JP2005147836A - Stacked-type gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked-type gas sensor element having high durability and reliability. <P>SOLUTION: This stacked type gas sensor element 1 is formed by directly connecting a solid electrolyte layer 11 containing zirconia and alumina to the first and second insulating layers 21, 22 mainly composed of alumina by simultaneous baking. A portion MZ1 very close to an interference IF1 in the solid electrolyte layer 11 is irradiated with a laser beam, and stress σZ applied to the solid electrolyte layer 11 at the portion MZ1 is determined from the wave number value κpsz of an acquired fluorescence peak, by utilizing the fact that the wave number value of the fluorescence peak, emitted from Cr<SP>3+</SP>ions in alumina crystal particles, is changed by a stress when the laser light is irradiated. When the tensile stress applied to the solid electrolyte layer 11 is smaller than 300 MPa at the maximum, the durability is satisfactory. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a stacked gas sensor element including a solid electrolyte layer and an alumina insulating layer.

Conventionally, the absolute wave value (about 14400 cm ⁻¹ ) of the peak of fluorescence generated when Cr ³⁺ ions contained as inevitable impurities in alumina crystal particles are irradiated with laser light depends on the stress applied to the alumina crystal particles. There is an example in which the residual stress generated in the alumina crystal particle itself is analyzed in the composite material of zirconia and alumina using the phenomenon of changing (shifting).
The absolute wave value is the reciprocal of the wavelength.
In this case, a reference sample made of an alumina ceramic material not containing zirconia or the like is used as the reference sample in advance, and external stress is applied to the reference sample, and each external stress value and the absolute wave value of the fluorescence peak or a certain value The relationship with the relative wave value from the reference absolute wave value is obtained. Based on this relationship, the residual stress applied to the alumina crystal particles in the composite material of zirconia and alumina is obtained from the absolute wave value or relative wave value of the fluorescence peak obtained by actually measuring the sample.

Acta mater. Vol.46. No.5. Pp.1701-1710. 1998

  By the way, a multilayer gas sensor element is known which includes a solid electrolyte layer containing zirconia and an alumina insulating layer laminated in direct contact with at least a part thereof by simultaneous firing. Among them, as a solid electrolyte layer, there is a multilayer gas sensor element using not only zirconia but also alumina, that is, a zirconia crystal particle and an alumina crystal particle dispersed in each other.

However, in the multilayer gas sensor element, cracks may occur in the vicinity of the interface between the solid electrolyte layer and the alumina insulating layer during the manufacturing process, specifically, in the fired multilayer gas sensor element. Further, cracks may occur near the interface between the solid electrolyte layer and the alumina insulating layer during use of the gas sensor element or during a durability test.

This is considered to be due to the following reason. That is, in the multilayer gas sensor element, due to the difference between the coefficient of thermal expansion of the solid electrolyte layer and the coefficient of thermal expansion of the alumina insulating layer, the solid electrolyte layer having a relatively large coefficient of thermal expansion has a tensile stress. It is considered that the alumina insulating layer having a small rate is subjected to compressive stress, and a stress difference is generated between the two.
And if this stress difference becomes too large, it is considered that cracks occur near the interface including the solid electrolyte layer during the manufacturing process, during use, or during the durability test in the vicinity of the interface between the two. Or, considering that ceramic materials are generally strong against compressive stress but weak against tensile stress, if the tensile stress applied to the solid electrolyte layer becomes too large, the manufacturing process will be performed near the interface between the two. It is considered that cracks occur in the vicinity of the interface including the solid electrolyte layer during use or during the durability test.

  The present invention has been made in view of such problems, and an object thereof is to provide a stacked gas sensor element having high durability and reliability.

The solution includes a solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other, and is laminated in direct contact with the solid electrolyte layer at least partially by co-firing. ^A laminated gas sensor element comprising an alumina insulating layer containing alumina crystal particles containing ³⁺ ions as a main component, wherein the solid electrolyte layer receives a maximum tensile stress in the immediate vicinity of the interface with the alumina insulating layer. However, it is a laminated gas sensor element of 300 MPa or less.

In the multilayer gas sensor element of the present invention, the solid electrolyte layer and the alumina insulating layer having different materials and, therefore, different thermal expansion coefficients are laminated in direct contact with each other. As described above, it is considered that tensile stress is applied to the solid electrolyte layer having a relatively large coefficient of thermal expansion. And the stress is considered to become the maximum in the immediate vicinity of the interface. In general, ceramic materials are strong against compressive stress but weak against tensile stress. Accordingly, it is understood that when the tensile stress applied to the solid electrolyte layer is excessive, the solid electrolyte layer, particularly, the breakage based on the immediate vicinity of the interface occurs and causes a crack.
On the other hand, in the multilayer gas sensor element of the present invention, the tensile stress received by the solid electrolyte layer in the vicinity of the interface with the alumina insulating layer is 300 MPa or less at the maximum. For this reason, the solid electrolyte layer is prevented from being broken by tensile stress, and a laminated gas sensor element with high durability and reliability can be obtained.

In addition, a solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other, and at least partly in direct contact with the solid electrolyte layer and laminated, Cr ³⁺ ions A laminated gas sensor element comprising an alumina insulating layer containing alumina crystal particles containing as a main component, and a first reference sample having the same composition as the solid electrolyte layer is prepared. A portion with a known stress is irradiated with a laser beam having a predetermined wavelength, and the fluorescence emitted by the Cr ³⁺ ions contained in the first reference sample is positioned near an absolute wave value of 14400 cm ^−1. And measuring the wave value of the fluorescent peak to obtain a first relationship between each stress value and the wave value of the fluorescent peak, while the boundary between the solid electrolyte layer and the alumina insulating layer. The closest portion is irradiated with the laser beam of the predetermined wavelength, the wave value of the fluorescence peak is measured, and the solid electrolyte is obtained near the interface from the measured wave value of the fluorescence peak based on the first relationship. It is preferable that the laminated gas sensor element has a tensile stress of 300 MPa or less at the maximum.

  Also in this laminated gas sensor element, the tensile stress received by the solid electrolyte layer in the vicinity of the interface with the alumina insulating layer is 300 MPa or less at the maximum. For this reason, the solid electrolyte layer is prevented from being broken by tensile stress, and a laminated gas sensor element with high durability and reliability can be obtained.

Further, in order to obtain the stress value applied to the solid electrolyte layer, a first reference sample having the same composition as that of the solid electrolyte layer is prepared, and the stress value and the wave value of the fluorescence peak are calculated using the first reference sample. Find the first relationship. Further, each part in the solid electrolyte layer is irradiated with laser light, and the stress value received at each part in the solid electrolyte layer is obtained from the measured wave value of the fluorescence peak based on the first relationship.
By irradiating the laser in this way and using the fluorescence emitted by Cr ³⁺ ions, the stress actually applied to the solid electrolyte layer can be measured in the form of the stacked gas sensor element.
As the wave value of the fluorescence peak, an absolute wave value can be used, or a relative wave value of the fluorescence peak with respect to a predetermined absolute wave value (for example, the absolute wave value of the irradiated laser beam) can be used. .

Another solution is a solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other, and the solid electrolyte layer is laminated in direct contact with at least part of the solid electrolyte layer by co-firing. A laminated gas sensor element comprising an alumina insulating layer mainly composed of alumina crystal particles containing Cr ³⁺ ions, wherein the solid electrolyte layer is interposed through an interface between the solid electrolyte layer and the alumina insulating layer. In the multilayer gas sensor element, a difference between the stress received and the stress received by the alumina insulating layer is 400 MPa or less.

As described above, in the stacked gas sensor element, due to the difference between the thermal expansion coefficient of the solid electrolyte layer and the thermal expansion coefficient of the alumina insulating layer, a tensile stress is relatively applied to the solid electrolyte layer having a relatively large thermal expansion coefficient. In addition, it is considered that the alumina insulating layer having a small coefficient of thermal expansion is subjected to compressive stress and a stress difference is generated between the two through the interface. Accordingly, it is understood that when the stress difference between the solid electrolyte layer and the alumina insulating layer is excessive, the breakage occurs near the interface, causing cracks.
On the other hand, in the multilayer gas sensor element of the present invention, the difference between the stress received by the solid electrolyte layer and the stress received by the alumina insulating layer via the interface between the solid electrolyte layer and the alumina insulating layer is as follows. 400 MPa or less. For this reason, the solid electrolyte layer and the alumina insulating layer are prevented from being destroyed in the vicinity of the interface, and a laminated gas sensor element with high durability and reliability can be obtained.

In addition, a solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other, and at least partly in direct contact with the solid electrolyte layer and laminated, Cr ³⁺ ions A laminated gas sensor element comprising an alumina insulating layer containing alumina crystal particles containing as a main component, and a first reference sample having the same composition as the solid electrolyte layer is prepared. A portion with a known stress is irradiated with a laser beam having a predetermined wavelength, and the fluorescence emitted by the Cr ³⁺ ions contained in the first reference sample is positioned near an absolute wave value of 14400 cm ^−1. A second reference sample having the same composition as that of the alumina insulating layer, by measuring the wave number of the fluorescent peak to obtain a first relationship between each stress value and the wave number of the fluorescent peak Prepared, the second applying stress to the reference sample, the portion known stressed irradiated with laser light of the predetermined wavelength, the fluorescence the Cr ³⁺ ions contained in the second reference sample emits While measuring the wave value of the peak of each of the two to obtain a second relationship between each stress value and the wave value of the fluorescent peak, the portion of the solid electrolyte layer closest to the interface and the interface of the alumina insulating layer Each of the nearest sites or on the interface is irradiated with the laser beam of the predetermined wavelength to measure the wave value of the fluorescence peak, and is obtained from the measured wave value of the fluorescence peak based on the first relationship. In addition, the laminate type in which the difference between the stress value received by the solid electrolyte layer in the immediate vicinity of the interface and the stress value received by the alumina insulating layer in the immediate vicinity of the interface is 400 MPa or less. Gas Preferably in the support element.

  In this laminated gas sensor element, the difference from the stress value applied to the alumina insulating layer in the vicinity of the interface is 400 MPa or less. For this reason, the solid electrolyte layer and the alumina insulating layer are prevented from being broken near the interface, and a laminated gas sensor element with high durability and reliability can be obtained.

In addition, in order to obtain the stress value received by the solid electrolyte layer in the immediate vicinity of the interface, a first reference sample having the same composition as that of the solid electrolyte layer is prepared, and the stress value and the fluorescence peak wave are prepared using the first reference sample. The first relationship with the numerical value is obtained. Further, a portion of the solid electrolyte layer near the interface is irradiated with laser light, and the stress value received by the solid electrolyte layer in the vicinity of the interface is obtained from the measured wave value of the fluorescence peak based on the first relationship. Similarly, in order to obtain the stress value received by the alumina insulating layer in the immediate vicinity of the interface, a second reference sample having the same composition as that of the alumina insulating layer is prepared, and each stress value and fluorescence peak are obtained using this second reference sample. A second relationship with the wave value is obtained. Further, a portion of the alumina insulating layer in the vicinity of the interface is irradiated with laser light, and the stress value received by the alumina insulating layer in the vicinity of the interface is obtained from the measured wave value of the fluorescence peak based on the second relationship.
By irradiating the laser in this way and using the fluorescence emitted by Cr ³⁺ ions, the stress actually received by the solid electrolyte layer and the alumina insulating layer, and further, the difference in stress between them is obtained. Can be measured.
As the wave value of the fluorescence peak, an absolute wave value can be used, or a relative wave value of the fluorescence peak with respect to a predetermined absolute wave value (for example, the absolute wave value of the irradiated laser beam) can be used. .

  Embodiments of the present invention will be described below with reference to FIGS. First, the laminated gas sensor element 1 according to the present embodiment will be described with reference to FIGS. Among these, FIG. 1 is an exploded perspective view of the multilayer gas sensor element 1. FIG. 2 is a cross-sectional view of the laminated gas sensor element 1 that is orthogonal to the longitudinal direction (left and right direction in FIG. 1) and includes a detection electrode 12, a reference electrode 13, and a heating portion 24 described below. It is sectional drawing.

The multilayer gas sensor element 1 is an element formed by laminating a plurality of ceramic layers as shown in FIG. The stacked gas sensor element 1 is roughly divided into an oxygen concentration cell element 10 and a base body 20.
Among these, the oxygen concentration cell element 10 is a solid electrolyte layer for oxygen concentration cell (hereinafter also referred to as a solid electrolyte layer) 11, a detection electrode 12 and a reference electrode 13 sandwiching the solid electrolyte layer, and a detection electrode 12. It has an electrode protective layer 18 and a reinforced protective layer 19 which are laminated with the electrolyte layer 11. The solid electrolyte layer 11 includes partially stabilized zirconia and alumina (zirconia crystal particles and alumina crystal particles) to which a predetermined amount (5 mol%) of yttria is added, and has a property as a solid electrolyte by zirconia. The solid electrolyte layer 11 includes a detection electrode 12 made of Pt on the upper surface 11u (upward in the drawing). The detection electrode 12 is drawn out to the base end side (right side in the figure) by the extension lead 14. The solid electrolyte layer 11 also includes a reference electrode 13 made of Pt on the lower surface 11d (lower side in the figure). The reference electrode 13 is also extended to the base end side (right side in the drawing) by the extension lead 15, and the base end side of the upper surface 11 u of the solid electrolyte layer 11 by the through-hole conductor 16 penetrating the solid electrolyte layer 11. It is connected to the terminal pad 17 formed in.

  Furthermore, on the upper surface 11u of this solid electrolyte layer 11 (upper side in the figure), a porous electrode protection layer 18 is disposed so as to cover the detection electrode 12, and protects the detection electrode 12 from poisoning, In order to protect the solid electrolyte layer 11, a reinforced protective layer 19 mainly composed of the same alumina as the first and second insulating layers 21 and 22 is formed. As can be easily understood from FIG. 1, the reinforced protective layer 19 is arranged and formed so that the base end portion 14b of the extended lead 14 and the terminal pad 17 are exposed to the outside.

  The base body 20 includes two layers of first and second insulating layers 21 and 22 and a resistance heating element 23 sandwiched therebetween. Of these, the first and second insulating layers 21 and 22 are both insulating layers mainly composed of alumina. Further, the resistance heating element 23 is made of Pt, is located immediately below the detection electrode 12 and the reference electrode 13 and has a zigzag shape, and a heat generating portion 24 that generates heat by energization, and a base end side (right side in the figure). Through hole pad portions 26 and lead portions 25 extending from both ends of the heat generating portion 24 to the through hole pad portions 26, respectively. Furthermore, it has a terminal pad 28 and a through-hole conductor 27 that penetrates through the second insulating layer 22 and connects the terminal pad 28 and the through-hole pad portion 26.

  The laminated gas sensor element 1 is manufactured as follows. First, an unfired sheet for a solid electrolyte layer is created. Specifically, a zirconia powder in which a predetermined amount (5 mol%) of yttria is dissolved, an alumina powder, a binder (polyvinyl butyral), and a solvent are mixed and kneaded to obtain a slurry, which is not yet obtained by a known casting method. Processed into a fired sheet. The green sheet is cut into a predetermined shape.

  A through-hole is drilled at a predetermined position of the green sheet, and a conductive paste containing Pt as a main component and serving as a through-hole conductor 16 is applied to the inner peripheral surface of the through-hole. In addition, a conductive paste containing Pt as a main component is printed in a predetermined pattern on the front and back surfaces of the green sheet in a predetermined pattern to be the detection electrode 12, the reference electrode 13, and the extended leads 14 and 15, and dried. Thus, an unsintered sheet for the solid electrolyte layer is obtained.

  Separately, unfired sheets for the first and second insulating layers and the reinforced protective layer are prepared. Specifically, alumina powder or a zirconia powder in which a predetermined amount of alumina powder and yttria are dissolved, a binder (polyvinyl vinyl), and a solvent are kneaded to form a slurry, which is a green sheet by a known casting method. To process. The green sheet is cut into a plurality having a predetermined shape. These unfired sheets become the first insulating layer 21, the second insulating layer 22, and the reinforced protective layer 19.

Among the unfired sheets, the unfired sheet to be the second insulating layer 22 is made of a conductive paste mainly composed of Pt, in which through holes are drilled at predetermined positions and through-hole conductors 27 are formed on the inner peripheral surface thereof. Apply. In addition, a conductive paste mainly composed of Pt is printed in a predetermined pattern to be the resistance heating element 23 and the terminal pad 28 in a predetermined region of the front and back surfaces, and dried, so that it is not fired for the second insulating layer. A sheet.

Next, the unfired sheet for the first insulating layer and the unfired sheet for the second insulating layer are laminated and pressure-bonded so that the pattern of the resistance heating element 23 is between the layers. Further, the unfired sheet for the first insulating layer and the unfired sheet for the solid electrolyte layer are laminated so that the pattern of the reference electrode 13 is between the layers, and pressure-bonded.
Separately, a slurry obtained by kneading alumina powder, a pore-forming material (carbon powder), a binder (butyral resin and dibutyl terephthalate), and a dispersing agent is cut into a sheet, and an unfired sheet for an electrode protective layer is obtained. Create it. The unfired sheet for the electrode protective layer is covered with the pattern to be the detection electrode 12, and the unfired sheet for the reinforcing protective layer is laminated and pressure-bonded, cut into a predetermined shape, and the unfired laminate is obtained. Obtained.

  Thereafter, the green laminate is fired by a known method. Specifically, degreasing is performed by raising the temperature at a rate of temperature increase of 20 ° C./H in an air atmosphere and holding at 450 ° C. for 1 hour. Next, the temperature was raised and the laminate was fired at 1500 ° C. for 1 hour to obtain a multilayer gas sensor element 1 (see FIGS. 1 and 2).

Next, the wave number measuring apparatus 100 used in the present embodiment will be described with reference to FIG. This wave number measuring apparatus 100 is a Raman spectroscopic analysis apparatus possessed by the Ceramic Physics Laboratory (Professor Pezzotti) of the Department of Materials Engineering, Kyoto Institute of Technology. In this wave number measuring apparatus 100, laser light of an Ar ion laser 120 (wavelength 488 nm) is guided and irradiated to the measurement sample SM placed on the XY table 170 by the microscopic optical system 130. The reflected light is received again by the microscopic optical system 130 and guided to the spectroscope 140. The spectroscope 140 uses a high precision triple monochromator (T-64000, manufactured by Jobin-Yvon / HoribaGroup ISA). Furthermore, when the spectroscope 140 targets a stable and high intensity peak such as a fluorescence peak of Cr ³⁺ ions, the spectroscope 140 separates a light beam from a neon lamp light source in order to manage a measurement temperature and suppress mechanical variation. The reference peak obtained in this way is monitored, and the measurement conditions are optimized, such as peak correction using this, and the resolution is increased to 0.01 cm ⁻¹ .

  Of the reflected light, the light split by the spectroscope 140 is input to the CCD array 150 serving as a one-dimensional line sensor. In the CCD array 150, since the wavelength (wave number) of light incident on each CCD element is different, the intensity of light for each wavelength (wave number) can be measured by obtaining the output of each CCD element. That is, the spectral intensity distribution can be measured. This is taken into the computer 160 and further processed.

By the way, as described above, it has been found that the alumina crystal particles contain slight Cr ³⁺ ions as inevitable impurities of aluminum ions. By the way, when the alumina crystal particles containing Cr ³⁺ ions are irradiated with laser light having a wavelength of 694 nm or less (for example, 488 nm or 514 nm), the Cr ³⁺ ions emit fluorescence having an absolute wave value of about 14400 cm ^{−1 at} the peak PK. (See FIG. 4).

  Furthermore, it has been found that the absolute wave value (relative wave value) of this fluorescence peak changes according to the magnitude of stress applied to the alumina crystal particles. From this, the magnitude of the stress applied to the alumina crystal particles can be estimated by measuring the wave number of the fluorescence peak.

  Therefore, it is considered that the gas sensor element 1 according to the present embodiment is also used to measure the stress generated in the solid electrolyte layer 11, the stress generated in the first insulating layer 21, and the stress difference generated therebetween. .

The solid electrolyte layer 11 for an oxygen concentration cell contains a certain amount of zirconia and has a relatively low alumina content (for example, 50%, 30%, 10%, or 3%, see FIG. 7 described later), whereas the first The insulating layer 21 has a high content of alumina (for example, 90% or 100%, see FIG. 7 described later). As described above, the solid electrolyte layer 11 and the first insulating layer 21 have different alumina contents, and thus are considered to have different coefficients of thermal expansion. In general, for alumina-zirconia composites, the higher the alumina content, the lower the coefficient of thermal expansion. Therefore, different alumina-zirconia composite layers having different alumina contents, or alumina-zirconia composite layers When the alumina layer is laminated and simultaneously sintered, a difference in thermal expansion occurs between them. Specifically, the alumina-zirconia composite material layer or the alumina layer having a high alumina content is subjected to a compressive stress from the alumina-zirconia composite material having a low alumina content. Conversely, an alumina-zirconia composite material having a low alumina content is subjected to tensile stress from the alumina-zirconia composite material or alumina layer having a high alumina content.
These stresses are residual stresses as a whole, but they act as external forces from the respective layers.
Therefore, in the stacked gas sensor element 1, the solid electrolyte layer 11 is subjected to tensile stress by the first insulating layer 21, and conversely, the first insulating layer 21 is subjected to compressive stress by the solid electrolyte layer 11. It is predicted that a stress difference will occur between these two layers.

Therefore, in the present embodiment, first, a reference sample SB having the same composition as the solid electrolyte layer 11 or the same composition as the first insulator layer 21 (see FIG. 7 described later) is prepared. Next, the reference sample SB is irradiated with laser light while applying stress to measure fluorescence, and the relationship between the stress value and the fluorescence peak wave value κp (fluorescence peak relative wave value κps) is obtained.
As the reference sample SB, in addition to a sample made of 100 wt% alumina, a reference sample SB made of an alumina-zirconia composite material having an alumina content of 90, 70, 50, 20, 3 wt% was prepared as follows.
That is, alumina powder and 5 mol% Y ₂ O ₃ -containing stabilized zirconia powder as raw material powders were weighed in the above-mentioned alumina mass fraction, ball mill mixed, molded, and then fired at 1500 ° C. × 1 Hr in an air atmosphere. . Thereafter, the sample was processed into a 3 × 4 × 40 mm rectangular parallelepiped test piece shape, and further annealed at 1200 ° C. × 1 Hr to obtain a reference sample SB. The annealing is performed in order to remove distortion caused by processing.

Then, using these reference samples SB, the stress value applied to these reference samples and the relative wave value κps of the fluorescence peak with respect to the reference absolute wave value (20491 cm ⁻¹ : wave number of Ar ion laser light) Is obtained as follows.
Since the wave number measuring apparatus 100 used in this embodiment is a Raman spectroscopic analyzer, the wave number of light is not displayed as an absolute wave number, but an Ar ion laser laser beam (wavelength 488 nm) irradiated on the sample. ) Has a relative wave value κs based on the absolute wave value (κa = 20491 cm ⁻¹ ). For this reason, also in the present embodiment, the wave number of light is represented not by an absolute wave value but by a relative wave value. Further, the wave value κp of the fluorescence peak is represented by the relative wave value κps of fluorescence, which is the relative wave value expression.
Incidentally, easily as it can be appreciated, if the absolute wave value of the reference (κa = 20491cm ^-1) subtracting the relative wave value of the fluorescence peak (κps = about 6087cm ^-1), the absolute wave numerical representation of the fluorescence peak (Kappapa = About 14400 cm ^-1 ).

  First, means for applying stress to the reference sample SB will be described. In this embodiment, in accordance with JIS-R-1601, as shown in FIG. 5, a four-point bending stress applying jig 80 is used to apply stress to the reference sample SB by the four-point bending method. In this jig 80, cylindrical rollers 83a and 83b having a diameter of 2 mmφ are arranged between the first pedestal 81 located in the upper part of the drawing and the second pedestal 82 located in the lower part with an interval of the upper span L1. To do. Further, cylindrical rollers 84a and 84b having a diameter of 2 mmφ are also arranged at intervals of the lower span L2. Further, between the two pairs of cylindrical rollers 83a, 83b and 84a, 84b, the reference sample SB is arranged such that the two pairs of cylindrical rollers 83a, 83b and 84a, 84b are arranged symmetrically, respectively. A load P is applied by the pusher 85 through the load cell 91. Thereby, the reference sample SB is subjected to stress by so-called four-point bending. The output of the load cell 91 is input to the computer 160 through the charge amplifier 90 (see FIG. 3).

The distribution of stress applied to each reference sample is known to be a linear uniaxial stress field on a virtual center line (indicated by a broken line A-O-B) on the side surface of the reference sample. As shown, the tensile stress is lower in the figure than the center O, and the compressive stress is higher in the figure. Further, the maximum tensile stress value σtmax at the lower end B of the virtual center line is given by σtmax = 3P (L2−L1) / (2Ws · Ts ² ).
In the above equation, P is the load, L1 is the upper span (= 10 mm), L2 is the lower span (= 30 mm), Ws is the width of the reference sample (= 3 mm), and Ts is the thickness of the reference sample (= 4 mm). is there.
Therefore, if the position is known on the virtual center line AOB on the side surface of the reference sample, the magnitude of the stress applied to the reference sample at that position can also be determined.

  Therefore, the four-point bending stress applying jig 80 in a state where the load P is continuously applied to the reference sample SB is placed on the XY table 170, and the wave number is placed on the virtual center line AOB on the side of the reference sample. Ar ion laser light is irradiated using the measuring apparatus 100. The spot diameter of the laser beam was 2 μmφ and the output was 200 mW.

Further, the reflected light is dispersed to obtain a spectral intensity distribution of fluorescence emitted by Cr ³⁺ ions (see FIG. 4). Next, the position of the peak PK (relative wave value κps) is obtained from this spectrum distribution. In this embodiment, in order to obtain the relative wave value of the peak PK from the spectral intensity distribution of fluorescence, it is assumed that this distribution is a mixture of Laurentian and Gaussian, and known software (Grams386, manufactured by Galactic Co.) Was used.

  Further, the reference sample is moved together with the jig 80 by the XY table 170, the spot irradiation position of the laser beam is moved along the virtual center line AOB, and the stress value at each point is calculated. The relationship with the relative wave value of the fluorescence peak was obtained. The results for each reference sample SB are shown in FIG. In this way, the relative wave value of the fluorescence peak and various stress values can be obtained simply by measuring the relative wave value of the fluorescence peak while moving the irradiation position of the laser beam along the virtual center line AOB. Therefore, it is very easy to obtain relationship data between the two.

In FIG. 6, the vertical axis on the left shows the relative wave value of the fluorescence peak obtained at the point of zero external stress (κps = 6085.3 cm ⁻¹ : absolute in the 100% alumina reference sample (indicated as 100A). A wave value κpa = 14405.7 cm ⁻¹ ) is used as a reference point (Δκ = 0), and is indicated by a wave value shift amount Δκ. On the other hand, the vertical axis on the right side indicates the relative wave value κps and the absolute wave value κpa of the fluorescence peak.
In FIG. 6, in addition to a reference sample of 100% alumina (indicated as 100A), 90 wt%, 70 wt%, 50 wt%, 20 wt%, 3 wt% (indicated as 90A, 70A, 50A, 20A, 3A in the figure) This case is shown.

From these results, it can be predicted that the relationship between the stress value and the relative wave value of the fluorescence peak is a linear relationship. In addition, since the measurement points are arranged almost linearly, there is an extremely strong correlation between the stress value and the relative wave value of the fluorescence peak, and it can be predicted that the values can be mutually converted with high accuracy. The relationship between the stress value and the absolute wave value of the fluorescence peak is the same.

Therefore, the relationship between the stress value σ applied to each reference sample SB shown in FIG. 6 and the relative wave value κps of the fluorescence peak was obtained by calculating a regression line equation.
When alumina is 100%: κps100 = −0.00248 × 3 × σ + 6085.3 Formula (2)
When alumina is 90%: κps90 = −0.00248 × 3 × σ + 6085.9 Equation (3)
When alumina is 70%: κps70 = −0.00215 × 3 × σ + 6086.5 Formula (4)
When alumina is 50%: κps50 = −0.00230 × 3 × σ + 6087.6 (5)
When alumina is 20%: κps20 = −0.00246 × 3 × σ + 6088.8 Formula (6)
When alumina is 3%: κps3 = −0.00289 × 3 × σ + 6089.2 Equation (7)
Note that κps100, κps90, and the like are relative wave values (cm ⁻¹ ) of the fluorescence peak in the case of each alumina content, and σ is a stress value (MPa). Further, among these relational expressions, “−0.00248” or the like corresponds to a piezoelectric spectroscopic coefficient. The coefficient “3” multiplied by the stress value σ is a uniaxial stress field generated in the above-described four-point bending, whereas a stress field generated in an actually measured sample described later is a triaxial stress field. Because this is a field, it is a coefficient that adjusts this difference.
In any of the relational expressions (2) to (7), there is a very strong correlation between the stress value σ and the relative wave values κps100, κps90, etc. of the fluorescence peak. It can be seen that the relative wave value κps100 and the like and the stress value σ can be converted to each other with high accuracy.

On the other hand, the stacked gas sensor element 1 according to the present embodiment is cut as shown in FIG. 2, and an actual measurement sample is prepared by mirror-polishing the end surface (measurement surface) MS. Then, as shown on the left side of FIG. 2, laser light is irradiated to a portion MZ1 of the solid electrolyte layer 11 closest to the interface IF1 and a portion MA1 of the first insulating layer 21 immediately to the interface IF1, The relative wave values κpsz and κpsa of the fluorescence peaks at the site MZ1 of the solid electrolyte layer 11 and the site MA1 of the first insulating layer 21 were measured, respectively. However, since the positions of the part MZ1 and the part MA1 are very close to each other, the relative wave values κpsz and κpsa of the fluorescence peaks at these positions are almost the same value (κpsz≈κpsa). This is because there is no sudden and sudden change near the interface IF1, and the wave number of the obtained fluorescence peak changes gradually and continuously. Therefore, the relative wave value κpsb of the fluorescence peak obtained by irradiating the part MB1 on the interface IF1 with the laser light is almost the same value (κpsz≈κpsa≈κpsb).
The spot diameter of the laser beam was 2 μmφ and the output was 200 mW.

Therefore, the part MZ1 and the part MA1 of the laminated gas sensor elements 1 according to Examples 1 to 3 and the comparative example prepared by changing the alumina contents of the solid electrolyte layer 11 and the first and second insulating layers 21 and 22 are different. The relative wave values κpsz and κpsa of the fluorescence peak at were measured. When the measurement results are converted into stress values σ (σZ, σA) according to the formula (any one of formulas (2) to (7)) obtained for each composition based on the results shown in FIG. 6, the table of FIG. The result is as follows.
According to the table of FIG. 7, as the difference between the alumina content in the solid electrolyte layer 11 and the alumina content in the first insulating layer 21 increases, the stress value σZ (this portion near the interface of the solid electrolyte layer 11) Is a point of maximum stress of the solid electrolyte layer). Similarly, it can be seen that the stress value σA (this portion becomes the point of the maximum stress of the first insulating layer) near the interface of the first insulating layer 21 also increases. The stress value indicates a tensile stress when the value is positive, and indicates a compressive stress when the value is negative.

  Further, the stress difference Dσ (= σZ− (σA)) generated in the solid electrolyte layer 11 and the first insulating layer 21 via the interface IF1 is also shown in the table of FIG. It can be seen that this stress difference Dσ also increases as the difference between the alumina content in the solid electrolyte layer 11 and the alumina content in the first insulating layer 21 increases.

Subsequently, the thermal cycle test (endurance test) was performed 50000 times for the laminated gas sensor elements 1 of Examples 1, 2, 3 and Comparative Examples having different compositions of the solid electrolyte layer 11 and the first and second insulating layers 21, 22. It was. The quality determination results of the stacked gas sensor element 1 thereafter are shown in the table of FIG.
In the cold cycle endurance test, a voltage of 12 V was applied to the resistance heating element 23 for 10 seconds to heat the laminated gas sensor element 1, and then the temperature of the surface of the electrode protective layer 18 was about 150 ° C. by applying wind. Air cooling for 60 seconds is performed once so that the temperature decreases to 50,000 times. Thereafter, a red check is performed on the tested multilayer gas sensor element 1 and the presence or absence of cracks is confirmed with a stereomicroscope (magnification 4 times). Things are OK.

  From the results in the table of FIG. 7, when the stress value σZ in the vicinity of the interface of the solid electrolyte layer 11 is 300 MPa or less, cracks do not occur even when the thermal cycle durability test is performed (Examples 1, 2, 3). However, when 300 MPa is exceeded, it turns out that a crack arises by a cold cycle endurance test (refer to a comparative example). That is, it turns out that it is inferior to durability and reliability.

  In addition, when the stress difference Dσ generated between the solid electrolyte layer 11 and the first insulating layer 21 via the interface IF1 is 400 MPa or less, no crack is generated even if the thermal cycle durability test is performed. (See Examples 1, 2, and 3). However, when it exceeds 400 MPa, it can be seen that a crack is caused by a cold cycle endurance test (see comparative example). That is, it turns out that it is inferior to durability and reliability.

  From the above, it can be seen that the stress value σZ in the vicinity of the interface of the solid electrolyte layer 11 should be 300 MPa or less. It can also be seen that the stress difference Dσ generated between the solid electrolyte layer 11 and the first insulating layer 21 via the interface IF1 should be 400 MPa or less.

In order to obtain the stress value σZ, as described above, a reference sample SB having the same composition as that of the solid electrolyte layer 11 is prepared in advance, and the wave number of the fluorescence peak is measured while applying stress to the reference sample SB. A first relationship between the stress value and the wave value of the fluorescence peak is obtained. On the other hand, in the cross section of the solid electrolyte layer 11 of the multilayer gas sensor element 1, when the wave value κpsz of the fluorescence peak at the portion MZ1 closest to the interface IF1 is measured, and the wave value κpsz is converted into the stress value σZ based on the first relationship. Good.
In obtaining the stress difference Dσ, in addition to obtaining the stress value σZ as described above, the stress value σA may be obtained as follows and the difference between them may be calculated. A reference sample SB having the same composition as that of the first insulating layer 21 is prepared in advance, and the wave value of the fluorescence peak is measured while applying stress to the reference sample SB, and the second relationship between the stress value and the wave value of the fluorescence peak is obtained. Get it. On the other hand, in the cross section of the first insulating layer 21 of the stacked gas sensor element 1, the wave value κpsa of the fluorescence peak at the portion MA1 closest to the interface IF1 is measured, and the wave value κpsa is converted into the stress value σA based on the second relationship. To do.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the above embodiment, the relative wave value κps is used as the wave value of the fluorescence peak, but it is obvious that an absolute wave value may be used.
Moreover, in the said embodiment, it showed about the laminated | stacked gas sensor element 1 of the form shown to FIG.1 and FIG.2. However, any multilayer gas sensor element having a solid electrolyte layer made of an alumina-zirconia composite material and an alumina insulating layer mainly composed of alumina laminated in direct contact with the solid electrolyte layer may be used. An air inlet may be formed, or an oxygen pumping element may be stacked via an insulating layer in which a hollow measurement chamber is formed on the solid electrolyte layer.

Further, in the above-described embodiment, the wave value κpsz of the fluorescence peak at the portion MZ1 closest to the interface IF1 in the cross section of the solid electrolyte layer 11 is measured, and converted to obtain the stress value σZ. In the cross section, the wave value κpsa of the fluorescence peak at the portion MA1 closest to the interface IF1 was measured and converted to obtain the stress value σA.
However, it does not change discontinuously suddenly near the interface IF1, and the wave value of the obtained fluorescence peak gradually and gradually changes. For this reason, the three values are almost the same (κpsz≈κpsa≈κpsb) including the relative wave value κpsb of the fluorescence peak obtained by irradiating the part MB1 on the interface IF1 with laser light. Therefore, the relative wave value κpsb of the fluorescence peak at the site MB1 on the interface IF1 is measured, the first relationship between the stress value in the solid electrolyte layer 11 and the wave value of the fluorescence peak, and the stress value and fluorescence in the first insulating layer 21 are measured. The stress values σZ and σA may be obtained by conversion using the second relationship with the peak wave value. If it does in this way, the frequency | count of a measurement in the lamination type gas sensor element 1 can be reduced.

It is a disassembled perspective view of the lamination type gas sensor element concerning this embodiment. It is sectional drawing of the lamination type gas sensor element concerning this embodiment. It is explanatory drawing which shows the structure of the apparatus used for the wavenumber measurement of the fluorescence peak which concerns on this embodiment. It is explanatory drawing which shows the spectrum intensity distribution of the fluorescence which Cr3 ⁺ ion emits. It is explanatory drawing which shows the form of the jig | tool for applying the stress by a 4-point bending method to a reference | standard sample, in order to irradiate a laser beam, applying a stress to a reference | standard sample. Graph obtained by changing the alumina content to show the relationship between the stress applied to the reference sample and the shift amount Δκ of the wave value of the fluorescence peak or the relative wave value (absolute wave value) of the fluorescence peak It is. The maximum stress σZ of the solid electrolyte layer, the maximum stress σA of the first insulating layer, and the interface at the interface when the alumina content in the solid electrolyte layer and the first insulating layer is changed (Examples 1, 2, 3 and Comparative Example) It is a table | surface shown about the relationship between stress difference D (sigma) and a thermal cycle durability test.

Explanation of symbols

1 Stacked Gas Sensor Element 10 Oxygen Concentration Battery Element 11 Oxygen Concentration Battery Solid Electrolyte Layer (Solid Electrolyte Layer)
12 sensing electrode 13 reference electrode 20 base 21 first insulating layer (alumina insulating layer)
22 Second insulating layer (alumina insulating layer)
23 resistance heating element 24 heating part IF1 interface 100 (solid electrolyte layer 11 and first insulating layer 21) interface 100 wave number measuring device 120 laser 130 optical system 140 spectroscope 150 CCD array 160 computer 170 XY table 90 charge amplifier SB reference Sample (first reference sample, second reference sample)
MS measurement surface PK Fluorescence peak position Fs, Fs100, Fs90, Fs70, Fs50, Fs20, Fs3 Fluorescence peak relative wave value σ Stress κs Relative wave value κp Fluorescence peak wave value Dσ Stress difference

Claims (2)

A solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other;
An alumina insulating layer mainly composed of alumina crystal particles containing Cr ³⁺ ions, laminated in direct contact with at least a part of the solid electrolyte layer and co-firing;
A laminated gas sensor element comprising:
A laminated gas sensor element in which the tensile stress received by the solid electrolyte layer in the vicinity of the interface with the alumina insulating layer is 300 MPa or less at the maximum. A solid electrolyte layer in which zirconia crystal particles and alumina crystal particles containing Cr ³⁺ ions are dispersed with each other;
An alumina insulating layer mainly composed of alumina crystal particles containing Cr ³⁺ ions, laminated in direct contact with at least a part of the solid electrolyte layer and co-firing;
A laminated gas sensor element comprising:
A multilayer gas sensor element, wherein a difference between a stress received by the solid electrolyte layer and a stress received by the alumina insulating layer via an interface between the solid electrolyte layer and the alumina insulating layer is 400 MPa or less.

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