RU2642596C2 - Method of metallic coating application to microspheres - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method of metallic coating application to microspheres by pyrolytic decomposition of organo-metallic compounds involves the interaction of organo-metallic compound vapours with the microsphere surface, heated up to a temperature below the softening temperature, stirring the microspheres. The microsphere stirring is performed in the presence of organo-metallic compound vapours. The quantity of the organo-metallic compound as related to the quantity of the microspheres is determined by the dependence on the required coating thickness

where m_MS is the charging weight of microspheres, g; m_OMS is the weight of the organo-metallic compound, g; ρ_d is the coating density, g/cm³;

is the specific surface of the microspheres, cm²/g; k₁ is the factor of conversion of the parent compound into the coating material, k₂ is the material utilisation rate and determined by the chamber volume and the ratio of the microsphere area to the chamber (varies from 0.30 to 0.95).

EFFECT: improvement of the method.

5 cl, 3 tbl, 7 ex, 5 dwg

Description

The present invention relates to chemical technology for applying metal, oxide and carbide coatings to microspheres to increase chemical resistance and sheath strength and reduce gas permeability and can be used in the production of composite materials, as well as for the storage and storage of helium and hydrogen.

A known method of surface treatment of glass microspheres with organosilicon compounds described in the patent of the Russian Federation No. 20159530, IPC С03С 17/00, publ. 09/15/1994. As organosilicon compounds, hydride-containing cyclic, cyclolinear or low molecular weight linear oligomers, including the corresponding disiloxane, are used, and the process is carried out with the microspheres vibro-boiling, the softening temperature of which is higher than the boiling point of the organosilicon compound.

The disadvantages of this method is that as a result of processing the microspheres by this method, the gas permeability and strength of the microspheres remain at the level of the original shells.

A known method of hardening glass hollow microspheres, described in the article "Strength of glass microspheres with ultrathin element oxide coatings," Journal of Applied Chemistry, No. 11, 1986, pp. 2472-2475. The coating is applied as a result of sequential alternation of irreversible chemisorption of precursors with the surface of the microspheres.

The disadvantage of this method is to maintain the gas permeability of the microspheres at the initial level.

A known method of hardening glass microspheres, protected by A.S. USSR No. 1203047, IPC S03C 17/245, publ. 07/01/1986. The method consists in treating glass microspheres with vapors of metal chlorides or oxychlorides of groups III-VI of the periodic system at elevated temperatures, additionally treating the chlorine-substituted agent in pairs, which is carried out repeatedly and alternately, and then removing unreacted products.

The disadvantages of this method is that the decomposition of metal chlorides and oxychlorides occurs at temperatures of ~ 400 ° C, at which a reaction between the pairs of chlorides and the shell of the microspheres with the destruction of the latter is possible. In the presence of microdefects on the surface of microspheres, the rate of destruction of microspheres can only increase due to reactions at the boundary of microdefects. In addition, the treatment with vapors of metal chlorides and oxychlorides produces highly toxic and aggressive decomposition products, as well as highly toxic reaction products between the oxide shell of microspheres and metal chloride vapors, for example, in the form of phosgene vapors (COCl ₂ ), which can lead to equipment corrosion and pollution the environment.

Closest to the claimed method according to the technical nature and the achieved result, selected as a prototype, is a method of metallization of powders, including and microspheres, from the gas phase (patent RU 2307004, IPC B22F 1/00, publ. 09/27/2007). The method includes filling the coated powder into one of the reactor chambers, heating the powder to the decomposition temperature of the volatile organometallic metal compound (MOC) of the metal, rotating the reactor 180 ° about the axis of rotation, pouring the powder from one reactor chamber to another through the reaction zone, in which, in the direction perpendicular to the movement of the microspheres, served MOS. The process of pouring powder from one chamber to another is carried out with forced dispersion of the powder in the reaction zone. The flow of MOS moves continuously, the powder is poured periodically.

The disadvantage of this method is that the metallization of the powder, which occurs during its interaction with the MOS, is determined by the conditions of passage of the batch of powder through the reaction zone. In this case, the contact time and the interaction conditions of individual powder particles with metal compounds differ significantly. For one metallization cycle, layers of various thicknesses are formed on the powder particles both in the diameter of an individual particle and in different particles in a batch.

The objective of the invention is to ensure uniformity of the metal-containing coating both on the surface of single microspheres and throughout the batch of microspheres in one coating cycle, while ensuring high reproducibility of the coating process from cycle to cycle.

The technical result from the use of the invention is to increase the strength properties and reduce the gas permeability of the microspheres.

, где m_MC - масса загрузки микросфер, г; m_MOC - масса металлоорганического соединения, г; ρ_П - плотность покрытия, г/см³;

- удельная поверхность микросфер, см²/г; k₁ - коэффициент перехода исходного соединения в материал покрытия (при использовании ХОЖ «Бархос» для получения покрытия из Cr k₁=0,16, для получения покрытия из Cr₃C₂ k₁=0,18), k₂ - коэффициент использования материала - определяется объемом камеры и соотношением площадей микросфер и камеры (варьируется от 0,30 до 0,95).To solve this problem and achieve a technical result, a method for applying metal-containing coatings to microspheres by pyrolytic decomposition of organometallic compounds is claimed, consisting in the interaction of organometallic vapor with the surface of microspheres heated to a temperature below the softening temperature of the wall of microspheres, and mixing the microspheres, in which according to the invention the mixing of microspheres is carried out in the presence of vapors of an organometallic compound, and the amount of metallo the organic compound in relation to the number of microspheres is determined depending on the required coating thickness

where m _MC is the load mass of microspheres, g; m _MOC — mass of organometallic compound, g; ρ _P is the density of the coating, g / cm ³ ;

- specific surface of the microspheres, cm ² / g; k ₁ is the coefficient of transition of the starting compound into the coating material (when using Barkhos® HCL to obtain a coating of Cr k ₁ = 0.16, to obtain a coating of Cr ₃ C ₂ k ₁ = 0.18), k ₂ is the utilization coefficient material - is determined by the volume of the camera and the ratio of the areas of microspheres and the camera (varies from 0.30 to 0.95).

Before heating the microspheres in a chamber with microspheres create a pressure of not more than 10 ^-1 PA.

The feed of the organometallic compound into the chamber can be carried out portionwise; between the feed portions of the organometal compound, the decomposition products are removed.

To obtain a carbide coating on microspheres, they are heated to a temperature of 280-300 ° C.

To metallize the microspheres, they are heated to a temperature of 450-500 ° C.

. Загрузив микросферы и МОС, камеру герметично закрывают, снижают давление до значения не более 10^-1 Па и начинают вращать со скоростью, необходимой для постоянного перемешивания микросфер. Во вращающейся камере постепенно повышают температуру до достижения в ней оптимальной температуры, необходимой для качественного осаждения покрытия. Температура зависит от выбранного МОС, но не должна превышать температуру размягчения микросфер. МОС переходит в газовую фазу и равномерно распределяется по всему объему камеры. При достижении в камере температуры разложения МОС происходит распад паров МОС на внешней поверхности микросфер с образованием покрытия. Процесс осаждения при оптимальной температуре проходит в течение от 0,5 до 8 часов. Затем камеру охлаждают до комнатной температуры. Выбранное соотношение количества МОС и микросфер, температура осаждения, перемешивание микросфер в присутствии паров металлорганического соединения обеспечивают однородность покрытия по поверхности микросфер и одинаковую толщину покрытия во всей партии микросфер. Давление в камере не более 10^-1 Па позволяет получать покрытия с минимальным содержанием примесей - продуктов разложения МОС. Однородность покрытия, низкие значения разнотолщинности и минимальное содержание примесей позволяют повышать прочностные свойства и снижать газопроницаемость при минимальных толщинах покрытий.This result is achieved by the fact that microspheres are loaded into the chamber in an amount that allows them to mix freely during rotation of the chamber. Then add a certain amount of MOS, calculated depending on the required thickness of the resulting coating according to

. Having loaded the microspheres and MOS, the chamber is hermetically sealed, the pressure is reduced to a value of not more than 10 ^-1 Pa and they begin to rotate at the speed necessary for constant mixing of the microspheres. In a rotating chamber, the temperature is gradually increased until it reaches the optimum temperature necessary for high-quality deposition of the coating. The temperature depends on the selected MOS, but should not exceed the softening temperature of the microspheres. MOS passes into the gas phase and is evenly distributed throughout the chamber. Upon reaching the decomposition temperature of the MOC in the chamber, the MOC vapor decomposes on the outer surface of the microspheres to form a coating. The deposition process at the optimum temperature takes place from 0.5 to 8 hours. Then the chamber is cooled to room temperature. The selected ratio of the number of MOC and microspheres, the deposition temperature, mixing of the microspheres in the presence of vapors of the organometallic compound ensure uniformity of the coating over the surface of the microspheres and the same coating thickness throughout the batch of microspheres. The pressure in the chamber of not more than 10 ^-1 Pa allows to obtain coatings with a minimum content of impurities - decomposition products of MOS. The uniformity of the coating, low values of the thickness difference and the minimum content of impurities can increase the strength properties and reduce gas permeability with minimum coating thicknesses.

The proposed method allows to obtain metal, oxide, carbide or combined coatings on the surface of microspheres, depending on the starting organometallic compound and deposition conditions.

Volatile compounds with a decomposition temperature lower than the softening temperature of microspheres, such as carbonyls and arene complexes of transition metals, β-diketonates and metal alcoholates, are used as organometallic compounds.

The effect of all the classes of organometallic compounds presented on the surface of the microspheres is approximately the same and proceeds by the method of chemical vapor deposition of organometallic compounds (MOCVD method). All of them, upon thermal decomposition on the surface of microspheres, form protective hardening coatings. During the decomposition of metal carbonyls, depending on the process conditions, it is possible to obtain coatings from metals and metal oxycarbides. During the decomposition of arena metal complexes, the coating composition can be changed from metallic to carbide of the corresponding metal. In the decomposition of β-diketonates and metal alcoholates, the coating will be an oxide of the corresponding metal.

Moreover, it should be especially noted that when using all the classes of organometallic compounds given above for the purpose of hardening the shell of microspheres, microdefects are grown on the surface of the microspheres.

In FIG. 1 shows an installation for implementing the inventive method, comprising microspheres 1, a chamber 2, an electric furnace 3 to maintain the optimum temperature inside the chamber 2, an electric motor 4 for rotating the chamber 2 with microspheres 1, a bypass valve system 5, 6, 7 for removing the decomposition products of the MOC and feeding new portion of MOS. Valve 6 is connected to the MOS batcher, valve 7 is connected to a vacuum pump.

In FIG. 2 shows photographs of samples of ash microspheres of the original (2A) and coated with the carbidechrome coating according to the proposed method (2b).

In FIG. Figure 3 shows photographs of the surface of samples of fly ash microspheres with a combined coating of Cr ₃ C ₂ , Cr ₇ C ₃ , Cr.

In FIG. 4 shows the hydrogen permeability dependences of ash microspheres: 1H - initial microspheres;

2H - microspheres coated with aluminum by magnetron sputtering;

3H - microspheres coated with carbide-chromium coatings according to our technology.

In Fig.5 presents the dependence of the hydrogen permeability of the microspheres of the brand MS-A9 gr. B2, starting and coated with Fe, filled with H ₂ . 1 - coated Fe, 2 - initial.

The method is as follows.

. Создают в камере давление не более 10^-1 Па, электропечью 3 нагревают камеру до температуры ниже температуры размягчения микросфер, при этом перемешивают микросферы путем вращения камеры 2 электродвигателем 4.Microspheres 1 are loaded into chamber 2. Then, MOS (in liquid or solid form, or in the form of vapors) is added. In liquid or solid form - charged directly to the chamber in a vapor - fed through a system of valves 5, 6, 7. The weight MOS _MOS m is calculated depending on the desired thickness of the coating _P h depending on

. Create a pressure in the chamber of not more than 10 ^-1 Pa, electric furnace 3 heat the chamber to a temperature below the softening temperature of the microspheres, while mixing the microspheres by rotating the chamber 2 with an electric motor 4.

Depending on the set temperature, a metal, carbide, oxide or mixed protective coating is formed on the surface of heated microspheres in the chamber from organometallic vapors. The process is carried out at a pressure of not more than 10 ^-1 Pa. The heating temperature of the microspheres should exceed by about ~ 100 ° C the decomposition temperature of the organometallic compound, but not exceed the softening temperature of the microspheres. As organometallic compounds, carbonyls and arene complexes of transition metals, β-diketonates and metal alcoholates can be taken.

The following examples illustrate the invention.

Example No. 1. Precipitation of carbidechrome coatings on the outer surface of microspheres by pyrolysis of a mixture of so-called chromium bis-arene complexes Organochromium Chromium Fluid (CLC) “Barchos” (TU 6-01-1149-78) was carried out in a plant, the scheme of which is shown in FIG. 1. ~ 50 cm ^{3 of} ash microspheres of the Cherepetskaya state district power station with a size of 112≤d <125 μm were loaded into a chamber with a volume of ~ 150 cm ³ , a certain volume of Barchos coke was added, 3 cm ³ , a pressure of 6 × 10 ^-2 Pa was created in it and hermetically closed the camera. Then, a rotational motion was imparted by the electric motor 4, and the temperature in the electric furnace 3 and, accordingly, in the chamber 2 was gradually increased. Within 2 hours, the temperature in the chamber 2 was raised to the optimum temperature necessary for high-quality deposition of the carbide-chromium coating. In this case, the organochromium liquid passed into the gas phase and was evenly distributed over the entire volume of the ampoule. When the temperature reached 380 ° C, the vapor of the organochromic liquid decomposed on the outer surface of the microspheres with the formation of a hardening carbidochrome coating. The deposition process at the optimum temperature (380 ° C) was carried out for 3-4 hours. Then the chamber 2 was cooled to room temperature, the samples of microspheres coated with a carbidochrome coating were opened and unloaded. Various modes of deposition of carbide-chromium coatings were tested. As a result, the conditions for the deposition of carbide-chromium coatings on the surface of ash microspheres were optimized.

The optimal conditions for the deposition of carbide-chromium coatings on the ash microspheres from the Barkhos HLC obtained for this installation are as follows:

- the initial temperature of heating of the microspheres is 80 ° C (the temperature of the transition of the organochromic liquid to steam);

- the volume of ash microspheres placed in the chamber is 50 cm ³ ;

- the volume of the fluid “Barhos” 3 cm ³ ;

- camera rotation speed of 10 rpm;

- the pre-heating time of the microspheres is 1-1.5 hours;

- the deposition time of the carbidochrome coating 4 hours;

- pressure - 6 × 10 ^-2 Pa.

Examples 2-5 (table 1) carried out analogously to example No. 1. At the same time, the volume of the Barkhos CJSC amounted to:

- Example 2 Hozh volume "Barhos" - 2.5 cm ^3, the pressure - 5 × 10 ^-2 Pa, the deposition coating karbidohromovogo 3.5 hours, - the rotation speed of the camera 15 rev / min;

- example 3, the volume of the Coke “Barhos” is 2 cm ³ , the pressure is 6 × 10 ^-2 Pa, the deposition time of the carbide-chromium coating is 3 hours, and the chamber rotation speed is 15 rpm;

- Example 4 volume Hozh "Barhos" - 1.5 cm ^3, the pressure - 5,5 × 10 ^-2 Pa, the deposition coating karbidohromovogo 2 hours - the rotation speed of the camera 20 rev / min;

- example 5, the volume of the CFC “Barchos” is 1.0 cm ³ , the pressure is 6 × 10 ^-2 Pa, the deposition time of the carbide-chromium coating is 1.5 hours, and the chamber rotation speed is 15 rpm.

The surface of the samples of ash microspheres is coated uniformly with carbidochrome coatings, microdefects are not observed (Fig. 3). The study of microspheres was carried out by optical microscopy (Leica MZ6 Fig. 2) and electron probe x-ray microanalyzer JSMA-733 (Fig. 3).

In FIG. 2 shows photographs of samples of ash microspheres of the original (2A) and coated with the carbidechrome coating according to the proposed method (2b). It can be seen from the photographs that the carbidochrome coating on the surface of the samples is uniform, completely covers all microspheres.

Studies of the strength characteristics of the obtained samples were carried out and their comparison with the initial samples of microspheres. After applying a carbide-chromium coating with a thickness of 130 nm to the outer surface of the ash microspheres, the hydrostatic strength increases at least one and a half times in comparison with the initial samples (table 1).

Table 2 presents the phase composition of the coating depending on the initial MOC and the deposition temperature, coating thickness and hydrostatic density.

Next, studies were conducted of the hydrogen permeability of ash microspheres with carbide-chromium coating. For comparison, tests were carried out on three batches of ash microspheres of the Cherepetskaya state district power station, having a size of 20≤d <350 microns. The results of such tests are presented in FIG. four:

1H - source microspheres,

2H - microspheres coated with A1 by magnetron sputtering,

3H - microspheres coated with carbide-chromium coatings according to our technology.

The results obtained on the measurement of gas evolution from three batches of ash microspheres allow us to speak about the possibility of controlling the permeability of the walls of microspheres to hydrogen over a fairly wide range. But for microspheres with a carbide-chromium coating of a thickness of the order of 130 nm, the gas evolution rate is about 3-4 times lower compared to the original microspheres and two times lower compared to samples of microspheres coated with aluminum by magnetron sputtering.

Thus, the proposed method allows to improve the strength properties of the microspheres and to reduce gas emission compared to the original microspheres, which is an important condition for the development of high-strength microspheres capable of encapsulating hydrogen for a longer time.

Example No. 6

The deposition of pyrolytic iron coatings on the outer surface of glass microspheres of the brand MS-A9 gr. B2 by pyrolysis of iron pentacarbonyl was carried out in a plant, the scheme of which is shown in FIG. 1. ~ 50 cm ³ glass microspheres ~ 100 μm in size were loaded into a chamber with a volume of ~ 150 cm ³ , a portion of iron pentacarbonyl was added and hermetically closed, and a pressure of not more than 10 ^-1 Pa was created. Then, a rotational movement was imparted by the electric motor 4, and the temperature in the electric furnace 3 and, accordingly, in the chamber 2 were gradually raised. Within 30 minutes, the temperature in the chamber 2 was raised to the optimum temperature necessary for the qualitative deposition of pyrolytic iron. In this case, iron pentacarbonyl passed into the gas phase and was evenly distributed over the entire volume of the ampoule. When the temperature reached 160 ° С, the pentacarbonyl iron vapor decomposed on the outer surface of the microspheres with the formation of reinforcing iron carbide. The deposition process at an optimum temperature of 160 ° C was carried out for 30 min. Then chamber 2 was cooled to room temperature, samples of microspheres coated with Fe coating were opened and unloaded.

The optimal conditions for the deposition of pyrolytic iron coatings on the surface of microspheres using iron pentacarbonyl obtained by us for this installation are as follows:

- the volume of microspheres loaded into the reaction volume is 15 cm ³ ;

- the temperature of the deposition process is 160 ° C,

- the rotation speed of the MOCVD reactor is 60 rpm;

- the time of the deposition process coated with a sample of pentacarbonyl iron 2.5 g - 30 min;

- the time of the deposition process of the coating using a portion of iron pentacarbonyl 1.36 g - 15 min;

- the time of the process of deposition of the coating using a portion of pentacarbonyl iron 0.25 g - 5 min;

- pressure - 7 × 10 ^-2 Pa.

The coating thickness is determined through the true density of the microspheres, which was measured by the cyclometric method. The density of the microspheres coated with pyrolytic iron with a deposition time of 3, 15 and 30 minutes was respectively 0.35, 0.37 and 0.39 g / cm ³ . The density of the initial microspheres is 0.33 g / cm ³ , the coating thickness was 71 nm, 45 nm and 21 nm, respectively.

Next, studies were conducted of the hydrogen permeability of microspheres of the brand MS-A9 gr. B2 coated with pyrolytic iron. Microspheres coated with 71 nm were compared with the original microspheres. The results of such tests are presented in FIG. 5:

Example No. 7

The deposition of pyrolytic tungsten coatings on the outer surface of the ash microspheres of the Cherepetskaya TPP with a size of 40 to 200 μm by pyrolysis of tungsten hexocarbonyl was carried out in the installation, the scheme of which is shown in FIG. 1. 33 to 50 cm ³ ash microspheres were loaded into a chamber with a volume of ~ 150 cm ³ , a weighed portion of tungsten hexocarbonyl was added and hermetically closed, and a pressure of not more than 10 ^-1 Pa was created. Then, a rotational motion was imparted by the electric motor 4, and the temperature in the electric furnace 3 and, accordingly, in the chamber 2 were gradually increased. Within 40 minutes, the temperature in the chamber 2 was raised to 245 ° C. In this case, tungsten hexocarbonyl passed into the gas phase and was evenly distributed over the entire volume of the ampoule. Upon reaching a temperature of 245 ° C, the vapor of hexocarbonyl tungsten decomposed on the outer surface of the microspheres with the formation of a hardening coating — tungsten carbide. The deposition process was carried out for 20 minutes. The rotation speed of the MOCVD reactor was 60 rpm, the pressure in the chamber was 7 × 10 ^-2 Pa. After completing one coating cycle from chamber 2, opening valves 5 and 7, the decomposition products of tungsten hexocarbonyl were pumped out. Having removed the decomposition products into chamber 2 through valve 6, a new portion of tungsten hexocarbonyl was fed. Depending on the required coating thickness, the required number of coating cycles can be carried out.

Table 3 shows the main parameters of the process of coating pyrolytic tungsten on the surface of ash microspheres.

Sample 3 was obtained after six consecutive cycles of deposition of pyrolytic tungsten. From table 3 it is seen that by the method of layering (sequential deposition of the coating of pyrolytic tungsten) you can adjust the thickness of the coating.

The true density of ash microspheres of a fraction of 40-80 μm coated with pyrolytic tungsten was determined by liquid pycnometry.

It is experimentally shown that the inventive method allows to obtain metal, oxide on the surface of microspheres. carbide or combination coatings depending on the starting organometallic compound and deposition conditions. This ensures uniformity of the coating on the surface of the microspheres, increases the strength properties of the microspheres due to the reduction of defects on their surface and decreases gas permeability.

Claims (6)

1. The method of applying metal-containing coatings to the microspheres, which consists in the interaction of the vapors of the organometallic compound with the surface of the microspheres, heated to a temperature below the softening temperature, mixing the microspheres, characterized in that the mixing of the microspheres is carried out in the presence of vapors of the organometallic compound, and the amount of organometallic compound in relation to the amount microspheres are determined depending on the required coating thickness h _P

where m _MC is the load mass of microspheres, g; m _MOC — mass of organometallic compound, g; ρ _P is the density of the coating, g / cm ³ ;

- specific surface of the microspheres, cm ² / g; k ₁ is the coefficient of transition of the starting compound into the coating material; k ₂ - utilization of the material - is determined by the volume of the camera and the ratio of the areas of microspheres and the camera (varies from 0.30 to 0.95). 2. The method according to p. 1, characterized in that before heating the microspheres in the chamber create a pressure of not more than 10 ^-1 PA. 3. The method according to p. 1, characterized in that the organometallic compound is fed into the chamber portionwise, between the servings of the organometallic compound, microspheres are mixed and decomposition products are removed. 4. The method according to p. 1 or 2, characterized in that to obtain a carbide coating on the microspheres they are heated to a temperature of 280-300 ° C. 5. The method according to p. 1 or 2, characterized in that for metallization of the microspheres they are heated to a temperature of 450-500 ° C.

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