JP3000692B2 - Sensor for measuring oxygen and metal concentration in molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration measuring element and a deoxidizing material for measuring the partial pressure of oxygen present in a molten metal using mullite, which is an oxygen ion conductor based on oxygen deficiency in a crystal structure. The present invention relates to a metal concentration measuring element (hereinafter simply referred to as a sensor) for quickly and accurately measuring the concentration of silicon or aluminum in a molten metal to be obtained.

[0002]

_2. Description of the Related Art Mullite is an oxygen ion conductor based on oxygen vacancies in the crystal structure, and is the only compound that exists stably under normal pressure in a binary system of Al ₂ O ₃ —SiO ₂ , and 3Al ₂
O ₃ · 2SiO ₂ is well known as the central composition. However, mullite can be obtained as a sintered body consisting of a single phase of mullite even if the respective components, Al ₂ O ₃ and SiO ₂ , are mixed in a molar ratio of 3: 2 and fired at a high temperature. It is difficult. Therefore, conventionally, mullite ceramics
Had been produced using a natural aluminum silicate and alumina, this time to form a glass phase consisting of alkali metal oxides and included as excess SiO ₂ and impurities from 3Al ₂ O ₃ · 2SiO ₂ composition, such The liquid phase sintering using a glass phase as a liquid phase resulted in a mullite phase-based sintered body.

[0003] Haber et al. (1906) found that such multi-phase coexisting ceramics had ionic conductivity.
However, they assumed that ionic conduction due to alkaline impurities was the main. Schuh et al. (1968) found that ceramics with an intermediate composition of mullite and sillimanite (Al ₂ O ₃ · SiO ₂ ) have oxygen ion conductivity. This property is based on the fact that Si atoms in crystals are replaced by Al atoms. It was argued that this was due to the oxygen ion vacancies generated in the reaction.

Further, Fischer and Janke (1969) have confirmed that mullite is an almost perfect oxygen ionic conductor at high temperatures and is superior to zirconia. However, the glass phase due to the alkali component coexisting in mullite ceramics causes the deterioration of corrosion resistance at high temperatures and has the disadvantage that the life of the crystal is short. Was not put to practical use.

In the refining of metals, it is important to quickly measure not only the oxygen concentration but also the silicon and aluminum concentrations in the metal. For example, in steel refining, dephosphorization and desulfurization of hot metal are frequently performed as pretreatment of a converter, but the reaction efficiency of the treating agent is greatly reduced by silicon in the hot metal. Therefore, it is necessary to change the addition amount of the treating agent according to the silicon concentration in the hot metal, and it is essential to quickly grasp the silicon concentration in the hot metal.

[0006] In steel refining, molten steel is deoxidized as a post-treatment of a converter. The treating agent is aluminum or an alloy containing aluminum as a main component. The addition of a large amount of aluminum is effective for deoxidation, but when the aluminum concentration in the molten steel is excessive, the mechanical properties of the steel are rather deteriorated. For this reason, it is indispensable to quickly grasp the aluminum concentration in the molten steel after the deoxidation treatment. Conventionally, chemical or instrumental analysis has been used to measure the silicon or aluminum concentration.However, even with emission spectroscopy, which is said to be the fastest, it takes about 10 minutes from sampling to obtaining measurement results. It does not satisfy quickness.

[0007] Today, a zirconia-based solid electrolyte is used as an oxygen sensor for molten metal. This zirconia-based solid electrolyte is composed of ZrO ₂ with CaO,
It is a sintered body to which MgO or Y ₂ O ₃ is added, and is known as an oxygen ion conductor through oxygen ion vacancies generated when Zr atoms in a crystal are replaced with atoms such as Ca. In terms of stability, reproducibility, and corrosion resistance of measured values at high temperatures,
Widely used as oxygen sensor for molten metal. By the way, the electromotive force E generated in the oxygen ion conductor is expressed by the following equation.

[0008]

(Equation 1)

Here, R: gas constant, T: absolute temperature, F: Faraday constant, Po ₂ : oxygen partial pressure of the standard electrode, Po ₂ ': oxygen partial pressure in the metal melt to be measured. This is a correction term due to conduction, and can be ignored if the solid electrolyte is sufficiently ionic conductive.

However, the zirconia solid electrolyte is
Under the environment of high temperature and low oxygen partial pressure, there is a disadvantage that electron conduction occurs in addition to ion conduction.In use, it is necessary to perform correction calculation using Pθ in equation (1) to obtain oxygen partial pressure, Therefore, the accuracy of the Pθ value becomes a problem. Further, in the case of zirconia, if carbon exists in the molten metal, zirconium carbide is generated on the surface of the solid electrolyte, and a correct oxygen partial pressure value cannot be obtained.

On the other hand, in recent years, a sensor for measuring silicon (aluminum) concentration using an oxygen concentration cell has been disclosed. These are roughly classified into the following three types. I) A so-called sub-electrode type in which an oxide or fluoride having a known activity of SiO ₂ or Al ₂ O ₃ is applied to the surface of a zirconia-based solid electrolyte used for oxygen concentration measurement (Japanese Patent Application Laid-Open No. 61-142455, JP-A-61-260155, JP-A-61-260156, JP-A-64-459, and JP-A-1
-203971). II) Stabilized or partially stabilized zirconia mixed with 1.5 to 25% by weight of silicate compound, molded and sintered
(JP-A-63-151846). III) those using molten slag mainly comprising CaO -SiO ₂ system as the electrolyte (JP-59-73763 JP).

[0012] The silicon concentration (
(Aluminum concentration) Among the sensors for measurement, those of the type I) above are based on oxygen partial pressure measurement using a zirconia solid electrolyte, so that the measurement error due to electron conductivity in zirconia at high temperature has been sufficiently solved. Is hard to say. Further, the electromotive force value and its stability vary depending on the thickness and the form of the coating film containing SiO ₂ or Al ₂ O ₃ . Furthermore, there are many problems, such as high cost due to fixing to the electrolyte by reheating.

On the other hand, in the case of the type II), the electromotive force changes due to the change in the activity of SiO ₂ in the electrolyte depending on the type of the compound, the amount of SiO ₂ and the firing conditions. In addition, it is necessary to strictly control the amount of the silicate compound in the electrolyte. Further, similarly to I), a measurement error due to electron conductivity in zirconia at a high temperature becomes a problem.

In the type III), since the electrolyte is a melt, it is difficult to hold the electrolyte at the interface between the hot metal and the reference electrode, and the reaction with the hot metal cannot be ignored. In these sensors, it is important to keep the activity of SiO ₂ or Al ₂ O _{3 on the} surface in contact with the hot metal constant. The reason is described below. When the sensor is immersed in hot metal, hot metal and Si
The equilibrium of equation (2) is established with O ₂ .

Si + 20 = SiO ₂ (electrolyte) (2) The equilibrium constant K of this reaction is expressed by the following equation (3). K = a _sio2 / (a _si · a ₀ ² ) = a _sio2 / (f _si [% Si] · a ₀ ² ) (3) where a _sio2 is the activity of SiO _{2 on} the electrolyte surface. , A _si and a ₀ are the activities of silicon and oxygen in the hot metal, respectively, f
_si and [% Si] are the activity coefficient and the weight% of silicon in the hot metal, respectively.

By transforming equation (3), equation (4) is obtained.

[% Si] = a _sio ² / a ₀ ² · 1 / (K · f _si ) ≒ C · a _sio ² / a ₀ ² (4) where C is represented by equation (4). You. log C = −log K−log f _si = −log K−Σe _si ⁽ⁱ⁾ [% i] (5) e _si ⁽ⁱ⁾ is a mutual representing the effect of the i component on the activity coefficient of Si. It is an operation assistance coefficient. According to Sigworth and Elliott, 16
At 00 ° C., the absolute value of e _si ⁽ⁱ⁾ other than C and O is 0.1
In the following, C can be regarded as a constant in a region where [% i] is small. On the other hand, e _si ^(c) is 0.18, and it is necessary to use different values of C between hot metal having a high C concentration and molten steel having a low C concentration. In any case, if a _sio2 is known in the equation (3), [% Si] can be obtained by measuring the electrolyte a ₀ .

On the other hand, a similar relationship holds between the hot metal and Al ₂ O ₃ . Al + 3/2 0 = 1/2 Al ₂ O ₃ (electrolyte) ・ ・ ・
(6) The equilibrium constant K for this reaction is expressed by equation (2). ^{_{K = a Al2o3 1/2 / (a}} Al · a 0 3/2) = a Al2o3 1/2 / (f Al [% Al] · a 0 3/2) ··· (7)
Where a _Al2o3 is the activity of Al ₂ O _{3 on} the electrolyte surface, a _Al
And a ₀ are the activities of silicon and oxygen in the hot metal, respectively, and f _Al and [% Al] are the activity coefficient and the weight% of aluminum in the molten metal, respectively.

By transforming equation (7), equation (8) is obtained. ^{_{[% Al] = a Al2o3 1/2}} / a 0 3/2 · 1 / (K · f Al) ≒ C · a Al2o3 1/2 / a 0 3/2 ··· (8) where, C is It is expressed by equation (9). log C = −log K−log f _Al = −log K−Σe _Al ⁽ⁱ⁾ [% i] (9) e _Al ⁽ⁱ⁾ is a mutual expression indicating the effect of the i component on the activity coefficient of Al. It is an operation assistance coefficient. As in the case of silicon described above,
According to Sigworth and Elliott, in an iron-based melt at 1600 ° C, the absolute value of e _Al ⁽ⁱ⁾ other than C and O is 0.06 or less, and C is regarded as a constant in the region where [% i] is small. Can be. On the other hand, e _Al ^(c) is 0.09. In equation (8), a
If _Al2o3 is known, by measuring the electrolyte a _0, can be obtained [% Al].

[0020]

As described above, zirconia-based solid electrolytes which have been widely used in the past can be used in a measurement environment in which a low oxygen partial pressure or carbon coexists at a high temperature, for example, in the case of vacuum degassing of molten steel. , It is not possible to directly and accurately measure the oxygen partial pressure in the molten metal. However, in the field of vacuum processing of non-ferrous metals, the need to directly measure the oxygen partial pressure in the molten metal with high accuracy has increased, and the development of an oxygen sensor applicable to such an environment has been demanded.

Further, in the conventional sensor for measuring silicon concentration (aluminum concentration), the coating form of the sub-electrode, coating thickness, and peeling at high temperature are important issues. In addition, it is not possible to quickly and accurately measure the concentrations of silicon and aluminum in hot metal, such as the fact that the amount of raw materials must be strict, the contribution of electron conduction cannot be ignored, and it easily reacts with hot metal at high temperatures. . Here, one object of the present invention is to provide an oxygen sensor for molten metal which directly and precisely measures the oxygen partial pressure in the molten metal under high temperature and low oxygen partial pressure or in the presence of carbon. Another object of the present invention is to provide a metal concentration measurement sensor for a molten metal that directly and accurately measures the concentration of a deoxidizer (silicon concentration and aluminum concentration) in the molten metal particularly at high temperatures and low oxygen partial pressures or in the presence of carbon. It is to provide.

[0022]

Means for Solving the Problems Accordingly, the present inventors have:
Focusing on the oxygen ion conductivity of mullite, various studies have been conducted, and regarding the deterioration of corrosion resistance and permeability as described above, the amount of impurities such as alkali metal oxides and other low melting point oxides has been reduced, and pores have been reduced. The inventors have found that the problem is solved by limiting the rate, and completed the present invention. Therefore, according to the present invention, in order to improve thermal shock resistance, corrosion resistance at high temperatures, and penetration resistance, oxygen ion conductivity at high temperatures is mainly controlled by setting the impurity concentration to 1% by weight or less and the porosity to 5% or less. Thus, an oxygen sensor made of a mullite solid electrolyte having a small effect on electron conductivity can be obtained.

In order to further improve the thermal shock resistance,
In addition, the mullite solid electrolyte is composed of 15% by weight or less of SiO ₂ and 20% by weight or less of Al ₂ O ₃ and / or 20% by weight or less of ZrO ₂ in order to improve corrosion resistance. And add. Meanwhile, mullite is itself a SiO ₂ -Al ₂ O ₃ -based compound, SiO ₂ excess and Al
Constant SiO ₂ activity and Al in both composition regions in excess of ₂ O ₃
Has ₂ O ₃ activity. Therefore, according to the present invention, as described above, the oxygen partial pressure is quickly measured with high accuracy, and the oxygen partial pressure and the oxygen activity are almost equal, and it is considered that the oxygen partial pressure is in a certain proportional relationship. According to the equations (4) and (8), the metal deoxidizer in equilibrium with oxygen in the molten metal, that is, the silicon concentration and the aluminum concentration can be quickly measured with high accuracy. completed.

Therefore, in order to improve the thermal shock resistance, corrosion resistance at high temperature, and permeation resistance, the present invention has an impurity concentration of 1%.
A sintered body made of a mullite solid electrolyte mainly containing oxygen ions at a high temperature and having little effect on electron conductivity by setting the porosity to 5% or less and the porosity to 5% or less ;
15% by weight or less of SiO ₂ and / or
Or 20% by weight or less of Al ₂ O ₃ and / or 20% by weight of ZrO ₂
%, Further comprising measuring the concentration of at least one of oxygen, silicon, and aluminum in the molten metal. As described above, according to the present invention, since the oxygen ion conductivity is higher than that of the zirconia-based material at a high temperature, the polarization phenomenon due to the contribution of electron conduction can be suppressed. In addition, a sensor that does not require a sub-electrode agent, can ignore errors due to electron conductivity, and is solid at the hot metal temperature and has excellent corrosion resistance.

[0025]

Next, the reason why the composition is limited in the present invention as described above will be described in detail. First, regarding the structure of mullite itself, according to Taylor (1933), sillimanite (A
l ₂ O ₃ · structure of SiO ₂₎ consists of AlO ₆ infinite octahedra chain, SiO ₄
And AlO ₄ are linked to each other via a double tetrahedral chain. Scholz (1955) describes the fourth Si of sillimanite
When the atoms were replaced by Al atoms and the number of oxygen atoms was appropriately reduced, the structure was distorted, resulting in mullite having oxygen ion vacancies. The generation of such oxygen ion vacancies is caused by the Zr atom in the crystal of the zirconia-based solid electrolyte.
It is similar to the formation of oxygen ion vacancies when substituted with an atom such as Ca. However, at higher temperatures in zirconia, mullite becomes an oxygen ion conductor because the Si-O bonds in mullite are stronger than the Zr-O bonds in zirconia.

[0026] Figure 1, SiO ₂ -Al ₂ O ₃ phase diagram and SiO ₂
The relationship between concentration and SiO ₂ activity and the relationship between Al ₂ O ₃ concentration and Al ₂ O ₃ activity are conceptually shown. SiO ₂ excess or Al over mullite composition
_{Since the} SiO ₂ activity and the Al ₂ O ₃ activity are each constant when the amount of ₂ O _{3 is} excessive, the degree of freedom in selecting the composition is large. In the mullite single-phase region, the SiO ₂ activity and Al ₂ O ₃ activity change according to the composition, so it is necessary to strictly control the composition. The problem is solved by making it to come to.

The mullite solid electrolyte is produced by molding and sintering high-purity mullite powder, and a mixture of silica and alumina in the high-purity mullite powder can also be used as a raw material. Therefore, these are collectively hereinafter referred to as a mullite sensor for measuring silicon concentration or measuring aluminum concentration. The mullite that constitutes the solid electrolyte oxygen sensor according to the present invention is 3Al ₂ O ₃ 2S
The basic composition is iO ₂ . However, the concentration of impurities such as alkali metal oxides and low melting point oxides in mullite must be 1% by weight or less in total. If the impurity concentration is higher than this, the thermal shock resistance and corrosion resistance of the mullite sintered body may be reduced. The porosity of the sintered body is
From the viewpoint of corrosion resistance and prevention of molten metal penetration, 5% or less is preferable.

At this time, SiO ₂ is used to improve thermal shock resistance.
15 wt% or less, and / or, Al ₂ O ₃ and, respectively 20 wt% to improve the corrosion resistance at least one of ZrO ₂ or less, Ru added alone or complexed in a ratio of. Addition of a larger amount than this is not preferable because it lowers the oxygen ion conductivity of mullite. Here, the method for producing the mullite ceramics according to the present invention will be described. First, 3Al ₂ O ₃ .2SiO _{2 as} a main raw material is coprecipitated, hydrothermal synthesis, spray pyrolysis, sol-gel method, alkoxide method. etc,
Either method may be used. It suffices if the concentration of impurities such as alkali metal oxides and other low melting point oxides is suppressed to 1% or less. In particular, the starting material may be highly purified to reduce the impurity level of the product.

To the raw material powder thus prepared, a molding aid such as polyvinyl alcohol is added according to a molding method, and the mixture is molded by a rubber press, a mold press, casting, injection, HIP or the like. 15 using gas furnace, high-frequency furnace, etc.
Bake at 00-1700 ° C for 1-5 hours. At this time, the porosity is 5
For example, the raw material particle size, the molding pressure, and the sintering temperature may be appropriately adjusted in order to make the content of the raw material or less. The mullite ceramic thus obtained may be used as it is as an oxygen sensor, or may be further pulverized, and then the additional compounding agent (Al ₂ O ₃ , SiO ₂ , ZrO ₂ ) ) May be added and then molded and sintered again. The sintering conditions at this time may be the same as in the case of the mullite sintering described above. In the present specification, mullite is generally referred to as a product containing such an additional compounding agent.

As described above, the mullite quality is 3Al ₂
Although the basic composition is O ₃ · 2SiO ₂ , the composition of the raw material powder does not necessarily need to be adjusted to this ratio, and Al ₂ O ₃ or SiO ₂
Can be added in excess of this proportion. in this case,
Components added in excess of the mullite solid solution region remain as they are after sintering. Therefore, the same effects as when Al ₂ O ₃ or SiO ₂ is added as an additional compounding agent as described above are expected. In particular, when the sensor according to the present invention is used for measuring the concentration of silicon or aluminum in molten metal,
In any of the above manufacturing methods, Al ₂ O ₃ or Si
It is preferable that the O ₂ excess amount.

[0031]

Embodiments will be described below. (Example 1)
A mullite oxygen sensor having the composition shown in Table 1 was prepared, immersed in molten carbon iron, and the temperature dependence of the oxygen partial pressure was measured. The mullite sensor is prepared by mixing the raw material into a predetermined structure (based on a molar ratio of Al ₂ O ₃ : SiO _{2 of} 3: 2), adding water to the mixture, pouring it into a gypsum mold, and discharging the slurry. And dried and then fired at 1650 ° C. for 3 hours. Its dimensions were an outer diameter of 5 mm, an inner diameter of 3.5 mm, a length of 40 mm, and a tubular shape.

For comparison, a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO, outer diameter 6 mm, inner diameter 4 mm, length 50
mm). FIG. 2 shows the procedure for measuring the electromotive force at this time. The solid electrolyte according to the present invention has a standard electrode inside, and an electrode is provided as a counter electrode opposite to the standard electrode. In the illustrated example, the temperature of the molten iron is simultaneously measured by a thermocouple.

Operating conditions Standard electrode: mixed powder of Mo and MoO ₂ Electrode: Mo rod (solid electrolyte side) Graphite rod (carbon saturated molten iron side) Crucible: graphite Atmosphere: high-purity argon Temperature: 1200-1500 ° C Are shown in Table 1 and FIG.

An impurity concentration of 1% by weight or less and a porosity of 5%
When the following mullite oxygen sensor according to the present invention was used, measurement was possible up to a high temperature of 1500 ° C.
Also, when 15% by weight or less of SiO ₂ was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al ₂ O ₃ and ZrO ₂ were mixed, excellent results were obtained. . In contrast, as shown in FIG. 3, the results with the zirconia solid electrolyte did not show correct temperature dependence. FIG. 3 shows the electromotive force of Sample No. 1 as an example of the present invention.

[0035]

[Table 1]

(Example 2) A mullite oxygen sensor shown in Table 2 was prepared, immersed in molten copper, and the change over time in oxygen partial pressure was measured. The measurement procedure was the same as in Example 1. The mullite oxygen sensor was obtained by molding a high-purity mullite raw material powder generated in advance by a rubber press and calcining the powder at 1650 ° C. for 3 to 5 hours. Its dimensions are 8mm outside diameter and 5 inside diameter
mm, length 36 mm, tubular shape. For comparison, a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO,
(mm, inner diameter 4 mm, length 50 mm).

Operating conditions Standard electrode: mixed powder of Mo and MoO ₂ Electrode: Mo rod Crucible: high-purity alumina Atmosphere: high-purity argon containing 5% by volume of hydrogen or high-purity argon Temperature: 1350 ° C. It is shown in FIG. FIG. 4 shows the change over time of the measured values.

An impurity concentration of 1% by weight or less and a porosity of 5%
When the following mullite oxygen sensor according to the present invention was used, there was no erosion and long-term measurement was possible.
On the other hand, in the measurement using an oxygen sensor made of a zirconia solid electrolyte, the electromotive force value decreased after a long time.
FIG. 5 shows changes in oxygen partial pressure when the atmosphere was changed from high-purity argon containing 5% by volume of hydrogen to high-purity argon. The value measured by the mullite oxygen sensor corresponded to the change in the oxygen partial pressure of the atmosphere, that is, the change in the oxygen partial pressure in the molten copper, whereas the value measured by the zirconia solid electrolyte did not change correctly. The test materials in FIGS. 4 and 5 are all sample Nos. In Table 2. One was used.

[0039]

[Table 2]

Example 3 A mullite oxygen sensor shown in Table 3 was prepared, immersed in molten iron containing no carbon, and the oxygen partial pressure was measured. The mullite oxygen sensor was prepared by mixing raw materials into a predetermined composition, molding the raw material by a rubber press, and firing at 1650 ° C. for 3 to 5 hours. Its dimensions are outer diameter 8mm, inner diameter 5mm, length 36
mm and bag-shaped. For comparison, a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO, outer diameter 6 mm, inner diameter 4
mm, length 50 mm). The measurement procedure was the same as in Example 1.

Operating conditions Standard electrode: mixed powder of Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod Crucible: high-purity alumina Atmosphere: high-purity argon or high-purity containing 5% by volume of hydrogen Argon temperature: 1600 ° C Table 3 shows the measurement results.

An impurity concentration of 1% by weight or less and a porosity of 5%
When the following mullite oxygen sensor according to the present invention was used, there was little erosion and continuous measurement was possible. In addition, when Al ₂ O ₃ or ZrO ₂ of 20% by weight or less is mixed,
Furthermore, the result which was excellent in corrosion resistance was obtained. FIG. 6 shows changes in the electromotive force when the atmosphere is changed from high-purity argon containing 5% by volume of hydrogen to high-purity argon. When the zirconia solid electrolyte was used, the corrosion resistance was better than that of the mullite type, but the change in the electromotive force value due to the change in the oxygen partial pressure was smaller than that of the mullite type oxygen sensor according to the present invention.

[0043]

[Table 3]

(Example 4) Sensors for measuring mullite silicon concentration shown in Table 4 were prepared, immersed in molten carbon saturated iron having variously changed silicon concentrations, and the dependency of electromotive force on silicon concentration was measured. In addition, the same sensor was immediately immersed in the carbon-saturated molten iron immediately from room temperature, and the thermal shock resistance was determined based on the electromotive force value. The mullite sensor is prepared by mixing the raw materials to a predetermined composition (Al ₂ O ₃ : SiO ₂ molar ratio of 3: 2
), Water was added thereto, and the slurry was poured into a plaster mold, molded by drainage, dried, and dried at 1650.
C. for 3 hours. Its dimensions are 5mm outside diameter,
The inner diameter was 3.5 mm, the length was 40 mm, and the bag was tubular. For comparison, a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO
, An outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 50 mm).

Operating conditions Standard electrode: Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod (solid electrolyte side) Graphite rod (carbon saturated molten iron side) Crucible: graphite or alumina Atmosphere: high purity argon Temperature: 1200-1500 ° C Table 4 shows the measurement results. When a mullite sensor having an impurity concentration of 1% by weight or less and a porosity of 5% or less was used, there was no erosion and measurement was possible up to a high temperature. Also,
When 15% by weight or less of SiO ₂ is mixed, it has thermal shock resistance,
When 20% by weight or less of Al ₂ O ₃ was mixed, excellent results were obtained in durability.

Using a mixed powder of Mo and MoO _{2 as} a standard electrode, 1500
FIG. 7 shows the result of examining the relationship between the silicon concentration and the electromotive force by melting the Fe-Si-4.5% C alloy in an alumina crucible at ℃. On the other hand, in the measurement using the zirconia solid electrolyte, it took more than 30 seconds for the electromotive force to stabilize, and the value did not show the correct silicon concentration dependency. The samples of Nos. 5 and 6 in Table 4 were used as examples of the present invention.

[0047]

[Table 4]

Example 5 A sensor for measuring mullite silicon concentration shown in Table 5 was prepared, immersed in molten copper, and the change with time of the oxygen partial pressure and the silicon concentration dependency were measured. Mullite Shitsuse Nsa is a raw material in the same manner as in Example 4 was formulated into a predetermined composition, which was molded by a rubber press, and fired at 1650 ° C. 3 to 5 hours. Its dimensions were an outer diameter of 8 mm, an inner diameter of 5 mm, a length of 36 mm, and a tubular shape. For comparison, a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% Ca
O, outer diameter 6 mm, inner diameter 4 mm, length 50 mm) were also measured at the same time.

Operating conditions Standard electrode: Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod Crucible: high-purity alumina Atmosphere: high-purity argon containing 5% by volume hydrogen Temperature: 1350 ° C. Measurement result Are shown in Table 5.

Next, FIG. 8 shows the change over time of the measured values when a mixed powder of Mo and MoO ₂ is used as the standard electrode and immersed in molten copper having a silicon concentration of 0.1%. Impurity concentration is 1% by weight
If the porosity with 5% or less of mullite Shitsuse Nsa is below melting without any was possible for a long time measurement.
Further, when 15% by weight or less of SiO ₂ was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al ₂ O ₃ was mixed, excellent results were obtained in durability. On the other hand, in the measurement using the zirconia solid electrolyte, the dependency on the silicon concentration was not obtained, and the electromotive force value decreased after a long time.

[0051]

[Table 5]

Example 6 A sensor for measuring mullite aluminum concentration shown in Table 6 was prepared, immersed in molten iron of carbon having various aluminum concentrations, and the dependence of electromotive force on aluminum concentration was measured. Further, the same sensor was immediately immersed in molten carbon iron immediately from room temperature, and the thermal shock resistance was determined based on the electromotive force value. The mullite sensor is prepared by mixing the raw materials into a predetermined composition (Al ₂ O ₃ : SiO ₂ molar ratio of 3: 2 as a reference composition), adding water to the mixture and pouring it into a gypsum mold and discharging. Molded with mud, dried and fired at 1650 ° C for 3 hours. Its dimensions were an outer diameter of 5 mm, an inner diameter of 3.5 mm, a length of 40 mm and a tubular shape. For comparison, measurements were also made with a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO, outer diameter 6 mm, inner diameter 4 mm, length 50 mm).

Operating conditions Standard electrode: Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod (solid electrolyte side) Graphite rod (carbon saturated molten iron side) Crucible: graphite or alumina Atmosphere: high purity argon Temperature: 1200-1500 ° C Table 6 shows the measurement results. When a mullite sensor having an impurity concentration of 1% by weight or less and a porosity of 5% or less was used, there was no erosion and measurement was possible up to a high temperature. Further, when 15% by weight or less of SiO ₂ was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al ₂ O ₃ was mixed, excellent results were obtained.

Next, a mixed powder of Mo and MoO ₂ was
FIG. 9 shows the result of examining the relationship between the aluminum concentration and the electromotive force by melting the Fe-Al-4.5% C alloy in an alumina crucible at 00 ° C. On the other hand, in the measurement using the zirconia solid electrolyte, it took more than 30 seconds for the electromotive force to stabilize, and the value did not show correct aluminum concentration dependence. In addition, the sample was used for No. 8 and No. 9 of Table 6 as an example of the present invention.

[0055]

[Table 6]

Example 7 A sensor for measuring mullite aluminum concentration shown in Table 7 was prepared, immersed in molten copper, and the change over time in oxygen partial pressure and the dependence on aluminum concentration were measured. Mullite Shitsuse capacitors <br/> over is a raw material in the same manner as in Example 6 were formulated into a predetermined composition, which was molded by a rubber press, and fired at 1650 ° C. 3 to 5 hours. The outer diameter is 8mm and the inner diameter is 5
mm, length 36 mm and bag-shaped tubular. For comparison, a commercially available zirconia solid electrolyte _(ZrO 2 _-11mo
1% CaO, outer diameter 6mm, inner diameter 4mm, length 50mm)
Was also measured at the same time.

Operating conditions Standard electrode: Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod Crucible: high-purity alumina Atmosphere: high-purity argon containing 5% by volume hydrogen Temperature: 1350 ° C. Are shown in Table 7. In particular, for the sample No. 1 and the zirconia solid electrolyte, FIG. 10 shows the change over time of the measured values when a mixed powder of the standard electrode Mo and MoO ₂ was used.

[0058] As can be seen from these results, when the impurity concentration porosity at 1 wt% or less with 5% or less of mullite Shitsuse <br/> Nsa is melting also without long Measurement was possible. When 15% by weight or less of SiO ₂ is mixed, 20% by weight or less of Al ₂ O
_In the case of mixing No. ₃ , excellent results were obtained in durability. On the other hand, in the measurement using the zirconia solid electrolyte, the aluminum concentration dependency cannot be obtained, and
The electromotive force value decreased after a long time.

[0059]

[Table 7]

Example 8 A mullite aluminum concentration measurement sensor shown in Table 8 was prepared, immersed in molten iron containing no carbon, and the aluminum concentration was measured. Mullite Shitsuse Nsa is a raw material in the same manner as in Example 6 were formulated into a predetermined composition, which was molded by a rubber press, and fired at 1650 ° C. 3 to 5 hours. Its dimensions are 8mm outside diameter, 5mm inside diameter, 36 length
mm in tubular shape. For comparison, a measurement was also performed simultaneously using a commercially available zirconia solid electrolyte (ZrO ₂ -11 mol% CaO, outer diameter 6 mm, inner diameter 4 mm, length 50 mm).

Operating conditions Standard electrode: Mo and MoO ₂ or mixed powder of Cr and Cr ₂ O ₃ Electrode: Mo rod Crucible: high-purity alumina Atmosphere: high-purity argon containing 5% by volume of hydrogen or high-purity argon : 1600 ° C Table 8 shows the measurement results.

An impurity concentration of 1% by weight or less and a porosity of 5%
When the following mullite sensor was used, there was little erosion and continuous measurement was possible. When 15% by weight or less of SiO ₂ was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al ₂ O ₃ was mixed, excellent results were obtained in durability. Next, Cr and Cr
FIG. 11 shows the dependency of the electromotive force value on the aluminum concentration when the mixed powder of ₂ O ₃ is used. As an example of the present invention, the sample No. 1, No. 2 was used. When using a zirconia solid electrolyte, corrosion resistance although better than that of mullite, a change in electromotive force due to the change of the aluminum concentration was less than mullite Shitsuse Nsa.

[0063]

[Table 8]

[0064]

As described above, the mullite oxygen sensor of the present invention can accurately measure the oxygen partial pressure, the silicon concentration, and the aluminum concentration in the molten metal at a higher temperature or in the presence of carbon than the zirconia sensor. It can be widely used as a sensor for measuring the concentration of oxygen and metal for molten metal.

[Brief description of the drawings]

FIG. 1 is a SiO ₂ —Al ₂ O ₃ system phase diagram and a graph showing the relationship between the concentration and activity of SiO ₂ and Al ₂ O ₃ .

FIG. 2 is an explanatory diagram of a measurement procedure of an electromotive force E in the embodiment.

FIG. 3 is a graph showing the temperature dependence of the electromotive force values measured by the mullite and zirconia sensors when measuring the oxygen partial pressure in the carbon-saturated molten iron.

FIG. 4 is a graph showing a change over time of an electromotive force value by a mullite and a zirconia sensor immersed in molten copper.

FIG. 5 is a graph showing a change in electromotive force by a mullite and zirconia sensor immersed in molten copper when the atmosphere is changed.

FIG. 6 is a graph showing a change in an electromotive force value by a mullite and a zirconia sensor immersed in molten iron when an atmosphere is changed.

FIG. 7 is a graph showing the silicon concentration dependency of the electromotive force value by the mullite and zirconia sensors when measuring the silicon concentration in the carbon-saturated molten iron.

FIG. 8 is a graph showing a change over time in an electromotive force value by a mullite and a zirconia sensor immersed in molten copper.

FIG. 9 is a graph showing the aluminum concentration dependency of the electromotive force value by the mullite and zirconia sensors when measuring the aluminum concentration in the carbon-saturated molten iron.

FIG. 10 is a graph showing a change over time of an electromotive force value by a mullite and a zirconia sensor immersed in molten copper.

FIG. 11 is a graph showing the aluminum concentration dependency of the electromotive force value by the mullite and zirconia sensors when measuring the aluminum concentration in the molten iron containing no carbon.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Chuji Kawai 1-3-1 Otemachi, Chiyoda-ku, Tokyo Sumitomo Metal Industries, Ltd. (72) Inventor Tadahisa Arahori 4-5-33 Kitahama, Chuo-ku, Osaka-shi No. Sumitomo Metal Industries Co., Ltd. (72) Inventor Kazuo Yamana 1st Tomicho, Kanazawa-shi Ishikawa Pref. Kuniaki Nakagawa 7-84 Matsumura, Kanazawa-shi Sumikin Hot-tonse Lamix Co., Ltd. Kawauchi Housing First District 3-203 (56) References Castings, 49 [7] (1977) p. 417-423 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/411

Claims (3)

(57) [Claims] 1. An oxygen ion conductor comprising a mullite solid electrolyte having an impurity of 1% by weight or less and a porosity of 5%.
The following sintered body, wherein the mullite solid electrolyte contains SiO ₂
A sensor for measuring the concentration of oxygen and metal in a molten metal, further comprising 15% by weight or less and / or 20% by weight or less of Al ₂ O ₃ . 2. A mullite solid electrolyte, which is an oxygen ion conductor, having an impurity of 1% by weight or less and a porosity of 5%.
The following sintered body, wherein the mullite solid electrolyte contains ZrO ₂
Oxygen in molten metal further containing up to 20% by weight
Sensor for measuring metal concentration. 3. The method according to claim 1, wherein the concentration of at least one of oxygen, silicon, and aluminum in the molten metal is measured.
Sensor for measuring metal concentration.