Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C4/00—Compositions for glass with special properties
  • C03C4/04—Compositions for glass with special properties for photosensitive glass
  • C03C4/06—Compositions for glass with special properties for photosensitive glass for phototropic or photochromic glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C15/00—Surface treatment of glass, not in the form of fibres or filaments, by etching
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B23/00—Re-forming shaped glass
  • C03B23/0006—Re-forming shaped glass by drawing
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
  • C03B32/02—Thermal crystallisation, e.g. for crystallising glass bodies into glass-ceramic articles
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
  • C03C14/006—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix the non-glass component being in the form of microcrystallites, e.g. of optically or electrically active material
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C23/00—Other surface treatment of glass not in the form of fibres or filaments
  • C03C23/007—Other surface treatment of glass not in the form of fibres or filaments by thermal treatment

Definitions

• a birefringent effect can be generated in these crystal-containing glasses by stretching the glass within a certain viscosity range
• the glass is placed under stress at a temperature above the glass strain point temperature This elongates the glass, and thereby elongates and orients the crystals
• the elongated article is then exposed to a reducing atmosphere at a temperature above 250°C, but not over 25°C above the glass annealing point This develops a surface layer in which at least a portion of the halide crystals are reduced to elemental metal
• the elongated elemental crystals provide an array of electric dipoles which preferentially interact with the electric field vector of incident light This provides a method to polarize transmitted light waves
• the production of a polarizing glass then, involves, broadly, these four steps:
• temperatures above the annealing point are preferred for crystal precipitation.
• temperatures up to 50°C above the softening point of the glass can be employed.
• the halide crystals should have a diameter of at least about 200 A in order to assume upon elongation, an aspect ratio of at least 5: 1.
• the particles having an aspect ratio of at least 5:1 will display an aspect ratio greater than 2: 1. This places the long wavelength peak at least near the edge of the infrared region of the radiation spectrum, while avoiding serious breakage problems during the subsequent elongation step. At the other extreme, the diameter of the initial halide particles should not exceed about 5000 A.
• the dichroic ratio is a measure of the polarizing capability of a glass. It is defined as the ratio existing between the absorption of radiation parallel to the direction of elongation and the absorption of radiation perpendicular to the direction of elongation.
• the aspect ratio of the elongated halide crystals must be at least 5 1 so that the reduced metal particles have an aspect ratio of at least 2 1
• Crystals having a small diameter demand very high elongation stresses to develop a necessary aspect ratio
• the likelihood of glass body breakage during a stretching-type elongation process is directly proportional to the surface area of the body under stress This creates a very practical limitation as to the level of stress that can be applied to a glass sheet, or other body of significant mass
• a stress level of a few thousand psi has been deemed to comprise a practical limit
• Stress levels above 3000 psi are customarily used
• Firing of the elongated body in a reducing atmosphere is undertaken at temperatures above 250°C, but no higher than 25°C above the annealing point of the glass
• the firing temperature is somewhat below the annealing point of the glass to prevent any proclivity of the particles to respheriodize
• contrast Contrast comprises the ratio of the amount of radiation transmitted with its plane of polarization perpendicular to the elongation axis to the amount of radiation transmitted with its plane of polarization parallel to the elongation axis
• contrast Contrast comprises the ratio of the amount of radiation transmitted with its plane of polarization perpendicular to the elongation axis to the amount of radiation transmitted with its plane of polarization parallel to the elongation axis
• the level of contrast attainable in a polarizing glass body is dependent upon the amount of reduction occurring during the step of firing in a reducing atmosphere Typically, the greater the extent of reduction the greater the level of contrast Thus, the degree of contrast can be increased by employing either higher temperatures, longer times, or higher pressures of reducing gas species for reduction.
• That practice is limited, however, by the tendency of the metal halide particles to respheriodize. That tendency is also enhanced by higher temperatures and longer times of firing. Respheriodization can result in a decrease in contrast and/or a narrowing of the peak absorption band, or a shifting of the peak absorption band in the direction of shorter wavelengths.
• a process for preparing polarizing glass articles in accordance with prior knowledge has utilized firing in a hydrogen atmosphere for 4 hours at 425° C. When the firing time was extended to 7 hours, the contrast was increased somewhat, but with a concurrent reduction in the bandwidth of high contrast.
• United States Patent No. 4,908,054 proposes a method of producing a polarizing glass body that obviates the effect of respheriodization during a heat treatment such as the reduction step. This method conducts the thermal reducing treatment under a pressure of at least twice atmospheric pressure. The effect of the pressure is to inhibit respheriodization and to produce a polarizing glass article that exhibits a relatively broad range of high contrast polarizing properties in the infrared region. This expedient is not required in the present invention, but may be employed.
• the invention resides in a method of producing a glass article that exhibits a broad band of high contrast polarizing properties in the infrared region of the radiation spectrum, that is phase-separated, or exhibits photochromic properties, based on silver, copper, or copper-cadmium halide crystals precipitated in the glass within a size range of 200-5000 A, and that contains elongated silver, copper, or copper-cadmium metal particles, the method comprising thermally forming and precipitating large halide crystals in the glass article by subjecting it to a time-temperature cycle in which the temperature is at least 75 °C above the glass softening point, preferably greater and the time is sufficient to form the crystals, preferably over one hour, and elongating the glass article at a temperature between the strain point and the softening point of the glass.
• the invention further resides in a method for making a glass article exhibiting a relatively broad band of high contrast polarizing properties in the infrared region of the radiation spectrum from glasses which are phase-separable, or exhibit photochromic properties, through the presence of silver, copper, or copper-cadmium halide crystals, the method comprising the steps of:
• FIGURE 1 is a graphical representation comparing the stress levels required in accordance with the present invention, as compared to prior practice, to achieve a given center wavelength in a polarizing glass.
• FIGURE 2 is a graphical representation of a typical contrast ratio curve obtained with the present invention as compared to a similar curve obtained with prior practice.
• FIGURE 3 is a graphical representation comparing maximum transmission values for a polarizing article produced in accordance with the present invention as compared to one produced in accordance with prior practice.
• the present invention adopts, and improves on, the known method of producing a polarizing glass body. Basically, it embodies the steps of melting, and forming an article from, a glass containing a source of silver, copper, or copper-cadmium and a halogen or combination thereof other than fluorine. The article is cooled and then heat treated to form and precipitate halide crystals of silver, copper, or copper-cadmium.
• the article is then heated and subjected to stress to elongate the halide crystals.
• the glass is then subjected to a thermal reduction step, preferably in a hydrogen atmosphere, to reduce a portion of the silver or copper halide crystals in a surface layer on the article to elongated metal particles.
• the glass employed may be any glass that can be phase-separated to form silver, copper, or copper-cadmium crystals in the glass.
• Such glasses are disclosed, for example, in United States Patent Nos. 4, 190,451 (Hares et al.) and 3,325,299 (Araujo) disclosing photochromic glasses and 5,281,562 (Araujo et al.) disclosing non- photochromic glasses.
• Each of these patents is incorporated by reference, particularly for its teaching of glass composition ranges and their production.
• Preferred glasses are those disclosed in the Hares et al. patent.
• the present invention is concerned with a modification of the step in which the glass is heat treated to form and precipitate the halide crystal phase.
• this step may be carried out at any temperature in the range of 500-900°C.
• the Jones et al. patent specifies what has been accepted as good practice. The temperature is specified to be above the glass strain point, but not over 75 °C above the glass softening point. Temperatures considerably below the 75 °C over the glass softening point are disclosed in examples. The time is stated to be a sufficient time to generate halide crystals.
• the maximum temperature is dependent on the viscosity characteristics of the glass. In general, the temperature should not be so high that the glass becomes undesirably soft, a viscosity point of about 10 5 poises being a practical limit.
• the glass is heat treated at a temperature of at least 75° above the softening point, and for time sufficient to develop the crystals, usually at least greater than about an hour.
• These higher heat treatment temperatures have produced glass blanks with larger, and a wider variety of, crystal sizes.
• the increase in metal halide crystal size permits elongating the glass at a much lower stress level, preferably not over 3000 psi.
• FIGURE 1 This improves the operation and lessens the chance for breakage during the stretching process. The dramatic decrease in required pulling forces is shown in FIGURE 1.
• FIGURE 1 is a graphical representation in which stress levels are plotted in psi on the vertical axis and center wavelengths (CWLs) in nm are plotted on the horizontal axis.
• the center wavelength is that wavelength at the center or peak of a given range of polarizing capability. Treatment conditions will be targeted to the desired wavelength for a particular application.
• the stress levels required to achieve a given center wavelength are compared for two heat treatment cycles.
• the upper line A represents data from a standard heat treatment at a temperature of 710°C for 4 hours. This cycle is typical of the cycles employed for several commercial polarizing glass products. It will be observed that a product having a center wavelength at 1310 nm requires a stress level around 3400 psi.
• the lower line B presents data for a new high temperature heat treatment of 750°C for 8 hours. This cycle is in accordance with the present invention. In this case, the stress level needed to achieve 1310 nm center wavelength is only about 1600 psi.
• a second benefit achieved by the new heat treatment process is a wider dispersion of crystal sizes.
• a flatter contrast absorption curve over a wider wavelength band is obtained than that normally obtained with the prior lower temperature heat treatment process. This relationship is shown graphically in FIGURE 2.
• FIGURE 2 is a graphical representation in which Contrast Ratio is plotted on the vertical axis and wavelength is plotted in nm on the horizontal axis.
• the upper curve C shows the relationship of contrast ratio to wavelength for a commercial polarizing glass article. This article was processed on a schedule of 710°C for 4 hours to precipitate halide crystals.
• the lower curve D shows the same relationship for the same article produced from the same glass, but heat treated at 750°C for 8 hours to develop halide crystals in accordance with the method of the present invention. It is apparent that curve D is a broader, flatter curve.
• FIGURE 3 is a graphical representation in which maximum transmission (T max ) is plotted on the vertical axis in %. Wavelength is again plotted in nm on the horizontal axis. As shown, the difference in transmission loss becomes less than 10% at wavelengths above about 800 nm, and becomes insignificant above about 1100 nm.
• the glass employed in making test pieces to obtain the data presented in the drawings has the following composition in % by weight as calculated from the batch on an oxide basis: SiO 2 56.3 ZrO 2 5.0

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Ceramic Engineering (AREA)
• Dispersion Chemistry (AREA)
• Glass Compositions (AREA)
• Polarising Elements (AREA)

Priority Applications (2)

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Publications (1)

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• 1997
  • 1997-09-08 WO PCT/US1997/015895 patent/WO1998014409A1/en not_active Application Discontinuation
  • 1997-09-08 KR KR10-1999-7002719A patent/KR100490316B1/ko not_active IP Right Cessation
  • 1997-09-08 JP JP10516549A patent/JP2001501163A/ja not_active Ceased
  • 1997-09-08 EP EP97941471A patent/EP0931029A4/de not_active Withdrawn

Patent Citations (4)

Non-Patent Citations (1)

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