Hard solder and method for preparing a sample, and method for joining for a silicon carbide lining

Description

FIELD OF THE INVENTION

[0001] The invention relates to the technical field of nuclear fuels, in particular to a brazing filler material and a method for preparing the brazing filler material, and a joining method for a silicon carbide cladding.DESCRIPTION OF THE RELATED ART

[0002] Silicon carbide (SiC) ceramics have the characteristics of high strength, high hardness, low density, oxidation resistance and corrosion resistance. In addition, the SiC ceramics have excellent properties such as small coefficient of thermal expansion, high thermal conductivity, good high temperature performance, and low neutron absorption cross section, such that they have been widely used in nuclear applications such as clad fuel elements, inner walls of nuclear reactor vessels, and linings of reactor pipes.

[0003] A cladding is mainly composed of a cladding tube and an end plug joined together, which serve in high temperature, high pressure, high radiation and hydrothermal corrosion environments. Since SiC is a strong covalent bond compound with high melting point and small self-diffusion coefficient, it is rather difficult to achieve direct joining between the cladding tube and the end plug. What is needed, therefore, is a brazing filler material and a joining method that can adapt to the above environmental conditions. At present, silicon carbide joining methods used in the nuclear field mainly include precursor joining method, glass-ceramic brazing method, MAX phase joining method, NITE phase joining method and mechanical joining.

[0004] Each of the above methods has its own advantages and disadvantages. The precursor joining method has the advantages of low joining pressure, low joining temperature, small thermal stress at the joint, good hydrothermal corrosion resistance and radiation resistance. However, a large amount of gas will be released during the precursor pyrolysis process, which causes a volume shrinkage and the formation of pores, resulting in a poor joining strength and hermeticity of the SiC joint. The glass-ceramic joining method can form a joint with good sealing performance and good heat resistance and thermal shock resistance, but the glass ceramics have poor radiation resistance and poor hydrothermal corrosion resistance. The MAX phase joining method can achieve a joint with good thermal shock resistance and oxidation resistance, but the joint is easy to decompose at high temperature and has poor radiation resistance. Although the joint formed by the NITE phase joining method has a good joining strength, the joining pressure is too high, which is unfavorable for the cladding joining.

[0005] In view of the advantages of precursor joining in the field of nuclear applications, especially that the joints have good hydrothermal corrosion resistance and radiation resistance, in order to increase the shear strength of the precursor joining, it is highly desirable to improve the precursor joining method to reduce the volume shrinkage during the joining process. In addition, if the thickness of the interlayer is too small, the difficulty in assembling the cladding tube with the end plug may be increased, and the issue of poor hermeticity may easily occur.

[0006] Publications ZHAO CHENG-CAI ET AL: "Facile joining of SiC ceramics with screenprinted polycarbosilane without pressure", JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, ELSEVIER, AMSTERDAM, NL, vol. 41, no. 3, 28 October 2020 (2020-10-28), pages 2157-2161, XP086375658; FERRARIS M ET AL: "Joining of SiC-based materials for nuclear energy applications", JOURNAL OF NUCLEAR MATERIALS, vol. 417, no. 1 , pages 379-382, XP028305663; JP H07 53278 A; and FRANCIS A ET AL: "Fabrication and cytotoxicity assessment of novel polysiloxane / bioactive glass films for biomedical applications", CERAMICS INTERNATIONAL, ELSEVIER, AMSTERDAM, NL, vol. 42, no. 14, 29 June 2016 (2016-06-29), pages 15442-15448, XP029686861, are considered to be relevant to the present application.SUMMARY OF THE INVENTION

[0007] The technical problem to be solved by the present invention is to provide a brazing filler material for use in joining of a silicon carbide cladding and a method for preparing the brazing filler material, and a joining method for a silicon carbide clad using the brazing filler material. This problem is solved by a brazing filler material having the features of claim 1, a method for preparing a brazing filler material having the features of claim 4 and a joining method for a silicon carbide cladding having the features of claim 5.

[0008] The technical solution the present invention adopts to solve the technical problem is that a brazing filler material is provided for use in joining of a silicon carbide cladding, and the brazing filler metal includes the following raw materials: precursor, glass powder and organic solvent; the mass ratio of the precursor to the glass powder is 90-98 : 2-10.

[0009] The precursor is at least one of polycarbosilane and polysilazane.

[0010] The raw materials of the glass powder include the raw material of the glass powder comprises one or more of CA, SARe 2 O 3 and SMRe 2 O 3 ; in the CA, SARe 2 O 3 and SMRe 2 O 3 : C represents CaO; A represents Al 2 O 3 ; S represents SiO 2 ; M represents MgO; Re represents Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

[0011] Preferably, the mass ratio in the CA is that CaO : Al 2 O 3 = 45-55 : 55-45; the mass ratio in the SARe 2 O 3 is that SiO 2 : Al 2 O 3 : Re 2 O 3 = 30-60 : 15-30 : 25-40; the mass ratio in the SMRe 2 O 3 is that SiO 2 : MgO : Re 2 O 3 = 30-60 : 15-30 : 25-40.

[0012] Preferably, the glass powder is obtained by water quenching and then milling after heating the one or more of CA, SARe 2 O 3 and SMRe 2 O 3 at 1400°C to 1750°C for 0.5h to 4h

[0013] Preferably, the organic solvent is at least one of xylene, toluene, absolute ethanol and acetone.

[0014] The present invention also provides a method for preparing a brazing filler material, comprising the following steps: mixing and ball milling the precursor and the glass powder to obtain mixed powder, mixing uniformly the mixed powder and the organic solvent to obtain a slurry which is the brazing filler material.

[0015] The present invention also provides a joining method for a silicon carbide cladding, comprising the following steps: S1. applying the brazing filler material according to any one of the above brazing filler materials between a cladding tube and an end plug that match with each other; S2, sequentially performing a precursor curing treatment, a precursor pyrolysis treatment and a heat treatment on the brazing filler material; S3. forming a interlayer by the brazing filler material that has undergone the heat treatment, the interlayer joining the cladding tube and the end plug together.

[0016] Preferably, in step S2, the temperature for the precursor curing treatment is 100°C to 300°C; the temperature for the precursor pyrolysis treatment is 800°C to 1200°C; the temperature for the heat treatment is 1300°C to 1500°C.

[0017] Preferably, in the precursor curing treatment, the temperature is raised to 100°C to 300°C at a heating rate of 2°C / min, and the temperature is maintained for 0.5h to 2h; the precursor curing pressure is 0.01MPa to 1MPa; in the precursor pyrolysis treatment, the temperature is raised to 800°C to 1200°C at a heating rate of 5°C / min to 20°C / min, and the temperature is maintained for 0.5h to 2h; the precursor pyrolysis pressure is 0.01MPa to 1MPa; in the heat treatment, the temperature is raised to 1300°C to 1500°C at a heating rate of 1°C / min to 20°C / min, and the temperature is kept for 0.5h to 2h.

[0018] Preferably, in step S3, a thickness of the interlayer is 50µm to 100µm.

[0019] In the brazing filler material of the invention for use in the joining of the silicon carbide cladding, the additive of glass phase formed by the glass powder has good wettability to silicon carbide, resulting in a high joining strength. The ratio of the glass powder is adjustable, so that the coefficient of thermal expansion of the glass addition phase is adjustable, and the stress of the formed joint is controllable. A thick dense interlayer can be achieved with good hermeticity, which is beneficial to the assembly of the silicon carbide cladding in industry.

[0020] The brazing filler material of the invention is applied in the joining of the cladding to improve the structural strength and integrity of the cladding, thereby improving the safety of the nuclear reactor, and actively promoting the application of the new cladding material in the nuclear reactor.DETAILED DESCRIPTION OF EMBODIMENTS

[0021] The brazing filler material of the present invention is used for joining of silicon carbide cladding in which an end plug is joined to a cladding tube.

[0022] The brazing filler material includes the following raw materials: precursor, glass powder and organic solvent.

[0023] Among them, the mass ratio of the precursor to the glass powder is 90-99 : 10-1.

[0024] The precursor is polycarbosilane (PCS).

[0025] The raw material of the glass powder includes one or more of CA, SARe 2 O 3 and SMRe 2 O 3 , and the glass powder is obtained by water quenching and then milling the one or more of CA, SARe 2 O 3 and SMRe 2 O 3 after the raw material is maintained at 1400°C to 1750°C for 0.5h to 4h.

[0026] In CA, SARe 2 O 3 and SMRe 2 O 3 , C represents CaO; A represents Al 2 O 3 ; S represents SiO 2 ; M represents MgO; Re represents Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

[0027] Further, the mass ratio in CA is that CaO : Al 2 O 3 = 45-55 : 55-45; the mass ratio in SARe 2 O 3 is that SiO 2 : Al 2 O 3 : Re 2 O 3 = 30-60 : 15-30 : 25-40; The mass ratio in SMRe 2 O 3 is that SiO 2 : MgO : Re 2 O 3 = 30-60 : 15-30 : 25-40.

[0028] The organic solvent is at least one of xylene, toluene, absolute ethanol and acetone.

[0029] The brazing filler material for joining of the present invention is prepared by the following method: mixing the precursor and the glass powder, ball milling the precursor and the glass powder to obtain mixed powder, mixing uniformly the mixed powder and the organic solvent to obtain a slurry which is the brazing filler material. The amount of the organic solvent is designed so that a solid content of the obtained slurry is 30wt% to 60wt%.

[0030] Specifically, a planetary ball mill is used to ball-mill and mix the precursor and the glass powder, the ball-milling time is 8h-24h, and the ball-milling speed is 400r / min.

[0031] The brazing filler material of the present invention is applied in the joining of the silicon carbide cladding, and the joining method for the silicon carbide cladding may include the following steps: S1. applying the brazing filler material between a cladding tube and an end plug that match with each other.

[0032] It can be understood that the end plug is mainly joined at an end opening of the cladding tube, and the brazing filler material is applied on a surface at the end opening of the cladding tube or a joining end of the end plug, or on both the surface of the end opening of the cladding tube and the joining end of the end plug according to needs. After the end plug is fitted into the end opening of the cladding tube, the brazing filler material is placed between the cladding tube and the end plug to form a to-be-joined sample.

[0033] A thickness of the applied brazing filler material can be adjusted according to a desired thickness of the interlayer to be formed.

[0034] S2. sequentially performing a precursor curing treatment, a precursor pyrolysis treatment and a heat treatment on the brazing filler material.

[0035] In step S2, the to-be-joined sample is first placed at 100°C to 300°C to perform a precursor curing treatment, so as to cure the precursor in the brazing filler material. During the precursor curing treatment, the temperature is raised to 100°C to 300°C at a heating rate of 2°C / min, and the temperature is maintained for 0.5h to 2h; a curing pressure of the precursor is 0.01MPa to 1MPa.

[0036] The to-be-joined sample that has undergone the precursor curing treatment is then placed at 800°C to 1200°C to perform the precursor pyrolysis treatment, so as to pyrolyze the precursor in the brazing filler material. During the precursor pyrolysis treatment, the temperature is raised to 800°C to 1200°C at a heating rate of 5°C / min to 20°C / min, and the temperature is maintained for 0.5h to 2h; the precursor pyrolysis pressure is 0.01MPa to 1MPa.

[0037] Finally, the to-be-joined sample that has undergone the precursor pyrolysis treatment is placed at 1300°C to 1500°C to perform the heat treatment. During the heat treatment, the temperature is raised to 1300°C to 1500°C at a heating rate of 1°C / min to 20°C / min, and the temperature is maintained for 0.5h to 2h.

[0038] The heat treatment can adjust the degree of crystallization of the glass phase at the interlayer, and improve the radiation resistance and corrosion resistance of the joint of the cladding tube and the end plug.

[0039] S3. forming a interlayer by the brazing filler material that has undergone the heat treatment, the interlayer joining the cladding tube and the end plug together.

[0040] Wherein, the interlayer formed by the brazing filler material is dense and has a good hermeticity. The thickness of the interlayer is 50µm to 100µm.

[0041] The room temperature shear strength is 40MPa to100MPa, the high temperature shear strength at 1200°C is 45MPa to 120MPa, and the leak-rate is 0 to 1×10 -9< Pa·m 3< / s.

[0042] The present invention will be further described below by way of specific embodiments.Example 11. Preparation:

[0043] Polycarbosilane (PCS) and glass powder CA (C=CaO, A=Al 2 O 3 ) are used as raw materials; wherein, CA has been obtained by water quenching and then milling the raw material after the raw material was maintained at 1650°C for 2h. PCS and CA are uniformly mixed in a mass ratio of 95:5, and the mixed powder is mixed with xylene to form a brazing filler material with a solid content of 50wt%. The brazing filler material is applied between the cladding tube and the end plug to form a to-be-joined sample; the to-be-joined sample undergoes a precursor curing treatment at 300°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1200°C and a pyrolysis pressure of 1MPa, and finally undergoes a subsequent heat treatment at 1500°C for 2h to obtain the silicon carbide cladding.2. Performance test:

[0044] The thickness of the interlayer formed by the brazing filler material is 50µm, the room temperature shear strength is 100MPa, the high temperature shear strength at 1200°C is 110MPa, and the leak-rate is 0.5×10 -9< Pa·m 3< / s.Example 21. Preparation:

[0045] Polycarbosilane (PCS) and glass powder CA (C=CaO, A=Al 2 O 3 ) are used as raw materials; wherein, CA has been obtained by water quenching and then milling the raw material after the raw material was maintained at 1700°C for 2 h. PCS and CA are uniformly mixed in a mass ratio of 98 : 2, and the mixed powder is mixed with xylene to form a brazing filler material with a solid content of 60wt%. The brazing filler material is applied between the cladding tube and the end plug to form a to-be-joined sample; the to-be-joined sample undergoes a precursor curing treatment at 250°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1100°C and a pyrolysis pressure of 0.1MPa, and finally undergoes a subsequent heat treatment at 1350°C for 1h to obtain the silicon carbide cladding.2. Performance test:

[0046] The thickness of the interlayer formed by the brazing filler material is 100µm, the room temperature shear strength is 60MPa, the high temperature shear strength at 1200°C is 80MPa, and the leak-rate is 0.8× 10 -9< Pa·m 3< / s.Example 31. Preparation:

[0047] Polycarbosilane (PCS) and glass powder SAY (S=SiO 2 , A=Al 2 O 3 , Y=Y 2 O 3 ) are used as raw materials; wherein, the glass powder SAY has been obtained by water quenching and then milling the raw material after the raw material was maintained at 1700°C for 2h. The PCS and SAY are uniformly mixed in a mass ratio of 90 : 10, and the mixed powder is mixed with xylene to form a brazing filler material with a solid content of 30wt%. The brazing filler material is applied between the cladding tube and the end plug to form a to-be-joined sample; the to-be-joined sample undergoes a precursor curing treatment at 280°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1150°C and a pyrolysis pressure of 0.5MPa, and finally undergoes a subsequent heat treatment at 1500°C for 0.5h to obtain the silicon carbide cladding.2. Performance test:

[0048] The thickness of the interlayer formed by the brazing filler material is 60µm, the room temperature shear strength is 55MPa, the high temperature shear strength at 1200°C is 70MPa, and the leak-rate is 0.2× 10 -9< Pa·m 3< / s.Example 41. Preparation:

[0049] Polycarbosilane (PCS) and glass powder SMY (M=MgO, Y=Y 2 O 3 ) are used as raw materials; wherein, the glass powder SMY has been obtained by water quenching and then milling the raw material after the raw material was maintained at 1750°C for 1h. The PCS and SMY are uniformly mixed in a mass ratio of 96:4, and the mixed powder is mixed with xylene to form a brazing filler material with a solid content of 45wt%. The brazing filler material is applied between the cladding tube and the end plug to form a to-be-joined sample; the to-be-joined sample undergoes a precursor curing treatment at 300°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1200°C and a pyrolysis pressure of 1MPa, and finally undergoes a subsequent heat treatment at 1500°C for 2h to obtain the silicon carbide cladding.2. Performance test:

[0050] The thickness of the interlayer formed by the brazing filler material is 80µm, the room temperature shear strength is 80MPa, the high temperature shear strength at 1200°C is 100MPa, and the leak-rate is 0.5× 10 -9< Pa·m 3< / s.Example 51. Preparation:

[0051] Polycarbosilane (PCS) and glass powder SANd (A=Al 2 O 3 , Nd=Nd 2 O 3 ) are used as raw materials; wherein, the glass powder SANd has been obtained by water quenching and then milling the raw material after the raw material was maintained at 1550°C for 1.5h. The PCS and SANd are uniformly mixed in a mass ratio of 95 : 5, and the mixed powder is mixed with xylene to form a brazing filler material with a solid content of 35wt%. The brazing filler material is applied between the cladding tube and the end plug to form a to-be-joined sample; the to-be-joined sample undergoes a precursor curing treatment at 280°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1200°C and a pyrolysis pressure of 0.5MPa, and finally undergoes a subsequent heat treatment at 1500°C for 1h to obtain the silicon carbide cladding.2. Performance test:

[0052] The thickness of the interlayer formed by the brazing filler material is 85µm, the room temperature shear strength is 80MPa, the high temperature shear strength at 1200°C is 100MPa, and the leak-rate is 0.4× 10 -9< Pa·m 3< / s.Comparative Example 1

[0053] Polycarbosilane (PCS) is used as the raw material, the PCS and xylene are mixed in a mass ratio of 1 : 1 to prepare a slurry, the prepared slurry is applied between the cladding tube and the end plug to form a to-be-joined sample. The to-be-joined sample undergoes a precursor curing treatment at 300°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1200°C and a pyrolysis pressure of 1MPa, and finally undergoes a heat treatment at 1500°C to obtain the silicon carbide cladding.

[0054] The obtained silicon carbide cladding has many pore defects, and the thickness of the interlayer is less than 5µm. This is because the precursor generates a large amount of pyrolysis gas during the pyrolysis process, which causes great loss of the joining material during the joining process, resulting in the small thickness of the interlayer and a large amount of pore defects present in the interlayer. A room temperature shear strength test shows that the room temperature shear strength is only 10.57MPa. A high temperature shear test performed at 1200°C shows that the high temperature shear strength is only 6.01MPa, and the leak-rate is greater than 10 -4< Pa·m 3< / s.Comparative Example 2

[0055] CA (49.7 wt% CaO; 50.3 wt% Al 2 O 3 ) was maintained at 1500 °C for 2h, and was then water quenched and milled; CA is used as the raw material, the CA and xylene are mixed at a mass ratio of 1 : 1 to prepare a slurry, and the prepared slurry is applied between the cladding tube and the end plug to form a to-be-joined sample. The above to-be-joined sample first undergoes a precursor curing treatment at 300°C, and then undergoes a precursor pyrolysis treatment at a pyrolysis temperature of 1200°C and a pyrolysis pressure of 1MPa, and finally undergoes a heat treatment at 1500°C to obtain the silicon carbide cladding.

[0056] The thickness of the interlayer of the silicon carbide cladding is about 50µm, and the room temperature joining strength reaches 60MPa, but the shear strength at 1200°C is only 8.27MPa, and the leak-rate is 10 -9< Pa·m 3< / s.

[0057] In summary, compared with Comparative Examples 1-2, Examples 1-5 adopt the combination of the precursor and the glass powder as the brazing filler material to achieve a thicker dense interlayer which has a high joining strength at both room temperature and high temperature of 1200°C and a satisfying leak-rate.

[0058] The above are only embodiments of the present invention and do not limit the scope of the present invention. The scope of the invention is defined by the claims.

Claims

1. A brazing filler material for use in joining of a silicon carbide cladding, characterized in that the brazing filler material comprises the following raw materials: precursor, glass powder and organic solvent; wherein the mass ratio of the precursor to the glass powder is 90-98 : 2-10; wherein the precursor is at least one of polycarbosilane and polysilazane; and wherein the raw material of the glass powder comprises one or more of CA, SARe2O3 and SMRe2O3; wherein in the CA, SARe2O3 and SMRe2O3: C represents CaO; A represents Al2O3; S represents SiO2; M represents MgO; and Re represents Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

2. The brazing filler material according to claim 1, characterized in that the mass ratio in the CA is that CaO : Al2O3 = 45-55 : 55-45; the mass ratio in the SARe2O3 is that SiO2 : Al2O3 : Re2O3 = 30-60 : 15-30 : 25-40; the mass ratio in the SMRe2O3 is that SiO2 : MgO : Re2O3 = 30-60 : 15-30 : 25-40.

3. The brazing filler material according to claim 1, characterized in that the organic solvent is at least one of xylene, toluene, absolute ethanol and acetone.

4. A method for preparing a brazing filler material according to any one of claims 1-3, characterized in that it comprises the following steps: mixing and ball milling the precursor and the glass powder to obtain mixed powder, mixing uniformly the mixed powder and the organic solvent to obtain a slurry which is the brazing filler material.

5. A joining method for a silicon carbide cladding, <b>characterized by comprising the following steps: S1. applying the brazing filler material according to any one of claims 1-3 between a cladding tube and an end plug that match with each other; S2, sequentially performing a precursor curing treatment, a precursor pyrolysis treatment and a heat treatment on the brazing filler material; S3. forming a interlayer by the brazing filler material that has undergone the heat treatment, the interlayer joining the cladding tube and the end plug together.

6. The joining method for a silicon carbide cladding according to claim 5 characterized in that, in step S2, the temperature for the precursor curing treatment is 100°C to 300°C; the temperature for the precursor pyrolysis treatment is 800°C to 1200°C; the temperature for the heat treatment is 1300°C to 1500°C.

7. The joining method for a silicon carbide cladding according to claim 6, characterized in that, in the precursor curing treatment, the temperature is raised to 100°C to 300°C at a heating rate of 2°C / min, and the temperature is maintained for 0.5h to 2h; the precursor curing pressure is 0.01MPa to 1MPa; in the precursor pyrolysis treatment, the temperature is raised to 800°C to 1200°C at a heating rate of 5°C / min to 20°C / min, and the temperature is maintained for 0.5h to 2h; the precursor pyrolysis pressure is 0.01MPa to 1MPa; in the heat treatment, the temperature is raised to 1300°C to 1500°C at a heating rate of 1°C / min to 20°C / min, and the temperature is maintained for 0.5h to 2h.

8. The joining method for a silicon carbide cladding according to any one of claims 5 to 7, characterized in that, in step S3, a thickness of the interlayer is 50µm to 100µm.