Infrared transparent fluoride glass prepn. - in which hydrogen fluoride treatment is used to remove oxide and hydroxyl ions

摘要

Infrared transparent glass compsns. based on fluorides of Zr. Th, and Ba are prepd. by forming a fused mixt. of ultra pure ZrF4, BaF2 and ThF4 in predetermined proportions under an atmos. of HF and He and holding the melt in contact with this atmos. for long enough to reach a negligible concn. of OH ions and/or O2 ions in the melt. The atmos. is then replaced with a rectification mixt. of CCl4 and He to reestablish the reduction of the colour centre produced in the HF/He mixt. Then casting, annealing and cooling to form a glass in the presence of this rectification atmosphere. The preferred glass compsn. comprises 0.58 mole ZrF4 0.33 mole BaF2 and 0.09 mole ThF4. The glasses are used in laser windows, and optical fibre elements. Absorption bands in prior art fluoride glasses due to oxide and hydroxyl ions are avoided. The mechanical strength density, hardness and usefulness of the glass compsns. are also markedly improved.