KR101033868B1 - Manufacturing method of SiC composite using calcined Al-B-C sintering additive - Google Patents

Abstract

The present invention relates to a method for producing a silicon carbide composite using an Al-BC-based sintering aid prepared by calcining, and more particularly to a composite of fibrous silicon carbide (SiC fiber) and particulate silicon carbide (SiC particle). For example, as a sintering aid, a mixture of Al + B + C, Al + B ₄ C + C, Al ₄ C ₃ + B + C, or Al ₄ C ₃ + B ₄ C + C, the temperature in the range of 1300 ~ 1900 ℃ Powders obtained by calcining at are selected, for example, at least one selected from Al ₈ B ₄ C ₇ and Al ₃ BC ₃ and mixed with particulate silicon carbide to prepare a high concentration slurry, and then the slurry is fibrous By impregnating and sintering the silicon carbide matrix, the present invention provides a method for producing a silicon carbide composite, which can realize a fine fiber pulling phenomenon despite the sintering at a temperature lower than the conventional silicon carbide sintering temperature.

The present invention is characterized in that to produce a composite by sintering silicon carbide, to synthesize the above-mentioned sintering aid separately, the sintering aid is mixed with particulate silicon carbide to produce a certain level of slurry despite the high level of slurry By maintaining the viscosity below, it is possible to smoothly penetrate into the fibrous silicon carbide matrix, and thus there is an advantage of obtaining a densified silicon carbide composite due to the high concentration slurry.

 Silicon carbide, fibrous, particulate, composite, sintering aid, calcining, Al8B4C7, Al3BC3, slurry, impregnation, sintering temperature, densification, fiber pulling phenomenon

Description

Manufacturing Method of SiC Composite Using Calcined Al-B-C Sintering Additive Using Calcination Process

The present invention relates to a method for producing a silicon carbide composite using an Al-BC-based sintering aid prepared by calcining, and more particularly to a composite of fibrous silicon carbide (SiC fiber) and particulate silicon carbide (SiC particle). For example, as a sintering aid, a mixture of Al + B + C, Al + B ₄ C + C, Al ₄ C ₃ + B + C, or Al ₄ C ₃ + B ₄ C + C, the temperature in the range of 1300 ~ 1900 ℃ Powders obtained by calcining at are selected, for example, at least one selected from Al ₈ B ₄ C ₇ and Al ₃ BC ₃ and mixed with particulate silicon carbide to prepare a high concentration slurry, and then the slurry is fibrous By impregnating and sintering the silicon carbide matrix, the present invention provides a method for producing a silicon carbide composite, which can realize a fine fiber pulling phenomenon despite the sintering at a temperature lower than the conventional silicon carbide sintering temperature.

Recently, the development of fusion power commercialization technology is in progress. In order to solve this problem, important technical problems to be solved include the technology of exchanging fusion energy with heat and generating fusion fuel in addition to the plasma stability problem. Particularly, the part where tritium (T) growth and heat exchange occurs by neutron irradiation is called a growth blanket, which is composed of tritium growth material and neutron multiplier, structural material, coolant, shield, etc. According to the type of growth material to be classified into a solid growth blanket and a liquid growth blanket. As a solid growth blanket, a ceramic propagation material containing Li is used, and water and helium are used as a cooling material. Representative solid propagation materials include Li ₂ TiO ₃ , Li ₂ ZrO ₃ , Li ₄ SiO ₄ and the like, and solid proliferation blankets require Be, Be-Ti alloys such as neutron multipliers. Representative growth agents of the liquid growth blanket include liquid type Li, PbLi, FLiBe (LiF-BeF ₂ ), FLiNaBe including molten salt, and liquid growth blanket does not require a separate neutron multiplier, and liquid type. The propagation material itself plays the role of the propagation and multiplier as well as the coolant. The solid growth blanket is a proliferative blanket of the type which is promising for use in a nuclear fusion reactor due to its relatively high technical maturity.

Meanwhile, as the blanket material, a metal-based and SiC / SiC composite have been studied, and the SiC / SiC composite has a good neutron damage characteristic, and the SiC / SiC composite has a good physical property in a long time use and a high temperature environment. It is known to be very suitable. However, there is a lot of room for material development since the physical property research, manufacturing, and bonding research of such SiC / SiC composites have not been established, and a lot of research and development is required due to insufficient data on performance under high temperature and irradiation environment.

Conventional methods for preparing such SiC / SiC composites include melt infiltration (MI), precursor impregnation and pyrolysis (PIP), and chemical vapor infiltration (CVI). Despite the method of injecting a precursor into the fibrous silicon carbide matrix, a problem occurs in that open pores are formed, which is not only difficult to realize as expected of the final density of the composite, but also remains unreacted and remains. Due to the presence of silicon, the value of use as an internal material of a fusion power plant is extremely low.

In order to solve this problem, the NITE (Nano-Infiltration and Transient Eutectic) method, which performs the sintering process by applying the hot press method (HP), has been developed. In this case, the high sintering temperature of the silicon carbide powder having the sintering ability The nanometer sized silicon carbide powder is used for the low reactivity, and such nanometer sized silicon carbide is not only very expensive in itself, but also maintains a sintering temperature of more than 1800 ° C in the sintering process. In addition, there is a problem in that the pressing device and the capacity of the device is limited in capacity so that only a specific type of blanket can be manufactured or a blanket of a certain size cannot be manufactured.

The present invention has been made to solve the problems described above, the present invention is to produce a silicon carbide composite used as a blanket material of the fusion reactor, during the manufacturing process of the sintering aid and particulate silicon carbide mixture as a slurry It is intended to produce a densified silicon carbide composite at the same time to reduce the sintering temperature by making the overall impregnation in the fibrous silicon carbide matrix by maintaining a high concentration while maintaining the slurry at a high concentration.

In addition, the present invention enables to obtain a densified silicon carbide composite even by low temperature sintering, and in the sintering method, it is possible to use a general sintering method rather than a high-pressure sintering method. It is another object to be able to select and to reduce the manufacturing cost of a silicon carbide sintered compact.

Further, another object of the present invention is to produce a silicon carbide sintered body which is not inferior to that used as a blanket material of a fusion furnace, although it is produced by low temperature sintering.

In order to achieve the object as described above, the present invention, in the preparation of a silicon carbide composite using fibrous silicon carbide and particulate silicon carbide, the calcined Al-BC-based sintering aid, particulate silicon carbide and a solvent Mixing to prepare a slurry; Impregnating the prepared slurry into a fibrous silicon carbide matrix; And sintering the impregnated fibrous silicon carbide matrix. Provides a method for producing a silicon carbide composite using an Al-B-C-based sintering aid prepared by calcining.

The sintering aid is preferably prepared by calcining at least any one selected from Al and Al ₄ C ₃ , at least one selected from B and B ₄ C, and stoichiometrically mixing C.

The calcination temperature is in the range of 1300 ~ 1900 ℃, it is preferably prepared by heat treatment for 30 minutes to 4 hours in a reducing atmosphere.

The Al-BC-based sintering aid is preferably at least one selected from Al ₈ B ₄ C ₇ and Al ₃ BC ₃ .

The slurry, the silicon carbide is 30 to 55% by volume relative to the total volume of the slurry, the Al-B-C-based sintering aid is preferably prepared to 2.5 to 15% by weight relative to the total weight of the slurry.

The slurry preferably has a viscosity of 5 to 120 mPa · s measured upon stirring.

The particulate nano silicon carbide has a size of 25 ~ 200 nm, the sintering temperature is preferably in the range of 1525 ~ 1700 ℃, the density of the composite is 96 ~ 99.5% of the theoretical density.

Sintering holding time in the sintering process is preferably in the range of 1 minute to 3 hours.

The particulate submicron silicon carbide has a size of 0.2 ~ 0.8 ㎛, the sintering temperature is preferably in the range of 1525 ~ 1700 ℃, the density of the composite is 97 ~ 99.5% of the theoretical density.

Sintering holding time in the sintering process is preferably in the range of 1 minute to 3 hours.

In addition, the present invention provides a silicon carbide composite prepared by using an Al-B-C-based sintering aid prepared by calcining, in order to achieve the object as described above, the fiber pull phenomenon when broken.

According to the present invention as described above, in the process of producing a silicon carbide composite to effectively impregnate the particulate silicon carbide uniformly between the fibrous silicon carbide by effectively controlling the concentration and viscosity of the slurry mixed with particulate silicon carbide and the sintering aid. And, despite the low temperature sintering, there is an effect that can produce a dense silicon carbide composite.

In addition, according to the present invention, since a high density can be obtained in the molding step of the composite, it is not necessary to use nano-sized silicon carbide powder in order to increase the reactivity, and it is possible to use a general sintering method rather than pressurization when sintering. There is no restriction on the shape or size of the product, such as a blanket, there is an effect that greatly reduces the overall process cost.

Moreover, according to this invention, there exists an effect which can manufacture the composite which can fully function as the blanket material of a fusion furnace.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

The invention provides Al + B + C, Al + B ₄ C + C, Al ₄ C ₃ + B + C, or Al ₄ C ₃ + B ₄ to rule out the limitations of existing methods that must use existing NITE processes. Powders obtained by calcining a mixture of C + C at a temperature in the range of 1300-1900 ° C., for example at least one selected from Al ₈ B ₄ C ₇ and Al ₃ BC _3, are used as a sintering aid and are much more conventional than conventional processes. By sintering at low temperature, even though inexpensive submicron-sized granular silicon carbide raw materials are used, they are practically dense due to their compactness, fiber bending occurs, and carbonization can freely control the shape and size of the final product such as blankets. To produce a silicon composite.

(1) Preparation of sintering aid

Al-BC-based composite used as a sintering aid in the present invention was made of Al ₈ B ₄ C ₇ or Al ₃ BC ₃ as an example, preferably synthesized in powder form, aluminum (Al) and aluminum carbide ( Al ₄ C ₃ ), at least one selected from boron (B) and boron carbide (B ₄ C) and carbon (C) after stoichiometric mixing, followed by a reduction of 1300 to 1900 ° C., preferably about 1800 ° C. It was prepared by heat treatment in an atmosphere for 30 minutes to 4 hours, preferably 1 to 3 hours. In this case, the sintering process is preferably performed in an argon atmosphere. The obtained sintering aid was found to be substantially pure single phase as a result of XRD analysis.

The above heat treatment temperature and time range have a critical significance for the production of Al ₈ B ₄ C ₇ or Al ₃ BC ₃ free of stoichiometric defects.

The sintering aid prepared as described above is also characterized by the present invention in that it is used by separately preparing and sintering, which is not synthesized separately, and separately prepares Al, B and C, respectively, and fibrous silicon carbide matrix It should be noted that there are differences that cannot be achieved when used impregnated with.

In Figure 1 was prepared by mixing the sintering aid Al ₈ B ₄ C ₇ and Al, B and C mixed powder prepared according to the present invention into a slurry, and then stirred, and measured the viscosity about it immediately after stirring, As described above, the slurry for the sintering aid according to the present invention was about 50% by volume, and the mixed powder slurry was about 10% by volume, but it was found that the viscosity was very similar under all stirring conditions.

That is, for the impregnation process, a slurry having an appropriate level of viscosity should be prepared. In the case of the conventional mixed powder, despite the low concentration, the slurry has a high viscosity value, thus making it difficult to increase the concentration. Therefore, it was found that when using such a slurry, a densified composite could not be obtained.

That is, it is a conventional technique to use the mixed powder of Al, B and C as stoichiometrically identical to the sintering aid according to the present invention and use it as a sintering aid by itself. Since the Al and B powders in size have the effect of filling the narrow voids present inside the fibrous silicon carbide matrix, the gastric mixed powder cannot penetrate deep into the silicon carbide matrix, thus achieving densification of the composite produced. Of course, the fibrous silicon carbide of the non-penetrated portion is in direct contact with each other during high-temperature high-pressure sintering, there is a problem that the composite is easily deformed as a whole around the stomach fibrous.

Meanwhile, in FIG. 2, the composite prepared by using the sintering aid according to an embodiment of the present invention and the mixed powder of Al, B, and C as the sintering aid were used as an electron microscope with the fibrous silicon carbide as a cross section. The observed picture is shown.

(a) is a silicon carbide composite prepared by using a mixed powder of Al, B, and C as a sintering aid, and (b) is a silicon carbide composite prepared using the sintering aid according to an embodiment of the present invention. Similarly, in the case of (a), the sintering aid was not impregnated properly between the fibrous silicon carbides, and thus the fibrous silicon carbides were in contact with each other during the sintering process. It can be seen that the sintering aid according to the present invention is impregnated properly between the fibrous silicon carbides to support each fibrous phase, thereby preventing contact between the fibers, thereby maintaining the original shape of the individual fiber cross sections. Therefore, when the sintering aid according to the present invention is used, the effect of maintaining the shape of fibrous silicon carbide during the sintering process could be proved.

In the case where the fiber phases are deformed by contact with each other, when a stress is applied, a fracture path is easily generated between the contacted fiber phases, so that the fiber breaks instead of the fiber pulling phenomenon.

In addition, when Al ₈ B ₄ C ₇ or Al ₃ BC ₃ is separately synthesized as a sintering aid, the synthesized sintering aid is high enough to be easily pulverized into fine powder of about 0.5 micrometer or less by a simple milling process. As long as the material is low and the dispersion conditions are satisfied, it can be easily impregnated even when mixed with the particulate silicon carbide powder, so that it can easily penetrate deep into the fibrous silicon carbide matrix to achieve densification upon sintering. It is possible to suppress the deformation of the fibrous phase.

In other words, the difference between whether to use the sintering aid separately synthesized or directly mixed with each constituent material is very large, and the technical idea regarding the synthesis of such a sintering aid has its own characteristics.

The sintering aid used in the conventional NITE process is a mixture of Al ₂ O ₃ and Y ₂ O ₃ , which makes it difficult to produce a slurry of higher concentration than single phase Al ₃ BC ₃ or Al ₈ B ₄ C ₇ , and the same amount of sintering Even when the aid is added, there is a problem that a higher temperature is required for densification of silicon carbide, and the present invention has improved these problems by using the above sintering aids.

(2) Preparation of the mixture

The sintering aid synthesized as described above was pulverized and mixed with varying the content of silicon carbide in granules. At this time, the above mixture was wet mixed to impregnate the fibrous silicon carbide matrix to prepare a slurry.

In preparing the slurry according to one embodiment of the present invention, particulate silicon carbide was used in the nano-range size and sub-micron size range, respectively, the silicon carbide is 30 to 50% by volume, the total slurry relative to the total volume of the slurry The Al-BC-based sintering aid to weight was prepared by mixing 5 to 15% by weight.

In FIG. 3, the slurry of the sintering aid and the silicon carbide mixture according to one embodiment of the present invention and a slurry composed of purely silicon carbide are prepared and stirred, respectively, and the viscosity of the slurry is measured immediately after the stirring. Represented by. At this time, the particulate silicon carbide was used as a sub-micron silicon carbide as an example. On the other hand, although not shown, nano-sized particulate silicon carbide tends to have a higher viscosity at the same concentration.

As shown, it was found that the slurry prepared by the present invention under the same stirring conditions, the viscosity is lower than the slurry prepared only with silicon carbide, the viscosity of the slurry produced so as to be practically meaningful by the present invention is 30 ~ 30 The range of 5 to 80 mPa.s in the range of 45% by volume, the slurry consisting of only 45% by volume of pure silicon carbide shows a value of about 100 mPa.s, so that the slurry according to the present invention is purely silicon carbide It was inferred that the fibrous silicon carbide matrix could be more easily impregnated compared to the slurry produced.

This is between the pure Al ₃ BC _3, while the slurry is possible up to 50% by volume pure silicon carbide represents an excellent dispersion property than Al ₃ BC SiC ₃ is pure enough to be up to 45 vol%, with Al ₃ BC ₃ and SiC This is because no aggregation reaction inhibits dispersion.

(3) Preparation of Composite by Sintering Process

By sintering the composite molded body completed the impregnation process as described above to prepare a silicon carbide composite. As mentioned above, the composite produced by the present invention exhibited about 99.4% of theoretical density.

In the present invention, silicon carbide composites were prepared using particulate silicon carbide each having two size ranges, one of which was silicon carbide having a size range of 25 nanometers to 200 nanometers, in which case the sintering temperature was 1525-1700. It was in the range of ℃, the density of the composite showed a relative density corresponding to 96.5 ~ 99.5% of the theoretical density. At this time, the sintering holding time was adjusted in the range of 3 hours to 1 minute.

The above sintering temperature range is a critical range that is set to realize the fiber pulling phenomenon and at the same time have a practical meaning, when sintering at a temperature below 1525 ℃, it is difficult to realize a meaningful relative density of the composite, 1700 ℃ When the temperature exceeds the temperature range of the fiber fracture phenomenon can hardly occur due to the fiber fracture phenomenon, it has a critical significance in the above sintering temperature range. This is more than 100 ℃ lower than the sintering temperature 1800 ℃ used in the existing NITE process. On the other hand, in the present invention, the sintering holding time also becomes an important factor, and the fiber pulling phenomenon and densification can be simultaneously achieved in the holding time range of 3 hours to 1 minute.

In this regard, Figure 4 shows the fracture surface of the composite prepared at each sintering temperature using the granular silicon carbide having a nano-size range and the fracture surface is shown by electron micrograph. Unlike the composite prepared by sintering at 1700 ° C. for 10 minutes as shown in (a), as shown in (b), the composite prepared by sintering at 1600 ° C. for 3 minutes has a fibrous silicon carbide shape. It is well shown that, from this, the composite according to the present invention was able to obtain a silicon carbide composite having good physical properties in which fiber pulling was well observed despite sintering at a temperature lower than the conventional silicon carbide sintering temperature.

In the case of ceramics, low reliability due to brittle fracture is a major obstacle to commercialization. Ceramic composites prevent the catastrophic progression of cracking by absorbing energy used to destroy materials. Therefore, when the fiber pulling phenomenon is expressed, the ceramic composite shows high fracture toughness and reliability despite being a brittle material, and thus the superiority of the physical properties of the composite can be determined from the expression of the fiber pulling phenomenon. On the other hand, when sintered at a higher temperature, fiber fracture did not occur due to fiber fracture, and it was found that all surfaces were brittle in the plane of the same level.

Meanwhile, according to one embodiment of the present invention, a composite using particulate silicon carbide having a size in the submicron range is manufactured. The particulate silicon carbide has a size of 0.2 micrometers to 0.8 micrometers, and the sintering temperature is 1525. It is in the range of ~ 1700 ℃, the density of the composite is 97 ~ 99.5% of the theoretical density. At this time, the sintering holding time was in the range of 3 hours to 1 minute.

From the above sintering temperature and holding time range, a silicon carbide composite having optimum physical properties was obtained. This is more than 100 ℃ lower than the sintering temperature 1800 ℃ used in the existing NITE process. The critical significance of the above sintering temperature and the holding time is the same as in the case of using the nanometer-sized silicon carbide, and thus will be replaced by the above contents.

In this regard, Figure 5 shows the fracture surface of the composite prepared at each sintering temperature using particulate silicon carbide having a submicron size range and the fracture surface is shown by an electron micrograph. As shown, in the case of a composite prepared by sintering at 1650 ° C. for 10 minutes, the fibrous silicon carbide shape does not appear well, but in the case of a composite prepared by sintering at a lower temperature of 1550 ° C. for 10 minutes, the fibrous silicon carbide shape is shown. It was observed that the fiber pulling phenomenon was good.

Although the present invention has been described in more detail with reference to the embodiments, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not stabilized by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a graph showing the viscosity of the sintering aid Al ₈ B ₄ C ₇ and Al, B and C prepared by one embodiment of the present invention after preparing a slurry, and measuring the viscosity thereof, (a) Is a viscosity measurement of 50% by volume of the sintering aid according to the present invention relative to the total volume of the slurry, and (b) is a viscosity measurement of 10% by volume of Al, B, C mixture sintering aid relative to the total volume of the slurry.

2 is a cross-sectional view of a composite prepared by (a) a composite powder of Al, B and C as a sintering aid, and (b) a composite prepared by using the sintering aid according to an embodiment of the present invention. It is a photograph observed with an electron microscope.

3 is a graph showing a slurry of a sintering aid and a mixture of silicon carbide according to one embodiment of the present invention and a slurry composed of purely silicon carbide, each of which is prepared and stirred. (C) a viscosity value of a slurry prepared by mixing 30% by volume particulate silicon carbide with respect to the total volume of the slurry and 10% by weight of Al ₃ BC ₃ relative to the total weight of the slurry, and (d) 45% by volume with respect to the total volume of the slurry. Viscosity of slurry prepared from particulate silicon carbide and Al ₃ BC ₃ mixture (the amount of preparation is 10% by weight of silicon carbide), (e) 45% by volume of particulate silicon carbide The viscosity value of a slurry is shown, respectively.

FIG. 4 is a photograph of a composite prepared at each sintering temperature using particulate silicon carbide having a nano-sized range according to an embodiment of the present invention, and the fracture surface thereof was observed with an electron microscope (a) 1700 ° C. FIG. The composites sintered by holding for 10 minutes at and (b) the composites sintered by holding at 1600 ° C for 10 minutes are respectively shown.

FIG. 5 is a photograph of a composite prepared at each sintering temperature using particulate silicon carbide having a submicron size range according to an embodiment of the present invention, and the fracture surface thereof is observed with an electron microscope, (a) 1650 The composite sintered by holding at 10 ° C. for 10 minutes and the composite sintered by holding at 1550 ° C. for 10 minutes are shown.

Claims (11)

In preparing a silicon carbide composite using fibrous silicon carbide and particulate silicon carbide, Preparing a slurry by mixing the calcined Al-B-C-based sintering aid, particulate silicon carbide, and a solvent; Impregnating the prepared slurry into a fibrous silicon carbide matrix; And Sintering the impregnated fibrous silicon carbide matrix; Method for producing a silicon carbide composite using an Al-B-C-based sintering aid prepared by calcining comprising a. The method of claim 1, The sintering aid is prepared by calcining, characterized in that at least any one selected from Al and Al ₄ C ₃ , at least any one selected from B or B ₄ C, by stoichiometric mixing and then calcining, respectively Method for producing silicon carbide composite using Al-BC sintering aid. The method of claim 2, The calcination temperature is 1300 ~ 1900 ℃, a method for producing a silicon carbide composite using the calcined Al-B-C-based sintering aid, characterized in that the reduced atmosphere is prepared by heat treatment for 30 minutes to 4 hours. The method of claim 2, The Al-BC-based sintering aid is a method of producing a silicon carbide composite using the Al-BC-based sintering aid prepared by calcining, characterized in that at least one selected from Al ₈ B ₄ C ₇ and Al ₃ BC ₃ . The method of claim 1, The slurry, The silicon carbide is 30 to 50% by volume relative to the total volume of the slurry, the Al-BC-based sintering aid is prepared by calcining the Al-BC-based sintering aid, characterized in that the prepared by 5 to 15% by weight Method for producing a silicon carbide composite using. The method of claim 5, The slurry is a method for producing a silicon carbide composite using an Al-B-C-based sintering aid prepared by calcining, characterized in that the viscosity measured at stirring is 5 ~ 120 mPa.s. The method of claim 1, The particulate silicon carbide has a size of 25 ~ 200 nm, the sintering temperature is in the range of 1525 ~ 1700 ℃, the density of the composite is calcined Al-BC system, characterized in that 96.5 ~ 99.5% of the theoretical density Method for producing silicon carbide composite using sintering aid. The method of claim 7, wherein The sintering holding time in the sintering process is a method of producing a silicon carbide composite using the Al-B-C-based sintering aid prepared by calcining, characterized in that the range of 3 hours to 1 minute. The method of claim 1, The particulate silicon carbide has a size of 0.2 ~ 0.8 ㎛, sintering temperature is in the range of 1525 ~ 1700 ℃, density is 97 ~ 99.5% of the theoretical density calcined Al-BC-based sintering aid Method for producing a silicon carbide composite using. The method of claim 9, The sintering holding time in the sintering process is a method of producing a silicon carbide composite using the Al-B-C-based sintering aid prepared by calcining, characterized in that the range of 3 hours to 1 minute. Prepared by the method of any one of claims 1 to 10, Silicon carbide composite prepared using an Al-B-C-based sintering aid prepared by calcining, characterized in that the fiber pull phenomenon when broken.

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