JP4573939B2 - Gas sensor element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor element that directly detects a gas such as nitrogen oxide (hereinafter sometimes simply referred to as NOx) in exhaust gas in an internal combustion engine such as an automobile, and more specifically, a sensor unit and a heater unit. And a heater-integrated gas sensor element having excellent thermal shock resistance and a short activation time.
[0002]
[Prior art]
Conventionally, an internal combustion engine such as an automobile is provided with a NOx sensor for combustion control. The NOx sensor is, for example, ZrO having oxygen ion conductivity.₂Is known which detects the concentration of NOx gas present in the exhaust gas by using the above-mentioned.
[0003]
As shown in the schematic cross-sectional view of FIG. 15, such a NOx sensor includes a laminate of oxygen ion conductive flat solid electrolyte plates 51 and 52 and an insulating plate 53, and the solid electrolyte plates 51 and 52. Two measurement chambers a and b are formed between the gas diffuser 54 and the porous partition wall 55. A small air introduction hole 56 that communicates with the atmosphere is formed on the surface of the solid electrolyte plate 51 opposite to the measurement chamber side.
[0004]
A pair of electrodes 57 and 58 are formed on the measurement chamber a side and the opposite side of the solid electrolyte plate 52 to form a first pump cell. A pair of electrodes 59 and 60 are also formed on the measurement chamber a side and the air introduction hole 56 side of the solid electrolyte plate 51 to form a light and dark battery cell. Furthermore, an electrode 61 is also formed on the measurement chamber b side of the solid electrolyte plate 51, and a second pump cell is formed between the electrode 60 and the electrode 61.
[0005]
In such an element, exhaust gas is introduced from the outside into the measurement chamber a through the gas diffuser 54, and oxygen in the exhaust gas is first discharged to the outside of the element by the first pump electrodes 57 and 58, and then the porous partition The remaining exhaust gas is guided to the measurement chamber b through 55, and the NOx concentration in the exhaust gas is detected by decomposing the remaining NOx by the pump electrodes 60 and 61 in the measurement chamber b and measuring the oxygen concentration. To do.
[0006]
At this time, in the measurement chamber a, in order to suppress decomposition of NOx in the exhaust gas, the partial pressure of oxygen in the measurement chamber a is measured using the electrodes 60 and 59 commonly used with the pump electrodes 60 and 61. Is done. A heater part in which a heating element 63 is embedded in an insulating layer 62 is formed integrally with the sensor part and a spacer 64 below the NOx sensor element, and the sensor part is formed by the heater part. The sensor is operated by heating to a temperature of 700 to 900 ° C.
[0007]
[Problems to be solved by the invention]
However, since the operating temperature of the flat plate element is as high as 700 to 900 ° C., when the temperature cycle from room temperature to the operating temperature is repeatedly applied, the solid electrolyte plates 51 and 52 have a flat plate shape. As a result, cracks occur in the solid electrolyte plates 51 and 52 of the NOx sensor element, the sealing performance of the measurement chambers a and b is impaired, and the measurement accuracy is significantly reduced. In some cases, there was a fatal problem that the sensor element was destroyed.
[0008]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cylindrical heater-integrated gas sensor element in which a heater portion is integrally formed with the gas sensor element as described above and has excellent thermal shock resistance such as rapid temperature rise. To do.
[0009]
[Means for Solving the Problems]
As a result of studying the above problems, the present inventors have provided a solid electrolyte layer outside a cylindrical tube made of a ceramic solid electrolyte having oxygen ion conductivity through a predetermined space region, and the space is gas permeable. The first space chamber and the second space chamber are separated by a certain partition wall, and a ceramic insulating layer in which a heating element for heating the element is embedded is disposed around the first and second space chambers. The present inventors have found that a heater-integrated gas sensor element that is resistant to temperature cycles can be provided by adopting a cylindrical structure as a whole.
[0010]
  That is, the gas sensor element of the present invention includes a cylindrical tube made of a ceramic solid electrolyte having at least oxygen ion conductivity and sealed at one end, and the cylindrical tube.ExteriorA ceramic insulating layer having a predetermined space region and a heating element embedded in the space region, and a solid electrolyte layer formed at a position closing the space region of the ceramic insulating layer; A first space chamber and a second space chamber in which the space region is separated and formed by a gas-permeable partition; and the first space chamber side of the solid electrolyte layerofInsideAnd the solid electrolyte layerA first electrode pair formed at positions facing each other on the outer surface of the cylindrical tube, and the cylindrical tubeThe first2 space sideOutsidesurfaceAnd said cylindrical tubeA second electrode pair formed on the inner surface facing each other; and a diffusion hole for taking the gas to be measured into the first space chamber.TheIt is a feature.
[0011]
At this time, the diffusion hole is preferably formed in the solid electrolyte layer or the ceramic insulating layer.
[0012]
In a flat plate type gas sensor element integrated with a conventional heater, when the temperature is rapidly increased, thermal stress concentrates on the edge portion of the element, and the element is easily broken. In contrast, the gas sensor element of the present invention has a cylindrical shape as a whole by providing a sensor portion outside a cylindrical tube made of a ceramic solid electrolyte having oxygen ion conductivity and sealed at one end. Is uniformly distributed over the entire element, so that concentration of thermal stress is prevented, and excellent thermal shock properties that cannot be obtained with a flat plate element can be obtained.
[0013]
In addition, according to the sensor element of the present invention, the ceramic insulating layer containing the heating element is disposed around the sensor unit, so that the heating efficiency of the sensor unit by the heating element can be increased and rapid temperature increase can be performed. The activation time of the sensor element can be shortened.
[0014]
As will be described later, the gas sensor element of the present invention has an electrode pattern, a ceramic insulating layer, and a heating element pattern embedded in the surface of the solid electrolyte sheet on the surface of the sensor element including a cylindrical tube made of a solid electrolyte. Since the sheet-like laminated body can be wound and the heater element body and the sensor element body can be fired at the same time, the manufacturing cost is extremely low, which is excellent from the viewpoint of economy.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a NOx sensor element will be described as an example of the heater-integrated gas sensor element of the present invention. The structure of the NOx sensor element of the present invention is shown in the schematic perspective view of FIG. 1 and the X of FIG. 1 shown in FIG.₁-X₁A cross-sectional view of the X shown in FIG.₂-X₂A cross-sectional view of the
[0016]
  According to the NOx sensor element 1 of the present invention, one end made of a ceramic solid electrolyte having oxygen ion conductivity is sealed, in other words, the longitudinal section of the cylindrical tube 2 having a U-shape.ExteriorIs provided with a ceramic insulating layer 4 having a predetermined space region and a heating element 3 embedded around the space region, and the space region of the ceramic insulating layer 4 includes a space region. A solid electrolyte layer 5 having a predetermined thickness is formed at a position to close the surface.
[0017]
A space region surrounded by the ceramic insulating layer 4 and the solid electrolyte layer 5 is separated into a first space chamber 7 and a second space chamber 8 by a gas-permeable partition wall 6.
[0018]
  Also, the first space chamber 7 side of the solid electrolyte layer 5ofInsideAnd the solid electrolyte layer 5First electrode pairs 9 and 10 are formed on the outer surfaces of the first electrode pair 9 and 10 at opposite positions. Furthermore, the second space chamber 8 side of the cylindrical tube 2OutsidesurfaceAnd the cylindrical tube 2At positions facing each other on the inner surfaceIsSecond electrode pairs 11 and 12 are formed by deposition.
[0019]
The solid electrolyte layer 5 and the first electrode pair 9 and 10 in the first space chamber 7 are provided with diffusion holes 13 for taking the gas to be measured into the first space chamber 7.
[0020]
In the NOx sensor element 1, oxygen ions are pumped by the solid electrolyte layer 5 and the first electrode pair 9 and 10 so that the oxygen concentration is constant so that the NOx in the first space chamber 7 is not decomposed. The exhaust gas pumped from the first space chamber 7 and maintained at this constant oxygen concentration is further guided to the second space chamber 8 through the gas permeable partition 6. In the second space 8, NOx in the exhaust gas is completely decomposed by the electrode 12, and oxygen produced is pumped by the cylindrical tube 2 and the second electrode pair 11, 12 to discharge the oxygen into the cylindrical tube 2. To do. The NOx sensor element 1 of the present invention has a mechanism for detecting the concentration of NOx in the exhaust gas from the pumping current values of the electrode pairs 11 and 12.
[0021]
At this time, the heating element 3 embedded in the ceramic insulating layer 4 is connected to the terminal electrode 15 via the lead electrode 14, and the heating element 3 is heated by passing a current through the heating element 3 through these. The sensor unit comprising the cylindrical tube 2 made of a solid electrolyte comprising the second electrode pairs 11 and 12 and the solid electrolyte layer 5 comprising the first electrode pairs 9 and 10 is heated efficiently. .
[0022]
As the overall size of the NOx sensor element, by setting the outer diameter to 3 to 6 mm, particularly 3 to 4 mm, the power consumption of the element can be reduced and the sensing performance can be enhanced.
[0023]
Although not shown in FIGS. 1 and 2 for convenience of explanation, the first electrode pair 9, 10, second electrode formed on the solid electrolyte layer 5 except for the electrode 11 inside the cylindrical tube 2. Of the electrode pairs 11 and 12, the electrode 12 formed on the second space chamber 8 side is desirably formed with a porous ceramic protective layer on the surface from the viewpoint of preventing poisoning by exhaust gas.
[0024]
Further, in the present invention, rapid decomposition of NOx in the first space chamber 7 is suppressed, and the oxygen partial pressure is set to a constant value (10^-83, it is desirable to form third electrode pairs 16 and 17 on the surface of the cylindrical tube 2 and the inner surface of the cylindrical tube 2 in the first space chamber 7 as shown in FIG. At that time, the electrode 11 in the cylindrical tube 2 of the second electrode pair 11 and 12 and the electrode 17 in the cylindrical tube 2 of the third electrode pair 16 and 17 can be formed as the same electrode. It is.
[0025]
Using the third electrode pairs 16 and 17 formed in the cylindrical tube 2, the electromotive force generated inside and outside the cylindrical tube 2 is measured, and the oxygen partial pressure in the first space chamber 7 is controlled to be constant. Accordingly, it is preferable to control the pumping current of the first electrode pair 9 and 10 from the viewpoint of measurement accuracy and sensitivity of the NOx concentration.
[0026]
Next, the material used for the sensor element of the present invention and the structure of each part of the element will be described.
(Solid electrolyte material)
In the NOx sensor element of the present invention, the solid electrolyte forming the cylindrical tube 2 and the solid electrolyte layer 5 is ZrO.₂It is preferable to be made of a ceramic containing ZrO, specifically, ZrO₂And Y₂O_ThreeAnd Yb₂O_Three, Sc₂O_Three, Sm₂O_Three, Nd₂O_Three, Dy₂O_ThreePartially stabilized ZrO containing 1 to 30 mol%, preferably 3 to 15 mol% of a rare earth oxide such as₂Or stabilized ZrO₂Is used. ZrO₂ZrO in which 1 to 20 atomic% of Zr was substituted with Ce₂By using, there is an effect that oxygen ion conductivity is increased and responsiveness is further improved.
[0027]
Furthermore, for the purpose of improving the sinterability, the above ZrO₂In contrast, Al₂O_ThreeAnd SiO₂However, if a large amount is added, the creep characteristics at high temperatures deteriorate, so Al₂O_ThreeAnd SiO₂The total amount of added is preferably 5% by weight or less, particularly 2% by weight or less.
(Ceramic insulation layer)
On the other hand, a ceramic material such as alumina, spinel, forsterite, zirconia, or glass is preferably used as the ceramic insulating layer 4 in which the heating element 3 is embedded. Furthermore, glass can be used for the glass insulating layer as the ceramic insulating layer 4, but in this case, from the viewpoint of heat resistance, at least one of BaO, PbO, SrO, CaO, and CdO is contained by 5% by weight or more. It is desirable that the glass be crystallized glass.
[0028]
The ceramic insulating layer 4 is preferably composed of a dense ceramic having a relative density of 80% or more and an open porosity of 5% or less. This is because the mechanical strength of the sensor element itself can be increased as a result of the strength of the insulating layer being increased because the ceramic insulating layer 4 is dense.
(Heating element)
The heating element 3 embedded in the ceramic insulating layer 4 is preferably made of one kind of metal selected from the group consisting of platinum, rhodium, palladium and ruthenium, or two or more kinds of alloys. From the viewpoint of co-sinterability with the ceramic insulating layer 4, it is desirable to select a metal or alloy having a melting point higher than the firing temperature of the ceramic insulating layer 4.
[0029]
In addition to the above metals, the heating element 3 contains alumina, spinel, an alumina / silica compound, forsterite, or zirconia that can be used as the above electrolyte in volume from the viewpoint of preventing sintering and increasing the adhesion between the insulating layers. It is desirable to mix in the range of 5 to 50%, particularly 10 to 20% in proportion.
(Heater structure)
As shown in the sectional view of FIG. 3, the structure of the heater portion in which the heating element 3 is embedded inside the ceramic insulating layer 4 has the heating element 3 embedded in the surface of the cylindrical tube 2 made of a solid electrolyte. It has a structure in which ceramic insulating layers 4 are laminated. That is, a ceramic insulating layer 4 made of alumina, spinel, forsterite or the like with a heating element 3 embedded therein is formed on the outer surface of the cylindrical tube 2. It is desirable to form the solid electrolyte layer 5 as well as on the second space chambers 7 and 8.
[0030]
The solid electrolyte layer 5 on the ceramic insulating layer prevents heat from being emitted from the heating element 3, and stress caused by a difference in thermal expansion or firing between the cylindrical tube 2 ceramic insulating layer 4 of the solid electrolyte. It works to reduce thermal stress as much as possible.
[0031]
The heating element 3 needs to be disposed in the ceramic insulating layer 4 so as not to be in direct contact with the cylindrical tube 2, the solid electrolyte layer 5, and the electrode, and the heating element 7, the cylindrical tube 2, and The thickness of the ceramic insulating layer between the heating element 7 and the solid electrolyte layer 5 is preferably in the range of 2 to 100 μm. This is because if the thickness of the ceramic insulating layer is less than 2 μm, the electrical insulating property is deteriorated and a leakage current is generated, which affects sensing. On the other hand, when the thickness of the ceramic insulating layer exceeds 100 μm, the thermal stress due to the difference in thermal expansion coefficient from the solid electrolytic material increases and the thermal shock resistance of the device deteriorates. The thickness of the insulating layer is particularly preferably 5 to 30 μm.
(electrode)
A first electrode pair 9, 10, a second electrode pair 11, 12, and a third electrode pair 16 formed on the surface of the solid electrolyte layer 5 above the first space chamber 7 and the cylindrical tube 2 of the second space chamber 8. , 17 may be one or two or more alloys selected from the group consisting of platinum, rhodium, palladium, ruthenium and gold. In addition, for the purpose of preventing the grain growth of the metal in the electrode during the sensor operation and for the purpose of increasing the contact at the so-called three-phase interface between the metal particles, the solid electrolyte and the gas related to the responsiveness, The components may be mixed in the electrode in a proportion of 1 to 50% by volume, particularly 10 to 30% by volume.
[0032]
  A first electrode pair 9, 10 formed on the solid electrolyte layer 5 of the first space chamber 7;Third electrode pair16 and 17 need to be an inactive electrode with respect to NOx from the viewpoint of suppressing decomposition of NOx. Therefore, platinum containing 1 to 30%, particularly 1 to 10% of gold in terms of weight is used. desirable. On the other hand, for the second electrode pair 11, 12, the cylindrical tube 2 made of a solid electrolyte is used.InsideThe electrode 11 and the electrode 17 may be formed on an area larger than the area of the electrode 12 and the electrode 16 on the second space chamber 8 side or the first space chamber 7, for example, on the entire inner surface of the cylindrical tube 2.
[0033]
Further, as another form, the diffusion hole 13 is not only formed in the solid electrolyte layer 5, but also as shown in the schematic sectional view of FIG. It can also be formed in a groove shape in the longitudinal direction of 2.
[0034]
As another embodiment, as shown in the schematic cross-sectional view of FIG. 6, a part of the ceramic insulating layer 4 on the tip side of the sensor element is partially replaced by a porous body 19, and the porous body 19 is replaced with a diffusion hole 13. It is also possible to substitute.
(Gas permeable partition)
It is necessary to separate the NOx sensor element of the present invention, the first space chamber 7 and the second space chamber 8 by the gas permeable partition 6. The partition wall 6 may be any material as long as it has a property of allowing gas to pass therethrough, and may be a dense material in which small diffusion holes are formed or a porous material.
As a material for forming the partition wall 6, at least one ceramic material selected from the group consisting of alumina, spinel, forsterite, zirconia, and glass is preferably used. In the case of using glass, from the viewpoint of heat resistance, it is a glass containing 5% by weight or more of at least one of BaO, PbO, SrO, CaO, and CdO, and is particularly preferably a crystallized glass. When the partition walls are formed of a porous body, the open porosity is preferably 20 to 70%, particularly preferably 40 to 50%, although it depends on the pore size.
(Electrode protective layer)
The electrode protective layer not shown in the drawing is provided for the purpose of preventing the other electrodes 9, 10, 12, 16 exposed to the exhaust gas from being poisoned except for the electrodes 11, 17 inside the cylindrical tube. It is formed on the surface of the electrode exposed to exhaust gas as a porous protective layer made of at least one selected from the group consisting of alumina, spinel, forsterite, zirconia and magnesia, and has an open porosity of 20 to 60 % Of the porous ceramic body, and the thickness is preferably in the range of 10 to 200 μm, particularly 50 to 150 μm, depending on the open porosity.
[0035]
Further, for the purpose of protecting the electrodes 10 and 12 inside the space chambers 7 and 8, the space chamber 7 is formed by forming a porous body 20 in the first space chamber 7 around the diffusion hole 13 as shown in FIG. , 8 may not be directly exposed to the exhaust gas.
(Element body manufacturing method)
Next, the method for manufacturing the sensor element of the present invention will be described by taking as an example the method for manufacturing the NOx sensor element having the structure shown in FIGS.
(1) First, a hollow cylindrical tube 21 having one end sealed as shown in FIG. This cylindrical tube 21 is well-known such as extrusion molding, isostatic pressing (rubber press) or press formation by appropriately adding a molding organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity such as zirconia. It is produced by the method.
[0036]
At this time, the solid electrolyte powder used is a mixed powder obtained by adding various stabilizers as described above to the zirconia powder, or a coprecipitation raw material powder of zirconia and the stabilizer. ZrO₂ZrO in which 1 to 20 atomic% of Zr was substituted with Ce₂A powder or a coprecipitation raw material can also be used. Furthermore, for the purpose of improving the sinterability, the solid electrolyte powder is mixed with Al.₂O_ThreeAnd SiO₂It is also possible to add 5% by weight or less, particularly 2% by weight or less.
(2) Then, as shown in FIG. 8B, the electrode patterns 22 and 23 to be the second electrode pairs 11 and 12 are formed on the inner and outer surfaces of the cylindrical tube 21 made of the above solid electrolyte, for example, a conductive material containing platinum. It is formed by a slurry dip method using a conductive paste, or screen printing, pad printing, or roll transfer. At this time, it is efficient to print the electrode on the inner surface of the cylindrical tube 21 by filling and discharging the conductive paste and coating the entire inner surface. In this way, the element body A is produced.
(3) Next, as shown in FIG. 9A, a slurry is prepared by appropriately adding an organic binder for molding to the zirconia powder, and using this insulator slurry, a doctor blade method, an extrusion molding method, A zirconia green sheet 24 for forming the ceramic insulating layer 4 having a predetermined thickness is produced by a pressing method or the like. The thickness of one green sheet 24 is preferably 50 to 500 μm, particularly preferably 100 to 300 μm from the viewpoint of handling the sheet.
[0037]
Thereafter, as shown in FIG. 9 (a), the first electrode is formed by a slurry dip method using a conductive paste of gold containing gold at predetermined positions on both sides of the green sheet 24, or by screen printing, pad printing, or roll transfer. In order to form 9 and 10, electrode patterns 25 and 26 including leads are formed.
[0038]
  nextAs shown in FIG. 9B, a ceramic powder such as alumina, spinel, forsterite, zirconia, glass or the like is used to appropriately add a molding organic binder to prepare a slurry. The ceramic insulating layer 27 is applied and formed on one side of the green sheet 24 with a predetermined thickness by screen printing or the like except for the region where the second space chamber 8 is formed. Thereafter, as shown in FIG. 9C, a conductive paste containing platinum powder is printed on the surface of the ceramic insulating layer 27 by a screen printing method, a pad printing method, a roll transfer method, or the like, thereby generating the heating element pattern 2.9Form. And again, figure9As shown in (d), the above-described insulator slurry is applied, and the heating element pattern 29 is embedded in the insulating layer 27. At this time, the partition wall 28 between the first space chamber 7 and the second space chamber 8 is also printed and formed by screen printing or the like using a slurry capable of forming a porous body in the same manner as described above, and the schematic perspective view of FIG. An element body B as shown in the figure is produced.
(4) Then, as shown in FIG. 11, a plate-like element B is wound around the surface of the cylindrical element A to produce a cylindrical laminate. At this time, in order to wind the element B around the element A, an adhesive such as an acrylic resin or an organic solvent is interposed between the element B and the element A, or pressure is applied with a roller or the like. It can be mechanically bonded.
[0039]
  At this time, FIG.)As shown, in the present invention, the seam of the wound element body B is desirably set so that the end face opening θ is in the range of θ = 5 to 50 ° in circumferential angle after firing. If the opening of the end face is smaller than 5 °, the heater element body partly overlaps easily from the viewpoint of the size of the element body B and the manufacturing variation of the element body A, which increases the yield during mass production of elements. There is a risk of impact. On the other hand, if the opening of the end face exceeds 50 °, the element is deformed into an ellipse during firing, and as a result, the thermal shock resistance may be lowered. The opening θ of the end face is particularly preferably 10 to 20 ° in terms of a circumferential angle.
(Diffusion hole formation) In forming the diffusion hole 13 of FIG. 1, before the element body B and the element body A are integrated, as shown in FIG. Or the like is used to form a hole 30 having a diameter of 100 to 500 μm after firing. Further, the hole 30 may be formed after forming the cylindrical laminated body by integrating the element body A and the element body B, or may be formed after firing described later. However, from the viewpoint of workability and yield, it is preferably formed by the above method before firing.
[0040]
Further, as shown in FIG. 5, when the diffusion hole 13 is formed on the tip side of the ceramic insulating layer 4, the ceramic insulating layer 4 is formed at the stage of forming the element body B before firing as shown in FIG. It is also possible to form a groove penetrating to the tip. Moreover, it is also possible to form using a micro drill from the front-end | tip after baking.
[0041]
  Furthermore, as shown in FIG.13In the case of substituting with a porous body 19, in the stage of FIGS. 9B to 9D, a slurry made of ceramic powder such as alumina, spinel, forsterite, zirconia, glass or the like having a large particle diameter at the tip portion, Or the slurry which added the pore formation which consists of organic substance to the said raw material powder should just be apply | coated.
(Baking) And, by burning the cylindrical laminate composed of the above-mentioned element body A and element body B into one body at a temperature at which the element body A and the element body B can be simultaneously fired, The body B can be completely integrated. For example, when zirconia is used as the solid electrolyte, simultaneous firing can be performed by firing at 1300 to 1700 ° C. for about 1 to 10 hours in an inert atmosphere such as argon gas.
(Formation of electrode protective layer) The electrode protective layer is formed on the surface of the electrode pattern of the element B, the electrode patterns 25 and 26 in the element B, or the electrode pattern in the element A before firing the cylindrical laminate. A ceramic slurry such as alumina, spinel, forsterite, zirconia, and magnesia that becomes porous after firing is formed on the surface of 22 by a screen printing method and a slurry dipping method. After winding and integrating, it may be fired. This ceramic electrode protective layer desirably has an open porosity of 20 to 60%, particularly 30 to 40% from the viewpoint of gas permeability.
(Other Manufacturing Method) In addition to the method shown in FIG. As shown in FIG. 12, the slurry is formed using a conductive paste containing platinum containing gold at predetermined positions on both sides of a green sheet 31 made of a solid electrolyte such as zirconia.
The electrode patterns 32 and 33 to be the first electrode pair are formed by the lead dip method, screen printing, pad printing, or roll transfer, and porous slurry is applied to one surface of the electrode patterns 32 and 33 to form the first space chamber and the second space. A partition wall 28 is formed for separating the chambers.
[0042]
On the other hand, an opening 35 is formed in the green sheet 34 made of a ceramic insulating material by a method such as punching to form the first space chamber and the second space chamber. Further, a similar opening 35 is formed in the green sheet 36 made of a ceramic insulating material, and a heat generation pattern 37 is printed and applied around the opening 35.
[0043]
Thereafter, the green sheets 31, 34, and 36 are aligned and stacked and integrated to produce the element body B of FIG. 10.
[0044]
Further, when the element B is wound around the surface of the element A, the electrode pattern 22 on the outer surface side of the element A is printed on the surface of the green sheet 38 made of the same solid electrolyte as the cylindrical tube 21 as shown in FIG. Then, after being previously laminated with the element body B, the laminated body of the element body B and the green sheet 38 is wound around the surface of the element body A in which only the electrode pattern 23 is formed inside the cylindrical tube 21, and is integrated. It is also possible to fire. This is because it is difficult to form an electrode pattern on the curved surface of the cylindrical tube 21, so that mass productivity can be improved by performing all patterning on the element body B side. In that case, the electrode pattern 23 inside the cylindrical tube 21 can be easily formed by filling and discharging the electrode paste inside the cylindrical tube 21 and forming the electrode pattern 23 on the entire inner surface of the cylindrical tube 21.
[0045]
The NOx sensor element of the present invention is not limited to the structure and manufacturing method shown in FIGS. 1 to 13. For example, the first space chamber 7 and the second space chamber 8 are interchanged, and the tip side of the cylindrical tube 2 is replaced. You may provide the 2nd space chamber 8 in. Further, the sensor element of the present invention can be used as an SOx sensor element or an HC sensor element having excellent measurement accuracy and sensitivity in addition to the NOx sensor element for detecting the NOx concentration in the exhaust gas of an automobile internal combustion engine.
[0046]
【Example】
Example 1
As an example, the gas sensor element structure shown in FIG. 1 is taken as an example, and the element of the present invention will be described using the manufacturing method of FIG.
Commercially available alumina powder and 5 mol% Y with an average particle size of 0.5 μm and 3 μm₂O_ThreeContaining zirconia powder and 10 vol% ZrO₂Platinum powder containing 5% by weight of gold and ZrO₂Each of platinum powders containing 10 wt% was prepared.
[0047]
First, as shown in FIG. 8A, 5 mol% Y having a particle diameter of 0.5 μm.₂O_ThreeA polyvinyl alcohol solution was added to the contained zirconia powder to prepare a clay, and after sintering by extrusion molding, a cylindrical molded body with one end sealed to an outer diameter of about 4 mm and an inner diameter of 1 mm was manufactured.
[0048]
Then, on the surface of the cylindrical molded body, ZrO as a second electrode pair as shown in FIG.₂A rectangular electrode pattern made of a platinum paste containing 10% by volume is printed and applied, and the platinum paste is filled and discharged on the entire inner surface of the cylindrical molded body to form an electrode on the entire inner surface of the cylindrical molded body. Element A was prepared. At this time, the thickness of the electrode was adjusted to about 10 μm after firing.
[0049]
Moreover, 5 mol% Y with a particle diameter of 0.5 μm₂O_ThreeA slurry was prepared by adding an acrylic binder and a toluene solution to the contained zirconia powder, and a zirconia green sheet having a thickness of about 300 μm was prepared by a doctor blade method.
[0050]
Using this green sheet, as shown in FIG. 9 (a), 5% by weight of gold and ZrO are provided at positions facing both sides of the sheet.₂A first electrode pair was formed using a platinum paste containing 10% by volume. Then, in order to form an insulating layer, as shown in FIG. 9B, a slurry containing alumina powder was applied by screen printing so as to have a thickness of about 10 μm after firing. Moreover, in order to form a porous partition, 5 mol% Y having a particle diameter of 3 μm₂O_ThreeA partition wall pattern was printed by screen printing using a slurry composed of the contained zirconia powder.
[0051]
Further, a platinum heating element pattern of FIG. 9C is formed on the surface of the insulating layer, and an alumina insulating layer having a thickness of about 10 μm is formed by the above method as shown in FIG. The pattern was embedded in the insulating layer, and the element body B was produced.
[0052]
After that, as shown in FIG. 11, the element body B made of the above-mentioned sheet-like laminate is wound around the surface of the cylinder-like element A on which the second electrode is formed using an acrylic binder, and the cylinder-like laminate And a heater-integrated nitrogen oxide (NOx) sensor element was completed at 1400 ° C. in the air for 1 hour. At this time, the opening angle (θ) of the end face by the element body B was set to about 15 °.
[0053]
The manufactured gas sensor element was heated from room temperature to 1000 ° C. in 20 seconds and air-cooled from 1000 ° C. to room temperature as one cycle, and this was repeated 50,000 times to determine the probability of the element breaking. At this time, 100 samples were used. For comparison, a similar test was performed on a flat plate type NOx sensor element integrated with a commercially available heater.
[0054]
As a result, in the commercially available flat plate type NOx sensor element, the breakage rate was 92%, whereas the cylindrical type NOx sensor element of the present invention was as low as 32%. It can be seen that the gas sensor element has an extremely low damage rate due to thermal cycling as compared with a commercially available flat sensor element. From this result, it can be fully understood that the cylindrical sensor element of the present invention has excellent thermal shock properties.
(Example 2)
Using the sample of Example 1, oxygen concentrations of 0.4 and 4.0% at 800 ° C. (N as the balance gas)₂The relationship between the NOx concentration and the pumping current of the second electrode pair was determined. The results are shown in FIG. From this, it can be seen that the element of the present invention has a stable ability to detect NOx concentration in a wide oxygen concentration range regardless of the oxygen concentration in the atmosphere.
[0055]
【The invention's effect】
  As detailed above, the present inventionThe mothThe sensor elementat leastCylindrical tube made of ceramic solid electrolyte with oxygen ion conductivity and sealed at one endAnd the cylindrical tubeOn the outsideA ceramic insulating layer that is formed and has a predetermined space region, and a heating element is embedded around the space region, and a solid electrolyte layer formed at a position that covers the space region of the ceramic insulating layer; Space areaGas permeationGenderwallBySeparationFormation1st space roomandSecond space roomWhen,SaidOf the solid electrolyte layerOn the first space room sideInside andOf the solid electrolyte layerExternalEach otherIn the opposite positionBeen formedFirst electrode pairAnd saidCylindrical tubeThe outer surface of the second space chamber side and the inner surface of the cylindrical tube are formed at positions facing each other.Second electrode pairAnd a diffusion hole for taking the gas to be measured into the first space chamberBy doing so, it is possible to provide a gas sensor element excellent in thermal shock properties such as rapid temperature rise that cannot be obtained by a conventional flat sensor element. As a result, the activation time of the sensor element can be shortened.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a NOx sensor element as an example of a gas sensor element of the present invention.
[Figure 2](A)X of the NOx sensor element of FIG.₁-X₁ lineSchematic cross sectionAnd (b) isX₂-X₂ lineIt is a schematic sectional drawing.
FIG. 3 shows the present invention.ofIt is a schematic sectional drawing for demonstrating the other example of a NOx sensor element.
FIG. 4 shows the present invention.ofIt is a schematic sectional drawing for demonstrating the further another example of a NOx sensor element.
FIG. 5 shows the present invention.ofIt is a schematic sectional drawing for demonstrating the further another example of a NOx sensor element.
FIG. 6 shows the present invention.ofIt is a schematic sectional drawing for demonstrating the further another example of a NOx sensor element.
FIG. 7 shows the present invention.ofIt is a schematic sectional drawing for demonstrating the further another example of a NOx sensor element.
[Fig. 8]Figure1 for explaining the manufacturing method of the gas sensor element of(A) (b)5 is a process diagram for explaining a method for producing an element body A.
FIG. 9Figure1 for explaining the manufacturing method of the gas sensor element of(A) to (d)5 is a process diagram for explaining a method for producing an element body B. FIG.
FIG. 10Figure9 is a schematic perspective view of an element body B manufactured according to FIG.
FIG. 11Figure1 for explaining the manufacturing method of the gas sensor element 1 for explaining the process of winding the element body A around the element body B.Outline perspectiveFIG.
FIG.FigureFIG. 6 is a process diagram for explaining another method for producing the element body B, for explaining a method for producing the gas sensor element 1.
FIG. 13FigureFIG. 6 is a process diagram for explaining another method for producing the element body B, for explaining a method for producing the gas sensor element 1.
FIG. 14 shows the present invention.ofIt is the figure which showed the relationship between NOx density | concentration of a NOx sensor element, and a pumping current.
FIG. 15 is a schematic sectional view of a conventional flat-plate-type NOx sensor element.
[Explanation of symbols]
1 Gas sensor element
2 Cylindrical tube
3 Heating elements
4 Ceramic insulation layer
5 Solid electrolyte layer
6 Gas-permeable partition
7 1st space room
8 Second space room
9, 10 First electrode pair
11, 12 Second electrode pair
13 Diffusion hole

Claims (3)

A cylindrical tube made of a ceramic solid electrolyte having at least oxygen ion conductivity and sealed at one end, and having a predetermined space region formed on the outer surface of the cylindrical tube, and a heating element embedded in the space region A ceramic insulating layer formed, a solid electrolyte layer formed at a position closing the space region of the ceramic insulating layer, and a first space chamber and a second space chamber formed by separating the space region by a gas-permeable partition. a first electrode pair formed on opposing positions of an outer surface of said solid inner surface of the first space chamber side of the electrolyte layer and the solid electrolyte layer, the outer surface of the second space chamber side of the cylindrical tube and the second electrode pair and the gas sensor element characterized by comprising a diffusion hole for taking in the measurement gas in the first space chamber formed at mutually opposing positions of the inner surface of the cylindrical tube. Claim 1 Symbol mounting of the gas sensor element the diffusion hole is formed before Symbol solid electrolyte layer. Claim 1 Symbol mounting of the gas sensor element the diffusion hole is formed in the ceramic insulating layer.

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