GB1136593A - Infra-red transmitting glasses - Google Patents

Abstract

1,136,593. Selenide glass purification. MINISTER OF TECHNOLOGY. 14 Jan., 1966 [15 Oct., 1964], No. 42176/64. Heading C1M. Infra-red transmitting selenide glasses are purified by distilling the glass in a stream of reducing gas. The glass constituents are selenium with one or more of the following elements: arsenic, germanium, sulphur, tellurium. A glass, in atoms per cent, initially As 20; Ge 30; Se 50 purifies to As 8; Ge 34; Se 58 and As 20; Se 80 to As 14À4; Se 85À6. The initial glass may be prepared by weighing out the quantities of each element into thick walled silica glass ampoules which are evacuated and sealed under vacuum. The ampoules are heated to 1000‹ C. in a tube furnace, which is rocked to and fro to mix the constituents, for 5 to 6 hours and allowed to cool naturally. The melts are then purified in a still consisting of a silica furnace tube 1 with an inner recessed outgassed silica distillation tube 3 having three recesses 3A, 3B, 3C located respectively in independent furnaces A, B, C surrounding tube 1. Upstream ends of tubes 1, 3 contain wads 7, 9 of silica wool. An electrical lead 5 is taken to thermocouples 5A, 5B, 5C in the furnaces A, B, C. Glass is placed in recess 3B and H 2 or H 4 Se/H 2 mixture passed through and burnt at the outlet end of tube 1. The furnaces A, B, C are maintained at 120‹ C. for 1 to 2 hours to dry the apparatus, then furnace A adjusted to 370‹ C., a temperature at which selenium dioxide and arsenious oxide are volatile and then furnace B heated rapidly to 900‹ C., the selenide glass distilling into the recess A. To compensate for the loss of As and /or Se in distillation, the initial glass may be adjusted or additional As and/or Se at particular temperatures may be placed in the recesses such as recess 3C. After distillation, furnace A is heated to 600‹ C. to melt the condensed glass into more compact shape and the glass allowed to cool, still in the stream of H 2 .