JPH04291146A - Element for measuring concentration of oxygen within melted metal - Google Patents

Abstract

PURPOSE:To enable a stable measurement to be made without any release of a film layer or generation of cracks when dipping in a melted steel by mixing a powder with two types of grain size distributions with an oxide containing a fluoride for forming the film layer. CONSTITUTION:A film layer 2 is provided on a surface which contacts a melted metal on an outer-periphery surface for a solid electrolyte 1 consisting of zirconia. This layer 2 is an oxide containing fluoride and is formed by mixing a powder with two types of grain size distributions and a filling density of the powder can be increased and the intricate layer 2 can be formed since small particles fill a gap of large particles. Therefore, by reducing sintering shrinkage, release of the layer 2 or generation of cracks can be reduced. Also, an amount of added fluoride with a binding effect within high temperature can be suppressed to a small amount owing to their reduction and a melting point of the layer 2 can be increased, thus preventing expansion or melting of the layer 2. Therefore, a stable measurement can be made.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an element used for measuring the oxygen concentration of molten metal, which 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. This invention relates to a concentration measuring element.

0002

[Prior Art] Conventionally, an oxygen ion conductive solid electrolyte such as zirconia is used to form a cylindrical shape with a closed end on one side, a solid electrode made of a metal-metal oxide mixture is enclosed inside the cylindrical shape, and a solid electrode made of a metal-metal oxide mixture is enclosed inside the cylindrical shape. 2. Description of the Related Art Sensor elements having a structure provided with a coating layer made of metal oxide or the like are known. In the sensor element with the above structure, when the element is placed in molten metal, the coating layer shrinks due to sintering 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 was a problem that a stable electromotive force waveform could not be obtained. In addition, in order to prevent peeling and cracking of the coating layer, it is possible to make the thickness of the coating layer 100 μm or more.
This has caused a problem of slow response time.

0003

[Problems to be Solved by the Invention] In order to solve the above-mentioned problems such as peeling of the coating layer, a technology has been developed in recent years in which CaF2, which has a binder effect at high temperatures, is included in the coating layer. It is disclosed in the publication No. However, in the past, in order to exhibit this binder effect, a large amount of CaF2 had to be added, and when a large amount of CaF2 was added, the melting point of the coating layer decreased, resulting in foaming and melting, which caused the molten metal to melt. There was a problem in that the contact area of the solid electrolyte changed, making it impossible to obtain a stable electromotive force waveform.

[0004] The purpose of the present invention is to solve the above-mentioned problems,
The object of the present invention is to provide an element for measuring oxygen concentration in molten metal that can utilize the binder effect of fluoride and that does not cause peeling of the coating layer or generation of cracks.

[0005]

[Means for Solving the Problems] An element for measuring oxygen concentration in molten metal of the present invention has a structure in which a coating layer is provided on the outer peripheral surface of a solid electrolyte element in contact with molten metal. The coating layer is characterized in that it is composed of a mixture of fluoride-containing oxide powders having two types of particle size distributions.

[0006]

[Operation] In the above structure, by forming a coating layer by mixing powders of fluoride-containing oxides with two types of particle size distribution, the small particles fill the gaps between the large particles. Since it is possible to increase the packing density and form a dense coating layer, sintering shrinkage can be reduced, and as a result, peeling and cracking of the coating layer can be reduced. In addition, as mentioned above, the aggregate of the coating layer itself becomes densified, reducing cracks and peeling, making it possible to suppress the addition of fluoride, which has a binder effect, to a small amount at high temperatures, and lowering the melting point of the coating layer. 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, which speeds up the time to reach thermal equilibrium between the molten metal and the solid electrode provided inside the solid electrolyte element, improving responsiveness. .

[0007] As is clear from the examples described below, the powders having two types of particle size distribution have an average particle size of:
10-50% by weight of powder with particle size range: 0.1-7μm and average particle size: 1.5-2.5
Particle size range in μm: 0.1-15 μm powder 50-9
It is preferable to use a mixture with 0% by weight because the denseness of the coating layer increases.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a partial sectional view showing the structure of an example of an element for measuring oxygen concentration in molten metal according to the present invention. In FIG. 1, 1 is a solid electrolyte body made of zirconia that exhibits oxygen ion conductivity, and 2 is a coating layer provided on the outer peripheral surface of the solid electrolyte body 1 in contact with the molten metal. This constitutes the element 3 for use. In the present invention, it is necessary to use a mixture of fluoride-containing oxide powders having two types of particle size distributions as the coating layer 2.

In the present invention, the solid electrolyte body 1 made of zirconia and the oxygen concentration measuring element are manufactured as follows. First, for example, zirconia powder 92 mol%
8 mol% of magnesia powder and 1% by weight of alumina powder based on the total amount are mixed. Next, the obtained mixture is ground with water and zirconia cobbles until it reaches a predetermined particle size. After pulverization, polyvinyl alcohol is added as a binder and then granulated using a spray dryer to obtain a magnesia partially stabilized zirconia raw material. Next, the obtained raw material is rubber pressed into a predetermined shape, the outer periphery is cut to form a bottomed cylindrical molded body, and then fired at a temperature of 1700° C. or higher to obtain a solid electrolyte body 1 made of zirconia. . Finally, fluoride-containing oxide powders having two types of particle size distributions are mixed on the outer circumferential surface of the solid electrolyte body 1 having a cylindrical shape with a bottom, which is in contact with the molten metal, and coated by the method described below. By forming the coating layer 2, the element for measuring oxygen concentration in molten metal of the present invention is obtained.

Next, the covering layer 2 will be explained in detail. The coating layer 2 is composed of an oxide containing fluoride having two types of particle size distribution and an organic binder. Examples of oxides that can be used include alumina, magnesia spinel, alumina strontia, and the like, which are composite oxides of alumina, magnesia, calcia, zirconia, and alumina. Further, as examples of fluorides, calcium fluoride, magnesium fluoride, aluminum fluoride, strontium fluoride, etc. can be used. The manufacturing method is as follows: First, 80 to 90% by weight of one of the above oxides and 10 to 20% by weight of one of the above fluorides.
% by weight. The resulting blended powder is then ground in a trommel using water and zirconia cobblestones. In order to obtain powders with different particle size distributions, after pulverizing with different pulverizing times, the obtained pulverized product is dried and the fluoride-containing powder is preferably average particle size: 0.7 to 1.4 μm and particle size range:
Oxide powder of 0.1 to 7 μm and average particle size: 1.5
to 2.5 μm and particle size range: 0.1 to 15 μm. Next, two types of oxide powders containing fluorides having different particle size distributions, water, and an organic binder are mixed to form a coating liquid. The surface of the solid electrolyte body on which the coating layer is to be provided is immersed in this coating liquid and then dried to obtain an oxygen concentration measuring element in which the coating layer 2 of the present invention is provided on the outer periphery of the solid electrolyte body 1.

An actual example will be explained below. Example 1 2 having the average particle size and particle size distribution as shown in Table 1
An element for measuring oxygen concentration was prepared by providing a 100 μm thick coating layer on the outer periphery of a zirconia solid electrolyte body consisting of various types of spinel powder and 15% by weight of CaF2 based on the total amount of spinel powder, and placed in a 10 kg high frequency induction furnace. So 165
Immersed and held in Fe-C-O-based molten steel at 0°C for a certain period of time,
Thereafter, it was pulled up and the state of the coating layer was visually observed. Note that the particle size distribution was measured by a laser scattering method. Also,
FIG. 2 shows an example of a particle size distribution obtained by mixing powders with two types of particle size distributions. The results are shown in Table 1.

0012

[Table 1]

As is clear from the results in Table 1, Test Nos. 2 to 10, which used powders with two types of particle size distributions, had a lower percentage of defects than Tests Nos. 1 and 11, which used only one type of powder. Among them, Test Nos. 6 to 10, in which the amounts of powders with two different particle size distributions were added, had the lowest percentage of defects.

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

[0015]

[Table 2]

[0016] From the results in Table 2, it can be seen that in Test Nos. 17 to 24, which used powders having two types of particle size distribution, either one
The percentage of defects was lower than in Test Nos. 12 to 16, in which only different types were used. Also, among them, test No. 18,
19, 21, and 22 are the best, and the two types of average particle size ranges are a powder with an average particle size of 0.7 to 1.4 μm and a powder with an average particle size of 1.5 to 2.5 μm. It was found to be advantageous to use it.

Example 3 In order to investigate the relationship between the thickness of the coating layer and the response, Example 1 was conducted.
Similarly, oxygen measuring elements were prepared using two types of spinel powders having average particle diameters as shown in Table 3 as raw materials, and the state of the coating layer was visually examined in the same manner as in Example 1. The electromotive force and response time were measured and the responsiveness was compared. The results are shown in Table 3.

[0018]

[Table 3]

From the results in Table 3, Test Nos. 29 to 32, which used powders with two types of average particle diameters, had no defects and had a shorter response time than Tests Nos. 25 to 28, which used only one type of powder. The response was good. Also, 2
When using powder with a different average particle size, test No. 3
As shown in Test No. 1, there was no defect even when the thickness of the coating layer was 50 μm, and as shown in Test No. 32, Ca
It was also found that there were no defects even when the amount of F2 added was reduced, and that the response time was further improved as the thickness was reduced.

[0020]

Effects of the Invention As is clear from the above description, according to the element for measuring oxygen concentration in molten metal of the present invention, powders of fluoride-containing oxides having two types of particle size distributions are mixed. By forming the coating layer in this manner, it is possible to obtain a stable electromotive force waveform without peeling or cracking of the coating layer during immersion in molten steel.

[Brief explanation of the drawing]

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

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

[Explanation of symbols]

1 Solid electrolyte body 2 Coating layer 3 Oxygen concentration measurement element

Claims (2)

[Claims] 1. An oxygen concentration measuring element having a structure in which a coating layer is provided on the outer peripheral surface of the solid electrolyte element in contact with molten metal, wherein the coating layer is made of fluoride-containing oxide powder, An element for measuring oxygen concentration in molten metal, characterized in that it is composed of a mixture of powders having two types of particle size distributions. 2. The coating layer made of oxide powder containing the two types of fluorides has an average particle size of 0.7 to 1.4 μm.
A claim consisting of 10-50% by weight of a powder with a particle size range of 0.1-7 μm and 50-90% by weight of a powder with an average particle size of 1.5-2.5 μm and a particle size range of 0.1-15 μm. Item 1. The element for measuring oxygen concentration in molten metal according to item 1.