WO2016053070A1

WO2016053070A1 - Method for preparing a flexible metal-ceramic carrier having a nanocrystalline surface layer

Info

Publication number: WO2016053070A1
Application number: PCT/LT2014/000011
Authority: WO
Inventors: Римантас ПАКАМАНИС; Александр ХИНСКИЙ; Кристина КЛЯМКАИТЕ - РАМАНАУСКЕ; Нериюс ЛАУРИНАИТИС
Original assignee: Уаб "Вердиго"
Priority date: 2014-10-03
Filing date: 2014-10-03
Publication date: 2016-04-07
Also published as: ES2654858A2; ES2654858B1; ES2654858R1

Abstract

The invention relates to the field of producing ceramic coatings, having a developed surface, on metal objects having complex shapes, and can be used in applied chemistry for preparing catalyst elements, in mechanical engineering, shipbuilding, the aviation industry, and in preparing objects of space technology when applying protective coatings including anti-corrosion coatings, thermal-barrier coatings, coatings resistant to ice formation, and other coatings. A method for preparing a flexible metal-ceramic carrier having a nanocrystalline surface layer includes the plasma spraying of a special aluminum-based coating onto a metal strip carrier, with the subsequent hydrothermal processing of the flexible semi-finished product. The invention is novel in that the hydrothermal processing, which provides for optimal microstructure, nanostructure and porosity, is carried out in two stages, wherein the first stage of processing is carried out at a pressure of 20-26 atm and temperatures of 200-230 degrees centigrade for 6-12 hours, and the second stage is carried out at a pressure of 4-8 atm and temperatures of 150-170 degrees for 120-160 hours.

Description

A method of manufacturing a ceramic-metal flexible carrier with

nanocrystalline surface layer

Technical field

The invention relates to the field of producing ceramic coatings with a developed surface on complex metal objects and can find its application in applied chemistry for the manufacture of catalytic elements, in mechanical engineering, shipbuilding, the aircraft industry and the manufacture of space technology objects * when applying protective, including anticorrosive, heat barrier, anti-icing and other coatings.

State of the art

The application of ceramic coatings on a metal carrier is widely used in industry, providing reliable protection against various factors of influence of both natural and artificial environments. For example: CN101438439, 2009-05-20, A multi-layer coating, Halvor Larsen Peter; EP2088225 (Al), 2009-08-12, Erosion and corrosion-resistant coating system and process therefore, Pabla Surinder Singh; CA2664929 (Al), 2008-04-03, Method and device for depositing a non-metallic coatings by means of cold-gas spraying, Luethen Volkmar; CA2668736, 2008-05-15, A method for the production of thin layers of metal-ceramic composite materials, Clasen Rolf. However, ceramic coatings on a metal substrate also have a number of drawbacks proceeding from the specifics of their nature. First of all, this is a significant difference in the coefficient of linear expansion (ctp) of ceramics and metals (see Table 1).

Tab. 1. The linear expansion coefficients of metallic materials and ceramics,.

Therefore, when operating a metal-ceramic composite material at elevated or lowered temperatures, which is necessarily associated with a heating and cooling process, high thermal stresses arise at the boundary between the metal and ceramics, which in many cases can cause distortion of the structure of both the metal substrate and ceramic coating, and in some cases - destruction of the ceramic layer, which manifests itself in intense shedding or even peeling of the coating.

The situation is even more complicated when the coating is used in conditions of thermal shock, thermal cycles with the simultaneous influence of factors such as corrosion or gas erosion.

To provide compensation for thermal stresses, intermediate layers are often used that are located between the metal substrate and the ceramic coating and provide complete or partial relaxation of thermal stresses arising in the intermediate layer.

Very stringent requirements are imposed on the intermediate layers, namely, they must provide reliable adhesion both to the substrate metal and to the ceramic coating, to provide quick relaxation of stresses at their minimum level due to plastic deformation, which is possible only with the maximum plasticity of the material of the intermediate layer . In addition, the material of the intermediate layer should be minimally brittle during application temperature gradients (or embrittlement should be removed due to specific relaxation mechanisms directly during operation).

In addition, the intermediate layer should, on the basis of general provisions, have a minimum thickness. All this imposes a number of serious restrictions on the material of the intermediate layer and sharply narrows the range of materials that can be used for these purposes.

As an intermediate layer, metals such as aluminum, nickel and copper are often used, which, along with high ductility, have good adhesion to the metal and ceramic substrates, as well as high processability, which makes it possible to use existing processes for their application, such as thermal spraying ( plasma and flame), ion-plasma and magnetron sputtering, as well as electrolytic coating methods.

Assessing the effectiveness of the mentioned methods of applying an intermediate layer in terms of adhesion to a metal (steel) substrate, only ion-plasma and magnetron sputtering methods can claim first place, thermal sputtering methods are second and galvanic methods are last.

The main advantage of physical deposition methods (ion-plasma and magnetron sputtering) is the gradual layer-by-layer deposition of metal ions, in which the first layer firmly adheres to the surface layer of the substrate, and subsequent layers already ideally adhere to the first, second, etc. layer. A significant drawback of these methods is the very low rate of build-up of this intermediate layer. Therefore, these methods are applicable only to create an intermediate adhesive layer and cannot be used to obtain a catalytic support layer on the surface of a metal substrate. Other methods must be used to obtain the catalyst support layer. spraying or deposition, providing a layer of sufficient thickness, which provides a high degree of surface development.

For example, technical solutions are known in which a very thin layer of aluminum is used as an intermediate layer, which is sprayed by the ion-plasma method onto the surface of a steel strip. Then, a layer of a catalytic support based on alumina alpha modification is deposited on its surface by the plasma method.

In the case of using thermal spraying and electroplating methods, it is possible to obtain sufficiently thick coatings that can be used as adhesion coatings, as well as to form a layer of catalytic support on their surface.

Such a solution is proposed in a number of patents.

So, for example, in the patent US5362523 (Gorinin IV, Farmakovsky BV, Khinsky A.R. and others) from 1994 describes a method for producing a catalytic tape material, which includes a steel substrate, which is first applied by plasma spraying an adhesive sublayer, and then using the same method, a catalytic multilayer coating is applied in which the concentration of catalytically active elements gradually increases from 0 at the interface between the adhesive sublayer and the catalytically active layer to 100% on the surface. Increased adhesion of the adhesive layer to the steel substrate is achieved by forming an effective diffusion layer in the area of contact of the adhesive layer with the substrate.

In the patent US5820940 (Gorinin IV, Farmakovsky BV, Khinsky A.R. and others) from 1998 describes a method for producing an adhesive coating (intermediate layer) on a metal tape carrier by plasma spraying of thermally reactive composite powders (such as nickel-aluminum). The described method provides an intermediate adhesive layer, very firmly bonded to a steel tape carrier, which is confirmed by the test results. However, the problem of reliable adhesion of the catalytic layer sprayed onto the surface of the intermediate layer remains unresolved, and the adhesion strength of these layers, although this is not given in the patent materials, will obviously be lower than the adhesion strength of the intermediate layer to a metal substrate. When operating catalytic elements made of catalytic ribbon material of this kind under rather severe conditions, including thermal cycles, intense gas erosion, etc., partial shedding of the catalytic layer is possible with a corresponding decrease in its characteristics.

Attempts to increase the adhesion strength of the intermediate layer to the catalytic layer due to intermediate heat treatments (US2001014648, Hums E., Khinsky A. from 2001), the use of various places of introduction of powder materials into the plasma jet during the spraying process (WO2004079035, Khinsky A.R., from 2004), the use of the HVOF (high velocity oxygen fuel) method of spraying composite powder (WO2008063038, Khinsky A.R., Klemkaite K. from 2008) lead to some increase in the adhesion strength, but do not provide a high level of adhesion of the intermediate layer to metal m substrate.

The use of coatings obtained by thermal spraying of ductile metals and alloys (aluminum, nickel, copper, etc.) provides high adhesion to the sprayed surface due to the high kinetic energy of the sprayed particles (spraying is often carried out at speeds close to or even faster than the speed of sound) and high dynamics of their cooling, which almost always leads to amorphization (or transition to the microcrystalline state) of the metal of the sprayed particles. Moreover, compounds formed upon instantaneous contact of molten particles with a metal substrate during thermal spraying and representing mainly intermetallic compounds of various compositions and stoichiometries that form in the contact zone in the form of very thin films sharply differ in physical and mechanical characteristics from ordinary intermetallics formed in the process of conventional metallurgical processes, ^{^""} including casting, heat treatment, etc., and special steels alloys. It is known that ordinary intermetallic compounds formed under equilibrium conditions are characterized by high hardness and brittleness, while film non-stoichiometric intermetallic compounds formed during thermal spraying, as practice shows, do not exhibit such properties and, in addition, provide very good adhesion of the sprayed layer to the substrate.

Coatings obtained by thermal spraying provide another important advantage over galvanic and ion-plasma and magnetron sputtering. This advantage lies in the ability to form a surface microstructure during thermal spraying. A typical thickness of such a coating is 10 to 20 microns.

The surface structure of the sprayed layer can be significantly improved due to the formation of nanostructured "protrusions" in the form of nanocrystals of various configurations (A.V. Lukashin, Creating functional nanocomposites based on oxide matrices with an ordered porous structure, Abstract of a doctoral dissertation, 2009, Moscow State University, Moscow.)

The creation of a similar type of nanostructure on the surface increases catalytic activity, resistance to the formation of an ice film at low temperatures, optical characteristics of the coating, etc.

Thus, the use of coatings obtained by thermal (especially plasma) spraying as an intermediate layer makes it possible, along with obtaining high adhesion of the sprayed layer, to provide the formation of a developed microstructure of its surface.

The application of a layer of a catalytic support (with or without a catalyst) to the intermediate layer can be carried out in various ways, however, in any case, the applied layer should provide the following characteristics:

- A sufficiently high free surface with an optimal structure of porosity;

- High adhesion of the catalytic carrier layer to the intermediate - A sufficiently high level of catalytic properties when interacting with the actual catalyst.

Unfortunately, almost all existing methods of applying a catalytic carrier cannot provide a high level of catalytic properties and high adhesion to the intermediate coating at the same time. Therefore, the choice of the optimal method for the formation of a catalytic support layer on metal substrates is often very difficult.

In addition, the technological process, including the mentioned intermediate stages, namely, the stage of applying the intermediate adhesive layer and the subsequent stage of applying the catalytic support, as well as possibly another stage of applying the catalyst, is very complex and expensive.

For example, in the case of applying a catalytic carrier to a metal honeycomb structure from an aqueous suspension by successive dipping and drying, a very unpleasant factor that reduces the wide applicability of this method is the slow draining of the suspension down the channels during the drying process and the formation of specific sagging in the lower part of the cellular structure, which can lead, in some cases, to the complete blocking of its channels.

From this point of view, it seems very promising to combine the processes of deposition of an adhesive coating (intermediate layer) and the subsequent transformation of its surface into a catalytic carrier. In this case, on the one hand, a strong adhesion of the adhesive coating to the metal substrate is ensured, which, as noted earlier, is characteristic of coatings deposited by plasma spraying, and, on the other hand, the organic transition of the coating metal to the oxide (or hydroxide) phase . As the material of the adhesive coating, plastic metals and alloys, in particular aluminum, nickel, copper and their alloys, are usually used, as mentioned earlier.

In principle, all these materials can, under certain conditions, transform from the surface to oxides and hydroxides, which is accompanied, in some cases, associated development of the porous structure. The latter circumstance is very important from the point of view of the formation of a catalytic coating.

However, for the above metals used to apply the adhesive coating, the formation of the porous structure necessary for the catalytic support is observed only in the case of aluminum.

Aluminum and a number of its alloys can, under certain conditions, be converted from the surface into aluminum hydroxide. Under ordinary conditions, a thin and very dense oxide film is formed on the surface of aluminum metal, which is instantly restored upon its destruction. This film prevents further oxidation of aluminum. However, under certain conditions - at elevated pressure and temperature in the atmosphere of superheated steam - a gradual transition of aluminum to aluminum hydroxide (boehmite) is observed. This process, as shown in a number of works, is carried out due to the sequential hydration of the oxide film formed on the surface of aluminum metal. In a series of articles (Tikhov S.F., Fenelonov V.B. et al., Kinetics and Catalysis, 2000, Volume 41, Ne 6, pp. 907-915. Tikhov S.F., Zaikovsky V.I. et al. ., Kinetics and Catalysis, 2000, Volume 41, Ν ° 6, pp. 916-924.) It is shown that this process can be applied to obtain porous cellular ceramic supports based on aluminum oxide.

The articles describe the procedure for producing porous cermet of aluminum oxide / metal aluminum composition during processing of an aluminum powder compact with a sufficiently high porosity (sufficient for free passage of air inside). The processing was carried out in a special thermal baroclave, which provides the processing of pressing in a vapor medium at a temperature of 150 to 250 C and a pressure of 5 to 50 atmospheres. A patent is also known based on the technology described in the articles (Patent RU2256499 (O), authors Pakhomov N.A., Tikhov S.F. et al. From 2004).

This patent proposes a ceramic catalyst for a process for the dehydrogenation of hydrocarbons and a method for its preparation. The catalyst contains in its composition chromium oxide, an alkali metal deposited on a carrier, which is a composite material comprising aluminum oxide and aluminum.

The above-described laws governing the conversion of metallic aluminum to aluminum hydroxide followed by its decomposition to produce a catalytic carrier suggest the idea of building a technology based on these principles to produce a catalytic carrier after applying an aluminum adhesive sublayer to the surface of a metal tape carrier. Patents JP9217178, 1997-08-19, Kanbe Yumi and JP 10120499, 1998-05-12, Kanbe Yumi describe a method for producing a multilayer thin coating. The coating should provide a porous structure of a metal oxide onto which an electrically insulating material is deposited, filling the pores of the metal oxide layer. According to the patent, at the first stage of the process, the formation of a thin and porous metal oxide film on the surface of the substrate during its hydrothermal treatment in solutions of the corresponding salts occurs.

JP9156927, 1997-06-17, Nakayama Naomi describes a method for producing a multilayer oxide coating in selected areas of a substrate, which includes the following operations: forming an oxide coating on the surface of the substrate, removing masking material, then processing in an oxidizing medium to form an oxide coating and etc. The final operation is the hydrothermal treatment of the resulting coating in aqueous alkaline solutions. In the patent JP3284356,1991-12-16, Kameyama Hideo describes the manufacturing technology of a flat low-temperature catalyst element, which includes the following operations. A flat substrate made of an aluminum alloy is annealed at high temperature, preferably in the range of 900 - 1000 C, to form an oxide film based on aluminum oxide on its surface. Then the substrate is hydrothermally treated in the range temperatures of 50 - 350 C and a metal having catalytic activity is deposited on a catalytic support based on alumina formed on the surface of a flat substrate as a result of hydrothermal treatment. The catalytic support obtained as a result of hydrothermal treatment should be gamma-modified alumina with a developed free surface. A metal having catalytic activity can also be deposited at the hydrothermal treatment stage.

JP2000178792, 2000-06-27, Ishizawa Hitoshi describes a coating method based on titanium oxide with a high free surface on a metal substrate. The method includes the step of preparing the surface of the metal substrate, the step of anodizing at least one surface of the substrate to form an anodic oxide film, and the step of applying a slurry based on aqueous solutions of metal salts and alkoxides containing dispersed metal oxide particles. After the anodizing step, hydrothermal treatment is recommended.

US2004058066, 2004-058066, Wei Zhiqiang describes a method for forming a thin film metal oxide coating.

The method includes the following steps: a step of applying a sol-gel coating containing at least one metal component to the surface of the metal substrate, a step of drying said sol-gel coating, a step of impregnating the resulting coating in alkaline aqueous solutions containing at least one metal component, a drying step and a hydrothermal treatment step.

Of the above patents, it is obvious that the method of applying an aluminum coating to the surface of a tape carrier is of great, in some cases, decisive importance.

For applying aluminum powder to the surface, the technological process described in the patent can be used (Patent RU2295588, A. Khinsky, March 20, 2007) A distinctive feature of the described coating in this process is its high adhesion to the steel tape used as a substrate. The resulting semi-finished product - a steel strip with a sprayed coating - has such a high adhesion strength that it allows you to carry out almost any machining operation, such as cutting, corrugating, perforating, etc. without peeling or shedding of the sprayed layer.

SUMMARY OF THE INVENTION

The use of this technological process for spraying an aluminum layer will make it possible to create a coating that combines the functions of an intermediate adhesive layer (on the surface adjacent to the steel tape carrier) and a catalytic carrier (on the surface of the coating itself) if it could be converted into a porous carrier on Alumina based on the technology described above.

Moreover, the sequence of processes for applying an aluminum coating and its conversion into a catalytic carrier must be changed. Since it is assumed that the adhesion strength of the coating to the steel substrate will be so high that it will allow mechanical processing of the semi-finished product obtained after spraying, it seems reasonable to include this stage immediately after spraying, and to make the hydrothermal treatment stage final.

In this case, the technological process, taking into account the above patents, should consistently include the following steps:

1. Application of an aluminum adhesive layer on the surface of a metal tape substrate by thermal spraying. 2. Carrying out mechanical processing (including cutting, corrugation, perforation, etc.) to form the catalytic element in its final form. 3. Processing of the obtained catalytic element in a vapor-air medium at elevated pressure and temperature to partially convert the surface of the adhesive layer to aluminum hydroxides.

4. Thermal decomposition of the obtained hydroxide coating with its transformation into alumina with the formation of a porous surface structure.

5. Application of catalysts by impregnation.

To implement the proposed method for producing a catalytic carrier, work was carried out on the 1st, 2nd, 3rd and 4th stages of the technological process, since the 5th stage is very trivial and can be carried out without preliminary preparation.

Stage 1.

Application of an aluminum adhesive layer on the surface of a metal tape substrate by thermal spraying.

The following materials were used to apply the aluminum layer to the surface of a metal tape tape substrate:

- Cold-rolled steel strip made of ferritic stainless steel chromium steel with a thickness of 40 microns and a width of 100 and 90 mm manufactured by Sandvik (Sweden). Data on the chemical composition and applications are shown in Table 2.

Tab. 2. Characteristics of cold rolled steel tape Sandvik OS404

- Aluminum powder grade PA-1 and aluminum powder grade PAP-2 (GOST

5494-95). Supplier - Volgograd Aluminum Company (Valkom-PM). The main characteristics of the mentioned materials are given in Tables 3 and 4. Tab. 3. The main characteristics of aluminum powder grade PA-1

Tab. 4. The main characteristics of aluminum powder brand PAP-2

To apply the aluminum adhesive layer, we used the plasma spraying method, which was carried out on a specially developed installation in air using a plasma torch and a dispenser of an original design (for the description of the installation and plasmatron see patents RU2295588, WO2008063038, WO2004079035, US2001014648) Plasma spraying of aluminum powder and as well as other process parameters are given in table 5. Tab. 5. The main parameters of the plasma spraying process.

As a result of the experiments, a solid aluminum coating with a thickness of 18-24 microns was obtained. The chemical composition of the sprayed coating is presented by X-ray diffraction data (Fig. 1), which was carried out using the usual Bragg-Brentano technique on a DRON-6 radiographic unit equipped with a secondary graphite monochromator. The radiation source was used Cu radiation (λ = 1.541838 A). In FIG. 1 is a radiograph of a sprayed aluminum layer.

The adhesion strength of the aluminum coating with the metal substrate was evaluated by the results of the machining of the obtained semi-finished product by visual inspection for violations of the integrity of the sprayed coating (peeling, shedding, etc.). Corrugation and perforation were chosen as two typical and rather rigid machining operations for assessing the integrity. Stage 2.

Carrying out mechanical processing (including cutting, corrugation, perforation, etc.) to form the catalytic element in its final form. This step has already been partially described in Step 1 (see above), so further description of this step seems unnecessary.

Stage 3.

Processing the obtained catalytic element (semi-finished product) in a vapor-air medium at elevated pressure and temperature to partially convert the surface of the adhesive layer to aluminum hydroxides.

The hydrothermal treatment of the carrier semi-finished products after plasma spraying and the catalytic elements (honeycomb structures) made of this carrier was carried out on a special installation designed and manufactured to solve this problem. The installation is a thermobaroclave (Fig. 2), designed to operate in the temperature and pressure range (shown in Table 6) and includes a reaction chamber representing the working volume for placing the semi-finished products of the carrier and catalytic elements (honeycomb structures) during hydrothermal treatment , a lock chamber, providing preliminary placement of the catalytic elements for their subsequent transportation to the reaction chamber, and an unloading chamber, where the processed atalytic elements.

Tab. 6. Intervals of operating temperatures and pressures of the thermobaroclave.

Additional equipment of the installation includes a device that provides adjustment and maintenance of the main process parameters (temperature, pressure, humidity, flow rate, etc.) in automatic mode.

Processing in a thermobaroclave was carried out according to the modes shown in table 7. Tab. 7. The main modes of processing a semi-finished carrier in a thermal baroclave.

Studies have shown that hydrothermal treatment in all modes (1, 2, and 3) is accompanied by a transition of the surface layer of the aluminum coating to gamma alumina, the development of the free surface of the coating, and the formation of an optimal porosity structure.

The value of the relative free surface, characterizing the development of porosity, after hydrothermal treatment according to 2 and 3 is in the range of 60 - 100 m2 / g, which is an acceptable result.

However, if during processing according to regimes 1 and 2, the surface, as a whole, morphologically preserves the microstructure of the sprayed layer and in the surface layer the presence of spherical particles of various sizes (from several microns to tens of microns), partially deformed (flattened) and firmly bonded to each other, can be noted another, which is a typical structure of the sprayed layer, a completely different picture is observed when processing according to mode 3.

In this case, it was experimentally established that an ordered "forest" of needle-shaped nanocrystallites having a fairly uniform orientation relative to the substrate is formed on the surface of the sprayed layer. In FIG. 3 shows, at various magnifications, the surface structure of the aluminum sprayed layer after processing in a thermal baroclave according to mode 3 (see Table 7).

A similar structure is stably formed on the surface of the sprayed aluminum layer in the following temperature and pressure ranges (see Table 8). Tab. 8. The intervals of formation of the coating nanostructure during the processing of the sprayed semi-finished product in a stepwise mode (mode 3).

In FIG. 3 shows the surface structure of the aluminum sprayed layer after processing in a thermal baroclave according to a stepwise mode with decreasing the treatment temperature.

As shown by studies of the fine structure of the surface after hydrothermal treatment, an increase in temperature and pressure causes an increase in the conversion rate of the aluminum coating and the process gradually moves from the surface into the depth of the coating. In this case, in the sprayed layer of pure aluminum, a gradual layer-by-layer conversion of metallic aluminum into the corresponding oxide and the formation of a specific microstructure are observed.

As for the specific effect of the formation of a nanostructured “forest” of crystals under the conditions of a stepwise regime with a decrease in temperature and pressure in the second stage, this is probably due to an increase in the selectivity of growth points during the crystallization of nanocrystals.

Claims

Claim

A method of manufacturing a ceramic-metal flexible carrier with a nanocrystalline surface layer, including plasma spraying of a special coating on the basis of aluminum on a metal tape carrier followed by hydrothermal treatment of a flexible semi-finished product, and characterized in that the hydrothermal treatment, providing optimal micro- and nanostructure and porosity, is carried out in two stages, the first stage of processing being carried out at a pressure in the range from 20 to 26 atm and temperatures in the range of 200 to 230 C for 6 - 12 hours and the second stage at a pressure of 4 to 8 atmospheres and temperatures ranging from 150 to 170 for 120 - 160 hours.