Oxygen sensor for molten copper, oxygen sensor device for molten copper, method for detecting oxygen concentration in molten copper, and method for manufacturing copper wire

Abstract

To provide an oxygen sensor for molten copper including a solid electrolyte with high durability, an oxygen sensor device for molten copper, a method for detecting the concentration of oxygen in molten copper, and a method for manufacturing a copper wire.SOLUTION: An oxygen sensor 10 has an oxygen cell 2 that is formed of a zirconia-based solid electrolyte having oxygen ion conductivity, and outputs a detection voltage according to the potential difference generated due to the oxygen concentration difference between the concentration of oxygen in gas supplied to the inside of the oxygen cell 2 and the concentration of oxygen in molten copper with which at least part of the oxygen cell 2 is impregnated. A partially stabilized zirconia in which a zirconia crystal is partially stabilized by a stabilizer is used as the solid electrolyte. The absolute value of the coefficient of thermal expansion of the oxygen cell is 8.2×10-6 / K or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oxygen sensor for molten copper, an oxygen sensor device for molten copper, a method for detecting the oxygen concentration of molten copper, and a method for manufacturing a copper wire. [Background technology]

[0002] Conventionally, oxygen sensors have been used to measure the oxygen concentration of high-temperature molten copper melted in a melting furnace. Patent Document 1 describes an oxygen concentration measurement probe previously filed by the applicant.

[0003] This oxygen concentration measurement probe is equipped with a cylindrical external electrode, a solid electrolyte tube placed inside the external electrode, and a reference electrode and an internal electrode placed inside the solid electrolyte tube. A potentiometer is connected between the external electrode and the internal electrode, and a potential difference signal is sent to the control unit. The material of the solid electrolyte tube is stabilized zirconia (ZrO2+MgO), whose crystal structure is stabilized by magnesium oxide, and oxygen ions (O 2- The solid electrolyte tube has the property of selectively passing oxygen and other gases. The reference electrode is either a solid oxygen reference electrode made of a metal / metal oxide such as Fe / FeO powder, or an air reference electrode made of a gas such as air. The internal electrode is a metal conductor wire made of stainless steel, platinum, or other metal. The lower end of the solid electrolyte tube forms an immersion section that protrudes downward from the external conductor. When this immersion section and a portion of the cylindrical external electrode are immersed in molten copper, oxygen ions move from the inner surface of the solid electrolyte tube to the outer surface due to the oxygen partial pressure difference, generating a potential difference between the internal and external electrodes. The control unit monitors the oxygen concentration in the molten copper by inputting the potential difference signal output by the potentiometer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-132617 Summary of the Invention [Problem to be solved by the invention]

[0005] In oxygen sensors using stabilized zirconia as described above, microcracks (crazing) may occur in the solid electrolyte tube after one or two immersions due to thermal shock when the immersion portion is immersed in molten copper. The present inventors have confirmed that when such microcracks occur, molten copper penetrates the cracked portion, making it impossible to accurately detect the oxygen concentration in the molten copper, especially when the oxygen concentration in the molten copper is extremely low. Therefore, the present inventors have conducted extensive research to realize an oxygen sensor that can be immersed a long average number of times before microcracks occur, and have arrived at the present invention.

[0006] That is, an object of the present invention is to provide an oxygen sensor for molten copper, which has a highly durable solid electrolyte that selectively passes oxygen ions, an oxygen sensor device for molten copper, a method for detecting the oxygen concentration of molten copper, and a method for manufacturing a copper wire. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides an oxygen sensor for molten copper, which comprises an oxygen cell formed of a zirconia-based solid electrolyte having oxygen ion conductivity, and outputs a detection voltage corresponding to a potential difference generated by an oxygen concentration difference between the oxygen concentration of a gas supplied to the inside of the oxygen cell and the oxygen concentration of molten copper in which at least a part of the oxygen cell is immersed, wherein partially stabilized zirconia in which zirconia crystals are partially stabilized by a stabilizer is used as the solid electrolyte, and the absolute value of the thermal expansion coefficient of the oxygen cell is 8.2 × 10 -6 / K or less the law of nature , a thermocouple formed by connecting a pair of metal conductor wires is arranged so that a connection point of the pair of metal conductor wires is in contact with an inner surface of the oxygen cell, and one of the pair of metal conductor wires is used as an internal electrode for detecting the potential difference; We provide oxygen sensors for molten copper.

[0008] Furthermore, in order to solve the above-mentioned problems, the present invention provides an oxygen sensor device for molten copper, comprising: the above-mentioned oxygen sensor for molten copper; a voltage detection unit that detects a voltage between the internal electrode and the external electrode; and a calculation unit that calculates the oxygen concentration of the molten copper based on a detection value of the voltage detection unit.

[0009] Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for detecting an oxygen concentration in molten copper, which uses an oxygen sensor for molten copper according to claim 6, in which the internal electrode and the external electrode are made of different metals, and calculates the oxygen concentration in the molten copper from a value obtained by subtracting a thermoelectromotive force generated due to the difference in material between the internal electrode and the external electrode from a voltage between the internal electrode and the external electrode.

[0010] Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for manufacturing a copper wire, in which an oxygen sensor for molten copper is arranged in a flow path of the molten copper, and casting is performed while the oxygen concentration of the molten copper is continuously detected by the oxygen sensor for molten copper. [Effects of the Invention]

[0011] According to the oxygen sensor for molten copper, the oxygen sensor device for molten copper, the method for detecting an oxygen concentration in molten copper, and the method for manufacturing a copper wire according to the present invention, it is possible to increase the durability of a solid electrolyte that selectively passes oxygen ions. [Brief explanation of the drawings]

[0012] [Figure 1] 1A is a cross-sectional view showing the configuration of an oxygen sensor device including an oxygen sensor according to an embodiment of the present invention, and FIG. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] 3(a) and 3(b) are perspective views showing the lower end portion of the oxygen sensor. [Figure 4] FIG. 1 is a perspective view showing a part of an oxygen sensor, shown as a comparative example, in which conventionally used stabilized zirconia is used as the material of the oxygen cell. [Figure 5] 1 is a diagram showing a schematic configuration of a manufacturing apparatus for manufacturing a copper wire from a copper raw material. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment Mode] FIG. 1(a) is a cross-sectional view showing the configuration of an oxygen sensor device 1 equipped with an oxygen sensor according to an embodiment of the present invention. FIG. 1(b) is a partially enlarged view of FIG. 1(a). FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIGS. 3(a) and 3(b) are perspective views showing the lower end of the oxygen sensor. In the description of this embodiment, "upper" and "lower" refer to the upper and lower directions in the vertical direction when the oxygen sensor is in use. In addition, in FIG. 1(a), the symbol M indicates molten copper, and the symbol M1 indicates the surface of the molten copper.

[0014] (Configuration of oxygen sensor and oxygen sensor device) The oxygen sensor device 1 includes an oxygen sensor 10, an oxygen gas supply unit 11, a voltage detection unit 12, and a calculation unit 13. The oxygen sensor 10 includes a cylindrical oxygen cell 2 with a bottom, a tubular insulating tube 3 made of an electrically insulating material such as alumina, a thermocouple 4 formed by connecting a first metal conductor wire 41 and a second metal conductor wire 42 that are a pair of metal conductor wires housed in the insulating tube 3, a cylindrical external electrode 5, a sealing material 6 disposed between the oxygen cell 2 and the external electrode 5, and a support mechanism 7 that supports the external electrode 5 and biases the insulating tube 3 toward the lower end of the oxygen cell 2.

[0015] The oxygen cell 2 is formed of a zirconia-based solid electrolyte having oxygen ion conductivity. Specifically, this solid electrolyte is partially stabilized zirconia, in which zirconia (ZrO2) is partially stabilized with a stabilizer. The stabilizer can be a rare earth oxide such as magnesium oxide (MgO), calcium oxide (CaO), or yttrium oxide (YO3).

[0016] The oxygen cell 2 integrally has a cylindrical portion 21 and a bottom portion 22, and the bottom portion 22 closes the lower end portion of the cylindrical portion 21 in the vertical direction. A portion of the oxygen cell 2 including the bottom portion 22 protrudes downward from the plugging material 6 to form an immersion portion 20 that is immersed in the molten copper M. The plugging material 6 is made of a refractory material such as refractory cement, and prevents the molten copper M from penetrating into the external electrode 5 from between the oxygen cell 2 and the external electrode 5. The temperature of the molten copper M is, for example, 1083°C or higher and 1200°C or lower.

[0017] 2, first to fourth through holes 31 to 34 are formed in the insulating tube 3. The first to fourth through holes 31 to 34 penetrate the insulating tube 3 in the longitudinal direction. A portion of the insulating tube 3 in the longitudinal direction is disposed inside the oxygen cell 2, and the other portion protrudes upward from the oxygen cell 2. The outer diameter of the insulating tube 3 is smaller than the inner diameter of the oxygen cell 2, and a gap is formed between the outer peripheral surface 3a of the insulating tube 3 and the inner peripheral surface 21a of the cylindrical portion 21 of the oxygen cell 2, through which air (oxygen gas, described later) can flow.

[0018] A first metal conductor wire 41 is inserted through the first through-hole 31, and a second metal conductor wire 42 is inserted through the second through-hole 32. The first metal conductor wire 41 and the second metal conductor wire 42 are connected to each other at their portions that protrude downward from the lower end of the insulating tube 3. In this embodiment, the ends of the first metal conductor wire 41 and the second metal conductor wire 42 are welded to each other below the insulating tube 3, and this welded portion forms a spherical welded portion 43. The welded portion 43 is in contact with the inner surface 22a of the bottom 22 of the oxygen cell 2.

[0019] As an example, the first metal conductor wire 41, which is the positive electrode, is made of a platinum-rhodium alloy (PtRh) containing 13% rhodium, and the second metal conductor wire 42, which is the negative electrode, is made of platinum (Pt). Note that such a thermocouple combining a platinum-rhodium alloy and platinum is generally called an R thermocouple, and is used to measure temperatures in high temperature ranges, for example, above 1000°C.

[0020] Oxygen gas containing a predetermined oxygen content is supplied from the oxygen gas supply unit 11 to the third through-hole 33 and the fourth through-hole 34 of the insulating tube 3. This oxygen gas is, for example, pure oxygen with an oxygen content of 100%, but may also be air with an oxygen content of approximately 21% as long as the oxygen content is known. Oxygen gas is supplied from the upper end of the insulating tube 3 to the third through-hole 33 and the fourth through-hole 34, and the supplied oxygen gas escapes to the lower end of the insulating tube 3. The oxygen gas that escapes to the lower end of the insulating tube 3 is discharged above the oxygen cell 2 through the gap between the insulating tube 3 and the oxygen cell 2. The amount of oxygen gas supplied from the oxygen gas supply unit 11 is such that the oxygen concentration inside the oxygen cell 2 is kept constant.

[0021] The external electrode 5 is cylindrical with open upper and lower ends, and is disposed outside the oxygen cell 2. A seal 6 seals the gap between the inner peripheral surface 5a at the lower end of the external electrode 5 and the outer peripheral surface 21b of the cylindrical portion 21 of the oxygen cell 2. The external electrode 5 supports the oxygen cell 2 via the seal 6. In this embodiment, the external electrode 5 is made of stainless steel. More specifically, SUS310S (JIS G 4303), which has excellent heat resistance, can be suitably used as this stainless steel. A portion of the insulating tube 3 protrudes upward from the upper end of the external electrode 5.

[0022] The support mechanism 7 includes a holding member 71 that holds the upper end of the external electrode 5, a cover member 72 that is fixed to the holding member 71 and covers a portion of the upper opening of the external electrode 5, an annular spring bearing member 73 that is fixed to the outer peripheral surface 3a of the insulating tube 3, and a coil spring 74 that is disposed between the spring bearing member 73 and the cover member 72. The holding member 71 integrally includes a fitting cylindrical portion 711 into which the upper end of the external electrode 5 is fitted, and a plate portion 712 to which the cover member 72 is fixed by a plurality of bolts 70. An insertion hole 721 through which the insulating tube 3 is inserted is formed in the cover member 72, and the upper end of the insulating tube 3 protrudes upward from the insertion hole 721. The restoring force of the coil spring 74 presses the insulating tube 3 downward. As a result, the welded portion 43 of the thermocouple 4 is pressed against and in contact with the inner surface 22a of the bottom 22 of the oxygen cell 2.

[0023] The oxygen sensor 10 configured as described above outputs a detection voltage corresponding to a potential difference generated by the difference in oxygen concentration between the oxygen concentration of the oxygen gas supplied to the inside of the oxygen cell 2 and the oxygen concentration of the molten copper in which at least a part of the oxygen cell 2 is immersed. This potential difference is generated by the migration of oxygen ions from the inner surface 2a of the oxygen cell 2 (the inner circumferential surface 21a of the cylindrical portion 21 and the inner surface 22a of the bottom portion 22) to the outer surface 2b of the oxygen cell 2 in the immersion portion 20 (the outer circumferential surface 21b of the cylindrical portion 21 and the outer surface 22b of the bottom portion 22) due to the difference in oxygen partial pressure between the inside and outside of the oxygen cell 2.

[0024] That is, on the inner surface 2a side where the oxygen concentration is relatively high, oxygen molecules take in electrons and become oxygen ions (O2 + 4e - →2O 2- ), and on the outer surface 2b side where the oxygen concentration is relatively low, oxygen ions release electrons and return to oxygen molecules (2O 2- →O2+4e - ) This generates an electromotive force according to the oxygen partial pressure difference. The electromotive force due to this oxygen partial pressure difference is expressed by the following relational equation (Nernst equation) using the temperature (absolute temperature) of the oxygen cell 2 as a coefficient:

[0025] E=(R·T / (n·F))×ln(PO2(A) / PO2(B)) In this formula, E is the electromotive force generated by the oxygen partial pressure difference [V] R is the gas constant (8.3144598 [J·mol -1 ·K -1 ]) T is the absolute temperature [K] n is the number of electrons involved in the reaction (n=4 in the above reaction) F is the Faraday constant (96485.3329 [C mol -1 ]) PO2(A) is the partial pressure of oxygen in the high concentration side (inside oxygen cell 2) [atm] PO2(B) is the oxygen partial pressure [atm] on the low concentration side (outside oxygen cell 2) Then, if E and T are known (PO2(A) is known), PO2(B) can be calculated from the above formula, and the oxygen concentration of molten copper M can be calculated from PO2(B).

[0026] (Method for detecting oxygen concentration in molten copper) Next, a method for detecting the oxygen concentration of the molten copper M in the oxygen sensor device 1 will be described.

[0027] 1(a), the voltage detection unit 12 receives the potentials of the first metal conductor wire 41 and the second metal conductor wire 42 of the thermocouple 4 and the potential of the external electrode 5. The voltage detection unit 12 detects the voltage (potential difference) between the first metal conductor wire 41 and the second metal conductor wire 42, and also detects the voltage (potential difference) between the second metal conductor wire 42, which serves as the internal electrode 40, and the external electrode 5. That is, in this embodiment, of the first metal conductor wire 41 and the second metal conductor wire 42, the second metal conductor wire 42 is used as the internal electrode 40 for detecting a voltage corresponding to the difference in oxygen concentration between the inside and outside of the oxygen cell 2. However, this is not limiting, and the first metal conductor wire 41 may be used as the internal electrode.

[0028] A longitudinal portion of the external electrode 5, including its lower end portion, is immersed in the molten copper M together with the immersed portion 20 of the oxygen cell 2. As a result, the external electrode 5 and the outer surface 2b of the oxygen cell 2 at the immersed portion 20 are electrically connected via the molten copper M. In this embodiment, since the external electrode 5 is made of stainless steel as described above, the internal electrode 40 (the second metal conductor wire 42 made of platinum) and the external electrode 5 are made of different metals.

[0029] Hereinafter, the voltage between the first metal conductor wire 41 and the second metal conductor wire 42 will be referred to as the temperature-sensitive voltage, and the voltage between the internal electrode 40 and the external electrode 5 will be referred to as the oxygen-concentration-sensitive voltage. The voltage detection unit 12 has an AD converter, and outputs digital signals obtained by converting the detected values of the temperature-sensitive voltage and the oxygen-concentration-sensitive voltage to the calculation unit 13. The calculation unit 13 calculates the oxygen concentration of the molten copper M based on the detected values output by the voltage detection unit 12.

[0030] To calculate the oxygen concentration of the molten copper M, the calculation unit 13 first determines the temperature of the oxygen cell 2 (T in the above relational expression) based on the temperature-sensitive voltage. This temperature of the oxygen cell 2 corresponds to the temperature of the molten copper M. Next, the calculation unit 13 determines the thermoelectromotive force generated due to the difference in material between the internal electrode 40 and the external electrode 5 based on the determined temperature, and subtracts the determined thermoelectromotive force from the oxygen concentration-sensitive voltage to determine the electromotive force due to the oxygen partial pressure difference between the inside and outside of the oxygen cell 2 (E in the above relational expression). The calculated E and T are then applied to the above relational expression to determine the oxygen concentration of the molten copper M.

[0031] (Oxygen cell material) Next, the material of the oxygen cell 2 will be described in detail. As is well known, pure zirconia without the addition of stabilizers is monoclinic at room temperature, but as the temperature is increased, its crystal structure changes from monoclinic to tetragonal and then from tetragonal to cubic. This phase transition is accompanied by a volume change, with volume contraction occurring during the phase transition from monoclinic to tetragonal, and volume expansion occurring during the phase transition from tetragonal to cubic. This volume change makes microcracks more likely to occur, especially when the temperature changes suddenly. On the other hand, when a stabilizer is added to zirconia, the cubic crystals remain stable even at room temperature, and it is known that mechanical properties such as strength and toughness are improved compared to zirconia without the addition of stabilizers.

[0032] In partially stabilized zirconia, not all of the zirconia crystals are cubic at room temperature, but single crystals and tetragonal crystals are dispersed. The inventors have confirmed that partially stabilized zirconia is less susceptible to microcracks than stabilized zirconia with a stabilization rate of 100%. The reason for this is thought to be that when a crack occurs, the surrounding tetragonal crystals change to monoclinic crystals through stress-induced transformation, causing volume expansion, which generates a force that suppresses the propagation of the crack and suppresses its progression.

[0033] Fig. 4 is a perspective view showing a portion of an oxygen sensor 10A, as a comparative example, in which conventionally used stabilized zirconia is used as the material for the oxygen cell 2A. In Fig. 4, a portion of the immersion portion 20A of the oxygen cell 2A is cut horizontally and removed to show the inside of the oxygen cell 2A. This oxygen sensor 10A has the same configuration as the above-mentioned oxygen sensor 10, except for the material of the oxygen cell 2A.

[0034] As shown in Figure 4, if the oxygen cell 2A is immersed in molten copper without sufficient preheating, a sudden change in volume will cause microcracks C to form, and molten copper M may enter these microcracks C. The molten copper M that has entered the microcracks C will form a current path that short-circuits the inside and outside of the oxygen cell 2A, causing the voltage generated between the internal electrode 40 (second metal conductor wire 42) and the external electrode 5 to deviate from a value corresponding to the difference in oxygen concentration between the inside and outside of the oxygen cell 2A. This may result in inaccurate measurement of the oxygen concentration, particularly in the low oxygen concentration range of 20 ppm or less.

[0035] The present inventors have discovered that by adjusting the stabilization rate of zirconia crystals by increasing or decreasing the amount of stabilizer added, the thermal expansion coefficient of partially stabilized zirconia can be set to a predetermined value or less, and the occurrence of microcracks in the immersion portion 20 of the oxygen cell 2 when immersed in molten copper M can be suppressed. Then, through repeated experiments in which many prototypes with different amounts of stabilizer added were immersed in molten copper M, the inventors have found that if partially stabilized zirconia that satisfies the following conditions (1) to (3) is used as the material for the oxygen cell 2 of the oxygen sensor 10 for molten copper, the occurrence of microcracks can be significantly suppressed compared to conventional materials. (1) The stabilization rate of zirconia crystal is 10% or more and 50% or less. (2) The absolute value of the thermal expansion coefficient is 8.2 × 10 -6 / K or less (3) The stabilizer content is between 2 mol% and 9 mol%.

[0036] Here, "the stabilization rate of zirconia crystal is 10% or more and 50% or less" means that the proportion of cubic zirconia crystal at room temperature is 10 to 50%. -6 / K or less" means that the absolute value of the thermal expansion coefficient is 8.2 × 10 / K or less over the entire operating temperature range of the oxygen sensor 10 (room temperature to the temperature of molten copper). -6 / K or less. In particular, the absolute value of the average thermal expansion coefficient at temperatures between 20°C and 1000°C is 8.2 × 10 -6 It is desirable that it be / K or less.

[0037] Furthermore, when magnesium oxide (MgO) or calcium oxide (CaO) is used as the stabilizer, the lower limit of the stabilizer content in the partially stabilized zirconia is preferably 7 to 8 mol %. If the stabilization rate (stabilizer concentration) of the partially stabilized zirconia is too low, the mechanical strength of the partially stabilized zirconia against heat deteriorates, making it unsuitable for use in continuously measuring the oxygen concentration in molten copper M.

[0038] (Copper wire manufacturing equipment and manufacturing method) Next, a copper wire manufacturing apparatus and manufacturing method will be described with reference to Fig. 5. Fig. 5 is a configuration diagram showing a schematic configuration of a manufacturing apparatus 8 that manufactures copper wire from copper raw material. This manufacturing apparatus 8 is a continuous casting and rolling apparatus that continuously casts and rolls copper wire (copper wire rod), which is a copper alloy material.

[0039] The manufacturing equipment 8 includes a melting furnace 80 for heating and melting copper raw materials, an upper trough 81 for transporting the molten copper flowing out of the melting furnace 80, a holding furnace 82 for temporarily storing the molten copper transported by the upper trough 81 at a predetermined temperature, a metal element adding device 83 for adding metal elements to the molten copper, a lower trough 84 for transporting the molten copper to which the metal elements have been added by the metal element adding device 83, a tundish 85 for temporarily storing the molten copper transported by the lower trough 84, a pouring nozzle 86 for pouring the molten copper from the tundish 85, a continuous casting machine 87, a hot rolling mill 88 for continuously rolling cast bars 91 transported from the continuous casting machine 87, and a winder (coiler) 89 for winding up copper wire 92 transported from the hot rolling mill 88 via a surface cleaning treatment device.

[0040] The metal elements added to the molten copper by the metal element adding device 83 are, for example, titanium (Ti), indium (In), tin (Sn), magnesium (Mg), etc. Note that there are cases where no metal elements are added to the molten copper, in which case the metal element adding device 83 is not necessary.

[0041] The continuous casting machine 87 is a belt-wheel type device for performing continuous casting, and includes a casting ring 871 with a groove formed on its outer periphery, a belt 872, and a cylindrical holder 873 for holding the casting ring 871. The casting ring 871 is driven to rotate by a motor (not shown). The belt 872 is guided by multiple pulleys 874 and rotates in a circular motion while contacting a portion of the outer periphery of the casting ring 871.

[0042] Molten copper flows down from a tundish 85 through a pouring nozzle 86 and is supplied between the grooves of the casting ring 871 and the belt 872. The casting ring 871 and the belt 872 are cooled with cooling water while rotating. The molten copper supplied to the continuous casting machine 87 is cooled and solidified between the casting ring 871 and the belt 872 to form a rod-shaped cast bar (cast material) 91.

[0043] The oxygen sensor 10 is disposed in the flow path of molten copper from the melting furnace 80 to the continuous casting machine 87. Casting is performed while the oxygen sensor 10 continuously detects the oxygen concentration of the molten copper. Here, "continuous detection" means that the oxygen concentration is constantly detected without interruption while the immersion unit 20 is immersed in the molten copper from the start to the end of production of the cast material (here, the cast bar 91).

[0044] The oxygen sensor 10 may be located in the upper trough 81, the holding furnace 82, or the lower trough 84. However, it is more preferable to locate it in the tundish 85 immediately before the molten metal is supplied to the continuous casting machine 87, and it is even more preferable to locate it directly above the pouring nozzle 86 in the tundish 85. By locating the oxygen sensor 10 in this manner, it is possible to detect a change in the oxygen concentration in the flow path, for example, if the sealing in the upper trough 81 or the lower trough 84 becomes insufficient for some reason. It is also effective to locate multiple oxygen sensors at multiple locations among those mentioned above. In this way, if a change in the oxygen concentration indicated by the oxygen sensor directly above the pouring nozzle 86 occurs during operation, it is possible to determine which upstream location caused the change.

[0045] The oxygen concentration of the molten copper detected by the oxygen sensor 10 is used for quality control purposes, such as for producing oxygen-free copper with a residual oxygen content of 10 ppm or less in the casting material, low-oxygen copper with a residual oxygen content of 20 ppm or less, and tough pitch copper with a purity of about 99.9%. The oxygen concentration of the molten copper detected by the oxygen sensor 10 can also be used to control the amount of active metals, such as titanium and magnesium, added by the metal element adding device 83. Titanium and magnesium easily bond with oxygen, and the oxygen concentration in the molten copper changes depending on the amount of these metals added. Therefore, the amount of active metal to be added can be estimated from the oxygen concentration in the molten copper.

[0046] The temperature detected by the thermocouple 4 is used to calculate the oxygen concentration using the above relational expression, and can also be used to check whether the oxygen cell 2 has been preheated properly, for example. Preheating the oxygen cell 2 can more reliably prevent the occurrence of microcracks. The specific method of preheating is not particularly limited, but it may be performed using a gas burner, or by bringing the immersion portion 20 of the oxygen cell 2 close to the surface of the molten copper before immersion in the molten copper.

[0047] (Experimental results) Table 1 shows the results of using magnesium oxide (MgO) as a stabilizer, with a stabilizer concentration of 9 mol%, a stabilization rate of 30%, and an absolute value of the thermal expansion coefficient of 6.2 × 10 -6 K, yttrium oxide (Y2O3) was used as a stabilizer. The stabilizer concentration was 8 mol%, the stabilization rate was 100%, and the absolute value of the thermal expansion coefficient was 10.1 × 10 -6 An oxygen cell [Comparative Example 1] formed by a solid electrolyte of 1000K, and calcium oxide (CaO) was used as a stabilizer, and the stabilizer concentration was 15 mol%, the stabilization rate was 100%, and the absolute value of the thermal expansion coefficient was 10.2 × 10 -6 10 is a table showing the results of measuring the average number of repeated immersion measurements using an oxygen cell [Comparative Example 2] formed with a solid electrolyte of K.

[0048] [Table 1] The measurement directions for the average number of times that repeated immersion measurements can be performed shown in Table 1 are as follows: Steps 1 to 5 below.

[0049] (Step 1) Three test samples are prepared for each of the three types of oxygen sensors for molten copper using oxygen cells shown in Example 1, Comparative Example 1, and Comparative Example 2. (Step 2) The first test sample of each of the three types of molten copper oxygen sensors was subjected to one cycle (one time, approximately 1.5 hours) of the following: preheating ⇒ immersion in molten pure copper held at approximately 1200°C (for one hour) ⇒ removal from the molten copper and slow cooling. (Step 3) It is determined whether the oxygen concentration can be measured during immersion in one cycle, and whether cracks have occurred in the test sample at the end of the slow cooling cycle. (Step 4) If the judgment result in Step 3 shows that the oxygen concentration could be measured while immersed in molten copper and that no cracks have occurred in the test sample, the test sample is subjected to the same cycle as Step 2 again, and then judgment is made in Step 3. On the other hand, if the oxygen concentration could not be measured while immersed in molten copper or if cracks have occurred in the test sample, it is replaced with the next test sample of the same type, and the replaced test sample is subjected to the same cycle as Step 2, and then judgment is made in Step 3. (Step 5) For each of the three types of test samples, if an abnormality is found in the third test sample in the judgment of Step 3, the test for that type of test sample is terminated. Then, the average number of cycles in which the judgment result of Step 3 for the three test samples was passed is calculated.

[0050] In the measurements of steps 1 to 5, the average value obtained in step 5 for the oxygen sensor for molten copper using the oxygen cell of Example 1 was larger than the average values obtained in step 5 for the oxygen sensors for molten copper using the oxygen cells of Comparative Examples 1 and 2. Furthermore, for all three oxygen sensors for molten copper using the oxygen cell of Example 1, the number of cycles for which the judgment result in step 3 was pass was greater than the number of cycles for which the judgment result in step 3 was pass for the oxygen sensors for molten copper using the oxygen cells of Comparative Examples 1 and 2. That is, the oxygen sensors for molten copper using the oxygen cell of Example 1 demonstrated stable high durability.

[0051] (Actions and Effects of the Embodiments) According to the embodiment described above, it is possible to suppress the occurrence of microcracks in the oxygen cell 2 and improve the durability of the oxygen sensor 10. Furthermore, by using the second metal conductor wire 42 constituting the thermocouple 4 as the internal electrode 40, it is possible to suppress the number of parts of the oxygen sensor 10 and reduce costs.

[0052] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0053] [1] An oxygen sensor (10) for molten copper, comprising an oxygen cell (2) formed of a zirconia-based solid electrolyte having oxygen ion conductivity, which outputs a detection voltage corresponding to a potential difference generated by the difference in oxygen concentration between the oxygen concentration of a gas supplied to the inside of the oxygen cell (2) and the oxygen concentration of molten copper (M) in which at least a part of the oxygen cell (2) is immersed, wherein partially stabilized zirconia in which zirconia crystals are partially stabilized by a stabilizer is used as the solid electrolyte, and the absolute value of the thermal expansion coefficient of the oxygen cell (2) is 8.2 × 10 -6 / K or less oxygen sensor for molten copper (10).

[0054] [2] The oxygen sensor (10) for molten copper according to the above [1], wherein the content of the stabilizer in the partially stabilized zirconia is 2 mol % or more and 9 mol % or less.

[0055] [3] The oxygen sensor (10) for molten copper according to the above [1] or [2], wherein the stabilization rate of the zirconia crystal in the oxygen cell (2) is 10% or more and 50% or less.

[0056] [4] The oxygen sensor (10) for molten copper according to any one of [1] to [3] above, wherein a thermocouple (4) formed by connecting a pair of metal conductor wires (41, 42) is arranged so that a connection point (43) of the pair of metal conductor wires (41, 42) is in contact with an inner surface of the oxygen cell (2), and one of the pair of metal conductor wires (41, 42) is used as an internal electrode (40) for detecting the potential difference.

[0057] [5] The oxygen sensor (10) for molten copper according to the above item [4], further comprising a metal conductor disposed outside the oxygen cell (2) to support the oxygen cell (2), the metal conductor being used as an external electrode (5) for detecting the potential difference between the metal conductor and the internal electrode (40).

[0058] [6] An oxygen sensor device (1) for molten copper, comprising: the oxygen sensor (10) for molten copper according to the above [5]; a voltage detection unit (12) for detecting a voltage between the internal electrode (40) and the external electrode (5); and a calculation unit (13) for calculating an oxygen concentration of the molten copper (M) based on a detection value of the voltage detection unit (12).

[0059] [7] The oxygen sensor device (1) for molten copper according to the above item [6], wherein the internal electrode (40) and the external electrode (5) are made of different metals, and the calculation unit (13) calculates the oxygen concentration of the molten copper (M) from a value obtained by subtracting a thermoelectromotive force generated due to the difference in material between the internal electrode (40) and the external electrode (5) from the detection value of the voltage detection unit (12).

[0060] [8] A method for detecting an oxygen concentration in molten copper (M), comprising: using the oxygen sensor (10) for molten copper (10) according to the above item [5], in which the internal electrode (40) and the external electrode (5) are made of different metals; and calculating the oxygen concentration in the molten copper (M) from a value obtained by subtracting a thermoelectromotive force generated due to the difference in material between the internal electrode (40) and the external electrode (5) from a voltage between the internal electrode (40) and the external electrode (5).

[0061] [9] A method for manufacturing a copper wire (91), comprising: arranging the oxygen sensor (10) for molten copper (10) according to any one of [1] to [5] above in a flow path of the molten copper (M); and performing casting while continuously detecting the oxygen concentration of the molten copper (M) with the oxygen sensor (10) for molten copper.

[0062] Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. [Explanation of symbols]

[0063] 1...Oxygen sensor device 10, 10A...Oxygen sensor 2,2A...Oxygen cell 20,20A...Immersion section 3...Insulating tube 4...Thermocouple 40...internal electrode 41...first metal conductor wire 42... second metal conductor wire 43... welded portion 5...External electrode 6...Sealing material 7...Support mechanism 8...Manufacturing equipment

Claims

1. An oxygen sensor for molten copper, comprising an oxygen cell formed of a zirconia solid electrolyte having oxygen ion conductivity, and outputting a detection voltage corresponding to a potential difference generated by an oxygen concentration difference between an oxygen concentration of a gas supplied to the inside of the oxygen cell and an oxygen concentration of molten copper in which at least a portion of the oxygen cell is immersed, As the solid electrolyte, partially stabilized zirconia in which zirconia crystals are partially stabilized by a stabilizer is used, The absolute value of the thermal expansion coefficient of the oxygen cell is 8.2 × 10 －６ / K or less, a thermocouple formed by connecting a pair of metal conductor wires is arranged so that a connection point of the pair of metal conductor wires is in contact with an inner surface of the oxygen cell; one of the pair of metal conductor wires is used as an internal electrode for detecting the potential difference; Oxygen sensor for molten copper.

2. The content of the stabilizer in the partially stabilized zirconia is 2 mol% or more and 9 mol% or less. The oxygen sensor for molten copper according to claim 1.

3. the stabilization rate of the zirconia crystal in the oxygen cell is 10% or more and 50% or less; 3. The oxygen sensor for molten copper according to claim 1 or 2.

4. An insulating tube that houses the pair of metal conductor wires, and a support mechanism that urges the insulating tube toward a lower end of the oxygen cell, the support mechanism has a coil spring that presses the insulating tube downward; the insulating tube is pressed downward by the restoring force of the coil spring, and the connection point of the pair of metal conductor wires is pressed against the inner surface of the oxygen cell; The oxygen sensor for molten copper according to any one of claims 1 to 3.

5. a metal conductor disposed outside the oxygen cell to support the oxygen cell, the metal conductor being used as an external electrode for detecting the potential difference between the metal conductor and the internal electrode; The oxygen sensor for molten copper according to claim 4.

6. 6. An oxygen sensor for molten copper, comprising: the oxygen sensor for molten copper according to claim 5; a voltage detection unit that detects a voltage between the internal electrode and the external electrode; and a calculation unit that calculates an oxygen concentration of the molten copper based on a detection value of the voltage detection unit. Oxygen sensor device for molten copper.

7. the internal electrode and the external electrode are made of different metals, The calculation unit calculates the oxygen concentration of the molten copper from a value obtained by subtracting a thermoelectromotive force generated due to a difference in material between the internal electrode and the external electrode from a detection value of the voltage detection unit. The oxygen sensor device for molten copper according to claim 6.

8. The oxygen sensor for molten copper according to claim 5, wherein the internal electrode and the external electrode are made of different metals, The oxygen concentration of the molten copper is calculated from a value obtained by subtracting a thermoelectromotive force generated due to a difference in material between the internal electrode and the external electrode from a voltage between the internal electrode and the external electrode. A method for detecting oxygen concentration in molten copper.

9. A method for producing a copper wire, comprising: disposing the oxygen sensor for molten copper according to any one of claims 1 to 5 in a flow path of the molten copper; and performing casting while continuously detecting the oxygen concentration of the molten copper with the oxygen sensor for molten copper.

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