A high melting point lanthanum-lead intermetallic compound LaPb3 and its synthesis method

Abstract

The present invention discloses a high melting point lanthanum-lead intermetallic compound LaPb3 and a synthesis method thereof. The present invention belongs to the technical field of new materials, and specifically relates to the technical field of nuclear fusion neutron multiplier materials. The synthesis method thereof comprises the steps of: pulverizing and mixing lead and lanthanum by ball milling in an inert gas environment; vacuum sealing the tube after mixing; and then sintering at 500-700°C to obtain the final product. The present invention prepares the lanthanum-lead intermetallic compound LaPb3 for the first time by a solid phase reaction method, and avoids the problem of volatile burning loss of metal lead and metal lanthanum raw materials by regulating the proportion of raw materials and vacuum sealing sintering, and controls the sintering parameters to achieve full reaction of raw materials in a temperature range below the melting point. The present invention synthesizes the lead-based intermetallic compound LaPb3 with a melting point exceeding 1100°C for the first time, meets the performance requirements of a high melting point solid neutron multiplier, and can be applied to fields such as fusion reactors. The application range of lead-based materials is expanded, the process is simple and feasible, and has significant economic and application value.

Description

Technical Field

[0001] The invention belongs to the technical field of new materials, in particular to the technical field of nuclear fusion neutron multiplier materials, and specifically to a high melting point lanthanum-lead intermetallic compound LaPb3 and a synthesis method thereof. Background Art

[0002] In the framework of the development of the breeder blanket for the future fusion demonstration reactor (DEMO), the blanket design needs to meet the tritium breeding capability. Due to the natural loss of neutrons in the blanket structure, neutron multipliers are needed to produce additional neutrons to compensate for this effect, otherwise the tritium breeding will always be lower than the design requirements. International research has identified two metals with the most suitable physical properties for use as neutron multipliers in breeder blankets: beryllium and lead.

[0003] In the typical DEMO blanket neutron spectrum, beryllium has the lowest (n, g) and sufficiently high (n, 2n) reaction rates (threshold is about 1.85 MeV). However, due to its limited natural reserves, its cost is quite high and its toxicity is strong. In order to reduce costs, researchers are studying alternative neutron multiplier solutions based on lead. However, lead has a low melting point (327°C) and is mostly used in liquid form. However, there is a risk of liquid metal corrosion and liquid metal solidification. The most promising solution is to form intermetallic compounds with lead metal and rare earth elements to increase the melting point of lead-based materials so that they can be filled and used in solid form. The LaPb3 system material with the highest lead content in the lanthanum-lead system can increase the melting point, avoid the use of liquid lead loops, and reduce corrosion problems. In terms of cost, rare earth lanthanum is widely used in the manufacture of material composites and catalysts, and its use cost is much lower than that of beryllium-based materials. Compared with the proliferation layer using solid beryllium-based neutron multipliers, the proliferation layer filled with LaPb3 blocks will greatly reduce the investment in DEMO, thus realizing a compact and economical DEMO design.

[0004] One of the key factors to be considered in solid neutron multipliers is the melting point of the neutron multiplier material. High melting point multiplier materials can better ensure the reliability and safety of the material during use. Therefore, for lead-based materials, achieving high melting point lead-based metal compounds is the key to realizing its nuclear fusion scientific application. There are few reports on the synthesis of LaPb3 materials at home and abroad, because the synthesis of this material is difficult. The raw materials, lead metal and lanthanum metal, both have different degrees of volatilization and burning loss at high temperatures, and the melting points of lead metal and lanthanum metal are quite different. The difference in volatilization and burning loss between the raw materials during the sintering process is huge, which seriously affects the chemical reaction process and product composition. At the same time, lanthanum metal is active and easy to oxidize or agglomerate. During the sintering process, the oxide residues and lanthanum metal agglomeration will hinder the chemical reaction between lanthanum metal and lead metal, resulting in incomplete reaction and too many impurities remaining. In addition, LaPb3 has a low formation energy, and heat treatment at too high a temperature will cause material decomposition and raw material volatilization. The low melting point metal lead and the poorly stable lanthanum metal residues do not meet the application requirements of the high melting point intermetallic compound LaPb3 as a neutron multiplier. A combination of factors make the synthesis of LaPb3 difficult, and precise control of the reaction process is required to obtain high-melting-point LaPb3 that meets the application requirements of neutron multipliers. Summary of the invention

[0005] The purpose of the present invention is to provide a high melting point lanthanum lead intermetallic compound LaPb3 and a synthesis method thereof, by precisely controlling the raw material ratio, using vacuum packaging and sintering below the melting point of LaPb3, optimizing the volatilization burning loss and oxidation problems, achieving full reaction of the raw materials, and preparing a high melting point lanthanum lead intermetallic compound LaPb3 material. The melting point of the lanthanum lead intermetallic compound exceeds 1100°C, and it can be applied to the field of fusion reactor research to meet the special performance requirements of solid blanket neutron multipliers. Specifically, the present invention adopts the following technical solutions:

[0006] First, the present invention provides a method for synthesizing a high melting point lanthanum-lead intermetallic compound LaPb3, characterized in that it comprises the following steps:

[0007] (1) Using metal powders of lead and lanthanum as raw materials, ball milling and mixing is performed under an inert gas environment;

[0008] (2) vacuum sealing the raw materials in step (1) to control burning and oxidation reactions of the raw materials;

[0009] (3) The step (2) is subjected to high temperature sintering to obtain a final product.

[0010] As one of the preferred embodiments of the present invention, in the step (1), the raw materials of lead and lanthanum are mixed in a molar ratio of 3:1.05-1.15, preferably 3:1.1. Micro-control of the raw material ratio can comprehensively compensate for the volatilization and burning loss of the raw materials of lead and lanthanum during the sintering process. Both the raw materials of lanthanum and lead are easy to volatilize, and there is volatilization and burning loss during the high-temperature sintering process. The burning loss of lanthanum is more serious. Therefore, it is necessary to adjust the raw materials to excessive lanthanum to achieve full reaction to obtain the pure phase of the intermetallic compound LaPb3. Excessive Pb content in the raw material will lead to the presence of residual metal Pb in the product. The low melting point of metal Pb will seriously affect the application needs of the neutron multiplier scenario of the intermetallic compound LaPb3. Excessive La content will lead to the presence of residual metal La in the product. The melting point of metal La is lower than 1110°C and it is unstable in the air. It will react rapidly with water and oxygen, resulting in hydrolysis and deterioration of the compound, which seriously affects the stability of the intermetallic compound LaPb3 and its application function.

[0011] As one of the preferred embodiments of the present invention, in the step (1), the mixing is carried out by ball milling, the rotation speed is 100 to 200 revolutions per minute, and the cumulative operation time is more than 12 hours, so as to ensure that the raw material size is less than 10 microns and the mixing is uniform. The raw materials are refined by ball milling to ensure that the raw material size is less than 10 microns and the mixing is uniform, so as to achieve full reaction during the high-temperature sintering process. If the rotation speed is too low during the ball milling mixing process, the ball milling mixing efficiency is low. If the rotation speed is too high, the raw material temperature will be too high and agglomeration will occur, which is not conducive to the full mixing of the raw materials.

[0012] As one of the preferred embodiments of the present invention, in step (1), the operating environment is an inert gas environment, which is one or more of high-purity nitrogen, argon, and helium.

[0013] As one of the preferred embodiments of the present invention, in the step (2), the mixed raw materials are loaded into a crucible for vacuum packaging in a glass tube. The crucible is made of one of tantalum, tungsten and graphene, and the vacuum degree of the tube sealing treatment is maintained below 10Pa. During the sintering process, the vacuum degree needs to be guaranteed to be below 10Pa to ensure that the oxygen content is low, and the metal lanthanum and metal lead will not be oxidized during the high-temperature reaction. The comparative example proves that other treatment methods such as inert gas purge gas cannot eliminate the oxidation problem. A sufficient vacuum chamber is required during the chemical reaction of metal lanthanum and metal lead, otherwise La will agglomerate during the high-temperature sintering process, which is not conducive to the full reaction of the raw materials. Therefore, the volume of the raw materials needs to be guaranteed to be less than 1 / 10 of the volume of the vacuum sealing tube.

[0014] As one of the preferred embodiments of the present invention, in the step (3), the temperature is raised from room temperature to the sintering temperature zone at a heating rate of 5°C-15°C per minute, the sintering temperature is in the range of 500-700°C for more than 12 hours, and then dropped to room temperature at a rate of 5°C-15°C per minute. Since the melting point of metal lead is relatively low (about 327°C, volatile and oxidizable at high temperature) and the melting point of metal lanthanum (melting point is about 920°C, volatile and oxidizable at high temperature), the difference between the two melting points is relatively large, and the sintering process will seriously affect the burning problem of the raw materials, so it is necessary to restrict the sintering process. The heating and cooling treatment is carried out at a rate of 5°C-15°C per minute. If the heating rate is too slow, the volatilization and burning of the raw materials will be aggravated, and if the cooling rate is too slow, the decomposition of the compounds will be aggravated. The sintering temperature is in the range of 500-700°C, and the synthesis of LaPb3 is achieved at a temperature lower than the melting point of lanthanum and LaPb3. If the temperature is too low, the reaction process will be slow, and the heat treatment at too high a temperature will aggravate the volatilization of the raw materials and cause the decomposition of the intermetallic compounds.

[0015] As a better preferred embodiment of the present invention, the method for synthesizing the high melting point lead-based intermetallic compound LaPb3 of the present invention may include the following steps:

[0016] (1) using metal powders of lead and lanthanum in a molar ratio of 3:1.1 as raw materials, ball milling and mixing them uniformly in an inert gas environment at a ball milling speed of 150-160 revolutions per minute;

[0017] (2) placing the raw materials mixed in step (1) into a glass tube and sealing the tube at a vacuum degree of less than 10 Pa, wherein the volume of the raw materials accounts for less than 1 / 10 of the volume of the vacuum sealed tube;

[0018] (3) subjecting the raw material after vacuum sealing in step (2) to high-temperature sintering, heating the temperature from room temperature to a sintering temperature zone at a heating rate of 5°C-15°C per minute, maintaining the sintering temperature at 500-700°C for 12-20 hours, and then cooling the temperature to room temperature at a rate of 5°C-15°C per minute to obtain a final product.

[0019] Secondly, the present invention prepares a pure phase high melting point lanthanum-lead intermetallic compound LaPb3 by a vacuum solid phase sintering method. The melting point of this material is greater than 1100°C, which meets the application scenario requirements of solid neutron multiplier in fusion reactors.

[0020] The present invention uses a solid phase reaction method to prepare the lanthanum-lead intermetallic compound LaPb3 for the first time. The problem of volatile burning of metal lead and metal lanthanum raw materials is avoided by adjusting the raw material ratio and vacuum sealing tube sintering, and the sintering parameters are controlled in a temperature range below the melting point to achieve full reaction of the raw materials. The present invention synthesizes the lead-based intermetallic compound LaPb3 with a melting point exceeding 1100°C for the first time, which meets the performance requirements of a high melting point solid neutron multiplier and can be applied to technical fields such as fusion reactors. Moreover, the method has a simple process, low economic cost, is suitable for mass production, and has significant economic and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a photo of the appearance of the high melting point lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0022] Figure 2 This is a schematic diagram of XRD of the high melting point lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0023] Figure 3 This is a graph showing the melting point test results of the high melting point lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0024] Figure 4 This is a photo of the appearance of the sample obtained in Comparative Example 1;

[0025] Figure 5 Schematic diagram of XRD of the sample obtained in Comparative Example 1;

[0026] Figure 6 This is a photo of the appearance of the sample obtained in Comparative Example 2;

[0027] Figure 7 Schematic diagram of XRD of the sample obtained in Comparative Example 2;

[0028] Figure 8 This is a photo of the appearance of the sample obtained in Comparative Example 3;

[0029] Fig. 9 This is a photo of the appearance of the sample obtained in Comparative Example 4;

[0030] Fig.10 This is a schematic diagram of the XRD pattern of the sample obtained in Comparative Example 4. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with specific implementation examples so that those skilled in the art can better understand the present invention. However, the protection scope of the present invention is not limited to the following embodiments, and the scope of rights of the present invention shall be subject to the scope of the claims.

[0032] Example 1

[0033] The preparation process of a high melting point lanthanum-lead intermetallic compound LaPb3 is as follows:

[0034] (1) Use lead and lanthanum as raw materials in a molar ratio of 3:1.1, and mix them by ball milling in a high-purity nitrogen environment for more than 12 hours to ensure uniform mixing. The ball milling speed is 150-160 revolutions per minute. If the speed is too low during the ball milling mixing process, the ball milling mixing efficiency is low. If the speed is too high, the raw material temperature will be too high and agglomeration will occur, which is not conducive to the full mixing of the raw materials.

[0035] (2) The mixed raw materials are placed in a glass tube and sealed at a vacuum degree of 5Pa. The vacuum degree needs to be kept below 10Pa to ensure that the oxygen content is low and that metal lanthanum and metal lead will not be oxidized during the high-temperature reaction. The volume of the raw materials accounts for 1 / 10 of the volume of the vacuum sealed tube. A sufficient vacuum chamber is required during the synthesis of lanthanum-based compounds to avoid La agglomeration, which is not conducive to the full reaction of the raw materials. Therefore, the volume of the raw materials needs to be kept below 1 / 10 of the volume of the vacuum sealed tube.

[0036] (3) The encapsulated raw materials are sintered in a muffle furnace, and the temperature is raised from room temperature to the sintering temperature zone at a heating rate of 10°C per minute. The sintering temperature is maintained in the range of 600°C for 15 hours, and then dropped to room temperature at a rate of 10°C per minute. If the heating rate is too slow, the volatilization and burning of the raw materials will be aggravated, and if the cooling rate is too slow, the decomposition of the compounds will be aggravated. The sintering temperature is in the range of 500-700°C, and the synthesis of LaPb3 is achieved at a temperature below the melting point. If the temperature is too low, the reaction process is slow and cannot be fully reacted. If the temperature is too high, the heat treatment will aggravate the volatilization of the raw materials and cause the decomposition of intermetallic compounds.

[0037] Through the above steps, a high melting point lead-based intermetallic compound LaPb3 can be prepared, and its appearance is as follows Figure 1 shown.

[0038] The obtained LaPb3 sample was characterized by X-ray diffractometer. The XRD results are as follows: Figure 2 As shown, the characteristic peaks match PDF#65-7232 and the sample has a LaPb3 structure.

[0039] The melting point of the LaPb3 sample was tested by differential scanning calorimetry (DSC) under nitrogen atmosphere protection. The results are as follows: Figure 3 As shown, the heat flow corresponding to the thermogravimetric change area suddenly changes to the reaction heat related to the melting point, and the melting point temperature is 1162.25℃.

[0040] Comparative Example 1

[0041] Different from Example 1, in this case, step 1) the raw material mixing is not performed under the protection of inert gas, and the preparation process is as follows:

[0042] (1) Using lead and lanthanum as raw materials, the mixture is mixed in a molar ratio of 3:1.1 and ball milling is used to mix the raw materials for more than 12 hours to ensure uniform mixing.

[0043] (2) The mixed raw materials are placed in a glass tube and sealed at a vacuum degree of 5 Pa. The volume of the raw materials accounts for 1 / 10 of the volume of the vacuum sealed tube.

[0044] (3) The vacuum-encapsulated raw materials were sintered at 600°C, the annealing heating and cooling rate was 10°C per minute, and the sintering time was 12 hours.

[0045] The appearance of the sample obtained after the above steps is as follows Figure 4 shown.

[0046] The obtained samples were characterized by XRD results. Figure 5 As shown, the characteristic peaks match those of PDF#65-2873 and PDF#058-0602, and the main components of the sample are lead and lanthanum oxide.

[0047] This is because the raw material lanthanum metal is easily oxidized and will gradually oxidize into lanthanum oxide in the air environment. Its oxidation product will seriously affect the chemical reaction between lanthanum metal and lead metal. Therefore, the final product is lead metal and lanthanum oxide, rather than lanthanum-lead intermetallic compound LaPb3, which does not meet the application requirements of neutron multiplier materials.

[0048] Comparative Example 2

[0049] The lanthanum-lead intermetallic compound is LaPb3. Different from Example 1, the sintering reaction in this case is carried out under the protection of nitrogen purge gas rather than vacuum packaging conditions.

[0050] The preparation process is as follows:

[0051] (1) Using lead metal and lanthanum metal as raw materials, the mixture is mixed in a molar ratio of 3:1.1 and ball milled in a high-purity nitrogen environment for more than 12 hours to ensure uniform mixing.

[0052] (2) The mixed raw materials were placed in a tubular furnace and continuously purged with nitrogen. The mixture was sintered at 600°C for 12 hours. The annealing heating and cooling rate was 10°C per minute.

[0053] The appearance of the sample obtained after the above steps is as follows Figure 6 shown.

[0054] The obtained samples were characterized by XRD results. Figure 7As shown, the characteristic peaks match those of PDF#65-2873 and PDF#05-0602, and the sample is mainly composed of lead and lanthanum oxide, as well as weak LaPb3 (PDF#65-7232).

[0055] This is because the raw material lanthanum metal is very easy to oxidize, and its oxidation products will seriously affect the chemical reaction between lanthanum metal and lead metal. The metal raw material volatilizes and burns under heating, making the chemical reaction incomplete. Therefore, the final product is mainly lead metal and lanthanum oxide, as well as a trace amount of intermetallic compound LaPb3. This method cannot solve the oxidation problem of lanthanum metal. The prepared product has more impurities and the melting point of lead metal is low, which does not meet the application requirements of neutron multiplier materials.

[0056] Comparative Example 3

[0057] The lanthanum-lead intermetallic compound is LaPb3. Different from Example 1, the sintering reaction in this case is directly carried out in an air environment. The preparation process is as follows:

[0058] (1) Using lead metal and lanthanum metal as raw materials, the mixture is mixed in a molar ratio of 3:1.1 and ball milled in a high-purity nitrogen environment for more than 12 hours to ensure uniform mixing.

[0059] (2) The mixed raw materials are placed in a muffle furnace and sintered at 600°C for 12 hours in an air environment. The annealing heating and cooling rate is 10°C per minute.

[0060] The appearance of the sample obtained after the above steps is as follows Figure 8 As shown in the figure, the sample is a mixture of oxides of various colors, rather than pure LaPb3. This is because the volatilization and oxidation process of low-melting-point metal lead is very intense during high-temperature sintering in air, which hinders the chemical reaction between the raw materials lead and lanthanum, and is not suitable for the preparation of intermetallic compound LaPb3.

[0061] Comparative Example 4

[0062] The lanthanum-lead intermetallic compound is LaPb3, and the difference from Example 1 is that the ratio of raw materials in this case is different. The preparation process is:

[0063] (1) Using lead metal and lanthanum metal as raw materials, the mixture is mixed in a molar ratio of 3:1 and ball milled in a high-purity nitrogen environment for more than 12 hours to ensure uniform mixing.

[0064] (2) The mixed raw materials are placed in a glass tube and sealed at a vacuum degree of 5 Pa. The volume of the raw materials accounts for 1 / 10 of the volume of the vacuum sealed tube.

[0065] (3) The vacuum-encapsulated raw material is sintered at 600°C, the annealing heating and cooling rate is 10°C per minute, and the sintering time is 12 hours.

[0066] The appearance of the sample obtained after the above steps is as follows Fig. 9 shown.

[0067] The obtained samples were characterized by XRD results. Fig.10 As shown, the characteristic peaks match those of PDF#65-1873 and PDF#65-7232, and the main components of the sample are lead and intermetallic compound LaPb3.

[0068] This is because the raw material lanthanum metal is volatile, and the burnout during high-temperature sintering is more serious than that of metal lead. If the raw material compensation is not performed, the original chemical reaction process will be affected, so there is a large amount of metal lead in the final product. This case proves that if the raw material composition is not regulated during the synthesis of lanthanum-lead intermetallic compounds, pure phase LaPb3 cannot be obtained. The product prepared by this method has more impurities and the melting point of metal lead is low, which does not meet the application requirements of neutron multiplier materials.

Claims

1. A method for synthesizing a high melting point lead-based intermetallic compound LaPb3, characterized in that: The following steps are involved: (1) using metal powders of lead and lanthanum as raw materials and subjecting them to ball milling and mixing under an inert gas environment; the lead and lanthanum are in a molar ratio of 3:1.05-1.15; (2) vacuum sealing the raw materials mixed in step (1); (3) high-temperature sintering the raw materials after vacuum sealing in step (2) to obtain a final product; specifically, the vacuum-sealed raw materials are subjected to high-temperature sintering, the temperature is raised from room temperature to a sintering temperature zone at a heating rate of 5°C-15°C per minute, the sintering temperature is within a range of 500-700°C for more than 12 hours, and then the temperature is reduced to room temperature at a rate of 5°C-15°C per minute.

2. The method for synthesizing the high melting point lead-based intermetallic compound LaPb3 according to claim 1, characterized in that: In step (1), the inert gas is one or more of high-purity nitrogen, argon, and helium.

3. The method for synthesizing the high melting point lead-based intermetallic compound LaPb3 according to claim 1, characterized in that: In step (1), the ball mill rotates at a speed of 100 to 200 revolutions per minute, and operates for a cumulative period of more than 12 hours to ensure uniform mixing.

4. The method for synthesizing the high melting point lead-based intermetallic compound LaPb3 according to claim 1, characterized in that: In step (2), the mixed raw materials are placed in a glass tube and sealed at a vacuum degree of less than 10 Pa.

5. The method for synthesizing the high melting point lead-based intermetallic compound LaPb3 according to claim 1, characterized in that: In step (2), the volume of the raw material is less than 1 / 10 of the volume of the vacuum sealed tube.

6. The method for synthesizing the high melting point lead-based intermetallic compound LaPb3 according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) using metal powders of lead and lanthanum in a molar ratio of 3:1.1 as raw materials, ball milling and mixing them uniformly in an inert gas environment at a ball milling speed of 150-160 revolutions per minute; (2) placing the raw materials mixed in step (1) into a glass tube and sealing the tube at a vacuum degree of less than 10 Pa, wherein the volume of the raw materials accounts for less than 1 / 10 of the volume of the vacuum sealed tube; (3) subjecting the raw material after vacuum sealing in step (2) to high-temperature sintering, heating the temperature from room temperature to a sintering temperature zone at a heating rate of 5°C-15°C per minute, maintaining the sintering temperature at 500-700°C for 12-20 hours, and then cooling the temperature to room temperature at a rate of 5°C-15°C per minute to obtain a final product.

7. A high melting point lead-based intermetallic compound LaPb3, characterized in that: It is prepared by the synthesis method described in any one of claims 1 to 6.

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