JPS59109852A - Reference oxygen electrode of oxygen sensor for molten metal - Google Patents

Abstract

PURPOSE:To obtain a reference oxygen electrode suitably used for a sensor with high responsiveness for measuring an oxygen concn. in molten metal by mixing metallic powder or metallic powder and metallic oxides having higher m.p. than Cr with powder of Cr or Cr and Cr2O3 in a specified ratio. CONSTITUTION:50-200pts.wt. metallic powder having higher m.p. than Cr such as Mo or W or powder of the oxides of the same metals are mixed with 100pts.wt. powder of Cr or Cr and Cr2O3 and pulverized. The pulverized mixture is packed in the bottom of a zirconia tube 2 closed at one end as a reference oxygen electrode 1, and an electrode 4 consisting of Mo wire and a standard electrode containing rod 3 are inserted to assemble an oxygen sensor. The Cr2O3 powder is regulated to <=50wt% of the Cr and the metallic oxide to <=10wt% of the added metals (Mo, W). When the Cr and Cr2O3 are previously sintered in a gaseous CO atmosphere, pulverized and mixed with the added metals (oxides), the responsiveness of the sensor is further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the oxygen reference electrode of an oxygen sensor for measuring dissolved oxygen concentration in molten metal.

More specifically, by adding a specific substance to the constituent material of the solid oxygen reference electrode of the oxygen sensor and by slightly changing the oxygen reference polarization generated by the reference electrode, the electromotive force exhibited when immersed in molten metal can be reduced. This invention relates to a so-called oxygen reference electrode for an oxygen sensor with excellent responsiveness, which can quickly change the electromotive force 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 an oxygen ion conductor have been rapidly used for automobile exhaust gas control, combustion management in boilers, etc., and even as oxygen analyzers in molten metal in the steelmaking field. It is widely used because it provides a good 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. 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 only requires filling the bottom of the zirconia tube.

Oxygen sensors for molten metal are mainly used in the steel industry, and are used for determining the end point of converters, vacuum degassing in RH and DH furnaces, preliminary analysis of deoxidation reactions and confirmation analysis after the reaction, and tundish during continuous casting. Oxygen measurement is mainly used for measurement in steel manufacturing fields or process control in various steel manufacturing fields. Since the measurement is performed 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, in 5 to 10 seconds). An oxygen sensor that can obtain such a quick response uses an MpO partially stabilized zirconia tube with excellent thermal shock resistance as a solid electrolyte, and uses a metal/metal oxide mixture or sintered body such as Mo/MOO2, 0r10r20a as a solid oxygen standard. The most extreme one is known. However, when such a component is used as an oxygen reference electrode, a phenomenon in which the response is different is observed. For example, as shown in the attached M1 diagram <Cr/Cr20
The electromotive force change exhibited by the B-based reference electrode is a rapid increase in electromotive force value immediately after immersion, followed by a change to an equilibrium value after a subsequent decrease.
The electromotive force difference is larger than that of the MO/MOO2 system reference pole, and therefore it takes a long time to reach the equilibrium value. Although the Cr/Cr20B reference electrode has the above-mentioned drawbacks, when the dissolved oxygen concentration in molten steel (usually 1 to 101000 ppm or less (e.g. less than IO ppm)), the oxygen partial pressure indicated by the reference electrode itself (1600' 28P in molten steel at C
Since it is close to Pm (equivalent to Pm), measurement errors based on oxygen partial pressure differences are theoretically small, and it is suitable for oxygen sensors such as e-free steel and light carbon steel.

On the other hand, as shown in Figure 2, the B4o/MoO2-based reference electrode corresponds to the saturated oxygen of molten steel with an oxygen partial pressure of 1600'C or higher, and is a solid oxygen reference electrode for measuring high oxygen concentrations. However, when used for low-oxygen molten steel, the partial pressure difference is large and the measurement error becomes large. Therefore, in principle, a Cr/Cr2O5 reference electrode is more advantageous in a low oxygen concentration region.

Under these circumstances, the inventors of the present invention have conducted extensive studies on improving the response of the 0r10r20s reference electrode, and have found that the above objective is satisfied when a specific metal or an oxide of the metal is added to the coexistence of the metal. The inventors discovered a Cr/Cr2O5 solid oxygen reference electrode and a scale, and completed the present invention.

That is, the present invention uses metallic chromium powder or metallic rim powder (!: Cr5Os powder 100 Tf, R part Ni Cr
Powder of a metal that forms an oxide that is more unstable than rOs and has a higher melting point than metallic chromium, or composed of 50 to 20 Oi parts of the metal powder and oxide powder of the metal coexisting. An object of the present invention is to provide an oxygen reference electrode for an oxygen sensor for molten metal, which is characterized by:

The present invention will be explained in more detail below.

The oxygen sensor for molten metal that is the object of the present invention is
/conial oxide as solid electrolyte, cr/Cr2O5
A well-known general-purpose diJL/conia oxidizer using as an oxygen reference electrode, for example, a so-called partially stabilized or stabilized zirconia oxide consisting of at least one of Y2OB, (:aO, TA0) and zirconia. This is an oxygen sensor that uses Or/CrrOs as a solid electrolyte and uses Or/CrrOs as an oxygen reference pole during use.The shape of the sensor is, for example, a plug type in which a solid electrolyte chip is glued to the tip of a glass tube such as quartz, a solid electrolyte, It can be applied to any type of tube formed by molding and sintering the solute.

The oxygen reference electrode of the present invention is made of Cr powder or Cr powder and Or
100 parts by weight of Cr2O5 powder of a metal that forms an unstable oxide and has a melting point higher than Or, or 50 to 20 parts by weight of the metal and its oxide powder.
This is a solid reference electrode constructed by adding and mixing 0 parts by weight.

Here, a metal powder that forms an oxide that is more unstable than Or sos and has an axis point higher than Or, or the metal powder and the metal oxide powder are at an angle of 1500 to 1800°.
Cr2O is produced by the reaction of metallic chromium with a metal oxide (e.g. MxOy) that falls under the above definition in the temperature range of C.
5 and metal M, and oxides of the metals, specifically molybdenum (Mo), molybdenum dioxide (MOO2), tungsten (W), and tungsten dioxide (WO2).

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 Or/ Since a waveform of Cr+Oa occurs, the response time becomes longer as a result, which is not preferable.

Or and Cr2 constituting the solid oxygen reference electrode in the present invention
A mixing ratio of 0 g is usually used in a range where the ratio of Cr 20B powder to Or powder ζ is 50% by weight or less. If the mixing ratio of Or 20a to Or exceeds 50% by weight, it is not suitable because the oxygen in the air remaining in the tube will not be removed quickly and the conductivity of the reference electrode will deteriorate. On the other hand, when the zirconia solid electrolyte container is packed with Cr powder constituting the reference electrode in an oxidizing atmosphere, the Cr powder generates oxides due to oxygen in the atmosphere.
It is also possible to use only the Cr powder without the 8 powder.

Such Cr powder or 20g Cr/Cr powder may be used as it is by being packed into a zirconia solid electrolyte container, but if it is sintered in advance and then pulverized for use, shrinkage due to sintering while immersed in molten steel etc. may occur. << is more preferable since the time to reach equilibrium is shorter. Furthermore, when sintering is performed in the presence of carbon and used after being crushed, the waveform characteristic of the Or/Cr20a reference electrode becomes V.
This is particularly recommended as it does not cause sagging and therefore significantly reduces response times.

In the present invention, M added to Cr/Cr20B
The proportion of metal such as oA1o02 and/or W/W02 and metal oxide is usually 10% by weight or less based on the metal powder. If the mixing ratio exceeds 10%, 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 the reason is that a small amount of the metal oxide as an additive is only present in the initial stages of Cr/Cr2.
The partial pressure of O3 is also higher than that of O3, so the difference in electromotive force shown in Figure 1 is compensated, and since the proportion of metal oxide in the additive is small, the difference in electromotive force is compensated for. The added metal oxide immediately completes its decomposition and does not significantly change the electromotive force value of the original reference electrode, and the remaining added metal acts as a sintering inhibitor for Crlorga8, and these two effects work together. Therefore, it is believed that the effects of the present invention can be achieved.

As detailed above, the present invention is achieved by simply mixing specific amounts of Mo and/or W metal powders and respective metal oxide powders with 20 g of Cr/Cr powder, which is the constituent material of the oxygen reference electrode conventionally used. This makes it possible to provide an oxygen sensor for melting and forging that stably indicates electromotive force and has excellent responsiveness, and its industrial value is extremely high.

EXAMPLES 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 70 parts by weight of metallic chromium powder and 30 parts by weight of Or 20B powder were mixed in a ball mill, sintered at 1300°C for 2 hours in a CO atmosphere, and then crushed and ground in a mortar to form Cr/20B powder with an average particle size of 5 μm. A Cr2O5 mixed powder was obtained.

The Cr/Cr+Oa mixed powder thus obtained is shown in Table 1 (
Mo/MoO2 and/or W/ shown in experimental points 2 to 7)
After adding WO2 mixed powder and mixing in a ball mill, the obtained mixed powder was made into a powder having an outer diameter of 5.6 rrm as shown in Fig. 3.
The bottom of a closed tube (2) of zirconia partially stabilized with 7 mol% MgO with a length of 35 mm was filled to form an oxygen reference electrode (1), and the reference electrode (1) was made of a molybdenum wire. The oxygen sensor was assembled by inserting the electrode (4) and further inserting and installing the reference electrode holding rod (3).

The oxygen sensor thus constructed was immersed in 1600°C molten steel melted by high frequency in an alumina crucible.
The electromotive force was observed and recorded for 0 seconds. The obtained results are shown in Sections 4 to 1.
Shown in Figure 0.

Further, a mixed powder consisting of 90 parts by weight of Or powder and 10 parts by weight of Cr 20Jl 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, it was crushed and crushed in a mortar, and the average particle size was 311 m (7).
Or/CrzOs% gold powder Table 1 Experiment A
The additives shown in No. 8 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 1-1 *Results of weight percent of oxide to metal powder in additives Experiments A 2 and 6 corresponding to the present invention.

7.8 shows that the response is significantly improved compared to the conventional oxygen sensor using an oxygen reference electrode made of Or/Crs+08 alone.

[Brief explanation of drawings]

Figures 1, 2, and 4 to 11 show electromotive force waveform diagrams shown by the oxygen sensor, and Figure 8 is a vertical cross-sectional view showing an outline of the oxygen sensor used in the example. 2 is a zirconia closed tube at one end, 3 is a reference pole holding rod,
4 indicates an electrode. Resident Aluminum 14 Lagoon, Lee Zhumu Company 4 Figure 5 Country 12 ALL 7 AIL Otsu No. 61 Garden Figure 7 15 AJL Ko 10 AQ
L No. 3 Fig. 8 Fig. 1 AAL E. 10 Fig. 72 Su - Country 9 No. 11 Concave 15i0

Claims (1)

[Claims] 1) Metal chromium powder or metal chromium powder and Cr20a
Powder 100! A powder of a metal that forms an oxide more unstable than 0r20a and has a melting point higher than that of metal chromium, or a powder of the metal and an oxide powder of the metal is added in an amount of 50 to 20%.
An oxygen reference electrode for an oxygen sensor for molten metal, characterized in that the oxygen reference electrode is configured such that 0 parts by weight coexist. 2) The oxygen reference electrode according to claim 1, wherein the ratio of Cr 20B powder to metal chromium powder is 50% by weight or less. 3゜3) Oxygen according to claim 1, wherein the proportion of the metal oxide to the metal chromium powder or the metal powder added to the metal chromium powder and the Or 20!1 powder is 10% by weight or less Reference pole. 2. The oxygen reference electrode according to claim 1, wherein the metal powder, or the metal powder and oxide of the metal, added to and coexisting with the metal powder is molybdenum and/or tungsten, and oxides of these metals. 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 2011 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 Cr20B powder.