United States Patent (19) 11 Patent Number: 5,045,510 Kohli Et Al
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United States Patent (19) 11 Patent Number: 5,045,510 Kohli et al. 45) Date of Patent: Sep. 3, 1991 54 PROCESS FOR PREPARING ASURFACE 56) References Cited DARKENED GLASS U.S. PATENT DOCUMENTS 75 Inventors: Jeffrey T. Kohli, Alfred; James E. 3,419,370 2/968 Craner et al. ..................... 65/30. 3,449,103 6/1969 Stookey ............. ... 6.5/30. Shelby, Alfred Station, both of N.Y. 3,689,242 9/1972 Platakis et al. ....................... 65/32.3 O 3,756,798 9/1973 Ernsberger .......................... 65/32.3 (73). Assignee: Alfred University, Alfred, N.Y. 4,065,283 12/1977 Asahara et al. ......................... 65/6 4,130,680 12/1978 Ference et al. ................... 65/30. *) Notice: The portion of the term of this patent 4,240,836 12/1980 Borrelli et al.................... S01/3 subsequent to Jul. 31, 2007 has been 4,475,059 10/1984 Sink ..................................... 33/534 disclaimed. 4,613,786 9/1986 Holland et al. ......................... 65/61 Primary Examiner-William R. Dixon, Jr. (21) Appl. No.: 557,913 Assistant Examiner-Anthony J. Green Attorney, Agent, or Firm-Howard J. Greenwald 22 Filed: Jul. 25, 1990 (57) ABSTRACT 8 8 A process for preparing a surface-darkened glass is Related U.S. Application Data disclosed. In the first step of this process, a specified 63 Continuation-in-part of Ser. No. 431,633, Nov. 3, 1989, silicate glass which contains a minor amount of anti Pat. No. 4,944,784. mony trioxide is provided. Thereafter, this glass is heated to a temperature of from about 350 to about 51 Int. Cl. ...................... C03C 3/091; CO3C 23/00; 1,000 degrees Celsius while being contacted with hy CO3B 32/OO drogen-containing gas. The presence of the antimony 52 U.S. Cl. ........................................ 501/66; 501/13; trioxide in the glass facilitates the darkening of its sur 501/65; 65/30. 11; 65/32.3; 313/534 face. 58) Field of Search ....................... 65/30. 11, 32.3, 61; 501/13, 65, 66; 313/534 13 Claims, 2 Drawing Sheets U.S. Patent Sep. 3, 1991 Sheet 1 of 2 5,045,510 U.S. Patent Sep. 3, 1991 Sheet 2 of 2 5,045,510 38 40 42 44 ALL O 5,045,510 1. 2 per million of silver ion, less than 10 parts (by weight) PROCESS FOR PREPARING A SURFACE per million of halide ion, less than about 0.01 weight DARKENED GLASS percent of elemental iron, and less than about 0.01 weight percent of iron ions, is heated to a temperature CROSS-REFERENCE TO RELATED 5 of at least about 350 degrees Celsius while being con APPLICATION tacted with hydrogen-containing gas. This is a continuation-in-part application of appli cants' copending patent application U.S. Ser. No. BRIEF DESCRIPTION OF THE DRAWINGS 07/431,633, filed Nov. 3, 1989, U.S. Pat. No. 4,944,784. The present invention will be more fully understood 10 by reference to the following detailed description FIELD OF THE INVENTION thereof, when read in conjunction with the attached A process for darkening the surface of a glass compo drawings, wherein like reference numerals refer to like sition in which a silicate glass containing antimony ion elements, and wherein: and less than 20 parts per million of silver ion or halide FIG. 1 is a transparent glass blank which may be used ion is contacted with a hydrogen-containing gas while 15 to prepare a window by a preferred process of the in being heated to a temperature of at least about 350 de vention; grees Celsius. FIG. 2 is a machine-ground object produced from the glass blank of FIG. 1; BACKGROUND OF THE INVENTION FIG. 3 is a surface-darkened glass object produced It is known that glasses whose surfaces are darkened from the machine-ground object of FIG. 2; may be used to prepare many different products. Thus, FIG. 4 is a reground glass object produced from the for example, a surface-darkened glass in the form of a surface-darkened object of FIG. 3; disc may have its faces polished so that they transmit FIG. 5 is an aperture to which a gallium arsenide light through the visible region of the spectrum but wafer has been bonded; have its perimeter substantially absorb such light. The 25 lens so formed will absorb stray light near its perimeter FIG. 6 is a schematic of a means for determining the but transmit such light near its center. absorbance characteristics of one surface-darkened arti The prior art describes a process for the preparation cle; and of a surface-darkened glass in which a clear glass core is FIG. 7 is a plot of the absorbance per thickness of the enveloped with a dark glass cladding and both are then 30 article of FIG. 6. subjected to heat and applied pressure to fuse them into DESCRIPTION OF THE PREFERRED a single unit. This prior art process often produces glass EMBODIMENTS objects with imperfections at the interface of the core and the cladding; and, when the surface of such a glass The process of applicants invention produces a dark object is polished, pitting and other imperfections often 35 ened glass, that is, a glass with one or more darkened appear at the interface. These surface imperfections regions whose optical absorbance throughout the ultra cause problems when one attempts to bond the surface violet, visible, and near-infrared regions of light spec to another surface. trum is substantially higher than glass regions not It is an object of this invention to provide a process treated by the process. for the preparation of a surface-darkened glass which 40 The glass produced by the process of this invention has substantially fewer surface imperfections and is may be used to collimate light and produce treated substantially more uniform than prior art surface-dark apertures for cameras and scopes for night vision appli ened glass; cations, for example. It is another object of this invention to provide a The process of this invention may be used with sili process for the preparation of surface-darkened glass 45 cate glasses. As used in this specification, the term sili which does not necessitate the joining of two different cate glass refers to a glass composition which contains glass bodies; less than about 20 parts per million of silver ion, less It is yet another object of this invention to provide a than about 20 parts per million of halide ion, and at least process for the preparation of a surface-darkened glass about 40 weight percent of silica. with a relatively low amount of deformation; 50 In the first step of the process of this invention, from It is yet another object of this invention to provide a about 0.1 to about 10 weight percent of antimony ion relatively low-temperature process for the preparation (by weight of antimony trioxide) is incorporated into a of surface-darkened glass; silicate glass. The antimony ion is preferably selected It is yet another object of this invention to provide a from the group consisting of trivalent antimony ion, process for the preparation of surface-darkened glass in 55 pentavalent antimony ion, and mixtures thereof. How which the reaction time is relatively short; and ever, as will be apparent to those skilled in the art, other It is yet another object of this invention to provide a antimony compounds also may be used. surface-darkened glass object which contains at least In general, the antimony ion is incorporated into the about 40 weight percent of silica, elemental antimony, glass by adding an antimony compound, such as anti less than about 20 parts per million of halide ion, less 60 mony trioxide, to either the glass batch and/or the glass than about 20 parts per million of silver ion, less than melt. When the antimony compound used is not anti about 0.01 weight percent of iron, and less than about mony trioxide, the amounts added should be adjusted SO 0.01 weight percent of ferric ion. that, on an equivalent basis, from about 0.1 to about 10 SUMMARY OF THE INVENTION weight percent of antimony trioxide is added. In deter 65 mining how much of other antimony compound(s) must In accordance with this invention, there is provided a be added to be equivalent to a specified amount of anti process for preparing a glass object in which a specified mony trioxide, one may calculate the number of anti silicate glass containing less than 20 parts (by weight) mony ions per cubic centimeter furnished by the anti 5,045,510 3 4. mony trioxide and then use an amount of the other preferred that the other components of the batch have antimony compound(s) which will furnish the same all of their particles be from about 0.5 to about 10 mi concentration antimony ions. crons in size. The batch components should be thor It is to be understood that, once the glass batch has oughly mixed so that a homogeneous batch is produced. been melted, antimony is not present in the glass in the When the antimony compound is added during the form of antimony compound but is present as antimony glass melting, it also should have substantially all of its ion. Thus, when reference is made to a glass containing particles be from about 0.5 to about 5.0 microns in larg from about 0.1 to about 10 weight percent of antimony est dimension. The antimony compound should be thor ion, it will be understood that such glass contains a oughly mixed in the melt so that a homogeneous melt sufficient amount of antimony ion to correspond to the O results.