JP3472608B2 - Activation method for zirconia oxygen sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to activation treatment of a zirconia oxygen sensor for detecting oxygen concentration in an ambient atmosphere by using a zirconia element having porous electrodes formed on both sides of an oxygen ion conductive solid electrolyte made of zirconia. Regarding the method.

[0002]

2. Description of the Related Art A sensor element used in a zirconia oxygen sensor has a sensor body made of partially stabilized zirconia, stabilized zirconia or the like formed in a plate shape, and electrodes made of platinum or the like are laminated on both sides of the body. Is produced by baking in a furnace at a predetermined temperature. In the sensor element after firing manufactured in this way, oxygen is bonded to the electrode, and the internal resistance of the sensor element becomes large. Therefore, it cannot be used as it is. Therefore, in the past, for example, Japanese Patent Laid-Open No. 3-15
As disclosed in Japanese Patent No. 6361, the internal resistance of the sensor element after firing is reduced by the activation process of flowing an alternating current between the electrodes of the sensor element.

[0003]

However, the above-mentioned conventional activation treatment is applied to the zirconia oxygen sensor in the range of 1 to 1 of the limiting current.
An internal current of the sensor element can be reduced because an internal current of the sensor element is reduced by pouring an alternating current of 5 times to make the surface of the metal particles forming the electrode finer. There was a problem that the zirconia was blackened during the activation treatment and the durability of the sensor element was lowered.

That is, first, when the sensor element is activated by applying an alternating current 1 to 5 times the limiting current as in the conventional case, oxygen at the zirconia-electrode interface is activated during the activation. Since the concentration becomes extremely low, a reaction of ZrO ₂ → Zr + O ₂ occurs on the surface of zirconia, the structural structure of that portion is broken, and blackening occurs, which causes black embrittlement.

Further, when the blackening occurs during the activation process as described above, if the blackening can be confirmed even after the activation process, the occurrence of the blackening can be detected in an inspection process or the like, but there is no problem. In addition to providing an alternating current, depending on the execution conditions of the activation process, for example, the process current is relatively small and the process temperature is relatively high, blackening may occur once during the activation process. However, most of them may be lost, and it may not be possible to confirm the occurrence of substantial blackening after the activation treatment. In such a case, the sensor element is used as it is as a normal sensor element.

However, since the internal structure of zirconia that has undergone blackening has been deteriorated, if activating treatment is periodically performed during use, for example, to activate the sensor, the zirconia deteriorates. As a result, the durability is reduced, and the usable period thereof is significantly reduced.

It is to be noted that it is not only after the activation treatment that the occurrence of blackening cannot be confirmed after the activation treatment,
Even during use after treatment, the surface of the zirconia that had undergone blackening was Zr + O ₂ → Z due to oxygen in the ambient atmosphere.
It is also considered that the reaction of rO ₂ occurs, and the surface of the zirconia that has once become brittle in black returns to the original color (white).

The present invention has been made in view of these problems, and the sensor element can be satisfactorily activated without causing a physical structural change such as blackening in zirconia even during the activation treatment. An object of the present invention is to provide a method for activating a zirconia oxygen sensor that can be activated.

[0009]

In order to achieve this object, the invention according to claim 1 forms at least a pair of porous electrodes on both surfaces of a plate-like oxygen ion conductive solid electrolyte made of zirconia. A method for activating a zirconia oxygen sensor having a sensor element according to claim 1, wherein the oxygen partial pressure value at the electrode-solid electrolyte interface of the sensor element is the solid electrolyte under the condition of a temperature of 500 ° C. to 800 ° C. Is characterized in that a predetermined voltage having an oxygen partial pressure value larger than a limiting oxygen partial pressure value at which blackening occurs is alternately applied between the electrodes.

According to a second aspect of the present invention, in the activation treatment method for a zirconia oxygen sensor according to the first aspect, the plate-like oxygen ion conduction made of the same zirconia as the sensor element for performing the activation treatment is used. Of a pair of porous electrodes on both sides of a porous solid electrolyte, and a measurement element in which one of the pair of electrodes is closed in a substantially airtight manner with respect to the external atmosphere, and the measurement is performed in a predetermined atmosphere. The limit electromotive force value of the sensor element under a predetermined atmosphere is measured by applying a direct current voltage between the pair of electrodes of the working element as a cathode for a sufficient time, and the measured limit electromotive force value is set. Based on this, the voltage value applied alternately between the electrodes of the sensor element is set.

Next, the invention according to claim 3 is the method for activating the zirconia oxygen sensor according to claim 2, wherein the limiting electromotive force under a predetermined atmosphere is measured by using the measuring element. Value and the oxygen partial pressure value of the ambient atmosphere at the time of the measurement, a limit oxygen partial pressure value at the cathode side electrode is calculated, and based on the calculated limit oxygen partial pressure value, alternating between the electrodes of the sensor element. It is characterized by setting the voltage value applied to.

Furthermore, in the invention described in claim 4, in the activation treatment method for a zirconia oxygen sensor according to claim 3, the external atmosphere of the sensor element when performing the activation treatment is atmospheric air or When a combustion gas atmosphere containing oxygen obtained by burning a fuel mixture having an excess air ratio λ> 1, the oxygen content under the thermodynamic equilibrium state in the above-mentioned external atmosphere or an atmosphere having a lower oxygen concentration than the external atmosphere. Along with calculating the pressure value, calculate the limit electromotive force value using the Nernst equation based on the calculated oxygen partial pressure value and the calculated limiting oxygen partial pressure value, based on the calculated limit electromotive force value, It is characterized in that the voltage value applied alternately between the electrodes of the sensor element is set.

The invention according to claim 5 is the method for activating the zirconia oxygen sensor according to claim 3, wherein the ambient atmosphere of the sensor element when performing the activating process is an excess air ratio. In a combustion gas atmosphere containing an oxygen compound obtained by burning a fuel mixture having λ ≦ 1, the oxygen partial pressure under a thermodynamic equilibrium state in the external atmosphere or an atmosphere having a lower oxygen compound concentration than the external atmosphere. Along with calculating the value, the limiting electromotive force value is calculated using the Nernst equation based on the calculated oxygen partial pressure value and the calculated limiting oxygen partial pressure value, and based on the calculated limiting electromotive force value, It is characterized in that the voltage value applied alternately between the electrodes of the sensor element is set.

On the other hand, the invention according to claim 6 is the sensor element for measurement, which is produced in advance under the conditions for performing the activation treatment in the activation treatment method of the zirconia oxygen sensor according to claim 1. Apply DC voltage for sufficient time,
The electrode of the sensor element-a partial voltage value at which the oxygen partial pressure value at the solid electrolyte interface becomes a limit oxygen partial pressure value at which the solid electrolyte causes blackening, is obtained, and between the electrodes of the sensor element during the activation treatment. It is characterized in that the voltage value applied to the alternation is set to a value smaller than the limit voltage value.

According to a seventh aspect of the invention, in the activation treatment method for a zirconia oxygen sensor according to any one of the first to sixth aspects, the voltage applied alternately between the electrodes of the sensor element is 0. It is characterized in that it is 0.4 V or more. Next, the invention according to claim 8 is the activation treatment method for a zirconia oxygen sensor according to any one of claims 1 to 7, wherein the frequency of application of the predetermined voltage between the electrodes of the sensor element is It is characterized in that it is 0.5 Hz or less.

Further, the invention according to claim 9 is the activation treatment method for a zirconia oxygen sensor according to any one of claims 1 to 8, wherein the activation treatment is performed during operation of the zirconia oxygen sensor. Alternatively, it is characterized in that it is carried out regularly or as required before and after the operation.

[0017]

First, when a voltage is applied between the electrodes of the sensor element, a current flows in the sensor element and flows in the direction opposite to that of the current, that is, from the electrode (cathode) side which becomes a low potential by the voltage application. Oxygen moves to the side of the electrode (positive electrode) that has a high potential.

When the current flowing through the sensor element becomes large, oxygen cannot be taken in from the cathode side, and the oxygen partial pressure at the zirconia-electrode interface (hereinafter referred to as the three-phase interface) on the electrode side significantly decreases. The reaction of ZrO ₂ → Zr + O ₂ occurs on the surface of the zirconia on the cathode side, and blackening occurs in the zirconia.

Therefore, in the activation treatment method of the present invention, an electric current is alternately applied to the sensor element to reduce the internal resistance of the sensor element, and during the energization of the sensor element, even if temporarily, the three-phase interface The oxygen partial pressure is controlled so as not to fall below the limit oxygen partial pressure at which blackening occurs in zirconia.

That is, in the activation treatment method of the zirconia oxygen sensor according to claim 1, the temperature is from 500 ° C to
Under the condition of 800 ° C., the oxygen partial pressure value at the electrode-solid electrolyte interface of the sensor element is the solid electrolyte (that is, zirconia).
The blackening occurs during the activation process by alternately applying a predetermined voltage between the electrodes of the sensor element, the predetermined voltage having the oxygen partial pressure value larger than the limiting oxygen partial pressure value that causes blackening. I try to prevent it.

That is, in the prior art, for the sensor element,
A large current enough to miniaturize the electrode surface
(5 times), the internal resistance of the sensor element was lowered, so that blackening will always occur in the zirconia during the activation process. However, in the present invention, only during the activation process. However, in order to prevent blackening of zirconia, the activation process is performed by limiting the voltage value applied alternately to the sensor element as described above.

Therefore, according to the present invention, during the activation process, even a relatively slight blackening that disappears after the activation process is not generated, and the activation process is not performed. Therefore, the durability of the sensor element can be improved. The limiting oxygen partial pressure at which blackening occurs in zirconia cannot be uniquely determined because it varies depending on the structure, material, temperature conditions, etc. of the sensor element, but since approximate values can be known from experiments, etc., If the limiting oxygen partial pressure is assumed from the value, the processing voltage can be set as follows.

That is, between the electrodes of the sensor element, according to the oxygen concentration at the three-phase interface on each electrode side, Nernst (Nerst)
nst), the electromotive force E expressed by the following equation (1), which is well known.
Since MF occurs, EMF = (RT / nF) × ln (PO1 / PO2) (1) where R: gas constant T: absolute temperature n: valence of oxygen
F: Faraday constant PO1, PO2: Vp is the voltage applied between the oxygen partial pressure electrodes at the three-phase interface on each electrode side, Ip is the current flowing through the sensor element, and Ri is the internal resistance of the sensor element. It can be expressed as the following equation (2).

Vp = Ip × Ri + EMF (2) Accordingly, the assumed limiting oxygen partial pressure value is P02, the oxygen partial pressure value in the ambient atmosphere during the activation process is P01, and the temperature of the sensor element is the absolute temperature T2. Using the above equation (1),
Limiting electromotive force EM that causes blackening in zirconia
The processing voltage may be set such that F is obtained and the applied voltage Vp satisfies the following expression (3).

Vp <limit electromotive force EMF + Ip × Ri (3) In the present invention, the activation treatment temperature range is 500.
The temperature is set to ℃ to 800 ℃ because it is within this range that the effect of the activation treatment by the application of the alternating voltage is obtained, and this value is determined by the experiment described later.

By the way, the limit electromotive force EMF can be measured extremely accurately by experiments without assuming the limit oxygen partial pressure value P02. That is, one of the pair of electrodes of the sensor element is closed, and the closed electrode is used as a cathode to sequentially apply a DC voltage for a sufficient period of time, whereby the applied voltage Vp that is the limit of zirconia blackening. By measuring, the limiting electromotive force EMF can be easily known from the applied voltage Vp. That is, when one of the electrodes is cut off from the external atmosphere, the current Ip converges to 0 unless the zirconia element is blackened, so that the applied voltage Vp = the limit electromotive force EMF, and the limit electromotive force EMF can be known very accurately. Can be done.

Therefore, in the method for activating the zirconia oxygen sensor according to the second aspect, the limiting electromotive force EMF is measured by using the measuring sensor element (measuring element) in which one of the electrodes is closed. Then, the processing voltage is set based on the measured limit electromotive force EMF.

Therefore, according to the invention described in claim 2,
Limiting electromotive force E at which zirconia actually causes blackening
Since the processing voltage can be set from the MF, it is possible to more accurately prevent the occurrence of blackening during the activation processing. Next, when the limiting electromotive force EMF at which zirconia reaches blackening is measured in this way,
The measured limiting electromotive force EMF can be used as it is if the oxygen partial pressure of the ambient atmosphere at the time of measuring the limiting electromotive force EMF and the oxygen partial pressure at the three-phase interface at the time of executing the activation process are substantially the same. If the oxygen partial pressure at the three-phase interface changes, the measured limiting electromotive force EMF cannot be used as it is.

However, this measured limit electromotive force EMF
Can be described as in the above equation (1), and the oxygen partial pressure PO1 at the three-phase interface of the positive electrode that is not blocked can be known from the known oxygen concentration in the ambient atmosphere at the time of measurement. By substituting the partial pressure value PO1 and the limiting electromotive force EMF into the above equation (1), the limiting oxygen partial pressure PO2 at which blackening occurs in zirconia can be obtained from the above equation (1).

Therefore, in the activation treatment method of the zirconia oxygen sensor according to the third aspect, the limit electromotive force value in an atmosphere of known oxygen partial pressure measured using the measuring element as described above, and its From the oxygen partial pressure value at the time of measurement, a limit oxygen partial pressure value at the cathode side electrode is calculated, and based on the calculated limit oxygen partial pressure value, the processing voltage applied alternately between the electrodes of the sensor element is set. I am trying.

Therefore, according to the invention described in claim 3,
The limit electromotive force E is measured by using the measuring element with one electrode closed.
When MF is measured, even if the ambient atmosphere at the time of measurement and the ambient atmosphere at which the activation process is actually performed are different, the processing voltage at which the activation process is performed causes blackening during the activation process. It can be set exactly to a value that does not.

Further, in this way, when the limiting oxygen partial pressure value is obtained from the measured value of the limiting electromotive force EMF, the limiting oxygen partial pressure value is set in order to set the processing voltage so as to satisfy the above equation (3). Electromotive force EM in the ambient atmosphere for activation treatment from
It is necessary to ask for F. Therefore, in the activation treatment method of the zirconia oxygen sensor according to claim 4, in realizing the method according to claim 3 as described above, the ambient atmosphere of the sensor element when performing the activation treatment is atmospheric air. Alternatively, in a combustion gas atmosphere containing oxygen (so-called lean atmosphere) obtained by burning a fuel mixture having an excess air ratio λ> 1, a thermodynamic equilibrium in an external atmosphere or an atmosphere having a lower oxygen concentration than the external atmosphere. The oxygen partial pressure value under the condition is calculated, and based on the calculated oxygen partial pressure value and the limiting oxygen partial pressure value obtained as described above, using the formula (1) (that is, the Nernst's formula), The limit electromotive force in a lean atmosphere in which the activation process is performed is calculated, and the voltage value applied alternately between the electrodes of the sensor element is set based on the calculated limit electromotive force value.

Further, in the activation treatment method of the zirconia oxygen sensor according to the fifth aspect, the ambient atmosphere of the sensor element at the time of performing the activation treatment has an excess air ratio λ≤.
In the combustion gas atmosphere (rich atmosphere) containing an oxygen compound obtained by burning the fuel mixture of No. 1, the oxygen content under the thermodynamic equilibrium state in the external atmosphere or an atmosphere having a lower oxygen compound concentration than the external atmosphere. The pressure value is calculated, and based on the calculated oxygen partial pressure value and the limiting oxygen partial pressure value obtained as described above, the above equation (1) (that is, the Nernst equation)
Is used to calculate the limit electromotive force value in a rich atmosphere in which the activation process is performed, and based on the calculated limit electromotive force value, the voltage value to be applied alternately between the electrodes of the sensor element is set. .

Therefore, according to the fourth and fifth aspects of the invention, the limiting oxygen partial pressure value of the sensor element obtained by the third aspect of the invention is used to create an ambient atmosphere for activation treatment. The corresponding processing voltage can be optimally set. Next, in the inventions described in claims 2 to 5, the limiting electromotive force when zirconia reaches blackening is measured using a measuring element, and the processing voltage is set based on the measured value. However, the processing voltage that does not cause blackening in zirconia can also be measured by applying a DC voltage to the sensor element.

That is, when an alternating current is passed through the sensor element for the activation process, the voltage applied to each electrode periodically changes between positive and negative, so that blackening occurs in the zirconia during the activation process. However, the blackening that occurs during the activation process disappears after the activation process, and the blackening that occurs during the activation process disappears after the activation process. In order to prevent the occurrence of blackening, a voltage value at which blackening does not occur in zirconia even if it is applied to the sensor element in one direction for a sufficient time may be set as the processing voltage. Then, this voltage value can be obtained by applying a DC voltage to the sensor element for a sufficient time and measuring the limit voltage value at which blackening occurs.

Therefore, in the method for activating the zirconia oxygen sensor according to the sixth aspect, the sensor element is prepared by applying a DC voltage to the previously prepared sensor element for measurement under the condition of performing the activation processing. The oxygen-partial pressure value at the electrode-solid electrolyte interface of is determined as a limit voltage value that is the limit oxygen partial pressure value at which zirconia causes blackening, and a value smaller than this limit voltage value is used as a sensor element for activation treatment. The processing voltage is alternately applied between the electrodes.

Therefore, also in the present invention, the activation treatment for lowering the internal resistance can be performed without causing blackening in the sensor element, and the durability of the zirconia oxygen sensor can be improved. Further, when the predetermined voltage is applied alternately between the electrodes of the sensor element to lower the internal resistance of the sensor element, it is preferable that the processing voltage is too low. It is preferable to set the processing voltage to 0.4 V or higher, as described in claim 7, because such a processing effect cannot be obtained.

If the cycle of the processing voltage alternately applied between the electrodes of the sensor element is too short, no current effectively flows through the sensor element even if the processing voltage is applied, and a good processing effect cannot be obtained. Therefore, the cycle of the processing voltage alternately applied between the electrodes of the sensor element, in other words, the frequency of the processing voltage is preferably 0.5 Hz or less as described in claim 8.

The lower limit value (0.4 V) of the processing voltage and the frequency (0.5 Hz) of the processing voltage described in claims 7 and 8 are set by an experiment described later. Next, in the zirconia oxygen sensor, oxygen is bound to the electrode immediately after the sensor is fired, and the internal resistance of the zirconia increases. Therefore, conventionally, the zirconia oxygen sensor is activated immediately after manufacturing (that is, before shipment). I was trying to process it.

However, when the zirconia oxygen sensor is used for a long time, the internal resistance tends to rise again.
This tendency becomes particularly remarkable when a voltage is applied in a direction in which oxygen ions are taken in from the electrode side exposed to the oxidizing atmosphere at a relatively low temperature for a long time and used. This cause is considered to be gas adsorption or polarization (distortion). For example, when the zirconia oxygen sensor is used as an air-fuel ratio sensor for controlling the air-fuel ratio of the internal combustion engine to a desired air-fuel ratio such as the theoretical air-fuel ratio. In this case, the control center shifts as the internal resistance increases, which is a serious problem.

Therefore, in the activation treatment method of the zirconia oxygen sensor according to the ninth aspect, the activation treatment is not performed only once immediately after the production of the zirconia oxygen sensor, but during the operation of the zirconia oxygen sensor. Before and after operation,
We do it regularly or as needed.

Therefore, according to the invention described in claim 9, it is possible to prevent characteristic deterioration caused by the use of the zirconia oxygen sensor and to activate the sensor at all times. It is possible to improve the control accuracy when performing control and the like.

[0043]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic configuration of an air-fuel ratio sensor for detecting an air-fuel ratio of a fuel mixture supplied from an exhaust gas component of an internal combustion engine to an internal combustion engine by using two sensor elements (sensor cells) which are zirconia oxygen sensors. It is sectional drawing showing.

As shown in FIG. 1, in this air-fuel ratio sensor, a plate-shaped heater plate 1, a spacer 2, a pump cell 3, a spacer 4, an electromotive force cell 5, and a shield plate 6 are laminated. The heater plate 1 has a heater 7
By energizing the heater 7 by a control circuit (not shown), the pump cell 3 and the electromotive force cell 5, which are sensor elements, can be maintained at a temperature of about 800 ° C. The spacers 2 and 4 are insulators made of alumina.

The pump cell 3 is formed of stabilized zirconia or partially stabilized zirconia which is an oxygen ion conductive solid electrolyte material, and is provided with porous electrodes 11 and 12 formed of platinum on the front surface and the back surface, respectively. There is. The one porous electrode 11 of the pump cell 3 is directly exposed to the measurement gas atmosphere.

Like the pump cell 3, the electromotive force cell 5 is made of stabilized zirconia or partially stabilized zirconia, and the porous electrodes 13 and 14 made of platinum are formed on the front surface and the back surface, respectively. Is equipped with. And
A diffusion chamber 15 is formed between the pump cell 3 and the electromotive force cell 5 and is in communication with the measurement gas atmosphere through a small hole or a gas diffusion limiting portion 16 formed by filling the small hole with a porous material. Has been done.

An internal reference oxygen chamber 17 is formed on the back surface of the electromotive force cell 5, and the internal reference oxygen chamber 17 has a leakage resistance portion 18 formed by filling a small hole or a porous material. It is connected to the diffusion chamber 15 via the. The air-fuel ratio sensor thus configured is drive-controlled as follows by a control circuit (not shown).

That is, the control circuit first detects the electromotive force cell 5
By constantly flowing a constant current Icp to draw oxygen in the diffusion chamber 15 into the internal reference oxygen chamber 17, the electromotive force cell 5 controls the oxygen partial pressure in the internal reference oxygen chamber 17 to a predetermined value. The electromotive force Vs corresponding to the generated oxygen partial pressure ratio between the internal reference oxygen chamber 17 and the diffusion chamber 15 is detected. Then, the current value Ip flowing through the pump cell 3 is bidirectionally controlled so that the electromotive force Vs is always constant, that is, the oxygen partial pressure in the diffusion chamber 15 is constant, and the inside of the diffusion chamber 15 is controlled. Oxygen is moved into the measurement gas atmosphere, or oxygen in the measurement gas atmosphere is bidirectionally moved into the diffusion chamber 15, and the air-fuel ratio of the fuel mixture supplied to the internal combustion engine is detected from the current value Ip.

Therefore, in the electromotive force cell 5 of such an air-fuel ratio sensor, a voltage is constantly applied between the electrodes 13 and 14 so that oxygen ions always move from the electrode 13 to the electrode 14 side. When operated for a long time, the electrode 14
It is thought that this is due to the adsorption of oxygen into the electromotive force, but the internal resistance of the electromotive force cell 5 increases.

When the air-fuel ratio of the internal combustion engine is controlled to the excess air ratio λ> 1 for a long time by using the air-fuel ratio sensor, the pump cell 3 is also supplied with oxygen ions from the diffusion chamber 15 into the measurement gas atmosphere for a long time. Since a voltage is applied to move oxygen, it is considered that oxygen is adsorbed on the electrode 11 side, but its internal resistance increases.

Therefore, in the air-fuel ratio sensor of this embodiment, the activity of the present invention can be obtained not only after firing the sensor cells 3 and 5 but also during execution of air-fuel ratio control of the internal combustion engine or before and after air-fuel ratio control. By performing the conversion process, it is possible to advantageously prevent the characteristic deterioration of the sensor cells 3 and 5 described above.

The activation process for reducing the internal resistance of the air-fuel ratio sensor of this embodiment will be described below. First, the activation process is performed by applying an alternating voltage between the electrodes of each sensor cell 3, 5, but if this applied voltage is too large, each sensor cell 3, 5 is configured during the activation process. Blackening occurs in the zirconia present, and even if the blackening disappears after the activation treatment due to the reoxidation of the part where the blackening occurs, the part where the blackening occurs deteriorates.

Therefore, in order to solve these problems,
In this example, the alternating voltage applied between the electrodes of each sensor cell 3.5 in performing the activation process was set as follows. First, as shown in FIG. 2, each sensor cell 3,
A porous zirconia Z made of the same material as the above-mentioned sensor cells 3 and 5 was formed on the front and back surfaces of a flat zirconia Z made of the same material as the No. 5 and the same production method, and one platinum electrode was covered with a cover C. A measurement cell 30 that was almost completely shielded from the outside air was produced.

Then, in air, at 727 ° C. (absolute temperature 10
00 degree), both platinum electrodes using the platinum electrode as a cathode
By applying a DC voltage Vp in between, the limit voltage at which zirconia reaches blackening was measured. In addition,
The application time of the DC voltage Vp was set to 3 hours, which was sufficient to confirm the blackening generated in zirconia.

As a result, at the temperature of 727 ° C. in the atmosphere, the limit voltage at which the measuring cell 30 reaches the blackening is 1.7.
It was found to be larger than V and smaller than 2.0V. By the way, the applied voltage Vp can be expressed by the above-mentioned equation (2). Also, the electromotive force E of the measuring cell 30 when a voltage is applied
The MF can be obtained by the Nernst equation (equation (1) above). When the temperature condition at the time of measuring the limit voltage is 727 ° C. (absolute temperature 1000 ° C.) as described above,
From the Nernst equation, the electromotive force EMF is given by the following equation (4).

EMF = 50 × log (PO1 / PO2) (4) Since one platinum electrode of the measuring cell 30 is completely shielded from the outside air by the cover C, zirconia (ZrO ₂ ) is blackened. Unless otherwise, the current Ip converges to zero.

Therefore, from the above equations (2) and (4), the applied voltage Vp is given by the following equation (5). Vp [V] × 1000 = EMF [mV] = (RT / nF) × ln (PO1 / PO2) = 50 × log (PO1 / PO2) (5) The atmospheric oxygen partial pressure is about 0.2 atm. Therefore, the oxygen partial pressure P at the platinum electrode side three-phase interface at the time of measuring the above limit voltage is
O1 is also about 0.2 atm.

Therefore, in the above equation (5), 0.
By substituting 2 atm into Vp with a voltage of 1.7 V and calculating the oxygen partial pressure PO2 at the platinum electrode side three-phase interface, this value becomes 10 ^-34.7 atm. As a result, in each of the sensor cells 3 and 5 of the air-fuel ratio sensor of the present embodiment, the oxygen partial pressure at the three-phase interface on the electrode side that becomes the cathode when a voltage is applied is 10 ⁻³⁴ atm as the safe side limit oxygen partial pressure value. If it is above,
It turns out that blackening does not occur.

From the above measurement results, when the sensor cells 3 and 5 are activated in the atmosphere, if the electromotive force of each sensor cell 3 and 5 is limited to 1.7 V or less, each sensor cell 3 and 5 is It can be seen that blackening that occurs in the can be prevented. Therefore, the processing voltage (alternating voltage) when activating the sensor cells 3 and 5 in the atmosphere is set so as to satisfy the condition of Vp ≦ 1.7 + Ip × Ri [V] from the equation (3). In the present embodiment, the processing voltage used for activating the sensor cells 3 and 5 in the atmosphere was set to 1.5V. Then, this voltage was applied alternately to perform activation treatment.

As described above, the air-fuel ratio sensor mounted on the exhaust system of the internal combustion engine may be operated after the vehicle has been stopped for a sufficiently long time before starting.
The processing voltage when the activation processing is performed in the atmosphere or the atmosphere equivalent to the time of fuel cut engine braking can be set by the measurement result of the limit voltage using the measurement cell 30. When the activation process is performed, since the sensor cells 3 and 5 are exposed to the exhaust gas of the internal combustion engine, the processing voltage in the atmosphere cannot be used as it is.

Exhaust gas during normal operation of the internal combustion engine is changed from a state (lean atmosphere) containing oxygen exhausted when the internal combustion engine is operated with a fuel mixture having an excess air ratio λ> 1.
Since the internal combustion engine greatly changes in accordance with the operating state of the internal combustion engine up to a state (rich atmosphere) containing almost no oxygen discharged when operating the internal combustion engine with a fuel mixture having an excess air ratio λ ≦ 1, When performing activation processing during operation,
It is necessary to set the processing voltage so that blackening does not occur in each of the sensor cells 3 and 5 even when the blackening is most likely to occur in each of the sensor cells 3 and 5 even in the rich atmosphere.

Therefore, in the present embodiment, the processing voltage for activating the air-fuel ratio sensor mounted on the exhaust system of the internal combustion engine during the operation of the internal combustion engine is as follows. ， The minimum air excess ratio is λ when the fuel ratio in the fuel mixture is the largest, such as during high load operation.
= 0.8, the following settings were made so that the activation process can be executed without causing blackening in each sensor cell 3, 5.

First, when a DC voltage is applied between the electrodes in a state where the sensor cells 3 and 5 are exposed to a rich atmosphere containing almost no oxygen, oxygen in the rich atmosphere is generated at the three-phase interface on the electrode side serving as the cathode. The compound causes dissociation of oxygen, and an electric current flows through each of the sensor cells 3 and 5.

That is, H ₂ O is contained in the exhaust gas of the internal combustion engine.
, CO _{2 and the} like are contained, even when oxygen is hardly contained in the exhaust gas, H ₂ O and CO ₂ which are oxygen compounds in the exhaust gas cause dissociation of oxygen and each sensor cell 3 , 5 flows.

Next, such dissociation of oxygen is caused by H ₂ O and C.
Since it is almost the same as that of O ₂ , consider the case where a current flows through the sensor element due to the dissociation of oxygen from H ₂ O. First, the equilibrium constant of H ₂ O is (PH ₂ × PO ₂ ^1/2 ) / PH ₂ O = 8.73 × 10 ^{-11 at} an absolute temperature of 1000 ° C. Also, the combustion system of H ₂ is modeled, and the combustion system is Assuming that the excess air ratio λ of the fuel mixture supplied to the engine is 0.8, which is the minimum value in the case of an internal combustion engine, the combustion of the fuel mixture is H ₂ + 0.4 · O ₂ → 0.8H It becomes ₂ O + 0.2H ₂ . At this time, according to the above equilibrium constant from H ₂ O, P
O ₂ oxygen is dissociated, but since it is very small, H ₂ O,
Neglecting H ₂ results in (0.2 × PO ₂ ^1/2 ) /0.8=8.73×10 ^-11 , which is the oxygen partial pressure P on the electrode side exposed to the reducing atmosphere.
O1 is PO1 = PO ₂ = (3.49 × 10 ^-11 ) ² = 1.2 × 10
^-21 .

Therefore, in the exhaust gas (rich atmosphere) with the excess air ratio λ = 0.8, the limit voltage that is the limit of blackening is EMF = 50 log (10 ⁻²⁰ / 10) from the above equation (5). ^-34.7 ) = 0.73
5 and when the sensor cells 3, 5 are activated during the operation of the internal combustion engine, if the electromotive force of each sensor cell 3, 5 is limited to 0.7 V or less, the blackening that occurs in each sensor cell 3, 5 It turns out that this can be prevented.

Therefore, the processing voltage (alternating voltage) when activating the sensor cells 3 and 5 in the atmosphere is (3) above.
From the formula, it may be set so as to satisfy the condition of Vp ≦ 0.7 + Ip × Ri [V]. In the present embodiment, the air-fuel ratio sensor provided in the exhaust system of the internal combustion engine is activated during the operation of the internal combustion engine. The processing voltage used for the chemical treatment is 0.9
Set to V.

Next, various experiments were carried out to measure the effect of the activation treatment by alternately applying the treatment voltage set as described above to the sensor cell and the treatment conditions suitable for the activation treatment. Hereinafter, this experiment will be described. First, the two air-fuel ratio sensors shown in FIG. 1 are attached to the exhaust pipe of an internal combustion engine, operated for a long time to increase the internal resistance of the electromotive force cell 5 of each air-fuel ratio sensor, and then activated in the atmosphere. As a result of the chemical conversion treatment, the internal resistance of the electromotive force cell 5 could be reduced as shown in FIGS.

In FIGS. 3A and 3B, the waveforms A1 and A2 shown by the solid lines are the pulse voltage as shown in FIG. 4 at the processing voltage ± 1.5 V and the frequency 0.0083 Hz, and the processing temperature 650. Simultaneously with the start of energization of the heater after activation of the electromotive force cell 5 by applying the voltage between the electrodes 13 and 14 of the electromotive force cell 5 continuously in the atmosphere for 3 cycles under the condition of ° C. The result of measuring the voltage Vs change result of the electromotive force cell 5 by applying a constant current of 27.5 μA to the electromotive force cell 5 is shown, and the waveforms of B1 and B2 shown by the dotted lines are as follows: The result of measuring the voltage Vs change result of the electromotive force cell 5 by applying a constant current of 27.5 μA to the electromotive force cell 5 at the same time when the heater energization is started is shown.

From the measurement results, in the activated air-fuel ratio sensor, a smooth decrease in resistance was observed along with a temperature rise due to energization of the heater. In the air-fuel ratio sensor before performing the treatment, the internal resistance slows down as the temperature rises due to the energization of the heater, and two reduction peaks are seen.
Moreover, it can be seen that there are variations depending on the sample.

The activation process in this case is +1.5.
It was performed by applying a pulse signal having a time ratio of V to -1.5 V of 1: 1 to the electromotive force cell 5. However, according to other experiments, the time ratio needs to be set to 1: 1. However, it has been found that the same effect as above can be obtained even with, for example, 3:10. Therefore, in the case of the electromotive force cell 5 of the air-fuel ratio sensor as in this embodiment, for example, the diffusion chamber 15
It is also possible to increase the energization time for moving the oxygen in the inside to the internal reference oxygen chamber 17 side and perform the activation treatment while keeping the oxygen partial pressure in the internal oxygen reference chamber 17 constant. Then, in this case, even if the activation process is regularly performed during the execution of the air-fuel ratio control, the air-fuel ratio can be promptly detected after the activation process is completed. The stop time of the air-fuel ratio control for execution can be shortened.

Next, in order to set an appropriate range such as the temperature and the processing voltage which are the conditions for executing the activation treatment, platinum electrodes are screen-printed on both sides of the partially stabilized zirconia green sheet having a thickness of 0.5 mm. As shown in FIG.
A large number of samples as shown in Fig. 3 were prepared, each sample was subjected to activation treatment under various conditions, and the results were examined. The results will be described below. The size of the electrode part 21 of the sample is 2 mm × 4 mm.

First, a plurality of samples are sampled from 400 ° C. to 850 ° C.
Up to a temperature of 0.0083 between the electrodes of each sample.
The activation processing was performed by applying a pulse signal of Hz for 3 cycles for 6 minutes. Then, after that, between the electrodes of the respective samples having different treatment temperatures, in the atmosphere of 800 ° C., 1.5
The current value when V was applied was measured to determine the degree of activation effect.

As a result, as shown in FIG. 6, at the activation temperature of 550 ° C. to 750 ° C., a relatively large current flows and 55
It was found that the current value was extremely small at temperatures of 0 ° C. or lower and 750 ° C. or higher, and the difference reached 4 to 6 times. Therefore, the activation process is from 500 ℃ to 80
It is understood that the temperature may be within the temperature range of 0 ° C, preferably within the temperature range of 550 ° C to 750 ° C.

Next, a plurality of samples were inserted into a furnace (atmosphere) at 650 ° C., and the treatment voltage was varied between ± 0.1 V and ± 0.1 V between the electrodes.
Pulse signals set to different values up to 2.0 V were applied to carry out activation processing. The frequency of the pulse signal in this case is 0.0083 Hz, as described above, and the activation processing time is 3 cycles and 6 minutes. The result is shown in FIG. 7.

In FIG. 7, the vertical axis represents the ratio of the current at the end of the activation process for 6 minutes in 3 cycles to the initial initial current value,
That is, it shows the rate of increase in current due to activation processing. Then, as is clear from FIG. 7, the processing voltage is 0.6
Above V, the saturation current value greatly increases from the initial current value, whereas below 0.6, the saturation current value does not increase much from the initial current value, and below 0.4 V, this tendency is remarkable. Therefore, it is understood that the processing voltage should be set to at least 0.4 V or higher, preferably 0.6 V or higher in order to obtain a favorable effect.

Next, a plurality of samples were inserted into a furnace (atmosphere) at 650 ° C., and a pulse signal with a frequency of 0.0083 Hz to 10 Hz was applied between the electrodes to perform activation treatment. . The processing voltage in this case is ±
It is 1.5 V and the activation time is 6 minutes. The result is shown in FIG.

In FIG. 8, the vertical axis represents the ratio of the current at the end of the activation process for 6 minutes to the initial initial current value, that is, the rate of increase in the current due to the activation process, as in FIG. Then, as is apparent from FIG. 8, the effect is exhibited in the region where the frequency of the processing voltage is 0.5 Hz or less, particularly 0.2
It can be seen that a large effect can be obtained in the region below Hz.
Therefore, the frequency of the processing voltage is 0.5 Hz or less,
It can be seen that the frequency is preferably set to 0.2 Hz or less.

Next, a plurality of samples were inserted into a furnace (atmosphere) at 650 ° C., the processing voltage was ± 1.5 V, and the frequency was 0.
008Hz, 0.016Hz, 0.05Hz, 0.5H
Applying four kinds of pulse signals different from z and changing the application cycle in which one cycle is from the rising of the processing voltage to the next rising as shown in FIG. 3, 1 cycle, 2 cycles, 3 cycles, ... Thus, the relationship between this application cycle (that is, the activation treatment time) and the effect of the activation treatment was investigated. The result is shown in FIG.

In FIG. 9, the vertical axis represents the ratio of the current at the end of the activation process for 6 minutes to the initial initial current value, that is, the rate of increase in the current due to the activation process, as in FIGS. ing. As is clear from FIG. 9, the effect of the activation treatment is obtained by applying the treatment voltage for one cycle or more at any frequency, and the effect of the activation treatment is substantially stable in the region of three cycles or more. I understand that
Therefore, the execution time of the activation processing is 1 of the processing voltage.
It can be seen that it is sufficient to set the time for one cycle, preferably three cycles.

Next, FIGS. 10 to 13 show Cole-Cole plot diagrams in which the impedances of the activated sample and the untreated sample are measured by the well-known complex impedance measuring method. Note that FIG. 10 shows the untreated sample at 650 ° C.
FIG. 11 shows the sample after the activation treatment at 650 ° C.
Is a Cole-Cole plot diagram in which the untreated sample was measured at 800 ° C., and the sample after the activation treatment was measured at 800 ° C., respectively.

Further, in this measurement, the sample activation treatment was carried out in a furnace (atmosphere) at 650 ° C.
, A voltage of ± 1.5 V and a frequency of 0.
It was performed by applying a pulse signal (processing voltage) of 008 Hz for 6 minutes. The conditions for executing the complex impedance measurement method are the same except for the temperature, and the upper limit frequency is 6
5 kHz, lower limit frequency 0.1 Hz, voltage peak value 100 m
V.

Measurement conditions Measurement results at 650 ° C. (FIG. 10,
Comparing Fig. 11), the low-frequency resistance value is scaled out in the untreated sample, and the internal resistance is several k.
It is estimated to be Ω. On the other hand, in the sample after the activation treatment, the low-frequency resistance value (point A in the figure) is about 430Ω, and when the high-frequency resistance value (point B in the figure) of 140Ω is subtracted, about 290Ω is the platinum electrode. Is estimated to be the resistance value between the solid electrolyte interface and the solid electrolyte interface.

Further, the measurement result at the measurement condition of 800 ° C. (see FIG. 1)
2 and FIG. 13), in the untreated sample, the low frequency resistance value (point A in the figure) 0 is about 170 Ω, and the high frequency resistance value (point B in the figure) is about 40 Ω. Is estimated to be the resistance value between the platinum electrode and the solid electrolyte interface. On the other hand, in the sample after the activation treatment, the low-frequency resistance value is about 65Ω, and when the high-frequency resistance value of 40Ω is subtracted, about 25Ω is estimated to be the resistance value between the platinum electrode and the solid electrolyte interface. .

That is, at any temperature, the resistance component between the platinum electrode and the solid electrolyte interface is extremely reduced by the activation treatment, and it can be seen that the activation treatment can reduce the internal resistance of the sensor element. Above, FIG.
When the activation treatment is performed in the atmosphere by subjecting the sample shown in 1 above to the activation treatment in the air, the temperature range is
500 ° C. to 800 ° C., preferably 550 ° C. to 750 ° C., and the lower limit value of the processing voltage is 0.4 V, preferably 0.6 V
It was found that the frequency of the processing voltage should be 0.5 Hz or less, preferably 0.2 Hz or less, and the application cycle of the processing voltage should be 1 cycle or more, preferably 3 cycles or more. The frequency of the processing voltage may be 0.5 Hz or less, but if the period is too long, the effect of the activation treatment tends to decrease, so the frequency of the processing voltage is 0, which is the minimum value in the above experiment. It is preferably set to 0.0083 Hz or more.

Next, the above experiment was carried out in the atmosphere using the sample shown in FIG. 5 in which both electrodes were opened. In the air-fuel ratio sensor shown in FIG. 1, one of the sensor cells 3 and 5 was used. Diffusion chamber 15 whose electrodes are diffusion limited to the outside atmosphere
And is also performed while the internal combustion engine is in operation after being installed in the exhaust pipe of the internal combustion engine.

Therefore, in the air-fuel ratio sensor shown in FIG. 1, in order to confirm that the effect of the activation process can be obtained in the atmosphere and the atmosphere equivalent to the rich operation exhaust gas of the internal combustion engine,
The following experiment was conducted. First, the processing voltage ± 1.
By applying an alternating voltage of 5 V and a frequency of 0.0083 Hz to each sensor cell 3 and 5 for 6 minutes, and sequentially changing the temperature of the pump cell 3 by controlling the energization of the heater 7, the processing temperature in the atmosphere and the activation processing are performed. The relationship with the effect of was measured. In addition, the atmosphere equivalent to the exhaust gas (C ₃ H ₈ + N ₂ + C when the internal combustion engine is operated with the air-fuel ratio of 12.0)
O + CO ₂ + H ₂ + H ₂ O), an alternating voltage with a processing voltage of ± 0.9 V and a frequency of 0.0083 Hz is applied to each sensor cell 3,
5 was applied for 6 minutes, and the temperature of the pump cell 3 was sequentially changed by controlling the energization of the heater 7 to measure the relationship between the treatment temperature in the rich atmosphere and the effect of the activation treatment. The measurement results are shown in [Table 1]. The measurement result is the value in the pump cell 3.

[0088]

[Table 1]

Next, the temperature of each sensor cell 3 and 5 is set to 700.
The temperature, the frequency of the treatment voltage, and the application time were the same as in the above experiment, and the treatment voltage was sequentially changed to measure the relationship between the treatment voltage in the atmosphere and the atmosphere equivalent to the exhaust gas and the effect of the activation treatment. did. The measurement results are shown in [Table 2]. In addition, this measurement result is a value in the pump cell 3 similarly to [Table 1].

[0090]

[Table 2]

As is clear from [Table 1] and [Table 2], as a result of the above experiment, (1) In the activation treatment in the rich atmosphere, it is expected that the internal resistance of the sensor cells 3 and 5 is lowered. Although the effect is obtained, compared to the activation treatment in the atmosphere, the pump cell 3
The change rate of the internal resistance is small and the effect of the activation treatment is small.

(2) In the atmosphere, the effect of the activation treatment can be obtained in a temperature range substantially similar to the measurement result of the sample shown in FIG. 5, whereas in the rich atmosphere, the treatment temperature at which a good effect is obtained can be obtained. The range becomes narrow. I knew that.

As described above, as one embodiment of the present invention, the limiting electromotive force when zirconia reaches blackening in the atmosphere is measured using the measuring element 30, and the activation treatment is performed in the atmosphere based on the measured value. Set the processing voltage when performing
Calculate the limiting oxygen concentration based on the limiting electromotive force in the atmosphere, calculate the limiting electromotive force in a rich atmosphere, and set the processing voltage when performing the activation process during operation of the internal combustion engine based on this calculation result. By doing so, it is possible to reduce the internal resistance of each sensor cell 3, 5 without causing blackening in each sensor cell 3, 5 even in the atmosphere and the operation of the internal combustion engine. However, it is not always necessary to set the processing voltage by using the measuring element 30, and for example, FIG.
By applying a predetermined DC voltage to both electrodes of the sample, for example, for 3 hours in the same atmosphere as in the case where the activation treatment is performed using the sample shown in FIG. Even if you measure and set a voltage below the measured voltage value as the processing voltage,
The activation process can be executed without causing blackening in each sensor cell 3, 5.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an air-fuel ratio sensor of an embodiment.

FIG. 2 is a cross-sectional view showing a schematic configuration of a measuring element used to determine a limit electromotive force that is a limit of occurrence of blackening.

FIG. 3 is a diagram showing an example of an effect obtained when the activation process of the present invention is applied to the air-fuel ratio sensor of FIG.

FIG. 4 is an explanatory diagram showing a processed voltage waveform when the activation process is performed on the air-fuel ratio sensor of FIG. 1.

FIG. 5 is a perspective view showing a sample used in an experiment for setting an appropriate range of execution conditions for activation processing.

FIG. 6 is a diagram showing a measurement result for setting an appropriate range of activation processing temperature.

FIG. 7 is a diagram showing a measurement result for setting an appropriate range of a processing voltage.

FIG. 8 is a diagram showing a measurement result for setting an appropriate range of a frequency of a processing voltage.

FIG. 9 is a diagram showing a measurement result for setting an appropriate range of activation processing time.

FIG. 10 is a Cole-Cole plot diagram at 650 ° C. of an untreated sample.

FIG. 11 is a Cole-Cole plot diagram at 650 ° C. of the sample after the activation treatment.

FIG. 12 is a Cole-Cole plot diagram at 800 ° C. of an untreated sample.

FIG. 13 is a Cole-Cole plot diagram at 800 ° C. of the sample after the activation treatment.

[Explanation of Codes] 1 ... Heater plate 2 ... Spacer 3 ... Pump cell
4 ... Spacer 5 ... Electromotive force cell 6 ... Shield plate 11, 12, 1
3, 14 ... Electrode 15 ... Diffusion chamber 16 ... Gas diffusion limiting part 17 ... Internal reference oxygen chamber 18 ... Leakage resistance part 30 ... Measuring cell

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-156361 (JP, A) JP-A-5-18938 (JP, A) JP-A-55-39096 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01N 27/419 G01N 27/41 G01N 27/409

Claims (9)

(57) [Claims] 1. A method for activating a zirconia oxygen sensor, comprising a sensor element having at least a pair of porous electrodes formed on both surfaces of a plate-shaped oxygen ion conductive solid electrolyte made of zirconia, wherein a temperature of 500 The oxygen partial pressure value at the electrode-solid electrolyte interface of the sensor element is larger than the critical oxygen partial pressure value at which the solid electrolyte causes blackening under the condition of ℃ to 800 ℃. A method for activating a zirconia oxygen sensor, characterized in that a predetermined voltage is applied alternately between the electrodes. 2. The activation treatment method for a zirconia oxygen sensor according to claim 1, wherein a pair of porous bodies is provided on both sides of a plate-like oxygen ion conductive solid electrolyte made of the same zirconia as the sensor element for performing the activation treatment. Using a measuring element in which an electrode is formed and one of the pair of electrodes is closed in a substantially airtight manner with respect to the external atmosphere, the above-mentioned closing between the pair of electrodes of the measuring element under a predetermined atmosphere The limit electromotive force value of the sensor element under a predetermined atmosphere is measured by applying a DC voltage for a sufficient time using the side electrode as a cathode, and the alternating electromotive force is applied between the electrodes of the sensor element based on the measured limit electromotive force value. A method for activating a zirconia oxygen sensor, which comprises setting a voltage value applied to the zirconia oxygen sensor. 3. The activation treatment method for a zirconia oxygen sensor according to claim 2, wherein the limit electromotive force value under a predetermined atmosphere measured using the measuring element and the measured oxygen in a predetermined ambient atmosphere. From the partial pressure value, the limiting oxygen partial pressure value at the cathode side electrode is calculated, and based on the calculated limiting oxygen partial pressure value, the voltage value to be alternately applied between the electrodes of the sensor element is set. A method for activating an oxygen sensor of zirconia. 4. The activation treatment method for a zirconia oxygen sensor according to claim 3, wherein the ambient atmosphere of the sensor element when performing the activation treatment is the atmosphere or a fuel mixture having an excess air ratio λ> 1. When the combustion gas atmosphere containing oxygen obtained by burning, calculates the oxygen partial pressure value under thermodynamic equilibrium in the external atmosphere or an atmosphere having a lower oxygen concentration than the external atmosphere, and the calculated oxygen Based on the partial pressure value and the calculated limiting oxygen partial pressure value, a limiting electromotive force value is calculated using the Nernst equation, and based on the calculated limiting electromotive force value, it is alternately applied between the electrodes of the sensor element. A method for activating a zirconia oxygen sensor, characterized by setting a voltage value. 5. The activation treatment method for a zirconia oxygen sensor according to claim 3, wherein the external atmosphere of the sensor element at the time of performing the activation treatment burns a fuel mixture having an excess air ratio λ ≦ 1. When a combustion gas atmosphere containing an oxygen compound obtained by the above, the oxygen partial pressure value under thermodynamic equilibrium state in the above-mentioned external atmosphere or an atmosphere having a lower oxygen compound concentration than the external atmosphere is calculated, and the calculated oxygen is calculated. Based on the partial pressure value and the calculated limiting oxygen partial pressure value, a limiting electromotive force value is calculated using the Nernst equation, and based on the calculated limiting electromotive force value, it is alternately applied between the electrodes of the sensor element. A method for activating a zirconia oxygen sensor, characterized by setting a voltage value. 6. The activation treatment method for a zirconia oxygen sensor according to claim 1, wherein a DC voltage is applied to a previously prepared sensor element for measurement for a sufficient time under the conditions for performing the activation treatment, The electrode of the sensor element-a partial voltage value at which the oxygen partial pressure value at the solid electrolyte interface becomes a limit oxygen partial pressure value at which the solid electrolyte causes blackening, is obtained, and between the electrodes of the sensor element during the activation treatment. A method for activating an zirconia oxygen sensor, characterized in that the voltage value applied to the alternation is set to a value smaller than the limit voltage value. 7. The activation treatment method for a zirconia oxygen sensor according to claim 1, wherein the voltage applied alternately between the electrodes of the sensor element is 0.4 V or more. Method for activating zirconia oxygen sensor. 8. The activation treatment method for a zirconia oxygen sensor according to claim 1, wherein the applied frequency of the predetermined voltage between the electrodes of the sensor element is 0.
A method for activating a zirconia oxygen sensor, which is 5 Hz or less. 9. The activation treatment method for a zirconia oxygen sensor according to any one of claims 1 to 8, wherein the activation treatment is carried out periodically or before or during the operation of the zirconia oxygen sensor. A method for activating a zirconia oxygen sensor, which is performed according to the method.