CN112194498B - Method for improving density of carbon/ceramic composite material by reducing viscosity of polycarbosilane - Google Patents
Method for improving density of carbon/ceramic composite material by reducing viscosity of polycarbosilane Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 64
- 229920003257 polycarbosilane Polymers 0.000 title claims abstract description 61
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 37
- 239000000919 ceramic Substances 0.000 title claims abstract description 34
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 33
- 239000002131 composite material Substances 0.000 title claims abstract description 33
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims abstract description 239
- 239000011259 mixed solution Substances 0.000 claims abstract description 39
- 230000008569 process Effects 0.000 claims abstract description 28
- 238000005336 cracking Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 12
- 238000005303 weighing Methods 0.000 claims abstract description 10
- 238000002791 soaking Methods 0.000 claims abstract description 7
- 239000002243 precursor Substances 0.000 claims description 88
- 239000003795 chemical substances by application Substances 0.000 claims description 26
- 238000003756 stirring Methods 0.000 claims description 18
- 238000007792 addition Methods 0.000 claims description 17
- 238000007598 dipping method Methods 0.000 claims description 17
- 238000007605 air drying Methods 0.000 claims description 15
- 239000012300 argon atmosphere Substances 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 8
- 239000013618 particulate matter Substances 0.000 claims 1
- 239000011148 porous material Substances 0.000 abstract description 5
- 239000003960 organic solvent Substances 0.000 abstract description 4
- 230000009467 reduction Effects 0.000 abstract description 4
- 229910010293 ceramic material Inorganic materials 0.000 abstract description 2
- 230000007547 defect Effects 0.000 abstract description 2
- 231100000086 high toxicity Toxicity 0.000 abstract 1
- 238000005470 impregnation Methods 0.000 description 13
- 238000009736 wetting Methods 0.000 description 13
- 230000008859 change Effects 0.000 description 7
- 238000001035 drying Methods 0.000 description 7
- 239000003054 catalyst Substances 0.000 description 6
- 230000007123 defense Effects 0.000 description 6
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- 229920000049 Carbon (fiber) Polymers 0.000 description 4
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- 230000003247 decreasing effect Effects 0.000 description 4
- 229910002804 graphite Inorganic materials 0.000 description 4
- 239000010439 graphite Substances 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical group C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
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- 150000003384 small molecules Chemical class 0.000 description 3
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- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 231100000053 low toxicity Toxicity 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 1
- 238000004566 IR spectroscopy Methods 0.000 description 1
- 238000002679 ablation Methods 0.000 description 1
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- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
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- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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- C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
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Abstract
The invention discloses a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane, relates to the field of carbon/ceramic composite materials, and aims to solve the problems that in the prior art, an additional organic solvent has high toxicity, energy is consumed by heating, and the performance of the prepared carbon/ceramic material has defects due to the slow curing phenomenon of PCS. The method comprises the following steps: firstly, weighing; secondly, preparing a uniform mixed solution; thirdly, soaking the uniform mixed solution; fourthly, volatilizing the acetone. The method is simple and convenient to operate, the viscosity of the polycarbosilane can be reduced to 6.0mpas from 243.0mpas, two orders of magnitude of reduction can be achieved, meanwhile, the porosity generated in the subsequent curing-cracking process of PCS can be greatly reduced, and the diameter of the pores can be reduced. The method is used for preparing the high-density carbon/ceramic composite material.
Description
Technical Field
The invention belongs to the field of carbon/ceramic composite materials, and particularly relates to a method for reducing viscosity of polycarbosilane and improving impregnation efficiency in a PIP (poly-p-phenylene-imide) process for preparing a carbon/ceramic composite material.
Background
The carbon/ceramic composite material has high specific strength and high specific modulus, excellent room-temperature and high-temperature mechanical properties and good oxidation and ablation resistance, and is expected to become an important candidate material for high-temperature structural components such as a nose cone, a wing leading edge and the like of a hypersonic aircraft. The most common material in the carbon/ceramic composite material system is carbon fiber toughened SiC or ultrahigh temperature ceramic modified SiC-based composite material, and the SiC matrix phase is mainly provided by impregnation cracking supply of polycarbosilane precursor. The traditional polycarbosilane Precursor (PCS) is high in viscosity and poor in wettability with fibers, so that the SiC ceramic phase in the carbon/ceramic composite material is low in introduction amount and needs to be impregnated for multiple times, and finally, the preparation period of the composite material is long and the cost is high. Therefore, reducing the viscosity of PCS while improving the wettability between fibers and ceramics is a core process for breaking through the bottleneck problems of long preparation period and high cost of carbon/ceramic composite materials. In view of the technical bottleneck, researchers at home and abroad carry out a great deal of research work, and at first, organic solvents such as xylene DVB and the like are utilized to dilute and dissolve polycarbosilane precursors, but the viscosity reduction effect is not obvious, and the highly toxic organic solvents such as xylene and the like easily cause environmental pollution. In addition, the PCS/xylene system is very easy to generate foaming phenomenon at high temperature, and the densification efficiency is reduced. In addition, the viscosity of the precursor can be reduced within a certain range by increasing the temperature of the polycarbosilane precursor, but the polycarbosilane precursor is easily cured and loses efficacy when the temperature is too high (more than 80 ℃), and the viscosity of the precursor is sharply increased after the temperature is increased for a period of time, so that the impregnation efficiency is reduced. Therefore, reducing the viscosity of the precursor and improving the wettability between fibers and ceramics are the key points for preparing the high-performance carbon/ceramic composite material with high efficiency and low cost.
Disclosure of Invention
The invention aims to solve the problems that in the prior art, the toxicity of an additional organic solvent is high, energy is consumed by heating, and the prepared carbon/ceramic material has defects due to the slow curing phenomenon of PCS. The invention provides a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane. The method is simple and convenient to operate, has low toxicity, can improve the density of the later-stage curing-cracking process of the PCS, can greatly improve the impregnation efficiency, and saves the cost.
The invention relates to a method for improving the density of a carbon/ceramic composite material by a process for reducing viscosity of polycarbosilane, which comprises the following steps:
firstly, weighing: measuring acetone and a curing agent and placing the acetone and the curing agent in a beaker;
secondly, preparing a uniform mixed solution: fully stirring acetone, a curing agent and a polycarbosilane precursor to obtain a uniformly mixed polycarbosilane-acetone mixed solution;
thirdly, impregnating polycarbosilane-acetone mixed solution: dipping the mixed solution in the previous step into a block to be dipped;
fourthly, volatilizing acetone: volatilizing acetone in the block by a heating mode;
fifthly, placing polycarbosilane after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 1-2 hours at the temperature of 180-200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking the sample for 0.5 to 1 hour in an argon atmosphere at the temperature of 1200 to 1300 ℃ to finish the method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of the polycarbosilane;
the acetone measured in the step one is 1-40% of the mass fraction of the polycarbosilane precursor;
the mass fraction of the curing agent measured in the first step is 1% of that of the polycarbosilane precursor;
the dipping time in the third step is 6-24 h;
in the third step, the mixed solution is soaked into the block to be soaked by adopting the combination of vacuum soaking and vibration-assisted soaking processes;
in the fourth step, the temperature rise is 20-100 ℃;
the acetone volatilization in the fourth step means that the mass fraction of the acetone is less than 0.5 percent.
The block body to be soaked is a carbon fiber woven body.
The invention has the following beneficial effects:
firstly, the reagent added in the invention has low cost and low toxicity.
Compared with a heating method, the invention adopts a combined process of vacuum impregnation (20MPa) and vibration-assisted impregnation (2000Hz) for impregnation, wherein, an absolute closed environment is created by vacuumizing, and certain pressure is generated to fully fuse PCS and acetone; the two are placed on a vibration table, vibration is utilized to replace stirring, the two are further fully fused, the effect of reducing the viscosity of PCS is more remarkable, the viscosity of polycarbosilane can be reduced to 6.0mpas from 243.0mpas, and the impregnation efficiency is improved. Energy is saved, and the viscosity can not be greatly increased in a long time.
The invention improves the surface tension coefficient, reduces the wetting angle between the mixed solution and the carbon fiber surface and the viscosity of polycarbosilane, optimizes three influencing factors and greatly improves the dipping efficiency.
The invention can not accelerate the curing effect of the PCS at normal temperature, does not change the chemical bond, elements and internal structure of the PCS, and can also improve the density of the PCS after subsequent curing and cracking.
The invention can improve the impregnation effect of various blocks to be impregnated in PCS and can be popularized in a large scale and industrialized.
Drawings
FIG. 1 is a plot of the change in PCS viscosity after the addition of different acetone levels in example one; wherein,
in order to avoid the addition of acetone, the method comprises the following steps of,
is added in an amount of 1 wt.% of acetone,
is added in an amount of 2 wt.% of acetone,
is added in an amount of 5 wt.% acetone,
is added in an amount of 10 wt.% acetone,
is added in an amount of 30 wt.% acetone,
40 wt.% acetone addition;
FIG. 2 is an infrared spectrum of PCS after addition of different amounts of acetone in example one; wherein a is no acetone added, b is 1 wt.% acetone added amount, c is 2 wt.% acetone added amount, d is 5 wt.% acetone added amount, e is 10 wt.% acetone added amount, f is 30 wt.% acetone added amount, and g is 40 wt.% acetone added amount;
FIG. 3 is a graph showing the variation of wetting angle between polycarbosilane and graphite surface under different acetone content in the first example;
FIG. 4 is a graph of PCS viscosity change after heating, acetone addition, and standing for 3 hours; wherein, a is a PCS viscosity change diagram after being heated and kept stand for 3 hours, and b is a PCS viscosity change diagram after being added with acetone and kept stand for 3 hours;
FIG. 5 is a microscopic topography of polycarbosilane after curing with different acetone additions;
FIG. 6 is a microscopic morphology of polycarbosilane after cracking after different acetone additions.
Detailed Description
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.
To make the objects, aspects and advantages of the embodiments of the present invention more apparent, the following detailed description clearly illustrates the spirit of the disclosure, and any person skilled in the art, after understanding the embodiments of the disclosure, may make changes and modifications to the technology taught by the disclosure without departing from the spirit and scope of the disclosure.
The exemplary embodiments of the present invention and the description thereof are provided to explain the present invention and not to limit the present invention.
The first embodiment is as follows: the method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane is specifically completed according to the following steps:
firstly, weighing: measuring acetone and a curing agent and placing the acetone and the curing agent in a beaker;
secondly, preparing a uniform mixed solution: fully stirring acetone, a curing agent and a polycarbosilane precursor to obtain a uniformly mixed polycarbosilane-acetone mixed solution;
dipping polycarbosilane-acetone mixed solution: dipping the mixed solution in the previous step into a block to be dipped;
fourthly, volatilizing acetone: volatilizing acetone in the block by a heating mode;
fifthly, placing polycarbosilane after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 1-2 hours at the temperature of 180-200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 0.5-1 hour in an argon atmosphere with a gas flow rate of 10mL/min at 1200-1300 ℃ to finish the method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of the polycarbosilane;
the acetone measured in the step one is 1-40% of the mass fraction of the polycarbosilane precursor;
the mass fraction of the curing agent measured in the first step is 1% of that of the polycarbosilane precursor;
the dipping time in the third step is 6-24 h;
in the third step, the mixed solution is soaked into the block to be soaked by adopting the combination of vacuum soaking and vibration-assisted soaking processes;
in the fourth step, the temperature rise is 20-100 ℃;
the acetone volatilization in the fourth step means that the mass fraction of the acetone is less than 0.5 percent.
The block body to be soaked is a carbon fiber woven body.
The heating rate in the fifth step is 3 ℃ per minute, and the heating rate in the fifth step is 5 ℃ per minute.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 1 wt.%. The rest is the same as the first embodiment.
The third concrete implementation mode: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 2 wt.%. The rest is the same as the first embodiment.
The fourth concrete implementation mode: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 5 wt.%. The rest is the same as the first embodiment.
The fifth concrete implementation mode: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 10 wt.%. The rest is the same as the first embodiment.
The sixth specific implementation mode: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 30 wt.%. The rest is the same as the first embodiment.
The seventh embodiment: the first difference between the present embodiment and the specific embodiment is: the acetone content in step one was 40 wt.%. The rest is the same as the first embodiment.
The specific implementation mode is eight: the first difference between the present embodiment and the specific embodiment is: and in the second step, the mixing mode is manual stirring. The rest is the same as the first embodiment.
The specific implementation method nine: the first difference between the present embodiment and the specific embodiment is: the equipment used in the fourth step is a common drying oven. The rest is the same as the first embodiment.
The detailed implementation mode is ten: the first difference between the present embodiment and the specific embodiment is: in step four, the temperature is room temperature (25 ℃). The rest is the same as the first embodiment.
The concrete implementation mode eleven: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 30 ℃. The rest is the same as the first embodiment.
The specific implementation mode twelve: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 40 ℃. The rest is the same as the first embodiment.
The specific implementation mode is thirteen: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 60 ℃. The rest is the same as the first embodiment.
The specific implementation mode is fourteen: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 70 ℃. The rest is the same as the first embodiment.
The concrete implementation mode is fifteen: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 80 ℃. The rest is the same as the first embodiment.
The specific implementation mode is sixteen: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 90 ℃. The rest is the same as the first embodiment.
Seventeenth embodiment: the first difference between the present embodiment and the specific embodiment is: in the fourth step, the temperature is 100 ℃. The rest is the same as the first embodiment.
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 0.1g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 5 min.
For the mixed solution obtained in the first example, the viscosity of the mixed solution was 205.5 mPas by a viscometer, the wetting angle with the graphite surface was 17.8 degrees, as shown in FIG. 1 and FIG. 3, FIG. 1 is a graph showing the variation of viscosity of PCS with rotation speed under different acetone contents, FIG. 3 is a graph showing the variation of wetting angle of polycarbosilane with the graphite surface under different acetone contents,
the wetting angles of the surfaces of PCS and graphite under different acetone contents are measured, the results show that the wetting angles show a decreasing trend along with the increase of the acetone content, the wetting angle values and other measured values are calculated by combining the following two formulas, the surface tension coefficient (formula 1) and the dipping height (formula 2) in unit time both show an increasing trend, and the addition of acetone into PCS can effectively improve the dipping efficiency.
Wherein, the symbols in the formulas 1 and 2 represent the following meanings: σ is the surface tension coefficient, l is the unitThe time impregnation height is rho, the density of the polycarbosilane-acetone mixed solution with different contents, the wetting angle theta, the density of the mixed solution mu, the pore radius of the impregnated block r, the height of the impregnated block h, the pore diameter of the impregnated block d and the local gravity acceleration value g (usually 9.8 m/s)2)。
The molecular weights before and after addition of acetone were measured by gel permeation chromatography, and table 1 is a table of PCS molecular weight changes before and after addition of acetone.
The chemical bond of PCS was characterized for different acetone contents using infrared spectroscopy, and fig. 2 is a liquid phase FT-IR plot of PCS for different acetone contents. From fig. 1, table 1, fig. 2, and fig. 3, it can be seen that the viscosity of PCS decreases as the acetone content increases, and the introduction of acetone does not change the molecular weight and original chemical bonds of PCS, so that the example one is suitable for decreasing the viscosity of PCS.
TABLE 1
As can be seen from Table 1, the weight average molecular weight of PCS before and after acetone introduction fluctuated within a range of 2100. + -.50, indicating that the chain length of PCS molecules was not changed by acetone introduction. When the acetone incorporation was 30 wt%, the percentage of small molecules (<1500) decreased from 27% to 23%, resulting in an increasing trend in both PCS number average molecular weight and weight average molecular weight. In addition, this example also calculated the PCS cure yield before and after acetone introduction, with a 30 wt% acetone introduction cure yield of 86.6% lower than that of pure PCS (90.6%) due to volatilization of small molecules carrying PCS during acetone volatilization. Therefore, acetone carrying small molecules volatilize to promote the solidification of PCS into a more compact body.
Example two: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor PCS (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 0.2g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 5 min.
The viscosity of the mixed solution obtained in example two was 117.0 mPas by a viscometer, and the wetting angle was 17.1 ℃.
Example three: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor PCS (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 0.5g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 10 min.
The viscosity of the mixed solution obtained in example three was 93.0 mPas by a viscometer, and the wetting angle was 16.8 ℃.
Example four: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor PCS (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 1.0g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 15 min.
The viscosity of the mixed solution obtained in example four was 45.0 mPas by a viscometer, and the wetting angle was 13.6 ℃.
Example five: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor PCS (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 3.0g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 20 min.
The viscosity of the mixed solution obtained in example four was 10.5 mPas by a viscometer, and the wetting angle was 12.8 ℃.
Example six: a method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane and an application thereof are specifically completed according to the following steps:
weighing 10g of polycarbosilane precursor PCS (the polycarbosilane precursor is directly purchased from national defense science and technology university), and adding 4.0g of acetone and 0.1g of curing agent;
the curing agent in the first step is KARSTEDT catalyst;
secondly, mixing acetone and PCS, and stirring by using a magnetic stirrer to obtain a PCS-acetone mixed solution which is uniformly stirred;
the rotating speed of the magnetic stirrer in the step two is 200r/min, and the stirring time is 10 min;
thirdly, dipping the mixed solution into a block to be dipped;
fourthly, placing the block body in a vacuum forced air drying oven to be heated until the acetone is completely volatilized;
fifthly, placing the PCS after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 2 hours at the temperature of 200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking for 1 hour in an argon atmosphere (10mL/min) at 1300 ℃ to obtain a cracked sample (namely a final finished product);
the drying oven in the fourth step is set at 60 ℃ and the volatilization time is 20 min.
The viscosity of the mixed solution obtained in example four was 6.0mPas by a viscometer, and the wetting angle was 12.2 ℃.
EXAMPLE seven
This example is to examine the change in viscosity of PCS after 3 hours of standing (where standing is just after the addition of the corresponding ratio of acetone/polycarbosilane and stopping heating and standing after reaching the set target temperature in order to compare the effective durations of the two viscosity reduction methods of acetone addition and temperature rise) after treatment by the method of example 1, and the results are shown in FIG. 4, from which it can be seen that the effect of acetone on viscosity reduction is more durable. Although both methods can reduce the viscosity of PCS in the initial stage of heating/adding acetone, after standing for 3 hours, the viscosity of the heated PCS is remarkably increased, and even rebounding occurs, and the viscosity exceeds the initial viscosity value of the PCS; in contrast, the PCS after acetone addition was still at rest for 3 hours, and the viscosity was kept at a small value, which helps the PCS to maintain a low viscosity state for a long time. In addition, in the actual production process, the impregnation process is generally a longer process, so that the impregnation efficiency of the actual production can be effectively improved by adding acetone to reduce the viscosity of PCS.
Example eight
The difference between this example and example 1 is that the addition amount of acetone is changed to examine the states of the cured and cracked samples, and the results are shown in fig. 5 and 6, and it can be seen from fig. 5 and 6 that the pores of the cured and cracked samples show a trend of significantly decreasing with the increase of the acetone content, which indicates that the addition method of acetone can not only decrease the viscosity of PCS and improve the impregnation efficiency, but also greatly reduce the pores of the prepared samples, improve the density, and further improve the mechanical properties.
Claims (9)
1. A method for improving the density of a carbon/ceramic composite material by a process for reducing the viscosity of polycarbosilane is characterized by comprising the following steps:
firstly, weighing: measuring acetone and a curing agent and placing the acetone and the curing agent in a beaker;
secondly, preparing a uniform mixed solution: fully stirring acetone, a curing agent and a polycarbosilane precursor to obtain a uniformly mixed polycarbosilane-acetone mixed solution;
dipping polycarbosilane-acetone mixed solution: dipping the mixed solution in the previous step into a block to be dipped;
fourthly, volatilizing acetone: volatilizing acetone in the block by a heating mode;
fifthly, placing polycarbosilane after acetone is completely volatilized in a vacuum forced air drying oven to be cured for 1-2 hours at the temperature of 180-200 ℃;
sixthly, placing the completely cured sample in a tube furnace, and cracking the sample for 0.5 to 1 hour in an argon atmosphere at the temperature of 1200 to 1300 ℃ to finish the method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of the polycarbosilane;
the acetone measured in the step one is 1% -40% of the mass fraction of the polycarbosilane precursor;
the mass fraction of the curing agent measured in the first step is 1% of that of the polycarbosilane precursor;
the dipping time in the third step is 6-24 h;
in the third step, the mixed solution is soaked into the block to be soaked by adopting the combination of vacuum soaking and vibration-assisted soaking processes;
in the fourth step, the temperature rise is 20-100 ℃;
the acetone volatilization in the fourth step means that the mass fraction of the acetone is less than 0.5 percent.
2. The method of claim 1, wherein the curing agent added in step one is KARSTEDT curing agent.
3. The method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane according to claim 1, wherein the acetone measured in the step one is 5-40% of the mass fraction of the polycarbosilane precursor.
4. The method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane according to claim 1 or 3, wherein the acetone is taken in the step one, and the content of the acetone is 10% -30% of the mass fraction of the polycarbosilane precursor.
5. The method for improving the density of the carbon/ceramic composite material according to the claim 1, wherein the acetone is added in 2 times, and the addition amount of each time is 50% of the total addition amount of the acetone.
6. The method for improving the compactness of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane according to claim 1, wherein the stirring time in the second step is 10 min.
7. The method of claim 1, wherein the step two of uniformly mixing means that no white particulate matter is generated.
8. The method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane according to claim 1, wherein the temperature rise in the fourth step is 30-80 ℃.
9. The method for improving the density of the carbon/ceramic composite material by the process for reducing the viscosity of polycarbosilane according to claim 1, wherein the acetone is volatilized by the fourth step of heating, adjusting the pressure to-0.1 MPa and then standing at normal temperature and normal pressure.
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