JP5071809B2 - Solid electrolyte type oxygen partial pressure control method - Google Patents

Description

  The present invention relates to a solid electrolyte type oxygen partial pressure control method for controlling an oxygen concentration partial pressure in a gas passing through a solid electrolyte.

  Conventionally, in an apparatus that removes oxygen from an inert gas or the like by applying a bias voltage to a solid electrolyte, the oxygen partial pressure measured by the oxygen sensor and the target are used to control the target oxygen partial pressure. A bias voltage value has been calculated by PID calculation from comparison with oxygen partial pressure (Patent Document 1).

The control by the PID calculation is a method of obtaining a necessary output by trial and error from a difference between a value at the time of operation and a target value and a change with time. In this case, when the target oxygen partial pressure is higher than the oxygen partial pressure during operation, that is, when it is necessary to take in oxygen from the outside, a negative bias voltage is applied. This often results in destruction of the solid electrolyte. In addition, it tends to cause a phenomenon that tends to occur in PID control such as hunting (the oxygen partial pressure value during operation vibrates around the target oxygen partial pressure value). On the other hand, since a bias voltage that is too large causes destruction of the solid electrolyte, a limit is usually provided. When operating under such a restriction, when the oxygen partial pressure is 10 ⁻² atm to 10 ⁻⁵ atm, it takes a very long time to exhaust oxygen, and the efficiency of the oxygen pump is poor.
JP 2005-331339 A

  The present invention has been made in view of conventional drawbacks, and provides a solid electrolyte oxygen partial pressure control method capable of efficiently exhausting oxygen in a very short time and accurately controlling the oxygen partial pressure. It is to provide.

The oxygen partial pressure control method of the solid electrolyte type oxygen molecule discharging apparatus according to claim 1 is a solid electrolyte type oxygen molecule discharging apparatus and oxygen partial pressure control method comprising a solid electrolyte type oxygen molecule discharging apparatus and a bias power source. When the predetermined current flowing in the oxygen molecule discharging apparatus becomes smaller than the target bias voltage (Vtarget) / internal resistance (R) of the oxygen molecule discharging apparatus system , the constant current mode is switched to the constant voltage mode. A bias voltage is applied so as to cancel out the reverse bias voltage generated by the oxygen partial pressure.

  According to a second aspect of the present invention, there is provided an oxygen partial pressure control method for a solid oxide oxygen molecule discharging apparatus, wherein the bias power source is switched between a constant current source operation and a constant voltage source operation in accordance with the oxygen partial pressure.

  Oxygen can be exhausted efficiently in a very short time, and the oxygen partial pressure can be controlled with high accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a main part schematic diagram showing an oxygen molecule discharging apparatus constituting an extremely low oxygen concentration gas generating apparatus.
The oxygen molecule discharging apparatus 20 includes a zirconia solid electrolyte body 21 having oxygen ion conductivity, and net-like electrodes 22 and 23 made of gold or platinum and disposed on both the inner and outer surfaces of the solid electrolyte body 21. The zirconia solid electrolyte body 21 is fixed to the metal pipe body 25 at both ends. The electrode and tube of the solid electrolyte body constitute an inner electrode.

FIG. 2 is a schematic view showing the operation of the oxygen molecule discharging apparatus 20. When a voltage I of 2 volts is applied to the DC power source E between the electrodes 22 and 23 of the oxygen molecule discharging apparatus 20 to flow a current I, oxygen molecules in the gas flowing through the hollow space of the solid electrolyte body are ionized in the solid electrolyte, Oxygen ions are transported from the inside to the outside due to the oxygen ion conductivity of the solid electrolyte, and are released out of the solid electrolyte body. As described above, the extremely low oxygen partial pressure gas generating apparatus discharges oxygen molecules in the gas to the outside air while passing the gas introduced into the solid electrolyte body 21 through the solid electrolyte body 21, thereby extremely low oxygen partial pressure. An extremely low oxygen concentration gas having the above is generated and supplied from the solid electrolyte body to the manufacturing apparatus. In FIG. 2 , ● is a gas, OO is an oxygen molecule, and ◯ is an oxygen ion.

  The solid electrolyte constituting the solid electrolyte body 21 is, for example, a general formula (ZrO2) 1-xy (In2O3) x (Y2O3) y (0 <x <0.20, 0 <y <020). A zirconia system represented by 0.08 <x + y <0.20) can be used. Among them, 0 <x <0.20 and y = 0 are preferable, and 0.06 <x <0.12 and y = 0 are more preferable.

  In addition to those exemplified above, the solid electrolyte is, for example, a composite B oxide containing Ba and In, in which a part of Ba of the composite oxide is replaced by solid solution with La, in particular, the number of atoms The ratio {La / (Ba + La)} is set to 0.3 or more, or a part of In is substituted with Ga, or the general formula {Ln1-xSrxGa1- (y + z) MgyCo z O 3, provided that one or two of Ln = La, Nd, x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.005 to 0.3}, General formula {Ln (1-x) AxGa (1-y-z) B1yB2zO3-d, where Ln = La, Ce, Pr, Nd, Sm, one or more, A = Sr , Ca, Ba 1 or more, B 1 = Mg, Al, or 1 or more, B 2 = Co, Fe, Ni, C or a general formula {Ln2-xMxGe1-yLyO5, where 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, Zn or more} , General formula {La (1-x) SrxGa (1-y-z) MgyAl2O3, where 0 <x ≦ 0.2, 0 <y ≦ 0.2, 0 <z <0.4} {La (1-x) AxGa (1-y-z) B1yB2zO3, where Ln = La, Ce, Pr, Sm, Nd, one or more, A = Sr, Ca , Ba 1 or more, B 1 = Mg, Al, In 1 or more, B 2 = Co, Fe, Ni, Cu 1 or Seed above, x = 0.05~ 0.3, y = 0~ 0.29, z = 0.01~ 0.3, y + z = 0.025~ 0.3} and the like can be employed.

  FIG. 3 shows an equivalent circuit of the oxygen molecule discharging apparatus and the bias power source. The equivalent circuit includes a direct current source and an oxygen molecule discharging device, and the oxygen molecule discharging device includes an internal resistance R (solid electrolyte resistance + electrode contact resistance) and an internal electromotive force (reverse bias). In the oxygen molecule discharging apparatus, the current I flowing through the oxygen molecule discharging apparatus is generated only when oxygen ions move in the solid electrolyte. In that case, the current I is proportional to the oxygen exhaust rate. In the oxygen molecule discharging apparatus, if the bias circuit is open, a voltage proportional to the logarithm of the ratio of the oxygen concentration inside and outside the tube is generated between the electrodes. This is described in the equivalent circuit as internal electromotive force (reverse bias). When the oxygen partial pressure in the oxygen molecule discharging apparatus is lower than the external oxygen partial pressure, the upper side of the symbol of the battery in the circuit diagram becomes a higher potential than the lower side.

  The circuit operation will be described below. When a gas having the same oxygen partial pressure (0.2 atm) as that of the atmosphere is contained in the oxygen molecule discharge device, and the gas is confined in a closed loop including the oxygen molecule discharge device, the oxygen content inside and outside the solid electrolyte tube Since there is no pressure difference, no reverse bias occurs. All voltages applied from the bias power supply are consumed by R (resistance) I (current). Oxygen is exhausted at a rate proportional to the current I. A reverse bias occurs when the oxygen partial pressure of the gas in the system decreases, and the current I decreases even when the same bias voltage is applied. Further, when the reverse bias voltage increases and becomes equal to the applied voltage V, I = 0 and the oxygen partial pressure does not change. Control to the target oxygen partial pressure can be obtained by applying a bias voltage equal to the reverse bias obtained from the Nernst equation.

  Therefore, in order to efficiently remove oxygen from the higher oxygen partial pressure with the oxygen molecule discharging apparatus, it is necessary to flow a large amount of current I. In order to increase the current without increasing the voltage, the resistance may be decreased, but the range is limited. Therefore, it is necessary to increase the current according to the flow rate of oxygen molecules to be exhausted. Here, the flow rate of oxygen molecules to be exhausted can be determined by measuring the oxygen concentration of the gas before entering the oxygen molecule discharging apparatus with an oxygen sensor and measuring the gas flow rate with a mass flow meter. It can be calculated by multiplication. The predetermined current [A] is defined by the oxygen molecular flow rate [mol / s] × 4F (Faraday constant) to be exhausted.

  While the oxygen partial pressure is high, the bias power supply is operated in the constant current power supply mode so that a necessary amount of current flows through the circuit. If the oxygen partial pressure of the gas entering the oxygen molecule discharging apparatus decreases as the oxygen exhaust proceeds, the required current of the oxygen molecule discharging apparatus also decreases in proportion to the target bias voltage (Vtarget). / Becomes less than the internal resistance (R) of the oxygen molecule ejector system. After that, the bias power supply is moved to the constant voltage power supply mode, and the bias voltage may be applied so as to cancel the reverse bias voltage generated by the target oxygen partial pressure. The bias power source is switched between a constant current source operation and a constant voltage source operation according to the oxygen partial pressure.

  In this example, a zirconia tube doped with 6% mol of yttria having a length of 235 mm was used as the solid electrolyte body 21. A heater is disposed around the zirconia tube. Argon gas was introduced from the gas inlet, and the mass flow controller was set to 200 cc / min. The oxygen molecule discharging apparatus 20 heated to 600 ° C. was initially applied with 2 V as a voltage between the electrodes. Note that air was allowed to flow as a purge gas outside the solid electrolyte body. Subsequently, the gas with reduced oxygen partial pressure that passed through the zirconia tube in the oxygen molecule discharging apparatus was guided to the oxygen sensor, and the oxygen partial pressure was measured. The oxygen partial pressure was measured by using an electromotive force generated by a concentration cell reaction associated with a difference in oxygen partial pressure inside and outside the solid electrolyte body.

Hereinafter, the flowchart of the oxygen partial pressure control of the oxygen molecule discharging apparatus will be described with reference to FIG.
The target bias voltage (Vtarget) is calculated from the required oxygen pumping speed (pump current I) and the target oxygen partial pressure from the value of the oxygen sensor and the gas flow rate (step 1). As a result of the calculation, when the current I is smaller than Vtarget / R, a bias voltage is applied in the constant voltage mode so as to cancel the reverse bias caused by the target oxygen partial pressure (step 2). The process is terminated when the oxygen partial pressure becomes equal to the target value (step 3). As a result of the calculation, when the current I is not smaller than Vtarget / R, a bias current is passed in the constant current mode (step 4). Then, returning to step 1, the target voltage (Vtarget) is calculated from the required oxygen pumping speed (pump current I) and the target oxygen partial pressure from the value of the oxygen sensor and the gas flow rate (step 1).
Where Vtarget = (k _B T / 4e) ln [p (O ₂ ) _ref / p (O ₂ ) _target ], k _B is the Boltzmann constant, e is the charge of the electron, p (O ₂ ) _ref , p ( O ₂ ) _target is the oxygen partial pressure and the target oxygen partial pressure in the atmosphere outside the oxygen pump, respectively.
If Vtarget / R is used as a criterion, the current I is prevented from changing suddenly.

  FIG. 5 shows the time change of the oxygen partial pressure by constant voltage control. First, before starting the oxygen partial pressure control, when a bias voltage of 2 V was applied between the electrodes, the oxygen partial pressure dropped to 2.7 × 10 minus 30th atmospheric pressure. Thereafter, the bias voltage applied between the electrodes is set to an electromotive force (1.5 V and 0.75 V) that is a target oxygen partial pressure of 1.0 × 10 minus 24 squared atmospheric pressure and 1.0 × 10 minus 18 squared atmospheric pressure, respectively. As a result, it was found that the control can be performed very quickly and accurately as shown in the figure. In FIG. 5, a curve a is P (O2) measurement, a curve b is a target value, and a curve c is an actually applied bias voltage.

  The method of the present invention can be applied to the field of manufacturing products using a low oxygen partial pressure gas, semiconductor manufacturing equipment, liquid crystal manufacturing equipment, electrical / electronic component manufacturing equipment, food manufacturing equipment, and the like.

It is a top view which shows the principal part of the oxygen molecule discharging apparatus which concerns on this invention. It is a schematic structure sectional view explaining the principle of the oxygen molecule discharge device concerning the present invention. It is a figure which shows the equivalent circuit of an oxygen molecule discharge device and a bias power supply. It is a figure which shows the flowchart of oxygen partial pressure control of an oxygen molecule discharge device. It is a figure which shows the time change of the oxygen partial pressure by constant voltage control.

Explanation of symbols

20: Oxygen molecule discharging device 21: Solid electrolyte body 22, 23: Electrode 25: Tube

Claims (2)

In a solid electrolyte type oxygen molecule discharging apparatus and oxygen partial pressure control method including a solid oxide type oxygen molecule discharging apparatus and a bias power source, the oxygen partial pressure control is performed by using a bias voltage (Vtarget) targeted by a predetermined current flowing in the oxygen molecule discharging apparatus. ) / Switching from constant current mode to constant voltage mode when it becomes smaller than the internal resistance (R) of the oxygen molecule discharging system, and applying a bias voltage to cancel the reverse bias voltage generated by the target oxygen partial pressure A method for controlling the partial pressure of oxygen in a solid oxide oxygen molecule discharging apparatus, characterized in that:   2. The oxygen partial pressure control method for a solid oxide oxygen molecule discharging apparatus according to claim 1, wherein the bias power source is switched between a constant current source operation and a constant voltage source operation in accordance with an oxygen partial pressure.