RU2536536C1 - Method of obtaining of porous permeable ceramic article - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: deposition is performed by forming of monolayers at the expense of collisions of deposited particles of ceramic material with the surface of mandrel at a minimum angle 45°, except for zero. Each monolayer is formed with the maximum thickness 0.04 mm. The porosity is formed as through one, pores are parallel to each other and slant to working surface of an article with channel pores (2) with variable cross-section, from which the least is from the side of output of filtered medium. The geometry of a pore space increases penetrability of an article more than twice.

EFFECT: creation of conditions for obtaining of open channel porosity in a body of an article.

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Description

The invention relates to methods for the manufacture of porous ceramic products by plasma spraying and can be used to obtain porous permeable products from aluminum oxide.

The nature of the formation of the porous structure of products is greatly influenced by the method of their preparation. In addition, changing the technological parameters of the production of products, you can adjust both their porosity and the nature of the structure. One of the parameters characterizing porous products is such a structural characteristic as permeability - the ability to pass through a liquid or gas under the influence of an applied pressure gradient. (Porous permeable materials: Ref. Ed. / Under the editorship of Belova S.V. M., Metallurgy, 1987, p. 28).

Numerous methods are known for producing porous ceramic products by molding ceramic masses consisting of a filler mixed with a disperse bond (USSR author's certificate No. 5337974, IPC С04В 35/10, 10.04.75., Publ. 05.12.76., USSR author's certificate No. 952811, IPC С04В 38/00, 09/22/80., Publ. 08.23.82., USSR copyright certificate No. 1654290, IPC С04В 38/00, 08/15/08., Publ. 07/06/91.), As a result of which the products are uniform the distribution of enlarged pores in the volume of the entire product.

However, only an increase in pore size does not allow creating an active pore space to increase the permeability of products.

There are also known methods of forming porous ceramic products in which their permeability is increased by various methods of creating a pore orientation in the structure of the product: by introducing a fibrous component (RF patent No. 2386605, IPC SB04/00, publ. 04/20/10.), One-dimensional filler (And . S. Kaynarsky, Corundum Refractories and Ceramics. M., Metallurgy, 1981, p. 109), by drilling a plurality of unidirectional capillary holes in a molded workpiece or by joining tubular elements when they are heated by sintering (author's certificate ments USSR №381638, IPC C04 B38 / 00, 05.20.71., publ. 05.22.73.).

However, the cylindrical shape of the pores unchanged over the cross-section does not make it possible to create a sufficient hydraulic pressure of the filtered medium and to ensure high permeability of the product. In addition, it is possible that the roughness on the inner surface of the cylindrical pores arising from the implementation of these methods, such as drilling, or the surface roughness of the introduced components, also does not improve the permeability of the porous products.

There are also known methods for producing porous permeable ceramic products by impregnating a porous organic base with a ceramic slurry hardening it without clogging pores (USSR author's certificate No. 1294794, IPC SB 38/00, 07/01/85, publ. 07.03.87.), Or by impregnating ceramic basics with an organic solution (USSR author's certificate No. 1726448, IPC С04В 35/10, 04.11.89., publ. 15.04.92) to impart hydrophobicity to the porous structure.

However, in the base material, the pores are randomly distributed and have a large scatter in size, and therefore the required permeability of the products is not achieved.

Other methods are also known for producing porous permeable ceramic articles by impregnating a material base with a ceramic suspension (USSR copyright certificate 1661167, IPC SB04/00, 03/10/08., Publ. 07/07/91., USSR copyright certificate No. 1731762, IPC SB04/00, 06/01/89, publ. 07.05.92., USSR author's certificate No. 1759815, IPC СВВ 35/10, 08.01.90., Publ. 07.09.92.), In which a layer of granular filter material is applied to the working surface of the porous base layer. .

Despite the fact that the obtained products combine the filtering advantages of a porous base and granular filters, the permeability of the obtained products does not reach the required value. This is due to the fact that the pore shape changes from a layer of one material to a layer of another and hydraulic resistance of the filtered medium arises at the boundary of these layers.

Also known are methods for producing porous ceramic products by plasma spraying. In this way, the entire product is made from powder materials by spraying by forming the product from individual particles, heated and accelerated by a high-temperature gas jet.

The main technological operations for manufacturing a ceramic product are carried out in the following sequence: manufacturing a mandrel model that completely repeats the shape of the future product, spraying ceramic material on the mandrel to obtain a hollow product, and removing the mandrel. In technology, such products are called cortical (AF Puzryakov. Theoretical foundations of plasma spraying technology. M., Publishing House of MSTU named after NE Bauman, 2008, pp. 260, 329-333).

The plasma spraying process is determined by many factors, among which one of the most important are the factors characterizing the sprayed material and the factors determining the spraying process itself: the speed of movement of the plasma jet relative to the surface of the mandrel and the angle of inclination of the plasma jet relative to the mandrel is the angle at which the sprayed material particles collide with its surface.

Due to the fact that a whole ceramic product is usually obtained by forming from separate numerous monolayers at an angle of inclination of 60 ÷ 90 ° a plasma jet to the sprayed surface, and in cramped conditions - at an angle of at least 45 ° (Borisov Yu.S., Plasma powder coatings, Kiev, Technika, 1986, p. 26), it can be considered that the whole product is sprayed at given angles. In this case, the monolayers are dense, and the product as a whole is non-porous and impermeable.

There is also known a method of producing a porous ceramic product (US patent No. 4460529, IPC B28B 1/32 publ. 07/17/1984), which includes plasma spraying of oxide ceramic material, including aluminum oxide on a removable mandrel by forming a crust product with a large thickness walls - 5 mm, from monolayers with a thickness of 0.05 ÷ 0.15 mm. The method allows to obtain a product with a microporous structure due to the temperature gradient created in it. This becomes possible due to its internal cooling when the mandrel is cooled and its outer surface formed by plasma spraying is heated to a high temperature. The structure of the obtained product with a very small pore size of less than 5 μm (K.K. Strelov. Technical control of the production of refractory material. M., Metallurgy, 1986, p. 83) excludes the presence of permeability of the product.

The closest analogue adopted for the prototype is a method for producing a porous permeable ceramic product (international application WO 9820181 (A1), IPC С04В 38/00, 35/00, 35/653, С23С 4/10, publ. 05/14/1998 )

The method includes plasma spraying of particles containing together with other oxides and aluminum oxide in an amount of 1.49 wt.% Ceramic material. The material is obtained from industrial wastes with a ceramic phase - from by-products of the processing of harmful substances and converted into bulk material suitable for plasma spraying, but non-uniform in size. The ceramic material introduced into the plasma jet is heated to a working temperature at which an additional, but only partial removal of harmful substances occurs, and the material remains contaminated with them. Plasma spraying is carried out by a plasma jet on a removable mandrel by forming monolayers of particles of increasing size in each subsequent layer.

This method makes it possible to create a product with varying in its thickness layered porosity. However, due to the inhomogeneous size of the sprayed particles in each layer and particles with different sizes in adjacent layers, a product with randomly arranged pores both in each layer and the absence of their directed orientation in the product as a whole is obtained. Plasma spraying is carried out on a removable mandrel by forming monolayers, while the thickness of each layer is not specified. It is possible that its significant value leads to the appearance of internal cracks in the monolayers and in the whole product, and, consequently, to the inability to form through pores clearly directed along the thickness of the product.

In addition, the mode of the method is not specified regarding the angle of impact of the sprayed particles with the surface of the mandrel, which may be considered insignificant, therefore, it can be considered well known - 45 ÷ 90 ° (Borisov Yu.S. Plasma powder coatings. Kiev, Technique, 1986, p. 26), which also reduces the porosity and permeability of the product.

The disadvantage of this method is the lack of the ability to create directional open channel porosity in products manufactured with its help, which does not allow to obtain their high permeability.

The problem to which the invention is directed, is the creation of a ceramic porous product with a high degree of permeability.

The problem is solved due to the technical result that can be obtained by carrying out the invention: creating conditions for obtaining the geometry of the pore space from the open channel porosity of the product due to the surface relief of each monolayer with single pores and their directional union into through pores when applying monolayers.

The problem is achieved in that in a method for producing a porous permeable ceramic product, comprising plasma spraying particles of an aluminum oxide-containing ceramic material with a plasma jet onto a removable mandrel by forming monolayers, according to the invention, plasma spraying is carried out by particles of a uniformly sized aluminum oxide-based ceramic material and conduct it by impact of sprayed particles of ceramic material with the surface of the mandrel at an angle of less than 45 °, excluding zero , Wherein each monolayer is formed not more than 0.04 mm thick.

In addition, electrocorundum with a content of the main component of at least 98 wt.% Can be used as a ceramic material based on aluminum oxide.

In addition, as a particle size uniform ceramic material based on alumina, a material with a narrow range in particle size distribution, namely 80-63 μm, can be used.

In addition, in plasma spraying, a plasma jet with sprayed particles of ceramic material can be formed by air.

In addition, plasma spraying can be carried out by impact of the sprayed particles of ceramic material with the surface of the mandrel rotating at a speed of (20 ÷ 400) rpm during the translational movement of the plasma jet containing sprayed particles on this surface at a speed of (0.06 ÷ 2.50) m / min

When plasma spraying a ceramic material with the same particles having the same chemical composition, size, mass, density and thermal conductivity, their heating is uniform and crystallization conditions are equal, which allows the formation of directional porosity of the product to achieve the required permeability.

In the case of plasma spraying of ceramic material by particles of different chemical composition and different size, the pore shape is random. Pores have a large number of constrictions and extensions along the entire length; on the surface of the pores there are macro-irregularities in the form of protrusions and depressions. The pores are curved and the required permeability of the product is not achieved.

Plasma spraying in the proposed method is carried out by impact of the sprayed particles of ceramic material with the surface of the mandrel at an angle of less than 45 °, excluding zero. In this case, the angle at which the jet of the sprayed material meets the surface of the mandrel creates behind the particles already connected to it spaces that cannot be filled with the sprayed material. These spaces in the form of single pores in each monolayer, when monolayers are sequentially applied, are connected in unidirectional chains and, most likely, in this way form products with channel pores. These pores are through, parallel oriented to each other and inclined to the working surfaces of the product. In this case, the channel pores have an increasing cross section from the initially sprayed monolayers to the subsequent ones during the formation of the product thickness.

When plasma spraying in the present method, each monolayer is formed with a thickness of not more than 0.04 mm Such thin monolayers make it possible to avoid the propagation of transverse cracks accidentally arising in them into neighboring monolayers and over the entire thickness of the product. Thin monolayers make it possible to preserve the surface topography of each monolayer and the formation of solid extended channels from pore spaces free of sprayed material combined over the thickness of the product.

The formation of sprayed layers with a thickness of more than 0.04 mm probably leads to the appearance of cracks in them and their propagation across and along monolayers. This does not allow to obtain the channel porosity of the product, leads to the destruction of its structure.

Thus, the directional unification of the single pores of each monolayer during the deposition of monolayers formed by plasma spraying, allows to obtain ceramic material with an open directional channel porosity corresponding to high permeability of the product. The inventive modes of operations are necessary and sufficient to implement the objectives of the invention.

All the considered features that are different from the features of the prototype, and together with the features common to these objects provide the specified technical result, therefore, the claimed invention is new.

The present invention corresponds to the inventive step. Considering the totality of its essential features, it can be noted that they do not follow explicitly from the prior art. Since the distinguishing features are quantitative features of the invention, such features cannot be considered in isolation from the feature to which they relate, and in isolation from the subject as a whole. Given this, it should be noted that among the objects of the same purpose there is no known technology with the same set of essential features.

The modes of operations of the method, in combination with the special material to which the operations are directed, provide mutual communication and mutual influence of the features of the method, thereby achieving a new technical result.

The invention is illustrated by drawings and photographs showing the structure of the resulting porous permeable ceramic product obtained as a result of the proposed method on a portion of its wall.

The upper boundary of the drawings and photographs is the working surface of the product from the input side of the filtered medium, the lower border is from the output side of the filtered medium.

Figure 1 - Drawing of the structure in longitudinal section of the product, where:

1 - product body;

2 - channel pores.

Figure 2 - Drawing of the structure in the cross section of the product, namely in cross section across the channel pores, where:

1 - product body;

2 - channel pores.

Figure 3 is a photograph of the structure in longitudinal section of the product, magnification × 15,

Where:

1 - bright field, body of the product;

2 - dark stripes, channel pores.

Figure 4 is a photograph of the structure in the cross section of the product, namely in cross section across the channel pores, magnification × 15, where:

1 - bright field, body of the product;

2 - dark areas, outputs of channel pores.

The possibility of implementing the invention and its use in an industrial environment allows us to conclude in accordance with its criterion of "Industrial applicability".

To confirm the possibility of carrying out the invention, we give an example implementation of the method.

The method was carried out as follows.

We took the initial ceramic material for plasma spraying based on aluminum oxide, which was an electrocorundum of grade 25A according to GOST 28818-90, grit F180 according to GOST R 52381-2005, additionally scattered to a grit of 80-63 microns. Standard electrocorundum contained 99.67 wt.% Alumina, the rest was iron, silicon, sodium oxides, was uniform in chemical and physical composition, and was a powder consisting of particles with a narrow range of particle size distribution.

To obtain a porous permeable ceramic product, we used a plasma spraying machine with numerical control type 17B and a plasmatron of the brand EAJI.56.038.00.000.

A mandrel was selected with an outer surface repeating the shape of the desired product. The mandrel was a cylinder of steel 3 and was intended to form a cortical product - a pipe, with a diameter of 200 mm and a length of 1 m.

The mandrel was fixed in the rotation mechanism of the plasma spraying apparatus and brought into rotation around its central longitudinal axis at a speed of 40 rpm. Then, a separating layer of salt, sodium chloride, was deposited on the mandrel to prevent the ceramic material from sticking to it.

After this, the plasmatron was turned on, the plasma jet was formed by air and electrocorundum powder was introduced into it. The spraying parameters were: arc current of the plasma torch (160 ± 5) A, voltage across the arc of the plasma torch (220 ± 10) V.

Then, the spraying distance was chosen — the distance from the plasma torch nozzle to the sprayed surface, which was (200 ± 20) mm.

We also set the spraying angle of the plasma torch — the angle between the direction of the plasma jet along its central axis and the surface of the mandrel, which was 20 ° and determined the angle of impact of the sprayed particles of ceramic material with this surface.

Then the plasmatron was brought into translational motion with a speed of 0.1 m / min along the rotating mandrel and plasma spraying of ceramic material particles onto the surface of the mandrel was carried out by forming monolayers.

The speed of rotation of the surface of the mandrel and the movement of the plasma jet along it was selected so that the thickness of one monolayer in one pass of the plasma torch was 0.04 mm, which was measured on an image obtained by electron microscopy.

Layer-by-layer spraying was carried out until the wall thickness of the manufactured thick-walled product — the cylinder — reached the required value of 10 mm + 2 mm.

After the required wall thickness of the product was set, the spraying process was stopped, the product on the mandrel was cooled with compressed air to a temperature of 100 ° C.

Then the mandrel with the product was lowered into a bath with water, where the salt of the separation layer was dissolved and the product was removed from the mandrel. At the same time, the removed mandrel was suitable for subsequent reuse in the manufacture of other cortical products.

In addition, due to the fact that the obtained product consisted of alumina in the form of a γ-phase with reduced mechanical strength, to increase its operational properties by converting aluminum oxide into a strong α-phase, the product was fired at 1200 ° C for 2 h, while the porosity of the product did not change.

As a result of the implementation of the proposed method within the claimed parameters, a product with an open porosity of 28-29% was obtained.

Under the same conditions, but at different angles of impact of the sprayed particles with the surface of the mandrel, taken from the claimed range, the values of permeability of ceramic products with different open porosity were obtained. The data obtained were listed in table 1. From table 1 it can be seen that at impact angles of 45 ° or more, the open porosity of ceramic products decreases and their permeability sharply decreases.

It should be noted that such an indicator of the product as open porosity (P) was determined due to the fact that it is open pores that communicate with the surface of the porous product and participate in the filtration of the medium, the permeability coefficient (K), which characterizes the permeability of the porous product ( Porous permeable materials: Reference ed. / Under the editorship of Belova S.V. M., Metallurgy, 1987, pp. 15 and 28).

Open porosity (P) was determined by hydrostatic weighing according to GOST 2409-95.

To determine the coefficient of permeability (K) used non-destructive testing method of finished products.

The technique consisted in passing distilled water through a porous wall of a product of known thickness and filtration area (under laminar filtration conditions) and in determining the flow rate of distilled water, as well as the pressure gradient according to the method of URALINTECH CJSC Membranes. Programs and test procedures for prototypes PlK-3 72-01 (03) PM. ” According to the obtained data, the permeability coefficient was calculated (Porous permeable materials: Ref. Ed. / Under the editorship of Belova S.V. M., Metallurgy, 1987, p. 295).

To obtain comparative data of a new method with a method for producing a porous permeable ceramic material used in industry (Journal "Glass and Ceramics", section "Science - Ceramic Production", 2003, No. 3, pp. 17-18, table, example No. 10), the method of forming a ceramic material by pressing was chosen. The method used electrocorundum as a filler and alumina with oxides of magnesium and titanium in an amount of 30 wt.% As a binder. As a result of the method of pressing ceramic material in the product, pore space was obtained from randomly generated and randomly formed pores. From several examples of the implementation of the known method, we select one that is similar in magnitude to the open porosity of 29% in the product obtained in a known manner with the product according to the claimed method.

The implementation methods of both methods and the results are listed in table 2. As can be seen from table 2, the permeability of a porous ceramic product based on aluminum oxide by the proposed method, with the same value of the open porosity of the products, is more than 2 times higher than the known method, which It is connected with the geometry of the structure of open channel porosity of a new ceramic product and is most effective for liquids (melts, solutions) that wet the product.

In addition, due to the monocomponent nature of the ceramic material sprayed in the proposed method, the product has high strength and chemical resistance of aluminum oxide, while its refractory properties correspond to corundum ceramics.

The proposed method is a technology for producing high-purity cortical products with widely controlled open porosity and permeability, suitable for use in chemistry, metallurgy, and many other industries.

Claims (5)

1. A method of producing a porous permeable ceramic product, comprising plasma spraying particles of aluminum oxide-containing ceramic material with a plasma jet onto a removable mandrel by forming monolayers, characterized in that the plasma spraying is carried out by particles of a uniformly sized aluminum oxide-based ceramic material and is carried out by impact spraying particles of ceramic material with a mandrel surface at an angle of less than 45 °, excluding zero, with each monolayer forming a thickness no more than 0.04 mm. 2. The method according to claim 1, characterized in that electrocorundum with a content of the main component of at least 98 wt.% Is used as a ceramic material based on aluminum oxide. 3. The method according to claim 1, characterized in that a material with a narrow range of particle size distribution, namely 80-60 microns, is used as a uniform particle size ceramic material based on aluminum oxide. 4. The method according to claim 1, characterized in that during plasma spraying, a plasma jet with sprayed particles of ceramic material is formed by air. 5. The method according to claim 1, characterized in that the plasma spraying is carried out by impact of the sprayed particles of ceramic material with the surface of the mandrel rotating at a speed of (20 ÷ 400) rpm during the translational movement of the plasma jet containing sprayed particles on this surface at a speed of (0 , 06 ÷ 2.50) m / min.

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