CN114671674B

CN114671674B - Silicon dioxide foam ceramic and preparation method thereof

Info

Publication number: CN114671674B
Application number: CN202210257884.3A
Authority: CN
Inventors: 张雅; 程骞; 蒋湘芬; 金成�; 王学斌
Original assignee: Shanghai Xuanyi New Energy Development Co ltd
Current assignee: Shanghai Xuanyi New Energy Development Co ltd
Priority date: 2022-03-14
Filing date: 2022-03-14
Publication date: 2023-09-15
Anticipated expiration: 2042-03-14
Also published as: CN114671674A

Abstract

The invention discloses a silicon dioxide foam ceramic and a preparation method thereof, belonging to the technical field of heat insulation materials. The preparation method of the silicon dioxide foam ceramic comprises the following steps: (1) Uniformly mixing a carbon source, a foaming agent and silicon dioxide powder to obtain mixed powder; (2) And (3) placing the mixed powder into a forming die, heating to 1000-1250 ℃ in an air atmosphere, and carrying out heat preservation treatment to obtain the silicon dioxide foamed ceramic. During heating, the mixed powder undergoes two chemical processes of thermochemical foaming and etching carbon removal, but the two chemical processes do not need to be operated separately on a process route, but can be completed after one-step heating. The invention has simple process, short production period and recycling of foaming agent, and the prepared silicon dioxide foam ceramic has the characteristics of high porosity and low thermal conductivity.

Description

Silicon dioxide foam ceramic and preparation method thereof

Technical Field

The invention belongs to the technical field of heat insulation materials, and particularly relates to a silicon dioxide foam ceramic and a preparation method thereof.

Background

The heat insulation technology product has great application prospect in the field of new energy batteries which are rapidly developed at present, and development of new materials is also needed. In practice, the polyurethane foam or phenolic foam has a smaller use temperature range, and has potential safety hazards such as flammability. Fiber heat insulation materials such as glass wool have certain harm to health. The appearance shape of the vacuum insulation panel is not easy to control. Porous materials of heavy element oxides, such as porous silica, porous zirconia, are theoretically very suitable heat resistant, insulating materials.

The foam ceramic is a porous inorganic nonmetallic material and has important application in the aspects of heat resistance, heat insulation, filtration and separation under severe working conditions and the like. Oxide foams are typical representations of ceramic foams. The silicon dioxide foam ceramic has great application value in the fields of heat insulation, aerospace, hot filtration, medical treatment, new energy and the like because of high stability, low heat conductivity coefficient and thermal shock resistance.

The preparation methods commonly adopted by the prior silicon dioxide foam ceramics are a template method, a gel casting method and a direct foaming method. The template method uses polymer foam as a template, and uses ceramic suspension to permeate the template, and after the template coated with the ceramic coating is dried, the template is removed by pyrolysis and the like, and finally, the ceramic coating is further densified by calcination (Ceramics International 2021,47,14561). In practical application, the ceramic slurry has certain difficulty and complexity on uniform coating of the template and controllable distribution of pore-forming agents, the non-compact pore-size framework is unfavorable for the mechanical performance, and toxic gas is usually generated in the template removal process, so that the template has certain harm to the environment. The gel casting method utilizes in-situ reaction solidification molding of organic monomers to obtain stable foamed ceramics with better consistency, but longer process period and higher requirements on experimental process reduce the feasibility of industrialization (Ceramics International 2020,46,12282). The direct foaming method introduces bubbles into ceramic suspension or precursor components for foaming by a physical or chemical method, then performs steps such as liquid discharge solidification and the like, maintains a pore structure brought by the bubbles to the foamed ceramic, and sinters to obtain open-cell or closed-cell porous ceramic (Journal of the Ceramic Society of Japan 2017,125,7). The foaming of the direct foaming method has certain difficulty, the thermodynamic instability of a wet foam system can combine small bubbles into large bubbles, the pore size is uneven, a surfactant or biological macromolecules such as proteins and the like are usually required for carrying out surface modification on ceramic particles, and the preparation procedures such as pulping, drying and the like take longer time.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a silicon dioxide foam ceramic and a preparation method thereof. The preparation method has the advantages of simple process, short production period, controllable product appearance, high porosity and low heat conductivity coefficient, and has the application prospect of heat insulation.

The technical scheme adopted by the invention comprises the following steps:

the preparation method of the silicon dioxide foam ceramic comprises the following steps:

(1) Uniformly mixing a carbon source, a foaming agent and silicon dioxide powder to obtain mixed powder; preferably, the carbon source comprises at least one of chitosan, cellulose, starch, lignin, hemicellulose, chitin, cyclodextrin, levan, xylose. The foaming agent comprises at least one of ammonium chloride, ammonium sulfate, ammonium carbonate and ammonium nitrate. Further preferably, the mass ratio of the carbon source, the foaming agent and the silicon dioxide powder is 1 (0.1-1): 0.8-1.6.

(2) And (3) placing the mixed powder into a forming die, heating to 1000-1250 ℃ in an air atmosphere, and carrying out heat preservation treatment to obtain the silicon dioxide foamed ceramic. Preferably, the heating rate is 0.3-10 ℃/min, and the heat preservation treatment time is 10-180 min.

The invention also discloses a silicon dioxide foam ceramic, which is prepared by adopting the preparation method.

Compared with the prior art, the preparation method of the invention has the following outstanding advantages:

1) The invention has simple process route. During heating, the mixed powder undergoes two chemical processes of thermochemical foaming and etching carbon removal, but the two chemical processes are not required to be operated separately on a process route, and can be completed after one-step heating, so that a required product is obtained. Specifically, the carbon source organic powder may form a polymer when heated to a temperature of 400 ℃. Simultaneously, the foaming agent is decomposed by heat to generate gases, and the gases foam the polymer substances to form polymer foam. The foaming process also drives the silica powder to distribute the silica powder in the polymeric foam. When the heating is continued to 1000 ℃ or above, the polymer is continuously coked and carbonized, but all carbon elements are finally oxidized by air and disappear at 1000 ℃ or above. The silica may be stable at high temperatures and thus remain, eventually turning into silica foam. In appearance, resembles a white sponge.

2) The foaming agent is decomposed during heating, but is recombined into ammonium salt during cooling, and is deposited in an exhaust system and can be reused as a raw material.

3) The process route of the invention has low requirements on equipment and short production period, and can easily realize the mass preparation of the silica foam ceramic. Compared with the related prior art, the invention has the important technical improvement that the inert atmosphere is abandoned. The inventors found that most organics do not burn when heated to 400 ℃ in air, at which point polymerization and coking reactions with the participation of the oxygen molecules occur, and at which point the foaming operation can already be performed. Therefore, the carbon source, the foaming agent, and the silica powder are heated in air, and thermal foaming can be performed. Based on the technical progress, the production process is da Jian which is one-step heating operation, and the gas cost (only air is needed in the invention) and the production line equipment cost are greatly reduced.

4) The silicon dioxide foam ceramic provided by the invention has the characteristics of high porosity and low heat conductivity coefficient, and has important application prospects in the field of heat insulation. Compared with the alumina foam heat insulation material, the sintering temperature of the silicon oxide is lower than that of the alumina, so that the end temperature of the invention can be reduced to 1250 ℃ or lower, and the energy consumption is greatly saved. In addition, in terms of heat insulating performance, the intrinsic thermal conductivity of silicon oxide is lower than that of aluminum oxide, and the aluminum oxide has a high-temperature phase transition phenomenon, which causes structural collapse and degradation of heat insulating performance, so that the silicon oxide foam heat insulating material is more generally and more important than the aluminum oxide foam heat insulating material.

Drawings

FIG. 1 is an optical photograph of the intermediate product (product at 400 ℃) and silica foam ceramic (product at 1150 ℃) obtained in example 1.

FIG. 2 is an X-ray diffraction chart of the silica foam ceramic obtained in example 1 after grinding.

FIG. 3 is a scanning electron micrograph of a broken surface of the silica foam ceramic obtained in example 1.

Detailed Description

The invention will now be further described by way of specific examples in conjunction with the accompanying drawings, which are given by way of illustration only and not by way of limitation. The starting materials used in the examples below were all commercially available products, commercially available.

(1) 1.2g of silicon dioxide powder is weighed and mixed with 0.8g of ammonium chloride and 1g of chitosan to obtain mixed powder.

(2) Transferring the mixed powder into a muffle furnace, heating at a heating rate of 2.5 ℃/min, and obtaining an intermediate product (porous coke and silicon dioxide mixed foam) when the temperature is raised to 400 ℃; continuously heating to 1150 ℃, preserving heat for 1h, and cooling to obtain the target product, namely the silicon dioxide foam ceramic.

The intermediate product obtained in example 1, i.e., the porous coke and silica mixed foam, appears as a black foam in appearance (left in fig. 1); the silica foam ceramic obtained in example 1 was represented in appearance by a white light porous foam-like structure (right side of FIG. 1), and the X-ray diffraction pattern (see FIG. 2) thereof showed a partial amorphous phase, a partial quartz phase and a phosphoquartz phase; the scanning electron micrograph of which reveals the three-dimensional skeletal structure of the sample (fig. 3), resembling the structure of a foamed sponge.

Adopting a static weighing method based on an Archimedes principle, and calculating the porosity of a sample to be 97.6% according to a full-automatic true density instrument; the thermal conductivity of the silicon dioxide foamed ceramic is measured to be 0.038W/(m K) based on a transient plane heat source method (according to the national standard GB/T32064-2015 test) by a thermal conductivity tester.

Example 2:

the temperature rising rate in the step (2) of the example 1 was changed to 4 ℃/min, and the other operations were the same as those of the example 1, and the obtained silica foam ceramic had a porosity of 98.5% and a thermal conductivity of 0.038W/(m K).

Example 3:

the temperature rising rate in the step (2) of the example 1 was changed to 1 ℃/min, and the other operations were the same as those of the example 1, and the obtained silica foam ceramic had a porosity of 97.2% and a thermal conductivity of 0.042W/(m K).

Example 4:

the calcination temperature in step (3) of example 1 was changed to 1250℃and the other operations were the same as in example 1, except that the porosity of the obtained silica foam ceramic was 96.2% and the thermal conductivity was 0.065W/(m K).

Example 5:

the mass of ammonium chloride in the step (1) of the example 1 was changed to 0.5g, and the operations were the same as those of the example 1, except that the porosity of the obtained silica foam ceramic was 96.6%, and the thermal conductivity was 0.045W/(m K).

Example 6:

the mass of ammonium chloride in the step (1) of example 1 was changed to 0.2g, and the operations were the same as those of example 1, except that the porosity of the obtained silica foam ceramic was 94.1%, and the thermal conductivity was 0.058W/(m K).

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 those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Claims

1. A preparation method of silicon dioxide foam ceramic is characterized in that: the method comprises the following steps:

(1) Uniformly mixing a carbon source, a foaming agent and silicon dioxide powder to obtain mixed powder; the carbon source is chitosan, and the foaming agent is ammonium chloride; the mass ratio of the carbon source to the foaming agent to the silicon dioxide powder is 1 (0.1-1): 0.8-1.6;

(2) Placing the mixed powder into a forming die, heating to 1000-1250 ℃ in an air atmosphere, and carrying out heat preservation treatment to obtain silicon dioxide foamed ceramic; the heating rate of the heating is 0.3-10 ℃/min.

2. The method for producing a silica foam ceramic according to claim 1, wherein: the mass ratio of the carbon source to the foaming agent to the silicon dioxide powder is 1:0.8:1.2.

3. The method for producing a silica foam ceramic according to claim 1, wherein: the mass ratio of the carbon source to the foaming agent to the silicon dioxide powder is 1:0.5:1.2.

4. The method for producing a silica foam ceramic according to claim 1, wherein: the mass ratio of the carbon source to the foaming agent to the silicon dioxide powder is 1:0.2:1.2.

5. The method for producing a silica foam ceramic according to any one of claims 1 to 4, wherein: in the step (2), the heat preservation treatment time is 10-180 min.

6. A silica foam ceramic characterized in that: the silica foam ceramic is prepared by the preparation method according to any one of claims 1 to 5.