Preparation process of special-shaped zinc powder

Abstract

The invention discloses a preparation process of special-shaped zinc powder, which comprises the following steps: cleaning spherical powder, pressing into a thin pancake, coating a ferromagnetic material part on the surface of the spherical zinc powder through magnetron sputtering, and then carrying out oriented shearing ball milling by using a high-energy ball mill and an external magnetic field, so as to obtain the special-shaped zinc powder. And the processed special-shaped zinc powder is graded through magnetic separation and a special-shaped screen to prepare the non-magnetic or weakly-magnetic 1-5 [mu] m screened special-shaped zinc powder. By means of the technology, the special-shaped zinc powder which is appropriate in sphericity degree and high in one-time ball milling qualification rate can be efficiently prepared and used for production of zinc-rich paint.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a preparation process of special-shaped zinc powder. Background Art

[0002] Zinc metal offers superior corrosion protection compared to aluminum and is widely used in industries with demanding corrosion protection requirements, providing excellent surface protection for metal workpieces. Consequently, spherical zinc powder has been developed for applications in zinc-rich coatings and other fields. Flake zinc powder is produced by dry-grinding spherical zinc powder in a ball mill after adding a lubricant. Compared to spherical zinc powder, flake zinc powder exhibits enhanced hiding power, floatation, shielding properties, and metallic luster, resulting in its widespread use in the production of zinc-rich coatings and Dacromet coatings.

[0003] However, using spherical zinc powder directly as a coating requires a coating thickness of 50 to 80 μm due to the gaps between the particles, which is costly. Using flake zinc powder as a coating, a coating thickness of 5 to 10 μm is sufficient, but flake zinc powder is more expensive and dangerous.

[0004] Therefore, it is possible to produce irregularly shaped zinc powder. Shaped zinc powder uses spherical zinc powder as raw material and is milled into irregular shapes such as cakes. The particles are tightly bonded together, and a coating thickness of 30 to 50 μm is sufficient to meet the required thickness. Shaped zinc powder has an appearance and performance intermediate between spherical and flake forms, with similar hazardous properties to spherical zinc powder, while lacking the flammability of flake zinc powder.

[0005] However, the current existing technology does not have an efficient means to prepare and develop special-shaped zinc powder, which limits the preparation efficiency and production volume. The present invention is designed to improve the relevant preparation process. Summary of the Invention

[0006] In response to related problems, the present invention provides a preparation process for special-shaped zinc powder. The preparation process principle is: spherical zinc powder is partially coated with ferromagnetic material by magnetron sputtering, and then oriented ball milling is performed using a high-energy ball mill with an external magnetic field. The processed special-shaped zinc powder is classified through magnetic separation and special-shaped screening, and the zinc powder that fails the screening can continue to be ball milled.

[0007] The specific content of the invention is as follows:

[0008] A preparation process for special-shaped zinc powder includes pretreatment, partial coating with ferromagnetic materials, high-energy ball milling in a magnetic field, magnetic separation and special-shaped screening and classification. The specific steps include:

[0009] S1: Pretreatment: spherical zinc powder is cleaned, dried, and pressed into a pancake;

[0010] S2: Partial coating, magnetron sputtering the wafer to partially coat it with a ferromagnetic film, mechanically crushing it, and then magnetically screening out the ferromagnetic partially coated zinc powder;

[0011] S3: Magnetic field high-energy ball milling: a quantitative magnetic field is applied outside the ball milling jar, and a non-magnetic ball mill with non-magnetic grinding balls is used to shear the ferromagnetic partially coated zinc powder at high speed under nitrogen protection to prepare special-shaped zinc powder;

[0012] S4: Screening and grading, cleaning and drying the special-shaped zinc powder, magnetic separation to remove the powder with higher magnetism, and then sieving and grading with special-shaped mesh to complete the screening of special-shaped zinc powder.

[0013] Preferably, the particle size of the spherical zinc powder in step S1 is 10 to 50 μm.

[0014] More preferably, the particle size of the spherical zinc powder is 10 to 30 μm.

[0015] Preferably, the cleaning adopts one of ethanol, acetone and isopropyl ketone, ultrasonic cleaning for 10 minutes, and the drying adopts vacuum drying at 40-50° C. for 2-4 hours.

[0016] Preferably, the spherical zinc powder is dispersed with a surfactant before being pressed.

[0017] More preferably, the surfactant is one of stearic acid, oleic acid, and polyvinyl pyrrolidone.

[0018] More preferably, the added amount of the surfactant is 0.5 to 2% wt.

[0019] Preferably, 0.1 to 0.5% wt of a lubricant may be added to the spherical zinc powder before pressing, wherein the lubricant is one of polyethylene glycol and zinc stearate, so as to avoid agglomeration and adhesion caused by local overpressure.

[0020] Preferably, the spherical zinc powder is dispersed with a surfactant and then vacuum dried at 40-50° C. for 1-2 hours to prevent moisture from causing agglomeration during pressing.

[0021] Preferably, the working pressure of the pancake pressing is 10-50 MPa and the holding time is 3-5 minutes.

[0022] More preferably, the working pressure is 15-30 MPa.

[0023] The working pressure is set in direct proportion to the particle size of the spherical zinc powder and the thickness of the pancake.

[0024] More preferably, the pressing can be bidirectional pressing to achieve double-sided sputtering.

[0025] More preferably, the pressing is carried out under nitrogen protection.

[0026] Preferably, the thickness of the pancake is 300-500 μm.

[0027] More preferably, the pancake uses a metal matrix as a supporting skeleton, and the metal matrix material is one of Cu, Al, and Ti.

[0028] More preferably, the thickness of the metal substrate is 0.5-1 mm.

[0029] Preferably, the wafer is plasma cleaned before magnetron sputtering coating to remove surfactants, lubricants, oil stains, oxides, etc. on the surface, which is beneficial for ferromagnetic material coating.

[0030] More preferably, the working conditions of the plasma cleaning are 10-50 sccm nitrogen protection, 20-50 W power, 60-100 s processing time, and a chamber temperature less than 50°C.

[0031] Preferably, the ferromagnetic partial coating film is made of one of Fe, Ni, and Co target materials, and has a thickness of 50 to 150 nm.

[0032] More preferably, the thickness is 50-100 nm.

[0033] More preferably, the ferromagnetic partial coating film is a Ni film.

[0034] More preferably, the process parameters of the magnetron sputtering are: vacuum pressure 0.2-10 Pa, current 0.1-10 A, and voltage 400-600 V.

[0035] Preferably, after the magnetron sputtering of the ferromagnetic partial coating film is completed, it is mechanically crushed for 1 to 3 minutes using a low-speed ball mill at 50 to 100 r / min.

[0036] More preferably, the ball milling jar and grinding balls of the low-speed ball mill are made of non-magnetic materials.

[0037] More preferably, the ball mill jar is made of zirconia or agate, and the grinding balls are made of zirconia.

[0038] Preferably, the magnetic separation and screening is carried out using a high gradient magnetic separator with a magnetic field strength of 0.3 to 0.8 T, feeding under nitrogen conditions, a gas pressure of 0.2 to 0.5 MPa, and a gas flow rate of 1 to 2 m / s.

[0039] More preferably, the non-magnetic zinc powder after magnetic separation and screening is cleaned, caked, and coated again, and the zinc powder partially coated with weak or strong magnetism is subjected to high-energy ball milling in a magnetic field to prepare special-shaped powder.

[0040] Preferably, the zinc powder coated with the weakly magnetic or strongly magnetic part is modified with a surfactant before ball milling, so as to facilitate dispersion and prevent oxidation of the zinc powder surface.

[0041] More preferably, the surfactant is one of stearic acid, oleic acid, and polyvinyl pyrrolidone.

[0042] Preferably, the process parameters of the magnetic field high-energy ball milling are: under nitrogen protection, external magnetic field strength is 1-2T, ball-to-material ratio is 10-5:1, ball milling working time is 2-2.5h, and dry stirring ball milling speed is 650-750r / min.

[0043] When the ball milling time is 2-2.5 hours, a single, non-recirculating milling cycle yields shaped zinc powder with a sphericity of 16-25% and a pass rate of 69-81%, indicating the best anisotropic properties. When the milling time is less than 2 hours, the zinc powder becomes epitaxially thinner, but the cleavage deformation is incomplete, not reaching the ideal deformation level, and orientation formation is incomplete. However, when the milling time is too long, the particles are too fine after ball milling, resulting in a flaky zinc powder.

[0044] More preferably, the high-energy ball milling is operated for 10 to 30 minutes and stopped intermittently for 10 to 30 minutes, and the temperature in the tank is controlled to be lower than 50°C.

[0045] More preferably, the high-energy ball milling starts at 650 r / min, and after each pause, the ball milling speed is adjusted in an arithmetic or periodic manner to perform variable-speed ball milling.

[0046] Preferably, the process parameters of the magnetic field high-energy ball milling can also use wet ball milling, the ball milling medium is ethanol, the ball mill adopts a planetary ball mill, the revolution speed is 150-200r / min, the rotation speed is 500-600r / min, and the external magnetic field is set around the ball milling tank.

[0047] Preferably, the high-energy ball mill is further provided with a jacket cooling water to assist in controlling the temperature inside the tank to be lower than 50°C.

[0048] Preferably, the high-energy ball mill uses a non-magnetic ball mill jar and grinding balls.

[0049] More preferably, the non-magnetic ball mill is made of zirconia or agate, and the grinding balls are made of zirconia.

[0050] More preferably, the diameter of the grinding balls is 3-12 mm, and the grinding balls are arranged in at least three levels.

[0051] Preferably, the intensity of the magnetic field is achieved by arranging non-contact fixed symmetrical permanent magnets outside the non-magnetic ball mill.

[0052] More preferably, the central magnetic field of the symmetrical permanent magnet is arranged in the middle and lower part of the ball mill.

[0053] The external magnetic field is more conducive to the ferromagnetic partially coated zinc powder to form oriented shear in a specific direction during mechanical deformation in the high-energy ball mill. The ferromagnetic coating surface faces away from the shear surface of the grinding ball, avoiding the random processing caused by the non-directional impact caused by the rotation of the material in traditional ball milling without a magnetic field, thereby improving the efficiency of special-shaped processing and the consistency of the dispersion effect.

[0054] Meanwhile, traditional zinc powder is a ductile metal and will adhere to the milling medium during the ball milling process, thereby reducing the ball milling efficiency. The ferromagnetic partially coated zinc powder of the present invention can be pinned and fixed in an external magnetic field, easily detaching from the milling balls, ensuring the transfer of milling energy and improving the ball milling efficiency.

[0055] Preferably, the material after high-energy ball milling in a magnetic field is first subjected to magnetic separation classification, and then to special-shaped classification.

[0056] Preferably, the magnetic separation and classification is carried out using a high gradient magnetic separator with a magnetic field strength of 1.0 to 1.5 T, feeding under nitrogen conditions, a gas pressure of 0.2 to 0.5 MPa, and a gas flow rate of 0.5 to 1 m / s.

[0057] After magnetic separation and classification, non-magnetic or weakly magnetic powders are greatly deformed and enter the special-shaped screen for classification. The strong magnetic powder or ferromagnetic film material that falls off is ball milled again.

[0058] Preferably, the special-shaped screen grading system adopts a combination of multi-stage cyclone separation and airflow screening, and uses strip screens for grading by adjusting the airflow speed to 8-12 m / s.

[0059] More preferably, the special-shaped screen grading adopts a strip-shaped screen with a mesh size of 1 to 5 μm for grading, the powder larger than 5 μm is ball-milled again, and the powder smaller than 1 μm is graded into flaky zinc powder.

[0060] More preferably, the qualified powder classified by the special-shaped screen is surface modified, and the surface modification is completed in a fluidized bed reactor, and a 0.3% to 0.8% stearic acid ethanol solution is introduced for coating treatment, the temperature is maintained at 60 to 70°C, and the time is 20 to 30 minutes, which significantly improves the dispersibility and antioxidant capacity of the zinc powder.

[0061] Compared with the prior art, the present invention significantly improves the preparation efficiency of special-shaped zinc powder by selective ball milling with an external magnetic field; the prepared special-shaped zinc powder is used to make zinc-rich coatings ( Figure 1 Schematic diagram), compared with using spherical zinc powder ( Figure 2 Schematic diagram), reducing the amount of material used; compared with the use of flake zinc powder ( Figure 3 (as shown in the figure), special-shaped zinc powder does not have the dangers of flaky zinc powder and is easy to transport and use downstream. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0063] Figure 1 Schematic diagram of the application of the special-shaped zinc powder of the present invention in zinc-rich coating.

[0064] Figure 2 Schematic diagram of the application of spherical zinc powder in zinc-rich coatings.

[0065] Figure 3 Schematic diagram of the application of flake zinc powder in zinc-rich coatings.

[0066] Figure 4 This is a SEM image of the product of the special-shaped zinc powder prepared in Comparative Example 1 of the present invention.

[0067] Figure 5 This is a SEM image of the product of the irregularly shaped zinc powder prepared in Example 1 of the present invention.

[0068] Figure 6 This is a magnified SEM image of the product of the irregularly shaped zinc powder prepared in Example 1 of the present invention.

[0069] Figure 7 This is a SEM image of the product of the irregularly shaped zinc powder prepared in Example 2 of the present invention.

[0070] Figure 8 This is a magnified SEM image of the product of the irregularly shaped zinc powder prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0071] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this invention.

[0072] The present invention provides a process for preparing shaped zinc powder. The purpose is to efficiently prepare shaped zinc powder that meets the requirements through a new process, so as to increase the filling amount of zinc-rich coatings and avoid the storage and transportation risks of flaky zinc powder. The specific technical solution is as follows:

[0073] A preparation process for special-shaped zinc powder includes pretreatment, partial coating with ferromagnetic materials, high-energy ball milling in a magnetic field, magnetic separation and special-shaped screening and classification. The specific steps include:

[0074] S1: Pretreatment: spherical zinc powder is cleaned, dried, and pressed into a pancake;

[0075] S2: Partial coating, magnetron sputtering the wafer to partially coat it with a ferromagnetic film, mechanically crushing it, and then magnetically screening out the ferromagnetic partially coated zinc powder;

[0076] S3: Magnetic field high-energy ball milling: a quantitative magnetic field is applied outside the ball milling jar, and a non-magnetic ball mill with non-magnetic grinding balls is used to shear the ferromagnetic partially coated zinc powder at high speed under nitrogen protection to prepare special-shaped zinc powder;

[0077] S4: Screening and grading, cleaning and drying the special-shaped zinc powder, magnetic separation to remove the powder with higher magnetism, and then sieving and grading with special-shaped mesh to complete the screening of special-shaped zinc powder.

[0078] The present invention realizes high-energy ball milling under a strong external magnetic field by preparing zinc powder coated with a ferromagnetic part. The orientation shearing of the zinc powder is improved through the positioning pinning of the magnetic field, and the requirements for high-energy ball milling equipment are reduced. A dry stirring ball mill can be used instead of a planetary ball mill.

[0079] In the present invention, the spherical zinc powder is coated with a Ni film, and the Ni film remaining after classification can also be used as part of the anti-corrosion material for the preparation of zinc-rich paint.

[0080] The present invention has multiple key process parameters in the above specific steps. To illustrate the importance of selecting each process parameter, the following examples are given:

[0081] 1. Particle size selection of spherical zinc powder

[0082] The present invention uses spherical zinc powder with a D50 particle size of 10 to 50 μm for ball milling, and further selects spherical zinc powder with a particle size of 10 to 30 μm. Compared with spherical zinc powders with larger or smaller particle sizes, the particle size range of the present invention is more suitable for ball milling and shearing under magnetic field conditions, and the prepared shaped zinc powder has the best shaped structure. The numerical values and performance comparisons of the examples and comparative examples are shown in Table 1 below.

[0083] The particle size of the spherical zinc powder in Example 2 and Comparative Example 4 is 10-20 μm, the sphericity is greater than 95%, and the apparent density is 1.8-2.0 g / cm 3 , with a specific surface area of 0.083m 2 / g.

[0084] The specific preparation steps of Examples 1-2 and Comparative Examples 1-4 in Table 1 are as follows:

[0085] S1: Pretreatment: Spherical zinc powder of the given particle size in each example in Table 1 was washed with acetone for 10 minutes and vacuum-dried at 45°C for 4 hours. 1% wt of a surfactant, stearic acid, and 0.3% wt of polyethylene glycol were then added, followed by surface modification in ethanol, vacuum drying at 450°C for 1.5 hours, and pressing at 20 MPa under nitrogen for 4 minutes to form a 400 μm thick wafer.

[0086] S2: Partial coating, plasma cleaning of the wafer, plasma working conditions are 50sccm nitrogen, 40W power, processing time 80s, and then magnetron sputtering 80nm thick Ni partial coating film, magnetron sputtering parameters are vacuum less than 10Pa, current 2A, voltage 600V, sputtering rate 1.2~1.4A / s, after the completion of magnetron sputtering, crushing in a low-speed ball mill 50r / min, 3min, and magnetic separation and screening of ferromagnetic partially coated zinc powder by a high gradient magnetic separator, magnetic field strength of 0.5T, nitrogen protection, gas pressure 0.4MPa, gas flow rate 1.5m / s, to complete the screening of ferromagnetic partially coated zinc powder, and the non-magnetic or weakly magnetic zinc powder that has not been well coated is re-coated with the cake;

[0087] S3: Magnetic field high-energy ball milling: the ferromagnetic partially coated zinc powder prepared in step S2 was modified with 1%wt stearic acid for surfactant, and ball milling was performed in a dry mixer with an external magnetic field of 1.5T. The magnetic field device was a circular permanent magnet, which was fixed in the middle and lower part of the ball mill. Zirconia ball milling jars and three-graded zirconia grinding balls of 3mm, 6mm, and 12mm were used. The ball-to-material ratio was 6:1, the stirring speed was 700r / min, and the ball milling was carried out for 2.5h, with a ball milling working time of 15min and a rest time of 15min.

[0088] S4: Screening and grading, cleaning and drying of special-shaped zinc powder, cleaning with acetone, vacuum drying, and magnetic separation and screening by high gradient magnetic separator, with magnetic field strength of 1.5T, nitrogen protection, gas pressure of 0.3MPa, and gas flow rate of 0.8m / s. After magnetic separation and grading, non-magnetic or weakly magnetic powders are greatly deformed and enter special-shaped screen grading. The special-shaped screen grading system adopts multi-stage cyclone separation and airflow screening in combination, and grading is carried out by adjusting the airflow speed to 8-12m / s and the strip sieve holes of 1-5μm. Powders larger than 5μm are ball-milled again, and powders smaller than 1μm are classified as flake zinc powder.

[0089] Comparing the data in Table 1, Example 1 ( Figure 5 、 Figure 6 ) and 2 ( Figure 7 、 Figure 8The sphericity of the shaped zinc powder produced by this method is less than 25%, making it easier to shear and create the shaped effect through high-energy ball milling in a magnetic field. The bulk density and specific surface area meet the coating's requirements for high filler and anti-corrosion activity. The preparation process of this invention utilizes spherical zinc powder of the appropriate particle size, which is essential for improving the efficiency of producing shaped zinc powder.

[0090] Table 1. Ball diameter selection table

[0091]

[0092] 2. Selection of pancake pressing conditions

[0093] The wafer pressing conditions are determined to ensure wafer thickness, wafer bonding strength, and post-coating dispersion. Using Example 1 as a benchmark for other process conditions, the wafer pressing conditions were varied to produce examples to illustrate the effectiveness of the present invention's selection range. See Table 2 for a detailed comparison:

[0094] Table 2. Variation of pressing conditions

[0095]

[0096] The specific preparation steps of the examples and comparative examples in Table 2 are as follows:

[0097] S1: Pretreatment: Spherical zinc powder with a D50 distribution of 10-20 μm was washed with acetone for 10 min and vacuum-dried at 45°C for 4 h. 1% wt of the surfactant stearic acid and 0.3% wt of polyethylene glycol were then added to the powder for surface modification in ethanol. The powder was vacuum-dried at 45°C for 1.5 h and pressed into wafers under nitrogen using the wafer pressing parameters in Table 2.

[0098] S2: Partial coating, plasma cleaning of the wafer, plasma working conditions are 50sccm nitrogen, 40W power, processing time 80s, and then magnetron sputtering 80nm thick Ni partial coating film, magnetron sputtering parameters are vacuum less than 10Pa, current 2A, voltage 600V, sputtering rate of 1.2~1.4A / s, after the completion of magnetron sputtering, crushed in a low-speed ball mill at 50r / min, 3min, and magnetic separation and screening of ferromagnetic partially coated zinc powder by a high gradient magnetic separator, magnetic field strength of 0.5T, nitrogen protection, gas pressure 0.4MPa, gas flow rate 1.5m / s, to complete the screening of ferromagnetic partially coated zinc powder, and repeat the cake coating of the non-magnetic or weakly magnetic zinc powder that has not been well coated.

[0099] Comparison of the preparation and performance results of the Examples and Comparative Examples reveals that low pressure can cause the wafer to break, making it impossible to transport and sputter, while high pressure can cause the wafer to deform and the zinc powder to stick together, hindering mechanical crushing and subsequent ball milling. The wafers prepared in Examples 1 / 3 / 4 / 5 / 6 / 7 are suitable for subsequent steps, with suitable pressing conditions of 10-50 MPa, a hold time of 3-5 minutes, and a wafer thickness of 300-500 μm.

[0100] In Example 8, a metal matrix was used as a support frame for the pancake pressing. A 1 mm thick Al sheet was used for bidirectional pressing, and 300 μm thick pancakes were prepared on both sides of the Al sheet to increase the transport sputtering hardness of the thin layer of pancake.

[0101] 3. Relationship between ferromagnetic film thickness and magnetism

[0102] The thickness of the ferromagnetic film determines the relative shear strength during high-energy ball milling in an external magnetic field. Weak magnetism prevents oriented shearing, while strong magnetism easily causes powder agglomeration and reduces milling efficiency. An appropriate ferromagnetic film thickness is beneficial for improving milling shear efficiency. Using the process of Example 2 as a benchmark, varying the coating thickness is demonstrated in Table 3.

[0103] Table 3. Coating thickness variation

[0104]

[0105] The main difference between the embodiments in Table 3 is the thickness of the coating. The thickness change is achieved by controlling the coating time according to magnetron sputtering. The film is prepared at an average rate of 1.3A / s, and the preparation time range of the 40-200nm film is 300-1500s.

[0106] According to the sphericity and qualified product percentage of the irregularly shaped zinc powder prepared in Examples 1 / 9 / 10 and Comparative Examples 9 / 10 in Table 3, it can be seen that when the coating is thin (Comparative Example 9), the sphericity is too low, flaky, and the qualified product percentage is less than 50%. However, when the coating is thick (Comparative Example 10), the average sphericity is higher and the qualified product percentage is less than 50%. The influence of the appropriate coating on the relative shearing capacity and pinning position in an external magnetic field helps to efficiently obtain qualified irregularly shaped zinc powder.

[0107] IV. Progressive Screening of the Magnetic Field High-Energy Ball Milling Process. After screening the process conditions in the preceding steps, it was determined that the magnetic field and ball milling conditions are key to the preparation of the irregularly shaped zinc powder of the present invention. Efficient ball milling energy conduction and accurate oriented shearing contribute to shortened preparation time and improved product yield. Using the process conditions of Example 2 as a benchmark, with all other conditions unchanged, namely, 10-20 μm spherical zinc powder as the starting material, wafer pressing conditions of 20 MPa, 4 min, 400 μm, and magnetron sputtering of an 80 nm Ni film, the magnetic field and ball milling conditions were modified to carry out the preparation process of the present invention, as detailed in Table 4.

[0108] The conditions in step S3 of Example 1 were changed, specifically: high-energy ball milling in a magnetic field, the ferromagnetic partially coated zinc powder prepared in step S2 was modified with 1% wt stearic acid surfactant, ball milling was performed using a dry mixer, and multiple external magnetic fields of 0.5 / 1 / 1.5 / 2 / 2.5 T were applied. The magnetic field device was a circular permanent magnet, which was fixed in the middle and lower part of the ball mill. A zirconia ball mill and three-graded zirconia grinding balls of 3 mm, 6 mm, and 12 mm were used. The ball-to-material ratio was 3:1 / 6:1 / 8:1 / 10:1, the stirring speed was 550 / 650 / 700 / 850 r / min, the ball milling time was 1.5 / 2 / 2.5 / 3.5 h, and the ball milling worked for 15 min and rested for 15 min.

[0109] The examples in Table 4 show that an external magnetic field strength between 1 and 2 T is optimal. Excessively high magnetic field strengths result in a stronger shearing effect and lower sphericity, which in turn reduces the proportion of qualified products. A moderate ball-to-material ratio achieves optimal results; excessively high or low ratios can affect efficiency (as seen in Comparative Examples 13 and 14). The ball milling speed, which represents the efficiency of shear force transmission, is higher than the standard milling range but lower than the milling speed for flaky zinc powder. Under these conditions, the milling time is far less than the tens of hours required for flaky zinc powder, significantly improving milling efficiency and reducing milling costs.

[0110] Through the changes in the preparation process of the aforementioned Examples 1-14 and Comparative Examples 1-18, it can be seen that the embodiments of the present invention fully explain the technical importance of ball diameter, wafer pressing, partial coating of ferromagnetic materials and high-energy ball milling with an external magnetic field.

[0111] Table 4. Magnetic field and ball milling process changes

[0112]

[0113] In the present invention, due to the magnetic characteristics generated by the partial coating of ferromagnetic materials, it can be used to screen the special-shaped zinc powder. If the magnetism of the special-shaped zinc powder prepared by steps S1, S2, and S3 is too high, it means that the ball milling shear level is low and the special-shaped change is small, so it is screened out by a magnetic separator and ball milled again. The special-shaped zinc powder with weak residual magnetism or no magnetism is subjected to multi-stage cyclone separation and airflow screening in combination, which can screen out small particles or flaky particles, increase the proportion of qualified special-shaped zinc powder, and finally perform surface treatment to complete the preparation before delivery. The specific steps are as follows:

[0114] S4: Screening and grading, cleaning and drying of special-shaped zinc powder, cleaning with acetone, vacuum drying, and then magnetic separation and screening by high-gradient magnetic separator, with a magnetic field strength of 1.5T, nitrogen protection, gas pressure of 0.3MPa, and gas flow rate of 0.8m / s. After magnetic separation and classification, non-magnetic or weakly magnetic powders are greatly deformed and enter special-shaped screen classification. The special-shaped screen classification system adopts multi-stage cyclone separation and airflow screening in combination. The classification is carried out by adjusting the airflow speed to 10m / s and the strip sieve holes of 1-5μm. The powder larger than 5μm is ball-milled again, and the powder smaller than 1μm is classified as flake zinc powder.

[0115] S5: Surface treatment: The qualified powder classified by the special-shaped screen is subjected to surface modification. The surface modification is completed in a fluidized bed reactor. A 0.5%wt stearic acid ethanol solution is introduced for coating treatment. The temperature is maintained at 70°C for 30 minutes, which significantly improves the dispersibility and antioxidant capacity of the zinc powder.

[0116] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing special-shaped zinc powder, characterized in that: The following steps are involved: S1: Pretreatment: After cleaning and drying the 10-50 μm spherical zinc powder, a surfactant and / or lubricant is added, and the powder is pressed into a 300-500 μm wafer under nitrogen protection; S2: Partial coating: The wafer after plasma cleaning is partially coated with ferromagnetic material by magnetron sputtering with a coating thickness of 50-150 nm, and then mechanically crushed, and the ferromagnetic partially coated zinc powder is separated by magnetic separation; S3: Magnetic field high-energy ball milling, applying an external magnetic field of 1-2 T, using a non-magnetic ball mill and grinding balls in a high-energy ball mill under nitrogen protection, a ball milling speed of 650-750 r / min, a ball-to-material ratio of 10-5:1, and a ball milling time of 2-2.5 h to perform ferromagnetic partially coated zinc powder special shearing; S4: Screening and grading, cleaning and drying the ball-milled material, performing magnetic separation to remove powder with more ferromagnetic material on the surface, and then grading through a 1-5 μm special-shaped screen to complete the preparation of special-shaped zinc powder.

2. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The particle size of the spherical zinc powder in step S1 is 10 to 30 μm.

3. The process for preparing the special-shaped zinc powder according to claim 1, wherein: In the step S1, the surfactant is one of stearic acid, oleic acid, and polyvinyl pyrrolidone, and the addition amount is 0.5-2%wt; the lubricant is one of polyethylene glycol and polyvinyl alcohol, and the addition amount is 0.1-0.5%wt.

4. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The pressing pressure in step S1 is 10-50 MPa, and the holding time is 3-5 minutes.

5. The process for preparing the irregularly shaped zinc powder according to any one of claims 1 or 4, characterized in that: The pressing process can use a metal substrate as a supporting skeleton and perform bidirectional pressing to prepare the wafer.

6. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The ferromagnetic material partial coating in the step S2 uses one of Fe, Ni, and Co target materials, and the thickness is preferably 50 to 100 nm.

7. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The high-energy ball milling in step S3 uses a ball milling jar and grinding balls made of non-magnetic material, and the external magnetic field strength is achieved by arranging a symmetrical magnetic field device outside the non-magnetic ball milling jar.

8. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The magnetic separation and classification in the S4 step is carried out using a high gradient magnetic separator with a magnetic field strength of 1.0 to 1.5 T, feeding under nitrogen conditions, a gas pressure of 0.2 to 0.5 MPa, and a gas flow rate of 0.5 to 1 m / s. The special-shaped screen classification in the S4 step adopts a strip sieve hole of 1 to 5 μm for classification. The powder larger than 5 μm is ball-milled again, and the powder smaller than 1 μm is classified into flaky zinc powder.

9. The process for preparing the special-shaped zinc powder according to claim 1, wherein: The qualified powder classified by the special-shaped screen is subjected to surface modification, and the surface modification is completed in a fluidized bed reactor, and a 0.3% to 0.8% wt stearic acid ethanol solution is introduced for coating treatment, the temperature is maintained at 60 to 70°C, and the time is 20 to 30 minutes.

10. The process for preparing special-shaped zinc powder according to claim 1, characterized in that: The prepared special-shaped zinc powder has a sphericity of 16-25% and is used for the production of zinc-rich coatings.

Images