CN111205093A - Preparation method of ultra-light silicon nitride foamed ceramic - Google Patents
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Abstract
The invention relates to a preparation method of ultra-light silicon nitride foamed ceramic, which comprises the following steps: (1) dispersing silicon nitride particles, a sintering aid and a gelling agent in deionized water, and mixing to obtain silicon nitride slurry with the solid content of 45-60%; (2) adding a foaming agent into the obtained silicon nitride slurry, injecting the silicon nitride slurry into a mould after foaming treatment, and then curing, demoulding and drying to obtain a silicon nitride foamed ceramic blank, wherein the foaming agent is a composite foaming agent obtained by compounding an anionic surfactant and a cationic surfactant in advance; (3) and carrying out pressureless sintering on the obtained silicon nitride foamed ceramic blank in a nitrogen atmosphere to obtain the silicon nitride foamed ceramic.
Description
Technical Field
The invention relates to a preparation method of ultra-light silicon nitride foamed ceramics, belonging to the technical field of preparation of low-shrinkage foamed ceramics and ultra-stable foamed ceramics.
Background
The foamed ceramic is a porous ceramic with a three-dimensional network shape and an open-cell or closed-cell structure, has the characteristics of low density, high porosity (60-90%), high specific surface area and the like, has excellent performances of high temperature resistance, corrosion resistance and the like, and can be applied to the fields of hot gas filters, catalyst carriers, heat insulation materials, sound absorbers, biological materials and the like. Therefore, the preparation of foamed ceramics with high porosity, uniform pore size, high strength and stable performance is very important for the application of the foamed ceramics in various fields.
The preparation method of the foamed ceramic mainly comprises a pore-forming agent adding method, a template copying method and a direct foaming method. Compared with other methods, the direct foaming method has obvious advantages in preparing the foamed ceramic with high porosity and stable structure. The key point of the direct foaming method for preparing the foamed ceramic is the stability of foam, and the usually adopted method is a particle stable foaming method, wherein a surfactant is adopted to modify the surface of ceramic particles, so as to improve the hydrophobicity, and then the ceramic particles are stirred at a high speed for foaming so as to be stably adsorbed on a gas-liquid interface of the foam to form the ultra-stable foam. The method is considered to be a preparation method of the light high-strength foamed ceramic with development potential due to simple process, low production cost and environmental friendliness.
Disclosure of Invention
Therefore, the invention aims to provide the ultra-light silicon nitride foamed ceramic with good foam stability, high slurry casting performance, uniform foam pore size, controllable pore size and excellent mechanical property and the preparation method thereof.
On one hand, the invention provides a preparation method of ultra-light silicon nitride foam ceramic, which comprises the following steps:
(1) dispersing silicon nitride particles, a sintering aid and a gelling agent in deionized water, and mixing to obtain silicon nitride slurry with the solid content of 45-60%;
(2) adding a foaming agent into the obtained silicon nitride slurry, injecting the silicon nitride slurry into a mould after foaming treatment, and then curing, demoulding and drying to obtain a silicon nitride foamed ceramic blank, wherein the foaming agent is a composite foaming agent obtained by compounding an anionic surfactant and a cationic surfactant in advance;
(3) and carrying out pressureless sintering on the obtained silicon nitride foamed ceramic blank in a nitrogen atmosphere to obtain the silicon nitride foamed ceramic.
In the disclosure, a composite ionic surfactant (a mixture of an anionic surfactant and a cationic surfactant) is used as a foaming agent for the first time, and a gel casting process is combined to dry foam slurry at room temperature, so that the ultra-light silicon nitride foam ceramic (ultra-light porous silicon nitride) is prepared. Specifically, the anionic surfactant has excellent foamability, the cationic surfactant has excellent foam stability, and the anionic surfactant and the cationic surfactant can be combined by adopting the composite ionic surfactant (the anionic surfactant and the cationic surfactant can be combined into a composite of the surfactants under the electrostatic attraction of charges), so that the foamability can be improved, the surface tension can be reduced, and the average pore diameter of pores can be reduced. In addition, in the preparation of the foamed ceramic, the surfactant also has the function of adjusting the hydrophobic state of the surfaces of the silicon nitride particles on the surface of the powder of the silicon nitride ceramic, so that the foam pores are uniformly distributed, and the mechanical property of the high-porosity silicon nitride foamed ceramic is improved.
Preferably, the sintering aid is at least one of yttrium oxide, ytterbium oxide and aluminum oxide; the sintering aid accounts for 1-5 wt% of the total mass of the silicon nitride slurry.
Preferably, the gelling agent is an isobutylene-maleic anhydride copolymer; the gelling agent accounts for 0.3-0.9 wt% of the total mass of the silicon nitride slurry. For example, the invention combines the gel film-casting process and the direct foaming method, adopts the novel water-based gel agent isobutene-maleic anhydride copolymer as the dispersing agent and the gel agent at the same time, increases the fluidity and the stability of the slurry, reduces the shrinkage in the foam drying process and has high yield.
Preferably, the anionic surfactant is at least one of sodium lauroyl sarcosinate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and sodium hexadecyl sulfate; the cationic surfactant is at least one of cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cetyl hydroxyethyl dimethyl ammonium bromide and cetyl dihydroxyethyl methyl ammonium bromide; the addition amount of the foaming agent is 0.1-0.4% of the total mass of the silicon nitride slurry.
Preferably, the mass ratio of the anionic surfactant to the cationic surfactant in the foaming agent is 1: (0.7 to 1.3), preferably 1: 1. When the amounts of the anionic surfactant and the cationic surfactant are close to each other, the properties of the slurry are optimal, and when the amount of either surfactant is too large, the pore size distribution of the prepared ceramic foam is not uniform, and when the amount of the cationic surfactant is too large, the foamability of the slurry is lowered, the porosity of the ceramic foam is lowered, and when the amount of the anionic surfactant is too large, the foamability is good, but the stability of the foam is poor, and the strength of the ceramic foam is low.
Preferably, the median particle size of the silicon nitride particles is 0.42 μm, and α -Si in the silicon nitride particles3N4Is greater than 92 wt%.
Preferably, the foaming treatment is ball milling treatment, the rotation speed of the ball milling treatment is 300-450 r/min, and the time is 1.5-3 hours.
Preferably, the curing temperature is 25-45 ℃ and the curing time is 3-10 hours; the drying temperature is 25-40 ℃, and the drying time is 24-48 hours.
Preferably, the pressureless sintering temperature is 1680-1760 ℃ and the time is 1.5-2.5 hours.
Further, preferably, the temperature raising system for pressureless sintering includes: heating to 1000-1100 ℃ at a heating rate of 5-10 ℃, and then heating to the pressureless sintering temperature at a heating rate of 3-5 ℃. The temperature raising system is more beneficial to the growth of the silicon nitride crystal whisker so as to realize the preparation with high strength.
On the other hand, the invention also provides the ultra-light silicon nitride foamed ceramic prepared by the preparation method, wherein the average pore diameter of the ultra-light silicon nitride foamed ceramic is 120-290 mu m, and the porosity is more than 90%.
Has the advantages that:
(1) according to the invention, an anionic surfactant (such as sodium lauroyl sarcosinate) and cationic surfactant (such as hexadecyl trimethyl ammonium bromide) complex is used as a foaming agent, so that the foamability is improved, the surface tension is reduced, the foam pores are uniformly distributed, and the mechanical property of the high-porosity ultra-light silicon nitride foam ceramic is improved;
(2) the aperture size of the silicon nitride foam ceramic can be effectively adjusted by adjusting the content of the composite foaming agent, and the average aperture of the ultra-light silicon nitride foam ceramic prepared by the invention is about 120-290 mu m;
(3) the silicon nitride foamed ceramic with high porosity can be prepared, the porosity of the silicon nitride foamed ceramic is over 90 percent, and the silicon nitride foamed ceramic is expected to be applied to the fields of sound absorption and heat insulation.
Drawings
FIG. 1 is a process flow diagram of the ultra-light silicon nitride ceramic foam of the present invention;
FIG. 2 is a microscopic morphology of an ultralight silicon nitride foam ceramic prepared in example 4;
FIG. 3 is a graph showing the distribution of pore diameters of ultra-lightweight silicon nitride foam ceramics prepared in examples 1 to 4, wherein the abscissa is the size of the pore diameter and the ordinate is the probability of the distribution of the pore diameter.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
In the disclosure, a composite ionic surfactant (a mixture of an anionic surfactant and a cationic surfactant) is used as a foaming agent for the first time, and a gel casting process is combined to prepare the ultra-light silicon nitride foamed ceramic.
The following exemplarily illustrates a method for preparing an ultra-lightweight silicon nitride ceramic foam, as shown in fig. 1.
Silicon nitride powder (silicon nitride particles), deionized water, a sintering aid and a gel are prepared into silicon nitride water-based slurry (silicon nitride slurry) with the solid content of 45-60 wt%, wherein the median particle size of the silicon nitride particles is 0.42 mu m, and the content of α phase is more than 92%.
In an alternative embodiment, the sintering aid may be at least one of yttria, ytterbia, and alumina. The particle size of the sintering aid can be 400 nm-2 μm. The content of the sintering aid in the silicon nitride slurry can be 1-5 wt%.
In an alternative embodiment, the gellant is a novel water-based gel system "isobutylene-maleic anhydride copolymer (Isobam)". The content of the gel in the silicon nitride slurry can be 0.3-0.9%.
And adding a foaming agent into the silicon nitride slurry, and performing foaming treatment to obtain the ultra-stable silicon nitride foam slurry. The formula of the ultra-stable silicon nitride foam slurry comprises the following components in percentage by mass: 45-60 wt% of silicon nitride particles, 0.1-0.4 wt% of composite ionic surfactant, 1-5 wt% of sintering aid, 0.3-0.9 wt% of gelling agent and the balance of deionized water. Wherein, the foaming treatment can be ball milling treatment. Wherein the composite ionic surfactant (foaming agent) is a mixture of an anionic surfactant and a cationic surfactant. Namely, it can be obtained by simply compounding an anionic surfactant and a cationic surfactant. The total adding amount of the composite ionic surfactant is 0.1-0.4% of the total mass of the slurry. The rotational speed of the ball milling process can be 300-450 rpm, and the time can be 1.5-3 hours (e.g., 2 hours).
In alternative embodiments, the anionic surfactant used may be sodium lauroyl sarcosinate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, and the like. The cationic surfactant may be cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cetyl hydroxyethyl dimethyl ammonium bromide and cetyl dihydroxyethyl methyl ammonium bromide. Preferably, the mass ratio of the anionic surfactant to the cationic surfactant may be 1: (0.7-1.3) when more anionic and cationic surfactants are added, the size uniformity of the foam is poor, and the pore size distribution is large; and when more anionic surfactants are added, the foam stability is poor, and the final foam ceramic pore wall is incomplete.
And injecting the foamed silicon nitride slurry into a mold, and curing, demolding and drying to obtain the silicon nitride foamed ceramic blank. Wherein the curing temperature can be 25-45 deg.C, and the curing time can be 3-10 hr. The drying temperature can be 25-40 deg.C, and the drying time can be 24-48 hr. Wherein the injection molding process and the curing process may be collectively referred to as an injection molding process.
And sintering the silicon nitride foam ceramic blank under a nitrogen atmosphere and without pressure to obtain the silicon nitride foam ceramic. Wherein the temperature of the pressureless sintering can be 1680-1760 ℃, and the time can be 1.5-2.5 hours. As an example of pressureless sintering, the sintering process is performed under a nitrogen atmosphere by heating to 1000-1100 ℃ at a heating rate of 5-10 ℃, heating to 1680-1760 ℃ at a heating rate of 3-5 ℃, and then maintaining the temperature for 1.5-2.5 h.
According to the invention, the prepared ultra-light silicon nitride foamed ceramic foam has the advantages of good stability, good casting performance, uniform foam pore diameter, controllable pore diameter and excellent mechanical property, the average pore diameter is 120-290 mu m, and the porosity is more than 90%.
In the disclosure, the average pore diameter of the obtained ultra-light silicon nitride foamed ceramic is tested by adopting a linear ranging method of software nano measure to the random 100 pore diameters in a scanning electron microscope image of the foamed ceramic. And testing the porosity of the obtained ultra-light silicon nitride foamed ceramic by adopting an Archimedes drainage method. The compressive strength of the ultra-light silicon nitride foamed ceramic tested by a universal mechanical testing machine is 1.40-5.75 MPa. The resulting slurry was tested at 100S using a KINEXUS-PRO rheometer-1Viscosity of (2). The surface tension of the obtained slurry is 62.41-64.51mN/m by adopting a vertical drop method test.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
Weighing 53g of silicon nitride particles, adding 2.6g of sintering aid (yttrium oxide powder) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then adding 0.05g of compounded composite foaming agent (0.025g of hexadecyl trimethyl ammonium bromide and 0.025g of sodium lauroyl sarcosine) into the silicon nitride slurry (the viscosity of the silicon nitride slurry is 0.41PaS, and the surface tension of the silicon nitride slurry is 64.51mN/m), and continuing ball milling for 2 hours (the rotating speed is 300 r/min) for foaming treatment to obtain the ultra-stable silicon nitride foam slurry;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Example 2
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then adding 0.1g of compounded composite foaming agent (0.05g of hexadecyl trimethyl ammonium bromide and 0.05g of sodium lauroyl sarcosine) into the silicon nitride slurry (the viscosity of the silicon nitride slurry is 0.47PaS, and the surface tension of the silicon nitride slurry is 63.48mN/m), and continuing ball milling for 2 hours (the rotating speed is 300 r/min) to carry out foaming treatment to obtain the ultra-stable silicon nitride foam slurry;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Example 3
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then adding 0.15g of compounded composite foaming agent (0.075g of hexadecyl trimethyl ammonium bromide and 0.075g of sodium lauroyl sarcosine) into the silicon nitride slurry (the viscosity of the silicon nitride slurry is 0.55PaS, the surface tension of the silicon nitride slurry is 62.93mN/m), and continuing ball milling for 2 hours (the rotating speed is 300 r/min) to carry out foaming treatment to obtain the ultra-stable silicon nitride foam slurry;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Example 4
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then adding 0.2g of compounded composite foaming agent (0.1g of hexadecyl trimethyl ammonium bromide and 0.1g of sodium lauroyl sarcosine) into the silicon nitride slurry (the viscosity of the silicon nitride slurry is 0.67PaS, and the surface tension of the silicon nitride slurry is 62.41mN/m), and continuing ball milling for 2 hours (the rotating speed is 300 r/min) to carry out foaming treatment to obtain the ultra-stable silicon nitride foam slurry;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Example 5
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then 0.05g of composite foaming agent (0.025g of dodecyl trimethyl ammonium bromide and 0.025g of dodecyl sodium sulfate) is added into the silicon nitride slurry (the viscosity is 0.40PaS, the surface tension is 64.38mN/m), and the ball milling is continued for 2 hours (the rotating speed is 300 r/min) for foaming treatment, so that the ultra-stable silicon nitride foam slurry is obtained;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Comparative example 1
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then 0.05g of foaming agent (0.05g of hexadecyl trimethyl ammonium bromide and 0g of sodium lauroyl sarcosine) is added into the silicon nitride slurry (the viscosity is 1.35PaS, the surface tension is 65.32mN/m), and the ball milling is continued for 2 hours (the rotating speed is 300 r/min) for foaming treatment, so that the ultra-stable silicon nitride foam slurry is obtained;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature (25 ℃) to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Comparative example 2
Weighing 53g of silicon nitride powder, adding 2.6g of sintering aid (yttrium oxide) and 0.4g of gelling agent (isobutylene-maleic anhydride copolymer), adding 30g of deionized water, and performing ball milling for 12 hours to obtain silicon nitride slurry;
then 0.05g of foaming agent (0g of hexadecyl trimethyl ammonium bromide and 0.05g of sodium lauroyl sarcosine) is added into the silicon nitride slurry (the viscosity is 0.35PaS, the surface tension is 67.85mN/m), and the ball milling is continued for 2 hours (the rotating speed is 300 r/min) for foaming treatment, so that the ultra-stable silicon nitride foam slurry is obtained;
the obtained silicon nitride foam slurry is subjected to injection molding (injected into a mold and cured for 5 hours at 25 ℃), and then dried for 48 hours at normal temperature to obtain a dry foam ceramic blank;
and sintering the obtained dry foamed ceramic blank in a nitrogen atmosphere, heating to 1000 ℃ at a heating rate of 10 ℃/min, then heating to 1700 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 2 h.
Table 1 shows the performance parameters of the ultralight silicon nitride foam ceramics prepared in examples 1 to 4:
| viscosity/PaS | Surface tension (mN/m) | Porosity% | Average pore diameter/. mu.m | Compressive strength/MPa | |
| Example 1 | 0.41 | 64.51 | 94.43 | 236 | 1.41 |
| Example 2 | 0.47 | 63.48 | 94.24 | 209 | 1.61 |
| Example 3 | 0.55 | 62.93 | 93.98 | 183 | 2.08 |
| Example 4 | 0.67 | 62.41 | 93.83 | 146 | 2.78 |
| Example 5 | 0.40 | 64.38 | 94.59 | 241 | 1.37 |
| Comparative example 1 | 1.35 | 65.32 | 85.32 | 107 | 14.34 |
| Comparative example 2 | 0.35 | 67.85 | 95.43 | 283 | 0.46 |
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As can be seen from FIG. 2, the pore size distribution of the prepared silicon nitride ceramic foam is uniform. As can be seen from Table 1 and FIG. 3, the slurry foaming property is poor by adding only the cationic surfactant, and the final ceramic foam has a low porosity, while the slurry foaming property is good by adding only the anionic surfactant, but the foam has a high surface tension, and is unstable, and the final ceramic foam has a low strength. The more the composite foaming agent (cetyl trimethyl ammonium bromide/sodium lauroyl sarcosine) is added, the viscosity of the slurry is improved, and the surface tension of the foam is reduced, but the influence on the foaming rate of the slurry is small, so that the stability of the foam is improved, the average pore diameter of pores is reduced, the change of the porosity is small, and the mechanical property is obviously improved.
Claims (10)
1. A preparation method of ultra-light silicon nitride foamed ceramics is characterized by comprising the following steps:
(1) dispersing silicon nitride particles, a sintering aid and a gelling agent in deionized water, and mixing to obtain silicon nitride slurry with the solid content of 45-60%;
(2) adding a foaming agent into the obtained silicon nitride slurry, injecting the silicon nitride slurry into a mould after foaming treatment, and then curing, demoulding and drying to obtain a silicon nitride foamed ceramic blank, wherein the foaming agent is a composite foaming agent obtained by compounding an anionic surfactant and a cationic surfactant in advance;
(3) and carrying out pressureless sintering on the obtained silicon nitride foamed ceramic blank in a nitrogen atmosphere to obtain the silicon nitride foamed ceramic.
2. The production method according to claim 1, wherein the sintering aid is at least one of yttria, ytterbia, and alumina; the sintering aid accounts for 1-5 wt% of the total mass of the silicon nitride slurry.
3. The method of claim 1 or 2, wherein the gelling agent is an isobutylene-maleic anhydride copolymer; the gelling agent accounts for 0.3-0.9 wt% of the total mass of the silicon nitride slurry.
4. The production method according to any one of claims 1 to 3, wherein the anionic surfactant is at least one of sodium lauroyl sarcosinate, sodium dodecylbenzenesulfonate, sodium dodecylsulfate and sodium hexadecylsulfate; the cationic surfactant is at least one of cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, cetyl hydroxyethyl dimethyl ammonium bromide and cetyl dihydroxyethyl methyl ammonium bromide; the addition amount of the foaming agent is 0.1-0.4% of the total mass of the silicon nitride slurry.
5. The production method according to any one of claims 1 to 4, wherein the mass ratio of the anionic surfactant to the cationic surfactant in the foaming agent is 1: (0.7 to 1.3).
6. The method as claimed in any one of claims 1 to 5, wherein the silicon nitride particles have a median particle size of 0.42 μm, wherein the silicon nitride particles contain α -Si3N4Is greater than 92 wt%.
7. The method according to any one of claims 1 to 6, wherein the foaming treatment is a ball milling treatment, and the rotation speed of the ball milling treatment is 300 to 450 rpm and the time is 1.5 to 3 hours.
8. The method according to any one of claims 1 to 7, wherein the curing is carried out at a temperature of 25 to 45 ℃ for 3 to 10 hours; the drying temperature is 25-40 ℃, and the drying time is 24-48 hours.
9. The method of any one of claims 1-8, wherein the pressureless sintering is carried out at a temperature of 1680 to 1760 ℃ for 1.5 to 2.5 hours; preferably, the temperature-raising schedule of the pressureless sintering comprises: heating to 1000-1100 ℃ at a heating rate of 5-10 ℃, and then heating to the pressureless sintering temperature at a heating rate of 3-5 ℃.
10. The ultra-light silicon nitride foamed ceramic prepared by the preparation method according to any one of claims 1 to 9, wherein the average pore diameter of the ultra-light silicon nitride foamed ceramic is 120 to 290 μm, and the porosity is more than 90%.
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