SU958509A1 - Method for decolorizing natural colour crystals - Google Patents

Description

The invention relates to the technology of obtaining optically transparent muscovite mica from naturally colored crystals and can be found with. change in the production of optical: elements of pribr in polarization optics and television technology,.

A known method of bleaching colored natural crystals by ultraviolet irradiation of C However, this method is associated with ultraviolet radiation and does not always lead to positive results when irradiated by crystals with a different nature of optical absorption. Thus, ultraviolet treatment does not improve the light transmission of muscovite crystals.

There is also a known method of bleaching colored natural crystals of Iceland spar, which includes: thermal treatment in air. The method includes heating the crystals to 300-350 ° C and annealing them in air at this temperature for 10 hours 2.

However, this method does not improve the crystal transmittance. Muscovite fishing. Moreover, processing .ka specified, the method leads to

the opposite result, i.e. k an increase in the intensity of the ruby color and an increase in absorption with in the near ultraviolet and visible regions of the spectrum.

Natural muscovite crystals are usually naturally colored, they are characterized by improper absorption in the ultraviolet and visible regions of the spectrum, due to the presence of chemical in the crystal lattice. elements of impurities (in particular, ReZ and Fe ions) and impurity-defect centers. Approximately 80%.

five ; Natural muscovite crystals from domestic deposits have a ruby color. In the production of optical elements of muscovite devices, such as phase plates, linear polarizers for filters, photo cathodes, and langentcent screens, it is preferable to use crystals that have a maximum projecter in various areas

spectrum, as improper absorption increases the loss of light.

The purpose of the invention is the elimination,

Claims (2)

30 ruby color muscovite crystals. The goal is achieved by the fact that according to the method of bleaching natural; colored crystals by heating with the post-isothermal annealing in air, heating is performed up to 400-500 ° C and annealing is carried out for 1-22 hours. Example. Thermal processing of natural muscovite crystals of ruby color is carried out according to the known and proposed methods. Five natural muscovite crystals of ruby color are selected for the experiment. Optically homogeneous crystals are selected, i.e. crystals not containing cracks, inclusions, color inhomogeneities. Three plates of the same thickness (0.25 mm) are made from each crystal. As a result, a trigroup of five crystals was obtained, one plate from each crystal. The crystals of the first group are subjected to heat treatment by a known method - with isothermal annealing. At ZOO-ZBO With crystals of the second and third groups according to the proposed method with isothermal annealing at 400 and 500 ° C. Heat treatment is carried out in the air in a muffle. The average heating rate is 9 ° C per minute. To establish the time dependence of the process at each fixed temperature, a series of consecutive isothermal anneals with a total duration of up to 25 hours is carried out. To control the nature of the light transmission during heat treatment, the optical absorption spectra of the crystals are taken in the initial state and after each isothermal annealing. The absorption spectra are taken on a Beckman spectrophotometer of the Acta-M-IV brand in the wavelength range of 300-800. As a result of the experiments, it is established that heat treatment of a pot according to a known method, including heating to 300-350C and isothermal annealing for a period of 1-25 hours, with BP / dates to an increase in the ruby color, and thermium treatment, including isothermal annealing at 400 and 500 s, lead to elimination of ruby color. The above is illustrated in FIG. 1, which shows typical absorption spectra: curve 1 — the original crystal of a ruby oKpacKHf curve I — of the same crystal after processing according to the known method; curve MJ of the same crystal after treatment according to the proposed method. An increase in optical density in the region of wavelengths of 450–800 nm (curve M) as a result of heat treatment at –300–350 0 increases the intensity of the rub of a new color. As a result of thermal treatment at 400 and (curve III), a significant decrease in the optical density occurs in a narrow range of wavelengths and the ruby color disappears. In addition, the dependence of the decrease in ruby color intensity on the duration of isothermal annealing was revealed. Thus, at 400 s, the process of weakening ruby color to its disappearance takes 22 hours, at 500 ° C, the discoloration takes 1 hour. As an example in FIG. Figures 2 and 3 show the dependence of the optical density (0 (L)) at a wavelength of 510 nm on the HsoTeRmic annealing time (t) in hours. (Figure 2 at the annealing temperature; FIG. With the annealing temperature). Thus, heat treatment of naturally colored muscovite crystals at an isothermal annealing temperature of 400–500 ° C and its duration of 1 – S24, respectively, eliminates the ruby color of the crystals and improves their light transmission over a wide wavelength range, and found that the ruby color of muscovite crystals is due to , impurity-impaired centr sh. Apparently, the heat treatment of crystals at 300–350 ° C promotes the formation of these color centers and an increase in their concentration, while an increase in temperature causes their destruction. Using the proposed method allows to improve the quality of natural raw materials. The crystals treated by this method acquire a new positive quality (significantly higher (up to 50%) transparency in the visible and near ultraviolet regions of the spectrum) in comparison with the initial crystals of ruby color. The method of bleaching natural colored crystals by heating followed by isothermal annealing in air, characterized in that, in order to eliminate the ruby color of muscovite crystals, heating is performed up to 400-500 ° C and annealing is carried out within 1-22 hours. Sources of information taken into account during the examination 1.Kozlovsky V.Kh. et al. Investigation of the nature of the yellow color of Iceland spar crystals and the mechanism of their discoloration. Works VNIISIMS, .1969, t. X, p. 118-129. 2.Skropiyiyev A.V., Kukui L.L. Iceland spar. L., Nedra, 1973, p. 141 (prototype). R eight f2IS -W R ff, 3 2