JPH11242016A - Oxygen sensor for high temperature melt material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor for a high temperature melt material which can be simply manufactured by precisely and stably measuring a potential caused by an oxidation-reduction state at a position to be measured in a high temperature melt material or particularly a glass melt liquid in an arbitrary gas atmosphere. SOLUTION: A reference electrode 2 has a columnar stabilized zirconia 21 formed with a recess 211 extended clown from an upper end face. A coiled spring-like platinum lead wire 5 having an outer diameter larger than an inner diameter of the recess is elastically radially reduced, inserted into the recess, and fixed in the recess. And, a measuring electrode has a conductive core wire for an electrode, cylindrical ceramics having gas barrier properties and nonconductivity to cover the core wire in an end exposed state at a position including an interface between the high temperature melt material and an atmospheric gas, and a ceramic cement having gas barrier properties and nonconductivity charged in a gap between the wire and the ceramics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for a high-temperature melt for measuring the oxygen activity inside a high-temperature melt such as glass with high accuracy.

[0002]

2. Description of the Related Art Strict control is required because the redox state of a glass melt greatly affects the physical properties of the melt itself and the quality of a final product. In particular, in the manufacturing process of liquid crystal substrates and various optical glasses, which are frequently used in the field of optoelectronics in recent years, it is necessary to completely clarify fine bubbles, but the generation and disappearance of bubbles are caused by the generation of oxygen gas in the glass melt. It is considered to be closely related to solubility and the like. Therefore, it is extremely important to strictly control the redox state of the melt for a long time. Therefore, there is a need for the development of an oxygen sensor that can withstand a high temperature of about 1550 ° C., which is generally the melting temperature of commercially produced glass, for a long time and that can precisely measure the potential caused by the oxidation-reduction state.

Research on oxygen sensors that can be used in a high-temperature melt has been conducted for a long time. Generally, stabilized zirconia (yttria-added zirconia), which is a solid electrolyte, is used as a reference electrode, and platinum is used as a measurement electrode. The oxygen activity that accurately reflects the oxidation-reduction state is determined from the potential difference generated between these electrodes. For example, A. Lenhart et al. Have proposed a sensor using a cylindrical stabilizing zirconia point-contacted with a platinum paste and fixed with a platinum paste as a reference electrode, and using a platinum wire as a measurement electrode (Glasrech. Ber. 58 (1985) 139). -147). A similar sensor is also described by H.S. M. Simon et al. Also reported (Gl
asrech.Ber.61 (1988) 293-299), and online measurement in a glass melting tank for product production is also being attempted.

[0004]

However, the above-mentioned conventional oxygen sensor has the following problems. That is,
Since the stabilized zirconia, which is the reference electrode, and the platinum conductor are in point contact with each other, if they are exposed to a high-temperature atmosphere for a long time, there is a possibility that the contact point may be deviated due to a difference in thermal expansion coefficient between the two. Also,
When the measurement electrode is immersed in the melt, a local battery is formed at the interface between the melt and the atmosphere gas, and a slight variation in the atmosphere gas component causes an error in the measurement potential.

According to the present invention, it is possible to accurately and stably measure a potential caused by an oxidation-reduction state at a target portion in a high-temperature melt, particularly a glass melt, in an arbitrary gas atmosphere. It is another object of the present invention to provide a high-temperature melt oxygen sensor that can be easily manufactured.

[0006]

The inventor of the present invention has made intensive studies to solve the above-mentioned problems of the prior art.
It has been found that the above problem can be solved by an oxygen sensor having the following configuration.

That is, the present invention is an oxygen sensor for immersing a reference electrode and a measurement electrode in a high-temperature melt and measuring the oxygen activity of the high-temperature melt from a potential difference between the reference electrode and the measurement electrode. The reference electrode includes a columnar stabilizing zirconia having a recess extending downward from the upper end surface, and a coil spring-shaped platinum conductive wire having an outer diameter larger than the inner diameter of the recess is elastically reduced in the recess. The measuring electrode has a gas barrier property that covers the conductive core wire for the electrode and the position including the interface between the high-temperature melt and the atmosphere gas and in an exposed state at the tip end. And a cylindrical ceramic having non-conductivity, and a ceramic cement having gas barrier properties and non-conductivity filled in the gap between the core wire and the cylindrical ceramic. There is provided a hot melt-body oxygen sensor.

[0008] Preferably, a platinum paste is applied to a contact portion of the pillar-shaped stabilized zirconia with the platinum conductor on the inner surface of the concave portion.

Preferably, the ratio of the outer diameter of the core wire to the inner diameter of the cylindrical ceramic is 0.95 or more and less than 1. More preferably, the core wire is a platinum wire, and the cylindrical ceramic is It is made of alumina, and the ceramic cement is alumina cement.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view showing an example of a usage state of an oxygen sensor for a high-temperature melt according to an embodiment of the present invention. As shown in FIG. 1, an oxygen sensor 1 for a high-temperature melt according to the present invention includes a reference electrode 2, a measurement electrode 3, a voltmeter 4, a platinum conductor 5, and a platinum wire 6. When measuring the oxygen activity in the solution 7 with the oxygen sensor 1,
The reference electrode 2 is immersed in the melt 7, and the measurement electrode 3 is immersed in the melt 7 at a location where the oxygen activity is measured. The potential difference between the two electrodes 2 and 3 caused by this is measured by a voltmeter 4 via a platinum lead wire 5 and a platinum wire 6, respectively.
Calculate the nearby oxygen activity. The reference electrode 2 is desirably immersed near the surface of the melt 7. This is because, by reducing the immersion volume, the dissolution rate of zirconia is reduced, and the life of the reference electrode 2 is prolonged.

FIG. 2 is a longitudinal sectional view of the reference electrode 2 constituting the oxygen sensor 1. As shown in FIG.
Is formed with a concave portion 211 having a circular cross section at an upper end portion. The distal end of the platinum conductive wire 5 is in the form of a coil spring having an outer diameter larger than the inner diameter of the concave portion 211, and comes into close contact with the inner surface of the concave portion 211 in a state of being elastically reduced in diameter and inserted into the concave portion 211. Further, in order to reduce the electric resistance between the platinum conductor 5 and the stabilized zirconia 21, the platinum conductor 5 and the recess 211 are formed.
A platinum paste 22 is applied to the entire surface of the contact portion, and the platinum conductive wire 5 is fixed to the inner surface of the concave portion 211 by making contact with the paste. With this configuration, the columnar stabilized zirconia 2
Since the distance from the portion immersed in the melt 7 to the contact portion with the platinum conductor 5 in 1 is shortened, the effect of the thermoelectromotive force caused by the vertical temperature difference of the cylindrical stabilized zirconia 21 can be reduced.

In this embodiment, the columnar stabilized zirconia 21 has a length of 50 mm and an outer diameter of 5 mm.
If the inner diameter of the concave portion 211 is too small, it becomes difficult to insert the platinum conductive wire 5 and fix it with the platinum paste 22. Therefore, the inner diameter is preferably 30% or more, more preferably 40% or more, of the outer diameter of the stabilized zirconia 21. Is more preferred. On the other hand, if it is too large, the wall thickness of the peripheral wall of the concave portion 211 becomes thin and may be damaged during the measurement. Therefore, the outer diameter of the stabilized zirconia 21 is preferably 80% or less, more preferably 70% or less. More preferred. Further, in order to avoid breakage of the stabilized zirconia 21, the depth of the concave portion 211 is preferably smaller than the length of the portion of the stabilized zirconia 21 inserted into the alumina tube 23 described later. From such a viewpoint, the concave portion 211 in the present embodiment has an inner diameter of 3 mm and a depth of 10 mm.
It has been. On the other hand, if the diameter of the platinum wire 5 is too small, the pressing force of the coil spring-shaped tip of the platinum wire 5 against the inner wall of the recess 211 becomes weak, and the fixing is insufficient.
Preferably, the inner diameter is not less than 5% of the inner diameter of the concave portion 211.
% Is more preferable. Conversely, if it is too large, it becomes difficult to process the tip of the platinum conductive wire 5 into a spring shape. Therefore, it is preferable to set the inner diameter of the recess 211 to 40% or less, and more preferably 30% or less. In the present embodiment, the platinum conductive wire 5 has a diameter of 0.5 mm, and the tip is formed in a coil spring shape having an outer diameter of 3.1 mm.

A portion 12 mm below the upper end face of the stabilized zirconia 21 is inserted into an alumina tube 23 having an inner diameter of 5 mm, an outer diameter of 8 mm and a length of 600 mm, and is fixed to the alumina tube 23 via a zirconia cement 24. I have.
The alumina tube 23 is provided so that the vicinity of the contact portion between the recess 211 and the platinum conductor 5 is not affected by the gas above the melt 7. The alumina tube 23 may be a tube made of another material that does not allow air to permeate and has electrical insulation and heat resistance. Further, an air injection pipe 25 is provided to reduce the influence of the gas above the melt 7 permeating the zirconia cement 24 and to fill the vicinity of the contact surface between the recess 211 and the platinum conductor 5 with an air atmosphere. In the present embodiment, the air injection pipe 25 has an outer diameter of 3 mm and an inner diameter of 2 mm.
mm and an alumina tube having a length of 600 mm.

FIG. 3 is a longitudinal sectional view of the measuring electrode 3 constituting the oxygen sensor 1. As shown in FIG.
Has a diameter of 1.0 mm, and the potential measurement portion at the tip is formed in a spiral shape with an outer diameter of 20 mm in order to increase the contact area with the melt 7. Since a local battery is easily formed around the interface between the melt 7 and the atmospheric gas 8, the platinum wire 6 is electrically insulated by covering the portion other than the tip portion immersed in the melt 7 with the insulator 31. . In the present embodiment, the insulator 31 is a high-purity alumina tube with a high sinterability having an inner diameter of 1.1 mm and an outer diameter of 3 mm, which is a ceramic that is not easily eroded by the high-temperature melt 7.
The measuring electrode 3 configured in this manner depends on the time of immersion in the melt 7, the composition of the melt 7, and the temperature.
In the case of a soda-lime glass melt at 0 ° C., continuous measurement for 200 hours or more is possible with an alumina tube having a thickness of about 3 mm.
Furthermore, if the measurement is performed for a long time, the melt 7 permeates into the gap between the alumina tube 31 and the platinum wire 6, and a local battery may be formed at the interface with the gas in the alumina tube 31. In order to avoid this, it is desirable to block the infiltration of the melt 7 and gas into the gap between the alumina tube 31 and the platinum wire 6. In the present embodiment, the ceramic cement 32 having excellent insulation properties is filled. . In the present embodiment, as the ceramic cement 32, an alumina cement having a coefficient of thermal expansion close to that of the alumina tube 31 is used, and sintered at a temperature of 1200 ° C. for 3 hours after filling. If the ratio of the outer diameter of the platinum wire 6 to the inner diameter of the alumina tube 31 is small, the melt 7 may enter the gap even if the ceramic cement 32 is filled. (Alumina tube 31 and platinum wire 6 of the present embodiment satisfy this condition).

FIG. 4 shows the oxygen sensor 1 having a composition of 20 (mol%) of Na ₂ O, 10 (mol%) of CaO,
The results of immersion in a glass melt at 1200 ° C. to 1350 ° C. containing 70 (mol%) of O ₂ and measurement of the potential between electrodes, that is, the change in oxygen activity are shown. In FIG. 4, (A) shows a case where the measuring electrode 3 is immersed in the melt 7;
The result of repeated measurement under the same conditions as (A) is shown. (C) shows a measurement result when the measurement electrode 3 is immersed near the surface of the melt 7. As shown in FIG. 4, the oxygen sensor 1 responded with good reproducibility to the temperature fluctuation of the melt and the oxygen concentration fluctuation of the atmospheric gas. This means that fluctuations in oxygen activity in the melt caused by fluctuations in the temperature of the melt or fluctuations in the oxygen concentration of the atmosphere gas can be detected, and the measured values are not directly affected by the fluctuations in the oxygen concentration of the atmosphere gas. . This is more apparent from the comparison with the measurement result of FIG. Further, the measured value of (C) is almost equal to the atmospheric oxygen concentration, which means that the oxygen activity near the inner surface of the melt can be measured. Therefore, a difference in the oxygen activity in the depth direction of the melt can be detected.

The temperature of the glass melt is 1350 ° C.
Even in a high temperature range of up to 1400 ° C., the influence of the atmosphere gas on the melt could be detected without being directly influenced by the oxygen concentration fluctuation of the atmosphere gas, and accurate potential difference measurement was possible.

FIG. 5 shows that the oxygen sensor contains 1 (mol%) of Sb ₂ O ₃ as antimony and 20 (mol%) of Na ₂ O.
%), 10 (mol%) of CaO, and 70 (mol%) of SiO ₂ were immersed in a glass melt, and the results of measuring the fluctuation of the oxygen activity in the melt are shown. In FIG. 5, (a) shows the result of measurement with the measurement electrode 3 shown in FIG. 3, and (b) shows the result of measurement with the platinum wire 6 not covered with the alumina tube 31 shown in FIG. In this case, it is considered that there is almost no change in the oxygen activity in the melt due to the change in the oxygen concentration of the atmosphere gas due to the action of antimony in the melt. As shown in the figure, the measured value of (a) is hardly affected by the change in the oxygen concentration of the atmospheric gas. This means that the value measured by the measurement electrode 3 shown in FIG. 3 is not directly affected by the change in the oxygen concentration of the atmospheric gas. Further, the measured value (b) is directly affected by the change in the oxygen concentration of the atmosphere gas because a local battery is easily formed near the interface between the melt and the atmosphere gas.

As shown in FIG. 6, the measuring electrode 3 is
An alumina tube 31 having an inner diameter of 1.6 mm and a platinum wire 6 having an outer diameter of 1.5 mm were used, and the gap between the alumina tube 31 and the platinum wire 6 was not filled with alumina cement. When the oxygen activity of the melt was measured using the measurement electrode 3, air flowed through the gap, and a local battery was formed at the interface with the melt, and stable potential difference measurement could not be performed.

[0019]

As described above, according to the oxygen sensor of the present invention, the columnar stabilized zirconia having the concave portion extending downward from the upper end surface is used as the reference electrode, and the outer diameter of the concave portion is larger than the inner diameter of the concave portion. Since the spring-shaped platinum conductor having a diameter is elastically reduced in diameter and inserted and fixed in the recess, the influence of the difference in thermal expansion coefficient between the stabilized zirconia and the platinum conductor compared to the conventional oxygen sensor is reduced. Stable measurement that is difficult to receive is possible, and it is also possible to manufacture easily.

Further, since the measuring electrode is covered with ceramics and the gap between the measuring electrode and the ceramics is filled with ceramic cement, formation of a local battery at the interface between the melt and the atmosphere gas is prevented, and the measured value is reduced. It is possible to suppress errors.

Therefore, the oxygen sensor according to the present invention enables precise measurement of oxygen activity in a local region in a high-temperature melt.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a usage state of an oxygen sensor for a high-temperature melt according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a reference electrode included in the oxygen sensor shown in FIG.

FIG. 3 is a longitudinal sectional view of a measurement electrode constituting the oxygen sensor shown in FIG. 1;

FIG. 4 shows an example of a result obtained by immersing the oxygen sensor shown in FIG. 1 in a high-temperature glass melt and measuring a change in oxygen activity.

FIG. 5 shows an example of a result obtained by immersing an oxygen sensor in a high-temperature glass melt containing antimony and measuring a change in oxygen activity.

FIG. 6 is a longitudinal sectional view of a reference electrode used for comparison with the oxygen sensor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Reference electrode 3 Measurement electrode 4 Voltmeter 5 Platinum lead wire 6 Platinum wire 7 Melt 8 Atmospheric gas 21 Stabilized zirconia 22 Platinum paste 23 Alumina tube 24 Zirconia cement 25 Air injection tube 31 Alumina tube 32 Alumina cement 211 Recess

[Procedure amendment]

[Submission date] March 29, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

That is, the present invention relates to an oxygen sensor for immersing a reference electrode and a measurement electrode in a glass melt and measuring the oxygen activity of the glass melt from a potential difference between the reference electrode and the measurement electrode. the reference electrode is provided with a columnar stabilized zirconia recesses are formed extending downward from the upper end surface, pillar
The portion of the shape-stabilized zirconia below the recess is the
When immersed in the glass melt, the bottom surface of the concave portion is
Is lengthened As can be separated from the surface, in the recess, is fixed to the large coil spring-shaped platinum wire having an outer diameter is inserted is elastically reduced in diameter in the recess than the inner diameter of the recess The measurement electrode is a conductive core wire for an electrode, a cylindrical ceramic having a gas barrier property and a non-conductive property that covers the core wire at a position including an interface between the glass melt and the atmospheric gas and in a state in which a tip end is exposed, It is an object of the present invention to provide an oxygen sensor for a high-temperature melt, comprising: a core wire; and a ceramic cement having a gas barrier property and a non-conductivity filled in a gap between the cylindrical ceramics.

Claims (4)

[Claims] 1. An oxygen sensor for immersing a reference electrode and a measurement electrode in a high-temperature melt and measuring the oxygen activity of the high-temperature melt from a potential difference between the reference electrode and the measurement electrode, wherein the reference electrode is A column-shaped stabilizing zirconia having a concave portion extending downward from the upper end surface is provided, and a coil spring-shaped platinum conductive wire having an outer diameter larger than the inner diameter of the concave portion is elastically reduced in diameter and inserted into the concave portion. The measurement electrode is fixed in the concave portion, and the measurement electrode includes a conductive core wire for an electrode, and a gas barrier property and a non-conductive property that cover the core wire at a position including the interface between the high-temperature melt and the atmosphere gas and in a state where the tip is exposed. An oxygen sensor for a high-temperature melt, comprising: a cylindrical ceramic having: a core ceramic; and a ceramic cement having a gas barrier property and a non-conductivity filled in a gap between the core wire and the cylindrical ceramic. Sir. 2. The oxygen sensor for a high-temperature melt according to claim 1, wherein a platinum paste is applied to a contact portion of the pillar-shaped stabilized zirconia with the platinum conductor on an inner surface of the concave portion. 3. The oxygen sensor for a high-temperature melt according to claim 1, wherein a ratio of an outer diameter of the core wire to an inner diameter of the cylindrical ceramic is 0.95 or more and less than 1. 4. The method according to claim 1, wherein the core wire is a platinum wire, the cylindrical ceramic is made of alumina, and the ceramic cement is alumina cement.
4. The oxygen sensor for a high-temperature melt according to any one of items 1 to 3.