Tellurium and selenium halide-based glasses, their preparation a

Details Tellurium and selenium halide-based glasses, their preparation a Tellurium and selenium halide-based glasses, their preparation a

1993-03-11

1994-10-04

Group, Karl

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

501151, 501904, C03C 332

Patent

active

053526392

DESCRIPTION:

BRIEF SUMMARY
The present invention has for an object new tellurium halide based glasses, their preparation and their use principally in the field of infrared transmission.
In French patent application 2,594,115, there are described glasses based on the halide of tellurium and selenium or sulfur which possess good transmission properties in the infrared. However, these glasses have relatively low glass transition temperatures which do not permit their use at high temperatures. Moreover, these glass transition temperatures vary only very slightly when the amounts of sulfur or selenium are varied.
It has now been discovered that it is possible to improve the properties of glasses based on the halide of tellurium and selenium by the addition of a supplemental constituent such as arsenic, antimony or bismuth.
It has been discovered, in particular, that it is possible to increase the glass transition temperature by increasing the amount of this supplemental constituent, and that it even becomes possible to adjust the glass transition temperature to a predetermined value by regulating the amount of the said supplemental constituent. It is thus possible to obtain, because of the invention, glasses based on the halide of tellurium and selenium having glass transition temperatures greater than 130.degree. C., and even greater than 150.degree. C., although for glasses based on the halide of tellurium and sulfur or selenium, the glass transition temperature rarely exceeds 80.degree. C.
Moreover, the glasses of the invention are less brittle than glasses based on the halide of tellurium and selenium. They also exhibit the advantage of permitting to obtain large pieces by hot pressing, when the glass is in its plasticity zone, at a temperature greater than several dozens of degrees to the glass transition temperature. These glasses can be formed by moderate pressure, in pyrex glass enclosures. It has been noted in effect that the glasses of the invention, thus formed, are capable of duplicating the polished surface of the pyrex mold, so that later the polishing of the piece obtained is not necessary, that which permits to considerably lower the cost of production.
Besides, the glasses of the invention can be deposited in thin layers to obtain antireflection deposits or integrated optics. They also permit to easily produce preforms having double index for the production of optical fibers.
The present invention has then for an object vitreous solid compositions of formula I: iodine, X, Se and Z, 100, not greater than 12 and that the molar percentage of the element Sb, when it is present, is not greater than 20.
The restrictive conditions concerning the maximum amount of antimony and bismuth are conditions generally permitting to obtain glasses by simple cooling of the mixture of constituents in the melted state, without rapid cooling (without tempering).
Among the vitreous compositions of the invention, mention can be made in particular of:
those for which X represents iodine, bromine or their mixtures;
those for which w is a number varying from 10 to 40 and y is a number varying from 5 to 65;
those for which z is a number at least equal to 10.
Among the compositions of the invention, certain ones are particularly interesting in that their thermal analysis permits to observe no phenomenon linked to a crystallization. In other words, these compositions form glasses which are not susceptible to devitrification. Such compositions can be found principally in the following fields:
(a) compositions for which w is a number varying from 15 to 25, x from 5 to 15, y from 20 to 60 and z from 10 to 50; and in particular for which y can vary from 30 to 50 and/or z from 20 to 40; and principally for which y can vary from 35 to 45 and/or z can vary from 25 to 35; these compositions being principally those for which Z represents mostly As (preferably Z represents As), and in particular those for which X represents mostly iodine (X represents iodine preferably);
(b) compositions for which w can vary from 5 to 20, x from 5 to 15, y from 55 to 65 and z

REFERENCES:
"Vitrification, switching and memory effects of glasses in potassium-arsenic (antimony)-sulfur (selenium, tellurium)-bromine (iodine) systems", Khiminets et al., Chem. Abstracts, vol. 82, No. 2, Jan. 1975, Abstract No. 10326t.
"Chalcohalide glasses", Sanghera et al., Journal of Non-Crystalline Solid, vol. 103, Nos. 2-3, Jul. 1988, pp. 155-178.
"Electrophotographic properties of selenium tellurium-antimony-halogen alloy", Onozuka et al., Chem. Abstracts, vol. 106, No. 20, May 1987, Abstract No. 165971n.

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