Device and method for preparing special-shaped silicon carbide foam ceramics

Abstract

A device and method for preparing special-shaped silicon carbide foam ceramics, relating to the field of silicon carbide foam ceramics, wherein the slurry attachment device is composed of a bottom plate, a grid cover plate, a top cover, a middle channel, a bottom groove, a track groove, and sponge fragments; the sintering support device is composed of a plurality of ceramic pyramids; the method is as follows: 1) preparing ceramic slurry; 2) then performing surface activation treatment on the sponge; 3) secondly, immersing the treated sponge in the slurry to absorb the slurry; 4) placing the slurry-absorbing sponge in the center of the device, filling the gap between the device and the slurry-absorbing sponge with sponge fragments, and covering it with a cover plate; 5) pressing the cover plate, the slurry-absorbing sponge is compressed to form a slurry-attached sponge; 6) the slurry-attached sponge is dried and placed in a crucible for a low-temperature sintering process, and then rapidly heated after cooling for a second high-temperature sintering process. The method of the present invention effectively improves the phenomenon of uneven slurry distribution and excessive local pore blockage during the slurry attachment and slurry removal process of special-shaped foam ceramics, thereby increasing the porosity of the foam ceramics and improving the performance of the foam ceramics.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon carbide foam ceramics, and particularly relates to a device and method for preparing special-shaped small-pore silicon carbide foam ceramics. Background Art

[0002] Silicon carbide foam ceramics have a special open three-dimensional network skeleton structure, and have excellent properties such as large specific surface area, high porosity, high mechanical strength, low density, high temperature resistance, resistance to metal melt erosion, good thermal shock resistance, corrosion resistance and low thermal conductivity. They are widely used in metallurgy, chemical industry, energy, biology, electronics and environmental protection fields, such as high-temperature metal melt filtration, heat-resistant insulation materials, bioceramic materials, sound absorption and noise reduction materials and catalyst carriers.

[0003] Currently, the most widely used method for preparing foam ceramics is the organic foam impregnation method. This method involves pre-treating a polyurethane sponge template, applying slurry to the sponge, rapidly drying it, and sintering it to form the finished foam ceramic. This method has advantages such as a simple process flow, minimal equipment requirements, ease of operation, low production costs, and high porosity in the finished ceramic product. However, its disadvantages are that traditional slurry removal methods such as plate pressing and roller pressing cannot evenly discharge the slurry from all surfaces during the slurry treatment, and the degree of rebound varies greatly from surface to surface after squeezing the sponge. This is particularly prone to localized pore blockage when producing small-pore foam ceramics, and it is impossible to evenly apply slurry to irregular-shaped sponges. This significantly affects the performance and production efficiency of the finished foam ceramic product.

[0004] During the production process of small-pore foam ceramics, a lot of pore blockage often occurs, which can be solved by adding an appropriate amount of foaming agent. The foaming agent releases a large amount of gas through decomposition and oxidation reactions at high temperature, effectively eliminating some of the pore blockage of the foam ceramics, thereby increasing the porosity of the finished foam ceramics.

[0005] The sintering process of foam ceramics is primarily divided into low-temperature and high-temperature sintering stages. The primary purpose of the low-temperature sintering stage is to decompose and volatilize the polyurethane sponge and the organic binder. If the heating rate is too rapid, the decomposition products will evaporate at a rapid rate, damaging the ceramic body and causing local collapse. This is particularly impactful on small-pore foam ceramics, which can easily cause pulverization. Therefore, the heating rate during the low-temperature sintering stage must be strictly controlled. Foam ceramics will shrink during high-temperature sintering and densification. Uneven temperatures or excessively rapid heating rates during high-temperature sintering can lead to inconsistent shrinkage in different parts of the foam and deformation of the finished ceramic, compromising the strength of the finished foam ceramic. Summary of the Invention

[0006] The first purpose of the present invention is to provide a multifunctional device for preparing foam ceramics, which can achieve uniform sizing of irregular sponge blanks, improve the performance of the finished foam ceramics, and recycle the excess slurry generated during the slurrying process. The second purpose of the present invention is to provide a method that can effectively reduce the pore blockage of irregular small-pore foam ceramics, so that they have a higher porosity and better pore distribution. The third purpose of the present invention is to provide a bracket device that can be used in the high-temperature sintering process of foam ceramics to reduce the phenomenon of excessive local shrinkage of foam ceramics caused by uneven temperature during the high-temperature sintering process.

[0007] The device for preparing special-shaped silicon carbide foam ceramics of the present invention comprises a slurry hanging device and a sintering bracket device, the slurry hanging device is composed of a bottom plate, a grid cover plate, a track groove, a top cover, a middle passage, a bottom groove and sponge fragments; the bottom plate is in the shape of a rectangular parallelepiped, and is provided with a No. 1 channel and four grooves inside, and the sizes of the four grooves match the sizes of the track grooves; the four track grooves match the grid cover plate after being fixed; the lower surface of the upper grid cover plate is connected to the upper surface of the top cover to form an integrated structure, and the upper surface of the lower grid cover plate is connected to the bottom groove to form an integrated structure; the top cover, the middle passage and the bottom groove are combined into a cylindrical shape, and a spatial structure with a No. 2 channel is formed inside; the sponge to be hung is placed in the center position of the No. 2 channel, and the sponge fragments fill the remaining space. The size of the sponge fragments is determined according to the pore size of the hanging sponge. In order to avoid the sponge fragments entering the pores of the hanging sponge during the slurry discharge process, the size of the sponge fragments should be larger than the pore size of the hanging sponge; the sintering bracket device is composed of four ceramic brackets, and the shape of the slurry is a quadrangular pyramid.

[0008] In the above device, the central axes of the bottom plate, the grid cover plate, the top cover, the middle passage and the bottom groove coincide with each other.

[0009] In the above device, the top cover and the bottom tank have the same size and structure.

[0010] In the above device, the upper grid cover plate and the lower grid cover plate are of the same material, shape and size.

[0011] In the above device, the outermost height of the bottom trough is 1.5 to 3 times the innermost height, and the outer diameter of the bottom trough is 1.2 to 1.6 times the inner diameter.

[0012] In the above device, the inner height of the middle passage is 4 to 6 times the inner height of the bottom trough, the outer height of the middle passage is 2 to 2.5 times the outer height of the bottom trough, and the outer diameter of the middle passage is 1.2 to 1.4 times its inner diameter.

[0013] In the above device, the side length of the grid cover is 1.5 to 2 times the diameter of the top cover.

[0014] In the above device, the width of the track composed of the four track grooves is equal to the side length of the grid cover.

[0015] In the above device, the width of the bottom plate is 1.1 to 1.3 times the width of the No. 1 channel, and the height of the bottom plate is 1.5 to 2 times the height of the No. 1 channel.

[0016] In the above device, the height of the ceramic bracket is 1 to 1.2 times the width of the bottom surface, the bottom surface is square, and the material is zirconia.

[0017] In the above device, the base plate and the track groove are made of polyethylene plastic.

[0018] In the above device, the mesh cover is made of stainless steel.

[0019] In the above device, the top cover, the middle channel and the bottom groove are made of mesh nylon, which has a certain flexibility. It can shrink during the extrusion process and allow the slurry to pass through and be discharged during multiple uses.

[0020] In the above device, the sponge fragments are made of polyurethane sponge.

[0021] In the above device, after multiple uses, the excess slurry will flow out from the top to the bottom, leaving a channel at the bottom of the device for slurry recovery and reuse. After the slurry flows out of the lower device, it will not accumulate excessively on the upper device and affect the next slurry application.

[0022] The method for preparing foam ceramics of the present invention is implemented using the apparatus for preparing foam ceramics, and is carried out according to the following scheme:

[0023] (1) The untreated sponge is subjected to alkali corrosion treatment and surface activation treatment to prepare a sponge to be coated with pulp; the sponge has a variety of shapes, and its overall size should be smaller than the spatial structure of the second channel;

[0024] (2) Preparation of slurry: The slurry components are 75 parts by mass of SiC powder, 5 parts by mass of SiO2, 10 parts by mass of kaolin, 5 parts by mass of bentonite, 5 parts by mass of talc, 8 parts by mass of 30% silica sol solution, 0.3 parts by mass of 1% carboxymethyl cellulose, 0.4 parts by mass of 3% polyacrylamide, 1-5 parts by mass of 5% polyvinyl alcohol, 60-70 parts by mass of deionized water, 2-4 parts by mass of foaming agent, and 0.5 parts by mass of n-butanol; all the above components are ball-milled for 12-16 hours and then mixed uniformly to form a slurry;

[0025] (3) Install and fix the four track grooves at the four corners of the bottom plate, connect the upper surface of a grid cover plate to the lower surface of the bottom groove and place it on the bottom plate as a supporting plane, and place the middle channel on top of the bottom groove;

[0026] (4) Immerse the sponge to be coated with slurry in the slurry and squeeze it repeatedly so that the sponge can fully absorb the slurry to form a slurry-absorbing sponge;

[0027] (5) Take out the grouting sponge, place it in the center of the second channel, and use sponge fragments to fill the gaps between the grouting sponge and the top cover, middle channel, and bottom groove;

[0028] (6) Connect the lower surface of a mesh cover plate to the upper surface of the top cover and place it above the middle passage. At this time, due to the presence of four track grooves, the mesh cover plate can move freely up and down in parallel. Move the upper mesh cover plate downward to the position where the top cover and the middle passage are in contact.

[0029] (7) Press the upper grid cover plate downward to 1 / 4 to 1 / 5 of the original height and hold for more than 5 seconds. At this time, all sides of the slurry-absorbing sponge can be compressed to a certain extent, so that part of the slurry is discharged from all sides of the slurry-absorbing sponge. The discharged slurry will remain on the sponge fragments, top cover, middle hole, bottom groove and bottom plate. Move the upper grid cover plate upward. At this time, all sides of the sponge will rebound to a certain extent. The slurry that is not squeezed out will hang on the sponge pore ribs, forming a slurry-hanging sponge with less pore blockage and uniform slurry hanging on all parts of the sponge.

[0030] (8) taking out the slurry sponge and placing it in an oven for drying to form a foam ceramic embryo; placing the foam ceramic embryo in a crucible and using a ceramic bracket to keep the foam ceramic in a suspended state, and covering it with a cover plate; placing the crucible in a muffle furnace for a low-temperature slow sintering, and cooling it to room temperature after sintering to obtain a foam ceramic semi-finished product; then heating it again for a second high-temperature rapid sintering, and cooling it to room temperature after sintering to obtain a foam ceramic finished product.

[0031] In the above step (1), the untreated sponge is a polyurethane sponge with a pore size of 10 to 60 ppi.

[0032] In the above step (1), the untreated sponge is placed in a sodium hydroxide solution with a mass concentration of 15-25%, and heated in a water bath at 50-60°C for 1-4 hours for alkaline solution corrosion treatment. The sponge is taken out and the sodium hydroxide remaining on the sponge surface is rinsed with water, and then dried at 100-120°C for 1-2 hours.

[0033] In the above step (1), the sponge after the corrosion treatment is subjected to surface activation treatment; specifically, it is first placed in a carboxymethyl cellulose solution with a mass concentration of 1%, and heated in a water bath at 40-50°C for 2-4 hours, and then placed in a mixed solution of a polyvinyl alcohol solution with a mass concentration of 5% and a silica sol solution with a mass concentration of 30%, and heated in a water bath at 40-50°C for 2-4 hours. After the sponge is taken out, the excess solution inside the sponge is removed by squeezing, and the sponge is dried at room temperature for 2-4 hours.

[0034] In the above step (2), in order to improve the mechanical strength of the foam ceramic and reduce the pore blocking phenomenon, the proportions of the polyvinyl alcohol solution and the foaming agent need to be set according to the pore size of the sponge to be slurried; when the pore size of the sponge to be slurried is larger, that is, the ppi value is smaller, a larger proportion of the polyvinyl alcohol solution and the foaming agent is used; when the pore size of the sponge to be slurried is smaller, that is, the ppi value is larger, a smaller proportion of the polyvinyl alcohol solution and the foaming agent is used.

[0035] In the above step (2), the main components of the foaming agent are graphite and starch, and the proportions are divided into three types: starch, 20-40% starch + 60-80% graphite, and graphite.

[0036] In the above step (2), the SiC in the slurry component is α-SiC, and the SiC powder is the undersize material obtained by passing SiC through a 400-mesh sieve.

[0037] In the above step (2), the ball milling treatment is to add corundum balls according to a material-ball ratio of 1:3, the rotation speed during ball milling is 300-500 r / min, and the ball milling time is 12-15 h.

[0038] In the above step (5), the size of the sponge pieces is 0.5 to 2.5 cm, which can fully fill the gaps between the slurry sponge and the top cover, the middle channel and the bottom groove.

[0039] In the above step (8), the sponge is dried by placing it in a blast drying oven and setting the drying temperature at 100-140° C. for 2-4 hours.

[0040] In the above step (8), the first low-temperature slow sintering is to heat to 600°C ± 10°C at a heating rate of 1 to 2°C / min and keep the temperature for 2 to 3 hours.

[0041] In the above step (8), the secondary high-temperature rapid sintering is first heated to 1200±10℃ at a heating rate of 4~6℃ / min, then heated to 1450±10℃ at a heating rate of 5~7℃ / min, and kept at 1450±10℃ for 2~3h.

[0042] The porosity of the foam ceramic product is ≥80%.

[0043] The thermal shock resistance cycle number of the foam ceramic product is 13±2 times.

[0044] The finished product rate of the foam ceramics is ≥98%.

[0045] The method of the present invention can discharge excess slurry from all sides of the sponge evenly during the slurry discharge process of slurry sponges of various shapes, effectively reducing the pore blocking phenomenon of foam ceramics and effectively improving the application range of the method for preparing foam ceramics by organic foam impregnation method; the method of the present invention can ensure that the compression and rebound degrees of various parts of the sponge are the same during the sponge discharge process, so that the slurry is evenly distributed inside the sponge, effectively improving the porosity and performance of the foam ceramic product; the method of the present invention can remove part of the pore blocking of the foam ceramic during high-temperature sintering by adding a certain amount of foaming agent to the slurry, thereby further improving the porosity of the foam ceramic; the method of the present invention can recycle excess slurry, effectively reducing the foam The method of the present invention can effectively reduce the local embryonic body collapse phenomenon caused by too fast heating rate and uneven slurry distribution during the production of foam ceramics by uniformly coating the slurry on various parts of the sponge and controlling the heating rates in the low-temperature stage and the high-temperature stage, thereby improving the performance and yield of foam ceramics. The method of the present invention can make various parts of the foam ceramics evenly heated in the high-temperature sintering stage, avoiding the phenomenon of excessive local shrinkage of the foam ceramics due to uneven heating of the foam ceramics during sintering. The device of the present invention can effectively control the slurry discharge amount of different parts of the slurry-coated sponges of various shapes according to needs, and the foam ceramics have a high yield, controllable porosity, and good various performances. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the structure of the device for preparing special-shaped foam ceramics in an embodiment of the present invention;

[0047] Figure 2 Schematic diagram of a device for preparing a high-temperature sintered stent in an embodiment of the present invention;

[0048] Figure 3 Schematic diagram of the cross-sectional structure of the bottom plate in an embodiment of the present invention;

[0049] Figure 4 Schematic diagram of the cross-sectional structure of the track groove in an embodiment of the present invention;

[0050] Figure 5 Schematic diagram of the cross-sectional structure of the grid cover in an embodiment of the present invention;

[0051] Figure 6 Schematic diagram of the cross-sectional structure of the top cover and bottom trough in an embodiment of the present invention;

[0052] Figure 7 Schematic diagram of the cross-sectional structure of the embodiment of the present invention;

[0053] Figure 8 A partial schematic diagram of the finished foam ceramic product in Example 3 of the present invention;

[0054] Figure 9 This is an SEM image of the finished foam ceramic product in Example 3 of the present invention;

[0055] In the figure, 1-bottom plate, 2-grid cover plate, 3-track groove, 4-top cover, 5-middle channel, 6-bottom groove, 7-sponge fragments, 8-channel No. 1, 9-channel No. 2, 10-slurry sponge. DETAILED DESCRIPTION

[0056] The SiC, SiO2, kaolin, bentonite, talc, graphite and starch used in the examples of the present invention are commercially available products.

[0057] The carboxymethyl cellulose, polyacrylamide, polyvinyl alcohol solution and silica sol solution with a mass concentration of 30% used in the examples of the present invention are commercially available products.

[0058] The four track grooves in the embodiment of the present invention provide track support for the vertical parallel movement of the grid cover, ensuring that the top and bottom surfaces of the slurry sponge are evenly stressed during the pressing process.

[0059] In the embodiment of the present invention, the sponge fragments are used to fill the gaps to ensure that the various surfaces of the sponge are evenly stressed during the sponge slurry discharge process, and the discharged slurry can be separated from the sponge in a timely manner.

[0060] The ceramic bracket in the embodiment of the present invention is used to keep the foam ceramic in a suspended state during the high-temperature sintering stage, thereby reducing the phenomenon of excessive local shrinkage of the foam ceramic during the high-temperature sintering.

[0061] The polyvinyl alcohol solution in the embodiment of the present invention is used to change the viscosity of the slurry so as to perform slurry treatment on sponges with different pore sizes.

[0062] The graphite and starch in the embodiment of the present invention are used to eliminate partial pore blockage of foam ceramics with different pore diameters during high-temperature sintering.

[0063] The thermal shock cycle test in the embodiments of the present invention is conducted in accordance with the standard GB 25139-2010-T “Foam ceramic filter for casting”.

[0064] The material of the ceramic bracket in the embodiment of the present invention is zirconium oxide.

[0065] In the embodiment of the present invention, the silicon carbide powder is the undersize material obtained by passing silicon carbide through a 400-mesh sieve.

[0066] In the embodiment of the present invention, the sponge is dried by placing it in a blast drying oven and drying it at a temperature of 100 to 140° C. for 2 to 4 hours.

[0067] The foaming agent used in the embodiment of the present invention is a mixture of 30% starch and 70% graphite.

[0068] Example 1

[0069] A device for preparing special-shaped silicon carbide foam ceramics, the structure of which is as follows Figure 1-7 As shown, it includes a slurry hanging device and a bracket device.

[0070] The cross-sectional structure of the slurry hanging device is as follows: Figure 1 As shown, it consists of a bottom plate 1, a grid cover plate 2, a track groove 3, a top cover 4, a middle passage 5, a bottom groove 6 and sponge fragments 7; the bottom plate 1 is in the shape of a rectangular parallelepiped, wherein the upper and lower surfaces are square, and a No. 1 channel 8 and four grooves are provided inside; the four track grooves 3 match the structure of the bottom plate 1 and are fixed to the four corners of the bottom plate respectively, providing track support for the up and down parallel movement of the grid cover plate 2; the upper and lower surfaces of the two grid cover plates 2 are both square, the size of the grid cover plates 2 matches the size of the four track grooves, and the upper grid cover plate 2 moves up and down parallel to the lower grid cover plate 2; the upper surface of the top cover 4 is connected to the upper grid cover plate 2, and the lower surface of the bottom groove 6 is connected to the lower grid cover plate 2; the sizes of the top cover 4, the middle passage 5 and the bottom groove 6 match, and the combined shape is a cylinder, forming a spatial structure of a No. 2 channel 9 inside;

[0071] The cross-sectional structure of the ceramic stent is as follows Figure 2 As shown, the cross-sectional structure of the bottom plate 1 is as follows Figure 3 As shown, the cross-sectional structure of the track groove 4 is as follows Figure 4 As shown, the cross-sectional structure of the grid cover 2 is as follows Figure 5 As shown, the cross-sectional structure of the top cover 4 and the bottom groove 6 is as follows Figure 6 As shown, the cross-sectional structure of the middle pass is as follows Figure 7 As shown;

[0072] The bottom plate 1 and the track groove 3 are made of polyethylene plastic, the mesh cover 2 is made of stainless steel, the top cover 4, the middle channel 5 and the bottom groove 6 are made of mesh nylon, and the sponge fragments 7 are made of polyurethane sponge;

[0073] The central axes of the bottom plate 1, the grid cover 2, the top cover 4, the bottom groove 6 and the middle passage 5 coincide with each other;

[0074] The top cover 4 and the bottom groove 6 have the same structure. The outermost height of the bottom groove 6 is twice the innermost height, and the outer diameter of the bottom groove 6 is 1.5 times the inner diameter.

[0075] The inner height of the middle hole 5 is 5 times the inner height of the bottom groove 6, the outer height of the middle hole 5 is 2.3 times the outer height of the bottom groove 6, and the outer diameter of the middle hole 5 is 1.2 times the inner diameter;

[0076] The side length of the grid cover 2 is 1.6 times the diameter of the top cover 4;

[0077] The width of the track formed by the four track grooves 3 is equal to the side length of the grid cover 2;

[0078] The length of the bottom plate 1 is 1.2 times the length of the first channel 8, and the height of the bottom plate 1 is 1.5 times the height of the first channel 8;

[0079] The height of the second channel 9 is 1.2 times the inner height of the middle channel 5, and the outer diameter of the middle channel 5 is 1.2 times the outer diameter of the second channel 9;

[0080] The height of the ceramic bracket is equal to the width of its bottom surface, and the bottom surface is square.

[0081] A method for preparing special-shaped silicon carbide foam ceramics is implemented using the above-mentioned device, and the specific operating steps include:

[0082] Prepare an untreated sponge in the shape of a cuboid, 9cm long, 9cm wide, and 10cm high. The top and bottom are square, and the center has a groove, 3cm long, 9cm wide, and 3cm high. The overall dimensions are smaller than the space in channel 9.

[0083] The untreated sponge is subjected to alkali corrosion treatment and surface activation treatment to prepare a sponge to be slurried; the sponge to be slurried is a polyurethane sponge with a pore size of 30ppi; the alkali corrosion treatment of the sponge is performed by placing the sponge in a sodium hydroxide solution with a mass concentration of 20%, heating it in a water bath at 55°C for 2.5 hours, taking out the sponge for rinsing, and drying it at 110°C for 1.5 hours; the surface activation treatment of the sponge is performed by first placing the sponge in a carboxymethyl cellulose solution with a mass concentration of 1% and heating it in a water bath at 45°C for 3 hours, and then placing it in a mixed solution of a polyvinyl alcohol solution with a mass concentration of 5% and a silica sol solution with a mass concentration of 30%, heating it in a water bath at 45°C for 3 hours, taking out the sponge to remove the excess solution inside the sponge by squeezing, and drying it at room temperature for 3 hours;

[0084] The slurry components are 75 parts by mass of SiC powder, 5 parts by mass of SiO2, 10 parts by mass of kaolin, 5 parts by mass of bentonite, 5 parts by mass of talc, 8 parts by mass of 30% silica sol solution, 0.3 parts by mass of 1% carboxymethyl cellulose, 0.4 parts by mass of 3% polyacrylamide, 3 parts by mass of 5% polyvinyl alcohol, 65 parts by mass of deionized water, 3 parts by mass of a foaming agent (30% starch + 70% graphite), and 0.5 parts by mass of n-butanol. After mixing all the above components, corundum balls are added according to a material-to-ball ratio of 1:3, and the slurry is prepared by ball milling at 400 r / min for 14 hours. The SiC is α-SiC, and the SiC powder is the undersize material of SiC passed through a 400-mesh sieve.

[0085] Immerse the treated sponge in the slurry and squeeze it repeatedly to allow the sponge to fully absorb the slurry to form a slurry-absorbing sponge;

[0086] Take out the slurry absorbing sponge, place it in the center of the second channel 9, and fill the gap between the slurry absorbing sponge and the top cover 4, the middle channel 5 and the bottom groove 6 with sponge fragments 7. The size of the sponge fragments 7 is 1.5±0.1 cm.

[0087] Press the upper grid cover 2 to 1 / 4 to 1 / 5 of the original height and hold for more than 5 seconds; at this time, all sides of the slurry absorbing sponge can be compressed to a certain extent, so that part of the slurry is discharged from all sides of the slurry absorbing sponge; move the upper grid cover 2 upward to the original height, and the slurry that is not squeezed out will be hung on the sponge pore ribs, forming a slurry sponge 10 with less pore blockage and uniform slurry hanging on all parts of the sponge;

[0088] The slurry sponge 10 is taken out and placed in an oven, and dried at 120±5℃ for 3h to form a foam ceramic embryo; the foam ceramic is placed in a crucible and a ceramic bracket is used to keep the foam ceramic in a suspended state, and then a cover plate is covered; the crucible is placed in a muffle furnace for a low-temperature slow sintering, and after sintering, it is cooled to room temperature with the furnace to obtain a foam ceramic semi-finished product; the foam ceramic semi-finished product is placed in a muffle furnace for a second high-temperature rapid sintering, and after sintering, it is cooled to room temperature with the furnace to obtain a foam ceramic finished product; specifically, the first low-temperature slow sintering is to heat to 600℃±10℃ at a heating rate of 1.5℃ / h and keep warm for 2h; the second high-temperature rapid sintering is to first heat to 1200±10℃ at a heating rate of 5℃ / min, and then heat to 1450±10℃ at a heating rate of 6℃ / min, and keep warm at 1450±10℃ for 2.5h.

[0089] The strength and porosity of each part of the special-shaped foam ceramic are uniform; the porosity of the foam ceramic is 87%; the number of thermal shock resistance cycles of the foam ceramic is 13±2 times; and the foam ceramic finished product rate is 98%.

[0090] Example 2

[0091] The structure and method of the apparatus for preparing foam ceramics are the same as those in Example 1, except that:

[0092] (1) The shape and size of the sponge to be treated are the same as those in Example 1, and the pore size is 10 ppi; the alkali solution corrosion treatment is to place the sponge to be treated in a sodium hydroxide solution with a mass concentration of 25%, heat it in a water bath at 60°C for 4 hours, take out the sponge, rinse it, and dry it at 120°C for 2 hours; the surface activation treatment is to place the sponge in a mixed solution of a carboxymethyl cellulose solution with a mass concentration of 1%, a polyvinyl alcohol solution with a mass concentration of 5%, and a silica sol solution with a mass concentration of 30%, respectively, and heat them in a water bath at 50°C for 4 hours. After taking out the sponge, the excess solution is removed and the sponge is dried at room temperature for 4 hours;

[0093] (2) The size of the sponge pieces is 2 ± 0.1 cm, which is used to fill the gap between the slurry sponge and the middle hole;

[0094] (3) The amount of polyvinyl alcohol added to the slurry component is 5 parts;

[0095] (4) The amount of foaming agent (30% starch + 70% graphite) added to the slurry component is 4 parts;

[0096] (5) The amount of deionized water added to the slurry component is 60 parts;

[0097] (6) Ball milling treatment was performed at 300 r / min for 12 h;

[0098] (7) The sponge is dried at 140℃±5℃ for 4h;

[0099] (8) Low-temperature slow sintering is heating to 600±10℃ at a heating rate of 2℃ / min and keeping it warm for 3h; high-temperature fast sintering is first heating to 1200±10℃ at a heating rate of 6℃ / min, then heating to 1450±10℃ at a heating rate of 7℃ / min, and keeping it warm at this temperature for 3h;

[0100] (9) The strength and porosity of each part of the special-shaped foam ceramic are uniform; the porosity of the foam ceramic is 85%; the finished product rate of the foam ceramic is 99%.

[0101] Example 3

[0102] The structure and method of the apparatus for preparing foam ceramics are the same as those in Example 1, except that:

[0103] (1) The shape and size of the sponge to be treated are the same as those in Example 1, and the pore size is 60 ppi; the alkali solution corrosion treatment is to place the sponge to be treated in a sodium hydroxide solution with a mass concentration of 15%, heat it in a water bath at 50°C for 1 hour, take out the sponge, rinse it, and dry it at 100°C for 1 hour; the surface activation treatment is to place the sponge in a mixed solution of a carboxymethyl cellulose solution with a mass concentration of 1%, a polyvinyl alcohol solution with a mass concentration of 5%, and a silica sol solution with a mass concentration of 30%, respectively, and heat them in a water bath at 40°C for 2 hours, take out the sponge, drain the excess solution, and dry it at room temperature for 2 hours;

[0104] (2) The size of the sponge fragments is 1 ± 0.1 cm, and they are used to fill the gap between the sponge and the middle hole;

[0105] (3) The amount of polyvinyl alcohol added to the slurry component is 1 part;

[0106] (4) The amount of foaming agent (30% starch + 70% graphite) added to the slurry component is 2 parts;

[0107] (5) The amount of deionized water added to the slurry component is 70 parts;

[0108] (6) Ball milling treatment was performed at 500 r / min for 15 h;

[0109] (7) The sponge is dried at 100℃±5℃ for 2h;

[0110] (8) Low-temperature slow sintering is heating to 600±10℃ at a heating rate of 1℃ / min and keeping it warm for 2h; high-temperature fast sintering is first heating to 1200±10℃ at a heating rate of 4℃ / min, then heating to 1450±10℃ at a heating rate of 5℃ / min, and keeping it warm at this temperature for 2h;

[0111] (9) The strength and porosity of each part of the special-shaped foam ceramic are uniform; the porosity of the foam ceramic is 89%; the finished product rate of the foam ceramic is 98%.

[0112] Figure 8 A partial schematic diagram of the finished foam ceramic product in Example 3 of the present invention; Figure 9 This is an SEM image of the finished foam ceramic product in Example 3 of the present invention.

Claims

1. A device for preparing special-shaped silicon carbide foam ceramics, characterized in that: The invention mainly consists of a slurry hanging device and a sintering support device, wherein the slurry hanging device consists of a bottom plate (1), a grid cover plate (2), a track groove (3), a top cover (4), a middle passage (5), a bottom groove (6) and sponge fragments (7); a No. 1 channel (8) and four grooves are provided inside the bottom plate (1), and the sizes of the four grooves match the sizes of the track groove (3); the four track grooves (3) match the grid cover plate (2) after being fixed, the lower surface of the upper grid cover plate (2) is connected to the upper surface of the top cover (4) to form an integrated structure, and the upper surface of the lower grid cover plate (2) is connected to the bottom groove (6) to form an integrated structure; the top cover (4), the middle passage (5) and the bottom groove (6) are combined into a space structure with an outer shape of a cylinder, and a No. 2 channel (9) is formed inside; the sponge to be slurried is placed in the formed No. 2 channel (9), and the sponge fragments (7) fill the remaining space; the sintering support device consists of four ceramic supports, and the outer shape is a quadrangular pyramid; The top cover (4), the middle channel (5) and the bottom groove (6) are made of a mesh nylon material, which can shrink during the extrusion process and allow the slurry to pass through and be discharged; The size of the sponge fragments (7) is larger than the pore size of the sponge to be coated with slurry, and is used to fill the gaps between the sponge to be coated with slurry and the top cover (4), the middle channel (5), and the bottom groove (6) to ensure that the force on each surface of the sponge is uniform during slurry discharge.

2. The device for preparing special-shaped silicon carbide foam ceramics according to claim 1, characterized in that: The inner height of the middle hole (5) is 4 to 6 times the inner height of the bottom groove (6), the outer height of the middle hole (5) is 2 to 2.5 times the outer height of the bottom groove (6), and the outer diameter of the middle hole (5) is 1.2 to 1.4 times the inner diameter.

3. The device for preparing special-shaped silicon carbide foam ceramics according to claim 1, characterized in that: The outermost height of the bottom groove (6) is 1.5 to 3 times the innermost height, and the outer diameter of the bottom groove (6) is 1.2 to 1.6 times the inner diameter.

4. The device for preparing special-shaped silicon carbide foam ceramics according to claim 1, characterized in that: The width of the bottom plate (1) is 1.1 to 1.3 times the width of the first channel (8), and the height of the bottom plate (1) is 1.5 to 2 times the height of the first channel (8); the height of the ceramic bracket is 1 to 1.2 times the width of the bottom surface, and the bottom surface is square; the material is zirconia.

5. A method for preparing special-shaped silicon carbide foam ceramics, characterized in that: The device according to any one of claims 1 to 4 comprises the following steps: (1) Preparation of slurry: The slurry components are 75 parts by mass of SiC powder, 5 parts by mass of SiO2, 10 parts by mass of kaolin, 5 parts by mass of bentonite, 5 parts by mass of talc, 8 parts by mass of 30% silica sol solution, 0.3 parts by mass of 1% carboxymethyl cellulose, 0.4 parts by mass of 3% polyacrylamide, 1-5 parts by mass of 5% polyvinyl alcohol, 60-70 parts by mass of deionized water, 2-4 parts by mass of foaming agent, and 0.5 parts by mass of n-butanol; all the components are ball-milled and mixed to form a slurry; (2) subjecting the sponge to be coated with slurry to surface alkali corrosion treatment and surface activation treatment, and then drying; (3) Immerse the sponge to be coated with slurry in the slurry, and squeeze it repeatedly to make the sponge absorb the slurry to form a slurry-absorbing sponge; place the slurry-absorbing sponge in the center of the second channel (9), and use sponge fragments (7) to fill the gaps between the slurry-absorbing sponge and the top cover (4), the middle channel (5), and the bottom groove (6); (4) Press the upper grid cover (2) downward to 1 / 4 to 1 / 5 of the original height. At this time, part of the slurry is squeezed out through the various surfaces of the sponge and remains on the sponge fragments (7), the top cover (4), the middle hole (5) and the bottom groove (6). The excess slurry flows into the bottom plate (1) to achieve slurry recycling. The slurry will not accumulate on the surface of the sponge during the rebound process, thereby effectively reducing the pore blockage phenomenon on the sponge surface and forming a slurry-hanging sponge (10); (5) taking out the slurry sponge (10) and placing it in an oven for drying to remove moisture to form a foam ceramic embryo; placing the foam ceramic embryo on a ceramic bracket in a crucible; placing the crucible in a muffle furnace for a low-temperature slow sintering, and cooling it to room temperature with the furnace to obtain a foam ceramic semi-finished product; then performing a second high-temperature rapid sintering, and cooling it to room temperature with the furnace after sintering to obtain a foam ceramic finished product.

6. The method for preparing special-shaped silicon carbide foam ceramics according to claim 5, characterized in that: In the step (1), the main components of the foaming agent are graphite and starch, and the proportions are divided into three types: starch, 20-40% starch + 60-80% graphite, and graphite.

7. The method for preparing special-shaped silicon carbide foam ceramics according to claim 5, characterized in that: The SiC in the slurry component of step (1) is α-SiC, and the SiC powder is the undersize material obtained by passing SiC through a 400-mesh sieve; in step (2), the sponge to be coated with slurry is a polyurethane sponge with a pore size of 10 to 60 ppi.

8. The method for preparing special-shaped silicon carbide foam ceramics according to claim 5, characterized in that: In the step (2), the untreated sponge is placed in a sodium hydroxide solution with a mass concentration of 15-25%, and heated in a water bath at 50-60°C for 1-4 hours for alkali solution corrosion treatment, the sponge is taken out and the sodium hydroxide remaining on the sponge surface is rinsed with water, and then dried at 100-120°C for 1-2 hours; the sponge after the alkali solution corrosion treatment is subjected to surface activation treatment; specifically, firstly placed in a carboxymethyl cellulose solution with a mass concentration of 1%, heated in a water bath at 40-50°C for 2-4 hours, and then placed in a mixed solution of a polyvinyl alcohol solution with a mass concentration of 5% and a silica sol solution with a mass concentration of 30%, heated in a water bath at 40-50°C for 2-4 hours, and after taking out the sponge, the excess solution inside the sponge is removed by squeezing, and then dried at room temperature for 2-4 hours.

9. The method for preparing special-shaped silicon carbide foam ceramics according to claim 5, characterized in that: In the step (5), the low-temperature slow sintering is performed by heating to 600°C±10°C at a heating rate of 1-2°C / min and keeping the temperature for 2-3 hours.

10. The method for preparing special-shaped silicon carbide foam ceramics according to claim 5, characterized in that: In the step (5), the secondary high-temperature rapid sintering is first heated to 1200±10°C at a heating rate of 4-6°C / min, then heated to 1450±10°C at a heating rate of 5-7°C / min, and kept at 1450±10°C for 2-3 hours.

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