Preparation method of rare earth silicide

Abstract

The invention relates to a preparation method of rare earth silicide. The method comprises the following steps: placing a rare earth metal simple substance and a silicon simple substance in a boron nitride crucible for smelting treatment to obtain a first melt; and the first melt is subjected to forming treatment, and the rare earth silicide is obtained. In the preparation method, the rare earth metal and the silicon elementary substance are placed in a boron nitride crucible to be smelted. The boron nitride crucible has excellent chemical stability and is not prone to chemical reaction with metal, alloy and fused salt in a high-temperature vacuum environment, chemical reaction between the crucible and rare earth metal and silicon elementary substance can be effectively avoided, the purity of the rare earth silicide product is improved, and the rare earth silicide with a single phase is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and particularly to a method for preparing rare earth silicide. Background Art

[0002] Due to their excellent properties, rare earth silicides are applied in various industries. For example, in the steel field, rare earth silicides can be used as additives to improve the properties of steel, such as enhancing the strength, toughness, and corrosion resistance of steel. Specifically, in the production of some high-strength alloy steels and stainless steels, adding an appropriate amount of cerium silicon alloy can significantly improve the quality of steel. In the field of superalloys, rare earth silicides can improve the high-temperature strength, creep strength, and hot corrosion resistance of superalloys due to their good high-temperature resistance and oxidation resistance, meeting the stringent requirements of superalloys in high-temperature environments. In the field of electronic materials, rare earth silicides can be used as dopants or functional materials in semiconductor devices, magnetic materials, etc. to improve the properties of electronic materials. In the photovoltaic field, rare earth silicides can be used for modifying solar silicon wafers, protective coatings, and thermal management systems, etc.

[0003] Currently, among the traditional preparation methods of rare earth silicides, there are mainly carbothermal reduction method, molten salt electrolysis method, vacuum melting method, and powder metallurgy method. The most common preparation method is the vacuum melting method, such as the vacuum melting method using an intermediate frequency furnace. However, this method is prone to introducing impurities, generating impurity phases, and reducing the purity of single-phase rare earth silicides. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for preparing rare earth silicide, and the rare earth silicide prepared by this method has a single phase and high purity.

[0005] The first aspect of the present application provides a method for preparing rare earth silicide, including the following preparation steps:

[0006] Placing rare earth metal simple substance and silicon simple substance in a boron nitride crucible for melting treatment to obtain a first melt;

[0007] Performing shaping treatment on the first melt to obtain the rare earth silicide.

[0008] In the above preparation method, rare earth metal and silicon simple substance are placed in a boron nitride crucible for melting. Among them, the boron nitride crucible has excellent chemical stability and is not prone to chemical reactions with metals, alloys, and molten salts in a high-temperature vacuum environment. It can effectively avoid chemical reactions between the crucible and rare earth metal and silicon simple substance, improve the purity of rare earth silicide products, and obtain rare earth silicides with a single phase.

[0009] Furthermore, the boron nitride crucible has good demolding performance and good non-stickiness to most metals and alloys, making it easier for the smelted metal or alloy to be removed from the crucible, reducing material loss.

[0010] In some embodiments, the preparation method further comprises the following steps:

[0011] Placing the rare earth metal element, the silicon element, and the metal flux in the boron nitride crucible for the smelting treatment to obtain a second melt;

[0012] Performing the shaping treatment on the second melt to obtain a solid alloy;

[0013] Performing distillation purification on the solid alloy to remove the metal flux component to obtain the rare earth silicide.

[0014] In some embodiments, the shaping treatment is performed by casting.

[0015] In some embodiments, the metal flux can form a eutectic phase with a low melting point with silicon elements.

[0016] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0017] (1) The rare earth metal element is selected from one or more of yttrium, cerium, scandium, and samarium;

[0018] (2) The metal flux is selected from one or more of alkali metals or alkaline earth metals.

[0019] In some embodiments, the metal flux is selected from one or more of elemental magnesium and elemental calcium.

[0020] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0021] (1) The smelting treatment is carried out under a vacuum condition of 5×10 -3 Pa~5×10 -2 Pa;

[0022] (2) The heating program of the smelting treatment includes: first heating at a heating power of 10 kW to 12 kW for 10 min to 20 min until the temperature reaches 600 °C to 650 °C; then heating at a heating power of 20 kW to 22 kW for 10 min to 15 min until the temperature reaches 1100 °C to 1150 °C; then heating at a heating power of 30 kW to 32 kW until the temperature reaches 1450 °C to 1500 °C to completely melt the rare earth metal element, the silicon element, and the metal flux, and then keeping warm for 10 min to 20 min;

[0023] (3) The smelting treatment is carried out under a protective gas condition, and the protective gas is selected from one or more of argon and helium;

[0024] (4) The smelting treatment is carried out in an intermediate frequency furnace, an electric arc furnace or a suspension furnace.

[0025] In some embodiments, the step of subjecting the solid alloy to distillation purification to remove the metal flux component includes:

[0026] Crushing the solid alloy to obtain alloy particles, and subjecting the alloy particles to distillation purification; the average particle size of the alloy particles is 1 mm to 5 mm.

[0027] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0028] (1) The temperature of the distillation purification is 1000 °C to 1200 °C;

[0029] (2) The distillation purification is carried out in a carbon tube furnace.

[0030] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0031] (1) The purity of the rare earth metal simple substance is ≥ 99.99%;

[0032] (2) The purity of the silicon simple substance is ≥ 99.99%;

[0033] (3) The purity of the metal flux is ≥ 99.99%;

[0034] (4) The average particle size of the metal flux is 1 mm to 3 mm;

[0035] (5) The rare earth silicide has a single phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the disclosed drawings without creative efforts.

[0037] Figure 1 It is the XRD semi - quantitative spectrum of the commercially available CeSi2 alloy and the cerium - silicon alloy prepared in Example 1.

[0038] Figure 2 It is the XRD semi - quantitative spectrum of the commercially available YSi2 alloy and the yttrium - silicon alloy prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In order to facilitate the understanding of the present invention, the present invention is described more comprehensively below. And preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0042] The weight of the relevant components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the description of the embodiments of the present invention, it is within the scope disclosed in the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiments of the present invention may be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0043] Impurities are easily introduced into the rare earth silicide prepared by vacuum melting in medium frequency furnace, producing impurity phases and reducing the purity of single-phase rare earth silicide. After careful study, it is found that tungsten crucibles, graphite crucibles, corundum crucibles, magnesia crucibles and ceramic crucibles are often used in vacuum melting, but the chemical properties of rare earth metals such as cerium and yttrium and silicon are relatively active, and they are easy to react with the components in the above crucibles, thereby introducing impurities into the alloy material, and producing impurity phases such as silicon carbide and silicon tungsten.

[0044] Based on this, the present application provides a method for preparing rare earth silicide as described below.

[0045] In one embodiment of the present application, a method for preparing a rare earth silicide is provided, comprising the following preparation steps:

[0046] Placing a rare earth metal element and a silicon element in a boron nitride crucible for smelting to obtain a first melt;

[0047] The first melt is subjected to a shaping process to obtain rare earth silicide.

[0048] In the above preparation method, the rare earth metal and silicon element are placed in a boron nitride crucible for melting. Among them, the boron nitride crucible has excellent chemical stability and is not prone to chemical reactions with metals, alloys, and molten salts in a high-temperature vacuum environment. It can effectively avoid chemical reactions between the crucible and the rare earth metal and silicon element, improve the purity of the rare earth silicide product, and obtain a rare earth silicide with a single phase.

[0049] Furthermore, the boron nitride crucible has good demolding performance and good non-stickiness to most metals and alloys, making it easier for the smelted metal or alloy to be removed from the crucible, reducing material loss.

[0050] In some embodiments, the preparation method of rare earth silicide further includes the following steps:

[0051] The rare earth metal element, silicon element, and metal flux are placed in a boron nitride crucible for melting treatment; a second melt is obtained;

[0052] The second melt is subjected to a shaping process to obtain a solid alloy;

[0053] The solid alloy is subjected to distillation purification to remove the metal flux component to obtain rare earth silicide.

[0054] In the above method, the rare earth metal element, silicon element, and metal flux are placed in a boron nitride crucible for melting; among them, the addition of the metal flux can form a eutectic or compound with a low melting point with the silicon element component, thereby reducing the overall melting point of the alloy, enabling the alloy to reach a molten state at a relatively low temperature, saving energy and melting time. At the same time, the addition of the metal flux can also reduce the surface tension and viscosity of the alloy liquid, making the fluidity of the alloy liquid better; it helps the alloy to be more evenly mixed and reduces composition segregation. Furthermore, when the solid alloy is subjected to distillation purification, the metal flux component with a lower melting point and boiling point is evaporated, while the alloy components with a higher melting point and boiling point are retained, thereby improving the purity of the rare earth silicide and reducing the impurity phase brought by the metal flux; at the same time, distillation purification of the solid alloy is more convenient to operate, can also reduce losses, and further improve the distillation effect and product quality.

[0055] In some embodiments, when performing the melting treatment, the above boron nitride crucible is sleeved in a graphite crucible. Sleeving the boron nitride crucible in the graphite crucible can not only prevent the rare earth metal and silicon element to be melted from reacting with the graphite crucible to bring impurity phases, but also utilize the heat conduction of the graphite crucible to make the raw materials to be melted in the boron nitride evenly heated.

[0056] In some embodiments, the shaping process adopts casting.

[0057] In some embodiments, the rare earth metal element is selected from one or more of yttrium, cerium, scandium, and samarium.

[0058] In some embodiments, the metal flux can form a eutectic phase with low melting point with silicon element.

[0059] Optionally, when the rare earth metal element is yttrium, the melting point of the eutectic phase is lower than the melting points of yttrium and silicon elements; when the rare earth metal element is cerium, the melting point of the eutectic phase is lower than that of silicon element and 100°C - 200°C higher than the melting point of cerium.

[0060] In some embodiments, the metal flux is selected from one or more of alkali metals and alkaline earth metals.

[0061] In some embodiments, the metal flux is selected from one or more of elemental magnesium and elemental calcium.

[0062] In some embodiments, the purity of the rare earth metal element ≥ 99.99%.

[0063] In some embodiments, the purity of the silicon element ≥ 99.99%.

[0064] In some embodiments, the purity of the metal flux ≥ 99.99%.

[0065] In some embodiments, the average particle size of the metal flux is 1 mm - 3 mm.

[0066] In some embodiments, when the rare earth metal element is selected as cerium, the mass ratio of the rare earth metal element, the silicon element, and the metal flux is (2.3 - 2.7):1:(0.068 - 0.073).

[0067] In some embodiments, the step of placing the rare earth metal element, the silicon element, and the metal flux in a boron nitride crucible includes: first mixing the rare earth metal element, the silicon element, and the metal flux, and pressing them into a block, and then placing the block in the boron nitride crucible.

[0068] Pressing the raw materials into blocks can increase the contact area between the raw materials, reduce the diffusion distance, and improve the uniformity of the reaction. Specifically, when the raw materials exist in loose particles, the contact between each other is only point contact, and the actual contact area is small. After being pressed into blocks, the raw material particles are tightly squeezed together, and the contact mode changes from point contact to surface contact or even body contact, which greatly increases the contact area between the raw materials. In this way, during the reaction process, the reactant molecules can contact and collide with each other more fully, thereby increasing the reaction rate and making the reaction more fully. Further, after being pressed into blocks, the gaps between the raw material particles are reduced, the diffusion path of the substance therein becomes shorter, and the transmission and reaction process of the substance are accelerated. The uniformity of the reaction is improved because: the pressing process can make various raw materials evenly mixed together, avoiding the segregation and uneven distribution of the raw materials; in this way, during the reaction, the proportion of reactants in each part is relatively consistent, and the reaction conditions are more uniform, thereby ensuring that the reaction is carried out more evenly in the entire block, improving the overall effect of the reaction and the quality stability of the product.

[0069] In some embodiments, the smelting process is performed at 5×10 -3 Pa~5×10 -2 Pa under vacuum conditions.

[0070] In some embodiments, the heating procedure of the smelting treatment includes: first heating at a heating power of 10kW~12kW for 10min~20min to a temperature of 600℃~650℃; then heating at a heating power of 20kW~22kW for 10min~15min to a temperature of 1100℃~1150℃; then heating at a heating power of 30kW~32kW to a temperature of 1450℃~1500℃ to completely melt the rare earth metal element, silicon element and metal flux, and then continue to keep warm for 10min~20min.

[0071] Under the above-mentioned temperature control conditions, the smelting treatment is carried out, and the metal flux can form a low-melting-point eutectic phase with the silicon element, for example, magnesium and silicon can form a Mg2Si phase. The melting point of this phase is relatively low, so that at least one of silicon and rare earth metals exists in a liquid phase when the alloy system is at a temperature lower than the melting point of silicon and rare earth metals, which promotes the melting and mixing of silicon and rare earth elements and plays a fluxing effect. Furthermore, part of the metal flux in the smelting furnace will evaporate to form vapor, and these vapors move in the space inside the furnace, which can enhance the convection and diffusion of the gas in the furnace, thereby driving the material transport inside the alloy melt, accelerating the diffusion rate of elements such as silicon and rare earth in the melt, and helping them to melt into the melt evenly at a lower temperature, accelerating the smelting process.

[0072] As an example, the above "first heat for 10 min to 20 min at a heating power of 10 kW to 12 kW until the temperature reaches 600 °C to 650 °C" can be understood as follows: Heating can be carried out at a heating power of 10 kW, 10.5 kW, 11 kW, 11.5 kW, or 12 kW; further, the heating power can be any value within the range formed by any two of the above point values as the end values. The heating time can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, or 20 min. Further, the heating time can be any value within the range formed by any two of the above point values as the end values. Its temperature can be 600 °C, 610 °C, 620 °C, 630 °C, 640 °C, or 650 °C, and further, its temperature can be any value within the range formed by any two of the above point values as the end values.

[0073] The above "heat for 10 min to 15 min at a heating power of 20 kW to 22 kW until the temperature reaches 1100 °C to 1150 °C" can be understood as follows: Heating can be carried out at a heating power of 20 kW, 20.5 kW, 21 kW, 21.5 kW, or 22 kW; further, the heating power can be any value within the range formed by any two of the above point values as the end values. The heating time can be 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min. Further, the heating time can be any value within the range formed by any two of the above point values as the end values. Its temperature can be 1100 °C, 1110 °C, 1120 °C, 1130 °C, 1140 °C, or 1150 °C, and further, its temperature can be any value within the range formed by any two of the above point values as the end values.

[0074] The above "heat at a heating power of 30 kW to 32 kW until the temperature reaches 1450 °C to 1500 °C to completely melt the rare earth metal simple substance, silicon simple substance, and metal flux, and continue to keep warm for 10 min to 20 min" can be understood as follows: Heating can be carried out at a heating power of 30 kW, 30.5 kW, 31 kW, 31.5 kW, or 32 kW. Further, the heating power can be any value within the range formed by any two of the above point values as the end values. Its temperature can be 1450 °C, 1460 °C, 1470 °C, 1480 °C, 1490 °C, or 1500 °C, and further, its temperature can be any value within the range formed by any two of the above point values as the end values.

[0075] The holding time after the complete melting of rare earth metal simple substance, silicon simple substance and metal flux can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min. Further, the holding time after the complete melting of rare earth metal simple substance, silicon simple substance and metal flux can be any value within the range formed by any two of the above point values as the end values.

[0076] In some embodiments, the above smelting treatment is carried out under a protective gas condition. The protective gas is selected from one or more of argon and helium. Preferably, the protective gas is argon. Further, the purity of argon is 99.99%.

[0077] In some embodiments, the above smelting treatment is carried out in an intermediate frequency furnace, an electric arc furnace or a floating furnace. Preferably, the above smelting treatment is carried out in an intermediate frequency furnace.

[0078] In some embodiments, the step of removing the metal flux component by distillation purification of the solid alloy includes:

[0079] The solid alloy is crushed to obtain alloy particles, and the alloy particles are subjected to distillation purification.

[0080] The ingot is crushed to form smaller particles and then subjected to distillation purification. In this way, the alloy particles can have a larger specific surface area, enabling the metal flux to be in full contact with the surrounding gas phase. During the distillation process, it is beneficial to the volatilization and diffusion of impurity elements, causing the impurities to migrate from the inside of the alloy calcium particles to the surface and then volatilize from the surface into the gas phase, thereby improving the mass transfer efficiency and accelerating the removal speed of impurities. Further, the smaller alloy particles can reach the required distillation temperature faster during heating, and the heat transfer is more uniform, avoiding local overheating or overcooling, making the distillation process more stable and efficient. At the same time, the gaps between the particles are also appropriate, and the flow resistance of the gas between the particles is small, which is conducive to the smooth discharge of the volatilized impurity gas and prevents the accumulation of impurity gas in the particle accumulation layer, affecting the distillation effect.

[0081] In some embodiments, the average particle size of the above alloy particles is 1 mm to 5 mm.

[0082] In some embodiments, the temperature of distillation purification is 1000 °C to 1200 °C.

[0083] In some embodiments, the distillation purification is carried out in a carbon tube furnace.

[0084] In some embodiments, before placing the rare earth metal element, silicon element, and metal flux in a boron nitride crucible, it further includes the step of pre-treating the rare earth metal element, silicon element, and metal flux respectively to remove the surface oxide layer and impurities.

[0085] In some embodiments, the above-mentioned pre-treatment includes: respectively grinding and polishing the rare earth metal element, silicon element, and metal flux to remove the surface oxide layer and other impurities of the raw materials.

[0086] In some embodiments, the above-mentioned pre-treatment further includes ultrasonic cleaning the rare earth metal element, silicon element, or metal flux that has been ground and polished in an organic solvent, and then drying.

[0087] In some embodiments, the above-mentioned organic solvent is selected from ethanol or acetone. Cleaning by ultrasonic waves in an organic solvent is beneficial for removing grease and oil stains (lubricant, cutting fluid residues), organic coatings (paint, plastic residues), and particulate pollutants (dust, metal chips), etc.

[0088] In some embodiments, the above-mentioned drying is carried out in a vacuum drying oven. Further, the pressure of the vacuum drying oven is below -0.1 MPa.

[0089] In some embodiments, the drying temperature is 100 °C to 120 °C.

[0090] In some embodiments, the drying time is 4 h to 6 h.

[0091] In some embodiments, the rare earth silicide has a single phase.

[0092] In some embodiments, when the rare earth metal element is cerium, the cerium element in the rare earth silicide is 70.5 wt% to 73.5 wt%, the mass percentage content of the silicon element is 26.5 wt% to 29.5 wt%, the oxygen element content is 0 to 0.05 wt%, and the mass percentage content of other impurity elements is 0 to 0.1 wt%.

[0093] In some embodiments, when the rare earth metal element is yttrium, the yttrium element in the rare earth silicide is 58 wt% to 64 wt%, the mass percentage content of the silicon element is 36 wt% to 42 wt%, the oxygen element content is 0 to 0.05 wt%, and the mass percentage content of other impurity elements is 0 to 0.1 wt%.

[0094] In order to make the objectives, technical solutions and advantages of the present invention more concise and clear, the present invention will be described with the following specific embodiments. However, the present invention is by no means limited to these embodiments. The following described embodiments are only the preferred embodiments of the present invention and can be used to describe the present invention, and should not be construed as a limitation on the scope of the present invention. It should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

[0095] To better illustrate the present invention, the content of the present invention will be further described below in conjunction with embodiments. The following are specific embodiments.

[0096] Example 1

[0097] 1. Preparation of raw materials: The raw materials used are high-purity silicon particles (purity ≥ 99.99%), cerium metal (purity ≥ 99.9%), and high-purity calcium metal (purity ≥ 99.99%) as a metal flux. The raw material high-purity silicon particles, cerium metal particles, and metal flux calcium metal particles are all ground and polished to remove the oxide layer and other impurities on the surface of the raw materials. After washing the materials with deionized water, ultrasonic cleaning is carried out in an acetone solvent, and then the materials are transferred to a vacuum drying oven for drying. Drying is carried out for 4 h under the conditions that the vacuum gauge shows -0.1 MPa and the temperature is 100 °C, and the dried materials are taken. Weigh 275.0 g of high-purity silicon particles, 725.0 g of cerium metal, and 20.0 g of calcium metal, and mix the raw materials evenly and carry out briquetting.

[0098] 2. Melting preparation: Place the briquetted raw materials in a vacuum medium-frequency furnace. The crucible used is a boron nitride ceramic crucible placed inside a graphite sleeve. The materials are placed in the central area at the bottom of the boron nitride crucible. After ensuring that the casting position is appropriate, close the furnace lid.

[0099] 3. Melting: Open the vacuum system, evacuate the vacuum inside the equipment to 5×10 -2 Pa, introduce high-purity argon until the vacuum gauge shows -0.6 MPa as the protective gas, and then start melting. Under the condition of a heating power of 10 kW, preheat the crucible and the materials for 15 min, and at this time the temperature reaches 600 °C; then heat at a heating power of 20 kW for 10 min, and at this time the temperature reaches 1100 °C; then heat to 1500 °C under the condition of a heating power of 30 kW for melting. After the materials are completely melted, keep warm for 10 min, and then carry out casting to obtain an ingot.

[0100] 4. Purification and single-phasing: Crush the ingot to obtain alloy particles with an average particle size of 2 mm. Place the alloy particles in a carbon tube furnace for purification. The carbon tube furnace is continuously evacuated, and the compound vacuum gauge shows 5×10 -2After reaching Pa, the temperature is gradually increased, and the temperature is measured through the temperature measuring hole. When it reaches 1200 °C, it is kept warm for 6 h to remove the flux metal calcium, and the alloy ingot in the crucible is taken out after cooling.

[0101] For the alloy ingot obtained by the above method, the effective component of cerium is detected to be 72.48 wt%, the effective component of silicon is detected to be 27.42 wt%, its impurity content is lower than 0.1 wt%, and the oxygen content is lower than 0.05 wt%.

[0102] As Figure 1 shown, Figure 1 a in is the standard XRD semi - quantitative spectrum of commercially available single - phase CeSi2 alloy; Figure 1 b in is the RXD semi - quantitative spectrum of the cerium - silicon alloy prepared in Example 1. From Figure 1 it can be seen that the characteristic absorption peaks of the RXD semi - quantitative spectrum of the cerium - silicon alloy prepared in Example 1 are basically the same as those in the standard XRD semi - quantitative spectrum of CeSi2 alloy. This shows that the cerium - silicon alloy prepared in Example 1 is an alloy material with a single phase of CeSi2.

[0103] Example 2

[0104] 1. Preparation of raw materials: The raw materials used are high - purity silicon particles (purity ≥ 99.99%), metallic yttrium (purity ≥ 99.9%), and high - purity metallic magnesium (purity ≥ 99.99%) as the flux. The raw materials of high - purity silicon particles, metallic yttrium particles, and flux metallic magnesium particles are all ground and polished to remove the oxide layer and other impurities on the surface of the raw materials. After cleaning the materials with deionized water, ultrasonic cleaning is carried out in acetone solvent, and then the materials are transferred to a vacuum drying oven for drying. Drying is carried out for 4 h under the conditions that the vacuum gauge shows - 0.1 MPa and the temperature is 100 °C, and the dried materials are taken. Weigh 290.0 g of high - purity silicon particles, 610.0 g of metallic yttrium, and 20.0 g of metallic magnesium, and mix the raw materials evenly and carry out briquetting.

[0105] 2. Melting preparation: Place the briquetted raw materials in a vacuum medium - frequency furnace. Use a crucible which is a boron nitride ceramic crucible inside a graphite sleeve. Place the materials in the central area at the bottom of the boron nitride crucible. After ensuring that the casting position is appropriate, close the furnace lid.

[0106] 3. Melting: Open the vacuum system, evacuate the vacuum in the equipment to 5×10 -2Pass in high-purity argon until the vacuum gauge shows -0.6 MPa as the protective gas, and then start melting. Under the condition of a heating power of 10 kW, preheat the crucible and the material for 15 min. At this time, the temperature reaches 600 °C; then heat at a heating power of 20 kW for 10 min. At this time, the temperature reaches 1100 °C; then heat to 1500 °C under the condition of a heating power of 30 kW for melting. After the material is completely melted, keep it warm for 10 min, and then carry out casting to obtain an ingot.

[0107] 4. Purification and single-phase formation: Crush the ingot to obtain alloy particles with an average particle size of 2 mm. Place the alloy particles in a carbon tube furnace for purification. Continuously evacuate the carbon tube furnace. When the compound vacuum gauge shows 5×10 -2 Pa, start to gradually heat up. Measure the temperature through the temperature measuring hole, and keep it at 1000 °C for 6 h to remove the flux metal magnesium. After cooling, take out the alloy ingot in the crucible.

[0108] For the alloy ingot obtained by the above method, the effective component of yttrium is detected to be 60.94 wt%, the effective component of silicon is detected to be 31.96 wt%, its impurity content is less than 0.1 wt%, and the oxygen content is less than 0.05 wt%.

[0109] As Figure 2 shown, Figure 2 c in it is the standard XRD semi-quantitative pattern of commercially available single-phase YSi2 alloy; Figure 2 d in it is the RXD semi-quantitative pattern of the yttrium-silicon alloy prepared in Example 1. From Figure 2 it can be seen that the characteristic absorption peaks of the RXD semi-quantitative pattern of the yttrium-silicon alloy prepared in Example 2 are basically the same as those in the standard XRD semi-quantitative pattern of the YSi2 alloy. It shows that the yttrium-silicon alloy prepared in Example 2 is an alloy material with a single phase of YSi2.

[0110] Example 3

[0111] 1. Preparation of raw materials: The raw materials used are high-purity silicon particles (purity ≥ 99.99%) and metallic cerium (purity ≥ 99.9%). The raw high-purity silicon particles and metallic cerium particles are both ground and polished to remove the oxide layer and other impurities on the surface of the raw materials. After washing the materials with deionized water, perform ultrasonic cleaning in an acetone solvent, and then transfer the materials to a vacuum drying oven for drying. Dry for 4 h under the conditions that the vacuum gauge shows -0.1 MPa and the temperature is 100 °C, and take the dried materials. Weigh 275.0 g of high-purity silicon particles and 725.0 g of metallic cerium, mix the raw materials evenly and carry out briquetting.

[0112] 2. Melting Preparation: Place the pressed raw materials in a vacuum medium-frequency furnace. Use a graphite sleeve with a boron nitride ceramic crucible inside as the crucible. Place the materials in the central area at the bottom of the boron nitride crucible. After ensuring the proper casting position, close the furnace lid.

[0113] 3. Melting: Open the vacuum system and evacuate the vacuum inside the equipment to 5×10 -2 Pa. Then, introduce high-purity argon until the vacuum gauge shows -0.6 MPa as the protective gas and start melting. Under the condition of a heating power of 10 kW, preheat the crucible and the materials for 20 min. At this time, the temperature reaches 600 °C; then heat at a heating power of 20 kW for 20 min. At this time, the temperature reaches 1000 °C; then heat to 1500 °C under the condition of a heating power of 32 kW for melting. After the materials are completely melted, keep them warm for 10 min, and then carry out casting to obtain an ingot.

[0114] For the alloy ingot obtained by the above method, the detected effective component of cerium is 72.40 wt%, the detected effective component of silicon is 27.53 wt%, its impurity content is less than 0.1 wt%, and the oxygen content is less than 0.05 wt%.

[0115] In Example 3, no metal additive was added, and the obtained rare earth silicide had a single phase and high purity; however, compared with Example 1, its melting time increased, significantly increasing the difficulty of the melting process.

[0116] Comparative Example 1

[0117] The preparation method of this comparative example is basically the same as that of Example 1, except that when performing melting preparation in Step 2, the crucible material used is different. The crucible used in this comparative example is a graphite crucible, and the materials are placed in the central area at the bottom of the graphite crucible. Other preparation steps and process conditions are basically the same as those in Example 1.

[0118] For the alloy ingot obtained by the above method, the detected effective component of cerium is 72.06%, the detected effective component of silicon is 26.98%, its impurity content is 0.88%, and the oxygen content is 0.03%. Through XRD test analysis, it is found that the alloy prepared in this comparative example contains C phase and SiC phase.

[0119] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combinations of these technical features do not conflict, they should all be considered to be within the scope described in this specification.

[0120] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims, and the description can be used to explain the content of the claims.

Claims

1. A method for preparing rare earth silicide, characterized in that, It includes the following preparation steps: Placing rare earth metal simple substance and silicon simple substance in a boron nitride crucible for smelting treatment to obtain a first melt; Performing shaping treatment on the first melt to obtain the rare earth silicide.

2. The preparation method according to claim 1, characterized in that, The preparation method further includes the following steps: Placing the rare earth metal simple substance, the silicon simple substance and a metal flux in the boron nitride crucible for the smelting treatment to obtain a second melt; Performing the shaping treatment on the second melt to obtain a solid alloy; Performing distillation purification on the solid alloy to remove the metal flux component to obtain the rare earth silicide.

3. The preparation method according to any one of claims 1 to 2, characterized in that, The shaping treatment adopts casting.

4. The preparation method according to claim 2, characterized in that, The metal flux can form a eutectic phase with low melting point with silicon element.

5. The preparation method according to claim 2, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The rare earth metal simple substance is selected from one or more of yttrium, cerium, scandium and samarium; (2) The metal flux is selected from one or more of alkali metals and alkaline earth metals.

6. The preparation method according to claim 5, characterized in that, The metal flux is selected from one or more of simple substance magnesium and simple substance calcium.

7. The preparation method according to any one of claims 1 to 2, 4 to 6, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The smelting treatment is carried out under a vacuum condition of 5×10 -3 Pa to 5×10 -2 Pa; (2) The heating procedure of the smelting treatment includes: first heating at a heating power of 10kW - 12kW for 10min - 20min until the temperature reaches 600°C - 650°C; then heating at a heating power of 20kW - 22kW for 10min - 15min until the temperature reaches 1100°C - 1150°C; then heating at a heating power of 30kW - 32kW until the temperature reaches 1450°C - 1500°C to completely melt the rare earth metal simple substance, silicon simple substance and metal flux, and continue to keep warm for 10min - 20min; (3) The smelting treatment is carried out under a protective gas condition, and the protective gas is selected from one or more of argon and helium; (4) The smelting treatment is carried out in an intermediate frequency furnace, an electric arc furnace or a suspension furnace.

8. The preparation method according to any one of claims 2, 4 to 6, characterized in that, The step of performing distillation purification on the solid alloy to remove the metal flux component includes: Crushing the solid alloy to obtain alloy particles, and performing distillation purification on the alloy particles; the average particle size of the alloy particles is 1mm - 5mm.

9. The preparation method according to any one of claims 2 and 4 to 6, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The temperature of the distillation purification is 1000°C - 1200°C; (2) The distillation purification is carried out in a carbon tube furnace.

10. The preparation method according to any one of claims 2, 4 to 6, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The purity of the rare earth metal simple substance ≥ 99.99%; (2) The purity of the silicon simple substance ≥ 99.99%; (3) The purity of the metal flux ≥ 99.99%; (4) The average particle size of the metal flux is 1mm - 3mm; (5) The rare earth silicide has a single phase.

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