Method for preparing alumina foamed ceramic by alumina sol self-gel forming
Technical Field
The invention belongs to the technical field of foamed ceramics, and particularly relates to a method for preparing alumina foamed ceramics by alumina sol self-gel forming.
Background
The foamed ceramic combines the characteristics of a foamed material and a ceramic material, has the advantages of low density, high specific surface area, high specific strength, high temperature resistance, corrosion resistance, wear resistance and the like, and can be widely applied to the fields of filtration, adsorption, catalysis, heat insulation and heat preservation. The preparation process of the foamed ceramic mainly comprises a pore-forming agent adding method, an organic foam impregnation method and a direct foaming method. The pore-forming agent method can regulate the size and shape of pores, but has low porosity, generally below 50%, and is mainly applied to general filters. The organic foam impregnation method can prepare high-porosity and open-cell foamed ceramics, but the removal of organic matters in the foamed ceramics pollutes the environment. The direct foaming method can prepare foamed ceramics with high porosity and high strength, and the preparation process is simpler.
The direct foaming method is to directly introduce bubbles into the slurry by stirring and the like, and the formed foam slurry is a thermodynamically unstable system, and a surfactant, a high molecular polymer and solid particles can be added to stabilize the foam slurry. However, the strength of the green body obtained by only stabilizing the foam slurry is low, which is not favorable for subsequent processing and transportation. At this time, curing agent can be added in the preparation process to fix the foam structure and increase the strength of the blank. Common curing methods are organic curing and inorganic curing. The use of organic curing such as gel casting requires binder removal and some organic monomers are toxic, while the use of inorganic curing such as cement curing introduces impurities, and therefore a new manufacturing process is required to increase green strength.
High porosity ceramic foams have many excellent properties, but the compressive strength decreases with increasing porosity. In production and application, the strength of the foamed ceramics and the green body is improved, so that the foamed ceramics and the green body are beneficial to further processing, transportation and application, and have practical significance.
Disclosure of Invention
In view of the background and the existing problems, the invention develops a method for preparing alumina foamed ceramics by aluminum sol self-gel forming, combines a direct foaming method with sol-gel, has very simple operation and convenient injection molding, is beneficial to preparing the foamed ceramics with specific shapes by utilizing the self-gel curing forming of the aluminum sol, has no inorganic matter as a coagulant, has no gel discharging process and very small addition amount, only plays a role of accelerating gel, and is not used as a curing agent. The invention can prepare the foamed ceramic with high porosity and high strength, and the compressive strength of the foamed ceramic under the same porosity is about 2 times of that of the foamed ceramic prepared by other methods.
The technical scheme adopted by the invention is as follows.
A method for preparing alumina foamed ceramics by alumina sol self-gel forming comprises the following steps:
(1) dissolving the aluminum sol powder in deionized water to prepare aluminum sol with the solid content of 15-35 wt%.
(2) And mechanically stirring the aluminum sol at a high speed, and adding 0.03-0.24 wt% of surfactant sodium dodecyl sulfate for foaming.
(3) Adding a coagulant with the concentration of 0.03-0.09 mmol/g, and continuing to stir at a high speed.
(4) Pouring and injecting the mixture, quickly gelling and curing the foam slurry, and drying the foam slurry in a constant-temperature and constant-humidity environment at the temperature of 20-30 ℃ and the temperature of 80-95% after demolding.
(5) And sintering the dried sample at 400-1500 ℃.
The aluminum sol powder is AlO (OH) with the particle size of 10-20 nm. And dissolving the powder in deionized water to obtain the alumina sol.
The coagulant can be ammonium chloride, potassium hydroxide, calcium chloride, and other inorganic electrolytes. The addition of the coagulant can increase the ionic strength of the slurry, compress the double electric layers of the colloid, reduce the repulsion between the colloids and accelerate the gelation of the sol.
Sintering at 400 ℃, 600 ℃ and 800 ℃ in the step 5) to obtain the gamma-Al2O3Sintering at 1000 ℃ to obtain theta-Al2O3Sintering at 1200 ℃ and above to obtain alpha-Al2O3。
The pore diameter of the foamed ceramic is 10-60 mu m, and the alpha-Al2O3The wall of the foamed ceramic hole is provided with a secondary mesoporous structure, and the grain size is nano-scale.
The invention can obtain a high-porosity and high-strength green body and alumina foamed ceramics, the compressive strength of the green body is 0.4-7.9 MPa when the porosity of the green body is 63.1-94.5%, and the alpha-Al2O3The compressive strength of the foamed ceramic is 26.1-97.8 MPa when the porosity of the foamed ceramic is 66.0-92.6%, and the compressive strength of the foamed ceramic under the same porosity is about 2 times that of the foamed ceramic under the same porosity, so that the application requirement of the foamed ceramic in the mechanical direction can be met.
The invention has the beneficial effects that: (1) the invention combines the direct foaming method with the sol-gel, thereby avoiding the problem that the low-strength ceramic body is obtained only by the direct foaming method. The raw material is aluminum sol, and the high-strength ceramic blank can be obtained by self-gel curing under the action of a coagulant without a curing agent. (2) The prepared green body and the foamed ceramic have high porosity and high strength, the compressive strength under the same porosity is about 2 times of that of the foamed ceramic prepared by other methods, and the prepared green body and the foamed ceramic have obvious advantages and are beneficial to further processing, transportation and application of the foamed ceramic. (3) The coagulant can be various inorganic electrolytes, does not need to discharge gel, has very small addition amount, only plays a role in accelerating gel and does not serve as a curing agent. (4) The gel time can be effectively controlled by adjusting the content of the coagulant, so that the aluminum sol foam slurry with fluidity can be quickly cured into foam gel after injection molding, the uniform pore structure of the foam ceramic is ensured, the compressive strength is favorably improved, and the foam ceramic with a specific shape can be obtained. (5) The microstructure, porosity and compressive strength of the foamed ceramic can be effectively controlled by adjusting the content of the surfactant and the solid content of the alumina sol. (6) alpha-Al2O3The foamed ceramic has a secondary mesoporous structure and is expected to be applied to the field of filtration. (7) Worker's toolThe alumina powder needs a sintering temperature of more than 1500 ℃, and the alpha-Al can be obtained by sintering the alumina sol at 1200 DEG C2O3The sintering temperature is reduced, and the energy consumption is reduced. (8) The preparation raw material only contains the aluminum sol, and then a small amount of surfactant and coagulant are added, so that impurities are not introduced basically, and the preparation process is simplified by utilizing self-gel curing of the foaming aluminum sol.
Drawings
FIG. 1 is a photograph of a foam green after demolding according to the method of the present invention.
FIG. 2 is a photograph of the foam green bodies with different shapes prepared by the method of the present invention after drying.
FIG. 3 is a view showing the preparation of alpha-Al by the method of the present invention2O3Micrographs of the ceramic foam.
FIG. 4 is a view showing the preparation of alpha-Al by the method of the present invention2O3Microscopic photograph of the cell walls of the ceramic foam.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
FIG. 1 is a photograph of a foam green after demolding according to the method of the present invention. It can be seen that the wet pour-molded green body had a very smooth surface, was substantially free of defects, had good shape retention, and had a specific shape.
FIG. 2 is a photograph of the foam green bodies with different shapes prepared by the method of the present invention after drying. It can be seen that the dry blank can maintain a complete shape with a smooth surface.
FIG. 3 is a view showing the preparation of alpha-Al by the method of the present invention2O3Micrographs of the ceramic foam. Therefore, the air hole structure is uniform and 10-60 mu m, and the compressive strength is favorably improved.
FIG. 4 is a view showing the preparation of alpha-Al by the method of the present invention2O3Microscopic photograph of the cell walls of the ceramic foam. The crystal grains are fine, and the hole wall is provided with a secondary mesoporous structure.
Example 1
(1) Dissolving the aluminum sol powder in deionized water to prepare the aluminum sol with the solid content of 30 wt%.
(2) The alumina sol was stirred with a mechanical stirrer at 2000rpm and 0.09 wt% sodium lauryl sulfate was added for foaming.
(3) Ammonium chloride was added at a concentration of 0.03mmol/g and high-speed stirring was continued.
(4) Pouring and injecting the mold, quickly solidifying the sample, and drying the sample in a constant temperature and humidity environment of 80 percent at 20 ℃ after demolding.
(5) And sintering the dried sample, heating to 500 ℃ for 33h, keeping the temperature for 1h, heating to 1200 ℃ at the speed of 3 ℃/min, and keeping the temperature for 2 h.
The porosity of the dried green body was 81.90%, and the compressive strength was 3.34 MPa. The porosity of the obtained alumina foamed ceramic after sintering is 80.69%, and the compressive strength is 66.73 MPa.
Example 2
(1) Dissolving the aluminum sol powder in deionized water to prepare the aluminum sol with the solid content of 15 wt%.
(2) The alumina sol was stirred with a mechanical stirrer at 2000rpm and 0.24 wt% sodium lauryl sulfate was added for foaming.
(3) Ammonium chloride was added at a concentration of 0.09mmol/g and high-speed stirring was continued.
(4) Pouring and injecting the mold, quickly solidifying the sample, and drying the sample in a constant temperature and humidity environment of 80 percent at 20 ℃ after demolding.
(5) And sintering the dried sample, heating to 500 ℃ for 33h, keeping the temperature for 1h, heating to 1200 ℃ at the speed of 3 ℃/min, and keeping the temperature for 2 h.
The porosity of the dried green body is 94.5%, and the compressive strength is 0.4 MPa. The porosity of the obtained alumina foamed ceramic after sintering is 92.6 percent, and the compressive strength is 26.1 MPa.
Example 3
(1) Dissolving the aluminum sol powder in deionized water to prepare aluminum sol with the solid content of 25 wt%.
(2) The alumina sol was stirred with a mechanical stirrer at 2000rpm and 0.03 wt% sodium lauryl sulfate was added for foaming.
(3) Ammonium chloride was added at a concentration of 0.06mmol/g and high speed stirring was continued.
(4) Pouring and injecting the mold, quickly solidifying the sample, and drying the sample in a constant temperature and humidity environment of 30 ℃ and 95 percent after demolding.
(5) And sintering the dried sample, heating to 500 ℃ for 33h, keeping the temperature for 1h, heating to 1200 ℃ at the speed of 3 ℃/min, and keeping the temperature for 2 h.
The porosity of the dried green body was 63.1%, and the compressive strength was 7.9 MPa. The porosity of the obtained alumina foamed ceramic after sintering is 66.0 percent, and the compressive strength is 97.8 MPa.
Example 4
(1) Dissolving the aluminum sol powder in deionized water to prepare aluminum sol with the solid content of 35 wt%.
(2) The alumina sol was stirred with a mechanical stirrer at 2000rpm and 0.09 wt% sodium lauryl sulfate was added for foaming.
(3) Potassium chloride with a concentration of 0.03mmol/g was added and high speed stirring was continued.
(4) Pouring and injecting the mold, quickly solidifying the sample, and drying the sample in a constant temperature and humidity environment of 30 ℃ and 95 percent after demolding.
(5) And sintering the dried sample, heating to 500 ℃ for 33h, keeping the temperature for 1h, heating to 1500 ℃ at 3 ℃/min, and keeping the temperature for 2 h.
The porosity of the dried green body is 73.8%, and the compressive strength is 4.5 MPa. The porosity of the obtained alumina foamed ceramic after sintering is 72.0 percent, and the compressive strength is 72.5 MPa.
The above embodiments describe the technical solutions of the present invention in detail. It will be clear that the invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various changes, but any changes equivalent or similar to the present invention are within the protection scope of the present invention.