Preparation method of a porous alumina ceramic

Abstract

The present invention relates to the technical field of porous alumina ceramics, and particularly relates to a porous alumina ceramic material and a preparation method thereof. The porous alumina ceramic comprises the following raw materials: wood fiber, phenolic resin solution, absolute ethanol, and nano-alumina sol. Among them, the preparation method of the porous alumina ceramic comprises the following steps: (1) impregnating the wood fiber with the nano-alumina sol for 24 hours; (2) gelling and drying in an electrothermal constant temperature blast drying oven at 135 °C; (3) impregnating the wood fiber with the phenolic resin solution prepared with the absolute ethanol at a weight ratio of 30% for 4 days; (4) after impregnation, drying the wood fiber in a blast box, then putting it into a mold with a diameter of 25 mm and a thickness of 5 mm, and then placing it in a blast box at 60 °C for curing; (5) after curing for 12 hours, demolding and then carbonizing at 800 °C under a nitrogen atmosphere condition in a vacuum tube furnace; (6) continuing to immerse the carbonized sample in the nano-alumina sol for 24 hours, then replacing the new nano-alumina sol and continuing vacuum impregnation for 1 hour; (7) gelling the porous alumina ceramic sample after vacuum impregnation in a ventilated drying oven at 135 °C for 2 hours; (8) after gel forming, sintering and heat preserving at 1550 °C for 2 hours under a filtered air atmosphere condition in a vacuum tube furnace, and then cooling with the furnace.

Description

Technical Field:

[0001] The present invention relates to the technical field of porous alumina ceramics, and particularly relates to a preparation method of porous alumina ceramics. Background Art:

[0002] Porous alumina ceramic materials refer to materials in which independent closed pores or connected open pores are introduced into the interior of ceramic materials through physical, chemical and other means. The introduction of the pore structure endows the ceramic materials with various additional properties. For example, the introduction of open pores can increase the specific surface area and permeability of the materials, and thus can be applied to fields such as catalyst carriers, substance separation, and high energy density materials; the introduction of independent closed pores can reduce the thermal conductivity of the materials, and thus can be applied to fields such as thermal insulation materials.

[0003] Porous alumina ceramics combine the above advantages of porous alumina ceramic materials, and at the same time also have the advantages of good chemical stability, high toughness, and lower thermal conductivity than common ceramic materials such as alumina of alumina ceramic materials. They are widely used in the fields of thermal insulation materials, corrosion-resistant materials, and bioengineering, and are a kind of ceramic material with great development potential.

[0004] Compared with other materials, due to the characteristics of porous alumina, when processing porous alumina into products with specific shapes, it is necessary to cut porous alumina, so it is easy to damage its porous properties and does not have good processability. Summary of the Invention:

[0005] In order to overcome the disadvantages and deficiencies existing in the prior art, the purpose of the present invention is to provide a porous alumina ceramic material, so that alumina inherits the excellent porous properties of biomass possessed by wood fibers, and no secondary processing of the porous ceramic is required during the sintering process, and the obtained porous ceramic material combines the corrosion resistance and high temperature resistance characteristics of alumina with the multi-level pores after the burning of wood fibers, and also has good mechanical properties; another purpose of the present invention is to provide a preparation method of the porous ceramic material, and the preparation method is simple and efficient, which is conducive to industrial production.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A porous alumina ceramic material, comprising the following raw materials: wood fibers, phenolic resin solution, absolute ethanol, nano-alumina sol;

[0008] Wherein, the preparation method of the porous alumina ceramics comprises the following steps:

[0009] (1) Immerse wood fibers in nano-alumina sol for 24 hours;

[0010] (2) Gel and dry in an electrothermal constant temperature blast drying oven at 135 °C;

[0011] (3) Impregnate the wood fibers with a phenolic resin solution prepared with absolute ethanol at a weight ratio of 30% for 4 days;

[0012] (4) After drying the impregnated wood fibers in a blast box, place them in a mold with a diameter of 25 mm and a thickness of 5 mm, and then place them in the blast box for curing at 60 °C;

[0013] (5) After 12 hours of curing, demold and then carbonize at 800 °C under a nitrogen atmosphere in a vacuum tube furnace;

[0014] (6) Immerse the carbonized sample in nano-alumina sol for 24 hours, then replace the fresh nano-alumina sol and continue vacuum impregnation for 1 hour;

[0015] (7) The porous alumina ceramic sample after vacuum impregnation gels at 135 °C for 2 hours in a ventilated drying oven;

[0016] (8) After gel forming, sinter at 1550 °C for 2 hours under a filtered air atmosphere in a vacuum tube furnace and then cool with the furnace.

[0017] The preparation mechanism of the porous aluminum oxide ceramic material of the present invention is as follows: the sintering temperature of alumina is about 1200 °C, the carbonization temperature of wood fibers is about 550 °C, and the ignition point of carbon is about 600 - 700 °C. During the impregnation process of nano-alumina, alumina particles tightly wrap around the pore structure of the biological tracheids of wood fibers and still adhere to the wood fibers during the impregnation of phenolic resin. Then, during the carbonization process, it does not change with temperature. After secondary impregnation and drying, by burning in air, the carbon elements in the wood fibers and phenolic resin are gradually burned off. During the burning process, alumina sinters into ceramic-form alumina, and as the wood fibers are burned away, the biomass structure pores left with the wood fibers as a template further improve the multi-level porosity of the porous alumina ceramic material. Finally, the prepared porous alumina ceramic has the characteristics of high porosity (50% - 70%), and the prepared porous alumina ceramic is a porous alumina ceramic material with high temperature resistance, corrosion resistance, good mechanical properties and multi-level pores including biomass template pores.

[0018] Among them, the wood fibers are pine wood fibers with a moisture content of 2% - 5%. By controlling the type and moisture content of the wood fibers, the pore formation after the combustion of the wood fibers and the spatial distribution of the wood fibers in the porous alumina ceramic can be improved, which is beneficial to forming a porous alumina material with sparse pores and certain mechanical properties after burning.

[0019] Among them, in the step (1), the mass percentage of alumina in the nano-alumina sol used for impregnation is 15%.

[0020] Among them, the mixing time required for the phenolic resin solution with a weight ratio of 30% prepared with absolute ethanol is more than 1 hour.

[0021] Among them, in the step (3), the grade of the phenolic resin solution is 2130. Preferably, the absolute ethanol is super pure absolute ethanol.

[0022] Among them, in the step (4), the pressure in the mold after mold clamping shall not exceed 10 MPa.

[0023] Among them, the pine wood fiber is at least one of Korean pine, hazel pine, Chinese red pine, and bunge pine. Preferably, the wood fiber is composed of Korean pine wood fiber with a moisture content of 5% and hazel pine wood fiber with a moisture content of 2% in a weight ratio of 1:2. This wood fiber combination has good dispersion performance and pore connectivity performance. The wood fiber can be fully dispersed in the porous alumina ceramic compact and form a porous alumina ceramic material with high mechanical properties and corrosion resistance after calcination.

[0024] Among them, the vacuum degree in the vacuum nano-alumina sol impregnation is 10 -3 mbar to 10 -4 mbar.

[0025] Among them, the particle size of alumina in the nano-alumina sol is 5 -10 nm, and the purity is 99.95%.

[0026] For the porous alumina ceramic material as described above, after opening the furnace and taking out the sample at the end of step (8), the porous ceramic material is obtained.

[0027] The beneficial effect of the present invention is that the preparation mechanism of the porous alumina ceramic material of the present invention is as follows: the sintering temperature of alumina is about 1200 °C, the carbonization temperature of wood fiber is about 550 °C, and the ignition point of carbon is about 600 - 700 °C. During the impregnation process of nano-alumina, alumina particles tightly wrap around the pore structure of the biological tracheids of the wood fiber and still adhere to the wood fiber during the impregnation of phenolic resin. Then, during the carbonization process, it does not change with the temperature. After secondary impregnation and drying, by calcining in the air, the carbon elements in the wood fiber and phenolic resin are gradually burned out. During the calcination process, alumina sinters into ceramic form alumina, and as the wood fiber burns away, the biomass structure pores left with the wood fiber as a template further improve the multi-level porosity of the porous alumina ceramic material. Finally, the prepared porous alumina ceramic has the characteristics of high porosity (50% - 70%). The prepared porous alumina ceramic is a porous alumina ceramic material with high temperature resistance, corrosion resistance, good mechanical properties, and multi-level pores including biomass template pores.

[0028] This porous alumina ceramic material is prepared using a wood material as a biological template, and it inherits the natural micro-porous structure of the wood. In wood, tracheids are interconnected through pits to form a three-dimensional network through-hole structure with well-developed pores. It can be seen from the wood fiber porous ceramic material that the natural microporous structure of the wood is completely retained during the matrix carbonization and ceramization processes. Compared with existing porous alumina materials, this feature ensures that this porous alumina ceramic material has good fluid transport capabilities. Description of the Drawings:

[0029] Figure 1 This is the biomass pore of the porous alumina ceramic-related micro-scale porous material in Example 1 of the present invention.

[0030] Figure 2 This is the biomass pore of the porous alumina ceramic-related micro-scale porous material in Example 2 of the present invention. Detailed Implementation Modes:

[0031] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with embodiments. The content mentioned in the implementation modes does not limit the present invention.

[0032] Example 1

[0033] A porous alumina ceramic material, comprising the following raw materials: wood fiber, phenolic resin solution, absolute ethanol, nano-alumina sol

[0034] Among them, the preparation method of the porous alumina ceramic comprises the following steps:

[0035] (1) Immerse the wood fiber in the nano-alumina sol for 24 hours;

[0036] (2) Gel and dry in an electrothermal constant temperature forced air drying oven at 135 °C;

[0037] (3) Immerse the wood fiber in a phenolic resin with a weight ratio of 30% prepared with absolute ethanol for 4 days;

[0038] (4) After drying the impregnated wood fiber in a forced air oven, place it in a mold with a diameter of 25 mm and a thickness of 5 mm, and then place it in a forced air oven at 60 °C for curing;

[0039] (5) After curing for 12 hours, demold and carbonize at 800 °C under a nitrogen atmosphere in a vacuum tube furnace;

[0040] (6) Immerse the carbonized sample in the nano-alumina sol for 24 hours, then replace it with a new nano-alumina sol and continue vacuum impregnation for 1 hour;

[0041] (7) The porous alumina ceramic sample after vacuum impregnation gels at 135 °C in a ventilated drying oven for 2 hours;

[0042] (8) After the gel is formed, it is sintered and heat-preserved at 1550 °C for 2 hours under the condition of filtering the air atmosphere in a vacuum tube furnace and then cooled with the furnace.

[0043] Among them, in the step (1), the mass percentage of alumina in the nano-alumina sol used for impregnation is 15%.

[0044] Among them, the mixing time required for the phenolic resin solution with a weight ratio of 30% prepared with absolute ethanol needs to be more than 1 hour.

[0045] Among them, in the step (3), the grade of the phenolic resin solution is 2130. Preferably, the absolute ethanol is super pure absolute ethanol.

[0046] Among them, in the step (4), the pressure in the mold after the mold is closed shall not exceed 10 MPa.

[0047] Among them, the wood fiber is composed of red pine wood fiber with a moisture content of 5% and hazel pine wood fiber with a moisture content of 2% in a weight ratio of 1:2. This wood fiber combination has good dispersion performance and pore connectivity performance. The wood fiber can be fully dispersed in the porous alumina ceramic compact and form a porous alumina ceramic material with high mechanical properties and corrosion resistance after burning.

[0048] Among them, the vacuum degree in the vacuum nano-alumina sol impregnation is 10 -3 mbar to 10 -4 mbar.

[0049] Among them, the particle size of alumina in the nano-alumina sol is 5 -10 nm, and the purity is 99.95%.

[0050] For the porous alumina ceramic material as described above, after the furnace is opened and the sample is taken out at the end of step (8), the said porous ceramic material is obtained.

[0051] Example 2

[0052] A porous alumina ceramic material, comprising the following raw materials: wood fiber, phenolic resin solution, absolute ethanol, nano-alumina sol

[0053] Among them, the preparation method of the porous alumina ceramic comprises the following steps:

[0054] (1) Impregnate the wood fiber with nano-alumina sol for 24 hours;

[0055] (2) Gel and dry in an electrothermal constant temperature blast drying oven at 135 °C;

[0056] (3) Impregnate the wood fibers with phenolic resin at a weight ratio of 30% prepared with absolute ethanol for 4 days;

[0057] (4) After drying the impregnated wood fibers in a blast box, place them in a mold with a diameter of 25 mm and a thickness of 5 mm, and then place the mold in the blast box for curing at 60 °C;

[0058] (5) After curing for 12 hours, demold and then carbonize at 800 °C under a nitrogen atmosphere in a vacuum tube furnace;

[0059] (6) Immerse the carbonized sample in nano-alumina sol for 24 hours, then replace the fresh nano-alumina sol and continue vacuum impregnation for 1 hour;

[0060] (7) The porous alumina ceramic sample after vacuum impregnation gels at 135 °C in a ventilated drying oven for 2 hours;

[0061] (8) After gel forming, sinter at 1550 °C for 2 hours under a filtered air atmosphere in a vacuum tube furnace and then cool with the furnace.

[0062] Among them, in the step (1), the mass percentage of alumina in the nano-alumina sol used for impregnation is 15%.

[0063] Among them, the mixing time required for the phenolic resin solution prepared with absolute ethanol at a weight ratio of 30% is more than 1 hour.

[0064] Among them, in the step (3), the grade of the phenolic resin solution is 2130. Preferably, the absolute ethanol is of superior grade pure absolute ethanol.

[0065] Among them, in the step (4), the pressure in the mold after mold closing shall not exceed 10 MPa.

[0066] Among them, the pine wood fibers are composed of red pine wood fibers with a moisture content of 5% and white pine wood fibers with a moisture content of 5% in a weight ratio of 3:2. This wood fiber combination has good dispersion performance and pore connectivity performance, and the wood fibers can be fully dispersed in the porous alumina ceramic compact, forming a porous alumina ceramic material with high mechanical properties and corrosion resistance after burning.

[0067] Among them, the vacuum degree in the vacuum nano-alumina sol impregnation is 10 -3 mbar to 10 -4 mbar.

[0068] Among them, the particle size of alumina in the alumina sol is 5 -10 nm, and the purity is 99.95%.

[0069] The porous alumina ceramic material as described above is obtained by opening the furnace and taking out the sample after the end of step (8).

Claims

1. A method for preparing porous alumina ceramics, characterized in that, It includes the following raw materials: wood fiber, phenolic resin solution, absolute ethanol, nano-aluminum oxide sol; the preparation method of the porous alumina ceramic includes the following steps: the wood fiber is impregnated with the nano-aluminum oxide sol for 24 hours, gelled and dried in an electrothermal constant temperature blast drying oven at 135 °C, the wood fiber is impregnated with the phenolic resin solution with a weight ratio of 30% prepared with the absolute ethanol for 4 days, after impregnation, the wood fiber is dried in a blast box and then put into a mold with a diameter of 25 mm and a thickness of 5 mm and then placed in a blast box at 60 °C for curing, after curing for 12 hours, demolding is carried out and carbonization is carried out at 800 °C under the condition of nitrogen atmosphere in a vacuum tube furnace, the carbonized sample is continuously impregnated in the nano-aluminum oxide sol for 24 hours and then new nano-aluminum oxide sol is replaced and vacuum impregnation is continued for 1 hour, the porous alumina ceramic sample after vacuum impregnation gels at 135 °C in a ventilation drying oven for 2 hours, after gel forming, sintering is carried out at 1550 °C under the condition of filtered air atmosphere in a vacuum tube furnace for heat preservation for 2 hours and then cooled with the furnace.

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