CN114773092A - A method for improving mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels by oxidation treatment - Google Patents

Abstract

The invention discloses a method for improving the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogel by oxidation treatment, and belongs to the technical field of silicon carbide aerogel preparation. The thickness of the oxide layer of the silicon carbide nanowire aerogel is adjusted by reasonable oxidation treatment, and the microstructure of the silicon carbide nanowire is changed with the help of the oxide layer, which increases the number of nodes in the silicon carbide nanowire network and improves the strength and elasticity at the same time; oxidation; The intrinsic thermal conductivity of silicon is much lower than that of silicon carbide, and the content of silicon oxide increases, resulting in a decrease in thermal conductivity of the oxidized silicon carbide nanowire aerogel; the introduction of silicon carbide/silicon oxide interface enhances phonon scattering and achieves In order to simultaneously improve the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels. The invention realizes the improvement of the mechanical properties and thermal insulation properties of the silicon carbide nanowire aerogel through simple oxidation treatment, and is helpful for promoting the practical application of the silicon carbide nanowire aerogel.

Description

A method for improving mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels by oxidation treatment

technical field

The present invention relates to the technical field of preparation of silicon carbide nanowire aerogel, in particular to a method for improving the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogel by oxidation treatment.

Background technique

Aerogels are nano-scale porous lightweight materials built with open-pored network skeletons, which have many unexpected and excellent properties, such as ultra-low density, high porosity, low thermal conductivity and good chemical stability, attracting research. The attention of scholars is that aerogels have particularly attractive application prospects in harsh service conditions such as high temperature heat insulation, catalyst carriers, filters, etc., especially in high temperature and aerobic environments. According to the different compositions, aerogels can be divided into carbon-based aerogels, polymer-based aerogels and ceramic-based aerogels. Among them, carbon-based aerogels and polymer-based aerogels are prone to damage in high-temperature aerobic environments due to the poor high-temperature stability of their constituent elements (carbon materials, polymers). Due to the good thermal and chemical stability of ceramic materials, ceramic-based aerogels have become one of the ideal candidates for high-temperature thermal insulation materials, catalyst carriers, filters and other high-temperature aerobic environments. Traditional ceramic-based aerogel materials, such as silica (SiO ₂ ) aerogel, alumina (Al ₂ O ₃ ) aerogel, are usually composed of a necklace-like connection of nano-ceramic particles with low strength. In practical applications, it is often required to be used in combination with fibers. In addition, due to the inherent brittleness of ceramics, the application of traditional ceramic aerogels is greatly restricted. For example, when the temperature of pure SiO ₂ aerogel exceeds 600°C, due to the sintering of the internal amorphous SiO ₂ particles, a severe volume shrinkage occurs, which makes it difficult to apply SiO ₂ aerogel in a high temperature environment. Al ₂ O ₃ aerogel will undergo crystal transformation at 1000 ℃, from γ-type to α-type, which will produce obvious volume shrinkage, resulting in a rapid decrease in volume stability, which greatly limits the aerogelation of Al ₂ O ₃ Further application of glue.

Silicon carbide nanowire aerogel is a new type of ceramic aerogel, which is composed of one-dimensional silicon carbide nanowires lapped, wound and self-assembled to form a three-dimensional network structure. Not only has the high temperature stability and chemical stability of the silicon carbide ceramic body, but also the one-dimensional nanowires endow it with flexibility, so the silicon carbide nanowire small aerogel has good elastic recovery performance, excellent high temperature stability and fire resistance, low heat It overcomes the problems of high brittleness and poor thermal stability of traditional ceramic materials. However, because the silicon carbide nanowires inside the silicon carbide nanowire aerogel rely on van der Waals force to lap together, the strength and elastic modulus are very low, and the mechanical properties are poor. In addition, the thermal conductivity of SiC nanowire aerogels increases rapidly with increasing ambient temperature, resulting in poor thermal insulation performance.

Based on the above, considering the reliable and efficient service in high temperature aerobic environment, the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels need to be further improved. At present, the mainstream means to improve the mechanical properties of silicon carbide aerogel materials are to prepare them into composite aerogels of various components to improve the mechanical properties. By reducing the porosity, reducing the density of the material, reducing the thermal conductivity, etc. To achieve the purpose of improving the thermal insulation performance, but most of these methods have complex preparation processes and low controllability, and cannot achieve the purpose of simultaneously improving the mechanical properties and thermal insulation properties.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for improving the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels through oxidation treatment, which is simple in process, low in equipment requirements, and can simultaneously improve the Mechanical and thermal insulation properties of silicon carbide nanowire aerogels.

In order to achieve the above object, the present invention adopts the following technical solutions to be realized:

The invention discloses a method for improving the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogel through oxidation. Through high-temperature oxidation treatment, a silicon oxide layer is formed on the surface of the silicon carbide nanowire aerogel, so that the silicon carbide nanowire aerogel is The strength, compressive resilience and thermal insulation properties of the gel are all improved.

Preferably, the high temperature oxidation treatment temperature is 900-1200° C., and the treatment time is 0.5-1.6 h.

Preferably, the high temperature oxidation treatment is carried out in a high temperature box-type resistance furnace.

Preferably, the diameter of the silicon carbide nanowire aerogel used is 50 nm to 300 nm.

Preferably, the thickness of the silicon oxide layer is 10 nm˜160 nm.

Preferably, the mechanical properties and thermal insulation properties of the silicon carbide nanowire aerogel can be regulated by changing the high-temperature oxidation temperature or treatment time.

Preferably, the elastic modulus of the treated silicon carbide nanowire aerogel is increased from 49.4 kPa to 68.6 kPa˜265.0 kPa.

Preferably, the stress corresponding to a 40% compressive strain of the treated silicon carbide nanowire aerogel is increased from 21.7 kPa to 33.2 kPa˜78.5 kPa.

Preferably, the resilience of the treated silicon carbide nanowire aerogel is increased from 51.9% to 54.8%-63.5%.

Preferably, the thermal conductivity of the treated silicon carbide nanowire aerogel is reduced from 39.1 mW·m ^-1 ·K ^-1 to 27.7-37.4 mW·m ^-1 ·K ^-1 .

Compared with the prior art, the present invention has the following beneficial effects:

The method for improving the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels through oxidation treatment disclosed in the invention, by improving the oxidation degree of silicon carbide nanowires, the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels can be obtained. This is because the higher the degree of oxidation of the silicon carbide nanowire aerogel, the thicker the silicon oxide layer of the internal silicon carbide nanowires, the easier the oxide layer is to flow, and the easier the silicon carbide nanowires are bonded together. This structurally improves the strength and prevents the SiC nanowires from slipping and deforming, so the elastic modulus, strength and resilience of the SiC nanowire aerogel after oxidation are improved. The oxidized silicon oxide is an amorphous substance with low intrinsic thermal conductivity; at the same time, the interface between the oxide layer/silicon carbide introduced by oxidation will increase phonon scattering, so the oxidized silicon carbide nanowires The thermal conductivity of the aerogel is reduced and the thermal insulation performance is improved. The invention adopts a simple oxidation treatment method, requires simple equipment and process, and is suitable for greatly improving the mechanical properties and thermal insulation properties of the silicon carbide nanowire aerogel in the actual production process.

Further, after the method is processed, the elastic modulus of the silicon carbide nanowire aerogel increases by 38.9% to 436.4%, in the range of 68.6kPa to 265.0kPa; when the silicon carbide nanowire aerogel is subjected to a compressive strain of 40% The stress of silicon carbide nanowire aerogel increased by 53.9% to 261.8%, in the range of 33.2kPa to 78.5kPa; the rebound rate of silicon carbide nanowire aerogel under 40% compressive strain increased by 5.6% to 22.4%, and in the range of 54.8% ∼63.5%; the thermal conductivity of SiC nanowire aerogel decreased by 4.3%∼41.2%, ranging from 27.7mW·m ^-1 ·K ^-1 to 37.4mW·m ^-1 ·K ^-1 .

Description of drawings

Fig. 1 is the SEM image of silicon carbide nanowire aerogel;

Fig. 2 is the diameter distribution statistics (1000 pieces) of the silicon carbide nanowires contained in the silicon carbide nanowire aerogel;

Fig. 3 is the compressive stress-strain curve of the unoxidized silicon carbide nanowire aerogel;

4 is a compressive stress-strain curve of the silicon carbide nanowire aerogel in Example 1 after being oxidized at 1000° C. for 0.5h;

5 is a compressive stress-strain curve of the silicon carbide nanowire aerogel in Example 2 after being oxidized at 1000° C. for 1 h;

6 is a compressive stress-strain curve of the silicon carbide nanowire aerogel in Example 3 after being oxidized at 1000° C. for 8 hours;

7 is a compressive stress-strain curve of the silicon carbide nanowire aerogel in Example 4 after being oxidized at 1000° C. for 16h;

8 is a thermal conductivity diagram of the silicon carbide nanowire aerogels without oxidation treatment and after being oxidized at 1000° C. for 0.5 h, 1 h, 8 h and 16 h.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first", "second" and the like in the description and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used may be interchanged under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

Below in conjunction with accompanying drawing, the present invention is described in further detail:

The method for improving the mechanical properties and thermal insulation properties of the silicon carbide nanowire aerogel disclosed by the invention only controls the thickness range of the oxide layer through oxidation treatment, thereby realizing the improvement of the performance of the silicon carbide nanowire aerogel. A silicon oxide layer is formed on the surface of silicon carbide nanowires by high-temperature oxidation treatment, which can strengthen the overlap between nanowires in silicon carbide nanowire aerogel, and the silicon oxide layer acts as a binder to bond silicon carbide nanowires. Thus, the number of nodes in the nanowire skeleton is increased, so that the strength and elasticity of the silicon carbide nanowire network are simultaneously improved; in addition, the silicon carbide/silicon oxide interface is introduced, the thickness of the silicon oxide layer is increased, and the silicon carbide nanowire aerogel is reduced. The thermal conductivity of SiC nanowire aerogels can be synergistically improved, and the mechanical properties and thermal insulation properties of the aerogels are improved.

The thickness of the oxide layer of the silicon carbide nanowire aerogel is adjusted by a reasonable oxidation treatment, and the microstructure of the silicon carbide nanowire is changed with the help of the oxide layer, which increases the number of nodes in the silicon carbide nanowire network, and improves the strength and elasticity at the same time; oxidation; The intrinsic thermal conductivity of silicon is much lower than that of silicon carbide, and the content of silicon oxide increases, which reduces the thermal conductivity of the oxidized silicon carbide nanowire aerogel; the introduction of silicon carbide/silicon oxide interface enhances phonon scattering and achieves In order to simultaneously improve the mechanical properties and thermal insulation properties of silicon carbide nanowire aerogels.

The silicon carbide nanowire aerogel used in the present invention is prepared according to the method disclosed in Chinese invention patent CN109627006B. Referring to FIG. 1 , the microscopic SEM image of the silicon carbide nanowire aerogel is shown. Referring to FIG. 2 , the statistics of the diameter distribution of the silicon carbide nanowires contained in the silicon carbide nanowire aerogel are shown, with a total of 1000 counts.

The initial diameter distribution of the silicon carbide nanowires contained in the silicon carbide nanowire aerogel is between 50 nm and 300 nm, and the thickness of the oxide layer of the silicon carbide nanowire aerogel after oxidation treatment is between 10 and 160 nm.

The temperature range of high temperature oxidation treatment is: 900℃～1200℃; the oxidation time range is 0.5h～16h.

Example 1

In this example, the silicon carbide nanowire aerogel was oxidized at 1000°C for 0.5h, and the properties after oxidation were as follows:

1) The elastic modulus of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 0.5 h increased from 49.4 kPa to 68.6 kPa, an increase of 38.9%;

2) The SiC nanowire aerogel after being oxidized at 1000°C for 0.5h, its stress under 40% compressive strain increases from 21.7kPa to 33.2kPa, an increase of 53.0%;

3) The SiC nanowire aerogel after being oxidized at 1000 °C for 0.5 h, its resilience under 40% compressive strain increased from 51.9% to 54.8%, an increase of 5.6%;

4) The thermal conductivity of the silicon carbide nanowire aerogels oxidized at 1000 °C for 0.5 h decreased by 4.3% from 39.1 mW·m ^-1 ·K ^-1 to 37.4 mW·m ^-1 ·K ^-1 .

Example 2

In this example, the silicon carbide nanowire aerogel was oxidized at 1000 °C for 1 h, and the properties after oxidation were as follows:

1) The elastic modulus of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 1 h increased from 49.4 kPa to 76.8 kPa, an increase of 55.5%;

2) The SiC nanowire aerogel after being oxidized at 1000℃ for 1h, its stress under 40% compressive strain increases from 21.7kPa to 39.6kPa, an increase of 8.2%;

3) The SiC nanowire aerogel after being oxidized at 1000 °C for 1 h, its resilience under 40% compressive strain increased from 51.9% to 57.5%, an increase of 10.8%;

4) The thermal conductivity of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 1 h decreased from 39.1 mW·m ^-1 ·K ^-1 to 35.1 mW·m ^-1 ·K ^-1 , a decrease of 10.2%.

Example 3

In this example, the silicon carbide nanowire aerogel was oxidized at 1000 ° C for 8 hours, and the properties after oxidation were as follows:

1) The elastic modulus of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 8 h increased from 49.4 kPa to 235.4 kPa, an increase of 376.5%;

2) The SiC nanowire aerogel after being oxidized at 1000°C for 8h, its stress under 40% compressive strain increases from 21.7kPa to 47.8kPa, an increase of 120.3%;

3) The SiC nanowire aerogel after being oxidized at 1000°C for 8h, its resilience under 40% compressive strain increased from 51.9% to 66.5%, an increase of 28.1%;

4) The thermal conductivity of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 8 h decreased from 39.1 mW·m ^-1 ·K ^-1 to 27.8 mW·m ^-1 ·K ^-1 , a decrease of 28.9%.

Example 4

In this example, the silicon carbide nanowire aerogel was oxidized at 1000 ° C for 16 hours, and the properties after oxidation were as follows:

1) The elastic modulus of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 16 h increased from 49.40 kPa to 265.0 kPa, an increase of 436.4%;

2) For the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 16 h, the stress under 40% compressive strain increased from 21.7 kPa to 78.5 kPa, an increase of 261.8%;

3) For the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 16 h, its resilience under 40% compressive strain increased from 51.9% to 63.5%, an increase of 22.4%;

4) The thermal conductivity of the silicon carbide nanowire aerogel after being oxidized at 1000 °C for 16 h decreased from 39.1 mW·m ^-1 ·K ^-1 to 27.7 mW·m ^-1 ·K ^-1 , a decrease of 29.2%.

Comparative Example 1

The silicon carbide nanowire aerogel not treated by the method of the present invention is prepared according to the method disclosed in the Chinese invention patent CN109627006B. The specific preparation steps of the silicon carbide nanowire aerogel treated in the present invention are as follows: According to the Chinese invention patent The method disclosed in CN109627006B is prepared, and the specific steps are as follows:

1) Four raw materials, dimethyldimethoxysilane, methyltrimethoxysilane, deionized water and absolute ethanol, were prepared in a mass ratio of 2:0.5:5:3 to prepare a siloxane sol;

2) Add carbon fiber to the siloxane sol in a certain proportion, the mass ratio of carbon fiber and siloxane sol is 1:160, and uniformly disperse the carbon fiber into the siloxane sol by means of mechanical stirring, and the stirring time is 10min , the speed of the mechanical mixer is 1000r/min. ;

3) The method of vacuum filtration is adopted to make the chopped carbon fibers dispersed in the sol overlap each other into a block of three-dimensional structure;

4) Apply 10kPa pressure to the block;

5) Heating in air to curing temperature (80°C), heat preservation for 6 hours;

6) Raising the temperature to 1550°C in argon with a pressure of 0.25MPa for 3h, the xerogel is cracked to form silicon carbide nanowires;

7) Cooling to room temperature with the furnace, then raising the temperature to 700°C at a heating rate of 1°C/min, heat preservation for 3 hours, and oxidizing in the air to remove the carbon fiber skeleton to obtain a silicon carbide nanowire aerogel.

Referring to FIG. 3, the compressive stress-strain curve of the silicon carbide nanowire aerogel not treated by the method of the present invention is shown as follows: the stress when subjected to 40% compressive strain is 21.7 kPa, the elastic modulus is 49.4 kPa, The rebound rate was 51.9%, and the thermal conductivity was 39.1 mW·m ⁻¹ ·K ⁻¹ .

Referring to FIG. 4 , the compressive stress-strain curve of the silicon carbide nanowire aerogel treated by the present invention in Example 1 is shown. As can be seen from the figure, after oxidation at 1000 °C for 0.5h, its elastic modulus increased to 68.6kPa, which was 38.9% higher than that before oxidation; its stress under 40% compressive strain increased to 33.2kPa, which increased the 53.0%; rebound rate increased to 54.8%, an increase of 5.6%;

Referring to FIG. 5 , the compressive stress-strain curve of the silicon carbide nanowire aerogel treated by the present invention in Example 2 is shown. It can be seen from the figure that the elastic modulus increased to 76.8kPa after being oxidized at 1000℃ for 1h, an increase of 55.5% compared with that before oxidation; the stress under 40% compressive strain increased to 39.6kPa, an increase of 8.2% %; rebound rate increased to 57.5%, an increase of 10.8%;

Referring to FIG. 6 , the compressive stress-strain curve of the silicon carbide nanowire aerogel treated by the present invention in Example 3 is shown. It can be seen from the figure that the elastic modulus increased to 235.4kPa after being oxidized at 1000℃ for 8h, an increase of 376.5% compared with that before oxidation; the stress under 40% compressive strain increased to 47.8kPa, an increase of 120.3% %; rebound rate increased to 66.5%, an increase of 28.1%;

Referring to FIG. 7 , the compressive stress-strain curve of the silicon carbide nanowire aerogel treated by the present invention in Example 4 is shown. It can be seen from the figure that after 16h oxidation at 1000℃, its elastic modulus increased to 265.0kPa, an increase of 436.4% compared with that before oxidation; its stress under 40% compressive strain increased to 78.5kPa, an increase of 261.8% %; rebound rate increased to 63.5%, an increase of 22.4%;

Referring to FIG. 8 , the thermal conductivity changes of the silicon carbide nanowire aerogels of Examples 1-4 treated with the present invention are shown. It can be seen from the figure that the thermal conductivity decreased by 4.3% from 39.1mW·m ^-1 ·K ^-1 to 37.4mW·m ^-1 ·K ^-1 after oxidation at 1000℃ for 0.5h; oxidation at 1000℃ for 1h , its thermal conductivity decreased from 39.1mW·m ^-1 ·K ^-1 to 35.1mW·m ^-1 ·K ^-1 , a decrease of 10.2%; at 1000℃ for 8h, its thermal conductivity decreased from 39.1mW·m ^{- 1} ·K ^-1 dropped to 27.8mW·m ^-1 ·K ^-1 , a decrease of 28.9%. After being oxidized at 1000℃ for 16h, its thermal conductivity decreased from 39.1mW·m ^-1 ·K ^-1 to 27.7mW·m ^-1 ·K ^-1 , a decrease of 29.2%.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. A method for improving the mechanical property and the heat-insulating property of a silicon carbide nanowire aerogel through oxidation is characterized in that a silicon oxide layer is formed on the surface of the silicon carbide nanowire aerogel through high-temperature oxidation treatment, so that the strength, the compression resilience and the heat-insulating property of the silicon carbide nanowire aerogel are improved.

2. The method for improving the mechanical property and the heat-insulating property of the silicon carbide nanowire aerogel through oxidation according to claim 1, wherein the high-temperature oxidation treatment temperature is 900-1200 ℃, and the treatment time is 0.5-1.6 h.

3. The method for improving the mechanical property and the thermal insulation property of the silicon carbide nanowire aerogel through oxidation according to claim 1, wherein the high-temperature oxidation treatment is performed in a high-temperature box-type resistance furnace.

4. The method for improving the mechanical property and the heat-insulating property of the silicon carbide nanowire aerogel through oxidation according to claim 1, wherein the diameter of the silicon carbide nanowire aerogel is 50nm to 300 nm.

5. The method for improving the mechanical property and the heat-insulating property of the silicon carbide nanowire aerogel through oxidation according to claim 1, wherein the thickness of the silicon oxide layer is 10nm to 160 nm.

6. The method for improving the mechanical property and the heat-insulating property of the silicon carbide nanowire aerogel through oxidation according to claim 1, wherein the mechanical property and the heat-insulating property of the silicon carbide nanowire aerogel can be controlled by changing the high-temperature oxidation temperature or the treatment time.

7. The method for improving the mechanical property and the heat insulation property of the silicon carbide nanowire aerogel through oxidation according to any one of claims 1 to 6, wherein the elastic modulus of the treated silicon carbide nanowire aerogel is increased from 49.4kPa to 68.6kPa to 265.0 kPa.

8. The method for improving the mechanical property and the heat insulation property of the silicon carbide nanowire aerogel through oxidation according to any one of claims 1 to 6, wherein the stress corresponding to 40% of the compressive strain of the treated silicon carbide nanowire aerogel is increased from 21.7kPa to 33.2kPa to 78.5 kPa.

9. The method for improving the mechanical property and the heat insulation property of the silicon carbide nanowire aerogel through oxidation according to any one of claims 1 to 6, wherein the rebound rate of the treated silicon carbide nanowire aerogel is improved from 51.9% to 54.8% -63.5%.

10. The method for improving the mechanical property and the heat insulation property of the silicon carbide nanowire aerogel through oxidation according to any one of claims 1 to 6, wherein the thermal conductivity of the treated silicon carbide nanowire aerogel is 39.1 mW-m^-1·K^-1Reducing the power to 27.7-37.4 mW/m^-1·K^-1。

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