CN112811924B - Silicon nitride reinforced porous spinel-carbon ceramic filter and preparation method thereof - Google Patents

Silicon nitride reinforced porous spinel-carbon ceramic filter and preparation method thereof Download PDF

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CN112811924B
CN112811924B CN202110023635.3A CN202110023635A CN112811924B CN 112811924 B CN112811924 B CN 112811924B CN 202110023635 A CN202110023635 A CN 202110023635A CN 112811924 B CN112811924 B CN 112811924B
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porous spinel
fine powder
ceramic filter
silicon nitride
ceramic
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CN112811924A (en
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鄢文
鄢俊杰
梁雄
李亚伟
李楠
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Wuhan University of Science and Engineering WUSE
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Wuhan University of Science and Engineering WUSE
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Abstract

The invention relates to a silicon nitride reinforced porous spinel-carbon ceramic filter and a preparation method thereof. The technical scheme is as follows: the preparation method comprises the steps of taking modified porous spinel ceramic fine powder, modified coal tar pitch fine powder, elemental silicon powder and sodium carboxymethylcellulose as raw materials, mixing, adding alumina sol, a water reducing agent, a defoaming agent and deionized water, and stirring to obtain ceramic slurry with thixotropy (ceramic slurry for short). Immersing the pretreated polyurethane foam into the ceramic slurry, taking out, removing the redundant ceramic slurry, maintaining, drying, and reacting in N 2 Raising the temperature to 1150-1250 ℃ in the atmosphere, and preserving the heat. Soaking the obtained pre-sintered body of the porous spinel-carbon ceramic filter in ceramic slurry, standing in vacuum, centrifuging, and drying; in N 2 Heating to 500-600 ℃ in the atmosphere, preserving heat, heating to 1350-1450 ℃, and preserving heat to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter. The product prepared by the invention has high strength, good thermal shock stability and excellent filtration efficiency.

Description

Silicon nitride reinforced porous spinel-carbon ceramic filter and preparation method thereof
Technical Field
The invention belongs to the technical field of porous ceramic filters. In particular to a silicon nitride reinforced porous spinel-carbon ceramic filter and a preparation method thereof.
Background
The non-metallic inclusion is one of the important factors influencing the steel quality, and the removal of the inclusion and the improvement of the purity of molten steel are important ways for improving the steel quality. For example, in the smelting of ultra-low carbon steel, molten steel needs to be subjected to the processes of deoxidation, desulfurization, inclusion removal and the like, so that high-quality molten steel meeting the requirements is obtained. Therefore, the porous ceramic filter with high thermal shock stability and high filtering efficiency is introduced in the molten steel refining or casting link to filter the impurities in the molten steel, so that the method is an effective way for purifying the molten steel and improving the steel quality.
At present, ceramic filters for purifying molten steel have been reported. For example, in the patent technology of 'preparation method of alumina porous foamed ceramic filter' (CN 103848642A), industrial alumina micro powder, bauxite, bentonite and the like are used as raw materials, polyurethane sponge foam is used as a template to prepare the alumina porous foamed ceramic filter, but the raw materials used in the technology are all compact powder, the surface of a filter framework is compact, the adsorption capacity to impurities is limited, particularly small-size impurities, the filtering effect is poor, the framework has weak alkaline slag corrosion resistance, and the service life is limited. Also, for example, literature techniques (Nixin, et al. Addition of V) 2 O 5 For SiC-Al 2 O 3 The influence of the performance of the foamed ceramics, 2018.53 (4): 261-264), adopts industrial silicon carbide, electric white corundum powder and the like as raw materials and soft polyurethane sponge cylinders as a template to prepare SiC-Al 2 O 3 The foamed ceramic, on one hand, silicon carbide is a non-oxide, has poor affinity and weak interaction with oxide inclusions in molten steel, and on the other hand, the skeleton surface is compact, the adsorption capacity to the inclusions is weak, and the filtration efficiency needs to be improved. For another example, in the patent of "method for preparing zirconia alumina porous ceramic filter" (CN 1548214A), zirconia alumina powder and zircon powder are used as raw materials, and an organic foam impregnation method is used to prepare a zirconia alumina porous ceramic filter, but zirconia has strong high-temperature chemical stabilityThe zirconium oxide has weak interaction with impurities, poor chemical adsorption capacity to the impurities and limited filtering effect, and zirconium oxide is easy to lose a stabilizer when contacting with slag, and a product can be damaged due to volume change generated by crystal form conversion. Also, for example, in the literature technology (Yuerei, et al. Influence of solid content of slurry on microstructure of CaO-based foamed ceramics prepared by organic foam impregnation method, refractory material, 2019.53 (5): 342-347), although a CaO-based foamed ceramic is prepared by using calcium hydroxide, zirconium oxide and the like as raw materials and adopting the organic foam impregnation method, the product is limited in preparation, transportation and use due to the characteristic of easy hydration of CaO, and the skeleton strength of the product needs to be improved.
In summary, the existing porous ceramic filter technology for molten steel still has several problems: firstly, the filter framework has low strength, poor thermal shock stability and short service life; secondly, the surface of the filter framework is compact, the interaction with the non-metallic inclusions in the molten steel is weak, the adsorption capacity to the inclusions is limited, and the filtering effect is poor.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and aims to provide a preparation method of a silicon nitride reinforced porous spinel-carbon ceramic filter, and the silicon nitride reinforced porous spinel-carbon ceramic filter prepared by the method has high strength, good thermal shock stability and excellent filtering efficiency and is suitable for filtering ultra-low carbon molten steel.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 380-550 ℃ at the speed of 2.5-5 ℃/min, preserving the heat for 2-3.5 hours, and cooling to obtain the fine porous alumina agglomerate powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.35-0.4, and stirring for 1.5-3.5 hours to obtain mixed powder.
Step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 150-180 MPa, and drying the molded blank at the temperature of 110-150 ℃ for 12-24 hours; then heating to 1600-1680 ℃ at the speed of 2-4 ℃/min, preserving the temperature for 3-5 hours, and cooling to obtain the porous spinel ceramic with the nano aperture.
The nanoporous porous spinel ceramic: the apparent porosity is 23-32%, and the volume density is 2.5-2.83 g/cm 3 The average pore diameter is 500-980 nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 1.5-5.5, and stirring for 5-10 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 20-36, vacuumizing to 2-2.9 kPa, adding the modified solution, stirring for 15-30 minutes, closing a vacuumizing system, and naturally drying for 36-48 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 1-3 hours, taking out, washing with deionized water for 4-6 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam has a specification of 10 to 20ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter presintering body
Immersing the pretreated polyurethane foam into thixotropic ceramic slurry for 15-20 minutes, taking out, removing redundant thixotropic ceramic slurry by using a double-roller machine, curing for 10-20 hours at room temperature, and drying for 14-26 hours at 90-120 ℃; then theIn N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And (3) under the condition of Pa atmosphere, heating to 1150-1250 ℃ at the speed of 1-1.5 ℃/min, preserving the heat for 2-4 hours, and cooling to obtain the porous spinel-carbon ceramic filter pre-sintered body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
And (3) dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 1.9-3 kPa, standing for 10-25 minutes, taking out, and then treating in a centrifuge at the rotating speed of 220-480 r/min for 3-8 minutes to obtain a secondary slurry-coated porous spinel-carbon ceramic filter blank. Naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 24-46 hours, and then drying for 12-24 hours at the temperature of 90-120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 Under the atmosphere condition of Pa, firstly heating to 500-600 ℃ at the speed of 1-2 ℃/min, preserving heat for 30-60 minutes, then heating to 1350-1450 ℃ at the speed of 3-5 ℃/min, preserving heat for 3-5 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 and the step 5 is the same, and the preparation method of the thixotropic ceramic slurry comprises the following steps: 89.5-96.5 wt% of the modified porous spinel ceramic fine powder, 1-3 wt% of the modified coal tar pitch fine powder, 2-5 wt% of simple substance silicon powder and 0.5-2.5 wt% of sodium carboxymethyl cellulose are used as raw materials, the raw materials are firstly placed in a mixer to be mixed for 1.5-3 hours, then alumina sol, 0.05-0.15 wt% of water reducing agent, 0.3-1.2 wt% of defoaming agent and 22-40 wt% of deionized water which account for 2-5 wt% of the raw materials are added, and stirring is carried out for 40-60 minutes, so as to obtain ceramic slurry with thixotropy.
The particle size of the aluminum hydroxide fine powder is less than 44 mu m; al of the aluminum hydroxide fine powder 2 O 3 The content is 64 to 66 weight percent.
The particle size of the light-burned magnesite micro powder is less than 2 mu m; the MgO content of the light-burned magnesite micro powder is more than or equal to 95wt%.
The catalyst is one of ferric nitrate nonahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate; fe (NO) in the ferric nitrate nonahydrate 3 ) 3 ·9H 2 The content of O is more than or equal to 98wt percent, and Co (NO) in the cobalt nitrate hexahydrate 3 ) 2 ·6H 2 The content of O is more than or equal to 98wt percent, and the Ni (NO) in the nickel nitrate hexahydrate 3 ) 2 ·6H 2 The content of O is more than or equal to 98wt percent.
The concentration of the NaOH solution is 6-8 mol/L.
The particle size of the modified coal tar pitch fine powder is less than 74 mu m; the C content of the modified coal tar pitch fine powder is 70-80 wt%.
The particle size of the elemental silicon powder is less than 45 μm; the Si content of the elemental silicon powder is more than or equal to 98wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 20-45 wt%.
The defoaming agent is dimethyl silicone oil or polyether modified silicone oil.
The water reducing agent is sodium lignosulphonate or polycarboxylate; the lignin content in the sodium lignosulphonate is 45-60 wt%, and the side chain molecular weight in the polycarboxylate is 700-2300.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following positive effects:
(1) The invention adopts the modified porous spinel ceramic fine powder with nano-aperture as the raw material, thereby improving the strength of the product.
Compared with compact raw materials, the modified porous spinel ceramic fine powder has a porous structure with through nanometer apertures, and is beneficial to improving the strength of products.
Firstly, the modified porous spinel ceramic fine powder has a rough surface, the contact area of ceramic slurry with thixotropy and a polyurethane foam template is increased, the adhesion of the ceramic slurry with thixotropy is facilitated, the slurry coating performance is improved, the thickness of a framework is increased, and the strength of a product is improved.
Secondly, in the existing carbon-containing material, the surfaces of oxide particles are relatively smooth, the sintering degree between the oxide particles and carbon is weak, and good neck connection is difficult to form; compared with the existing carbon-containing material, the modified porous spinel ceramic fine powder is adopted, the surfaces of fine powder particles are rough, the contact areas among the modified porous spinel ceramic fine powder and between the modified porous spinel ceramic fine powder and the modified coal tar pitch powder are increased, the material transmission among all microparticles and the growth of sintering necks are promoted in the high-temperature sintering process, a sawtooth-meshed interface is formed among the particles, and the strength of a product is further improved.
(2) The silicon nitride whiskers with special distribution are generated in the product obtained by the invention, the thermal shock stability of the product is improved, and the strength of the product is further improved.
In the existing silicon nitride whisker reinforced materials, silicon nitride whiskers can only be formed in gaps of matrix powder, and have poor interface compatibility with oxide materials, so that the further improvement of the matrix strength and the thermal shock stability is limited; the modified porous spinel ceramic fine powder adopted by the invention has more pores and catalysts in the interior and on the surface, can provide a large number of landing sites for the growth of silicon nitride whiskers, silicon nitride whiskers can be generated in situ in the pores under the action of the catalysts, and silicon nitride whiskers can be generated in the pores among the micro particles, finally interlaced silicon nitride whiskers are formed among the modified porous spinel ceramic fine powder and between the modified porous spinel ceramic fine powder and the modified coal tar pitch powder, the sawtooth-shaped occlusion interfaces among the particles are further enhanced, the defect of poor interface compatibility of the existing silicon nitride whiskers and oxide materials is overcome, and the strength and the thermal shock stability of products are further improved.
(3) The product skeleton obtained by the invention has a micro-nano porous structure, has stronger adsorption capacity on nonmetallic inclusions, and has high filtration efficiency.
The skeleton of the product obtained by the invention is a porous pore wall structure with micro-nano pore diameter, and compared with the existing molten steel filter, the skeleton pore structure and the material design of the filter are innovative.
(1) The invention adopts the modified porous spinel ceramic fine powder as the raw material, so that the skeleton of the product has a porous pore wall structure with micro-nano pores, the specific surface area of the product skeleton is increased, and the physical adsorption capacity of the product on inclusions in molten steel is improved.
(2) The product obtained by the invention is a carbon-containing material, the surface of the framework is rough, the wetting angle of molten steel to the framework of the product is increased, and the adsorption capacity of the product to inclusions in the molten steel is enhanced.
(3) During the high-temperature service process, the magnesium aluminate spinel and carbon undergo carbothermic reduction reaction, mgAl 2 O 4 After being reduced, the alloy is mainly prepared from Al, alO and Al 2 O and Mg vapor. Al, alO, al 2 O and Mg vapor can escape to the surface of the product through micro-nano pores in the product and is oxidized again to form high-activity Al 2 O 3 /MgAl 2 O 4 Layer, which reduces the total oxygen content in the molten steel and simultaneously has high activity Al 2 O 3 /MgAl 2 O 4 The layer can still further adsorb impurities in the molten steel, so that the filtering effect is enhanced; the other part of the steam enters the molten steel to react with oxygen and other inclusions in the molten steel to form slag, and the slag floats upwards and is absorbed by the top slag, so that the total oxygen content and the inclusion content in the molten steel are further reduced, the molten steel is more effectively purified, and the purity of the molten steel is improved.
(4) In the high-temperature service process, gases such as CO and the like can be generated in the product, and the gases can escape into the molten steel through micro-nano air holes in the product to form micron-sized bubbles, so that the bubbles can capture small-size impurities in the floating process, the content of non-metallic inclusions in the molten steel is further reduced, and the molten steel is more effectively purified; and the escape of the internal gas through the porous structure can reduce the internal pressure of the product, so that the product is prevented from bursting due to excessive internal pressure.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared by the invention is detected as follows: the porosity is 78-90%; the volume density is 0.46-0.79 g/cm 3 (ii) a The compressive strength is 2.1-4.1 MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Therefore, the silicon nitride reinforced porous spinel-carbon ceramic filter prepared by the invention has high strength, good thermal shock stability and excellent filtering efficiency, and is suitable for filtering ultra-low carbon molten steel.
Detailed Description
The invention is further described with reference to specific embodiments, without limiting its scope.
A silicon nitride enhanced porous spinel-carbon ceramic filter and a preparation method thereof. The preparation method of the embodiment comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 380-550 ℃ at the speed of 2.5-5 ℃/min, preserving the heat for 2-3.5 hours, and cooling to obtain the fine porous alumina agglomerate powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.35-0.4, and stirring for 1.5-3.5 hours to obtain mixed powder.
Step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 150-180 MPa, and drying the molded blank at the temperature of 110-150 ℃ for 12-24 hours; then heating to 1600-1680 ℃ at the speed of 2-4 ℃/min, preserving the temperature for 3-5 hours, and cooling to obtain the porous spinel ceramic with the nano aperture.
The nanoporous porous spinel ceramic: the apparent porosity is 23-32%, and the volume density is 2.5-2.83 g/cm 3 The average pore diameter is 500-980 nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 1.5-5.5, and stirring for 5-10 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 20-36, vacuumizing to 2-2.9 kPa, adding the modified solution, stirring for 15-30 minutes, closing a vacuumizing system, and naturally drying for 36-48 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 1-3 hours, taking out, washing with deionized water for 4-6 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam has a specification of 10 to 20ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Immersing the pretreated polyurethane foam into thixotropic ceramic slurry for 15-20 minutes, taking out, removing redundant thixotropic ceramic slurry by using a double-roller machine, curing for 10-20 hours at room temperature, and drying for 14-26 hours at 90-120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 Under the condition of Pa atmosphere, heating to 1150-1250 ℃ at the speed of 1-1.5 ℃/min, preserving the heat for 2-4 hours, and cooling to obtain the porous spinel-carbon ceramic filter presintering body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 1.9-3 kPa, standing for 10-25 minutes, taking out the pre-sintered body of the porous spinel-carbon ceramic filter, and treating the pre-sintered body of the porous spinel-carbon ceramic filter for 3-8 minutes in a centrifuge at the rotating speed of 220-480 r/min to obtain a secondary slurry-hanging porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 24-46 hours, and then drying for 12-24 hours at the temperature of 90-120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressures less than 1.0X 10 -6.4 Under the atmosphere condition of Pa, firstly heating to 500-600 ℃ at the speed of 1-2 ℃/min, preserving heat for 30-60 minutes, then heating to 1350-1450 ℃ at the speed of 3-5 ℃/min, preserving heat for 3-5 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 is the same as the thixotropic ceramic slurry obtained in the step 5, and the preparation method of the thixotropic ceramic slurry comprises the following steps: 89.5-96.5 wt% of the modified porous spinel ceramic fine powder, 1-3 wt% of the modified coal tar pitch fine powder, 2-5 wt% of simple substance silicon powder and 0.5-2.5 wt% of sodium carboxymethyl cellulose are used as raw materials, the raw materials are firstly placed in a mixer to be mixed for 1.5-3 hours, then alumina sol, 0.05-0.15 wt% of water reducing agent, 0.3-1.2 wt% of defoaming agent and 22-40 wt% of deionized water which account for 2-5 wt% of the raw materials are added, and stirring is carried out for 40-60 minutes, so as to obtain ceramic slurry with thixotropy.
Al of the aluminum hydroxide fine powder 2 O 3 The content is 64-66 wt%.
The MgO content of the light-burned magnesite micro powder is more than or equal to 95wt%.
The catalyst is one of ferric nitrate nonahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate; fe (NO) in the ferric nitrate nonahydrate 3 ) 3 ·9H 2 The content of O is more than or equal to 98wt percent, and Co (NO) in the cobalt nitrate hexahydrate 3 ) 2 ·6H 2 The content of O is more than or equal to 98wt percent, and the Ni (NO) in the nickel nitrate hexahydrate 3 ) 2 ·6H 2 The content of O is more than or equal to 98wt percent.
The concentration of the NaOH solution is 6-8 mol/L.
The C content of the modified coal tar pitch fine powder is 70-80 wt%.
The Si content of the elemental silicon powder is more than or equal to 98wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 20-45 wt%.
The defoaming agent is dimethyl silicone oil or polyether modified silicone oil.
The water reducing agent is sodium lignosulphonate or polycarboxylate; the lignin content in the sodium lignosulphonate is 45-60 wt%, and the side chain molecular weight in the polycarboxylate is 700-2300.
In this embodiment:
the particle size of the aluminum hydroxide fine powder is less than 44 mu m;
the particle size of the light-burned magnesite micro powder is less than 2 mu m;
the particle size of the modified coal tar pitch fine powder is less than 74 mu m;
the particle size of the simple substance silicon powder is less than 45 μm.
The detailed description is omitted in the embodiments.
Example 1
A silicon nitride reinforced porous spinel-carbon ceramic filter and a preparation method thereof. The preparation method of the embodiment comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 380 ℃ at the speed of 2.5 ℃/min, preserving the heat for 2 hours, and cooling to obtain the fine porous alumina agglomerate powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.35, and stirring for 1.5 hours to obtain mixed powder.
Step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 150MPa, and drying the molded blank at the temperature of 110 ℃ for 12 hours; then heating to 1600 ℃ at the speed of 2 ℃/min, preserving the heat for 3 hours, and cooling to obtain the porous spinel ceramic with the nano aperture.
The nanoporous porous spinel ceramic: the apparent porosity is 32 percent, and the volume density is 2.5g/cm 3 The average pore diameter is 980nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 1.5, and stirring for 5 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 20, vacuumizing to 2kPa, adding the modified solution, stirring for 15 minutes, closing a vacuumizing system, and naturally drying for 36 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 1 hour, taking out, washing with deionized water for 4 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam had a specification of 10ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Immersing the pretreated polyurethane foam into thixotropic ceramic slurry for 15 minutes, taking out, removing redundant thixotropic ceramic slurry by using a double-roller machine, curing for 10 hours at room temperature, and drying for 14 hours at 90 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressures less than 1.0X 10 -6.4 And (3) under the atmosphere condition of Pa, heating to 1150 ℃ at the speed of 1 ℃/min, preserving the temperature for 2 hours, and cooling to obtain the porous spinel-carbon ceramic filter presintered body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 1.9kPa, standing for 10 minutes, taking out, and then treating the pre-sintered body in a centrifuge at a rotating speed of 220r/min for 3 minutes to obtain a secondary slurry-coated porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 24 hours, and then drying for 12 hours at the temperature of 90 ℃; then in N 2 Partial pressure of 1atm、O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And under the atmosphere condition of Pa, firstly heating to 500 ℃ at the speed of 1 ℃/min, preserving heat for 30 minutes, then heating to 1350 ℃ at the speed of 3 ℃/min, preserving heat for 3 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 is the same as the thixotropic ceramic slurry obtained in the step 5, and the preparation method of the thixotropic ceramic slurry comprises the following steps: 89.5wt% of the modified porous spinel ceramic fine powder, 3wt% of the modified coal tar pitch fine powder, 5wt% of elemental silicon powder and 2.5wt% of sodium carboxymethyl cellulose are used as raw materials, the raw materials are placed in a mixer to be mixed for 1.5 hours, then alumina sol accounting for 2wt% of the raw materials, 0.05wt% of water reducing agent, 0.3wt% of defoaming agent and 22wt% of deionized water are added, and stirring is carried out for 40 minutes, so that ceramic slurry with thixotropy is obtained.
Al of the aluminum hydroxide fine powder 2 O 3 The content was 64wt%.
The MgO content of the light-burned magnesite micro powder is 95wt%.
The catalyst is ferric nitrate nonahydrate; fe (NO) in the ferric nitrate nonahydrate 3 ) 3 ·9H 2 The O content was 98wt%.
The concentration of the NaOH solution is 6mol/L.
The C content of the modified coal tar pitch fine powder is 70wt%.
The Si content of the elemental silicon powder is 98wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 20wt%.
The defoaming agent is dimethyl silicone oil.
The water reducing agent is sodium lignosulphonate; the lignin content in the sodium lignosulfonate was 46wt%.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared in this example was tested: the porosity is 90%; the bulk density is 0.46g/cm 3 (ii) a The compressive strength is 2.1MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Example 2
A silicon nitride enhanced porous spinel-carbon ceramic filter and a preparation method thereof. The preparation method of the embodiment comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the aluminum hydroxide fine powder to 420 ℃ at the speed of 3 ℃/min, preserving the heat for 2.5 hours, and cooling to obtain porous alumina agglomerate fine powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.36, and stirring for 2 hours to obtain mixed powder.
Step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 160MPa, and drying the molded blank at the temperature of 130 ℃ for 16 hours; then raising the temperature to 1620 ℃ at the speed of 2.5 ℃/min, preserving the heat for 3.5 hours, and cooling to obtain the porous spinel ceramic with the nano-aperture.
The nanoporous porous spinel ceramic: the apparent porosity is 28.5%, and the volume density is 2.62g/cm 3 The average pore diameter was 813nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst in a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 3, and stirring for 7 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 28, vacuumizing to 2.3kPa, adding the modified solution, stirring for 20 minutes, closing a vacuumizing system, and naturally drying for 40 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 2 hours, taking out, washing with deionized water for 5 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam had a specification of 12ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Immersing the pretreated polyurethane foam into thixotropic ceramic slurry for 16 minutes, taking out, removing redundant thixotropic ceramic slurry by using a roll machine, curing for 16 hours at room temperature, and drying for 18 hours at 100 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And (3) heating to 1180 ℃ at the speed of 1.2 ℃/min under the condition of Pa atmosphere, preserving the heat for 3 hours, and cooling to obtain the porous spinel-carbon ceramic filter pre-sintered body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 2.2kPa, standing for 15 minutes, taking out, and then treating the pre-sintered body in a centrifuge at the rotating speed of 300r/min for 5 minutes to obtain a secondary slurry-coated porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 34 hours, and then drying for 18 hours at the temperature of 100 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And (3) under the condition of Pa atmosphere, firstly heating to 530 ℃ at the speed of 1.3 ℃/min, preserving heat for 40 minutes, then heating to 1380 ℃ at the speed of 4 ℃/min, preserving heat for 3.5 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 and the step 5 is the same, and the preparation method of the thixotropic ceramic slurry comprises the following steps: taking 91wt% of the modified porous spinel ceramic fine powder, 2.5wt% of modified coal tar pitch fine powder, 4.5wt% of elemental silicon powder and 2wt% of sodium carboxymethyl cellulose as raw materials, firstly placing the raw materials in a mixer to mix for 2 hours, then adding alumina sol accounting for 3wt% of the raw materials, 0.08wt% of water reducing agent, 0.6wt% of defoaming agent and 26wt% of deionized water, and stirring for 45 minutes to obtain thixotropic ceramic slurry.
Al of the aluminum hydroxide fine powder 2 O 3 The content was 65wt%.
The MgO content of the light-burned magnesite micro powder is 95.2wt%.
The catalyst is cobalt nitrate hexahydrate; co (NO) in the cobalt nitrate hexahydrate 3 ) 2 ·6H 2 The O content was 98.1wt%.
The concentration of the NaOH solution is 6.5mol/L.
The C content of the modified coal tar pitch fine powder is 73wt%.
The Si content of the elemental silicon powder is 98.2wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 30wt%.
The defoaming agent is polyether modified silicone oil.
The water reducing agent is polycarboxylate; the molecular weight of the side chain in the polycarboxylate is 1000.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared in this example was tested: porosity 86.5%; the bulk density is 0.55g/cm 3 (ii) a The compressive strength is 2.5MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Example 3
A silicon nitride enhanced porous spinel-carbon ceramic filter and a preparation method thereof. The preparation method of the embodiment comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 500 ℃ at the speed of 4 ℃/min, preserving heat for 3 hours, and cooling to obtain the fine porous alumina agglomerate powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.38, and stirring for 2.5 hours to obtain mixed powder.
1.3, mechanically pressing the mixed powder under 170MPa, and drying the formed blank at 140 ℃ for 20 hours; then heating to 1640 ℃ at the speed of 3 ℃/min, preserving the heat for 4 hours, and cooling to obtain the porous spinel ceramic with the nano aperture.
The nanoporous porous spinel ceramic: the apparent porosity is 25.4%, and the volume density is 2.72g/cm 3 The average pore diameter is 694nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 4, and stirring for 9 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 30, vacuumizing to 2.6kPa, adding the modified solution, stirring for 25 minutes, closing a vacuumizing system, and naturally drying for 44 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 2.5 hours, taking out, washing with deionized water for 5 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam had a specification of 16ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Immersing the pretreated polyurethane foam into ceramic slurry with thixotropy for 18 minutes, and taking outRemoving redundant thixotropic ceramic slurry by using a roll pair machine, maintaining for 18 hours at room temperature, and drying for 22 hours at 110 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressures less than 1.0X 10 -6.4 And (3) under the atmosphere condition of Pa, heating to 1200 ℃ at the speed of 1.3 ℃/min, preserving the heat for 3.5 hours, and cooling to obtain the porous spinel-carbon ceramic filter pre-sintered body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 2.5kPa, standing for 20 minutes, taking out, and then treating the pre-sintered body in a centrifuge at the rotating speed of 400r/min for 6 minutes to obtain a secondary slurry-coated porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 40 hours, and then drying for 21 hours at the temperature of 110 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And under the atmosphere condition of Pa, firstly heating to 560 ℃ at the speed of 1.6 ℃/min, preserving heat for 50 minutes, then heating to 1420 ℃ at the speed of 4.5 ℃/min, preserving heat for 4 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 is the same as the thixotropic ceramic slurry obtained in the step 5, and the preparation method of the thixotropic ceramic slurry comprises the following steps: 93wt% of modified porous spinel ceramic fine powder, 2wt% of modified coal tar pitch fine powder, 4wt% of elemental silicon powder and 1wt% of sodium carboxymethyl cellulose are used as raw materials, the raw materials are placed in a mixer to be mixed for 2.5 hours, then alumina sol, 0.12wt% of water reducing agent, 0.9wt% of defoaming agent and 34wt% of deionized water are added, and stirring is carried out for 50 minutes, so that thixotropic ceramic slurry is obtained.
Al of the aluminum hydroxide fine powder 2 O 3 The content was 65.5wt%.
The MgO content of the light-burned magnesite micro powder is 95.4wt%.
The catalyst is nickel nitrate hexahydrate; ni (NO) in the nickel nitrate hexahydrate 3 ) 2 ·6H 2 The O content was 98.3wt%.
The concentration of the NaOH solution is 7mol/L.
The C content of the modified coal tar pitch fine powder is 76wt%.
The Si content of the elemental silicon powder is 98.4wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 35wt%.
The defoaming agent is dimethyl silicone oil.
The water reducing agent is sodium lignosulphonate; the lignin content in the sodium lignin sulfonate is 58wt%.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared in this example was tested: the porosity was 80.3%; the bulk density is 0.71g/cm 3 (ii) a The compressive strength is 3.4MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Example 4
A silicon nitride reinforced porous spinel-carbon ceramic filter and a preparation method thereof. The preparation method of the embodiment comprises the following steps:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 550 ℃ at the speed of 5 ℃/min, preserving the heat for 3.5 hours, and cooling to obtain the fine porous alumina agglomerate powder.
Step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.4, and stirring for 3.5 hours to obtain mixed powder.
Step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 180MPa, and drying the molded blank at 150 ℃ for 24 hours; then heating to 1680 ℃ at the speed of 4 ℃/min, keeping the temperature for 5 hours, and cooling to obtain the porous spinel ceramic with the nano aperture.
The number of the nano-aperturesPore spinel ceramic: the apparent porosity is 23 percent, and the volume density is 2.83g/cm 3 The average pore diameter was 500nm.
And step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m.
Step 2, preparation of modified porous spinel ceramic fine powder
And 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 5.5, and stirring for 10 minutes to obtain a modified solution.
And 2.2, putting the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 36, vacuumizing to 2.9kPa, adding the modified solution, stirring for 30 minutes, closing a vacuumizing system, and naturally drying for 48 hours to obtain the modified porous spinel ceramic fine powder.
Step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 3 hours, taking out, washing with deionized water for 6 times, and airing to obtain pretreated polyurethane foam; the polyurethane foam had a specification of 20ppi.
Step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Immersing the pretreated polyurethane foam into thixotropic ceramic slurry for 20 minutes, taking out, removing redundant thixotropic ceramic slurry by using a roll machine, curing for 20 hours at room temperature, and drying for 26 hours at 120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And (3) under the condition of Pa atmosphere, heating to 1250 ℃ at the speed of 1.5 ℃/min, preserving the heat for 4 hours, and cooling to obtain the porous spinel-carbon ceramic filter pre-sintered body.
Step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing in a vacuum environment, vacuumizing to 3kPa, standing for 25 minutes, taking out, and then processing in a centrifuge at a rotating speed of 480r/min for 8 minutes to obtain a secondary slurry-coated porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 46 hours, and then drying for 24 hours at the temperature of 120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 And (3) under the condition of Pa atmosphere, heating to 600 ℃ at the speed of 2 ℃/min, preserving heat for 60 minutes, heating to 1450 ℃ at the speed of 5 ℃/min, preserving heat for 5 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter.
The thixotropic ceramic slurry obtained in the step 4 is the same as the thixotropic ceramic slurry obtained in the step 5, and the preparation method of the thixotropic ceramic slurry comprises the following steps: taking 96.5wt% of the modified porous spinel ceramic fine powder, 1wt% of the modified coal tar pitch fine powder, 2wt% of simple substance silicon powder and 0.5wt% of sodium carboxymethyl cellulose as raw materials, firstly placing the raw materials in a mixer for mixing for 3 hours, then adding 5wt% of alumina sol, 0.15wt% of water reducing agent, 1.2wt% of defoaming agent and 40wt% of deionized water into the raw materials, and stirring for 60 minutes to obtain the thixotropic ceramic slurry.
Al of the aluminum hydroxide fine powder 2 O 3 The content was 66wt%.
The MgO content of the light-burned magnesite micro powder is 95.6wt%.
The catalyst is ferric nitrate nonahydrate; fe (NO) in the ferric nitrate nonahydrate 3 ) 3 ·9H 2 The O content was 98.5wt%.
The concentration of the NaOH solution is 8mol/L.
The C content of the modified coal tar pitch fine powder is 80wt%.
The Si content of the elemental silicon powder is 98.6wt%.
Al of the aluminum sol 2 O 3 The content of (B) is 45wt%.
The defoaming agent is polyether modified silicone oil.
The water reducing agent is polycarboxylate; the molecular weight of the side chain in the polycarboxylate is 2000.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared in this example was tested: the porosity was 78%; the bulk density is 0.79g/cm 3 (ii) a The compressive strength is 4.1MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Compared with the prior art, the specific implementation mode has the following positive effects:
(1) The specific embodiment adopts the modified porous spinel ceramic fine powder with the nano-aperture as the raw material, so that the strength of the product is improved.
Compared with compact raw materials, the modified porous spinel ceramic fine powder has a porous structure with through nanometer apertures, and is beneficial to improving the strength of products.
Firstly, the surface of the modified porous spinel ceramic fine powder is rough, the contact area between the ceramic slurry with thixotropy and a polyurethane foam template is increased, the attachment of the ceramic slurry with thixotropy is facilitated, the slurry hanging performance is improved, the thickness of a framework is increased, and the strength of a product is improved.
Secondly, in the existing carbon-containing material, the surfaces of oxide particles are relatively smooth, the sintering degree between the oxide particles and carbon is weak, and good neck connection is difficult to form; compared with the existing carbon-containing material, the modified porous spinel ceramic fine powder is adopted in the specific embodiment, the surface of fine powder particles is rough, the contact areas among the modified porous spinel ceramic fine powder and between the modified porous spinel ceramic fine powder and the modified coal tar asphalt powder are increased, the material transmission among all microparticles and the length of a sintering neck in a high-temperature sintering process are promoted, a sawtooth occlusion-shaped interface is formed among the particles, and the strength of a product is further improved.
(2) The silicon nitride whiskers with special distribution are generated in the product obtained by the specific implementation mode, so that the thermal shock stability of the product is improved, and the strength of the product is further improved.
In the existing silicon nitride whisker reinforced materials, silicon nitride whiskers can only be formed in gaps of matrix powder, and have poor interface compatibility with oxide materials, so that the further improvement of the matrix strength and the thermal shock stability is limited; the modified porous spinel ceramic fine powder adopted by the specific embodiment has more holes and catalysts inside and on the surface, a large number of landing sites can be provided for the growth of silicon nitride whiskers, the silicon nitride whiskers can be generated in the holes in situ under the action of the catalysts, the silicon nitride whiskers can be generated in the holes among the micro particles, finally, interwoven silicon nitride whiskers are formed among the modified porous spinel ceramic fine powder and between the modified porous spinel ceramic fine powder and the modified coal tar pitch powder, the sawtooth occlusion interface among the particles is further enhanced, the defect that the interface compatibility of the existing silicon nitride whiskers and an oxide material is poor is overcome, and the strength and the thermal shock stability of a product are further improved.
(3) The product skeleton obtained by the embodiment has a micro-nano porous structure, has stronger adsorption capacity on nonmetallic inclusions, and is high in filtering efficiency.
The product skeleton obtained by the specific embodiment is a porous pore wall structure with micro-nano pore diameter, and compared with the existing molten steel filter, the product skeleton has innovation in the aspects of skeleton pore structure and material design of the filter.
(1) The specific embodiment adopts the modified porous spinel ceramic fine powder as the raw material, so that the skeleton of the product has a porous pore wall structure with micro-nano-sized pores, the specific surface area of the product skeleton is increased, and the physical adsorption capacity of the product on inclusions in molten steel is improved.
(2) The product obtained by the embodiment is a carbon-containing material, the surface of the framework is rough, the wetting angle of molten steel to the product framework is increased, and the adsorption capacity of the product to inclusions in the molten steel is enhanced.
(3) During the high-temperature service process, the magnesium aluminate spinel and carbon undergo carbothermic reduction reaction, mgAl 2 O 4 After being reduced, the alloy is mainly prepared from Al, alO and Al 2 O and Mg vapor. Al, alO, al 2 O and Mg vapor can escape to the surface of the product through micro-nano pores in the product and is oxidized againTo highly active Al 2 O 3 /MgAl 2 O 4 Layer, which reduces the total oxygen content in the molten steel and simultaneously has high activity Al 2 O 3 /MgAl 2 O 4 The layer can still further adsorb impurities in the molten steel, so that the filtering effect is enhanced; the other part of the steam enters the molten steel to react with oxygen and other inclusions in the molten steel to form slag, and the slag floats upwards and is absorbed by the top slag, so that the total oxygen content and the inclusion content in the molten steel are further reduced, the molten steel is more effectively purified, and the purity of the molten steel is improved.
(4) In the high-temperature service process, gases such as CO and the like can be generated in the product, and the gases can escape into the molten steel through micro-nano air holes in the product to form micron-sized bubbles, so that the bubbles can capture small-size impurities in the floating process, the content of nonmetallic inclusion in the molten steel is further reduced, and the molten steel is more effectively purified; and the escape of the internal gas through the porous structure can reduce the internal pressure of the product, so that the product is prevented from bursting due to excessive internal pressure.
The silicon nitride reinforced porous spinel-carbon ceramic filter prepared by the specific embodiment is detected as follows: the porosity is 78-90%; the volume density is 0.46-0.79 g/cm 3 (ii) a The compressive strength is 2.1-4.1 MPa; the phase composition mainly comprises spinel, graphite and beta-Si 3 N 4 。
Therefore, the silicon nitride reinforced porous spinel-carbon ceramic filter prepared by the embodiment has high strength, good thermal shock stability and excellent filtering efficiency, and is suitable for filtering ultra-low carbon molten steel.

Claims (10)

1. A method of making a silicon nitride enhanced porous spinel-carbon ceramic filter, the method comprising the steps of:
step 1, preparation of porous spinel ceramic fine powder
Step 1.1, heating the fine aluminum hydroxide powder to 380-550 ℃ at the speed of 2.5-5 ℃/min, preserving the heat for 2-3.5 hours, and cooling to obtain porous alumina agglomerate fine powder;
step 1.2, placing the porous alumina agglomerate fine powder and the light-burned magnesite micro powder in a stirrer according to the mass ratio of the porous alumina agglomerate fine powder to the light-burned magnesite micro powder of 1: 0.35-0.4, and stirring for 1.5-3.5 hours to obtain mixed powder;
step 1.3, performing mechanical pressing molding on the mixed powder under the condition of 150-180 MPa, and drying the molded blank at the temperature of 110-150 ℃ for 12-24 hours; then heating to 1600-1680 ℃ at the speed of 2-4 ℃/min, preserving the temperature for 3-5 hours, and cooling to obtain the porous spinel ceramic with the nano aperture;
the nanoporous porous spinel ceramic: the apparent porosity is 23-32%, and the volume density is 2.5-2.83 g/cm 3 The average pore diameter is 500-980 nm;
step 1.4, crushing and screening the porous spinel ceramic with the nano aperture to obtain porous spinel ceramic fine powder with the nano aperture, wherein the particle size of the porous spinel ceramic fine powder with the nano aperture is smaller than 30 mu m;
step 2, preparation of modified porous spinel ceramic fine powder
Step 2.1, placing the deionized water and the catalyst into a stirrer according to the mass ratio of the deionized water to the catalyst of 100: 1.5-5.5, and stirring for 5-10 minutes to obtain a modified solution;
step 2.2, placing the porous spinel ceramic fine powder with the nano aperture in a vacuum device according to the mass ratio of the porous spinel ceramic fine powder with the nano aperture to the modified solution of 100: 20-36, vacuumizing to 2-2.9 kPa, adding the modified solution, stirring for 15-30 minutes, closing a vacuumizing system, and naturally drying for 36-48 hours to obtain the modified porous spinel ceramic fine powder;
step 3, preparation of pretreated polyurethane foam
Soaking polyurethane foam in NaOH solution for 1-3 hours, taking out, washing with deionized water for 4-6 times, and airing to obtain pretreated polyurethane foam; the specification of the polyurethane foam is 10-20 ppi;
step 4, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter pre-sintered body
Subjecting the pretreated polyurethane to a treatmentSoaking the foam into ceramic slurry with thixotropy for 15-20 minutes, taking out, removing redundant ceramic slurry with thixotropy by using a roll-pair machine, maintaining for 10-20 hours at room temperature, and drying for 14-26 hours at 90-120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 Under the atmosphere condition of Pa, heating to 1150-1250 ℃ at the speed of 1-1.5 ℃/min, preserving the heat for 2-4 hours, and cooling to obtain a porous spinel-carbon ceramic filter presintered body;
step 5, preparation of silicon nitride reinforced porous spinel-carbon ceramic filter
Dipping the pre-sintered body of the porous spinel-carbon ceramic filter into the ceramic slurry with thixotropy, then placing the pre-sintered body in a vacuum environment, vacuumizing to 1.9-3 kPa, standing for 10-25 minutes, taking out the pre-sintered body of the porous spinel-carbon ceramic filter, and treating the pre-sintered body of the porous spinel-carbon ceramic filter for 3-8 minutes in a centrifuge at the rotating speed of 220-480 r/min to obtain a secondary slurry-hanging porous spinel-carbon ceramic filter blank; naturally drying the secondary slurry-coated porous spinel-carbon ceramic filter blank for 24-46 hours, and then drying for 12-24 hours at the temperature of 90-120 ℃; then in N 2 Partial pressure of 1atm, O 2 Partial pressure of less than 1.0X 10 -14.4 Pa and CO partial pressure less than 1.0X 10 -6.4 Under the condition of Pa atmosphere, firstly heating to 500-600 ℃ at the speed of 1-2 ℃/min, preserving heat for 30-60 minutes, then heating to 1350-1450 ℃ at the speed of 3-5 ℃/min, preserving heat for 3-5 hours, and cooling to obtain the silicon nitride reinforced porous spinel-carbon ceramic filter;
the preparation method of the ceramic slurry with thixotropy in the step 4 is the same as that in the step 5: 89.5-96.5 wt% of the modified porous spinel ceramic fine powder, 1-3 wt% of the modified coal tar pitch fine powder, 2-5 wt% of simple substance silicon powder and 0.5-2.5 wt% of sodium carboxymethyl cellulose are used as raw materials, the raw materials are firstly placed in a mixer to be mixed for 1.5-3 hours, then alumina sol, 0.05-0.15 wt% of water reducing agent, 0.3-1.2 wt% of defoaming agent and 22-40 wt% of deionized water which account for 2-5 wt% of the raw materials are added, and stirring is carried out for 40-60 minutes, so as to obtain ceramic slurry with thixotropy;
the water reducing agent is sodium lignosulphonate or polycarboxylate; the lignin content in the sodium lignosulphonate is 45-60 wt%, and the side chain molecular weight in the polycarboxylate is 700-2300.
2. The method of making a silicon nitride enhanced porous spinel-carbon ceramic filter of claim 1, wherein said aluminum hydroxide fine powder has a particle size of less than 44 μm; al of the aluminum hydroxide fine powder 2 O 3 The content is 64-66 wt%.
3. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein the particle size of the fine powder of the light-burned magnesite is less than 2 μm; the MgO content of the light-burned magnesite micro powder is more than or equal to 95wt%.
4. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein the catalyst is one of iron nitrate nonahydrate, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate; fe (NO) in the ferric nitrate nonahydrate 3 ) 3 ·9H 2 The content of O is more than or equal to 98wt percent, and Co (NO) in the cobalt nitrate hexahydrate 3 ) 2 ·6H 2 The content of O is more than or equal to 98wt percent, and the Ni (NO) in the nickel nitrate hexahydrate 3 ) 2 ·6H 2 The O content is more than or equal to 98wt percent.
5. The method for preparing a silicon nitride reinforced porous spinel-carbon ceramic filter according to claim 1, wherein the concentration of the NaOH solution is 6 to 8mol/L.
6. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein the modified coal tar pitch fine powder has a particle size of less than 74 μm; the C content of the modified coal tar pitch fine powder is 70-80 wt%.
7. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein the elemental silicon powder has a particle size of less than 45 μm; the Si content of the elemental silicon powder is more than or equal to 98wt%.
8. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein Al of the aluminum sol 2 O 3 The content of (B) is 20-45 wt%.
9. The method of preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to claim 1, wherein said defoaming agent is a dimethyl silicone oil or a polyether-modified silicone oil.
10. A silicon nitride-reinforced porous spinel-carbon ceramic filter, characterized in that it is a silicon nitride-reinforced porous spinel-carbon ceramic filter prepared according to the method for preparing a silicon nitride-reinforced porous spinel-carbon ceramic filter according to any one of claims 1 to 9.
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