RU2408741C2 - Procedure for production of high porous material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: certain volume of fluid mass containing powder is preliminary mixed with spherical granules. Produced mixture is placed in a mould. There is moulded a work piece of specified height by pressure and/or vibration. The fluid mass is strengthened and spherical granules are removed. Porous system is formed in their place and produced porous material is strengthened. Volume of fluid mass is preliminary determined by moulding a work piece of specified height by pressure and/or vibration in the mould with an upper and lower dies; also, there are used spherical granules and liquid not interacting with material of spherical granules.

EFFECT: production of material of high porosity with specified shape and dimension of pores.

3 cl, 6 ex

Description

The invention relates to highly porous materials, in particular to a method for producing highly porous material. The invention is intended for use at elevated temperatures in aggressive environments, for example, in filters for the purification of gases, solutions and melts, in catalyst carriers or thermal insulation.

Known methods for producing highly porous material from a ceramic powder by applying its suspension in a solution of organic matter to a porous polymeric material (polyurethane), removing excess suspension, drying, removing polymer material without destroying the structure and shape of the preform, which was then sintered according to the conditions known for this powder [ Guzman I.Ya. Some principles of the formation of porous ceramic structures. Properties and application (review). // Glass and ceramics. 2003. No9. - S. 28-31. Antsiferov V.N., Porozova S.E. Highly porous permeable materials based on aluminosilicates. - Perm: Publishing house Perm. state tech. University, 1996. - 207 p.].

The closest in technical essence and the achieved result is a method of producing a highly porous material, including preparing a suspension of a metal powder in an aqueous solution of an organic substance, applying the suspension to a substrate of porous polymeric material, drying the preform, after which the preform is subjected to heat treatment at 160-180 ° C, removal of organic matter by thermal degradation and sintering [USSR Author's Certificate No. 577095, cl. B22F 3/10, 1976]. First, a highly porous permeable polymer (most often polyurethane) matrix is prepared with the required characteristics of the porous frame. To increase the permeability of the frame, additionally remove the walls between the pores (cells). Then a fluid mass (suspension) is prepared from the powder with the addition of a water-soluble organic substance (carboxymethyl cellulose, polyvinyl alcohol, etc.). This fluid mass is used to impregnate the matrix, for example, by immersing it in a suspension. Excess suspension is removed from the pores using vibration or mechanical stress (compression-tension cycles by rolling through rolls, push-ups, or centrifugation). The mass layer applied to the surface of the pores is previously hardened by drying. The formation of cracks in the deposited layer during its drying is excluded by the choice of the type and amount of the organic binder, the particle size distribution of the powder, and the drying regime. Next, the polyurethane matrix is carefully removed (burned out) during heat treatment, and the remaining powder particles are further strengthened, for example, by sintering. By this method, highly porous materials from ceramic powders with a porosity of 70-95% and compressive strength up to 1 MPa were obtained.

Obtaining spherical pores of the same predetermined size in a polyurethane matrix is complex and increases its cost. It is even more difficult to obtain pores in a polyurethane matrix with a given shape (and not only spherical) and size. For maximum permeability of the carcass, it is necessary to additionally remove the partitions between the pores (cells) by etching in aggressive environments. It is difficult to apply an even layer of powder on the pore surface of a polyurethane matrix. After that, the fluid mass is hardened, mainly by drying. To maintain the dried fluid mass of the form of the polyurethane matrix while removing the organic component, heat treatment in the temperature range of the decomposition of the polyurethane matrix must be carried out slowly and in a certain mode. The gases released during the decomposition of polyurethane are toxic and must be trapped and neutralized.

The objective of the invention is to obtain a matrix of spherical easily removable granules, as well as facilitating the filling of pores in this matrix, while ensuring the predominant absence of contacts between spherical granules or the required size of the isthmuses between spherical granules in the matrix.

The problem is achieved by a method of obtaining a material with a highly porous structure, including determining the volume of the powder containing the fluid mass and the height of the workpiece using a liquid that does not interact with the material of the spherical granules and spherical granules that fill the mold using the upper and lower dies, compression and / or vibration, and the upper stamp has holes through which, if necessary, remove excess fluid, mixing the fluid mass and spherical granules, the placement obtained with mixtures in the mold and molding the workpiece using pressure and / or vibration, hardening the fluid by drying, removing spherical granules with the formation in their place of a pore system of a certain shape and size and hardening of the obtained porous material.

Pre-mixing spherical granules with a fluid mass significantly reduces the path of movement of the fluid mass to completely fill the space between the spherical granules in the matrix formed by them (reduces it to a small redistribution of the fluid mass). Upon subsequent removal of the granules, a pore system of a certain shape and size is formed in their place. Pre-mixing facilitates the filling of a fluid mass of the space between the spherical granules in the matrix formed by them, especially when the product is large and when small spherical granules are used.

To obtain a structure in which the spherical pores formed at the site of the removed spherical granules are not predominantly connected by isthmuses (isolated), it is necessary to ensure the predominant absence of contacts between the spherical granules in the manufacture of the workpiece. In this case, when determining the volume of the fluid mass, first pour a liquid that does not interact with the material of the spherical granules into the mold, then pour the granules into this liquid, enter a stamp with an opening to remove excess fluid from above, form a matrix of the required dimensions when using vibration without applying pressure, so that no isthmus formed between the granules. If the granules were small for the desired height of the workpiece, then the granules were refilled, if many were removed from the mold. After obtaining the desired height, the granules fell out and weighed. The volume of fluid mass for a certain mass of spherical granules take more than the volume of fluid defined above. This ensures the separation of the spherical granules and the predominant absence of contacts between them. The greater the excess fluid mass, the thicker, on average, the walls will be between the granules, and then between the pores, but the porosity will also decrease. The material from the previously hardened former fluid mass must contain permeable pores, through which the substance from which the spherical granules are composed is removed.

If it is necessary to ensure the interconnectedness of the pores through the isthmuses, it is first necessary to form the required size of the isthmuses between the spherical granules in the matrix. In this case, first spherical granules are placed in the mold, squeezed between the dies and / or vibration is applied to form a matrix of the required volume (workpiece height) with the required size of the isthmuses between the spherical granules.

The volume of the workpiece is reduced due to more perfect packaging of granules and the formation of isthmuses between them. The size (diameter) of the isthmuses is determined by geometric calculation, section control using a microscope or, more reliable, by the gas permeability of the workpiece. If the diameter of the isthmuses is too large, then the pressing pressure is reduced, but small is increased. So they select the required size of the isthmus between the granules. After that, the workpiece is removed from the mold, weighed (M ₁ ) and measure its height (H ₁ ). If the height of the workpiece must be changed to a height of H ₂ , then the required mass of granules (M _x ) is found by the ratio M ₁ / M _x = H ₁ / H ₂ . Subsequently, a weighted number of granules is placed in the mold and squeezed so that the distance between the dies is equal to the required height of the workpiece. After that, on such a workpiece, the required amount of fluid mass is determined by filling the pores with a liquid that does not interact with the material of the spherical granules, removing its excess through the hole in the upper die and determining the volume of liquid that fills all the pores between the granules. In addition, determine the mass of spherical granules and the height of the workpiece.

The volume of the fluid mass can be taken exactly equal to the volume of fluid defined above, mix the fluid mass with the number (mass) of spherical granules defined above and put into the mold between the dies. A mixture of fluid mass with spherical granules is squeezed between the dies and / or vibration is applied to form a workpiece with the required height (volume). In this case, the size of the isthmuses between the spherical granules will be the same as in the matrix of granules formed for the previous liquid filling.

Example 1. To obtain a polymer (paraffin) matrix used spherical granules with a size of 1.5 mm from paraffin. An α-alumina powder with an average particle size of 2-4 μm was mixed with a solution of polyvinyl alcohol (5 wt.%) In water using a ball mill to obtain a flowing mass (48 vol.% Alumina powder in flowing mass). To determine the volume of fluid mass, first 23 cm ^{3 of} water with 3% polyvinyl alcohol was poured into a mold with a diameter of 36 mm (to improve the wetting of paraffin), then 37.9 g of spherical granules were poured on top. A stamp with a cone-shaped cavity was introduced from above. The top of the cone was a hole with a diameter of 0.5 mm. Excess water was squeezed through this hole with 3% polyvinyl alcohol, which was removed using a syringe. The volume of water remaining in the preform filling all the pores was 18.9 cm ³ . Next, 19.9 cm ^{3 of} flowing ceramic mass was taken to ensure separation of the spherical granules and the absence of contacts between them, and carefully mixed manually with 37.9 g of paraffin spherical granules. The resulting mixture was placed in a mold and a preform was pressed using a pressure of 3 MPa.

To strengthen the ceramic mass, the preform was carefully dried at 40 ° C for 1 day, avoiding the deformation of the matrix. After hardening the fluid mass, the resulting material had permeable pores. After hardening the mass, the sample was placed on a grid placed over a porcelain cup, heated to 80 ° C in an oven and paraffin was melted, which was removed through the permeable pores of the material from the cured fluid mass, drained into the cup and reused. The sample was placed in a furnace with lanthanum chromite heaters and burned in air. The maximum firing temperature was 1700 ° C, the exposure time was 2 hours. After sintering, the sample had pores of about 1.3 mm in size (due to shrinkage of ceramics during sintering), and according to the data on thin sections, contacts between the spherical pores were mostly absent, the total porosity was 70%, compressive strength was 9.1 MPa.

Example 2. A sample was made in accordance with example 1, but they took 23.9 cm ^{3 of} flowing ceramic mass to ensure separation of spherical granules and the absence of contacts between them. After sintering, the sample had pores with a size of about 1.3 mm (due to shrinkage of ceramics during sintering), and according to the study of thin sections, contacts between the spherical pores were mostly absent, the total porosity was 64%, and the compressive strength was 11.2 MPa.

Example 3. To obtain highly porous material used spherical granules 1 mm in size from ammonium nitrate. From a mixture of heat-resistant chemical glass powder (average particle size of about 2-5 μm) and a solution of rubber glue (4 wt.%) In gasoline (technological bond), a flowing mass (54 vol.% Of glass powder) was obtained. To determine the volume of fluid mass, first 14 cm ^{3 of} kerosene was poured into the mold with a cross section of 20 × 30 mm, then 32.8 g of spherical granules were poured on top. Analogously to example 1, the volume of kerosene remaining in the preform was determined, which amounted to 10.8 cm ³ . Next, 12 cm ^{3 of} fluid mass was taken and carefully mixed manually with 32.8 g of spherical granules from urea. The resulting mixture was placed in the mold and, using vibration without the application of additional pressure, in addition to the weight of the upper die, the preform was formed.

To harden the ceramic mass, the preform was dried at room temperature for a day. After hardening the fluid mass, the resulting material had permeable pores. The sample was placed in water at a temperature of 50 ° C to dissolve ammonium nitrate and remove it through the permeable pores of the material from the cured fluid. The billets were placed in a furnace with lanthanum chromite heaters and burned in air. The maximum firing temperature was 850 ° C, the exposure time was 2 hours. After sintering, the sample had pores of about 0.9 mm in size (due to shrinkage of ceramics during sintering), and according to the data on thin sections, contacts between the spherical pores were mostly absent, the total porosity was 71%, compressive strength was 7.3 MPa.

Example 4. To obtain the matrix used spherical granules from (NH ₄ ) ₂ CO ₃ · 2H ₂ O with an average size of 1.8 mm From a tungsten powder (average particle size of about 1-2 μm) a solution of rubber glue (4 wt.%) In gasoline (technological bond) received a flowing mass (53 vol.% Tungsten powder). To determine the volume of fluid mass, first, 83.8 g of spherical granules were poured into a mold with a diameter of 36 mm and, with vibration and a pressure of 10 MPa, a blank of 60 mm in height was pressed using a punch with a cavity in the form of a cone. Then, from below, through the hole, the pores of the preform were filled with kerosene and, analogously to Example 1, the volume necessary to fill all the pores in the preform was determined. The volume of kerosene was 6.1 cm ³ . Then 6.1 cm ^{3 of the} prepared fluid mass was carefully manually mixed with 83.8 g of spherical granules, the mixture was placed in the mold and, under vibration without applying additional pressure, in addition to the weight of the upper die, a blank of 60 mm height was formed. For hardening, the powder mass was dried at room temperature for a day. After hardening the mass, the sample filled with it was placed in a tube furnace, heated to 70 ° C with air passing for sublimation of (NH ₄ ) ₂ CO ₃ • 2H ₂ O. Sublimated and entrained air components were collected in the refrigerator at the outlet of the furnace in the form of (NH ₄ ) ₂ CO ₃ • 2H ₂ O and reused. To prevent the oxidation of tungsten powder, the temporary process binder was removed in wet Furmer gas (a mixture of nitrogen and hydrogen). The final firing was carried out in a vacuum furnace at a temperature of 1750 ° C, the exposure time was 2 hours. After sintering, the sample had highly permeable pores about 1.6 mm in size (due to shrinkage during sintering), open porosity - 91%, compressive strength of the samples was 1, 4 MPa.

Example 5. To obtain highly porous material used spherical granules with a size of 1.2 mm from urea. The flowing mass was made of a mixture consisting of hydroxyapatite with a particle size of 1-2 microns and 15 wt.% Chemically resistant glass with an average particle size of 1-4 microns and paraffin. The volumetric content of the solid phase in the paraffin melt (paraffin slip) is 50%.

To prepare the samples, a mold with a cross section of 20 × 30 mm was used, into which 42.3 g of spherical granules were poured from above and, with vibration and a pressure of 5 MPa, a workpiece 60 mm high was pressed. Analogously to example 3, but using glycerol, its remaining volume in the preform was determined, which amounted to 3.96 cm ³ . Then, 3.96 cm ^{3 of} fluid mass (paraffin slip) was taken and carefully mixed manually with 42.3 g of spherical granules from urea at a temperature of 70 ° C. The resulting mixture was placed in a mold heated to 75 ° C, and an upper die with 8 holes of 0.9 mm was inserted from above. Then, using a pressure of 10 MPa and vibration, a workpiece 60 mm high was pressed.

Excess fluid mass filled holes in the upper die. The fluid mass was hardened by curing paraffin. Granules from urea were removed by dissolution in water at 30 ° C. The obtained sample was calcined in air at a temperature of 1150 ° C for 1 h. After firing, the sample had highly permeable pores 1.1 mm in size (due to shrinkage during firing), porosity of 88%, and compressive strength of 0.4 MPa.

Example 6. To obtain highly porous material used spherical granules of ice with an average size of 1.3 mm A fluid mass (52 vol.% Mullite powder) was obtained from a mixture of mullite powder (average particle size of about 1-2 μm) and a solution of polyurethane adhesive (3 wt.%) In gasoline (technological binder), which was cooled to -1 ° C. Analogously to example 3, from an ice granule in a refrigerated box, a blank of 60 mm high was formed on a mold with a diameter of 36 mm and the volume of fluid mass was determined using kerosene. The volume of kerosene was 6.1 m ³ . Then 6.1 cm ^{3 of the} prepared fluid was carefully manually mixed with 61.04 g of spherical granules, the mixture was placed in a mold cooled to 3 ° C, and a workpiece of 60 mm height was pressed under vibration and a pressure of 5 MPa. To strengthen the fluid mass due to the volatilization of gasoline, it was kept for 3 days at -3 ° C. After hardening the mass, the sample was removed from the freezer, placed in a bed of corundum powder and heated to 15 ° C. After removing water, the preform was dried at 90 ° C. The sample was placed in a furnace with lanthanum chromite heaters and burned in air. The maximum firing temperature was 1750 ° С, the exposure time was 2 h. After sintering, the sample had highly permeable pores of about 1.2 mm in size (due to shrinkage of ceramics during sintering), open porosity - 91%, compressive strength was 0.3 MPa.

Claims (3)

1. A method of obtaining a highly porous material, including preliminary determination of the volume of the powder containing the flowing mass by forming a workpiece of a given height using pressure and / or vibration in a mold containing upper and lower dies, using spherical granules and a liquid that does not interact with spherical material granules, mixing a predetermined volume of a powder containing a flowing mass and spherical granules, placing the resulting mixture in a mold, molding a preform height using pressure and / or vibration, hardening the fluid mass by drying, removing spherical granules with the formation of a pore system in their place and hardening of the obtained porous material. 2. The method according to claim 1, characterized in that when forming a blank containing non-spherical granules in contact with each other, to determine the volume of fluid mass, first fill the mold with a liquid that does not interact with the material of the spherical granules, then spherical granules are poured into the liquid, form a workpiece of a given height by vibration and remove excess fluid through the holes in the upper stamp. 3. The method according to claim 1, characterized in that when forming a workpiece with isthmuses between spherical granules to determine the volume of fluid mass, first spherical granules are poured into the mold and a workpiece of a given height is formed using pressure and vibration, then the mold is filled with liquid not interacting with the material of the spherical granules, ensuring complete filling of the pores, and remove excess fluid through the holes in the upper stamp.