DE1496524C - Lead-free, devitrification stable optical glass with a refractive index of at least 1.65 and its use in particular in fiber optics - Google Patents

Description

In the production of fiber optics, the 10 must be at least 1.65, which is suitable for optical core glass, the highest possible refractive index, a purpose, in particular for the production of fiber medium to high softening point, a wide optics, and in addition to the highest possible working range and for most applications, refractive index and a low Verfärbungsten * a relatively high thermal expansion tendency _T a very great stability in the drawing and having coefficients. Of particular importance has 15 working temperatures and does not tend to have a high stability in the drawing and glass and which continues to have a medium to working temperature and high permeability in the high softening point and a relatively visible spectrum. has a high coefficient of thermal expansion.

So far, glasses with a high refractive index contain 'This object is achieved according to the invention by a typically large amount of lead and / or titanium a ° glass, which has the following composition in oxides or ZrO ₂ , WO ₃ , HfO ₂ or ThO ₂ . As a percentage by weight: Use in fiber optics is a larger proportion ■ ·, '

Lead oxide is disadvantageous, while because of the practical difficulty of producing titanium oxide or other titanium compounds sufficiently free from coloring impurities, glasses with sufficient amounts of titanium to give a sufficiently high refractive index turn out to be too strongly colored with long fiber lengths. The other above-mentioned heavy metal oxides ZrO ₂ , WO ₃ , HfO ₂ and ThO _{2 are} also ruled out because of their easy discoloration. In addition, glasses with a significant proportion of lead or titanium generally have too small a working area or easily devitrify at working temperatures.

In the case of glasses that are to be used for fiber optics, the usual, the Refractive index-increasing additives the above-mentioned heavy metal oxides, especially lead oxide, out. In the case of fiber optic glasses, other additives that increase the refractive index must therefore be used.

It has now been found that these difficulties
by omitting lead and titanium as well as such
Heavy metals such as zirconium, hafnium and tho-. 45 can be suppressed. It is particularly astonishing, except in relatively small amounts, that the glass according to the invention can contain 5 to and their replacement by relatively large amounts 40 percent by weight of niobium oxide and 15 to 45 percent by weight of niobium oxide as mainly for the high percent of barium oxide and still chung index responsible ingredient avoided does not tend to devitrify. Such a stable one, can be. The presence of tantalum oxide, the glass containing 5 ° niobium and barium in the specified amount in addition to commercially available niobium compounds, is not yet known.

Lanthana is apart in its influence on the physical properties of the fiber optic core glasses in terms of refractive index, very similar to barium oxide, so that both oxides are fairly broader within Glass composition ranges interchangeable

5 to 40 Nb ₂ O ₅ and optionally Ta ₂ O ₅ , with at least 90% of this amount of Nb ₂ O ₅ ,

25 to 40 SiO ₂ and optionally B ₂ O ₃ , with at least 70% of this amount of SiO ₂ ,

15 to 45 BaO,

O to 36 La ₂ O _3,.

O to 15 CaO and / or SrO,

O to 10 ZnO and / or CdO,

O to 5 Na ₂ O and / or K ₂ O and / or Li ₂ O,

at most 5 TiO ₂ and / or ZrO ₂ and / or HfO ₂ and / or ThO ₂ .

It has now surprisingly been found that with this in terms of the selected ingredients and proportions of very special glass composition, the devitrification tendency of niobium oxide and glasses containing barium oxide largely

any natural contamination present, in amounts not exceeding 10 percent by weight of the amount of niobium, has no disadvantage and improves the stability of the glasses in smaller quantities.

From the publication S c hm id tV ο ss, "Die Rohstoffe zur Glaserzeugung", Leipzig, 1958, a number of glass raw materials are known which cause the glass to have a high refractive index, including BaO, Nb ₂ O ₅ , Ta ₂ O ₅ and La ₂ O ₃ . A major problem with the use of niobium in optical glasses, however, is precisely the high tendency of such glasses to devitrify. The same also applies to high barium oxide contents of around 20 percent by weight and more. The latter is clear from the above-mentioned prior publication, p. 199, lines 31 and 32. Barium glasses with up to 42 percent by weight BaO are already known. However, their influence on the refractive index is quite different, and the index increases with the larger La: Ba ratio.

Particularly useful are glasses with the same in the remaining composition is 20 to 40 weight percent Nb ₂ O ₅ and, optionally, Ta ₂ O _5, with at least 90 ° / ₀ of this amount of Nb ₂ O _5, but no, or 10 to 36 percent by weight La ₂ O ₃ included.

The following table lists a number of examples of optical glasses according to the invention, with the proportions of the oxides are given in percent by weight are:

example
3 I 4

SiO ₂

B ₂ O ₃

BaO

CaO

ZnO

Nb ₂ O ₃

La ₂ O ₃

Na ₂ O

Li ₂ O

Refractive index

V (Abbe dispersion value)
specific weight

25th

10

42

10

1.70
48
3.8.

22nd

45

5 20

1.78 39 4.4 25

30th

10

28

1.79
36
3.9

1.81
33
3.8

22nd

31

17th
20th

1.78
29
4.4

31

43

5
15th

1.68
43
4.1

The glasses according to the invention can be produced by mixing the ingredients melts in common crucibles free of harmful contaminants. Are particularly suitable Platinum crucible. The insert consists of oxides or compounds that develop under the melting conditions decompose to oxides, in appropriate proportions, to obtain the specified composition. in the in general, niobium, lanthanum, zinc and cadmium are added as oxides. Barium can be used as an oxide or carbonate or partly or wholly as peroxide are added; Calcium, strontium, sodium, Potassium and lithium can expediently be added as carbonates. Silicon dioxide can be used as high quality quartz sand and boron are added as boric acid.

The glasses melt and refine easily at temperatures between 1344 and 1427 ° C. You can reheated and drawn into rods or fibers at 816 ° C or below. The invention Glasses are practically colorless even in long fiber lengths and are very stable at working temperatures.

Although the glasses according to the invention are used as core glasses are particularly useful for fiber optics, their use is by no means limited thereto. The optical properties of the glasses according to the invention are comparable to those of the so-called "Lanthanum flint glasses," and they are therefore excellent optical glasses. Because of their relative proportions They are also extremely hard and resistant to chemical attack for Abbe refractometers can be used, the prisms of which were previously made of soft, easily scratched and blinding lead-containing glasses getting produced. The glasses according to the invention with a higher niobium content are considerably lighter than customary optical glasses corresponding to them and therefore offer advantages for solid optical elements, in which weight plays a significant role.

Claims (5)

Patent claims: 1. Lead-free, devitrification stable optical glass with a refractive index of at least 1.65, which is particularly suitable for the production of glass fiber optics by the following composition in percent by weight: 5 to 40 Nb ₂ O ₅ and optionally Ta ₂ O ₅ , with at least 90% of this amount of Nb ₂ O ₅ , 25 to 40 SiO ₂ and optionally B ₂ O ₃ , with at least 70% of this amount of SiO ₂ , 15 to 45 BaO, 0 to 36 La ₃ O ₃ , 0 to 15 CaO and / or SrO, 0 to 10 ZnO and / or CdO, 0 to 5 Na ₂ O and / or K ₂ O and / or Li ₂ O, at most 5 TiO ₂ and / or ZrO ₂ and / or HfO ₂ and / or ThO ₂ . 2. Glass according to claim 1, characterized in that it contains 20 to 40 percent by weight of Nb ₂ O ₅ and optionally Ta ₂ O ₅ , with at least 90% of this amount of Nb ₂ O ₅ , but no La ₂ O _{3, with otherwise the same composition} contains. 3. Glass according to claim 2, characterized in that it additionally contains 10 to 36 percent by weight of La ₂ O ₃ . 4. Use of glasses according to one of claims 1 to 3 as fiber optic core glass. 5. Use of glasses according to one of claims 1 to 3 as prisms in Abbe refractometers.