Patent GB-704374-A (GB)
Title: Improved light-absorbing glasses and methods of making same
IPC: C03C3/078
Filed: 1951-12-04
Abstract: 704,374. Light-absorbing glasses. ABBEY, A. (American Optical Co.). Dec. 4, 1951, No. 28443/51. Drawings to Specification. Class 56 An infra red and ultra violet absorbing glass having its dominant wave length of transmission adjacent the middle part of the visible region of the spectrum and the transmission characteristics at each side of the dominant wave length progressively decreasing to nearly complete absorption in the ultra violet and infra red areas consists of a silica-alkali-lime base combined with about 1.5-6.5 per cent. by weight of a mixture of ferric and ferrous oxides, and a fraction of 1 per cent. of vanadium oxides and/or chromium oxides, with or without fining agents selected from the group consisting of Cl 2  0-1 per cent., SO 3  0-1.5 per cent., and AS 2 O 3  0-1 per cent., the silica comprising the predominant constituent. The glass is green, can be reworked without devitrification, and will readily fuse with ophthalmic, flint, borium, and crown glasses, e.g. in multifocal lenses, colour wedges &c. Preferred composition ranges, in percentages by weight, are as follows: SiO 2  67-70, Na 2 O 0-17, K 2 O 0-17, CaO 4-13, Cl 2  0-1, SO 3  0-1.5, As 2 O 3  0-1, Iron oxides (expressed as Fe 2 O 3 ) 1.5-6.5, Vanadium oxides (expressed as V 2 O 5 ) 0.05-0.8, either Na 2 O or K 2 O must be present. A particular example comprises SiO 2  70.3, Na 2 O 6.6, K 2 O 10.7, CaO 7.0, Cl 2  0.6, SO0.6, As 2 O 3  0.4, Fe 2 O 3  3.6, V 2 O 5  0.2, and the latter may be replaced by Cr 2 O 3  0.05. Cr 2 O 3  can be included from 0.01-0.2 per cent. by weight, but when both Cr 2 O 3  and V 2 O 5  are included the most suitable proportions are 0.1-0.2 per cent. V 2 O 5  and 0.05-0.1 per cent. Cr 2 O 3 , although 0.1-0.8 per cent. V 2 O 5  can be included with 0.05-0.2 per cent. Cr 2 O 3 . The light transmission properties are given of several glasses as above but with an iron oxide content of 4.8 per cent., and the V 2 O 3 , Cr 2 O 3  content varying between 0.1 per cent. V 2 O 5  0.05 per cent. Cr 2 O 3  and 0.8 per cent. V 2 O 5  0.4 per cent. Cr 2 O 3 . Vanadium in the valency of 3 gives a pale green colour and slight I.R. absorption, in the valency of 4 has no significant absorption effects, and in the valency of 5 strongly absorbs U.V., but correctly combined with iron the vanadium increases the U.V. absorption and gives a green colour. By controlling the atmosphere in the furnace and the batch by reducing agents such as carbon, phosphorus, silicon, sugar &c. the relative valencies are balanced to give the desired colour and absorption. The batch is melted between 2450 and 2750‹C. The refractive index for the above glass is 1.523, and this can be adjusted by varying the silica alkalies, and lime plus iron, the index increasing with increase of lime and iron oxide and vice versa. The effect of the interchange of CaO, SiO 2 , Na 2 O and K 2 O is illustrated by examples, the refractive index varying from 1.521-1.531. When AS 2 O 5  is added to the batch the carbon content must be increased. The transmission data is given of several examples in which the iron oxide is 4.8 per cent., the carbon varying from 0.15-0.30 per cent. for V 2 O 5  varying between 0.2-1.6 per cent. The colour becomes too blue or green if melting conditions are too reducing and too yellow or green if too oxidising. The Specification describes with tables and graphs the desired and obtained absorptions &c. of the glasses, the iron oxide content of three particular glasses being approximately 4.7 per cent., 3.5 per cent., and 2.2 per cent.