JPH05312775A - Oxygen sensor using zirconia containing gadorinium oxide - Google Patents

Abstract

PURPOSE:To provide a zirconia solid electrolyte internal vessel containing Gd2O3 as an improved zirconia oxygen sensor which permits stable measurement of oxygen potential of alloys or molten metals having low melting point and low oxygen potential for an extended period. CONSTITUTION:A zirconia oxygen sensor, for measuring oxygen potential of alloys or a molten metal 5 whose melting point is as low as 350-550 deg.C, comprises a reference electrode 2 forming a system consisting of a metal which shows liquid phase at the temperature of measuring the molten metal 5 or the alloy and the oxides distributed in it, a vessel 1 of zirconia solid electrolyte containing 5-15mol%, Gd2O3 of (6-12)mol% desirable, being let to receive the system and contact the molten metal or the alloy, lead wires 3 and 4 connected to either the reference electrode 2 or the molten metal 5 or each alloy and a means 6 for measuring electromotive force between the lead wires 3 and 4. By using the zirconia solid electrolyte internal vessel 1 containing Gd2O3, oxygen potential of alloys or the molten metal 5 of low melting point and oxide potential can be stably measured for an extended period, more effectively as a zirconia oxygen sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia oxygen sensor for measuring the oxygen potential of low melting point molten metal and alloy (hereinafter referred to as molten metal) baths.

[0002]

2. Description of the Related Art In recent years, with the diversification of metal materials, the quality required for metal materials has become stricter, and in the process of handling various molten metals, it is important to control the concentration of impurity elements etc. that directly relate to the quality. It has started to be done. Among them, the measurement of oxygen potential in molten metal is
It is also very important for controlling the oxygen concentration in the molten metal and the concentration of the impurity element in equilibrium with it. An example of this is the measurement of oxygen potential in molten steel and molten copper.

Conventionally, as a zirconia oxygen sensor for measuring oxygen potential in molten metal, an oxygen sensor for molten steel or molten copper utilizing the electromotive force of a solid electrolyte is known. However, the operating temperature range of the oxygen sensor is
1500 ~ 1800 ℃ for molten steel, 100 for molten copper
It is limited to a fairly high temperature of 0 to 1300 ° C.

However, as the object of the present invention, 55
A low melting point metal in a molten state at 0 ° C. or lower, such as zinc,
For lead, tin, bismuth, indium, gallium and alloys of these metals, the zirconia oxygen sensor conventionally used to measure the oxygen potential in molten steel or molten copper has an oxygen content in the molten metal of 550 ° C or lower. Since it was thought that it was impossible to measure the potential, there are few measurement examples. In particular, relatively low temperatures (450-500), such as hot dip galvanizing baths.
At (° C.), The oxygen ion conductivity of the zirconia solid electrolyte becomes small, so it was considered difficult to measure the electromotive force itself.

As an oxygen sensor for molten metal at low temperature, there is an oxygen sensor for liquid sodium using a thoria solid electrolyte as disclosed in JP-A-52-53494. However, the thoria solid electrolyte used in this sensor is a radioactive substance, is very difficult to handle, and is expensive, which is disadvantageous for industrial use for this purpose. As described above, there has been almost no conventional zirconia oxygen sensor for measuring the oxygen potential in a molten metal having a low melting point.

[0006]

[Solution to Problem] Conventionally, a reference electrode of a zirconia oxygen sensor for molten steel or molten copper is Cr-Cr ₂ O ₃ system, Mo-MoO ₂ system, etc. for molten steel. Is a solid electrode of Ni-NiO system, Fe-FeO system, or the like. In these cases, since the operating temperature is as high as 1000 to 1800 ° C., the response of electromotive force is sufficiently fast. However, when these solid electrodes are used for a relatively low temperature molten metal having a temperature of 350 to 550 ° C., the time required for the electromotive force to stabilize becomes impractically long or unstable. The present inventors have paid attention to this point, and have a reference electrode having a melting point equal to or lower than that of a low melting point molten metal and forming a liquid phase at a measurement temperature, and a zirconia solid electrolyte containing Y ₂ O ₃ or CaO. By using the container as a zirconia oxygen sensor, we have already obtained the knowledge that the oxygen potential in molten metal can be measured reliably. The present inventors have further reported that Gd ₂ O ₃
It is known that the zirconia electrolyte containing Y ₂ O ₃ has a higher ionic conductivity than the zirconia electrolyte containing Y ₂ O ₃ and CaO, but contains Gd ₂ O ₃ in an environment of low temperature and low oxygen potential such as a molten zinc bath. It has been found that when the zirconia electrolyte is used as a container for the zirconia electrolyte in the zirconia oxygen sensor, the electromotive force is more stable for a longer time than when the zirconia electrolyte containing Y ₂ O ₃ and CaO is used. The present invention provides an improved zirconia oxygen sensor based on the above findings.

[0007]

According to the present invention, a metal having a melting point equal to or lower than that of a molten metal in a low melting point of 350 to 550 ° C. and forming a liquid phase at the measurement temperature in the molten metal. And a reference electrode, which is a system consisting of the oxide dispersed therein, and 5 to 15 mol%, preferably 6 to 12 that can contain the system and contact it with a molten metal or alloy.
A container of zirconia solid electrolyte containing mol% of Gd ₂ O ₃ , a lead wire connected to each of a reference electrode and a molten metal or alloy, and means for measuring an electromotive force between the lead wires. An improved zirconia oxygen sensor is provided, which is capable of stably measuring the oxygen potential for a long time.

The zirconia oxygen sensor determines the oxygen concentration by measuring the electromotive force of an oxygen concentration cell composed of a reference electrode, a zirconia solid electrolyte, a molten metal and a lead wire. The low melting point metal which is in a molten state at a temperature of 350 to 550 ° C. in the present invention includes zinc, lead, tin, bismuth, indium, gallium and alloys of these metals. In the present invention, the zirconia solid electrolyte functions as a conductor for oxygen ions. By bringing the zirconia solid electrolyte into contact with the molten metal, an electromotive force is generated due to the difference in oxygen potential between the reference electrode and the molten metal or alloy. 5 as a zirconia solid electrolyte
15 mol%, preferably 6～12Mol% of Gd ₂
Zirconia containing O ₃ (ZrO ₂ ) is preferably used.
When the Gd ₂ O ₃ content of ZrO ₂ is less than 5%, the electromotive force is not stable and the response is extremely poor. Also, ZrO ₂ Gd ₂ O ₃
If the content exceeds 15 mol%, the oxygen ion conductivity of the zirconia solid electrolyte decreases and it cannot be put to practical use. It is preferable to contain 6 to 12 mol% of Gd ₂ O ₃ . Further, when the operating temperature is 350 ° C. or lower, the oxygen ion conductivity of the zirconia solid electrolyte becomes extremely small, and measurement becomes impossible.

As the reference electrode, an electrode made of a metal having a melting point equal to or lower than the temperature of the molten metal and its oxide and always exhibiting a liquid phase at the measurement temperature is used. In the measurement state, the reference electrode is in a state where oxide particles of the metal are dispersed in the molten metal, and it is considered that oxygen is dissolved in the reference electrode metal in a saturated state. Given oxygen potential is given. At a measurement temperature in a molten metal having a low melting point of 350 to 550 ° C., a reference electrode, which is a system including a liquid phase metal and its oxide dispersed therein, is an In—In ₂ O ₃ system, a Bi— system. Bi ₂ O ₃ system, Zn-Zn
O type is preferable.

Next, as lead materials connected to the reference electrode and the low melting point molten metal, C, W, Mo, Re and T are used.
Preferred are a, Ir, Os and stainless steel.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Relationship between ionic conductivity of ZrO ₂ -M ₂ O ₃ (MO) solid electrolyte and guest solid solution amount (800
(° C.) is shown in FIG. (T. Tannenberg e
t al. , Proc. J. Int'l Etud
e Piles Combust. p19 (196
5)). From FIG. 1, it can be seen that Gd ₂ O ₃ has a higher ionic conductivity than Y ₂ O ₃ and CaO. A schematic diagram of the zirconia oxygen sensor according to the present invention is shown in FIG. As shown in FIG. 2, it comprises a zirconia solid electrolyte container containing Gd ₂ O ₃ , a reference electrode 2, a lead wire 3 (reference electrode side), a potentiometer 6, and a lead wire 4 (molten metal side). ..

[0012]

EXAMPLES AND COMPARATIVE EXAMPLES Reference was made at a temperature of 450 ° C. using a zirconia solid electrolyte container containing 9 mol% Gd ₂ O ₃ and a zirconia solid electrolyte container containing 8 mol% Y ₂ O ₃ in the above zirconia oxygen sensor. The result of measuring the time change of the electromotive force mV generated between the reference electrode and the molten zinc by immersing the zirconia solid electrolyte container in the molten zinc bath using the electrode (In-In ₂ O ₃ system) 3 shows. From FIG. 3, when the zirconia solid electrolyte containing Gd ₂ O ₃ is used as the inner container in an environment of low temperature and low oxygen potential such as a molten zinc bath, the electromotive force is Y ₂
It can be seen that the zirconia solid electrolyte containing O ₃ is more stable for a longer period of time than when it is used.

[0013]

According to the present invention, by using the zirconia solid electrolyte inner container containing Gd ₂ O ₃ , it is possible to stably measure the oxygen potential of a molten metal or alloy having a low melting point and a low oxygen potential for a long time. It can be effectively used as a zirconia oxygen sensor.

[0014]

[Brief description of drawings]

FIG. 1 is a graph showing the relationship (800 ° C.) between the ionic conductivity of a ZrO ₂ —M ₂ O ₃ (MO) -based solid electrolyte and the amount of guest solid solution.

FIG. 2 is a schematic view showing a usage state of a zirconia oxygen sensor.

FIG. 3 is a graph showing a time change of an electromotive force generated between a reference electrode and a molten metal.

[Explanation of symbols]

 1 ... Solid electrolyte container 2 ... Reference electrode 3, 4 ... Lead wire 5 ... Molten metal bath 6 ... Potentiometer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Issei Nakamoto 1 Tsurumachi, Amagasaki City, Hyogo Prefecture Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. To measure the oxygen potential of a molten metal or alloy bath having a low melting point of 350 ° C. to 550 ° C., a metal in a liquid phase at a measurement temperature in the molten metal or alloy and its oxidation dispersed therein. A reference electrode which is a system consisting of a substance, a container of zirconia solid electrolyte containing 5 to 15 mol% of Gd ₂ O ₃ which is contained in the system and brought into contact with a molten metal or alloy, and a reference electrode and a molten metal or alloy, respectively. An improved zirconia oxygen sensor comprised of connected leads and means for measuring the electromotive force between the leads. 2. The zirconia solid electrolyte is 6 to 12 mol.
The zirconia oxygen sensor according to claim 1, comprising% Gd ₂ O ₃ .