Method of obtaining crystalline workpieces from silver halides and their solid solutions for infrared fibrous lightguides

FIELD: chemistry.

SUBSTANCE: invention relates to improved method of obtaining workpieces from silver halides and their solid solutions for fibrous infrared lightguides, which includes application on silver halide crystal-core of crystalline shell of crystalline silver halide with refraction index lower than in crystal-core, and thermal processing. Shell on crystal-core is applied by ion-exchange diffusion in ion-exchange source, as the latter taken is finely disperse silver halide powder with coarseness 1-20 mcm, diffusion is carried out at temperature, close to melting temperature of crystal-core in atmosphere of mixture of vapours of halides, included into composition of crystal material and powder, taken in equal ratio under pressure 0.2-0.5 atm.

EFFECT: method makes it possible to reduce optic loss of lightduides, operating in infrared spectrum range.

2 ex

 

The invention relates to the field of materials transparent in the infrared spectral range 0.4 to 40 μm, namely crystals of silver halides which can be used for the manufacture of optical elements, infrared, laser, acousto-optic and fiber-optic technology.

A method of obtaining crystalline pieces of silver halides for the extrusion of fibers. From a crystal of silver halide mechanically cutting a workpiece of a given size, heated and extruded through the die plate, the light guide (U.S. Patent No. 5182790, publ. 26.01.1993, IPC C30B 15/24, NPK 385/141).

The disadvantage of this method is to obtain a fiber with high optical losses due to the insecurity of the boundaries of the fiber environment. Such a fiber is exposed to heat and ultraviolet dissociation of silver halides. The outer polymer shell such fibers only protects from mechanical influences and does not reduce optical loss.

An object of the invention is the reduction of optical losses of the optical fibers operating in the infrared region of the spectrum.

A method of obtaining crystalline pieces of silver halides and their solid solutions for the extrusion of the fibre, in which the billet for extrusion is made of two parts - the crystal heart is eveny and shell, made in the form of a hollow cylinder made of a material with a smaller refractive index than the refractive index of the core material. Before extrusion of the two parts assembled in type design "rod in the tube", is heated and mechanically compresses to improve the contact rod and the inner surface of the tube. The extrusion is carried out at a heating to the softening pieces and high pressure. Get a blank shell of the fibre (I. S. young, W. F. Golovanov, G. C. Polyakov "single Crystals of silver halides for fiber optics". Surface x-ray, synchronous and neutron studies. 2003, No. 7, S. 22-25).

The disadvantage of a relatively high optical loss in the fiber, related to the fact that the contact surface of the core-shell is not optical and clean, there are always mechanical impurities: organic material, the pores of the shell.

The technical result of the claimed method is the reduction of optical loss of the fiber.

The technical result is achieved that the way to get pieces of silver halides and their solid solutions for fiber infrared optical fibers, comprising applying to the crystal core of the silver halide crystal shell of crystalline silver halide indicator prelo the population, less than crystal-core, and heat-treated according to the invention the shell on the crystal core is applied by ion diffusion in the ion source, which take the fine powder of the silver halide particle size of 1-20 μm, the diffusion is carried out at a temperature close to the melting point of the crystal core, in an atmosphere of a mixture of vapor of the halogen included in the composition of the crystal and powder, taken in equal proportions at a pressure of 0.2-0.5 ATM.

The essence of the method lies in the fact that, by subjecting the ion-exchange diffusion crystal of silver halide in an ion source, which take crystalline fine powder of silver halide particle size of 1-20 μm, with a smaller refractive index in the crystal core is formed a radial gradient of chemical composition, resulting in a gain radial gradient layer of refractive index in the crystal of silver halide, which prevents the light output outside of the workpiece and, therefore, optical loss.

When used as an ion vapor source halides of silver, due to the low concentration of ions in the gas phase, in the crystalline core is not formed, the gradient of the chemical composition.

Use as an ion source of the melt is of halogenide silver is impossible, as the temperature of the melt of silver halide with a refractive index lower than that of the crystalline core, significantly above the temperature of melting of the core. The location of the core in the melt leads to its destruction.

The process of diffusion at low temperature reduces the rate of diffusion and productivity of the process.

The dispersion of powder of silver halide than 20 microns violates the integrity and uniformity of the resulting gradient layer. The dispersion of less than 1 μm is difficult and complicates the work of creating a gradient layer due to toxicity and explosive powder.

Conducting ion diffusion at the melting temperature close to the melting point of the crystal of silver halide in the air or in vacuum, it is impossible due to the dissociation of silver halide, and therefore it is impossible to obtain a gradient layer of refractive index in the crystal. Formed by the decomposition of fine metal colloidal silver reduces the spectral transmittance of the crystal at 90-99%, and formed in the gas phase halogen enough to suppress dissociation.

To suppress the dissociation of the halide of the silver diffusion process leads to a mixture of vapor of the halogen contained in the composition of the solid solution of silver halide is, taken in equal proportions at a pressure of 0.2-0.5 ATM. Pressure of the mixture of Halogens in the gas phase 0.1 ATM is not enough to suppress the dissociation of the silver halides. To create more pressure 0.5 ATM impractical due to increased corrosion damage of the equipment elements.

Examples of the method

Example 1. In a glass container of heat-resistant borosilicate glass download cylindrical crystal of silver bromide with a diameter of 25 mm, length 100 mm, the refractive index of which is within the working range of wavelengths (0.4 to 12 microns) is 2.21 are 2,30. Crystal fall asleep from all sides and mechanically compacted fine powder of silver chloride. The dispersion of powder of silver chloride is 10.0 μm. The refractive index 1,90-2,00. The container is filled with a mixture of vapors of the Halogens chlorine and bromine in the ratio of 1:1 at a pressure of 0.3 ATM and sealed. A sealed container is heated to a temperature of 410°C and kept at this temperature for 200 hours. From chilled to room temperature container retrieve the crystal, cut off the ends. End surface of the grind, Polish and measure optical and chemical characteristics. Measurement of the gradient of the chemical composition of the resulting sample is carried out by a chemical method on the content of chlorine and bromine with an accuracy of ±2% by successive removal of layers of the crystal is and from forming to the center. The chemical composition of the layers of the cylindrical workpiece adjacent to the forming amounted to 20% of silver bromide - 80% of silver chloride to 95% of silver bromide and 5% of silver chloride on the axis of the crystal. The refractive index of the workpiece, as measured by x-ray microanalyzer "Comebax" (accuracy ±1,5%), amounted to 2.29 from along the axis of the workpiece to 2.10 along. From the obtained crystalline workpiece by extrusion made of polycrystalline fiber diameter of 1.0 mm, the optical loss which amounted to 0.05 dB/m For comparison, extruded from the original billet silver bromide fiber with a shell of silver chloride (core/shell - 0,5/0,5 mm) optical loss was 0.3 dB/m

Example 2. In a glass container of heat-resistant borosilicate glass download cylindrical crystal of a solid solution of chloride - bromide of silver composition: 25% of the mass. silver chloride - 75% of the mass. bromide silver with a diameter of 18 mm, a length of 100 mm, a refractive index which is within the working range of wavelengths (0.4 to 12 microns) is 2,18-2,19. Crystal fall asleep from all sides and mechanically compacted fine powder of silver chloride. The dispersion of powder of silver chloride is of 20.0 μm. The refractive index 1,90-2,00. The container is filled with a mixture of vapors of the Halogens chlorine and bromine in the ratio of 1:1 while allowing the attachment of 0.4 ATM and sealed. A sealed container is heated to a temperature of 400°C and kept at this temperature for 200 hours. From chilled to room temperature container retrieve the crystal, cut off the ends. End surface of the grind, Polish and measure optical and chemical characteristics. Measurement of the gradient of the chemical composition of the resulting sample is carried out by a chemical method on the content of chlorine and bromine with an accuracy of ±2% by successive removal of layers of crystal from forming to the center. The chemical composition of the layers of the cylindrical workpiece adjacent to the forming amounted to 60% of silver bromide - 40% of silver chloride to 70% of silver bromide - 30% of silver chloride on the axis of the crystal. The refractive index of the workpiece, as measured by x-ray microanalyzer "Comebax" (accuracy ±1,5%), ranged from 2,20 axis of the workpiece to 2.09 along. From the obtained crystalline workpiece by extrusion made of polycrystalline fiber diameter of 1.0 mm, the optical loss which amounted to 0.01 dB/m For comparison, extruded from the original piece chloride - bromide of silver composition: 25% of the mass. silver chloride - 75% of the mass. bromide silver fiber with a shell of silver chloride (core/shell - 0,5/0,5 mm) optical loss was 0.3 dB/m

As seen from the above examples, the proposed JV the property allows you to create crystal billet for extrusion of the fibre with a radial gradient of refractive index is non-defective, exposed to the possibility of contamination of the inner surface design of the rod in the tube", which greatly reduces the optical loss in extruded optical fiber.

The way to get pieces of silver halides and their solid solutions for fiber infrared optical fibers, comprising applying to the crystal core of the silver halide crystal shell of crystalline silver halide with a refractive index lower than that of the crystal core, and heat treatment, characterized in that the shell on the crystal core is applied by ion diffusion in the ion source, which take the fine powder of the silver halide particle size of 1-20 μm, the diffusion is carried out at a temperature close to the melting point of the crystal core, in the atmosphere of a vapor mixture of halogen, included in the material composition of the crystal and powder, taken in equal proportions at a pressure of 0.2-0.5 ATM.



 

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