A method for controllably reducing sodium to produce low-oxygen titanium powder

Abstract

The application provides a method for preparing low-oxygen titanium powder by controllable sodium reduction, which comprises the following steps: filtering and purifying metal sodium through a molten sodium system to obtain purified sodium; placing molten salt containing TiCl2 in a reactor, vacuumizing and heating, then slowly adding the purified sodium to perform sodium reduction, and obtaining a mixture containing titanium powder after the reaction; crushing the mixture containing titanium powder into fine-grained material with a particle size of no more than 10 mm, washing the molten salt in the fine-grained material with deionized water and dilute hydrochloric acid solution, then washing with water until neutral, vacuum drying, and obtaining fine titanium powder; reducing the oxygen of the fine titanium powder in a hydrogen atmosphere by using magnesium and magnesium chloride, washing with dilute hydrochloric acid solution and deionized water, and finally vacuum drying to obtain low-oxygen titanium powder. 50 The particle size of the prepared low-oxygen titanium powder is 10-50 μm, D 50 is 20-30 μm, and the oxygen content is ≤1000 ppm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of titanium powder preparation, in particular to a method for preparing low-oxygen titanium powder by controllable sodium reduction. BACKGROUND

[0002] Metallic titanium has the advantages of low density, low elastic modulus, high specific strength, good corrosion resistance and biocompatibility, and is widely used in aerospace, chemical industry, medicine and other fields. Additive manufacturing, also known as 3D printing, is a technology that uses a layer-by-layer accumulation method to manufacture specific geometric structures. Additive manufacturing can produce complex structural parts that are difficult to produce by traditional processing methods, and has become a new method for producing titanium and titanium alloy parts. With the rapid development of metal additive manufacturing technology, the demand for spherical titanium powder is also increasing.

[0003] Radio frequency plasma spheroidization method has the characteristics of high temperature and high heat enthalpy. The prepared powder has high spheroidization rate and spherical degree, narrow particle size distribution, high fine powder yield and low cost. It is the most potential technology for industrial production of spherical titanium powder at present. Jing Li et al. used sponge titanium hydrogenated dehydrogenated titanium powder as raw material when spheroidizing titanium powder by plasma, but the oxygen content was generally high (>2000ppm), which led to high oxygen content of the spheroidized powder, which could not meet the demand of additive manufacturing for low-oxygen titanium powder, and calcium needed to be used for deoxidation, increasing the process flow and cost (Jing Li, Zhenhua Hao, Yongchun Shu, Jilin He. Fabrication of spherical Ti-6Al-4V powder for additive manufacturing by radio frequency plasma spheroidization and deoxidation using calcium [J]. Journal of materials research and technology, 2020; 9(6): 14792-14798.). Therefore, it is urgent to develop a low-oxygen titanium powder raw material preparation technology with particle size of 10-50μm and D 50 20-30μm, oxygen content ≤1000ppm for plasma spheroidization, to meet the requirements of 3D printing materials.

[0004] Sodium reduction method (also known as Hunter method) is one of the methods for industrial production of titanium powder. At present, sodium reduction two-stage method uses metallic sodium to reduce titanium tetrachloride in both stages, resulting in large sodium consumption and high cost. In addition, the molten salt in the reaction process is mainly sodium chloride, and no other diluent molten salt is added. The reaction temperature is greater than 850℃, and the adjustable range is narrow (Zhu Xiaofang, Li Qing, Zhang Ying, Fang Zhigang, Zheng Shili, Sun Pei, Xia Yang. Research progress on preparation of metallic titanium by thermochemical reduction method [J]. Journal of Process Engineering, 2019, 19(03): 456-464), and it is difficult to accurately control the particle size and morphology of titanium powder.

[0005] Patents CN112705720B and CN112756621B propose HAMR method for preparing low-oxygen titanium powder, which first discovers the regulation mechanism of solid solution H on the thermodynamic stability of Ti-O solid solution, and solves the problem of difficult deoxidation of magnesium hot reduction of titanium oxide from the chemical principle, but it uses titanium dioxide as the precursor, and the content of metal impurities in the end product is easily affected by the precursor. In order to obtain titanium powder with high purity, high quality precursor needs to be used, and the mass ratio of reducing agent to titanium oxygen intermediate needs to be large, which is (0.05-5):1. SUMMARY

[0006] The present application proposes a method for preparing low-oxygen titanium powder by controllable sodium reduction, and the particle size range of the prepared low-oxygen titanium powder is 10-50μm, D 50 20-30μm, and the oxygen content is ≤1000ppm.

[0007] The technical scheme of the present application is realized as follows: a method for preparing low-oxygen titanium powder by controllable sodium reduction, comprising the following steps:

[0008] (1) filtering, purifying and purifying the metallic sodium through a molten sodium system to obtain purified sodium;

[0009] (2) placing the molten salt containing TiCl2 in a reactor, slowly adding purified sodium after vacuumizing and heating, and carrying out sodium reduction, to obtain a mixture containing titanium powder after the reaction is completed;

[0010] (3) crushing the mixture containing titanium powder into fine particle materials with a particle size not greater than 10mm, washing the molten salt in the fine particle materials with deionized water and dilute hydrochloric acid solution, then washing with deionized water until neutral, and vacuum drying to obtain fine titanium powder;

[0011] (4) reducing the fine titanium powder obtained in step (3) in a hydrogen atmosphere by using magnesium and magnesium chloride, and then washing with dilute hydrochloric acid solution and deionized water in sequence, and finally vacuum drying to obtain low-oxygen titanium powder.

[0012] Further, in step (2), the molten salt containing TiCl2 is prepared by the following method: vacuumizing and heating (heating to 300℃ for 2-12h) the diluent molten salt and titanium sponge under sealed condition, further removing the water in the diluent molten salt, then filling argon and heating to the reaction temperature of the molten salt, injecting TiCl4 under micro-negative pressure of -0.01 to -0.1 MPa, so that the titanium sponge and TiCl4 react to generate the molten salt containing TiCl2.

[0013] Further, in step (2), the molten salt containing TiCl2 is prepared by the following method: vacuumizing and heating (heating to 300℃ for 2-12h) the diluent molten salt and titanium sponge under sealed condition, further removing the water in the diluent molten salt, then filling argon and heating to the reaction temperature of the molten salt, injecting TiCl4 under micro-negative pressure of -0.01 to -0.1 MPa, so that the titanium sponge and TiCl4 react to generate the molten salt containing TiCl2.

[0014] Further, the diluent molten salt is heated and stored at 60-100℃ for 2-24h before use to remove the water in the diluent molten salt.

[0015] Further, the diluent molten salt is NaCl, KCl, LiCl, CaCl2, MgCl2, NaF and KF.

[0016] Further, the diluent molten salt is NaCl, KCl, LiCl, CaCl2, MgCl2, NaF and KF.

[0017] Further, the mass ratio of the diluent molten salt to the titanium sponge is (10-200):1.

[0018] Further, the mass of TiCl4 is 0.4-1kg, the mass of the titanium sponge is 0.2-0.5kg, the reaction temperature is 700-900℃, and the reaction time is 2-12h.

[0019] Further, in step (1), the purified sodium contains Na≥99.7wt.%, K≤0.003wt.%, Fe≤0.001wt.%, heavy metals≤0.005wt.%, and C content≤30ppm; the filtration and purification process of the molten sodium system is as follows: heating the metallic sodium to 150℃ for melting, then removing oil at 130℃ and -0.08MPa vacuum, coarsely filtering with a stainless steel mesh at 130℃, finely filtering with a ceramic filter at 130℃, transferring into a cold trap at 150℃ for treatment, and then storing in a storage tank.

[0020] Further, in step (2), the mass ratio of TiCl2 to the purified sodium is (2.3-2.6):1, the reaction temperature is 700-950℃, and the sodium adding speed is 0.8%-3.5% of the total sodium amount per minute.

[0021] Further, in steps (3) and (4), the dilute hydrochloric acid solution refers to a hydrochloric acid aqueous solution with a mass concentration of 0.5% to 10%, and the pickling stirring time is 0.5 to 6 hours.

[0022] Further, in step (4), the mass of the fine titanium powder is 1 kg, the mass of the magnesium is 0.002 to 0.05 kg, the mass of the magnesium chloride is 0.3 to 0.5 kg, the reaction temperature is 700 to 900 ℃, and the reaction time is 1 to 6 hours.

[0023] The present application has the following beneficial effects:

[0024] 1. The present application controls the particle size of titanium powder by regulating the composition of the diluent molten salt, the reaction temperature, the sodium addition speed, etc. in the sodium reduction process to affect the nucleation and growth of titanium grains, and adopts magnesium to reduce oxygen, so that a high-purity low-oxygen titanium powder product can be prepared.

[0025] 2. The particle size D 50 of general titanium powder is smaller, and the oxygen content is higher. Through the preparation method of the low-oxygen titanium powder of the present application, the particle size range of the low-oxygen titanium powder is controlled to be 10 to 50 μm, and the D 50 is controlled to be 20 to 30 μm, and the oxygen content is ≤1000 ppm.

[0026] 3. The present application adopts a two-stage reduction method to prepare the metal titanium powder, and compared with the Hunter method, sponge titanium is used as the reducing agent in the first-stage reduction instead of the traditional sodium, so that the consumption of sodium is saved, and the cost is saved. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0028] Embodiment 1:

[0029] A method for preparing low-oxygen titanium powder by controllable sodium reduction comprises the following steps:

[0030] (1) The diluent molten salt NaCl is heated to 80 ℃ in an oven for 24 hours to remove the water in the NaCl;

[0031] (2) Put the NaCl and titanium sponge treated by step (1) into a reactor according to a mass ratio of 25:1, seal the reactor, and then replace the reactor with argon for at least 3 times after vacuumizing the reactor. Further remove the water in the NaCl by heating the reactor to 300℃ for 2h after vacuumizing, and then fill the reactor with argon to make the pressure in the reactor 0.03 MPa. Start to heat the reactor, and then inject TiCl4 into the reactor under a micro negative pressure of -0.01 MPa at 850℃, wherein the mass ratio of titanium tetrachloride to titanium sponge is 2:1, and the heating is kept for 4h to generate a molten salt containing TiCl2;

[0032] (3) Purify the metallic sodium by filtering and purifying the sodium through a molten sodium system to obtain purified sodium;

[0033] (4) Put the molten salt containing TiCl2 into a reactor, inject the purified sodium into the reactor after vacuumizing and heating, wherein the mass ratio of TiCl2 to purified sodium is 2.5:1, and the sodium injection speed is 1% of the total sodium dosage per minute. Perform a sodium reduction reaction at 850℃, and then naturally cool the reactor to obtain a mixture containing titanium powder;

[0034] (5) Open the reactor to take out the mixture, crush the mixture into fine particles with a particle size of no more than 10 mm, and then stir and wash the fine particle material in deionized water and a 1 wt.% hydrochloric acid solution for 2h respectively to obtain an acid-washed powder. After washing the residual acid with deionized water, dry the acid-washed powder in a vacuum drying oven for 4h to obtain fine titanium powder;

[0035] (6) Put the fine titanium powder, magnesium chips and magnesium chloride into a crucible according to a mass ratio of 1:0.01:0.4, heat to 800℃ in a hydrogen atmosphere, and then heat for 2h to reduce the oxygen in the titanium powder. Then stir and wash the titanium powder in a 1 wt.% dilute hydrochloric acid solution for 2h, and then wash and dry the titanium powder to obtain low-oxygen titanium powder.

[0036] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size analyzer, and has a purity of 99.9%, an oxygen content of 969 ppm, and a particle size D 50 of 30 μm.

[0037] Example 2:

[0038] A method for preparing low-oxygen titanium powder by controllable sodium reduction includes the following steps:

[0039] (1) Dilute the NaCl and KCl diluent with a molar ratio of 1:1 in an oven, heat to 100℃, and then heat for 12h to remove the water in the NaCl+KCl mixed molten salt;

[0040] (2) Put the NaCl+KCl mixed molten salt and sponge titanium treated in step (1) into a reactor in a mass ratio of 100:1, seal the reactor, and then replace the reactor with argon for at least 3 times after vacuumizing the reactor. Remove the water in the reactor by heating to 300℃ for 2h after vacuumizing, and then fill argon to make the pressure in the reactor 0.01 MPa. Start to heat, and then inject TiCl4 from the top under a micro negative pressure of -0.01 MPa when the temperature is 750℃. The mass ratio of sponge titanium to TiCl4 is 2:1, and the heating is kept for 3.5h to generate TiCl2 mixed molten salt;

[0041] (3) Purify the sodium metal by filtering and purifying through a molten sodium system to obtain purified sodium;

[0042] (4) Put the molten salt containing TiCl2 into a reactor, inject the purified sodium after vacuumizing and heating, and the mass ratio of TiCl2 to purified sodium is 2.5:1. The sodium injection speed is 1.7% of the total sodium amount per minute. Perform sodium reduction reaction at 750℃, and then naturally cool to obtain a mixture containing titanium powder;

[0043] (5) Open the reactor to take out the mixture, crush the mixture into fine particles with a particle size of no more than 10mm, and then add the fine particle material into deionized water and 5wt.% hydrochloric acid solution respectively for stirring and washing for 5h to obtain pickled powder. After washing the pickled powder with deionized water to remove residual acid, dry the pickled powder in a vacuum drying box for 3h to obtain fine titanium powder;

[0044] (6) Put the fine titanium powder, magnesium chips and magnesium chloride into a crucible in a mass ratio of 1:0.02:0.4, heat to 850℃ in a hydrogen atmosphere, and then heat for 2h to reduce the oxygen in the titanium powder. Then, use 3wt.% dilute hydrochloric acid solution to stir and wash the titanium powder for 4h, and then wash and dry the titanium powder to obtain low-oxygen titanium powder.

[0045] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size instrument. The purity is 99.8%, the oxygen content is 875ppm, and the particle size D 50 is 25μm.

[0046] Example 3:

[0047] The step (2) in the embodiment provides a method for preparing low-oxygen titanium powder by controllable sodium reduction. The diluent molten salt in the step (2) is NaCl and KCl in a molar ratio of 1:1, and the rest are the same as those in the example 1.

[0048] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size instrument. The purity is 99.9%, the oxygen content is 920ppm, and the particle size D 50 is 21μm.

[0049] Example 4:

[0050] The present example provides a method for preparing low-oxygen titanium powder by controllable sodium reduction. Step (2) is omitted, and commercially available TiCl2 is purchased. The commercially available TiCl2 is mixed with the diluent molten salt in step (4) at a mass ratio of TiCl2 to diluent molten salt of 1:8, and then placed in the reactor. The rest is the same as in Example 1.

[0051] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size analyzer. The purity is 99.9%, the oxygen content is 910 ppm, and the particle size D 50 is 28 μm.

[0052] Comparative Example 1:

[0053] The present example provides a method for preparing low-oxygen titanium powder by controllable sodium reduction. Step (2) is omitted, and commercially available TiCl2 is purchased. The commercially available TiCl2 is mixed with the diluent molten salt in step (4) at a mass ratio of TiCl2 to diluent molten salt of 1:8, and then placed in the reactor. The rest is the same as in Example 1.

[0054] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size analyzer. The purity is 99.9%, the oxygen content is 910 ppm, and the particle size D 50 is 28 μm.

[0055] Comparative Example 1:

[0056] The present example provides a method for preparing low-oxygen titanium powder by controllable sodium reduction. Step (2) is omitted, and commercially available TiCl2 is purchased. The commercially available TiCl2 is mixed with the diluent molten salt in step (4) at a mass ratio of TiCl2 to diluent molten salt of 1:8, and then placed in the reactor. The rest is the same as in Example 1.

[0057] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size analyzer. The purity is 99.9%, the oxygen content is 910 ppm, and the particle size D 50 is 28 μm.

[0058] Comparative Example 1:

[0059] The present example provides a method for preparing low-oxygen titanium powder by controllable sodium reduction. Step (2) is omitted, and commercially available TiCl2 is purchased. The commercially available TiCl2 is mixed with the diluent molten salt in step (4) at a mass ratio of TiCl2 to diluent molten salt of 1:8, and then placed in the reactor. The rest is the same as in Example 1.

[0060] The prepared titanium powder is detected by ICP, nitrogen and oxygen analyzers, and a laser particle size analyzer. The purity is 99.9%, the oxygen content is 910 ppm, and the particle size D 50 is 28 μm.

[0061] Comparative Example 1 and Example 3 can be seen that in Example 1, the diluent molten salt in step (2) is NaCl, the particle size D 50 of the titanium powder is 30 μm, while in Example 3, the diluent molten salt in step (2) is NaCl and KCl, and the particle size D 50 of the titanium powder is 21 μm. This indicates that by controlling the composition of the diluent molten salt in sodium reduction, the particle size of the titanium powder can be controlled.

[0062] From the comparison of Example 1 and Comparative Example 1, it can be seen that Comparative Example 1 does not add step (6), and the oxygen content of the powder is higher, being 1640 ppm, while Example 1 adds step (6), and the oxygen content of the titanium powder is lower, being 969 ppm, thus indicating that the oxygen content of the titanium powder can be effectively reduced by hydrogen gas in cooperation with magnesium.

[0063] From the comparison of Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, the sodium addition speed in step (6) is 4% of the total sodium dosage per minute, and the titanium powder particle size is 56 μm, while in Example 1, the sodium addition speed in step (6) is 1% of the total sodium dosage per minute, and the titanium powder particle size is 30 μm, thus indicating that the particle size of the titanium powder can be controlled by controlling the sodium addition speed.

[0064] From the comparison of Example 2 and Comparative Example 3, it can be seen that in Comparative Example 3, the reaction temperature in step (4) is 1000℃, and the titanium powder particle size D 50 53 μm, which does not meet the requirements of 3D printing on the particle size of the titanium powder, while in Example 2, the reaction temperature in step (4) is 750℃, and the titanium powder particle size D 50 25 μm, which meets the requirements of 3D printing on the particle size of the titanium powder, thus indicating that the particle size of the titanium powder can be controlled by controlling the reaction temperature of sodium reduction.

[0065] The purity, oxygen content and particle size distribution of the titanium powder of Examples 1-4 of the present application all meet the requirements of the raw material powder for radio frequency induction plasma spheroidization.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of controllably reducing sodium to produce low-oxygen titanium powder, characterized by, The method comprises the following steps: (1) filtering and purifying molten sodium to obtain purified sodium; (2) placing a molten salt containing TiCl2 in a reactor, vacuumizing and heating, then slowly adding the purified sodium to perform sodium reduction, and obtaining a mixture containing titanium powder after the reaction is completed; (3) crushing the mixture containing titanium powder into fine-grained materials with a particle size of not more than 10 mm, washing the fine-grained materials with deionized water and a dilute hydrochloric acid solution, then washing to neutral with deionized water, and vacuum drying to obtain fine titanium powder; (4) reducing the oxygen of the fine titanium powder obtained in step (3) by using magnesium and magnesium chloride in a hydrogen atmosphere, washing with a dilute hydrochloric acid solution and deionized water after the reduction is completed, and finally vacuum drying to obtain low-oxygen titanium powder; In step (2), the molten salt containing TiCl2 is prepared by the following method: vacuumizing and heating the diluent salt and the sponge titanium under a sealed condition, further removing the water in the diluent salt, then filling argon and heating to the reaction temperature of the molten salt, and injecting TiCl4 under a micro-negative pressure of -0.01 to -0.1 MPa to make the sponge titanium and TiCl4 react to generate the molten salt containing TiCl2; The mass ratio of the diluent salt to the sponge titanium is (10-200):1; the mass of TiCl4 is 0.4-1 kg, the mass of the sponge titanium is 0.2-0.5 kg, the reaction temperature is 700-900 DEG C, and the reaction time is 2-12 h; In step (2), the mass ratio of TiCl2 to the purified sodium is (2.3-2.6):1, the reaction temperature is 700-950 DEG C, and the sodium adding speed is 0.8%-3.5% of the total sodium amount per minute; The particle size range of the low-oxygen titanium powder is 10 to 50 µm, D 50 20 to 30 µm, while the oxygen content is ≤ 1000 ppm.

2. A method of producing low oxygen titanium powder with controllable sodium reduction as claimed in claim 1, characterized in that, The diluent salt is preserved at 60-100 DEG C for 2-24 h before use to remove the water in the diluent salt.

3. A method of producing low oxygen titanium powder with controllable sodium reduction as claimed in claim 1, wherein, The diluent salt is any one or more of alkali metal chlorides, alkaline earth metal halides and alkali metal fluorides.

4. A method of producing low oxygen titanium powder with controllable sodium reduction according to claim 3, characterized in that, The diluent salt is any one or more of NaCl, KCl, LiCl, CaCl2, MgCl2, NaF and KF.

5. A method of producing low oxygen titanium powder with controllable sodium reduction as claimed in claim 1, wherein, In step (1), the purified sodium contains Na≥99.7wt.%, K≤0.003wt.%, Fe≤0.001wt.%, heavy metals≤0.005wt.% and C content≤30ppm.

6. A method of producing low oxygen titanium powder with controllable sodium reduction as claimed in claim 1, wherein, In steps (3) and (4), the dilute hydrochloric acid solution refers to a hydrochloric acid aqueous solution with a mass concentration of 0.5%-10%, and the acid pickling stirring time is 0.5-6 h.

7. A method of producing low oxygen titanium powder with controllable sodium reduction as claimed in claim 1, wherein, In step (4), the mass of the fine titanium powder is 1 kg, the mass of the magnesium is 0.002-0.05 kg, the mass of the magnesium chloride is 0.3-0.5 kg, the reaction temperature is 700-900 DEG C, and the reaction time is 1-6 h.