JPH033903B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the oxygen reference electrode of an oxygen sensor for measuring the concentration of dissolved oxygen in molten metal. More specifically, by adding a specific substance to the solid oxygen reference electrode constituent material of the oxygen sensor and causing it to coexist, it is possible to prevent sintering of the oxygen reference electrode constituent material and to slightly change the oxygen reference polarization generated in the reference electrode. This invention relates to a so-called oxygen reference electrode for an oxygen sensor with excellent responsiveness, which can quickly change the electromotive force exhibited when immersed in molten metal and stably indicate the electromotive force after the change. In recent years, oxygen sensors using stabilized or partially stabilized zirconia as a solid electrolyte and oxygen ion conductor have been used for automobile exhaust gas control, combustion management in boilers, etc., and even as oxygen analyzers in molten metal in the steel and copper manufacturing fields. It is widely used because it provides a quick response and is inexpensive. Conventionally, air has often been used as the oxygen reference electrode in oxygen sensors, but when air is used as the oxygen reference electrode, the structure of the oxygen sensor becomes complicated, so it is particularly difficult to use consumable oxygen sensors for molten metal. In this case, a solid reference electrode made of a mixture of a specific metal and an oxide of that metal is used because of its simple structure, which allows it to be simply packed in the bottom of a zirconia tube. Oxygen sensors for molten metal are mainly used in the steel industry, and are used for determining the end point of converters, RH furnaces, DH
The main uses are vacuum degassing in furnaces, preliminary analysis of deoxidation reactions and confirmation analysis after the reaction, measurements in tundishes during continuous casting, and oxygen measurements for process control in various steelmaking fields. Since the measurement is carried out by immersing the oxygen sensor in high-temperature molten steel at around 1600°C, it is necessary to determine a stable equilibrium electromotive force before the oxygen sensor components are eroded (for example, within 5 to 10 seconds). An oxygen sensor that can obtain such a quick response uses a MgO partially stabilized zirconia tube with excellent thermal shock resistance as a solid electrolyte, and a mixture of metals/metal oxides such as Mo/MoO ₂ , Cr/Cr ₂ O ₃ or sintered zirconia tubes. It is known to use a solid oxygen reference electrode as a solid oxygen reference electrode. However, when using such a component as an oxygen reference electrode,
Phenomena with different responses are observed. For example, as shown in the attached Figure 1, the electromotive force change exhibited by the Cr/Cr ₂ O ₃ reference electrode is a sudden increase in electromotive force value immediately after immersion.
In the subsequent change to the equilibrium value after the decrease, the electromotive force difference is larger than that of the Mo/MoO ₂ reference pole, and therefore the time to reach the equilibrium value is longer. The Cr/Cr ₂ O ₃ reference electrode has the drawbacks mentioned above, but when the dissolved oxygen concentration in molten steel (usually 1 to 1000 ppm) is low (e.g. 100 ppm or less), the Cr/Cr ₂ O ₃ reference electrode itself Since the oxygen partial pressure is close to the indicated oxygen partial pressure (equivalent to 28 ppm in molten steel at 1600°C), measurement errors due to oxygen partial pressure differences are theoretically small, making it suitable for oxygen sensors such as deoxidized steel and high carbon steel. On the other hand, as shown in Figure 2, the Mo/MoO _2- based reference electrode has an oxygen partial pressure equivalent to or higher than the saturated oxygen concentration of molten steel at 1600°C, and is therefore suitable as a solid oxygen reference electrode for measuring high oxygen concentrations. is suitable, but when used for low-oxygen molten steel, the partial pressure difference is large and the measurement error becomes large. Therefore, in principle, a Cr/Cr ₂ O ₃ reference electrode is more advantageous in a low oxygen concentration region. Under these circumstances, the present inventors conducted intensive studies on improving the response of the Cr/Cr ₂ O ₃ based reference electrode, and as a result, found that
The above objective is satisfied when a specific metal or an oxide of the metal is added and made to coexist.
It was discovered that a solid oxygen reference electrode based on Cr/Cr ₂ O ₃ could be used, and the present invention was completed. That is, the present invention provides metallic chromium powder, or a metal powder that forms an oxide more unstable than Cr ₂ O ₃ in 100 parts by weight of metallic chromium powder and Cr ₂ O ₃ powder and has a higher melting point than metallic chromium. Another object of the present invention is to provide an oxygen reference electrode for an oxygen sensor for molten metal, characterized in that the metal powder and the metal oxide powder coexist in an amount of 50 to 200 parts by weight. The present invention will be explained in more detail below. The oxygen sensor for molten metal, which is the object of the present invention, uses zirconia oxide as a solid electrolyte,
Known general-purpose zirconia oxygen sensors using Cr/Cr ₂ O ₃ as an oxygen reference electrode, such as Y ₂ O ₃ , CaO, MgO
An oxygen sensor configured with a so-called partially stabilized or stabilized zirconia oxide consisting of at least one of the following and zirconia as a solid electrolyte, and Cr/Cr ₂ O ₃ as an oxygen reference electrode during use,
The shape of the sensor can be either a plug type in which a solid electrolyte chip is bonded to the tip of a glass tube made of quartz or the like, or a tube type in which a solid electrolyte is molded and sintered. The oxygen reference electrode of the present invention is made of Cr powder or Cr powder.
Add to 100 parts by weight of Cr ₂ O ₃ powder a powder of a metal that forms an oxide that is more unstable than Cr ₂ O ₃ and has a higher melting point than Cr, or a powder of the metal and its oxide.
This is a fixed reference electrode constructed by adding and mixing 50 to 200 parts by weight. Here, the powder of a metal that forms an oxide that is more unstable than Cr ₂ O ₃ and has a melting point higher than that of Cr, or the metal powder and the oxide powder of the metal, is 1500~
Metals and oxides of such metals that form Cr ₂ O ₃ and metal M by the reaction of metallic chromium with oxides of metals falling under the above definition (e.g. MxOy) in the temperature range of 1800 ° C. , specifically molybdenum (Mo), molybdenum dioxide (MoO ₂ ), tungsten (W), and tungsten dioxide (WO ₂ ). If the amount added is less than 50 parts by weight, the response speed improvement effect will not be sufficient, while if it exceeds 200 parts by weight, a waveform due to the oxygen partial pressure of the additive will appear, and then Cr/ Since a Cr ₂ O ₃ waveform occurs, the response time becomes longer as a result, which is undesirable. Cr constituting the solid oxygen reference electrode in the present invention
The mixing ratio of Cr ₂ O 3 and Cr 2 O ₃ is usually such that the ratio of Cr ₂ O ₃ powder to Cr powder is 50% by weight or less.
If the mixing ratio of Cr ₂ O ₃ to Cr exceeds 50% by weight, oxygen in the air remaining in the tube will not be removed quickly and the conductivity of the reference electrode will deteriorate, which is not suitable. On the other hand, when filling a zirconia solid electrolyte container with Cr powder constituting the reference electrode in an oxidizing atmosphere, the Cr powder generates oxides due to oxygen in the atmosphere, so the Cr powder is packed without the Cr ₂ O ₃ powder. It is also possible to use only one. Such Cr powder or Cr/Cr ₂ O ₃ powder may be used as it is by being packed into a zirconia solid electrolyte container, but if it is sintered in advance and used after being crushed, it may be sintered while immersed in molten steel etc. This is more preferable because it is less likely to cause shrinkage and the time required to reach equilibrium is shorter. Furthermore, when sintering is performed in the presence of carbon and used after being crushed, Cr/Cr ₂ O ₃
It is particularly recommended because the waveform does not fall into a V-shape, which is a characteristic of the system reference pole, and the response time is therefore significantly shortened. In the present invention, Cr/Cr ₂ O ₃ is added to coexist.
The proportion of metal such as Mo/MoO ₂ and/or W/WO ₂ and metal oxide is usually 10% by weight or less based on the metal powder. If the mixing ratio exceeds 10% by weight, the influence of the metal oxide will be strong, two levels of electromotive force will be exhibited, and the response time will be long, which is not appropriate. It is not clear why the configuration described above improves the observed electromotive force waveform, that is, the response, but a small amount of the metal oxide as an additive causes the Cr/Cr ₂ O ₃ to react only in the initial stage. Therefore, since the proportion of metal oxide in the additive is small, the added metal oxide after compensating for the electromotive force difference is The material immediately finished decomposing, and there was no significant change in the electromotive force value of the original reference electrode, and the remaining added metal acted as a sintering inhibitor for Cr/Cr ₂ O ₃ , and both effects were combined. It is believed that the effects of the present invention will be achieved in combination. As described in detail above, the present invention simply replaces Cr/Cr ₂ O ₃ powder, which is the constituent material of the oxygen reference electrode used conventionally.
By simply mixing specific amounts of Mo and/or W metal powder and each metal oxide powder, it is possible to provide an oxygen sensor for molten steel that can stably indicate the electromotive force and has excellent responsiveness. , its industrial utility value is extremely great. The present invention will be explained in more detail with reference to Examples below, but the Examples show embodiments of the present invention, and the present invention is not limited by these Examples. Example After mixing 70 parts by weight of metallic chromium powder and 30 parts by weight of Cr ₂ O ₃ powder in a ball mill, the mixture was heated at 1300°C in a CO atmosphere for 2
The mixture was sintered for a period of time, and then crushed and ground in a mortar to obtain a Cr/Cr ₂ O ₃ mixed powder with an average particle size of 5 μm. The Mo/MoO ₂ and/or W/WO ₂ mixed powder shown in Table 1 (Experiment Nos. 2 to 7) was added to the Cr/Cr ₂ O ₃ mixed powder obtained in this way, and the mixture was mixed in a ball mill. The obtained mixed powder was filled in the bottom of a zirconia tube 2 with an outer diameter of 5.6 mm and a length of 35 mm, one end of which was partially stabilized with 7 mol% MgO, as shown in Fig. 3, and the oxygen reference electrode 1 was filled with the mixed powder. Then, an electrode 4 made of a molybdenum wire was inserted into the reference electrode 1, and a reference electrode holding rod 3 was further inserted and installed, thereby assembling an oxygen sensor. The oxygen sensor thus constructed was immersed in high-frequency molten steel at 1600°C in an aluminum crucible, and the electromotive force was observed and recorded for 30 seconds. The results obtained are shown in Figures 4-10. Further, a mixed powder consisting of 90 parts by weight of Cr powder and 10 parts by weight of Cr ₂ O ₃ powder was mixed using a ball mill, and then sintered at 1300°C for 2 hours in an argon atmosphere and in the presence of carbon.
After that, crush and crush in a mortar to obtain an average particle size of 3 μm.
Table 1 Experiment No. 8 for Cr/Cr ₂ O ₃ mixed powder
The additives listed above were mixed, an oxygen sensor was constructed in the same manner as above, and its performance was measured. The results are shown in FIG.

【table】

[Table] * Weight percent of oxide to metal powder in additives
As a result of the above, Experiment Nos. 2, 6, which correspond to the present invention,
It can be seen that samples No. 7 and No. 8 have significantly improved responsiveness compared to the conventional oxygen sensor using an oxygen reference electrode made of Cr/Cr ₂ O ₃ alone.

[Brief explanation of the drawing]

Figures 1, 2, and 4 to 11 show electromotive force waveform diagrams shown by the oxygen sensor, and Figure 3 is a vertical cross-sectional view showing an outline of the oxygen sensor used in the example. The electrode constituent materials include a zirconia tube with one end closed, 3 a reference electrode holding rod, and 4 an electrode.

Claims (1)

[Claims] 1 Metal chromium powder or metal chromium powder and
To 100 parts by weight of Cr ₂ O ₃ powder, add 50 parts by weight of a metal powder that forms an oxide that is more unstable than Cr ₂ O ₃ and has a higher melting point than metallic chromium, or the metal powder and the oxide powder of the metal. An oxygen reference electrode for an oxygen sensor for molten metal, characterized in that the oxygen reference electrode is made up of 200 parts by weight. 2 The ratio of Cr ₂ O ₃ powder to metal chromium powder is
The oxygen reference electrode according to claim 1, wherein the oxygen content is 50% by weight or less. 3 Metallic chromium powder or metallic chromium powder
2. The oxygen reference electrode according to claim 1, wherein the proportion of the oxide of the metal to the metal powder added and coexisting with the Cr ₂ O ₃ powder is 10% by weight or less. 4. Claims in which the metallic chromium, the metallic powder added to the metallic chromium and the Cr ₂ O ₃ powder, or the metallic powder and its metal oxide are molybdenum and/or tungsten, and their metallic oxides. The oxygen reference electrode according to item 1. 5. The oxygen reference electrode according to claim 1, which uses metallic chromium powder that has been sintered in advance and then pulverized, or metallic chromium powder and Cr ₂ O ₃ powder. 6. The oxygen reference electrode according to claim 1, which uses metallic chromium powder that has been sintered in advance in the presence of carbon and then pulverized, or metallic chromium powder and Cr ₂ O ₃ powder.