Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/18—Stirring devices; Homogenisation
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/18—Stirring devices; Homogenisation
  • C03B5/183—Stirring devices; Homogenisation using thermal means, e.g. for creating convection currents
  • C03B5/185—Electric means
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/18—Stirring devices; Homogenisation
  • C03B5/187—Stirring devices; Homogenisation with moving elements
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
  • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

• the present invention relates to processes and apparatuses for abating particles during the handling of glass melt.
• the present invention relates to processes and apparatuses for making glass using a platinum-containing metal delivery system where platinum oxidation and subsequent reduction can cause platinum defects in glass.
• the present invention is useful, e.g., in the manufacture of high-quality glass (such as glass suitable for making a glass substrate of a LCD display) using a glass melt delivery system comprising platinum.
• a process for making glass comprising:
• the refractory vessel comprises a refractory metal exposed to the atmosphere, and the atmosphere is oxidative such that the reaction between the refractory metal and the atmosphere produces at least part of the air-borne particle.
• the refractory metal vessel comprises platinum or an alloy thereof.
• the electric field generates a corona in the atmosphere.
• all metal in direct contact with the glass melt is subjected to essentially the same electrical potential.
• the refractory vessel comprises a glass melt stirring device comprising (a) a stir chamber defined by a chamber wall comprising a refractory metal and (b) a stirrer shaft comprising a refractory metal.
• the electric field is at least partly generated by an electrical potential gradient between (i) the stir chamber wall and the stirrer shaft, which together function as a first electrode; and (ii) an opposite second electrode placed above the surface of the glass melt.
• a barrier for receiving particle is provided between the second electrode and the surface of the glass melt.
• step (B) the electrical field between the first electrode and the second electrode is effected by an electric potential gradient of at least 100 V.
• step (B) the second electrode is provided with a higher electric potential than the first electrode.
• the glass melt is suitable for making a glass substrate for LCD displays.
• At least part of the wall of the stir chamber and at least part of the stir shaft are exposed to an oxygen-containing atmosphere.
• a glass melt handling device comprising a refractory vessel adapted for operating at an elevated temperature, wherein the glass melt is exposed to an atmosphere comprising an air-borne particle, comprising an electrostatic precipitator comprising: (i) a first electrode; and (ii) a second electrode for collecting the particle.
• the refractory vessel comprises a refractory metal exposed to the atmosphere.
• At least part of the refractory vessel functions as the first electrode of the electrostatic precipitator.
• an identical electric potential is applied to the surface of refractory metal exposed to the glass melt.
• the refractory vessel comprises a glass melt stirring device comprising a stir chamber and a stir shaft.
• the devices comprises a barrier between the second electrode and the surface of the glass melt to be handled by the device during operation, wherein the barrier is adapted for intercepting particles falling off the second electrode.
• the second electrode has a higher electric potential than the first electrode.
• the device further comprises a third electrode having a differing electric potential from that of the first electrode.
• the third electrode has essentially the same electric potential as the second electrode.
• the third electrode has an electric potential higher than that of the first electrode.
• At least one electrode is capable of generating a corona.
• the surface of the second electrode is a different material than the surface of the first electrode.
• One or more embodiments of the present invention have one or more of the following advantages.
• First, the present invention can enable the reduction of platinum inclusions in glass materials delivered, fined, formed and/or stirred in platinum- containing refractory vessels, thereby improving the glass yield.
• FIG. 1 is a schematic illustration of a stirring device according to one embodiment of the present invention.
• FIG. 2 is a schematic illustration of a laboratory set-up testing the efficacy of the present invention for platinum condensation abatement.
• FIG. 3 is a schematic illustration of respective temperature zones of the tube enclosing the electrodes in the electrostatic precipitator illustrated in FIG. 2.
• FIGS. 4-21 are electronic microscopic images of the different zones of the two electrodes of the electrostatic precipitator as illustrated in FIG. 2 at the end of the test.
• glass melt handling device means a device for processing a glass melt, including but not limited to: a glass melt delivery device, a glass melt homogenizing device such as a stirring device, a glass melt forming device such as a glass melt rolling device, a glass melt pressing device, a fusion draw system which forms glass sheet from glass melt, a slot draw system which forms glass sheet from glass melt, and the like. Since glass melt is typically held at an elevated temperature, a glass melt handling device typically comprises a refractory vessel, including but not limited to a pipe, a container, a chamber, a block, and the like, directly in contact with the glass melt.
• the term "handling of glass” as used herein can include, inter alia, glass melt delivery, glass melt homogenization (such as stirring and mixing), glass melt fining, glass forming (rolling, pressing, fusion forming, slot forming, drawing), and the like.
• glass melt handling and “handling of glass melt” is the step of glass melting in which raw materials such as oxides, minerals, cullets, and the like, are heated and allowed to react to form the glass melt with a determined composition.
• the present invention is concerned with process steps after a glass melt is formed in a glass melting tank.
• electrostatic precipitation means the collection of air-borne particles by subjecting the particles to an electric field.
• air-borne means the particles may be present in the atmosphere, either transiently or stably. Thus such particles could include, inter alia, those particles that can suspend relatively stably in the atmosphere, as well as those particles that travel in the air temporarily (falling due to gravity, or entrained by air flow, e.g.).
• the electric field is generated by two electrodes. In certain embodiments, the electric field is generated by more than two electrodes.
• At least one of the electrodes desirably an electrode having a higher electric potential, produces a corona that can provide electric charges to the air-borne particles.
• At least one of the electrodes serves as a particle collector on which the particles are collected via, e.g., a force exerted thereto by the electric field generated by the electrodes.
• a glass melt is formed in a glass tank, before the glass melt is allowed to cool down to a rigid glass article (such as a glass sheet, a glass plate, and the like), the glass melt is typically subjected to various handling steps mentioned above. During those steps, the glass melt may be exposed to an atmosphere.
• the atmosphere may comprise air-borne particles due to various reasons. Such particles, if allowed to fall into the glass melt, can form unwanted inclusions in the final formed glass article, reducing the quality and yield. Abatement of such particles in the atmosphere is thus necessary, especially for optical glass articles.
• Contaminating particles can be generated by a number of factors, including, inter alia, air supply devices, evaporation and condensation of glass melt and/or components thereof, evaporation, reaction and condensation of refractory materials used in the handling process, mechanical force exerted on the refractories, and the like.
• LCD glass substrates are required of a high quality, both in terms of surface and bulk.
• the fusion draw technology was developed by Corning Incorporated, Corning, NY, U.S.A. for forming thin glass sheets having pristine optical surfaces suitable for forming semiconductor components such as thin-fikn-transistors thereon.
• the stringent requirements imposed on the optical quality of the bulk of the glass sheet also call for very low level of inclusions therein.
• refractory materials such as precious metals including Pt, Rh, Ir, Os, Pd, Au, Ru, Re and the like, may be employed, along with non-metallic refractories such as SiO 2 , ZrO 2 , zircon, Al 2 O 3 , SiC, and the like, in the equipment handling the glass melt. It is known that the following factors, inter alia, can contribute to the formation of unwanted inclusions in the glass sheet. [0043] First, oxidation and subsequent reduction of precious metals such as Pt and Rh contribute to forming precious metal defects in glass. For example, as the temperature of platinum rises, such as from room temperature to the typical temperature at which LCD glass melt is handled, the equilibrium of the following reaction is favored to shift to the right:
• the hot surface of a Pt vessel can be oxidized into PtO 2 gas in the presence of O 2 in the ambient atmosphere, which, upon contacting another surface or medium (such as the atmosphere) at a lower temperature, may dissociate to form solid Pt.
• the solid Pt can grow over time into particles sufficiently large, subsequently fall into the glass melt, and form inclusions in the final glass article formed.
• refractory materials used in constructing the refractory vessels may chip or otherwise produce fine particles. Given the refractory nature of these particles, they can form blisters and other inclusions in the final glass article.
• the ambient air that comes into contact with the glass melt may be contaminated by particles such as dust generated by other equipment or process steps.
• the downstream process such as glass scoring, breaking, edge finishing, and the like, may produce glass particles that find their way into the atmosphere which the glass melt may contact. This is especially true in the glass forming area, where the glass melt is formed in an atmosphere with considerable air flow from the down-stream process.
• the glass melt is allowed to fill partly in the finer vessel, which can be a tube.
• the inner surface of the finer above the glass line is thus exposed to an atmosphere which can be oxygen-containing. Bubbles inside the glass melt are allowed to exit the glass melt and escape the glass finer. Due to the above mechanism, Pt particles may be formed on the inner surface of the finer, or on the surface of the outlet for exhaust gas, accumulate overtime, and fall when it grows sufficiently large, into the glass melt to form Pt inclusions.
• the downcomer is a pipe delivering glass melt into the inlet of the isopipe, where glass melt is formed into a glass sheet.
• the downcomer can be made of a Pt or Pt alloy.
• the glass melt is exposed to an oxygen-containing atmosphere when it exits the downcomer.
• the metal forming the downcomer can be oxidized according to the above mechanism to form Pt particles which could eventually make their way into the glass melt to form inclusion defects.
• the isopipe is the device over which glass melt overflows, joins at the bottom, and fuses into a single glass sheet.
• Pt or Pt alloy which can be used for building part of or supplementary components of the isopipe, is typically exposed to air and elevated temperature. According to the same mechanism, Pt particles can be produced and brought into the glass melt during forming. In this area, significant air flow can take place, increasing the probability of contamination by other particles as well.
• the stirring device is a component of the glass melt handling system which is highly prone to Pt particle condensation and contamination.
• FIG. 1 includes a schematic illustration of a typical glass melt stirring device. In this device, a stir chamber is defined by a stir chamber wall 103 and a bottom 104.
• Glass melt 113 is delivered into the chamber through inlet 109 and fills the chamber up to glass line 115.
• Stirrer shaft 105 comprising a plurality of blades 107, stirs the glass melt 113 by the shearing stress it produces by rotation.
• Stirrer shaft 105 and the chamber wall 103 are made of Pt or Pt alloy in certain advantageous embodiments.
• the stir chamber may be further covered by stir chamber cover 117. Above the glass line 115, the stir chamber is filled with an oxygen-containing atmosphere, such as air, in certain embodiments.
• the glass melt has the highest temperature inside the chamber; and the temperature in the chamber cover area is lower than the glass melt.
• the present invention uses an electric field to attract and capture air-borne particles, including metal particles, such as Pt and Pt-alloy particles, particles formed from glass components, and particles that exist in ambient air, thereby abating them and preventing them from entering into the glass melt.
• the electric field is generated by at least two electrodes having differing electric potential.
• a typical electrostatic precipitator used e.g., in a power plant for the abatement of fly-ash
• at least one electrode of the precipitator has the capability to provide a corona which provides the electrical charges to the particles, which is then attracted and collected by the opposite electrode. Once reaching the opposite electrode, the charges borne by the particles are neutralized by the opposite charges supplied by the opposite electrode.
• the electrodes are routinely made of metal.
• the electrodes may be made of metal, and other materials, as long as the material has sufficient electrical conductivity at the operating temperature.
• a corona is desirably formed by at least one electrode in certain embodiments of the present invention
• the generation is corona is not necessary as indicated by the Example below.
• the present inventors believe in certain embodiments, at least some of the particles formed or present in the atmosphere of the glass-handling device is already charged with various amounts of electrical charges, and thus can be attracted and captured by an opposite electrode.
• the glass melt stirring device 100 schematically illustrated in FIG. 1 represents an embodiment of the present invention.
• stirring device 100 in addition to the above components typical of a glass melt stirring device described and discussed above, an electric field is generated by applying a voltage between the chamber wall 103, the stir shaft 105, the stir chamber cover 117 (all three are grounded as illustrated) and a second electrode 119 inserted into the stir chamber, hi this embodiment, the stir chamber wall 103, the stir shaft 105 and the stir chamber cover 117 collectively function as a first electrode in the meaning of the electrostatic precipitator in the present application. Between the second electrode 119 and the glass line (the surface of the glass melt exposed to the atmosphere), barrier 123 is attached to the end of rods 121 extending from stir chamber cover 117.
• Barrier 123 has the capability to intercept any particles, such as Pt particles, that may fall from the surface of the second electrode 119.
• the extending rods 121, which hold barrier 123 in place, and the barrier 123 are made of electrically insulating materials, such as oxides, ceramics, and the like.
• any air-borne particle is first attracted to the surface of the second electrode 119, collected on the surface of the second electrode 119, and further collected by the barrier 123 in case the particles fall from the surface of the second electrode 119.
• the second electrode 119 and barrier 123 may be cleaned from time to time, without significant interference with the continuous glass handling process.
• One approach to this end is to impose a substantially identical electrical potential to all metals in direct contact with the glass melt during operation thereof.
• the refractory metal wall 103 and the bottom 104 of the chamber, as well as the metal stir shaft are all grounded, effectively subjecting them to the same electrical potential in the system, thereby avoiding the application of an electrical potential gradient to the glass melt via these metals.
• multiple electrodes may be utilized in the atmosphere to achieve an optimal particle collection efficiency and efficacy.
• it is desired that at least one of the electrodes is capable of generating a corona, which can facilitate the charging of the particles, thus further enhancing the efficiency and efficacy of particle collection.
• FIG. 2 schematically illustrates the laboratory set-up.
• set-up 201 inside furnace 203, an alumina tube 205 is inserted.
• Electrically grounded platinum mesh 219 was placed in the middle of alumina tube 205.
• negative electrode 211 and positive electrode 217 were inserted at locations essentially symmetrical relative to platinum mesh 219.
• electrodes 211 and 217 were enclosed by alumina tubes 207 and 213, respectively.
• the tubes 207 and 213 were secured to the ends of alumina tube 205 by insulating fire bricks 209 and 215, respectively.
• Essentially identical DC voltages 221 and 223 were applied (i) between platinum mesh 219 and the negative electrode 211 and (ii) between positive electrode 217 and platinum mesh 219.
• an electric field is established in the atmosphere inside tube 205.
• the temperature profile inside furnace 203 was held substantially constant.
• the temperature of the various locations along tubes 207 and 213 were measured and recorded.
• FIG. 3 illustrates the locations measured on the electrode enclosure tubes 207 and 213 in greater detail. The temperature of the parts are included in the following TABLE I.
• electrode enclosure tubes 207 and 213 have essentially the highest temperature in the tip areas, which is closest to platinum mesh 219, and the temperature decreases gradually from the tip to the end in contact with insulating fire bricks 209 and 215.
• the temperature of the platinum mesh 219 has a higher temperature than the tip zones of the two electrodes. Insulating fire bricks 209 and 215 are not air-tight.
• the atmosphere inside tube 205 contains air, and is supplied with additional O 2 when O 2 is consumed over time by the oxidation of Pt via convection and/or diffusion. Due to the temperature gradient between platinum mesh 219 and electrode enclosures 207 and 213, Pt was found to have migrated from the mesh to the electrode enclosures, presumably by the oxidation-condensation mechanism described above.
• the present invention can be used to abate both non-metallic particles (such as oxide, glass and ceramic particles) and metallic particles (such as Pt defects and the like), in a glass-handling device.
• non-metallic particles such as oxide, glass and ceramic particles
• metallic particles such as Pt defects and the like

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
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• Glass Compositions (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
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• Manufacture And Refinement Of Metals (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)

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• 2008
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• 2009
  • 2009-11-10 JP JP2011537497A patent/JP5713915B2/ja not_active Expired - Fee Related
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