JP4758117B2 - Gas sensor element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a gas sensor element and a manufacturing method thereof, and more particularly to a gas sensor element suitable for an oxygen sensor element and a manufacturing method thereof.

  In general, a gas sensor element such as an oxygen sensor element includes a sensor unit having a function of detecting a gas concentration, a heater unit that is integrally formed with the sensor unit and for heating the sensor unit, and the sensor unit and the heater unit. It is comprised from the poisoning prevention layer which coat | covered. This gas sensor element operates and functions at a high temperature, and is required to function in a severe use environment. For this reason, the sensor part and the heater part are covered with a poisoning prevention layer having a porous ceramic structure, in particular for the purpose of preventing the sensor part from directly touching water droplets and contaminants. In general, the poisoning prevention layer is coated by a thermal spraying method or a dipping method.

  The thermal spraying method is a method in which a composition for poisoning prevention layer made of ceramic particles or the like is sprayed on the sensor part and the heater part at a high temperature, and the sensor part and the heater part are covered with the poisoning prevention layer. However, this method has a problem of requiring an expensive thermal spraying apparatus. Furthermore, in the case of a flat plate type gas sensor element capable of rapidly raising temperature, which is becoming mainstream in recent years, it is difficult to efficiently coat the sensor part and the heater part with the poisoning prevention layer because the spraying distance is not uniform. There's a problem.

  On the other hand, the dipping method is a method in which the sensor part and the heater part are covered with the poisoning prevention layer by immersing the sensor part and the heater part in the composition for poisoning prevention layer and baking after drying. Patent Document 1 describes an oxygen sensor including a sensor element having a predetermined poisoning prevention layer. The poisoning prevention layer in this oxygen sensor is covered with the poisoning prevention layer by immersing the sensor element in a prescribed poisoning prevention layer forming paste (composition for poisoning prevention layer) and then baking at a prescribed temperature. is doing. Patent Document 2 discloses another example of the dipping method.

  FIG. 14 is a schematic cross-sectional view showing a gas sensor element manufactured by a conventional dipping method as in Patent Document 1. As shown in FIG. As shown in FIG. 14, the gas sensor element 51 includes a fired body 52 obtained by integrating a sensor part and a heater part by firing, a protective layer 53 provided on a detection electrode part of the sensor part, a sensor part, It is comprised from the poisoning prevention layer 54 which coat | covered the heater part. As shown in FIG. 14, in the gas sensor element 51 produced by the conventional dipping method, the composition for poisoning prevention layer tends to sag in the drying step after dipping, that is, the portion corresponding to the electrode portion is thin, and the tip portion However, the thickness of the poisoning prevention layer 54 is biased. This uneven thickness is not preferable because the durability (poisoning durability) of the poisoning prevention layer is lowered and the poisoning prevention layer is damaged by vibration. That is, when the gas sensor element 51 is exposed to moisture contained in the gas to be detected, the gas sensor element 51 is easily affected by a sudden thermal shock, and the portion corresponding to the electrode portion is a thin poisoning prevention layer 54. The gas sensor element 51 covered with the sensor part and the heater part has a problem that its durability to water is low, so that it is easily broken and has a short life. Further, when the tip is thick, there is a problem that it is easily affected by vibration and the poisoning prevention layer is easily damaged.

JP 2002-195977 A JP 2002-323471 A

  The subject of this invention is providing the gas sensor element which coat | covered the sensor part and the heater part with the poisoning prevention layer which has high poisoning durability and high moisture tolerance, and its manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have determined that the gas sensor element having a predetermined sensor part, heater part and poisoning prevention layer has a thickness T of the poisoning prevention layer on the sensor part side. However, when the maximum value Tmax is within the range of the heat generating portion length L of the heating element, there is no bias in the thickness of the poisoning prevention layer, so that it has high poisoning durability and is affected by a sudden thermal shock. The present inventors have found a new finding that it is difficult to receive and high water durability is obtained, and the present invention has been completed.

That is, the gas sensor element and the manufacturing method thereof according to the present invention have the following configurations.
(1) A sensor part in which a detection electrode is formed on one side of a solid electrolyte layer and a reference electrode is formed on the other side, and a sensor part that is in contact with the solid electrolyte layer on the side of the reference electrode and formed integrally with the sensor part A gas sensor element having a long plate shape, comprising a heater part in which a heating element is embedded, and a poisoning prevention layer covering the sensor part and the heater part, wherein the thickness of the poisoning prevention layer on the sensor part side A gas sensor element, wherein T has a maximum value Tmax within a range of a heat generating portion length L of the heat generating element.
(2) The gas sensor element according to (1), wherein a thickness T of the poisoning prevention layer on the sensor unit side is 0.4Tmax ≦ T ≦ Tmax within a range of a heat generating portion length L of the heat generating element.
(3) The gas sensor element according to (1) or (2), wherein the Tmax exists on the tip side within a range of the heat generating portion length L of the heat generating element.
(4) The gas sensor element according to any one of (1) to (3), wherein the gas sensor element is an oxygen sensor element.
(5) The gas sensor element according to any one of (1) to (4), wherein the poisoning prevention layer has at least a substantially spherical pore having a pore diameter of 10 to 100 μm.
(6) In the cross section of the poisoning prevention layer, any one of the above (1) to (5), wherein the ratio S _v / S of the occupied area S _v of the pores to the total cross sectional area S is 0.05 to 0.70 A gas sensor element according to any one of the above.
(7) In any one of the above (1) to (6), the width in the direction orthogonal to the longitudinal direction of at least the long plate-like gas sensor element is 2.0 to 3.5 mm in the sensor portion. The gas sensor element described.
(8) The gas sensor element according to any one of (1) to (7), wherein the poisoning prevention layer is formed using a slurry made of a ceramic powder containing a pore-forming agent that burns down or vaporizes after firing. .

(9) a step of forming a sensing electrode on one side of the solid electrolyte layer and a reference electrode on the other side to form a sensor unit; a step of embedding a heating element inside to form a heater unit; and the heater A method of manufacturing a gas sensor element, comprising: a step of contacting a portion with the solid electrolyte layer on the reference electrode side and integrally forming the sensor portion; and a step of covering the sensor portion and the heater portion with a poisoning prevention layer. The sensor part and the heater part are inserted into a concave mold filled with the composition for the poisoning prevention layer, and the composition for the poisoning prevention layer is solidified to prevent the sensor part and the heater part from being poisoned. Then, the sensor part and the heater part covered with the poisoning prevention layer are extracted from the concave mold, and the poisoning prevention layer is subjected to heat treatment to burn the poisoning prevention layer onto the sensor part and the heater part. With Method for manufacturing a gas sensor element characterized Rukoto.
(10) The method for producing a gas sensor element according to (9), wherein the concave mold is a metal mold.
(11) The method for producing a gas sensor element according to (9), wherein the concave mold is a resin mold.
(12) The method for producing a gas sensor element according to any one of (9) to (11), wherein the poisoning prevention composition contains a thermosetting resin.
(13) The method for producing a gas sensor element according to any one of (9) to (11), wherein the poisoning prevention composition contains a thermoplastic resin.

(14) forming a sensing electrode on one side of the solid electrolyte layer, forming a reference electrode on the other side to form a sensor part, forming a heater part by embedding a heating element therein, and the heater A method of manufacturing a gas sensor element, comprising: a step of contacting a portion with a solid electrolyte layer on the reference electrode side and joining to a sensor portion; and a step of covering the sensor portion and the heater portion with a poisoning prevention layer. The sensor part and the heater part are immersed in the composition for poisoning prevention layer in which the difference ΔT between the shear stress at the time of ascending and the shear stress at the time of descending at a shear rate of 50 (1 / S) is 200 Pa or more. A manufacturing method of a gas sensor element characterized by the above.
(15) The gas sensor according to (14), wherein the difference ΔT between the shear stress during ascending and the shear stress during descending at a shear rate of 50 (1 / S) of the composition for poisoning prevention layer is 300 Pa or more. Device manufacturing method.
(16) The method for producing a gas sensor element according to the above (14) or (15), wherein the composition for poisoning prevention layer contains a granular organic substance.
(17) The method for producing a gas sensor element according to any one of (14) to (16), wherein the composition for poisoning prevention layer contains a ceramic sol.

  According to the above (1), since the thickness T of the poisoning prevention layer on the sensor part side has the maximum value Tmax within the range of the heating part length L of the heating element, the thickness of the poisoning prevention layer is determined by the gas sensor element. Because it has a high poisoning durability and a sudden thermal shock due to water, the temperature gradient to the sensor unit and heater unit is reduced. It is possible to prevent the gas sensor element from being broken, and it is possible to prevent the poisoning prevention layer from being broken due to vibration that occurs when the tip of the gas sensor element is biased and extremely thick. As a result, there is an effect that a gas sensor element having a high detection capability over a long period of time can be obtained.

  According to the above (2), by setting the thickness of the poisoning prevention layer to 0.4 Tmax or more in the range of the heat generating portion length L, there is no extreme bias in the thickness of the poisoning prevention layer, and abrupt due to water exposure. Thermal shock is effectively reduced, and destruction of the gas sensor element can be reliably prevented. According to the above (3), the portion corresponding to the Tmax is formed on the tip side within the range of the heat generating portion length L. For example, even when the measurement gas is introduced from the tip side of the gas sensor element, the thermal shock Can be sufficiently relaxed. In addition, the poisoning substance on the tip side to which the poisoning substance easily adheres can be efficiently collected. According to the above (4), it is possible to obtain an oxygen sensor element in which the sensor unit and the heater unit are covered with the poisoning prevention layer having high poisoning durability and high water durability.

  According to the above (5), since the poisoning prevention layer has substantially spherical pores having a pore diameter of 10 to 100 μm, the thickness can be increased while maintaining the gas permeability of the poisoning prevention layer. Thus, the rapid thermal shock due to water is effectively reduced, and the destruction of the gas sensor element can be surely prevented. Moreover, since it is excellent in heat retention, activation time can be shortened at the time of restart after an engine stall etc.

According to the above (6), in the cross section of the poisoning prevention layer, the ratio S _v / S of the occupied area S _v of the pores to the total cross sectional area S is 0.05 to 0.70. Since the thickness can be increased while maintaining the gas permeability of the poisoning prevention layer, the rapid thermal shock due to the water can be effectively reduced, and the destruction of the gas sensor element can be surely prevented.

  According to the above (7), at least the width in the direction perpendicular to the longitudinal direction of the long plate-like gas sensor element is 2.0 to 3.5 mm in the sensor portion, so that the sensor can be miniaturized. , Material cost can be reduced. According to said (8), the said poisoning prevention layer is efficiently manufactured by forming the said poisoning prevention layer using the slurry which consists of a ceramic powder containing the pore formation agent burnt down or vaporized after baking. be able to.

  According to the above (9), the sensor part and the heater part are inserted into a predetermined mold filled with the composition for poisoning prevention layer, and in this state, the composition for poisoning prevention layer is solidified. Since the heater part is covered with a poisoning prevention layer, there is no bias in the thickness of the poisoning prevention layer, and gas sensor elements equipped with a poisoning prevention layer with high poisoning durability and high water durability can be used easily and efficiently. Can be manufactured well. In addition, since the shape of the poisoning prevention layer can be easily controlled, there is no variation in shape, the production yield is improved, and an expensive thermal spraying device is not required, so that the cost can be reduced.

  According to the above (10), since the metal mold has high thermal conductivity, the temperature of the poisoning prevention composition can be controlled efficiently. According to (11) above, the demolding process can be simplified from the point that the resin mold itself can be burned out in the baking process of the poisoning prevention layer, and damage during demolding can be prevented. In addition, the gas sensor element can be manufactured at a lower cost than when the mold is a metal mold. According to (12) above, when the poisoning prevention composition contains a thermosetting resin, the strength of the poisoning prevention layer before baking is high, thus preventing damage to the poisoning prevention layer during handling. can do. According to the above (13), when the poisoning-preventing composition contains a thermoplastic resin, the solidification rate is fast, so that it can be removed from the mold in a short time, and the tact time can be shortened. .

  According to the above (14), since the sensor part and the heater part are immersed in the composition for poisoning prevention layer whose shear stress difference ΔT in rheological characteristics is controlled to a predetermined value, the poisoning prevention layer in the drying process. Gas sensor element with a poisoning prevention layer that can prevent sagging of the composition for use, suppress the uneven thickness of the poisoning prevention layer, and have high poisoning durability and high water durability. can do. In addition, an expensive thermal spraying device is not required and the manufacturing yield is improved, so that the cost can be reduced. According to the above (15), the sagging of the composition for poisoning prevention layer can be reliably prevented. According to the above (16) and (17), the shear stress difference ΔT can be increased.

Hereinafter, a gas sensor element and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings.
<Gas sensor element>
FIGS. 1A and 1B are schematic views showing an oxygen sensor element according to an embodiment of the gas sensor element of the present invention. FIGS. 2A and 2B are oxygen sensors of this embodiment. It is a top view which shows the heat generating body of an element, FIG. 3 is a schematic sectional drawing of the oxygen sensor element of this embodiment. As shown in FIGS. 1, 2, and 3, the oxygen sensor element 1 according to the present embodiment is in the shape of a long plate, and the sensor unit A having a function of detecting the oxygen concentration and the sensor unit A are heated. And a poisoning prevention layer 2 covering the sensor part A and the heater part B. The present invention is not limited to the oxygen sensor element described above, and can be suitably used, for example, for NOx, CO ₂ sensor elements, etc., but the oxygen sensor element is particularly suitable for ease of manufacturing. is there.

(Sensor part)
As shown in FIG. 3, the sensor part A includes a solid electrolyte layer 9 made of flat zirconia and having oxygen ion conductivity, a reference electrode 10 in contact with air formed on one side of the solid electrolyte layer 9, and the like. The detection electrode 11 is in contact with the exhaust gas formed on the surface. Further, a protective layer 3 is formed on the detection electrode 11. The solid electrolyte layer 9 is integrated with a heater base 4 having a flat plate-like hollow shape whose end is sealed, which will be described later, and this hollow portion forms an air introduction hole 12. As shown in FIG. 3, the width W in the direction perpendicular to the longitudinal direction of the long plate-like gas sensor element 1 is preferably 2.0 to 3.5 mm in the sensor portion A.

(Heater part)
As shown in FIG. 3, the heater part B is provided to heat the sensor part A to a predetermined temperature and to function, and a heating element 5 is embedded in the heater base 4 that is a ceramic insulating layer. ing. 2A and 2B, the heating element 5 includes a heating part 6 and a lead part 7. The heating part 6 has a narrower line width or a smaller thickness than the lead part 7. For example, the resistance during energization is set high. It is preferable that the pattern shape of the heat generating portion 6 has a meander structure that is folded back multiple times. The heating part length L of the heating element in the present invention means, for example, the length between the folded portions. That is, it corresponds to a portion where the temperature distribution becomes particularly high due to heat generation when energized.

(Poison prevention layer)
The poisoning prevention layer 2 mainly prevents the poisoning due to the pollutants contained in the gas to be detected, or the heat at the time of the flooding due to the moisture contained in the gas to be detected in the usage environment of the gas sensor. Has the function of mitigating impact. Compared to a protective layer described later, it is more porous and the gas itself has a permeable structure. In the present invention, the thickness T of the poisoning prevention layer on the sensor portion side means a thickness in a direction perpendicular to the surface of the sensor portion A as shown in FIG. Then, as shown in FIG. 1B, in the longitudinal section of the oxygen sensor element 1, the thickness T of the poisoning prevention layer on the sensor unit side becomes the maximum value Tmax within the range of the heat generating unit length L. This is a major feature of the present invention.

  As a result, the poisoning prevention layer is not formed extremely thick on the tip side of the gas sensor element, the deviation of the thickness of the poisoning prevention layer is reduced, and the poisoning prevention layer has high poisoning durability and a rapid thermal shock. High water durability is obtained. Moreover, it is preferable that the thickness T of the poisoning prevention layer 2 on the sensor part side is 0.4 Tmax ≦ T ≦ Tmax at the maximum within the range of the heat generating part length L. If the thickness T of the poisoning prevention layer is outside the above range, the thickness deviation of the poisoning prevention layer becomes large, so that the poisoning durability is lowered and the effect of preventing thermal shock due to water is reduced. It is not preferable. Further, it is preferable that Tmax is on the tip side of the gas sensor element within the range of the heat generating portion length L, since the poisoning substance on the tip side to which the poisoning substance easily adheres can be efficiently collected. The thickness T of the poisoning prevention layer on the sensor portion side in the present invention is a value obtained by nondestructive measurement with a microfocus X-ray flaw detector, for example, as will be described later.

  As the poisoning prevention layer 2, for example, alumina, spinel, titania, and a mixture thereof can be used. The thickness can be selected as appropriate, and the thickness T may exceed 500 μm. In the present invention, in particular, the thickness T is preferably 700 μm or more in order to obtain high water durability. Moreover, the shape of the poisoning prevention layer 2 is not limited to FIGS. 1-3, For example, a shape like the poisoning prevention layer 33 shown in FIG.8 (c) mentioned later may be sufficient.

(Solid electrolyte layer)
The solid electrolyte layer 9 is made of a ceramic containing ZrO ₂ (zirconia), and Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , Dy ₂ are used as stabilizers. O _3, 1 to 30 mol% of rare earth oxide in terms of oxide, preferably can be used partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol%. Moreover, it is preferable to use ZrO ₂ in which 1 to 20 atomic% of Zr in ZrO ₂ is substituted with Ce in order to increase the ionic conductivity and further improve the responsiveness. Furthermore, for the purpose of improving the sinterability, Al ₂ O ₃ and SiO ₂ can be added to the ZrO ₂ , but if it is contained in a large amount, the creep properties at high temperatures are deteriorated. The total amount of Al ₂ O ₃ and SiO ₂ is preferably 5% by weight or less, particularly 2% by weight or less.

(electrode)
The reference electrode 10 and the detection electrode 11 deposited and formed on both surfaces of the solid electrolyte layer 9 are both platinum or an alloy of platinum and one selected from the group of rhodium, palladium, ruthenium and gold. . Further, for the purpose of preventing metal grain growth in the electrode during sensor operation and for increasing the contact at the so-called three-phase interface between platinum particles, solid electrolyte and gas related to responsiveness, the above-mentioned ceramic solid electrolyte is used. The components may be mixed in the electrode in a proportion of 1 to 50% by volume, particularly 10 to 30% by volume. Further, the electrode shape may be a quadrangle or an ellipse. The thickness of the electrode is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.

(Heater base)
The heater base 4, which is an insulating ceramic in which the heating element 5 is embedded, is preferably composed of a dense ceramic made of alumina ceramics with a relative density of 80% or more and an open porosity of 5% or less. At this time, Mg, Ca, and Si may be contained in a total amount of 1 to 10% by mass for the purpose of improving the sinterability. However, the content of alkali metals such as Na and K is migrated to generate a heating element. In order to deteriorate the electrical insulation of 5, the alkali metal is desirably controlled to 100 ppm or less in terms of oxide. In addition, by setting the relative density within the above range, the substrate strength increases, and as a result, the mechanical strength of the oxygen sensor itself can be increased.

(Protective layer)
The protective layer 3 formed on the surface of the detection electrode 11 is provided mainly for the purpose of directly protecting the detection electrode and at the same time controlling the gas responsiveness. It is desirable to be formed of at least one selected from the group consisting of zirconia, alumina, γ-alumina and spinel having a thickness of 10 to 400 μm and a porosity of 10 to 60%. When the thickness of the protective layer 3 is less than 10 μm or the porosity exceeds 60%, the slight electrode poisoning substances P, Si, etc. that could not be collected by the poisoning prevention layer easily reach the electrode. Electrode performance is reduced. Further, if the thickness of the protective layer 3 exceeds 400 μm or the porosity is less than 10%, the diffusion rate of gas in the protective layer 3 is slowed, and the gas responsiveness of the electrode is deteriorated. In particular, the thickness of the protective layer 3 is appropriately 20 to 350 μm although it depends on the porosity. The protective layer 3 may be formed as necessary.

(Heating element)
The heating element 5 is composed of a heating part 6 and a heating element lead part 7, and as the material of the heating part 6 and the heating element lead part 7, for example, platinum alone as a metal, or a group of platinum and rhodium, palladium, ruthenium An alloy with one selected from the group consisting of: In this case, it is preferable to control the resistance ratio between the heat generating portion 6 and the heat generating lead portion 7 within a range of 9: 1 to 7: 3 at room temperature. Moreover, the heat generating body 5 may be comprised from the heat generating part which has tungsten as a main component, and a heat generating body lead part.

  In the oxygen sensor element of the present embodiment, the reference air (oxygen) is introduced into the air introduction hole 12 in a state where the heating element 5 is energized and the solid electrolyte layer 9 is heated to about 400 to 1000 ° C. It arrange | positions in measurement atmospheres, such as waste gas. Then, the electromotive force generated between the detection electrode 11 and the reference electrode 10 is measured, and the oxygen concentration in the exhaust gas is measured. As a measurement method, for example, a concentration cell type in which an electromotive force generated between the detection electrode 11 and the reference electrode 10 is measured to measure an oxygen concentration in exhaust gas, a current is detected by applying a constant voltage. For example, a limiting current type for measuring the oxygen concentration may be used.

Next, oxygen sensor elements according to other embodiments will be described in detail with reference to the drawings. FIG. 4 is a schematic cross-sectional view of the oxygen sensor element according to this embodiment, FIG. 5 is a view for explaining the total cross-sectional area S, and FIG. 6 is a view for explaining the occupied area _Sv . It is. In FIG. 4, the same reference numerals are given to the same or equivalent parts as those in FIGS. As shown in FIG. 4, in the oxygen sensor element 61 according to this embodiment, the poisoning prevention layer 62 includes at least approximately spherical pores 63 having a pore diameter of 10 to 100 μm. As a result, the thickness of the poisoning prevention layer 62 can be increased while maintaining gas responsiveness without impeding gas permeability, so that the oxygen sensor element is resistant to sudden thermal shock due to moisture and has excellent heat retaining properties. 61. On the other hand, if the pore diameter is less than 10 μm, gas responsiveness tends to be insensitive, and if it exceeds 100 μm, poisonous substances cannot be collected effectively, which is not preferable.

  The poisoning prevention layer 62 can be formed using a slurry made of ceramic powder containing a pore-forming agent that burns down or vaporizes after firing. Examples of the pore forming agent include resin beads as an organic pore material, and more specifically, polyethylene beads.

In the cross section of the poisoning prevention layer 62, the ratio S _v / S of the occupied area S _v of the pores 63 to the total cross sectional area S is preferably 0.05 to 0.70. Thus, the thickness of the poisoning prevention layer 62 can be increased while effectively maintaining the gas permeability of the poisoning prevention layer 62, so that a rapid thermal shock due to moisture is effectively reduced, and the oxygen sensor element. The destruction of 61 can be reliably prevented.

Here, the total cross-sectional area S is a cross-sectional area of only the poisoning prevention layer 62 excluding the pores 63, the sensor part A, and the heater part B in the oxygen sensor element 61 as shown in FIG. The cross-sectional area within the range of the part length L is meant. Further, as shown in FIG. 6, the occupied area S _v is a cross section for measuring the cross sectional area, and means a total area of the substantially spherical pores 63 having a pore diameter of 10 to 100 μm, and S _v = ΣS It can be represented by _vi .

<Manufacturing method of gas sensor element>
Next, with respect to the method for manufacturing the oxygen sensor element according to the embodiment, an exploded perspective view showing the sensor part and the heater part of FIG. 7 and a schematic view showing a procedure for covering with the poisoning prevention layer of FIG. And explained.
(Sensor part)
First, as shown in FIG. 7, the green sheet 13 for solid electrolyte layers is produced. For example, the green sheet 13 may be formed by appropriately adding an organic binder for molding to a ceramic solid electrolyte powder having oxygen ion conductivity, such as partially stabilized zirconia, by a doctor blade method, extrusion molding, or isostatic pressing (rubber press). Or it produces by well-known methods, such as press formation.

  Next, patterns 14 and 15, lead patterns 16 and 17, electrode pads 18, through holes (not shown), which are to be the measurement electrode 11 and the reference electrode 10, respectively, are formed on both surfaces of the green sheet 13, for example, platinum. The sensor portion A is manufactured by printing using the contained conductive paste by a slurry dip method, screen printing, pad printing, roll transfer, or the like. The through hole has a role of electrically connecting the lead pattern inside the element and the electrode pad, and transmitting an output signal to the outside of the element. And the porous slurry 19 for forming the protective layer 3 on the surface of the pattern 14 used as the measurement electrode 11 is formed by printing.

The conductive paste containing platinum used at this time is platinum particles containing 1 to 50% by volume, particularly 10 to 30% by volume of zirconia composed of the ceramic solid electrolyte component described above. Those containing organic resin components such as are desirable. In order to produce such platinum particles including a zirconia phase inside, for example, a platinum powder, a zirconia fine powder having a specific surface area of 30 m ² / g or more in BET value, a binder and a three roll are used. By mixing for 12 hours or more, zirconia can be accommodated in the platinum powder.

(Heater part)
The heater part B produces an insulating ceramic green sheet 20. This green sheet 20 is a known method such as a doctor blade method, extrusion molding, isostatic pressing (rubber press) or press formation by appropriately adding a molding organic binder to, for example, an insulating ceramic powder of alumina. It is produced by. Next, a pattern 21 and a lead pattern 22 to be the heating elements 5 are formed on one side of the green sheet 20, an electrode pad 23, a through hole (not shown), etc. are formed on the other side, and a conductive paste containing platinum, for example. It is used for printing by slurry dip method, screen printing, pad printing, roll transfer or the like. The through hole has a role of electrically connecting the lead pattern inside the element and the electrode pad to enable voltage application to the heater. Moreover, 10-20 micrometers can be used conveniently for printing thickness. At this time, the printing paste for the heating element is 10 μm or less, preferably 8 μm or less as measured by a grind gauge.

  The air introduction hole 12 for supplying air to the reference electrode 10 includes an acrylic resin or an organic solvent formed on an alumina green sheet 24 that has been previously punched and an alumina green sheet 25 that has no holes. The adhesive may be bonded mechanically while applying pressure under heating with a roller or the like. In addition, the green sheet 20 on which the heating element is printed is also bonded and laminated at the same time to produce the heater part B.

(Integration and firing of sensor and heater)
Sensor unit A and heater unit B obtained above are bonded and integrated by interposing an adhesive such as acrylic resin or organic solvent, or by mechanically bonding the two while applying pressure under heating with a roller or the like. Then, these are fired to obtain a fired body 26 of the sensor part and the heater part. Firing is performed in the air or in an inert gas atmosphere at a temperature of 900 to 1500 ° C. for 1 to 10 hours. At the time of firing, in order to suppress warping of the sensor part A during firing, the amount of warpage can be reduced by placing a smooth substrate such as alumina on the laminate as a weight.

  Further, when the sensor part A and the heater part B are simultaneously fired and integrated, in order to reduce the occurrence of stress due to the difference in thermal expansion coefficient between them, for example, the solid electrolyte component forming the sensor part A and the heater It is desirable to interpose a composite material with an insulating component forming the ceramic insulating layer of the part. In the above-described method, the case where the sensor part A and the heater part B are formed by simultaneous firing has been described. However, after the sensor part A and the heater part B are separately fired, appropriate inorganic materials such as glass are used. It is also possible to integrate by bonding with a bonding material.

(Poison prevention layer)
Next, the sensor part A and the heater part B are covered with a poisoning prevention layer. Specifically, as shown in FIG. 8A, the concave mold 31 is filled with the poisoning prevention composition 32. The material of the mold 31 can be metal, resin, or the like. As the metal, for example, aluminum, duralumin, iron, carbon steel, stainless steel, copper or the like can be used. As the resin, for example, Teflon (registered trademark), PVC, PE, PP or the like can be used. Further, a surface treatment may be applied to improve the releasability.

  The composition 32 for poisoning prevention layer should just consist of a ceramic material, a solvent, resin, etc., and should solidify within the shaping | molding die 31. FIG. Here, solidifying means curing when the resin is a thermosetting resin, and means that the resin solidifies while forming a three-dimensional network structure by reaction. When the resin is a thermoplastic resin, it means solidification by cooling.

  As the ceramic material, for example, alumina, spinel, titania and a mixture thereof can be used. As the solvent, for example, organic solvents such as hydrocarbon organic substances and alcohols, and plasticizers such as phthalate esters can be appropriately selected. As the hydrocarbon-based organic material, a hydrocarbon-based organic material having a melting point of 20 ° C. or less is preferable, and examples thereof include paraffin mixtures having 10 to 16 carbon atoms, mineral oil, normal hydrocarbons having 10 carbon atoms, styrene, vinyl toluene, and the like. preferable. As the alcohols, for example, lower alcohols having 12 to 9 carbon atoms, alkylene oxide alcohols such as ethoxyethanol, ethoxyethoxyethanol, ethoxybutoxyethanol and the like are preferable. Examples of the phthalic acid ester include diethyl phthalate, dioctyl phthalate, and methylbutyl phthalate.

  Examples of the resin include a thermosetting resin and a thermoplastic resin. Examples of the thermosetting resin include an unsaturated polymer, a crosslinked product having a vinyl group, an acroyl group, or a methacryloyl group. Examples of the thermoplastic resin include paraffin wax, wax, hydroxy fatty acid, alkylene oxide derivative, fatty acid ester, and fatty acid amide. Examples of the hydroxy fatty acid include 8-hydroxy stearic acid and 6-hydroxy stearic acid, examples of the alkylene oxide derivative include polyethylene glycol, and examples of the fatty acid ester include 6-hydroxy stearic acid ethylene glycol ester and 6-hydroxy stearic acid. For example, stearic acid triglyceride and the like, and examples of the fatty acid amide include acetamide.

  Next, as shown in FIG. 8B, the sensor unit and the fired body 26 of the heater unit are inserted into the molding die 31 filled with the poisoning prevention layer composition 32 in the direction of the arrow to a predetermined position. To do. Insertion may be performed in a vacuum, or vacuuming may be performed after insertion to perform a defoaming process. The position where the fired body 26 is inserted is preferably at least a position where the protective layer 19 is immersed.

  Then, when the said poisoning prevention layer composition 32 contains a thermosetting resin, it can be heat-processed and hardened | cured and solidified. Although heat processing temperature is not specifically limited, About 60-120 degreeC is preferable from handling property. Moreover, when it contains a thermoplastic resin, it can be cooled and solidified. As temperature of the composition 32 for poisoning prevention layers before cooling, about 60-120 degreeC is preferable on handling property. And the oxygen sensor element 27 in which the poisoning prevention layer before baking was formed can be obtained by volatilizing and drying a solvent.

  Next, as shown in FIG. 8C, the oxygen sensor element 27 is extracted from the mold 31, and the oxygen sensor element 27 on which the poisoning prevention layer before baking is formed is subjected to heat treatment, and the poisoning prevention layer 33 is baked. The oxygen sensor element 27 can be obtained by integrating the poisoning prevention layer 33 and the fired body 26. The temperature and time of the heat treatment are not particularly limited and can be selected as appropriate. However, in order to prevent oversintering of the heater in the oxygen sensor element, the temperature ranges from 500 to 1000 ° C. in the atmosphere for 10 minutes to 5 hours. It is better to apply a degree of heat treatment.

  The present invention is not limited to the concave mold 31 and may be, for example, a concave mold 34 as shown in FIG. The mold 34 is configured by combining a pair of substantially symmetrical molds 34a and 34b so that the thickness T of the poisoning prevention layer on the sensor unit side is maximized within the range of the heat generating part length L. It has a concave shape. When the molding die 34 is used, the poisoning prevention wearing composition is filled into the molding die 34, and then the fired bodies of the sensor part and the heater part are inserted into the molding die 34 to a predetermined position, and the poisoning prevention wearing is performed. After the composition is solidified, the molds 34a and 34b can be removed to produce an oxygen sensor element in which a poisoning prevention layer before baking is formed. An oxygen sensor element can be obtained by the same method as described above. Note that when the mold 34 is a resin mold, the mold can be burned out. Therefore, the molds 34a and 34b are not limited to a configuration in which a pair of substantially symmetrical molds 34a and 34b are combined. May be a integrally formed mold.

<Other manufacturing method of gas sensor element>
Next, with respect to another method for manufacturing the oxygen sensor element according to the embodiment, a block diagram showing a procedure when the oxygen sensor element is coated with the poisoning prevention layer shown in FIG. 10, and a relationship between the shear stress and the shear rate shown in FIG. A description will be given based on a graph and a schematic diagram showing a procedure for coating with the poisoning prevention layer of FIG.

  First, as shown in FIGS. 10 and 12A, a ceramic material, a solvent, an organic binder, and a thixotropy imparting material are prepared as a poisoning prevention composition 41 in a container 40. As the ceramic material, for example, alumina, spinel, titania or the like can be used. As said solvent, organic solvents, such as water and toluene, can be selected suitably, for example. In the present invention, in particular, when forming the poisoning prevention layer so that the surface tension is high and the thickness T of the poisoning prevention layer on the sensor part side is the maximum value Tmax within the range of the heating part length L, Is preferably used. Moreover, in order to control the porosity of a poisoning prevention layer, the organic pore material etc. which can be burned out can also be added as needed.

  As the organic binder, for example, an aqueous binder such as PVA, a solvent binder such as an acrylic resin and a butyral resin, and the like can be appropriately selected. As the thixotropy-imparting material, for example, an organic material such as acrylic or polyethylene, or a ceramic sol such as alumina sol or titania sol can be used. Next, the poisoning composition prepared above is stirred and mixed. As a means for stirring and mixing, for example, known ball mill mixing, roll mixing, centrifugal mixing and the like can be used. In the present invention, in particular, centrifugal mixing can be suitably used in terms of simplicity.

  As shown in FIG. 11, the poisoning prevention composition 41 obtained above was increased in shear rate from 0 (1 / s) to 200 (1 / s) with a viscometer, and 200 (1 / s) for about 1 minute and then descending from 200 (1 / s) to 0 (1 / s) at 50 (1 / s) at the time of ascending and shearing stress at the time of descending The difference ΔT is 200 Pa or more. Thereby, even when forming a poisoning prevention layer by dipping, dripping of the composition for poisoning prevention layer can be prevented in the drying step. In the present invention, it is desirable that the difference ΔT between the shear stress at the time of ascending and the shear stress at the time of descending is 300 Pa or more, particularly from the viewpoint that the protective layer can be easily formed thick. The shear stress in the present invention is a value obtained by measuring with a viscometer, and can be measured by, for example, a trade name “RS100” manufactured by Haake, as described later.

  Next, as shown in FIGS. 12A and 12B, the fired body 26 of the sensor part and the heater part produced by the same method as the above-described manufacturing method is used as the poisoning prevention composition 41, as shown in FIG. Immerse to a predetermined position along the direction of the arrow shown in a). The position where the fired body 26 is immersed is preferably at least the position where the protective layer 19 is immersed. In addition, immersion time, temperature, etc. can be selected suitably.

  And as shown in FIG.12 (c), the oxygen sensor element 43 by which the sensor part and the heater part were coat | covered with the poisoning prevention layer 42 was obtained by pulling up the baking body 26 along the direction of the arrow, and drying. It is done. At this time, by adjusting the pulling speed, the thickness T of the poisoning prevention layer on the sensor part side can be formed to be the maximum within the range of the heat generating part length L. In addition, although immersion time, temperature, etc. can be selected suitably, it is preferable to prevent the poisoning prevention layer 42 from cracking, for example, drying at a relatively low temperature of about room temperature to 100 ° C. Next, after drying, the poisoning prevention layer 42 is baked. Although baking time, temperature, etc. can be selected suitably, in order to prevent the oversintering of the heater in an oxygen sensor element, it is good to perform the heat processing for about 10 minutes-about 5 hours in the temperature range of 500-1000 degreeC in air | atmosphere.

  The present invention is not limited to the poisoning prevention composition 41, and the sensor part and the heater part fired body 26 are soaked in various known poisoning prevention compositions that can be used in the dipping method. Even when producing an oxygen sensor element, it can be suitably used. The method for producing the oxygen sensor element in this case can be produced in the same manner as in the case of using the poisoning prevention composition 41 described above.

  EXAMPLES Hereinafter, although an Example is given and the gas sensor element of this invention and its manufacturing method are demonstrated still in detail, this invention is not limited to a following example.

[Examples 1 to 8]
<Production of oxygen sensor element>
(Heater part)
The oxygen sensor element shown in FIGS. 1, 3, and 5 was produced. Specifically, alumina powder having a commercial purity of 99.9% and an average particle size of 0.5 μm (containing 0.1% by weight of silica) and a platinum powder having an average particle size of 0.5 μm were prepared. Subsequently, a butyral binder, toluene, and ethanol were added to the alumina powder to prepare a slurry, and an alumina green sheet having a sheet thickness of 0.3 mm was prepared by a doctor blade method.

  A paste made of platinum powder containing 40% by volume of the above-mentioned alumina powder was prepared, and a heater pattern and a lead pattern were used so that the resistance value after firing on the surface of the alumina green sheet was about 7.5Ω at room temperature. Was printed by screen printing. Then, two alumina green sheets on the upper surface of these heater patterns and lead patterns, and three alumina green sheets punched with a die corresponding to the air introduction hole are laminated and thermocompression-bonded to contain a heater. A laminated body (heater part B) was prepared.

(Sensor part)
A zirconia powder having an average particle size of 0.5 μm was prepared, and a butyral binder, toluene and ethanol were mixed to prepare a slurry. Next, a zirconia green sheet 13 having a thickness of 0.3 mm was prepared by a doctor blade method. Then, the patterns 14 and 15, the lead patterns 16 and 17, the electrode pads 18, the through holes (not shown) and the like that become the detection electrode 11 and the reference electrode 10, respectively, and zirconia in a ratio of 15% by volume on both surfaces of the green sheet 13 Is formed by screen printing using a conductive paste containing platinum contained in the above, and a porous alumina slurry 19 containing polyethylene beads having an average particle diameter of 5 μm is printed on the surface of the pattern 14 and applied to the protective layer 3. The sensor part A was produced.

(Integrated / fired)
The laminated body (heater part B) and sensor part A obtained above are joined and integrated with an adhesion liquid composed of alumina powder, butyral resin and solvent, and then fired to obtain fired bodies of the heater part and sensor part. Obtained. Firing was performed at 1500 ° C. in the atmosphere for 2 hours.

(Poison prevention layer)
A ceramic material, a resin, and a solvent were mixed and stirred with a centrifugal stirrer (revolution 2000 rpm, rotation 800 rpm) in the combinations shown in Table 1 to prepare a composition for a poisoning prevention layer. Next, the fired body obtained above is inserted into the obtained composition for poisoning prevention layer to a position where the protective layer is coated, immersed for 10 seconds, and then pulled up as shown in Table 1 and FIG. It pulled up at speed and dried at room temperature (immersion method). Then, it baked at 950 degreeC in air | atmosphere, and obtained the oxygen sensor element. Note that “position L2” in Table 1 and FIG. 14 means a position 75% from position L5, which is the tip of the heat generating portion length L, and “position L4” means 25% from position L5 in the heat generating portion length L. Means the position of

  For each of the five oxygen sensor elements of Examples 1 to 8, the thickness T of the poisoning prevention layer on the sensor unit side corresponding to each position of the heat generating unit length L was measured, and the water resistance durability was evaluated. The evaluation method of each characteristic is shown below, and the evaluation results are shown in Table 1.

<Measurement method of thickness T of poisoning prevention layer>
The thickness T of the poisoning prevention layer on the sensor unit side corresponding to each position of the heat generating part length L of the sensor element is measured nondestructively with a microfocus X-ray flaw detector, and corresponds to each position of the heat generating part length L. The average thickness was determined (n = 5). Note that “position L5” in Table 1 and FIG. 14 means the tip of the heat generating portion length L, and “position L3” means a position 50% from the position L5 in the heat generating portion length L. “L1” means the rear end portion of the heat generating portion length L.

<Evaluation method of water durability>
10 μl of water droplets are repeatedly dropped onto the sensor element side of the sensor element that has been heated so that the maximum heat generation part on the sensor side is 400 ° C., and the insulation resistance between the reference electrode of the sensor part and the outside is less than 500 MΩ The number of repetitions until the value was measured and the average number of repetitions was determined (n = 5).

表１から、実施例１〜８の酸素センサー素子は、被水耐久性に優れているのがわかる。

From Table 1, it can be seen that the oxygen sensor elements of Examples 1 to 8 are excellent in water resistance.

[Examples 9 to 17]
<Production of oxygen sensor element>
Except having used the ceramic material, resin, and solvent as shown in Table 2, it carried out similarly to Examples 1-8, and obtained the poisoning prevention layer composition, the heater part, and the sintered body of the sensor part. Next, the obtained composition for poisoning prevention layer was filled into a concave mold made of the materials shown in Table 2 and the surface of which was subjected to mold release treatment. Next, the fired body is inserted into the mold until the protective layer is covered, and after solidified by heating at 80 ° C. or cooling from 80 ° C. to room temperature, it is baked at 950 ° C. in the atmosphere to provide an oxygen sensor element. Obtained. Note that the mold 31 shown in FIG. 8 was used as the mold.

  For each of the five oxygen sensor elements in Examples 9 to 17, the variation in thickness and the wet durability were evaluated in the same manner as in Examples 1 to 8. The evaluation method of thickness variation is shown below, and the evaluation results are also shown in Table 2.

<Evaluation method of thickness variation>
The thickness of the poisoning prevention layer on the sensor portion side at the central position of the heating element L was measured nondestructively with a microfocus X-ray flaw detector, and the thickness variation was determined (n = 5).

表２から、実施例９〜１７のセンサー素子は、被毒防止層の厚みにバラツキがなく、被水耐久性が高いのがわかる。

From Table 2, it can be seen that the sensor elements of Examples 9 to 17 have no variation in the thickness of the poisoning prevention layer and have high water resistance.

[Examples 18 to 29]
<Production of oxygen sensor element>
Except having used the ceramic material, the thixotropy imparting material, and the solvent as shown in Table 3, the poisoning prevention layer composition, the fired part of the heater part and the sensor part were obtained in the same manner as in Examples 1-8.

(Poison prevention layer)
A ceramic material, a thixotropy-imparting material and a solvent were mixed and stirred with a centrifugal stirrer (revolution 2000 rpm, rotation 800 rpm) in the combinations shown in Table 3 to prepare a composition for a poisoning prevention layer. Subsequently, the shear stress of the obtained composition for poisoning prevention layer was measured by a trade name “RS100” manufactured by HAAKE. In the measurement, the shear rate was increased from 0 (1 / s) to 200 (1 / s), held at 200 (1 / s) for 1 minute, and then from 200 (1 / s) to 0 (1 / s ), The shear stress at the time of ascending and the shear stress at the time of descending at 50 (1 / s) were measured, and the difference ΔT between the shearing stress at the time of ascending and the descending speed was calculated. The results are shown in Table 3.

  The fired body was immersed in the composition for poisoning prevention layer at room temperature for 10 seconds and then dried at room temperature. At this time, similarly to Examples 1 to 8, the thickness T of the poisoning prevention layer on the sensor unit side corresponding to each position of the heat generating unit length L of the gas sensor element was obtained (n = 20). The measurement results are also shown in Table 3. Subsequently, it baked at 950 degreeC in air | atmosphere for 1 hour, and the oxygen sensor element was obtained. The evaluation was performed with the sensor element after drying at room temperature before firing. The evaluation method is shown below, and the results are also shown in Table 3.

表３から、実施例１８〜２９の酸素センサー素子は、被水耐久性に優れているのがわかる。

From Table 3, it can be seen that the oxygen sensor elements of Examples 18 to 29 are excellent in water resistance.

(A), (b) is the schematic which shows the oxygen sensor element concerning one Embodiment of this invention. (A), (b) is a top view which shows the heat generating body of the oxygen sensor element concerning one Embodiment. It is a schematic sectional drawing of the oxygen sensor element concerning one Embodiment. It is a schematic sectional drawing of the oxygen sensor element concerning other embodiment. It is a figure for demonstrating the total cross-sectional area S concerning other embodiment. It is a diagram for explaining the area occupied S _v according to another embodiment. It is a disassembled perspective view which shows a sensor part and a heater part. (A), (b), (c) is the schematic which shows the procedure at the time of coat | covering with a poisoning prevention layer. It is sectional drawing which shows the other concave shaping | molding die concerning this invention. It is a block diagram which shows the procedure at the time of coat | covering with a poisoning prevention layer. It is a graph which shows the relationship between a shear stress and a shear rate. It is the schematic which shows the procedure at the time of coat | covering with a poisoning prevention layer. It is a figure which shows each position of the heat generating part length L in Examples 1-8. It is a schematic sectional drawing which shows the gas sensor element produced with the conventional immersion method.

Explanation of symbols

1, 27, 61 Oxygen sensor element 2, 33, 42, 62 Poisoning prevention layer 3 Protective layer 4 Heater base 5 Heating element 6 Heating part 7 Lead part 9 Solid electrolyte layer 10 Reference electrode 11 Detection electrode 12 Air introduction hole 13 Solid Green sheet for electrolyte layer 19 Porous slurry 20 Green sheet of insulating ceramic 26 Sintered body of sensor part and heater part 31, 34 Concave mold 32, 41 Poisoning prevention composition 63 Pore

Claims (17)

A sensor part in which a detection electrode is formed on one side of the solid electrolyte layer and a reference electrode is formed on the other side, and a heating element formed integrally with the sensor part in contact with the solid electrolyte layer on the reference electrode side A gas sensor element having a long plate-like shape, comprising a heater section embedded with a poisoning prevention layer covering the sensor section and the heater section,
The gas sensor element characterized in that a thickness T of the poisoning prevention layer on the sensor part side has a maximum value Tmax within a range of a heat generating part length L of the heat generating element.   2. The gas sensor element according to claim 1, wherein the thickness T of the poisoning prevention layer on the sensor part side is 0.4Tmax ≦ T ≦ Tmax within the range of the heat generating part length L of the heat generating element.   3. The gas sensor element according to claim 1, wherein the Tmax exists on a tip side within a range of a heat generating portion length L of the heat generating element.   The gas sensor element according to claim 1, wherein the gas sensor element is an oxygen sensor element.   The gas sensor element according to any one of claims 1 to 4, wherein the poisoning prevention layer has at least a substantially spherical pore having a pore diameter of 10 to 100 µm. Wherein in the cross section of the poisoning prevention layer, a gas sensor according to claim 1 ratio S _v / S of the area occupied by S _v of the pore to the total cross-sectional area S is 0.05 to 0.70 element.   The gas sensor element according to any one of claims 1 to 6, wherein a width in a direction orthogonal to a longitudinal direction of at least the long plate-shaped gas sensor element is 2.0 to 3.5 mm in the sensor portion.   The gas sensor element according to any one of claims 1 to 7, wherein the poisoning prevention layer is formed using a slurry made of a ceramic powder containing a pore-forming agent that burns down or vaporizes after firing. Forming a sensing electrode on one side of the solid electrolyte layer and forming a sensor part by forming a reference electrode on the other side; forming a heater part by embedding a heating element therein; and A method for producing a gas sensor element, comprising: a step of forming a single contact with a solid electrolyte layer on a reference electrode side; and a step of covering the sensor portion and the heater portion with a poisoning prevention layer.
The sensor part and the heater part are inserted into a concave mold filled with the composition for the poisoning prevention layer, the composition for the poisoning prevention layer is solidified, and the sensor part and the heater part are covered with the poisoning prevention layer. Then, the sensor part and the heater part covered with the poisoning prevention layer are extracted from the concave mold, and the poisoning prevention layer is subjected to a heat treatment to burn the poisoning prevention layer onto the sensor part and the heater part. A method for manufacturing a gas sensor element.   The method for manufacturing a gas sensor element according to claim 9, wherein the concave mold is a metal mold.   The method for manufacturing a gas sensor element according to claim 9, wherein the concave mold is a resin mold.   The method for producing a gas sensor element according to claim 9, wherein the poisoning prevention composition contains a thermosetting resin.   The method for producing a gas sensor element according to any one of claims 9 to 11, wherein the poisoning prevention composition contains a thermoplastic resin. Forming a sensing electrode on one side of the solid electrolyte layer and forming a sensor part by forming a reference electrode on the other side; forming a heater part by embedding a heating element therein; and A method for producing a gas sensor element, comprising: a step of contacting a solid electrolyte layer on a reference electrode side and bonding to a sensor portion; and a step of covering the sensor portion and the heater portion with a poisoning prevention layer.
The sensor unit and the heater unit are immersed in a composition for a poisoning prevention layer in which a difference ΔT between a shear stress at ascending speed and a shear stress at descending speed at a shear rate of 50 (1 / S) is 200 Pa or more. A manufacturing method of a gas sensor element characterized by the above.   The method for producing a gas sensor element according to claim 14, wherein the difference ΔT between the shearing stress during ascending and the shearing stress during descending at a shear rate of 50 (1 / S) of the composition for poisoning prevention layer is 300 Pa or more. .   The method for producing a gas sensor element according to claim 14 or 15, wherein the composition for poisoning prevention layer contains a granular organic substance. The method for producing a gas sensor element according to any one of claims 14 to 16, wherein the composition for poisoning prevention layer contains a ceramic sol.

Images