JP2562198B2 - Sensor element for measuring components in molten metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a component measuring sensor element for measuring components such as oxygen in molten metal.

(Prior Art) Conventionally, a cylindrical body having one side closed by an oxygen ion conductive solid electrolyte such as zirconia, a solid electrode mixed with a metal-metal oxide is enclosed inside, and a metal oxide is formed outside. Sensor elements provided with a uniform coating layer are known, for example, from Japanese Patent Publication Nos. 61-47377 and 60-52763.

(Problems to be Solved by the Invention) The above-mentioned JP-B-61-47377 and JP-A-60-527 are mentioned above.
In the technique described in Japanese Patent Laid-Open No. 63-63, the point where the coating layer sinters and shrinks due to high temperature and is easily peeled off is attempted by uniformly dispersing the fluoride in the coating layer.

However, even in the above-mentioned technique, there is a problem that the operating temperature range is limited because the sintering proceeds excessively to a higher temperature molten metal, cracks occur in the coating layer, and the coating layer peels off.

An object of the present invention is to solve the above-mentioned problems and to provide a sensor element for measuring a component in a molten metal which can be used in a wide operating temperature range without peeling or cracking of a coating layer at a high temperature.

(Means for Solving the Problems) The component measuring sensor element in molten metal of the present invention is a component measuring sensor element in molten metal in which a coating layer is provided on the surface in contact with the molten metal on the outer peripheral surface of the solid electrolyte element, Each of the at least two kinds of powdery substances forms an aggregate containing the powdery substance as a main component, and the coating layer is composed of a plurality of kinds of the aggregates.

(Operation) In the above-mentioned configuration, by forming an aggregate in each of a plurality of types of powdery substances and forming an inhomogeneous coating layer having a structure in which the aggregates are stacked, peeling or large This is due to the finding that cracks do not occur. It is considered that this is because even if the individual aggregates are sintered, the small gaps formed between the aggregates absorb the stress, so that peeling and cracks do not occur. In this case, the coating layer preferably has a thickness of 50 to 300 μm, more preferably 100 to 200 μm.

Here, the aggregate refers to, for example, granulated powder, and refers to an aggregate of several hundreds of powder particles having an average particle diameter of about 1 μm, and the average particle diameter of the aggregate is preferably 5 to 30 μm.

It is preferable that the two or more kinds of substances include at least two kinds of oxides and fluorides as an aggregate, because the effect of preventing cracks and peeling is increased. The reason for this is thought to be that the fluoride acts to prevent the small gaps formed between the aggregates from developing into large cracks.

Further, it is preferable that the amount of fluoride increases in the coating layer from the sensor element side toward the outside. The reason is that since the outer side of the coating layer is more easily sintered, the gap between the aggregates is usually larger, but the gap is reduced by increasing the amount of fluoride. If the amount of fluoride is too large, the signal output of the sensor element is affected, so the amount of fluoride is limited.

Further, the oxide to be used is preferably any one or a mixture of alumina, alumina magnesia spinel, magnesia, alumina barrier spinel (barium aluminate), and alumina strontia (strontium aluminate).

(Example) FIG. 1 is a partial cross-sectional view showing a configuration of an example of a sensor element for measuring a component in a molten metal of the present invention. In FIG.
Reference numeral 1 denotes a zirconia solid electrolyte body, and 2 denotes a coating layer, which constitutes a component measuring sensor element having a bottomed cylindrical shape.

The zirconia solid electrolyte body 1 is manufactured as follows. First, for example, 92 mol% of zirconia powder, 8 mol% of magnesia powder, and 1 wt% of alumina powder with respect to the total amount.
And mix. Next, the above-mentioned prepared powder is mixed and ground in water and zirconia cobblestone in a trommel, and then dried.
The dried powder is calcined at 1200 to 1500 ° C., and after calcining, is ground using water and zirconia cobblestone to a predetermined particle size.
After pulverization, polyvinyl alcohol is added as a binder, and then granulated by a spray drier to obtain a partially stabilized zirconia raw material for magnesia. Next, the obtained raw material is rubber-pressed into a predetermined shape, the outer periphery is cut to form a bottomed cylindrical shaped body, and the body is fired at a temperature of 1700 ° C. or higher to obtain a zirconia solid electrolyte body 1. Finally, a coating layer 2 having a structure in which two or more kinds of aggregates of powder particles are provided in layers on the outer peripheral surface of the bottomed cylindrical solid electrolyte body 1 in contact with the molten metal.
Is provided by the method described below to obtain the component measuring sensor element in the molten metal of the present invention.

FIG. 2 is a schematic sectional view showing the structure of an example of the coating layer of the sensor element of the present invention. In this example. The covering layer is composed of three kinds of aggregates. This structure can be observed with a scanning electron microscope or the like after cutting or breaking the sensor element. In the example shown in FIG. 2, 3 is an aggregate of alumina fine powder, 4 is an aggregate of calcium fluoride fine powder, and 5 is an aggregate of alumina magnesia spinel fine powder. The average particle size of these aggregates is preferably 5 to 30 μm. The composition of the coating layer is, for example, 30% by weight of alumina, 50% by weight of spinel, and 20% by weight of calcium fluoride. Although not shown in FIG. 2, it is preferable in terms of the film strength of the coating layer that the aggregate and the interface of the aggregate include an organic bonding agent such as polyvinyl alcohol or a surfactant.

Although this aggregate is preferably a single substance, it may contain a small amount of a different kind of oxide or fluoride. Further, by increasing the amount of fluoride-based aggregates on the outer surface of the coating layer, the effect of improving durability is also recognized. Examples of oxides include alumina, alumina magnesia spinel, alumina barrier spinel, magnesia, alumina toronthia, and the like. Examples of fluorides include calcium fluoride, magnesium fluoride, strontium fluoride and the like.

As a method for applying the coating layer, a dipping method, a spray method, or the like can be considered. In the case of the dipping method, the aggregate may be obtained by a method of granulating the fine powder of each substance by a method such as a spray dryer, or a method of putting the fine powder in a ceramic crucible or the like, calcining it at a low temperature, and then coarsely pulverizing it. it can. In the case of a calcined body, a calcining temperature at which the fine powders react and sinter only at their contact points is preferable. These aggregates are mixed in a predetermined amount and then mixed with an organic bonding agent (for example, polyvinyl alcohol) in a solvent such as water to form a dipping liquid. The surface of the solid electrolyte body on which the coating layer is provided is dipped in this dipping solution and then dried to obtain the coating layer of the present invention.

Next, in the case of the spray method, first, the fine powder raw material and the solvent,
Make a spray solution with the addition of organic binder and dispersant. This spray liquid is prepared for each aggregate type, spray guns are prepared for each type of aggregate, and the spray liquid of each aggregate is simultaneously sprayed from the spray gun while rotating the solid electrolyte body on which the coating layer should be provided. To obtain a coating layer. In the spray method, the size of the aggregate can be controlled by changing the spray conditions to adjust the size of the liquid. Moreover, a coating layer having a predetermined composition ratio can be obtained by adjusting the spray amount. For example, in order to increase the amount of fluoride in the thickness direction, it is sufficient to increase the spray amount as the thickness increases. As a result, the distribution amount of fluoride in the coating layer can be increased from the side closer to the solid electrolyte element to the other side.

Actually, when the component measuring sensor element having the coating layer of the present invention having the structure shown in FIG. 2 was immersed in molten steel at 1700 ° C. for 10 seconds, no peeling occurred and fine cracks were observed on the coating layer surface. Only some of them were present, showing a good appearance.

The present invention is not limited to the above-described embodiments, but various modifications and changes can be made. For example, it is clear that the composition of the coating layer shown in the above-mentioned example is not limited to this, and it is also clear that the composition and shape of the solid electrolyte are not limited to the above-described embodiment.

(Effects of the Invention) As is clear from the above description, according to the component measuring sensor element in the molten metal of the present invention, by providing the structure of the coating layer in a non-homogeneous manner in two or more kinds of aggregates, at high temperature It is possible to measure components such as oxygen in the molten metal in a wide temperature range without peeling or cracking of the coating layer.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing the structure of an example of a sensor element for measuring a component in molten metal of the present invention, and FIG. 2 is a schematic cross-sectional view showing the structure of an example of a coating layer of the sensor element of the present invention. DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte body, 2 ... Coating layer 3 ... Aggregate of fine alumina powder 4 ... Aggregate of fine powder of calcium fluoride 5 ... Aggregate of alumina magnesia spinel fine powder

Claims (3)

(57) [Claims] 1. In a sensor element for measuring a component in a molten metal, wherein a coating layer is provided on a surface of an outer peripheral surface of a solid electrolyte element which is in contact with the molten metal, at least two kinds of powdered substances each contain the powdered substance as a main component. A sensor element for measuring a component in molten metal, characterized in that the above-mentioned coating layer is formed by a plurality of kinds of the above-mentioned assembly. 2. A sensor element for measuring a component in a molten metal according to claim 1, wherein the aggregate is an aggregate of oxides and an aggregate of fluorides. 3. The component measuring sensor element in molten metal according to claim 2, wherein the distribution amount of fluoride in the coating layer increases from the side closer to the solid electrolyte element toward the other side.