Hydrotalcite nanofluid and preparation method thereof

Abstract

The invention belongs to the technical field of nanofluid materials, and particularly relates to hydrotalcite nanofluid and a preparation method thereof. The preparation method comprises the following steps: mixing a mixed salt solution (divalent metal salt and aluminum salt) and a mixed alkali solution (sodium hydroxide and sodium carbonate), carrying out a co-precipitation reaction, carrying out solid-liquid separation, and washing the obtained precipitate to obtain a hydraulically gypsum-like precipitate; and dispersing the hydraulically gypsum-like precipitate in an alcohol-water mixed solvent for high-temperature crystallization to obtain the hydrotalcite nanofluid. According to the invention, a one-step process route is innovatively adopted to realize technical breakthrough, rich hydroxyl groups on the surface of the hydrotalcite material endow the nanoparticles with hydrophilicity, the main body laminate has positive charges to maintain dispersion stability through electrostatic repulsion, and a long-term stable system can be formed without depending on an exogenous stabilizer. The hydrotalcite nanofluid prepared by the invention has super-long stability, can be kept at room temperature for 8 months without generating sedimentation, and can meet the requirements of practical application.

Description

Technical Field

[0001] This invention belongs to the field of nanofluid materials technology, specifically relating to a hydrotalcite nanofluid and its preparation method. Background Technology

[0002] Heat transfer is a common phenomenon in production and daily life. Traditional heat transfer fluids include water, ethylene glycol, and glycerol, which are widely used in applications such as hot steel plate spray cooling, engine heat dissipation, and battery cooling. However, as industrial technology evolves towards high power density and miniaturization, the heat exchange efficiency of traditional fluids is no longer sufficient to meet the demands of extreme operating conditions. Early research attempted to improve the performance of the base fluid by adding micron / millimeter-sized solid particles, but its engineering application was significantly limited by the sedimentation tendency of large-sized particles, poor dispersion stability, and the risk of pipe wear and blockage.

[0003] Breakthroughs in nanotechnology have provided a new path for upgrading heat transfer media: introducing nanoparticles such as metal oxides or carbon materials into the base liquid to form nanofluid (sol) systems can significantly improve the thermal conductivity of the medium. However, such nanofluid systems face a core bottleneck of poor long-term dispersion stability—the current mainstream process uses a two-step "synthesis-dispersion" method (first synthesizing nanopowders and then preparing nanofluids). Due to their high surface energy, the synthesized nanopowders are prone to agglomeration during dispersion, leading to defects in the thermal conductivity network structure and severely weakening the actual performance of the material. Although adding surfactants can extend the stabilization time of nanofluid systems, under high-temperature conditions, surfactants are prone to foaming due to increased solubility and intensified molecular motion, which exacerbates system instability and greatly limits the prospects for industrial application. Therefore, there is an urgent need to develop a nanofluid system that can achieve long-term stable dispersion without the need for exogenous stabilizers. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a hydrotalcite nanofluid, its preparation method, and its applications. The preparation method provided by this invention can obtain a long-term stable hydrotalcite nanofluid system without the addition of an exogenous stabilizer.

[0005] This invention provides a method for preparing hydrotalcite nanofluids, comprising the following steps:

[0006] A mixed salt solution and a mixed alkali solution are provided; the solute in the mixed salt solution includes a divalent metal salt and an aluminum salt, wherein the divalent metal salt includes one or more of magnesium salt, zinc salt, and nickel salt; the solute in the mixed alkali solution includes sodium hydroxide and sodium carbonate.

[0007] The mixed salt solution and the mixed alkali solution were mixed and subjected to a coprecipitation reaction. The solid and liquid were separated, and the resulting precipitate was washed to obtain a hydrotalcite-like precipitate.

[0008] The hydrotalcite nano-fluid is obtained by dispersing the hydrotalcite gossy precipitate in an alcohol-water mixed solvent for crystallization.

[0009] Preferably, the molar ratio of the divalent metal salt and the aluminum salt is 1.5-2.5:1.

[0010] Preferably, the molar ratio of the sodium hydroxide and the sodium carbonate is 10-12:1.

[0011] Preferably, the concentration of the divalent metal salt in the mixed salt solution is 0.01-1 mol / L, and the concentration of the aluminum salt is 0.005-0.5 mol / L; the concentration of the sodium hydroxide in the mixed alkali solution is 0.15-3 mol / L, and the concentration of the sodium carbonate is 0.0013-0.27 mol / L.

[0012] Preferably, the molar ratio of the aluminum salt and the sodium hydroxide is 0.1-0.17:1.

[0013] Preferably, the solid-liquid separation is centrifugation, the centrifugation speed is 3000-5000 r / min, and the centrifugation time is 3-5 min; the washing is water washing, and the number of water washing is 3-5 times.

[0014] Preferably, the alcohol in the alcohol-water mixed solvent is ethylene glycol or glycerol, and the volume ratio of the alcohol and water is 2-8:8-2.

[0015] Preferably, the crystallization temperature is 80-120℃, and the crystallization time is 12-20 hours.

[0016] The application further provides the hydrotalcite nano-fluid prepared by the preparation method.

[0017] The application further provides the application of the hydrotalcite nano-fluid as a heat transfer medium.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] The application provides a preparation method of a hydrotalcite nano-fluid, which comprises the following steps: providing a mixed salt solution and a mixed alkali solution; the solute of the mixed salt solution comprises a divalent metal salt and an aluminum salt, the divalent metal salt comprises one or more of a magnesium salt, a zinc salt and a nickel salt; the solute of the mixed alkali solution comprises sodium hydroxide and sodium carbonate; the mixed salt solution and the mixed alkali solution are mixed for a coprecipitation reaction, solid-liquid separation is performed, the obtained precipitate is washed to obtain a hydrotalcite gossy precipitate; and the hydrotalcite gossy precipitate is dispersed in an alcohol-water mixed solvent for crystallization to obtain the hydrotalcite nano-fluid.

[0020] This invention first generates hydrotalcite precipitate through a nucleation reaction between salt and alkali solutions. After solid-liquid separation and washing to remove impurity ions, a high-purity paste is obtained. Subsequently, it is dispersed in an alcohol-water mixed solvent and subjected to high-temperature crystallization to finally obtain hydrotalcite nanofluid. This invention innovatively employs a one-step process (eliminating the need for prior nanopowder preparation) to achieve a technological breakthrough. The abundant hydroxyl groups on the surface of the hydrotalcite material endow the nanoparticles with hydrophilicity, and the main layer itself carries a positive charge, maintaining dispersion stability through electrostatic repulsion. A long-term stable system can be formed without relying on external stabilizers. The hydrotalcite nanofluid obtained by this invention exhibits ultra-long-term stability, remaining at room temperature for 8 months without sedimentation, meeting the needs of practical applications.

[0021] The data from the embodiments show that the hydrotalcite nanosheets in the hydrotalcite nanofluid obtained by the present invention have nanoscale dimensions and ultrathin thickness; thermophysical performance tests show that the hydrotalcite nanofluid has good thermal conductivity.

[0022] The raw materials for preparing hydrotalcite nanofluids are readily available and inexpensive. The preparation method is simple, efficient, and environmentally friendly, offering significant advantages for industrial-scale production. Hydrotalcite nanofluids can be applied on a large scale to diverse industrial applications such as battery thermal management and solar thermal energy regulation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows the XRD pattern of the hydrotalcite nanofluid obtained in step E of Example 1 after drying.

[0025] Figure 2 SEM image of the hydrotalcite nanofluid obtained in step E of Example 1;

[0026] Figure 3 The image shows the AFM pattern of the hydrotalcite nanofluid obtained in step E of Example 1.

[0027] Figure 4 This is a digital photograph of the hydrotalcite nanofluid obtained in step E of Example 1 at 8 months.

[0028] Figure 5 Digital photographs of hydrotalcite nanofluids with different magnesium-aluminum ratios on day 10.

[0029] Figure 6The thermal conductivity results are for hydrotalcite nanofluids with different solid contents;

[0030] Figure 7 The temperature rise curve for hydrotalcite nanofluid and ethylene glycol-water mixed solvent in Example 1 is shown.

[0031] Figure 8 The temperature drop diagram is shown for the hydrotalcite nanofluid and ethylene glycol-water mixed solvent in Example 1. Detailed Implementation

[0032] This invention provides a method for preparing hydrotalcite nanofluids, comprising the following steps:

[0033] A mixed salt solution and a mixed alkali solution are provided; the solute in the mixed salt solution includes a divalent metal salt and an aluminum salt, wherein the divalent metal salt includes one or more of magnesium salt, zinc salt, and nickel salt; the solute in the mixed alkali solution includes sodium hydroxide and sodium carbonate.

[0034] The mixed salt solution and the mixed alkali solution were mixed and subjected to a coprecipitation reaction. The solid and liquid were separated, and the resulting precipitate was washed to obtain a hydrotalcite-like precipitate.

[0035] The hydrotalcite precipitate was dispersed in an alcohol-water mixed solvent and crystallized to obtain hydrotalcite nanofluid.

[0036] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0037] The present invention provides a mixed salt solution and a mixed alkali solution; the solute of the mixed salt solution includes a divalent metal salt and an aluminum salt, wherein the divalent metal salt includes one or more of magnesium salt, zinc salt and nickel salt; the solute of the mixed alkali solution includes sodium hydroxide and sodium carbonate.

[0038] In this invention, the magnesium salt is preferably magnesium chloride hexahydrate or magnesium nitrate hexahydrate, the zinc salt is preferably zinc nitrate hexahydrate, and the nickel salt is preferably nickel nitrate hexahydrate. The aluminum salt is preferably aluminum chloride hexahydrate or aluminum nitrate nonahydrate.

[0039] In this invention, the molar ratio of the divalent metal salt to the aluminum salt is preferably 1.5 to 2.5:1, specifically 2:1. The molar ratio described in this invention results in a hydrotalcite nanofluid with good stability and minimal sedimentation.

[0040] In this invention, the concentration of the divalent metal salt in the mixed salt solution is preferably 0.01–1 mol / L, more preferably 0.1–1 mol / L, specifically 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, or 1.0 mol / L; the concentration of the aluminum salt is preferably 0.005–0.5 mol / L, more preferably 0.05–0.5 mol / L, specifically 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or 0.5 mol / L.

[0041] In this invention, the solvent of the mixed salt solution is preferably an alcohol-water mixed solvent, wherein the alcohol is preferably ethylene glycol or glycerol, and the volume ratio of the alcohol to water is preferably 2-8:8-2, specifically 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or 8:2.

[0042] In this invention, the molar ratio of sodium hydroxide to sodium carbonate is preferably 10 to 12:1, specifically 11:1, 11.5:1 or 12:1.

[0043] In this invention, the concentration of sodium hydroxide in the mixed alkaline solution is preferably 0.15–3 mol / L, specifically 0.15 mol / L, 0.3 mol / L, 0.45 mol / L, or 0.75 mol / L; the concentration of sodium carbonate is preferably 0.0013–0.27 mol / L, specifically 0.013 mol / L, 0.026 mol / L, 0.039 mol / L, or 0.065 mol / L, and the sodium carbonate is preferably anhydrous sodium carbonate.

[0044] In this invention, the solvent of the mixed alkaline solution is preferably the same as the solvent of the mixed salt solution, which will not be elaborated further here.

[0045] In this invention, the mixed salt solution and the mixed alkali solution are mixed to carry out a co-precipitation reaction, the solid and liquid are separated, and the obtained precipitate is washed to obtain a hydrotalcite-like precipitate.

[0046] In this invention, the volume ratio of the mixed salt solution to the mixed alkali solution is preferably 0.25 to 2:1, specifically 1:1, 1:2 or 1:4.

[0047] In this invention, the molar ratio of the aluminum salt to sodium hydroxide is preferably 0.1 to 0.17:1, specifically 0.17:1.

[0048] In this invention, the mixing of the mixed salt solution and the mixed alkali solution is preferably completed within 5 seconds. Rapid mixing allows all metal ions to reach supersaturation simultaneously, promoting uniform co-precipitation and forming a well-structured hydrotalcite. Slow mixing can lead to asynchronous nucleation and growth, with pre-formed nuclei potentially continuing to grow, resulting in a wide particle size distribution or the formation of impurity phases (such as isolated metal hydroxides). The co-precipitation reaction is preferably carried out under stirring for a period of 15–25 minutes, specifically 20 minutes.

[0049] In this invention, the solid-liquid separation is preferably performed by centrifugation. The centrifugation speed is preferably 3000–5000 r / min, specifically 4500 r / min, and the centrifugation time is preferably 3–5 min, specifically 4 min. This invention can remove unreacted free ions (such as excess OH-, CO32-) from the reaction system through centrifugation. 2- (and metal ions), soluble byproducts or salts, to avoid these impurities interfering with subsequent colloid formation.

[0050] In this invention, the washing is preferably a water wash, and the water wash preferably uses deionized water, and the number of washes is preferably 3 to 5 times, specifically 4 times. The water wash can further remove impurity ions (such as CO3). 2- ).

[0051] After obtaining the hydrotalcite precipitate, the present invention disperses the hydrotalcite precipitate in an alcohol-water mixed solvent for crystallization to obtain hydrotalcite nanofluid.

[0052] In this invention, the alcohol in the alcohol-water mixed solvent is preferably ethylene glycol or glycerol, and the volume ratio of the alcohol to water is preferably 2-8:8-2, specifically 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or 8:2.

[0053] In this invention, the crystallization is preferably carried out in a polytetrafluoroethylene reactor, the crystallization temperature is preferably 80–120°C, specifically 100°C, and the crystallization time is preferably 12–20 hours, specifically 16 hours. During the high-temperature crystallization process, the layered structure of the hydrotalcite rearranges, the grains grow, and neat hexagonal flakes are formed.

[0054] The present invention also provides a hydrotalcite nanofluid obtained by the preparation method described above, wherein the solid content of the hydrotalcite nanofluid is 0.25wt% to 2.5wt%.

[0055] In this invention, the solid content of the hydrotalcite nanofluid is preferably 1wt% to 2.5wt%, specifically 1wt%, 1.5wt%, or 2.5wt%; the hydrotalcite nanofluid is preferably stored in a sealed container.

[0056] The present invention also provides the application of the hydrotalcite nanofluid described in the above technical solution as a heat transfer medium.

[0057] In this invention, the preferred application areas include hot steel plate spray cooling, new energy vehicle battery thermal management, or solar thermal energy regulation.

[0058] To further illustrate the present invention, the following detailed description of the hydrotalcite nanofluid, its preparation method, and its application, in conjunction with the accompanying drawings and embodiments, is provided but should not be construed as limiting the scope of protection of the present invention.

[0059] In the following examples or comparative examples, the concentration M in parentheses represents the concentration of the component in the mixed solvent (mol / L); the solid content is calculated based on the actual solid content of the prepared colloid (5g of hydrotalcite nanofluid is weighed, placed in a constant temperature drying oven at 60℃, and dried to obtain x grams of hydrotalcite solid, (x / 5)*100% is the solid content of the nanofluid); unless otherwise specified, the centrifugation and washing conditions in step D are the same as in Example 1.

[0060] Example 1

[0061] Step A: Dissolve magnesium chloride hexahydrate (concentration 0.4M) and aluminum chloride hexahydrate (concentration 0.2M) in 50 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50 at a molar ratio of 2:1 to obtain a mixed salt solution.

[0062] Step B: Dissolve sodium hydroxide (0.3M concentration) and anhydrous sodium carbonate (0.026M concentration) in 200mL of ethylene glycol-water mixed solvent at a molar ratio of 12:1 to obtain a mixed alkaline solution.

[0063] Step C: Pour the mixed salt solution and mixed alkali solution into a three-necked flask simultaneously and stir rapidly. This process should be completed within 5 seconds. Stir for 20 minutes and then collect the sample.

[0064] Step D, Preparation of hydrotalcite precipitate: Centrifuge the sample from step C (4500 r / min, 4 min), collect the precipitate and wash it repeatedly with deionized water (add deionized water to the precipitate obtained by centrifugation and wash-centrifuge, repeat 5 times, each time using about 150 mL of deionized water) to obtain hydrotalcite precipitate.

[0065] Step E, Preparation of hydrotalcite nanofluid: The paste-like precipitate obtained in step D was redispersed in 200 mL of a 50:50 volume ratio ethylene glycol-water mixed solvent, placed in a polytetrafluoroethylene reactor, and crystallized at 100 °C for 16 hours to obtain hydrotalcite nanofluid with a solid content of 1.0 wt%, which was then stored in a sealed container.

[0066] Example 2

[0067] Step A: Dissolve magnesium chloride hexahydrate (concentration 0.6M) and aluminum chloride hexahydrate (concentration 0.3M) in 50 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50 at a molar ratio of 2:1 to obtain a mixed salt solution.

[0068] Step B: Dissolve sodium hydroxide (0.45M concentration) and anhydrous sodium carbonate (0.039M concentration) in 200mL of ethylene glycol-water mixed solvent at a molar ratio of 12:1 to obtain a mixed alkaline solution.

[0069] Step C: Pour the mixed salt solution and mixed alkali solution into a three-necked flask simultaneously and stir rapidly. This process should be completed within 5 seconds. Stir for 20 minutes and then collect the sample.

[0070] Step D, Preparation of hydrotalcite precipitate: Centrifuge the sample from step C, collect the precipitate and wash it repeatedly with deionized water to obtain hydrotalcite precipitate.

[0071] Step E, Preparation of hydrotalcite nanofluid: The paste-like precipitate obtained in step D was redispersed in 200 mL of a 50:50 volume ratio ethylene glycol-water mixed solvent, placed in a polytetrafluoroethylene reactor, and crystallized at 100 °C for 16 hours to obtain hydrotalcite nanofluid with a solid content of 1.5 wt%, which was then stored in a sealed container.

[0072] Example 3

[0073] Step A: Dissolve magnesium chloride hexahydrate (concentration 0.2M) and aluminum chloride hexahydrate (concentration 0.1M) in 50 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50 at a molar ratio of 2:1 to obtain a mixed salt solution.

[0074] Step B: Dissolve sodium hydroxide (0.15M concentration) and anhydrous sodium carbonate (0.013M concentration) in 200mL of ethylene glycol-water mixed solvent at a molar ratio of 12:1 to obtain a mixed alkaline solution.

[0075] Step C: Pour the mixed salt solution and mixed alkali solution into a three-necked flask simultaneously and stir rapidly. This process should be completed within 5 seconds. Stir for 20 minutes and then collect the sample.

[0076] Step D, Preparation of hydrotalcite precipitate: Centrifuge the sample from step C, collect the precipitate and wash it repeatedly with deionized water to obtain hydrotalcite precipitate.

[0077] Step E, Preparation of hydrotalcite nanofluid: The paste obtained in step D is redispersed in 200 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50, placed in a polytetrafluoroethylene reactor, and crystallized at 100 °C for 16 hours to obtain hydrotalcite nanofluid with a solid content of 0.5 wt%, which is then stored in a sealed container.

[0078] Figure 1 The image shows the XRD pattern of the dried hydrotalcite nanofluid obtained in step E of Example 1, where the horizontal axis represents 2Theta (degrees) and the vertical axis represents intensity. Figure 1 The XRD patterns of magnesium aluminum hydrotalcite can be observed, such as the (003), (006), and (009) peaks, which correspond to the standard card peak PDF89#0460, indicating the successful synthesis of hydrotalcite nanofluids.

[0079] Figure 2 The image shows a SEM image of the hydrotalcite nanofluid obtained in step E of Example 1, where the inset shows the average particle size of the hydrotalcite particles, which is 70 nm. The testing procedure was as follows: the hydrotalcite nanofluid was pipetted into a sample tube, diluted with ethanol, sonicated, dropped onto a silicon wafer to prepare the sample, dried, and then observed by SEM.

[0080] Figure 3 The image shows the AFM diagram of the hydrotalcite nanofluid obtained in step E of Example 1, where the inset shows the average thickness of the hydrotalcite particles, which is 5 nm.

[0081] Figure 4 This is a digital photograph of the hydrotalcite nanofluid obtained in step E of Example 1 at 8 months. It can be seen that the hydrotalcite nanofluid exhibits excellent dispersion stability (uniform dispersion) and long-term stability (can be stored for extended periods). Testing showed that the hydrotalcite nanofluid can still be stored stably for one year.

[0082] Comparative Example 1

[0083] The difference from Example 1 is as follows, while the remaining steps and conditions are the same.

[0084] Step A: Dissolve magnesium chloride hexahydrate (concentration 0.6M) and aluminum chloride hexahydrate (concentration 0.2M) in 50 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50 at a molar ratio of 3:1 to obtain a mixed salt solution.

[0085] Comparative Example 2

[0086] The difference from Example 1 is as follows, while the remaining steps and conditions are the same.

[0087] Step A: Dissolve magnesium chloride hexahydrate (concentration 0.8M) and aluminum chloride hexahydrate (concentration 0.2M) in 50 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50 vol% at a molar ratio of 4:1 to obtain a mixed salt solution.

[0088] Figure 5 Digital photographs of hydrotalcite nanofluids with different magnesium-aluminum ratios on day 10. The hydrotalcite nanofluid with a magnesium-aluminum ratio of 4:1 (Comparative Example 2) settled within 3 days; the hydrotalcite nanofluid with a magnesium-aluminum ratio of 3:1 (Comparative Example 1) settled within 10 days; and the hydrotalcite nanofluid with a magnesium-aluminum ratio of 2:1 (Example 1) did not settle after being stored at room temperature for 8 months.

[0089] Figure 6 The thermal conductivity results for hydrotalcite nanofluids with different solid contents (0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0 wt%) are shown. LDH / EG-W represents hydrotalcite nanofluids in an ethylene glycol-water mixed solvent, with 0 solid content corresponding to a volume ratio of 50:50 ethylene glycol-water mixed solvent. It can be seen that hydrotalcite has a high thermal conductivity and good thermal conductivity. This is because the Brownian motion and microconvection of hydrotalcite nanoparticles lead to intensified molecular collisions, which is conducive to the formation of a thermal network and promotes heat transfer. The hydrophilicity of hydrotalcite causes the formation of a nanolayer around it. This nanolayer state, which is between solid and liquid, is more conducive to heat transfer than the base liquid (ethylene glycol-water mixed solvent).

[0090] Figure 7 This is a temperature rise graph of the hydrotalcite nanofluid and ethylene glycol-water mixed solvent in Example 1. Figure 8 This is a cooling graph of the hydrotalcite nanofluid and the ethylene glycol-water mixed solvent in Example 1. The thermal conductivity and heat dissipation capabilities of the hydrotalcite nanofluid and the base liquid during heating and cooling were evaluated using a constant-temperature oil bath apparatus. The hydrotalcite nanofluid or the base liquid (ethylene glycol-water mixed solvent, volume ratio 50:50) in Example 1 was uniformly heated, and the internal temperature changes of the fluid were recorded in real time. The hydrotalcite nanofluid took only 13 minutes to heat to 100°C, a reduction of 40.9% compared to the base liquid (22 minutes); it took 16 minutes to cool to 40°C, an increase of 23.8% compared to the base liquid (21 minutes). The results indicate that the hydrotalcite nanofluid has higher thermal conductivity and heat dissipation capabilities compared to the base liquid.

[0091] Comparative Example 3

[0092] The difference from Example 1 is as follows, while the remaining steps and conditions are the same.

[0093] Steps A through C are the same; step D is skipped.

[0094] Step E: Disperse the hydrotalcite reaction solution sample obtained in step C in 200 mL of ethylene glycol-water mixed solvent with a volume ratio of 50:50, place it in a polytetrafluoroethylene reaction vessel, and crystallize it at 100 °C for 16 hours to obtain a hydrotalcite paste precipitate and two phases separated by the ethylene glycol-water mixed solvent.

[0095] The mixture obtained in step E was separated to obtain a hydrotalcite-like precipitate. This precipitate was then redispersed in 200 mL of an ethylene glycol-water mixed solvent (volume ratio 50:50) and sonicated for 30 min. However, a stable dispersion of nanofluid could not be formed; the resulting product was still a two-phase mixture of the hydrotalcite-like precipitate and the ethylene glycol-water mixed solvent. It can be seen that omitting the centrifugation and washing steps in step D prevents the formation of a stable hydrotalcite nanofluid.

[0096] The preparation method provided by this invention first prepares hydrotalcite precipitate through nucleation reactions in salt and alkali solutions. After repeated centrifugation (3-5 times) and washing, a hydrotalcite paste is obtained. This paste is then dispersed in an ethylene glycol-water mixed solvent and subjected to high-temperature crystallization treatment in a polytetrafluoroethylene reactor, ultimately yielding hydrotalcite nanofluids. This invention successfully prepares hydrotalcite nanofluids with long-term stability by utilizing the unique hydrophilic properties of the surface hydroxyl groups of hydrotalcite and the positive charge stabilization mechanism of the main layers. This invention not only overcomes the dispersion defects of traditional nanofluids but also enables the prepared hydrotalcite nanofluids to exhibit excellent thermal conductivity.

[0097] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing hydrotalcite nanofluids, characterized in that, Includes the following steps: A mixed salt solution and a mixed alkali solution are provided; the solute in the mixed salt solution includes a divalent metal salt and an aluminum salt, wherein the divalent metal salt includes one or more of magnesium salt, zinc salt, and nickel salt; the solute in the mixed alkali solution includes sodium hydroxide and sodium carbonate. The mixed salt solution and the mixed alkali solution were mixed and subjected to a coprecipitation reaction. The solid and liquid were separated, and the resulting precipitate was washed to obtain a hydrotalcite-like precipitate. The hydrotalcite precipitate was dispersed in an alcohol-water mixed solvent and crystallized to obtain hydrotalcite nanofluid.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the divalent metal salt to the aluminum salt is 1.5 to 2.5:

1.

3. The preparation method according to claim 1, characterized in that, The molar ratio of sodium hydroxide to sodium carbonate is 10 to 12:

1.

4. The preparation method according to claim 1, characterized in that, The concentration of divalent metal salt in the mixed salt solution is 0.01–1 mol / L, and the concentration of aluminum salt is 0.005–0.5 mol / L; the concentration of sodium hydroxide in the mixed alkaline solution is 0.15–3 mol / L, and the concentration of sodium carbonate is 0.0013–0.27 mol / L.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the aluminum salt to sodium hydroxide is 0.1 to 0.17:

1.

6. The preparation method according to claim 1, characterized in that, The solid-liquid separation is performed by centrifugation, with a centrifugation speed of 3000-5000 r / min and a time of 3-5 min; the washing is performed by water washing, with the number of water washing cycles being 3-5.

7. The preparation method according to claim 1, characterized in that, The alcohol in the alcohol-water mixed solvent is ethylene glycol or glycerol, and the volume ratio of the alcohol to water is 2-8:8-2.

8. The preparation method according to claim 1 or 7, characterized in that, The crystallization temperature is 80–120°C, and the time is 12–20 hours.

9. The hydrotalcite nanofluid obtained by the preparation method according to any one of claims 1 to 8, characterized in that, The solid content of the hydrotalcite nanofluid is 0.25 wt% to 2.5 wt%.

10. The application of the hydrotalcite nanofluid as described in claim 9 as a heat transfer medium.

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