CN112374902A - Preparation method of high-densification SiCf/SiC clad composite pipe - Google Patents

Abstract

The invention discloses a preparation method of a high-densification SiCf/SiC cladding composite pipe, which comprises the following steps: s1: preparation of Low Density SiC_fThe SiC preform: weaving or winding the SiC fiber tube, and then carrying out PyC interface layer deposition and short-time SiC matrix deposition on the surface of the fiber by a CVI process to obtain low-density SiC_fa/SiC preform; s2: preparation of SiC_fA SiC blank: dispersing the nano SiC sintered powder and organic additive in an organic dispersant to prepare NITE-SiC slurry, and diffusing the NITE-SiC slurry into the low-density SiC by infiltration_fPores of SiC preformsDrying to obtain SiC_fA SiC blank; s3: and (3) heat treatment: mixing SiC_fCarrying out degumming heat treatment on the SiC blank under the protection of inert gas atmosphere; s4: and (3) hot isostatic pressing sintering: the blank after the heat treatment is subjected to gas phase pressure sintering in the inert gas atmosphere to obtain the high-densification SiC_fthe/SiC cladding composite pipe. The preparation method can obtain the SiCf/SiC cladding composite material with high density and solves the problem of SiC_fThe problem that the SiC pipe fitting is difficult to form.

Description

Preparation method of high-densification SiCf/SiC clad composite pipe

Technical Field

The invention relates to the field of preparation of silicon carbide ceramic matrix composite materials, in particular to a preparation method of a high-densification SiCf/SiC cladding composite pipe.

Background

Silicon carbide fiber toughened silicon carbide ceramic matrix composite (SiC)_f/SiC) is an excellent high temperature ceramic structural material, which is applied to cladding design and is expected to improve certain operating properties of Light Water Reactor (LWR) cores. The high temperature resistance (capable of operating at 900 ℃) can improve the power by 30 percent; neutron irradiation resistance (can bear 200dpa) and increase of burnup can further prolong the refueling period; the SiC slowly reacts with water at high temperature in a contact way, and hydrogen is not generated, so that the structural integrity of the cladding can be maintained, and the risk of hydrogen explosion can be reduced; particularly, under the condition of loss of coolant accident (LOCA), the high-temperature corrosion resistance can improve the safety of the power station and avoid the catastrophic consequences of a large amount of radioactivity leakage caused by multiple hydrogen explosions similar to the Fudao power plant. Thus, SiC_fthe/SiC composite cladding becomes the first candidate for development of Accident-resistant nuclear Fuel (ATF) cladding materials.

However, SiC_f/The SiC cladding composite material has the problems of difficult molding and low densification degree. For example, chemical vapor deposition (CVI) employs diffusion of gaseous reactants into an isothermal or temperature-graded porous fiber preform and deposit formation, but with progressive deposition of the SiC matrix, of the SiC fibersPossibly forming closed cells and interlaminar spaces between the two layers of fibers, as shown in figure 1. The nano-penetration and eutectic transformation technology (NITE) adopts a liquid phase sintering method to manufacture the matrix of the SiC composite cladding, and SiC with low void ratio and high density can be obtained_fThe technique requires hot-pressing sintering to prepare large-Size (SiC)>1m) and the difficulty of pipe forming are very large.

In summary, the conventional chemical vapor deposition (CVI) method can produce SiC_fThe composite material being/SiC-clad, but the SiC produced_fThe density of the/SiC cladding composite material is low; although the nano-penetration and eutectic transformation technology (NITE) can obtain SiC with low void ratio and high density_fthe/SiC composite material is difficult to form and cannot be applied to SiC_f/And preparing the SiC cladding composite material.

Disclosure of Invention

The invention aims to provide a preparation method of a high-densification SiCf/SiC cladding composite pipe, which can be used for obtaining a high-density SiCf/SiC cladding composite material and solving the problem of SiC cladding composite pipe_fThe problem that the SiC pipe fitting is difficult to form.

The invention is realized by the following technical scheme:

high-densification SiC_fThe preparation method of the/SiC clad composite pipe comprises the following steps:

s1: preparation of Low Density SiC_fThe SiC preform: weaving or winding the SiC fiber tube, and then carrying out PyC interface layer deposition and short-time SiC matrix deposition on the surface of the fiber by a CVI process to obtain low-density SiC_fa/SiC preform;

s2: preparation of SiC_fA SiC blank: dispersing the nano SiC sintered powder and organic additive in an organic dispersant to prepare NITE-SiC slurry, and diffusing the NITE-SiC slurry into the low-density SiC by infiltration_fDrying the SiC preform in the pores to obtain SiC_fA SiC blank;

s3: and (3) heat treatment: mixing SiC_fCarrying out degumming heat treatment on the SiC blank under the protection of inert gas atmosphere;

s4: heat, etcStatic pressure sintering: the blank after the heat treatment is subjected to gas phase pressure sintering in the inert gas atmosphere to obtain the high-densification SiC_fthe/SiC cladding composite pipe.

The deposition time of the SiC matrix is short and is about 15-50 h.

According to the method, the SiC matrix is deposited in the SiC fiber preform with the PyC interface in a short time, the deposition time is about 15-50 h, the deposition is used for filling the inner pores of the fiber bundle in the SiC fiber preform, paths are reserved for the slightly larger pores and the interlayer large pores, CVI deposition is stopped before a closed hole is formed, the closed hole is prevented from being generated, the mechanical strength is certain, the phenomenon that the SiC fiber bundle is not deformed in subsequent operation is guaranteed, and the SiC fiber preform is guaranteed to be subjected to SiC matrix deposition in a short time_fThe circularity of the SiC pipe fitting is beneficial to the forming of the cladding composite pipe, and the deposited SiC_fThe initial density of the SiC preform does not exceed 2.2g/cm³(ii) a Less than 2.2g/cm³The initial density of the NITE process is better, the preform has enough strength and structure shape, and enough infiltration channels are ensured in the preform to avoid forming closed pores.

The prepared NITE-SiC slurry is used for impregnating low-density SiC_fA SiC preform, crosslinked during heat treatment, fixing the SiC nanoparticles to the low-density SiC_fOn SiC preforms, enabling the invention to obtain structurally compact SiC by hot isostatic pressing sintering_fthe/SiC composite cladding simplifies the hot-pressing sintering step of the traditional NITE technology.

The invention realizes SiC by using CVI process as a basic process_fForming the/SiC cladding composite pipe, filling CVI-SiC by taking an NITE process as an auxiliary process_fResidual pores in the SiC composite material, and simultaneously, the NITE process flow is optimized, so that tiny closed pores and interlayer gaps in a pure CVI method can be avoided, a complex NITE forming die is not required, and SiC is solved_fThe problem of difficult forming of SiC pipe fittings enables the invention to prepare long-size SiC_fSiC pipe fitting with improved SiC_fThe density of the SiC pipe fitting is more than 2.7g/cm, and the density of the SiCf/SiC cladding composite pipe prepared by the preparation method is³High density requirement of more than 2.7g/cm³Preferably close to 2.8g/cm³Is of high density.

Further, in step S1, a PyC interface layer is deposited with C₃H₆The deposition temperature is 1000-1050 ℃ and the thickness of the PyC interface layer is less than or equal to 500 nm.

Further, the SiC matrix is deposited with MTS-H in step S1₂Ar is a reaction source gas, the deposition temperature is 1050-1100 ℃, the deposition pressure is 200Pa, and the deposition time is 15-50 h.

The method carries out short-time SiC matrix deposition for filling the pores in the fiber bundles in the fiber preform, simultaneously reserves a path for slightly larger pores and interlaminar macropores, stops CVI deposition before forming a closed hole, avoids the generation of the closed hole, has certain mechanical strength, ensures that the closed hole is not deformed in subsequent operation, and ensures that SiC is not deformed_fCircularity of SiC pipe.

Further, the NITE-SiC slurry in step S2 includes the following components in wt%:

10% of sintering aid, 0-5% of silicon carbide precursor, 10-40% of adhesive, 0-10% of plasticizer and the balance of nano SiC micropowder.

The average particle size of solid particles of the NITE-SiC slurry is less than 100nm, and the mass ratio of solid to liquid is 1-3: 10.

According to the invention, the silicon carbide precursor is added into the traditional NITE slurry, and the silicon carbide precursor can be crosslinked in the heat treatment process, so that the nano SiC particles are fixed in the SiC particles in the previous step_fOn SiC preforms, enabling the invention to obtain structurally compact SiC by hot isostatic pressing sintering_fthe/SiC composite cladding simplifies the hot-pressing sintering step of the traditional NITE technology.

Further, the sintering aid is Al₂O₃And Y₂O₃Or Al and Y₂O₃Mixture of (1), Al₂O₃And Y₂O₃Or Al and Y₂O₃The mass ratio of (A) to (B) is 1.5-4: 1.

Preferably, the sintering is carried outThe auxiliary agent can be added with a small amount of MgO, ZrC and SiO according to the requirement₂Micronizing to adjust the subsequent sintering temperature and the ratio of the matrix C, Si.

Further, the silicon carbide precursor is solid or liquid polycarbosilane; the adhesive is polyvinyl butyral (PVB), and the plasticizer is dibutyl phthalate.

Further, the NITE-SiC slurry is prepared by uniformly dispersing all the components in an organic dispersing agent and uniformly mixing the components by a ball milling method, wherein the organic dispersing agent is a mixed solution of toluene and ethanol.

The ball-material ratio in the mixing process of the ball-milling method is 4-10: 1, and the time is 12-24 h.

The conventional slurry comprises three parts of sintering aid, adhesive and plasticizer, the specific components and the proportion of the three parts can be adjusted according to the process, and the NITE-SiC slurry is specially set according to the process requirement.

Further, in the step S2, the impregnation is vacuum impregnation or electrophoresis impregnation, and the impregnation time is 1 to 2 hours.

Further, the degumming heat treatment in step S3 is:

slowly raising the temperature within the range of 0-400 ℃ at the temperature raising rate of 1-5 ℃/min, and preserving the temperature for 1-4 h at 400 ℃; heating at a temperature rise rate of 5-10 ℃/min within a range of 400-1200 ℃, and preserving heat for 1-2 h at 1200 ℃.

The conventional degumming comprises that the temperature is slowly increased within the range of 0-400 ℃ at the temperature increase rate of 1-5 ℃/min, and the temperature is maintained at 400 ℃ for 1-4 h; since the silicon carbide precursor is added in the present application, the heat treatment of the latter half is a special treatment for the silicon carbide precursor: heating at a temperature rise rate of 5-10 ℃/min within the range of 400-1200 ℃, and preserving heat for 1-2 h at 1200 ℃.

Further, the gas phase pressure sintering in step S4 is:

the sintering temperature is 1700-1850 ℃, the heating rate is 10-20 ℃/min, the gas phase pressure is 20-50 MPa, and the temperature and pressure holding time is 2-4 h.

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

the invention realizes SiC by using CVI process as a basic process_fForming the/SiC cladding composite pipe, filling CVI-SiC by taking an NITE process as an auxiliary process_fResidual pores in the SiC composite material, and simultaneously, the NITE process flow is optimized, so that tiny closed pores and interlayer gaps in a pure CVI method can be avoided, a complex NITE forming die is not required, and SiC is solved_fThe problem of difficult forming of SiC pipe fittings enables the invention to prepare long-size SiC_fSiC pipe fitting with improved SiC_fThe density of the SiC pipe fitting is more than 2.7g/cm, and the density of the SiCf/SiC cladding composite pipe prepared by the preparation method is³。

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 shows plain CVI-SiC_fAnd a microscopic morphology map of the/SiC composite cladding tube.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limitations of the present invention.

Example 1:

high-densification SiC_fThe preparation method of the/SiC clad composite pipe comprises the following steps:

s1: preparation of Low Density SiC_fThe SiC preform: weaving SiC fibers into tubes in a 2D manner, with C₃H₆The deposition temperature is 1000 ℃, and the thickness is 200 nm; with MTS-H₂Carrying out CVI deposition (SiC matrix deposition) for 16h at 1100 ℃ and 200Pa by using Ar as a reaction source gas to obtain low-density SiC_fA SiC preform having a density of 2.02g/cm³；

S2: preparation of SiC_fA SiC blank: 10 percent of sintering aid and silicon carbideDispersing 5% of precursor, 40% of adhesive, 10% of plasticizer and 35% of nano SiC micropowder in organic dispersant, uniformly mixing by ball milling method, the ball-material ratio is 10:1, the time is 12h, preparing NITE-SiC slurry, and diffusing the NITE-SiC slurry into low-density SiC by infiltration_fImpregnating the pores of the SiC preform for 1 hour, and drying the impregnated pores in an oven at 90 ℃ for 5 hours to obtain SiC_fA SiC green body, wherein the sintering aid is Al with the mass ratio of 3:2₂O₃/Y₂O₃The silicon carbide precursor is solid polycarbosilane; the adhesive is polyvinyl butyral (PVB), the plasticizer is dibutyl phthalate, and the dispersing agent is a toluene/ethanol solution with the mass ratio of 3: 2; the average particle size of solid particles in the NITE-SiC slurry is 50nm, and the mass ratio of solid to liquid is 1: 10; a NITE slurry;

s3: and (3) heat treatment: mixing SiC_fHeating the SiC blank from room temperature to 400 ℃ at the speed of 2 ℃/min under the protection of Ar atmosphere, preserving heat for 4h, then continuously heating to 1000 ℃ at the speed of 5 ℃/min, and preserving heat for 1 h; then stopping heating, and cooling the sample along with the furnace;

s4: and (3) hot isostatic pressing sintering: heating the heat-treated blank to 1800 ℃ at the speed of 15 ℃/min in Ar atmosphere, pressurizing the meteorological pressure to 25MPa, preserving heat and pressure for 2h, and then cooling along with the furnace to obtain SiC_fComposite SiC pipe and SiC produced therefrom_fThe density of the/SiC composite pipe is 2.75g/cm³。

Example 2:

high-densification SiC_fThe preparation method of the/SiC clad composite pipe comprises the following steps:

s1: preparation of Low Density SiC_fThe SiC preform: weaving SiC fibers into tubes in shallow crossing (2.5D) mode, with C₃H₆The deposition temperature is 1050 ℃ and the thickness is 400 nm; with MTS-H₂CVI deposition is carried out for 30h under the conditions of 1050 ℃ and 200Pa by taking Ar as a reaction source gas, and low-density SiC is obtained_fThe density of the/SiC preform was 2.11g/cm³；

S2: preparation of SiC_fA SiC blank: sintering aid10％，SiO₂Dispersing 2% of micropowder, 3% of silicon carbide precursor, 10% of adhesive, 5% of plasticizer and 70% of nano SiC micropowder in an organic dispersant, uniformly mixing by a ball grinding method, wherein the ball-material ratio is 4:1, the time is 24h, preparing NITE-SiC slurry, and diffusing the NITE-SiC slurry into low-density SiC by infiltration_fImpregnating for 2 hours in pores of a/SiC prefabricated body, and then drying for 2 hours in a 90 ℃ oven to obtain SiC_fA SiC green body, wherein the sintering aid is Al with the mass ratio of 3:2₂O₃/Y₂O₃The silicon carbide precursor is solid polycarbosilane; the adhesive is polyvinyl butyral (PVB), the plasticizer is dibutyl phthalate, and the dispersing agent is a toluene/ethanol solution with the mass ratio of 3: 2; the average particle size of solid particles in the NITE-SiC slurry is 80nm, and the mass ratio of solid to liquid is 1: 5; a NITE slurry;

s3: and (3) heat treatment: mixing SiC_fHeating the SiC blank from room temperature to 400 ℃ at the speed of 2 ℃/min under the protection of Ar atmosphere, preserving heat for 2h, then continuously heating to 1100 ℃ at the speed of 5 ℃/min, and preserving heat for 1 h; then stopping heating, and cooling the sample along with the furnace;

s4: and (3) hot isostatic pressing sintering: heating the heat-treated blank to 1780 ℃ at the speed of 15 ℃/min in Ar atmosphere, pressurizing the meteorological pressure to 50MPa, preserving heat and pressure for 1h, and then cooling along with the furnace to obtain SiC_fComposite SiC pipe and SiC produced therefrom_fThe density of the/SiC composite pipe is 2.71g/cm³。

Example 3:

high-densification SiC_fThe preparation method of the/SiC clad composite pipe comprises the following steps:

s1: low density SiC_fThe SiC preform: braiding SiC fibers into a tube in a winding manner, with C₃H₆The PyC interface layer is deposited by taking argon as a diluent gas as a source gas, the deposition temperature is 1000 ℃, and the thickness is 300 nm; with MTS-H₂Carrying out CVI deposition for 40h at 1100 ℃ and 200Pa by taking Ar as a reaction source gas to obtain low-density SiC_fThe density of the/SiC preform was 2.15g/cm³；

S2: preparation of SiC_fA SiC blank: dispersing 10% of sintering aid, 2% of MgO micropowder, 5% of silicon carbide precursor, 30% of adhesive, 5% of plasticizer and 48% of nano SiC micropowder in organic dispersant, uniformly mixing by ball milling method, wherein the ball-material ratio is 5:1, and the time is 24h to prepare NITE-SiC slurry, and diffusing the NITE-SiC slurry into low-density SiC by infiltration_fImpregnating for 2 hours in pores of the SiC preform, and drying for 3 hours in a 90 ℃ oven to obtain SiC_fA SiC green body, wherein the sintering aid is Al/Y with the mass ratio of 4:1₂O₃The silicon carbide precursor is solid polycarbosilane; the adhesive is polyvinyl butyral (PVB), the plasticizer is dibutyl phthalate, and the dispersing agent is a toluene/ethanol solution with the mass ratio of 3: 2; the average particle size of solid particles in the NITE-SiC slurry is 60nm, and the mass ratio of solid to liquid is 3: 10; a NITE slurry;

s3: and (3) heat treatment: mixing SiC_fHeating the SiC blank from room temperature to 400 ℃ at the speed of 2 ℃/min under the protection of Ar atmosphere, preserving heat for 2h, then continuously heating to 1200 ℃ at the speed of 5 ℃/min, and preserving heat for 1 h; then stopping heating, and cooling the sample along with the furnace;

s4: and (3) hot isostatic pressing sintering: heating the heat-treated blank to 1780 ℃ at the speed of 15 ℃/min in Ar atmosphere, pressurizing the meteorological pressure to 50MPa, preserving heat and pressure for 1h, and then cooling along with the furnace to obtain SiC_fComposite SiC pipe and SiC produced therefrom_fThe density of the/SiC composite pipe is 2.78g/cm³。

Example 4:

the present example is based on example 3, and differs from example 3 in that:

the deposition time of SiC matrix deposition in the step S1 is 60h, and the obtained low-density SiC_fThe density of the/SiC preform was 2.29g/cm³Prepared SiC_fThe density of the/SiC composite pipe is 2.61g/cm³。

Comparative example 1:

the present example is based on example 3, and differs from example 3 in that:

the deposition time of SiC matrix deposition in the step S1 is 10h, and the obtained low-density SiC_fDensity of SiC preformIs 1.91g/cm³SiC due to too short a deposition time_fthe/SiC preform failed to maintain strength and was unable to complete subsequent testing.

Comparative example 2:

this comparative example is based on example 3, differing from example 3 in that:

the deposition time of SiC matrix deposition in the step S1 is 80h, and the obtained low-density SiC_fThe density of the/SiC preform was 2.38g/cm³Finally prepared SiC_fThe density of the/SiC composite pipe is 2.56g/cm³。

Comparative example 3:

this comparative example is based on example 3, differing from example 3 in that:

the deposition time of SiC matrix deposition in the step S1 is 120h, and the obtained low-density SiC_fThe density of the/SiC preform was 2.58g/cm³Finally prepared SiC_fThe density of the/SiC composite pipe is 2.59g/cm³。

Comparative example 4:

this comparative example is based on example 3, differing from example 3 in that: the formula of the NITE-SiC sizing agent is as follows:

dispersing 10% of sintering aid, 2% of MgO micropowder, 30% of adhesive, 5% of plasticizer and 53% of nano SiC micropowder in organic dispersant, uniformly mixing by ball milling method, wherein the ball-material ratio is 5:1, the time is 24h, preparing NITE-SiC slurry, and finally preparing SiC_fThe density of the/SiC composite pipe is 2.61g/cm³。

Comparative example 5:

this comparative example is based on example 3, differing from example 3 in that: the formula of the NITE-SiC sizing agent is as follows:

dispersing 5% of sintering aid, 2% of MgO micropowder, 10% of silicon carbide precursor, 30% of adhesive, 5% of plasticizer and 48% of nano SiC micropowder in organic dispersant, uniformly mixing by ball milling method, wherein the ball-material ratio is 5:1, and the time is 24h, preparing NITE-SiC slurry, and finally preparing SiC_fThe density of the/SiC composite pipe is 2.70g/cm³。

Comparative example 6:

this comparative example is based on example 3, differing from example 3 in that: the formula of the NITE-SiC sizing agent is as follows:

dispersing 5% of sintering aid, 2% of MgO micropowder, 20% of silicon carbide precursor, 30% of adhesive, 5% of plasticizer and 38% of nano SiC micropowder in organic dispersant, uniformly mixing by ball milling method, wherein the ball-material ratio is 5:1, and the time is 24h, preparing NITE-SiC slurry, and finally preparing SiC_fThe density of the/SiC composite pipe is 2.65g/cm³。

Comparative example 7:

this comparative example is based on example 3, differing from example 3 in that: the formula of the slurry is as follows:

uniformly mixing polycarbosilane and xylene according to the mass ratio of 1:5 to obtain slurry, and finally preparing SiC_fThe density of the/SiC composite pipe is 2.71g/cm³。

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. High-densification SiC_fThe preparation method of the/SiC clad composite pipe is characterized by comprising the following steps:

s1: preparation of Low Density SiC_fThe SiC preform: weaving or winding the SiC fiber tube, and then carrying out PyC interface layer deposition and short-time SiC matrix deposition on the surface of the fiber by a CVI process to obtain low-density SiC_fa/SiC preform;

s2: preparation of SiC_fA SiC blank: dispersing the nano SiC sintered powder and organic additive in an organic dispersant to prepare NITE-SiC slurry, and diffusing the NITE-SiC slurry into the low-density SiC by infiltration_fDrying the SiC preform in the pores to obtain SiC_fA SiC blank;

s3: and (3) heat treatment: mixing SiC_f/SiCCarrying out degumming heat treatment on the blank under the protection of inert gas atmosphere;

s4: and (3) hot isostatic pressing sintering: the blank after the heat treatment is subjected to gas phase pressure sintering in the inert gas atmosphere to obtain the high-densification SiC_fthe/SiC cladding composite pipe.

2. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that a PyC interface layer is deposited with C in the step S1₃H₆The deposition temperature is 1000-1050 ℃ and the thickness of the PyC interface layer is less than or equal to 500 nm.

3. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that in the step S1, MTS-H is deposited on the SiC matrix₂Ar is a reaction source gas, the deposition temperature is 1050-1100 ℃, the deposition pressure is 200Pa, and the deposition time is 15-50 h.

4. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that the NITE-SiC slurry in the step S2 comprises the following components in percentage by weight:

8-10% of sintering aid, 5% of silicon carbide precursor, 10-40% of adhesive, 0-10% of plasticizer and the balance of nano SiC micropowder.

5. High densification SiC according to claim 4_fThe preparation method of the/SiC cladding composite pipe is characterized in that the sintering aid is Al₂O₃And Y₂O₃Or Al and Y₂O₃Mixture of (1), Al₂O₃And Y₂O₃Or Al and Y₂O₃The mass ratio of (A) to (B) is 1.5-4: 1.

6. High densification SiC according to claim 4_f/Preparation method of SiC clad composite pipeThe silicon carbide precursor is characterized by being solid or liquid polycarbosilane; the adhesive is polyvinyl butyral, and the plasticizer is dibutyl phthalate.

7. High densification SiC according to claim 4_fThe preparation method of the/SiC cladding composite pipe is characterized in that the NITE-SiC slurry is prepared by uniformly dispersing all components in an organic dispersing agent and uniformly mixing the components by a ball milling method, wherein the organic dispersing agent is a mixed solution of toluene and ethanol.

8. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that in the step S2, the impregnation is vacuum impregnation or electrophoresis impregnation, and the impregnation time is 1-2 hours.

9. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that the degumming heat treatment in the step S3 is as follows:

slowly raising the temperature within the range of 0-400 ℃ at the temperature raising rate of 1-5 ℃/min, and preserving the temperature for 1-4 h at 400 ℃; heating at a temperature rise rate of 5-10 ℃/min within a range of 400-1200 ℃, and preserving heat for 1-2 h at 1200 ℃.

10. High densification SiC according to claim 1_fThe preparation method of the/SiC clad composite pipe is characterized in that the gas-phase pressure sintering in the step S4 is as follows:

the sintering temperature is 1700-1850 ℃, the heating rate is 10-20 ℃/min, the gas phase pressure is 20-50 MPa, and the temperature and pressure holding time is 2-4 h.

Images