RU2677173C1 - MODIFIED BY THE SiO2 NANOPARTICLES BaSO4 POWDER BASED PIGMENT - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention can be used in the space technology, in the construction industry, as well as in the chemical, food, light industries for the devices or technological objects temperature control. Pigment for the “solar optical reflectors” class thermal control coatings is prepared from barium sulfate powder, which is modified by the silicon nanoparticles in an amount of 3 wt.%.EFFECT: invention allows to increase the pigment radiation resistance.1 cl, 1 tbl, 6 ex

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 sulfate powders are pigments that are promising for the preparation of temperature-controlled coatings, since they have a large band gap, which ensures a small value of the integral absorption coefficient of solar radiation ( a _s ). In combination with a large integrated hemispherical emissivity in the infrared region of the spectrum (ε), they provide a small value of the ratio a _s / ε, which allows us to attribute them to promising pigments for TRPs of the class “optical solar reflectors”. In addition, the powders of this compound have a relatively high radiation resistance, which allows them to be used as TRP pigments operating under the action of charged particles of outer space (KP).

But under the influence of outer space radiation, barium sulfate 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. In this case, the temperature of spacecraft will increase, the thermal modes of operation of devices and devices will be violated, and their active existence will be reduced. To increase the resistance of barium sulfate powders to the effects of outer space radiation, various methods developed for oxide pigments can be applied.

Barium sulfate powders, as well as powders of zinc and aluminum oxides, titanium and zirconia, are not stoichiometric in oxygen, and color centers on biographical anion vacancies are formed in them under the influence of radiation. 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 pigment powders after irradiation with 30 keV electrons showed that changes in the spectra occur mainly in those spectral regions which are located the absorption bands of defects of the anionic sublattice of the band of F ^- and F ⁺ centers.

These studies have shown that the formation of photo- or radiation defects occurs by the ionization mechanism. The primary processes of interaction of various types of radiation with powders - pigments TRP ZnO, TiO ₂ , ZrO ₂ , Al ₂ O ₃ , etc. 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 [V. Neshchimenko Study of the structure, properties and radiation resistance of oxide powders modified by nanoparticles // Abstract of the dissertation of the doctor a fiz.-floor-mat. Science, Tomsk, TUSUR, 2017, 34 pp.].

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 30 keV electrons due to changes in the particle size distribution and specific surface of another rutile pigment 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. 73-77].

Method number 1

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.

The disadvantage of this composition is that the pigment has a large number of components and a large number of technological operations for applying layers of various metal oxides on the surface of titanium dioxide particles - the main component of the pigment, of other sizes.

Method number 2

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.

The disadvantage of this composition is that on the surface of the main component of the pigment - titanium dioxide, layers of cerium dioxide, silicon dioxide and aluminum hydroxide are applied. A large number of applied components requires a large number of technological operations and, accordingly, increases the time of their execution and the cost of the resulting product.

Method number 3

The composition [Reflective Coating Composition. Application: 2008150546/15, 12.19.2008. Effective date for property rights: 12.19.2008. Inventor (s): Zhabrev VA, Kuznetsova LA, Efimenko LP et. al. Proprietor (s): Uchrezhdenie Rossijskoj akademii nauk Institut khimiisilikatov imeni IV Grebenshchikova (IKhS RAN)] to obtain a light-resistant reflective coating, comprising as a filler a mechanical mixture of metal oxides ZrO ₂ (30-55 wt.%) And MgO (25-35- .%) with a particle size of 80-120 nm, liquid glass (20-25 wt.%) as a binder.

The disadvantage of this composition is that the pigment is completely 100% composed of nanoparticles, the cost of which is many times higher than the cost of the same compounds with micron particles. Nanopowders are not used effectively from the point of view of increasing light resistance, since for this purpose a few percent of the nanoparticles of the mass of the pigment that they envelop is sufficient, creating layers that act as relaxation centers for the primary defects formed by irradiation.

Method number 4

A known method of producing pigment based on micro- and nanopowders of aluminum oxide [Pigment based on micro- and nanopowders of aluminum oxide // RF Patent No. 2533723 from 09/20/2014]. The invention relates to compositions of pigments for white paints and coatings, including for temperature-controlled coatings used in the field of passive methods of thermal control 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.

Alumina refers to pigments that are especially promising for the preparation of thermoregulatory coatings, since it has a large band gap (Eg> 6 eV), therefore it does not absorb a significant part of ultraviolet radiation and has a low absorption coefficient of solar radiation a _s and a large emissivity in infrared spectral region ε.

The pigment is obtained by mixing a mixture containing 4.0 wt. % nanopowder Al ₂ O ₃ and 96.0 wt. % alumina micropowder in a magnetic stirrer with distilled water added, evaporating the resulting solution in an oven at 150 ° C for 6 hours, grinding in an agate mortar and heating at 800 ° C for 2 hours, and grinding again in an agate mortar.

Method number 5

A method has been developed to increase the radiation resistance of zirconia powders modified with their own ZrO ₂ nanoparticles [Pigment based on micro- and nanopowders of zirconium dioxide // RF Patent No. 2532434 from 09/08/2014]. The method consists in preparing a mixture of zirconia micropowder and zirconia nanopowder containing 5-7 wt. % ZrO2 nanopowder and 93-95 mass. % ZrO ₂ micropowder, which is stirred in a magnetic stirrer with the addition of distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, ground in an agate mortar and heated at a temperature of 800 ° C for 2 hours. After warming up, the resulting mixture is again triturated in an agate mortar, polyvinyl alcohol is added, and applied to metal substrates to study radiation resistance.

The calculation results of the integrated absorption coefficient from the experimentally obtained diffuse reflection spectra before irradiation with accelerated electrons of unmodified and modified powders show that the concentration of nanoparticles is 5-7 mass. % is optimal. The integrated absorption coefficient of the samples decreases with increasing concentration of ZrO ₂ nanoparticles from zero to 5-7 wt. % decreases, and in the concentration range of 10-20 wt. % increases.

After irradiation, Δ a s of modified powders is significantly less compared to unmodified zirconia micropowder. The greatest increase in radiation resistance occurs when the concentration of nanopowder 5-7 wt. %, the maximum increase determined by the powder.

The obtained decrease in the absorption coefficient before irradiation at C = (1 ÷ 5 wt.%) Is determined by the fact that the addition of nanoparticles to micropowder leads to an increase in the diffuse reflection coefficient of the mixture due to an increase in the scattering coefficient on smaller nanoparticles compared to microparticles. With a further increase in the concentration, nanoparticles do not settle on the surface of grains and granules due to its filling; therefore, aluminum cations diffuse into the zirconia lattice and create absorption centers, which leads to an increase in the integral absorption coefficient a _so .

The resulting increase in radiation resistance is determined by the fact that with an increase in the concentration of nanoparticles from 1 to 5-7 wt. % increases the number of relaxation centers on the surface of grains and granules of zirconia powder. And such a number of nanoparticles (5-7 wt.%) On the surface is enough to form the necessary density of these centers. A further increase in the concentration of nanoparticles from 7 to 20 wt. % leads to the diffusion of zirconium cations into the zirconium dioxide lattice, to the creation of interstitial atoms, which, when irradiated, turn into absorption centers and increase the values of the integral absorption coefficient a _s and its changes Δ a _s .

Method number 6

A method for producing a titanium dioxide pigment modified by nanoparticles is described [Pigment based on titanium dioxide powder modified by nanoparticles // RF Patent No. 2555484 of 08/07/2015]. The invention relates to compositions of pigments for white paints and coatings, including for temperature-controlled coatings used in the field of passive methods of thermal control of objects, namely, temperature-controlled coatings of spacecraft. The invention can be used in space technology, in the construction industry and in other industries.

Titanium dioxide refers to pigments that are especially promising for the preparation of temperature-controlled coatings, since it has a low absorption coefficient of solar radiation a _s and a large emissivity in the infrared spectrum ε.

The technology for producing the pigment is to prepare a mixture of micropowder of titanium dioxide and nanopowder SiO ₂ at a concentration of 7 wt. %, which is stirred in a magnetic stirrer with the addition of distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, fray in an agate mortar and heated at a temperature of 800 ° C for 2 hours. After heating, the resulting mixture is crushed, polyvinyl alcohol is added, applied to metal substrates to study radiation resistance.

The results of calculations of changes in the absorption coefficient Δas from the experimentally obtained diffuse reflection spectra before and after irradiation with an electron fluence of 2⋅10 ¹⁶ cm ^-2 with an energy of 30 keV. The increase in radiation resistance, determined by the change in the integral absorption coefficient of unmodified and modified pigments, is 37%.

In the present invention, in order to increase radiation resistance, the pigment BaSO ₄ was modified with SiO ₂ nanoparticles _of various concentrations and the optimal concentration was selected according to the change in the integral absorption coefficient of solar radiation after irradiation with 30 keV electrons.

This method of increasing the resistance to radiation of titanium dioxide powders is notable for its simplicity, does not require complex and expensive equipment, low material costs in execution, and high efficiency. It is selected as a prototype.

Example 1

Distilled water is added to the BaSO ₄ powder, stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, rubbed in a porcelain cup, pressed into a metal substrate by low pressure pressure, Р = 1 MPa.

Example 2

SiO ₂ nanoparticles are added to BaSO ₄ powder in an amount of 1 mass. % and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, ground in a porcelain cup, pressed into a metal substrate by hand pressing at low pressure, P = 1 MPa.

Example 3

To the powder BaSO ₄ add nanoparticles of SiO ₂ in the amount of 3 mass. % and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, ground in a porcelain cup, pressed into a metal substrate by hand pressing at low pressure, P = 1 MPa.

Example 4

To the powder BaSO ₄ add nanoparticles of SiO ₂ in the amount of 5 mass. % and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, ground in a porcelain cup, pressed into a metal substrate by hand pressing at low pressure, P = 1 MPa.

Example 5

To the powder BaSO ₄ add nanoparticles of SiO ₂ in the amount of 7 mass. % and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, ground in a porcelain cup, pressed into a metal substrate by hand pressing at low pressure, P = 1 MPa.

Example 6

SiO ₂ nanoparticles in an amount of 10 masses are added to BaSO ₄ powder. % and distilled water. The prepared mixture is stirred in a magnetic stirrer for 10-12 hours, evaporated in an oven at a temperature of 150 ° C, cooled to room temperature, ground in a porcelain cup, pressed into a metal substrate by hand pressing at low pressure, P = 1 MPa.

Obtained in examples 1-6, the samples are mounted on the stage of the Spectrum KP conditions simulator, a vacuum of P≤10 ^-6 torr is obtained in the installation, diffuse reflectance spectra are measured in the solar range from 0.25 to 2.5 μm in the original state (ρ _λ0 ). Then, all samples are sequentially irradiated with 30 keV electrons with a fluence of 1 × 10 ¹⁶ cm ^-2 and after irradiation, the spectra of the irradiated samples (ρ _λt ) are measured in vacuum at the irradiation site (in situ). From the obtained spectra ρ _λo calculate the integral absorption coefficient of solar radiation before irradiation (a _so ) and after irradiation (a _st ) of each powder. The absorption coefficient a _{s is} calculated by the formula (1):

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.

The change in the absorption coefficient a _s after irradiation is determined by the difference in its values before (a _s0 ) and after (a _sf ) irradiation: Δa _s = a _s0 -a _sf . The dependence of Δa _s on irradiation time is obtained, which is a measure of the radiation resistance of the powders.

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 with a fluence of 1⋅10 ¹⁶ cm ^-2 at a temperature of 25 ° C of powders No. 1-No. 6 are shown in the table.

From the table it follows that the Δa _s values of various BaSO ₄ pigment powders at the same electron fluence values are significantly different. The least radiation resistance is possessed by unmodified powder No. 1 and powder No. 6 with a nanoparticle concentration of 10 mass. % The highest radiation resistance has a powder modified with SiO ₂ nanoparticles with a concentration of 3 masses. %

Thus, the BaSO ₄ powder, modified as SiO ₂ nanoparticles at a concentration of 3 masses, is proposed as a pigment for temperature-controlled coatings. %, has a greater radiation resistance compared to unmodified powder.

Claims (1)

Pigment for thermoregulating coatings of the class “solar optical reflectors”, prepared from barium sulfate powder, characterized in that in order to increase the radiation resistance, the powder is modified with silicon dioxide nanoparticles in an amount of three weight percent.