JP2006250577A - Oxygen concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen sensor for accurately measuring the concentration of dissolved oxygen by preventing the oxidation of a lead wire on the standard side. <P>SOLUTION: The oxygen sensor S is constituted so that a container-shaped measuring part 27, which comprises a solid electrolyte and comes into contact with a liquid metal, is connected to the leading end of a conductive hollow tubular extension sleeve 25, and a standard electrode 33 is housed in the container-shaped measuring part 27, while a lead wire 30 for a standard electrode 33 is inserted in the standard electrode 33 to measure the voltage applied across the standard electrode 33 and the extension sleeve 25. This oxygen sensor S is filled with an oxidation preventing gas (g). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of an oxygen concentration sensor for measuring the oxygen concentration in a low-melting-point liquid metal such as lead / bismuth, bismuth, or lead.

  Conventionally, various types of apparatuses for measuring the dissolved oxygen concentration in molten metal (liquid metal) such as molten lead and bismuth have been proposed. And liquid metal is used as a coolant because it is stable against heat and radiation and has excellent thermal conductivity.

  A typical example of this is liquid sodium metal that cools the heat generated in a fast breeder reactor. The metal used for such applications is a low-melting-point metal such as Na, Na-K, Li, Bi, or Pb. When these liquid metals are used as a coolant, a liquid low-melting-point metal is used. Corrosion of equipment piping and structural materials due to the above becomes a problem.

  Corrosion caused by liquid metal is mainly due to dissolution of a metal element in liquid metal, not an electrochemical process for corrosion of an aqueous solution or the like. Therefore, as a problem when the liquid metal used as the coolant circulates between the high temperature part and the low temperature part for heat recovery, the element dissolved from the structural material in the high temperature part is supersaturated and precipitates in the low temperature part. This is because a so-called mass transfer phenomenon occurs.

  This mass transfer phenomenon is repeated, and structural materials such as equipment and piping continue to be corroded, and impurities are deposited in the low temperature portion in the low temperature portion. In particular, when the cross-sectional area of the portion where the liquid moves, such as a small-diameter tube, is small, the liquid metal channel may be blocked by the impurities. The cause that governs the dissolution rate of the metal depends on the degree of unsaturation in the high temperature part, but the state of the equipment such as the configuration and shape of the loop through which the liquid metal flows, the flow rate and temperature of the liquid metal, the surface roughness of the piping, etc. It depends on various conditions such as impurity concentration.

  Among them, it is known that impurities in the liquid metal, particularly “dissolved oxygen concentration”, greatly affects the corrosion phenomenon and the corrosion rate. And by controlling an appropriate oxygen concentration, the soundness of the structural material in contact with the liquid metal can be maintained.

  Conventionally, various types of oxygen sensors for measuring the oxygen concentration in a liquid metal are known. Specifically, it is as follows.

  1) In an oxygen sensor including a reference electrode made of a reference material filled in a cylindrical chamber facing a reference portion of a solid electrolyte element and an internal electrode made of a metal rod embedded in the reference material, the internal electrode is A sealing agent filled in the cylindrical chamber so as to be embedded is a stable protective layer selected from Al2 O3 powder and / or Zr O2 powder, an oxygen adsorption layer selected from graphite powder and / or carbide powder, There has been proposed a “molten metal probe” having a four-layer structure comprising a relaxation layer selected from quartz wool and / or alumina wool and / or ceramic wool and a consolidated layer made of refractory cement. In the molten metal probe of the present invention, a solid electrolyte having a tube shape or a test tube is used (see Patent Document 1).

  2) In addition, an oxygen gas serving as a reference for comparison is filled inside at a predetermined pressure, and a flow path for circulating the test fluid is provided outside, and oxygen gas contained in the test fluid flowing in the flow path A hollow solid electrolytic sensor that generates an electromotive force according to the difference between the pressure and the pressure of the oxygen gas that serves as a reference, and the electromotive force generated from the solid electrolytic sensor are measured. An invention relating to an “oxygen concentration measuring apparatus and a plant to which it is applied” having an oxygen concentration calculating means for calculating the concentration of oxygen gas contained in a specific detection fluid based on the pressure of oxygen gas serving as a reference is proposed Has been. In this invention, the stationary electrolyte is tube-shaped and the outer periphery of the sensor is protected by a mesh-shaped member (see Patent Document 2).

  3) As shown in FIG. 6, the oxygen concentration sensor 1 is immersed in a liquid metal 2 such as lead bismuth filled in the apparatus or the container 3, and measurement of the solid electrolyte provided at the tip of the oxygen concentration sensor 1 is performed. An oxygen concentration meter that calculates an electromotive force between the oxygen sensor standard electrode side lead wire 4 connected to the unit 3 and the oxygen sensor counter electrode side lead wire 4a by an electromotive force calculator 5 and measures the oxygen concentration by the electromotive force. Is known (see Patent Document 3).

  As shown in FIG. 5, the specific structure of the oxygen concentration sensor 1 is such that a container-shaped solid electrolyte portion 12 is fitted and fixed by an inlay through a corrosion-resistant sleeve 11 having a seal portion at the tip of an extension sleeve 10. Further, an insulating tube 15 is supported at the center of the end joint 13 that closes the upper end of the extension sleeve 10, and the tip thereof is fixed so as to be positioned at the opening of the solid electrolyte portion 12.

  Then, the solid electrolyte part 12 (measuring part) is filled with a standard electrode 16 made of metal bismuth and a standard electrode made of bismuth oxide 17, and penetrates the end joint 13 and the insulating tube 15 to lead the standard electrode. 18 is extended and its tip is connected to the standard electrodes 16 and 17.

  Further, the counter electrode side lead wire 20 is connected to the extension sleeve 10, and a minute voltage (electromotive force) E generated between the standard electrode side lead wire 18 and the counter electrode side lead wire 20 is used. Thus, the oxygen concentration in the liquid metal 2 is calculated from the following formula.

The measurement of the oxygen concentration in the liquid metal is based on the Nernst principle, which is obtained by the following calculation formula.
E = (R × T) / (4 × F) × 1n (P (reference) / P) (1)
Here, the symbols of the formula are as follows.
E: electromotive force (V), R: gas constant, T: absolute temperature (K)
F: Faraday constant (C / mol)
P (reference): Reference gas oxygen partial pressure (atm)
P: Partial pressure of oxygen gas contained in lead-based metal (atm)
JP-A-10-253582 JP 2001-215212 A JP 2003-294692 A

  The conventional oxygen concentration sensor 1 is configured as shown in FIGS. 5 and 6, and the standard electrode lead wire 18 is composed of standard electrode materials (Bi / Bi2 O3, Pb / Pb O, In / In2 O3, Mo wire or W wire is used as a metal wire having high corrosion resistance against (Pb-Bi / PbO) (Note: A / B means a mixture with metal A / B oxide).

  In the conventional oxygen concentration sensor 1, the atmosphere in the hollow extension sleeve 10, that is, the atmosphere around the standard electrode lead wire 18, is air. While the oxygen concentration sensor 1 is in use, the standard electrode lead wire 18 is heated, and at this time, it reacts with oxygen contained in the atmosphere in the sensor, causing deterioration, that is, oxidation.

  When the standard electrode lead wire 18 is “oxidized” in this way, the resistance value increases, and the electromotive force generated between the standard electrode lead wire 18 and the counter electrode side lead wire 20 increases. As a result, there is a problem that the correct electromotive force is not exhibited, and as a result, the oxygen concentration in the molten metal cannot be accurately measured (see FIG. 2).

  The present invention provides an oxygen concentration sensor that can accurately measure the electromotive force due to the oxygen concentration in the liquid metal, and further prevents oxidation of the lead wire for the standard electrode that sends the electromotive force. An object of the present invention is to provide an oxygen concentration sensor that prevents abnormal fluctuations in electromotive force due to deterioration and has no error in measurement values.

In order to achieve the above object, the oxygen concentration sensor in the liquid metal according to the present invention is equipped with a container-shaped measuring unit made of a fixed electrolyte at the tip of a hollow tubular extension sleeve, and a standard in the container-shaped measuring unit. An oxygen concentration characterized by containing an electrode and inserting a lead wire for a standard electrode into the standard electrode, and supplying an antioxidant gas into the extension sleeve so as to protect the periphery of the lead wire for the standard electrode The oxygen concentration sensor is characterized in that the inside of the oxygen sensor is vacuum-sealed so as to protect the periphery of the sensor and the lead wire for the standard electrode.
It is.

  Each component in the oxygen concentration sensor according to the present invention is as follows.

  A. Antioxidant gas filling method: The antioxidant gas is supplied into the extension sleeve, flows around the lead wire for the standard electrode, and then discharged from the extension sleeve; and the antioxidant gas is introduced into the extension sleeve. There is a method of supplying and enclosing and retaining this.

  B. Liquid metal: Lead (Pb), bismuth (Bi), and lead bismuth alloy (Pb-Bi) are essentially suitable as the liquid metal using the oxygen concentration sensor of the present invention.

  C. Kind of antioxidant gas: The antioxidant gas supplied to the oxygen concentration sensor is an inert gas, specifically, one or more of helium, argon, nitrogen, neon, krypton, xenon, radon, and nitrogen. It is a mixed gas.

D. Another antioxidant gas: The antioxidant gas supplied into the oxygen concentration sensor is not limited to the inert gas, but is carbon dioxide or a mixed gas of water vapor and oxygen, and its oxygen partial pressure is 10 ^−5. 10 ^-30 (equilibrium oxygen partial pressure of the standard electrode material).

  E. Solid electrolyte: Yttria (Y2 O3) -added zirconia (ZrO2), calcia (CaO) -added zirconia, or magnesia (MaO) -added zirconia is suitable as the solid electrolyte constituting the measuring section.

  F. Standard electrode: As the material of the standard electrode, Bi / Bi2 O3, Pb / PbO, In / In2 O3, Pb-Bi / PbO-based metal / metal oxide is preferable.

  In the present invention, the lead wire connected to the standard electrode as described above is protected by filling with an inert gas or maintaining a vacuum state, so that the lead wire is prevented from being oxidized. The resistance value suppresses the increase so that the electromotive force of the oxygen sensor is abnormally increased so that a considerably high electromotive force is not generated.

  In the conventional oxygen sensor, the standard electrode side lead wire is oxidized and the electromotive force increases greatly. Therefore, it is difficult to directly measure the concentration of oxygen dissolved in the liquid metal. The line is protected with an inert gas so as not to oxidize or is kept in a vacuum, so that even if the oxygen concentration sensor is used for a very long time, there is virtually no error in measuring its oxygen concentration. .

  The structure of the oxygen concentration sensor S according to the embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a front sectional view of an oxygen concentration sensor S according to a first embodiment of the present invention. A container-shaped solid electrolyte 27 (measurement unit) is hermetically sealed at the tip of a corrosion-resistant sleeve 26 at the tip of an extension sleeve 25. Or it is fixed with ceramic cement.

  Further, the rear opening portion of the extension sleeve 25 is closed by an end joint 28, and is supported and guided through the standard electrode side lead wire 30 by an insulating tube 29 fixed to the center portion thereof. Further, in parallel with the insulating tube 29, an antioxidant gas introduction nozzle 31 particularly employed in the present invention is fixed, and the antioxidant gas discharge hole 31a is opened in the end joint 28. An antioxidizing gas g is supplied from the nozzle 31 into the extension sleeve 25, and a gas g supply passage is formed so as to be discharged from a discharge hole 31 a opened in the end joint 28.

  And the metal bismuth which comprises the standard pole 33 is accommodated in the measuring part which consists of the said container-shaped solid electrolyte 27, Furthermore, the bismuth oxide 35 which comprises a standard pole is arrange | positioned on it, and a measuring part is put in a liquid metal. When immersed, an accurate electromotive force corresponding to the oxygen concentration is generated.

  Next, the material of each part will be described. The extension sleeve 25 is a tubular body made of austenitic stainless steel or carbon steel, and the corrosion-resistant sleeve 26 is ferritic stainless steel. As the solid electrolyte 27 (measurement unit), yttria (Y2 O3) -added zirconia (ZrO2), calcia (CaO) -added zirconia, or magnesia (MaO) -added zirconia is suitable.

  The standard electrode side lead wire 30 is molybdenum (Mo) or tungsten (W), and a thin wire having a diameter of about 0.5 mm is used. The lead wire 30 does not oxidize at a low temperature, but, for example, at a temperature of 400 ° C. or higher, the lead wire 30 reacts with oxygen contained in the atmosphere existing in the extension sleeve 25 to generate oxidation. As a result, the electrical resistance increases rapidly, and it is necessary to prevent this oxidation action.

  The antioxidant gas g for preventing deterioration of the lead wire 30 on the standard electrode side connected to the container-shaped solid electrolyte 27 is one of helium, argon, nitrogen, neon, krypton, xenon, radon and nitrogen, or An inert gas such as a mixed gas of two or more.

Carbon dioxide or a mixed gas of water vapor and oxygen can also be used, but the oxygen partial pressure in that case is preferably 10 ⁻⁵ to 10 ⁻³⁰ (equilibrium oxygen partial pressure of the standard electrode material).

  According to the oxygen concentration sensor shown in FIG. 1, the atmosphere containing oxygen in the extension sleeve 25 is replaced by the antioxidant gas g supplied through the antioxidant gas introduction nozzle 31. As a result, the standard electrode Therefore, the deterioration of the lead wire 30 due to oxidation can be prevented.

  FIG. 2 is a graph showing the change over time in the electromotive force of the oxygen concentration sensor, and is a characteristic graph drawn with the elapsed time (h) used by the oxygen concentration sensor as the horizontal axis and the oxygen sensor electromotive force (mV) as the vertical axis. It is.

  In FIG. 2, the line (a) supplies the theoretical value of the electromotive force of the oxygen sensor, the line (b) supplies the measured value of the electromotive force of the oxygen concentration sensor of the present invention, and the line (c) supplies the conventional antioxidant gas. The electromotive force in the case of not performing is shown respectively.

  As can be understood from the graph, the value of the electromotive force generated by the oxygen concentration sensor S for supplying the antioxidant gas according to the present invention is stable even when a considerable measurement time has elapsed, and therefore, in liquid metal. This oxygen concentration sensor S can be used to accurately control the oxygen concentration in the liquid metal.

  FIG. 3 is a front sectional view showing an oxygen concentration sensor S1 according to the second embodiment.

  The end joint 28 that closes one end of the extension sleeve 25 includes an antioxidant gas introduction nozzle 31 having a jet at a position almost reaching the tip of the extension sleeve 25 and an antioxidant having a discharge port near the end joint 28. A pair of gas discharge nozzles 37 is provided, and valves 38 and 38a are provided on the antioxidant gas introduction nozzle 31 and the antioxidant gas discharge nozzle 37, respectively.

  When the oxygen concentration sensor S1 according to the present invention is used, the antioxidant gas g is supplied from the antioxidant gas introduction nozzle 31 and discharged from the antioxidant gas discharge nozzle 37 with the valves 38 and 38a opened. By maintaining this state for a certain period of time or longer, the air in the hollow extension sleeve 25 is replaced with the antioxidant gas g, and then the valves 38 and 38a of both nozzles 31 and 37 are closed to create an atmosphere in the extension sleeve 25. Replace with an antioxidant gas g.

  Deterioration (oxidation) of the standard electrode lead wire 30 can be prevented by sealing the antioxidant gas g (helium gas), and as a result, the electromotive force related to the dissolved oxygen concentration in the molten metal is accurately measured. Can do it. It is preferable to increase the effect by adding or exchanging the sealed antioxidant gas by operating the valves 38 and 38a from time to time.

  In the comparative example shown in the graph of FIG. 2, lead bismuth is used as the liquid metal, and the dissolved oxygen concentration is measured.

  FIG. 4 is a front sectional view of an oxygen sensor S2 according to the third embodiment. Unlike the two embodiments, the oxygen sensor S2 is provided with a vacuum exhaust nozzle 40 having an on-off valve 41 at an end joint 28 that closes the upper portion of the extension sleeve 25, and this vacuum exhaust nozzle 40 is used as a vacuum pump (not shown). Connected.

  When this oxygen sensor S2 is used, the vacuum pump is driven to evacuate the inside of the oxygen sensor S2 to be in a vacuum state, and then the on-off valve 41 is closed to keep the inside of the oxygen sensor S2 in a vacuum state. Thus, the lead wire 30 on the standard electrode 27 side is prevented from being deteriorated due to oxidation, and the electromotive force is accurately measured.

In this oxygen sensor S2, it is important to increase the degree of vacuum. However, since it is sufficient that the lead wire 30 can be prevented from being oxidized, the degree of vacuum is actually about 10 to 100 Pa. It may be sustainable, and if a vacuum is applied from time to time as the measurement time elapses, the effects of air leaks can be prevented.
(About the actual measurement method)
As an object to be measured, the composition of lead bismuth was a eutectic composition of 45% by weight of lead and 55% by weight of bismuth, and the temperature was maintained at 450 ° C. A lead oxide ball (2-5 mm in diameter) was immersed in lead bismuth to saturate oxygen in the lead bismuth.

  FIG. 2 shows a graph in which the oxygen concentration sensor S or S1 and S2 is immersed in a liquid metal and the change with time of electromotive force up to 1000 hours is continuously measured.

  While the oxygen saturation theoretical electromotive force (a) is 76 mV, the electromotive force of the oxygen concentration sensor S or S1 in which an antioxidant gas (for example, helium) is flowed to the vicinity of the standard electrode is shown in the line (b). As shown in the figure, it changes at a substantially constant value between 85 mV and 90 mV.

  On the other hand, the electromotive force generated by the conventional oxygen concentration sensor shown in FIGS. 5 and 6 increased rapidly from about 50 hours, and finally exceeded 600 mV. Therefore, the conventional oxygen concentration sensor cannot measure the oxygen concentration stably for a long time, and it is dangerous to use this sensor for controlling the oxygen concentration of a heating furnace using a liquid metal. On the other hand, it was confirmed that the oxygen concentration sensor of the present invention was highly accurate and highly reliable.

  Therefore, by using the oxygen sensor according to the present invention, it is possible to accurately measure the oxygen concentration of the liquid metal of a low melting point metal such as Bi, Pb, Pb-Bi alloy during the operation of the apparatus.

  Also in the case of the oxygen sensor S2 of the third embodiment shown in FIG. 4, the first and second lead wires 25 are maintained at a predetermined vacuum level to prevent oxidation of the standard electrode side lead wires. Excellent measurement values similar to those of the oxygen sensors S and S1 shown in the examples can be shown.

It is a front sectional view of oxygen concentration sensor S of Example 1 of the present invention. It is a graph which shows the elapsed time / electromotive force which compared the oxygen concentration sensor which concerns on this invention, and the conventional sensor. It is a front sectional view of oxygen concentration sensor S1 of Example 2 of the present invention. It is a front sectional view of oxygen concentration sensor S2 of Example 3 of the present invention. It is a front sectional view of a conventional oxygen concentration sensor. It is a principle figure which measures the oxygen concentration in a liquid metal.

Explanation of symbols

25 Extension sleeve 26 Corrosion resistant sleeve
27 Container-shaped fixed electrode quality (measurement part)
28 End joint 29 Insulation tube
30 Standard electrode side lead wire 31 Antioxidation gas introduction nozzle 31a Gas discharge hole 33 Standard electrode (metal bismuth)
35 Standard electrode (bismuth oxide)

Claims (8)

A container-shaped measuring unit that is made of a solid electrolyte and is in contact with the liquid metal is connected to the tip of the conductive hollow tubular extension sleeve, and a standard electrode is accommodated in the container-shaped measuring unit. In the oxygen sensor, which is configured to insert a lead wire and measure the voltage between the standard electrode and the liquid metal,
An oxygen sensor is characterized in that an antioxidant gas is supplied into the oxygen sensor, and the antioxidant gas is circulated and discharged. A container-shaped measuring unit that is made of a solid electrolyte and is in contact with the liquid metal is connected to the tip of the conductive hollow tubular extension sleeve, and a standard electrode is accommodated in the container-shaped measuring unit. In the oxygen sensor, which is configured to insert a lead wire and measure the voltage between the standard electrode and the liquid metal,
An oxygen sensor comprising an antioxidant gas sealed inside the oxygen sensor.   The antioxidant gas is an inert gas composed of one kind or a mixture of two or more kinds selected from helium, argon, nitrogen, neon, krypton, xenon, radon and nitrogen. The oxygen sensor described in 1. The oxygen sensor according to claim 1 or 2, wherein the antioxidant gas is carbon dioxide or a mixed gas of water vapor and oxygen, and an oxygen partial pressure thereof is ^10-15 to ^10-30 . A container-shaped measuring unit that is made of a solid electrolyte and is in contact with the liquid metal is connected to the end of the conductive hollow tubular extension sleeve, and a standard electrode is accommodated in the container-shaped measuring unit. In the oxygen sensor, which is configured to insert a lead wire and measure the voltage between the standard electrode and the liquid metal,
An oxygen sensor, wherein the inside of the oxygen sensor is sealed in a vacuum.   6. The oxygen sensor according to claim 1, wherein the liquid metal in contact with the container-shaped measuring unit made of a solid electrolyte is essentially lead, bismuth, or lead bismuth alloy.   6. The oxygen sensor according to claim 1, wherein the solid electrolyte is yttria (Y2 O3) added zirconia (ZrO2), calcia (CaO) added zirconia, or magnesia (MgO) added zirconia.   6. The oxygen sensor according to claim 1, wherein the standard electrode is Bi / BiO3, Pb / PbO, In / In2O3, Pb-Bi / PbO system.

Images