JPH0428655B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a fluoride glass that has good transmission characteristics for infrared rays and is suitable as a material for optical fibers and optical components, and has excellent chemical durability and mechanical properties. The present invention also relates to a fluoride glass with improved devitrification resistance. [Prior art] Fluoride glass transmits a wide wavelength range from ultraviolet to infrared, and has unique optical properties such as low refraction and low dispersion, making it suitable for use in low-loss optical communications and infrared radiation temperature measurement. It is expected to have a wide range of applications, including fibers, lenses, window glass, and laser host glass. Conventional fluoride glass
Glass systems whose main components are BeF ₂ , AlF ₃ and ZrF ₄ (or HfF ₄ ) are known, and recently,
Optical fibers are being developed using fluoride glass containing _ZrF4 as a main component. Like SiO _{2 ,} BeF 2 is stable enough to form a glass by itself, so glasses containing a large amount of BeF ₂ as a glass-forming fluoride are the most stable against crystallization among fluoride glasses. Therefore, when it was first discovered, research was conducted with the aim of improving the chemical durability, which was a drawback of this glass. However, since BeF ₂ itself is deliquescent, there was a limit to the ability to improve the chemical durability of glasses containing a large amount of BeF 2. Also, Bef ₂
The higher the content, the shorter the infrared transmission limit wavelength becomes, so from this point of view as well, it is not preferable to have a large amount of BeF ₂ . U.S. Patent No. 2466506 and No. 2466509 are
It teaches that when BeF ₂ coexists with a large amount of PbF ₂ , the amount of BeF ₂ can be reduced. In the former example, BeF ₂ 10, AlF ₃ 30, PbF ₂ 45,
Like MgF ₂ 15, containing as much as 45 mol% of PbF ₂
Glasses with BeF ₂ reduced to 10 mol% are shown. This US patent limits BeF ₂ to 10-25 mol%, but the reason for this limitation is not specified. The latter also discloses that in glasses containing 20-55 mol% _PbF2 , up to 10 mol% _BeF2 can be included. Glasses based on these US patents contain a large amount of PbF ₂ , so as fluoride glasses, they have a drawback of high Rayleigh scattering due to their high refractive index. Due to its properties, it is not suitable as an optical fiber material. Furthermore, when glass containing a large amount of PbF ₂ is melted, the PbF ₂ is reduced and it is easy to form an alloy with a _platinum crucible or a gold _crucible . Although a method of adding it alone is employed, it is difficult to obtain a homogeneous glass with such a method, and the composition also fluctuates widely, resulting in poor reproducibility. Fluoride glasses containing ZrF ₄ and/or HfF ₄ as main components have been obtained that are relatively stable against crystallization, but they have poor chemical durability and low hardness and Young's modulus, making them difficult to absorb light. Not sufficient as a fiber material. On the other hand, fluoride glass whose main component is AlF ₃ has relatively good chemical durability and mechanical properties, but it tends to crystallize, requires rapid cooling to obtain good glass, and is not suitable for large shapes. It is difficult to draw optical fiber, let alone to obtain glass of this type. [Problems to be Solved by the Invention] As described above, fluoride glasses according to the prior art have serious drawbacks in stability against crystallization, glass properties, and production, and truly useful glasses have not yet been obtained. do not have. Therefore, an object of the present invention is to provide a glass that is stable against crystallization, has excellent chemical durability and mechanical properties, and can be easily produced. [Means for solving the problems] The present invention provides AlF ₃ glass that does not contain PbF ₂ and has excellent chemical durability and mechanical properties.
This book was developed based on the discovery that introducing a small amount of BeF ₂ significantly improves the stability against crystallization, which is a drawback of AlF ₃ glass, without impairing its chemical durability or mechanical properties. The fluoride glass of the invention is characterized by having the following composition. That is, the glass composition of the present invention is expressed in mol%: AlF ₃ 20-45, BeF ₂ 1-9, CaF ₂ 0-42,
SrF ₂ 0-25, BaF ₂ 0-25, CaF ₂ +SrF ₂ +
Total amount of BaF ₂ 20-70, ZrF ₄ and/or HfF ₄ 0
~25, MgF2 ₀ ~15, _YF3 and/or lanthanide elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,
Fluorides of Tb, Dy, Ho, Er, Tm, Yb, Lu) 0-25, ZnF ₂ 0-15, InF ₃ 0-10, GaF ₃ 0
~10, characterized by 0 to 20 fluorides of alkali metals (Li, Na, K, Rb, Cs). The preferable glass composition of the present invention is also expressed in mol%: AlF ₃ 25-40, BeF ₂ 2-9,
CaF ₂ 10-38, SrF ₂ 3-20, BaF ₂ 3-22,
Total amount of CaF ₂ + SrF ₂ + BaF ₂ 30-60, ZrF ₄ and/
or HfF ₄ 0-20, MgF ₂ 0-10, YF ₃ and/or lanthanide elements (La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Fluoride of Lu) 0-15, ZnF ₂ 0-10, InF ₃
0-8, GaF ₃ 0-8, alkali metals (Li, Na,
K, Rb, Cs) fluorides range from 0 to 15. [Function] The glass composition of the present invention includes AlF ₃ as the main component for forming the glass network, BeF ₂ as its auxiliary component, and
Since it is composed of CaF ₂ , SrF ₂ , and BaF ₂ as network modifying components, it can be easily vitrified, especially when small amounts of
The presence of BeF ₂ has the effect of improving the stability of glass against crystallization. In addition, since AlF ₃ is the main component, the bond is strong, and since it contains no components other than BeF ₂ that are easily soluble in water, it has good chemical durability and mechanical properties. On the other hand, optional components such as ZrF ₄ , HfF ₄ , YF ₃ , fluorides of lanthanide elements, InF ₃ , and GaF ₃ complement defects or increase irregularity in the network structure of fluoride glass, thereby stabilizing it against crystallization. and works to improve chemical durability and mechanical properties. In addition, alkali metal fluorides make it easier to dissolve glass, and
It acts to increase the disorder of the glass structure and increase its stability against crystallization. Next, the reason for limiting the content of each component will be described. In terms of mol%, the content of AlF ₃ is 20 to 45, preferably 25 to 40. If the amount is less than the lower limit or more than the upper limit, crystallization tends to occur, making it difficult to obtain a stable glass. Furthermore, if the amount is less than the lower limit, the surface hardness cannot be increased. BeF ₂
The content of is 1 to 9, preferably 2 to 9,
If the amount is less than the lower limit, the stabilizing effect on crystallization will be poor, and if it is more than 9, crystals will tend to precipitate.
In addition, chemical durability and mechanical properties are reduced, and infrared transparency is also deteriorated. The content of _CaF2 is 0-25,
Preferably in the range of 3 to 20, the content of _SrF2 is 0
-25, preferably 3-20, and the content of _BaF2 is selected in the range 0-25, preferably 3-22, but the total amount of _CaF2 , _SrF2 and _BaF2 is 20-70. , preferably 30 to 60, and if the total amount of these three components is less than the lower limit or more than the upper limit, crystallization is likely to occur, making it difficult to obtain a stable glass. On the other hand, the content of optional ZrF ₄ and/or HfF ₄ expressed in mol% is 0 to 25, preferably 3
~20, the content of _MgF2 is 0-15, preferably 0-10, _YF3 and/or lanthanide elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
The content of fluorides (Dy, Ho, Er, Tm, Yb, Lu) is 0 to 25, preferably 0 to 15, and ZnF ₂
The content of is 0 to 15, preferably 0 to 10,
The content of InF ₃ or GaF ₃ is 0 to 10, preferably 0
~8. If the amount of these components is more than the upper limit, crystallization tends to occur and it becomes difficult to obtain a stable glass. The content of fluorides of alkali metals (Li, Na, K, Rb, Cs) is 0 to 20, preferably 0 to 15, expressed as mol%, and if the amount is greater than the upper limit, chemical durability will deteriorate. [Example] Table 1 shows the effect of BeF ₂ on fluoride glasses according to the present invention. Sample Nos. 1 and 2 are a typical ZrF ₄ -based glass according to the prior art and the glass of Example No. 4 of US Patent No. 2,466,506, respectively, and Sample No. 3 is an AlF ₃ -based glass.

[Table] Glasses with sample numbers 1 to 7 were made by adding 10 g of acidic ammonium fluoride to a total of 100 g of fluoride raw material having the composition shown in the table, and mixing the mixture into a gold crucible in an argon atmosphere at 900°C. After being melted for 2 hours, it was slowly cooled to form a glass with a diameter of about 45 mm and a thickness of about 15 mm. However, the glass of sample number 2 according to US Patent No. 2,466,506 did not vitrify under the above glass manufacturing conditions, and no glass could be obtained.
The glass of sample number 3, which does not contain BeF ₂ , was transparent only in the rapidly cooled peripheral part, and the rest was crystallized and devitrified, whereas the glass of sample numbers 4 to 7, which contained BeF ₂ , was transparent.
The glass and the ZrF ₄ glass of sample number 1 were transparent. However, sample number 6 containing a large amount of BeF ₂
In samples Nos. 4 and 7, fine crystals were observed inside the glass, and when a He-Ne laser beam was applied to the glass, a ray trajectory due to light scattering that was not observed in samples Nos. 4 and 5 was observed. This result shows that the glasses of sample numbers 4 and 5 according to the invention are extremely stable against crystallization compared to glasses of other compositions. Furthermore, in terms of water resistance and Knoop hardness measured based on the Japan Optical Glass Industry Association standard JOGIS-1975, the glass according to the present invention is also a typical fluoride glass according to the prior art, as shown in Table 1.
Significantly superior to ZrF ₄ glass, and
Better than glass containing a lot of BeF ₂ . These facts indicate that the fluoride glass according to the present invention is excellent not only in stability against crystallization but also in chemical durability and mechanical properties. The attached drawings show the Rayleigh ratio (R90° ₎ to the wavelength of light [incidence Scattered light intensity in a direction of 90° to the light].
In the figure, 1 is a line segment indicating the wavelength dependence of the Rayleigh ratio of sample number 1, and 2 is a line segment indicating the wavelength dependence of the Rayleigh ratio of sample number 4. At 1, the Rayleigh ratio is proportional to the -2.5th power of the wavelength, and at 2, it is proportional to approximately the -4th power. This is because the glass of sample number 1 has Mie scattering due to particles of a certain size, whereas the glass of sample number 4 has scattering peculiar to glass caused by fluctuations in density and composition. This shows that only Rayleigh scattering exists, and it is clear that the glass of sample number 4 is extremely homogeneous. Further, the refractive index n _d and dispersion ν _d of the glass of sample number 5 are 1.4097 and 102.2, respectively, whereas the ZrF ₄ glass of sample number 1 according to the prior art has n _d = 1.4990, ν _d =
Since the refractive index is significantly lower than that of 76.0, the Rayleigh scattering itself of the glass of the present invention is essentially smaller than that of ZrF ₄ glass, making it suitable as a material for low-loss optical fibers.

【table】

[Table] Table 2 shows another composition example of the fluoride glass according to the present invention. Samples Nos. 8 to 17 were made into glass by the method described above using fluoride as a raw material. The obtained fluoride glasses of sample numbers 8 to 17 were observed with the naked eye, with a microscope, and with He-Ne laser light incident, but no crystals or light ray trajectories were observed in any of the fluoride glasses, indicating that they were not susceptible to crystallization. It was stable. In addition, the chemical durability of these glasses is such that the water resistance weight loss is 0.05 to 0.3%, and the Knoop hardness is 280 to 360 Kg/mm ² , making them superior in practical use compared to ZrF ₄ glass, which is a typical fluoride glass made by conventional technology. with possible characteristics. [Effects of the Invention] The fluoride glass of the present invention is extremely stable against crystallization, and a large glass with no light scattering other than Rayleigh scattering can be obtained without using special cooling means. Good durability,
Therefore, there is no need to worry about deterioration during use, the surface hardness is high and it is difficult to scratch, and the refractive index is low.
Since Rayleigh scattering is small, it is suitable as a low-loss optical fiber material for optical communications. In addition to this,
The fluoride glass of the present invention has excellent infrared transparency,
Because it has lower refraction and lower dispersion than _CaF2 crystal, it is also useful as a material for optical components.

[Brief explanation of drawings]

The attached drawing is a diagram showing the wavelength dependence of the Rayleigh ratio, and 1 is a diagram of sample number 1, which is one of the conventional techniques.
2 shows the wavelength dependence of the Rayleigh ratio of the ZrF ₄ -based fluoride glass of sample number 4 according to the present invention.

Claims (1)

[Claims] In 1 mol%, AlF ₃ 20-45, BeF ₂ 1-45
9, CaF ₂ 0-42, SrF ₂ 0-25, BaF ₂ 0-25,
Total amount of CaF ₂ + SrF ₂ + BaF ₂ 20-70, ZrF ₄ and/or HfF ₄ 0-25, MgF ₂ 0-15, YF ₃ and/or lanthanide elements (La, Ce, Pr, Nd, Pm, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
Fluorides of 0-25, ZnF ₂ 0-15, InF ₃ 0-10,
GaF ₃ 0-10, alkali metals (Li, Na, K,
A fluoride glass having a composition of 0 to 20 fluorides of Rb, Cs). 2 In claim 1, AlF ₃
25-40, BeF ₂ 2-9, CaF ₂ 10-38, SrF ₂ 3
~20, BaF ₂ 3 ~ 22, total amount of CaF ₂ + SrF ₂ + BaF ₂
30-60, ZrF ₄ and/or HfF ₄ 0-20, MgF ₂
0-10, _YF3 and/or lanthanide elements (La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Fluorides of Ho, Er, Tm, Yb, Lu) 0 to 15,
A fluoride glass having a composition of 0 to 10 _ZnF2 , 0 to 8 _InF3 , 0 to ₈ GaF3, and 0 to 15 fluorides of alkali metals (Li, Na, K, Rb, Cs).