JP5229508B2 - Oxygen partial pressure control apparatus and solid electrolyte recovery method for oxygen partial pressure control - Google Patents

Description

The present invention relates to an oxygen partial pressure control apparatus capable of supplying a gas whose oxygen partial pressure is controlled in the range of 0.2 to 10 ^-30 atm, and in particular, under the conditions of low material cost and low operation cost, the atmosphere of the processing apparatus The present invention relates to an electrochemical oxygen partial pressure control device capable of controlling an oxygen partial pressure of gas or the like in a range of 0.2 to 10 ^-30 atm, and a solid electrolyte recovery method for extending the life of the oxygen partial pressure control device.

  Conventionally, a method of producing a single crystal sample using an atmospheric gas whose oxygen partial pressure is controlled by an electrochemical oxygen pump containing a solid electrolyte is known. Specifically, while sealing both ends of a flat cylindrical solid electrolyte, a sealed cylindrical solid electrolyte provided with net-like electrodes made of platinum on the inner and outer surfaces of the cylindrical peripheral surface portion as an oxygen pump, A technique for reducing the partial pressure of oxygen in the inert gas by supplying an inert gas into the solid electrolyte and applying a voltage to both electrodes to exclude oxygen in the inert gas from the solid electrolyte. It is. (See Patent Document 1.)

  Furthermore, the present inventor, as an improved technique, provides a conductance means and an exhaust speed variable means in the return path from the sample preparation device as a mechanism for recycling waste gas, and maintains a positive pressure therebetween, Proposes a technology to prevent contamination caused by outside air. (Refer to the description and drawings attached to the application for Japanese Patent Application No. 2003-42403.)

  In addition, it is made of solid electrolyte material such as strontium-doped, lanthanum, manganate, etc., has a cylinder structure such as honeycomb, and feedback control of operation voltage etc. based on oxygen partial pressure value from the sensor to prevent damage. An oxygen pump for producing atmospheric gas from high pressure to extremely low oxygen is known. (See Patent Document 2.)

  There is known a floating zone device in which a plurality of gas supply circuits are connected in parallel, and a mass flow controller is provided for each of them so that the atmosphere can be changed over a wide range and the vapor pressure fluctuation can be dealt with. (See Patent Document 3)

  On the other hand, in an electrochemical oxygen sensor that monitors exhaust gas from an internal combustion engine, a method for regenerating the oxygen sensor by applying a voltage equal to or higher than a saturation voltage is known. (See Patent Document 4)

JP 2002-326887 A JP 10-500450 gazette JP 2001-114589 A Special table 2003-510588 gazette

However, in the system including the oxygen pump with the circulation mechanism described in the specification and drawings attached to the application of Japanese Patent Application No. 2003-42403, which is an improvement technique of the above-mentioned Patent Document 1, the oxygen partial pressure is set to 10 ^-30 atm. Although it can be reduced to the vicinity, it has been found that there is a problem that the zirconia tube, which is a solid electrolyte, breaks in about one week to 10 days when operated continuously in such extremely low oxygen conditions.

Further, when assuming an operation in an extremely low oxygen partial pressure region near 10 ^-30 atm, for example, an oxygen pump with a circulation mechanism exemplified in the specification and drawings of Japanese Patent Application No. 2003-42403 is used. In addition to one zirconia tube for the oxygen pump, two zirconia tubes are required for the oxygen sensor for controlling the oxygen partial pressure, which increases the material cost for the zirconia tube. Since each zirconia tube requires a heating furnace for raising the temperature to the operating temperature as a solid electrolyte, there is a problem that the apparatus cost and the operation cost increase.

  Moreover, considering airtight piping to the zirconia pipe, it is necessary to attach a sealing mechanism such as an O-ring or bellows with an adhesive that can keep the airtightness, but since these are not sufficiently heat resistant, the zirconia pipe is lengthened. Thus, it is necessary to take a long exposed portion from the heating furnace and seal it in a low temperature region. Accordingly, there are problems that the material cost is further increased due to the lengthening of the zirconia pipe and the size of the apparatus is increased.

On the other hand, as exemplified in Patent Document 2, in order to control the oxygen partial pressure of the gas used with a predetermined accuracy, feedback control based on the output of the oxygen sensor is performed even in normal oxygen pump operation. Although it is desirable, the adoption of the PID control type oxygen pump for the drive control is not only made by the present inventors, but the oxygen partial pressure level required for the operation is 0.2 to 10 ^{−. Since} the control system has a wide gain characteristic of ³⁰ atm and its characteristic gain curve depends on the oxygen partial pressure, simply incorporating a conventional PID constant-fixed PID controller into the oxygen pump does not provide sufficient controllability. , Which contributed to increase operating costs. Also, determining the gain curve characteristics according to the individual operating conditions itself is a work that requires a great deal of labor.

  Moreover, since the conventional oxygen partial pressure control devices are assumed to be processing devices having an internal volume of less than 1 liter, they are not suitable for manufacturing processes for mass-produced products such as semiconductor devices that require a large amount of gas. is there. As exemplified in Patent Document 3, it is conceivable to connect a considerable number of oxygen partial pressure control devices in parallel to satisfy the supply capacity. However, it is assumed that the equipment cost and the operation cost become enormous.

  On the other hand, the method for recovering the solid electrolyte exemplified in Patent Document 4 is only for dealing with a decrease in the performance of the oxygen sensor. When this method is applied to an over-reduced oxygen pump, the lifetime is shorter. It does not contribute to the reduction of equipment costs.

  In order to solve the above-mentioned various problems, the present inventors have made improvements from both the apparatus configuration such as an oxygen pump and the operation method, and create an invention capable of realizing a high practical operation level and low cost. It came to. The present invention is an invention specified by the following technical matters.

In the present invention (1), air or pure oxygen is supplied into a heating furnace capable of being heated and held at the operating temperature of the solid electrolyte, and at least one oxygen pump including a solid electrolyte having a tubular structure and a solid having a tubular structure are provided. Contains at least two oxygen sensors containing electrolyte,
The at least one oxygen pump and the at least two oxygen sensors are arranged in parallel to each other so that the air or pure oxygen is used as an extra-purge gas for each solid electrolyte, and the inside of each solid electrolyte pipe is shared. Process gas is connected to be able to distribute
Furthermore, the oxygen partial pressure control device is characterized in that it is electrically connected to oxygen pump operation control means for controlling the operation of the oxygen pump based on the oxygen partial pressures detected by the two oxygen sensors.
According to the present invention (2), both ends of the solid electrolyte having a tubular structure of the oxygen pump are extended to the outside of the heating furnace, and both ends of the pipe protruding from the heating furnace are hermetically sealed by sealing means, The oxygen partial pressure control device according to the present invention (1), further comprising a cooling means for cooling the sealing means.
According to the present invention (3), the oxygen sensor includes a porous electrode provided on the entire surface of the tube and a porous electrode provided in a strip shape on the outer periphery of the tube, and detects an oxygen partial pressure by detecting a potential difference generated between the two electrodes. It is an oxygen partial pressure control device according to any one of the present invention (1) and the present invention (2), characterized in that
According to the present invention (4), each time the oxygen pump operation control means has its PID constant defined as a function of the oxygen partial pressure and the current value of the oxygen partial pressure is sampled by the oxygen sensor, Any one of the present invention (1) to the present invention (3), wherein the operation of the oxygen pump is PID controlled based on the PID constant after the adjustment. 1 is an oxygen partial pressure control device of the invention.
In the present invention (5), the heating furnace includes at least one cylindrical resistance heating element, and is arranged in parallel to each of the solid electrolytes, and the number of the solid electrolytes and the number of the resistance heating elements. The oxygen partial pressure control device according to any one of the present invention (1) to the present invention (4) is characterized in that the ratio of the above is 1 / 2-6.
In the present invention (6), the axial center of each solid electrolyte is positioned at each vertex of the honeycomb structure centering on the axial center of the resistance heating element as viewed in the axial direction of the resistance heating element and the solid electrolyte. Thus, the oxygen partial pressure control device according to the present invention (5) is characterized by being arranged at equal intervals.
The present invention (7) includes a step of heating a heating furnace including at least one solid electrolyte separating at least two spaces to an operating temperature of the solid electrolyte,
Applying a voltage between the electrodes provided on the front and back of the solid electrolyte, and discharging oxygen from the gas in one of the spaces to the gas in the other space through the solid electrolyte;
Introducing a pure oxygen or air at atmospheric pressure into the solid electrolyte surface on the side that has been in contact with the gas having a reduced oxygen partial pressure, and reoxidizing the solid electrolyte surface;
A method of recovering a solid electrolyte for controlling oxygen partial pressure, comprising at least a step of lowering the temperature of the heating furnace from the solid electrolyte operating temperature.
The present invention (8) is characterized in that an average rate of temperature increase in the step of increasing temperature is 3 to 6 ° C./min, and an average rate of temperature decrease in the step of decreasing temperature is 3 to 6 ° C./min. This is a method for recovering a fixed electrolyte for controlling oxygen partial pressure according to the present invention (7).

  In addition, as an apparatus configuration in which a very low oxygen partial pressure is required as the oxygen partial pressure level of the processing gas, the apparatus further includes a second heating furnace that houses a second oxygen pump including a tubular solid electrolyte, The solid electrolyte of the second oxygen pump is connected between the oxygen pump and the oxygen sensor, and serves as an inert gas whose oxygen partial pressure is controlled as its extra-purge gas. The tubular structure of the oxygen partial pressure control device of the present invention (1) and the oxygen pump is a double tube structure including an outer tube and an inner tube coaxial with each other, and is formed in a space between the inner tube and the outer tube. The present invention is characterized in that the processing gas whose oxygen partial pressure is reduced by the solid electrolyte in the outer tube is guided to the space in the inner tube, and the oxygen partial pressure is further reduced by the solid electrolyte in the inner tube ( 1) Oxygen partial pressure control device It may be employed as an invention.

The figure which shows the outline | summary of the oxygen partial pressure control apparatus concerning this invention The figure which shows the electrode structure of the oxygen sensor concerning this invention, and the sealing structure of a solid electrolyte edge part The figure which shows an example of the oxygen partial pressure behavior of the gas processed by the oxygen partial pressure control apparatus concerning this invention The figure which shows the layout at the time of oxygen pump installation concerning this invention The figure which shows the profile of the PID constant according to the oxygen partial pressure employ | adopted in the oxygen partial pressure control apparatus concerning this invention. The figure which shows an example of the oxygen partial pressure fluctuation | variation log | history observed when the PID constant is fixed in the oxygen partial pressure control apparatus concerning this invention.

  FIG. 1 shows an outline of an oxygen partial pressure control apparatus according to the present invention, in particular, an apparatus cross-sectional view around a heating furnace. The left side of FIG. 1 is a cross-sectional view of the side of the device as viewed in the axial direction of the solid electrolyte, while the right side is a cross-sectional view of the front of the device, and each cut surface is a point marked with a dashed line in the other figure. The cut surface is shown.

  Here, in the tubular heating furnace 1, a solid electrolyte pipe 2 for an oxygen pump, a first oxygen sensor, and a second oxygen sensor is disposed with flanges 3 in parallel at equal intervals, and both ends of each fixed electrolyte pipe. However, it sticks out of the heating furnace.

  In FIG. 1, a configuration in which both ends are open to the atmosphere is adopted, but a sealed type may be used. In that case, a purge gas introduction hole is provided in the center of the flange side surface, and a supply purge gas flow made of pure oxygen or air is introduced from the introduction hole so that the external atmosphere of the solid electrolyte tube in the heating furnace 1 is kept constant. In addition, it is possible to employ a configuration in which the inside of the heating furnace is swept and the exhaust purge gas flow is exhausted from the purge gas discharge hole provided in the flange at the other end. The flow rate of the purge gas is desirably 2300 to 3400 sccm per 1 l of the heating furnace volume.

Here, as the solid electrolyte constituting the oxygen pump, for example, the general formula (ZrO ₂ ) _1-xy (In ₂ O ₃ ) _x (Y ₂ O ₃ ) _y (0 <x <0.20, 0 <y <0.20, 0.08 <x + y <0.20) can be used. In addition, for example, a composite B oxide containing Ba and In, in which a part of Ba of this composite oxide is replaced by solid solution with La, in particular, the atomic ratio {La / (Ba + La)} and those with 0.3 or more, and those further substituted for part of in in Ga, formula _{{Ln 1-x Sr x Ga} 1- (y + z) Mg y Co z O 3, however, Ln = La, One or two of Nd, x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.025 to 0.3}, or a general formula {Ln _(1-x) A _{x Ga (1-yz) B1} y B2 z O 3-d, however, Ln = La, Ce, Pr , Nd, 1 or more kinds of Sm, a = Sr, Ca, 1 kind of Ba or two above, B1 = Mg, Al, 1 or more kinds of in, B2 = Co, Fe, Ni, and those represented by one or more of Cu}, the formula {Ln _2-x MxGe _{1- y} LyO ₅ , t However, Ln = La, Ce, Pr, Sm, Nd, Gd, Yd, Y, Sc, M = Li, Na, K, Rb, Ca, Sr, Ba, or more, L = Mg, Al , Ga, in, Mn, Cr , Cu, 1 kind or 2 or more kinds of Zn} and formula _{{La (1-x) Sr} x Ga (1-yz) Mg y Al 2 O 3, where 0 < x ≦ 0.2, 0 <y ≦ 0.2, 0 <z <0.4} and the general formula {Ln _(1-x) A _x Ga _(1-yz) B1 _y B2 _z O ₃ , where Ln = La, Ce, One or more of Pr, Sm, Nd, one or more of A = Sr, Ca, Ba, one or more of B1 = Mg, Al, In, B2 = Co, Fe, Ni , Cu or one or more of them, x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.025 to 0.3} and the like can be employed. An electrochemical oxygen pump including such a solid electrolyte having an oxide ion conductor may be used alone, but for example, by combining with a getter material, control of oxygen partial pressure may be promoted. Good.

  In addition, a tubular solid electrolyte made of such a material is provided with a net-like electrode made of platinum or the like on the inner and outer peripheral surfaces thereof, and a current from a DC power source is passed through the electrode to generate gas in the solid electrolyte tube. The contained oxygen molecules are electrically reduced by the solid electrolyte, oxygen ionized and taken into the solid electrolyte, while being released as oxygen molecules from the outer surface of the solid electrolyte tube and discharged out of the system by the purge gas flowing outside the tube. The

  In order to reduce the material cost of the solid electrolyte tube 2 of the oxygen pump or oxygen sensor, the length of the solid electrolyte tube extending from the heating furnace was shortened by 7 cm, and the length of the solid electrolyte tube was 20 cm. As a result, since the tube end becomes high temperature due to heat conduction through the solid electrolyte, an air cooling fan 8 for cooling the tube end seal mechanism is provided in the vicinity of the solid electrolyte tube. FIG. 2 shows a schematic diagram of the peripheral configuration of the solid electrolyte tube of the oxygen sensor. Here, the air cooling method is adopted, but other cooling means can also be adopted.

  Further, the platinum electrodes 4 and 5 provided on the inner and outer surfaces of the solid electrolyte tube 2 of the oxygen sensor are as shown in FIG. 2 in order to eliminate the influence of the temperature gradient in the high temperature portion of the zirconia tube operating as the solid electrolyte. The inner surface is coated with a platinum paste and baked, and the entire inner surface is made into the inner surface porous electrode 4 and the platinum wire 6 is bonded, while the outer surface is near the center of the solid electrolyte tube 2. A platinum paste is applied only to a belt-like region having a width of about 1 to 2 cm and baked to form an outer surface porous electrode 5, and a platinum wire 7 inserted into an insulating glass tube is bonded to the outer surface electrode 5. It is desirable that the potential difference with the platinum wire 6 be measured. Thereby, it is not necessary to perform calibration work for each oxygen sensor, and the oxygen partial pressure can be directly calculated by the Nernst equation based on thermodynamics.

[Example 1]
In this embodiment, in particular, the solid electrolyte tube 2 of the oxygen pump, the solid electrolyte 2 of the first oxygen sensor, and the solid electrolyte 2 of the second oxygen sensor are arranged at the vertices of an equilateral triangle with the axis of each solid electrolyte tube 2. Are arranged in parallel so that they match each other. Since the flange 3 is an open type, the atmosphere in which the oxygen pump, the first oxygen sensor, and the second oxygen sensor are installed is common.

  Then, argon gas was introduced at 200 sccm into the solid electrolyte tube 2 of the oxygen pump. A voltage of −2 to 2 V was applied between the inner and outer electrodes of the solid electrolyte 2 of the oxygen pump according to the feedback gain. In the heating furnace of this embodiment, an open type is adopted and carried out in the air. However, a closed type can be used and pure oxygen can be used as a purge gas.

Subsequently, the argon gas having passed through the solid electrolyte tube 2 of the oxygen pump and having a reduced oxygen partial pressure was introduced into the solid electrolyte tube 2 of the first oxygen sensor, and the oxygen partial pressure in the argon gas was measured. For measuring the oxygen partial pressure, an electromotive force due to the concentration cell reaction accompanying the difference in oxygen partial pressure inside and outside the solid electrolyte tube 2 was used. The change with time in the oxygen partial pressure is shown in FIG. It showed about ^10-26 atm in about 2 hours, and showed stable oxygen partial pressure value of ^10-30 atm after about 20 hours of operation.

[Example 2]
Next, in order to meet the needs for mass production of oxygen partial pressure control gas, the design for consolidating the heating furnace of the present invention was further advanced, and a mode in which a plurality of solid electrolyte tubes 2 were arranged in one heating furnace was implemented. .

  The solid electrolyte tube 2 and the resistance heating element 9 were arranged in parallel as shown in FIG. That is, the axis of each solid electrolyte 2 was disposed at each apex of the honeycomb structure centered on the axis of the cylindrical resistance heating element 9. As a result, the temperature unevenness of each solid electrolyte tube 2 can be suppressed to less than 1 ° C.

  Here, the layout in FIG. 4 is not limited to this number, and the layout ratio can be further expanded, and the number ratio of the solid electrolyte tube 2 and the resistance heating element 9 is in the range of 1 / 3-6. Can be changed freely. In FIG. 4, each solid electrolyte tube is selected as one of the solid electrolyte tubes for the oxygen pump by selecting any two of those described as the solid electrolyte 2 for the oxygen pump. Is.

[Example 3]
On the other hand, in this embodiment, in order to meet the oxygen partial pressure needs of a wide range of atmospheric gases in actual operation of 0.2 to 10 ^-30 atm, the following PID control is performed to quickly control to the control target partial pressure. As a result, the operation cost was reduced.

  Specifically, as illustrated in FIG. 5 (particularly on the right side), a configuration is adopted in which the PID constant can be variably set automatically and smoothly according to the oxygen partial pressure at that time. In addition, as a standard of the value of each constant with respect to the oxygen partial pressure level, the values in the table shown on the left side of FIG. 5 were used. However, this table does not indicate that the change is made in multiple stages. In actual operation, each constant is defined as a continuous function based on the oxygen partial pressure.

The PID constant in FIG. 5 is based on the premise that the heating furnace has an internal volume of 0.03 l, the zirconia tube has a length of 200 mm × diameter of 10 mm, and an operating temperature of 600 to 700 ° C. However, it is desirable to modify the PID constant according to the apparatus configuration to be adopted. For reference, FIG. 6 shows the result after the oxygen partial pressure is lowered to 10 ^-10 atm when pure argon gas is introduced into a device fixed at an optimum PID constant at an oxygen partial pressure of 10 ^-20 atm. Oxygen partial pressure behavior is shown. As described above, in the control using the fixed PID constant, the oxygen partial pressure oscillates greatly periodically, and it takes a long time to obtain a stable oxygen partial pressure. This is significantly different from the behavior when the PID constant in FIG. 3 is variable.

[Example 4]
Considering the use in harsh environments where the oxygen partial pressure in the oxygen pump is ~ 10 ^-30 atm and the temperature is 600 ~ 700 ° C, in order to extend the life of the zirconia tube, the temperature increase rate during preparation and the temperature decrease at the end It is desirable to reduce the speed within the range allowed by the operation efficiency, and it is also desirable to take measures for recovering the inner surface of the solid electrolyte partially reduced by being used under an extremely low oxygen partial pressure for a long time.

  Therefore, temperature control is performed so that the average temperature rise rate / average temperature drop rate is 3-6 ° C / min so that the temperature rises and falls slowly between room temperature and operating temperature 600-700 ° C over 2-3 hours. At the same time, after starting the oxygen pump, before starting to lower the temperature, a process of flowing 1 atm of pure oxygen or air into the solid electrolyte such as an oxygen pump was added. Specifically, a pipe for flowing supplied pure oxygen or air flow into each solid electrolyte pipe, and a pipe for flowing exhaust pure oxygen or air flow out of the system after flowing through the pipe. It is desirable to reoxidize the inner surface of the solid electrolyte tube that has been partially reduced with pure oxygen or air after operation of the solid electrolyte under ultra-low oxygen partial pressure.

  As a result, the zirconia tube that had been damaged in the normal continuous operation for about one week to 10 days can be extended in life until no damage has been reported yet even after 5 months from the start of the experiment. did it.

  In the present invention, the solid electrolyte purge gas is shared by the oxygen pump and the oxygen sensor, so that the solid electrolyte can be compactly accommodated in one heating furnace, which reduces the equipment cost and the operation cost. An oxygen partial pressure control device is provided.

  On the other hand, the present invention adopts an operation method and a post-treatment process with a small load on the solid electrolyte during operation of the oxygen partial pressure control device, thereby extending the life of the solid electrolyte and reducing the maintenance cost. A method for recovering a solid electrolyte for a pressure control device is provided.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Zirconia pipe 3 Flange 4 Inner surface porous electrode 5 Outer surface porous electrode 6 Platinum wire for inner surface electrode 7 Platinum wire for outer surface electrode 8 Cooling means 9 Resistance heating body

Fin External processor gas supply pipe Fout External processor gas exhaust pipe Gin supply Ar gas flow Gout exhaust Ar gas flow

Claims (2)

Heating a heating furnace including at least one solid electrolyte separating at least two spaces to an operating temperature of the solid electrolyte;
Applying a voltage between the electrodes provided on the front and back of the solid electrolyte, and discharging oxygen from the gas in one of the spaces to the gas in the other space through the solid electrolyte;
Introducing a pure oxygen or air at atmospheric pressure into the solid electrolyte surface on the side that has been in contact with the gas having a reduced oxygen partial pressure, and reoxidizing the solid electrolyte surface;
A method for recovering a solid electrolyte for controlling oxygen partial pressure, comprising at least a step of lowering the temperature of the heating furnace from the solid electrolyte operating temperature.   2. The oxygen content according to claim 1, wherein an average temperature increase rate in the temperature increasing step is 3 to 6 ° C./min, and an average temperature decrease rate in the temperature decreasing step is 3 to 6 ° C./min. Recovery method for pressure control fixed electrolyte.

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