Mixed molten salt heat transfer and storage material and preparation method thereof
By adding a specific proportion of titanium dioxide, magnesium oxide, silicon dioxide nanoparticles, and expanded graphite to the mixed molten salt, the problem of insufficient thermal conductivity and specific heat capacity of the mixed molten salt heat transfer and storage material was solved, achieving efficient heat storage and release, and optimizing the operating efficiency and economy of the CSP system.
Patent Information
- Application Number
- CN202511388156.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-26
- Publication Date
- 2025-12-05
AI Technical Summary
Existing mixed molten salt heat transfer and storage materials have insufficient thermal conductivity and specific heat capacity, and unsatisfactory thermal cycle stability, resulting in limited heat storage and release efficiency, requiring larger system equipment scale, increased land area and construction investment.
By adding a specific proportion of composite nanoparticles composed of titanium dioxide, magnesium oxide, and silicon dioxide to a binary mixed molten salt composed of KNO3 and NaNO3, and adding expanded graphite, more diverse interface structures and defect sites are formed, thereby improving the thermal conductivity and specific heat capacity of the material.
It significantly improves the thermal conductivity and specific heat capacity of the mixed molten salt heat transfer and storage material, enhances heat transfer and storage efficiency, reduces material usage, lowers system volume and construction costs, and maintains component homogeneity under high-temperature conditions, thus extending system service life.
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of physical heat transfer and energy storage, and particularly relates to a mixed molten salt heat transfer and storage material and a preparation method thereof. BACKGROUND
[0002] Concentrated solar power (CSP) technology concentrates solar radiation onto a receiver through mirrors or lenses, which heats the heat transfer medium and then drives a steam turbine to generate electricity. In this process, molten salt, due to its excellent thermophysical properties and stability, has become the current mainstream heat transfer and storage medium. The core advantage of the molten salt system lies in its high compatibility with thermal energy storage (TES). By storing excess heat during the day in a high-temperature molten salt tank, heat is released at night or on cloudy days to continue power generation, achieving the schedulability of power output, which is a unique advantage that photovoltaic + battery energy storage cannot completely replace. A typical CSP power station can be configured with 6-15 hours of energy storage capacity, greatly enhancing the stability of the power grid and the penetration rate of renewable energy.
[0003] In addition, molten salt works at atmospheric pressure, the system pressure is low, the safety is high, and the corrosion to the equipment is relatively mild, prolonging the service life of the key components. Although there is a risk of low-temperature solidification, which requires heat preservation, modern power stations have effectively responded through intelligent temperature control and system design. However, traditional molten salt has the defects of weak thermal conductivity and small specific heat capacity, which limits the efficiency of heat storage and release and slows down the heat transfer response. To meet the energy storage needs, the equipment scale often needs to be expanded, which in turn increases the system footprint and construction investment. Therefore, improving the thermal conductivity and heat capacity of molten salt materials has become a key path to optimizing the operating efficiency and economy of CSP systems. Malik in the article “Evaluation of composite alumina nanoparticle and nitrate eutectic materials for use in concentrating solar power plants” found that adding nano-alumina trioxide to the heat transfer and storage material can improve the specific heat capacity of the material. However, the thermal conductivity and specific heat capacity of the mixed molten salt heat transfer and storage material in the prior art cannot meet the market demand, and the thermal cycle stability is not ideal. SUMMARY
[0004] The purpose of the present application is to provide a mixed molten salt heat transfer and storage material and a preparation method thereof.
[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:
[0006] A kind of mixed molten salt heat transfer and heat storage material, the material includes KNO 3 、NaNO 3 、expanded graphite and composite nanoparticles;The composite nanoparticles include titanium dioxide, magnesium oxide and silicon dioxide.
[0007] Preferably, the mass ratio of KNO 3 、NaNO 3 It is (3-5) :(5-7) ;The mass fraction of the composite nanoparticles in the material is 1.2-1.5%;The mass fraction of the expanded graphite in the material is 10-13%.
[0008] Preferably, the mass ratio of the composite nanoparticles and expanded graphite is (1.2-1.3) :(12-13).
[0009] The present application can improve the average specific heat capacity of mixed molten salt heat transfer and heat storage material by adding composite nanoparticles composed of titanium dioxide, magnesium oxide and silicon dioxide in the binary mixed molten salt composed of KNO 3 、NaNO 3.Analysis is that the addition of nanoparticles in molten salt forms a large number of solid-liquid interfaces, induces special ordered arrangement of molten salt molecules at the interface, and the energy state of this part of ordered structure is higher, which needs to absorb more heat energy to increase temperature, so that the specific heat capacity is significantly enhanced macroscopically.The nanoparticles of specific ratio have synergistic effect between them, which can create more diversified interface structure and defect site, thereby increasing the proportion of interface area.The present application simultaneously adds expanded graphite in the system, which can improve the average specific heat capacity of mixed molten salt heat transfer and heat storage material, and when the composite nanoparticles and expanded graphite are in a specific ratio, the average specific heat capacity has higher stability.Under the condition of this ratio, the composite nanoparticles and expanded graphite have synergistic effect, which better perfect the internal structure of the material.
[0010] Preferably, the composite nanoparticles include titanium dioxide, magnesium oxide and silicon dioxide with a mass ratio of 1 :(0.2-0.4) :(1.3-1.5).
[0011] Preferably, the preparation method of the silicon dioxide includes the following steps:
[0012] (1) mix silicon precursor and ethanol, stir uniformly, to obtain mixed solution A;
[0013] (2) mix water, ammonia and ethanol, stir uniformly, to obtain mixed solution B;
[0014] (3) inject mixed solution A and mixed solution B into the reactor at the same time, react at 30-40 ℃ for 12-15 h, centrifuge, collect the lower layer precipitate, wash, vacuum dry, to obtain silicon dioxide.
[0015] Preferably, the reaction condition in step (3) is: react at 30-40 ℃ for 12-15 h.
[0016] Preferably, the silicon precursor comprises tetraethyl orthosilicate and tetramethoxysilane in a volume ratio of (1.5-2):(2.5-3).
[0017] Preferably, the average particle size of the titanium dioxide is 15 nm, and the specific surface area is 30-100 m 2 / g.
[0018] Preferably, the particle size of the magnesium oxide is 30-50 nm, and the specific surface area is 30-50 m 2 / g.
[0019] The present application can improve the thermal stability and heat conduction capacity of the mixed molten salt heat transfer and storage material by using specific proportions of titanium dioxide, magnesium oxide and silicon dioxide. The analysis is that the different surface chemical properties of the nanoparticles have different adsorption preferences for the ions of different polarities of the molten salt, thereby forming a more complex and stable interface layer structure that can resist thermal stress damage; at the same time, the nanoparticles form an efficient heat transfer channel in the molten salt, and change the microstructure of the molten salt matrix, thereby significantly enhancing the heat conduction rate.
[0020] The preparation method of the mixed molten salt heat transfer and storage material comprises the following steps:
[0021] (1) uniformly mix KNO3 and NaNO3, put them into a muffle furnace and heat to 420℃, keep the temperature constant for 15h, after cooling, crush to less than 100 mesh, to obtain a binary nitrate;
[0022] (2) after heating and melting the binary nitrate, add the composite nanoparticles, stir, and naturally cool to obtain a primary material;
[0023] (3) add expanded graphite to the primary material, stir uniformly, and cool to room temperature to obtain the mixed molten salt heat transfer and storage material.
[0024] Compared with the prior art, the present application has the following advantages and beneficial effects:
[0025] 1. The mixed molten salt heat transfer and storage material prepared by the present application has excellent heat conduction capacity and high specific heat capacity, significantly improving the efficiency of heat transfer and storage. The high thermal conductivity can accelerate the thermal response speed of the molten salt in the heat exchange process, reduce the temperature difference and thermal resistance of heat transfer, and improve the efficiency of the heat exchanger; and the high specific heat capacity means that more heat energy can be stored per unit mass of molten salt, thereby reducing the material usage, system volume and construction cost under the same energy storage capacity. At the same time, the material has excellent thermal chemical stability, can maintain uniform composition under long-term high-temperature operating conditions, prolongs the system maintenance cycle and service life.
[0026] 2、The application can improve the specific heat capacity of the mixed molten salt heat transfer and storage material by adding the composite nanoparticles composed of titanium dioxide, magnesium oxide and silicon dioxide in the binary mixed molten salt composed of KNO3 and NaNO3; meanwhile, the average specific heat capacity of the mixed molten salt heat transfer and storage material can be improved by adding the expanded graphite in the system, and when the composite nanoparticles and the expanded graphite are in a specific ratio, the average specific heat capacity stability is higher.
[0027] 3、The application can improve the heat conduction capacity and thermal stability of the mixed molten salt heat transfer and storage material by using the titanium dioxide, magnesium oxide and silicon dioxide in a specific ratio. DETAILED DESCRIPTION
[0028] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.
[0029] The raw materials used in the following embodiments of the application are all commercially available goods:
[0030] Expanded graphite, item number: 101104, Jiangsu Xianfeng Nanometer Material Technology Co., Ltd.
[0031] Embodiment 1
[0032] The embodiment provides a mixed molten salt heat transfer and storage material, the material comprising KNO3, NaNO3, expanded graphite and composite nanoparticles; the mass ratio of the KNO3 and the NaNO3 is 4:6; the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide in a mass ratio of 1:0.3:1.4; the mass fraction of the composite nanoparticles in the material is 1.3%; and the mass fraction of the expanded graphite in the material is 12%.
[0033] The average particle size of the titanium dioxide is 15 nm, and the specific surface area is 30-100 m 2 / g; purchased from Beijing Deke Island Gold Technology Co., Ltd.
[0034] The particle size of the magnesium oxide is 30-50 nm, and the specific surface area is 30-50 m 2 / g, model number DK-MgO-001; Beijing Deke Island Gold Technology Co., Ltd.
[0035] The preparation method of the silicon dioxide comprises the following steps:
[0036] (1) 2 mL of tetraethyl orthosilicate, 3 mL of tetramethoxysilane and 45 mL of ethanol are mixed and stirred uniformly to obtain a mixed solution A;
[0037] (2) 2.5 mL of water, 4 mL of ammonia water with a concentration of 25 wt%, and 41 mL of ethanol were mixed and stirred uniformly to obtain a mixed solution B;
[0038] (3) The mixed solution A and the mixed solution B were simultaneously injected into the reactor at a speed of 3 mL / min, and after the injection was completed, the reaction was carried out at 35℃ for 13 h, centrifuged, and the lower precipitate was collected and washed with anhydrous ethanol three times, and vacuum dried at 80℃ for 24 h to obtain the silicon dioxide.
[0039] The preparation method of the mixed molten salt heat transfer and storage material comprises the following steps:
[0040] (1) KNO3 and NaNO3 were uniformly mixed and placed in a muffle furnace and heated to 420℃, and kept at this temperature for 15 h, and after cooling, the mixture was crushed to less than 100 mesh to obtain a binary nitrate;
[0041] (2) After the binary nitrate was melted by heating to 450℃, the composite nanoparticles were added, and stirred at 700 r / min for 20 min to obtain a primary material;
[0042] (3) The primary material was kept at 450℃, and the expanded graphite was added, and stirred at 500 r / min for 40 min, and cooled to room temperature to obtain the mixed molten salt heat transfer and storage material.
[0043] Example 2
[0044] The example provides a mixed molten salt heat transfer and storage material, which comprises KNO3, NaNO3, expanded graphite and composite nanoparticles; the mass ratio of KNO3 to NaNO3 is 3:5; the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide with a mass ratio of 1:0.2:1.5; the mass fraction of the composite nanoparticles in the material is 1.2%; and the mass fraction of the expanded graphite in the material is 13%.
[0045] The average particle size of the titanium dioxide is 15 nm, and the specific surface area is 30-100 m 2 / g; purchased from Beijing Deke Island Gold Technology Co., Ltd.
[0046] The particle size of the magnesium oxide is 30-50 nm, and the specific surface area is 30-50 m 2 / g, model DK-MgO-001; Beijing Deke Island Gold Technology Co., Ltd.
[0047] The preparation method of the silicon dioxide comprises the following steps:
[0048] (1) 2 mL of tetraethyl orthosilicate, 3 mL of tetramethoxysilane and 45 mL of ethanol were mixed and stirred uniformly to obtain a mixed solution A;
[0049] (2) Mix 2.5 mL of water, 4 mL of ammonia water with a concentration of 25 wt%, and 41 mL of ethanol, stir until uniform, to obtain a mixed solution B;
[0050] (3) Inject mixed solution A and mixed solution B into the reactor at a speed of 3 mL / min at the same time, after all injection, react at 35℃ for 13h, centrifuge, collect the lower precipitate, wash with anhydrous ethanol three times, and vacuum dry at 80℃ for 24h to obtain silicon dioxide.
[0051] The preparation method of the mixed molten salt heat transfer and storage material comprises the following steps:
[0052] (1) Mix KNO3 and NaNO3 uniformly, heat to 420℃ in a muffle furnace, keep constant temperature for 15h, after cooling, crush to less than 100 mesh to obtain binary nitrate;
[0053] (2) After the binary nitrate is melted by heating to 450℃, add composite nanoparticles, stir at 700 r / min for 20 min to obtain a primary material;
[0054] (3) Keep 450℃, add expanded graphite to the primary material, stir at 500 r / min for 40 min, cool to room temperature to obtain the mixed molten salt heat transfer and storage material.
[0055] Example 3
[0056] The example provides a mixed molten salt heat transfer and storage material, the material comprises KNO3, NaNO3, expanded graphite and composite nanoparticles; the mass ratio of KNO3 and NaNO3 is 5:7; the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide with a mass ratio of 1:0.4:1.3; the mass fraction of the composite nanoparticles in the material is 1.25%; the mass fraction of the expanded graphite in the material is 12.4%.
[0057] The average particle size of the titanium dioxide is 15 nm, and the specific surface area is 30-100 m 2 / g; purchased from Beijing Deke Island Gold Technology Co., Ltd.
[0058] The particle size of the magnesium oxide is 30-50 nm, and the specific surface area is 30-50 m 2 / g, model DK-MgO-001; Beijing Deke Island Gold Technology Co., Ltd.
[0059] The preparation method of the silicon dioxide comprises the following steps:
[0060] (1) Mix 2 mL of tetraethyl orthosilicate, 3 mL of tetramethoxysilane and 45 mL of ethanol, stir until uniform, to obtain a mixed solution A;
[0061] (2) 2.5 mL of water, 4 mL of ammonia water with a concentration of 25 wt%, and 41 mL of ethanol were mixed and stirred uniformly to obtain a mixed solution B;
[0062] (3) The mixed solution A and the mixed solution B were simultaneously injected into the reactor at a speed of 3 mL / min, and after the injection was completed, the reaction was carried out at 35°C for 13 h, centrifugation was performed, the lower precipitate was collected and washed with anhydrous ethanol three times, and vacuum drying was performed at 80°C for 24 h to obtain the silicon dioxide.
[0063] The preparation method of the mixed molten salt heat transfer and storage material comprises the following steps:
[0064] (1) KNO3 and NaNO3 were uniformly mixed and placed in a muffle furnace and heated to 420°C, and the temperature was kept constant for 15 h. After cooling, the mixture was ground to less than 100 mesh to obtain a binary nitrate salt;
[0065] (2) After the binary nitrate salt was melted by heating to 450°C, the composite nanoparticles were added, and stirring was performed at 700 r / min for 20 min to obtain a primary material;
[0066] (3) The primary material was kept at 450°C, and the expanded graphite was added, and stirring was performed at 500 r / min for 40 min, and the temperature was cooled to room temperature to obtain the mixed molten salt heat transfer and storage material.
[0067] Comparative Example 1
[0068] The difference between the comparative example and Example 1 is that the composite nanoparticles are replaced by silicon dioxide. The preparation method of the silicon dioxide is the same as that of Example 1.
[0069] Comparative Example 2
[0070] The difference between the comparative example and Example 1 is that the average particle size of the silicon dioxide is 10 nm, and the average specific surface area is 380 m 2 / g, which is purchased from Jinlei Technology, JL-SiO2-N10.
[0071] Comparative Example 3
[0072] The difference between the comparative example and Example 1 is that the particle size of the magnesium oxide is 0.5-1 μm, and the specific surface area is 5-10 m 2 / g, Model DK-MgO-001. Beijing Deke Daojin Technology Co., Ltd.
[0073] Comparative Example 4
[0074] The difference between the comparative example and Example 1 is that the average particle size of the titanium dioxide is 50 nm, and the specific surface area is 5-15 m 2 / g. Beijing Deke Daojin Technology Co., Ltd.
[0075] Comparative Example 5
[0076] The difference between the present comparative example and Example 1 is that the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide at a mass ratio of 0.9:0.1:1.6.
[0077] Comparative Example 6
[0078] The difference between the present comparative example and Example 1 is that the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide at a mass ratio of 1.1:0.5:1.2.
[0079] Comparative Example 7
[0080] The difference between the present comparative example and Example 1 is that the mass fraction of the composite nanoparticles in the material is 1.0%.
[0081] Comparative Example 8
[0082] The difference between the present comparative example and Example 1 is that the mass fraction of the composite nanoparticles in the material is 1.7%.
[0083] Comparative Example 9
[0084] The difference between the present comparative example and Example 1 is that the preparation method of the silicon dioxide comprises the following steps:
[0085] (1) 5 mL of tetraethyl orthosilicate and 45 mL of ethanol were mixed and stirred uniformly to obtain a mixed solution A;
[0086] (2) 2.5 mL of water, 4 mL of ammonia water with a concentration of 25 wt%, and 41 mL of ethanol were mixed and stirred uniformly to obtain a mixed solution B;
[0087] (3) The mixed solution A and the mixed solution B were simultaneously injected into a reactor at a speed of 3 mL / min, and after all were injected, the reaction was carried out at 35°C for 13 h, centrifuged, and the lower precipitate was collected and washed with anhydrous ethanol for three times, and vacuum dried at 80°C for 24 h to obtain silicon dioxide.
[0088] Comparative Example 10
[0089] The difference between the present comparative example and Example 1 is that the mass fraction of the expanded graphite in the material is 15%.
[0090] Comparative Example 11
[0091] The difference between the present comparative example and Example 1 is that the mass fraction of the composite nanoparticles in the material is 1.0% and the mass fraction of the expanded graphite in the material is 15%.
[0092] The mixed molten salt heat transfer and heat storage materials of Examples 1-3 and Comparative Examples 1-11 were subjected to performance testing.
[0093] 1. Average specific heat capacity in the range of 250-430℃ was measured using a differential scanning calorimeter (DSC, Q20 TA Instruments). c̄ = Q / [m × (T2 - T1)], c̄: average specific heat capacity, unit is J / (g·K) or kJ / (kg·K). Q: total heat absorbed from temperature T1 to T2, unit is J. m: mass of the material, unit is g. T2 - T1: change in temperature, unit is K.
[0094] 2. Average thermal conductivity in the range of 250-430℃ was measured using transient hot wire method. λ_avg = (Q × L) / (A × ΔT × t); Q: total heat through the material in time t (J). A: cross-sectional area perpendicular to the direction of heat flow (m²). ΔT: temperature difference between the two ends of the material. t: measurement time (s). L: material thickness along the direction of heat flow (m).
[0095] 3. Thermal cycle stability: the mixed molten salt heat transfer and storage material was heated to 400℃ at 20℃ / min in a muffle furnace, cooled to room temperature at 20℃ / min, and cycled 150 times, and the average specific heat capacity after cycling was determined.
[0096] The results are shown in Table 1.
[0097] Table 1 Performance test results
[0098] Average specific heat capacity J / (g K) Average thermal conductivity W / (m K) Thermal cycle stability J / (g K) Example 1 4.70 10.16 4.65 Example 2 4.61 10.02 4.52 Example 3 4.65 10.05 4.58 Comparative Example 1 3.32 7.11 3.06 Comparative Example 2 3.75 8.13 3.59 Comparative Example 3 4.23 9.17 4.17 Comparative Example 4 4.04 8.82 3.99 Comparative Example 5 3.68 8.04 3.33 Comparative Example 6 3.85 8.32 3.57 Comparative Example 7 4.36 9.45 4.21 Comparative Example 8 4.17 9.06 4.04 Comparative Example 9 4.09 8.83 3.98 Comparative Example 10 4.25 9.24 4.13 Comparative Example 11 4.15 9.03 4.00
[0099] As can be seen from Table 1, the average specific heat capacity and average thermal conductivity of the mixed molten salt heat transfer and storage materials of Examples 1-3 are high, and the stability is good.
[0100] In Comparative Example 1, only silica nanoparticles were used, and the performance of the mixed molten salt heat transfer and storage material decreased significantly.
[0101] In Comparative Examples 2-6, the parameters and ratios of the nanoparticles were different, and the performance of the mixed molten salt heat transfer and storage material decreased.
[0102] In Comparative Examples 7-8, the amount of composite nanoparticles was too high, which was prone to agglomeration in the system, and the amount was too low, which was insufficient to play a role, both of which would lead to a decrease in material performance.
[0103] In Comparative Example 9, only tetraethyl orthosilicate was used as the silicon precursor, and the performance was poor. It was analyzed that the hydrolysis and condensation reaction rates of tetraethyl orthosilicate and tetramethoxysilane were different, and by controlling the hydrolysis and condensation rates of the precursors, the particle size and morphology of the final product could be accurately controlled, and the compounding effect of the prepared silica with titanium dioxide and magnesium oxide was better.
[0104] It can be seen from Comparative Examples 10 and 11 that when the amount of added expanded graphite is too high, the performance of the heat storage material also decreases, which is analyzed to be caused by the increased interfacial thermal resistance between the expanded graphite and the nitrate / nanoparticles. Meanwhile, there is an obvious synergistic effect between the expanded graphite and the composite nanoparticles, but the effect can only be fully exerted within a specific addition range, so that the synergistic effect of the expanded graphite and the nanoparticles is optimal, which can significantly improve the thermal conductivity of the material, and also maintain good thermal cycle stability and heat storage capacity.
[0105] In summary, the mixed molten salt heat transfer and storage material prepared by the present application has excellent thermal conductivity and high specific heat capacity, which significantly improves the efficiency of heat transfer and storage. The high thermal conductivity can accelerate the thermal response speed of the molten salt in the heat exchange process, reduce the temperature difference and thermal resistance of heat transfer, and improve the efficiency of the heat exchanger; and the high specific heat capacity means that more heat energy can be stored per unit mass of molten salt, thereby reducing the material usage, the system volume and the construction cost under the same energy storage capacity. Meanwhile, the material has excellent thermal chemical stability, can maintain uniform composition under long-term high-temperature operation conditions, and prolongs the system maintenance cycle and service life.
[0106] The above describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application.
Claims
1. A hybrid molten salt heat transfer and thermal storage material, characterized in that, The material comprises KNO3, NaNO3, expanded graphite and composite nanoparticles; the composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide.
2. The molten salt heat transfer and storage material of claim 1, wherein, The mass ratio of KNO3 and NaNO3 is (3-5):(5-7); the mass fraction of the composite nanoparticles in the material is 1.2-1.5%; the mass fraction of the expanded graphite in the material is 10-13%.
3. The molten salt heat transfer and storage material of claim 2, wherein, The mass ratio of the composite nanoparticles and the expanded graphite is (1.2-1.3):(12-13).
4. The molten salt heat-transfer and heat-storage mixture of claim 1, wherein The composite nanoparticles comprise titanium dioxide, magnesium oxide and silicon dioxide in a mass ratio of 1:(0.2-0.4):(1.3-1.5).
5. The molten salt heat-transfer and heat-storage mixture of claim 4, wherein The preparation method of the silicon dioxide comprises the following steps: (1) mixing a silicon precursor and ethanol, stirring uniformly to obtain a mixed solution A; (2) mixing water, ammonia and ethanol, stirring uniformly to obtain a mixed solution B; (3) injecting the mixed solution A and the mixed solution B into a reactor simultaneously, reacting, centrifuging, collecting the lower precipitate, washing, vacuum drying to obtain silicon dioxide.
6. The molten salt heat-transfer and heat-storage mixture of claim 5, wherein The reaction condition in step (3) is: reacting at 30-40℃ for 12-15h.
7. The molten salt heat-transfer and heat-storage mixture of claim 5, wherein The silicon precursor comprises tetraethyl orthosilicate and tetramethoxysilane in a volume ratio of (1.5-2):(2.5-3).
8. The molten salt heat-transfer and heat-storage mixture of claim 4, wherein The average particle size of the titanium dioxide is 15 nm, and the specific surface area is 30-100 m 2 / g.
9. The molten salt heat-transfer and heat-storage mixture of claim 4, wherein, Magnesium oxide having a particle size of 30-50 nm and a specific surface area of 30-50 m 2 / g.
10. A method of producing the molten salt heat transfer and storage mixture according to any one of claims 1 to 9, characterized in that The method comprises the following steps: (1) mixing KNO3 and NaNO3 uniformly, heating, cooling, crushing to obtain a binary nitrate; (2) adding the composite nanoparticles to the binary nitrate after heating and melting, stirring, naturally cooling to obtain a primary material; (3) adding the expanded graphite to the primary material, stirring uniformly, cooling to room temperature to obtain a mixed molten salt heat transfer and storage material.