CN113999015A - Light high-strength elastic ceramic and preparation method thereof - Google Patents

Light high-strength elastic ceramic and preparation method thereof Download PDF

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CN113999015A
CN113999015A CN202111328041.XA CN202111328041A CN113999015A CN 113999015 A CN113999015 A CN 113999015A CN 202111328041 A CN202111328041 A CN 202111328041A CN 113999015 A CN113999015 A CN 113999015A
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ceramic
nanowires
strength elastic
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王红洁
冯靖雅
侯丽娟
涂昂
易振宇
卢德
苏磊
牛敏
庄磊
彭康
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Xian Jiaotong University
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Abstract

The invention discloses a light high-strength elastic ceramic and a preparation method thereof, belonging to the technical field of porous ceramic preparation, wherein the light high-strength elastic ceramic is formed by mutually bonding ceramic nanowires to form a continuous porous layered network, the light high-strength elastic ceramic takes ceramic nanowire aerogel as a raw material, and the preparation method comprises the following steps: forming a layered structure, and placing the ceramic nanowire aerogel in a mold and axially compressing the ceramic nanowire aerogel; and welding the ceramic nanowires, performing heat preservation treatment in a high-temperature oxygen-free environment, and welding the ceramic nanowires which are in contact with each other by an oxide layer on the surfaces of the nanowires to obtain the light-weight high-strength elastic ceramic.

Description

Light high-strength elastic ceramic and preparation method thereof
Technical Field
The invention belongs to the technical field of porous ceramic material preparation, and particularly relates to a light high-strength elastic ceramic and a preparation method thereof.
Background
The porous ceramic has the characteristics of light weight, low heat conduction, high specific surface area, excellent chemical and high-temperature stability and the like, and is widely applied to the fields of heat insulation, heat protection, high-temperature filtration, adsorption and the like. However, the strength of the material is rapidly reduced with the increase of porosity, and the ceramic has a natural brittleness problem, so that the high-porosity ceramic material has low mechanical reliability and is easily broken during actual transportation or use. The strength of high-porosity ceramics obtained by the traditional methods for preparing the high-porosity ceramics, such as a direct foaming method, a sacrificial template method, gel casting and the like, is generally low. For example, the foamed ceramic disclosed in chinese patent CN 110092650 a and the preparation method thereof can obtain a foamed ceramic with a porosity as high as 88%, but the strength is low and the ceramic is still brittle.
Recent studies have found that the brittleness problem of ceramics can be greatly improved by reasonable material selection and structural design, for example, ding et al make the ceramic aerogel with ultra-high porosity maintain structural stability under high compressive strain by assembling flexible nano ceramic units into a three-dimensional block, but the strength of the material is too low (up to tens of kPa level), and the practical application is difficult.
Therefore, how to realize that the ceramic still keeps high strength and compressibility under the condition of porosity as high as possible is a key factor for determining the practical application of the porous ceramic in wider fields.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a light-weight high-strength elastic ceramic and a preparation method thereof, and aims to solve the problems of low strength and high brittleness of the current elastic ceramic material.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the invention discloses a light high-strength elastic ceramic, which has a layered structure, wherein highly crosslinked ceramic nanowires are mutually overlapped in a layer to form a porous continuous network, and fixed silicon oxide nodes are formed among the ceramic nanowires; wherein:
the diameter of the ceramic nanowire is 30nm-3 mu m;
the elastic ceramic has a bulk density of 0.10 to 0.50g/cm3。
Due to the fact that the layered structure brings performance anisotropy, the light high-strength elastic ceramic has compression resilience in the direction perpendicular to the layers, the structure can be kept not to collapse under the condition of bearing large compression strain (60%), the shape can be almost completely recovered after load removal under the condition of 40% compression strain, and when the strain is 40%, the corresponding compression stress is 0.4-14.2 MPa, and meanwhile, the heat conductivity is low (0.071-0.121W/m.K).
Preferably, the diameter of the ceramic nanowire is 30nm to 300 nm.
Further preferably, the diameter of the ceramic nanowires is between 30nm and 1 μm, more preferably between 30nm and 300 nm.
Preferably, the ceramic nanowires are silicon carbide (SiC) nanowires or silicon nitride (Si)3N4) A nanoribbon. The ceramic nanowire with high length-diameter ratio has excellent deformability, and the nanowire network prepared by taking the ceramic nanowire as a basic construction unit also has excellent deformability, so that the defect that the traditional porous ceramic is fragile can be overcome.
Further preferably, the raw materials SiC nanowire and Si3N4The nanobelts have a core-shell structure, and the surface of the nanobelt is provided with an oxide layer with the thickness of 5 nm-30 nm, wherein the oxide layer is silicon oxide and is used for bonding mutually lapped ceramic nanowires.
The invention also discloses a preparation method of the light high-strength elastic ceramic, which comprises the following steps:
1) forming a layered structure: ceramic nanowire aerogel is used as a raw material and is filled in a mould to be axially compressed to form a layered structure;
2) welding the ceramic nanowires: preserving the heat of the layered structure obtained in the step 1) for at least 0.5 hour in a high-temperature oxygen-free environment, and cooling to room temperature to obtain the light-weight high-strength elastic ceramic.
Preferably, the temperature of the high-temperature oxygen-free environment is 1100-1600 ℃.
Preferably, the high temperature oxygen-free environment is selected from protective atmospheres well known to those skilled in the art, and even more preferably, the high temperature oxygen-free environment is selected from a nitrogen environment.
Preferably, the operation of performing heat treatment on the prepared light high-strength elastic ceramic in an air atmosphere is further included, and the thickness of an oxide layer on the surface of the ceramic nanowire in the elastic ceramic is increased through the heat treatment, so that the thermal conductivity of the elastic ceramic is further reduced, and the thermal conductivity of the elastic ceramic is reduced by 35%.
Still more preferably, the heat treatment temperature is 1000 ℃ to 1200 ℃.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a light high-strength elastic ceramic which has a layered structure and a low volume density (0.10-0.50 g/cm)3) The inside of the layer is a porous continuous network formed by mutually lapping highly-crosslinked ceramic nanowires with the diameters of 30nm-3 mu m, and an oxide layer on the surfaces of the ceramic nanowires can serve as a binder to weld the mutually-contacted ceramic nanowires to form the porous ceramic nanowire network with fixed nodes. On one hand, the ceramic nanowire with high length-diameter ratio has excellent deformability, and the nanowire network prepared by taking the ceramic nanowire as a basic construction unit also has excellent deformability, so that the defect that the traditional porous ceramic is fragile can be overcome; on the other hand, the layered structure brings anisotropy of performance, and the light high-strength elastic ceramic has compression resilience in the direction vertical to the layer and can bear large compression stressThe structure can be kept without collapse under the condition of 60 percent of strain, the shape can be almost completely recovered after the load is removed under the condition of 40 percent of compressive strain, the corresponding compressive stress is 0.4-14.2 MPa when the strain is 40 percent, and the thermal conductivity is low (0.071-0.121W/m.K), so that the thermal insulation tile is suitable for being used as a new-generation thermal insulation tile. Therefore, the light high-strength elastic ceramic prepared by the invention has the characteristics of high porosity, low density, high strength, processability, compressibility and resilience, high specific surface area, low thermal conductivity, excellent high-temperature stability and the like, and can be used in the fields of heat insulation and fire prevention, catalyst carriers, high-temperature filtration and the like.
According to the preparation method of the light high-strength elastic ceramic, disclosed by the invention, the light high-strength elastic ceramic can be prepared only by axially compressing the ceramic nanowires to form a layered structure and then performing heat preservation treatment in a high-temperature oxygen-free environment, wherein the ceramic nanowires in contact with each other can be welded by the oxide layer on the surfaces of the nanowires. The method effectively avoids the problem of raw material dispersibility in the traditional preparation process, does not need to add a binder, has simple process, low requirement on equipment and high preparation efficiency, and is easy to produce high-porosity ceramics with various shapes and sizes.
Drawings
FIG. 1 is a microscopic morphology of a lightweight high-strength elastic ceramic;
FIG. 2 is a microscopic morphology of a lightweight high-strength elastic ceramic;
FIG. 3 is a TEM and corresponding elemental surface distribution diagram of the lightweight high-strength elastic ceramic;
FIG. 4 is a stress-strain curve of a lightweight, high-strength elastic ceramic in a direction perpendicular to the layers; wherein (a) is the density of 100mg/cm3Stress diagram corresponding to the elastic ceramic of (1); (b) is at a density of 100mg/cm3Stress diagram corresponding to the elastic ceramic of (1); (c) the density is 100mg/cm3Stress diagram corresponding to the elastic ceramic.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, 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 in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the accompanying drawings:
the following embodiments of the present invention employ SiC nanowire aerogel disclosed in chinese invention patent 201811626203.6 and Si disclosed in chinese invention patent 201811626361.13N4The nanobelt aerogel is used as a raw material.
Example 1
This example produced a density of 100mg/cm3The light high-strength elastic ceramic comprises the following specific steps:
1) 2g of SiC nanowire aerogel disclosed in Chinese patent 201811626203.6 is used as a raw material and is filled in a graphite mold with the inner diameter of 40mm, and the filled height is kept fixed to be 15.9 mm;
2) placing in 1100 deg.C nitrogen atmosphere for 2h, cooling with furnace to obtain density of about 0.10g/cm3The elastic ceramic has light weight and high strength.
Example 2
This example systemPrepared with a density of 300mg/cm3The light high-strength elastic ceramic comprises the following specific steps:
1) 4g of Si disclosed in Chinese patent 201811626361.13N4The nanobelt aerogel is used as a raw material and is filled in a graphite mold with the inner diameter of 40mm, and the filling height is kept fixed to be 10.6 mm;
2) placing in nitrogen atmosphere at 1200 deg.C for 2 hr, cooling with furnace to obtain product with density of 0.30g/cm3The elastic ceramic has light weight and high strength.
It can be seen from fig. 1 that the lightweight high-strength elastic ceramic prepared by the present example has a distinct layered structure.
As can be seen from fig. 2, in the lightweight high-strength elastic ceramic prepared in this example, a porous network structure formed by mutually cross-linked SiC nanowires is in the layer.
As can be seen from fig. 3, in the lightweight high-strength elastic ceramic prepared in this example, SiC nanowires are well welded together by silicon oxide on the surface thereof.
Example 3
This example produced a density of 500mg/cm3The light high-strength elastic ceramic comprises the following specific steps:
1) using 6g of SiC nanowire aerogel disclosed in Chinese patent 201811626203.6 as a raw material, filling the SiC nanowire aerogel into a graphite mold with the inner diameter of 40mm, and keeping the height of the filled SiC nanowire aerogel fixed to be 9.5 mm;
2) placing in 1100 deg.C nitrogen atmosphere for 2h, cooling with furnace to obtain density of 0.50/cm3The elastic ceramic has light weight and high strength.
From fig. 4, it can be seen that the compressive stress-strain diagram of the light weight, high strength elastic ceramic prepared in this example in the direction perpendicular to the layer shows a brittle behavior different from that of the conventional ceramic in this direction, when the compressive strain is less than 20%, the obtained light weight, high strength elastic ceramic can achieve complete recovery, and when the compressive strain is 20%, the density is 100mg/cm3The stress corresponding to the elastic ceramic of (1) is 0.23MPa, see (a) in FIG. 4; the density is 300mg/cm3The stress corresponding to the elastic ceramic is 1.92MPa, see (b) in FIG. 4; the density is 500mg/cm3The stress corresponding to the elastic ceramic of (2) is 5.81MPa, see (c) in FIG. 4. When the compressive strain is continuously increased, the compressive stress is increased along with the increase of the compressive strain, the phenomenon of abrupt stress reduction is not generated, and the light high-strength elastic ceramic can keep stable structure and does not generate the phenomenon of structural collapse. .
The performance test data of the lightweight, high-strength elastic ceramics prepared in examples 1 to 3 are shown in table 1 below:
TABLE 1
Figure BDA0003347643060000061
As shown in Table 1, the resulting lightweight, high-strength elastic ceramic has lower thermal conductivity in the direction perpendicular to the layers than in the direction parallel to the layers, compressive stress and compressive strength increase with increasing density in both directions, and when the density reaches 500mg/cm3When the method is used, the maximum service temperature of the obtained light high-strength elastic ceramic in the air can reach 1200 ℃.
In addition, the light high-strength elastic ceramic prepared by the embodiment is subjected to heat treatment in an air atmosphere, so that the thickness of an oxide layer on the surface of the ceramic nanowire in the elastic ceramic can be increased, and the thermal conductivity of the elastic ceramic is further reduced.
100mg/cm prepared for the examples3The sample was incubated at 1000 ℃ for 6 hours in an air atmosphere to reduce the thermal conductivity to 0.041W/m.K, 300mg/cm as prepared in example 23The sample was kept at 1100 ℃ for 4 hours in air and the thermal conductivity was reduced to 0.078W/m.K, 500mg/cm as prepared in example 33The sample is kept at 1200 ℃ for 2 hours in an air atmosphere, and the thermal conductivity is reduced to 0.092W/m.K. It can be seen that the maximum reduction in thermal conductivity can be as much as 35%.
In conclusion, the light high-strength elastic ceramic disclosed by the invention is formed by mutually bonding ceramic nanowires to form a continuous porous layered network, the traditional porous ceramic is formed by mutually stacking or sintering ceramic particles which cannot deform, and once the traditional porous ceramic is subjected to the action of external force, the ceramic particles cannot deform, so that stress concentration is easy to occur, and the structure collapses; in contrast, the ceramic nanowires with high aspect ratio have excellent deformability, and the nanowire network prepared by using the ceramic nanowires as basic construction units also has excellent deformability, so that the defect that the conventional porous ceramic is fragile can be overcome. The lightweight high-strength elastic ceramic has compression resilience in the direction perpendicular to the layer, can still keep the structure from collapsing under the condition of bearing large compression strain (60%), can almost completely recover the shape after load unloading under the condition of 40% of compression strain, has the corresponding compression stress of 0.4-14.2 MPa when the strain is 40%, and has stronger service reliability compared with the traditional porous ceramic.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (10)

1. The light high-strength elastic ceramic is characterized by having a layered structure, wherein highly crosslinked ceramic nanowires are mutually overlapped in a layer to form a porous continuous network, and fixed silicon oxide nodes are formed among the ceramic nanowires; wherein:
the diameter of the ceramic nanowire is 30nm-3 mu m;
the elastic ceramic has a bulk density of 0.10 to 0.50g/cm3。
2. The lightweight, high-strength elastic ceramic according to claim 1, wherein the diameter of the ceramic nanowires is 30nm to 300 nm.
3. The lightweight, high strength resilient ceramic of claim 1, wherein said ceramic nanowires are silicon carbide nanowires or silicon nitride nanoribbons.
4. The light-weight high-strength elastic ceramic according to claim 1, wherein the ceramic nanowire has a core-shell structure, and the surface of the ceramic nanowire is an oxide layer with a thickness of 5nm to 30 nm; the oxide layer is used for bonding the mutually lapped ceramic nanowires.
5. The lightweight high strength elastic ceramic according to claim 1, wherein the lightweight high strength elastic ceramic has a compression resilience in a vertical direction, and a corresponding compressive stress of 0.4 to 14.2MPa at a strain of 40%.
6. The method for preparing a lightweight high-strength elastic ceramic according to any one of claims 1 to 5, comprising the steps of:
1) forming a layered structure: ceramic nanowire aerogel is used as a raw material and is filled in a mould to be axially compressed to form a layered structure;
2) welding the ceramic nanowires: preserving the heat of the layered structure obtained in the step 1) for at least 0.5 hour in a high-temperature oxygen-free environment, and cooling to room temperature to obtain the light-weight high-strength elastic ceramic.
7. The method for preparing a lightweight high-strength elastic ceramic according to claim 6, wherein the temperature of the high-temperature oxygen-free environment is 1100 ℃ to 1600 ℃.
8. The method for preparing a lightweight, high strength, elastic ceramic according to claim 6, wherein the high temperature, oxygen-free environment is a nitrogen environment.
9. The preparation method of the light-weight high-strength elastic ceramic according to any one of claims 6 to 8, further comprising a heat treatment operation of the prepared light-weight high-strength elastic ceramic in an air atmosphere, wherein the thickness of the oxide layer on the surface of the ceramic nanowire in the elastic ceramic is increased through the heat treatment, so that the thermal conductivity of the elastic ceramic is reduced by 35%.
10. The method for preparing a lightweight high-strength elastic ceramic according to claim 9, wherein the heat treatment temperature is 1000 ℃ to 1200 ℃.
CN202111328041.XA 2021-11-10 2021-11-10 Light high-strength elastic ceramic and preparation method thereof Pending CN113999015A (en)

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CN114702328A (en) * 2022-04-13 2022-07-05 西安交通大学 SiC nanowire network reinforced layered porous SiC ceramic and preparation method thereof
CN114773092A (en) * 2022-04-29 2022-07-22 西安交通大学 Method for improving mechanical property and heat-insulating property of silicon carbide nanowire aerogel through oxidation treatment
CN114853482A (en) * 2022-05-11 2022-08-05 西安交通大学 High-toughness silicon nitride nanowire/silicon nitride layered ceramic and preparation method thereof
CN114956858A (en) * 2022-05-11 2022-08-30 西安交通大学 Layered elastic-plastic silicon nitride ceramic and preparation method thereof

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114702328A (en) * 2022-04-13 2022-07-05 西安交通大学 SiC nanowire network reinforced layered porous SiC ceramic and preparation method thereof
CN114773092A (en) * 2022-04-29 2022-07-22 西安交通大学 Method for improving mechanical property and heat-insulating property of silicon carbide nanowire aerogel through oxidation treatment
CN114853482A (en) * 2022-05-11 2022-08-05 西安交通大学 High-toughness silicon nitride nanowire/silicon nitride layered ceramic and preparation method thereof
CN114956858A (en) * 2022-05-11 2022-08-30 西安交通大学 Layered elastic-plastic silicon nitride ceramic and preparation method thereof
CN114956858B (en) * 2022-05-11 2023-06-06 西安交通大学 Layered elastoplastic silicon nitride ceramic and preparation method thereof

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