Method for preparing high-purity metal through electron beam melting

Abstract

The invention discloses a strengthening method for preparing high-purity metal through electron beam melting, and relates to the technical field of high-purity metal preparation. The method comprises the steps of raw material pretreatment, smelting furnace preparation, quasi-vacuum atmosphere construction, electron beam smelting impurity removal and product collection, and the core is that specific gas is introduced into an initial vacuum system of 10 <-2 >-10 <-4 > Pa, and a quasi-vacuum atmosphere of 10 <-1 >-10 <-3 > Pa is constructed; during electron beam melting, metal raw materials (including noble metals such as ruthenium, refractory metals and conventional metals) are molten, specific gas is ionized into active particles, the active particles react with evaporated impurities to generate low-boiling-point and high-vapor-pressure compounds, the compounds are extracted and removed through a vacuum system, and the thermodynamic and dynamic conditions of the impurity removal process are enhanced. According to the method, the vacuum degree requirement and the production cost are reduced, the impurity removal rate is increased to 90% or above, the final metal purity can reach 99.999% or above, and the method is suitable for ultra-pure preparation of multiple kinds of metal.

Description

Technical Field

[0001] This invention belongs to the field of high-purity metal preparation technology, specifically relating to a method for preparing high-purity metals based on electron beam melting in a quasi-vacuum atmosphere, applicable to the ultra-high purity purification and preparation of refractory metals such as ruthenium, titanium, zirconium, tantalum, and niobium, as well as conventional metals such as copper. Background Technology

[0002] Electron beam melting technology, with its advantages of high energy density, high melting temperature, and controllable vacuum environment, has become one of the key technologies for preparing high-purity metals. Its core principle is to use a high-energy electron beam to bombard the metal raw material, causing the metal to melt and evaporate rapidly. The difference in vapor pressure between the metal and impurity elements is used to remove impurities, thereby improving the purity of the metal.

[0003] However, traditional electron beam melting technology typically relies on high vacuum or even ultra-high vacuum environments (vacuum levels are generally below 10). -4 This technical approach has the following significant drawbacks: First, the construction and operation costs of the high-vacuum system are high, the vacuum pump group consumes a lot of energy, and maintaining the vacuum is difficult, resulting in limited production efficiency; Second, for some impurity elements with small vapor pressure differences from the main metal or that easily form solid solutions (such as oxygen, carbon, iron, and nickel in ruthenium, and oxygen and nitrogen in titanium), the impurity removal effect achieved solely by vapor pressure difference is limited, making it difficult to reduce their content to 10. -5 The following are ultra-high purity levels; thirdly, in a high vacuum environment, the metal evaporation process lacks the participation of an active medium, and the impurity removal process relies solely on physical evaporation. Both the thermodynamic driving force and the kinetic rate are bottlenecks, which cannot meet the increasingly stringent requirements of modern electronics, aerospace, precision instruments and other fields for the purity of precious metals and refractory metals.

[0004] To address the aforementioned issues, existing technologies have attempted to introduce gases into the melting system. However, these are mostly inert gas protection methods, used only to prevent metal oxidation, and do not employ specific gas and atmosphere parameters designed for impurity reactions, thus failing to achieve efficient impurity removal. Therefore, developing an electron beam melting method that can reduce vacuum requirements, enhance the impurity removal process, and improve metal purity, especially suitable for the preparation of high-purity ruthenium and other precious metals, has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of traditional electron beam melting technology, such as high cost of high vacuum, low impurity removal efficiency, and incomplete impurity removal, and to provide a method for preparing high-purity metals by electron beam melting. By constructing a quasi-vacuum atmosphere and utilizing the active particles generated by the ionization of a specific gas to react with impurities, the thermodynamic and kinetic conditions of the impurity removal process are enhanced, thereby achieving the preparation of ultra-high-purity metals (especially high-purity ruthenium) at low vacuum cost.

[0006] To achieve the above objectives, the core technical solution adopted by this invention is as follows: A method for preparing high-purity metals by electron beam melting, comprising the following steps:

[0007] Raw material pretreatment: Select the metal raw material to be purified, remove surface oil, oxide scale and mechanical impurities, and cut the raw material into blocks or granules suitable for the electron beam melting furnace crucible for later use.

[0008] Furnace preparation: Place the pretreated metal raw material into the water-cooled copper crucible of the electron beam melting furnace, close the furnace door, and start the vacuum system to evacuate the furnace to an initial vacuum level of 10. -2 Pa~10 -4 Pa.

[0009] Quasi-vacuum atmosphere construction: A specific gas is introduced into the melting furnace, which is initially under vacuum, and the introduction rate of the specific gas is controlled to stabilize the vacuum level inside the furnace at 10. -1 Pa~10 -3 The near-vacuum range of Pa, where the partial pressure of a specific gas in the furnace is 10. -3 Pa~10 -2 Pa; The specific gas is a gas capable of reacting with the impurity element to be removed from the metal raw material to be purified to generate a low-boiling-point, high-vapor-pressure compound. The gas is selected according to the type of metal to be purified and the target impurity, specifically: when the impurity element to be removed is oxygen or sulfur, hydrogen (H2) or ammonia (NH3) is selected; when the impurity element to be removed is nitrogen or carbon, oxygen (O2) or carbon dioxide (CO2) is selected; when the impurity element to be removed is a mixture of multiple impurities, a mixture of H2, NH3, O2, and CO2 is selected. The specific gas is selected from H2, NH3, O2, CO2, or mixtures thereof, and is used to react with the target impurity to generate a compound that is easily removed or easily separated from the melt under the conditions of this invention.

[0010] Electron beam melting and impurity removal: The electron gun is activated, and the electron beam accelerating voltage is adjusted to 20kV~40kV, and the beam current to 50mA~200mA, so that the high-energy electron beam is focused on the surface of the metal raw material, bombarding the raw material and melting it to form a molten pool; during the melting process, the high-energy electron beam simultaneously bombards a specific gas in the quasi-vacuum atmosphere inside the melting furnace, ionizing it into gases containing active atoms (such as H·, O·) or active ions (such as NH2). + CO3 2－ The active particles react rapidly with impurity elements (such as O, N, S, C, Fe, Ni) evaporated from the molten metal pool to generate stable compounds (such as H2O, CO2, FeO, NiO) with low boiling points and high vapor pressures.

[0011] Product collection and post-processing: During the smelting process, the gaseous compounds generated in the smelting furnace are continuously removed by the vacuum system, and the temperature of the molten pool is controlled to be stable at 200℃~500℃ above the melting point of the metal to be purified, and the smelting time is maintained at 1min~60min; after the smelting is completed, the electron gun is turned off, and after the molten pool is naturally cooled to room temperature, the solidified metal ingot is taken out to obtain the high-purity metal product.

[0012] Furthermore, the purity of the specific gas mentioned in step 3 is not less than 99.999% to avoid introducing new impurities.

[0013] Furthermore, in step 4, the electron beam is scanned in a spiral pattern, with the scanning range covering the entire surface of the molten pool to ensure uniform temperature and improve the reaction efficiency between active particles and impurities.

[0014] Furthermore, in step 5, the pumping rate of the vacuum system is adjusted according to the generation rate of impurity compounds to keep the quasi-vacuum level inside the furnace stable within the set range.

[0015] Compared with the prior art, the present invention has at least the following advantages:

[0016] (1) Reduce vacuum costs: This invention uses 10 -1 Pa~10 -3 The near-vacuum environment of Pa replaces the traditional high vacuum environment, significantly reducing the pumping load of the vacuum system, reducing the energy consumption of the vacuum pump group by 30% to 50%, and reducing equipment investment and operating costs by more than 40%.

[0017] (2) Enhanced impurity removal effect: The active particles generated by the ionization of specific gases react with impurity elements in a directional manner. The vapor pressure of the generated compound is much lower than that of the impurity element itself, which greatly reduces the partial pressure and chemical potential of the impurity in the quasi-vacuum environment, and significantly enhances the thermodynamic trend of the impurity removal process. At the same time, the high reactivity of the active particles accelerates the kinetic rate of impurity removal. For impurities such as oxygen, carbon, iron, and nickel that are difficult to remove by traditional methods, the removal rate is increased to more than 90%, and the purity of the final metal product can reach more than 99.999% (5N), and some metals can achieve the 99.9999% (6N) level.

[0018] (3) Strong applicability: By adjusting the type and ratio of specific gases, it can be adapted to the purification needs of different metal raw materials (such as precious metals such as ruthenium, refractory metals, and conventional metals), and can achieve targeted impurity removal for different combinations of impurities, with a wide range of applications;

[0019] (4) Stable and controllable process: The parameters of the quasi-vacuum atmosphere and the electron beam melting conditions can be precisely adjusted, the temperature uniformity of the molten pool is good, the composition of the metal products is stable, and the purity fluctuation between batches is less than 0.0001%. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0021] Examples 1-3 require the use of the upper limit, lower limit, and any intermediate value within the range defined by weight 1. For example, weight 1 defines "the initial vacuum degree as 10". -2 Pa~10 -4 Pa” Therefore, Examples 1-3 must use 10 -2 Pa and 10 -4 Pa, and also need 10 -3 Pa or 10 -3.5 Pa, other range requirements are the same, please make appropriate modifications to Examples 1-3.

[0022] Example 1: Preparation of High-Purity Ruthenium

[0023] This embodiment uses industrial-grade ruthenium (99.0% purity, main impurities being O: 0.6%, C: 0.2%, Fe: 0.15%, Ni: 0.05%) as raw material to prepare high-purity ruthenium. To address the high carbon and metallic impurities (Fe, Ni) content in the raw material, oxygen was selected as the specific gas to oxidize them into volatile CO / CO2 and low-boiling-point oxides, which were then removed through vacuum extraction and zone enrichment, respectively. The steps are as follows:

[0024] Raw material pretreatment: The industrial pure ruthenium raw material is polished with diamond sandpaper to remove the surface oxide scale and attached impurities, ultrasonically cleaned with anhydrous ethanol for 20 minutes to remove oil stains, and cut into blocks with a size of 40mm×40mm×8mm (fitting the inner diameter of the water-cooled copper crucible).

[0025] Furnace preparation: Place the ruthenium ingot into the water-cooled copper crucible of the electron beam melting furnace, close the furnace door, start the molecular pump group to evacuate the furnace, and make the initial vacuum degree inside the furnace reach 1×10⁻⁶. -4 Pa.

[0026] Quasi-vacuum atmosphere construction: Oxygen with a purity of 99.9995% was introduced into the furnace at a rate of 4 mL / min to stabilize the vacuum level inside the furnace at 1 × 10⁻⁶. -3 Pa, the partial pressure of oxygen is 1×10⁻⁶. -4 Pa;

[0027] Electron beam melting and impurity removal: The electron gun is started, the accelerating voltage is set to 40kV, the beam current is 200mA, and the electron beam covers the surface of the molten pool in a spiral scan (scanning frequency 5Hz), bombarding the ruthenium block to melt it. The temperature of the molten pool is controlled at 2800℃ (ruthenium melting point 2334℃, higher than the melting point 466℃). The high-energy electron beam ionizes oxygen into O· active particles. O· reacts with C evaporated from ruthenium to generate CO2, and reacts with Fe and Ni to generate FeO and NiO (both low-boiling-point, high vapor pressure compounds). O2 formed by combining with O in the raw material further participates in the impurity reaction.

[0028] Product collection and post-processing: CO2, FeO, NiO, and other compound gases were continuously removed using a vacuum pump system (the pumping rate was adjusted to 15 L / s according to the gas generation rate), maintaining a melting time of 5 minutes. After melting, the electron gun and vacuum system were turned off, and the molten pool was allowed to cool naturally to room temperature (cooling time approximately 4 hours) before the ruthenium ingot was removed. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the ruthenium ingot had a purity of 99.9993%, with O content reduced to 0.0004%, C content to 0.0001%, Fe content to 0.0002%, Ni content to 0.0001%, and the total content of other impurities below 0.0003%.

[0029] Example 2: Preparation of High-Purity Copper

[0030] This embodiment uses electrolytic copper (99.9% purity, with main impurities being S: 0.06%, P: 0.03%, Fe: 0.01%) as raw material to prepare high-purity copper. The steps are as follows:

[0031] Raw material pretreatment: The electrolytic copper is crushed into particles with a diameter of 20~30mm, soaked in dilute sulfuric acid (mass fraction 5%) for 10min to remove the surface oxide layer, rinsed with clean water 3 times and dried at 120℃;

[0032] Furnace preparation: Load copper granules into a water-cooled copper crucible, close the furnace door, and evacuate to an initial vacuum level of 1×10⁻⁶. - 2 Pa;

[0033] Quasi-vacuum atmosphere construction: A mixture of hydrogen and ammonia gas with a purity of 99.999% (volume ratio 1:1) was introduced at a rate of 8 mL / min to stabilize the vacuum level inside the furnace at 1 × 10⁻⁶. -1 Pa, the partial pressure of the mixed gas is 1×10⁻⁶ Pa. -2 Pa;

[0034] Electron beam melting and impurity removal: The electron gun accelerating voltage is set to 20kV, the beam current to 50mA, and the molten pool temperature is controlled at 1300℃ (copper melting point 1083℃, 217℃ higher); the high-energy electron beam ionizes the mixed gas into H· and NH2.+ Active particles react with sulfur (S) to produce hydrogen sulfide (H2S) and with phosphorus (P) to produce phosphorus sulfide (PH3).

[0035] Product collection and post-processing: H2S and PH3 were continuously removed (vacuuming rate 10L / s), and the smelting time was 30min; after cooling, the copper ingots were taken out, and the purity was tested to be 99.9995%, S content 0.0003%, P content 0.0002%, and Fe content less than 0.0001%.

[0036] Example 3: Preparation of High-Purity Titanium

[0037] This embodiment uses industrial pure titanium (purity 99.5%, main impurities are O: 0.35%, N: 0.08%, C: 0.05%) as raw material to prepare high-purity titanium. The steps are as follows:

[0038] 1. Raw material pretreatment: The industrial pure titanium raw material is sanded to remove the surface oxide scale, ultrasonically cleaned with anhydrous ethanol for 15 minutes to remove oil stains, and cut into blocks with a size of 50mm×50mm×10mm.

[0039] 2. Furnace Preparation: Place the titanium block into the water-cooled copper crucible of the electron beam melting furnace, close the furnace door, and start the molecular pump group to evacuate the furnace, achieving an initial vacuum level of 5 × 10⁻⁶. -3 Pa;

[0040] 3. Establishment of a near-vacuum atmosphere: Hydrogen gas with a purity of 99.9995% was introduced into the furnace at a rate of 5 mL / min to stabilize the vacuum level inside the furnace at 2 × 10⁻⁶. -2 Pa, the partial pressure of hydrogen is 8 × 10⁻⁶. -3 Pa;

[0041] 4. Electron beam melting and impurity removal: The electron gun is activated, the accelerating voltage is set to 30kV, and the beam current is 120mA. The electron beam scans in a spiral pattern, covering the surface of the molten pool and bombarding the titanium block to melt it. The temperature of the molten pool is controlled at 1800℃ (the melting point of titanium is 1668℃, which is 132℃ higher than the melting point). After hydrogen ionization, H· active atoms are generated, which react chemically with C and N impurities to generate high vapor pressure compounds (such as CH4 and NH3), which can be efficiently removed by the vacuum system. At the same time, within the range of hydrogen partial pressure and melting time described in this invention, the oxygen content and hydrogen embrittlement sensitivity of titanium will not be significantly deteriorated.

[0042] 5. Product Collection and Post-processing: CH4, NH3, and other compounds were continuously removed using a vacuum pump system, maintaining a melting time of 10 minutes. After melting, the product was cooled to room temperature, and the titanium ingot was removed. Testing revealed that the titanium ingot had a purity of 99.9992%, with the O content reduced to 0.0005%, the N content to 0.0002%, and the C content to 0.0001%.

[0043] Comparative Example 1

[0044] The same ruthenium raw material and electron beam melting equipment as in Example 1 were used, but no gas was introduced (i.e., conventional method). The vacuum level inside the furnace was evacuated to <5 × 10⁻⁶. -4 Pa, and other smelting parameters (temperature, time) were kept as consistent as possible with those in Example 1. After smelting, the metal ingot was analyzed as a whole, and the final purity was 99.995%, with the C content reduced to 0.0015%, the O content reduced to 0.003%, the Fe content to 0.012%, and the Ni content to 0.003%.

[0045] As can be seen from the above embodiments and comparative examples, the present invention has at least the following advantages:

[0046] 1. While significantly reducing the requirements and operating costs of the vacuum system, it achieves better impurity removal and higher purity of the final product.

[0047] 2. By using a directed chemical reaction in an active atmosphere, the thermodynamic and kinetic bottlenecks of traditional physical methods for impurity removal are overcome, making it particularly effective for removing impurities with similar vapor pressures.

[0048] 3. The process is highly versatile; by flexibly adjusting the type of specific gas, it can specifically remove characteristic impurities in different metal systems.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-purity metals by electron beam melting, characterized in that, Includes the following steps: Step 1: Raw material pretreatment: After removing oxides or adsorbed impurities from the surface of the metal raw material to be purified by pickling, alcohol washing or grinding, cut it into a shape suitable for the crucible. Step 2: Furnace preparation: Place the pretreated metal raw material from Step 1 into the water-cooled copper crucible of the electron beam melting furnace, and evacuate the furnace until the initial vacuum level is 10. -2 Pa~10 -4 Pa; Step 3: Establishing a quasi-vacuum atmosphere: Introduce a specific gas into the melting furnace, which is initially under vacuum, to stabilize the vacuum level inside the furnace at 10. -1 Pa~10 -3 Pa, the partial pressure of a specific gas is 10. -2 Pa~10 -4 Pa; The specific gas is a gas that can react with the impurity elements to be removed from the metal raw material to be purified to generate low-boiling-point, high-vapor-pressure compounds; Step 4: Electron beam melting and impurity removal: The electron gun is activated to bombard the raw material with a high-energy electron beam with an acceleration voltage of 20kV~40kV and a beam current of 50mA~200mA, causing it to melt and form a molten pool. At the same time, the electron beam bombards and ionizes a specific gas into active particles. The active particles react with the impurity elements evaporated from the molten metal pool to generate compounds. Step 5 Product Collection: Remove the gaseous compound, maintain the melting process for 5 to 30 minutes, then cool and remove the metal ingot to obtain high-purity metal.

2. The method for preparing high-purity metals by electron beam melting according to claim 1, characterized in that, In step 3, the purity of the specific gas is not less than 99.999%, and the specific gas is selected according to the impurity element to be removed, and is selected from H2, NH3, O2, CO2 or a mixture thereof.

3. The method for preparing high-purity metals by electron beam melting according to claim 2, characterized in that, When the impurity element to be removed is oxygen or sulfur, H2 or NH3 is selected; when the impurity element to be removed is nitrogen or carbon, O2 or CO2 is selected; when the impurity element to be removed is a mixture of multiple impurities, a mixture of H2, NH3, O2 and CO2 is selected.

4. The method for preparing high-purity metals by electron beam melting according to claim 1, characterized in that, In step 4, the electron beam is used for spiral scanning, and the scanning range covers the surface of the molten pool. The temperature of the molten pool is controlled at 100°C to 500°C above the melting point of the metal to be purified.

5. The method for preparing high-purity metals by electron beam melting according to claim 1, characterized in that, In step 5, the vacuum level inside the furnace is kept stable by adjusting the pumping rate of the vacuum system.

6. The method for preparing high-purity metals by electron beam melting according to any one of claims 1-5, characterized in that, The metal to be purified is ruthenium, titanium, zirconium, tantalum, niobium, copper, or aluminum.

7. The method for preparing high-purity metals by electron beam melting according to claim 6, characterized in that, The high-purity metal obtained in step 5 has a purity of not less than 99.999%.

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