1. Field of the Invention
The present invention relates to a method for forming a thin-film layer on the outer surface of a sensor and to a sensor fabricated using such a method.
2. Description of the Related Art
In order of increase the degree of refining obtained by adjusting the concentration of melt components to a control standard values and to increase the refining rate in metal refining plants which are typical for steelmaking industry, it is very important to measure rapidly the concentration of elements that require concentration control during refinement, such as oxygen, silicon, and phosphorus that are contained in the molten metal. Accordingly, methods have been developed for measuring the concentration of those elements by using electrochemical sensors. A basic measurement method that can be used when the measurement object has electron conductivity, as a molten metal, is illustrated by
The sensor 51 shown in
Concentration measurements of the elements contained in a molten metal, which is the measurement object, are based on using a sensor employing a concentration cell principle as the electrochemical sensor, as described hereinabove. As a rule, an electrolyte having ion conductivity of the element which is to be measured is required as a solid electrolyte for the aforesaid measurements. However, there is also a measurement method which does not use an electrolyte having ion conductivity of the element which is to be measured, when this element is metal. With this method, as described in Unexamined Japanese Patent Application Laid-open No. S61-260155, the activity value of the element is found and the concentration thereof is measured by using a zirconia solid electrolyte employed in the oxygen sensor as the solid electrolyte, measuring the oxygen potential, that is, the partial pressure of oxygen in the molten metal by bringing the activity value of the oxide to a constant value in the vicinity of zirconia solid electrolyte-molten metal interface with the aforesaid auxiliary electrode, from the oxidation reaction of the element in the molten metal.
Measurement of the concentration of elements such as Cr, Mn, Si, Al, and P contained in the molten metal, which is the measurement object 54, as described, for example, in Unexamined Japanese Patent Application Laid-open No. H5-60726, is an example of using the sensor 51 shown in
When the measurement object is gas of slag of molten oxides that have no electron conductivity, the sensor 51 shown in
The above-described thin-film layer serving as an auxiliary electrode or a measurement electrode formed on the surface of a solid electrolyte has been conventionally formed by a method comprising the steps of mixing the above-described mixed oxide or the like or a platinum powder or the like with an organic solvent or the like to obtain a paste and applying this paste in the dot-like or spiral-like fashion to the surface of the solid electrolyte, for example in the same manner as described in Unexamined Japanese Patent Application Laid-open No. S61-260155.
However, from the standpoint of increasing the concentration measurement speed, it is preferred that the aforesaid three-phase interface be enlarged. For this purpose, is it described that patterns be formed which incorporate the pattern shape of the thin-film layer in a complex fashion when the thin-film layer, which is a mixed oxide or the like, is formed on the surface of the solid electrolyte in such a manner that part of the surface is exposed. However, it is not easy to coat the paste-like oxide or the like so as to obtain such a complex pattern. Furthermore, it is desirable that the aforesaid patterns be arranged as uniformly as possible to increase the efficiency of concentration measurements. Such an arrangement is, however, not easy to realize with a coating process. Moreover, when a method for coating a paste-like mixed oxide prepared by mixing with an organic solvent was used to form the aforesaid thin-film layer, the thin-film layer always had a large thickness. As a result, when the sensor fabricated in such a manner was used for measurements, because a molten metal had a rather high temperature, the organic solvent was evaporated and the thin-film layer sometimes peeled off and fell down under the weight of the coated mixed oxide.
The present invention was created to resolve the above-described problems and it is an object of the present invention to provide a method for forming a thin-film layer on the outer surface of a sensor, by which a thin-film layer formed on the surface of a sensor used for measuring the concentration of elements contained in the measurement object such as a molten metal, slag, or gas, can be easily provided with a complex pattern shape of small thickness and a uniformly arranged pattern shape.
The method for forming a thin-film layer of a sensor in accordance with the present invention is a method for forming a thin-film layer of a sensor composed of a solid electrolyte which is a molded body having an inner space, a reference substance filled in the inner space, a reference electrode connected to the reference substance and led out to the outside of the inner space, and a thin-film layer comprising a ceramic powder or a metal powder as the main component and formed on the outer surface of the solid electrolyte in such a manner that part of the outer surface is exposed, wherein the thin-film layer is formed by printing. The molded body as referred to herein means that it is in the form of a solid body. No specific limitation is placed on the method for fabrication thereof, and it can be molded by a method other than that using a mold such as a metal mold for molding.
In the above-described method for forming a thin-film layer of a sensor, the pattern shape of the surface of the thin-film layer may be an assembly of independent patterns or a continuous shape.
By applying the above-described method for forming a thin-film layer of a sensor to a sensor in which a thin-film layer lead wire is connected to the thin-film layer it is possible to create a sensor for measurement objects that have no electron conductivity, such as slags and gases.
In the above-described method for forming a thin-film layer of a sensor, screen printing or pad printing may be used for the printing.
In the above-described method for forming a thin-film layer of a sensor, the recommended thickness of the thin-film layer is 500 μm or less.
In the above-described method for forming a thin-film layer of a sensor, the molded body of the solid electrolyte may be in the form of a cylindrical Tammann tube which is closed at one end thereof.
The sensor in accordance with the present invention is composed of a solid electrolyte which is a molded body having an inner space, a reference substance filled in the inner space, a reference electrode connected to the reference substance and led out to the outside of the inner space, and a thin-film layer comprising a ceramic powder or a metal powder as the main component and formed on the outer surface of the solid electrolyte in such a manner that part of the outer surface is exposed, wherein the thin-film layer is formed by printing.
In the aforesaid sensor, the pattern shape of the surface of the thin-film layer may be an assembly of independent patterns or a continuous shape.
By applying the above-described configuration to a sensor in which a thin-film layer lead wire is connected to the thin-film layer it is possible to create a sensor for measurement objects that have no electron conductivity, such as slags and gases.
In the aforesaid sensor, screen printing or pad printing may be used for the printing.
In the aforesaid sensor, the thickness of the thin-film layer may be 500 μm or less.
In the aforesaid sensor, the molded body of the solid electrolyte may be in the form of a cylindrical Tammann tube which is closed at one end thereof.
The present invention will be described below in greater detail based on the embodiments thereof illustrated by the appended drawings. The present invention relates to a method for forming a thin-film layer which is to be formed on the surface of a sensor used for measuring the concentration of elements contained in a measurement object such as a molten metal, a slag which is the oxide melt, or a gas. The present invention also relates to a sensor formed by using this formation method. In the present embodiments, explanation will be conducted with respect to a sensor in which a thin-film layer was formed as the aforesaid auxiliary electrode.
Referring to
The aforesaid sensor is based on the principle of an oxygen concentration cell. As described hereinabove, a zirconia solid electrolyte comprising ZrO2 as the main component, such as a zirconia solid electrolyte partially stabilized with magnesia, is used as the solid electrolyte 1a, a mixture of Cr and Cr2O3 or Mo and MoO2 with known partial pressure of oxygen is used as the reference substance 1b, Mo is used as the reference electrode 1c, and alumina cement is used as the sealing portion 1e. The substance used for the thin-film layer 1d formed on the outer surface of the solid electrolyte 1a differs depending on the element which is to be measured. For example, when the element to be measured is Cr, Mn, Si, Al, or P, mixed oxides are used which contain as the main component an inorganic compound comprising an oxide of the element. Those mixed oxides can be referred to as ceramic powders. More specifically, when the element to be measured is P, a mixture of Al2O3 and AlPO4 is used. In order to form a three-phase interface of a molten metal, the thin-film layer 1d serving as an auxiliary electrode, and the solid electrolyte when the sensor is used for measurements, the thin-film layer 1d has to be formed in such a manner that part of the outer surface of the zirconia solid electrolyte serving as the solid electrolyte 1a is exposed.
Described hereinbelow is a method for forming the thin-film layer 1d on the outer surface of the Tammann tube which is formed from a zirconia solid electrolyte serving as the solid electrolyte 1a of the above-described sensor. With this method, the thin-film layer 1d is formed by screen printing.
Further, as shown in
Then, as shown in
The assembly of the sensor is then completed by inserting and installing the aforesaid reference substance and solid electrolyte inside the Tammann tube 14 that has a thin-film layer formed on the outer surface thereof by screen printing conducted in the above-described manner and forming a sealing portion. The sensor 22 thus assembled is usually used, as shown in
In the above-described embodiment, the pattern of the thin-film layer 18 formed on the outer surface of the Tammann tube 14 was a continuous pattern shown in
With the above-described embodiment, a thin-film layer is formed on the outer surface of the Tammann tube 14 by screen printing. Therefore, a pattern of complex shape and small thickness can be easily obtained. Furthermore, a constant product quality can be maintained and the production efficiency can be increased. Furthermore, obtaining a uniform pattern shape in the printing pattern formed on the screen printing mask 11 makes it possible to obtain a pattern shape of the thin-film layer which is uniformly disposed on the outer surface of the Tammann tube and to form a variety of patterns according to the desired object. Furthermore, thin-film layers using a variety of materials corresponding to the elements which are to be measured can be formed by changing the composition of the printing paste.
In the above-described embodiment, screen printing was used as the printing method. However, pad printing may be also used.
In the above-described embodiment, the explanation was provided with respect to a sensor in which the thin-film layer was formed as an auxiliary electrode. However, the thin-film layer can be also formed in the same manner on the surface of a sensor in which the thin-film layer serves as the above-described measurement electrode, this sensor being used when the object of measurement is a slag or gas having no electric conductivity.
With the above-described method for forming a thin-film layer of a sensor in accordance with the present invention, the thin-film layer is formed on the outer surface of a solid electrolyte such as a Tammann tube by printing such as screen printing or pad printing. Therefore, a complex pattern shape of small thickness can be easily obtained, products of constant quality can be obtained, and production efficiency can be increased. Moreover, the pattern of the thin-film layer can be uniformly disposed on the outer surface of a solid electrolyte such as a Tammann tube 14 and a variety of patterns can be formed according to application. Furthermore, changing the composition of the printing paste makes it possible to form a thin-film layer using a variety of materials corresponding to the application of the sensor.
Number | Date | Country | Kind |
---|---|---|---|
2003-052275 | Feb 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP04/02364 | 2/27/2004 | WO | 5/19/2006 |