CN114622442A

CN114622442A - Novel insulating paper material and preparation method and application thereof

Info

Publication number: CN114622442A
Application number: CN202110756855.7A
Authority: CN
Inventors: 孙魄韬; 司马文霞; 袁涛; 杨鸣
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2021-07-05
Filing date: 2021-07-05
Publication date: 2022-06-14
Anticipated expiration: 2041-07-05
Also published as: CN114622442B

Abstract

The invention discloses a novel insulating paper material, a preparation method and application thereof. The novel insulating material has an amorphous nano-pore-rich structure, and forms novel ceramic fiber reinforced silicon-based nano-pore-rich insulating paper. The preparation method comprises the following steps: mixing ethyl orthosilicate, water and absolute ethyl alcohol according to a certain proportion, adjusting the pH of the mixture by hydrochloric acid to form a silica sol solution, adjusting a mixed sol system by ammonia water, pouring the sol into a mould to cover common ceramic fiber insulation paper (CFP), and heating to obtain wet gel; replacing the solvent in the wet gel by adopting a gradual replacement method, and pouring the surface grafting solution; and finally, carrying out surface cleaning, sealing soaking and drying at normal pressure to prepare the ceramic fiber reinforced silicon-based nanopore-rich insulating paper. Compared with the common ceramic fiber insulating paper, the generated nano-pore-rich silicon-based medium has the advantages of improved thermal stability, obviously enhanced hydrophobic property and obviously improved AC and DC breakdown field strengths. As the pore size decreases, the composite dielectric breakdown voltage increases.

Description

Novel insulating paper material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of insulating material preparation, and particularly relates to a novel insulating material, a preparation method and application thereof.

Background

The continuous development of high-performance advanced power equipment puts extremely stringent requirements on the performance of insulating materials, and the research and development of high-performance insulating materials are concerned about the miniaturization, low cost and safe operation of electric equipment. The nano composite technology is considered as an important means for improving the dielectric insulation performance, the current research mostly takes a filling type composite material as a main part, namely inorganic oxide is added into a polymer matrix, and the materials still face a plurality of problems after being developed for more than 20 years up to now: such as limited electrical performance enhancement (usually less than 30%), high dielectric loss, poor long-term stability and dispersion uniformity of nanoparticles, etc., which severely restrict their industrial application.

Disclosure of Invention

Based on the technical problems in the prior art, the method provided by the invention bypasses the traditional nano composite technology route, constructs a novel silicon-based dielectric material with a structure rich in nano holes by a sol-gel method, and develops systematic experimental research and theoretical analysis on a multi-performance parameter and structure-effect correlation mechanism of the novel silicon-based dielectric material. Research results show that the breakdown field strength of the material can be greatly improved by constructing the structure rich in the nano-pores, and the breakdown field strength is gradually increased along with the reduction of the pore diameter.

The relative dielectric constant, the dielectric loss and the volume conductivity of the material can be reduced to a certain extent by constructing a nano-porous structure. Under the measurement frequency of 50Hz, compared with the common ceramic fiber insulation paper, the ceramic fiber reinforced silicon-based nanopore-rich insulation paper has the advantages that the relative dielectric constant is reduced by 12.4%, the dielectric loss tangent value is reduced by 39.2%, and the volume conductivity is reduced by 52.5%. The method has very important significance for improving the ageing damage resistance of the transformer insulation system and reducing the dielectric loss.

The invention provides a novel insulating material and a preparation method and application thereof.

The first purpose of the invention is to provide a preparation method of ceramic fiber reinforced silicon-based nanopore-rich insulating paper, which comprises the following steps:

s1, preparation of silica sol: ethyl orthosilicate, deionized water and absolute ethyl alcohol are mixed according to a molar ratio of 1: (2-4): 7, mixing, dropwise adding hydrochloric acid to adjust the pH value to 4, stirring at room temperature for 20-30 minutes to fully hydrolyze TEOS (tetraethyl orthosilicate) to obtain a mixed system, heating the mixed system to 40 ℃, adding ammonia water to adjust the pH value of the mixed system to 7-10, mixing and stirring to form silica sol for later use; preferably, the method comprises the following steps of mixing ethyl orthosilicate, deionized water and absolute ethyl alcohol according to a molar ratio of 1: (3-4): 7, mixing;

s2, impregnating ceramic fiber insulation paper with silica sol: placing the ceramic fiber insulation paper in the silica sol prepared in S1, placing the ceramic fiber insulation paper in a vacuum drying oven after the silica sol completely covers the ceramic fiber insulation paper, and taking out the ceramic fiber insulation paper after vacuum impregnation at normal temperature to obtain a ceramic fiber insulation paper-silica sol mixed system for later use;

s3, preparation of wet gel: placing the ceramic fiber insulation paper-silica sol mixed system obtained in the step S2 in an environment with the temperature of 35-45 ℃ to convert the ceramic fiber insulation paper-silica sol mixed system into wet gel;

preferably, the ceramic fiber insulation paper-silica sol mixed system obtained in the step S2 is placed in an environment with the temperature of 35-45 ℃ at 45 degrees, and when the mixed system does not flow, the gel point is reached, so that wet gel is obtained;

s4, aging of wet gel: soaking the wet gel obtained in the step S3 in absolute ethyl alcohol, and removing the absolute ethyl alcohol after reaction after the wet gel becomes transparent to obtain a primarily aged wet gel; soaking the preliminarily aged wet gel in a mixed solution of tetraethoxysilane and absolute ethyl alcohol at normal temperature and normal pressure, wherein the volume ratio of tetraethoxysilane to absolute ethyl alcohol in the mixed solution of tetraethoxysilane and absolute ethyl alcohol is 1:10, soaking for 24 hours, and then removing the reacted tetraethoxysilane/absolute ethyl alcohol mixed solution to obtain aged wet gel;

s5, replacing the solvent in the wet gel by adopting a step-by-step replacement method: soaking the aged wet gel obtained by S4 in ethanol, ethanol mixed solution of 50 vol% of n-hexane and n-hexane in sequence to obtain a displaced wet gel; in the step, n-hexane is adopted to replace water and ethanol in the aged wet gel obtained from S4, so that the surface tension of the gel is reduced;

s6, surface modification treatment: soaking the wet gel obtained after the replacement in the S5 in trimethylchlorosilane for 2 days in a sealed way, and pouring out the residual surface grafting solution of the trimethylchlorosilane to obtain a gel mixture; adding n-hexane into the gel mixture for surface cleaning to ensure that the wet gel is completely covered by the n-hexane, sealing and soaking for 6 hours after soaking, and then removing the residual n-hexane to obtain surface modified wet gel; in the step, trimethylchlorosilane is adopted to carry out surface grafting treatment on the gel obtained from S5.

S7, drying wet gel: and (4) placing the surface modified wet gel obtained in the step (S6) in an electric heating air blast drying box, and performing gradient temperature rise drying under normal pressure to prepare the ceramic fiber reinforced silicon-based nanopore-rich insulating paper.

Further, in S1, ethyl orthosilicate, deionized water and absolute ethyl alcohol are mixed according to a molar ratio of 1: 3: and 7, mixing, wherein the concentration of the ammonia water is 0.5mol/L, adjusting the pH of the mixed system to 10 by using the ammonia water, and mixing and stirring for 2-5 minutes.

Further, in S5, the specific operations are as follows:

s5-1, adding ethanol to soak the aged wet gel obtained in S4, replacing for 10-12 hours, and removing the ethanol;

s5-2, adding ethanol mixed solution of 50 vol% n-hexane, soaking, displacing for 12 hours, and discarding the ethanol mixed solution of 50 vol% n-hexane;

s5-3, adding n-hexane for soaking, and replacing for 12 hours to obtain the wet gel after replacement.

Further, in S7, in order to put the surface modified wet gel obtained in S6 into an electrothermal blowing dry box for normal pressure gradient temperature rise drying,

preferably, the temperature-raising procedure of the normal-pressure gradient temperature raising is as follows:

more preferably, the temperature-raising procedure of the normal-pressure gradient temperature raising is as follows:

further, in S7, the temperature-raising procedure of the atmospheric gradient temperature raising is:

the second purpose of the invention is to provide ceramic fiber reinforced silicon-based nanopore-rich insulating paper, which is prepared by adopting the preparation method.

Further, the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 10-1500 nm; preferably, the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 10-127 nm, and further preferably, the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 10-20 nm; still more preferably, the ceramic fiber reinforced silicon-based nanopore-rich insulating paper has an average pore diameter of 14 nm.

The third purpose of the invention is to provide the application of the preparation method in improving the breakdown field strength of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper, wherein the breakdown field strength is direct current breakdown field strength and/or power frequency breakdown field strength.

The fourth purpose of the invention is to provide the application of the preparation method in reducing the relative dielectric constant and/or the dielectric loss and/or the volume conductivity of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper.

The fifth purpose of the invention is to provide the application of the preparation method in improving the intrinsic electrical properties of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper medium.

The invention has the beneficial effects that:

1) research shows that the generated silica-based medium rich in the nano holes has a typical amorphous structure, and compared with common ceramic fiber insulating paper, the thermal stability of the medium is improved, and the hydrophobic property is obviously enhanced. The common ceramic fiber insulating paper has extremely weak hydrophobicity, and the contact between water drops and fibers instantly shows hydrophilic contact, and the hydrophobic angle of the common ceramic fiber insulating paper is 3.5 degrees. The ceramic fiber reinforced silicon-based nanopore-rich insulating paper has good hydrophobic performance, and the hydrophobic angle is 141 degrees. The TG curve of a common ceramic fiber insulating paper sample has a weight loss step at about 75 ℃, and the mass loss is about 10%, while the TG curve of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper has a weight loss step at about 300 ℃, and the mass loss is about 0.9%.

2) The method obtains the breakdown field intensity of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper by constructing the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper, and compared with the common ceramic fiber insulating paper, the AC and DC breakdown field intensities of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper are obviously improved. Compared with a dry test sample which is not soaked in oil, the ceramic fiber reinforced silicon-based nanopore-rich insulating paper has larger breakdown field strength promotion amplitude after being soaked in insulating oil, and can reach 120.5 percent (under direct current voltage) and 90.4 percent (under power frequency voltage); as the pore size decreases, the composite dielectric breakdown voltage increases.

3) The nano-pore-rich structure of the ceramic fiber reinforced silicon-based nano-pore-rich insulating paper constructed by the method can reduce the relative dielectric constant, the dielectric loss and the volume conductivity of the material to a certain extent. Under the measurement frequency of 50Hz, compared with the common ceramic fiber insulating paper, the relative dielectric constant of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is reduced by 12.4%, the dielectric loss tangent value is reduced by 39.2%, and the volume conductivity is reduced by 52.5%. The method has very important significance for improving the ageing damage resistance of the transformer insulation system and reducing the dielectric loss.

4) According to the invention, the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is constructed, the trap energy level and density in the medium are reduced, and the local defects in the medium are reduced. And deducing by combining a space charge test result, constructing a nano-pore-rich structure is favorable for improving a charge injection potential barrier, blocking charge injection, weakening local field intensity distortion in the medium and realizing the improvement of the intrinsic electrical performance of the medium.

Drawings

FIG. 1 is a plot of the DC breakdown field intensity Weibull, where: (a) the direct current breakdown field intensity Weibull distribution of the dry sample; (b) the direct current breakdown field strength Weibull of the oil immersed test sample is distributed;

FIG. 2 is a power frequency breakdown field Weibull distribution, wherein: (a) the power frequency breakdown field strength Weibull of the dry sample is distributed; (b) the power frequency breakdown field intensity Weibull of the oil immersed sample is distributed;

FIG. 3S3 shows the macroscopic morphology of the CF-PSIP (0#) wet gel;

FIG. 4S3 shows the macroscopic morphology of the wet gels CF-PSIP (1#), CF-PSIP (2#), and CF-PSIP (3#), wherein (a) is the sample CF-PSIP (1#), (b) is the sample CF-PSIP (2#), and (c) is the sample CF-PSIP (3 #);

FIG. 5 is a diagram showing the micro-patterns of CFP and CF-PSIP (1#), CF-PSIP (2#), CF-PSIP (3#), wherein (a) is CFP, (b) is CF-PSIP (1#), wherein (c) is CF-PSIP (2#), and wherein (d) is CF-PSIP (3 #);

FIG. 6 is a graph showing the pore size distribution of CF-PSIP at different molar ratios of CFP to TEOS, DI water and absolute ethanol, wherein (a) is CFP, (b) is CF-PSIP (1#), (c) is CF-PSIP (2#), and (d) is CF-PSIP (3 #);

FIG. 7 is the adsorption-desorption isotherm of N2 for CF-PSIP (2 #);

FIG. 8 is a schematic diagram of electron impact ionization;

FIG. 9 is a schematic of electron impact ionization in a nanopore;

FIG. 10 is a schematic diagram of the development of electron avalanche within natural pores and nanopores;

FIG. 11 shows the effect of the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper on the relative dielectric constant of an oil-immersed insulating medium;

FIG. 12 shows the effect of the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper on the loss tangent of an oil-immersed insulating medium;

FIG. 13 shows the influence of the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper on the conductivity σ of the oil-immersed insulating medium;

FIG. 14CFP sample space charge accumulation characteristics;

FIG. 15CF-PSIP (2#) sample space charge accumulation characteristics;

FIG. 16 shows the space charge dissipation characteristics of CFP and CF-PSIP (2#) samples;

FIG. 17 thermal stimulation currents for CFP and CF-PSIP (2#) samples;

FIG. 18 thermogravimetric analysis curves of CFP and CF-PSIP (2#) samples;

FIG. 19 is a comparison of the hydrophobic properties of CFP and CF-PSIP (2#) samples, (a) conventional ceramic fiber insulation paper; (b) ceramic fiber reinforced silicon-based nanopore-rich insulating paper.

Detailed Description

The sources and purities of the chemical reagents used for sample preparation in the method of the invention are shown in table 1:

table 1 summary of main experimental materials

The model and source of the main experimental apparatus for sample preparation in the method of the invention are shown in Table 2:

table 2 summary of sample preparation main experimental apparatus

The present invention is further illustrated by the following examples so that those skilled in the art may better understand the invention and practice it, but the examples are not intended to limit the invention.

Example 1

S1, preparation of silica sol: ethyl orthosilicate, deionized water and absolute ethyl alcohol are mixed according to a molar ratio of 1: 1: 7, mixing, dropwise adding hydrochloric acid to adjust the pH value to 4, stirring at room temperature for 30 minutes to fully hydrolyze TEOS (tetraethyl orthosilicate) to obtain a mixed system, heating the mixed system to 40 ℃, adding 0.5mol/L ammonia water solution to adjust the pH value of the mixed system to 7-10, mixing and stirring to form silica sol for later use;

s2, silica sol impregnated ceramic fiber insulation paper: the silica sol obtained in S1 was poured into a glass mold (the glass mold in this example was a petri dish with a diameter of 60mm, purchased from Chongqing glass Co., Ltd.), then a CFP of ceramic fiber insulation paper was placed in the silica sol, and then the remaining silica sol was poured from the mold side so that it gradually penetrated into the CFP from the mold side until the CFP was completely covered. Then placing the mould in a vacuum drying oven, vacuum impregnating at normal temperature and taking out to obtain a ceramic fiber insulation paper-silica sol mixed system for later use;

s3, preparation of wet gel: placing the ceramic fiber insulation paper-silica sol mixed system obtained in the step S2 on a heating table at 40 ℃ to enable the ceramic fiber insulation paper-silica sol mixed system to start sol-gel transformation, inclining the mould by 45 degrees, and when the mixture does not flow, reaching a gel point to transform into wet gel;

s4, aging of wet gel: pouring absolute ethyl alcohol into a mold filled with wet gel, soaking the wet gel obtained in the step S3, pouring out the absolute ethyl alcohol after reaction is discarded after the wet gel becomes transparent, and obtaining preliminarily aged wet gel; pouring mixed liquor of tetraethoxysilane and absolute ethyl alcohol with the volume ratio of 1:10 into a mould at normal temperature and normal pressure, soaking the primarily aged wet gel at normal temperature and normal pressure, and removing the reacted tetraethoxysilane and/or absolute ethyl alcohol mixed liquor after 24 hours to obtain aged wet gel;

s5, replacing the solvent in the wet gel by stepwise replacement: soaking the aged wet gel obtained by S4 with ethanol, 50 vol% n-hexane/ethanol mixed solution and n-hexane in sequence to obtain a displaced wet gel;

the specific operation is as follows:

s5-1, adding ethanol into the mould to soak the aged wet gel obtained in S4, replacing for 12 hours, and removing the ethanol;

s5-2, adding 50 vol% n-hexane/ethanol mixed solution into the mould for soaking, displacing for 12 hours, and discarding 50 vol% n-hexane/ethanol mixed solution;

s5-3, adding n-hexane into the mould for soaking, and replacing for 12 hours to obtain the wet gel after replacement.

S6, surface modification treatment: pouring trimethyl chlorosilane serving as a surface grafting solution into a mold to soak the wet gel obtained after the replacement in the S5, sealing and standing for 2 days, and pouring out the rest surface grafting solution after the treatment to obtain a gel mixture; adding normal hexane into the gel mixture for surface cleaning to completely cover the wet gel, pouring out the normal hexane, removing residual chemical reagents in the mixture, pouring the normal hexane again to completely cover the wet gel in order to ensure that the gel is fully soaked, sealing and soaking for 6 hours after soaking, and discarding the residual normal hexane to obtain surface modified wet gel; in the step, trimethylchlorosilane is adopted to carry out surface grafting treatment on the gel obtained from S5.

S7, drying wet gel: and (3) placing the surface modified wet gel obtained in the step (S6) in an electrothermal blowing drying oven, and performing gradient temperature rise drying under normal pressure to prepare the ceramic fiber reinforced silicon-based nanopore-rich insulating paper CF-PSIP (0 #). The temperature-raising procedure of the normal-pressure gradient temperature raising is as follows:

example 2

In this example, except for S1, tetraethoxysilane, deionized water and absolute ethyl alcohol were mixed in a molar ratio of 1: 2: 7 mixing, and the rest is the same as the example 1, and preparing the ceramic fiber reinforced silicon-based nanopore-rich insulating paper CF-PSIP (1 #).

Example 3

In this example, except for S1, tetraethoxysilane, deionized water and absolute ethyl alcohol were mixed in a molar ratio of 1: 3: 7 mixing, and the rest is the same as the example 1, and the ceramic fiber reinforced silicon-based nanopore-rich insulating paper CF-PSIP (2#) is prepared.

Example 4

In this example, except for S1, tetraethoxysilane, deionized water and absolute ethyl alcohol were mixed in a molar ratio of 1: 4: 7 mixing, and the rest is the same as the example 1, and the ceramic fiber reinforced silicon-based nanopore-rich insulating paper CF-PSIP (3#) is prepared.

Example 5 macroscopic and microscopic morphological analysis of CF-PSIP

This example examines the addition ratio of ethyl orthosilicate to deionized water in the preparation step of the silica sol.

The experiment was divided into 4 groups, the differences between each group being shown in table 3:

table 3 reaction addition ratio screening variable table

Group of	The molar ratio of the ethyl orthosilicate to the deionized water to the absolute ethyl alcohol	Name of product
			Example 1	1：1：7	CF-PSIP(0#)
Example 2	1：2：7	CF-PSIP(1#)
			Example 3	1：3：7	CF-PSIP(2#)
Example 4	1：4：7	CF-PSIP(3#)

(1) During the preparation process, the macro morphology of the nanopore-rich medium is shown in fig. 3 and 4:

for the CF-PSIP (0#) sample, the state from the preparation step to the preparation of S3 wet gel is as shown in fig. 3, when the molar ratio of ethyl orthosilicate, deionized water and absolute ethanol is 1: 1: when the concentration of the reactant is too high at 7 hours, the ammonia water is dripped into the mixture to generate precipitate instantly, and a stable nano-pore-rich structure cannot be generated.

The macro-topography of the remaining set of samples prepared up to the preparation step of the S3 wet gel as the silicon source dilution concentration increased is shown in fig. 4.

CF-PSIP (1#) sample, when the molar ratio of ethyl orthosilicate, deionized water and absolute ethyl alcohol is 1: 2: at 7, there was a small amount of precipitation in the silicon based medium and significant internal cracking.

For the CF-PSIP (2#) sample, when the molar ratio of ethyl orthosilicate, deionized water and absolute ethanol is 1: 3: and 7, the silicon-based medium is relatively clear, no precipitate is generated, and no crack exists on the surface and the inside.

For the CF-PSIP (3#) sample, when the molar ratio of ethyl orthosilicate, deionized water and absolute ethyl alcohol is 1: 4: and 7, the silicon-based medium is relatively clear, no precipitate is generated, but micro cracks appear inside the silicon-based medium.

In summary, from the state of the wet gel obtained in step 3, i.e., the silicon-based medium, it can be seen that no precipitate is generated inside both the CF-PSIP (2#) and CF-PSIP (3#) samples, but the CF-PSIP (2#) sample has the best integrity.

(2) The microscopic morphology of the CF-PSIP was observed at different molar ratios of CFP to tetraethoxysilane, deionized water and absolute ethanol, as shown in FIG. 5.

It can be observed from the figure that the inside of the CFP is composed of fibers, and there are many large pores between the fibers, and the size of the large pores is about several micrometers to tens of micrometers.

For the CF-PSIP (0#) sample, a complete sample cannot be formed, and the micro-morphology of the sample cannot be observed.

For the CF-PSIP (1#) sample, the structure of the medium rich in the nanometer pores collapses, the particles are easy to agglomerate, the average pore diameter is large, and the number of the big pores and the connected pores is increased. This is because the condensation polymerization rate is too fast because of the high concentrations of the reactants tetraethylorthosilicate and deionized water. At this time, a large amount of hydroxyl groups were present in the mixture, and shrinkage was severe during drying, and the shrinkage of the sample was large, and the structure collapsed during drying.

For a CF-PSIP (2#) sample, the framework structure is compact, the average pore diameter is small, the distribution is uniform, and the molar ratio of tetraethoxysilane to deionized water to absolute ethyl alcohol is 1: 3: the optimal ratio is 7.

With TEOS and H₂The molar ratio of O is further reduced, and some pores still exist between the porous silicon-based medium and the ceramic fiber for the CF-PSIP (3#) sample. The reason for the formation of the holes is that before SEM test, the surface medium of the sample needs to be opened by a needle point to carry out gold spraying treatment on the inside, so that the internal structure of the sample can be damaged; on the other hand, the molar ratio of the ethyl orthosilicate to the deionized water to the absolute ethyl alcohol is 1: 4: and 7, when the concentration of the reactant is too low, the formed polymer network skeleton rich in the nano holes is fine, excessive water is retained in the network after the network is formed, and the structure collapse is easily caused by the action of capillary force in the drying process, so that the network structure of the sample is incomplete under the concentration ratio of the precursor reactant, and the microstructure is loose.

(3) Observing the pore size distribution of CF-PSIP under the molar ratio of CFP to different tetraethoxysilane, deionized water and absolute ethyl alcohol

The pore size distribution diagram of the CF-PSIP under the molar ratio of CFP to tetraethoxysilane, deionized water and absolute ethyl alcohol is obtained by measuring with a full-automatic specific surface and micropore physical adsorption analyzer, and is shown in figure 6.

For the CF-PSIP (0#) sample, a complete sample could not be formed, and the pore size distribution could not be observed.

From the above pore size distribution results, it is found that the pore structure of the CF-PSIP (2#) sample is uniformly distributed and concentrated around 10 to 20 nm. Although the other samples had a pore size distribution in the nm scale range, the distribution was too dispersed. Based on the BJH method and the aperture distribution diagram, the aperture parameters of the sample can be calculated, and the average aperture of CF-PSIP under the condition of CFP and different concentration ratios of precursor reactants is shown in a table 4. It can be seen that the average pore size of the CF-PSIP (2#) is the smallest, 14nm, which is the optimum concentration for the CF-PSIP sample preparation. The average pore diameter of pure CFP is the largest and is 8571nm, and the pore diameter of the CF-PSIP sample prepared by the method is greatly reduced compared with that of the conventional CFP.

TABLE 4 average pore diameter of CF-PSIP at CFP to different precursor reactant concentration ratios

Screening tetraethoxysilane, deionized water and absolute ethyl alcohol according to the experiment results of (1) - (3) in a molar ratio of 1: (2-4): 7, mixing, wherein when the tetraethoxysilane, the deionized water and the absolute ethyl alcohol are mixed according to a molar ratio of 1: 3: and 7, when mixing, the prepared ceramic fiber reinforced silicon-based nanopore-rich insulating paper has the optimal effect.

(4) Observe N of CF-PSIP (2#)₂Adsorption-desorption isotherm

The adsorption isotherms are classified according to the adsorption isotherm proposed by IUPAC (International Union of Pure and Applied chemistry), and belong to the type III isotherm. The low pressure region, with concave isotherms, indicates that the interactions between the adsorbate molecules are stronger than between the adsorbate and the adsorbent, making adsorption difficult at the initial stage. In the medium pressure region, the adsorption amount is increased, and in P/P₀＝0.7, a desorption lag ring appears, which indicates that mesopores (2 nm) exist in the medium<Pore diameter<50 nm). In the high pressure region, the isotherm extends upward, indicating that the medium contains a small number of macropores. The isothermal lines in the adsorption and desorption processes are not coincident, a mesoporous hysteresis ring is formed, and the IUPAC divides the mesoporous hysteresis ring into four types of H1-H4. Because practical materials often have complex pore structures, the hysteresis loop obtained by experiments cannot be simply classified into a certain class, and the material is characterized by a mixed pore structure. As can be seen from FIG. 7, the hysteresis loop of the adsorption-desorption curve of CF-PSIP (2#) nitrogen is represented by H₂A type hysteresis loop. The hysteresis loop of the type shows that the medium contains an obvious mesoporous structure, wherein most of the pore channels are tubular capillary pore structures with two open ends or dense-packed spherical particle mesopores. Therefore, the supposing pipe-shaped hole is formed by a gap between the silica-based medium rich in the nano-pores and the ceramic fiber, and the slit hole accumulated by the spheres is formed by the nano-pores in the silica-based medium rich in the nano-pores.

Example 6

(1) The relationship between the failure probability and the electric field strength of a sample is calculated by Weibull distribution and is shown in figure 1 by performing a direct current breakdown test on the CFP of the common ceramic fiber insulation paper and the ceramic fiber reinforced silicon-based nanopore-rich insulation paper prepared in the embodiment 1, the embodiment 2, the embodiment 3 and the embodiment 4.

FIG. 1(a) is a distribution diagram of a DC breakdown field strength Weibull by a uniform boosting method for a dry sample, and FIG. 1(b) is a distribution diagram of a DC breakdown field strength Weibull by a uniform boosting method for an oil-immersed sample.

The method for treating the oil immersed sample comprises the following steps:

cutting the common ceramic fiber insulating paper and the ceramic fiber reinforced silicon-based nanopore-rich insulating paper into square paper patterns with side lengths of 4cm, and drying in a vacuum drying oven at 90 ℃ and a pressure of 50Pa for 48 hours. The insulating oil for the transformer used herein is cramayo 25# naphthenic transformer oil. The pretreatment method of the transformer oil comprises the following steps: filtering mineral insulating oil to remove gas, moisture and impurities in the mineral insulating oil, then placing the transformer oil in a vacuum drying oven for vacuum drying for 48 hours, finally placing the dried sample in the dried and filtered insulating oil, and carrying out oil immersion treatment for 24 hours at the temperature of 60 ℃ and under the condition of 50 Pa. And (4) placing the pretreated oil-immersed sample in a sealed glass tank and storing the oil-immersed sample in a dry place for later use.

The characteristic parameters of the sample failure characteristic curves of different precursor reactant concentration ratios under direct current voltage are shown in Table 5, and since CF-PSIP (0#) cannot be prepared to obtain samples, CFP, CF-PSIP (1#), CF-PSIP (2#), and CF-PSIP (3#) are examined in the experiment.

TABLE 5 sample failure characteristic curve characteristic parameters of different precursor reactant concentration ratios under direct current voltage

The results show that compared with the common ceramic fiber insulation paper CFP sample, the preparation method provided by the invention is adopted to construct the nanopore-rich structure, namely the direct-current breakdown field strengths of the dry sample and the oil-immersed sample of the ceramic fiber reinforced silicon-based nanopore-rich insulation paper are greatly improved. As the average pore size of the sample is reduced, the DC breakdown field strength is increased. Simultaneously, the range of lift of oily sample is bigger than dry sample. For a CF-PSIP (2#) sample, the breakdown field strength is increased to the maximum extent, and the direct-current breakdown field strength of the oil-immersed ceramic fiber reinforced silicon-based nanopore-rich insulating paper oil-immersed sample is increased by 120.5% compared with that of a common ceramic fiber insulating paper sample.

(2) The relationship between the failure probability and the electric field strength of a sample is shown in figure 2 by using Weibull distribution statistics, wherein the work frequency breakdown test is carried out on the CFP of the common ceramic fiber insulation paper and the ceramic fiber reinforced silicon-based nanopore-rich insulation paper prepared in the embodiment 1, the embodiment 2, the embodiment 3 and the embodiment 4.

And (a) in the figure 2 is that power frequency breakdown field strength Weibull distribution is carried out on a dry sample according to GB T1408.1-2016, and (b) in the figure 2 is that power frequency breakdown field strength Weibull distribution is carried out on an oil immersed sample according to GB T1408.1-2016.

The method for treating the oil immersed sample comprises the following steps:

Characteristic parameters of sample failure characteristic curves of different precursor reactant concentration ratios under the power frequency voltage are shown in table 6, and since CF-PSIP (0#) cannot be prepared to obtain samples, CFP, CF-PSIP (1#), CF-PSIP (2#), and CF-PSIP (3#) are examined in the experiment.

TABLE 6 characteristic parameters of sample failure characteristic curves of different precursor reactant concentration ratios under power frequency voltage

Research shows that compared with a common ceramic fiber insulation paper CFP sample, the ceramic fiber reinforced silicon-based nanopore-rich insulation paper prepared by the preparation method disclosed by the invention has the advantages that the power frequency breakdown field intensity of the dry and oil-immersed samples is greatly improved. According to the result of the pore structure characteristic analysis of each sample, the power frequency breakdown field strength of the sample is improved along with the reduction of the average pore diameter of the sample. Simultaneously, the range of lift of oily sample is bigger than dry sample. For a CF-PSIP (2#) sample, the power frequency breakdown characteristic field intensity of the oil-immersed ceramic fiber reinforced silicon-based nanopore-rich insulating paper sample is improved by 90.4% compared with that of a common ceramic fiber insulating paper sample.

In the combination of the samples in examples 5, (2) and (3), the analysis results of the pore structure characteristics of the samples show that the power frequency breakdown field strength of the samples is increased along with the reduction of the average pore diameter of the samples.

EXAMPLE 7 dielectric Property testing of CFP and CF-PSIP

The dielectric property tests of CFP and CF-PSIP (2#) are carried out by adopting a Novocontrol Concept 80 broadband dielectric impedance spectrometer, and comprise a relative dielectric constant experiment, a loss tangent experiment and a conductivity sigma experiment.

The test results of constructing the influence of the nanopore-rich structure on the relative dielectric constant of the oil-immersed insulating medium are shown in fig. 11, the influence of constructing the nanopore-rich structure on the loss tangent of the oil-immersed insulating medium is shown in fig. 12, and the influence of constructing the nanopore-rich structure on the conductivity sigma of the oil-immersed insulating medium is shown in fig. 13.

Under the measurement frequency of 50Hz, the dielectric property of the composite insulating paper can be effectively improved by constructing the nanopore-rich structure of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper. The relative dielectric constant of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper sample is reduced by 12.4%, the dielectric loss tangent value is reduced by 39.2%, and the volume conductivity is reduced by 52.5%.

Example 8

In this embodiment, the internal space charge distribution characteristics of the CFP sample and the CF-PSIP (2#) sample are measured by a Pulsed Electro-acoustic Method (PEA).

The CFP sample space charge accumulation characteristic measurement results are shown in fig. 14, the CF-PSIP (2#) sample space charge accumulation characteristics are shown in fig. 15, and the CFP and CF-PSIP (2#) sample space charge dissipation characteristics are shown in fig. 16.

Compared with a common ceramic fiber insulating paper sample, the charge accumulation amount of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper sample in the polarization process is reduced by 28.6%, and the charge surplus amount in the depolarization process is reduced by 33.3%.

Example 9

In this example, the trap characteristics of the CFP and CF-PSIP (2#) samples were characterized by Thermally Stimulated Current (TSC, model Novocontrol concentrate 80, temperature-20-80 ℃).

The results of the CFP and CF-PSIP (2#) sample thermal stimulation current tests are shown in FIG. 17.

The result shows that a nano-pore-rich structure is constructed, the trap energy level and density in the medium are reduced, and local defects in the medium are reduced. And deducing by combining a space charge test result, constructing a nano-pore-rich structure is favorable for improving a charge injection potential barrier, blocking charge injection, weakening local field intensity distortion in the medium and realizing the improvement of the intrinsic electrical performance of the medium.

Example 10

In this example, thermogravimetric analysis curves of CFP and CF-PSIP (2#) were determined using a relaxation-tolerant STA449F5 synchronous thermal analyzer. As shown in fig. 18, the TG curve of the CFP sample shows a weight loss step at about 75 ℃, the mass loss is about 10%, the substances thermally decomposed at this temperature stage are the residual moisture and — OH groups in the medium, at this time, the — OH groups are condensed and evaporated together with the residual moisture to cause weight loss, and then the curve is maintained stable, indicating that the medium structure tends to be stabilized. The TG curve of CF-PSIP (2#) has a weight loss step at about 300 ℃, and the mass loss is about 0.9%. According to the analysis of chemical reaction in the preparation process of the composite insulating medium, the substance which is thermally decomposed after 300 ℃ is-CH on the nano-pore-rich silicon-based medium skeleton₃A group. In this temperature phase, -CH₃Radical decomposition to CO₂And cause weight loss. Obviously, compared with CFP, the thermal cracking temperature is increased, the weight loss rate is reduced, the thermal weight loss rate is reduced by 91.3 percent compared with CFP, and the thermal stability is greatly improved.

In this example, the contact angle of CFP and CF-PSIP (2#) samples was measured by a German dataphysics contact angle tester. As shown in fig. 19, the hydrophobicity of the conventional ceramic fiber insulation paper is very weak, and the contact between water drops and the fibers is instantly hydrophilic, and the hydrophobic angle is 3.5 °. The ceramic fiber reinforced silicon-based nanopore-rich insulating paper has good hydrophobic performance, and the surface energy of the nanopore-rich insulating paper is reduced and the hydrophobic angle is 141 degrees due to the fact that the surface grafting treatment is carried out on the composite medium in the preparation process. The improvement of the hydrophobic property is beneficial to keeping a complete skeleton structure in the drying process of the composite medium, and is beneficial to reducing the moisture content of the insulating medium and reducing the medium loss of the insulating medium.

In conclusion, the molar ratio of the ethyl orthosilicate to the deionized water to the absolute ethyl alcohol is 1: 3: 7 is the optimal proportion when mixed, the CF-PSIP (2#) sample prepared under the proportion has a uniform structure, the average pore diameter is 14nm at least, the thermal weight loss rate is reduced by 91.3 percent compared with CFP, and the hydrophobic angle is 141 degrees.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.

Claims

1. A preparation method of ceramic fiber reinforced silicon-based nanopore-rich insulating paper is characterized by comprising the following steps:

s2, silica sol impregnated ceramic fiber insulation paper: placing the ceramic fiber insulation paper in the silica sol prepared in S1, placing the ceramic fiber insulation paper in a vacuum drying oven after the silica sol completely covers the ceramic fiber insulation paper, and taking out the ceramic fiber insulation paper after vacuum impregnation at normal temperature to obtain a ceramic fiber insulation paper-silica sol mixed system for later use;

s4, aging of wet gel: soaking the wet gel obtained in the step S3 in absolute ethyl alcohol, and removing the absolute ethyl alcohol after reaction after the wet gel becomes transparent to obtain a primarily aged wet gel; soaking the primarily aged wet gel in a mixed solution of tetraethoxysilane and absolute ethyl alcohol at normal temperature and normal pressure, wherein the volume ratio of tetraethoxysilane to absolute ethyl alcohol in the mixed solution of tetraethoxysilane and absolute ethyl alcohol is 1:10, and removing the reacted mixed solution of tetraethoxysilane and absolute ethyl alcohol after soaking for 24 hours to obtain aged wet gel;

s5, replacing the solvent in the wet gel by adopting a step-by-step replacement method: soaking the aged wet gel obtained by S4 in ethanol, ethanol mixed solution of 50 vol% of n-hexane and n-hexane in sequence to obtain a displaced wet gel;

s6, surface modification treatment: soaking the wet gel obtained after the replacement in the S5 in trimethylchlorosilane for 2 days in a sealed way, and pouring out the residual surface grafting solution of the trimethylchlorosilane to obtain a gel mixture; adding n-hexane into the gel mixture for surface cleaning to ensure that the wet gel is completely covered by the n-hexane, sealing and soaking for 6 hours after soaking, and then removing the residual n-hexane to obtain surface modified wet gel;

s7, drying wet gel: and (4) heating and drying the surface modified wet gel obtained in the step S6 at normal pressure gradient to prepare the ceramic fiber reinforced silicon-based nanopore-rich insulating paper.

2. The method for preparing ceramic fiber reinforced silicon-based nanopore-rich insulating paper according to claim 1, wherein in S1, ethyl orthosilicate, deionized water and absolute ethyl alcohol are mixed according to a molar ratio of 1: 3: and 7, mixing, wherein the concentration of the ammonia water is 0.5mol/L, adjusting the pH of the mixed system to 10 by using the ammonia water, and mixing and stirring for 2-5 minutes.

3. The method for preparing ceramic fiber reinforced silicon-based nanopore-rich insulating paper according to claim 1, wherein in S5, the specific operations are as follows:

4. The method for preparing ceramic fiber reinforced silicon-based nanopore-rich insulating paper according to claim 1, wherein in S7, the surface modified wet gel obtained in S6 is placed in an electrothermal blowing dry box for atmospheric pressure gradient temperature rise drying, preferably, the temperature rise procedure of the atmospheric pressure gradient temperature rise is as follows:

5. the method for preparing ceramic fiber reinforced silicon-based nanopore-rich insulating paper according to claim 4, wherein in S7, the temperature rise procedure of the normal pressure gradient temperature rise is as follows:

6. the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is characterized by being prepared by the preparation method of any one of claims 1 to 5.

7. The ceramic fiber reinforced silicon-based nanopore-rich insulating paper according to claim 6, wherein the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 10-1500 nm; preferably, the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 10-127 nm; further preferably, the average pore diameter of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper is 14 nm.

8. The application of the preparation method of any one of claims 1 to 5 in improving the breakdown field strength of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper, wherein the breakdown field strength is a direct current breakdown field strength and/or a power frequency breakdown field strength.

9. Use of the preparation method of any one of claims 1 to 5 for reducing the relative dielectric constant and/or the dielectric loss and/or the bulk conductivity of the ceramic fiber reinforced silicon-based nanopore-rich insulating paper.

10. Use of the preparation method of any one of claims 1 to 5 in improving the intrinsic electrical properties of ceramic fiber reinforced silicon-based nanopore-rich insulating paper media.