CN117800755A - Preparation method of high-strength foamed ceramic under freeze-thawing cycle - Google Patents
Preparation method of high-strength foamed ceramic under freeze-thawing cycle Download PDFInfo
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- 238000000034 method Methods 0.000 claims abstract description 27
- 239000000463 material Substances 0.000 claims abstract description 26
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- 238000005187 foaming Methods 0.000 claims abstract description 21
- 238000010304 firing Methods 0.000 claims abstract description 20
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- UQGFMSUEHSUPRD-UHFFFAOYSA-N disodium;3,7-dioxido-2,4,6,8,9-pentaoxa-1,3,5,7-tetraborabicyclo[3.3.1]nonane Chemical compound [Na+].[Na+].O1B([O-])OB2OB([O-])OB1O2 UQGFMSUEHSUPRD-UHFFFAOYSA-N 0.000 claims description 6
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- Porous Artificial Stone Or Porous Ceramic Products (AREA)
Abstract
The invention provides a preparation method of high-strength foamed ceramics under freeze-thawing cycle, belonging to the technical field of foamed ceramics preparation. The method comprises the steps of firstly grinding and drying raw materials to prepare first ceramic powder, further adding a fluxing agent, grinding to obtain second ceramic powder, then spraying a foaming material obtained by mixing gel and water on the second ceramic powder to obtain third ceramic powder, adding a pore-forming agent into the third ceramic powder to obtain a pre-firing material after grinding, further pre-firing the pre-firing material for pre-firing and degassing, pouring the pre-firing material into a mould for cyclic freeze thawing, and finally firing the pre-firing material in a nitrogen atmosphere to obtain the high-strength foaming ceramic. The method ensures that the foamed ceramic has good performance after being subjected to freeze-thawing cycle treatment.
Description
Technical Field
The invention relates to the technical field of foamed ceramic preparation, in particular to a preparation method of high-strength foamed ceramic under freeze thawing cycle.
Background
In addition to the traditional colloidal forming methods, such as slip casting, injection molding and the like, the novel colloidal forming methods, such as gel casting, direct solidification injection molding and the like, have also been developed in the ceramic forming method, and the method is good in particle stacking uniformity and few in defects, is more suitable for preparing high-reliability complex-shape components, and is particularly suitable for near-net forming of ceramic composite materials.
The gel casting method is to use the idea of forming a three-dimensional entangled state-space macromolecular network by monomer reaction, so that ceramic particles are fixed on a required shape. Compared with other molding methods, the gel casting molding has the advantages of short curing time, high blank strength, low processing cost, high yield and the like, and is more suitable for preparing ceramics with complex shapes. However, the most commonly used gel systems such as acrylamide-N, N' -methylenebisacrylamide (AM-MBAMM) are relatively toxic and limit their further application, so many researchers have been devoted to developing low-toxic or non-toxic gel systems in recent years.
Direct solidification casting (DCC) has been attracting attention to date as another common method of colloid forming of near net shape ceramic components. It exploits the instability of the suspension, by shifting its pH to the isoelectric point (IEP) or increasing its ionic strength, to obtain a uniform green body. However, the low strength of the wet-set samples of around 10kPa should be quite large, the long setting time and cumbersome operating conditions limit the mass production of ceramic components.
Polyvinyl alcohol (PVA) is a water-soluble polymer with good biocompatibility and no toxicity, is a semi-crystalline polymer, has good chemical stability and thermal stability, and is widely applied in the fields of medical treatment, cosmetics, packaging and the like. Interestingly, repeated freezing and thawing treatments of PVA can result in high strength PVA gels, which may be caused by intramolecular and intermolecular hydrogen bonds.
Based on the method, the invention takes the coal-fired furnace slag as a main raw material system to research the influence of PVA gel on the composition, pore structure and performance of the furnace slag foamed ceramic under different freezing and thawing periods and freezing time, discloses the formation mechanism and influencing factors of the pore structure of the foamed ceramic, defines the compression destructive behavior and the enhancement mechanism of the foamed ceramic, and provides the design principle and the preparation method of the high-strength foamed ceramic.
Disclosure of Invention
The invention provides a preparation method of high-strength foamed ceramic under freeze thawing cycle. The method can reduce the occurrence of uneven foaming, improve the freezing resistance of the foamed ceramic and increase the heat preservation and insulation performance of the foamed ceramic.
In order to solve the above-mentioned purpose, the technical scheme provided by the invention is as follows:
a preparation method of high-strength foamed ceramics under freeze thawing cycle comprises the following steps:
s1, respectively ball-milling and drying raw materials, and then preparing the raw materials into first ceramic powder according to a proportion;
s2, transferring the first ceramic powder into a ball mill, adding sodium tetraborate and metal wires serving as fluxing agents, and stirring in the ball mill to obtain second ceramic powder;
s3, uniformly spraying and adding the foaming material into the second ceramic powder to obtain third ceramic powder;
s4, transferring the third ceramic powder into a ball mill, adding pore-forming agent powder, and stirring in a stirrer to obtain a pre-firing material;
s5, placing the pre-fired material into a die for presintering, and then strongly stirring and degassing;
s6, pouring the mixture subjected to degassing in the step S5 into a mold for cyclic freeze thawing;
and S7, firing the mixture subjected to the cyclic freeze thawing in the step S6 in a nitrogen atmosphere to obtain the high-strength foamed ceramic.
The raw materials in the step S1 are lepidolite tailings, ceramic polishing waste, fly ash and borax, wherein the mass ratio of the lepidolite tailings to the ceramic polishing waste to the fly ash to the borax is 16-20:32-40:16-20:14-26.
The ball milling rotating speed in the step S1 is 150r/min-210r/min;
the ball milling time of lepidolite tailings in the raw materials is 12-24 hours; the ball milling time of the ceramic polishing waste is 8-15h; the ball milling time of the fly ash is 6-10h; the ball milling time of borax is 6-8h;
the drying temperature is 90-120 ℃ and the drying time is 6-12 h.
In the step S2, the dosage of sodium tetraborate is 14-26% of the mass of the first ceramic powder, and the dosage of metal wires is 30-50% of the mass of the first ceramic powder; the rotating speed of the ball mill is 45r/min-70r/min, the ball milling and stirring time in the ball mill is not less than 1h, and the granularity of the obtained second ceramic powder is less than 75 mu m.
The diameter of the metal wire is less than or equal to 1mm, the length of the metal wire is 0.5-1.0cm, and the melting point of the metal wire is not lower than 1200 ℃.
The foaming material in the step S3 is obtained by mixing PVA gel and water according to the mass ratio of 7-15:100, and the use amount of the foaming material is 7-15% of the mass of the second ceramic powder.
The pore-forming agent in the step S4 is Si 3 N 4 The average grain diameter of the pore-forming agent is 20-60 mu m, the dosage of the pore-forming agent is 16-21% of the mass of the third ceramic powder, and the stirring time in a stirrer is not less than 12h.
And (3) sintering the presintered material in the step (S5) in a nitrogen atmosphere, wherein the nitrogen pressure is 0.05-0.2 Mpa, the sintering temperature is 900-1000 ℃, and the sintering time is 20-40 min. The incomplete reduction of metal oxide in ceramic is avoided, and the surface oxidation of ceramic material and the generation of impurities are also avoided.
And in the step S5, the rotating speed is 210r/min-340r/min when the strong stirring and degassing are carried out.
The circulating freeze thawing in the step S6 specifically comprises the following steps: freezing for 20-30 h at the temperature of minus 10-minus 15 ℃, then thawing for 20-30 h at room temperature, and continuously drying for 12-24h in a baking oven at 70-110 ℃ to realize one cycle of freezing and thawing;
and the number of times of cyclic freezing and thawing in the step S6 is not less than 2.
The firing temperature in the step S7 is 900-1000 ℃ and the firing time is 30-90 min.
Preferably, the drying temperature in the step S1 is 100-120 ℃, and the drying time is 12-24 hours.
Preferably, in step S2, the first ceramic powder, the metal wire and the flux sodium tetraborate are ball milled in a ball mill for 4 hours. The melting point of the added metal wire is not lower than 1200 ℃, certain strength is ensured while high-temperature foaming is carried out, the diameter of the added metal strip is not more than 1 millimeter, the length is not more than 1 centimeter, and metals such as copper, iron, aluminum, titanium and the like can be selected.
Preferably, the polymerization degree of the foaming material in step S3 is not lower than 1700.
Preferably, the pore-forming agent powder in the step S4 has a diameter of 20-60 micrometers, so that the metal strip can well participate in the foaming process during foaming, and the effects of improving the heat conductivity and reducing the fluidity of liquid phase crystals are achieved; the pore-forming agent powder adopts silicon nitride hollow spheres.
Preferably, the pre-sintering temperature in step S5 is 900-950 ℃.
And (5) carrying out vacuum treatment on the fired product in a vacuum furnace, wherein the degassing time is not less than 10min, and avoiding generating bubbles in the firing process, so that the density and the quality of the fired foamed ceramic are ensured.
Preferably, in step S7, the nitrogen atmosphere pressure is not lower than 0.5MPa.
According to the invention, by adding the metal wires and utilizing the heat conduction and catalysis effects of the metal strips, the ceramic powder can be better sintered together, so that the strength and heat resistance of the foamed ceramic are improved, the formation of a pore structure of the foamed ceramic is promoted, and the heat preservation and heat insulation performance of the foamed ceramic is improved to a certain extent.
By adding fluxing agent, borax pentahydrate can be decomposed to form Na during high-temperature foaming of the foamed ceramic 2 O and [ BO ] 3 ]Triangle, sodium oxide produced can induce the decomposition of Si-O bond, and [ BO 3 ]Can be inserted into [ [ SiO ]] 4 ]Tetrahedra break the vitreous structure, thereby lowering the glass softening temperature and allowing sintering at low temperatures.
The polyvinyl alcohol solution is added by spraying, and the polyvinyl alcohol aqueous solution is sprayed on the surface of the ceramic powder to be uniformly attached on the particles so as to form a uniform coating. This can improve the adhesion between ceramic particles, promoting green body formation and sintering. Secondly, the ceramic particles can be wetted and wrapped in the ceramic particles, so that the ceramic particles are dispersed and uniformly distributed, a uniform green body is formed, and nonuniform pore distribution is avoided in the sintering process. Again, the surface tension of the liquid can be reduced so that the surface of the ceramic powder can be better covered and wetted during spraying, which helps to improve the fluidity and dispersibility of the ceramic particles while reducing the voids and interstices between the particles. Finally, the ceramic powder and the polyvinyl alcohol aqueous solution can be uniformly mixed to form slurry with better plasticity. This helps to improve the plasticity and formability of the green body during the forming process, making it easier to form into the desired shape.
By adding the pore-forming agent, tiny bubbles can be formed, and further closed pores are realized in the ceramic, so that a pore structure is formed.
Compared with the prior art, the technical scheme has at least the following beneficial effects:
according to the scheme, the added metal strips can enhance the heat conductivity and catalysis during foaming, and enhance the strength and heat insulation of the foamed ceramic; the added fluxing agent can reduce the temperature required by foaming, and can also perform foaming at low temperature, so that the energy loss during foaming is reduced; the dispersion, wetting and adhesion of ceramic powder can be better realized by adopting spraying polyvinyl alcohol solution, so that the forming performance and sintering quality of green bodies are improved; and finally, the pore-forming agent is added, so that the uniformity of air holes generated during foaming can be ensured, and various performances of the foamed ceramic are improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a process flow diagram of a method for preparing high strength foamed ceramics under freeze-thawing cycle according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without creative efforts, based on the described embodiments of the present invention fall within the protection scope of the present invention.
The invention provides a preparation method of high-strength foamed ceramic under freeze thawing cycle.
As shown in fig. 1, the method comprises the steps of:
s1, respectively ball-milling and drying raw materials, and then preparing the raw materials into first ceramic powder according to a proportion;
s2, transferring the first ceramic powder into a ball mill, adding sodium tetraborate and metal wires serving as fluxing agents, and stirring in the ball mill to obtain second ceramic powder;
s3, uniformly spraying and adding the foaming material into the second ceramic powder to obtain third ceramic powder;
s4, transferring the third ceramic powder into a ball mill, adding pore-forming agent powder, and stirring in a stirrer to obtain a pre-firing material;
s5, placing the pre-fired material into a die for presintering, and then strongly stirring and degassing;
s6, pouring the mixture subjected to degassing in the step S5 into a mold for cyclic freeze thawing;
and S7, firing the mixture subjected to the cyclic freeze thawing in the step S6 in a nitrogen atmosphere to obtain the high-strength foamed ceramic.
The following describes specific embodiments.
Ball milling lepidolite tailings, ceramic polishing waste, fly ash and borax for 4-8 hours respectively according to the flow shown in figure 1, drying for 6-12 hours at 110 ℃, and then configuring according to the mass ratio of 16:35:18:20; transferring the prepared ceramic powder into a ball mill, adding metal wires with the diameters not exceeding 1mm and the lengths not exceeding 1cm, which are 40% of the mass of the ceramic powder, and sodium tetraborate pentahydrate with the mass of 20% of the mass of the ceramic powder, and stirring in the ball mill for not less than 4 hours; uniformly mixing polyvinyl alcohol (PVA) gel and water according to the proportion of 7:100 to obtain the foaming materialThen uniformly spraying the solution on the ceramic powder, stirring, adding the pre-sintered material obtained by stirring into a pore-forming agent silicon nitride hollow sphere, and transferring the pore-forming agent silicon nitride hollow sphere into a ball mill for stirring; transferring the stirred pre-fired material into a mould, and presintering for 20-40 min at 900-950 ℃ under the nitrogen atmosphere of 0.05-0.2 MPa; transferring the sintered material into a ball mill for strong stirring; transferring the stirred sintering material into a vacuum furnace for vacuum treatment, wherein the degassing time is not less than 10min; pouring the deaerated sintering material into a mould; transferring the mould to a refrigerator with the temperature of minus 10 ℃ to minus 15 ℃ for 24 hours; thawing the frozen sample at room temperature for 20h; transferring the thawed sample into an oven at 70-100 ℃ for drying for 24 hours; repeating the freezing-thawing-drying cycle for the sample; transferring the sample subjected to 2 times of circulating freeze thawing into a mould, and firing for 65min at 950-100 ℃ under the nitrogen atmosphere of 0.5-1 MPa to obtain the porous material with the porosity of 73.37-75.78% and the volume density of 1.53-2.13 g/cm 3 The bending strength is 62.1-166.3 MPa, and the crack resistance toughness is 1.78-3.54 MPa m 1/2 The dielectric coefficient is 3.74-4.76 ℃, the temperature is 10GHz, the heat conductivity coefficient is 2.19-2.41W/(m.K), and the water absorption rate is more than 4 percent.
The present invention is not limited to the above embodiments, but the scope of the invention is defined by the claims.
Claims (10)
1. The preparation method of the high-strength foamed ceramic under the freeze thawing cycle is characterized by comprising the following steps:
s1, respectively ball-milling and drying raw materials, and then preparing the raw materials into first ceramic powder according to a proportion;
s2, transferring the first ceramic powder into a ball mill, adding sodium tetraborate and metal wires serving as fluxing agents, and ball milling and stirring in the ball mill to obtain second ceramic powder;
s3, uniformly spraying and adding the foaming material into the second ceramic powder to obtain third ceramic powder;
s4, transferring the third ceramic powder into a ball mill, adding pore-forming agent powder, and stirring in a stirrer to obtain a pre-firing material;
s5, placing the pre-fired material into a die for presintering, and then strongly stirring and degassing;
s6, pouring the mixture subjected to degassing in the step S5 into a mold for cyclic freeze thawing;
and S7, firing the mixture subjected to the cyclic freeze thawing in the step S6 in a nitrogen atmosphere to obtain the high-strength foamed ceramic.
2. The method for preparing the high-strength foamed ceramic under the freeze-thawing cycle according to claim 1, wherein the raw materials in the step S1 are lepidolite tailings, ceramic polishing waste, fly ash and borax, and the mass ratio of the lepidolite tailings, the ceramic polishing waste, the fly ash and the borax is 16-20:32-40:16-20:14-26.
3. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the ball milling rotation speed in the step S1 is 150r/min-210r/min;
the ball milling time of lepidolite tailings in the raw materials is 12-24 hours; the ball milling time of the ceramic polishing waste is 8-15h; the ball milling time of the fly ash is 6-10h; the ball milling time of borax is 6-8h; the drying temperature is 90-120 ℃ and the drying time is 6-12 h.
4. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein in the step S2, the amount of sodium tetraborate is 14% -26% of the mass of the first ceramic powder, and the amount of metal wire is 30% -50% of the mass of the first ceramic powder; the rotating speed of the ball mill is 45r/min-70r/min, the ball milling and stirring time in the ball mill is not less than 1h, and the granularity of the obtained second ceramic powder is less than 75 mu m;
the diameter of the metal wire is less than or equal to 1mm, the length of the metal wire is 0.5-1.0cm, and the melting point of the metal wire is not lower than 1200 ℃.
5. The method for preparing high-strength foamed ceramic under freeze thawing cycle according to claim 1, wherein the foaming material in the step S3 is obtained by mixing PVA gel and water according to a mass ratio of 7-15:100, and the amount of the foaming material is 7% -15% of the mass of the second ceramic powder.
6. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the pore-forming agent in step S4 is Si 3 N 4 The average grain diameter of the pore-forming agent is 20-60 mu m, the dosage of the pore-forming agent is 16-21% of the mass of the third ceramic powder, and the stirring time in a stirrer is not less than 12h.
7. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the pre-sintering material in step S5 is fired under nitrogen atmosphere at a nitrogen pressure of 0.05-0.2 Mpa, a firing temperature of 900-1000 ℃ and a sintering time of 20-40 min.
8. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the rotation speed is 210r/min-340r/min when the gas is removed by strong stirring in the step S5.
9. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the cycle freeze-thawing in step S6 is specifically: freezing for 20-30 h at the temperature of minus 10-minus 15 ℃, then thawing for 20-30 h at room temperature, and continuously drying for 12-24h in a baking oven at 70-110 ℃ to realize one cycle of freezing and thawing;
and the number of times of cyclic freezing and thawing in the step S6 is not less than 2.
10. The method for preparing high-strength foamed ceramic under freeze-thawing cycle according to claim 1, wherein the firing temperature in the step S7 is 900-1000 ℃ and the firing time is 30-90 min.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311723464.0A CN117800755A (en) | 2023-12-14 | 2023-12-14 | Preparation method of high-strength foamed ceramic under freeze-thawing cycle |
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