JP2006104035A - Method for removing oxygen in float bath atmosphere - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for preventing the occurrence of tin faults in a float bath. <P>SOLUTION: The method for preventing the occurrence of tin faults is provided for removing oxygen existing in the form of oxygen or water vapor in a float bath atmosphere, the method comprises: arranging an oxygen removing means in which a first thin-layer electrode, a base body having a thin-layer structure and made of a solid electrolyte ceramic having oxygen ion conductivity, and a second thin-layer electrode are laminated in this order, in such a manner that the first thin-layer electrode is brought into contact with the float bath atmosphere and the second thin-layer electrode is brought into contact with the atmosphere outside the float bath; and then discharging oxygen existing in the form of oxygen or water vapor to the atmosphere outside the float bath through the second thin-layer electrode by catalytically reducing oxygen or water vapor existing in the float bath atmosphere with the first thin-layer electrode by applying negative electric charge and positive electric charge to the first thin-layer electrode and the second thin-layer electrode, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for removing oxygen in a float bath atmosphere. More specifically, the oxygen or water vapor in the float bath atmosphere is removed by catalytic reduction using a solid electrolyte having oxygen ion conductivity to remove oxygen or oxygen present in the float bath atmosphere. On how to do.
The present invention also relates to a method for reducing the oxygen concentration in a float bath atmosphere or the oxygen concentration present in the state of water vapor using the above-described method.
The present invention also relates to a method for reducing the oxygen concentration in molten tin using the above-described method.
The present invention also relates to a method for reducing the amount of hydrogen supplied to the float bath atmosphere using the method described above.

The float process is extremely excellent in that glass with high flatness can be produced continuously and in large quantities by continuously pouring molten glass at a controlled flow rate into a float bath containing molten tin. Is the method.
In order to maintain tin in a molten state, it is necessary to keep the inside of the float bath at a high temperature, specifically, 600 ° C. or higher. When oxygen is present in such a high-temperature float bath atmosphere, oxygen is dissolved in the molten tin to produce tin oxide. When this tin oxide adheres to the molten glass (glass ribbon) flowing in the float bath, it becomes a so-called tin defect, and the yield of the glass manufactured by the float process decreases.

  In order to prevent oxygen from entering, it is preferable that the float bath has a completely sealed structure. However, the float bath cannot be completely sealed because of its structure. For this reason, the float bath atmosphere is kept in a reducing atmosphere by introducing nitrogen and hydrogen. Here, in order to prevent the occurrence of tin defects, it is preferable to increase the hydrogen concentration in the float bath atmosphere. However, an increase in the amount of hydrogen supplied to the float bath atmosphere leads to an increase in glass manufacturing costs.

In order to reduce defects derived from metal oxides such as tin oxide defects during float glass production, a part of the molten metal in the molten metal bath (float bath) is extracted from the molten metal bath to remove oxygen. Patent Document 1 discloses a method of controlling the oxygen concentration in the molten metal to be less than the saturation solubility by returning to the molten metal bath after that. However, in the method described in Patent Document 1, it is necessary to provide a circulation system for circulating the molten metal outside the molten metal bath, and in order to remove oxygen in the molten metal, the molten metal is removed from the molten metal. It is necessary to cool to a temperature below the minimum temperature in the bath and reheat the molten metal before returning to the molten metal bath.
Moreover, in order to prevent the equipment in the float bath from deteriorating due to the reducing atmosphere, the gas composition in the upper space of the molten metal bath surface covered with the strip glass flow (glass ribbon) and the strip glass flow Japanese Patent Application Laid-Open No. H10-228707 describes a method for making the gas composition of the uncovered region different. However, since it is necessary to provide a partition that separates the two areas in the upper space of the molten metal bath, it is necessary to significantly modify the equipment in order to apply it to the existing float bath, and the existing equipment is suspended. It is practically impossible to remodel without it.

  Patent Document 3 discloses an apparatus for removing moisture present in a gas by dry electrolysis using a solid electrolyte ceramic. However, the moisture removing device disclosed in Patent Document 3 is based on an adsorption device that adsorbs and removes moisture in the gas described in the prior art in Patent Document 3 and a cold trap that uses liquid nitrogen as a refrigerant. Similar to a moisture adsorption device, a getter device, etc., it is intended to remove moisture in the air to obtain dry air. For this reason, in the moisture removing apparatus described in Patent Document 3, the problem to be solved by the invention is the miniaturization of the moisture removing apparatus. Further, the moisture removing device described in Patent Document 3 introduces a process gas for removing moisture into a primary flow path formed on the inner peripheral side of a cylindrical electrolyte partition wall. Therefore, it aims at removing the water | moisture content in gas locally in the space limited very much.

That is, in order to prevent the occurrence of tin defects in the float bath, it has been considered necessary to introduce hydrogen into the float bath atmosphere to make the float bath atmosphere a reducing atmosphere. As another method, a method described in Patent Document 1 or 2 has been proposed, but in order to implement these methods using an existing float bath, it is necessary to modify the equipment.
On the other hand, Patent Document 3 discloses an apparatus for removing moisture in a gas by dry electrolysis using a solid electrolytic ceramic. However, the apparatus locally removes moisture in a gas within a very limited space. The device is applied to a large-scale region such as a float bath atmosphere to remove oxygen in the atmosphere and has not been studied. It was.

JP 2000-247658 A Japanese Patent Laid-Open No. 11-21137 JP-A-8-24555

Therefore, an object of the present invention is to provide a novel method for preventing the occurrence of tin defects in a float bath.
In order to solve this problem, an object of the present invention is to provide a method for removing oxygen present in the state of oxygen or water vapor in a float bath atmosphere.
Another object of the present invention is to provide a method for reducing the oxygen concentration in a float bath atmosphere or the oxygen concentration present in the state of water vapor in order to solve this problem.
Another object of the present invention is to provide a method for reducing the oxygen concentration in molten tin in order to solve this problem.
It is a further object of the present invention to provide a method for reducing the amount of hydrogen supplied to a float bath atmosphere to maintain a reducing atmosphere.

To achieve the above object, the present invention is a method for removing oxygen present in the state of oxygen or water vapor in a float bath atmosphere,
A first thin layer electrode, an oxygen removing means in which a substrate having a thin layer structure made of a solid electrolyte ceramic having oxygen ion conductivity and a second thin layer electrode are laminated in this order, the first thin layer electrode being floated Arranged in contact with the bath atmosphere, the second electrode in contact with the atmosphere outside the float bath, and applying a negative charge to the first thin layer electrode and a positive charge to the second thin layer electrode to float Oxygen or water vapor present in the bath atmosphere is contact-reduced by the first thin layer electrode, and oxygen present in the state of oxygen or water vapor is transferred to the atmosphere outside the float bath via the second thin layer electrode. By releasing, there is provided a method for removing oxygen existing in the state of oxygen or water vapor in a float bath atmosphere (hereinafter sometimes simply referred to as “oxygen removal method of the present invention”).

In the oxygen removing means, the base has a bottomed cylindrical shape with one end opened, and the first thin layer electrode is formed on an outer surface of the bottomed cylindrical shape, and the second thin layer electrode Is preferably formed on the inner surface of the base having a bottomed cylindrical shape.
Here, by allowing gas to flow inside the bottomed cylindrical base of the oxygen removing means, oxygen that has moved inside the base is released to the atmosphere outside the float bath via the second thin layer electrode. It is preferable to make it.

In the oxygen removal method of the present invention, the solid electrolyte ceramic is preferably made of stabilized zirconia.
In the oxygen removal method of the present invention, the first and second thin layer electrodes are preferably at least one selected from the group consisting of platinum, titanium carbide, titanium nitride, graphite, and glassy carbon.

  The present invention also provides a method for reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration existing in the state of water vapor (hereinafter simply referred to as “in the float bath atmosphere of the present invention”) using the above-described oxygen removal method of the present invention. It is also sometimes referred to as a “method of reducing the oxygen concentration of”.

  In addition, the present invention uses the above-described method for reducing the oxygen concentration in the float bath atmosphere to reduce the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor, thereby reducing the oxygen concentration. A method is provided for reducing the oxygen concentration in molten tin that is in equilibrium with the concentration.

  The present invention also provides a float bath by reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor using the above-described method for reducing the oxygen concentration in the float bath atmosphere. A method is provided for reducing the amount of hydrogen supplied to an atmosphere.

The oxygen removal method of the present invention can reduce the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the water vapor state by removing oxygen present in the state of oxygen or water vapor in the float bath atmosphere. it can.
The oxygen removing method of the present invention has a structure in which thin layer electrodes are formed on the inner surface and the outer surface of a solid electrolyte ceramic substrate having oxygen ion conductivity, and has a bottomed cylindrical shape with one end opened. Can be implemented by inserting from the side wall of the float bath. For this reason, compared with the conventional method that requires a circulation system for circulating molten metal outside the float bath or a partition wall in the upper space of the molten metal bath, the equipment is used when the existing float bath is used. Less remodeling is required.

In the method for reducing the oxygen concentration in the float bath atmosphere of the present invention, the occurrence of tin defects during the production of float glass is prevented by reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor. The yield of float glass is improved.
According to the method for reducing the oxygen concentration in the float bath atmosphere of the present invention, the oxygen concentration in the molten tin can be reduced by reducing the oxygen concentration in the float bath or the oxygen concentration present in the state of water vapor. it can. And the production | generation of the tin oxide in this molten tin is effectively prevented by reducing the oxygen concentration in molten tin. By reducing the oxygen concentration in the molten tin, the oxygen concentration in the molten tin can be kept below the saturation solubility even on the downstream side of the float bath where the temperature of the molten tin is low. This is particularly effective in preventing the formation of tin oxide in the molten tin.

  According to the method of the present invention, by reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor, the amount of hydrogen supplied to the float bath atmosphere is reduced for the purpose of reducing the atmosphere. can do. Thereby, the manufacturing cost of float glass can be reduced.

The present invention will be further described below with reference to the drawings.
FIG. 1A is a side view of oxygen removing means used in the oxygen removing method of the present invention, and FIG. 1B is a side sectional view of the oxygen removing means. The oxygen removing means 1 shown in FIGS. 1A and 1B includes a base 2 having a bottomed cylindrical shape with one end opened, and a cap 6 attached to the open end of the base 2. The base 2 having a bottomed cylindrical shape is made of a solid electrolyte ceramic having oxygen ion (O ²⁻ ) conductivity. Thin layer electrodes 3 and 4 are respectively formed on the outer surface and the inner surface of the substrate 2. That is, when viewed from the outer surface side of the base body 2, the oxygen removing means 1 has a structure in which the thin layer electrode 3, the base body 2, and the thin layer electrode 4 are laminated in this order.

  A part of the thin layer electrode 4 laminated on the inner surface of the substrate 2 is folded at the opening end of the substrate 2 and drawn out on the outer surface of the substrate 2. That is, the thin layer electrode 3 and a part of the thin layer electrode 4 are present on the outer surface of the substrate 2. With this configuration, the oxygen removing unit 1 can easily apply a DC voltage from an external power source. It should be noted that the material corresponding to the portion between the thin layer electrodes 3 and 4 is made of the base 2 material so that a short circuit does not occur between the portion of the thin layer electrode 4 located on the outer surface of the base 2 and the thin layer electrode 3. By providing the portion (insulating portion) 9 where the solid electrolytic ceramic is exposed, the electrodes 3 and 4 are insulated.

  A gas supply pipe 7 and a discharge pipe 8, each of which is a hollow pipe through which gas can flow, are attached to the cap 6 attached to the open end of the base 2. As will be described in detail later, when the method of the present invention is carried out, a gas such as nitrogen or dry air is supplied into the substrate 2 from the gas supply pipe 7. The gas supplied into the substrate 2 is discharged from the discharge pipe 8. That is, a flow path through which gas flows is formed in the order of the gas supply pipe 7, the inside of the base 2 and the discharge pipe 8. By having such a configuration, oxygen that has moved from the float bath atmosphere to the inside of the substrate 2 by catalytic reduction at the thin layer electrode 3 is removed from the inside of the substrate 2 by the gas flow.

The material which comprises the base | substrate 2 can be widely selected from the solid electrolyte ceramic which has oxygen ion conductivity. Specific examples of the solid electrolyte ceramic that can be used as the base material 2 include stabilized zirconia stabilized with yttria, magnesia, calcia, ceria, scandia, alumina, and the like. Among these, stabilized zirconia stabilized with yttria, magnesia, calcia, ceria or scandia is preferable because of its stable characteristics at high temperatures and excellent oxygen ion conductivity. As a specific example of such stabilized zirconia, a stabilized zirconia stabilized with scandia represented by (Sc ₂ O ₃ ) _0.1 (ZrO ₂ ) _0.9 is preferable. Specific examples of stabilized stabilized zirconia with yttria, commercially, ZR-6Y of Nikkato Corporation (Y ₂ O ₃ 6mol% _{doping), ZR-8Y (Y 2} O 3 8mol% doped) Exists. As specific examples of stabilized zirconia stabilized with magnesia, there are ZR-9M (9 mol% magnesia dope) and ZR-15M (15 mol% magnesia dope) manufactured by Nikkato Co., Ltd. as commercially available products. As specific examples of stabilized zirconia stabilized with calcia, there are ZR-11 (11 mol% calcia dope) and ZR-15 (15 mol% calcia dope) manufactured by Nikkato Co., Ltd. as commercially available products. Among these, (Sc ₂ O ₃ ) _0.1 (ZrO ₂ ) _0.9 and ZR-8Y are particularly preferable.

  The material of the thin layer electrodes 3 and 4 has oxygen ion conductivity, a small specific resistance value, a float bath atmosphere, that is, a high temperature of 600 to 1200 ° C., and a gas composition having a reducing atmosphere composed of nitrogen and hydrogen. Need to be done. Furthermore, the oxygen reduced by the contact reduction by the thin layer electrode 3 that is in contact with the float bath atmosphere moves inside the substrate 2 and becomes rich in oxygen. For this reason, the thin layer electrode 4 formed on the inner surface of the substrate 2 is also required to have excellent oxidation resistance. Examples of the electrode material satisfying these include platinum, titanium carbide, titanium nitride, graphite, and glassy carbon. Among these, platinum is particularly preferable because it is excellent in oxygen ion conductivity, has a small specific resistance value, and is excellent in both reduction resistance and oxidation resistance.

  The thickness of the thin layer electrodes 3 and 4 is not particularly limited as long as the oxygen ion conductivity is not impaired. For example, when platinum is used as the thin layer electrode material, the electroless platinum is electrolessly formed so that the inner surface and the outer surface of the base body 2 have a thickness of about 30 μm in a state where a mask is provided in a portion corresponding to the insulating portion 9 on the outer surface of the base body 2. It only has to be plated. In this case, the insulating portion 9 is a recess having a height of about 30 μm provided between the thin layer electrodes 3 and 4.

  Since the cap 6, the gas supply pipe 7 and the exhaust pipe 8 exist in the atmosphere outside the float bath at the time of use, there are fewer restrictions on the materials than the base 2 and the thin layer electrodes 3 and 4. Specifically, these materials may be selected from the viewpoints of workability, mechanical strength, weather resistance, and ease of joining to the substrate 2. In the examples described later, stainless steel caps 6, gas supply pipes 7 and exhaust pipes 8 were used. However, the material of the cap 6, the gas supply pipe 7 and the exhaust pipe 8 is not limited to this, and may be a normal steel material, an alloy steel other than stainless steel, or another metal material such as aluminum, or alumina. Or a ceramic material such as mullite. The base 2 and the cap 6 and the cap 6 and the gas supply pipe 7 or the exhaust pipe 8 are joined using a known joining means, specifically, for example, an organic or inorganic adhesive. Alternatively, metal solder or glass solder may be used. In the examples described later, the cap 6, the gas supply pipe 7 and the exhaust pipe 8 were joined using metal solder. As described above, since the cap 6 is mainly made of a conductive material, a zirconia-based adhesive was used for bonding the base 2 and the cap 6 for the purpose of insulation.

FIG. 2 is a view for explaining the oxygen removing method of the present invention, and schematically shows a float bath. In FIG. 2, the float bath 10 includes a bath portion 11 that accommodates molten tin 20, and a ceiling portion 12 and a side wall portion 121 that are located above the bath 11 and isolate the float bath atmosphere from the outside.
A ribbon-like molten glass (glass ribbon) 30 floats on the molten tin 20 and moves in the float bath 10 in the downstream direction. In FIG. 2, the front side or the back side of the drawing is the moving direction of the glass ribbon 30.

  In this specification, the float bath atmosphere refers to an atmosphere of a space surrounded by the bath part 11, the ceiling part 12 and the side wall part 121. The temperature of the float bath atmosphere is in the range of 600 to 1200 ° C., although it depends on the specifications of the float bath 10 and the position in the float bath 10. The gas composition of the float bath atmosphere is a mixed gas of nitrogen and hydrogen (hydrogen content: 4 to 10 vol%). An example is a mixed gas of 10 vol% hydrogen and 90 vol% nitrogen.

  In order to prevent tin defects, it is desirable that the float bath atmosphere be completely isolated from the outside and be substantially oxygen-free. However, due to the structure of the float bath 10, it is impossible to completely prevent oxygen from entering the float bath atmosphere. Oxygen that has entered the float bath atmosphere at a high temperature and in a reducing atmosphere usually reacts with hydrogen in the float bath atmosphere and exists in the state of water vapor.

The oxygen removal method of the present invention is mainly intended to remove oxygen present in the state of water vapor in the float bath atmosphere, and as a result, to reduce the oxygen concentration in the float bath atmosphere.
When carrying out the oxygen removing method of the present invention, the oxygen removing means 1 shown in FIG. 1 is inserted into the float bath atmosphere from the side wall 121 of the float bath 10 as shown in FIG. The important point here is that the oxygen removing means 1 is not completely inserted into the float bath atmosphere. Specifically, the bottom side of the oxygen removing means 1 having a bottomed cylindrical shape is disposed in the float bath atmosphere, and the opening end, that is, the side on which the cap 6 is attached is disposed in the atmosphere outside the float bath. Like that. As long as this condition is satisfied, most of the oxygen removing means 1 is preferably disposed in the float bath atmosphere. Thereby, the effective area of the thin layer electrode 3 used for the catalytic reduction of oxygen or water vapor in the float bath atmosphere increases. However, for the convenience of applying a DC voltage from the external power source 50, at least a part of the thin layer electrode 3 and a portion drawn out on the outer surface of the base 2 of the thin layer electrode 4 are arranged in an atmosphere outside the float bath. It is preferable.

  As described above, the thin layer electrodes 3 and 4 are thin films having a thickness of about 30 μm made of an oxygen ion conductive material such as platinum. Therefore, there is a possibility that the thin layer electrodes 3 and 4 may be damaged when the oxygen removing means 1 is inserted from the side wall portion 121 that is generally made of refractory bricks. For this reason, in FIG. 2, in order to prevent damage to the thin-layer electrodes 3 and 4, the protective tube 100 is attached to a portion that contacts the side wall 121 on the outer periphery of the oxygen removing means 1. The protective tube 100 is made of a material that can withstand the high temperature and reducing atmosphere of the float bath atmosphere and has sufficient mechanical strength. As such a material, ceramics such as alumina and mullite can be used.

The dimensions of the oxygen removing means 1 are not particularly limited, and various conditions, specifically, for example, the dimensions of the float bath 10 including the thickness of the side wall 121, the required oxygen removal level, and the oxygen used. The number can be appropriately selected according to the number of removal means 1. However, as shown in FIG. 2, the oxygen removing means 1 is substantially the same as the width of the portion inserted in the float bath atmosphere not covered with the glass ribbon 30 of the molten tin 20 or It is preferable that it is more.
It is known that tin oxide is likely to be generated in the portion of the molten tin 20 that is not covered with the glass ribbon 30 for the following reason. First, oxygen present in the state of oxygen or water vapor in the float bath atmosphere can be dissolved directly in the molten tin 20. As a result, tin oxide is produced. Secondly, when the molten tin is vaporized, tin oxide is generated by reacting with oxygen or oxygen present in the state of water vapor in the float bath atmosphere.
Therefore, in the float bath atmosphere, the oxygen that is present in the state of oxygen or water vapor is removed at the portion not covered with the glass ribbon 30 of the molten tin 20, and the oxygen concentration in the float bath atmosphere or the state of water vapor is present. It is preferable to reduce the oxygen concentration in order to prevent the generation of tin oxide in the float bath and thereby the generation of tin defects.

When carrying out the method of the present invention, a gas such as nitrogen or dry air is supplied from the gas supply pipe 7 attached to the cap 6 to the inside of the oxygen removing means 1 (base 2). 1 A path through which gas flows is formed in the order of the inside and the exhaust pipe 8.
Subsequently, a DC voltage is applied from the external power supply 50 so that a negative charge is applied to the thin layer electrode 3 provided on the outer surface of the oxygen removing means 1 (base 2) and a positive charge is applied to the thin layer electrode 4 provided on the inner surface. Apply. In other words, the thin layer electrode 3 in contact with the float bath atmosphere is connected to the cathode of the external power source 50, and the thin layer electrode 4 in contact with the atmosphere outside the float bath is connected to the anode of the external power source 50.

In the thin layer electrode 3 to which a positive charge is applied, oxygen or water vapor in the float bath atmosphere is catalytically reduced. In the case of oxygen (O ₂₎ is reduced to oxygen ions (O ^2-). Oxygen ions pass through the solid electrolyte constituting the substrate 2 and move to the thin layer electrode 4. The oxygen ions are oxidized by the thin layer electrode 4 to which a positive charge is applied, returned to oxygen (O ₂ ), and released into the oxygen removing means 1. In the case of water vapor, it is electrolyzed into hydrogen and oxygen. Oxygen is released into the oxygen removing means 1 as described above. On the other hand, hydrogen is released into the float bath atmosphere in contact with the thin layer electrode 3. As described above, since the gas is supplied into the oxygen removing unit 1, the oxygen released into the oxygen removing unit 1 is removed to the outside by this gas.

  In this way, oxygen is removed from the float bath atmosphere, and the oxygen concentration in the float bath atmosphere is reduced. In addition, since the fundamental object of the present invention is to prevent tin defects when producing glass by the float process, it is not always necessary to reduce the oxygen concentration in the entire float bath atmosphere. It is only necessary to prevent the occurrence of tin defects by reducing the oxygen concentration at a specific portion of the above. Therefore, when viewed as the entire float bath atmosphere, it is not always necessary to reduce the oxygen concentration. In the float bath atmosphere, molten tin 20 is mainly generated where tin oxide that causes tin defects is generated. It is preferable that the oxygen concentration is reduced in a portion corresponding to a portion not covered with the glass ribbon 30.

  The temperature of the float bath atmosphere is not uniform in the float bath 10, and is higher on the upstream side of the float bath 10 and lowers as it goes downstream. When carrying out the method of the present invention, the oxygen removing means 1 is preferably installed on the upstream side of the float bath 10 where the temperature of the float bath atmosphere is high. For this reason, the electric conductivity of the solid electrolyte constituting the substrate 2 generally increases as the temperature rises. The same applies to stabilized zirconia which is a solid electrolyte suitable as the material for the substrate 2. When the electrical conductivity increases, the transport rate of oxygen ions as a medium also increases, so that the amount of oxygen released into the oxygen removing means 1 increases.

  In principle, the amount of oxygen released into the oxygen removing means 1 increases according to the magnitude of the direct current applied to the thin layer electrodes 3 and 4. However, as will be shown later in the examples, the amount of oxygen released into the oxygen removing means 1 depends on the conversion efficiency in the thin layer electrodes 3 and 4 (in the thin layer electrode 3, the conversion efficiency from oxygen to oxygen ions, thin The layer electrode 4 reaches saturation at a certain stage due to the conversion efficiency of oxygen ions to oxygen. Therefore, the magnitude of the direct current applied to the thin layer electrodes 3 and 4 depends on the oxygen removing means 1 to be used, specifically, the material, surface area or thickness of the thin layer electrodes 3 and 4, and the solid electrolyte constituting the substrate 2. May be selected as appropriate in accordance with various conditions such as the type or thickness of the glass, the temperature of the float bath atmosphere, or the gas composition. For example, in the examples described later, a direct current of 0.1 A to 0.3 A was applied.

The present invention also provides a method for reducing the oxygen concentration in molten tin using the method for reducing the oxygen concentration in the float bath atmosphere of the present invention.
The oxygen partial pressure P (O ₂ ) in the float bath atmosphere and the oxygen activity a (O) in the molten tin have a relationship represented by the following formula.
a (O) = {(P (O ₂ )) × exp (−ΔG / RT)} ^1/2
Here, a (O): oxygen activity P (O ₂ ): oxygen partial pressure ΔG = −88.816 + 0.02234 × T
R = 1.98648
According to the above equation, if the oxygen partial pressure in the float bath atmosphere is lowered, the oxygen activity in the molten tin, in other words, the oxygen concentration in the molten tin can be lowered. The oxygen partial pressure in the float bath is directly related to the oxygen concentration in the float bath atmosphere. Therefore, the oxygen concentration in molten tin can be reduced by reducing the oxygen concentration in the float bath atmosphere using the method of the present invention. By reducing the oxygen concentration in the molten tin, it is possible to prevent the formation of tin oxide in the molten tin, thereby preventing the occurrence of tin defects.

FIG. 3 is a graph showing the relationship between the temperature of molten tin (T (° C.)) and the oxygen activity in molten tin (a (O) (ppm)), H ₂ = 8%, dew point = −. The relationship at 30 ° C. is shown. As is apparent from FIG. 3, the oxygen activity in the molten tin decreases as the temperature of the molten tin decreases. For this reason, on the downstream side of the float bath where the temperature is low, the oxygen concentration in the molten tin may exceed the oxygen activity, that is, it may be supersaturated. It is known that tin oxide is particularly easily generated when oxygen is supersaturated in molten tin. Therefore, in order to prevent tin defects, it is important to always keep the oxygen concentration in the molten tin below the oxygen activity. According to the present invention, by reducing the oxygen concentration in the molten tin, the oxygen concentration in the molten tin can be kept below the oxygen activity even on the downstream side of the low temperature float bath.
Therefore, it is preferable to install the oxygen removing means upstream of the float bath where the temperature of molten tin is high and the oxygen activity in the molten tin is high. If the oxygen removal means is installed upstream of the float bath having a high oxygen activity in the molten tin and the oxygen concentration in the molten tin is reduced in advance, the molten tin reaches the downstream side of the float bath, Even when the temperature of the molten tin decreases and the oxygen activity in the molten tin decreases, the oxygen concentration in the molten tin can be kept below the oxygen activity.

Further, according to the present invention, the amount of hydrogen supplied to the float bath atmosphere can be reduced in order to obtain a reducing atmosphere by reducing the oxygen concentration in the float bath atmosphere. That is, the present invention provides a method for reducing the amount of hydrogen supplied to the float bath atmosphere by using the method for reducing the oxygen concentration in the float bath atmosphere.
When the oxygen removal amount (0.58 mL / min (applied with a direct current of 0.2 A applied)) obtained in the examples described later is calculated, the method for reducing the oxygen concentration in the float bath atmosphere of the present invention is not implemented. As compared with the case of the case, the amount of hydrogen supplied to the float bath atmosphere can be reduced by about 40%.

As mentioned above, although the method of this invention was demonstrated using drawing, the method of this invention is not limited to the form shown in figure. For example, in FIG. 2, the oxygen removing means 1 is inserted from the side wall 121 of the float bath 10, but the oxygen removing means may be inserted from the ceiling 12 if practicable. Also, as the oxygen removing means 1, a bottomed cylindrical shape having an open end is used, but the oxygen removing means includes a first thin layer electrode, a substrate having a thin layer structure, and a second thin layer electrode. The layers may be stacked in this order, and the first thin layer electrode may be in contact with the float bath atmosphere and the second electrode may be in contact with the atmosphere outside the float bath. Therefore, all or part of the ceiling 12 or the side wall 121 of the float bath 10 is formed of a laminated body in which the first thin layer electrode, the thin layer base, and the second thin layer electrode are laminated in this order. You may have done. However, when the method of the present invention is carried out with an existing float bath, the oxygen removal means 1 shown in FIG. 1 can be used because of the balance between the degree of modification required for the float bath and the effect of reducing the oxygen concentration obtained. preferable.
Further, as long as the oxygen concentration in the float bath atmosphere can be reduced to prevent the occurrence of tin-based defects, it may be carried out not at the upstream side of the float bath but at other portions, for example, the downstream side. .

Hereinafter, the present invention will be further described by examples.
In this example, the oxygen removing means 1 shown in FIG. 1 was used. The oxygen removing means 1 is a base 2 made of yttria-stabilized zirconia (Y ₂ O ₃ 8 mol% dope, stability 100%) having a bottomed cylindrical shape (inner diameter 17 mm, outer diameter 21 mm, length 600 mm). The thin layer electrodes 3 and 4 were formed by electrolessly plating platinum on the inner surface and the outer surface. Here, the degree of stabilization of 100% refers to the case where the sintered body having the same composition is prepared and pulverized, and the crystallinity is evaluated by X-ray diffraction.
When plating on the outer surface side of the substrate 2, plating was performed with a mask on a part of the outer surface in order to form the insulating portion 9. In addition, a stainless steel cap 6 was fixed to the open end of the base 2 using a commercially available zirconia-based adhesive (Response (trade name) 904, manufactured by COTRONICS). The cap 6 is provided with two stainless steel pipes having an inner diameter of 4 mm and an outer diameter of 6 mm as a gas supply pipe 7 and an exhaust pipe 8.

  The oxygen removing means 1 prepared according to the above was inserted into the float bath 10 from the side wall 121 of the float bath 10 as shown in FIG. The oxygen removing means 1 was inserted at a position 200 mm above the liquid level of the molten tin 20 so that the tip portion was positioned 200 mm from the side wall portion 121. In order to prevent the thin-layer electrodes 3 and 4 from being damaged at the time of insertion, it was inserted with the protective tube 100 made of alumina attached to the outer surface of the oxygen removing means 1. The oxygen removing means 1 and the protective tube 100, and the protective tube 100 and the penetrating portion of the side wall 121 were joined using water glass. The oxygen removing means 1 was attached to the upstream side of the float bath 10.

The float bath atmosphere near the portion where the oxygen removing means 1 was inserted was as follows.
Temperature: about 1100 ° C
Gas composition: nitrogen about 90 vol%, hydrogen about 10 vol%

Nitrogen gas was supplied from the gas supply pipe 7 to the oxygen removing means 1 at 30 mL / min. The nitrogen gas supplied to the oxygen removing means 1 is exhausted from the exhaust pipe 8. The exhaust pipe 8 is connected to an oxygen concentration meter 60 and analyzed the oxygen concentration in the gas discharged from the oxygen removing means 1.
After confirming with the oxygen concentration meter 60 that the inside of the oxygen removing means 1 (substrate 2) has been sufficiently substituted with nitrogen, an external charge is applied so that a negative charge is applied to the thin layer electrode 3 and a positive charge is applied to the thin layer electrode 4. A direct current was applied from the power source 50. Note that a direct current of 0.1 A (4 V), 0.2 A (6 V), 0.25 A (7 V), or 0.3 A (8 V) was applied. After the DC current application was started, the oxygen concentration in the gas discharged from the oxygen removing means 1 was analyzed by the oxygen concentration meter 60. The average value of oxygen concentration measured from 60 minutes to 65 minutes after the start of direct current application was defined as the oxygen removal amount. The results are shown in FIG.

Furthermore, the dew point in the float bath atmosphere was measured, and the water vapor concentration was determined based on the obtained results. Specifically, similarly to the oxygen removing means 1 shown in FIG. 2, the stainless steel tube of the dew point measuring device (capacitance type) is connected from the side wall 121 of the float bath 10 to the wall surface of the side wall 121 of the float bath 10. The dew point was measured over 30 minutes from 300 minutes after the start of application of the direct current (0.1 A) by inserting it at positions of 0 mm, 100 mm and 200 mm. Based on the measured dew point, the water vapor concentration in the float bath atmosphere was determined. In addition, the dew point before direct current application was previously measured in the same procedure, and the water vapor concentration in the float bath atmosphere was obtained. The results are shown in FIG. FIG. 5 is a graph showing the relationship between the distance (dew point measurement position) from the wall surface 121 of the float bath 10 to the tip of the stainless pipe of the dew point measuring device and the water vapor concentration in the float bath atmosphere. The water vapor concentration in the atmosphere is shown as a relative ratio to the water vapor concentration before the DC current application starts at the dew point measurement position of 0 mm. As is clear from FIG. 5, the water vapor concentration before the DC current application increases remarkably as the dew point measurement position decreases from 200 mm to 0 mm. This portion is considered to correspond to a portion where the molten tin 20 is not covered with the glass ribbon 30. It was confirmed that the application of a direct current significantly reduced the water vapor concentration in the float bath atmosphere. Therefore, when the water vapor concentration in the float bath atmosphere is reduced, the oxygen concentration existing in the water vapor state, that is, oxygen is reduced.
Further, as described above, these dew point measurement positions correspond to the portions where the molten tin 20 is not covered with the glass ribbon 30, so that the oxygen concentration decreases in this portion of the float bath atmosphere, so that the molten tin 20 Therefore, the oxygen concentration in the molten tin 20 can be kept below the oxygen activity. As a result, the production of tin oxide in the molten tin 20 can be prevented, and the occurrence of tin defects can be prevented.

1 (a) and 1 (b) are views showing an oxygen removing means used in the method of the present invention, FIG. 1 (a) is a side view of the oxygen removing means, and FIG. 1 (b) is an oxygen removing means. Figure 2 is a side sectional view of the means. FIG. 2 is a diagram for explaining the method of the present invention, in which a float bath is schematically shown. FIG. 3 is a graph showing the relationship between the temperature of molten tin and the oxygen activity in the molten tin. FIG. 4 is a graph showing the relationship between the direct current applied to the oxygen removing means and the oxygen removal amount in the example. FIG. 5 is a graph showing the relationship between the water vapor concentration in the float bath atmosphere and the dew point measurement position in the example, and the water vapor concentration is shown as a relative ratio to the water vapor concentration before the start of DC current application at the dew point measurement position of 0 mm. ing.

Explanation of symbols

1: Oxygen removing means 2: Substrate 3, 4: Thin layer electrode 6: Cap 7: Gas supply pipe 8: Exhaust pipe 9: Insulating part 10: Float bath 11: Bath part 12: Ceiling part 121: Side wall part 20: Melting Tin 30: Glass ribbon 50: External power supply 60: Oxygen concentration meter 100: Protection tube

Claims (8)

A method for removing oxygen present in a state of oxygen or water vapor in a float bath atmosphere,
A first thin layer electrode, an oxygen removing means in which a substrate having a thin layer structure made of a solid electrolyte ceramic having oxygen ion conductivity and a second thin layer electrode are laminated in this order, the first thin layer electrode being floated Arranged in contact with the bath atmosphere, the second electrode in contact with the atmosphere outside the float bath, and applying a negative charge to the first thin layer electrode and a positive charge to the second thin layer electrode to float Oxygen or water vapor present in the bath atmosphere is contact-reduced by the first thin layer electrode, and oxygen present in the state of oxygen or water vapor is transferred to the atmosphere outside the float bath via the second thin layer electrode. A method of removing oxygen present in the state of oxygen or water vapor in a float bath atmosphere by releasing.   In the oxygen removing means, the base has a bottomed cylindrical shape with an open end, the first thin layer electrode is formed on an outer surface of the base having a bottomed cylindrical shape, and the second thin layer electrode is 2. The method for removing oxygen present in a state of oxygen or water vapor in a float bath atmosphere according to claim 1, wherein the base is formed on the inner surface of the base having a bottomed cylindrical shape.   3. The float bath according to claim 2, wherein the oxygen that has moved into the substrate through the second thin layer electrode is removed by flowing a gas through the bottomed cylindrical substrate. 4. A method for removing oxygen present in the state of oxygen or water vapor in an atmosphere.   The method for removing oxygen present in a state of oxygen or water vapor in a float bath atmosphere according to any one of claims 1 to 3, wherein the solid electrolyte ceramic is made of stabilized zirconia.   5. The float according to claim 1, wherein each of the first and second thin layer electrodes is at least one selected from the group consisting of platinum, titanium carbide, titanium nitride, graphite, and glassy carbon. A method for removing oxygen present in the state of oxygen or water vapor in a bath atmosphere.   A method for reducing the oxygen concentration in a float bath atmosphere or the oxygen concentration present in the state of water vapor using the method according to claim 1.   The method according to claim 6 is used to reduce the oxygen concentration in the molten tin in equilibrium with the oxygen concentration by reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor. Method.   A method for reducing the amount of hydrogen supplied to a float bath atmosphere by reducing the oxygen concentration in the float bath atmosphere or the oxygen concentration present in the state of water vapor using the method according to claim 6.

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