A method for the reductive preparation of metallic hafnium

Abstract

The application relates to the technical field of rare metals, and discloses a method for preparing metal hafnium by reduction, which comprises the following steps: S1, mixing hafnium oxide, calcium and calcium chloride, and carrying out a thermal reduction reaction under a protective gas to obtain a solid mixture; S2, carrying out acid pickling, water washing and drying on the solid mixture to obtain metal hafnium powder; S3, melting the metal hafnium powder under the protective gas, and cold-pressing and forming the metal hafnium powder to obtain the metal hafnium; the calcium chloride is composed of first calcium chloride and second calcium chloride, and the first calcium chloride and the second calcium chloride are in different forms. Through the technical scheme, the problem of high oxygen content in the related art when metal hafnium is prepared by reduction is solved.

Description

A method for preparing metallic hafnium by reduction Technical Field

[0001] This invention relates to the field of rare metals technology, and more specifically, to a method for the reduction preparation of metallic hafnium. Background Technology

[0002] In the reduction process of preparing metallic hafnium, thermal reduction methods often utilize magnesium, calcium, aluminum, etc., as reducing agents to reduce the chlorides or oxides of metallic hafnium. Among them, the calcium reduction method has the advantages of relatively simple process and high recovery rate. However, in the reaction of calcium reducing hafnium oxide, the generated metallic hafnium easily coats calcium oxide, resulting in a high oxygen content. Since the calcium oxide particles are mechanically wrapped inside the hafnium powder, it is difficult to completely remove them through conventional physical separation (such as acid washing and sieving). Therefore, flux is added. However, the effect of existing fluxes is limited and cannot effectively solve the problem of metallic hafnium coating calcium oxide. As a result, the oxygen content of the product is still high. When the oxygen content is too high, oxygen, as an interstitial impurity atom, will be embedded in the metallic hafnium lattice, causing lattice distortion, significantly reducing the plasticity and toughness of the material. Moreover, excessive oxygen content will also limit the application scenarios of metallic hafnium.

[0003] Therefore, it is necessary to propose a method for the reduction preparation of metallic hafnium. Summary of the Invention

[0004] This invention proposes a method for the reduction preparation of metallic hafnium, which solves the problem of high oxygen content in the reduction preparation of metallic hafnium in related technologies.

[0005] The technical solution of the present invention is as follows: The present invention proposes a method for preparing metallic hafnium by reduction, comprising the following steps:

[0006] S1. Hafnium oxide, calcium, and calcium chloride are mixed and subjected to a thermal reduction reaction under a protective gas to obtain a solid mixture;

[0007] S2. The solid mixture is acid-washed, water-washed, and dried to obtain hafnium metal powder;

[0008] S3. The metal hafnium powder is melted under a protective gas and then cold-pressed to obtain metal hafnium.

[0009] The calcium chloride is composed of a first calcium chloride and a second calcium chloride, which have different forms.

[0010] As a further technical solution, the first calcium chloride is in the form of spiky granules, the second calcium chloride is in the form of powder, and the mass ratio of the first calcium chloride to the second calcium chloride is 1~1.2:5.

[0011] In the process of reducing and preparing metallic hafnium in this invention, the first calcium chloride is in the form of spiky granules, and the second calcium chloride is in the form of powder. The powdered calcium chloride can melt first to form a low-viscosity liquid phase, which comes into contact with calcium oxide. The spiky granules of calcium chloride have a porous structure and a larger particle size, and have a lower melting rate than the powdered calcium chloride. This can avoid a sudden increase in overall viscosity after melting. Furthermore, the continuous melting of the spiky granules of calcium chloride can continuously release calcium ions into the molten salt in the later stages of the reaction, replenishing the calcium chloride concentration lost due to reaction or volatilization, forming a dynamic dissolution equilibrium. This ensures that calcium oxide can be efficiently captured and dissolved throughout the entire thermal reduction process, further reducing the oxygen content of metallic hafnium.

[0012] In the process of reducing and preparing metallic hafnium in this invention, the mass ratio of the first calcium chloride and the second calcium chloride is 1~1.2:5. This ratio ensures that the rapid melting stage dominated by powdered calcium chloride is dominant, preferentially forming a molten salt environment to meet the need for rapid capture of calcium oxide in the early stage of the reaction. In the middle and late stages of the reaction, the spiky granular calcium chloride gradually melts, releasing the calcium ions stored inside, maintaining a high concentration of calcium chloride in the molten salt, and avoiding a decrease in solubility due to excessive consumption of powdered calcium chloride, thereby further reducing the oxygen content of metallic hafnium.

[0013] As a further technical solution, in step S2, the acid solution used for pickling is composed of a hydrochloric acid aqueous solution and an acid solution containing phenolic hydroxyl groups in a mass ratio of 4:1~1.5.

[0014] In the process of reducing and preparing metallic hafnium in this invention, the acid solution used for pickling consists of hydrochloric acid aqueous solution and acid solution containing phenolic hydroxyl groups, with hydrochloric acid accounting for a large proportion to ensure strong acidity of the system, which is used to dissolve most impurities. The addition of acid solution containing phenolic hydroxyl groups not only prevents metallic hafnium from being excessively corroded by hydrochloric acid, but the phenolic hydroxyl groups it contains also have antioxidant properties, which can slow down the oxidation of metallic hafnium powder during the pickling process, thereby improving the purity of metallic hafnium.

[0015] As a further technical solution, the acid solution containing phenolic hydroxyl groups includes one or more of p-hydroxycinnamic acid alcohol solution, 2,4,5-trihydroxybenzoic acid alcohol solution, and 3,4-dihydroxycinnamic acid alcohol solution, preferably 3,4-dihydroxycinnamic acid alcohol solution.

[0016] In the process of reducing and preparing metallic hafnium in this invention, the acid solution containing phenolic hydroxyl groups is preferably a 3,4-dihydroxycinnamic acid alcohol solution. The 3,4-dihydroxycinnamic acid alcohol solution contains an appropriate amount of phenolic hydroxyl groups, which can avoid the problem of insufficient antioxidant performance caused by too little phenolic hydroxyl content, and can also avoid the problem of excessive viscosity of the pickling solution caused by too much phenolic hydroxyl content, which would affect the pickling efficiency of the acid solution.

[0017] As a further technical solution, the solvents for the p-hydroxycinnamic acid alcohol solution, the 2,4,5-trihydroxybenzoic acid alcohol solution, and the 3,4-dihydroxycinnamic acid alcohol solution are all anhydrous ethanol.

[0018] As a further technical solution, the mass concentration of the hydrochloric acid aqueous solution is 8%~12%, for example, it can be 8%, 9%, 10%, 11%, 12%, preferably 10%, and the mass concentration of the acid solution containing phenolic hydroxyl groups is 5%~10%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, preferably 8%.

[0019] In the process of reducing and preparing metallic hafnium in this invention, the mass concentration of hydrochloric acid aqueous solution during pickling is 8%~12%. If the hydrochloric acid concentration is too low, it is difficult to effectively dissolve impurities, and if the concentration is too high, it will aggravate the corrosion of metallic hafnium powder. In addition, hydrochloric acid is volatile and generates a large amount of HCl acid mist, which corrodes equipment and endangers the health of operators. The mass concentration of acid solution containing phenolic hydroxyl groups is 5%~10%, which maintains the balance between the antioxidant activity and viscosity of the pickling solution. The two solutions are mixed at specific concentrations to exert their synergistic effect and further improve the purity of metallic hafnium.

[0020] As a further technical solution, in step S1, the protective gas includes one of argon and helium, preferably argon.

[0021] In the process of reducing and preparing metallic hafnium in this invention, the protective gas for the thermal reduction reaction is preferably argon. As an inert gas, argon will not react chemically with the raw materials in the thermal reduction reaction, thus avoiding the generation of impurities such as oxides and nitrides due to the participation of the gas in the reaction and improving the purity of metallic hafnium.

[0022] As a further technical solution, in step S1, the mass ratio of hafnium oxide to calcium is 1:1 to 2, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2, preferably 1:1.7.

[0023] As a further technical solution, in step S1, the mass ratio of hafnium oxide to calcium chloride is 1:1 to 3, for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, or 1:3, preferably 1:3.

[0024] As a further technical solution, in step S1, the temperature of the thermal reduction reaction is 900~1200℃, for example, it can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, preferably 1000℃, and the time is 2~4h, for example, it can be 2h, 2.3h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h, 4h, preferably 3h.

[0025] As a further technical solution, in step S2, the number of acid washings is 3 to 5 times, for example, 3 times, 4 times, or 5 times, preferably 3 times, and the number of water washings is 1 to 2 times, for example, 1 time or 2 times, preferably 1 time.

[0026] As a further technical solution, in step S3, the protective gas includes one of argon and helium, preferably argon.

[0027] The working principle and beneficial effects of this invention are as follows:

[0028] In the reduction preparation of metallic hafnium of this invention, calcium chloride is used as a flux, composed of different forms of calcium chloride (first and second). These two forms work synergistically to further promote the dissolution of calcium oxide and reduce the oxygen content of metallic hafnium. In existing technologies, calcium chloride is often added as a flux to reduce oxygen content, but the effect of existing fluxes is limited. This invention focuses on the influence of the different forms of calcium chloride on the dissolution efficiency of calcium oxide. By mixing different forms of calcium chloride (first and second), this invention adjusts the melting rate and uniformity of calcium chloride, and modulates the fluidity and viscosity of the molten salt, enabling efficient dissolution and separation of calcium oxide in the molten salt, further reducing the oxygen content of metallic hafnium. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following examples and comparative examples:

[0031] Hafnium oxide: purity 97.5 wt%, zirconium oxide content 1.8 wt%;

[0032] First calcium chloride: spiky granules, purchased from Shandong Haihua Supply Chain Co., Ltd., product number 6879;

[0033] Second calcium chloride: powder, purchased from Shandong Haihua Supply Chain Co., Ltd., product number 20210331;

[0034] The solvents for p-hydroxycinnamic acid alcohol solution, 2,4,5-trihydroxybenzoic acid alcohol solution and 3,4-dihydroxycinnamic acid alcohol solution are all anhydrous ethanol.

[0035] Example 1

[0036] A method for preparing metallic hafnium by reduction includes the following steps:

[0037] S1. Mix 10g of hafnium oxide, 17g of calcium and 30g of calcium chloride, and heat to 900℃ for thermal reduction reaction for 3h under argon protection to obtain a solid mixture; wherein the calcium chloride is composed of first calcium chloride and second calcium chloride in a mass ratio of 1:5;

[0038] S2. The solid mixture is subjected to three acid washes, one water wash, and drying to obtain metallic hafnium powder; the acid solution used in the three acid washes is an 8wt% hydrochloric acid aqueous solution.

[0039] S3. Metal hafnium powder is melted under argon protection and then cold-pressed to obtain metal hafnium.

[0040] In this embodiment, the purity of the metallic hafnium is 99.27 wt%, and the oxygen content is 382 ppm.

[0041] Example 2

[0042] A method for preparing metallic hafnium by reduction includes the following steps:

[0043] S1. Mix 10g of hafnium oxide, 17g of calcium and 30g of calcium chloride, and heat to 1000℃ for 3h under argon protection to obtain a solid mixture; wherein the calcium chloride is composed of first calcium chloride and second calcium chloride in a mass ratio of 1:5.

[0044] S2. The solid mixture is subjected to three acid washes, one water wash, and drying to obtain metallic hafnium powder; the acid solution used in the three acid washes is a 10wt% hydrochloric acid aqueous solution.

[0045] S3. Metal hafnium powder is melted under argon protection and then cold-pressed to obtain metal hafnium.

[0046] In this embodiment, the purity of the metallic hafnium is 99.42 wt%, and the oxygen content is 227 ppm.

[0047] Example 3

[0048] A method for preparing metallic hafnium by reduction includes the following steps:

[0049] S1. Mix 10g of hafnium oxide, 17g of calcium and 30g of calcium chloride, and heat to 1200℃ for thermal reduction reaction for 3h under argon protection to obtain a solid mixture; wherein the calcium chloride is composed of first calcium chloride and second calcium chloride in a mass ratio of 1:5;

[0050] S2. The solid mixture is subjected to three acid washes, one water wash, and drying to obtain metallic hafnium powder; the acid solution used in the three acid washes is a 12wt% hydrochloric acid aqueous solution.

[0051] S3. Metal hafnium powder is melted under argon protection and then cold-pressed to obtain metal hafnium.

[0052] In this embodiment, the purity of the metallic hafnium is 99.34 wt%, and the oxygen content is 309 ppm.

[0053] Example 4

[0054] The difference between Example 4 and Example 2 is that the calcium chloride is composed of first calcium chloride and second calcium chloride in a mass ratio of 1.2:5.

[0055] The purity of the metallic hafnium is 99.45 wt%, and the oxygen content is 164 ppm.

[0056] Example 5

[0057] Compared with Example 4, the difference in Example 5 is that the acid solution used for pickling in step S2 is different. In this example, the acid solution is an 8% p-hydroxycinnamic acid alcohol solution.

[0058] In this embodiment, the purity of the metallic hafnium is 90.01 wt%, and the oxygen content is 176 ppm.

[0059] Example 6

[0060] Compared with Example 4, Example 6 differs in that the acid solution used for pickling in step S2 is different. In this example, the acid solution consists of a hydrochloric acid aqueous solution (mass concentration of 10%) and a p-hydroxycinnamic acid alcohol solution (mass concentration of 8%) with a mass ratio of 4:1.

[0061] In this embodiment, the purity of the metallic hafnium is 99.73 wt%, and the oxygen content is 158 ppm.

[0062] Example 7

[0063] Compared with Example 6, Example 7 differs in that the acid solution in this example is composed of a hydrochloric acid aqueous solution (mass concentration of 10%) and a p-hydroxycinnamic acid alcohol solution (mass concentration of 8%) with a mass ratio of 4:1.5.

[0064] In this embodiment, the purity of the metallic hafnium is 99.79 wt%, and the oxygen content is 150 ppm.

[0065] Example 8

[0066] The difference between Example 8 and Example 7 is that the p-hydroxycinnamic acid alcohol solution is replaced with an equal mass of 2,4,5-trihydroxybenzoic acid alcohol solution.

[0067] In this embodiment, the purity of the metallic hafnium is 99.81 wt%, and the oxygen content is 141 ppm.

[0068] Example 9

[0069] The difference between Example 9 and Example 7 is that the p-hydroxycinnamic acid alcohol solution is replaced with an equal mass of 3,4-dihydroxycinnamic acid alcohol solution.

[0070] In this embodiment, the purity of the metallic hafnium is 99.87 wt% and the oxygen content is 132 ppm.

[0071] Comparative Example 1

[0072] The difference between Comparative Example 1 and Example 2 is that calcium chloride is only the first calcium chloride;

[0073] In this comparative example, the purity of metallic hafnium was 99.18 wt%, and the oxygen content was 671 ppm.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 2 is that the calcium chloride used is only the second calcium chloride;

[0076] In this comparative example, the purity of metallic hafnium was 99.23 wt%, and the oxygen content was 584 ppm.

[0077] Comparing Examples 1-4 with Comparative Examples 1 and 2, it can be seen that when calcium chloride is composed of first calcium chloride and second calcium chloride, the oxygen content of metallic hafnium can be reduced.

[0078] Comparing Examples 4 and 5 with Examples 6 and 7, it can be seen that when the acid solution during pickling consists of hydrochloric acid aqueous solution and acid solution containing phenolic hydroxyl groups, the purity of metallic hafnium can be further improved.

[0079] Comparing Examples 7-9, it can be seen that when the acid solution containing phenolic hydroxyl groups contains an appropriate amount of phenolic hydroxyl groups, that is, preferably a 3,4-dihydroxycinnamic acid alcohol solution, the purity of metallic hafnium can be further improved.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing metallic hafnium by reduction, characterized in that, Includes the following steps: S1. Hafnium oxide, calcium, and calcium chloride are mixed and subjected to a thermal reduction reaction under a protective gas to obtain a solid mixture; S2. The solid mixture is acid-washed, water-washed, and dried to obtain metallic hafnium powder; S3. The metallic hafnium powder is melted under a protective gas and cold-pressed to obtain metallic hafnium; The calcium chloride is composed of first calcium chloride and second calcium chloride, which have different forms; the first calcium chloride is in the form of spiky granules, and the second calcium chloride is in the form of powder, with a mass ratio of 1~1.2:5; In step S2, the acid solution used for acid washing is composed of hydrochloric acid aqueous solution and phenolic hydroxyl-containing acid solution in a mass ratio of 4:1~1.5; The phenolic hydroxyl-containing acid solution is 3,4-dihydroxycinnamic acid alcohol solution.

2. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, The hydrochloric acid aqueous solution has a mass concentration of 8% to 12%, and the acid solution containing phenolic hydroxyl groups has a mass concentration of 5% to 10%.

3. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, In step S1, the protective gas includes either argon or helium.

4. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, In step S1, the mass ratio of hafnium oxide to calcium is 1:1~2.

5. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, In step S1, the mass ratio of hafnium oxide to calcium chloride is 1:1~3.

6. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, In step S1, the temperature of the thermal reduction reaction is 900~1200℃ and the time is 2~4h.

7. The method for preparing metallic hafnium by reduction according to claim 1, characterized in that, In step S2, the acid washing is performed 3 to 5 times, and the water washing is performed 1 to 2 times.