A method for preparing high-purity terbium-iron alloy

Abstract

This invention discloses a method for preparing high-purity terbium-iron alloy, utilizing ferric fluoride as a chemical decalcification agent in the refining stage. Compared with existing technologies that rely solely on high-temperature volatilization and physical adsorption for calcium removal, this method provides a clear chemical driving force, converting calcium dissolved in the alloy melt into an insoluble calcium fluoride slag phase through a displacement reaction, thereby achieving efficient calcium removal. This invention can reduce the calcium content in terbium-iron alloy from 0.011-0.015% in traditional processes to 0.002-0.004%, a reduction of 70-85%. This method requires no special equipment; only the addition of ferric fluoride in the refining stage is needed, resulting in low process modification costs and good industrial applicability.

Description

Technical Field

[0001] This invention belongs to the field of alloy material manufacturing technology, specifically relating to a method for preparing high-purity terbium-iron alloy. Background Technology

[0002] Terbium-iron alloys are crucial foundational materials in the field of rare-earth functional materials, widely used in high-tech areas such as giant magnetostrictive materials, magneto-optical storage materials, and permanent magnet materials. Terbium-iron-based giant magnetostrictive materials possess excellent magnetostrictive properties, making them irreplaceable in applications such as precision actuators, sonar transducers, and micro-displacement controllers. With the increasing demands for material performance in the high-end equipment manufacturing industry, more stringent requirements have been placed on the purity of terbium-iron alloys. The presence of impurities in the alloy, especially calcium and oxygen, significantly affects the magnetic, mechanical properties, and service life of the material. Therefore, improving the purity of terbium-iron alloys has significant technical and economic value.

[0003] Currently, the mainstream industrial method for preparing terbium-iron alloys is the calcium thermal reduction method, which uses terbium fluoride as a raw material and metallic calcium as a reducing agent to produce terbium-iron alloys through a reduction reaction at high temperatures. This method has advantages such as mature technology, low cost, and suitability for large-scale production. However, the inherent technical characteristics of the calcium thermal reduction method inevitably result in the presence of residual calcium impurities in the product. To ensure the completeness of the reduction reaction, industrial production typically uses an excess of about 25% metallic calcium, which remains in the alloy melt after the reaction. Although subsequent refining processes can remove some of the residual calcium, the complex thermodynamic behavior of calcium in rare earth alloy melts, coupled with the limited volatilization rate of calcium at refining temperatures despite its high vapor pressure, and the lack of effective chemical driving forces to separate calcium from the melt during refining, makes it difficult to further reduce the calcium content in the final product, typically maintaining a level above 0.01%. This technical bottleneck restricts the further improvement of the purity of terbium-iron alloys and limits their widespread use in high-end applications.

[0004] Therefore, there is a need for a preparation process that can effectively remove residual calcium during the refining stage and significantly reduce the calcium content in terbium-iron alloys. Summary of the Invention

[0005] The existing calcium thermal reduction process for terbium-iron alloy preparation includes: uniformly mixing terbium fluoride powder, iron powder, metallic calcium granules, and sodium chloride powder, and placing the mixture in a tungsten crucible; evacuating the furnace under vacuum and then purging it with argon gas for protection; heating to 1350-1400℃ and holding for 30 minutes to carry out the reduction reaction; separating the slag and refining at 1500-1550℃ for 25-30 minutes; and finally casting to obtain the terbium-iron alloy. In this process, the amount of metallic calcium added is 1.25 times the theoretically calculated amount to ensure complete reduction. The existing refining stage mainly relies on the high-temperature volatilization of calcium and slag adsorption to remove residual calcium, lacking active chemical calcium removal methods, resulting in limited calcium removal efficiency.

[0006] Based on the above scheme, the improvement of this scheme is as follows: In the refining stage, iron fluoride powder is added to the alloy melt as a calcium removal agent. The substitution reaction between iron fluoride and residual calcium generates calcium fluoride and metallic iron. The calcium fluoride floats into the slag phase and is removed, while the metallic iron directly melts into the alloy matrix to become an alloy component, thereby achieving efficient calcium removal without introducing any foreign impurity elements.

[0007] To achieve the above and other related objectives, this invention provides a method for preparing high-purity terbium-iron alloy, specifically comprising the following steps:

[0008] Ingredients: Weigh out terbium fluoride powder, iron powder, metallic calcium granules and sodium chloride powder according to the formula. The amount of metallic calcium is 1.20-1.50 times the theoretically calculated amount of reduced terbium fluoride.

[0009] Mixing: Place terbium fluoride powder, iron powder, metallic calcium granules and sodium chloride powder in a mixer and mix evenly to obtain a mixture;

[0010] Thermal reduction reaction: The mixture is transferred to a reaction vessel, vacuumed, filled with high-purity argon, heated to 1350-1400℃ and held to complete the reduction reaction; during the reduction reaction, terbium fluoride reacts with metallic calcium to produce metallic terbium and calcium fluoride, metallic terbium fuses with iron powder to form terbium-iron alloy melt, and calcium fluoride reacts with sodium chloride to form mixed slag that floats on the surface of the melt;

[0011] First slag separation: After the reduction reaction is completed, solid-liquid separation is performed to remove the calcium fluoride-sodium chloride mixed slag on the surface and obtain the primary alloy melt; at this time, the primary alloy melt contains excess unreacted metallic calcium.

[0012] Calcium removal in ferric fluoride refining: The furnace is re-evacuated to below 1 Pa, then filled with high-purity argon. The primary alloy melt is heated to 1480-1560℃. Ferric fluoride powder is added to the surface of the melt in batches, with stirring and maintaining the temperature after each batch to ensure full contact and reaction with the melt. The ferric fluoride undergoes a displacement reaction with the residual calcium in the melt, producing calcium fluoride and metallic iron. The reaction formula is: The generated calcium fluoride has a low density and floats to the surface of the melt to form a slag layer; the generated metallic iron melts directly into the alloy matrix. The total amount of iron fluoride added is 0.5-2.0% of the mass of the alloy melt.

[0013] Secondary slag separation: After the calcium removal process of ferrofluoride refining is completed, the calcium fluoride slag layer on the surface of the melt is removed to obtain the refined alloy melt.

[0014] Casting: The refined alloy melt is poured into a preheated mold and cooled to obtain a high-purity terbium-iron alloy ingot.

[0015] Furthermore, in the thermal reduction step, the reactor is a tungsten crucible. Specifically, the mixture is transferred to the tungsten crucible, and the tungsten crucible is placed in the induction coil of the vacuum induction melting furnace.

[0016] Furthermore, in the thermal reduction step, high-purity argon gas is introduced to 0.03-0.08 MPa, and the heating and holding time is 25-35 minutes.

[0017] Furthermore, during the calcium removal process of ferric fluoride refining, the furnace body is re-vacuumed to below 1 Pa.

[0018] Furthermore, in the calcium removal step of ferric fluoride refining, the furnace body is evacuated to below 1 Pa and then filled with high-purity argon gas to 0.03-0.08 MPa.

[0019] Furthermore, a stabilization and refining step can be added to the secondary slag separation and casting process, namely, stabilization and refining after removing the calcium fluoride slag layer. This step further homogenizes the alloy composition and removes any trace impurities that may be present through vacuum volatilization.

[0020] Furthermore, the stabilization and refining step specifically involves holding the temperature at 1500-1550℃.

[0021] Furthermore, the heat preservation time is 10-20 minutes.

[0022] The present invention also provides a high-purity terbium-iron alloy, which is prepared by the method described above.

[0023] Furthermore, the calcium content in the high-purity terbium-iron alloy is less than 0.004%.

[0024] From a thermodynamic perspective, at refining temperatures (1480-1560℃), the affinity of calcium for fluorine is much stronger than that of iron for fluorine. The free energy of formation of calcium fluoride is significantly lower than that of iron fluoride, therefore the reaction... It has a strong thermodynamic driving force, and the reaction tends to proceed to completion.

[0025] From a thermodynamic perspective, at refining temperatures (1480-1560℃), the affinity of calcium for fluorine is much stronger than that of iron for fluorine. The free energy of formation of calcium fluoride is significantly lower than that of iron fluoride, therefore the reaction... It has a strong thermodynamic driving force, and the reaction tends to proceed to completion.

[0026] From a kinetic perspective, in the molten state, ferric fluoride powder rapidly melts and disperses upon addition to the melt, reacting with dissolved calcium atoms. By adding the powder in batches and maintaining a constant temperature with stirring, the reaction can be ensured to proceed fully. The resulting calcium fluoride, due to its significantly lower density (approximately 3.18 g / cm³) compared to the terbium-iron alloy melt (approximately 8.5-9.0 g / cm³), spontaneously rises to form a slag layer, which is easily separated and removed.

[0027] From the perspective of impurity control, the outstanding advantage of this scheme lies in the cleanliness of the reaction products. The metallic iron generated by the displacement reaction is itself one of the matrix components of the terbium-iron alloy, and its direct melting into the alloy will not introduce any foreign impurity elements. Compared with traditional vacuum volatilization for calcium removal or slag refining methods, this scheme has significant advantages in calcium removal efficiency and impurity control. Furthermore, since the reaction is carried out under an inert atmosphere or vacuum conditions, no gaseous products are generated, avoiding the risk of introducing harmful gaseous impurities such as nitrogen and hydrogen.

[0028] From the perspective of process controllability, the amount of ferric fluoride added can be precisely calculated and adjusted based on the calcium excess coefficient and the target calcium content. By adding it in batches, the formation of the slag layer can be observed in real time, avoiding potential problems caused by excessive addition of ferric fluoride.

[0029] Due to the adoption of the above technologies, the significant advantages of this invention compared with the prior art are as follows:

[0030] 1) The core innovation of this solution lies in using ferric fluoride as a chemical decalcification agent in the refining stage. Compared with existing technologies that rely solely on high-temperature volatilization and physical adsorption for calcium removal, this solution provides a clear chemical driving force, converting calcium dissolved in the alloy melt into an insoluble calcium fluoride slag phase through a displacement reaction, thereby achieving efficient calcium removal;

[0031] 2) Implementing this solution can reduce the calcium content in terbium-iron alloys from 0.011-0.015% in traditional processes to 0.002-0.004%, a reduction of 70-85%. Since the iron generated from the reaction of ferric fluoride is directly added to the alloy, the terbium-iron ratio of the alloy can be pre-compensated by adjusting the amount of iron powder in the original feedstock, ensuring that the composition of the final product meets the target requirements. This solution has no special requirements for existing equipment; it only requires adding ferric fluoride during the refining stage. The process modification cost is low, and it has good industrial applicability. Detailed Implementation

[0032] To better understand the present invention, the following detailed description is provided in conjunction with specific embodiments. These embodiments are used to illustrate the main reactions and basic features of the present invention and are not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements. Implementation conditions not specified are generally those in conventional experiments.

[0033] The raw materials involved in this solution include: terbium fluoride powder, with a purity of ≥99% and a particle size of 100-200 mesh; iron powder, with a purity of ≥99.5% and a particle size of 100-300 mesh; metallic calcium particles, with a purity of ≥98% and a particle size of 2-5 mm; ferric fluoride powder, anhydrous ferric fluoride, with a purity of ≥98% and a particle size of 100-200 mesh, which needs to be dried in an inert atmosphere or vacuum drying oven at 150-200℃ for 2 hours before use to remove adsorbed moisture; and sodium chloride powder, with a purity of ≥99% and a particle size of 80-150 mesh.

[0034] The main equipment involved in this plan includes: a mixer with a rotation speed of 10-30 r / min; a vacuum induction melting furnace with an ultimate vacuum degree better than 0.5 Pa and a maximum heating temperature of not less than 1800℃, equipped with a feeding device to add powdered materials to the melt under vacuum or inert atmosphere; and a tungsten crucible with a purity greater than or equal to 99.5%.

[0035] The theoretical amount of metallic calcium required is calculated based on the stoichiometric relationship of the reduction reaction. The reduction reaction equation is: According to the reaction formula, approximately 0.283 kg of metallic calcium is theoretically required to reduce 1 kg of terbium fluoride powder.

[0036] The theoretical amount of ferric fluoride used is calculated based on the stoichiometric relationship of the calcium removal reaction. The calcium removal reaction equation is: According to the reaction formula, approximately 1.88g of ferric fluoride is theoretically required to remove 1g of calcium. Considering factors such as reaction efficiency and slag entrainment, the actual amount added is taken as 1.2-1.5 times the theoretical value.

[0037] Compensation for iron formation in the ferric fluoride reaction: According to the calcium removal reaction formula, approximately 0.49g of metallic iron will be generated for every 1g of ferric fluoride added. To maintain the terbium-iron ratio in the final product, the amount of iron powder used in the initial batch should be reduced accordingly, or a slight increase in iron content should be accepted.

[0038] The present invention will be further described below with reference to the embodiments.

[0039] Example 1

[0040] Weigh the raw materials according to the following formula: 2.00 kg of terbium fluoride powder, 0.95 kg of iron powder, 0.71 kg of metallic calcium granules (1.25 times the theoretical amount of 0.566 kg), and 0.40 kg of sodium chloride powder.

[0041] The above raw materials were placed in a mixer and mixed at 20 r / min for 30 minutes until homogeneous, yielding a total of 4.06 kg of mixture.

[0042] Transfer the mixture to a 2L tungsten crucible and place the crucible in the induction coil of the vacuum induction melting furnace. Start the vacuum system and evacuate to 0.8Pa, then fill with 99.999% pure argon gas to 0.05MPa.

[0043] The induction heating system is activated, and the temperature is increased to 1380℃ at a rate of 10-15℃ / min. The temperature is then maintained for 30 minutes to carry out the thermal reduction reaction. During the reduction reaction, terbium fluoride reacts with metallic calcium to produce metallic terbium and calcium fluoride. The metallic terbium fuses with iron powder to form a terbium-iron alloy melt, while calcium fluoride and sodium chloride form a mixed slag that floats on the surface of the melt.

[0044] After the reduction reaction is complete, about 0.85 kg of calcium fluoride-sodium chloride mixed slag on the surface is removed by tilting the crucible or using a slag spoon to obtain the primary alloy melt.

[0045] The furnace body was evacuated again to 0.8 Pa, and high-purity argon gas was introduced to 0.05 MPa. The primary alloy melt was heated to 1520℃.

[0046] Weigh 30g of dried anhydrous iron fluoride powder. Using the feeding device of a vacuum induction melting furnace, add 10g of iron fluoride powder to the surface of the melt in three batches. After each batch is added, maintain the temperature and stir for 5 minutes, observing the formation of a white calcium fluoride slag layer on the melt surface. After all three batches are added, continue to maintain the temperature for 10 minutes to ensure the reaction proceeds fully. The amount of iron fluoride added is approximately 1.5% of the mass of the primary alloy melt.

[0047] Use a slag spoon to remove approximately 35g of the newly formed calcium fluoride slag layer from the surface of the melt.

[0048] After removing the calcium fluoride slag, continue to hold at 1520℃ for 15 minutes for stabilization refining to further homogenize the alloy composition.

[0049] The refined alloy melt was poured into a graphite mold preheated to 200°C, allowed to cool naturally to room temperature, and then demolded to obtain a terbium-iron alloy ingot of approximately 1.95 kg.

[0050] Chemical analysis of the product revealed the following results: terbium content 58.8%, iron content 40.6%, calcium content 0.0028%, oxygen content 0.12%, and total other impurities less than 0.1%. Compared to products refined using traditional methods (without adding ferric fluoride), the calcium content decreased from 0.012-0.014% to 0.0028%, a reduction of approximately 78%.

[0051] Physical performance tests were conducted on the product, which showed a density of 8.6 g / cm³ and a coercivity of approximately 15 Oe at room temperature, meeting the technical requirements for terbium-iron alloys used in super magnetostrictive materials.

[0052] Example 2

[0053] The difference from Example 1 is that the amount of ferric fluoride added is 0.5% of the mass of the primary alloy melt, i.e., 10g.

[0054] The raw material ratios and reduction reaction process parameters were the same as in Example 1. During the iron fluoride refining and calcium removal stage, iron fluoride powder was added in two batches, 5g per batch, with stirring and maintaining the temperature for 5 minutes after each addition. Other process parameters were the same as in Example 1.

[0055] The chemical analysis results of the product are as follows: terbium content 59.0%, iron content 40.3%, calcium content 0.0055%, and oxygen content 0.13%. The calcium content is reduced by approximately 55% compared to the traditional process.

[0056] This example demonstrates that a lower amount of ferric fluoride can still significantly reduce calcium content, but the calcium removal effect is not as good as in Example 1.

[0057] Example 3

[0058] The difference from Example 1 is that the amount of ferric fluoride added is 2.0% of the mass of the primary alloy melt, i.e., 40g.

[0059] The raw material ratios and reduction reaction process parameters were the same as in Example 1. During the iron fluoride refining and calcium removal stage, iron fluoride powder was added in four batches of 10g each, with stirring and maintaining the temperature for 5 minutes after each addition. Other process parameters were the same as in Example 1.

[0060] The chemical analysis results of the product are as follows: terbium content 58.5%, iron content 41.0%, calcium content 0.0018%, and oxygen content 0.11%. The calcium content is reduced by approximately 85% compared to the traditional process.

[0061] This example demonstrates that increasing the amount of ferric fluoride added can further reduce the calcium content, but at the same time leads to a slight increase in the iron content. For applications with strict requirements on the terbium-iron ratio, the amount of iron powder used in the original batching needs to be reduced accordingly to compensate.

[0062] Example 4

[0063] The difference from Example 1 is that the amount of iron generated by the reaction of iron fluoride is deducted in advance during the original ingredient preparation.

[0064] The amount of ferric fluoride added is 30g, which, according to the reaction formula, will generate approximately 14.7g of iron. Therefore, the amount of iron powder in the original ingredients is reduced from 0.95kg to 0.935kg.

[0065] The other raw material ratios and process parameters are the same as in Example 1.

[0066] The chemical analysis results of the product are as follows: terbium content 59.2%, iron content 40.1%, calcium content 0.0026%, and oxygen content 0.12%.

[0067] This embodiment demonstrates that by pre-deducting the amount of iron powder, the target terbium-iron ratio can be maintained while achieving efficient calcium removal.

[0068] Example 5

[0069] The difference from Example 1 is that the refining temperature of ferric fluoride is 1480°C, which is lower than 1520°C in Example 1.

[0070] The raw material ratios and reduction reaction process parameters were the same as in Example 1. During the calcium removal stage of the ferrofluoride refining process, the primary alloy melt was heated to 1480°C before adding ferrofluoride powder. Other process parameters were the same as in Example 1.

[0071] The chemical analysis results of the product are as follows: terbium content 58.9%, iron content 40.5%, calcium content 0.0035%, and oxygen content 0.12%. The calcium content is reduced by approximately 72% compared to the traditional process.

[0072] This example demonstrates that the calcium removal reaction of ferric fluoride can still proceed effectively at lower refining temperatures, although the calcium removal efficiency decreases slightly.

[0073] Example 6

[0074] The difference from Example 1 is that the refining temperature of ferric fluoride is 1560°C, which is higher than 1520°C in Example 1.

[0075] The raw material ratios and reduction reaction process parameters were the same as in Example 1. During the calcium removal stage of the ferrofluoride refining process, the primary alloy melt was heated to 1560°C before adding ferrofluoride powder. Other process parameters were the same as in Example 1.

[0076] The chemical analysis results of the product are as follows: terbium content 58.7%, iron content 40.6%, calcium content 0.0022%, and oxygen content 0.105%. The calcium content is reduced by approximately 82% compared to the traditional process.

[0077] This example demonstrates that higher refining temperatures are beneficial for improving the calcium removal efficiency of ferric fluoride and reducing oxygen content.

[0078] Example 7

[0079] The difference from Example 1 is that the feed coefficient of metallic calcium is 1.20 times (i.e. 1.20 times the theoretical amount), which is lower than 1.25 times that of Example 1.

[0080] The amount of metallic calcium granules was adjusted to 0.68 kg. Due to the reduction in excessive calcium, the expected amount of residual calcium was also reduced, so the amount of ferric fluoride added was adjusted to 20 g accordingly.

[0081] The other raw material ratios and process parameters are the same as in Example 1.

[0082] The chemical analysis results of the product are as follows: terbium content 59.1%, iron content 40.3%, calcium content 0.0030%, and oxygen content 0.12%.

[0083] This example demonstrates that appropriately reducing the calcium feed coefficient in conjunction with iron fluoride refining to remove calcium can effectively control calcium residue while ensuring complete reduction reaction.

[0084] Example 8

[0085] The difference from Example 1 is that the feeding coefficient of metallic calcium is 1.30 times, which is higher than 1.25 times in Example 1, and the amount of iron fluoride added is increased.

[0086] The dosage of metallic calcium granules was adjusted to 0.74 kg. Due to the excessive increase in calcium, the dosage of ferric fluoride was adjusted to 45 g, to be added in 4-5 batches.

[0087] The other raw material ratios and process parameters are the same as in Example 1.

[0088] The chemical analysis results of the product are as follows: terbium content 58.4%, iron content 41.1%, calcium content 0.0025%, and oxygen content 0.11%.

[0089] This example shows that a higher calcium feed coefficient helps ensure complete reduction reaction, and with the corresponding increase in the amount of ferric fluoride added, effective calcium removal can still be achieved, but the iron content of the final product is slightly higher.

[0090] Example 9

[0091] The difference from Example 1 is that the target composition ratio of the terbium-iron alloy is different, and it is a high terbium ratio.

[0092] The ingredients are adjusted as follows: 2.00 kg terbium fluoride powder, 0.55 kg iron powder, 0.71 kg metallic calcium granules, and 0.40 kg sodium chloride powder. The amount of ferric fluoride added is 25 g.

[0093] Other process parameters are the same as in Example 1.

[0094] The chemical analysis results of the product are as follows: terbium content 65.1%, iron content 34.2%, calcium content 0.0032%, and oxygen content 0.12%.

[0095] This embodiment demonstrates that the method is applicable to the preparation of alloys with different terbium-iron ratios.

[0096] Example 10

[0097] The difference from Example 1 is that the process parameters of the reduction reaction stage are adjusted.

[0098] The reduction reaction temperature was adjusted to 1400℃, and the holding time was adjusted to 35 minutes. The addition of ferric fluoride and other parameters during the refining stage were the same as in Example 1.

[0099] The chemical analysis results of the product are as follows: terbium content 58.9%, iron content 40.5%, calcium content 0.0025%, and oxygen content 0.115%.

[0100] Example 11

[0101] The difference from Example 1 is that the ferric fluoride is added all at once instead of in batches.

[0102] During the calcium removal stage of ferric fluoride refining, 30g of ferric fluoride powder is added to the surface of the alloy melt at 1520℃ in one go, and then kept warm and stirred for 20 minutes.

[0103] The chemical analysis results of the product are as follows: terbium content 58.8%, iron content 40.6%, calcium content 0.0038%, and oxygen content 0.13%.

[0104] This example demonstrates that adding ferric fluoride in a single step is slightly less effective at removing calcium than adding it in batches. Adding it in batches allows for better contact and reaction between the ferric fluoride and the calcium in the melt, avoiding side reactions caused by excessive local ferric fluoride or loss due to volatilization.

[0105] Comparative Example 1

[0106] The difference from Example 1 is that no iron fluoride is added during the refining stage, and a traditional vacuum refining process is used.

[0107] The raw material ratio and reduction reaction process parameters were the same as in Example 1. After the reduction reaction was completed, the slag was removed, and the primary alloy melt was vacuum refined at 1520℃ for 30 minutes (vacuum degree 0.8Pa) and then cast into shape.

[0108] The chemical analysis results of the product are as follows: terbium content 58.9%, iron content 40.2%, calcium content 0.0125%, and oxygen content 0.15%.

[0109] The comparative example is the traditional calcium thermal reduction refining process, and the calcium content of the product is 0.0125%, which is 4.5 times that of Example 1 (0.0028%), demonstrating the significant effect of iron fluoride refining on calcium removal in reducing calcium residue.

[0110] Comparative Example 2

[0111] The difference from Example 1 is that the vacuum refining time is extended in the refining stage, but iron fluoride is not added.

[0112] The raw material ratio and reduction reaction process parameters were the same as in Example 1. In the refining stage, the primary alloy melt was subjected to intensive vacuum refining at 1550°C and a vacuum degree of 0.5 Pa for 60 minutes.

[0113] The chemical analysis results of the product are as follows: terbium content 59.0%, iron content 40.1%, calcium content 0.0088%, and oxygen content 0.13%.

[0114] This comparative example illustrates that extending the vacuum refining time can reduce the calcium content to some extent through the high-temperature volatilization of calcium, but the effect is limited, and the calcium content is still more than three times that of Example 1. Furthermore, extending the refining time increases energy consumption and production cycle, resulting in poor economic efficiency.

[0115] Comparative Example 3

[0116] The difference from Example 1 is that calcium chloride is added during the refining stage as a calcium removal and slag-forming agent to replace iron fluoride.

[0117] The raw material ratio and reduction reaction process parameters were the same as in Example 1. During the refining stage, 30g of calcium chloride powder was added to the surface of the alloy melt at 1520℃, and the mixture was kept at that temperature for 20 minutes before slag separation.

[0118] The chemical analysis results of the product are as follows: terbium content 58.7%, iron content 40.3%, calcium content 0.0095%, and oxygen content 0.14%.

[0119] This comparative example illustrates that calcium chloride, as a slag-forming agent, does not possess the thermodynamic driving force to undergo a displacement reaction with calcium in the melt. It can only remove a small amount of calcium through adsorption in the slag phase, and its calcium removal effect is far inferior to that of ferric fluoride.

[0120] Comparative Example 4

[0121] The difference from Example 1 is that the amount of iron fluoride added is too high, which is 5% of the mass of the primary alloy melt, i.e., 100g.

[0122] The raw material ratios and reduction reaction process parameters were the same as in Example 1. During the refining stage, ferric fluoride powder was added in 5 batches, 20g per batch.

[0123] The chemical analysis results of the product are as follows: terbium content 57.2%, iron content 42.5%, calcium content 0.0008%, oxygen content 0.10%, but trace amounts of unreacted fluoride residues were detected in the product.

[0124] This comparative example illustrates that while adding excessive amounts of ferric fluoride can reduce calcium content to extremely low levels, it will lead to a significant increase in iron content, deviating from the target ratio. Furthermore, excess ferric fluoride may not be completely reacted and consumed, remaining in the product. The recommended amount of ferric fluoride added is 0.5-2.0%.

[0125] The above embodiments are merely preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The scope of protection of the present invention should be the technical solution described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing a high-purity terbium-iron alloy, characterized in that, Specifically, the steps include the following: Ingredients: Weigh out terbium fluoride powder, iron powder, metallic calcium granules and sodium chloride powder according to the formula. The amount of metallic calcium is 1.20-1.50 times the theoretically calculated amount of reduced terbium fluoride. Mixing: Place terbium fluoride powder, iron powder, metallic calcium granules and sodium chloride powder in a mixer and mix evenly to obtain a mixture; Thermal reduction reaction: The mixture is transferred to a reaction vessel, vacuumed, filled with high-purity argon, heated to 1350-1400℃ and held to complete the reduction reaction; First slag separation: After the reduction reaction is completed, solid-liquid separation is performed to remove the calcium fluoride-sodium chloride mixed slag on the surface and obtain the primary alloy melt; Refining and removing calcium from ferric fluoride: The furnace body is evacuated to below 1 Pa and filled with high-purity argon. The primary alloy melt is heated to 1480-1560℃. Ferric fluoride powder is added to the surface of the melt in batches. After each batch is added, the furnace is kept warm and stirred to ensure that it fully contacts and reacts with the melt. Secondary slag separation: After the calcium removal process of ferrofluoride refining is completed, the calcium fluoride slag layer on the surface of the melt is removed to obtain the refined alloy melt. Casting: The refined alloy melt is poured into a preheated mold and cooled to obtain a high-purity terbium-iron alloy ingot.

2. The preparation method according to claim 1, characterized in that, In the thermal reduction step, the reactor is a tungsten crucible. The specific operation involves transferring the mixture into the tungsten crucible and placing the tungsten crucible in the induction coil of the vacuum induction melting furnace.

3. The preparation method according to claim 1, characterized in that, In the thermal reduction step, high-purity argon gas is introduced to a pressure of 0.03-0.08 MPa, and the heating and holding time is 25-35 minutes.

4. The preparation method according to claim 1, characterized in that, In the calcium removal process of ferric fluoride refining, the furnace body is re-vacuumed to below 1 Pa.

5. The preparation method according to claim 4, characterized in that, In the calcium removal step of ferric fluoride refining, the furnace body is evacuated to below 1 Pa and then filled with high-purity argon gas to 0.03-0.08 MPa.

6. The preparation method according to claim 1, characterized in that, A stabilization and refining step can be added to the secondary slag separation and casting process, that is, stabilization and refining is carried out after removing the calcium fluoride slag layer.

7. The preparation method according to claim 6, characterized in that, The stabilization and refining step specifically involves holding the temperature at 1500-1550℃.

8. The preparation method according to claim 7, characterized in that, The heat preservation time is 10-20 minutes.

9. A high-purity terbium-iron alloy, characterized in that, The high-purity terbium-iron alloy is prepared by the method described in any one of claims 1-8.

10. The high-purity terbium-iron alloy as described in claim 9, characterized in that, The calcium content in the high-purity terbium-iron alloy is less than 0.004%.