JP2011075582A - Method for selecting oxygen sensor for oxygen copper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for selecting an oxygen sensor for copper having a high measurement accuracy to measure an oxygen partial pressure and an oxygen concentration of a fused oxygen copper and a copper alloy. <P>SOLUTION: When the predicted oxygen concentration of an oxygen-free copper or a copper alloy is about 0.5 ppm, that is, the level of an oxygen partial pressure is at a level of 10<SP>-13</SP>, either of Fe/FeO and Mo/MoO<SB>2</SB>is selected as a reference electrode. When the predicted oxygen concentration of an oxygen-free copper or a copper alloy is about 0.005 ppm, that is, the level of oxygen partial pressure is at a level of 10<SP>-17</SP>, Cr/Cr<SB>2</SB>O<SB>3</SB>is selected as a reference electrode. When the predicted oxygen concentration of copper is about 150 ppm, that is, the level of oxygen partial pressure is presumably at a level of 10<SP>-8</SP>, Ni/NiO is selected as a reference electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for selecting an oxygen sensor for oxygen copper.

  Conventionally, technology for in-line measurement of oxygen partial pressure or oxygen concentration in a general copper melt with a concentration cell type oxygen sensor probe using stabilized zirconia as a solid electrolyte in real time has been established. It is effectively used in the copper melting process.

  By the way, in oxygen-free copper, oxygen of extremely low concentration (10 ppm or less) is dissolved as compared with a general copper melt, and if this oxygen partial pressure or oxygen concentration can be measured, production of oxygen-free copper is possible. It is preferable because quality control can be improved.

  However, compared with the case of measuring a conventional copper or copper alloy melt with a relatively high oxygen concentration, oxygen-free copper has a very low oxygen concentration, so it is highly accurate. It is difficult to measure the oxygen partial pressure and oxygen concentration in it, and it is considered impossible to measure the oxygen concentration and oxygen partial pressure, so there are hardly any measurement examples.

  The present invention has been made paying attention to such problems existing in the prior art. An object of the present invention is to provide a method for selecting an oxygen sensor for copper with high measurement accuracy in order to measure the oxygen partial pressure and oxygen concentration of molten oxygen copper and copper alloys.

To achieve the above objective,
The invention of claim 1 predicts the oxygen partial pressure level of the oxygen copper or copper alloy to be measured from the manufacturing conditions, and the level and the equilibrium oxygen partial pressure of the reference electrode of the oxygen sensor for copper at the measurement temperature. The gist of the method for selecting a copper oxygen sensor is to select a copper oxygen sensor based on a comparison of sizes.

According to the present invention, the following effects can be exhibited.
According to claim 1, in order to measure the oxygen partial pressure and oxygen concentration of molten oxygen copper or a copper alloy, it is possible to select a copper oxygen sensor with good measurement accuracy.

(A) is a schematic front view which shows an oxygen sensor, (b) is a schematic front view which decomposes | disassembles and shows an oxygen sensor probe and a holder, (c) is a schematic rear view which shows a calculator. (A) is the front view which fractures | ruptures and shows the principal part of the oxygen sensor probe in 1st Embodiment, (b) is a side view when a cap is removed in the state of (a). Sectional drawing which expands and shows an oxygen sensor element. Explanatory drawing which shows the relationship between oxygen partial pressure and oxygen concentration. The graph which shows the relationship between the immersion time of an oxygen sensor probe in a melt, electromotive force, and temperature. The schematic sectional drawing of the oxygen sensor of other embodiment. The graph which shows the relationship between the immersion time of an oxygen sensor probe in a melt, electromotive force, and temperature.

(First embodiment)
Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings.
FIG. 1A is a schematic front view showing a solid electrolyte type oxygen sensor in the present embodiment, FIG. 1B is a schematic front view showing an exploded view of an oxygen sensor probe and a holder, and FIG. 1C is a schematic view showing a computing unit. It is a rear view. As shown in these drawings, the oxygen sensor includes a columnar oxygen sensor probe 11, a bottomed cylindrical holder 12 that accommodates and holds the oxygen sensor probe 11, and a connection in which one end is connected to the oxygen sensor probe 11. The cable 13 and an arithmetic unit 15 connected to the other end of the connection cable 13 via a connector 14 are configured. The oxygen sensor probe 11 of this embodiment is a consumable (use-up) sensor probe.

  The oxygen sensor probe 11 is immersed in a molten liquid of molten oxygen-free copper or molten copper alloy, which is a measurement target medium, and measures oxygen partial pressure or oxygen concentration. The computing unit 15 is formed in a square box shape, and a temperature display unit 16 and a concentration or partial pressure display unit 17 are provided on the surface thereof. On the back surface of the calculator 15, a concentration / partial pressure display switching unit 18 and a power switch 19 are provided. The calculator 15 calculates the oxygen concentration based on the signal from the oxygen sensor probe 11 or calculates and displays the oxygen partial pressure.

  Next, the oxygen sensor probe 11 will be described in detail. FIG. 2A is a front view showing a principal part of the oxygen sensor probe 11 in a broken state, and FIG. 2B is a side view when the cap 30 is removed in the state of FIG. FIG. 3 is a cross-sectional view showing the oxygen sensor probe 11. As shown in these drawings, a cylindrical ceramic base 20 is disposed at the distal end portion 11a of the oxygen sensor probe 11, and a positive side wire 21 and a negative side made of a conductive wire are provided at almost the center of the ceramic base 20. A thermocouple 23 formed in an arc shape is provided by joining the element wire 22 at the tip. The thermocouple 23 is disposed in the quartz tube 24 and protected. The thermocouple 23 having the + side strand 21 and the − side strand 22 and the quartz tube 24 constitute a temperature measuring unit. The + side strand 21 is made of an alloy containing 13% by mass of rhodium in platinum, and the − side strand 22 is made of platinum.

  An oxygen sensor element 25 protrudes from a side position of the thermocouple 23 so as to be higher than the thermocouple 23. The + side strand 21 and the − side strand 22 are connected to the computing unit 15 via the connection cable 13. A connection electrode 26 protrudes at a position opposite to the oxygen sensor element 25 across the thermocouple 23 so as to be almost the same height as the oxygen sensor element 25. The connection electrode 26 is electrically connected to the calculator 15 via the connection cable 13. The connection electrode 26 corresponds to a connection member.

  As shown in FIG. 3, the oxygen sensor element 25 is configured such that a reference material 28 functioning as a reference electrode is accommodated in a bottomed cylindrical solid electrolyte tube 27 placed in a molten metal. The reference material 28 is connected to a lead wire (not shown), and is connected to the computing unit 15 via the connection cable 13. The lead wire and the connection cable 13 correspond to a connection member.

And the oxygen-free copper or copper alloy which is a measuring object medium becomes a measurement pole, and an electric signal is sent from the connection electrode 26 to the measurement pole.
A copper cap 30 having a covered cylindrical shape is attached and fixed to the ceramic base 20 so as to cover the thermocouple 23, the oxygen sensor element 25, and the connection electrode 26. A through hole 31 is formed through the center of the tip of the cap 30, and the outside and the inside of the cap 30 communicate with each other through the through hole 31. The through hole 31 allows the melt to enter the cap 30 when the oxygen sensor probe 11 is immersed in the melt of oxygen-free copper or copper alloy.

(Fixed electrolyte)
As the solid electrolyte used for the solid electrolyte tube 27, zirconia (ZrO ₂ ) doped with 9 mol% magnesia (MgO) is used.

In the present embodiment, the zirconia solid electrolyte functions as an oxygen ion conductor, and is brought into contact with molten oxygen-free copper or molten copper alloy so that the molten oxygen-free copper or molten metal melts with the reference electrode. An electromotive force is generated due to a difference in oxygen partial pressure in the copper alloy. When zirconia (ZrO ₂ ) is used alone, no electromotive force is generated in the oxygen concentration cell, but by adding magnesia (MgO), which is the oxide, an electromotive force is generated in the oxygen concentration cell.

(Reference electrode)
As the reference material 28 of the present embodiment, a mixture of any of the following Cr / Cr ₂ O ₃ , Fe / FeO, and Mo / MoO ₂ metals and an oxide of the metal is used, and its mass The ratio is set to metal: metal oxide = 9: 1.

(1) Chromium (Cr) and chromium oxide (Cr ₂ O ₃ )
(2) Fe (iron) and iron oxide (FeO)
(3) Mo (molybdenum) and MoO ₂ (molybdenum oxide)
As for these metals and metal oxides, those that do not melt are selected at 1000 ° C. to 1500 ° C., which is the melting temperature of oxygen-free copper or copper alloy, and always exhibit a solid phase at the measurement temperature. Incidentally, the melting point of chromium is 1905 ° C, iron is 1535 ° C, and molybdenum is 2622 ° C.

  Which reference electrode is used, that is, which oxygen sensor probe 11 with which reference electrode is used depends on the level of oxygen concentration expected to be contained in oxygen-free copper or copper alloy, that is, , Determined according to the level of oxygen partial pressure.

  This predicted value of oxygen concentration (predicted value) is not exact, and in the manufacturing process that is the manufacturing condition of oxygen-free copper or copper alloy, the melting temperature, the melting time, or the mixing ratio of other metals to be mixed It is a value predicted based on the above, and indicates a level of size. Note that the crude copper produced in the refining process has an oxygen concentration of 0.2% or less. After that, when the copper is made tough pitch copper through electrolytic copper, the oxygen concentration is about 0.02%. Oxygen-free copper is obtained by further removing oxygen from the tough pitch copper molten copper. Therefore, it is easy to predict the oxygen concentration level of oxygen-free copper. In addition, a predicted value may be selected from a database of manufacturing results such as melting temperature, melting time, or mixing ratio of other metals to be mixed in the past manufacturing process of oxygen-free copper or copper alloy. .

Next, which reference pole is selected will be specifically described.
Table 1 shows the equilibrium oxygen partial pressure of the metal / metal oxide at 1150 ° C.

なお、表１において、「Ｎｉ／ＮｉＯ」は、酸素濃度が１０ｐｐｍ以下ではなく、一般の溶融銅の酸素分圧、又は酸素濃度の測定の場合に使用されている従来の基準極である。

In Table 1, “Ni / NiO” is not the oxygen concentration of 10 ppm or less, but is a conventional reference electrode used in the measurement of the oxygen partial pressure or oxygen concentration of general molten copper.

  Table 2 shows the electromotive force of the oxygen sensor when each metal / metal oxide is a solid reference electrode and the oxygen concentration in copper is different at 1150 ° C.

表２に示すように、無酸素銅又は銅合金中の酸素濃度が、１５０ｐｐｍ、０．５ｐｐｍ、０．００５ｐｐｍの場合における酸素分圧（すなわち、前述した酸素分圧のレベル）は、それぞれ１０^−８ａｔｍ、１０^−１３ａｔｍ、１０^−１７ａｔｍである（図４参照）。

As shown in Table 2, when the oxygen concentration in the oxygen-free copper or copper alloy is 150 ppm, 0.5 ppm, or 0.005 ppm, the oxygen partial pressure (that is, the above-mentioned oxygen partial pressure level) is 10 ^{− 8} atm, 10 ⁻¹³ atm, 10 ⁻¹⁷ atm (see FIG. 4).

Compared with the equilibrium oxygen partial pressure of metal / metal oxide shown in Table 1, Fe / FeO is 1.97 × 10 ⁻¹³ and Mo / MoO ₂ is 4.88 × 10 ⁻¹³ . it is found that as much as ^{10 -13} level of oxygen concentration 0.5ppm in copper. For this reason, it is understood that when the oxygen concentration in copper includes 0.5 ppm, the electromotive force is reduced when Fe / FeO or Mo / MoO ₂ is selected as the reference electrode.

Further, when compared with the equilibrium oxygen partial pressure of the metal / metal oxide shown in Table 1, Cr / Cr ₂ O ₃ is 1.64 × 10 ⁻¹⁹ , so the oxygen concentration in copper is 0.005 ppm. It turns out that it is a grade close ^| similar to the level of ^10-17 . For this reason, it can be seen that, at a small level including an oxygen concentration of 0.005 ppm in copper, when this Cr / Cr ₂ O ₃ is selected as the reference electrode, the electromotive force is reduced.

  When the oxygen concentration in the oxygen-free copper or copper alloy is 150 ppm, 0.5 ppm, or 0.005 ppm, when the combination of each metal / metal oxide is used as a reference electrode, the electromotive force of the oxygen sensor is shown in Table 2. It becomes as follows.

  As described above, the predicted oxygen partial pressure level (that is, the oxygen concentration level) of the measurement electrode at the measurement temperature (eg, 1150 ° C.) and the equilibrium oxygen partial pressure of the reference electrode are the same or close to each other. By selecting, a reference electrode having a small absolute value of electromotive force can be selected.

Here, the reason why the absolute value of the electromotive force of the oxygen sensor element 25 should be as small as possible is described.
This is because, when the electromotive force of the oxygen sensor element 25 increases, electrochemical leakage (short circuit) occurs in the solid electrolyte from the thicker oxygen concentration to the thinner oxygen concentration. In addition, if the oxygen concentration difference is large, there is an influence of gas leakage in the melt from the gas line of the oxygen sensor (which means a space area where air exists in the oxygen sensor probe 11), and measurement is started. After that (that is, after being immersed in molten copper), the electromotive force is not constant and stable, and the measurement accuracy is deteriorated.

  On the other hand, if the reference electrode and the measurement electrode (oxygen-free copper or copper alloy) have the same concentration (level), the generated electromotive force is reduced, and the above-described electrochemical leakage or gas line The effect of leakage can be reduced, and the electromotive force after the start of measurement is stabilized, so that measurement can be performed early.

In the case of 0.5 ppm, the absolute value of the electromotive force to be measured is the same level of Fe / FeO and Mo / MoO ₂ , and the absolute value of these electromotive forces is higher than that of Cr / Cr ₂ O _3. Since it is small, an oxygen sensor having either of the two as a reference electrode is selected.

In the case of 0.005 ppm, since Cr / Cr ₂ O ₃ has a smaller absolute value than other reference electrodes, an oxygen sensor using Cr / Cr ₂ O ₃ as a reference electrode is selected.
In the case of general copper that is not oxygen-free copper, when the oxygen concentration is 150 ppm, since the absolute value of the electromotive force of Ni / NiO is small as the reference electrode, Cr / Cr ₂ O ₃ is used as the reference electrode. An oxygen sensor is good.

(Connection electrode 26)
The connection electrode 26 is made of molybdenum in this embodiment, but is not limited to this material. The connection electrode 26 may be selected from those that do not react or dissolve with oxygen-free copper or copper alloy.

Next, the principle of the oxygen sensor probe 11 will be described.
When the oxygen concentration or oxygen partial pressure in the reference electrode and the measurement electrode existing on both sides of the solid electrolyte tube 27 is different, the electromotive force E generated between the reference electrode and the measurement electrode is based on the Nernst equation shown below. Calculated.

但し、Ｅは理論起電力、Ｒは気体定数、Ｆはファラデー定数及びＴは絶対温度を表す。又、

However, E represents a theoretical electromotive force, R represents a gas constant, F represents a Faraday constant, and T represents an absolute temperature. or,

は基準極側における酸素濃度又は酸素分圧を表す。

Represents the oxygen concentration or oxygen partial pressure on the reference electrode side.

は測定極側における酸素濃度又は酸素分圧を表す。

Represents the oxygen concentration or oxygen partial pressure on the measurement electrode side.

  By using this Nernst equation, when one oxygen concentration or oxygen partial pressure and temperature are known, the other oxygen concentration or oxygen partial pressure can be calculated from the generated electromotive force. Therefore, the function as the oxygen sensor probe 11 can be achieved.

(Operation of the embodiment)
For example, when measuring the oxygen concentration in the melt of oxygen-free copper or copper alloy, the oxygen sensor probe 11 is directed toward the melt and the cap 30 portion is immersed in the melt. In this state, the oxygen sensor element 25 measures the electromotive force (E), and the thermocouple 23 measures the temperature (T) of the melt (that is, the measured temperature). The oxygen concentration on one side of the solid electrolyte tube 27 is known. Accordingly, the calculator 15 of the oxygen sensor probe 11 calculates the oxygen concentration in the melt based on the Nernst equation and displays it on the concentration or partial pressure display unit 17. The temperature of the melt is measured by the thermocouple 23, calculated by the calculator 15, and displayed on the temperature display unit 16.

According to the first embodiment described in detail above, the following effects are exhibited.
In the first embodiment, the reference electrode that reduces the absolute value of the electromotive force of the oxygen sensor element 25 according to the predicted oxygen concentration of the oxygen-free copper or copper alloy that is the measurement electrode, that is, the oxygen partial pressure level. Is selected, the influence of electrochemical leakage and leakage from the gas line can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

For example, when the predicted oxygen concentration of oxygen-free copper or copper alloy is about 0.5 ppm, that is, when the oxygen partial pressure level is ^10-13 , Fe / FeO and Mo / MoO ₂ If any of these is used as a reference electrode, the absolute value of the electromotive force of the oxygen sensor can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

- In addition, the oxygen concentration in the oxygen-free copper or copper alloy is expected, by the case of the order of 0.005 ppm, when the level of the oxygen partial pressure of ^{10 -17} level, the _Cr / Cr 2 _{O 3} as a reference electrode For example, the absolute value of the electromotive force of the oxygen sensor can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

・ In addition, as shown in Table 2, when the oxygen concentration of copper is predicted to be about 150 ppm, that is, when the oxygen partial pressure level is predicted to be 10 ⁻⁸ , Ni / NiO is selected as the reference electrode. Then, the absolute value of the electromotive force of the oxygen sensor for copper can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

FIG. 5 shows Ni / NiO and Cr / Cr ₂ O ₃ as reference electrodes, Ni / NiO as Comparative Example 1, and Cr / Cr ₂ O ₃ as Example 1 immersed in an oxygen-free copper melt. The elapsed time and the electromotive force measurement test results are shown. The measurement temperature is 1150 ° C.

  As shown in the figure, in Comparative Example 1, it can be seen that the electromotive force is not stable after the measurement is started, and as a result, the measurement accuracy is poor. On the other hand, in Example 1, since the electromotive force is stabilized early, it is possible to measure the electromotive force stabilized early.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 6 is an explanatory diagram showing a schematic configuration of an oxygen sensor that constitutes the oxygen sensor 150 using gas as a reference electrode.

The oxygen sensor 150 includes a computing unit 110, a connection terminal 120, an oxygen sensor element 125, and a temperature sensor 140. In FIG. 6, the oxygen sensor element 125 includes an outer shell tube 126 and an inner shell tube 134. The outer tube 126 is made of alumina. The tip of the outer shell tube 126 is closed with a solid electrolyte 127. The solid electrolyte 127 extends to the tip side along the axial direction of the outer shell tube 126. In this embodiment, zirconia (ZrO ₂ ) doped with 9 mol% magnesia (MgO) is used as the solid electrolyte.

  The upper part of the solid electrolyte 127 and the tip of the outer tube 126 are covered with a cap 128 made of alumina. Furthermore, a part of the lower end portion of the outer shell tube 126, the cap 128, and the lower end peripheral surface of the solid electrolyte 127 are covered with a covering member 129 made of alumina cement. The lower end surface of the solid electrolyte 127 is exposed. Further, the space surrounded by the lower end surface of the cap 128, the solid electrolyte 127, and the covering member 129, and the space surrounded by the upper end surface of the cap 128, the outer shell tube 126, and the covering member 129 are glass seals. Sealed by 130 and 131.

  A porous platinum electrode 132 is formed on the upper surface of the solid electrolyte 127 facing the space in the outer shell tube 126. An electrically conductive inner shell tube 134 is inserted and disposed in the outer shell tube 126. In this embodiment, the inner shell tube 134 is formed of stainless steel. The lower end of the inner shell tube 134 is disposed in contact with the platinum electrode 132, and a gas serving as a reference electrode is introduced into the platinum electrode 132. Then, the introduced gas passes through the platinum electrode 132 and is led out through the space between the outer shell tube 126 and the inner shell tube 134. The platinum electrode 132 is electrically connected by being in contact with the inner shell tube 134. The platinum electrode 132 and the outer shell tube 126 correspond to connection members.

  Further, the inner tube 134 of the oxygen sensor element 125 is electrically connected to the calculator 110, and a detection signal of the oxygen sensor element 125 can be input to the calculator 110. Since the calculator 110 has the same configuration as the calculator 15 of the first embodiment, a detailed description thereof is omitted.

  The connection terminal 120 includes a tube 121 made of alumina. The lower end of the tube 121 is closed with a conductive cap 122. In the present embodiment, the cap 122 is made of graphite. A conductive rod 123 is inserted into the tube 121 and is electrically connected to the cap 122. The conductive rod 123 is electrically connected to the calculator 110. As shown in FIG. 6, the connection terminal 120 can be immersed in the molten copper D.

The conductive rod 123 and the cap 122 correspond to connection members.
The temperature sensor 140 is made of a thermocouple (not shown), is covered with a heat-resistant material, and can be immersed in the molten copper D. The temperature sensor 140 can input a temperature detection signal to the computing unit 110.

Now, the reference electrode of the second embodiment will be described.
As the reference electrode, which is the reference material of the present embodiment, the following H ₂ / O ₂ / Ar-based and CO / CO ₂ / Ar-based mixed gases are used.

(1) 4% H ₂ -0.5% O ₂ -95.5% Ar (hereinafter referred to as mixed gas A)
(2) 10% CO-0.1% CO ² -89.9% Ar (hereinafter referred to as mixed gas B)
Which reference electrode is used, that is, which oxygen sensor element 125 with which reference electrode is used, is the level of oxygen concentration expected to be contained in oxygen-free copper or copper alloy, that is, , Determined according to the level of oxygen partial pressure.

The value of oxygen concentration (predicted value) is predicted in the same manner as in the first embodiment.
Next, which reference pole is selected will be specifically described.
Table 3 shows the equilibrium oxygen partial pressure of the mixed gas at 1150 ° C.

表４は、各混合ガスを基準極とし、１１５０℃において、銅中の酸素濃度が異なる場合の酸素センサの起電力を示している。

Table 4 shows the electromotive force of the oxygen sensor when the oxygen concentration in copper is different at 1150 ° C. with each mixed gas as a reference electrode.

なお、表４において、「基準極の空気」は、酸素濃度が１０ｐｐｍ以下ではなく、一般の溶融銅の酸素分圧、又は酸素濃度の測定の場合に使用されている従来の基準極である。

In Table 4, “air of reference electrode” is a conventional reference electrode that is used in the measurement of the oxygen partial pressure or oxygen concentration of general molten copper, not the oxygen concentration of 10 ppm or less.

As shown in Table 4, when the oxygen concentration in the oxygen-free copper or copper alloy is 150 ppm, 0.5 ppm, or 0.005 ppm, the oxygen partial pressure (that is, the above-mentioned oxygen partial pressure level) is 10 ^{− 8} atm, 10 ⁻¹³ atm, 10 ⁻¹⁷ atm.

Shown in Table 3, when compared with the equilibrium oxygen partial pressure of the mixed gas, the mixed gas A are the 4.36 × ^{10 -14,} than the mixed gas B, 10 of the oxygen concentration 0.5ppm in copper ^- It can be seen that the level of ¹³ is closer to the mixed gas B. For this reason, it is understood that when the oxygen concentration in copper includes 0.5 ppm, the electromotive force is reduced when the mixed gas A is selected as the reference electrode.

In contrast to the equilibrium oxygen partial pressure of the mixed gas shown in Table 3, since the mixed gas B is 5.62 × 10 ⁻¹⁸ , the oxygen concentration in copper is 10 ⁻¹⁷ level with 0.005 ppm. It turns out that it is a near degree. For this reason, it can be seen that the electromotive force is reduced when the mixed gas B is selected as the reference electrode at a level including an oxygen concentration of 0.005 ppm in copper.

  When the oxygen concentration in the oxygen-free copper or copper alloy is 150 ppm, 0.5 ppm, or 0.005 ppm, the electromotive force of the oxygen sensor is as shown in Table 4 when air and the mixed gases A and B are used as reference electrodes. Street.

  As described above, the predicted oxygen partial pressure level (that is, the oxygen concentration level) of the measurement electrode at the measurement temperature (eg, 1150 ° C.) and the equilibrium oxygen partial pressure of the reference electrode are the same or close to each other. By selecting, a reference electrode having a small absolute value of electromotive force can be selected.

According to the second embodiment described in detail above, the following effects are exhibited.
In the second embodiment, as in the first embodiment, the absolute value of the electromotive force of the oxygen sensor element 25 is reduced according to the predicted oxygen concentration level of the oxygen-free copper or copper alloy that is the measurement electrode. Since the reference electrode is selected, the influence of electrochemical leakage and leakage from the gas line can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

  For example, when the oxygen concentration level of oxygen-free copper or copper alloy is about 0.5 ppm, the absolute value of the electromotive force of the oxygen sensor can be reduced by using the mixed gas A as a reference electrode. As a result, since the electromotive force is stabilized early, measurement can be performed early.

  If the oxygen concentration level of oxygen-free copper or copper alloy is about 0.005 ppm, the absolute value of the electromotive force of the oxygen sensor can be reduced by using the mixed gas B as a reference electrode. As a result, since the electromotive force is stabilized early, measurement can be performed early.

・ Also, as shown in Table 4, when the predicted oxygen concentration in copper is predicted to be about 150 ppm, that is, when the oxygen partial pressure level is predicted to be 10 ⁻⁸ , air is used as a reference. If selected as the pole, the absolute value of the electromotive force of the oxygen sensor can be reduced. As a result, since the electromotive force is stabilized early, measurement can be performed early.

  FIG. 7 shows the elapsed time and the electromotive force when air and mixed gas A are respectively used as reference electrodes, air is set as Comparative Example 2, and mixed gas A is immersed in an oxygen-free copper melt as Example 2. The result of the measurement test is shown. The measurement temperature is 1150 ° C. In Comparative Example 2, as shown in FIG. 7, the elapsed time is between 0.8 h and 1.4 h when the mixed gas A is supplied instead of air. It shows that the same electromotive force measurement was possible.

  In Comparative Example 2, as shown in FIG. 7, the measured electromotive force is shifted downward from the start of measurement in the section described as air (air reference in FIG. 7). It can be seen that the electromotive force is not stable, and as a result, the measurement accuracy is poor. On the other hand, in Example 2, since the electromotive force is stabilized early, it is possible to measure the electromotive force stabilized early.

  -In 2nd Embodiment, the surface which faces the space in the outer shell tube 126 of the solid electrolyte 127 is equipped with the porous platinum electrode 132, and the mixing which is a reference electrode from the inner shell tube 134 with respect to the platinum electrode 132 Gas was introduced. As a result, the mixed gas enters the porous electrode, and it is easy to conduct oxygen ions between the mixed gas and the solid electrolyte.

In addition, embodiment of this invention is not limited to the said embodiment, You may change as follows.
-In the said embodiment and the said Example, although the measurement temperature was 1150 degreeC, it is not limited to this temperature, The range of 1000 degreeC-1500 degreeC within the range of the melting temperature of oxygen free copper or a copper alloy If it is in.

· In the first embodiment, _Cr / Cr 2 _{O 3} system, Fe / FeO system, changing the mixing ratio of the components of Mo / MoO ₂ system.
In the second _embodiment, H _{2 /} O 2 / Ar system, CO / _CO 2 / each Ar-based mixed gas of varying the mixing ratio of the components.

13: Connection cable (connection member),
26: Connection electrode (connection member),
27 ... Solid electrolyte tube (solid electrolyte),
28: Reference material (reference electrode).

Claims (1)

  The oxygen partial pressure level of the oxygen copper or copper alloy to be measured is predicted from the manufacturing conditions, and based on a comparison between the level and the equilibrium oxygen partial pressure of the reference electrode of the oxygen sensor for copper at the measurement temperature. A method for selecting a copper oxygen sensor, comprising: selecting a copper oxygen sensor.

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