Optical fluorophosphate glass with anomalous positive incrementa

Details Optical fluorophosphate glass with anomalous positive incrementa Optical fluorophosphate glass with anomalous positive incrementa

1990-04-10

1991-11-26

Dixon, Jr., William R.

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

501 44, C03C 606, C03C 3247

Patent

active

050682091

DESCRIPTION:

BRIEF SUMMARY
The application relates to an optical fluorophosphate glass having anomalous positive partial dispersion, in which the tendency toward crystallization is extremely low.
An optical glass based on metaphosphates and fluorides of alkaline-earth metals and aluminum with the following composition is already known:


______________________________________ Ca(PO.sub.3).sub.2 : 2.53% by weight Ba(PO.sub.3).sub.2 : 18.01% by weight Al(PO.sub.3).sub.3 : 22.94% by weight MgF.sub.2 : 9.70% by weight CaF.sub.2 : 7.40% by weight SrF.sub.2 : 21.80% by weight AlF.sub.3 : 6.69% by weight BaO: 9.93% by weight KHF.sub.2 : 1.00% by weight ______________________________________
This known glass has a refractive index n.sub.e of 1.544 and an Abbe number .nu..sub.e of 73.1. However, melting is only possible with great technological difficulty. The yield is extremely low, due, inter alia, to the high tendency of this glass towards crystallization.
It is therefore an object of the present invention to provide a glass with analogous optical properties, i.e. with an identical refractive index n.sub.e and an identical Abbe number .nu..sub.e, in which the above mentioned technological difficulties in melting are avoided. It is a further object to indicate a process for crystallization-free melting of the glass in large units.
This object is achieved according to the invention by providing a fluorophosphate optical glass produced by melting a mixture having the following composition (in % by weight):


______________________________________ Ca(PO.sub.3).sub.2 1.0-2.5 Ba(PO.sub.3).sub.2 23.0-25.5 Al(PO.sub.3).sub.3 12.0-14.5 MgF.sub.2 6.5-8.5 CaF.sub.2 5.5-8.0 SrF.sub.2 16.0-19.0 AlF.sub.3 10.0-12.5 SrO 2.0-3.0 BaO 12.5-14.5 K.sub.2 TiF.sub.6 0.2-0.7 ______________________________________ by weight; the total content of all fluorides is between 38.2 and 48.7% by weight, and the F/P ratio is between 1.8 and 2.4; said glass having a refractive index n.sub.e between 1.53 and 1.55, an Abbe number .nu..sub.e between 72.8 and 73.5, and an anomalous positive partial dispersion .DELTA..nu..sub.e between +11.8 and +12.5.
The glasses according to the invention have the following elemental composition: (in wt. %)


TABLE 1 ______________________________________ (in atom-%): Range of the Preferred Preferred single invention range example ______________________________________ Mg 2.0-3.5 2.0-3.0 2.93 Ca 2.4-4.5 3.0-4.0 3.88 Sr 13.0-16.0 14.0-15.0 14.51 Ba 22.0-25.0 23.0-24.0 23.55 Al 4.5-6.0 5.0-6.0 5.05 K 0.1-0.3 0.1-0.2 0.16 P 9.0-12.0 10.0-11.0 10.51 O 17.0-20.0 18.0-19.0 18.14 F 20.0-23.0 21.0-22.0 21.27 n.sub.e 1.53-1.55 1.54-1.55 1.544 .nu..sub.e 72.8-73.5 73.0-73.2 73.10 .DELTA..nu..sub.e 11.8-12.5 12.1-12.2 12.17 ______________________________________ compositions: (in wt. %)


TABLE 2 ______________________________________ (in % by weight): Preferred Preferred Range of the interval of individual invention the invention example ______________________________________ Ca(PO.sub.3).sub.2 1.0-2.5 1.6-1.8 1.7 Ba(PO.sub.3).sub.2 23.0-25.5 24.0-25.0 24.2 Al(PO.sub.3).sub.3 12.0-14.5 13.0-14.0 13.9 MgF.sub.2 6.5-8.5 7.0-8.0 7.5 CaF.sub.2 5.5-8.0 6.0-7.0 6.9 SrF.sub.2 16.0-19.0 17.0-18.0 17.9 AlF.sub.3 10.0-12.5 11.0-12.0 11.3 SrO 2.0-3.0 2.3-2.5 2.4 BaO 12.5-14.5 13.0-14.0 13.7 K.sub.2 TiF.sub.6 0.2-0.7 0.4-0.6 0.5 ______________________________________ crucible. The glass molten from the initial quantity is colorless, ream-free, stable to crystallization and can be produced in significantly higher yield than the known glass. After slow cooling, the individual example shown has the following optical data:
The symbols here have the following meanings: applies: ##EQU1## In this equation, the subscripts have the following meanings: g=blue mercury line (435.84 nm); straight line", as shown in diagrammatic form and described in greater detail in, for example, the draw

REFERENCES:
patent: 3451829 (1969-06-01), Bromer et al.
patent: 3492136 (1970-01-01), Bromer et al.
patent: 3671276 (1972-06-01), Bromer et al.
patent: 4859635 (1989-08-01), Meinert et al.

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