22 and a reference electrode unit 40, A first surface P facing the outer surface of the gas sensor and an outer surface covering the outer surface of the gas sensor 100 including the portion 60 and the tunnel electrode 70, 2 surface (Q).

Specifically, the porous protective layer 200 for a gas sensor according to the present invention may be formed to cover all of the upper portions of the external sensing electrodes 22 included in the gas sensor 100. In other words, the porous protective layer 200 of the present invention protects the external sensing electrode 22 located at the top of the gas sensor 100 from external physical impact and physical / chemical external factors such as liquid and poisonous substances in the gas under test can do.

The porous protective layer of the present invention will be described in more detail with reference to FIG.

2, the porous protective layer 200 for a gas sensor of the present invention includes a first surface P facing the sensing electrode and a second surface Q opposed to the first surface P, Through pores (80). In this case, the through pores 80 mean a structure in which pores are not blocked, and the sensing electrode may include an external sensing electrode 22 as an electrode included for sensing a gas to be inspected of the gas sensor.

In other words, the porous protective layer 200 for a gas sensor of the present invention has a structure in which the through pores 80 penetrate the second surface Q and the first surface P, that is, the through pores of the porous protective layer 200 (80) is formed in a direction perpendicular to the surface of the sensing electrode contacting the first surface (P), so that gas permeability can be obtained only in a direction perpendicular to the surface of the sensing electrode.

In other words, it is possible to prevent the penetration of the exhaust gas which can permeate from the horizontal direction to the surface of the sensing electrode, and to supply a proper amount of target gas to the gas sensor while keeping the diffusion distance of the target gas to be measured constant in the exhaust gas So that the target gas concentration can be measured more quickly and accurately.

The average diameter of the through pores 80 may be 5.5 to 42 탆, preferably 5.95 to 35 탆, and more preferably 16 to 30 탆. If the average diameter of the through pores 80 is less than 5.5 占 퐉, the gas permeability to the porous protective layer 200 lowers and the supply and / or discharge of the target gas to the gas sensor is difficult to proceed smoothly The output of the gas sensor can be reduced. If the thickness exceeds 42 탆, the liquid and poisonous substances in the exhaust gas, which can permeate into the through pores 80, can penetrate into the porous protective layer 200 and reach the gas sensor It may be difficult to protect the gas sensor from such a material, and it may become difficult to measure the target gas concentration more accurately because it is difficult to supply an appropriate amount of the target gas to the gas sensor.

On the other hand, the diameter of the through pores 80 may become larger from the second surface Q of the porous protective layer 200 toward the first surface P. For example, if the diameter of the through pores 80 of the second surface Q is 16 占 퐉, the diameter of the through pores 80 of the first surface P may be 20 占 퐉 larger than 16 占 퐉.

The reason why the through pores 80 are formed to have a larger diameter toward the first surface P from the second surface Q of the porous protective layer 200 is as follows.

First, when the diameter of the first surface P is large, the total volume of the through pores 80 of the first surface P becomes large, and the heat insulating property is given. When the second surface (Q) is cooled by the liquid material as described above, the gas sensor is hardly quenched due to the heat insulating property of the first surface (P), and damage due to the liquid material can be effectively suppressed.

Secondly, the diffusion rate of the gas passing through the porous protective layer 200 is affected not only by the average porosity per unit volume of the porous protective layer 200, but also by the diameter of the through pores 80. For example, when the diameter of the through pores 80 is large, a plurality of gas molecules are gathered into the through pores 80, and the diffusion resistance to diffuse while colliding with each other becomes small, and the diffusion speed becomes large. On the other hand, if the diameter of the through pores 80 is small, the diffusion resistance for diffusing the gas molecules into the through pores 80 and colliding with each other becomes small, and the diffusion rate becomes small. Accordingly, when the diameter of the through pores 80 increases from the second surface Q to the first surface P, the pores of the first surface P become higher than the porosity of the second surface Q The gas diffusion resistance from the second surface Q to the first surface P is greatly reduced.

The porous protective layer 200 of the present invention has a small diameter of the through pores 80 of the second surface Q so that the penetration of the liquid material can be sufficiently blocked, The diameter of the through pores 80 of the gas sensor 80 can be increased and the heat insulating property can be imparted so that damage caused by the liquid material of the gas sensor can be effectively suppressed and a smooth target gas can be supplied to the gas sensor, The concentration can be measured.

Further, the through pores 80 may have a ratio of the diameter of the second surface Q of the porous protective layer 200 to the diameter of the first surface P of 1: 1.8 to 6, preferably 1: 2.0 to 4 have. When the diameter of the first surface and the second surface pore have such a diameter ratio, the porous protective layer 200 can sufficiently block the penetration of the liquid material into the gas sensor, and the first surface P 2 is larger than the diameter of the through pores 80 of the surface Q so that the gas sensor can be provided with a heat insulating property so that damage caused by the liquid material of the gas sensor can be effectively suppressed and the target gas can be smoothly supplied to the gas sensor, The damage caused by the liquid material of the sensor can be effectively suppressed.

Meanwhile, the porous protective layer 200 of the present invention 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 protective layer 200 is less than 20%, the gas permeability is lowered and the supply and / or discharge of the target gas to the gas sensor is difficult to proceed smoothly, If it is more than 60%, the mechanical strength may be remarkably lowered, and the pores may be collapsed, cracked or peeled off.

Further, the present invention relates to a porous protective layer for a gas sensor according to the present invention; And an electrode for a gas sensor.

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 to a thickness of less than 20 mu m. In addition, if it is formed to have 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 target gas concentration more quickly and accurately.

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.

3 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 a sensing unit including the electrode sensing unit 20 and the reference electrode unit 40, 60 may be stacked in order from the top to the bottom.

The electrode sensing unit 20 may include an external sensing electrode 22 and a sensor sheet 24 that can measure and / or sense a difference in electromotive force 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 or yttrium stabilized zirconia may be used as the material.

The reference electrode portion 40 may include an insulating layer 42, 46, an internal reference electrode 44, and a reference sheet 48, which can collect and / or sense a specific target gas ion. Preferably, 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 trap and / or sense a particular target gas ion. 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 can be made of various materials having thermal conductivity and high temperature durability, and preferably zirconia or yttrium stabilized 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 remaining gas sensors 100 except for 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 serves to connect an external terminal for supplying power to the gas sensor 100 and 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, preferably one surface including the external sensing electrode, according to the above-described porous protective layer according to the present invention. Specifically, The porous protective layer 200 may be formed so as to cover only the upper portion of one surface of the gas sensor 100 including the external sensing electrode 22 and may be configured to cover the upper surface of the gas sensor 100 including the external sensing electrode 22, The portion covering the outer surface can be selected differently.

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

Furthermore, the present invention provides a method for forming a porous protective layer.

First, in the method of forming a porous protective layer of the present invention, the composition including the porous formed body and the low melting point short fiber provided on the sensing electrode is heated in step (1) to form pores by eliminating the low melting point short fibers.

First, the composition of step (1) may be put on the sensing electrode before heating. The sensing electrode is an electrode included for sensing the gas to be inspected of the gas sensor. As mentioned above, the gas sensor can be used without limitation in the case of a sensor that normally detects gas.

Also, the sensing electrode phase is inserted to face at least one side of the sensing electrode, and includes another layer on at least one side of the sensing electrode, such that the composition faces the other layer.

The method of applying the composition onto the sensing electrode may vary depending on the properties of the composition and the specific method of placing the composition on the surface of the sensing electrode. If the composition is in powder form, And if the composition is a liquid paste, the paste can be placed in such a manner as to be applied on the sensing electrode.

In the case of using the vacuum powder spraying method at room temperature, a method known in the art can be used. In a non-limiting method, first, the composition is introduced into a powder container, a gas sensor is attached to the deposition chamber, A process of supplying a carrier gas from a carrier gas cylinder located inside the cylinder can be performed. 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.

When the composition is applied on a sensing electrode in the form of a liquid, the composition may further include a binder component and a solvent. The binder component serves to further improve the adhesive force between the porous protective layer and the composition, which is produced on the sensing electrode surface, preferably the external sensing electrode, through the step (2) described later. As a non-limiting example, a binder component commonly used in the art may be used. Examples of the binder component include polyvinyl, ethylcellulose, polyester, epoxy, terpineol such as polyvinyl butyral, 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 be contained in an amount of 8 to 26 parts by weight based on 100 parts by weight of the porous formed body and 20 to 50 parts by weight of the solvent. When the binder component is contained in an amount of less than 8 parts by weight, the adhesion between the sensing electrode and the porous protective layer to be produced is weakened, so that the porous protective layer is separated from the sensing electrode, or the bonding force between the porous forming body and / or the porous forming body and the low- If the porous protective layer is contained in an amount exceeding 26 parts by weight, the porous protective layer may be cracked due to a decrease in mechanical strength, The shrinkage ratio is increased and a desired thickness may cause a problem that formation of the porous protective layer becomes difficult.

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.

In the step (1), the dissolution temperature may be 200 to 400 ° C, preferably 300 to 400 ° C. The composition is heated at such a temperature to dissolve the low melting point staple fibers to form pores.

Next, the low melting point staple fibers contained in the composition will be described.

First, the low-melting-point staple fiber acts as a pore-forming agent in the composition. By heating the low-melting staple fiber, the low-melting staple fiber disappears and pores are formed in the lost portion.

In general, resin balls are used as a pore forming agent. When forming pores by using a resin ball, a window between the pores formed through the resin balls can not be formed, and the pores may be clogged have. In addition, the pores may not be opened on the surface of the porous protective layer due to the surface tension of the composition including the resin balls.

In order to solve such a problem, in the present invention, low melting point staple fibers can be used as a pore-forming agent.

The low melting point staple fibers may pass through a first surface facing the sensing electrode of the porous protective layer and a second surface facing the first surface.

The low-melting-point staple fibers thus formed disappear to form through pores passing through the first surface and the second surface of the porous protective layer, and the average diameter of the through pores formed is 5.5 to 42 탆, preferably 5.95 to 35 Mu] m, more preferably from 16 to 30 [mu] m.

The low melting point staple fibers may have a fineness of 0.5 to 5 denier, preferably 0.8 to 3 denier, and more preferably 1.0 to 2.0 denier. As mentioned above, the through pores are formed by eliminating the low melting point staple fibers. By including the low melting staple fibers having the fineness as described above in the composition, the through pores have an average diameter of 5 탆 to 40 탆, preferably 5.95 탆 To 35.9 占 퐉, and more preferably from 16 占 퐉 to 24 占 퐉.

In other words, when the fineness of the low melting point staple fiber is less than 0.5 denier, the average diameter of the through pores formed by disappearance of the low melting point staple fibers can be formed to be less than 5 탆, and the gas permeability of the porous protective layer is lowered The output of the gas sensor can be reduced as the supply and / or discharge of the target gas to the gas sensor is difficult to smoothly proceed, and when the fineness of the low melting point staple fiber exceeds 5 denier, The average diameter of the through pores formed by the short fibers disappearing can be formed to be larger than 40 mu m so that the liquid material and the poisonous substance in the exhaust gas that can permeate through the through pores penetrate into the porous protective layer and reach the gas sensor It may be difficult to protect the gas sensor from such a material, and it may be difficult to measure the target gas concentration more accurately because it is difficult to supply a proper amount of the target gas to the gas sensor The.

On the other hand, the fineness staple fibers may have a smaller fineness from one end to the other end. By using such low melting point staple fibers, the through pores formed by disappearance of the low melting point staple fibers can be formed to have a larger diameter from the second surface to the first surface of the porous protective layer.

Specifically, one end of the low melting point staple fiber having a large fineness is located on the first surface of the porous protective layer, and the other end thereof having a small fineness is located on the second surface of the porous protective layer, and the low melting point staple fiber is disappeared to form through pores , The through pores can be formed to have a larger diameter as the porous protective layer moves from the second surface to the first surface.

As mentioned above, the diameter of the through-pores of the porous protective layer of the present invention is increased from the second surface to the first surface because the diameter of the through-pores of the second surface is small, And the diameter of the through pores of the first surface is large, so that it is possible to impart heat insulation, thereby effectively suppressing the damage caused by the liquid material of the gas sensor, and to provide a smooth target gas to the gas sensor, It is possible to accurately measure the target gas concentration.

Further, the through pores may have a ratio of the diameter of the second surface of the porous protective layer to the diameter of the first surface of 1: 1.8 to 6, preferably 1: 2.0 to 4. When the diameter of the first surface and the second surface pore has such a diameter ratio, the porous protective layer can sufficiently block the penetration of the liquid material into the gas sensor, and the first surface has a larger diameter than the through pores of the second surface It is possible to effectively provide the gas sensor with the target gas, and it is possible to effectively suppress the damage caused by the liquid material of the gas sensor have.

On the other hand, the fiber having a fiber length longer than the average thickness of the porous protective layer may be used as the low melting point staple fiber. As described above, since the low melting point staple fibers are fired to form through pores passing through the first and second surfaces of the porous protective layer, if the fiber length of the low melting point staple fibers is shorter than the average thickness of the porous protective layer, It is difficult to form through pores passing through the first surface and the second surface of the substrate. For example, when the average thickness of the porous protective layer is 100 mu m, the fiber length of the low melting point staple fibers may be at least 100 mu m or more.

Further, the low melting point staple fibers may be polyester fibers having a melting point of 70 to 150 ° C, preferably 80 to 120 ° C.

As mentioned above, in the above step (1), the disintegration temperature of the low melting point staple fibers may be 200 to 400 ° C., preferably 300 to 400 ° C. At this time, the disintegration temperature of the low melting staple fibers If the melting point exceeds 150 ° C, incomplete combustion or pyrolysis reaction may occur in the disappearance reaction and carbonization may occur to generate amorphous carbon. This may lead to incomplete pore generation. For example, if a through-hole is formed with a polyethylene terephtalalate (PET) fiber having a melting point of 250 to 280 ° C, the polyetylene terephtalalate (PET) fiber is partially carbonized due to pyrolysis reaction, It is possible to prevent the flow of the measurement gas smoothly to the through pores.

On the other hand, if the low melting point staple fiber is contained in an amount of 25 to 60 parts by weight based on 100 parts by weight of the porous forming material, if the low melting staple fiber is contained in an amount of less than 25 parts by weight, the average porosity per unit volume of the porous protective layer The output of the gas sensor can be reduced, and if it exceeds 60 parts by weight, it is difficult to form the porous protective layer. .

Next, the porous formed body included in the composition will be described as follows.

The porous formed body is a part constituting the basic skeleton of the porous protective layer and has porosity and can protect the gas sensor from external physical / chemical factors.

The porosity of the porous formed body can be controlled by controlling the average porosity per unit volume of the pores having a desired diameter and the desired porous protective layer, Zirconium oxide, zirconium oxide, yttrium oxide, lithium oxide, calcium oxide, magnesium oxide, cesium oxide and mullite, preferably at least one selected from alumina, spinel, zirconia and yttrium stabilized zirconia can do.

Next, the method for forming a porous protective layer of the present invention includes a step of firing a composition in which the low melting point staple fiber is removed in step (2) to form a porous protective layer.

The firing in the step (2) may be performed at a temperature of preferably 1,100 to 1,800 ° C, more preferably 1,200 to 1,700 ° C, and still more preferably 1,300 to 1,600 ° C under an atmosphere of air and / or nitrogen. If it is carried out at less than 1100 ° C, it may be difficult to realize a porous protective layer having a desired porosity and pore diameter. If the temperature is higher than 1800 ° C, the gas sensor may be damaged by heat.

When zirconia or yttrium-stabilized zirconia is used as the porous body in the present invention, the calcination proceeds in an air atmosphere in step (2), and if it is carried out under a nitrogen atmosphere, blackening ) May occur. In addition, if the firing temperature is lower than 1100 ° C, zirconia or yttrium-stabilized zirconia may be microscopically damaged, resulting in a problem of mechanical strength deterioration.

The firing can be performed for 20 minutes to 5 hours, but the firing time is not limited thereto.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood that various changes and modifications may be made without departing from the scope of the present invention. For example, each component specifically illustrated in the embodiments of the present invention can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

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

Example  One

(1) 70 g of yttrium-stabilized zirconia powder, 12 g of polyvinyl butyral as a binder component, 25 g of butyl alcohol as a solvent, and 5 g of polyetylene terephthalalate (PET) fiber having a fineness of 0.5 denier and a fineness of 3 Denier, melting point 90 DEG C, fiber length 100 mu m) was applied onto a sensing electrode of a stacked type oxygen gas sensor including a platinum sensing electrode having the structure shown in Fig. 2, and then heated to 300 DEG C, The fibers were lost.

The low melting point staple fiber of the composition is designed so that one end is located on the first surface facing the sensing electrode and the other end is located on the second surface facing the first surface.

(2) The composition having the low melting point staple fiber disappeared was fired at 1450 占 폚 to prepare a gas sensor including the porous protective layer as shown in Table 1 so that the average thickness after firing was 70 占 퐉.

Example  2 to 10

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 types of PET fibers were changed as shown in Tables 1 and 2.

Comparative Example  1-2

A gas sensor including a porous protective layer as shown in Table 3 below was prepared by changing the kind of PET fibers as shown in Table 3.

Comparative Example  3 to 4

The same procedure as in Example 1 was carried out except that the types of PET fibers were changed as shown in Table 3 and the low melting point staple fibers of the composition were designed to be positioned horizontally with the sensing electrodes.

Experimental Example  One

The following properties of the gas sensor including the porous protective layer prepared through the above Examples and Comparative Examples were measured and shown in Table 1.

1. Measurement of pore diameter, carbide formation of pores and average porosity per unit volume

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 of the pores included in the area of 100 mu m x 100 mu m, the presence or absence of carbide formation of the pores, and the average porosity per unit volume were measured.

2. Whether the gas sensor is cracked or not

With the temperature of the gas sensor at 800 占 폚, 10 占 퐇 of water drops were dripped twice onto the porous protective layer. 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.

division Example
One Example
2 Example
3 Example
4 Example
5 PET fiber A piece of fineness 0.5D 0.5D 0.5D 0.5D 1D The other end 3D 2.5D 2D 1.5D 3D Melting point 90 ° C 90 ° C 90 ° C 90 ° C 90 ° C

The porous protective layer Second Surface pore average diameter 5.8 탆 5.8 탆 5.8 탆 5.8 탆 11.1 탆 First surface pore average diameter 34.22 탆 27.84 탆 22.62 탆 17.98 탆 32.19 탆 Second surface pore average diameter:
First surface pore average diameter 1: 5.9 1: 4.8 1: 3.9 1: 3.1 1: 2.9 Average porosity per unit volume 41% 39% 37% 35% 43% Carbide formation of pores × × × × × gas
sensor Crack occurrence One One One One 2 Evaluation of output of gas sensor -3.1 -2.9 -2.3 -1.9 -2.1

division Example
6 Example
7 Example
8 Example
9 Example
10 PET fiber A piece of fineness 1D 1.5D 0.5D 1.5D 3D The other end 2D 3D 4D 1.5D 3D Melting point 90 ° C 90 ° C 90 ° C 90 ° C 90 ° C

The porous protective layer Second surface pore average diameter 11.1 탆 17.2 탆 5.8 탆 17.98 탆 32.19 탆 First surface pore average diameter 22.61 탆 30.96 탆 44.66 탆 17.98 탆 32.19 탆 Second surface pore average diameter:
First surface pore average diameter 1: 1.9 1: 1.8 1: 7.7 1: 1 1: 1 Average porosity per unit volume 40% 45% 45% 41% 54% Carbide formation of pores × × × × × gas
sensor Crack occurrence 2 2 2 3 4 Evaluation of output of gas sensor -1.6 -1.5 -10.3 -7.3 -8.3

division Comparative Example
One Comparative Example
2 Comparative Example
3 Comparative Example
4 PET fiber A piece of fineness 0.5D 1D 0.5D 1D The other end 1.5D 2D 1.5D 2D Melting point 250 ℃ 250 ℃ 90 ° C 90 ° C

The porous protective layer Second surface pore average diameter 5.2 탆 10.7 탆
Pore formed horizontally with gas sensor surface First surface pore average diameter 15.6 탆 19.38 탆 Second surface pore average diameter:
First surface pore average diameter 1: 3 1: 1.9 Average porosity per unit volume 28% 30% 35% 40% Carbide formation of pores 0 0 × × gas
sensor Crack occurrence 3 3 3 4 Evaluation of output of gas sensor -12.3 -12.2 -15.8 -14.5

Specifically, as shown in Tables 1 to 3, in Examples 1 to 10 using PET fibers having a melting point of 90 占 폚, no carbides of pores were formed, but Comparative Examples 1 to 2 using PET fibers having a melting point of 250 占 폚 The carbide of the pore was formed.

In Examples 1 to 10, it was confirmed that the output of the gas sensor was superior to those of Comparative Examples 1 and 2, and it was confirmed that less cracks were generated.

Comparing Examples 4 and 6 with Comparative Examples 3 and 4 shows that Examples 4 and 5 formed in a direction perpendicular to the abutting surface of the gas sensor were compared with Comparative Examples 3 and 4 in which pores were formed in a direction parallel to the abutting surface of the gas sensor And 4, and it was confirmed that cracks were generated less.

Comparing Examples 1 to 7 and Example 8, Examples 1 to 7, in which the ratio of the diameter of the second surface of the porous protective layer to the diameter of the first surface is 1: 1.8 to 5.9, It was confirmed that the output of the gas sensor was superior to that of Example 8 in which the ratio of the diameter of the surface to the diameter of the first surface was 1: 7.7.

Finally, comparing Example 4 with Example 9, Example 4, in which the pores become larger from the second surface to the first surface of the porous protective layer, is larger than the second surface of the porous protective layer and the pores of the first surface It was confirmed that not only the output of the gas sensor but also the cracks was less than that of Example 9 having the same size. Comparing Examples 5 and 7 and Example 10, it can be seen that pores are formed on the second surface of the porous protective layer Examples 4 and 7 in which the diameter increases toward the first surface are superior to those of Example 10 in which the second surface and the first surface of the porous protective layer have the same pore size, .

20: Electrode sensing part 22: External sensing electrode
24: sensor sheet 40: electrode reference portion
42, 46, 62, 66: insulating layer 44: internal reference electrode
48: reference sheet 60: heater part
64: heater electrode 68: tunnel sheet
70: Tunnel electrode 80: Through-hole porosity
100: gas sensor 200: porous protective layer

Claims (19)

A porous protective layer for a gas sensor for protecting a sensing electrode of a gas sensor,
Wherein the porous protective layer comprises a through pore formed through a first surface facing the sensing electrode and a second surface opposite the first surface, the through hole being formed by the disappearance of the low melting point staple fibers,
The diameter of the through pores increases from the second surface to the first surface,
Wherein the ratio of the diameter at the second surface of the through pores to the diameter at the first surface is 1: 1.8-6. The method according to claim 1,
Wherein the average diameter of the through pores is 5.5 to 42 占 퐉. The method according to claim 1,
Wherein the porous protective layer has an average porosity of 20 to 60% per unit volume of the porous protective layer. delete delete A porous protective layer for a gas sensor according to any one of claims 1 to 3; And an electrode for a gas sensor. The method according to claim 6,
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 6 as an external sensing electrode. A porous protective layer for a gas sensor according to any one of claims 1 to 3; .
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