JPH04213050A - Sensor for measuring oxygen/metal concentration in fused metal - Google Patents

Abstract

PURPOSE:To measure the oxygen partial pressure in fused metal directly and accurately under the high temperature/low oxygen partial pressure or coexistence of carbon by using a sintered body which comprises mullite solid electrolyte that is an oxygen ion conductor and wherein the amount of impurities is a specified amount or less and porosity is a specified value or less. CONSTITUTION:Impurity concentration is made less than 1weight% and porosity is made less than 5% in order to improve thermal shock property and corrosion resistance and permeability resistance at high temperature. Thus, an oxygen sensor comprising mullite solid electrode wherein oxygen ion conductivity at high temperature is main and the effect of electron conductivity is less is obtained. It is preferable that SiO2 of 15weight% or less is added into the mullite solid electrolyte in order to improve the thermal shock property furthermore and Al2O3 of 20weight% or less and/or ZrO2 of 20weight% or less are added in order to improve the corrosion resistance. Therefore, the oxygen partial pressure is quickly measured in high accuracy. The components of metallic deoxidizing material which is in balance with oxygen in the fused metal, i.e., the concentration of silicon and the concentration of aluminum, can be quickly measured in high accuracy.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention uses mullite, which is an oxygen ion conductor based on oxygen vacancies in the crystal structure, to be used as an oxygen concentration measuring element for measuring the partial pressure of oxygen present in molten metal, and as a deoxidizing material. The present invention relates to a metal concentration measuring element (hereinafter simply referred to as a sensor) that quickly and accurately measures the silicon or aluminum concentration in molten metal.

0002

[Prior Art] Mullite is an oxygen ion conductor based on oxygen vacancies in the crystal structure, and is an oxygen ion conductor based on the 2
It is the only compound in the component system that exists stably under normal pressure, and 3Al2O3.2SiO2 is well known as the central composition. However, mullite has a ratio of powders of Al2O3 and SiO2, which are its constituent components, in a ratio of 3:2.
It is difficult to obtain a sintered body consisting of a single mullite phase even if the mixture is mixed at a molar ratio of Therefore,
Conventionally, mullite ceramics were manufactured using natural aluminum silicate and alumina, but at that time, 3A
A glass phase consisting of SiO2 in excess of the composition and alkali metal oxides contained as impurities was formed, and liquid-phase sintering using this glass phase as a liquid phase produced a sintered body mainly composed of a mullite phase. .

Haber et al. (1
(906), but they assumed that ionic conduction was mainly caused by alkali impurities. Schuh et al. (1968
) are mullite and sillimanite (Al2O3・SiO2
) was found to have oxygen ion conductivity in ceramics with an intermediate composition, and it was argued that this property was due to oxygen ion vacancies created when Si atoms in the crystal were replaced with Al atoms.

Furthermore, Fischer and Janke (
(1969) confirmed that mullite is a nearly perfect oxygen ion conductor at high temperatures, superior to zirconia. However, the glass phase caused by alkaline components that coexist in mullite ceramics causes deterioration of corrosion resistance at high temperatures and has the drawback of shortening the lifetime of the crystalline body.Although its existence has been known until now, its characteristics It was never put into practical use.

By the way, in the melting and refining of metals, it is important to quickly measure not only the oxygen concentration but also the silicon concentration and aluminum concentration in the metal. For example, in steel refining, dephosphorization and desulfurization of hot metal are frequently performed as pretreatment for converters, but the reaction efficiency of the treatment agent is greatly reduced by silicon in the hot metal. Therefore, it is necessary to change the amount of the treatment agent added depending on the silicon concentration in the hot metal, and it is essential to quickly grasp the silicon concentration in the hot metal.

Furthermore, in steel refining, molten steel is deoxidized as a post-treatment in a converter, and the treatment agent used is aluminum or an alloy containing aluminum as a main component. Addition of a large amount of aluminum is effective in deoxidizing, but
If the aluminum concentration in molten steel becomes excessive, the mechanical properties of the steel will rather deteriorate. Therefore, it is essential to quickly determine the aluminum concentration in molten steel after deoxidizing treatment. Conventionally, chemical analysis or instrumental analysis has been used to measure the silicon or aluminum concentration, but even with emission spectrometry, which is said to be the fastest method,
It takes about 10 minutes from sample collection to obtaining measurement results, which does not satisfy speed.

[0007] Today, oxygen sensors for molten metal that are in practical use are those made of a zirconia solid electrolyte. This zirconia-based solid electrolyte contains C in ZrO2.
It is a sintered body containing aO, MgO or Y2O3,
It is known as an oxygen ion conductor through oxygen ion vacancies created when Zr atoms in the crystal are replaced with atoms such as Ca. It is widely used as an oxygen sensor for molten metals due to its stability of measured values at high temperatures, reproducibility, and corrosion resistance. By the way, the electromotive force E generated in the oxygen ion conductor is expressed by the following equation.

[0008]

[Math 1]

[0009] Here, R: Gas constant, T: Absolute temperature, F: Faraday constant, Po2: Oxygen partial pressure at the standard electrode, Po2': Oxygen partial pressure in the metal melt to be measured. Also, Pθ
is a correction term due to electron conduction, and can be ignored if the solid electrolyte has sufficient ionic conductivity.

However, the zirconia solid electrolyte
It has the disadvantage that electronic conduction occurs in addition to ionic conduction in an environment of high temperature and low oxygen partial pressure, and when using it, it is necessary to perform correction calculations using Pθ in equation (1) to determine the oxygen partial pressure. Therefore, the accuracy of the Pθ value becomes a problem. Furthermore, in the case of a zirconia-based metal, if carbon is present in the molten metal, zirconium carbide is generated on the surface of the solid electrolyte, making it impossible to obtain a correct oxygen partial pressure value.

On the other hand, in recent years, a sensor for measuring silicon (aluminum) concentration using an oxygen concentration battery has been proposed. They can be roughly divided into the following three types. I) A so-called auxiliary electrode type in which an oxide or fluoride with a known SiO2 activity or Al2O3 activity is coated on the surface of a zirconia solid electrolyte used for oxygen concentration measurement (JP-A-61-142455) Publication, JP-A-61-260155, JP-A-61-260156
No. 1, JP-A-64-459, JP-A-1-20
Publication No. 3971). II) Stabilized or partially stabilized zirconia mixed with 1.5 to 25% by weight of a silicate compound, molded and sintered (Japanese Unexamined Patent Publication No. 151846/1984). III) Using molten slag mainly composed of CaO-SiO2 system as electrolyte (Japanese Unexamined Patent Publication No. 59-73
Publication No. 763).

[0012] The above silicon concentration (
Aluminum concentration) Among the measurement sensors, the above
Since type I) is based on oxygen partial pressure measurement using a zirconia solid electrolyte, it cannot be said that measurement errors due to electronic conductivity in zirconia at high temperatures have been sufficiently resolved. Furthermore, the electromotive force value and its stability vary depending on the thickness of the coating film containing SiO2 or Al2O3 and the form of coating. Furthermore, there are many problems such as high cost because it is fixed to the electrolyte by reheating.

On the other hand, in the type II), S in the electrolyte depends on the type of compound, the amount of SiO2, and the firing conditions.
Since the iO2 activity changes and the electromotive force changes, it is necessary to strictly control the amount of silicate compound in the electrolyte to improve the reproducibility of silicon concentration measurements. Also, similar to I), measurement errors due to the electronic conductivity in zirconia at high temperatures pose a problem.

In the type III), since the electrolyte is a melt, it is difficult to maintain it at the interface between the hot metal and the reference electrode, and furthermore, the reaction with the hot metal cannot be ignored. In these sensors, it is important to keep the SiO2 activity or Al2O3 activity of the surface in contact with the hot metal constant. The reason for this is explained below. When the sensor is immersed in hot metal, the equilibrium expressed by equation (2) is established between the hot metal and SiO2.

[0015] Si + 2 0 = SiO2 (electrolyte)
... (2) The equilibrium constant K of this reaction is (
3) Expressed by the formula. K = asio2/(asi・a02) =
asio2/(fsi[%Si]・a02)
...(3) Here, a sio2 is S on the electrolyte surface
The activity of iO2, asi and a0 are the activities of silicon and oxygen in hot metal, fsi and [%Si], respectively.
are the activity coefficient and weight percent of silicon in hot metal, respectively.

[0016] Equation (3) is transformed into equation (4).

[%Si] = asio2/a02 ・1/(K・f
si) ≒ C・asio2/a02
...(4) Here, C is expressed by the formula (4). log C = -log K- log fsi
= −log K− Σesi(i
)[%i] (5) esi(i) is an interaction co-efficient representing the influence of the i component on the Si activity coefficient. According to Sigworth and Elliott,
At 1600° C., the absolute value of esi(i) other than C and O is 0.1 or less, and in the region where [%i] is small, C can be regarded as a constant. On the other hand, esi(c)
is 0.18, and it is necessary to use different C values for hot metal with a high C concentration and molten steel with a low C concentration. In any case, (
3) If a sio2 is known in the formula, electrolyte a
By measuring 0, [%Si] can be determined.

On the other hand, a similar relationship holds true between hot metal and Al2O3. Al + 3/2 0 = 1/2 Al2O
3 (electrolyte)... (6) The equilibrium constant K of this reaction is expressed by the formula (2). K = aAl2o31/2/(aAl・a03/2
) = aAl2o31/2/(fAl[%Al
]・a03/2) ...(7) Here, aAl2o3 is Al2O3 on the electrolyte surface.
, aAl and a0 are the activities of silicon and oxygen in the hot metal, respectively, and fAl and [%Al] are the activity coefficient and weight % of aluminum in the molten metal, respectively.

[0019] Equation (7) is transformed into equation (8). [%Al] = aAl2o31/2/a03/2 ・
1/(K・fAl) ≒ C・aAl2o
31/2/a03/2 (8) Here, C is represented by the formula (9). log C = -log K- log fAl
= −log K− ΣeAl(i
)[%i] (9) eAl(i) is an interaction co-factor representing the influence of the i component on the activity coefficient of Al. As in the case of silicon mentioned above, Sigwort
According to H and Elliott, the absolute value of eAl(i) other than C and O in an iron-based melt at 1600°C is 0.
．． 06 or less, and in a region where [%i] is small, C can be regarded as a constant. On the other hand, eAl(c) is 0.0
It is 9. If a Al2o3 is known in equation (8), [%Al
] can be found.

[0020]

[Problems to be Solved by the Invention] As described above, zirconia-based solid electrolytes that have been widely used in the past cannot be used in measurement environments with high temperatures, low oxygen partial pressures, or carbon coexistence, such as in the case of vacuum degassing treatment of molten steel. , it is not possible to directly measure the oxygen partial pressure in the molten metal with high accuracy. However, today there is an increasing need to directly and accurately measure the oxygen partial pressure in molten metals in the field of vacuum processing of nonferrous metals, and there is a need to develop oxygen sensors that can be applied to such environments.

[0021] Furthermore, the silicon concentration (
For sensors for measuring aluminum concentration, important issues are the coating form of the sub-electrode, coating thickness, and peeling at high temperatures. In addition, it is not possible to quickly and precisely measure the silicon and aluminum concentrations in hot metal due to the necessity of exacting the blending amount of raw materials, the inability to ignore the contribution of electronic conduction, and the fact that they easily react with hot metal at high temperatures. . Here,
One object of the present invention is to provide an oxygen sensor for molten metal that directly and accurately measures the oxygen partial pressure in molten metal, particularly at high temperatures and low oxygen partial pressures or in the presence of carbon. Another object of the present invention is to provide a metal concentration measurement sensor for molten metal that directly and accurately measures the concentration of deoxidizing agents (silicon concentration and aluminum concentration) in molten metal, especially under high temperature, low oxygen partial pressure, or coexistence of carbon. The goal is to provide the following.

[0022]

[Means for solving the problem] Therefore, the present inventors
Various studies have been conducted focusing on the oxygen ion conductivity of mullite, and in order to reduce the amount of impurities such as alkali metal oxides and other low melting point oxides, as well as to reduce the amount of pores in order to prevent the deterioration of corrosion resistance and permeability as mentioned above. They discovered that the problem can be solved by limiting the rate, and have completed the present invention. Therefore, according to the present invention, in order to improve thermal shock resistance, corrosion resistance, and permeation resistance at high temperatures, the impurity concentration is set to 1% by weight or less and the porosity is set to 5% or less, so that the oxygen ion conductivity is mainly maintained at high temperatures. Thus, an oxygen sensor made of a mullite solid electrolyte with little influence on electronic conductivity can be obtained.

Furthermore, preferably, in order to further improve thermal shock resistance, SiO2 is added to the mullite solid electrolyte.
15% by weight or less, and to improve corrosion resistance, 20% by weight or less Al2O3 and/or ZrO2
Up to 20% by weight of these are added individually or in combination. On the other hand, mullite itself is SiO2-Al2
It is an O3-based compound, with excess SiO2 and Al2O3
Both excess composition regions have constant SiO2 activity and Al2O3 activity, respectively. Therefore, as described above, according to the present invention, the oxygen partial pressure can be measured quickly with high accuracy, and since the oxygen partial pressure and the oxygen activity are almost equal and are considered to have a certain proportional relationship, the above-mentioned ( 4) We learned that the metal deoxidizer components in equilibrium with oxygen in molten metal, namely silicon concentration and aluminum concentration, can be rapidly measured with high accuracy according to equations and (8), and we developed the present invention. completed.

[0024] Therefore, from another aspect, the present invention aims to improve thermal shock resistance, corrosion resistance at high temperatures, and permeation resistance.
By setting the impurity concentration to 1% by weight or less and the porosity to 5% or less, oxygen, silicon, and a sensor for measuring the concentration of at least one of aluminum. As described above, according to the present invention, since the oxygen ion conductivity is higher than that of the zirconia type material at high temperatures, it is possible to suppress the polarization phenomenon due to the contribution of electron conduction. Furthermore, a sensor that does not require an auxiliary electrode material, can ignore errors due to electronic conductivity, and is solid at hot metal temperatures and has excellent corrosion resistance.

[0025]

[Operation] Next, the reason for limiting the composition as described above in the present invention will be explained in detail. First, regarding the structure of mullite itself, according to Taylor (1933), the structure of sillimanite (Al2O3・SiO2) is AlO
It consists of 6 infinite octahedral chains, which are interconnected through double tetrahedral chains of SiO4 and AlO4. Scholz
(1955) proposed that each fourth Si atom in sillimanite is replaced by an Al atom, and oxygen atoms are appropriately reduced, causing distortion in the structure and forming mullite with oxygen ion vacancies. The generation of such oxygen ion vacancies is similar to the generation of oxygen ion vacancies when Zr atoms in the crystal are replaced with atoms such as Ca in a zirconia-based solid electrolyte. However, because the Si-O bonds in mullite are stronger compared to the Zr-O bonds in zirconia, mullite becomes an oxygen ion conductor at higher temperatures in zirconia.

FIG. 1 shows the SiO2-Al2O3 system phase diagram, SiO2 concentration, SiO2 activity, and Al2O
The relationship between Al2O3 concentration and Al2O3 activity is conceptually shown. Since the SiO2 activity and the Al2O3 activity are each constant when SiO2 or Al2O3 is in excess of the mullite composition, there is a large degree of freedom in composition selection. In the mullite single phase region, SiO2 activity and Al2O3 vary depending on the composition.
Since the activity changes, it is necessary to strictly control the composition, but the problem can be solved by preparing the raw material powder of mullite composition in advance so that it is in the excess region as described above.

The mullite solid electrolyte is produced by molding and sintering high-purity mullite powder, but a mixture of silica and alumina with the high-purity mullite powder can also be used as a raw material. Therefore, these will be collectively referred to as mullite sensors for silicon concentration measurement or aluminum concentration measurement. The mullite constituting the solid electrolyte oxygen sensor according to the present invention is 3Al2O
The basic composition is 3.2SiO2. However, the total concentration of impurities such as alkali metal oxides and low melting point oxides in mullite must be 1% by weight or less. If the impurity concentration is higher than this, the thermal shock properties of the mullite sintered body,
This is because corrosion resistance may decrease. Further, the porosity of the sintered body is preferably 5% or less from the viewpoint of corrosion resistance and prevention of penetration of molten metal.

At this time, SiO2 is used alone in a proportion of 15% by weight or less in order to improve thermal shock resistance, and/or at least one of Al2O3 and ZrO2 is individually contained in a proportion of 20% by weight or less in order to improve corrosion resistance. Or it can be added in combination. Addition of a larger amount than this is not preferable because it lowers the oxygen ion conductivity of mullite. Here, to explain the method for manufacturing mullite ceramics according to the present invention, first, 3Al, which is the main raw material,
2O3.2SiO2 may be produced by any method such as a coprecipitation method, a hydrothermal synthesis method, a spray pyrolysis method, a sol-gel method, or an alkoxide method. It is sufficient that 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 materials may be highly purified to reduce the level of impurities in the product.

[0029] A molding aid such as polyvinyl alcohol is added to the raw material powder prepared in this way according to the molding method, and the mixture is processed by rubber press, mold press, casting, injection, HIP.
After molding using an electric furnace, gas furnace, high frequency furnace, etc., it is fired at 1500 to 1700°C for 1 to 5 hours. At this time, in order to make the porosity 5% or less, for example, the particle size of the raw material,
The molding pressure and sintering temperature may be adjusted as appropriate. The mullite ceramic thus obtained may be used as it is as an oxygen sensor, or it may be further pulverized and then added with additional compounding agents (Al2O3, SiO3) in an amount within the above range.
2. One or more types of ZrO2) may be added and molded and sintered again. The sintering conditions at this time may be the same as in the case of sintering the mullite described above. In this specification, products containing such additional ingredients are collectively referred to as mullite.

[0030] As mentioned above, the mullite quality is 3A
The basic composition is 12O3.2SiO2, but the composition of the raw material powder does not necessarily need to be adjusted to this ratio;
It is also possible to add 2O3 or SiO2 in excess of this proportion. In this case, the components added in excess from the mullite solid solution region remain as they are after sintering, so as mentioned above, A
Similar effects are expected when 12O3 or SiO2 is added as an additional compounding agent. In particular, when the sensor according to the present invention is used to measure the concentration of silicon or aluminum in molten metal, it is preferable to incorporate an excessive amount of Al2O3 or SiO2 in any of the above-mentioned manufacturing methods.

[0031]

[Example] Examples will be described below. (Example 1
) A mullite oxygen sensor having the composition shown in Table 1 was prepared,
The temperature dependence of oxygen partial pressure was measured by immersing it in carbon-saturated molten iron. Mullite sensors are made by mixing raw materials into a predetermined structure (based on an Al2O3:SiO2 molar ratio of 3:2).
This was made into a slurry by adding water, poured into a plaster mold, molded by draining the slurry, dried, and then fired at 1650°C for 3 hours. Its dimensions are outer diameter 5mm and inner diameter 3.5mm.
mm, length 40 mm, and shaped like a bag tube.

For comparison, measurements using a commercially available zirconia solid electrolyte (ZrO2-11 mol % CaO, outer diameter 6 mm, inner diameter 4 mm, length 50 mm) were also carried out at the same time. FIG. 2 shows how to measure the electromotive force at this time. The solid electrolyte according to the present invention includes a standard electrode therein, and an electrode is provided as a counter electrode in opposition to the standard electrode. In the illustrated example, the temperature of the molten iron is also measured at the same time by a thermocouple.

[0033] Operating conditions Standard electrode: mixed powder of Mo and MoO2 Electrode: Mo rod (solid electrolyte side) Graphite rod (carbon saturated molten iron side) Crucible: graphite Atmosphere: High purity argon Temperature: 1200-1500℃ The measurement results are shown in Table 1 and FIG. 3.

[0034] Impurity concentration is 1% by weight or less and porosity is 5%.
When the following mullite oxygen sensor according to the present invention was used, measurement up to a high temperature of 1500°C was possible. Further, when 15% by weight or less of SiO2 was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al2O3 and ZrO2 were mixed, excellent results were obtained in durability. On the other hand, as shown in FIG. 3, the results using the zirconia solid electrolyte did not show correct temperature dependence. In addition, FIG. 3 shows sample No. 3 as an example of the present invention. Indicates the electromotive force of 1.

[0035]

[Table 1]

(Example 2) Mullite oxygen sensors shown in Table 2 were manufactured and immersed in molten copper to measure changes in oxygen partial pressure over time. The measurement procedure was the same as in Example 1. The mullite oxygen sensor is made by molding pre-generated high-purity mullite raw material powder using a rubber press and heating it at 1650°C for 3 to 30 minutes.
It was baked for 5 hours. Its dimensions are 8mm outside diameter
, had an inner diameter of 5 mm, a length of 36 mm, and was shaped like a bag tube. For comparison, a commercially available zirconia solid electrolyte (ZrO2-1
1 mol% CaO, outer diameter 6 mm, inner diameter 4 mm, length 50
Measurements in mm) were also carried out at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 Electrode: Mo rod Crucible: High purity alumina Atmosphere: High purity argon containing 5% by volume hydrogen or high purity argon Temperature: 1350°C Measurement results are shown in Table 2. Shown below. Figure 4 shows the changes in measured values over time.

[0038] Impurity concentration is 1% by weight or less and porosity is 5%.
When the following mullite oxygen sensor according to the present invention was used, there was no erosion loss and long-term measurement was possible. On the other hand, when measured using a temperature sensor made of a zirconia solid electrolyte, the electromotive force value decreased after a long period of time. Further, FIG. 5 shows the change in oxygen partial pressure when the atmosphere was changed from high purity argon containing 5% hydrogen by volume to high purity argon. While the values measured by the mullite oxygen sensor corresponded to changes in the partial pressure of oxygen in the atmosphere, that is, the partial pressure of oxygen in the molten copper, the values measured by the zirconia solid electrolyte did not change correctly. The test materials in FIGS. 4 and 5 are all sample No. 2 in Table 2. 1 was used.

[0039]

[Table 2]

(Example 3) Mullite oxygen sensors shown in Table 3 were produced and immersed in carbon-free molten iron to measure oxygen partial pressure. The mullite oxygen sensor was prepared by mixing raw materials to a predetermined composition, molding the molded material using a rubber press, and firing it at 1650° C. for 3 to 5 hours. Its dimensions are outer diameter 8mm and inner diameter 5mm.
It had a length of 36 mm and a bag tube shape. For comparison, a commercially available zirconia solid electrolyte (ZrO2-11 mol% Ca
Measurements were also made at the same time. The measurement procedure was the same as in Example 1.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2
O3 mixed powder electrode: Mo bar Crucible: High purity alumina Atmosphere: High purity argon containing 5% by volume hydrogen or high purity argon Temperature: 1600°C The measurement results are shown in Table 3.

[0042] Impurity concentration is 1% by weight or less and porosity is 5%
When the following mullite oxygen sensor according to the present invention was used, there was little erosion loss and continuous measurement was possible. Further, when 20% by weight or less of Al2O3 and ZrO2 were mixed, even better corrosion resistance was obtained. FIG. 6 shows the change in the electromotive force value when the atmosphere was changed from high-purity argon containing 5% hydrogen by volume to high-purity argon. When a zirconia solid electrolyte was used, the corrosion resistance was superior to that of a mullite type electrolyte, but the change in electromotive force value due to a change in oxygen partial pressure was smaller than in the case of the mullite type oxygen sensor according to the present invention.

[0043]

[Table 3]

(Example 4) Mullite silicon concentration measurement sensors shown in Table 4 were prepared and immersed in carbon-saturated molten iron with various silicon concentrations to measure the dependence of electromotive force on silicon concentration. In addition, the same sensor was immediately immersed in the carbon-saturated molten iron from room temperature repeatedly.
Thermal shock resistance was determined based on the electromotive force value. Mullite sensors are manufactured by mixing raw materials into a predetermined composition (Al2O3:SiO
The standard composition was a molar ratio of 3:2), which was made into a slurry by adding water to it, poured into a plaster mold, molded by draining the slurry, dried, and then fired at 1650°C for 3 hours. Its dimensions are outer diameter 5mm, inner diameter 3.5mm, length 4
It was 0 mm and had a bag-tubular shape. For comparison, a commercially available zirconia solid electrolyte (ZrO2-11mol%CaO
, outer diameter 6 mm, inner diameter 4 mm, and length 50 mm) were also measured at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2O3 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 The measurement results are shown in Table 4. When a mullite sensor with an impurity concentration of 1% by weight or less and a porosity of 5% or less was used, there was no melting loss and measurement was possible up to high temperatures. Also, 1
When 5% by weight or less of SiO2 was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al2O3 was mixed, excellent results were obtained in durability.

A mixed powder of Mo and MoO2 was used as a standard electrode, and Fe-Si-4.5 was heated in an alumina crucible at 1500°C.
%C alloy was melted and the relationship between silicon concentration and electromotive force was investigated. The results are shown in FIG. On the other hand, in measurements using a zirconia solid electrolyte, it took more than 30 seconds for the electromotive force to stabilize, and the value did not show correct dependence on silicon concentration. Note that No. 4 in Table 4 is an example of the present invention. 5, No.
6 samples were used.

[0047]

[Table 4]

(Example 5) A sensor for measuring mullite silicon concentration shown in Table 5 was produced and immersed in molten copper to measure the temporal change in oxygen partial pressure and silicon concentration dependence. The mullite oxygen sensor was prepared by mixing raw materials to a predetermined composition in the same manner as in Example 4, molding this using a rubber press, and baking it at 1650° C. for 3 to 5 hours. Its dimensions are outer diameter 8mm and inner diameter 5mm.
It had a length of 36 mm and a bag tube shape. For comparison, commercially available zirconia solid electrolyte (ZrO2-11mol%C
aO, outer diameter 6 mm, inner diameter 4 mm, length 50 mm) was also measured at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2O3 Electrode: Mo rod Crucible: High purity alumina Atmosphere: High purity argon containing 5% by volume hydrogen Temperature:
Table 5 shows the measurement results at 1350°C.

Next, FIG. 8 shows the change in measured values over time when the standard electrode was immersed in molten copper with a silicon concentration of 0.1% using a mixed powder of Mo and MoO2. When a mullite oxygen sensor with an impurity concentration of 1% by weight or less and a porosity of 5% or less was used, there was no melting damage and long-term measurement was possible. Furthermore, when 15% by weight or less of SiO2 was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al2O3 was mixed, excellent results were obtained in durability. On the other hand, in measurements using a zirconia solid electrolyte, silicon concentration dependence was not obtained and the electromotive force value decreased after a long period of time.

[0051]

[Table 5]

(Example 6) Mullite aluminum concentration measurement sensors shown in Table 6 were produced and immersed in carbon-saturated molten iron with various aluminum concentrations to measure the dependence of electromotive force on aluminum concentration. In addition, the same sensor was repeatedly immersed in carbon-saturated molten iron immediately from room temperature, and the thermal shock resistance was determined based on the electromotive force value. Mullite sensors are manufactured by mixing raw materials into a predetermined composition (Al2O3:SiO2 molar ratio 3:2).
(standard composition), water was added to this to form a slurry, which was then poured into a plaster mold, molded by removing mud, and after drying,
It was fired at 1650°C for 3 hours. Its dimensions were an outer diameter of 5 mm, an inner diameter of 3.5 mm, and a length of 40 mm, and was shaped like a bag tube. For comparison, measurements using a commercially available zirconia solid electrolyte (ZrO2-11 mol % CaO, outer diameter 6 mm, inner diameter 4 mm, length 50 mm) were also conducted at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2O3 Electrode: Mo rod (solid electrolyte side) Graphite rod (carbon saturated molten iron side) Crucible: graphite or alumina Atmosphere: High purity argon Temperature: 1200 Table 6 shows the measurement results at ~1500°C. When a mullite sensor with an impurity concentration of 1% by weight or less and a porosity of 5% or less was used, there was no melting loss and measurement was possible up to high temperatures. In addition, SiO of 15% by weight or less
When 2 was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al2O3 was mixed, excellent results were obtained in durability.

Next, a mixed powder of Mo and MoO2 was used as a standard electrode, and Fe-Al-4.
Figure 9 shows the results of melting a 5% C alloy and examining the relationship between aluminum concentration and electromotive force. On the other hand, in measurements using a zirconia solid electrolyte, it takes 30 minutes until the electromotive force stabilizes.
It took more than a second, and the value did not show correct dependence on aluminum concentration. Note that No. 6 in Table 6 is an example of the present invention. 8
, No. Sample No. 9 was used.

[0055]

[Table 6]

(Example 7) A sensor for measuring mullite aluminum concentration shown in Table 7 was produced and immersed in molten copper to measure the temporal change in oxygen partial pressure and the dependence on aluminum concentration. The mullite oxygen sensor is prepared by mixing raw materials to a predetermined composition in the same manner as in Example 6,
This was molded using a rubber press and heated to 1650°C for 3 to 5 minutes.
It is baked for hours. Its dimensions were an outer diameter of 8 mm, an inner diameter of 5 mm, and a length of 36 mm, and was shaped like a bag tube. For comparison, a commercially available zirconia solid electrolyte (ZrO2-11m
ol%CaO, outer diameter 6mm, inner diameter 4mm, length 50
Measurements in mm) were also carried out at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2O3 Electrode: Mo rod Crucible: High purity alumina Atmosphere: High purity argon containing 5% by volume hydrogen Temperature:
Table 7 shows the measurement results at 1350°C. Especially sample no. Regarding No. 1 and the zirconia solid electrolyte, FIG. 10 shows the changes over time in the measured values when a mixed powder of standard electrode Mo and MoO2 was used.

[0058] As can be seen from these results, when a mullite oxygen sensor with an impurity concentration of 1% by weight or less and a porosity of 5% or less is used, long-term measurement is possible without erosion loss. there were. In addition, when 15% by weight or less of SiO2 is mixed, the thermal shock resistance is improved, and when 20% by weight or less of Al is mixed.
When 2O3 was mixed, excellent results in durability were obtained. In contrast, in measurements using a zirconia solid electrolyte, no dependence on aluminum concentration was obtained, and the electromotive force value decreased after a long period of time.

[0059]

[Table 7]

(Example 8) A mullite aluminum concentration measuring sensor shown in Table 8 was prepared and immersed in carbon-free molten iron to measure the aluminum concentration. The mullite oxygen sensor was prepared by mixing raw materials to a predetermined composition in the same manner as in Example 6, and molding this using a rubber press.
It was baked at ℃ for 3 to 5 hours. Its dimensions were an outer diameter of 8 mm, an inner diameter of 5 mm, and a length of 36 mm, and was shaped like a bag tube. For comparison, a commercially available zirconia solid electrolyte (ZrO
2-11mol%CaO, outer diameter 6mm, inner diameter 4mm
, length 50 mm) was also measured at the same time.

Operating conditions Standard electrode: Mixed powder of Mo and MoO2 or Cr and Cr2O3 Electrode: Mo rod Crucible: High purity alumina Atmosphere: High purity argon containing 5% by volume hydrogen or high purity argon Temperature: 1600°C Measurement The results are shown in Table 8.

[0062] Impurity concentration is 1% by weight or less and porosity is 5%.
When the following mullite sensor was used, there was little erosion and continuous measurement was possible. Furthermore, when 15% by weight or less of SiO2 was mixed, excellent results were obtained in thermal shock resistance, and when 20% by weight or less of Al2O3 was mixed, excellent results were obtained in durability. Next, add Cr and C to the standard electrode.
FIG. 11 shows the aluminum concentration dependence of the electromotive force value when a mixed powder of r2O3 is used. As an example of the present invention, sample No. in Table 8 is used. 1.No. 2 was used. When a zirconia solid electrolyte was used, the corrosion resistance was superior to that of a mullite type sensor, but the change in electromotive force value due to changes in aluminum concentration was smaller than that of a mullite type oxygen sensor.

[0063]

[Table 8]

[0064]

[Effects of the Invention] As described above, the mullite oxygen sensor of the present invention can accurately measure oxygen partial pressure, silicon concentration, and aluminum concentration in molten metal at high temperatures or in the presence of carbon, compared to zirconia-based sensors. It can be widely used as a sensor for measuring oxygen and metal concentration in molten metal.

[Brief explanation of the drawing]

[Figure 1] SiO2-Al2O3 system phase diagram and SiO
2 is a graph showing the relationship between concentration and activity of Al2O3 and Al2O3.

FIG. 2 is an explanatory diagram of a procedure for measuring electromotive force E in an example.

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

FIG. 4 is a graph showing changes over time in electromotive force values of mullite and zirconia sensors immersed in molten copper.

FIG. 5 is a graph showing changes in electromotive force values of mullite and zirconia sensors immersed in molten copper when the atmosphere is changed.

FIG. 6 is a graph showing changes in electromotive force values of mullite and zirconia sensors immersed in molten iron when the atmosphere is changed.

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

FIG. 8 is a graph showing changes over time in electromotive force values of mullite and zirconia sensors immersed in molten copper.

FIG. 9 is a graph showing the dependence of electromotive force values on aluminum concentration using mullite and zirconia sensors when measuring aluminum concentration in carbon-saturated molten iron.

FIG. 10 is a graph showing changes over time in electromotive force values of mullite and zirconia sensors immersed in molten copper.

FIG. 11 is a graph showing the dependence of electromotive force values on aluminum concentration using mullite and zirconia sensors when measuring aluminum concentration in molten iron that does not contain carbon.

Claims (4)

[Claims] [Claim 1] Consists of a mullite solid electrolyte that is an oxygen ion conductor, contains impurities of 1% by weight or less, and has a porosity of 5.
A sensor for measuring oxygen and metal concentration in molten metal, characterized by being a sintered body of less than %. [Claim 2] SiO2 in the mullite solid electrolyte
The sensor for measuring oxygen/metal concentration in molten metal according to claim 1, further comprising 15% by weight or less and/or 20% by weight or less Al2O3. [Claim 3] ZrO2 is added to the mullite solid electrolyte.
Claim 1 or 2 further containing 20% by weight or less
The sensor for measuring oxygen and metal concentration in molten metal described above. 4. The method for measuring oxygen/metal concentration in molten metal according to any one of claims 1 to 3, which measures the concentration of at least one of oxygen, silicon, and aluminum in molten metal. sensor.