CN111875404B

CN111875404B - Preparation method of silicon carbide slurry applied to free direct-write forming technology

Info

Publication number: CN111875404B
Application number: CN202010742002.3A
Authority: CN
Inventors: 茹红强; 孙是昊
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2022-02-11
Anticipated expiration: 2040-07-29
Also published as: CN111875404A

Abstract

The invention discloses a preparation method of silicon carbide slurry applied to a free direct-write forming technology, which belongs to the technical field of materials and comprises the following specific steps: (1) uniformly mixing SiC powder with a sintering aid through ball milling; (2) putting the suspension obtained after ball milling into a constant-temperature oven for drying, grinding and sieving; (3) pouring the sieved powder into an aqueous solution dissolved with a dispersant to prepare a sol ceramic suspension, and stirring at a high speed; (4) adjusting the pH value, adding a thickening agent, and stirring; (5) and ball-milling the stirred slurry to prepare the SiC ceramic slurry applied to free direct writing. The method has simple steps and relatively low requirement on equipment, the prepared slurry can meet the rheological property requirement of free direct-writing forming on the slurry, and various porous SiC ceramic products with complex shapes can be produced.

Description

Preparation method of silicon carbide slurry applied to free direct-write forming technology

The technical field is as follows:

the invention belongs to the technical field of materials, and particularly relates to a preparation method of silicon carbide slurry applied to a free direct-write forming technology.

Background art:

silicon carbide (SiC) ceramics have excellent properties of high strength, high hardness, good thermal stability, small thermal expansion coefficient, high thermal conductivity, wear resistance, thermal shock resistance, chemical corrosion resistance and the like, are widely applied to the fields of petrochemical industry, aerospace, microelectronics, steel, automobiles and the like, and are widely valued by people. The demand for SiC materials is increasing, and the extensive research on the relationship between its manufacture and performance is being promoted. At present, the forming modes of SiC ceramics mainly comprise dry pressing, slip casting, gel casting, direct solidification and the like. Although the relevant molding processes are well-established, the biggest defects of the molding methods are that the restrictions of a mold on ceramic production cannot be removed, and the molding methods are not suitable for preparing porous SiC ceramic samples with high precision.

In order to solve the above-mentioned problems associated with the restriction on the production of SiC ceramics, the present study is to produce SiC porous ceramic articles with high precision and high aspect ratio by means of the free-write forming technique. As one of the most widely used ceramic 3D technologies, the direct write forming technology has an advantage of being unique in preparing porous ceramics. The ceramic part is prepared by utilizing a free direct-writing forming process, and three steps of slurry preparation, slurry forming and drying sintering are generally required. The preparation of the slurry is the basis of the free direct-writing forming process and is also the key for determining the forming performance. However, there is no patent concerning SiC slurry applied to direct-write forming technology, and there is no SiC porous ceramic article produced by applying direct-write forming technology on the market.

The invention content is as follows:

the invention aims to overcome the defects in the prior art and provide a preparation method of silicon carbide slurry applied to a free direct-writing forming technology. And the SiC slurry prepared by the formula is used for preparing the SiC porous ceramic material with high precision and high aspect ratio, so that the practical application condition of the formula is verified.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of silicon carbide slurry applied to a free direct-write forming technology comprises the following steps:

(1) uniformly mixing SiC powder with a sintering aid by ball milling to obtain a suspension, wherein the sintering aid is two of boron carbide, aluminum oxide, silicon nitride, calcium oxide, yttrium oxide, zirconium oxide and carbon black; the addition amount of the sintering aid is 2-5 wt% of the total mass of the powder;

(2) drying the suspension to obtain dry powder, grinding, and screening by a 50-500-mesh screen;

(3) and pouring the sieved powder into an aqueous solution in which a dispersing agent is dissolved, and uniformly stirring to prepare the sol ceramic suspension. Wherein the addition amount of the dispersing agent is 0.5-5 wt% of the total mass of the powder;

(4) and adding 0.2-20 mol/L sodium hydroxide (NaOH) or hydrochloric acid (HCl) aqueous solution into the sol ceramic suspension, adjusting the pH to 8-11.5, continuously stirring for 0.1-10 h, adding a thickening agent, stirring and ball-milling to obtain the SiC ceramic slurry applied to free direct writing. Wherein the addition amount of the thickening agent is 10-30mg/L of the total volume of the free direct-writing SiC ceramic slurry.

In the step (1), the total mass of the powder is the sum of the mass of the SiC powder and the mass of the sintering aid, and the ball milling process comprises the following steps: the rotating speed is 50-500 rpm, and the ball milling time is 2-24 h. The ball milling medium is one of water, ethanol, glycerol and toluene. The ball milling ball is made of one of zirconia, alumina, titanium oxide, silicon carbide and silicon nitride balls with the diameter of 2-50 mm.

In the step (1), the sintering aid is preferably a mixture of boron carbide and carbon black in a mass ratio of 1: 1.

In the step (2), the drying operation is carried out in a constant-temperature oven, the drying temperature is 50-300 ℃, and the drying time is 1-24 hours.

In the step (3), the stirring speed is 200-10000 rpm, and the stirring time is 0.1-10 h.

In the step (3), the dispersant is one or more of sodium silicate, sodium citrate, ammonium polyacrylate, tetramethylammonium hydroxide, polyethyleneimine, polymethacrylic acid, polyacrylamide and cellulose.

In the step (3), the dispersant is preferably Polyethyleneimine (PEI) with a molecular weight of 75000.

In the step (3), the solid content of the sol ceramic suspension is 42-60 vol%.

In the step (3), the solid content of the sol-state ceramic suspension is preferably 42-54 vol%.

In the step (4), the concentration of the aqueous solution of sodium hydroxide (NaOH) or hydrochloric acid (HCl) is 2 mol/L.

In the step (4), the addition amount of the thickening agent is 20mg/L of the total volume of the SiC ceramic slurry applied to free direct writing.

In the step (4), the stirring time after the thickening agent is added is 0.1-10 h, and the stirring speed is 200-10000 rpm.

In the step (4), the thickener is one of cellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, phenolic resin, ammonium polyacrylate and polyethyleneimine.

In the step (4), the thickening agent is preferably methylcellulose, and the viscosity of the thickening agent is 5000 cp.

In the step (4), the ball milling time is 2-48 h, and the ball milling rotating speed is 20-10000 rpm.

In the step (4), the prepared SiC ceramic slurry applied to free direct writing has a solid content (phi) of 40-58 vol%. The slurry has an obvious shear thinning phenomenon, and the shear thinning index n is 0.25-0.47. And the slurry has obvious viscoelasticity and shear yield stress (tau)_y) 56.77 to 455.89pa, balance storage modulus (G'_eq) Is 2464.86 to 23381.87 pa.

In the step (4), the prepared SiC ceramic slurry applied to free direct writing has a solid content (phi) of 41-53 (vol%).

In the step (4), the prepared SiC ceramic slurry applied to free direct writing has a shear thinning index n of 0.25-0.37.

The method for preparing the porous SiC ceramic by adopting the SiC ceramic slurry prepared in the step (4) to carry out free direct writing forming comprises the following steps:

(1) placing SiC ceramic slurry into a stainless steel barrel with the volume of 10ml, assembling a nozzle with the diameter of 0.15-2.5 mm at the front end of the barrel, extruding the SiC ceramic slurry through the nozzle according to a designed three-dimensional structure by means of free direct writing equipment, wherein the extrusion speed is 6-12 mm/s, and depositing the SiC ceramic slurry on a printing platform layer by layer;

(2) and after all samples are deposited, drying to remove moisture, and sintering the dried samples at high temperature under a vacuum condition to prepare the porous SiC ceramic sample.

In the step (2), the step of drying to remove water is drying for 10-24 hours at a specific temperature, wherein the drying temperature is 20-100 ℃.

In the step (2), the vacuum degree in the sintering process is less than or equal to 10Pa, and the sintering temperature is 1800-2100 ℃.

In the step (3), the prepared porous SiC ceramic sample has a cylindrical skeleton with the diameter of 0.26-2.2 mm and the aspect ratio of 4-20.

The invention has the beneficial effects that:

the preparation principle of the invention is as follows: firstly, preparing SiC sol suspension with high solid content and no aggregate, and then changing the molecular configuration and adsorption behavior of a dispersing agent by adjusting the pH value to induce a gel reaction, thereby preparing the strong gel ceramic slurry with obvious shear thinning and stronger viscoelasticity. Wherein, the obvious shear thinning behavior can ensure that the slurry is smoothly extruded from a thinner nozzle, and the stronger viscoelasticity can ensure that the slurry does not have obvious collapse and elastic deformation when forming a sample with obvious hollow and large-span characteristics.

Description of the drawings:

FIG. 1 is a Zeta potential diagram of the silicon carbide and two sintering aid raw powders of example 1 of the present invention and a Zeta potential diagram of three powders subjected to surface modification by a dispersant; wherein the sintering aid is boron carbide (B)₄C) And nano Carbon Black (CB);

FIG. 2 is a graph of the rheological properties of SiC slurries for free-write applications prepared in examples 1, 2 and 3 of the present invention; wherein, fig. 2(a) is a shear rate-shear stress curve, 2(b) is an oscillating stress-storage modulus curve, and 2(c) is a shear rate-viscosity curve;

FIG. 3 is a photograph taken by a scanning electron microscope at 25 times magnification of a SiC porous ceramic prepared by free direct write forming using the SiC slurry prepared in example 1 of the present invention;

FIG. 4 is a photograph taken by a scanning electron microscope of a SiC porous ceramic produced by free direct write forming using the SiC slurry produced in example 2 of the present invention; wherein, FIG. 4(a) and FIG. 4(b) are the scanning electron microscope photograph images of example 2; FIGS. 4(c) and 4(d) are sectional scanning electron microscope photographs of example 2; FIG. 4(a) is at 25 times magnification, FIG. 4(b) is at 50 times magnification, FIG. 4(c) is at 50 times magnification, and FIG. 4(d) is at 160 times magnification;

FIG. 5 is a photograph taken by a scanning electron microscope at 25 times magnification of a SiC porous ceramic prepared by free direct write forming using the SiC slurry prepared in example 3 of the present invention;

FIG. 6 is a photograph taken by means of a scanning electron microscope at 2000 times magnification of a SiC porous ceramic prepared by applying example 1 of the present invention;

FIG. 7 is a photomicrograph of a SiC porous ceramic prepared by free-write formation using the SiC slurry prepared in inventive example 1;

FIG. 8 is a photomicrograph of a SiC porous ceramic prepared by free-write formation using the SiC slurry prepared in example 2 of the present invention;

FIG. 9 is a photomicrograph of a SiC porous ceramic prepared by free-write formation using the SiC slurry prepared in example 3 of the present invention;

FIG. 10 is a graph of the rheological properties (shear rate-viscosity) of SiC slurries of varying solids content prepared using example 4 of the present invention;

FIG. 11 is a graph of the rheological properties (shear rate versus shear stress) of SiC slurries of varying solids content prepared using example 4 of the present invention;

FIG. 12 is a graph of the rheological properties (shear stress-storage modulus) of SiC slurries of different solids content prepared using example 4 of the present invention.

The specific implementation mode is as follows:

the present invention will be described in further detail with reference to examples.

Weight purity of SiC powder used in examples of the invention>99% by weight, particle size 0.5mm (d)₅₀＝0.5μm)。

The sintering aid adopted in the embodiment of the invention is an industrial grade product, and the weight purity is more than 99%.

The ball milling and powder mixing equipment in the embodiment of the invention is a roller ball mill.

The stirrer adopted in the preparation process of the suspension in the embodiment of the invention is a JB300-SH type digital display constant speed strong stirrer of Shanghai balance company.

The sintering process in the embodiment of the invention adopts a vacuum high-temperature sintering furnace as equipment.

The equipment used for the Zeta potential test in the embodiment of the present invention is a Zeta potential instrument from Bedford Hills company.

The equipment used for the rheological property test in the embodiment of the invention is a rotational rheometer from TA company, and the model of the equipment is DHR-2.

The device used for Scanning Electron Microscope picture provided by the invention is Hitachi Scanning Electron Microscope, and the model of the device is s 4800.

Example 1

292gSiC and 4gB₄C (as sintering aid) and 4g of nano Carbon Black (CB) (as sintering aid) (the mass of the sintering aid accounts for 2.7 percent of the total mass of the powder) are put into a polytetrafluoroethylene ball milling tank, and 40 SiC ball milling balls with the diameter of 2mm and 400ml of alcohol are added. Ball milling is carried out for 24 hours at the rotating speed of 200rpm to prepare SiC and B₄C and CB mixed powder. And (4) sieving the mixed powder through a 400-mesh sieve, and drying for 24 hours at the temperature of 90 ℃. The dried powder was ground and pulverized in a mortar and sieved again through a 400-mesh sieve.

In this example, the Zeta potential diagrams of the raw powders of silicon carbide and two sintering aids and the Zeta potential diagrams after surface modification of the three powders by means of the dispersant are shown in fig. 1.

The mixed powder after sieving was slowly added to a solution containing 2.8g of a polyethyleneimine (PEI, m.w. ═ 75000) dispersant (0.93% of the total mass of the powder) and 80g of deionized water, and stirred while adding, thereby obtaining a ceramic slurry having a high solid content (53.3 vol%).

To the ceramic slurry, a 2mol/L aqueous solution of sodium hydroxide was added to a pH of 10.3, and stirred for 2 hours. And then continuously adding methyl cellulose as a thickening agent to obtain an adjusted slurry, wherein the mass ratio of the methyl cellulose in the adjusted slurry is 20 mg/L.

And (3) ball-milling the obtained adjusted slurry for 24 hours at the rotating speed of 750rpm by using a planetary ball mill to prepare the strong gel ceramic slurry. The solid content of the strong gel ceramic slurry is 52 vol%, and the strong gel ceramic slurry has obvious shear thinning phenomenon, wherein the shear thinning index n is 0.25. The slurry has a distinct viscoelasticity, its shear yield stress (tau)_y) Is 56.77pa, equilibrium storage modulus (G'_eq) 2464.86 pa.

The prepared strong gel ceramic slurry is applied to free direct-writing forming. The slurry was extruded from a 0.25mm diameter nozzle with the aid of a gas pressure of 0.5 MPa. And (3) obtaining porous SiC ceramic at the extrusion speed of 12mm/s, and drying the formed porous SiC ceramic for 24 hours at room temperature to obtain a biscuit. And sintering the dried biscuit at the high temperature of 2000 ℃ to obtain a final finished product. The linear shrinkage of the sintered product was 13.7%. FIG. 3 shows a scanning electron micrograph of the finished SiC porous ceramic at 25 Xmagnification, and FIG. 6 shows a scanning electron micrograph at 2000 Xmagnification, in which the skeleton is a cylinder having a diameter of 0.32mm and the aspect ratio is 2.7. The macro-photograph is shown in figure 7.

Example 2

292gSiC and 4gB₄C (sintering aid) and 4g of nano carbon black (sintering aid) powder are put into a polytetrafluoroethylene ball milling tank, and 40 SiC ball milling balls with the diameter of 2mm and 400ml of alcohol are added. Ball milling is carried out for 24 hours at the rotating speed of 200rpm to prepare SiC and B₄C and CB mixed powder. And (4) sieving the mixed powder through a 400-mesh sieve, and drying for 24 hours at the temperature of 90 ℃. The dried powder was ground and pulverized in a mortar and sieved again through a 400-mesh sieve.

The mixed powder after sieving was slowly added to a solution containing 3.5g of a polyethyleneimine (PEI, m.w. ═ 75000) dispersant (1.2% of the total mass of the powder) and 82g of deionized water, and stirred while adding, thereby obtaining a ceramic slurry having a high solid content (52.9 vol%).

To the ceramic slurry was added a 2mol/L aqueous solution of sodium hydroxide to a pH of 9, and stirred for 2 h. And then continuously adding methyl cellulose as a thickening agent to obtain an adjusted slurry, wherein the mass ratio of the methyl cellulose in the adjusted slurry is 20 mg/L.

And (3) ball-milling the obtained adjusted slurry for 24 hours at the rotating speed of 750rpm by using a planetary ball mill to prepare the strong gel ceramic slurry. The solids content of this slurry was 52 vol%. The slurry had a significant shear thinning behavior with a shear thinning index n of 0.36. And the slurry has obvious viscoelasticity and shear yield stress (tau)_y) 455.89pa, equilibrium storage modulus (G'_eq) 23381.87 pa.

The slurry prepared as described above was applied for free direct write forming. The slurry was extruded from a 0.2mm diameter nozzle with the aid of a gas pressure of 0.5 MPa. And (3) drying the molded porous SiC ceramic for 24 hours at room temperature at the extrusion speed of 8mm/s to obtain a biscuit. And sintering the dried biscuit at the high temperature of 2000 ℃ to obtain a final finished product. The linear shrinkage of the sintered product was 13.2%. Scanning electron micrographs of the finished SiC porous ceramic are shown in fig. 4, where fig. 4(a) and 4(b) are surface scanning electron micrographs; FIGS. 4(c) and 4(d) are sectional scanning electron micrographs; the skeleton is a cylinder with a diameter of 0.26mm and an aspect ratio of 4. The macro-photograph is shown in figure 8.

Example 3

The mixed powder after sieving was slowly added to a solution containing 4.2g of a polyethyleneimine (PEI, m.w. ═ 75000) dispersant (1.4% of the total mass of the powder) and 84g of deionized water, and stirred while adding, thereby obtaining a ceramic slurry having a high solid content (53.1 vol%).

To the slurry was added a 5mol/L aqueous hydrochloric acid solution to a pH of 8, and the mixture was stirred for 2 hours. And then continuously adding methyl cellulose as a thickening agent to obtain an adjusted slurry, wherein the mass ratio of the methyl cellulose in the adjusted slurry is 20 mg/L.

And (3) ball-milling the prepared slurry for 24 hours at the rotating speed of 750rpm by using a planetary ball mill to prepare the strong gel ceramic slurry. The solids content of this slurry was 52 vol%. The slurry had a significant shear thinning behavior with a shear thinning index n of 0.37. And the slurry has obvious viscoelasticity and shear yield stress (tau)_y) 237.26pa, equilibrium storage modulus (G'_eq) 5418.77 pa.

The slurry prepared as described above was applied for free direct write forming. The slurry was extruded from a 0.25mm diameter nozzle with the aid of a gas pressure of 0.5 MPa. And (3) drying the molded porous SiC ceramic for 24 hours at room temperature at the extrusion speed of 12mm/s to obtain a biscuit. And sintering the dried biscuit at the high temperature of 2000 ℃ to obtain a final finished product, wherein the linear shrinkage rate of the sintered finished product is 14.8%. FIG. 5 is a scanning electron micrograph of the finished SiC porous ceramic at 25 Xmagnification showing a skeleton having a cylindrical shape with a diameter of 0.28mm and an aspect ratio of 3.8. The macro-photograph is shown in figure 9.

The rheological property curves of the SiC slurries applied to free-direct-write prepared in the above examples 1, 2 and 3 are shown in fig. 2, in which fig. 2(a) is a shear rate-shear stress curve, 2(b) is an oscillating stress-storage modulus curve, and 2(c) is a shear rate-viscosity curve.

In FIG. 2(a), the solid line is a fitting curve, and the fitting model is a Herschel-Bulkley model. The ceramic slurry used for free-write forming must have suitable viscoelasticity, and the rheological properties thereof need to satisfy the Herschel-Bulkley formula:

wherein, tau is the actual shear stress, tau_yFor shear yield stress, γ is the actual shear rate, n is the shear thinning index, and K is the viscosity constant. When n is<1 and the applied stress to which the slurry is subjected exceeds the shear yield stress, the slurry will exhibit shear thinning behavior.

As can be seen, the flow curves of the SiC slurries prepared in examples 1, 2 and 3 all conform to the Herschel-Bulkley model, and the fitting degree R of examples 1, 2 and 3²0.989, 0.996 and 0.996 respectively. This demonstrates that the SiC slurries prepared in examples 1, 2, and 3 all have significant viscoelasticity.

The process and performance parameters for preparing the strong gel ceramic slurry of examples 1-3 above are shown in table 1 below.

Table 1.

Example 4

This example aims to investigate the effect of different solid phase contents on the rheological properties of a strongly gelled ceramic slurry. Strong gel ceramic slurry with solid contents of 41 vol%, 47 vol%, 53vol% and 57 vol% is prepared. The gel was prepared in the same manner as in example 3. The difference lies in that:

when the solid content of the strong gel ceramic slurry is 41 vol%, the preparation proportion of the sol suspension liquid at the early stage is as follows: 80g of water, 4.2g of polyethyleneimine (2.2% of the total mass of the powder) and 188.2g of mixed powder (including 182g of SiC and 3.1g of B)₄C and 3.1gCB, wherein the mass of the sintering aid accounts for 3.3 percent of the total mass of the powder; the obtained sol suspension had a solid content of 42 vol%;

when the solid content of the strong gel ceramic slurry is 47 vol%, the preparation proportion of the early-stage sol suspension is as follows: 80g of water, 4.2g of polyethyleneimine (1.7% of the total mass of the powder) and 241.8g of mixed powder (including 235g of SiC and 3.4g of B)₄C and 3.4gCB, wherein the mass of the sintering aid accounts for 2.8 percent of the total mass of the powder; the obtained sol suspension had a solid content of 48.5 vol%;

when the solid content of the strong gel ceramic slurry is 53vol%, the preparation proportion of the early-stage sol suspension is as follows: 80g of water, 4.2g of polyethyleneimine (1.3% of the total mass of the powder) and 319g of mixed powder (including 310g of SiC and 4.5g of B)₄C and 4.5gCB, wherein the mass of the sintering aid accounts for 2.8 percent of the total mass of the powder; the sol suspension obtained had a solids content of 54.4 vol%;

when the solid content of the strong gel ceramic slurry is 57 vol%, the preparation proportion of the sol suspension liquid at the early stage is as follows: 80g of water, 4.2g of polyethyleneimine (1.2% of the total mass of the powder), and 367.4g of a mixed powder (containing 357g of SiC and 5.2g of B)₄C and 5.2gCB, wherein the mass of the sintering aid accounts for 2.7 percent of the total mass of the powder; the sol suspension obtained had a solids content of 58 vol%.

The rheological parameters of the above obtained strong gel ceramic slurries of different solids contents are shown in table 2. SiC gels of different solids contents were fitted using the Herschel-Bulkley equation. Fitting result and degree of fitting (R) of relevant parameters²) As shown in table 2. The rheological properties (shear rate-viscosity) curve is shown in FIG. 10, the shear rate-shear stress curve is shown in FIG. 11,the (shear stress-storage modulus) graph is shown in fig. 12.

TABLE 2 relevant parameters for example 4

Claims

1. A preparation method of silicon carbide slurry applied to a free direct-write forming technology is characterized by comprising the following steps:

(1) uniformly mixing SiC powder with a sintering aid by ball milling to obtain a suspension, wherein the sintering aid is a mixture of boron carbide and carbon black in a mass ratio of 1: 1; the addition amount of the sintering aid is 2-5 wt% of the total mass of the powder;

(3) pouring the sieved powder into an aqueous solution in which a dispersing agent is dissolved, and uniformly stirring to prepare a sol ceramic suspension, wherein the addition amount of the dispersing agent is 0.5-5 wt% of the total mass of the powder, the dispersing agent is polyethyleneimine, and the molecular weight of the dispersing agent is 75000; the solid content of the sol ceramic suspension is 48.5-54.4 vol%;

(4) adding 2-5mol/L sodium hydroxide aqueous solution or hydrochloric acid aqueous solution into the sol ceramic suspension, adjusting the pH to 8-11.5, continuously stirring for 0.1-10 h, adding a thickening agent, stirring and ball-milling to obtain SiC ceramic slurry applied to free direct writing, wherein the solid content phi is 47-53 vol%, the shear thinning index n =0.25-0.37, and the shear yield stress isτ _y56.77-455.89 Pa, and balanced storage modulus G'_eq2464.86-23381.87 Pa; wherein the addition amount of the thickening agent is 10-30mg/L of the total volume of the free direct-writing SiC ceramic slurry;

the preparation method of the porous SiC ceramic sample is characterized in that the porous SiC ceramic sample is prepared from the SiC ceramic slurry applied to free direct writing, the skeleton of the porous SiC ceramic sample is cylindrical with the diameter of 0.26-2.2 mm, and the aspect ratio of the porous SiC ceramic sample is 4-20, and the preparation method of the porous SiC ceramic comprises the following steps:

(2) and after all samples are deposited, drying to remove water, sintering the dried samples in a vacuum sintering furnace at a high temperature of 1800-2100 ℃ under a vacuum condition, and preparing the porous SiC ceramic sample.

2. The method for preparing silicon carbide slurry for use in free-write forming technology according to claim 1, wherein in the step (1): the total mass of the powder is the total mass of the SiC powder and the sintering aid, and the ball milling process comprises the following steps: the rotating speed is 50-500 rpm, and the ball milling time is 2-24 h; the ball milling medium is one of water, ethanol, glycerol and toluene; the ball milling ball is made of one of zirconia, alumina, titanium oxide, silicon carbide and silicon nitride balls with the diameter of 2-50 mm.

3. The method for preparing silicon carbide slurry applied to the free-form direct-write forming technology according to claim 1, wherein in the step (2), the drying operation is performed in a constant-temperature oven, the drying temperature is 50-300 ℃, and the drying time is 1-24 hours.

4. The method for preparing silicon carbide slurry for use in free-write forming technology according to claim 1, wherein in the step (3): the stirring speed is 200-10000 rpm, and the stirring time is 0.1-10 h.

5. The method for preparing silicon carbide slurry for use in free-write forming technology according to claim 4, wherein in the step (4):

the addition amount of the thickening agent is 20mg/L of the total volume of the SiC ceramic slurry applied to free direct writing;

the thickener is one of cellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, phenolic resin, ammonium polyacrylate and polyethyleneimine;

the stirring time after the thickening agent is added is 0.1-10 h, the stirring rotating speed is 200-10000 rpm, the ball milling time is 2-48 h, and the ball milling rotating speed is 20-10000 rpm.

6. The method for preparing silicon carbide slurry for use in the free-write forming technology according to claim 5, wherein in the step (4), the thickening agent is methylcellulose and the viscosity is 5000 cp.