A method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling

Abstract

The present invention belongs to the field of magnetic materials, and specifically relates to a method for preparing nanocrystalline strips and nanoparticles based on gas-phase drive and liquid rolling. A crystallized thin strip with a width of 5 to 40 mm is obtained through processes such as alloy melting, pouring, and liquid rolling. The crystallized thin strip is subjected to heat treatment, crushing, chemical and physical driven particle separation, and other processes to finally obtain a magnetic particle powder. The powder is single crystal, with more than 85% of the particles being undamaged and more than 95% of the particles having a damaged volume of ≤10%. The six-dimensional particle size D80 is 8 to 10 nm and 20 to 30 nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.2 to 1.8:1, and the magnetic induction is 35 to 80 A·m. 2 / kg.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic materials, and in particular relates to a method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling. Background Art

[0002] With the rapid advancement of modern science and technology, nanoscience has demonstrated tremendous potential and application prospects in a wide range of fields, including materials science, information technology, and biomedicine. As an important branch of nanomaterials, magnetic nanoparticles have garnered extensive attention and research in data storage, biomedicine, and catalysis due to their unique physical and chemical properties, such as superparamagnetism, high specific surface area, and excellent biocompatibility.

[0003] Hard magnetic nanoparticles are in high demand in areas such as information storage, stealth coatings, and electromagnetic shielding. They demonstrate significant potential for application in these fields. In information storage, their high magnetic susceptibility and stability make them key materials for increasing storage density and speed. In stealth coatings, their electromagnetic properties can be tuned to achieve broadband stealth, enhancing target concealment. In electromagnetic shielding, their efficient absorption and attenuation capabilities provide reliable protection for electronic devices. These properties have established hard magnetic nanoparticles as crucial in numerous high-tech fields.

[0004] There are various methods for preparing magnetic nanocrystalline particles, including chemical, physical, and biological methods. Each of these methods has its own advantages and disadvantages. Patent CN115196954B uses a sol-gel process to spin-coat an amorphous thin film on a single-crystal silicon substrate. This method cannot be used for mass production. Patent US20110244271 A1 uses a molten alloy to flow directly into the roller gap through a water nozzle. After a relatively small casting force, an amorphous thin strip is obtained. After further heating and crystallization annealing, hexagonal ferrite magnetic powder is obtained. The molten alloy flows in the form of a liquid column over a long distance to reach the roller gap. The liquid column cools unevenly inside and outside, resulting in large structural fluctuations. The heat treatment process is crystallization annealing. Due to the large structural fluctuations of the amorphous structure and the uneven heating during the heating process, the crystallization size is uneven during this crystallization process. Summary of the Invention

[0005] In response to the problems in the prior art, the present invention provides a method for preparing nanocrystalline strips and nanoparticles based on gas-phase drive and liquid rolling. The nanocrystalline particles obtained thereby have uniform size, good dispersion, and excellent performance, which can meet the needs of hard magnetic nanoparticles in the fields of information storage, stealth coatings, electromagnetic shielding, etc.

[0006] The technical solution of the present invention is:

[0007] A method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling comprises the following steps:

[0008] Step (1) Alloy melting

[0009] Smelt the alloy according to the set composition. Use high-purity alumina or Pt-Rh alloy in the smelting crucible. Heat it to 1300-1450℃ and keep it warm for 2-3 hours. After the alloy powder is melted, add 1 / 3 of the weight of the melted powder into the alloy powder briquette. After it is completely melted, stir it thoroughly for more than 30 minutes to promote uniform distribution.

[0010] Step (2) Pouring

[0011] After the alloy is melted and the crucible is preheated and in place, the gate is heated online. The molten alloy is poured into the distribution nozzle by using the nozzle flow storage, small diameter gate flow control and spray deposition ring spraying method. The molten alloy is introduced through the nozzle nozzle. The liquid is dispersed into droplets by the spray deposition ring. The droplets enter the roll gap of the double rollers for rolling and cooling.

[0012] Step (3) Rolling

[0013] During the rolling process, when the molten liquid is poured, the double-roll surface rotates at a speed of 2-10m / s, and the double-roller frame moves back and forth along the axis as a whole, with a moving speed of 0-20mm / s, which facilitates the regulation of the heat exchange capacity of the roller surface. Constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 10-100kN. The diameter of the casting roller is 200-400mm, the width of the roller is 110-350mm, and the roller surface crown is +10-25μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied. The cooling water flux of the casting roller is 30-100m 3 / h; the casting rolls are driven by a direct servo motor to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to be 5~40mm;

[0014] Step (4) Collection of crystallized thin strips

[0015] The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects.

[0016] Step (5) Nanocrystallization diffusion heat treatment

[0017] Take the genuine crystallized thin ribbon and perform nano-crystallization diffusion heat treatment in a strong air circulation muffle furnace to make the boron diffuse more evenly to the grain boundary, which is convenient for the subsequent chemical and physical driven particle separation;

[0018] Step (6) Heat treatment of the strip and crushing

[0019] The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide or titanium oxide. Liquid nitrogen is added in a ratio of 1:2 to wet milling to refine the crystallized ribbon. The particle diameter distribution of the ball mill is controlled to be 0.1~0.5μm. The over-fine and over-coarse powders are removed and recycled.

[0020] Step (7) Chemical-physical driven particle separation

[0021] The ball-milled particles are subjected to a first pickling process using 1% acetic acid as the pickling solution, a powder particle to pickling solution mass ratio of 1:2-4, and pickling at 70°C for 5-10 minutes with stirring. After removing the upper layer of liquid, a primary pickling powder is obtained, and broken nanoparticles are removed. The primary pickling mixture is subjected to a second pickling process using 5% acetic acid as the pickling solution, a powder particle to pickling solution mass ratio of 1:5-10, and pickling at 85°C for 100-150 minutes with sufficient stirring. The magnetic nanoparticles are then obtained and collected after repeated centrifugal washing and drying.

[0022] Furthermore, in the above-mentioned method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling, the set composition in step (1) is (Fe2O3) by weight percentage. a (BaCO3) b (SrCO3) c (H3AlO3) d (H3BO3) e (CoO) f (TiO2) g (Bi2O3) h (Nd2O3) i , where the mass fraction is a: 10~30%; b: 30~40% or 1~6%; c: 1~5% or 30~40%; d: 0~3%; e: 10~25%; f: 0~1%; g: 0~1%; h: 0~5%; i: 0~5%.

[0023] Furthermore, in the above-mentioned preparation method of nanocrystalline strips and nanoparticles based on gas phase drive and liquid rolling, in step (2), a preheater is used to preheat a water nozzle, wherein the water nozzle is made of alumina or Pt-Rh, the preheating temperature is 1200-1300°C, the pouring water nozzle aperture is 1-3mm, the liquid level height is controlled at 100-180mm, a weighing device is used to measure the amount of molten alloy, and the pouring and pouring amount of molten alloy is controlled; the water nozzle is located in the middle of the spray deposition ring, the water nozzle is aligned with the center line of the spray deposition ring, the lower plane of the water nozzle is parallel to the lower plane of the spray deposition ring, the distance between the spray deposition ring and the roller gap is 200-240mm, the slit width of the spray deposition ring is 1-2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3-0.4MPa.

[0024] Furthermore, in the above-mentioned method for preparing nanocrystalline strips and nanoparticles based on gas phase drive and liquid rolling, the casting roller in step (3) is made of beryllium copper or chrome-plated mold steel, wherein the coating thickness of the beryllium copper roller sleeve is 50-250μm, and the coating thickness of the chrome-plated mold steel sleeve is 10-50μm, and the coating polishing roughness requirements are both ≤Ra0.8μm, and the hardness is both ≥60HRC.

[0025] Furthermore, in the above-mentioned method for preparing nanocrystalline strips and nanoparticles based on gas phase drive and liquid rolling, the heat treatment process in step (5) is as follows: the air flow velocity is 2-3 m / s, the crystallized strip is placed on a multi-unit shelf using a 304 stainless steel tray, and the thickness of a single tray does not exceed 10 mm; the temperature entering the furnace is not higher than 100°C, and the temperature is raised to 550~790°C at a rate of ≤10°C / min with the furnace and kept at this temperature for 0.5-5h for heat treatment.

[0026] Furthermore, the above-mentioned method for preparing nanocrystalline strips and nanoparticles based on gas-phase drive and liquid rolling, the nanoparticles prepared by this preparation method are single crystals, with more than 85% of the particles being undamaged, the damaged volume ≤10%, and the particle proportion being more than 95%.

[0027] Furthermore, the above-mentioned method for preparing nanocrystalline strips and nanoparticles based on gas phase drive and liquid rolling has the following characteristics: the particle size D80 of strontium-based and barium-based nanoparticles prepared by this method is 8-10nm and 20-30nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.2-1.8:1, and the magnetic induction is 35-80 A·m 2 / kg.

[0028] Advantages and beneficial effects of the present invention:

[0029] 1. Based on the liquid high-efficiency rolling process, the present invention provides a method for high-efficiency forming below 20 μm, which can be formed continuously and the obtained product is a uniform nanocrystalline thin strip;

[0030] 2. The present invention adopts a double-roll liquid rolling process, which overcomes the problems of uneven cooling rate and shape fluctuation between the roller surface and the free surface in the single-roll method, and creates a geometric foundation for subsequent diffusion heat treatment, chemical and physical driven particle separation, spheroidization and other processes;

[0031] 3. The present invention utilizes a process combining jet dispersion with twin-roll liquid rolling, which simultaneously applies a significant rolling forming force during cooling. This, in turn, induces intense high-temperature viscoplastic deformation, imparting a short-range, ordered, and large free volume of energy input to the nanocrystalline ribbon. This fully ensures that energy is high and uniform at every location during the forming process, satisfying crystallization conditions during rolling and allowing for nucleation and growth. Because the nucleation rate at each point is uniform, competitive growth is highly uniform, resulting in highly uniform nanoparticle size.

[0032] 4. The present invention adopts a comprehensive separation method of physical metallurgy and chemical physics, and the product obtained on the basis of the above is clearly divided into particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a process flow chart of the present invention;

[0034] Figure 2 TEM image of nanocrystalline particles prepared in Example 1 of the present invention;

[0035] Figure 3 Schematic diagram of gas phase drive and liquid rolling process;

[0036] In the figure, 1-water nozzle, 2-spray deposition ring, 3-casting roller. DETAILED DESCRIPTION

[0037] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0038] The following examples are based on the preparation methods of gas phase driven and liquid rolled nanocrystalline strips and nanoparticles using the following method: Figure 1 The process flow is shown. Example 1

[0039] This embodiment provides a method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling, comprising the following steps:

[0040] Step (1) Alloy melting

[0041] The alloy composition is set as (Fe2O3) by weight a (BaCO3) b (SrCO3) c (H3AlO3) d (H3BO3) e (CoO) f (TiO2) g (Bi2O3) h (Nd2O3)i , where the mass fractions are a: 30%; b: 30%; c: 5%; d: 2%; e: 25%; f: 1%; g: 1%; h: 3%; i: 3%; the melting crucible is made of high-purity alumina, heated to 1450℃ and kept warm for 3 hours. After the alloy powder is melted, 1 / 3 of the weight of the melted powder is added into the alloy powder briquette; after complete melting, stir thoroughly for 40 minutes to promote uniform distribution;

[0042] Step (2) Pouring

[0043] After the alloy is melted and the crucible is preheated in place, the gate is heated online, and the molten alloy is poured into the distribution water nozzle by adopting the method of water nozzle storage, small diameter gate flow control and spray deposition ring injection. The molten alloy is introduced through the water nozzle under the gate, and the liquid is dispersed into droplets by the spray deposition ring. The droplets enter the roll gap of the double rollers for rolling and cooling; specifically, a preheater is used to preheat the water nozzle, wherein the nozzle is made of alumina, the preheating temperature is 1300℃, the pouring nozzle aperture is 2mm, and the liquid level height is controlled at 150mm. A weighing device is used to measure the amount of molten alloy and control the amount of molten alloy poured in and out; the nozzle is located in the middle of the spray deposition ring, the nozzle is aligned with the center line of the spray deposition ring, the lower plane of the nozzle is parallel to the lower plane of the spray deposition ring, the spray deposition ring is 200mm away from the roll gap, the slit width of the spray deposition ring is 2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3MPa;

[0044] Step (3) Rolling

[0045] Rolling process such as Figure 3 As shown, it includes a water nozzle 1, a spray deposition ring 2 and two casting rollers 3. When the molten liquid is poured, the roller surface rotates at a speed of 10m / s, and the double-roller arch frame moves back and forth along the axial direction as a whole at a speed of 10mm / s, which is convenient for regulating the heat exchange capacity of the roller surface; constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 100kN; the diameter of the casting roller is 300mm, the roller width is 200mm, and the roller surface convexity is +15μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied; the casting roller is made of beryllium copper chrome-plated, and the beryllium copper roller sleeve coating thickness is 100μm; the coating polishing roughness requirement is ≤Ra 0.8μm, and the hardness is ≥60HRC; the casting roller cooling water flux is 50m 3 / h; the casting rolls are driven by a servo motor directly connected to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to 30mm;

[0046] Step (4) Collection of crystallized thin strips

[0047] The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects.

[0048] Step (5) Nanocrystallization diffusion heat treatment

[0049] Genuine crystallized ribbons were subjected to nanocrystallization diffusion heat treatment in a forced air circulation muffle furnace with an airflow velocity of 3m / s. The crystallized ribbons were placed on a multi-unit shelf using 304 stainless steel trays, with a single tray thickness of 6mm. The furnace temperature was set at 80°C and then heated to 580°C at a rate of 4°C / min for 5 hours to ensure more uniform diffusion of boron to the grain boundaries, facilitating subsequent chemical and physical driven particle separation.

[0050] Step (6) Heat treatment of the strip and crushing

[0051] The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide. Liquid nitrogen is added in a ratio of 1:2 to the crystallized ribbon for wet grinding and refinement. The diameter distribution of the ball milled particles is controlled to 0.3μm. The over-fine and over-coarse powders are removed and recycled.

[0052] Step (7) Chemical-physical driven particle separation

[0053] The ball-milled particles were pickled for the first time with 1% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:2, and pickling at 70°C for 10 minutes with stirring. After removing the upper liquid, the primary pickling powder was obtained and the broken nanoparticles were removed. The primary pickling mixture was pickled for the second time with 5% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:5, and pickling at 85°C for 120 minutes with sufficient stirring. The mixture was then repeatedly centrifuged and washed and dried to obtain the magnetic nanoparticles and collect them.

[0054] The magnetic nanoparticles prepared in this example are single crystals, with more than 85% of the particles being intact and more than 95% of the particles having a damage volume of ≤10%. The barium-based hexagonal particle size D80 is 25 nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.5:1, and the magnetic induction is 60 A·m 2 / kg, the TEM images of the prepared magnetic nanoparticles are shown in Figure 2 shown. Example 2

[0055] This embodiment provides a method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling, comprising the following steps:

[0056] Step (1) Alloy melting

[0057] The alloy composition is set as (Fe2O3) by weight a (BaCO3) b (SrCO3) c (H3AlO3) d (H3BO3) e (CoO) f(TiO2) g (Bi2O3) h (Nd2O3) i , where the mass fractions are a: 30%; b: 40%; c: 5%; d: 2%; e: 15%; f: 1%; g: 1%; h: 3%; i: 3%; the melting crucible is made of high-purity alumina, heated to 1450℃ and kept warm for 3 hours. After the alloy powder is melted, 1 / 3 of the weight of the melted powder is added into the alloy powder briquette; after complete melting, stir thoroughly for 40 minutes to promote uniform distribution;

[0058] Step (2) Pouring

[0059] After the alloy is melted and the crucible is preheated in place, the gate is heated online, and the molten alloy is poured into the distribution water nozzle by adopting the method of water nozzle storage, small diameter gate flow control and spray deposition ring injection. The molten alloy is introduced through the water nozzle under the gate, and the liquid is dispersed into droplets by the spray deposition ring. The droplets enter the roll gap of the double rollers for rolling and cooling; specifically, a preheater is used to preheat the water nozzle, wherein the nozzle is made of alumina, the preheating temperature is 1300℃, the pouring nozzle aperture is 2mm, and the liquid level height is controlled at 150mm. A weighing device is used to measure the amount of molten alloy and control the amount of molten alloy poured in and out; the nozzle is located in the middle of the spray deposition ring, the nozzle is aligned with the center line of the spray deposition ring, the lower plane of the nozzle is parallel to the lower plane of the spray deposition ring, the spray deposition ring is 200mm away from the roll gap, the slit width of the spray deposition ring is 2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3MPa;

[0060] Step (3) Rolling

[0061] Rolling process such as Figure 3 As shown, it includes a water nozzle 1, a spray deposition ring 2 and two casting rollers 3. When the molten liquid is poured, the roller surface rotates at a speed of 10m / s, and the double-roller arch frame moves back and forth along the axial direction as a whole at a speed of 10mm / s, which is convenient for regulating the heat exchange capacity of the roller surface; constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 100kN; the diameter of the casting roller is 300mm, the roller width is 200mm, and the roller surface convexity is +15μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied; the casting roller is made of beryllium copper chrome-plated, and the beryllium copper roller sleeve coating thickness is 100μm; the coating polishing roughness requirement is ≤Ra 0.8μm, and the hardness is ≥60HRC; the casting roller cooling water flux is 50m 3 / h; the casting rolls are driven by a servo motor directly connected to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to 30mm;

[0062] Step (4) Collection of crystallized thin strips

[0063] The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects.

[0064] Step (5) Nanocrystallization diffusion heat treatment

[0065] Genuine crystallized ribbons were subjected to nanocrystallization diffusion heat treatment in a forced air circulation muffle furnace with an airflow velocity of 3m / s. The crystallized ribbons were placed on a multi-unit shelf using 304 stainless steel trays, with a single tray thickness of 6mm. The furnace temperature was set at 80°C and then heated to 620°C at a rate of 4°C / min for 5 hours to ensure more uniform diffusion of boron to the grain boundaries, facilitating subsequent chemical and physical driven particle separation.

[0066] Step (6) Heat treatment of the strip and crushing

[0067] The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide. Liquid nitrogen is added in a ratio of 1:2 to the crystallized ribbon for wet grinding and refinement. The diameter distribution of the ball milled particles is controlled to 0.3μm. The over-fine and over-coarse powders are removed and recycled.

[0068] Step (7) Chemical-physical driven particle separation

[0069] The ball-milled particles were pickled for the first time with 1% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:2, and pickling at 70°C for 10 minutes with stirring. After removing the upper liquid, the primary pickling powder was obtained and the broken nanoparticles were removed. The primary pickling mixture was pickled for the second time with 5% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:5, and pickling at 85°C for 120 minutes with sufficient stirring. The mixture was then repeatedly centrifuged and washed and dried to obtain the magnetic nanoparticles and collect them.

[0070] The magnetic nanoparticles prepared in this example are single crystals, with more than 85% of the particles being intact and more than 95% of the particles having a damage volume ≤10%. The barium-based hexagonal particle size D80 is 20 nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.6:1, and the magnetic induction is 80 A·m 2 / kg. Example 3

[0071] This embodiment provides a method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling, comprising the following steps:

[0072] Step (1) Alloy melting

[0073] The alloy composition is set as (Fe2O3) by weight a (BaCO3) b (SrCO3) c (H3AlO3)d (H3BO3) e (CoO) f (TiO2) g (Bi2O3) h (Nd2O3) i , where the mass fractions are a: 30%; b: 5%; c: 30%; d: 2%; e: 25%; f: 1%; g: 1%; h: 3%; i: 3%; the melting crucible is made of high-purity alumina, heated to 1450℃ and kept warm for 3 hours. After the alloy powder is melted, 1 / 3 of the weight of the melted powder is added into the alloy powder briquette; after complete melting, stir thoroughly for 40 minutes to promote uniform distribution;

[0074] Step (2) Pouring

[0075] After the alloy is melted and the crucible is preheated in place, the gate is heated online, and the molten alloy is poured into the distribution water nozzle by adopting the method of water nozzle storage, small diameter gate flow control and spray deposition ring injection. The molten alloy is introduced through the water nozzle under the gate, and the liquid is dispersed into droplets by the spray deposition ring. The droplets enter the roll gap of the double rollers for rolling and cooling; specifically, a preheater is used to preheat the water nozzle, wherein the nozzle is made of alumina, the preheating temperature is 1300℃, the pouring nozzle aperture is 2mm, and the liquid level height is controlled at 150mm. A weighing device is used to measure the amount of molten alloy and control the amount of molten alloy poured in and out; the nozzle is located in the middle of the spray deposition ring, the nozzle is aligned with the center line of the spray deposition ring, the lower plane of the nozzle is parallel to the lower plane of the spray deposition ring, the spray deposition ring is 200mm away from the roll gap, the slit width of the spray deposition ring is 2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3MPa;

[0076] Step (3) Rolling

[0077] Rolling process such as Figure 3 As shown, it includes a water nozzle 1, a spray deposition ring 2 and two casting rollers 3. When the molten liquid is poured, the roller surface rotates at a speed of 10m / s, and the double-roller arch frame moves back and forth along the axial direction as a whole at a speed of 10mm / s, which is convenient for regulating the heat exchange capacity of the roller surface; constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 100kN; the diameter of the casting roller is 300mm, the roller width is 200mm, and the roller surface convexity is +15μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied; the casting roller is made of beryllium copper chrome-plated, and the beryllium copper roller sleeve coating thickness is 100μm; the coating polishing roughness requirement is ≤Ra 0.8μm, and the hardness is ≥60HRC; the casting roller cooling water flux is 50m 3 / h; the casting rolls are driven by a servo motor directly connected to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to 30mm;

[0078] Step (4) Collection of crystallized thin strips

[0079] The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects.

[0080] Step (5) Nanocrystallization diffusion heat treatment

[0081] Genuine crystallized ribbons were subjected to nanocrystallization diffusion heat treatment in a forced air circulation muffle furnace with an airflow velocity of 3m / s. The crystallized ribbons were placed on a multi-unit shelf using 304 stainless steel trays, with a single tray thickness of 6mm. The furnace temperature was set at 80°C and then heated to 620°C at a rate of 4°C / min for 5 hours to ensure more uniform diffusion of boron to the grain boundaries, facilitating subsequent chemical and physical driven particle separation.

[0082] Step (6) Heat treatment of the strip and crushing

[0083] The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide. Liquid nitrogen is added in a ratio of 1:2 to the crystallized ribbon for wet grinding and refinement. The diameter distribution of the ball milled particles is controlled to 0.3μm. The over-fine and over-coarse powders are removed and recycled.

[0084] Step (7) Chemical-physical driven particle separation

[0085] The ball-milled particles were pickled for the first time with 1% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:2, and pickling at 70°C for 10 minutes with stirring. After removing the upper liquid, the primary pickling powder was obtained and the broken nanoparticles were removed. The primary pickling mixture was pickled for the second time with 5% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:5, and pickling at 85°C for 120 minutes with sufficient stirring. The mixture was then repeatedly centrifuged and washed and dried to obtain the magnetic nanoparticles and collect them.

[0086] The magnetic nanoparticles prepared in this example are single crystals, with more than 85% of the particles being undamaged and more than 95% of the particles having a damage volume ≤10%. The strontium-based hexagonal particle size D80 is 10 nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.5:1, and the magnetic induction is 60 A·m 2 / kg. Example 4

[0087] This embodiment provides a method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling, comprising the following steps:

[0088] Step (1) Alloy melting

[0089] The alloy composition is set as (Fe2O3) by weight a (BaCO3) b (SrCO3) c(H3AlO3) d (H3BO3) e (CoO) f (TiO2) g (Bi2O3) h (Nd2O3) i , where the mass fractions are a: 30%; b: 5%; c: 40%; d: 2%; e: 15%; f: 1%; g: 1%; h: 3%; i: 3%; the melting crucible is made of high-purity alumina (, heated to 1450℃ and kept warm for 3 hours, the alloy powder is melted and then 1 / 3 of the weight of the melted powder is added to the alloy powder briquette; after complete melting, stir thoroughly for 40 minutes to promote uniform distribution;

[0090] Step (2) Pouring

[0091] After the alloy is melted and the crucible is preheated in place, the gate is heated online, and the molten alloy is poured into the distribution water nozzle by adopting the method of water nozzle storage, small diameter gate flow control and spray deposition ring injection, and the molten alloy is introduced through the water nozzle under the water nozzle, and the liquid is dispersed into droplets by the spray deposition ring, and the droplets enter the roll gap of the double rollers for rolling and cooling; specifically, a preheater is used to preheat the water nozzle, wherein the nozzle is made of alumina, the preheating temperature is 1300℃, the pouring nozzle aperture is 2mm, the liquid level height is controlled at 150mm, and a weighing device is used to measure the amount of molten alloy and control the amount of molten alloy poured in and out; the nozzle is located in the middle of the spray deposition ring, the nozzle is aligned with the center line of the spray deposition ring, the lower plane of the nozzle is parallel to the lower plane of the spray deposition ring, the spray deposition ring is 200mm away from the roll gap, the slit width of the spray deposition ring is 2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3MPa;

[0092] Step (3) Rolling

[0093] Rolling process such as Figure 3 As shown, it includes a water nozzle 1, a spray deposition ring 2 and two casting rollers 3. When the molten liquid is poured, the roller surface rotates at a speed of 10m / s, and the double-roller arch frame moves back and forth along the axial direction as a whole at a speed of 10mm / s, which is convenient for regulating the heat exchange capacity of the roller surface; constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 100kN; the diameter of the casting roller is 300mm, the roller width is 200mm, and the roller surface convexity is +15μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied; the casting roller is made of beryllium copper chrome-plated, and the beryllium copper roller sleeve coating thickness is 100μm; the coating polishing roughness requirement is ≤Ra 0.8μm, and the hardness is ≥60HRC; the casting roller cooling water flux is 50m 3 / h; the casting rolls are driven by a servo motor directly connected to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to 30mm;

[0094] Step (4) Collection of crystallized thin strips

[0095] The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects.

[0096] Step (5) Nanocrystallization diffusion heat treatment

[0097] Genuine crystallized ribbons were subjected to nanocrystallization diffusion heat treatment in a forced air circulation muffle furnace with an airflow velocity of 3m / s. The crystallized ribbons were placed on a multi-unit shelf using 304 stainless steel trays, with a single tray thickness of 6mm. The furnace temperature was set at 80°C and then heated to 670°C at a rate of 4°C / min for 5 hours to ensure more uniform diffusion of boron to the grain boundaries, facilitating subsequent chemical and physical driven particle separation.

[0098] Step (6) Heat treatment of the strip and crushing

[0099] The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide. Liquid nitrogen is added in a ratio of 1:2 to the crystallized ribbon for wet grinding and refinement. The diameter distribution of the ball milled particles is controlled to be 0.3 μm. The over-fine and over-coarse powders are removed and recycled.

[0100] Step (7) Chemical-physical driven particle separation

[0101] The ball-milled particles were pickled for the first time with 1% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:2, and pickling at 70°C for 10 minutes with stirring. After removing the upper liquid, the primary pickling powder was obtained and the broken nanoparticles were removed. The primary pickling mixture was pickled for the second time with 5% acetic acid as the pickling solution, a mass ratio of powder particles to pickling solution of 1:5, and pickling at 85°C for 120 minutes with sufficient stirring. The mixture was then repeatedly centrifuged and washed and dried to obtain the magnetic nanoparticles and collect them.

[0102] The magnetic nanoparticles prepared in this example are single crystals, with more than 85% of the particles being undamaged and more than 95% of the particles having a damage volume of ≤10%. The strontium-based hexagonal particle size D80 is 8 nm, the particle shape is a hexagonal prism structure, the aspect ratio is 1.3:1, and the magnetic induction is 70 A·m 2 / kg.

Claims

1. A method for preparing nanocrystalline strips and nanoparticles based on gas phase drive and liquid rolling, characterized in that: The following steps are involved: Step (1) Alloy melting Smelt the alloy according to the set composition. Use high-purity alumina or Pt-Rh alloy in the smelting crucible. Heat it to 1300-1450℃ and keep it warm for 2-3 hours. After the alloy powder is melted, add 1 / 3 of the weight of the melted powder into the alloy powder briquette. After it is completely melted, stir it thoroughly for more than 30 minutes to promote uniform distribution. Step (2) Pouring After the alloy is melted and the crucible is preheated and in place, the gate is heated online. The molten alloy is poured into the distribution nozzle by using the nozzle flow storage, small diameter gate flow control and spray deposition ring spraying method. The molten alloy is introduced through the nozzle nozzle. The liquid is dispersed into droplets by the spray deposition ring. The droplets enter the roll gap of the double rollers for rolling and cooling. Step (3) Rolling During the rolling process, when the molten liquid is poured, the double-roll surface rotates at a speed of 2-10m / s, and the double-roller frame moves back and forth along the axis as a whole, with a moving speed of 0-20mm / s, which facilitates the regulation of the heat exchange capacity of the roller surface. Constant casting and rolling force control is adopted, and the sum of the casting and rolling forces on both sides is 10-100kN. The diameter of the casting roller is 200-400mm, the width of the roller is 110-350mm, and the roller surface crown is +10-25μm. According to the matching of the roller surface material and the casting roller stiffness, the roller gap is balanced after the casting and rolling force is applied. The cooling water flux of the casting roller is 30-100m 3 / h; the casting rolls are driven by a direct servo motor to achieve synchronous dynamic adjustment; the width of the crystallized strip is controlled to be 5~40mm; Step (4) Collection of crystallized thin strips The casting machine outlet is designed with a multi-channel collection bin to distinguish and collect pouring heads, genuine products and cast residues. The cast residue bin is isolated from the genuine product bin with insulation materials to avoid annealing effects. Step (5) Nanocrystallization diffusion heat treatment Take the genuine crystallized thin ribbon and perform nano-crystallization diffusion heat treatment in a strong air circulation muffle furnace to make the boron diffuse more evenly to the grain boundary, which is convenient for the subsequent chemical and physical driven particle separation; Step (6) Heat treatment of the strip and crushing The ball mill is mixed with liquid nitrogen for ball milling. The grinding balls are made of zirconium oxide or titanium oxide. Liquid nitrogen is added in a ratio of 1:2 to wet milling to refine the crystallized ribbon. The particle diameter distribution of the ball mill is controlled to be 0.1~0.5μm. The over-fine and over-coarse powders are removed and recycled. Step (7) Chemical-physical driven particle separation The ball-milled particles are subjected to a first pickling process using 1% acetic acid as the pickling solution, a powder particle to pickling solution mass ratio of 1:2-4, and pickling at 70°C for 5-10 minutes with stirring. After removing the upper layer of liquid, a primary pickling powder is obtained, and broken nanoparticles are removed. The primary pickling mixture is subjected to a second pickling process using 5% acetic acid as the pickling solution, a powder particle to pickling solution mass ratio of 1:5-10, and pickling at 85°C for 100-150 minutes with sufficient stirring. The magnetic nanoparticles are then obtained and collected after repeated centrifugal washing and drying.

2. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: The set composition in step (1) is (Fe2O3) by weight percentage a (BaCO3) b (SrCO3) c (H3AlO3) d (H3BO3) e (CoO) f (TiO2) g (Bi2O3) h (Nd2O3) i , where mass fraction a: 10~30%; b: 30~40% or 1~6%; c: 1~5% or 30~40%; d: 0~3%; e：10~25%； f：0~1%； g：0~1%； h：0~5%； i：0~5%。 3. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: In step (2), a preheater is used to preheat a water nozzle, wherein the nozzle is made of alumina or Pt-Rh, the preheating temperature is 1200-1300°C, the pouring nozzle aperture is 1-3mm, the liquid level height is controlled at 100-180mm, a weighing device is used to measure the amount of molten alloy, and the amount of molten alloy poured in and out is controlled; the nozzle is located in the middle of the spray deposition ring, the nozzle is aligned with the center line of the spray deposition ring, the lower plane of the nozzle is parallel to the lower plane of the spray deposition ring, the distance between the spray deposition ring and the roller gap is 200-240mm, the slit width of the spray deposition ring is 1-2mm, the annular slit inclination angle is 45°, the focal length is 40mm, and the injection pressure is 0.3-0.4MPa.

4. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: In step (3), the casting roller is made of beryllium copper or chrome-plated mold steel, wherein the coating thickness of the beryllium copper roller sleeve is 50-250 μm, and the coating thickness of the mold steel chrome-plated sleeve is 10-50 μm, and the coating polishing roughness requirements are both ≤ Ra0.8 μm, and the hardness is both ≥ 60 HRC.

5. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: The heat treatment process in step (5) is as follows: the air flow velocity is 2-3 m / s, the crystallized strip is placed on a multi-unit shelf using a 304 stainless steel tray, and the thickness of a single tray does not exceed 10 mm; the temperature entering the furnace is not higher than 100 ° C, and the temperature is raised to 550~790 ° C at a rate of ≤10 ° C / min with the furnace and kept at this temperature for 0.5-5 hours for heat treatment.

6. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: The nanoparticles prepared by this preparation method are single crystals, with more than 85% of the particles being undamaged, the damaged volume being ≤10%, and the particle proportion being more than 95%.

7. The method for preparing nanocrystalline strips and nanoparticles based on gas phase driving and liquid rolling according to claim 1, characterized in that: The strontium-based and barium-based nanoparticles prepared by this preparation method have a particle size D80 of 8-10 nm and 20-30 nm, a hexagonal prism structure, an aspect ratio of 1.2-1.8:1, and a magnetic induction of 35-80 A·m 2 / kg.

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