RU2160294C2 - Modifier for zirconium dioxide-based light-reflecting coatings - Google Patents

Abstract

FIELD: space-system engineering. SUBSTANCE: aircraft zirconium dioxide pigment is coated by 4 wt % of modifying monolayer composed of 23-75% crystalline silicone dioxide and 77-25% silicone dioxide hydrate. Integral absorption coefficient is changed by 0.042-0.073. EFFECT: increased UV emission resistance. 1 tbl, 2 ex

Description

 The invention relates to the modification of pigments and can be used to obtain reflective coatings used in aircraft of space technology.

где A - коэффициент, зависящий от длины волны, объема и числа рассеивающих частиц и расстояния до источника;
ε_П,ε_М - диэлектрическая проницаемость пигмента и модификатора, соответственно.Known modifier for zirconium dioxide - SrO [Rempel S.I., Driker B.N., Rutman D.S. and others. A method of obtaining stabilized zirconia. 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.: Science, 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.

и образование монослоя, который дает меньшее рассеяние света по сравнению со SrO.Known modifier for zirconium dioxide [Mikhailov M.M., Kuznetsov N.Ya. , Stas N.F. et al., Izv. USSR Academy of Sciences. Inorganic Materials, 1990, v. 26, No. 9, p. 1889-1892], which is selected as a prototype. It is silicon dioxide, which is applied to the surface of ZrO ₂ granules by molecular layering by reaction
SiCl ₄ + (n + 2) H ₂ O ---> SiO ₂ • nH ₂ O + 4HCl (2)
Subsequently, heating to 670 ^o C in air takes place to remove water

and the formation of a monolayer, which gives less light scattering compared to SrO.

 But when building up several layers, the method does not give the expected effect. The reason for this is a violation of the continuity of the film during dehydration during heating and a violation of optical contact due to peeling of part of it on the surface of the pigment grains.

A characteristic of the pigment's resistance to radiation is the integral absorption coefficient of solar radiation a _s calculated by the formula
a _s = 1-R, (4)
where R is the integral coefficient of diffuse reflection.

The objective of the invention is to increase the resistance to radiation by reducing changes in the integral absorption coefficient (Δa _S ) when exposed to radiation on a reflective coating containing the pigment ZrO ₂ and the modifier SiO ₂ .

This task is achieved in that the modifier for reflective coatings based on ZrO ₂ , including a silicon compound to create a modified monolayer, according to the invention consists of crystalline silicon dioxide SiO ₂ cr and crystalline hydrate SiO ₂ nH ₂ O in the following ratio, wt.%:
SiO ₂ cr - 23 - 75
SiO ₂ nH ₂ O - 77 - 25
providing the creation of a granular monolayer around the grains of the pigment ZrO ₂ .

а масса зерна пигмента равна

где ρ - плотность модификатора, см³;
Δr прирост размера зерна, см.Suppose that a ZrO ₂ grain has a cubic shape with a volume of r ³ , then the surface on which the contact between the ZrO ₂ grain and SiO ₂ grains occurs is 6 g ² , and if there is a tightly packed SiO ₂ monolayer, then its volume is 6 g ² Δr.
The amount of modifier introduced on the mass, sufficient to fill this layer is

and the mass of the pigment is

where ρ is the density of the modifier, cm ³ ;
Δr increase in grain size, see

The average pigment particle size r _n, experimentally measured by the secant method, is 104 μm. The thickness of the coating layer should be 1-2 microns, which corresponds to the range of secondary electrons.

где ρSiO₂ = 2,65г/см³,ρZrO₂ = 5,73г/см³.
Для толщины слоя 1 мкм величина α будет в 2 раза меньше, но из-за неплотности упаковки его надо несколько больше, поэтому в эксперименте брали α = 4%.In this case, the mass ratio of the modifier and the pigment (α), according to (5, 6), is

where ρSiO ₂ = 2.65 g / cm ³ , ρZrO ₂ = 5.73 g / cm ³ .
For a layer thickness of 1 μm, the value of α will be 2 times less, but due to the leaking packaging it needs to be slightly larger, therefore, in the experiment, α = 4% was taken.

 Comparative results confirming the resistance to UV radiation of the pigment with various modifiers are presented in table 1.

The values of Δa _{S were} determined after exposure to sunlight in a Specter-1 simulator [Kositsyn LG, Mikhailov MM, Kuznetsov N.Ya., Dvoretsky MI // PTE, 1985, N 4, p. 176-180]. The radiation dose corresponded to 170 em.s. (1 e.s. p. - equivalent to a sunny day equal to 0.14 W / cm ² ). Data from the work [Mikhailov MM, Kuznetsov N.Ya., Stas N.Ya. et al., Izv. USSR Academy of Sciences. Inorganic materials, 1990, v. 26, No. 9, p. 1889-1892] obtained by extrapolating the dependence of Δa _S on the exposure time.

The maximum concentration value corresponding to SiO ₂ cr = 100% is determined by the need to create a layer of a modifier that provides a sufficient number of contacts and minimal light scattering with the ZrO ₂ pigment (ε _P = 4.75), according to formula (1).

The dielectric constant of silicon dioxide is 3.5 - 4.1 [Physico-chemical properties of oxides. Handbook Ed. G.V. Samsonova. - M.: Metallurgy, 1978, 471 p.]. Obviously, in the presence of a water molecule in the SiO ₂ • nH ₂ O crystalline hydrate, it leads to a larger value of ε _M and less light scattering so that the difference (ε _П -ε _M ) decreases. However, in the process of thermal exposure, crystallites with a developed surface are formed and the number of optical contacts of the SiO ₂ and ZrO ₂ grains decreases. Therefore, there should be an optimal ratio between the formation on the surface of intermediate compounds that are resistant to UV radiation and the property of light scattering at the contact points. This ratio determines the minimum value of pigment degradation (Δa _S values in table 1). Thus, the technical result of the invention is a complex modifier composition that increases the resistance of the pigment based on ZrO ₂ to the action of UV radiation compared to the prototype 2 times.

Example 1. A mixture of powders of zirconia 96% and anhydrous silica 4% is mixed in a roller mill with uralite balls, placed in a muffle furnace, heated at a speed of 200 deg / h to a temperature of 900 ^o C, kept for 1 hour, then cooled to 20 ^o C for 8-10 hours. The result (experiment N 4 table. 1).

Example 2. A mixture of powders of zirconia 96% with a total oxide content of 4%, including anhydrous silica 0.9% (23%) and crystalline silica crystalline hydrate 3.1% (77%), is mixed in a roller mill with uralite balls for 3 hours, heated at a speed of 200 deg / h to a temperature of 900 ^o C, incubated for 1 hour, then cooled to 20 ^o C for 8-10 hours. The result (experiment No. 1, table. 1).

Claims (1)

A modifier for reflective coatings based on ZrO ₂ , comprising a silicon compound to create a modifying monolayer, characterized in that the modifier consists of crystalline silicon dioxide (SiO ₂ cr) and crystalline hydrate (SiO ₂ • nH ₂ O) in the following ratio, wt.% :
SiO ₂ cr - 23 - 75
SiO ₂ • nH ₂ O - 77 - 25
providing the creation of a granular monolayer around the grains of the pigment ZrO ₂ .

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