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Proceedings Paper

Fabrication of Infrared Optical Ceramics in the CaLa[sub]2[/sub]S[sub]4[/sub] - La[sub]2[/sub]S[sub]3[/sub] Solid Solution System
Author(s): J. A. Savage; K. L. Lewis; B. E. Kinsman; A. R. Wilson; R. Riddle
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Paper Abstract

Calcium lanthanum sulphide optical ceramic has been identified as a potential 8-12 μm infrared window material. However, since there is a solid solution region in the phase diagram between CaLa2S4 and La2S3 other compositions from this region may also be of interest. The most promising synthesis route, also used in the present work, appears to be that of sintering a pure sulphide powder to closed porosity followed by hot isostatic pressing to achieve full density. A mixed oxide precursor powder has been made by the evaporative decomposition of solution (EDS) synthesis route in which a mixed nitrate solution was sprayed through a hot furnace. The mixed oxide powder was then fired in an H2S containing gas to synthesise a very fine sulphide powder of a number of compositions in the CaLa2S4 - La2S3 phase diagram. The evolution of the powder synthesis and ceramic processing techniques has enabled a continued improvement in ceramic quality. For example in 1983 a dark brown CaLa2S4 ceramic partially transmitting in the visible and IR but showing extrinsic S03= and SO4= absorptions was prepared by hot pressing followed by annealing in H2S. By 1985 extrinsic absorption free CaS 45 La2S3 55 mole % material transmitting in the visible and IR but showing visible and near IR scatter has been synthesised by sintering and hot isostatic pressing. In 1986 a range of compositions in the CaLa2S4 - La2S3 phase diagram have been prepared in a similar manner.

Paper Details

Date Published: 19 December 1986
PDF: 6 pages
Proc. SPIE 0683, Infrared and Optical Transmitting Materials, (19 December 1986); doi: 10.1117/12.936419
Show Author Affiliations
J. A. Savage, Royal Signals and Radar Establishment (United Kingdom)
K. L. Lewis, Royal Signals and Radar Establishment (United Kingdom)
B. E. Kinsman, BDH Ltd (United Kingdom)
A. R. Wilson, BDH Ltd (United Kingdom)
R. Riddle, BDH Ltd (United Kingdom)

Published in SPIE Proceedings Vol. 0683:
Infrared and Optical Transmitting Materials
Robert W. Schwartz, Editor(s)

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