Preparation process of nanoscale high-anti-evaporation ferromagnetic fluid with low cost and batch production

Abstract

This invention relates to a low-cost, mass-producible process for preparing nanoscale, highly evaporative ferrofluids. The process includes the following steps: 1) Adding an appropriate amount of acetic acid to water to dissolve ferric chloride and ferrous sulfate sequentially, forming an iron salt precursor solution; 2) Vigorously stirring the iron salt precursor solution and adding an appropriate amount of ammonia, then allowing it to stand until precipitation occurs, separating the supernatant and retaining the precipitate; 3) Preparing an oleic acid-ammonia mixed solution, mixing it with the precipitate, adding water and stirring, then adding acetic acid under stirring conditions to form a flake-like precipitate; 4) Separating the flake-like precipitate, drying it, and mixing it with kerosene to obtain the ferrofluid. The preparation process optimizes the dispersibility of magnetic particles and forms a stable surface modification layer by adding a surfactant, thereby reducing particle aggregation and inhibiting liquid evaporation. Simultaneously, through the synergistic effect of static sedimentation and a magnetic field, magnetic particles are enriched at the interface and form a particle layer, effectively reducing the liquid-gas contact area and lowering the evaporation rate.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a low-cost, mass-producible process for preparing nanoscale ferrofluids with high evaporation resistance. Background Technology

[0002] Nanoscale magnetofluids are stable colloidal systems composed of nanoscale magnetic particles, surfactants, and carrier liquids. They possess both solid-state magnetism and liquid-state fluidity, exhibiting reversible deformation and directional flow under an external magnetic field. Due to their unique physicochemical properties, they have broad application prospects in various high-end fields such as aerospace, electronic equipment, precision mechanical seals, biomedicine, and optical devices, and have become one of the current research hotspots in the field of nanomaterials. The nanoscale magnetic particles are mostly ferrite or metal nanoparticles such as Fe3O4, γ-Fe2O3, and CoFe2O4. Their particle size typically needs to be controlled within 100 nm, preferably within 50 nm, and further preferably within 10–20 nm per domain, to ensure the magnetic response sensitivity and dispersion stability of the magnetofluid and meet the requirements of end-applications.

[0003] Currently, the mainstream preparation processes for nanoscale magnetic fluids mainly include coprecipitation, microemulsion, thermal decomposition, and solvothermal methods. However, these existing processes generally suffer from complex manufacturing processes. Taking coprecipitation as an example, it requires multiple cumbersome steps, such as preparing a mixed iron salt solution, preparing an alkali solution, water bath heating under inert gas protection, surfactant modification, centrifugal washing, and ultrasonic dispersion. Each step requires strict control of reaction parameters, such as iron salt concentration, hydrogen ion concentration, reaction temperature, stirring time, and pH value. Fluctuations in any parameter will affect product performance. Although thermal decomposition can achieve precise particle size control, it relies on high-boiling-point organic solvents and expensive ligands, and subsequent hydrophilic phase inversion treatment is required, further increasing the process complexity. Microemulsion methods suffer from high surfactant residue rates and difficulties in subsequent purification. Solvothermal methods are difficult to scale up for large-scale production, and uneven heat transfer during scale-up can lead to a decrease in batch consistency. These factors combined result in lengthy and cumbersome existing manufacturing processes, requiring extremely high control over the production process.

[0004] The complexity of the process directly leads to high difficulty and cost in producing nanoscale magnetic fluids, making it difficult to achieve large-scale, low-cost mass production. On the one hand, the production process requires high-purity raw materials, such as electronic-grade ferric chloride, whose impurity content must be controlled below 1 ppm, resulting in high raw material costs. On the other hand, the complex process places stringent requirements on production equipment, operating environment, and the professional level of operators, necessitating specialized equipment such as inert gas protection devices, centrifuges, ultrasonic dispersion equipment, and high-temperature, high-pressure reactors, leading to high equipment investment costs. Simultaneously, the cumbersome process steps result in low production efficiency and a high likelihood of product defects, further increasing production losses and overall costs. For example, the cost per batch of the thermal decomposition method is approximately 4.2 times that of the co-precipitation method, while the solvothermal method has not yet overcome the bottleneck of stable preparation at the 100-gram level, making it difficult to meet the needs of large-scale industrial applications. These problems severely restrict the industrialization, promotion, and widespread application of nanoscale magnetic fluids.

[0005] In addition to the aforementioned issues in the preparation process, existing nanoscale magnetic fluid products also commonly suffer from the defect of easy evaporation, which seriously affects their long-term stability and service life. Studies have shown that the evaporation characteristics of nanoscale magnetic fluids are affected by multiple factors. Under natural environments or operating conditions, the carrier liquid is prone to evaporation, especially under extreme conditions such as high temperature and strong magnetic fields, where the evaporation rate is significantly accelerated. External magnetic fields promote carrier liquid evaporation by altering the internal convection dynamics, thermal gradient, and solute gradient of the magnetic fluid; the stronger the magnetic field and the higher the ambient temperature, the more pronounced the evaporation phenomenon. Simultaneously, existing surface modification and dispersion processes for magnetic fluids have significant limitations in microscopic control. Surfactants used in traditional preparation processes often only achieve basic coating of solid nanoparticles, making it difficult to construct a strongly interacting solvation layer within the colloidal system, nor can they effectively self-assemble at the gas-liquid interface of the magnetic fluid to form a dense, anti-volatile molecular barrier. This results in the carrier liquid molecules, as the continuous phase, lacking sufficient microscopic confinement, exhibiting high molecular activity, and easily escaping into the environment. Once the carrier liquid evaporates in large quantities, it will directly cause a sharp increase in the local concentration of nano-magnetic particles within the system, disrupting the original thermodynamic equilibrium and steric hindrance effect, leading to irreversible aggregation and sedimentation. This will not only cause it to lose its original magnetic response performance and fluidity, making it unable to meet the long-term stability requirements of products in fields such as precision mechanical seals and biomedicine, but also cause changes in key performance parameters such as the concentration and viscosity of the magnetic fluid, further affecting its application in end devices and limiting the widespread application of nanoscale magnetic fluids in high-end scenarios.

[0006] In summary, existing manufacturing processes for nanoscale magnetofluids are complex, difficult to produce, and costly. Furthermore, the products are prone to evaporation, severely restricting their large-scale production and widespread application. Therefore, developing a simple, low-cost nanoscale magnetofluid preparation technology that can effectively suppress evaporation and improve stability has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to disclose a low-cost, mass-producible process for preparing nanoscale high-evaporation-resistant ferrofluids, in order to solve one or more technical problems existing in the existing methods and provide at least one beneficial option or create conditions.

[0008] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention is to provide a process for preparing a magnetic fluid. The preparation process specifically includes the following steps: 1) Add an appropriate amount of acetic acid to water to dissolve ferric chloride and ferrous sulfate in sequence, forming an iron salt precursor solution; 2) Vigorously stir the iron salt precursor solution and add an appropriate amount of ammonia water, then let it stand and wait for the precipitate to form. Separate the supernatant and retain the precipitate. 3) Prepare an oleic acid-ammonia mixed solution, mix it with the precipitate, add water and stir, then add acetic acid under stirring conditions to form a flaky precipitate; 4) Separate the flaky precipitate, dry it, and mix it with an organic carrier liquid to obtain the magnetic fluid.

[0009] This invention uses conventional raw materials such as acetic acid, ferric chloride, ferrous sulfate, and ammonia as a base, eliminating the need for high-purity electronic-grade raw materials or expensive ligands, significantly reducing raw material and equipment costs and solving the technical problems of high production difficulty and cost in existing technologies. By modifying the precipitate with an oleic acid-ammonia mixed solution, combined with subsequent composite with an organic carrier liquid, a dense coating is formed on the surface of the magnetic particles to prevent aggregation. Furthermore, a strongly interacting solvation layer is constructed within the system to effectively bind the carrier liquid molecules, fundamentally inhibiting kerosene evaporation and overcoming the defects of easy evaporation and poor stability in existing magnetic fluids. Simultaneously, the entire process can be scaled up for mass production, improving production efficiency and ensuring batch consistency. The prepared magnetic fluid exhibits both good magnetic response performance and colloidal stability, with particle size stably controlled within the nanometer range, meeting the needs of high-end applications. The preparation process is simple and convenient, requiring no complex equipment or stringent operating conditions such as inert gas protection or high-temperature, high-pressure reactors, effectively solving the problem of complex manufacturing processes in existing technologies.

[0010] In a further embodiment of the first aspect of the present invention, in step 1), the water is first heated to 75±1 °C before the acetic acid is added. Preheating the water accelerates the dissolution rate of acetic acid and simultaneously improves the dissolution efficiency of ferric chloride and ferrous sulfate in the aqueous solution, ensuring that the two iron salts are fully dissolved and uniformly mixed, avoiding problems such as uneven magnetic particle size and agglomeration caused by insufficient iron salt dissolution. The temperature parameter of 75±1 °C is precisely controlled, which can ensure the uniformity of the iron salt precursor solution and avoid premature reaction of iron salts due to high temperature, ensuring the stability of the subsequent precipitation reaction, further improving the magnetic response sensitivity and dispersion stability of the magnetic fluid product, while eliminating the need for additional high-temperature heating equipment, thus balancing process simplicity and cost control.

[0011] In a further embodiment of the first aspect of the present invention, the mass ratio of ferric chloride to ferrous sulfate in step 1) is 5:3. This mass ratio allows for precise control of the Fe content in the iron salt precursor solution. 3+ with Fe 2+ The ratio ensures that high-purity, crystal-complete nanoscale magnetic particles (such as Fe3O4) can be generated during subsequent reactions with ammonia, avoiding the generation of impurities caused by ion imbalance, improving the magnetic properties of the magnetic fluid, simplifying process steps, ensuring that the magnetic particle size is stable within the target range, solving the problems of uneven magnetic particle performance and large batch differences in existing processes, reducing production losses, and further controlling production costs.

[0012] In a further embodiment of the first aspect of the present invention, after separating the precipitate in step 2) and / or step 4), the precipitate is rinsed, stirred, and drained with water, and the process is repeated 2 to 4 times. This cyclical operation of rinsing, stirring, and draining effectively removes impurities, excess ammonia, acetic acid, and other residual substances adhering to the surface of the precipitate, preventing residual impurities from affecting the subsequent modification reaction and preventing residual impurities from causing a decrease in the stability of the magnetic fluid and an acceleration of the carrier liquid evaporation rate.

[0013] In a further embodiment of the first aspect of the present invention, the separation in step 2) and / or step 4) is performed by applying an external magnetic field to separate the precipitate and / or the flaky precipitate. Separation by applying an external magnetic field is simpler and more efficient than existing methods such as centrifugation and filtration, eliminating the need for specialized equipment like centrifuges, reducing equipment investment costs, and solving the problems of high dependence on and high cost of existing processes. The separation process is gentle and does not damage the morphology and structure of the magnetic particles, ensuring the smooth progress of subsequent modification reactions, further improving the magnetic response performance and stability of the magnetofluid, and the separation process can be completed quickly, improving production efficiency and facilitating large-scale production.

[0014] In a further embodiment of the first aspect of the present invention, the oleic acid-ammonia mixed solution in step 3) comprises 200 parts ammonia water and 13 parts oleic acid by volume. This ratio not only uniformly coats the surface of the magnetic particles to form a dense hydrophobic layer, but also constructs a solvation layer with strong interactions within the colloidal system, and even self-assembles to form a molecular barrier at the gas-liquid interface. This micro-network structure can effectively bind the organic carrier liquid as a continuous phase, significantly reducing its molecular activity, thereby fundamentally inhibiting the escape and volatilization of the carrier liquid into the environment, solving the technical problems of easy evaporation and short service life of existing magnetic fluids; at the same time, the mixed solution of this ratio can improve the dispersibility of magnetic particles in the organic carrier liquid, avoid particle agglomeration, ensure the colloidal stability and flowability of the magnetic fluid, and eliminate the need for additional surfactants, simplifying the process steps, reducing costs, and ensuring that the magnetic response performance of the magnetic fluid meets the requirements of high-end applications.

[0015] In a further embodiment of the first aspect of the present invention, the organic carrier liquid is selected from at least one of kerosene, mineral oil, and silicone oil.

[0016] In a further embodiment of the first aspect of the present invention, the drying in step 4) is carried out by airflow at 50~90 °C, and the sheet-like precipitate is stirred at 100~240 rpm during the drying process to prevent agglomeration. Using airflow drying within a limited temperature range can avoid oxidation and morphological damage to the sheet-like precipitate caused by high-temperature drying, while preventing the magnetic particles from agglomerating and ensuring the dispersion of the precipitate, laying the foundation for subsequent mixing with the organic carrier liquid to form a stable magnetic fluid. The lower stirring speed can eliminate agglomeration and further improve drying efficiency. Compared with the high-temperature drying and vacuum drying methods in the prior art, the gentle heating airflow drying does not require special vacuum equipment, the process is simpler and the cost is lower, and it can retain the activity of the precipitate, ensuring the stability of the magnetic fluid performance after subsequent mixing, solving the problems of product performance degradation and high equipment costs caused by existing drying processes.

[0017] In a further embodiment of the first aspect of the present invention, the flake-like precipitate in step 4) is mixed with the organic carrier liquid at a mass / volume ratio of 1.0:(1.0~1.6). This ratio ensures that the magnetic fluid has good magnetic response performance and that the magnetic particles are uniformly dispersed in the organic carrier liquid, avoiding particle agglomeration. The resulting magnetic fluid has good fluidity and stability, while further enhancing the anti-evaporation performance of the carrier liquid. Combined with the coating layer, it can doubly suppress evaporation, solving the problems of easy evaporation and performance fluctuation of existing magnetic fluids.

[0018] A second aspect of this invention provides a magnetic fluid. The magnetic fluid is prepared using the process described in the first aspect of this invention. The magnetic fluid has a stable particle size in the range of 10-50 nm, exhibiting both excellent magnetic response performance and liquid flowability, as well as strong colloidal stability. The magnetic fluid demonstrates significantly improved anti-evaporation performance; under conditions such as natural environments, high temperatures, and strong magnetic fields, the evaporation rate of the carrier liquid is greatly reduced, effectively preventing the aggregation and sedimentation of magnetic particles, extending product service life, and overcoming the shortcomings of existing magnetic fluids, such as easy evaporation and poor stability.

[0019] The third aspect of this invention provides application directions for the magnetic fluid described in the second aspect. In the field of precision mechanical seals, the magnetic fluid can operate stably for extended periods under high-speed and high-temperature conditions, preventing seal failure due to carrier fluid evaporation, improving seal reliability, and reducing equipment maintenance costs. In the field of electronic component protection, it can achieve efficient heat dissipation and electromagnetic shielding, while its anti-evaporation performance prevents a decrease in heat dissipation efficiency due to carrier fluid evaporation, protecting electronic components for long-term stable operation. In the field of bio-implantable device protection, its anti-evaporation and impurity-free characteristics prevent carrier fluid evaporation and particle leakage from causing harm to the human body, ensuring the long-term safe service of implantable devices. In the field of biological detection, its stable dispersibility improves detection accuracy and repeatability, preventing particle agglomeration from affecting detection results, and solving the problems of insufficient performance and poor applicability of existing magnetic fluids in high-end application scenarios. Attached Figure Description

[0020] Figure 1 It is the nanoscale high evaporation-resistant ferrofluid prepared in Example 1; Figure 2 These are photographs of the control sample from Example 2; Figure 3 These are photographs of the two groups of samples before the start of the control experiment in Example 2; Figure 4 These are photographs of the two sets of samples after 30 minutes of heat treatment in Example 2; Figure 5 These are photographs of two sets of samples from Example 2 after 60 minutes of heat treatment without the application of a magnetic field; Figure 6 These are photographs of two sets of samples subjected to a magnetic field after being heated for 60 minutes in Example 2.

[0021] in, Figures 3-6 Sample No. 1 is EMG900, and sample No. 2 is the magnetic fluid prepared in Example 1. Detailed Implementation

[0022] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the present invention are within the scope of the present invention.

[0023] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0024] Example 1: Preparation of nanoscale triferroic oxide magnetic fluid The raw materials include 100 g of ferric chloride, 60 g of ferrous sulfate, 240 g of glacial acetic acid, 1200 mL of ammonia water, 13 mL of oleic acid, 100 mL of kerosene, and an appropriate amount of 3000 mL of water.

[0025] Preparation process: 1) Heat 3000 mL of water to about 75°C, add 40 g of glacial acetic acid and stir for 30 seconds to dissolve 100 g of ferric chloride and 60 g of ferrous sulfate in sequence to form an iron salt precursor solution. 2) Under vigorous stirring, quickly add 1000 mL of ammonia water to generate iron oxide precipitate in the solution. After standing for several minutes to complete the reaction and particle growth, apply an external magnetic field to separate the precipitate and drain the supernatant. The precipitate is then washed with water, stirred, and drained in a cycle to remove soluble impurities. 3) In a separate container, 200 mL of ammonia water is slowly added to 13 mL of oleic acid under strong stirring to prepare an oleic acid-ammonia mixed solution. The oleic acid-ammonia mixed solution is mixed with the precipitate and water is added to make up to a total volume of 2000 mL. After stirring for 3 minutes, 200 g of glacial acetic acid is added in a thin stream under stirring to induce the formation of a large amount of oleic acid-coated flaky precipitate. 4) The precipitate is separated under an external magnetic field and washed several times with water and anhydrous ethanol, followed by stirring and draining. The precipitate is then dried under a gentle heating airflow, with moderate stirring during the drying process to prevent clumping. 5) Add the dried powder to kerosene at a ratio of 1 g: 1.0~1.6 mL and disperse it fully to obtain kerosene-based ferromagnetic fluid.

[0026] The obtained sample is as follows Figure 1 As shown.

[0027] Example 2, Evapotranspiration Control Experiment The magnetic fluid obtained in Example 1 was compared with a commercially available similar product, EMG900 (Ferrotec, Japan, etc.). Figure 2A control experiment was conducted to investigate the evaporation and deactivation of two groups of magnetic fluids under high-temperature conditions, exploring their anti-evaporation performance and stability changes. By analyzing the evaporation rate, surface changes, and structural stability of EMG900 and the magnetic fluids during the heating process, the effects of factors such as carrier liquid volatilization, surfactant aging, and particle agglomeration on magnetic fluid deactivation were revealed. The experiment will evaluate the anti-evaporation ability and long-term storage stability of the magnetic fluids under harsh conditions under the same temperature and heating time conditions.

[0028] Experimental control conditions: The two groups of samples were placed on a heating platform at 60±0.5 ℃, and their flowability and evaporation were observed. The samples were observed every 30 minutes.

[0029] (1) Single variable method: In this experiment, the initial volume of the magnetic fluid was 0.3 mL. Its volume was strictly controlled and extracted using a syringe, injected into a circular open culture dish with an opening diameter of 3.5 cm. A permanent magnet was used to apply pressure to the bottom of the dish, ensuring the magnetic fluid covered the entire surface. A constant-temperature heating stage (Kaisi 818 model) was used to simulate the harsh conditions of high-temperature evaporation. The ambient temperature was set to (60±0.5 ℃) and the relative humidity to (40±5%). The culture dish was placed on the heating stage with the opening open. Every 30 minutes of heating, a circular permanent magnet was placed under the dish to test its flow properties and detect any inactivation, thus verifying the presence of Rosensweig instability. Heating was carried out for a total of one hour. To verify the successful modification of DNA onto gold nanoparticles, the experiment was conducted using ultraviolet spectroscopy, nanoparticle size and zeta potential analysis, and field emission scanning electron microscopy.

[0030] Initial state as Figure 3 As shown, both magnetofluids exhibit strong fluidity and can produce significant Rosensweig instabilities under magnetic fields.

[0031] After heating at 60 °C for 30 minutes, the surface stability of EMG900 significantly decreased. Wrinkled structures and localized collapses appeared on its surface, the liquid surface was no longer smooth, and there was a noticeable volume reduction. This phenomenon indicates that the sample exhibited strong evaporation behavior during heating, possibly related to base liquid volatilization, enhanced internal convection, and changes in interfacial tension, reflecting its limited resistance to evaporation. After being treated under the same 60 °C heating conditions for 30 minutes, the surface of the magnetic fluid showed wrinkles due to evaporation, but the overall morphology was relatively smooth. Compared to EMG900, its free surface did not show obvious wrinkles or collapses, with only a few minor inhomogeneities observed in localized areas. The change in liquid level was small, and the residue on the cup wall was not obvious, indicating that the magnetic fluid had a low evaporation rate during heating and good system stability (e.g., Figure 4 (As shown).

[0032] After being heated continuously at 60 °C for 1 hour, the EMG900 exhibited significant differences from the magnetic fluid. For example... Figure 5 As shown, EMG900 exhibited severe evaporation after heating, with a significant drop in liquid level and large areas of dryness and discontinuity visible on the surface, indicating significant deactivation of the magnetofluid. In contrast, the magnetofluid maintained a certain degree of fluidity under the same heating conditions, with a continuous and uniform liquid surface, showing no obvious signs of drying or deactivation. Figure 6 As shown, after inducing a magnetic field by placing a permanent magnet at the bottom of the culture dish, EMG900 exhibited Rosensweig instability only in a small area where it had not completely evaporated. This instability was characterized by uneven distribution, blunted morphology, and significant size differences in the spike structures. Most areas failed to form stable spike structures. These phenomena indicate that the magnetic response of EMG900 significantly decreased after prolonged heating, and its structural stability and reversible magnetostrictive ability were severely compromised. In contrast, the magnetic fluid, under the same magnetic field conditions, formed a uniformly distributed and regularly arranged Rosensweig unstable structure on its surface, with clear, sharp, and highly consistent spike morphology, demonstrating excellent magnetic response characteristics and structural stability. This suggests that the magnetic fluid possesses superior anti-evaporation ability and thermal stability, maintaining its functional integrity even under prolonged heating conditions.

[0033] The excellent anti-evaporation properties exhibited by the magnetic fluid are mainly due to its unique microstructure, rheological properties, and surface tension characteristics. First, magnetic particles accumulate at the liquid-gas interface, forming a particulate barrier layer that reduces liquid-gas contact and suppresses evaporation. Second, the magnetic fluid possesses high viscosity and yield stress, which effectively suppresses internal convection and surface disturbance, further slowing down the evaporation rate. Finally, the modified particles modulate the surface tension at the liquid-gas interface, suppressing Marangoni flow and maintaining liquid surface stability. In summary, these properties of the magnetic fluid prepared in Example 1 enable it to exhibit stronger stability and a lower evaporation rate at high temperatures.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A process for preparing a magnetic fluid, characterized in that, Including the following steps: 1) Add an appropriate amount of acetic acid to water to dissolve ferric chloride and ferrous sulfate in sequence, forming an iron salt precursor solution; 2) Vigorously stir the iron salt precursor solution and add an appropriate amount of ammonia water, then let it stand and wait for the precipitate to form. Separate the supernatant and retain the precipitate. 3) Prepare an oleic acid-ammonia mixed solution, mix it with the precipitate, add water and stir, then add acetic acid under stirring conditions to form a flaky precipitate; 4) Separate the flaky precipitate, dry it, and mix it with an organic carrier liquid to obtain the magnetic fluid.

2. The preparation process according to claim 1, characterized in that, In step 1), the water is first heated to 75±1 ℃ before the acetic acid is added.

3. The preparation process according to claim 1, characterized in that, In step 1), the mass ratio of ferric chloride to ferrous sulfate is 5:

3.

4. The preparation process according to claim 1, characterized in that, After separating the precipitate as described in step 2) and / or step 4), rinse, stir and drain with water, repeating 2 to 4 times.

5. The preparation process according to claim 1, characterized in that, The separation described in step 2) and / or step 4) is achieved by using an external magnetic field to separate the precipitate and / or the flaky precipitate.

6. The preparation process according to claim 1, characterized in that, Step 3) The oleic acid-ammonia mixed solution comprises 200 parts ammonia water and 13 parts oleic acid by volume ratio.

7. The preparation process according to claim 1, characterized in that, Step 4) The drying is carried out by airflow at 50~90 ℃, and the flaky precipitate is stirred at 100~240 rpm during the drying process to prevent clumping.

8. The preparation process according to claim 1, characterized in that, Step 4) The flaky precipitate and the organic carrier liquid are mixed at a mass / volume ratio of 1.0:(1.0~1.6).

9. A magnetic fluid, characterized in that, It is prepared by the preparation process described in any one of claims 1 to 8.

10. The application of the magnetic fluid of claim 9 in precision mechanical seals, electronic component protection, biological implantation device protection, or biological detection systems.

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