JP2868920B2 - Element for measuring oxygen 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 element used for measuring the oxygen concentration of a molten metal, wherein the element has a structure in which a coating layer is provided on the outer peripheral surface of a solid electrolyte body in contact with the molten metal. It relates to a concentration measuring element.

[0002]

2. Description of the Related Art Conventionally, an oxygen ion conductive solid electrolyte such as zirconia has been used to form a closed-end cylindrical shape with one side closed, and a solid electrode mixed with a metal-metal oxide is sealed inside the inside, and outside the solid electrode. 2. Description of the Related Art A sensor element having a structure provided with a coating layer of a metal oxide or the like is known. In the sensor element having the above-described structure, when the element is put into the molten metal, the coating layer sinters and shrinks in the high-temperature molten metal, causing peeling and cracking, and changing the contact area between the molten metal and the solid electrolyte. Therefore, there is a problem that a stable electromotive force waveform cannot be obtained. It is also conceivable that the thickness of the coating layer is set to 100 μm or more in order to eliminate peeling and cracking of the coating layer.
Then, the problem that response time becomes slow occurred.

[0003]

In order to solve the above-mentioned problems such as peeling of the coating layer, a technique of including CaF ₂ having a binder effect at a high temperature in the coating layer has recently been proposed, for example, in Japanese Patent Publication No. 61-1986. It is disclosed in Japanese Patent No. 47377. However, conventionally, in order to exert this binder effect, a large amount of CaF ₂ must be added, and if a large amount of CaF ₂ is added, the melting point of the coating layer decreases, and as a result, foaming and melting occur, and There is a problem that the contact area between the metal and the solid electrolyte changes, and a stable electromotive force waveform cannot be obtained.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an element for measuring the oxygen concentration in a molten metal which can utilize the binder effect of fluoride and does not cause peeling or cracking of a coating layer.

[0005]

According to the present invention, there is provided an element for measuring an oxygen concentration in a molten metal according to the present invention, which comprises a coating layer provided on a surface of the solid electrolyte element which is in contact with the molten metal on the outer peripheral surface. The coating layer is a powder of an oxide containing fluoride, which has an average particle diameter of 0.7 to 1.4 μm and a particle size range of 0.1 to 7 μm, and 10 to 50% by weight of the powder. 1.5 to 2.5 μm and particle size range: 0.1 to 15 μm
m of 50 to 90% by weight.

[0006]

In the above-described structure, a powder containing an oxide containing fluoride and having two kinds of particle size distributions is mixed to form a coating layer. Since the packing density can be increased and a dense coating layer can be formed, sintering shrinkage can be reduced, and as a result, peeling and cracking of the coating layer can be reduced. In addition, as described above, the aggregate itself of the coating layer is densified, and cracks and peeling are reduced, so that addition of fluoride having a binder effect at high temperatures can be suppressed to a small amount, and the melting point of the coating layer can be reduced. As a result, foaming and melting of the coating layer can be prevented. Furthermore, since the sintering shrinkage of the coating layer is reduced, the coating layer can be made thinner, and the time required to reach the thermal equilibrium between the molten metal and the solid electrode provided inside the solid electrolyte element is increased, and the responsiveness is improved. .

[0007] The powder having two types of particle size distributions has an average particle diameter, as will be apparent from Examples described later.
10% to 50% by weight of a powder having a particle size range of 0.1 to 7 μm in a size of 0.7 to 1.4 μm, and an average particle size of 1.5 to 2.5 μm
Particle size range: 0.1 to 15 μm powder 50 to 90% by weight
The use of a mixture with the above is preferred because the density of the coating layer is increased.

[0008]

FIG. 1 is a partial sectional view showing the structure of an example of an element for measuring the concentration of oxygen in a molten metal according to the present invention. In FIG. 1, reference numeral 1 denotes a solid electrolyte body made of zirconia exhibiting oxygen ion conductivity, and 2 denotes a coating layer provided on the outer peripheral surface of the solid electrolyte body 1 in contact with the molten metal. Element 3 for use. In the present invention, it is necessary to use as the coating layer 2 a mixture of powders of oxides containing fluoride having two types of particle size distribution.

In the present invention, the solid electrolyte member 1 made of zirconia and the element for measuring oxygen concentration are manufactured as follows. First, for example, 92 mol% of zirconia powder
And 8 mol% of magnesia powder and 1% by weight of alumina powder with respect to the total amount. Next, the obtained mixture is pulverized with water and zirconia cobblestone to a predetermined particle size. After pulverization, polyvinyl alcohol is added as a binder, and the mixture is granulated by a spray dryer to obtain a magnesia partially stabilized zirconia raw material. Next, after the obtained raw material is rubber-pressed into a predetermined shape, the outer periphery is cut into a cylindrical shape with a bottom, and then fired at a temperature of 1700 ° C. or more to obtain a solid electrolyte body 1 made of zirconia. . Finally, a powder having two kinds of particle size distributions of an oxide containing fluoride is mixed with the surface of the outer peripheral surface of the bottomed cylindrical solid electrolyte body 1 which is in contact with the molten metal, and coated by a method described later. By forming the coating layer 2, the element for measuring the oxygen concentration in the molten metal of the present invention is obtained.

Next, the coating layer 2 will be described in detail.
The coating layer 2 is composed of an oxide containing fluoride having two kinds of particle size distributions and an organic binder. Examples of the oxide include alumina, magnesia, calcia, zirconia, and a composite oxide of alumina, magnesia spinel, and alumina strontia. Examples of the fluoride include calcium fluoride, magnesium fluoride, aluminum fluoride, strontium fluoride and the like. First, one of the oxides is 80 to 90% by weight and one of the fluorides is 10 to 2%.
0% by weight. Next, the obtained prepared powder is ground in a trommel using water and zirconia cobblestone. In order to obtain powders having different particle size distributions, the resulting mixture is pulverized for different pulverization times, and the obtained pulverized product is dried, preferably containing fluoride and having an average particle size of 0.7 to 1.4 μm and a particle size range of:
0.1 to 7 μm oxide powder and average particle size: 1.5 to
An oxide powder having a particle size range of 0.1 to 15 μm at 2.5 μm is obtained. Next, two kinds of oxide powders containing fluorides having different particle size distributions, water and an organic binder were mixed,
Use as coating solution. After the surface on which the coating layer of the solid electrolyte body is provided is immersed in the coating liquid and dried, an element for measuring oxygen concentration in which the coating layer 2 of the present invention is provided on the outer peripheral portion of the solid electrolyte body 1 is obtained.

Hereinafter, an actual example will be described. Example 1 2 having an average particle size and particle size distribution as shown in Table 1
A 10 kg high-frequency induction furnace was prepared by preparing an element for measuring oxygen concentration in which a 100 μm-thick coating layer composed of various kinds of spinel powder and 15 wt% CaF ₂ with respect to the total amount of the spinel powder was provided on the outer periphery of the zirconia solid electrolyte body. 1650 ° C in
Was immersed and held in Fe-CO-based molten steel for a certain period of time, and then pulled up to visually observe the state of the coating layer. The particle size distribution was measured by a laser scattering method. FIG. 2 shows an example of a particle size distribution obtained by mixing powders having two types of particle size distributions. Table 1 shows the results.

[0012]

[Table 1]

As is clear from the results shown in Table 1, Test Nos. 2 to 10 using two kinds of powders having a different particle size distribution have a lower defective ratio than Test Nos. 1 and 11 using only one kind. Among them, Test Nos. 6 to 10 in which the amounts of the powders of the two kinds of particle size distributions were close to each other had the lowest defective rate.

Example 2 As in Example 1, two types of spinel powders having an average particle size and a particle size distribution as shown in Table 2 were used as raw materials.
An element for measuring oxygen concentration was prepared, and the state of the coating layer after immersion in molten steel was visually observed in the same manner as in Example 1. Table 2 shows the results.

[0015]

[Table 2]

From the results shown in Table 2, the test Nos. 17 to 24 using the powders having two kinds of particle size distributions showed a lower percentage of defects than the test Nos. 12 to 16 using only one kind. Also, among them, Test No. 18, 19,
21 and 22 are the best, and as a range of two types of average particle diameters, a mixture of powder having an average particle diameter of 0.7 to 1.4 μm and powder having an average particle diameter of 1.5 to 2.5 μm is used. It turned out to be favorable.

Example 3 In order to investigate the relationship between the thickness of the coating layer and the response, Example 1 was used.
In the same manner as in Example 1, two types of spinel powders having average particle diameters as shown in Table 3 were used as raw materials to prepare oxygen measurement elements, and the state of the coating layer was visually inspected in the same manner as in Example 1. The electromotive force and response time were measured and the response was compared. Table 3 shows the results.

[0018]

[Table 3]

From the results shown in Table 3, Test Nos. 29 to 32 using two kinds of powders having an average particle diameter had no defects compared with Test Nos. 25 to 28 using only one of the powders.
The response time was short and the response was good. When powders having two average particle diameters were used, there was no defect even when the thickness of the coating layer was 50 μm as shown in Test No. 31, and as shown in Test No. 32, the amount of CaF ₂ added It was also found that there was no defect even if the thickness was reduced, and the response time was further improved by the reduction in thickness.

[0020]

As is apparent from the above description, according to the element for measuring the oxygen concentration in the molten metal of the present invention, the oxide containing fluoride and the powder having two kinds of particle sizes are mixed. By forming the coating layer in this manner, a stable electromotive force waveform can be obtained without peeling or cracking of the coating layer during immersion in molten steel.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a configuration of an example of an element for measuring an oxygen concentration in a molten metal according to the present invention.

FIG. 2 is a graph showing an example of a particle size distribution obtained by mixing powders having two types of particle size distribution in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte body 2 Coating layer 3 Element for measuring oxygen concentration

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/411

Claims (1)

(57) [Claims] 1. An oxygen concentration measuring element having a structure in which a coating layer is provided on a surface of a solid electrolyte element that is in contact with a molten metal on an outer peripheral surface, wherein the coating layer is a powder of an oxide containing fluoride. Average particle size: 0.7 to 1.4 μm and particle size range:
10 to 50% by weight of a 0.1 to 7 μm powder, an average particle diameter of 1.5 to 2.5 μm and a particle size range of 0.1 to 15 μm
An element for measuring an oxygen concentration in a molten metal, comprising 50 to 90% by weight of a powder of