Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1997-09-26
2001-01-23
Bell, Mark L. (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S904000, C501S905000
Reexamination Certificate
active
06177372
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of high-density glasses. In particular, the present invention is directed to heavy metal fluoride glasses (HMFG), processes for the production of such heavy metal fluoride glasses, and apparatus embodying such heavy metal fluoride glasses.
More specifically, the present invention is directed to heavy metal fluoride glasses with extended ultraviolet (UV) and infrared (IR) transmission ranges, methods of producing heavy metal fluoride glasses with extended ultraviolet (UV) and infrared (IR) transmission ranges, and apparatus embodying heavy metal fluoride glasses with extended ultraviolet (UV) and infrared (IR) transmission ranges.
BACKGROUND ART
A number of glasses having high density and exhibiting a wide transmission window in the ultraviolet range are generally known. The high density and wide transmission window in the ultraviolet range allow high stopping power and high Cerenkov light yield. Consequently, such glasses are good materials for applications requiring either fast time measurements, or energy measurements at high energy.
The following are examples of patents directed to glasses and technology related to the present invention: U.S. Pat. No. 4,717,691, Lucas et al.; U.S. Pat. No. 4,749,666; U.S. Pat. No. 5,015,281, Hall et al.; U.S. Pat. No. 5,081,076, Rapp; EP 0 234 581, Minoru et al.; EP 0 282 155, Franz et al.; and GB 2,082,168, Lucas et al.
Fluoride glasses have good optical transparency both in the infrared and ultraviolet regions of the electromagnetic spectrum. In this field, new high density fluoride glasses were developed and characterized in terms of density, ultraviolet (UV)/visible/infrared (IR) transmission, chemical stability, and glass transition/crystallization temperatures. The family of glasses found in this field have a very high density, are free of any lead or radioactive elements, and are accompanied by a low UV cut-off as well as extended transmission into the mid-IR range.
Fluoride glasses were first discovered in 1974 by Michael and Marcel Poulain, who were working with Jacque Lucas at the University of Rennes in France. These glasses were found to have good optical transparency in the UV and visible ranges. High density fluoride glasses are of particular interest because they tend to have a low UV cut-off as well as extended transmission into the mid-IR range. Possible uses for these glasses are: Cerenkov detectors, scintillation hosts, x-ray detectors, optical amplifiers, and if stable enough, laser fibers.
Other high density glasses have been reported, including a family of glasses in the BaF
2
—YbF
3
—ThF
4
—ZnF
2
system with a reported density of 6.43 g/cc. The problem with glasses in this system is that they are relatively unstable against devitrification. Samples have been cast up to a maximum thickness of approximately 3 mm, but this system contains thorium which exhibits radioactive decay. Thorium based glasses do, however, have better chemical stability and extended IR transmission compared to traditional fluorozirconate glasses.
Another high density glass family, 6.0 g/cc, was discovered by Tick in the CdF
2
—Lif—AlF
3
—PbF
2
quaternary system, but these glasses can only be made up to a maximum thickness of 2 mm. This system also contains lead, which has been shown to have quenching affects for scintillation mechanisms in fluoride glasses.
Zhou, et al. reported glass formation in the PbF
2
—BaF
2
—HfF
4
—ZnF
2
—YbF
3
system having a density range of 6.0-6.9 g/cc, a maximum thickness of 3 mm, and a UV cut-off of 254 nm. However, these glasses were found to be very susceptible to attach by moisture as they exhibited a thick reaction layer after being immersed in water for a period of only one hour. This would make the glasses unsuitable for uses in an ambient atmosphere.
In his work, Zhou was originally trying to synthesize glasses the BaF
2
—YbF
3
—ZnF
2
—HfF
4
system by substituting Hf in place of the Th found in the BaF
2
—YbF
3
—ZnF
2
—ThF
4
system described above. However, these direct substitutions were not glass forming compositions so he varied the molar ratios of the four elements until he found some areas of glass formation. He later added lead in place of some of the barium and zinc in an effort to increase the glass forming character.
In the fall of 1995, several companies expressed interest in the lead free glass compositions reported by Zhou. This led to an effort, through the Iowa State University Research Foundation (ISURF) to reproduce some of these glasses. Attempts at reproducing his work failed as the compositions were found to have a severe tendency to crystallize at a thickness as small as 1 mm. It was later found that Zhou had used porcelain crucibles to melt some of his compositions. It is assumed that the alumina and silica oxides from the crucibles aided in glass formation, and may have actually produced an oxy-fluoride glass, as fluoride will readily attack any oxides present at elevated temperatures. During attempts reported herein to reproduce his work, platinum crucible, known not to contaminate fluoride glasses, were used.
Even though the lead free compositions were not good glass formers, there was evidence that maybe some of the compositions could be modified and/or stabilized to produce a family of good glass forming compositions. This evidence came from the fact that when a melt was quenched between two plates at room temperature, rather than at an elevated casting temperature, thin sheets of glass were formed.
The purpose of the present invention is not only to find a high density glass free of lead and radioactive elements, but also to find a stronger glass forming system since most applications would require a glass with a thickness greater than 3 mm.
SUMMARY OF THE INVENTION
The present invention relates to heavy metal fluoride glasses which have been discovered to exhibit extended transmission into ultra-violet (UV) and infra-red (IR) ranges.
In this regard, the present invention is also directed to heavy metal fluoride glasses, such as HfF
4
-based heavy metal glasses having extended UV and IR transmission ranges.
The glass forming region found in this work is: (16-30)BaF
2
.(8-26)HfF
4
.(0-16)CdF
2
.(6-24)YbF
3
.(4-26)ZnF
2
.(6-24)AlF
3
or GaF
3
or IfF
3
. These glasses have a density range of 5.8-6.0 g/cc, a UV cut-off of 260 nm, and had an IR cut-off of 9-10 &mgr;m, depending on the specific composition.
The heavy metal fluoride glasses of the present invention comprise a composition range (in mol percent) selected from the group consisting of:
(16-30)BaF
2
.(8-26)HfF
4
.(6-24)InF
3
or GaF
3
.(4-16)CdF
2
.(6-24)YbF
3
.(4-22)ZnF
2
; and
(16-30)BaF
2
.(8-26)HfF
4
.(6-24)InF
3
or GaF
3
or AlF
3
.(0-16)CdF
2
.(6-24)YbF
3
.(4-26)ZnF
2
.
A more preferred heavy metal fluoride glass produced in accordance with the present invention comprises a composition (in mol %) comprising about:
26BaF
2
.18HfF
4
.7InF
3
.5GaF
3
.10CdF
2
.18YbF
3
.16ZnF
2
(I)
A more preferred heavy metal fluoride glass produced in accordance with the present invention have a maximum thickness of most preferably about 3 mm.
Another more preferred heavy metal fluoride glass produced in accordance with the present invention comprises a composition (in mol %) comprising about:
26BaF
2
.18HfF
4
.12AlF
3
.10CdF
2
.18YbF
3
.16ZnF
2
(II)
A more preferred heavy metal fluoride glass produced in accordance with the present invention have a maximum thickness of most preferably greater than about 6 mm.
The heavy metal fluoride glasses produced in accordance with the present invention exhibit the following characteristics:
(II)
(I)
MORE
PREFERRED
CHARACTERISTICS
PREFERRED VALUES
VALUES
Glass Transition Tg
338° C.
326° C. @
heating rate of 5°
C./min
Onset of Crystallization Tx
421° C.
370° C.
Peak of Crystallization Tc
440° C.
399° C.
Bulk Density (Archimedes)
5.8g/cc
6.0g/cc
Ultra-violet cut-off
~268nm
~260nm
Infrared cut-off
~9&mgr;m
~10&mgr;m
The high density fluoride glasses in accordance with the present invention also exhibit transmis
Huebsch Jesse
Martin Steven W.
Bell Mark L.
Henderson & Sturm LLP
Iowa State University & Research Foundation, Inc.
Sample David
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