A high-density lanthanum-lead intermetallic compound LaPb3 and its preparation method

Abstract

The present invention discloses a high-density lanthanum-lead intermetallic compound LaPb3 and a preparation 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 preparation method of the present invention is as follows: raw materials of metal lead and metal lanthanum are mixed according to a specific molar ratio, suspended smelting is performed under the protection of an inert gas, and the lanthanum-lead intermetallic compound LaPb3 is obtained after sufficient reaction; water-cooled mold casting is adopted for rapid forming to ensure the density of the ingot. The present invention reduces the burning loss caused by the low melting point and volatility of the raw materials of metal lanthanum and metal lead through sufficient reaction of suspended smelting and rapid forming by water-cooled casting, avoids the decomposition of LaPb3 and segregation and agglomeration of lanthanum elements during the casting process, and the density of the prepared lanthanum-lead intermetallic compound LaPb3 ingot is greater than 90%, which meets the performance requirements of nuclear fusion neutron multiplier materials. The preparation method designed by the present invention is simple and is conducive to large-scale industrial production.

Description

Technical Field

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

[0002] The nuclear fusion reaction process is based on the reaction of deuterium (D) and tritium (T) to produce helium (He) and 14.1 MeV neutrons (D+T→He+n). T needs to be continuously supplied during the reaction, but this element cannot be directly obtained in the natural environment. Tritium needs to be produced by neutron irradiation of tritium breeder materials, that is, neutrons react with Li elements to produce T to achieve tritium self-sustaining in fusion reactors. Not all neutrons from fusion reactions can be used for T generation, and some of them are lost due to parasitic absorption of structural materials and non-functional materials. Therefore, neutron multiplication is required to produce additional neutrons to compensate for the lost neutrons.

[0003] At present, the two most widely studied neutron multiplication metal materials in the world are beryllium and lead. Beryllium has a sufficiently high (n, 2n) neutron multiplication reaction rate (threshold is about 1.86 MeV) and a high melting point (1287℃), so it can be used in solid form in the solid blanket of the fusion demonstration reactor (DEMO). However, Be-based multipliers also have many disadvantages, such as limited natural reserves, high cost, and strong toxicity. Compared with Be, lead (n, 2n) neutron multiplication reaction threshold is higher (about 6.76 MeV), but for 14.1MeV fusion neutrons, lead has a higher reaction cross section than Be. At the same time, lead-based materials are widely used as neutron multipliers because of their abundant reserves and low prices. LaPb3 can be used in solid form because of its melting point above 1100℃, making it one of the most promising lead-based solid compounds for solid neutron multipliers. In terms of cost, filling with dense LaPb3 material will greatly reduce the economic cost of the fusion reactor DEMO compared to the solid blanket using solid Be-based neutron multipliers.

[0004] The neutron multiplier of DEMO solid blanket needs to have a high density to meet the performance requirements. It has been reported abroad that LaPb3 materials can be prepared by induction melting and arc melting. Conventional induction melting methods do not react fully in a short period of time, and mechanical stirring is required to promote the reaction of raw materials. Long-term heating will aggravate the volatilization and burning of raw materials. The arc melting method heats to the high temperature zone instantly through plasma discharge. The raw material metal lead has a low melting point. The instantaneous high temperature will cause violent volatilization, and the prepared material has serious segregation and porosity. Therefore, the preparation processes that have been reported cannot produce the bulk material performance requirements required for solid neutron multipliers.

[0005] It is very difficult to prepare high-density intermetallic compound LaPb3 bulk materials, and there are no related reports at home and abroad. This is because the raw materials of lead and lanthanum are volatile. Conventional rare earth alloys or lead-based alloys are generally smelted with similar melting points or trace doping. The content of lanthanum and lead in the LaPb3 system is large, and the melting point difference between the two metal raw materials is huge. Excessive temperature treatment will cause uncontrollable volatilization and burning of the raw materials. Lanthanum metal is prone to agglomeration, and the raw materials need to be fully contacted and fully reacted during the smelting process. The binding energy of lanthanum-lead intermetallic compounds is low, and long-term heat treatment or high-temperature treatment may cause decomposition or volatilization of the material. In short, excessive volatilization and burning, lanthanum agglomeration and decomposition reactions in the reaction process of lanthanum and lead metals will lead to the formation of pores in the casting process, which seriously affects the density of the ingot. It is difficult to prepare a lanthanum-lead intermetallic compound LaPb3 ingot with a density greater than 90%. Summary of the invention

[0006] The purpose of the present invention is to provide a high-density lanthanum-lead intermetallic compound LaPb3 and its preparation process. By designing the full reaction of suspension smelting and rapid molding of water-cooled casting, the volatilization and burning loss of raw metal lead and metal lanthanum are regulated, the segregation and agglomeration behavior of metal lanthanum elements and the high-temperature decomposition of intermetallic compounds are avoided, and a lanthanum-lead intermetallic compound LaPb3 ingot with a density greater than 90% is prepared to meet the functional requirements of solid neutron multipliers. Thereby, an economically feasible large-scale industrial production plan is provided for the research and development of lead-based neutron multipliers. The technical solution adopted by the present invention is:

[0007] A high-density lanthanum-lead intermetallic compound LaPb3 and a preparation method thereof, comprising the following steps:

[0008] (1) Using metallic lead and metallic lanthanum as raw materials;

[0009] (2) Use cold crucible magnetic levitation vacuum melting equipment for suspension melting;

[0010] (3) Water-cooled mold casting to obtain a high-density lanthanum-lead intermetallic compound ingot;

[0011] 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 compensate for the different degrees of 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.

[0012] As one of the preferred embodiments of the present invention, in step (1), the size of the block material is less than 2 cm. Raw materials that are too large cannot be fully stirred in a short time after being melted.

[0013] As one of the preferred embodiments of the present invention, in step (2), a cold crucible magnetic suspension vacuum melting equipment is used for melting, and the melting environment gas is one or more of nitrogen, argon and helium.

[0014] As one of the preferred embodiments of the present invention, in step (2), the temperature is raised and smelted by the high-frequency magnetic field of a cold crucible magnetic suspension vacuum melting device. After reaching the melting point of the raw material (reaching the melting point of lanthanum, 920°C, i.e., both the raw material metal lead and the metal lanthanum are melted), the temperature is continued to be raised to overheat by 50-60°C to reach the melting temperature.

[0015] As one of the preferred embodiments of the present invention, in the step (2), the melting temperature is reached and the mixture is kept warm and stirred continuously for 10-20 minutes using magnetic flux lines.

[0016] As one of the preferred embodiments of the present invention, in step (2), after smelting is completed, heating is stopped and the material is allowed to cool naturally to room temperature in the crucible. The cooled and formed ingot is mechanically reversed to complete the ingot turning. The cumulative number of ingot turnings is greater than or equal to 2 times. For example, when the raw material reaches the melting point, it continues to be heated to 50-60°C, kept warm and stirred continuously for 10-20 minutes using magnetic flux lines, and then the heating is stopped to allow the material to cool naturally in the crucible. The cooled and formed ingot is mechanically reversed to complete an ingot turning. Then continue to repeat the heating treatment until the melting point is overheated by 50-60°C, kept warm and stirred continuously for 10-20 minutes using magnetic flux lines, and then turned over for the second time after cooling. Then repeat the high-frequency magnetic field heating treatment until the melting point is overheated by 50-60°C, kept warm and stirred continuously for 10-20 minutes using magnetic flux lines.

[0017] As one of the preferred embodiments of the present invention, in the step (3), the molten liquid is cast into a mold, and the mold material can be one or more of copper, stainless steel, and graphite.

[0018] As one of the preferred embodiments of the present invention, in step (3), a water-cooled mold is used for casting, and the mold temperature during the casting process is lower than 60°C.

[0019] The present invention reduces the burning loss caused by the low melting point and volatility of the raw materials lanthanum and lead metals through full reaction of suspension smelting and rapid molding by water-cooled casting, avoids the decomposition of LaPb3 and the segregation and agglomeration of lanthanum elements during the casting process, and the density of the prepared lanthanum-lead intermetallic compound LaPb3 ingot is greater than 90%, meeting the performance requirements of nuclear fusion neutron multiplier materials. The preparation method designed by the present invention is simple, and large-scale batch production of high-density lanthanum-lead intermetallic compound LaPb3 can be achieved at a relatively low economic cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the appearance morphology of the high-density lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0021] Figure 2 The XRD pattern of the high-density lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0022] Figure 3 This is a SEM image of the high-density lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0023] Figure 4 This is the EDS elemental analysis diagram of the high-density lanthanum-lead intermetallic compound LaPb3 obtained in Example 1;

[0024] Figure 5 This is the appearance morphology of the sample ingot obtained in Comparative Example 1;

[0025] Figure 6 This is the SEM image of the sample ingot obtained in Comparative Example 1;

[0026] Figure 7 This is the appearance morphology of the sample ingot obtained in Comparative Example 2. DETAILED DESCRIPTION

[0027] 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.

[0028] Example 1

[0029] A preparation process of a high-density lanthanum-lead intermetallic compound LaPb3 is as follows:

[0030] (1) Using metallic lead and metallic lanthanum particles as raw materials; the metallic lead and metallic lanthanum raw materials are mixed in a molar ratio of 3:1.1; and the size of the metallic lead and metallic lanthanum raw materials is less than 2 cm.

[0031] (2) Use cold crucible magnetic levitation vacuum melting equipment for melting. Under the protection of high-purity nitrogen, place the prepared raw materials in the copper crucible of the melting furnace and start heating and melting under the action of high-frequency magnetic field. After the raw materials reach the melting point, continue to heat up by 50°C, keep warm and stir continuously for 15 minutes using magnetic flux lines, then stop heating and let the material cool naturally to room temperature in the crucible. Mechanically reverse the cooled ingot to complete one ingot flipping. Then continue to repeat the heating treatment until the melting point is overheated by 50°C, keep warm and stir continuously for 15 minutes using magnetic flux lines, and then turn the ingot over for the second time after cooling. Then repeat the high-frequency magnetic field heating treatment until the melting point is overheated by 50°C, keep warm and stir continuously for 15 minutes using magnetic flux lines.

[0032] (3) The molten metal after smelting in stage (2) is cast into a mold using a stainless steel water-cooled mold. The mold temperature is maintained below 60°C. After the casting is completed, a LaPb3 ingot is obtained.

[0033] After the above steps, a high-density LaPb3 ingot can be prepared, and its appearance is as follows: Figure 1 shown.

[0034] The obtained LaPb3 ingot was characterized by XRD results. Figure 2 As shown, the characteristic peaks match PDF#65-7232 and the sample has a LaPb3 structure.

[0035] The LaPb3 ingot was subjected to microstructural analysis, and its SEM morphology is as follows: Figure 3 As shown in Figure 1, the surface of the micro-scale sample is dense. The ESD element analysis results of the sample are shown in Figure 1. Figure 4 As shown, the elements lanthanum and lead are evenly distributed without element segregation and agglomeration.

[0036] The density of the LaPb3 ingot was analyzed. The sample density was determined by the water displacement method (using alcohol and water as the medium). The sample volume was converted by the mass product of the liquid displacement. The density of the sample ingot was calculated. The density of the sample was obtained by comparing the theoretical density of the material. The results are shown in Table 1. The density of the materials is greater than 90%.

[0037] Table 1 Determination of density of LaPb3 ingot

[0038] medium Sample mass (dry weight), m, (g) Weight gain of sample in medium, Δm, (g) <![CDATA[Volume of the medium displaced by the sample, v = Δm / ρ, (cm 3 ).]]> <![CDATA[Sample density, ρ = m / v, (g / cm 3 ).]]> <![CDATA[Relative density (theoretical density of LaPb3 is 10.72 g / cm 3 )(%)]]> Alcohol 1.776 0.135 0.171 10.387 96.9 water 0.301 0.030 0.030 10.092 94.1

[0039] Comparative Example 1

[0040] The LaPb3 ingot is prepared by induction melting. The preparation process of the LaPb3 ingot is as follows:

[0041] Using lead and lanthanum as raw materials, the surface of the raw materials is cleaned, and the surface of the tooling is purified. A vacuum induction melting furnace is used for production, and the smelting is performed at a vacuum degree below 10Pa. After the lead liquid is heated to 950°C, the lanthanum metal begins to melt. After it is completely melted at 1250°C, it is left to stand for 10 minutes, and the temperature is repeated 3 times. The liquid stirring is strengthened to ensure the alloying of the liquid. After the alloy temperature rises to 1350°C, it is kept still and cast into the mold. After solidification and cooling for 3 hours, it is taken out of the furnace and demolded.

[0042] After the above steps, LaPb3 ingots can be prepared, and the appearance is as follows Figure 5 As shown in Figure 2, the surface of the ingot is uneven, and there are many pits and holes.

[0043] The LaPb3 ingot was subjected to microstructural analysis, and its SEM morphology is as follows: Figure 6 As shown, there is obvious element segregation on the surface of the microscopic sample, and there is an obvious porous structure in the lanthanum agglomeration area.

[0044] The density of the LaPb3 ingot was analyzed. The sample density was determined by the water displacement method (using alcohol and water as the medium). The sample volume was converted by the mass product of the liquid displacement. The density of the sample ingot was calculated. The theoretical density of the material was compared to obtain the density of the sample. The results are shown in Table 2. The density of the materials is less than 90%.

[0045] The experiment proves that induction heating melting and conventional mold casting cannot produce high-density LaPb3 ingots. This is because the method cannot quickly achieve a sufficient reaction between the raw metal lanthanum and metal lead, as well as the possible decomposition reaction of LaPb3 during the slow cooling process. The escape of these atmospheres and element segregation will cause obvious pore structures in the ingot, resulting in a low density of the ingot, which cannot meet the performance requirements of the neutron multiplier.

[0046] Table 2 Density determination of LaPb3 ingots prepared by induction melting

[0047] medium Sample mass (dry weight), m, (g) Weight gain of sample in medium, Δm, (g) <![CDATA[Volume of medium displaced by the sample, v = Δm / ρ, (cm 3 ).]]> <![CDATA[Sample density, ρ = m / v, (g / cm 3 ).]]> <![CDATA[Apparent density (theoretical density of LaPb3 is 10.72 g / cm 3 )(%)]]> water 5.511 0.607 0.607 9.079 84 Alcohol 7.125 0.617 0.782 9.114 85

[0048] Comparative Example 2

[0049] LaPb3 ingots are prepared by arc melting. The preparation process is as follows:

[0050] Lead and lanthanum are used as raw materials and mixed in a ball mill under inert gas protection. A vacuum arc melting furnace is used for preparation, and the vacuum degree is maintained below 10 Pa. The raw materials are melted at high temperature in the form of plasma arc discharge, and then cooled and demolded.

[0051] After the above steps, LaPb3 ingots can be prepared, and the appearance is as follows Figure 7 As shown in the figure, the surface of the ingot is uneven and there is serious raw material segregation. This is because the low-melting-point metal lead undergoes violent volatilization and burning at the instantaneous high temperature of arc melting.

[0052] The experiment proved that the arc melting method cannot produce high-density LaPb3 ingots. This is because the raw material metal lead has a low melting point, and the instantaneous high temperature will cause severe volatilization and burning of the raw material, resulting in serious element segregation in the sample and poor density, which does not meet the performance requirements of the neutron multiplier.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-density lanthanum-lead intermetallic compound LaPb3, characterized in that: The following steps are involved: (1) Using metallic lead and metallic lanthanum as raw materials; the metallic lead and metallic lanthanum are in a molar ratio of 3:1.05-1.15; (2) Use cold crucible magnetic levitation vacuum melting equipment for suspension melting; heat up and melt through the high-frequency magnetic field of the cold crucible magnetic levitation vacuum melting equipment. After reaching the melting point of the raw material, continue to heat up by 50-60°C to reach the melting temperature. Keep warm and use magnetic lines of induction to stir continuously for 10-20 minutes. After melting is completed, stop heating and let the material cool naturally to room temperature in the crucible. Mechanically reverse the cooled ingot to complete the ingot turning; (3) Water-cooled mold casting to obtain a high-density lanthanum-lead intermetallic compound LaPb3 ingot; the mold temperature during the water-cooled mold casting process is lower than 60°C.

2. The method for preparing the high-density lanthanum-lead intermetallic compound LaPb3 according to claim 1, characterized in that: In step (1), the metal lead and the metal lanthanum are both metal blocks with a size less than 2 cm.

3. The method for preparing the high-density lanthanum-lead intermetallic compound LaPb3 according to claim 1, characterized in that: In step (2), the ambient gas for suspension smelting is one or more of high-purity nitrogen, argon, and helium.

4. The method for preparing the high-density lanthanum-lead intermetallic compound LaPb3 according to claim 1, characterized in that: The cumulative number of ingot turning is greater than or equal to 2 times.

5. The method for preparing the high-density lanthanum-lead intermetallic compound LaPb3 according to claim 1, characterized in that: In step (3), the molten metal is cast into a mold, and the mold material is one or more of copper, stainless steel, and graphite.

6. A high-density lanthanum-lead intermetallic compound LaPb3 ingot, characterized in that: The preparation method is used as described in any one of claims 1 to 5.

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