CS263299B1 - Infrared-transmissive silicon glass in the spectral range of 780 to 2600 nm - Google Patents

Abstract

The glass is intended for the production of special optical filters, transmitting infrared radiation in the spectral range of 780 to 2,500 nm. The glass contains in percentages by weight 67 to 71 silicon dioxide SiO, 11 to 14 calcium oxide CaO, 12 to 20 sodium oxide NaO, 0.1 to 2 zinc oxide ZnO, 0.1 to 1.5 antimony Sb, 0.1 to 1 selenium Se and at most 0.02 iron oxide Fe2O3. Easier processing of glass and improvement of optical properties is achieved by adding 0.5 to 6 percent by weight of potassium oxide K2O.

Description

BACKGROUND OF THE INVENTION The present invention relates to the composition of infrared transmissive silica glass at spectral 780 to 2500 nm.

Infrared-transmitting filters are used in the production of various optical devices, e.g. The prior art filters are made of chalcogenide glasses of various compositions, such as those disclosed in U.S. Patent Nos. 3,511,672 and 3,511,673, which are glasses of the Ge - Se - Mn and Ge - Se - Zn system in France. No. 2 027 407, the glass of the Ge - Se - As system, etc.

A disadvantage of hitherto known chalcogenide glasses is that they only transmit infrared radiation in regions of wavelengths above 6,000 nm, making them impossible to use for special purposes where transmittance in the lower region of the spectral range of infrared radiation is required.

These disadvantages are overcome by the inventive silica glass which transmits infrared radiation in the spectral range of 780 to 2500 nm. SUMMARY OF THE INVENTION The glass composition comprises 67 to 71 SiO ₂ silica, 11 to 14 CaO, 12 to 20 Na 2 O, 0.1 to 2 ZnO, 0.1 to 1 5 antimony Sb, 0.1 to 1 selenium Se, and at most 0.02 ferric oxide Fe 2 O 4.

In order to achieve better processability of the glass as well as to improve the optical properties, the glass may preferably further comprise 0.5 to 6% by weight of K ₂ O.

The glass composition of the invention transmits infrared radiation in the lower region of the infrared spectral range, in the spectral range of 780 to 2500 nm, where it has a spectral transmission of 0.5 to 75%.

The glass, after melting and initial processing, is clear, light yellow in color and transparent. In order to achieve the required transmittance only in the infrared region, a secondary thermal exposure of the glass, the so-called start-up, during which nucleation and growth of the antimony selenide crystals SbjS ^ takes place, is necessary. The size and frequency of these crystals determine the nature and magnitude of the spectral transmission in the desired spectral range of infrared radiation. The resulting glass is black.

An exemplary embodiment of the invention is apparent from the examples.

Example 1

The glass contains in weight% 68.5 SiO ₂ , 11 CaO, 19.3 Na ₂ O, 0.2 ZnO, 0.8 antimony Sb and 0.2 selenium Se. Ferric oxide Fe ₂ O ₂ is contained as an impurity in trace amounts.

The glass was melted from a strain consisting of ground quartz, calcium carbonate CaCO 3 and precipitated sodium carbonate Na ₂ CO ₃ .

Furthermore, pure reducing agents, sugar, starch, dextrin and coloring raw materials of selenium Se and antimony Sb were used. Selenium Se was introduced in the elemental form, antimony Sb in the form of antimony trioxide Sb10.

Since it is known that the spectral transmission of glass in the infrared range adversely affects impurities constituting admixtures of the raw materials used, such as chromium chromium, copper Cu, and in particular iron Fe, it is necessary to use high purity raw materials.

The glass was melted in a ceramic pan at a temperature of 1380 to 1410 ° C, the glass was homogenized with a ceramic propeller stirrer. It was further processed by pressing in metal molds to produce the desired shape or by casting on a plate, rolling and cutting the shapes at 1200 ° C.

After coarse cooling, the products were subjected to secondary heat treatment - start-up - at temperatures of 580 to 620 ° C for 12 hours. The charging was carried out in an electric furnace with a minimum temperature gradient.

In the spectral range of infrared radiation, the glass exhibited these selected spectral progression values (in%) s at 850 nm-1; 900 nm-6; 950 nm-32; 1,000 nm - 60; 1,100 nm -70;

500 nm-70; 2000 nm - 70; 2500 nm - 70.

Example 2

The glass contains 67.3% SiO _{2 by} weight; 14 CaO; 16,4 of sodium oxide Na ₂ 0; 1 zinc oxide ZnO; 1 antimony Sb and 0.3 selenium Se. Ferric oxide Fe ₂ O ₃ is contained as an impurity in trace amounts.

The glass was melted from a batch consisting of the same raw materials as in Example 1.

The glass was melted in a ceramic pan at a temperature of 1380 to 1420 ° C, the glass was homogenized with a ceramic propeller stirrer. Further, the glass was treated as in Example 1.

After coarse cooling, the products were subjected to secondary heat treatment - start-up - at temperatures of 580 to 620 ° C for 10 hours. The charging was carried out in an electric furnace with a minimum temperature gradient.

In the spectral range of infrared radiation, the glass exhibited the following selected spectral transmittance values (δ): at 850 nm - 1.5; 900 nm-5; 950 nm-31+ 1000 nm-54; 1,100 nm -64;

500 nm -64; 2000 nm - 64; 2500 nm - 64.

Example 3

The glass contains in weight% 68.1 SiO ₂ ; 12.2 CaO;

15.0 sodium oxide Na ₂ O; 3.5 K ₂ O; 0.3 zinc oxide ZnO; 0.2 selenium Se and 0.7 antimony Sb. Fe ₂ O 3 3 ^{is present as} trace impurity.

The glass was melted from a batch consisting of the same raw materials as in Example 1, in addition potassium carbonate K ₂ CO ₃ was used. Further, the glass was treated as in Example 1.

After coarse cooling, the products were subjected to secondary heat treatment - start-up - at temperatures of 580 to 640 ° C for 12 hours. The charging was carried out in an electric furnace with a minimum temperature gradient.

In the spectral range of infrared radiation, the glass exhibited the following selected spectral transmittance values (δ): at 850 nm - 0.5; 900 nm-35; 1000 nm - 65; 1100 nm-75; 1500 nm-75; 2000 nm - 75; 2500 nm - 75.

Claims (2)

An infrared transmissive silica glass in the spectral range of 780 to 2500 nm, characterized in that it contains, by weight, 67 to 71 silica, 11 to 14 calcium oxide, 12 to 20 sodium oxide, 0.1 to 1 zinc oxide, 0.1 to 1.5 antimony, 0.1 to 1 selenium and not more than 0.02 iron oxide. 2. The silica glass according to claim 1, characterized in that it contains 0.5 to 6% by weight of potassium oxide.