CN114105134A - Matrix graphite powder for high-temperature gas cooled reactor fuel element and preparation method thereof - Google Patents
Matrix graphite powder for high-temperature gas cooled reactor fuel element and preparation method thereof Download PDFInfo
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Abstract
The invention provides matrix graphite powder for a high-temperature gas cooled reactor fuel element and a preparation method thereof. The preparation method comprises the following steps: step S1, obtaining microcrystalline graphite powder; step S2, natural flake graphite powder is obtained, and the microcrystalline graphite powder and the natural flake graphite powder are dry-mixed to obtain mixed dry powder; step S3, adding a binder or an organic solution of the binder into the mixed dry powder, and carrying out wet mixing to obtain a paste; and step S4, granulating and drying the paste, and then crushing to obtain the matrix graphite powder. According to the preparation method of the matrix graphite powder provided by the embodiment of the invention, the microcrystalline graphite powder and the natural crystalline flake graphite powder are used as raw materials, a certain resin is used as a binder, and the prepared matrix graphite powder can be directly used for preparing nuclear fuel elements of a high-temperature gas cooled reactor, is simple in production process and low in production cost, and can meet the increasing requirements of the nuclear power industry.
Description
Technical Field
The invention relates to the technical field of graphite powder preparation, in particular to matrix graphite powder for a high-temperature gas cooled reactor fuel element and a preparation method thereof.
Background
High temperature gas cooled reactors have been developed based on gas cooled reactors, which are classified into prismatic reactors and pebble bed reactors, which use spherical fuel elements, according to the fuel elements used. Spherical fuel elements, which are one of the types of elements used in fourth generation high temperature gas cooled reactors, consist essentially of two parts, a fuel zone of about 50mm diameter and a 5mm thick fuel-free envelope, with matrix graphite occupying more than 90% of the mass and volume.
Currently, the raw materials used to make spherical fuel elements are made from 64% natural graphite powder, 16% artificial graphite powder, and 20% resin binder, also known as a3-3 matrix graphite powder.
The fuel-free graphite nodules are made of A3-3 matrix graphite powder, do not contain fuel particles inside, have the same size as spherical fuel elements, and are mainly used for adjusting the reactivity of a reactor core and enabling the power distribution to be smooth.
As the main components of spherical fuel elements and fuel-free graphite nodules, the matrix graphite powder acts to moderate neutrons, conduct heat generated by fission to the coolant, protect the fuel particles from damage, and the like.
The HTR-10 and HTR-PM projects developed in China at present use spherical fuel elements and fuel-free graphite spheres prepared by the formula. Where HTR-10 has reached its limit in the end of 2000, the HTR-PM consumes about 300000 spherical fuel elements per year under normal operating conditions, and subsequently plans to build larger scale HTR-PM 600. With the rapid development of the nuclear power industry in China, the requirements for fuel elements and raw materials thereof are increasing day by day.
Chinese patent application No. 201610414446.8 discloses a method for preparing artificial graphite powder for high temperature gas cooled reactor nuclear fuel elements and graphite powder, wherein pitch coke is used as raw material, pitch is used as binder, the two are mixed and stirred for 4-8 hours according to a certain proportion, then crushed and formed under isostatic pressure for 60-70 minutes, and the product is densified through roasting and dipping, wherein the roasting time is about 600-700 hours each time, the dipping time is 1-2 hours, after the product is densified, the product needs to be purified at 3000 ℃ for 36-48 hours and then can be processed into artificial graphite powder, and the preparation of the powder needs to be ground, shaped and graded, and the high temperature purification of the graphite powder and other steps.
However, the method has the disadvantages of long production period and high production cost, and is not beneficial to the rapid development of the fourth-generation nuclear power industry.
In addition, the thermal expansion performance of the artificial stone toner obtained by the preparation method has a further improved space.
Therefore, it is highly desirable to provide a novel method for preparing graphite powder as a base for high-temperature gas-cooled reactor nuclear fuel elements.
Disclosure of Invention
Natural graphite is a strategic mineral resource in china, and includes microcrystalline graphite in addition to flake graphite. Compared with artificial graphite, the microcrystalline graphite has the advantages of high graphitization degree, high thermal conductivity, low thermal expansion coefficient and the like, and the higher thermal conductivity is favorable for transferring heat generated by nuclear fission to a gas coolant, so that the outlet temperature of the reactor is increased. The lower thermal expansion coefficient, especially the low isotropic thermal expansion coefficient, is beneficial to further improving the thermal expansion performance and isotropic performance of the matrix graphite of the fuel element, and the excellent performances enable the matrix graphite to have wide application prospects in the field of nuclear graphite.
If the natural microcrystalline graphite can replace the artificial graphite, the preparation period can be greatly shortened. The inventor finds that after repeated research, high-grade microcrystalline graphite concentrate is used as a raw material, and is subjected to high-temperature purification, crushing and classification to obtain a microcrystalline graphite powder with certain technical requirements, and the microcrystalline graphite powder, natural crystalline flake graphite powder and a binder are mixed according to a certain proportion to prepare matrix graphite, so that the microcrystalline graphite powder can be directly applied to preparation of spherical fuel elements and non-fuel graphite spheres, the production period and the production cost can be greatly reduced, meanwhile, the thermal expansion performance of the matrix graphite of the fuel elements can be improved, and better irradiation performance can be obtained. On the basis of this, the present invention has been completed.
The invention aims to provide a preparation method of matrix graphite powder for a high-temperature gas cooled reactor fuel element, which has the advantages of short production period, low production cost, excellent isotropy of the obtained fuel element and good thermal expansion performance.
The invention also aims to provide matrix graphite powder for the high-temperature gas cooled reactor fuel element.
In order to solve the technical problems, the invention adopts the following technical scheme:
the preparation method of the matrix graphite powder for the high-temperature gas cooled reactor fuel element according to the embodiment of the first aspect of the invention comprises the following steps:
step S1, obtaining microcrystalline graphite powder;
step S2, natural flake graphite powder is obtained, and the microcrystalline graphite powder and the natural flake graphite powder are dry-mixed to obtain mixed dry powder;
step S3, adding a binder or an organic solution of the binder into the mixed dry powder, and carrying out wet mixing to obtain a paste;
and step S4, granulating and drying the paste, and then crushing to obtain the matrix graphite powder.
Furthermore, in the matrix graphite powder, the content of the microcrystalline graphite powder is 10-30 wt%, the content of the natural crystalline flake graphite powder is 50-70 wt%, and the content of the binder is 10-30 wt%.
Further, the binder is phenolic resin, the organic solution of the binder is a solution obtained by dissolving the binder in ethanol, and the content of the binder in the organic solution of the binder is more than 50 wt%.
Further, the step S1 includes:
step S11, obtaining microcrystalline graphite raw ore;
step S12, purifying the microcrystalline graphite raw ore;
and step S13, crushing and grading the purified microcrystalline graphite to obtain the microcrystalline graphite toner.
Further, in the step S13, the pulverizing process conditions are as follows: the rotating speed of the crushing disc is 5000-6000rpm, the rotating speed of the grading wheel is 1500-2500rpm, the feeding frequency is 8-10Hz, the frequency of the fan is 25-40Hz, and the induced air flow is 15-20m3/min。
Further, the step S12 includes:
and S121, carrying out primary purification on the microcrystalline graphite raw ore in any one or more modes of flotation, acid treatment and alkali treatment to obtain primary purified powder.
Further, the step S12 further includes:
and S122, carrying out high-temperature purification on the primary purified powder to obtain secondary purified powder. In the step S13, the secondary purified powder is pulverized and classified to obtain the microlite toner.
Furthermore, the microcrystalline graphite powder is granular, and the particle size D50 is 10-30 μm.
Further, the step 4 comprises:
granulating the paste, drying by blowing at the temperature of 60-80 ℃ for 6-10 hours, crushing by a crusher, and sieving the crushed powder by a 100-mesh sieve to obtain the matrix graphite powder.
The matrix graphite powder for the high-temperature gas cooled reactor fuel element according to the embodiment of the second aspect of the invention comprises 10-30 wt% of microlite ink powder, 50-70 wt% of natural phosphorus flake graphite powder and 10-30 wt% of a binder.
The technical scheme of the invention at least has one of the following beneficial effects:
according to the preparation method of the matrix graphite powder for the high-temperature gas cooled reactor fuel element, the microcrystalline graphite powder and the natural crystalline flake graphite powder are used as raw materials and matched with a certain resin as a binder, the prepared matrix graphite powder can be directly used for preparing the high-temperature gas cooled reactor nuclear fuel element, the production process is simple, the production period is short, the production cost is low, and the method can meet the increasing requirements of the nuclear power industry;
furthermore, the microcrystalline graphite powder has a smaller thermal expansion coefficient and better isotropy, so that the thermal expansion coefficient and the isotropy of the matrix graphite obtained by configuration can be further improved, and the matrix graphite powder is used for preparing the fuel-free graphite nodules, the isotropy of the fuel-free graphite nodules is less than 1.15, and the good isotropy is shown; the thermal conductivity-TR measured at 900 ℃ is 35-40W/m K and the thermal conductivity-AX is 30-35W/m K.
Drawings
FIG. 1(a) is an SEM photograph of a microlite toner obtained after secondary purification and pulverization classification in example 1;
FIG. 1(b) is a graph showing the particle size distribution of a microlite toner obtained by the secondary purification and pulverization classification in example 1;
FIG. 2(a) is a linear thermal expansion coefficient plot of the fuel-free graphite nodules M-x obtained in example 1;
fig. 2(b) is a linear thermal expansion coefficient curve of the fuel-free graphite nodule T-x obtained in comparative example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
First, a method for preparing a base graphite powder for a high temperature gas cooled reactor fuel element according to an embodiment of the present invention will be described in detail.
The preparation method of the matrix graphite powder for the high-temperature gas cooled reactor fuel element according to the embodiment of the invention comprises the following steps:
and step S1, obtaining microcrystalline graphite powder.
That is, first, microcrystalline graphite powder is prepared.
The microcrystalline graphite raw ore powder can be used as a raw material, and granular microcrystalline graphite powder with a preset particle size distribution is obtained after purification and crushing.
Specifically, for example, the following steps may be included:
and step S11, obtaining the microcrystalline graphite raw ore.
For the slightly different grades of the microcrystalline graphite in different producing areas, the invention successfully prepares the fuel-free graphite nodules meeting the technical requirements by using the microcrystalline graphite powder produced in Nengmon Xing and county. However, the present invention is not limited to the microlite toners of the production sites.
And step S12, purifying the microcrystalline graphite raw ore.
The raw microcrystalline graphite ore contains a certain amount of impurities, and can be purified in order to increase the fixed carbon content.
Specifically, the purification may include:
and S121, carrying out primary purification on the microcrystalline graphite raw ore in any one or more modes of flotation, acid treatment and alkali treatment to obtain primary purified powder.
That is, the raw microcrystalline graphite ore is first chemically purified. Specific methods of chemical purification may include, for example, flotation, acid treatment, alkali treatment, and the like.
For example, the purification method used for the microcrystalline graphite raw ore is a hydrofluoric acid method, which removes SiO in the graphite raw ore by utilizing the principle that silicate impurities in graphite react with hydrofluoric acid to generate water-soluble compounds and volatile matters2、Al2O3And the like, thereby obtaining purified microcrystalline graphite. The specific purification method can be carried out by referring to the method disclosed in Chinese patent application CN 109437187A.
Further, after chemical purification, the method can also comprise the following steps:
and S122, carrying out high-temperature purification on the primary purified powder to obtain secondary purified powder.
The secondary purification of the microcrystalline graphite powder is carried out by high-temperature purification, and for example, the method can be as follows: placing the primarily purified microlite ink powder in a high-temperature graphitization furnace, heating to 2800-3000 ℃ at an average heating rate of 10 ℃/min under the protection of high-purity argon, and preserving heat for 30-60 min to remove impurities.
The primary purified powder can be purified at 2800-3000 ℃ to increase the fixed carbon content to over 99.9 percent.
Only chemical purification or only high-temperature purification may be performed, and in the case where the quality of the raw ore is extremely high, purification may not be performed.
And step S13, crushing and grading the purified microcrystalline graphite to obtain the microcrystalline graphite toner.
That is, the purified microcrystalline graphite is pulverized and classified to obtain microcrystalline graphite powder having a predetermined particle size distribution.
Specifically, in step S13, the powder may be classified by using a VT-300 mechanical pulverizer provided by suzhou; industrial equipment limited. Of course, other mills may be used for milling, and the present invention is not limited thereto.
As the process conditions for the pulverization, the following conditions may be set: the rotating speed of the crushing disc is 5000-6000rpm, the rotating speed of the grading wheel is 1500-2500rpm, the feeding frequency is 8-10Hz, the frequency of the fan is 25-40Hz, and the induced air flow is 15-20m3/min。
Taking the VT-300 mechanical pulverizer manufactured and provided by suzhou; industrial equipment limited, mentioned above, the equipment has pulverizing and classifying functions. The whole set of crushing system comprises a feeder, a VT-300 mechanical crusher main machine, a cyclone dust collector, a pulse bag dust collector, a safety filter, an induced draft fan, an air heat exchanger, an air supplementing system, an electric control system, a material connecting pipeline, a pneumatic valve, an operation platform and various detection instruments, wherein a crushing disc and a grading wheel are coaxially distributed in a crushing cavity of the crusher main machine, the grading wheel is positioned above the crushing disc, the two are respectively driven by a crushing motor and a grading wheel motor, the induced draft fan provides wind power for the whole set of system, and powder flows along the direction of the crusher, the material connecting pipeline and the dust collector. The mechanical pulverizer uses a super wear-resistant silicon nitride ceramic crushing disc imported from Japan, and crushes graphite particles through high-speed rotation of the crushing disc, so that the particle size of the graphite particles is reduced, under the rotating speed of a specific grading wheel, the particles smaller than a certain particle size can flow through the grading wheel and along a material connecting pipeline under the traction of wind power, the particles with larger particle sizes can not pass through the grading wheel, micro powder with undersize particle sizes can be collected by a cloth bag dust collector, and finally powder in a proper particle size range can be obtained at a pneumatic valve discharge port of a cyclone dust collector.
In the preparation process of the powder, the particle size and the particle morphology of the prepared powder in a particle size distribution state can be regulated and controlled by controlling the technological parameters of equipment such as the crushing rotating speed, the rotating speed of the grading wheel, the frequency of the feeding machine, the frequency of the fan, the induced air flow and the like.
The frequency of the fan and the induced air flow jointly determine the air volume and the air speed in the material pipeline, the induced air flow plays a main role in the frequency and the induced air flow, and when the induced air flow is smaller than a given parameter range, superfine powder in the powder cannot be rapidly collected by a dust collecting cloth bag, so that the content of the superfine powder in the powder is increased, and the particle size of the powder is relatively low; when the induced air flow is larger, the powder crushing time is reduced, the obtained powder has uneven particle size distribution, and excessive superfine powder is quickly absorbed into a dust collecting cloth bag, so that more waste is caused and the yield is reduced; the frequency of the fan in a given range can not cause excessive load on a power supply system, and is favorable for stable operation of equipment and production of powder.
The frequency of the feeder is lower than the given parameter range, so that the production efficiency is reduced, the material in the crushing cavity is excessive if the frequency of the feeder is higher than the given parameter range, extra burden is caused to the crusher, the crushing rotating speed under the corresponding equipment parameter is reduced due to the increase of the load, so that the particle size of the powder is thickened, meanwhile, a certain burden is caused to the fan, the air volume in the pipeline is reduced, and the particle size distribution range of the obtained powder is widened.
The grinding rotating speed and the grading rotating speed are the most main factors influencing the particle size distribution of the powder, when the grinding rotating speed is too low, the powder raw materials cannot be sufficiently ground, so that the obtained powder is thick, the phenomenon of material accumulation can also occur in a grinding cavity, and the production efficiency is reduced; when the crushing rotating speed is too high, the powder is crushed rapidly, so that the obtained powder is thin, a large load is caused to a system, and the production cost is increased; when the rotating speed of the grading wheel is too low, powder in the crushing cavity can be quickly sucked out of the crushing cavity by the suction force in the pipeline, so that the crushing time is reduced, and the powder is too coarse; when hierarchical rotational speed was too high, the classifying wheel can block that the powder gets into the material pipeline from the rubbing crusher, leads to the extension of crushing time, and the gained powder is thin excessively, and simultaneously, the classifying wheel rotational speed is too fast also can lead to smashing the intracavity and appearing long-pending material, reduces production efficiency, also can cause too big burden to the system, improves manufacturing cost, reduction equipment life.
The grinding rotating speed and the classifying wheel rotating speed jointly regulate and control the particle size distribution of the powder in the production process, so that the grinding rotating speed and the classifying wheel rotating speed are often required to be matched with each other in the selection of production parameters, when the grinding rotating speed is increased, the rotating speed of the classifying wheel is properly reduced, when the grinding rotating speed is reduced, the rotating speed of the classifying wheel is properly increased, the former is suitable for grinding powder raw materials with high hardness, and the latter is suitable for grinding powder raw materials with low hardness.
The obtained microcrystalline graphite powder after crushing and grading is granular, and the particle size D50 is 10-30 mu m.
In addition, in consideration of the possibility that a part of impurities may be introduced in the pulverization stage after the pulverization classification, further purification may be carried out, and in this case, for example, purification at a high temperature (for example, heating to 2800-. For a specific method, reference may be made to the secondary purification in step S12, which is not described herein again.
And step S2, obtaining natural crystalline flake graphite powder, and dry-mixing the microcrystalline graphite powder and the natural crystalline flake graphite powder to obtain mixed dry powder.
That is, after pulverization and classification, the obtained microlite toner can be directly mixed with natural crystalline flake graphite powder to prepare mixed dry powder.
Here, it should be noted that, for example, chemical purification, high-temperature purification, or the like may be performed on the natural flake graphite powder to remove impurities therein. Further, the powder may be subjected to a pulverization/classification treatment according to the particle size. The specific process may refer to the above-described treatment of the microlite toner, and a detailed description thereof is omitted here.
After obtaining the desired microlite toner and natural graphite flake powder, a dry blend powder may be prepared, for example, by dry blending by ball milling, stirring, or the like for 1 hour.
And step S3, adding a binder or an organic solution of the binder into the mixed dry powder, and carrying out wet mixing to obtain the paste.
That is, after mixing to obtain a mixed dry powder, a binder or an organic solution in which a binder is dissolved in an organic solvent is added thereto, and further wet mixing is performed to obtain a paste.
Wherein the content of the microlite toner may be, for example, 10 to 30% by weight, the content of the natural crystalline flake graphite powder is 50 to 70% by weight, and the content of the binder is 10 to 30% by weight, in terms of solid content (i.e., not containing liquid components such as organic solvents, dispersion liquids, etc.).
Further, the binder is phenolic resin, the organic solution of the binder is a solution obtained by dissolving the binder in ethanol, and the content of the binder in the organic solution of the binder is more than 50 wt%.
The solid content of the phenolic resin solution is 50 wt%, which means that the mass of the residual phenolic resin solid particles after the solvent (ethanol) in the solution is completely volatilized accounts for the total mass of the solution. The proper solution viscosity in the kneading stage is beneficial to the rapid and uniform mixing of the binder and the powder raw material, when the solid content of the phenolic resin binder is too high, the viscosity of the solution is remarkably increased, the mixing of the binder and the powder raw material is not facilitated, and the phenomena of prolonging the kneading time, nonuniform mixing and the like can be caused; when the solid content of the phenolic resin is lower, in order to meet the requirement that the content of the phenolic resin accounts for 10-30 wt% of the matrix powder, the using amount of the phenolic resin solution in the kneading stage is obviously increased, the fluidity of the obtained paste is increased, the subsequent granulation of the paste is not facilitated, the drying time is greatly increased, and the production efficiency is reduced.
And step S4, granulating and drying the paste, and then crushing to obtain the matrix graphite powder.
After the paste is obtained, the paste is subjected to treatments such as granulation, drying, pulverization, sieving, and the like, thereby obtaining matrix graphite powder.
The maximum particle size of the obtained matrix graphite powder is less than 150 mu m.
The fuel-free graphite nodules prepared from the matrix graphite powder have an isotropy (linear thermal expansion coefficient-AX/linear thermal expansion coefficient-TR) of 1.15 or less, and show good isotropy; the thermal conductivity-TR measured at 900 ℃ is 35-40W/m K and the thermal conductivity-AX is 30-35W/m K.
The degree of isotropy is defined as the coefficient of linear thermal expansion (CTE) against the direction of the particleAX) Its coefficient of linear thermal expansion (CTE) in the direction of the particleTR) Ratio of (i.e., CTE)AX/CTETR. The isotropic degree is between 1.00 and 1.10 and is called isotropic nuclear graphite; between 1.10 and 1.15 of a graphite called near-isotropic core; greater than 1.15 are referred to as anisotropic nuclear graphites.
That is, the closer the isotropy is to 1, the higher the isotropy performance is.
That is, the matrix graphite powder prepared according to the present invention has excellent isotropic properties.
The method for producing the base graphite powder for a high temperature gas cooled reactor fuel element, the base graphite powder, and the graphite nodules produced according to the present invention will be described in further detail with reference to specific examples.
Example 1
(1) Preparation of microcrystalline graphite powder
Raw materials: selecting microcrystalline graphite raw ore in Nemongol Xing and county.
Primary purification:
referring to the method of chinese patent application CN109437187A, the raw microcrystalline graphite is fully dispersed in hydrofluoric acid for purification, and after the immersion, the solid-liquid separation, water washing and drying are performed.
And (3) secondary purification:
placing the primarily purified microcrystalline graphite in a high-temperature graphitization furnace, heating to 3000 ℃ at an average heating rate of 10 ℃/min under the protection of high-purity argon, preserving the heat for 60min, and further purifying the raw material to ensure that the fixed carbon content of the raw material reaches more than 99.9 percent.
Crushing and grading:
crushing equipment: VT-300 type mechanical pulverizer provided by Suzhou; industrial equipment, Inc.
The crushing process comprises the following steps: specific process parameters are shown in table 1 below.
TABLE 1 milling Process parameters
The morphology of the microlite toner prepared as described above is shown in fig. 1(a), and the microlite toner is granular graphite powder with uniform size, and fig. 1(b) shows that the particle size is mainly several to several tens of micrometers, and specific particle size distribution data are shown in table 2 below.
Table 2 graphite powder particle size data
In table 2, for comparison, the particle size data of the natural flake graphite powder selected in this example and the artificial stone toner prepared according to the method described in chinese patent application No. 201610414446.8 are also shown.
As can be seen from table 2, after purification, pulverization, and classification, microcrystalline graphite powder having a smaller particle size and a more uniform distribution was obtained.
(2) Preparation of matrix graphite powder
The raw materials are prepared by mixing 60 wt% of natural crystalline flake graphite, 20 wt% of the obtained microcrystalline graphite powder and 20 wt% of phenolic resin.
First, natural flake graphite and microcrystalline graphite powder were dry-mixed for 1 hour, and thereafter, an ethanol solution of a phenol resin having a solid content of 50 wt% was added thereto, and wet-mixed for 2 hours. Thereafter, the resulting mixture was granulated, dried by blowing at 70 ℃ for 8 hours, and pulverized again by a small mechanical pulverizer, and the pulverized powder was passed through a 100-mesh screen to obtain matrix graphite powder (referred to as "M").
(3) Preparation of fuel-free graphite nodules
The specific process conditions for preparing the fuel-free graphite nodules are as follows:
1. molding:
pre-pressing: filling matrix graphite powder into a rubber mold with an ellipsoidal inner cavity, performing pre-pressing molding on a ball core under a lower pressure of about 3MPa, and maintaining the pressure for 10-30 s;
final pressure: putting the graphite spherical core into another silicon rubber mold with a larger ellipsoidal cavity, filling matrix graphite powder around the graphite spherical core to fill the whole mold with the powder, realizing cold quasi-isostatic pressing of a sample by the deformation capacity of the rubber mold, keeping the pressure at 300MPa for 3-5min, and obtaining a press-formed fuel-free graphite spherical green product;
2. and (3) heat treatment:
and (3) carbonization treatment:
carbonizing the sample under the protection of argon or nitrogen, wherein the average heating rate in the carbonization process is about 0.1-1 ℃/min, the temperature is increased to 900 ℃ of 700-;
high-temperature purification treatment:
placing the carbonized fuel-free graphite spheres into a graphitization furnace, and performing high-temperature purification under the protection of argon, wherein the average heating rate is about 10 ℃/min, heating to 1950 ℃, and preserving heat for 0.5-1 h;
3. turning:
turning the purified sample by using a special lathe to obtain the fuel-free graphite nodules with the diameter of 59.5-60.5 mm.
Comparative example
For comparison, when preparing the matrix graphite powder, the artificial stone toner is used to replace the microcrystalline graphite powder, and the other matrix graphite powder (denoted as T) is prepared by the traditional process ratio, namely 64 wt% of natural crystalline flake graphite, 16 wt% of artificial graphite powder and 20 wt% of phenolic resin under the same process conditions.
For comparison, fuel-free graphite nodules (denoted as T-x) were prepared using the above-described base graphite powder under the same process conditions.
The results of the performance tests on the fuel-free graphite nodules M-x and T-x obtained above are shown in tables 3-5 below.
TABLE 3 graphite ball Performance test results
Table 4 results of thermal conductivity test
TABLE 5 results of the linear thermal expansion coefficient test
Further, FIGS. 2(a) and 2(b) show linear thermal expansion coefficient curves at 50 to 500 ℃ respectively.
As can be seen from tables 3 to 5 and fig. 2(a) and 2(b), the thermal conductivity, thermal expansion coefficient and isotropy of the graphite nodules prepared from the matrix graphite powder prepared by the method of the present invention are significantly higher than those obtained from the artificial stone toner.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A preparation method of matrix graphite powder for a high-temperature gas cooled reactor fuel element is characterized by comprising the following steps:
step S1, obtaining microcrystalline graphite powder;
step S2, natural flake graphite powder is obtained, and the microcrystalline graphite powder and the natural flake graphite powder are dry-mixed to obtain mixed dry powder;
step S3, adding a binder or an organic solution of the binder into the mixed dry powder, and carrying out wet mixing to obtain a paste;
and step S4, granulating and drying the paste, and then crushing to obtain the matrix graphite powder.
2. The method according to claim 1, wherein the matrix graphite powder contains 10 to 30 wt% of the microcrystalline graphite powder, 50 to 70 wt% of the natural flake graphite powder, and 10 to 30 wt% of the binder.
3. The method according to claim 1, wherein the binder is a phenol resin, and the organic solution of the binder is a solution obtained by dissolving the binder in ethanol, and wherein the content of the binder in the organic solution of the binder is 50 wt% or more.
4. The method for preparing a composite material according to claim 1, wherein the step S1 includes:
step S11, obtaining microcrystalline graphite raw ore;
step S12, purifying the microcrystalline graphite raw ore;
and step S13, crushing and grading the purified microcrystalline graphite to obtain the microcrystalline graphite toner.
5. The method as claimed in claim 4, wherein in step S13, the pulverizing process conditions are as follows: the rotating speed of the crushing disc is 5000-6000rpm, the rotating speed of the grading wheel is 1500-2500rpm, the feeding frequency is 8-10Hz, the frequency of the fan is 25-40Hz, and the induced air flow is 15-20m3/min。
6. The method for preparing a composite material according to claim 4, wherein the step S12 includes:
and S121, carrying out primary purification on the microcrystalline graphite raw ore in any one or more modes of flotation, acid treatment and alkali treatment to obtain primary purified powder.
7. The method for preparing a composite material according to claim 6, wherein the step S12 further includes:
and S122, carrying out high-temperature purification on the primary purified powder to obtain secondary purified powder.
8. The method according to claim 4, wherein the microcrystalline graphite powder is in a granular form and has a particle size D50Is 10-30 μm.
9. The method for preparing according to claim 1, wherein the step 4 comprises:
granulating the paste, drying by blowing at the temperature of 60-80 ℃ for 6-10 hours, crushing by a crusher, and sieving the crushed powder by a 100-mesh sieve to obtain the matrix graphite powder.
10. A matrix graphite powder for a high temperature gas cooled reactor fuel element, comprising 10-30 wt% of a microcrystalline graphite powder, 50-70 wt% of a natural flaked graphite powder, and 10-30 wt% of a binder, wherein the microcrystalline graphite powder is prepared by the preparation method according to any one of claims 1 to 8, and the maximum particle size of the matrix graphite powder is less than 150 μm.
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