JP2010249629A - Nondestructive inspection device for solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems in a conventional nondestructive inspection device, wherein inspection takes up much space and is expensive, since an X-ray diffraction stress measuring instrument is large-scaled, and it is difficult to keep on applying X-rays to a solid oxide fuel cell at all times and detect an anomaly, while the fuel cell is in operation. <P>SOLUTION: A nondestructive inspection device includes a waveform generator 21, a piezoelectric vibrator 22, a piezoelectric transducer 24, a waveform analyzer 23, an analysis means, and a detection means. Vibration of a unit cell 1 due to the piezoelectric vibrator 22 is detected by the piezoelectric transducer 24 and is output to the waveform analyzer 23. Finite element software constitutes the analysis means for analyzing the characteristic frequency of the a unit cell 1. An electronic computer with the element software installed therein constitutes the detection means for detecting an anomaly produced inside a sample, by identifying the characteristics of the specimen through comparison of the characteristic frequency analyzed by the analysis means, with the resonance frequency measured by the piezoelectric transducer 24 and the waveform analyzer 23. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nondestructive inspection apparatus that nondestructively detects an abnormality occurring inside a solid oxide fuel cell using a resonance method.

  Conventionally, as this type of non-destructive inspection apparatus, for example, a stress measurement method using X-ray diffraction as disclosed in Patent Document 1 is used to measure residual stress in a sample and detect abnormalities inside the sample. There is something to do. In the stress measurement method disclosed in Patent Document 1, the residual stress of the minute portion of the aluminum nitride sintered body is determined by irradiating the characteristic nitrided X-rays on the aluminum nitride sintered body and examining the change in the diffraction angle of the diffraction peak. It enables non-destructive and accurate measurement.

  Conventionally, this type of non-destructive inspection device detects non-destructive abnormalities inside a sample by detecting acoustic waves generated when cracks occur inside the sample using acoustic emission. There is also.

JP-A-5-79926

  However, since the conventional non-destructive inspection apparatus using X-ray diffraction disclosed in Patent Document 1 requires a large X-ray diffraction stress measurement apparatus, the inspection takes a lot of space and is expensive. Become. Further, it is difficult to detect an abnormality by constantly irradiating X-rays while using the measurement object, that is, during operation of the solid oxide fuel cell. In addition, since the X-ray diffraction stress measuring apparatus cannot be used at high temperatures or in a gas atmosphere, it is impossible to detect abnormalities in a sample placed at high temperatures or in a gas atmosphere.

  In addition, since the conventional non-destructive inspection equipment using acoustic emission is a passive measurement method, it is difficult to detect an abnormality unless a large abnormality occurs in the sample. Is difficult.

The present invention has been made to solve such problems,
Contact with a sample consisting of a unit cell of a solid oxide fuel cell in which an electrolyte that transmits ions generated at an air electrode that supplies air to the fuel electrode that supplies battery fuel is provided between the fuel electrode and the air electrode And vibration means for vibrating the sample,
Measuring means for measuring the resonance frequency of the resonance vibration generated in the sample by the vibration means in contact with the sample;
Analysis means for analyzing the natural frequency of the sample;
A detection means for detecting an abnormality occurring in the sample by comparing the natural frequency analyzed by the analysis means and the resonance frequency measured by the measurement means to identify the characteristics of the sample, and a solid A non-destructive inspection device for oxide fuel cells was constructed.

  According to this configuration, when the characteristic of the sample is known by comparing the natural frequency analyzed by the analyzing means and the resonance frequency measured by the measuring means to identify the characteristic of the sample, Abnormalities that occur inside, for example, defects such as cracks and delamination, internal stresses such as residual stress and thermal stress, etc. can be detected easily and non-destructively in a short time. These defects and internal stress cause deterioration in performance, destruction, and accidents of the solid oxide fuel cell.

  In addition, since the characteristics of the sample can be identified by vibrating the sample using ultrasonic waves etc., the apparatus does not become large like the X-ray diffraction stress measurement device, and it does not take up a lot of space for inspection. In addition, nondestructive inspection of solid oxide fuel cells can be performed. In addition, non-destructive inspection can be performed on samples of various sizes and shapes. In addition, since non-destructive inspection can be performed by simply oscillating the sample without always irradiating the sample with X-rays, the sample is placed under high temperature or in a gas atmosphere even while the sample is in operation. Can also perform non-destructive inspection.

  Further, the present invention is characterized in that the sample is a stack of solid oxide fuel cells composed of a plurality of unit cells, and the vibration means vibrates the sample while the sample is in operation.

  According to this configuration, the characteristics of the sample consisting of a stack of solid oxide fuel cells composed of a plurality of unit cells are identified during the operation of the sample by exciting the sample with the vibration means during the operation. Can do. For this reason, the internal state of the solid oxide fuel cell can be constantly monitored, the abnormality occurring in the interior can be detected early, and the operating solid oxide fuel cell can be stopped due to failure. It will be possible to take measures before it reaches.

  According to the present invention, as described above, the characteristic of the sample is known by comparing the natural frequency analyzed by the analyzing means and the resonance frequency measured by the measuring means to identify the characteristic of the sample. In this case, an abnormality occurring inside the sample can be detected easily and non-destructively in a short time.

(A) is a figure which shows the outline of the structure at the time of inspecting the unit cell of a solid oxide fuel cell with the nondestructive inspection apparatus by one embodiment of this invention, (b) is one implementation of this invention It is a figure which shows the outline of a structure at the time of test | inspecting the stack structure of a solid oxide fuel cell with the nondestructive inspection apparatus by a form. It is a figure which shows the outline of operation | movement of the unit cell of the solid oxide fuel cell shown in FIG. (A) is the crystal structure of the electrolyte which comprises the solid oxide fuel cell shown in FIG. 1, (b) is the figure which showed the outline of the ion conduction mechanism in the electrolyte. It is a graph which shows the result of the eigenvalue analysis using the finite element software of the unit cell of the solid oxide fuel cell shown in FIG.

  Next, the form for implementing this invention is demonstrated.

  Fig.1 (a) is a figure which shows the outline of a structure of the nondestructive inspection apparatus by one embodiment of this invention. In this embodiment, this nondestructive inspection apparatus is used for nondestructive inspection of the product of the unit cell 1 which comprises a solid oxide fuel cell, and uses the unit cell 1 as a sample.

  The nondestructive inspection apparatus includes a waveform generator 21, a piezoelectric vibrator 22, a piezoelectric transducer 24, a waveform analyzer 23, and analysis means and detection means described later.

  The waveform generator 21 and the piezoelectric vibrator 22 constitute a vibrating means that vibrates the sample by contacting the sample of the unit cell 1. The piezoelectric vibrator 22 is made of a piezoelectric material, vibrates according to the electric signal waveform output from the waveform generator 21, and applies vibration to the unit cell 1 that is in contact therewith. The piezoelectric transducer 24 detects the vibration of the unit cell 1 generated by the piezoelectric vibrator 22, converts the vibration into an electric signal by the piezoelectric material, and outputs the electric signal to the waveform analyzer 23.

  The waveform analyzer 23 detects the vibration waveform of the unit cell 1 from the electrical signal input from the piezoelectric transducer 24. Then, the detected vibration waveform of the sample is automatically recorded. The piezoelectric transducer 24 and the waveform analyzer 23 constitute measurement means for measuring the resonance frequency of the resonance vibration generated in the sample by the vibration means in contact with the sample. When a frequency equal to the natural frequency of the sample is applied to the sample, the amplitude increases and the resonance state is obtained, and the resonance frequency is measured. In addition, the structure which detects the vibration of a sample using an acceleration sensor may be sufficient.

The unit cell 1 that is a measurement object of the nondestructive inspection apparatus includes a flat fuel electrode 2 that supplies battery fuel as hydrogen (H ₂ ), and a flat air that supplies air as oxygen (O ₂ ). The electrode 4 is composed of a flat electrolyte 3 provided between the fuel electrode 2 and the air electrode 4, which transmits oxygen ions (O ²⁻ ) generated in the air electrode 4 to the fuel electrode 2. The electrolyte 3 is made of stabilized zirconia (ZrO ₂ ) having a crystal structure to be described later and added with 8 mol% of yttria (Y ₂ O ₃ ). The fuel electrode 2 is made of nickel, cermet that is a mixture of nickel and stabilized zirconia, or the like. The air electrode 4 is made of LaMnO ₃ or LaCoO ₃ having electronic conductivity, or a perovskite oxide (LSM) in which a part of these La is replaced with Sr, Ca, or the like.

In the unit cell 1, as shown in FIG. 2, oxygen (O ₂ ) is supplied to the air electrode 4, and the oxygen (O ₂ ) receives electrons (e ⁻ ) in the air electrode 4 and converts them into oxygen ions (O ²⁻ ). Ionized. This oxygen ion (O ²⁻ ) moves to the fuel electrode 2 via the electrolyte 3 and reacts with hydrogen (H ₂ ), which is a cell fuel supplied to the fuel electrode 2, to produce a reaction product (H ₂ O) and electrons (e ⁻ ) are emitted. The load 5 consumes the electric power generated in this reaction process.

  3A is a diagram showing the crystal structure of the electrolyte 3, and FIG. 3B is a diagram showing an outline of the ion conduction mechanism in the electrolyte 3. FIG.

The stabilized zirconia that constitutes the electrolyte 3 is composed of a composite oxide of Y ₂ O ₃ and ZrO _{2 in} which yttria (Y ₂ O ₃ ) as an additive is substituted and dissolved in a zirconia (ZrO ₂ ) lattice. The stabilized zirconia has a cubic crystal structure composed of cations (Zr ⁴⁺ , Y ³⁺ ) 11 and anions (O ²⁻ ) 10 as shown in FIG.

As shown in FIG. 4B, by replacing and dissolving yttria in the zirconia lattice, Y ³⁺ ions 11b occupy a part of Zr ⁴⁺ ions 11a, and oxygen ion vacancies 12 are generated. When the oxygen ions (O ²⁻ ) 10 move through the oxygen ion vacancies 12, ion conduction responsible for supplying electric power is performed in the solid oxide fuel cell.

  FIG. 4 is a graph showing the result of eigenvalue analysis using the unit cell 1 finite element software (MSC.Marc2005).

  In this analysis, the unit cell 1 is made of yttria-added zirconia Ni-8YSZ to which the fuel electrode 2 has a thickness of 1.5 [mm] and Ni is added, and the electrolyte 3 has a thickness of 30 [μm]. The yttria-added zirconia 8YSZ and the air electrode 4 are made of LSM having a thickness of 20 [μm]. The size of the unit cell 1 is 27.5 [mm] × 27.5 [mm], and the boundary condition is that the four end faces around the unit cell 1 are fixed. Here, the finite element software and the electronic computer in which the finite element software is installed constitute analysis means for analyzing the natural frequency of the sample of the unit cell 1. By this analyzing means, the analysis results shown in FIGS.

FIG. 4A is a graph showing natural frequencies in various natural vibration modes of the unit cell 1. The horizontal axis of the graph represents the natural vibration mode number (Mode number), and the vertical axis represents the natural frequency (Resonant frequency) [KHz]. The mode number represents the number of wave nodes formed on the vibration surface. For example, the mode number ₂ R ₃ indicates that 2 × 3 vibration peaks and valleys are formed on the vibration surface. The vibration mode of the unit cell 1 basically shows the same tendency as a uniform thin plate. The graph of FIG. 6A shows that the natural frequency of the lowest-order natural vibration mode ( ₁ R ₁ ) is about 11 [kHz], and the higher-order natural vibration mode with more in-plane vibration nodes has more natural characteristics. It shows that the frequency increases.

FIG (b) shows a graph of when the number of modes of the natural oscillation modes shown in the diagram (a) is ₂ R _2, analysis shows the change in the natural frequency with respect to plane stress results. The horizontal axis of the graph represents in-plane stress at the end of the center surface of the electrolyte 3 of the unit cell 1 (MPa), and the vertical axis represents the natural frequency (KHz). . As shown by characteristic lines A, B, C, D and E in the graph, the in-plane stress is the stress on the vertical axis in the vicinity of both ends in the in-plane direction [mm] on the horizontal axis. (Stress) As shown in [MPa], the stress is high. Each plot A, B, C, D and E shows the natural frequency corresponding to the stress at this end. Negative in-plane stress is compression, and positive in-plane stress is tensile stress.

  As shown in the graph of FIG. 5B, the natural frequency increases as the in-plane stress of the electrolyte 3 becomes tensile. In addition, the natural frequency is changed by about 0.1 [kHz] with respect to the change of the in-plane stress of 100 [MPa], which is an order that can be actually measured. It shows that resonance measurement is effective for stress evaluation of the unit cell 1.

  The electronic computer in which the finite element software is installed compares the natural frequency analyzed by the analyzing means with the resonance frequency measured by the measuring means comprising the piezoelectric transducer 24 and the waveform analyzer 23 shown in FIG. By detecting the characteristics of the sample, detection means for detecting an abnormality occurring inside the sample is configured.

  In such a nondestructive inspection apparatus according to the present embodiment, it is possible to inversely analyze the material characteristics of the sample. When the characteristics of the sample are known, the shape error of the sample can be calculated from the natural frequency and the resonance frequency. You can see the initial defects, internal stress, etc. For example, when the resonance frequency of the product inspected by the nondestructive inspection apparatus according to the present embodiment is larger than the resonance frequency of a normal product measured in advance, the resonance frequency increases as the tensile stress increases (FIG. 4 ( From the analysis result of b), it can be seen that there is an abnormality due to the tensile stress acting inside the inspection product. Also, for example, if a product no longer resonates even if a resonance frequency corresponding to the natural frequency of a specific natural vibration mode of a normal product is added to the product, a defect occurs in the crystal structure corresponding to this natural vibration mode. I understand that. In addition, for example, by analyzing the natural frequency of products of various sizes that are not normal in advance, the resonance frequency of the product is measured at the time of product inspection, and this resonance frequency and the various sizes analyzed. By comparing with the natural frequency of the product, the size of the product can be identified, and the shape error of the product can be detected. Further, for example, by comparing the natural frequency of the unit cell 1 having the stress distribution shown in the characteristic lines A to E in the graph of FIG. 4B with the measured resonance frequency of the product, the stress distribution of the product And local measurement of product stress is possible.

  According to such a non-destructive inspection apparatus for a solid oxide fuel cell according to the present embodiment, the characteristic frequency of the unit cell 1 is compared by comparing the natural frequency analyzed by the analysis means with the resonance frequency measured by the measurement means. When the characteristics of the unit cell 1 are known, abnormalities that occur inside the unit cell 1, such as cracks or Defects such as peeling and internal stresses such as residual stress and thermal stress can be detected easily and non-destructively in a short time.

  In addition, since the characteristics of the unit cell 1 can be identified by vibrating the unit cell 1 using ultrasonic waves or the like, the apparatus does not become large like the X-ray diffraction stress measuring apparatus, and the space for the inspection is taken. In addition, the non-destructive inspection of the solid oxide fuel cell can be performed at low cost. Further, nondestructive inspection can be performed on the unit cells 1 having various sizes and shapes. In addition, since the non-destructive inspection can be performed by simply oscillating the unit cell 1 without always irradiating the unit cell 1 with the X-ray, the unit cell 1 can be kept at a high temperature even while the unit cell 1 is in operation. Nondestructive inspection can be performed even in a gas atmosphere.

  FIG. 1B shows a case where a stack structure 31 of a solid oxide fuel cell in which a plurality of unit cells 1 shown in FIG. 1A are connected in series by an interconnector 5 is inspected by the above-described nondestructive inspection apparatus. An outline of the configuration is shown.

  The piezoelectric transducer 24 that detects the vibration of the stack structure 31 is in contact with the interconnector 5 of the stack structure 31. The waveform generator 21 and the piezoelectric vibrator 22 constituting the excitation means are set to the stack structure 31 constantly or in advance during the operation of the stack structure 31, that is, during the power generation operation of the solid oxide fuel cell. Vibrated at a predetermined time. The waveform analyzer 23 measures the resonance frequency of the excited stack structure 31, and the detection means detects the measured resonance frequency, the natural frequency of the stack structure 31 previously analyzed by the analysis means, and the normal stack. The resonance frequency of the structure 31 is compared, and abnormalities such as cracks and internal stress inside the stack structure 31 are detected. If an abnormality is detected by the detection means, a stack structure that promptly outputs an audible alarm, lights a lamp, or displays information notifying the abnormal state on the screen of the electronic computer by controlling the electronic computer etc. 31 is notified that an abnormality has occurred. In this notification, a configuration for notifying the distribution of internal stress, the magnitude of the stress, the type of abnormality such as tensile stress or compressive stress may be used.

  In the solid oxide fuel cell non-destructive inspection apparatus shown in FIGS. 1A and 1B, a solid oxide fuel cell stack structure 31 composed of a plurality of unit cells 1 is applied with vibration means during operation. By shaking, the characteristics of the stack structure 31 can be identified during operation. For this reason, the internal state of the solid oxide fuel cell can be constantly monitored, the abnormality occurring in the interior can be detected early, and the operating solid oxide fuel cell can be stopped due to failure. It will be possible to take measures before it reaches.

DESCRIPTION ^{OF SYMBOLS} 1 ... Unit cell 2 ... Fuel electrode 3 ... Electrolyte 4 ... Air electrode 5 ... Interconnector 10 ... Oxygen ion 11 ... Positive ion 11a ... Zr ⁴⁺ ion 11b ... Y3 ⁺ ion 12 ... Oxygen ion hole 21 ... Waveform generator 22 ... Piezoelectric vibrator 23 ... Waveform analyzer 24 ... Piezoelectric transducer 31 ... Stack structure

Claims (2)

A sample comprising a unit cell of a solid oxide fuel cell in which an electrolyte that transmits ions generated at an air electrode that supplies air to a fuel electrode that supplies battery fuel is provided between the fuel electrode and the air electrode Vibrating means for vibrating the sample in contact with
Measurement means for measuring the resonance frequency of the resonance vibration generated in the sample by the vibration means in contact with the sample;
Analyzing means for analyzing the natural frequency of the sample;
And a detecting means for detecting an abnormality occurring in the sample by comparing the natural frequency analyzed by the analyzing means and the resonance frequency measured by the measuring means to identify the characteristics of the sample. Non-destructive inspection equipment for solid oxide fuel cells. The sample is a stack of solid oxide fuel cells composed of a plurality of the unit cells,
2. The non-destructive inspection apparatus for a solid oxide fuel cell according to claim 1, wherein the vibration means vibrates the sample during operation of the sample.

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