RU2555484C2 - Titanium dioxide based pigment modified with nanoparticles - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to pigments for white paints and coatings, including temperature-control coatings of spacecraft, and can be used in space engineering, in the construction industry and in various industries for temperature control of devices or processing facilities. The pigment for light-reflecting coatings is obtained by heating at 800°C and with a high vaporised and ground mixture of titanium dioxide microparticles with 7 wt % silicon dioxide nanoparticles.

EFFECT: invention enables to obtain a pigment with high radiation resistance using a simple technique which is efficient compared to similar pigments obtained using prior art.

1 tbl, 8 ex

Description

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.

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. But under the influence of outer space radiation, titanium dioxide 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 spacecraft in this case rises, the thermal modes of operation of devices and devices are violated and the time of their active existence is reduced. Various methods have been developed to increase the stability of titanium dioxide to the action of outer space radiation.

The pigment powders of titanium dioxide, like zirconia and alumina, 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 titanium dioxide powders with a rutile lattice [1] and anatase [2] after irradiation with 30 keV electrons showed that the changes in the spectra occur mainly in the near infrared region in which defects the absorption band located anion sublattice band F ^{- -} and F ⁺ centers. Similar qualitative changes in the ρ _λ spectra were also obtained after irradiation of TiO ₂ (rutile) powders with ultraviolet light from the solar spectrum [3] and hydrogen ions with an energy of 3 keV [4]. These studies have established 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 titanium dioxide powders are qualitatively identical. When irradiated, electron-hole pairs are formed. Holes move to a negatively charged surface, neutralize the lattice oxygen, which 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 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. Positive results were obtained earlier - an increase in 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 rutile powders [5].

A promising way is to increase the stability of the optical properties of titanium dioxide 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 TiO ₂ pigments with light quanta and charged particles. To date, the following methods are known to increase the photo and radiation resistance by saturating the surface and volume of titanium dioxide grains with oxygen

Method number 1

The work [6] 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.

Samples for studies were prepared by lightly pressing powders into metal cups with a diameter of 24 mm and a depth of 2 mm, fixed on the stage of the installation - a simulator of the space environment "Spectrum" [7] and measured the diffuse reflectance spectra (ρ _λ0 ) in vacuum no worse than 10 ^-4 Pa using the integrating sphere integrated in the vacuum chamber.

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. Studies were performed on five samples heated in various modes of TiO ₂ powders _, qualification P02. Sample No. 1 was not heated, samples No. 2-5 were heated in various modes: the temperature was varied within 110-150 ° C, the heating time was 17-120 min, 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 · 10 ¹⁶ cm ^-2 with an energy of 30 keV and the change in the integral absorption coefficient Δa _{s was} calculated.

The performed studies have shown 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 temperature and on the time of heating and in order 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 mmHg, average heating temperature of about 100 ° C, heating time of 120 min 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 of the powders in its atmosphere. Moreover, the effectiveness of the method is not very high.

Method number 2

Another similar way to increase the photo- and radiation resistance of the TiO ₂ pigment is its treatment with ultraviolet in oxygen [8].

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.

Comparison of the spectral degradation after irradiation with electrons of qualification Р02, pretreated with ultraviolet in oxygen, with degradation not treated with oxygen and not withstand oxygen - “fresh” TiO ₂ powders irradiated with 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 light 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 TiO ₂ powders during ultraviolet treatment in air [9]. 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. So, it was experimentally established that processing for 72 hours with an intensity 2 times higher than the intensity of solar radiation gives an increase in radiation resistance of only 1.23 times when exposed to 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 for 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 of primary photolysis and radiolysis products 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. 1-3. The pigment composite contains a base of titanium dioxide and layers of zirconium and aluminum oxides [10]. Particles of TiO _{2 are} dispersed in water, a dispersant (sodium hexametaphosphate) is added, the resulting suspension 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 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 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 [10]. 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 O ₃ . The resulting product is filtered off, washed with water and dried at 110 ° C. and chopped. The pigment composite has improved optical properties such as scattering, gloss, brightness and color, as well as durability.

Method number 6

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 [11]. The pigment may be further coated with aluminum hydroxide in an amount of 2-4 wt.% Of the amount of titanium dioxide. Next, water-soluble silicate is added in an amount of 1-6 wt.% And mineral acid to precipitate 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.

A common disadvantage of methods No. 4-6 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. 6, after applying the 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. 5 after applying the ZrO ₂ layer, the photo and radiation resistance of the obtained composition was not determined and the need for another Al ₂ O ₃ layer was not proven.

Method No. 6 is selected as a prototype, since in it to increase resistance to ionizing radiation; as in the proposed method, on the surface of grains and granules of TiO ₂ apply layers of silicon dioxide in an amount of 1-8 wt.% of the amount of titanium dioxide. The application is carried out by adding water-soluble silicate in an amount of 1-6 wt.% And mineral acid.

To achieve the goal, titanium dioxide micropowder Solikamskiy qualification with an average grain size of 0.2 μm was mixed in various proportions with a silicon dioxide nanopowder with an average grain size of 10–20 nm obtained by the action of an electron beam of nanosecond duration on silicon tetrachloride [12]. The mixture was dispersed in distilled water using a PE-6100 magnetic stirrer, which meets the requirements of TU 4321-009-23050963-98. The resulting solution was evaporated in an oven at 150 ° C for 6 hours, ground in an agate mortar and heated in a chamber electric furnace SNOL-1,4.2,5.1,2 / 12,5-I1 at a temperature of 800 ° C for 2 hours. After heating, the resulting mixture was crushed.

Polyvinyl alcohol was added to the modified pigment until a paste-like state was obtained, the paste was applied to metal substrates and dried in the atmosphere for 24 hours at room temperature. The diffuse reflection spectra of the prepared samples were studied, then the samples were irradiated with electrons (E = 30 keV, Ф = 1 · 10 ¹⁶ cm ^-2 , T = 300 K, P = 10 ^-4 Pa) and the diffuse reflection spectra of the irradiated samples were recorded in a setup simulator outer space "Spectrum" [7]. 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 [13]. The integral absorption coefficient of solar radiation was calculated by the formula:

where R _s is the integral coefficient of diffuse reflection of solar radiation, calculated as the arithmetic mean of the coefficient of diffuse reflection at 24 points located on equal-energy sections of the solar radiation spectrum. The mathematical expression for calculating the integral absorption coefficient of solar radiation has the form:

where ρ _λ is the spectral reflectivity, I _λ is the solar radiation spectrum, λ ₁ ÷ λ ₂ is the range of the solar spectrum (in the region of 0.2 ÷ 2.5 μm, the sun radiates 98% of all energy), n is the number of equal-energy sections of the solar spectrum .

The wavelengths correspond to the equi-energy portions of the Sun, at which the values of the diffuse reflection coefficient were chosen to calculate the integral reflection coefficient of solar radiation.

Example 1

The titanium dioxide micropowder 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 obtained powder is crushed, polyvinyl alcohol is added to obtain a pasty state that does not distort the measurement results, but increases the adhesion of the powder to the substrate, and is applied to metal substrates to study radiation resistance.

Example 2

A mixture of zirconia micropowder and alumina nanopowder containing 0.25 wt.% SiO ₂ nanopowder and 99.75 wt.% TiO _{2 was} stirred in a magnetic stirrer with distilled water, the resulting solution was evaporated in an oven at 150 ° C for 6 hours, rubbed 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

Example 3

A mixture of zirconia micropowder and alumina nanopowder containing 0.5 wt.% SiO ₂ nanopowder and 99.5 wt.% TiO _{2 is} stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, rubbed 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

Example 4

A mixture of zirconia micropowder and alumina nanopowder containing 1 wt.% SiO ₂ nanopowder and 99 wt.% TiO _{2 is} stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, grind 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.

Example 5

A mixture of zirconia micropowder and alumina nanopowder containing 3 wt.% SiO ₂ nanopowder and 97 wt.% TiO ₂ is stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, grind 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.

Example 6

A mixture of zirconia micropowder and alumina nanopowder containing 5 wt.% SiO ₂ nanopowder and 95 wt.% TiO ₂ is stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, grind 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.

Example 7

A mixture of zirconia micropowder and alumina nanopowder containing 7 wt.% SiO ₂ nanopowder and 93 wt.% TiO ₂ is stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, grind in an agate mortar and heated at a temperature of 800 ° C for 2 hours, crushed, add polyvinyl alcohol, applied to metal substrates to study radiation resistance.

Example 8

A mixture of zirconia micropowder and alumina nanopowder containing 10 wt.% SiO ₂ nanopowder and 90 wt.% TiO ₂ is stirred in a magnetic stirrer with distilled water, the resulting solution is evaporated in an oven at 150 ° C for 6 hours, grind 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 Δa _s from 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 Yes, unmodified and modified powders are given in the table.

Table. Dependence of changes in the integral absorption coefficient Δa _s upon electron irradiation of modified TiO ₂ powders _on the concentration of SiO ₂ nanoparticles C, wt.% 0 0.25 0.5 one 3 5 7 10 Δa _s 0.067 0.069 0.071 0.07 0.063 0.061 0.042 0.058

The Δa _s values of the modified powders at a concentration of silicon dioxide of 0.25-1 wt.% Are not significantly greater, and at a concentration of 3-10 wt.% More compared to unmodified micropowder of titanium dioxide. The greatest increase in radiation resistance, determined by the ratio:

37% compared to unmodified powder. Here Δa _s0 -Δa _{s of} unmodified powder, Δa _s7 -Δa _s at C = 7 wt.%.

The resulting increase in radiation resistance is determined by the fact that with an increase in the concentration of nanoparticles from 3 to 7 wt.%, The number of relaxation centers on the surface of grains and granules of titanium dioxide powder increases. And such a quantity of silicon dioxide nanoparticles (7 wt.%) On the surface is sufficient for the formation of the required density of these centers. With a further increase in the concentration of nanoparticles from 7 to 10 wt.%, A significant contribution to the creation of radiation defects is made by the diffusion of silicon cations into the titanium dioxide lattice and the creation of substitution defects due to the larger radius of Ti ³⁺ ions (r = 0.6 Å) compared to Si ³⁺ ions (r = 0.39 Å). When irradiated, these defects turn into absorption centers and increase the changes in the integral absorption coefficient Δa _s .

Thus, the proposed 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.

List of sources used

1. Mikhailov M.M., Butler M.I. Kinetics of the accumulation of color centers in rutile under electron irradiation // Izv. universities. Physics, 1983. - No. 3. - S.30-34.

2. Mikhailov M.M., Gordienko P.S., Senko I.V. et al. Effect of production technology on induced absorption spectra of TiO ₂ powders (anatase) // Izv. universities. Physics, 2002, No. 11, pp. 92-94.

3. Mikhailov M.M., Gordienko P.S., Senko I.V. and others. The reflectivity of titanium dioxide pigments with the structure of anatase and rutile and its change under the influence of electron irradiation and radiation that mimics the solar // Prospective materials, 2002, No. 2, pp. 40-44.

4. Mikhailov M.M., Butler M.I. Changes in the optical properties of TiO ₂ (rutile) upon irradiation with H ₂ ⁺ ions // Materials of the All-Union Conference "Interaction of Atomic Particles with a Solid" Minsk, 1981, pp. 118-120.

5. Mikhailov M.M., Vlasov V.A. 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 the specific surface and grain sizes of titanium dioxide powders / Journal of Applied Spectroscopy, 2006, vol. 73, No. 1, pp. 73-77.

6. 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.

7. Kositsyn L.G., Mikhailov M.M., Dvoretsky M.I. et al. Installation for studying the spectra of diffuse reflection and cathodoluminescence of solids in vacuum. Instruments and experimental technique. 1985, No. 4, p. 175-180.

8. Mikhailov M.M. 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.

9. Mikhailov M.M. 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.

10. K.E. Green, T.Ya. Brownbridge A method of obtaining a pigment composite, a pigment composite. RF patent №2135536. IPC 6 C09C 1/36, application. 04/09/1993, publ. 08/27/1999.

11. J.R. Brand, R.A. Baldwin, T.Ya. Brownbridge Pigmented titanium dioxide and method for its preparation. RF patent No. 2099372. // IPC 6 C09C 1/36, application. 11/23/1994, publ. 12/20/1997.

12. Ponomarev D.V., Pushkarev A.I., Remnev G.E. The method of obtaining nanosized powders of oxides. RF patent No. 2264888 // IPC 7 B22F 9/12; СВВ 33/18; B03C 3/00, application 12.24.2003, publ. 07.20.2005.

13. Mikhailov M.M. Prediction of optical degradation of temperature-controlled coatings of spacecraft. Novosibirsk: “Science”, 1998, 192 p.

Claims (1)

Reflective pigment for coatings with improved resistance to the action of radiation, comprising a mixture of titanium dioxide particles with micron sized silica nanoparticles obtained by heating ^at 800 ° C and rubbed vaporized mixture of particles of titanium dioxide having micron size of 7 wt.% Silica nanoparticles.