Preparation method of high-performance magnetic liquid for low-temperature sealed environment

Abstract

The invention belongs to the technical field of intelligent magnetic material preparation and low-temperature sealing environment application thereof, and particularly relates to a preparation method of high-performance magnetic liquid for a low-temperature sealing environment. The method comprises the following steps: (1) controllably doping different ions to prepare ferrite nanoparticles with high saturation magnetization at low temperature; (2) adjusting the pH value of the reaction liquid to change the zeta potential on the surface of the nano magnetic particles; (3) carrying out effective chemical coating on the particles by using oleic acid; and (4) uniformly dispersing the coated particles in low-temperature hydraulic oil to prepare the low-temperature-resistant magnetic liquid with high dispersion stability. The prepared magnetic liquid has a saturation magnetization value and fluidity which are obviously higher than those of conventional magnetic liquid at low temperature, and can be applied to the application fields of hydraulic mechanical sealing and low-temperature environment high-end sealing.

Description

Technical Field

[0001] This invention belongs to the technical field of intelligent magnetic material preparation and its application in low-temperature sealing environments, specifically a method for preparing a high-performance magnetic liquid for low-temperature sealing environments. Background Technology

[0002] Nanomagnetic fluids are colloidal solution systems composed of superparamagnetic nanoparticles, surfactants, and a base liquid. They do not stratify or settle under the influence of magnetic fields, gravity, or centrifugal forces, making them a high-end intelligent material. Their fluidity and magnetism change significantly under a magnetic field, leading to their widespread application in sealing, aerospace, and military fields. While magnetic fluid sealing technology at room temperature and high temperatures is relatively mature, with continuous advancements in industrial technology, magnetic fluids may operate over a wider temperature range, particularly at low temperatures. However, reports on the preparation and sealing applications of magnetic fluids at low temperatures are currently limited.

[0003] Patent No. CN 115083719 A—A Low-Temperature Resistant Magnetic Fluid and Its Preparation Method—discloses a low-temperature resistant magnetic fluid and its preparation method. This magnetic fluid is inexpensive, has a simple preparation process, exhibits excellent stability, and can be applied over a wide temperature range, making it particularly suitable for long-term stable operation at low temperatures. However, the base oil used in preparing the magnetic fluid is an alcohol-water mixture, which has high volatility, making it unsuitable for long-term stable sealing applications.

[0004] The patent—"A Method for Improving the Pressure Resistance of Magnetic Fluid Seals in Low-Temperature Operating Environments" (Patent No.: CN104405886 A)—points out that in low-temperature environments, temperature changes are significant in certain operating conditions; for example, the maximum temperature difference in the operating environment of a certain equipment can reach 100°C. At low temperatures, the viscosity of the magnetic fluid changes drastically. Combined with a large shaft diameter, this results in excessive starting torque on the rotating shaft, severely impacting the application of magnetic fluid seals in low-temperature fields. This patent improves the sealing pressure resistance by changing the material and design parameters of the seal, but does not improve the sealing effect by optimizing the performance of the magnetic fluid.

[0005] The patent—Magnetic Liquid Sealing Device for Cryogenic Gas Sealing (Patent No.: CN 116221413A) mentions that in the sealing application of magnetic liquid in equipment such as superconducting motors or cryogenic reactors, when the equipment is in standby or at a low speed, cryogenic helium or nitrogen gas leaks into the seal, causing the magnetic liquid to freeze and solidify, resulting in the failure of the magnetic liquid seal.

[0006] The patents "A Low-Temperature Resistant Magnetic Liquid Sealing Device" (Patent No.: CN118564654A) and "A Low-Speed ​​Medium-Low Temperature Magnetic Liquid Water-Cooled Sealing Device" (Patent No.: CN206845903U) also improve the sealing effect by optimizing the design of the sealing device.

[0007] However, there are currently very few patents on how to select the best low-temperature resistant base liquid to prepare magnetic liquids with high saturation magnetization, dispersion stability and flowability at low temperatures. Summary of the Invention

[0008] Current methods for preparing magnetic fluids are primarily suitable for sealing in room temperature and high-temperature environments. However, their fluidity changes at low temperatures, significantly limiting their sealing effectiveness. Therefore, this invention aims to provide a method for preparing a high-performance magnetic fluid for low-temperature sealing environments. This method involves preparing ferrite nanoparticles with high saturation magnetization at low temperatures by controlling the type and amount of ion doping. These nanoparticles are then chemically coated with oleic acid and uniformly dispersed in low-temperature resistant hydraulic oil, resulting in a high-performance magnetic fluid suitable for low-temperature environments, thereby improving the low-temperature sealing effect.

[0009] To achieve the above-mentioned objectives, the specific technical solution adopted by this invention is as follows: A method for preparing a high-performance magnetic fluid for cryogenic sealing environments includes the following steps: (1) Press Me x Fe 3-x The stoichiometric ratio of Me to Fe in the O4 molecular formula was determined by weighing substances containing Me and Fe and preparing a ferrite nanoparticle precursor solution through pre-reaction. (2) The ferrite nanoparticle precursor liquid prepared in step (1) is placed in a reaction vessel for further reaction to obtain a reaction liquid containing ferrite nanoparticles with high saturation magnetization at low temperature. (3) Add dilute hydrochloric acid to the reaction solution prepared in step (2) to adjust the zeta potential on the surface of the ferrite nanoparticles and obtain a reaction solution containing ferrite nanoparticles with a positive zeta potential. (4) Add oleic acid to the reaction solution containing ferrite nanoparticles with a positive zeta potential obtained in step (3) to perform chemical coating and obtain coated particles; (5) Disperse the coated particles obtained in step (4) evenly in the base liquid to obtain a high-performance magnetic liquid for low-temperature sealing environment.

[0010] In a preferred embodiment of this application, step (1) of the method for preparing a high-performance magnetic liquid for a low-temperature sealed environment involves preparing a ferrite nanoparticle precursor solution through a pre-reaction by controlling the type and amount of ion doping. The ion doping type is Me=Zn.2+ Dy 3+ Gd 3+ The doping amount is x =0.01-0.3 (specific values ​​can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, etc.).

[0011] In a preferred embodiment of this application, in step (1) of the method for preparing a high-performance magnetic liquid for a low-temperature sealing environment, the pre-reaction temperature is 60-80℃ (specifically, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, etc.), and the reaction time is 30-60min (specifically, it can be 30min, 40min, 50min, 60min, etc.).

[0012] As a preferred embodiment of this application, in step (2) of the method for preparing a high-performance magnetic liquid for a low-temperature sealed environment, the initial reaction liquid is placed in a reaction vessel and reacted at a high temperature (the temperature of further reaction) of 150-300℃ (specifically, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 250℃, 270℃, 280℃, 290℃, 300℃, etc.) for 2-5 hours (specifically, 2 hours, 3 hours, 4 hours, 5 hours, etc.).

[0013] In a preferred embodiment of this application, in step (3) of the method for preparing a high-performance magnetic liquid for a low-temperature sealing environment, the amount of dilute hydrochloric acid added is preferably such that the zeta potential on the surface of the nanoparticles is positive.

[0014] In a preferred embodiment of this application, in step (4) of the method for preparing a high-performance magnetic liquid for a low-temperature sealing environment, the mass ratio of oleic acid to ferrite nanoparticles with a positive zeta potential is 0.1-0.5.

[0015] As a preferred embodiment of this application, in step (4) of the method for preparing a high-performance magnetic fluid for a low-temperature sealing environment, the coating particles account for 20%-50% of the mass of the magnetic fluid (specifically, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.).

[0016] As a preferred embodiment of this application, in step (5) of the method for preparing a high-performance magnetic fluid for a low-temperature sealing environment, the base fluid is low-temperature hydraulic oil; the selected low-temperature hydraulic oil has better fluidity than non-low-temperature resistant base fluid magnetic fluid fluoroether oil under low-temperature conditions of -10℃.

[0017] As a preferred embodiment of this application, in step (5) of the method for preparing a high-performance magnetic liquid for a low-temperature sealing environment, the high-performance magnetic liquid has a saturation magnetization of up to 30-50 emu / g at a low temperature of -50°C.

[0018] This invention also protects the high-performance magnetic fluid for cryogenic sealing environments obtained by the above methods.

[0019] This invention also protects the application of the high-performance magnetic fluid for cryogenic sealing environments obtained by the above methods in cryogenic environment sealing.

[0020] The working principle of this invention is as follows: First, ferrite nanoparticles with high saturation magnetization at low temperatures were prepared by doping with different ions. The zeta potential on the surface of the nanoparticles was adjusted by dilute hydrochloric acid. A positive zeta potential, and the larger the positive value, the more favorable it is for the adsorption of electronegative functional groups; conversely, a negative zeta potential, and the larger the negative value, the more favorable it is for the adsorption of positively charged functional groups. To ensure a positive zeta potential, an appropriate amount of oleic acid was added. Insufficient oleic acid coating on the particle surface is detrimental to the dispersion stability of the magnetic liquid due to insufficient repulsion between particles. After adding oleic acid, a chemical reaction occurs between the oleic acid and the particles. The coated particles are then dispersed in low-temperature hydraulic oil to obtain a magnetic liquid with high saturation magnetization, high dispersion stability, and high fluidity at low temperatures.

[0021] In Zn x Fe 3-x There are three types of iron ions in O4, namely Fe occupying the B site. 2+ Ions and Fe occupying A and B sites 3+ Zn 2+ Prioritize occupying site A, and allocate a certain amount of Fe from site A. 3+ Fe is squeezed into the B site. 3+ Increased quantity. Zn 2+ Occupying the A-site disrupts the interaction between adjacent ions, weakening the Fe-O-Fe interaction at the A-site. Appropriate doping with Zn... 2+ This will increase the net magnetic moment of the molecules and the saturation magnetization of the particles. Dy 3+ Belongs to rare earth ions, Dy 3+ It exhibits strong exchange coupling with other ions, which effectively transmits magnetic moment alignment information, causing more magnetic moments to align in the same direction, thereby significantly increasing the specific saturation magnetization. Similarly, Gd... 3+ Exchange interactions with other particles can promote the coordinated alignment of magnetic moments, enhance magnetic order, and thus increase the specific saturation magnetization of nanoparticles.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (i) Magnetic liquids prepared in existing studies are usually used in room temperature and high temperature environments; the magnetic liquid prepared in this invention can be used in low temperature environments (for example, it still performs well at -50℃).

[0023] (ii) The magnetic liquid prepared by the present invention has significant advantages at low temperatures, possessing high saturation magnetization, high dispersion stability and high fluidity, and the required materials are readily available with low equipment requirements. Attached Figure Description

[0024] Figure 1 The images show the physical images of the magnetic liquids obtained in Comparative Example 1 and Example 1, respectively. The left side is Comparative Example 1, and the right side is Example 1; Figure 2 Magnetization curves of particles and magnetic liquids at -10℃; Figure 3 The graphs show the low-temperature fluidity curves of the magnetic liquids obtained in Example 1 and Comparative Example 3, respectively. Detailed Implementation

[0025] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0026] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0027] Any feature disclosed in this specification (including the claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0028] Unless otherwise specified, all processes used in this application are conventional methods; and all materials used, unless otherwise specified, are commercially available.

[0029] In this application, unless otherwise specified, all ratios are mass ratios, and % refers to mass percentage content, i.e., wt%.

[0030] The low-temperature resistant hydraulic oil used in the following examples is RP4350 aviation hydraulic oil, DuPont fluoroether oil, with the molecular formula F-(C3F6O). n-C2F5 exhibits superior fluidity compared to non-low-temperature resistant magnetic liquid fluoroether oils at a low temperature of -10°C.

[0031] Hydrochloric acid, commercially available product, analytical grade.

[0032] Example 1 A method for preparing a high-performance magnetic fluid for cryogenic sealing environments includes the following steps: (1) 0.4g DyCl3·H2O, 8g FeCl3·H2O and 5g FeSO4·H2O were placed in ultrapure water and mechanically stirred at 70℃ and 500r / min to dissolve. Then 10g NaOH was added and the pre-reaction was carried out for 40min to obtain ferrite nanoparticle precursor solution.

[0033] (2) The ferrite nanoparticle precursor liquid obtained in step (1) is placed in a high-temperature reactor and crystallized at 250°C for 3 hours to obtain a reaction liquid containing ferrite nanoparticles with high saturation magnetization at low temperature.

[0034] (3) Add dilute hydrochloric acid (the volume ratio of hydrochloric acid to ultrapure water is 1:3) to the reaction solution obtained in step (2) to change the zeta potential of the particle surface until its zeta value is positive, and obtain a reaction solution containing ferrite nanoparticles with a positive zeta potential.

[0035] (4) Add 2g of oleic acid to the reaction solution containing ferrite nanoparticles with a positive zeta potential obtained in step (3), and continue the reaction for 2h under mechanical stirring at 70℃ and 500r / min to achieve effective chemical coating and obtain coated particles.

[0036] (5) Take 10g of the coated particles obtained in step (4) and 15g of low-temperature hydraulic oil, and mechanically stir at 70℃ and 500r / min for 2h to uniformly disperse the coated particles in the low-temperature hydraulic oil, thus preparing a high-performance magnetic fluid for low-temperature sealing environments. This magnetic fluid also has high saturation magnetization and high dispersion stability, wherein the coated particles account for 40wt% of the mass of the magnetic fluid.

[0037] The resulting cryogenic sealing environment was left to stand in a high-performance magnetic fluid for one month. A photograph of the cryogenic sealing environment after one month of standing in the high-performance magnetic fluid is shown below. Figure 1 As shown on the right.

[0038] Example 2 A method for preparing a high-performance magnetic fluid for cryogenic sealing environments includes the following steps: (1) 0.6g ZnCl2, 8g FeCl3·6H2O and 4g FeSO4·7H2O were placed in ultrapure water and mechanically stirred at 70℃ and 500r / min to dissolve. Then 10g NaOH was added and the pre-reaction was carried out for 40min to obtain ferrite nanoparticle precursor solution.

[0039] (2) The ferrite nanoparticle precursor liquid obtained in step (1) is placed in a high-temperature reactor and the crystallization reaction is continued at a high temperature of 250°C for 3 hours to obtain a reaction liquid containing ferrite nanoparticles with high saturation magnetization at low temperature.

[0040] (3) Add dilute hydrochloric acid (hydrochloric acid to ultrapure water volume ratio 1:3) to the reaction solution obtained in step (2) to change the zeta potential of the particle surface until its zeta value is positive, and obtain a reaction solution containing ferrite nanoparticles with a positive zeta potential.

[0041] (4) Add 2g of oleic acid to the reaction solution obtained in step (3), and continue to react for 2h at 70℃ and 500r / min with mechanical stirring to coat the particles.

[0042] (5) Take 10g of the coated particles obtained in step (4) and 15g of low-temperature hydraulic oil. Mechanically stir the coated particles at 70℃ and 500r / min for 2h to uniformly disperse them in the low-temperature hydraulic oil, thus preparing a high-performance magnetic liquid for low-temperature sealing environments. This magnetic liquid also has high saturation magnetization and high dispersion stability, wherein the mass fraction of the coated particles is 40wt%.

[0043] The final magnetic fluid was tested, and the specific results are shown in [link to results]. Figure 2 ,Depend on Figure 2 It can be seen that the saturation magnetization of the final magnetic liquid at low temperature is approximately 37.6 emu / g.

[0044] Example 3 A method for preparing a high-performance magnetic fluid for cryogenic sealing environments includes the following steps: (1) Place 0.6g GdCl3, 7.5g FeCl3·6H2O and 5g FeSO4·7H2O in ultrapure water and dissolve them by mechanical stirring at 70℃ and 500r / min. Then add 10g NaOH and continue the pre-reaction for 40min to obtain ferrite nanoparticle precursor solution.

[0045] (2) The precursor liquid prepared in step (1) is placed in a high-temperature reactor and the crystallization reaction is continued at a high temperature of 250°C for 3 hours to obtain a reaction liquid containing ferrite nanoparticles with high saturation magnetization at low temperature.

[0046] (3) Add dilute hydrochloric acid (hydrochloric acid to ultrapure water volume ratio 1:3) to the reaction solution obtained in step (2) to change the zeta potential of the particle surface until its zeta value is positive, and obtain a reaction solution containing ferrite nanoparticles with a positive zeta potential.

[0047] (4) Add 2g of oleic acid to the reaction solution containing ferrite nanoparticles with a positive zeta potential obtained in step (3), and continue to react for 2h under mechanical stirring at 70℃ and 500r / min to coat them and obtain coated particles.

[0048] (5) Take 10g of coated particles and 15g of low-temperature hydraulic oil. Mechanically stir the coated particles at 70℃ and 500r / min for 2h to uniformly disperse them in the low-temperature hydraulic oil, thus preparing a high-performance magnetic fluid for low-temperature sealing environments. This magnetic fluid also has high saturation magnetization and high dispersion stability, wherein the mass fraction of the coated particles is 40wt%.

[0049] The final magnetic fluid was tested, and the specific results are shown in [link to results]. Figure 2 ,Depend on Figure 2 It can be seen that the saturation magnetization of the final magnetic liquid at low temperature is approximately 31.9 emu / g.

[0050] Comparative Example 1 A method for preparing a high-performance magnetic liquid for low-temperature sealed environments is described, with the same preparation method as in Example 1. The only difference is that step (3) is omitted, i.e., the step of adding dilute hydrochloric acid to the reaction solution obtained in step (2) is removed. In this case, since dilute hydrochloric acid is not added, and the reaction solution is strongly alkaline due to the addition of a large amount of NaOH, the zeta potential of the particle surface is negative. The remaining steps and parameters are the same as in Example 1, and the final magnetic liquid is obtained.

[0051] The obtained magnetic fluid was allowed to stand (the standing time was the same as in Example 1). A picture of the magnetic fluid after standing for one month is shown below. Figure 1 As shown on the left. By Figure 1 It can be seen that the prepared magnetic liquid has poor dispersion stability, and it exhibits stratification.

[0052] Comparative Example 2 A method for preparing a high-performance magnetic fluid for low-temperature sealed environments is described, with the same preparation method as in Example 2. The only difference is that the amount of ZnCl2 added in step (1) is changed to 2g.

[0053] The final magnetic fluid was tested, and the specific results are shown in [link to results]. Figure 2 ,Depend on Figure 2It can be seen that the final magnetic liquid has a saturation magnetization of approximately 19.8 emu / g at low temperature, indicating a relatively low specific saturation magnetization. Analysis suggests that Zn doping has a more significant effect on improving the specific saturation magnetization of the particles. x Fe 3-x O4 with Zn 2+ With increasing ion doping concentration, the specific saturation magnetization of the particles initially increases and then decreases. In Zn... x Fe 3-x There are three types of iron ions in O4, namely Fe occupying the B site. 2 + ions and Fe occupying A and B sites 3+ Zn 2+ Prioritize occupying site A, and allocate a certain amount of Fe from site A. 3+ Fe is squeezed into the B site. 3+ Increased quantity. Zn 2+ Occupying the A-site disrupts the interaction between adjacent ions, weakening the Fe-O-Fe interaction at the A-site. This leads to an increase in the net magnetic moment of the molecule. More Zn... 2+ Entering site A results in a greater amount of Fe. 3+ It was squeezed into the B site. Fe in the B site 3+ The increased amount of ions at the B site causes some of the ions to shift from a parallel alignment to an antiparallel alignment, which enhances the superexchange interaction at the BB site. This, in turn, affects the antiparallel alignment of the magnetic moments between the sublattices at the AB site, weakens the superexchange interaction between the AB sites, and results in a lower saturation magnetization of the magnetic liquid.

[0054] Comparative Example 3 A method for preparing a high-performance magnetic fluid for cryogenic sealing environments is disclosed, which is the same as in Example 3. The only difference is the amount of coated particles added in the final preparation of the high-performance magnetic fluid for cryogenic sealing environments; the mass fraction of the coated particles in the final high-performance magnetic fluid for cryogenic sealing environments is 60 wt%.

[0055] The final magnetic fluid was tested, and the specific results are shown in [link to results]. Figure 3 Measurements showed that this magnetic fluid had poor fluidity. Figure 3 It can be seen that the yield stress of the magnetic fluid gradually increases with increasing shear rate; comparing Comparative Example 3 with Example 1, it can be found that when the shear rate increases to 10... 3 s -1 At that time, the yield stress of the magnetic fluid in Comparative Example 3 increased to 10. 4 Pa, while the yield stress in Example 1 was only 10 Pa. 3 Pa.

[0056] Comparative Example 4 A method for preparing a high-performance magnetic liquid for low-temperature sealed environments is described, with the preparation method being the same as in Example 1. The only difference is that the 40-minute pre-reaction in step (1) is omitted, and instead, the dissolved solution is directly subjected to the reaction in step (2). The remaining steps are the same. As a result, the particles agglomerate after the crystallization reaction, and the resulting particles have a large morphology and particle size distribution range. Consequently, the dispersion stability of the prepared magnetic liquid is poor, and the sedimentation ratio is higher than 10% after standing for one month.

[0057] Comparative Example 5 A method for preparing a high-performance magnetic fluid for cryogenic sealing environments is described, with the preparation method being the same as in Example 1. The only difference is that step (4) is omitted, and the reaction solution obtained in step (3) is dried, then the powder is ground and dispersed together with oleic acid in cryogenic hydraulic oil. The resulting magnetic fluid exhibits very poor dispersion stability, with a sedimentation rate exceeding 30% after one month.

[0058] Comparative Example 6 A method for preparing a high-performance magnetic fluid for low-temperature sealing environments is described, with the same preparation method as in Example 1. The only difference is that 20g of the coated particles obtained in step (4) are mixed with 15g of low-temperature hydraulic oil to prepare the magnetic fluid, resulting in the loss of fluidity of the magnetic fluid, which approaches a gel state.

[0059] experiment: The ferrite nanoparticles and magnetic liquids obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and their low-temperature magnetization curves at -10°C are shown below. Figure 2 As shown. The specific saturation magnetization of the ion-doped powder and magnetic liquid at -10℃ were as follows: Example 1 (45 emu / g), Example 2 (38 emu / g), Example 3 (32 emu / g), and Comparative Example 2 (19 emu / g). Figure 2 It is evident that appropriate ion doping can significantly enhance the saturation magnetization of magnetic liquids at low temperatures. The flow curves of magnetic liquids prepared from three different ferrite particles are shown below. Figure 3 As shown in the figure, the fluidity of different magnetic liquids varies greatly at low temperatures. Compared with fluoroether oil-based magnetic liquids, the low-temperature resistant synthetic oil-based magnetic liquids clearly exhibit stronger fluidity.

[0060] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0061] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects described in this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A method for preparing a high-performance magnetic fluid for low-temperature sealed environments, characterized in that... Includes the following steps: (1) Press Me x Fe 3-x The stoichiometric ratio of Me to Fe in the O4 molecular formula was determined by weighing substances containing Me and Fe and preparing a ferrite nanoparticle precursor solution through pre-reaction. (2) The ferrite nanoparticle precursor liquid prepared in step (1) is placed in a reaction vessel for further reaction to obtain a reaction liquid containing ferrite nanoparticles with high saturation magnetization at low temperature. (3) Add dilute hydrochloric acid to the reaction solution prepared in step (2) to adjust the zeta potential on the surface of the ferrite nanoparticles and obtain a reaction solution containing ferrite nanoparticles with a positive zeta potential. (4) Add oleic acid to the reaction solution containing ferrite nanoparticles with a positive zeta potential obtained in step (3) to perform chemical coating and obtain coated particles; (5) Disperse the coated particles obtained in step (4) evenly in the base liquid to obtain a high-performance magnetic liquid for low-temperature sealing environment.

2. The method for preparing a high-performance magnetic fluid for low-temperature sealing environments as described in claim 1, characterized in that: In step (1), Me is Zn 2+ Dy 3+ or Gd 3+ ; x =0.01-0.

3.

3. The method for preparing a high-performance magnetic fluid for low-temperature sealed environments as described in claim 1, characterized in that: In step (1), the pre-reaction temperature is 60-80℃ and the reaction time is 30-60min.

4. The method for preparing a high-performance magnetic fluid for low-temperature sealed environments as described in claim 1, characterized in that: In step (2), the temperature for further reaction is 150-300℃ and the reaction time is 2-5h.

5. The method for preparing a high-performance magnetic fluid for low-temperature sealed environments as described in claim 1, characterized in that: In step (3), the amount of dilute hydrochloric acid added should be such that the zeta potential on the surface of the nanoparticles is positive.

6. The method for preparing a high-performance magnetic fluid for low-temperature sealed environments as described in claim 1, characterized in that: In step (4), the mass ratio of oleic acid to ferrite nanoparticles with a positive zeta potential is 0.1-0.

5.

7. The method for preparing a high-performance magnetic fluid for low-temperature sealing environments as described in claim 1, characterized in that: In the high-performance magnetic fluid for low-temperature sealing environment obtained in step (5), the coated particles account for 20%-50% of the mass of the magnetic fluid.

8. The method for preparing a high-performance magnetic fluid for low-temperature sealed environments as described in claim 1, characterized in that: Step (5) The base fluid selected is low-temperature hydraulic oil; low-temperature hydraulic oil has excellent fluidity at a low temperature of -10℃.

9. The high-performance magnetic fluid for cryogenic sealing environments prepared by the method according to any one of claims 1-8, characterized in that, The high-performance magnetic liquid has a saturation magnetization of 30-50 emu / g at a low temperature of -50℃.

10. The application of the high-performance magnetic fluid for cryogenic sealing environments according to claim 9 in cryogenic environment sealing.

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