RU2656660C1 - THERMO STABILIZING RADIATION RESISTANT COATING BaTiZrO3 - Google Patents

Abstract

FIELD: space technology.

SUBSTANCE: invention relates to the production of thermoregulatory coatings and can be used in space technology, in building industry, as well as in the chemical, food, light industry for thermostatic devices or process facilities. Thermoregulating coating of “solar optical reflectors” class is prepared from BaTiZrO₃ powder. Powder is deposited on base coat by the detonation method.

EFFECT: invention makes it possible to increase the radiation resistance of the thermoregulatory coating.

1 cl, 4 ex, 1 tbl

Description

The invention relates to temperature-controlled coatings designed to maintain the temperature of the objects on which they are applied, including temperature-controlled coatings used in the field of passive methods for controlling the temperature of objects, namely, temperature-controlled coatings of spacecraft. The invention can be used in space technology, in the construction industry, as well as in the chemical, food, light and other industries for thermostating of devices or technological objects.

Barium titanate refers to pigments that are especially promising for the preparation of thermoregulatory coatings, since it has a low coefficient of absorption of solar radiation a _s , a large emissivity in the infrared spectrum ε. In addition, this compound has the ability to vary over a wide range of emissivity depending on the temperature near the Curie point corresponding to a temperature of 120 ° C. Partial substitution of titanium cations by atoms of other elements, for example zirconium atoms, allows one to shift the temperature dependence of the emissivity to a region of lower temperatures. The property allows controlling the radiated heat fluxes from objects coated with coatings made on the basis of such compounds. Such coatings belong to the class of thermostabilizing or “smart” coatings.

But under the influence of outer space radiation, barium titanate forms radiation defects, which leads to the appearance of absorption bands due to these defects, a decrease in the reflection coefficient, an increase in the absorption coefficient a _s , and an increase in the fraction of absorbed energy. The temperature of the spacecraft will increase in this case, the thermal modes of operation of devices and devices will be violated and the time of their active existence will be reduced. To increase the resistance of barium titanates to the action of outer space radiation, various methods developed for oxide pigments can be applied.

Powders - pigments of barium titanate, like zinc and aluminum oxides, and titanium and zirconia are not stoichiometric in oxygen, and color centers on biographical anion vacancies are formed under the influence of radiation in them. Such pigments, in addition to reflective coatings of spacecraft and phosphors, where they are exposed to the flow of charged particles, are widely used in everyday conditions (paints, paper, rubbers), in which only solar electromagnetic radiation acts from ionizing factors.

Previous studies of diffuse reflectance spectra (ρ _λ ) and differential diffuse reflectance spectra (Δρ _λ ) of temperature-controlled coatings based on barium titanate powders after irradiation with 30 keV electrons showed that changes in the spectra occur mainly in the near infrared region, in which are located the absorption bands of defects of the anionic sublattice of the band of F ^- and F ⁺ centers [Mikhailov MM, Lapin AN Radiation resistance of thermostabilizing coatings based on barium titanate. Reshetnev readings. 2009.Vol. 1. No. 13. S. 342-343], [Mikhailov M.M., Lapin A.N. Grandfather N.V. Radiation resistance of temperature-controlled coatings based on barium titanate modified with micro- and nanopowders of aluminum oxide and zirconium dioxide. // Physics and chemistry of materials processing. 2010. No3. P. 45-50], [Mikhailov M.M., Burtseva T.A., Lapin A.N. Andriyanov D.I. The effect of synthesis temperature on the particle size distribution of Ba _0.65 Sr _0.35 TiO ₃ pigment on the optical properties and radiation resistance of coatings based on it // Surface. X-ray, synchrotron and neutron studies, 2010, No. 12, p. 23-29].

These studies have shown that if the formation of photo- or radiation defects occurs by the ionization mechanism, then the primary processes of interaction of various types of radiation with barium titanate powders are qualitatively identical, electron-hole pairs are formed, holes move to a negatively charged surface, neutralize the lattice oxygen that leaves the surface with the formation of anionic vacancies, first in the surface layers, then in the bulk of the powder grains.

At low radiation doses, the contribution of anionic vacancies to the total concentration of the formed electronic color centers can be decisive and even basic. Therefore, it seems important to research aimed at developing ways to increase the photo and radiation resistance of such pigments.

Previously, positive results were obtained on increasing the stability of diffuse reflection spectra to irradiation with electrons with an energy of 30 keV due to changes in the particle size distribution and specific surface of another pigment - rutile powder [Mikhailov MM, Vlasov VA On the size effect of the optical properties of TiO ₂ powders // Izv. universities. Physics, 1998, No. 12, p. 52-58], [Mikhailov M.M. Dependence of optical properties on specific surface and grain sizes of titanium dioxide powders. // Journal of Applied Spectroscopy, 2006, v. 73, No. 1, p. 73-7].

A promising way is to increase the stability of the optical properties of oxide powders by oxidizing the surface and saturating the volume with oxygen. The introduced oxygen, in addition to replacing biographical anionic vacancies, can be an oxygen supplier instead of the lattice leaving during photolysis or radiolysis during irradiation of treated powders with light quanta and charged particles. To date, the following methods for saturation with oxygen of the surface and volume of grains of titanium dioxide are known.

Method number 1

In the work [Mikhailov M.M. On the possibility of increasing the photo - and radiation resistance of TiO ₂ (rutile) powders by heating in oxygen // RAS. Surface. X-ray, synchrotron and neutron studies. 2007, No. 35, p. 102-106] presents the results of a study of one of the simplest methods of oxidizing powders and saturating them with oxygen - heating the powders in oxygen.

The radiation resistance of the samples over the entire range of the solar spectrum was evaluated by the change in the integral absorption coefficient, solar radiation (a _s ). Studies were performed on five samples heated in various modes of TiO ₂ powders _of qualification P02. Sample No. 1 was not heated, samples No. 2-No. 5 were heated in various modes: the temperature was varied within 110-150 ° C, the heating time was 17-120 minutes, the oxygen pressure was 0.2-760 mm Hg. The diffuse reflection spectra were measured before and after irradiation (ρ _λph ) with an electron fluence of ² × ^{16 16} cm ^-2 with an energy of 30 keV, and the change in the integral absorption coefficient Δa _{s was} calculated.

The performed studies showed that heating in oxygen leads to a decrease in the intensity of the absorption bands of defects in the anionic sublattice (F ^- and F ⁺ centers, neutral anionic vacancies, and conduction electrons) and weakly affects the formation of defects in the cationic sublattice when the powders are irradiated with electrons. The decisive role in increasing the radiation resistance of pigments under the given conditions of their processing in oxygen is apparently played by its diffusion into the bulk of the powder grains. It depends on both the temperature and the time of heating, and to obtain high radiation resistance of TiO ₂ powders by heating, it is necessary to create the following conditions: partial oxygen pressure of about ^10-1 mm Hg, average heating temperature of about 100 ° C, heating time of 120 minutes . The greatest increase in radiation resistance obtained under such optimal processing conditions is 1.4 times compared with the untreated sample. The disadvantage of this method is the large labor and energy costs associated with the need to obtain a high vacuum, oxygen inlet and heating, powders in its atmosphere. Moreover, the effectiveness of the method is not very high.

Method number 2

Another way to increase the photo and radiation resistance of oxide pigments is their treatment with ultraviolet in oxygen [Mikhailov MM On the possibility of increasing the photo and radiation resistance of TiO ₂ powders. UV ultraviolet treatment in oxygen // RAS. Surface. X-ray, synchrotron and neutron studies. 2007, No.8, p. 82-88]. The effect of a decrease in the concentration of anionic vacancies in the processed powders can manifest itself both during ultraviolet radiation and during subsequent irradiation by electrons processed in various modes of powders. If a decrease in anionic vacancies occurs during exposure to ultraviolet radiation, when oxygen is dissociated by reaction

then the effect can be recorded in the reflection spectra after irradiation with ultraviolet light. If there is no such manifestation, then we can assume that ultraviolet treatment in the atmosphere leads to saturation of the lattice with atomic oxygen without replacing them with anion vacancies. This oxygen will serve as a supplier of oxygen instead of leaving during irradiation, it will replace the newly formed vacancies when the pigment is irradiated with electrons. A comparison of the spectral degradation after electron irradiation of samples of qualification P02, pretreated with ultraviolet in oxygen, with the degradation of untreated oxygen and not soaked in oxygen - “fresh” TiO ₂ powders irradiated by electrons at the same fluence and energy values, shows a significantly greater degradation of “fresh” »Powders compared to the degradation of any of the processed samples. It follows from the table that the optimal time for ultraviolet treatment in oxygen of Р02 powder is 20 min, while the improvement of radiation resistance by the integral absorption coefficient is 2.2 times.

This method is highly effective, but has a significant drawback associated with the need to place the powders in a vacuum chamber, in which, after receiving the vacuum, an oxygen atmosphere should be created by inlet through a special device - leak and irradiate the powders with ultraviolet in it. Material and energy costs for the implementation of this method are the need for the acquisition and operation of a high vacuum system and a source of ultraviolet radiation.

Method number 3

The disadvantages indicated in the method No. 2 are partially eliminated in the method for increasing the photo- and radiation resistance of pigment powders during ultraviolet treatment in air [Mikhailov MM On the possibility of increasing the radiation resistance of TiO ₂ powders during UV irradiation in air // RAS. Surface. X-ray, synchrotron and neutron studies. 2007, No. 10, p. 68-72]. The experimental equipment in this method is greatly simplified, since a vacuum chamber is not required, only a source of ultraviolet radiation is needed to saturate the titanium dioxide powders with oxygen. But the processing efficiency is significantly reduced compared to method No. 2. Thus, it was experimentally established that treatment for 72 hours with an intensity 2 times the intensity of solar radiation gives an increase in radiation resistance of only 1.23 times under the action of electrons with the same parameters as in method No. 2 (E = 30 keV , Ф = 2⋅10 ¹⁶ cm ^-2 s ^-1 ). In addition to these three methods of increasing photo and radiation resistance by saturating the lattice of titanium dioxide powders with oxygen, methods have been developed based on creating layers of other compounds on the surface of grains and granules that act as relaxation centers for the primary products of photolysis and radiolysis and absorb part of the radiation energy falling on titanium dioxide - the role of protective layers.

Method number 4

The invention relates to the chemical industry and can be used in the manufacture of paints, i.e. the same coatings as in methods No. 1-No. 3. The pigment composite contains a base of titanium dioxide and layers of zirconium and aluminum oxides, the resulting suspension is heated to 46.11-50 ° C [RF Patent No. 2135536: TiO ₂ particles are dispersed in water, a dispersant (sodium hexametaphosphate) is added]. A solution of H ₂ SO _{4 is} added to maintain a pH of 7 to 9. A zirconium sulfate solution is introduced. Precipitated 0.1-2.5% zirconium hydroxide by weight of TiO ₂ in terms of ZrO ₂ . An aqueous solution of NaOH is added to maintain a pH of 7 to 9. An aqueous solution of sodium aluminate is introduced. Precipitated 3.5-4% aluminum hydroxide by weight of TiO ₂ in terms of Al ₂ O ₃ . The resulting product is filtered off, washed with water and dried at 110 ° C. Chopped. The pigment composite has improved optical properties such as scattering, gloss, brightness and color, as well as durability.

Method number 5

The invention relates to pigment rutile titanium dioxide, to a method for its production and can be used in the manufacture of paints, plastics and laminated plates on a paper basis. The invention consists in a pigment consisting of particles of titanium dioxide with cerium oxide deposited on them in an amount of 0.01-1 wt. % and dense amorphous silicon dioxide in an amount of 1-8 wt. % of the amount of titanium dioxide [RF Patent No. 2099372]. The pigment may be further coated with aluminum hydroxide in an amount of 2-4 wt. % of the amount of titanium dioxide. Then add water-soluble silicate in an amount of 1-6 wt. % and mineral acid for precipitation, at least at pH 8 of dense amorphous silica, while the sludge is continuously mixed and maintained at a temperature of 60-100 ° C throughout the entire deposition process. In addition to the sludge, an aqueous solution of sodium aluminate and sulfuric acid are added to precipitate aluminum hydroxide. The pigment according to the invention has improved strength, improved resistance to photochemical decomposition.

Method number 6

The invention relates to the chemical industry and can be used in the manufacture of dyes for paints, plates, ink and paper. The pigment composite contains a base of titanium dioxide and layers of zirconium and aluminum oxides [Patent No. 2135536 (US) on application 93004951/25 of 08.27.1999, Applicant: Kerr-McGee Chemical LLC (US) Authors: Kelly Ann Green (US); Thomas Ian Brownbridge (US)]. Particles of TiO _{2 are} dispersed in water, a dispersant (sodium hexametaphosphate) is added. The resulting suspension of titanium dioxide is heated to 46.11-50 ° C. A solution of H ₂ SO _{4 is} added to maintain a pH of 7 to 9. A solution of zirconium sulfate is introduced. Precipitated 0.1-2.5% zirconium hydroxide by weight of TiO ₂ in terms of ZrO ₂ . An aqueous solution of NaOH is added to maintain a pH of 7 to 9. An aqueous solution of sodium aluminate is introduced. Precipitated 3.5-4% aluminum hydroxide by weight of TiO ₂ in terms of Al ₂ Oz. The resulting product is filtered off, washed with water and dried at 110 ° C and ground. The pigment composite has improved optical properties such as scattering, gloss, brightness and color, as well as durability.

A common disadvantage of methods No. 4-No. 6 is the multi-stage chemical reactions and the large number of reagents necessary for their implementation, as well as the lack of data on the quality of the applied layers on the grain surface of titanium dioxide powders, which does not allow to determine the feasibility of applying subsequent layers after applying the previous ones. For example, in method No. 5 after applying a CeO ₂ layer, the photo and radiation resistance of the obtained composition was not determined and the need to apply another SiO ₂ layer was not proved, and in method No. 6 after applying a ZrO ₂ layer, the photo and radiation resistance of the obtained composition was not determined and the need for another layer of Al ₂ O ₃ was not proven.

Method number 7

Known modifier for zirconium dioxide - SrO [Rempel S.I., Driker B.N., Rutman D.S. and others. A method of obtaining stabilized zirconium dioxide. A. s. 522138 USSR // B.N. 1976, N 3, p. 66] to increase the resistance to light irradiation, the role of which is to capture and anihilate defects arising from irradiation. However, this modifier is not effective enough, as it creates additional light scattering at the boundaries. The magnitude of light scattering S according to the theory of Rayleigh is expressed by the formula [G. Landberg Optics. M .: Nauka, 1976, 926 p.]

where A is a coefficient depending on the wavelength, volume and number of scattering particles and the distance to the source;

ε _P , ε _M - dielectric constant of the pigment and modifier, respectively.

Method number 8

A method has also been developed to increase the radiation resistance of temperature-controlled coatings [RF Patent No. 2581278]. The method is based on their manufacture from powders without binders. The invention relates to temperature-controlled coatings and a method for their formation on the outer surfaces of spacecraft using the method of thermal spraying. The combined thermal control coating contains a sublayer of metallic material deposited on a substrate, a layer of ceramic material of the class “solar reflectors”, a non-continuous layer of material of the class “true reflectors”, applied by discrete drops on the surface of the layer of ceramic material. This method is selected as a prototype. It, as well as in the method proposed in the present invention, uses the method of spraying a metal material onto a substrate or onto the spacecraft’s body, followed by coating of the solar reflector class. The disadvantage of this method is its multi-stage and the presence of several layers of the applied material.

Example 1

To BaTiZrO ₃ powder, KO-859 polymer varnish is added in a mass ratio typical of thermally-controlled coatings of the class of “solar optical reflectors” equal to 0.75: 0.25. Add solvent in an amount of 1/4 of the volume of varnish and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, applied to a metal substrate and dried for 24 hours at room temperature. A thermally-regulating varnish-and-paint coating of the “solar optical reflectors” class is obtained on the basis of barium titanate pigment. The coating is placed in a vacuum chamber, the vacuum in the chamber is not worse than 10 ^-6 torr, the diffuse reflection spectra in the solar range are measured - from 0.25 to 2.5 microns in the initial state (ρ _λ0 ). Then, the coating is irradiated with electrons, and after each irradiation time, the spectrum of the irradiated sample (ρ _λt ) is _measured . From the obtained spectra ρ _{λo, the} integral absorption coefficient of solar radiation before irradiation (a _so ,) and after each irradiation time (a _st ) is calculated. The integral absorption coefficient of solar radiation was calculated from the diffuse reflection spectra, and its change after irradiation by the difference in the absorption coefficient before (a _s0 ) and after irradiation (a _sf ): Δa _s = a _s0 -a _sf [Kalistratova OV, Lyutak D.I., Kharlova E.V. et al. Combined thermoregulatory coating and method of its formation // http: // www. findpatent. com / patent / 258 / 2581278.html]. The absorption coefficient a _{s was} calculated by the formula:

where R _s is the arithmetic mean of the diffuse reflection coefficient calculated from 24 points at wavelengths corresponding to the equal-energy sections of the solar radiation spectrum; I _λ is the spectral intensity of solar radiation; (λ ₁ -λ ₂ ) is the spectral range of solar radiation; n is the number of points on the wavelength scale at which the diffuse reflection coefficient was calculated

After irradiation of powders or coatings, the change in the integral absorption coefficient with respect to the value before irradiation is calculated: Δa _s = a _st -a _s0 . The dependence of Δa _s values on the exposure time is obtained, which is a measure of the radiation resistance of a given coating.

Example 2

To the BaTiZrO ₃ powder, potassium liquid glass K ₂ SiO ₃ is added in the mass ratio typical of the thermo-regulating coatings of the class “solar optical reflectors” equal to 0.75: 0.25. Add solvent in an amount of 1/4 of the volume of liquid glass and distilled water.

The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, applied to a metal substrate and dried for 24 hours at room temperature. A ceramic thermal control coating of the class “solar optical reflectors” is obtained on the basis of a barium titanate pigment. The coating is placed in a vacuum chamber, the vacuum in the chamber is not worse than 10 ^-6 torr, the diffuse reflection spectra in the solar range are measured - from 0.25 to 2.5 microns in the initial state (ρ _λ0 ). Then, the coating is irradiated with electrons, and after each irradiation time, the spectrum of the irradiated sample (ρ _λt ) is _measured . From the obtained spectra ρ _{λo, the} integral absorption coefficient of solar radiation is calculated before irradiation (a _so ) and after each irradiation time (a _st ). The change in the integral absorption coefficient with respect to the value before irradiation is calculated: Δa _s = a _st -a _s0 . The dependence of Δa _s values on the exposure time is obtained, which is a measure of the radiation resistance of a coating of this type.

Example 3

The BaTiZrO ₃ powder is pressed into cups, and a thermoregulatory coating of the “solar optical reflectors” class is obtained on the basis of barium titanate pigment in the form of a ceramic tile. The coating is placed in a vacuum chamber, the vacuum in the chamber is not worse than 10 ^-6 torr, the diffuse reflection spectra in the solar range are measured - from 0.25 to 2.5 μm in the initial state (ρ _λ0 ) .Then the coating is irradiated with electrons and after each time irradiation measure the spectrum of the irradiated sample (ρ _λt ). From the obtained spectra ρ _{λo, the} integral absorption coefficient of solar radiation before irradiation (a _so ) and after each irradiation time (a _st ) is calculated. The change in the integral absorption coefficient with respect to the value before irradiation is calculated: Δa _s = a _st -a _s0 . The dependence of Δa _s values on the exposure time is obtained, which is a measure of the radiation resistance of a coating of this type.

Example 4

BaTiZrO ₃ powder is poured into the batcher of the detonation unit, a combustible mixture is ignited, and under the influence of a shock wave, this mixture is “driven” into a metal target, and a thermal control coating of the class “solar optical reflectors” based on barium titanate pigment is applied in the form of a deposited layer. The coating is placed in a vacuum chamber, the vacuum in the chamber is not worse than 10 ^-6 torr, the diffuse reflection spectra in the solar range are measured - from 0.25 to 2.5 microns in the initial state (ρ _λ0 ). Then, the coating is irradiated with electrons, and after each exposure time, the spectrum of the irradiated sample (ρ _λt ) is _measured . From the obtained spectra ρ _{λo, the} integral absorption coefficient of solar radiation before irradiation (a _so ) and after each irradiation time (a _st ) is calculated. The change in the integral absorption coefficient with respect to the value before irradiation is calculated: Δa _s = a _st -a _s0 . The dependence of Δa _s values on the exposure time is obtained, which is a measure of the radiation resistance of a coating of this type.

The results of calculations of changes in the absorption coefficient Δa _s from experimentally obtained diffuse reflection spectra before and after irradiation with accelerated electrons with an energy of 30 keV for 10, 20, 30, 40, 50 and 60 minutes with a flux of 1⋅10 ¹² cm ^-2 s ^-1 at temperature 25 ° C temperature-controlled coatings No. 1, No. 2, No. 3 and No. 4 are shown in the table.

It follows from the table that the values of Δa _s for the same irradiation time of different thermoregulatory coatings based on barium titanate powder differ significantly. Paint coating No. 1 has the lowest radiation resistance, followed by coating No. 2 with potassium liquid glass as a binder in order to increase radiation resistance. Ceramic tiles obtained by pressing barium titanate powder without the use of a binder have even greater radiation resistance. The highest radiation resistance for all values of the exposure time has a coating No. 4, applied by the detonation method. The Δa _s values of this coating are four times less than the values of all other coatings.

Thus, the proposed thermal control coating of barium titanate, applied by the detonation method, has the highest radiation resistance in comparison with all the studied coatings obtained by other methods.

Claims (1)

Thermoregulatory coating of the class “solar optical reflectors” prepared from BaTiZrO ₃ powder, characterized in that in order to increase radiation resistance, the powder is applied to the substrate by sputtering by the detonation method.