A method for integrated molding of metallic chromium powder and additives

Abstract

This invention discloses an integrated molding method for metallic chromium powder and additives, comprising: crushing chromite ore and mixing it with aluminum powder, adding additives, mixing and pressing the mixture into a compact, and then feeding it into an electric arc furnace for an electrothermal reaction; after the reaction, separating the slag and metallic chromium; crushing the prepared metallic chromium, adding a binder to the crushed metallic chromium powder, mixing, and then performing high-temperature sintering treatment to obtain high-temperature sintered metallic chromium powder, which is then cleaned and dried; pressing the dried metallic chromium powder into blocks to obtain the finished metallic chromium product. This invention addresses the issue of high carbon content in existing electrothermal methods for preparing metallic chromium by adding chromium trioxide, tin powder, or highly active tin powder to chromite ore. The reaction of chromium trioxide with carbon removes impurities, while the reaction of tin powder with sulfur generates volatile tin sulfide, thereby removing sulfur impurities from the metallic chromium and improving the purity of the finished metallic chromium product.

Description

Technical Field

[0001] This invention belongs to the field of metal powder processing technology, and more specifically, this invention relates to a method for the integrated molding of chromium metal powder and additives. Background Technology

[0002] Metallic chromium possesses advantages such as a high melting point and excellent corrosion resistance, making it crucial for industrial applications, especially in specialized equipment used in aerospace, nuclear power, and other fields where stringent requirements apply. Chromium naturally exists primarily in chromite ((Fe,Mg)Cr₂O₄). Industrially, metallic chromium is typically produced from chromium oxide using the electroaluminothermic process, or from chromium ammonium sulfate or chromic acid via electrolysis. The electroaluminothermic process is the most widely used method for producing metallic chromium due to its advantages of thorough conversion and low production costs.

[0003] Currently, the carbon content of ordinary metallic chromium prepared by the electrothermal method is relatively high, exceeding 0.5%. Furthermore, the resulting chromium powder contains impurities such as C and S. Since special equipment in aerospace, nuclear power, and other fields has extremely stringent requirements regarding the impurity content of metallic chromium, it is necessary to introduce appropriate impurity removal improvements to the existing electrothermal method to ensure that the impurity content of the prepared metallic chromium meets the requirements of these special equipment applications. Chinese invention patent CN113927040A discloses a method for preparing high-purity metallic chromium by carbon reduction. This patent uses graphite emulsion mixed with chromium oxide green (chromium trioxide), pressed into a compact, and vacuum sintered to obtain metallic chromium powder. While this patent can provide a conversion rate for chromium oxide, it cannot effectively remove sulfur impurities from chromite. Additionally, the prepared metallic chromium powder needs to be pressed into shape, and the molding method and style also significantly affect the properties of the metallic chromium product. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these objectives and other advantages according to the present invention, a method for integrally molding metallic chromium powder with additives is provided, comprising:

[0006] Step 1: After crushing chromite, mix it with aluminum powder and add additives. After mixing and pressing, put the mixture into an electric arc furnace for electrothermal reaction. After the reaction is completed, separate the slag liquid and metallic chromium.

[0007] Step 2: Crush the metallic chromium obtained in Step 1, add a binder to the crushed metallic chromium powder, mix the powder, and then perform high-temperature sintering treatment to obtain high-temperature sintered metallic chromium powder, which is then cleaned and dried.

[0008] Step 3: Press the dried chromium powder from Step 2 into blocks to obtain the finished chromium metal.

[0009] Preferably, in step one, the additives include chromium trioxide and tin powder, wherein the mass ratio of chromite, aluminum powder, chromium trioxide, and tin powder is 100-150:20-30:1-5:5-8; the chromite powder is crushed to a particle size of 100-200 mesh, the aluminum powder is crushed to a particle size of 100-300 mesh, the chromium trioxide is crushed to a particle size of 50-200 mesh, and the tin powder is crushed to a particle size of 30-100 mesh.

[0010] Preferably, in step one, the tin powder is highly active tin powder, and the preparation method of highly active tin powder includes:

[0011] S1. Select tin ingots with a purity greater than 99.99% and put them into a melting furnace for high-temperature melting. The melting temperature is 2000-2500℃ and the melting time is 1-3 hours.

[0012] S2. Atomize the molten tin through a nozzle at a temperature of 1000–1500°C for 20–60 minutes. After cooling to room temperature, obtain metallic tin powder.

[0013] S3. Spraying the surface of metallic tin powder with graphite emulsion to obtain highly active tin powder partially coated with graphite emulsion, wherein the mass ratio of graphite emulsion to metallic tin powder is 1-10:30-100.

[0014] Preferably, in step one, after the billet is fed in, the vacuum degree is first evacuated to 1×10⁻⁶. -3 ~5×10 - 3 Pa, then carbon dioxide is introduced to achieve a vacuum of 1 to 10 Pa.

[0015] Preferably, in step two, the binder added is one or more of sodium hexametaphosphate, sodium tripolyphosphate, and aluminum dihydrogen phosphate, and the mass ratio of the binder to the metallic chromium powder is 1-3:50-200.

[0016] Preferably, in step two, the sintering temperature is 1300–1800℃, the sintering time is 12–48 h, and the vacuum degree before sintering is less than 2.5 × 10⁻⁶. -2 Pa, then argon gas is introduced to standard atmospheric pressure.

[0017] Preferably, in step three, the pressure for forming the briquette is 20-60 MPa, and the pressure holding time is 20-60 s.

[0018] Preferably, in step one, after the chromite is crushed and mixed with aluminum powder, and after the additives are added, the pressed blank is cylindrical, honeycomb block or concentric spiral, and the blank has through holes of 2 to 20 mm pressed on it.

[0019] Preferably, in step two, after obtaining metallic chromium powder by high-temperature sintering, it is washed multiple times with clean water or deionized water, and the drying temperature is 100-120℃.

[0020] The present invention has at least the following beneficial effects: The integrated molding method of metallic chromium powder and additives provided by the present invention addresses the characteristic of high carbon content (approximately 0.5%) in the preparation of metallic chromium by the existing electrothermal method. By adding chromium trioxide, tin powder or highly active tin powder to chromite, the carbon impurities are removed by the reaction of chromium trioxide with carbon. At the same time, the tin powder reacts with sulfur to generate volatile tin sulfide, thereby removing sulfur impurities from metallic chromium and improving the purity of the finished metallic chromium product.

[0021] This invention uses smelting and nozzle atomization to obtain tin powder with uniform particle size distribution and small particle size. Since the boiling point of tin powder is lower than that of graphite emulsion, this invention uses graphite emulsion to coat the tin powder. During the electrothermal reaction, the graphite emulsion first reacts with chromium trioxide to generate carbon oxygen gas (carbon monoxide and carbon dioxide). Then, the tin powder reacts with sulfur impurities to generate tin sulfide, thereby removing sulfur impurities. This superior coating method avoids premature volatilization of tin powder and makes the removal of sulfur impurities more thorough.

[0022] The present invention also includes heat treatment after obtaining metallic chromium by the electrothermal process. The heat treatment improves the particle size distribution and density of the metallic chromium powder, thereby improving the quality and density of the subsequently pressed metallic chromium product.

[0023] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0024] Figure 1 This is a top view of the honeycomb block blank in Embodiment 1 of the present invention;

[0025] Figure 2 This is a top view of the concentric spiral ligand in Embodiment 2 of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0027] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0028] Example 1

[0029] This embodiment provides a method for integrally molding chromium powder and additives, including the following steps:

[0030] Step 1: Crush 100 kg of chromite (containing 0.6% carbon and 0.8% sulfur by mass) and mix it with 30 kg of aluminum powder. Add an additive consisting of 5 kg of chromium trioxide and 5 kg of tin powder. The particle size of the chromite is 100-200 mesh, the aluminum powder is 100-300 mesh, the chromium trioxide is 50-200 mesh, and the tin powder is 30-100 mesh. After mixing and pressing into honeycomb-shaped blocks, the mixture is fed into an electric arc furnace for electrothermal reaction. Figure 1 As shown, a honeycomb block-shaped blank 1 has 10mm through holes 2 pressed on it. After the blank is put in, the vacuum degree is first evacuated to 2×10. -3 Pa, then carbon dioxide is introduced to achieve a vacuum of 10 Pa, and after the reaction is completed, the slag liquid and metallic chromium are separated.

[0031] Step 2: Crush 20 kg of metallic chromium obtained in Step 1. Add 0.4 kg of sodium hexametaphosphate to the crushed metallic chromium powder. After mixing, perform high-temperature sintering treatment at 1300℃ for 24 hours. The vacuum degree before sintering is less than 2.5 × 10⁻⁶. -2 Pa, then argon gas is introduced to standard atmospheric pressure to obtain high-temperature sintered metallic chromium powder, which is washed multiple times with deionized water to remove sodium hexametaphosphate, and then dried at 110℃.

[0032] Step 3: Press the dried chromium powder from Step 2 into briquettes to obtain the finished chromium metal. The pressing pressure is 20 MPa, and the pressure holding time is 30 s.

[0033] Example 2

[0034] This embodiment provides a method for the integrated molding of metallic chromium powder and additives. Unlike Embodiment 1, in step one of this embodiment, the mixed materials are pressed into a concentric spiral blank. The blank 1 has 10mm through holes 2 pressed laterally. Each layer of the concentric spiral blank is 5mm thick. The top view of the blank 1 is as follows... Figure 2 As shown, the remaining processes in this embodiment are the same as in Embodiment 1.

[0035] Example 3

[0036] This embodiment provides a method for integrally molding chromium powder and additives, including the following steps:

[0037] Step 1: Crush 120 kg of chromite and mix it with 30 kg of aluminum powder. Add an additive consisting of 5 kg of chromium trioxide and 5 kg of tin powder. The chromite has a particle size of 100-200 mesh, the aluminum powder has a particle size of 100-300 mesh, the chromium trioxide has a particle size of 50-200 mesh, and the tin powder has a particle size of 30-100 mesh. After mixing and pressing into a concentric spiral shape, the mixture is fed into an electric arc furnace for electrothermal reaction. Figure 1 As shown, a 12mm through hole is pressed into the concentric spiral-shaped billet. Each layer of the concentric spiral-shaped billet is approximately 5mm thick. After the billet is inserted, the vacuum level is first evacuated to 3×10. -3 Pa, then carbon dioxide is introduced to achieve a vacuum of 6 Pa, and after the reaction is completed, the slag and liquid and metallic chromium are separated.

[0038] Step 2: Crush 20 kg of metallic chromium obtained in Step 1. Add 0.2 kg of sodium hexametaphosphate to the crushed metallic chromium powder. After mixing, perform high-temperature sintering treatment at 1500℃ for 36 hours. The vacuum degree before sintering is less than 2.5 × 10⁻⁶. -2 Pa, then argon gas is introduced to standard atmospheric pressure to obtain high-temperature sintered metallic chromium powder, which is washed multiple times with deionized water to remove sodium hexametaphosphate, and then dried at 120°C.

[0039] Step 3: Press the dried chromium powder from Step 2 into briquettes to obtain the finished chromium powder. The pressing pressure is 30 MPa and the pressure holding time is 10 s.

[0040] Example 4

[0041] This embodiment provides a method for integrally molding metallic chromium and additives, including the following steps:

[0042] Step 1: Crush 150 kg of chromite and mix it with 30 kg of aluminum powder. Add an additive consisting of 5 kg of chromium trioxide and 5 kg of tin powder. The particle size of the chromite is 100-200 mesh, the aluminum powder is 100-300 mesh, the chromium trioxide is 50-200 mesh, and the tin powder is 30-100 mesh. Mix and press the mixture. Figure 2 The spiral-shaped billet shown is then fed into an electric arc furnace for an electrothermal reaction, such as... Figure 1 As shown, a 15mm through hole is pressed into the concentric spiral-shaped billet. Each layer of the concentric spiral-shaped billet is 5mm thick. After the billet is inserted, the vacuum degree is first evacuated to 5×10. -3 Pa, then carbon dioxide is introduced to achieve a vacuum of 10 Pa, and after the reaction is completed, the slag liquid and metallic chromium are separated.

[0043] Step 2: Crush 20 kg of metallic chromium obtained in Step 1. Add 0.3 kg of sodium hexametaphosphate to the crushed metallic chromium powder. After mixing, perform high-temperature sintering treatment at 1800℃ for 48 hours. The vacuum degree before sintering is less than 2.5 × 10⁻⁶. -2 Pa, then argon gas is introduced to standard atmospheric pressure to obtain high-temperature sintered metallic chromium powder, which is washed multiple times with deionized water to remove sodium hexametaphosphate, and then dried at 120°C.

[0044] Step 3: Press the dried chromium powder from Step 2 into briquettes to obtain the finished chromium powder. The pressing pressure is 40 MPa and the pressure holding time is 60 s.

[0045] Example 5

[0046] This embodiment provides a method for integrally forming metallic chromium and additives. The difference from Embodiment 2 is that the tin powder used as the additive in step one is highly active tin powder. The preparation method of the highly active tin powder includes:

[0047] S1. Select 10 kg of tin ingots with a purity greater than 99.99% and put them into the melting furnace for high-temperature melting. The melting temperature is 2000℃ and the melting time is 2 hours.

[0048] S2. The molten tin is atomized through a nozzle at a temperature of 1000℃ for 30 minutes. After cooling to room temperature, metallic tin powder is obtained.

[0049] S3. Spray 1 kg of graphite emulsion onto the surface of metallic tin powder to obtain highly active tin powder partially coated with graphite emulsion.

[0050] Example 6

[0051] This embodiment provides a method for integrally forming metallic chromium and additives. The difference from Embodiment 2 is that the tin powder used as the additive in step one is highly active tin powder. The preparation method of the highly active tin powder includes:

[0052] S1. Select 10 kg of tin ingots with a purity greater than 99.99% and put them into the melting furnace for high-temperature melting at a temperature of 2500℃ for 2 hours.

[0053] S2. The molten tin is atomized through a nozzle at a temperature of 1500℃ for 20 minutes. After cooling to room temperature, metallic tin powder is obtained.

[0054] S3. Spray 1 kg of graphite emulsion onto the surface of metallic tin powder to obtain highly active tin powder partially coated with graphite emulsion.

[0055] Comparative Example 1

[0056] This comparative example provides a method for the integrated molding of metallic chromium and additives. The difference between this method and Example 1 is that the high-temperature sintering process in step two is not performed. The remaining processes are the same as in Example 1.

[0057] Comparative Example 2

[0058] This comparative example provides a method for integral molding of metallic chromium and additives. The difference between this method and Example 1 is that the additive in step one contains only chromium trioxide, while the rest of the process is the same as in Example 1.

[0059] Samples of the finished metallic chromium products prepared in Examples 1-6 and Comparative Examples 1-2 were taken respectively, and the carbon content, sulfur content, and tap density of the metallic chromium powder before pressing in step two or three were measured. The results are shown in the table below:

[0060] C content (%) S content (%) <![CDATA[Tap density (g / cm 3 )]]> Example 1 0.018 0.009 8.2 Example 2 0.017 0.008 8.1 Example 3 0.017 0.008 8.2 Example 4 0.016 0.007 8.3 Example 5 0.014 0.001 8.5 Example 6 0.016 0.001 8.6 Comparative Example 1 0.018 0.009 5.2 Comparative Example 2 0.017 0.061 7.2

[0061] As can be seen from the table above, the carbon content of Examples 1-6 and Comparative Examples 1-2 is less than 0.02%, meeting the target requirement. However, because the additives in Examples 5 and 6 contain highly active tin powder, the sulfur content of Examples 5 and 6 is significantly lower than that of Examples 1-4 and Comparative Examples 1-2. Meanwhile, the tap density of the metallic chromium powder prepared in Examples 1-6 and Comparative Example 2 is significantly greater than that in Comparative Example 1. This indicates that the carbon content of the metallic chromium powder prepared by the method of the present invention in Examples 1-6 all meets the requirement of ≤0.02%, while Examples 5-6 used highly active tin powder for sulfur impurity removal, resulting in the lowest sulfur content.

[0062] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0063] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for integrally molding metallic chromium powder and additives, characterized in that, Includes the following steps: Step 1: After crushing chromite, mix it with aluminum powder and add additives. After mixing and pressing, put the mixture into an electric arc furnace for electrothermal reaction. After the reaction is completed, separate the slag liquid and metallic chromium. Step 2: Crush the metallic chromium obtained in Step 1, add a binder to the crushed metallic chromium powder, mix the powder, and then perform high-temperature sintering treatment to obtain high-temperature sintered metallic chromium powder, which is then cleaned and dried. Step 3: Press the dried chromium powder from Step 2 into briquettes to obtain the finished chromium metal. In step one, the added additives include chromium trioxide and highly active tin powder, wherein the mass ratio of chromite, aluminum powder, chromium trioxide, and highly active tin powder is 100~150:20~30:1~5:5~8; the particle size of chromite is 100~200 mesh, the particle size of aluminum powder is 100~300 mesh, the particle size of chromium trioxide is 50~200 mesh, and the particle size of tin powder is 30~100 mesh; Methods for preparing highly active tin powder include: S1. Select tin ingots with a purity greater than 99.99% and put them into a melting furnace for high-temperature melting. The melting temperature is 2000~2500℃ and the melting time is 1~3h. S2. Atomize the molten tin through a nozzle at a temperature of 1000~1500℃ for 20~60 min, and then cool it to room temperature to obtain metallic tin powder. S3. Spraying the surface of metallic tin powder with graphite emulsion to obtain highly active tin powder partially coated with graphite emulsion, wherein the mass ratio of graphite emulsion to metallic tin powder is 1~10:30~100; In step two, the added binder is one or more of sodium hexametaphosphate, sodium tripolyphosphate, and aluminum dihydrogen phosphate, and the mass ratio of the binder to the metallic chromium powder is 1~3:50~200. The sintering temperature is 1300-1800℃, the sintering time is 12-48h, and the vacuum degree before sintering is less than 2.5x10 -2 Pa, and then argon gas is introduced to standard atmospheric pressure.

2. The method for integrated molding of metallic chromium powder and additives as described in claim 1, characterized in that, In the step one, after putting in the blank, the vacuum degree is first drawn to 1x10 -3 5x10 -3 Pa, then the carbon dioxide is introduced to make the vacuum degree reach 1~10 Pa.

3. The method for integrated molding of metallic chromium powder and additives as described in claim 1, characterized in that, In step three, the pressure for forming the briquette is 20~60MPa, and the pressure holding time is 20~60s.

4. The method for integrated molding of metallic chromium powder and additives as described in claim 1, characterized in that, In step one, after the chromite is crushed and mixed with aluminum powder, and after the additives are added, the pressed blank is cylindrical, honeycomb block or concentric spiral, and the blank has through holes of 2-20mm pressed on it.

5. The method for integrated molding of metallic chromium powder and additives as described in claim 1, characterized in that, In step two, after obtaining metallic chromium powder by high-temperature sintering, it is washed multiple times with clean water or deionized water, and the drying temperature is 100~120℃.

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