WO2008063038A1 - Procédé de projection thermique - Google Patents

Procédé de projection thermique Download PDF

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Publication number
WO2008063038A1
WO2008063038A1 PCT/LT2006/000010 LT2006000010W WO2008063038A1 WO 2008063038 A1 WO2008063038 A1 WO 2008063038A1 LT 2006000010 W LT2006000010 W LT 2006000010W WO 2008063038 A1 WO2008063038 A1 WO 2008063038A1
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Prior art keywords
aluminum
layer
hydrotalcite
coating
powder
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PCT/LT2006/000010
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English (en)
Russian (ru)
Inventor
Aleksander Pavlovich Khinsky
Kristina Klemkaite
Nerijus Laurinaitis
Avelino Corma
Eduardo Polomares
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Uab 'norta'
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Priority to PCT/LT2006/000010 priority Critical patent/WO2008063038A1/fr
Publication of WO2008063038A1 publication Critical patent/WO2008063038A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
    • C23C4/06—Metallic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating
    • B01J37/0225—Coating of metal substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0244—Coatings comprising several layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/16—Metallic particles coated with a non-metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/202—Alkali metals
    • B01D2255/2027—Sodium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/204—Alkaline earth metals
    • B01D2255/2047—Magnesium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20715—Zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20723—Vanadium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20746—Cobalt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/209—Other metals
    • B01D2255/2092—Aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/92—Dimensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

  • the invention relates to methods for coating by spraying a material in a molten state and may find application in various fields of chemistry, energy. State of the art
  • Known methods for applying protective coatings using compositions based on aluminum compounds by methods of thermal spraying Aluminum oxide is most widely used as a powder material for spraying coatings based on aluminum. As a rule, thermal spraying of ceramic coatings is carried out on a previously applied metal sublayer. Powder materials in pure form and / or their compounds - oxides, carbides, nitrides, etc. are used to spray coatings by thermal spraying methods. Often, sprayed powders are composite materials, for example, nickel particles coated with aluminum, tungsten, molybdenum.
  • composition of the metal core and the thin coating layer is dictated by the need to take into account many factors, including a set of mechanical and special properties (adhesion strength of the coating to the substrate, porosity, corrosion resistance, erosion resistance, abrasion and wear resistance), as well as economic factors (production cost) .
  • the powder material In the process of thermal spraying, the powder material, as a rule, undergoes some transformation. This is due to the obligatory stage of the passage of powder materials in a jet of gas plasma (with plasma spraying) or in a stream of combustion products (with flame spraying).
  • the particles of the sprayed material are heated to various temperatures, which causes various kinds of transformation in the particles - from surface heating and melting to complete melting and even transfer of the material into gas
  • the first and third tasks are polar opposites, since to ensure reliable contact with the substrate, it is desirable to completely melt the particles during their passage in the gas stream - this ensures reliable adhesion of the coating to the substrate, but the shape of the particles is lost and the substructure of the coating changes.
  • the process is often carried out in two or more stages. In this case, at the first stage, a special thin intermediate layer (sublayer) is sprayed, which, on the one hand, provides reliable adhesion to the substrate, and on the other hand, provides a good adhesion of the main layer, which is sprayed onto its surface.
  • powders As materials for spraying, powders, powder mixtures and special compositions of powders are used. As such compositions, powders are often used with a coating applied to their surface (the coating can be multilayered), powders with small particles of another material attached to their surface, and powders combined into whole complexes of particles connected to each other in a specific, ordered manner.
  • a known method of forming metal particles with an oxide coating for a plasma spraying process (US6582763, ⁇ r mecanicss SWs f adoptedrrrhafene so composedt Foodd fme metal r diaryt deadlinel Switzerlands).
  • the fundamental difference from the usual surface oxidation process is the fact that a thin layer of oxides of those metals that are not part of the metal core is formed on the surface of metal particles.
  • the process of applying an oxide coating includes the following stages - mixing a metal powder with an oxide, then feeding the mixture of powders into the thermal plasma stream to obtain a vapor phase; and finally, quenching (hardening) to fix the oxide layer on the surface of the particles.
  • JP2005068508 Metal rover coater with Iporpur superfme rapplic apd its product method.
  • the coating which contains particles of aluminum oxide, aluminum hydroxide or their complex compounds, boron or phosphorus, in the form of a gel is deposited on the surface of metal powder particles.
  • the final formation of the inorganic coating occurs during the heat treatment of the coated powder.
  • a known method for the production of powder with a titanium coating (RU2178341, Titapium roverdrodustiop rocess), in which during the joint grinding of a metal powder with a titanium sponge, a thin layer of titanium is applied to the surface of the powder.
  • Thermal spraying methods are usually used to obtain coatings that provide mechanical (increase in surface hardness, decrease in friction coefficient and increase in wear resistance), physical and chemical (increase corrosion resistance in water and gas, gas erosion, increase radiation resistance) and special (in particular catalytic) properties.
  • the catalytic activity of a material is determined by a number of factors, both chemical and technological.
  • the technological factors that determine the degree of catalytic activity is, in particular, the degree of development of the catalytic surface (Farrauto, RJ., Vartholom, CH, 1997. Pharmaceuticals Industrial Technologies ⁇ r Canalss Moscows ⁇ , 78-86: 122-134).
  • This term describes a parameter characterizing the total surface area of one gram of coating. In the case of conventional coatings, this parameter is 0.01-0.1 m 2 / g, while in the case of special, catalytic coatings, it reaches 100-400 m 2 / g.
  • Such a catalytic surface allows the placement of a proportionally larger volume of catalytic material.
  • the increase in the specific free surface, ceteris paribus is proportional to the increase in the catalytic activity of the coating.
  • a specific problem that must be solved by thermal spraying of catalytic coatings is the need to ensure a high specific surface.
  • One of the solutions to this problem may be to increase the porosity of the coating during the spraying process. High porosity of the coating for conventional coatings is undesirable, as it causes deterioration adhesion to the substrate, as well as a decrease in the physicochemical characteristics of the coating.
  • the sprayed powder materials are a mixture of powders, including catalytic materials (metal oxides), aluminum hydroxides, in particular gibbsite and boehmite, which ensure the development of the free surface of the coating during and / or after spraying and a metal binder, usually aluminum which provides adhesion of the sprayed particles to each other and to the substrate.
  • catalytic materials metal oxides
  • aluminum hydroxides in particular gibbsite and boehmite
  • a method for forming a catalytic coating is proposed (RU2126717C1, A method for manufacturing a catalytic unit for neutralizing gas emissions), in which a powder mixture consisting of aluminum - 0.5-5% and aluminum hydroxide is applied to the surface of a metal strip with high electrical resistance by plasma spraying with natural accompanying impurities.
  • a plasma-forming gas air or another oxygen-containing mixture is used.
  • spraying it is proposed to maintain regulated energy regimes that ensure, on the one hand, the melting of aluminum particles, but excluding the thermal decomposition of aluminum hydroxide.
  • the specified method allows you to get on the surface of a metal tape carrier thin composite layer with high adhesive strength.
  • aluminum hydroxide (gibbsite) dispersion less than 10 microns.
  • aluminum hydroxide (gibbsite) does not require chemical treatment, but is used with natural (technological) impurities - sodium, potassium, calcium, silicon, etc. - which are in this case thermostabilizing elements and provide an additional increase in thermal stability
  • a known method of manufacturing a composite coating (RU97101513A, a Method of manufacturing a composite coating), in which a porous coating comprising a metal oxide and a metal binder is applied to the initial substrate by plasma spraying.
  • plasma spraying use a mixture of powders, including aluminum oxide and / or titanium, aluminum as a metal binder and additionally aluminum hydroxide and / or titanium.
  • the value of the specific free surface after decomposition of the sprayed layer is 50-70 m 2 / g of coating.
  • a known method of applying a porous coating to metal and ceramic materials by plasma spraying (US6254938B1, Sprauipg metod for arrluipg and porous coatigot substitute).
  • a powder mixture which includes aluminum hydroxide, aluminum oxide and / or titanium, glass powder, as a component forming a microstructure, aluminum metal powder and / or titanium as a metal binder.
  • various components of the sprayed powder are introduced into different areas of the plasma flow. So, for example, aluminum hydroxide is introduced into the colder zone of the stream, and metals - aluminum and titanium - into the hotter one.
  • the resulting coating according to the authors, is characterized by high adhesion to the metal substrate and high porosity.
  • the intermediate layer must, firstly, have a thermal expansion coefficient (ctr) as close to the ctp of the substrate, and, secondly, be as integrated as possible into the structure substrates, i.e. atoms of the coating material should form metallic bonds with atoms of the substrate material. If the first condition can be quite easily satisfied by selecting the material of the intermediate layer with a c.t.p. as close as possible to the c.t.
  • the relative free surface in this case should be at least 10 m 2 / g (this means that one gram of the coating must have a total surface of 10 square meters), which should provide high adhesion of the sprayed coating.
  • recalculation of the maximum open porosity established for the intermediate layers sprayed in the usual way by the value of the relative free surface shows that the latter in this case does not exceed a value of the order of 1-2 m 2 / g, which is clearly not enough.
  • the sprayed layer must be dense (on the side adjacent to the substrate), which should provide high adhesion to the substrate, and, therefore, high thermomechanical characteristics of the coating, and, at the same time , the sprayed layer must be highly porous (on its surface) to ensure special, including catalytic, properties. This contradiction is resolved due to the specific chemical composition of the sprayed powders and the original technology of their spraying.
  • metal aluminum performs, firstly, the role of the metal sublayer, providing high adhesion strength of the sprayed layer to the substrate, and, secondly, the role of the metal bond to fix the particles of the porous surface of the sprayed layer.
  • Silicate glass powder provides the development of the macrostructure of the sprayed coating.
  • a composite layer consisting of aluminum, melted in a plasma jet and forming a plastic sublayer on the surface of the substrate. Glass particles partially melted from the surface are embedded in this layer, which ensures their strong adhesion to the layer. And finally, particles of aluminum hydroxide, which did not decompose during passage through the plasma jet, were introduced into the surface of this layer.
  • the composite coating obtained in this way is not the final product, because, firstly, it is not porous, and secondly, its phase composition does not meet the requirements for special coatings (for example, for using the coating in catalysis gamma and theta modifications of aluminum oxides should be predominantly on its surface) and, thirdly, the residual thermal stresses (the result of the plasma spraying process itself) are quite high.
  • Obtaining the necessary physical and chemical properties of the sprayed composite coating is achieved by conducting heat treatment in an oxidizing environment, mainly in air. During the decomposition of aluminum hydroxide in the temperature range 480-660 ° C during the heat treatment, the formation of aluminum oxide with a highly developed microporous surface occurs in accordance with reaction (1).
  • the process of heat treatment of the sprayed composite layer in an oxidizing medium provides, according to the authors, the preparation of the necessary chemical and phase composition on the surface with the simultaneous formation of a specific macro- and microstructure of the surface layer.
  • the method of thermal spraying described in detail above for the preparation of catalytic coatings has a number of significant drawbacks, the main of which is the problem of preventing thermal decomposition of aluminum hydroxide during its passage in a plasma jet.
  • any change in the mass of particles, air pressure in the plasmatron, or a small change in the electrical parameters of the source during the deposition process will lead to a change in the trajectory of the particles, and, therefore, to decomposition of particles in the process of spraying, or to their underheating - in this case, they simply will not adhere to the substrate.
  • a precursor is usually understood as a substance that contains the necessary catalytic materials and, after its application to the surface of the carrier, can be converted, after a series of procedures, into a catalyst (Farutauto, RJ., Pharmaceutical, C.H., 1997, Industrial Chemical Industrial Chemicals). As such procedures, heating, irradiation or other activation of the surface of the catalytic coating can be used.
  • complex powder materials as precursors can also solve a number of specific problems associated with the deposition of catalysts.
  • a spraying option using a mixed composition consisting of aluminum metal, aluminum oxide and hydroxides The proposed process allows to obtain a catalytic coating characterized by a relatively high free surface (50-70 m 2 / g) and a statistically uniform distribution of catalyst particles.
  • the optimal operation of the catalyst is possible only when the catalytic particles are on the surface of a special catalytic carrier, the role of which is played by gamma and theta alumina, as well as aluminum hydroxide in the form of gibbsite and / or boehmite.
  • the catalytic activity of the catalyst is higher, the higher the degree of development surface.
  • the thermal spraying process is constructed in such a way that aluminum hydroxide is applied to the surface of the product in an undecomposed or partially decomposed state. Subsequent heat treatment leads to thermal decomposition of the hydroxide and a strong increase in the free surface.
  • an increase in the free surface does not lead to migration and redistribution of catalyst particles on the surface of the catalytic carrier (see Fig. L).
  • the catalyst particle is rigidly fixed in the sprayed layer after thermal spraying and its position does not change during the decomposition of aluminum hydroxide. Therefore, an increase in the free surface is not accompanied by a proportional increase in catalytic activity.
  • the formation of the precursor occurs upon impregnation of boehmite, which has a certain crystallite size, namely, in the range of 4-30 nanometers.
  • solutions for coating formation aqueous solutions of salts and organic solvents are used.
  • a method for forming a precursor (EP 1462475 Al, Mg-Zn-
  • Albased bakedite-resin and resin composition containing theme in which the composite Mg-Zn-Al layer is formed on the surface of the core, consisting of Mg-Al hydrotalcite.
  • the particle size of the precursor is 0.1-1.0 microns.
  • JP2004255245 the Wellbearing method, the method of the method, the method consists of the aluminum, the surface is the hydrothermal method, which includes the aluminum surface and magnesium nickel.
  • This precursor is subjected to heat treatment in a reducing medium, where nickel oxide is reduced to nickel and its uniform distribution on the particle surface is ensured.
  • a known method for the manufacture of composite coatings (WO2004079035, Method for production and co-production) with plasma spraying.
  • the composite coating obtained in accordance with this method can be used as a substrate for applying various coatings, for example, polymer, as well as impregnation with various compositions, including catalytic ones.
  • the proposed method consists in the fact that in the sprayed powder, providing the development of the microstructure of the coating, enter the composite powder with a coating of the type hydrotalcite (composite precursor).
  • a coating of this composition is sprayed onto a metal or ceramic substrate, then machining and heat treatment are carried out by annealing.
  • the aim of the invention described above is to obtain a catalytic coating having enhanced characteristics, namely, the adhesion strength of the coating to the substrate and a high free surface.
  • a coating is applied to the substrate by thermal spraying, which includes a mixture of alumina powders, aluminum metal as a binder metal, glass powder, as a material for the formation of the coating macrostructure, as well as a composite precursor with a coating of hydrotalcite type.
  • Composite powder (precursor) rest As a composite powder in a coating according to the invention, an aluminum hydroxide-based powder material is used with a hydrotalcite type coating applied to its surface.
  • Gibbsite Al (OH) 3 has a monoclinic crystal lattice and dissociates in the temperature range
  • Hydrotalcite is usually understood to mean a natural mineral represented by the formula Mg 6 Al 2 (OH) 2 .16CO 3 . 4H 2 O.
  • the structure of hydrotalcite is derived from brucite Mg (OH) 2 , where magnesium ions form octahedra that line up in an infinite layer. These layers are superimposed on one another and are held together due to hydrogen bonds.
  • the layer receives an additional positive charge, which is compensated by the introduction of divalent CO 3 anions located between the layers.
  • hydrotalcite-type materials are isomorphic analogues in which the cations of magnesium and aluminum are partially replaced by divalent and trivalent metal cations with a close ionic radius.
  • the decomposition of materials such as hydrotalcite occurs, as a rule, in three stages.
  • the so-called crystallization water is released from hydrotalcite, which is retained in the structure during crystallization.
  • anions are separated from the structure, which are located between the cation layers and provide electrostatic equilibrium of the material.
  • the departure of anions is accompanied by the release of interplanar space and the primary development of the surface of the material. In this case, there is no destruction of the structure of the material, and it can be restored by holding the material in an atmosphere of saturated steam.
  • hydrotalcite decomposition occurs in three stages, which opens up great opportunities for multi-stage heat treatment, - within the second stage of hydrotalcite decomposition (350-450 ° C), its structure can be completely restored in an atmosphere of saturated steam,
  • the temperature of the interval of the third stage of decomposition of hydrotalcite is 650-750 0 C, which significantly exceeds the temperature range of the decomposition of aluminum hydroxide, which is 500-560 0 C, - the free surface after the complete decomposition of hydrotalcite is 200-400 m 2 / g.
  • hydrotalcites and aluminum hydroxides The most important fundamental difference between hydrotalcites and aluminum hydroxides is their ability to replace aluminum and magnesium cations with trivalent and, accordingly, divalent cations of most metals, the oxides of which are widely used in catalysis, provided that their ionic radius is not much different from the ionic radii of aluminum and magnesium. This allows one to introduce such metals directly into the structure of hydrotalcites and, thus, use the main features of their decomposition to obtain catalysts the necessary chemical composition in the form of a mixture of oxides or complex oxides
  • hydrotalcites with partially substituted magnesium and aluminum ions that are advisable to use as a material ensuring the creation of a highly efficient catalytically active surface with high microporosity.
  • the precursor when using a composite precursor, a high level of catalytic properties is achieved due to the fact that the precursor is a porous particle of aluminum hydroxide (gibbsite or boehmite), on the surface of which a thin layer of hydrotalcite is deposited.
  • the precursor core consisting of gibbsite or boehmite, transforms into aluminum oxide, and hydrotalcite on its surface into a mixture of oxides or, depending on the processing temperature, spinel.
  • An example is the attempt to reproduce the plasma spraying technology of a catalytic coating on a metal substrate in accordance with the patent WO2004079035 described above.
  • a thin (40 ⁇ m) strip of heat-resistant chromium-aluminum steel grade OC404 (Sandvik) was used as a substrate.
  • Plasma spraying was performed using an APP-403 type current source and an air plasma torch. Air was used as a plasma-forming gas.
  • the electrical parameters corresponded to those cited in the aforementioned patent, namely, voltage of 210 volts, current of 150 amperes. The regulation of these parameters was carried out in a rather narrow range (voltage within 200-220 volts, current within 140-160 amperes).
  • the only parameters that can be widely controlled with plasma spraying are the speed and flow rate of the sprayed powders.
  • the powder can be supplied in two ways - by introducing the powder into the plasma torch and feeding along the axial line in the plasma jet (to the most warmed up zone) and feeding directly to the peripheral (colder zone) plasma jet.
  • a mixture of powders was used, including, according to the patent, 85% of the composite powder (boehmite coated with hydrotalcite), 10% alumina of gamma modification, 3% aluminum and 2% glass powder (all powders with a fineness of less than 60 microns).
  • a mixture of powders was supplied:
  • Option 4 - separate feed a mixture of aluminum and glass powders into the peripheral zone of the jet 30 mm from the nozzle exit (hotter zone), a mixture of composite powder and aluminum oxide into the peripheral zone of the jet 70 mm from the nozzle exit (cooler zone).
  • the first embodiment of the powder supply is not acceptable in this case.
  • the powder mixture when the powder mixture was fed into the peripheral zone of the plasma jet at a distance of 30 mm from the nozzle exit, a coating was obtained with satisfactory properties about 10 microns thick. However when serving powder mixture in the peripheral zone was observed, as shown by weight analysis, an extremely irrational flow rate of the sprayed powder. The amount of powder deposited was not more than 3-5% of the total amount of powder supplied.
  • the powder mixture when the powder mixture was supplied to the peripheral zone of the plasma jet at a distance of 70 mm from the nozzle exit, the powder did not have time to warm up when passing through the plasma and did not form a coating on the surface of the carrier. Thus, the third embodiment of the powder supply is not acceptable.
  • the main problem is that although the particle diameter of the composite precursor is large enough (reaches 100 microns), their mass is insufficient for effective incorporation into the intermediate layer deposited on the surface of the substrate to increase adhesion.
  • aluminum particles included in the composition of the powder mixture are effectively embedded in the intermediate layer, capturing part of the sprayed particles and thereby increasing the efficiency of the process.
  • most of the powder - from 80 to 90% - does not spray and goes to waste, thereby reducing the efficiency of the spraying process.
  • it seems reasonable to significantly increase the particle mass of the composite precursor by introducing additional materials that are used in the spraying process and which, at least, will not reduce the level of catalytic properties of the coating. This will provide a sharp increase in the density of the deposited layer, and, consequently, the level of catalytic properties, as well as a reduction in the unproductive expenditures of the powder of the composite precursor by reducing losses during sputtering.
  • This problem can be solved by creating a composite precursor in which a metal aluminum particle is a core on which an intermediate layer of aluminum hydroxide is deposited, firmly adhered to the metal core and having a developed surface on which a layer of hydrotalcite is deposited.
  • Fig.Z is a diagram of the sequential development of the concept of a precursor.
  • the diagram shows the evolution of the precursor concept - starting with a hydrotalcite particle, through a composite powder in which aluminum hydroxide plays the role of a core (gibbsite or boehmite), and hydrotalcite is used as a coating, and to a precursor, which is a composition of an aluminum core, an intermediate hydroxide layer aluminum and hydrotalcite coatings.
  • the aluminum particle which is the core of the precursor, should have a size of 60-100 microns, which is due to the possibilities of feeding the powder from the dispenser and its passage through the plasma torch.
  • the process of creating an aluminum hydroxide layer on the particle surface is a rather complicated task, since it must ensure that the following conditions are met:
  • the process of growing a porous layer on the surface of an aluminum particle consists in sequentially hydrating the oxide layer to form a porous structure, then again forming the oxide layer, hydrating it, etc.
  • the process can be brought to a porous hydroxide layer of the required thickness or even complete hydration of the aluminum particle.
  • the series of articles (KINETICS AND CATALYSIS, 2000, volume 41, Xa 6, p.907-915, KINETICS AND CATALYSIS, 2000, volume 41, JV ° 6, p.916-924) describes the technology for producing porous cermet by forming aluminum particles coated with aluminum hydroxide on the surface and their subsequent pressing.
  • the formation of a porous layer of aluminum hydroxide on the surface of the particles is carried out during the oxidation of aluminum particles in an autoclave with a controlled temperature and pressure.
  • the basic laws of the kinetics of the formation of the surface layer of aluminum hydroxide (boehmite) during the oxidation of aluminum particles in the vapor phase (hydrothermal oxidation) are established in the articles.
  • boehmite layer As established during the research, at the initial stage of the process, the formation of aluminum oxide occurs, which then, during hydration, turns into boehmite.
  • the free surface of the boehmite layer With its volume of less than 10%, is 200-250 m 2 / g. With a further increase in the volume of the surface layer, the free surface decreases to 150-160 m 2 / g.
  • a known method for producing aluminum hydroxides (WO 2004 / 071950A1, A method for producing hydroxides or oxides of aluminum and hydrogen and a device for its implementation) from a powder of finely dispersed aluminum with a particle size of not more than 20 ⁇ m, from which an aqueous suspension is prepared, which is fed to the reactor, where the suspension is sprayed with drops with a diameter of 5-100 microns in water under a pressure of 20-40 MPa at a temperature of 220-900 ° C.
  • a hydrotalcite layer on the porous surface of aluminum hydroxide can be carried out by various methods, including methods of impregnation, coprecipitation, etc. (CN1483513, "sootipg”).
  • the objective of the invention was to develop a complex precursor for thermal spraying of catalytic coatings.
  • the complex precursor was supposed to be particles including an aluminum core, an intermediate coating of aluminum hydroxide and an outer layer of catalytic material based on synthetic hydrotalcite.
  • the catalytic coating obtained in the process of thermal spraying of a complex precursor should provide good adhesion to the substrate, a high specific free surface and high catalytic properties in the reaction of reduction of nitrogen oxides.
  • the essence of the invention consists in the fact that for the thermal spraying of catalytic coatings a special powder material is made - a precursor (resursor), each particle of which is a core of aluminum with an intermediate layer of aluminum hydroxide deposited on its surface and a surface layer of catalytic material deposited on the surface of the intermediate layer - synthetic hydrotalcite.
  • a precursor resursor
  • aluminum powder with a dispersion of 20-100 microns is used.
  • the technological process for obtaining a precursor includes two stages:
  • stage 1 For the production of the precursor, a technological process for hydration of aluminum powder (stage 1) was developed, which provides a porous intermediate layer of aluminum hydroxide on the surface of aluminum particles.
  • FIG. Figure 4 shows an X-ray diffraction pattern of an aluminum powder with a hydrated layer.
  • peaks corresponding to aluminum peaks corresponding to aluminum hydroxides, namely boehmite and bayerite, are clearly visible.
  • Figure 4 - x-ray aluminum powder with a hydrated layer.
  • the development of the chemical and phase composition of synthetic hydrotalcite for the deposition of a surface catalytic layer on a precursor was carried out as follows.
  • the development of the catalyst was carried out in relation to the task of reducing nitrogen oxides and oxidizing carbon monoxide in the exhaust gases of a diesel engine. This statement of the problem determined the requirements for both the catalyst and its operating conditions.
  • the catalyst under development should ensure the reduction of nitrogen oxides to molecular nitrogen and the oxidation of carbon monoxide to carbon dioxide.
  • hydrotalcites of the Mg-Al-Co system were selected with the possibility of introducing additional metal ions, such as sodium, vanadium, cerium, and / or ruthenium.
  • the catalyst obtained by the decomposition of hydrotalcites described above is active in the removal of nitrogen oxides at low temperatures and in the presence of oxygen, water vapor, and sulfur oxides, as well as in the oxidation of carbon-containing mixtures at low temperatures.
  • Catalysts can be prepared by coprecipitation of solutions containing magnesium, aluminum and cobalt with an alkali solution for the synthesis of Mg-Al-Co hydrotalcite.
  • a solution containing cobalt, magnesium and aluminum ions was obtained from the soluble salts of Mg (NO 3 ) 2 .6H 2 O, A1 (NO 3 ) 3 .9H 2 O and Co (NO 3 ) 2 .6H 2 O.
  • concentration of magnesium, aluminum, and cobalt ions, as well as the ratio (Mg + Co) / Al can vary over a wide range without exceeding the solubility limit.
  • the alkaline solution is formed by mixing alkaline hydroxides and carbonates, mainly NaOH and Na 2 CO 3 in adequate concentrations, ensuring complete precipitation of the components of the first solution.
  • the resulting gel was aged from 3 to 20 hours at temperatures in the range of 60-100 ° C. After aging, the resulting material was filtered and washed to obtain a pH in the range of 6.8-7.5. After calcination at temperatures up to 300 ° C, the resulting material was converted to Mg / Al / Co mixed oxides.
  • the catalytic properties of mixed oxides obtained by decomposition of hydrotalcites in the reaction of reduction of nitrogen oxides were carried out at a laboratory bench. The experiments were carried out in a special reactor, which is a quartz tube with a diameter of 22 mm and a length of 530 mm. Catalytic material, weighing 1 gram, in the form of particles with a size of 0.25-0.42 mm, was loaded into the reactor and heated to a temperature of 350 ° C with the passage of nitrogen or hydrogen. At this temperature, the material was aged for 30 minutes. After that, the desired reaction temperature was established and the supply of nitrogen oxides was ensured.
  • the gases supplied were a mixture of 300 million “1 NO, 900 million “ 1 C 3 H 8 , as well as varying amounts of oxygen and nitrogen.
  • the flow rate when the gas mixture was supplied was 650 ml / min.
  • experiments were carried out with the introduction of water in the range of 0-10% and SO 2 in the range of 0-60 ppm . 1.
  • the concentration of nitrogen oxides in the outlet of the reactor was constantly monitored using a chemo-luminescent detector 951 A.
  • the catalytic activity of mixed oxides obtained after decomposition of hydrotalcite in the oxidation reaction of carbon-containing mixtures was determined in a special reactor, which is a quartz tube with a diameter of 22 mm and a length of 530 mm.
  • Catalytic material weighing 1 gram, in the form of particles with a size of 0.25-0.42 mm, was loaded into the reactor and heated to 350 ° C with the passage of nitrogen or hydrogen. At this temperature, the material was aged for 30 minutes. After that, the catalyst was cooled in a stream of nitrogen to 120 ° C.
  • a reaction mixture was supplied, which consisted of a mixture of gases, including 300 million " NO, 900 million " 1 C 3 H 8 and 8% oxygen, the rest was nitrogen.
  • the flow rate when the gas mixture was supplied was 650 ml / min.
  • the gas mixture was heated from a temperature of 120 to 550 ° C at a rate of 5 ° C / min.
  • Propane oxidation was monitored by CO 2 content.
  • Example 1 Preparation of a catalyst based on Mg / Al / Co hydrotalcite with a molar ratio of 65/20/15.
  • Aqueous solutions were prepared: 0.975M solution of magnesium nitrate, 0, 3M solution of aluminum nitrate and 0.225M solution of cobalt nitrate. They mixed when shaken with 3, 3M aqueous NaOH and IM Na 2 CO 3 until pH is obtained
  • the resulting gel was ripened for 12 hours at 60 0 C, then washed and filtered to obtain a pH of 7. Then the material was calcined at 650 ° C for 6 hours. After calcination, the material had a relative free surface of 165 m 2 / g.
  • Example 2 Preparation of a catalyst based on Mg-Al-Co hydrotalcite with a molar ratio of 65/20/15 with Na and V.
  • Example 2 To the catalyst described in Example 1 was added, by impregnation, an IM solution of the vanadium salt and NaOH to obtain 1% vanadium and 6% sodium. Then, the material was dried and calcined at 550 ° C. After calcination, the material had a relative free surface of 55 m 2 / g.
  • Example 3 Catalytic activity in the NOx reduction reaction of the catalyst described in Example 2.
  • the catalyst described in Example 2 was used to remove NOx, as described above, at various temperatures.
  • a 95% conversion of nitrogen oxides was obtained with an experiment duration of 1 hour at temperatures in the range of 100-400 ° C and in the presence of 8% oxygen.
  • Example 4 Catalytic activity in the oxidation reaction of carbon-containing mixtures of the catalyst described in example 1.
  • the catalyst described in example 1 was used to remove carbon-containing mixtures, as described above. It was found that in the presence of this catalyst, propane oxidation occurs at temperatures 120 ° C lower than without catalyst.
  • the hydrotalcite compositions described above were applied to the intermediate layer of aluminum hydroxide on the surface of an aluminum particle (stage 2 of the preparation of a complex precursor) by the deposition method.
  • Example 5 The deposition of a layer of hydrotalcite on an intermediate layer of aluminum hydroxide (gibbsite / boehmite) in the production of a complex precursor. 50 g of aluminum powder with a layer of hydroxide on the surface
  • the resulting suspension was ripened for 24 hours at 80 ° C, then cooled to room temperature, filtered by distilled water, dried at room temperature and milled.
  • a thin layer of hydrotalcite was deposited on the surface of particles with a porous layer based on aluminum hydroxides (Fig. 5).
  • a steel strip made of heat-resistant steel 40 microns thick (Sandvik OC404) was used as a substrate for obtaining a catalytic coating. Spraying was carried out on both sides. When spraying, an APR-403 current source was used, as well as a plasma torch and dispensers of an original design, which provided a highly dispersed and light ceramic powder. The microstructure of the coating surface is presented in Fig.6.
  • the samples were corrugated with a step of 3 mm and rolled up into catalytic blocks with a diameter of 40 mm and a length of 50 mm.
  • the catalytic blocks thus obtained were heat-treated in the temperature range 650-850 0 C to decompose the intermediate hydroxide layer and the surface layer of cobalt hydrotalcite.
  • the heat treatment regime included slow heating (at a speed of no higher than 3 ° C min "1 ), holding for 3 hours in the temperature range 650-850 ° C and slow cooling (at a speed of no higher than 4 0 C min " 1 ) to room temperature .
  • the scheme of the stand is presented, which includes: a steam boiler 1, a gas inlet pipe 2, a gas outlet pipe 3, an EcoLipe 6000 gas analyzer 4, a filter 5, a counter 6, a pump 7, valves 8, a cylindrical furnace 9, and T9- thermocouples
  • Example 6 The manufacturing technology of the catalytic block (option 1).
  • a powder precursor based on the aluminum / gibbsite / cobalt hydrotalcite composition was prepared as follows. Aluminum particles with a dispersion of 60-100 microns were oxidized in a thermostat in the vapor phase at a temperature of 340 ° C and a pressure of 32 MPa for 24 hours, which led to the formation of a porous layer of aluminum hydroxide (gibbsite) with a developed surface on the surface of aluminum particles. Then, in a special installation, aluminum hydrotalcite was precipitated with a cobalt content of about 15%. The obtained powder, after filtration, drying, and grinding, was sprayed by thermal spraying onto OC404 steel tape from two sides. Then the tape was corrugated, rolled into a cylinder (to form a catalytic block) and fixed by sliding it into a thin pipe (G, Fig. 8).
  • Example 7 The manufacturing technology of the catalytic block (option 2). The technology corresponded to that given in Example 6, differing only in that, in the manufacture of the precursor, aluminum fractions of 20-60 microns were used (2 ?, Fig. 8).
  • Example 8 The manufacturing technology of the catalytic block (option S).
  • Example 9 The manufacturing technology of the catalytic block (option 4).
  • Example 10 The technology corresponded to that given in Example 6, differing only in that in the manufacture of the precursor, the oxidation of aluminum in the vapor phase was carried out at a temperature of 240 ° C and a pressure of 32 MPa, which led to the formation of an intermediate layer in the structure of bayerite (4 ', Fig. 8).
  • Example 10 The manufacturing technology of the catalytic block (option 5).
  • Example 11 The technology corresponded to that given in Example 6, differing only in that in the manufacture of the precursor, the oxidation of aluminum in the vapor phase was carried out at a temperature of 300 ° C and a pressure of 32 MPa, which led to the formation of an intermediate layer with a mixed structure of bayerite and boehmite (5 ', Fig. 8).
  • Example 11 The manufacturing technology of the catalytic block (option 6).
  • Example 12 The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, 0.2% cerium (6 ', Fig. 8).
  • Example 12 The manufacturing technology of the catalytic block (option 7).
  • Example 6 The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, 0.1% ruthenium (7 ', Fig. 8).
  • Example 13 The manufacturing technology of the catalytic block (option 8). The technology corresponded to that given in Example 6, differing only in that the surface layer of the precursor, namely hydrotalcite, contained, in addition to 15% cobalt, about 0.1% sodium (8 ', Fig. 8).
  • Fig. 8 presents the test results of samples (catalytic blocks) after various options for their manufacture and heat treatment.

Abstract

L'invention concerne des procédés de fabrication de revêtements catalytiques par projection thermique d'un matériau en poudre et peut s'utiliser dans différents domaines de la chimie, du génie énergétique et de l'industrie automobile. L'invention vise l'obtention d'un revêtement catalytique biface sur bande métallique qui possède, outre un niveau élevé de propriétés catalytiques dans des réactions de réduction d'oxydes d'azote et d'oxydation d'hydrocarbures, un niveau élevé de propriétés mécaniques et d'usage tels que l'adhérence élevée au substrat métallique et la résistance élevée à la contamination dans une atmosphère de gaz de dioxyde de soufre et de vapeurs d'eau. A cet effet, on propose d'utiliser dans le processus de projection thermique sur bande métallique une poudre composite spéciale constituée d'un noyau métallique d'aluminium, d'une couche intermédiaire à base d'hydroxyde d'aluminium et d'un revêtement à la surface de la particule à base d'hydrotalcite de cobalt qui est appliqué sur la couche intermédiaire. On propose une composition de la poudre composite, en termes de quantité comme en termes de qualité. Le revêtement catalytique de ce type est appliqué par un procédé de projection thermique sur une bande métallique, après quoi l'on effectue le traitement mécanique et la formation de l'article.
PCT/LT2006/000010 2006-11-23 2006-11-23 Procédé de projection thermique WO2008063038A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US850893A (en) * 1906-08-06 1907-04-23 Edward D Barton Sleigh-knee.
US5872075A (en) * 1996-08-19 1999-02-16 Mitsubishi Chemical Corporation Catalyst for oxidation of hydrogen, method for selective oxidation of hydrogen, and method for dehydrogenation of hydrocarbon
RU2126717C1 (ru) * 1995-03-06 1999-02-27 Хинский Александр Павлович Способ изготовления каталитического блока для нейтрализации газовых выбросов
RU2202414C1 (ru) * 1998-12-28 2003-04-20 Сименс Акциенгезелльшафт Способ изготовления катализатора и катализатор

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US850893A (en) * 1906-08-06 1907-04-23 Edward D Barton Sleigh-knee.
RU2126717C1 (ru) * 1995-03-06 1999-02-27 Хинский Александр Павлович Способ изготовления каталитического блока для нейтрализации газовых выбросов
US5872075A (en) * 1996-08-19 1999-02-16 Mitsubishi Chemical Corporation Catalyst for oxidation of hydrogen, method for selective oxidation of hydrogen, and method for dehydrogenation of hydrocarbon
RU2202414C1 (ru) * 1998-12-28 2003-04-20 Сименс Акциенгезелльшафт Способ изготовления катализатора и катализатор

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