CN114790118A - Method for preparing porous alumina ceramic by using hollow microspheres - Google Patents

Abstract

The invention provides a method for preparing porous alumina ceramics by using hollow microspheres. The preparation method has the advantages of a mechanical foaming method and a gel injection method, and simultaneously introduces the hollow resin microspheres to regulate and control the microstructure according to the particle size of the hollow microspheres. The porous alumina ceramic prepared by the method has excellent performance. The porosity can be improved by 50-200% and the pore size distribution can be improved by additionally adding 0.5-1% of hollow microspheres. The method has the advantages of cheap and easily obtained raw materials, simple process, low cost, suitability for large-scale production and the like, and the prepared porous ceramic can be applied to the field of large-scale industrial production.

Description

Method for preparing porous alumina ceramic by using hollow microspheres

Technical Field

The invention relates to a method for preparing porous alumina ceramics by using hollow microspheres, belonging to the technical field of porous ceramic materials.

Background

The porous ceramic has the advantages of good permeability, low density, large specific surface area, small thermal conductivity, high temperature resistance, corrosion resistance and the like due to pores with specific pore diameter and morphology, so that the porous ceramic is widely applied to the fields of metallurgy, chemical industry, environmental protection, energy, biology, food and the like. Generally, porous ceramics are used for filtration, heat insulation, sound absorption, chemical fillers, bioceramics, catalyst carriers and the like. The aluminum oxide is the preferred material for high-temperature heat insulation at present due to high melting point, high strength and the like. For example, the high-temperature muffle furnace heat preservation material is basically alumina-based porous ceramic material.

At present, a plurality of methods for preparing the porous ceramics comprise a gas foaming method, a method for adding pore-forming agents, an organic foam impregnation method, a sol-gel method, a freeze drying method and the like. The porosity and pore structure obtained by different preparation processes are different. The pore-forming agent method is difficult to obtain high-porosity materials, and the application of the pore-forming agent method is limited. The porous ceramic prepared by the foaming method has high porosity and high strength, so the development is rapid. However, the pore size of the porous ceramics prepared by mechanical foaming is usually large, and is often 50-300 microns. The size of the pore diameter has a significant influence on the strength, thermal conductivity, and the like of the porous ceramic. The researchers use PMMA microspheres as pore-forming agents to prepare porous ceramics, and the pore size distribution of the PMMA microspheres is uniform and is mainly influenced by the microspheres. Recently, the porous ceramic prepared by combining the mechanical foaming method and the gel injection method has good performance and has the advantages of the two methods. For example, the invention patent of 'an anorthite porous ceramic with controllable structure and adjustable performance and a preparation method patent thereof' (patent number 201410362715.1), but the gel monomer adopted by the method is toxic, and the prepared porous ceramic has large pores. If the pore size of the foaming process can be controlled to improve the pore structure, the performance of the porous ceramic is remarkably improved.

Therefore, the preparation method of the porous ceramic is improved and optimized by introducing the hollow microspheres with controllable pore size distribution, and the prepared alumina porous ceramic with high porosity, controllable pore size distribution and excellent force/thermal performance has important significance, and is beneficial to reducing the cost and improving the market competitiveness.

Disclosure of Invention

In view of the above problems in the prior art, the present invention aims to provide a method for preparing porous alumina ceramics by using hollow microspheres, so as to solve the problem of too large and uneven pore size distribution in the mechanical foaming method.

In order to realize the aim, the invention selects high-purity alumina powder as a raw material, combines a mechanical foaming and gel injection method, and introduces hollow microspheres to regulate and control a pore structure to prepare the alumina porous ceramic. The method mainly comprises the following steps:

a) preparing deionized water, an auxiliary binder, a cross-linking agent and a dispersing agent into a premixed solution;

b) adding alumina powder, and preparing ceramic slurry which is uniformly mixed by ball milling;

c) adding the hollow microspheres and uniformly mixing;

d) adding a foaming agent, and performing mechanical foaming;

e) preparing a porous ceramic biscuit;

f) and sintering at high temperature to prepare the porous ceramic.

In the foaming and injection-coagulation process stage, deionized water is used as a solvent, Isobam is used as a cross-linking agent and a dispersing agent, epoxy resin is used as an auxiliary binder, and lauryl triethanolamine sulfate is used as a foaming agent. The premix liquid comprises deionized water, a cross-linking agent and a dispersing agent; the content of the deionized water is related to the solid content proportion; the content of Isobam is determined by the mass of solid content (alumina powder) and is 0.2-0.5 wt%;

furthermore, the auxiliary binder water-based epoxy resin is added into the premixed liquid, and the addition amount is 0.2 to 0.5 weight percent of the alumina powder.

Further, the solid content of the alumina in the slurry is 25-50 wt%.

Furthermore, the ball milling time of the slurry is 1-6h, the slurry is slightly alkaline, and the pH value is 8-10.

Furthermore, in order to solve the problem of large aperture of the traditional mechanical foaming method, resin hollow microspheres are added for regulation, the content of the hollow microspheres is 0.1-2wt%, and the mixing time is 0.5-2 h.

The foaming ratio is the key for controlling the porosity by a mechanical foaming method. The foaming volume can be controlled to increase by 2-4 times according to the solid content and the content of the foaming agent.

The added Isobam has the function of a cross-linking agent, and the slurry can be spontaneously gelled after being injected into a mould for tens of minutes to hours.

The gelled sample needs to be dried in a constant temperature and humidity environment to avoid cracking; e.g., 40 ℃, 75% relative humidity, etc.

The biscuit prepared by the method has little organic content. Drying, placing the mixture into a muffle furnace, heating to 600 ℃ at the speed of 1-5 ℃/min, preserving heat for 2 hours, and fully dehydrating and degreasing; then heating to 1450-1650 ℃ at the speed of 2-5 ℃/min, preserving the heat for 2-6 hours, and cooling along with the furnace.

Compared with the prior art, the preparation method has the advantages of a mechanical foaming method and a gel injection method, and the average pore diameter is greatly reduced by introducing the hollow microsphere regulation pore structure, the structure with the main mechanical foaming macropore is improved, and the performance of the porous ceramic is favorably improved.

The method for preparing the porous ceramic by utilizing hollow power-up and flexion has the advantages of easily available raw materials, simple process, low cost, suitability for large scale and the like, and the prepared alumina porous ceramic has the advantages of high porosity, higher strength, controllable pore size distribution and the like and can be used in a high-temperature environment.

Drawings

FIGS. 1 and 2 are fracture morphology (SEM) diagrams of alumina porous ceramics before and after addition of microspheres prepared in example 1;

fig. 3 is an XRD spectrum of the porous ceramic prepared in example 1.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are only for illustrating the present invention and are not to be construed as limiting the scope of the present invention.

Example 1

Weighing 300 g of commercial alumina powder, 63ml of deionized water, 1g of Isobam powder, 0.6g of epoxy resin and 4g of pre-prepared 40wt% foaming agent. Firstly, 1g of Isobam powder and 0.6g of epoxy resin are dissolved in deionized water, then alumina powder is added, ball milling is carried out for 4 hours, then 1g of hollow microspheres are added, and mixing is carried out for 30 min. Then adding a foaming agent, quickly stirring and foaming by adopting an electric stirrer, wherein the stirring speed is 2500 revolutions per minute, and stopping foaming when the volume is increased to about 3 times. The foamed slurry is poured into a mold and the gel cured at room temperature, typically taking several hours. And (4) demolding the solidified biscuit, and drying in a constant temperature and humidity box. And (3) putting the completely dried biscuit sample into a muffle furnace, heating to 600 ℃ at the speed of 2 ℃/min in the air atmosphere, preserving heat for 2 hours, fully dehydrating and degreasing, heating to 1600 ℃ at the speed of 5 ℃/min, and preserving heat for 2 hours to obtain the porous alumina ceramic.

Fig. 1 and 2 are fracture morphology diagrams (SEM) of the prepared alumina porous ceramic before and after adding the microspheres, and it can be seen from fig. 1 that: after the microspheres are added, a large amount of small-size pores are introduced, and the pore distribution is greatly improved. Tests show that after the microspheres are added, the porosity is increased by 11 percent and is 71.7 percent; the average pore size was reduced by 43% to 46 microns; the compressive strength was 51MPa, and the thermal conductivity was 1.8W/m.K.

FIG. 2 is an XRD spectrum of the prepared alumina porous ceramic.

Finally, it is necessary to explain here: the above embodiments are only used for further detailed description of the technical solutions of the present invention, and should not be understood as limiting the scope of the present invention, and the insubstantial modifications and adaptations made by those skilled in the art according to the above descriptions of the present invention are within the scope of the present invention.

Claims (7)

1. A porous alumina ceramic prepared by utilizing hollow microspheres is characterized by comprising the following steps:

a) preparing deionized water, an auxiliary binder, a cross-linking agent and a dispersing agent into a premixed solution;

b) adding alumina powder, and preparing ceramic slurry by ball milling;

c) adding the hollow microspheres and uniformly mixing;

d) adding a foaming agent, and performing mechanical foaming;

e) preparing a porous ceramic biscuit;

f) and sintering at high temperature to prepare the porous ceramic.

2. The method of claim 1, wherein: in the step a), the dispersant and the cross-linking agent are Isobam, and the addition amount is 0.2-0.5 wt%; the auxiliary binder is water-based epoxy resin, and the addition amount is 0.2-0.5 wt%.

3. The method of claim 1, wherein: in the step b), the solid content of the alumina in the slurry is 25-50 wt%, and the ball milling time of the slurry is 1-6 h.

4. The method of claim 1, wherein: in the step c), the content of the hollow microspheres is 0.1-2wt%, and the mixing time is 0.5-2 h.

5. The method of claim 1, wherein: in the step d), the foaming agent is lauryl sulfuric acid triethanolamine, and the adding amount of the foaming agent is 0.5-1% of the total volume fraction of the slurry.

6. The method of claim 1, wherein: and e) drying the biscuit in the step e), wherein the biscuit is dried in a constant temperature and humidity environment to ensure that the biscuit does not crack.

7. The method of claim 1, wherein: in the step f), heating to 600 ℃ at the speed of 1-5 ℃/min in the air atmosphere, preserving the heat for 2 hours, and fully dehydrating and degreasing; then heating to 1450-1650 ℃ at the speed of 2-5 ℃/min, preserving the temperature for 2-6 hours, and cooling along with the furnace to obtain the porous alumina ceramic.

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