Patent GB-649514-A (GB)
Title: Improvements in and relating to optical glass
IPC: C03C3/23
Filed: 1947-02-07
Abstract: 649,514. Optical glasses. KODAK Ltd Feb. 7, 1947, Nos. 3682 and 3683. Convention dates, Feb. 9, 1946 and April 6, 1946. Drawings to Specification. [Class 56] Fluorescent glasses (having a refractive index for the D line greater than 2.2-0.01, where u is the Abbe value, or greater than 1.92 where v is less than 25) are made from batches consisting of Boron, Oxygen, and Fluorine in combined form, with one or more of Be, Mg, Ca, Zn, Sr, Cd, Ba, Pb, La, Ti, Th, Cb, Ta with or without Si with the atomic ratio of fluorine to boron up to 1.31. The compositions in weight per cent, the cationic percentage (i.e. the mol. percentage when the ingredients are expressed as containing only one metallic atom), the atomic ratio F/B, and some optical properties are given for various glasses of the following combinations: (1) B 2 O 3  with one of MgF 2 , CaF 2 , SrF 2 , BaF 2 , PbF 2 , LaF 2 ; (2) B 2 O 3 , La 2 O 3 , CaF 2 ; (3) B 2 O 3 , La 2 O 3 , SrF 2 ; (4) B 2 O 3 , La 2 O 3 , BaF,; (5) B 2 O 3 , La 2 O 3 , LaF 3 ; (6) B 2 O 3 , La 2 O 3 , ThF 4 ; (7) B 2 O 3 . La 2 O 3 , with two of CaF 2 , BaF 2 , LaF 3 , ThF 4 ; (8) B 2 O 3 , ThO 2 , La 2 O 3 , CaF 2 , SrF2, BaF 2 ; (9) B 2 O 3  with either BeO or BaO, and either CaF 2 , BaF 2 , or LaF,; (10) B 2 O 3  with either LaF 3  or ThF 4 ,and two or more of La 2 O 3 , TiO 3 , ThO 2 , Cb 2 O 5 , Ta 2 O 5 . The refractive indices extend from 1.55- 1.92 and lie above the line defined by the equation <SP>n</SP>D = 2.2- 0.01 u Another group of glasses with refractive index greater than 1.9 and dispensive index less than 25 result from batches containing Boron, Oxygen, Fluorine and at most two of Ba, La, Ti, Th, or divalent Pb, with the cationic percentage of boron oxide less than 50, and of metallic fluoride between 3 and 15. Examples are given using PbO, TiO 2  B 2 O 3 , and one or more of BaF 2 , LaF 3 , ThF A . The glasses are preferably made in a vessel with a SiO 2  content over 96 per cent. The fluorides must not be added until all water vapour has been removed, and in one method the B 2 O 3  and other oxide compounds are heated at a low temperature (e.g. 250‹C. with La 2 O 3 ) for 10-20 hours, the mixture ground, mixed with the fluorides, and melted in a Pt crucible at about 950‹- 1250‹C. Alternatively all ingredients except the fluorides are covered to prevent volatization, and melted at about 1200‹- 1300‹C. (e.g. one to one and a half hours at 1250‹C. for 500-grams batch), and the fluorides added and stirred with a Pt stirrer (for about 10 minutes), and the glass poured after further stirring for half an hour at a lower temperature; The best moulding temperatures are between 450‹- 650‹C. Preferably the cationic percentage of fluoride is greater than 17, and the atomic ratio F/B between 0.4 and 1.3. The Specification as open to inspection under Sect. 91 comprises also two glasses composed as follows: (1) LiF 15 per cent by wt., La 2 O 3  50 per cent by wt., and B 2 O 3  35 per cent by wt., and (2) CaF 2  52 per cent by wt., SiO 2  13 per cent by wt., and B 2 O 7  35 per cent by wt. This subject-matter does not appear in the Specification as accepted.