Patent GB-708031-A (GB)
Title: Improvements in light-absorbing glass and method of making same
IPC: C03C3/076
Filed: 1951-12-03
Abstract: 708,031. Ultra-violet light absorbing glass. ABBEY, A. (American Optical Co.) Dec. 3, 1951 No. 28340/51. Drawings to Specification. Class 56 An U.V. light absorbing optical crown glass comprises an oxidized glass which is substantially free of reducing agents and has the following weight percentage composition, SiO 2  67-70, V 2 O 5  0.2-1.2, MnO 2  0-0.45, with or without a trace of colour modifying oxide of a metal such as Fe, Co, Cr, Cu, Sn, As, Sb, or mixtures thereof, TiO 2  0-3, chlorine 0-2, sulphur dioxide 0-1.5, and the remainder consisting of CaO, K 2 O, and Na 2 O, with or without BaO replacing the CaO, the glass when of 2mm. thickness having a high percentage of transmission for all wave lengths of the visible spectrum and transmitting less than 5 per cent. for wave lengths of U.V. light shorter than 356 millimicrons. The glass has a refractive index of approximately 1-523, may be fused with standard crown, flint, or barium glasses in the manufacture of multifocal lenses, and may be worked and annealed with conventional equipment. Preferred glasses transmit less than 1 per cent. of U.V. light up to 365 millimicrons and 75 per cent. in the visible region. The manganese imparts a flesh colour to the glass which is otherwise substantially colourless. The batch of a suitable base contains, in parts by weight, sand 70.3, soda ash 14.9, potassium. nitrate 4.6, potassium carbonate 9.1, limestone 20.6, salt 1.0, salt cake 1.0, allowance being made for volatilization losses, hygroscopicity, impurities, and pot attack. The weight percentage composition of the preferred base glass is, SiO 2  70.4, Na 2 O 8.7, K 2 O 8.2, CaO 11.5, Cl 2  0.6, SO 3  0.6. The CaO content of the batch is lowered in accordance with the amount of V 2 O 5 , and the V 2 O 5  and MnO 2  must be balanced, e.g. 0.75 parts V 2 O 5  and 0.18 parts MnO 2 . The weight percentage composition range of desirable glasses is, SiO 2  67-70, Na 2 O 0-17, K 2 O 0-17, CaO 9-14, Cl 2  0-2, SO 3  0-1.5, V 2 O 5  0.2-1.2, lin0  2  0.15-0.45, either Na 2 O and/or K 2 O being present. A particular example comprises SiO 2  70.4, Na 2 O 8.7, K 2 O 8.2, CaO 10.5, Cl 2  0.6, SO 3  0.6, V 2 O 5  0.8, MnO 2  0.2. One pound batches are melted in an oxidizing atmosphere for 2 hours at 2550‹ F and soaked at 2200‹ F for 1 hour, and can be worked at 2200-1800‹F and annealed at 1100‹ F. Prolonged soaking! at 2200‹ F improves the quality of the glass, does not affect the colour development when the colour has been destroyed by high melting, 2550-2600‹ F, but appreciably deepens the colour after melting at a maximum of 2500‹ F. An oxygen evolver is necessary, regardless of the atmosphere of the furnace, to prevent the formation of a green glass. KNO 3  and NaNO are normally used, but Ca (NO 3 ) 2  can assist or replace alkali nitrate up to a very large excess. BaO 2  may be used as an oxygen source, the resultant BaO replacing CaO, but the refractive index is lowered. Too large a proportion of Na 2 SO 4  produces a green colour. The effects on colour and visual transmission by varying the level of oxidation and the proportions of MnO 2  is illustrated in four examples with the nitrate content per 100 parts sand being respectively 3.4, 11, 26, and 31, and a further table shows the variation in visual transmission caused by variation of the maximum melting temperature, the V 2 O 5  being 1 per cent. the MnO  2  0.20-0.30, melting for 1¢ hours at maximum temperature, and soaking 3¢ hours at 2200‹ F. With lowered V  2 O 5  the MnO 2  can be lowered, and examples are given with the V 2 O 5  varying from 1.20-0.70 and the MnO 2  from 0.30-0.15, the nitrate being 3 parts per 100 parts sand. Fused V 2 O 5  is a suitable grade of oxide for use, but other grades may be used or technical sodium orthovanadate. Additional, or modification of, colour may be obtained by the addition of other ingredients, e.g. Fe 2 O 3  up to 0.1 per cent. is desirable, Co 2 O 3  1 part per million to neutralize yellow tints, CuO 0.0005-0.005 per cent. to give a less red and more neutral colour and raise the visible transmission 1-2 per cent., chromium in fractional parts per million, and TiO 2  up to 3 per cent. also modify colour, and Sn, As, and Sb control the intensity of the manganese purple. Some oxides, e.g. rouge or TiO  2 , in separate pots in the furnace control the atmosphere and colour. The colour and transmission powers of the given and desired glasses are described at some length using graphs.