Preparation process of special-shaped zinc powder

Abstract

The application discloses a preparation process of special-shaped zinc powder, and the preparation process comprises the following steps: after cleaning treatment of spherical powder, pressing thin cakes, performing partial coating of the surface of the spherical zinc powder by a ferromagnetic material through magnetron sputtering, and then performing orientation shearing ball milling by using a high-energy ball mill and an additional magnetic field, and the processed special-shaped zinc powder is classified through magnetic separation and a special-shaped screen to prepare 1-5 mu special-shaped zinc powder with no magnetism or weak magnetism. The special-shaped zinc powder with suitable sphericity and high one-time ball milling qualified rate can be efficiently prepared through the technology, and is used for the production of zinc-rich paint.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a preparation process of special-shaped zinc powder. BACKGROUND

[0002] Metal zinc has better corrosion protection effect than aluminum, and is widely used in some industries with high corrosion resistance requirements, which can provide good protection to the surface of metal workpieces. Therefore, spherical zinc powder is developed and applied in zinc-rich paint and other fields. Flaky zinc powder is obtained by dry grinding of spherical zinc powder after adding lubricant through a ball mill, and flaky zinc powder has stronger covering ability, floating ability, shielding ability and metal luster than spherical zinc powder, so it is also widely used in the production of zinc-rich paint and Dacromet coating solution.

[0003] However, when using spherical zinc powder directly as paint, the coating thickness needs to be 50-80 mu m due to the gap between particles, and the cost is high. When using flaky zinc powder as paint, the coating thickness can be 5-10 mu m, but the cost of flaky zinc powder is high and the risk is high.

[0004] Therefore, special-shaped zinc powder can be prepared, which uses spherical zinc powder as raw material, is processed into irregular shapes such as cakes through ball milling, and can be tightly combined between particles to form a coating of 30-50 mu m to meet the requirements. The shape and performance of special-shaped zinc powder are between spherical and flaky, and the risk characteristics are close to spherical zinc powder, and it does not have the flammable characteristics of flaky zinc powder.

[0005] However, there is no efficient means to obtain special-shaped zinc powder in the prior art, which limits the preparation efficiency and preparation amount. The present application is designed to improve the related preparation process. SUMMARY

[0006] In view of the above problems, the present application provides a preparation process of special-shaped zinc powder, and the principle of the preparation process is as follows: the spherical zinc powder is partially coated with ferromagnetic material by magnetic control sputtering, and then oriented ball milling is performed by using a high-energy ball mill with an external magnetic field. The processed special-shaped zinc powder is classified by magnetic separation and special-shaped screening, and the zinc powder that does not pass the screening can continue to be ball milled.

[0007] The specific application content is as follows:

[0008] A preparation process of special-shaped zinc powder, including the steps of pretreatment, partial coating of ferromagnetic material, high-energy ball milling in a magnetic field, and classification by magnetic separation and special-shaped screening, and the specific steps include:

[0009] S1: pretreatment, the spherical zinc powder is cleaned, dried and pressed into a thin cake;

[0010] S2: partial coating, the thin cake is coated with a ferromagnetic coating film by magnetic control sputtering, and the ferromagnetic partially coated zinc powder is screened out by magnetic separation after mechanical crushing.

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

[0012] S4: Screening and grading, washing and drying the special-shaped zinc powder, screening and removing the powder with high magnetism by magnetic separation, and then screening and grading by special-shaped screen to complete the screening of the special-shaped zinc powder.

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

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

[0015] Preferably, the washing uses one of ethanol, acetone and isopropyl ketone, and the ultrasonic cleaning lasts for 10 min, and the drying uses vacuum drying at 40-50 °C for 2-4 h.

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

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

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

[0019] Preferably, 0.1-0.5% wt. of a lubricant, which is one of polyethylene glycol and zinc stearate, can be added to the spherical zinc powder before being pressed to avoid local overpressure and agglomeration.

[0020] Preferably, the spherical zinc powder is vacuum dried at 40-50 °C for 1-2 h after being dispersed by the surfactant to avoid water from causing caking during pressing.

[0021] Preferably, the working pressure for pressing the thin cake is 10-50 MPa, and the holding time is 3-5 min.

[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 thin cake.

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

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

[0026] Preferably, the thickness of the thin cake 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 to the coating of ferromagnetic materials.

[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 surface active agent is one of stearic acid, oleic acid, and polyvinylpyrrolidone.

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

[0043] When the ball milling working time is 2-2.5h, the non-circulating ball milling of single ball milling obtains the irregular zinc powder with sphericity 16-25% and qualified rate 69-81%, indicating that the anisotropic performance is the best. Less than 2h, the zinc powder is thinned in epitaxy, but the cleavage deformation is not complete, and the ideal deformation degree is not reached, and the orientation formation is not complete. However, if the time is too long, the particle is too fine after ball milling, leading to the bias of flaky zinc powder.

[0044] More preferably, the high-energy ball milling is ball milled for 10-30min, and then stopped for 10-30min, and the temperature in the tank is controlled to be lower than 50℃.

[0045] More preferably, the high-energy ball milling is ball milled at 650r / min, and after each intermittent stop, the ball milling speed is adjusted according to the arithmetic progression or periodically, and the variable speed ball milling is carried out.

[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 arranged around the ball milling tank.

[0047] Preferably, the high-energy ball milling is also provided with a jacket cooling water to assist in controlling the temperature in the tank to be lower than 50℃.

[0048] Preferably, the high-energy ball milling adopts a non-magnetic ball milling tank and grinding balls.

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

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

[0051] Preferably, the strength of the magnetic field is realized by arranging a non-contact fixed symmetrical permanent magnet outside the non-magnetic ball milling tank.

[0052] More preferably, the center magnetic field of the symmetrical permanent magnet is arranged at the middle and lower part of the ball milling tank.

[0053] The external magnetic field is more conducive to the formation of oriented shear in a specific direction of the ferromagnetic partially coated zinc powder during high-energy ball milling mechanical deformation, and the ferromagnetic coating surface is away from the shear surface of the milling ball, thereby avoiding random processing caused by non-directional impact of the self-rotation movement of the material under traditional non-magnetic field ball milling, and improving the special-shaped processing efficiency and dispersion effect consistency.

[0054] Meanwhile, the traditional zinc powder is a ductile metal, which will adhere to the ball milling medium during the ball milling process, thereby reducing the ball milling efficiency. The ferromagnetic partially coated zinc powder can be pinned and fixed under the external magnetic field, and is easy to separate from the milling ball, thereby ensuring the transmission of the ball milling energy and improving the ball milling efficiency.

[0055] Preferably, the material after the magnetic high-energy ball milling is subjected to magnetic separation grading, and then subjected to special-shaped grading.

[0056] Preferably, the magnetic separation grading is performed by using a high-gradient magnetic separator, the magnetic field strength is 1.0-1.5T, the feeding is under nitrogen condition, the gas pressure is 0.2-0.5MPa, and the gas flow rate is 0.5-1m / s.

[0057] After the magnetic separation grading, the non-magnetic or weak-magnetic powder is subjected to large deformation and enters the special-shaped screen grading. The strong-magnetic powder or the ferromagnetic film material is subjected to re-ball milling.

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

[0059] More preferably, the special-shaped screen grading is performed by using a strip-shaped screen hole with a size of 1-5μm, the powder with a size greater than 5μm is subjected to re-ball milling, and the powder with a size less than 1μm is graded as flaky zinc powder.

[0060] More preferably, the qualified powder after the special-shaped screen grading is subjected to surface modification, the surface modification is completed in a fluidized bed reactor, 0.3%-0.8% stearic acid ethanol solution is introduced for coating treatment, the temperature is maintained at 60-70°C, and the time is 20-30min, thereby significantly improving the dispersibility and oxidation resistance of the zinc powder.

[0061] Compared with the prior art, the preparation efficiency of the special-shaped zinc powder is significantly improved by the selective ball milling under the external magnetic field. Figure 1 Compared with the use of spherical zinc powder ( Figure 2 illustration), the material usage is reduced. Figure 3 Compared with the use of flaky zinc powder ( illustration), the special-shaped zinc powder does not have the danger of flaky zinc powder, and is convenient for transportation and downstream use.

[0062] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art of the present application, the drawings required to be used in the specific embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0063] Figure 1 Application diagram of the special-shaped zinc powder in the zinc-rich coating.

[0064] Figure 2 Application diagram of the spherical zinc powder in the zinc-rich coating.

[0065] Figure 3 Application diagram of the flaky zinc powder in the zinc-rich coating.

[0066] Figure 4 Product SEM diagram of the special-shaped zinc powder prepared in the comparative example 1 of the present application.

[0067] Figure 5 Product SEM diagram of the special-shaped zinc powder prepared in the example 1 of the present application.

[0068] Figure 6 Product SEM zoomed-out diagram of the special-shaped zinc powder prepared in the example 1 of the present application.

[0069] Figure 7 Product SEM diagram of the special-shaped zinc powder prepared in the example 2 of the present application.

[0070] Figure 8 Product SEM zoomed-out diagram of the special-shaped zinc powder prepared in the example 2 of the present application. DETAILED DESCRIPTION

[0071] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The endpoints of the ranges are provided as example of the upper and lower limits for the ranges. The endpoints of the ranges can be combined with one another to form new ranges. The ranges are not limited to the precise values stated.

[0072] The present application provides a preparation process of special-shaped zinc powder, which aims to efficiently prepare the special-shaped zinc powder meeting the requirements by a new process, so as to improve the filling amount of the zinc-rich coating and avoid the storage and transportation risk of the flaky zinc powder. The specific technical solution is as follows:

[0073] The preparation process of the special-shaped zinc powder comprises the steps of pretreatment, partial coating of ferromagnetic material, magnetic field high-energy ball milling, and magnetic separation plus special-shaped screening grading, and the specific steps comprise:

[0074] S1: pretreatment, spherical zinc powder is cleaned, dried, and pressed into a thin cake;

[0075] S2: partial coating, the thin cake is subjected to magnetron sputtering of a ferromagnetic partial coating film, and after mechanical crushing, the ferromagnetic partially coated zinc powder is screened out by magnetic separation;

[0076] S3: magnetic field high-energy ball milling, a quantitative magnetic field is applied outside the ball milling tank, and the ferromagnetic partially coated zinc powder is subjected to high-speed shearing under nitrogen protection by using a high-energy ball mill without a magnetic ball milling tank and a non-magnetic grinding ball to prepare a special-shaped zinc powder;

[0077] S4: screening and grading, the special-shaped zinc powder is cleaned and dried, the powder with high magnetism is screened out by magnetic separation, and then the special-shaped screen mesh screening and grading are performed to complete the screening of the special-shaped zinc powder.

[0078] The present application realizes high-energy ball milling under the condition of a strong external magnetic field by preparing ferromagnetic partially coated zinc powder, improves the oriented shearing of the zinc powder through the positioning pinning of the magnetic field, and reduces the requirements for the high-energy ball milling equipment, so that a dry stirring ball mill can be used instead of a planetary ball mill.

[0079] The residual Ni film after grading can also be used as a part of the anticorrosion material for the preparation of zinc-rich paint.

[0080] The present application has a plurality of key process parameters in the above specific steps, and the following examples are provided to illustrate the importance of the selection of the process parameters:

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

[0082] The present application uses spherical zinc powder with a D50 particle size of 10-50 μm as the ball milling object, and further uses spherical zinc powder with a particle size of 10-30 μm. Compared with spherical zinc powder with a particle size that is too large or too small, the particle size range of the present application is more suitable for ball milling shearing under the condition of a magnetic field, and the special-shaped structure of the prepared special-shaped zinc powder is optimal. The numerical values and performance of the examples and comparative examples are compared in Table 1 below.

[0083] The spherical zinc powder of Example 2 and Comparative Example 4 has a particle size of 10-20 μm, a sphericity of greater than 95%, and a loose bulk density of 1.8-2.0 g / cm 3 , and a specific surface area of 0.083 m 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, the spherical zinc powder with the given particle size in Table 1 was cleaned with acetone for 10 min, vacuum dried at 45°C for 4 h, then 1%wt of surfactant stearic acid and 0.3%wt of polyethylene glycol were added, surface modification was carried out in ethanol, vacuum dried at 450°C for 1.5 h, pressed into a 400 μm thick wafer under nitrogen protection at 20 MPa for 4 min;

[0086] S2: partial coating, the wafer was plasma cleaned, the plasma working conditions were 50 sccm of nitrogen, 40 W of power, and 80 s of treatment time, then a 80 nm thick Ni partial coating film was prepared by magnetron sputtering, the magnetron sputtering parameters were a vacuum lower than 10 Pa, a current of 2 A, a voltage of 600 V, a sputtering rate of 1.2-1.4 A / s, after the magnetron sputtering was completed, the ferromagnetic partially coated zinc powder was screened out by a high gradient magnetic separator, the magnetic field strength was 0.5 T, nitrogen protection, the gas pressure was 0.4 MPa, and the gas flow rate was 1.5 m / s, the screening of the ferromagnetic partially coated zinc powder was completed, and the non-magnetic or weakly magnetic zinc powder which was not well coated was repeated to make a wafer and coat it;

[0087] S3: high-energy ball milling in a magnetic field, the ferromagnetic partially coated zinc powder prepared in the step S2 was surface modified with 1%wt of stearic acid, dry stirring was carried out by using a ball mill, a 1.5 T external magnetic field was applied, a circular ring permanent magnet was fixed to the lower part of the ball mill tank, a zirconia ball mill tank and three-stage graded zirconia grinding balls with a size of 3 mm, 6 mm and 12 mm were used, the ball-to-material ratio was 6:1, the stirring speed was 700 r / min, and the ball milling was carried out for 2.5 h, with 15 min of work and 15 min of interval stop;

[0088] S4: screening and grading, after the irregular zinc powder was cleaned and dried, the magnetic screening was carried out by using a high gradient magnetic separator, the magnetic field strength was 1.5 T, nitrogen protection, the gas pressure was 0.3 MPa, and the gas flow rate was 0.8 m / s, after the magnetic screening and grading, the non-magnetic or weakly magnetic powder was greatly deformed, entered the irregular screen grading system, the irregular screen grading system adopted a combined operation of multi-stage cyclone separation and airflow screening, the airflow velocity was adjusted to 8-12 m / s, the strip-shaped screen hole with a size of 1-5 μm was used for grading, the powder larger than 5 μm was ball milled again, and the powder smaller than 1 μm was graded as flaky zinc powder.

[0089] According to the data in Table 1, the zinc powder in the examples 1 ( Figure 5 、 Figure 6 ) and 2 ( Figure 7 、 Figure 8The prepared irregular zinc powder has a sphericity of less than 25%, and is more easily sheared to form an irregular shape by high-energy ball milling in a magnetic field. The loose bulk density and specific surface area meet the requirements of high filling and corrosion resistance of the coating. The preparation process of the present application selects a suitable particle size of the spherical zinc powder as the basis for improving the efficiency of preparing the irregular zinc powder.

[0090] Table 1. Spherical diameter selection table

[0091]

[0092] II. Selection of wafer pressing conditions

[0093] The confirmation of the wafer pressing conditions is to ensure the thickness of the wafer, the bonding strength of the wafer, and the dispersion ability after plating. Based on the process conditions of Example 1, the wafer pressing conditions are changed to prepare the examples for illustrating the effectiveness of the selection range of the present application. The specific comparison is shown in Table 2:

[0094] Table 2. Wafer pressing condition change table

[0095]

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

[0097] S1: pretreatment, the spherical zinc powder with a D50 distribution of 10-20 μm particle size is cleaned with acetone for 10 min, vacuum dried at 45°C for 4 h, then 1%wt of a surfactant stearic acid and 0.3%wt of polyethylene glycol are added, surface modification is carried out in ethanol, vacuum dried at 45°C for 1.5 h, under nitrogen protection, the wafer pressing parameters in Table 2 are used to press the wafer;

[0098] S2: partial coating, the wafer is cleaned by plasma, the plasma working conditions are 50 sccm of nitrogen, 40 W of power, and 80 s of treatment time, then a 80 nm thick Ni partial coating film is prepared by magnetron sputtering, the magnetron sputtering parameters are a vacuum lower than 10 Pa, a current of 2 A, a voltage of 600 V, a sputtering rate of 1.2-1.4 A / s, after the magnetron sputtering is completed, the powder is crushed in a low-speed ball mill at 50 r / min for 3 min, the ferromagnetic partially coated zinc powder is screened out by a high-gradient magnetic separator, the magnetic field strength is 0.5 T, the nitrogen protection, the gas pressure is 0.4 MPa, and the gas flow rate is 1.5 m / s, the screening of the ferromagnetic partially coated zinc powder is completed, and the non-magnetic or weak-magnetic zinc powder which is not well coated is repeated to make a cake and coat.

[0099] From the preparation and performance results of the examples and comparative examples, it can be seen that too low pressure will cause the thin cake to break and be unable to be transported and sputtered, and too high pressure will cause the thin cake to deform and the zinc powder to be bonded, which is not conducive to mechanical crushing and subsequent ball milling. The thin cakes prepared in Examples 1 / 3 / 4 / 5 / 6 / 7 are suitable for subsequent steps, and the suitable pressing conditions are 10-50 MPa, the holding time is 3-5 min, and the thickness of the thin cake is 300-500 μm.

[0100] Example 8 is also prepared, which is a kind of thin cake pressing support skeleton containing a metal matrix, using a metal Al sheet with a thickness of 1 mm, bidirectional pressing, and preparing a thin cake with a thickness of 300 μm on both sides of the Al sheet. The transport and sputtering hardness of the thin layer of the thin cake is increased.

[0101] III. Relationship between thickness of ferromagnetic film and magnetism

[0102] The thickness of the ferromagnetic film determines the relative shear strength of high-energy ball milling in an external magnetic field. Weak magnetism cannot be oriented and sheared, and strong magnetism can easily cause powder agglomeration and reduce the efficiency of ball milling. A suitable thickness of the ferromagnetic film is beneficial to improve the shear efficiency of ball milling. Based on the process of Example 2, the plating film thickness is changed, and the specific description is made through the examples in Table 3:

[0103] Table 3. Change table of plating film thickness

[0104]

[0105] The main difference between the examples in Table 3 is the thickness of the plating film. The change in thickness is achieved by controlling the plating time of the magnetron sputtering. The film layer with a thickness of 40-200 nm is prepared at an average rate of 1.3 A / s, and the preparation time interval is 300-1500 s.

[0106] From the sphericity and qualified product ratio of the shaped zinc powder prepared in Examples 1 / 9 / 10 and Comparative Examples 9 / 10 in Table 3, it can be seen that when the plating layer is too thin (Comparative Example 9), the sphericity is too low, and there is a tendency to be flaky, and the qualified product is less than 50%. When the plating layer is too thick (Comparative Example 10), the average sphericity is higher and the qualified product is less than 50%. A suitable plating layer can help to obtain qualified shaped zinc powder efficiently by affecting the relative shear ability and pinning position in an external magnetic field.

[0107] IV. Progression of magnetic field and high-energy ball milling process After the process condition screening of the foregoing steps, the magnetic field and ball milling conditions are the key to the preparation of the special-shaped zinc powder of the present application. Efficient ball milling that can conduct and accurately orient shear is conducive to shortening the preparation time and the pass rate of the finished product. Based on the process conditions of Example 2, other conditions remain unchanged, i.e., 10-20 μm spherical zinc powder raw material, thin cake pressing conditions of 20 MPa, 4 min, 400 μm, and 80 nm Ni film by magnetron sputtering, the magnetic field and ball milling conditions are changed, and the preparation process of the present application is illustrated, which is shown in Table 4.

[0108] Based on the S3 step of Example 1, the conditions are changed, which are as follows: magnetic field high-energy ball milling, 1%wt stearic acid surface modification of the ferromagnetic partially coated zinc powder prepared in the S2 step, dry mixer is used for ball milling, multiple external magnetic fields of 0.5 / 1 / 1.5 / 2 / 2.5 T are applied, the magnetic field device is a circular ring permanent magnet, which is fixed to the lower part of the ball milling tank, zirconia ball milling tank and 3 mm, 6 mm, 12 mm three-stage graded zirconia grinding balls are used, the ball-to-material ratio is 3:1 / 6:1 / 8:1 / 10:1, the stirring speed is 550 / 650 / 700 / 850 r / min, the ball milling time is 1.5 / 2 / 2.5 / 3.5 h, and the ball milling works for 15 min with 15 min interval.

[0109] As can be seen from the examples in Table 4, the external magnetic field strength is preferably between 1-2 T, and too high a magnetic field strength causes stronger shear effect and lower sphericity, and the pass rate is reduced. The effect is best when the ball-to-material ratio is moderate, and too high or too low may affect the efficiency (such as Comparative Examples 13 and 14). The ball milling speed represents the transmission efficiency of shear force, which is higher than the ordinary ball milling interval but lower than the ball milling speed of flaky zinc powder. Under the above conditions, the ball milling working time is much lower than the dozens of working time required for flaky zinc powder, greatly improving the ball milling efficiency and reducing the ball milling cost.

[0110] As can be seen from the preparation processes of the foregoing Examples 1-14 and Comparative Examples 1-18, the examples of the present application fully explain the technical importance of the ball diameter, thin cake pressing, ferromagnetic material partial coating, and external magnetic field high-energy ball milling.

[0111] Table 4. Table of changes in magnetic field and ball milling process

[0112]

[0113] In the present application, due to the magnetic characteristics generated by the partial coating of ferromagnetic material, it can be used for the screening of shaped zinc powder. If the magnetic property of the shaped zinc powder prepared by S1, S2 and S3 steps is too high, it indicates that the ball milling shear level is low and the shape change is small, so it is screened out by the magnetic separator for re-ball milling. The weakly magnetic or non-magnetic shaped zinc powder is subjected to multi-stage cyclone separation and air flow screening operation, so that the small particles or flaky particles can be screened out, the qualified product ratio of the shaped zinc powder is improved, and finally the surface treatment is carried out to complete the preparation before delivery. The specific steps are as follows:

[0114] S4: screening and grading, cleaning and drying the shaped zinc powder, after cleaning with acetone and vacuum drying, magnetic separation and screening are carried out by high gradient magnetic separator, the magnetic field strength is 1.5T, nitrogen protection, gas pressure is 0.3MPa, gas flow rate is 0.8m / s, after magnetic separation and grading, the non-magnetic or weakly magnetic powder is deformed greatly, enters the shaped screen grading system, the shaped screen grading system adopts multi-stage cyclone separation and air flow screening operation, by adjusting the air flow rate of 10m / s, the strip-shaped screen hole of 1-5μm is used for grading, the powder larger than 5μm is re-ball milled, and the powder smaller than 1μm is graded as flaky zinc powder;

[0115] S5: surface treatment, the qualified powder of the shaped screen grading is subjected to surface modification, the surface modification is completed in a fluidized bed reactor, 0.5%wt of stearic acid ethanol solution is introduced for coating treatment, the temperature is maintained at 70°C, the time is 30min, the dispersibility and oxidation resistance of the zinc powder are significantly improved.

[0116] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, the above examples and descriptions in the specification are only to illustrate the principles of the present application, without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, which all fall within the scope of the claimed present application. The scope of protection of the present application 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 adopts a metal matrix as a supporting skeleton and prepares the wafer by bidirectional pressing.

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 with a thickness of 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.

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