Method for preparing nanowires and angstrom chains by extruding and stretching quick-freezing method
Nanowires and microchains were prepared by extrusion-stretching-freezing method, which solved the problems of consistency and stability in the preparation of nanowires and microchains, and realized efficient, green and large-scale preparation of nanomaterials.
Patent Information
- Application Number
- CN202511351319.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-22
- Publication Date
- 2025-12-12
AI Technical Summary
Existing methods for preparing nanowires suffer from problems such as structural and compositional inhomogeneity, unstable performance, catalyst residue, poor process repeatability, high cost, and difficulty in achieving batch-to-batch consistency and large-scale production. The preparation of microchains, on the other hand, faces challenges related to poor stability, environmental sensitivity, and difficulty in control and integration.
Nanowires and angstroms were prepared by extrusion-stretching-freezing method, using physical methods of extrusion, stretching and quick-freezing. A sandwich structure was formed between the substrate by polar molecules and ionic compounds, and then rapid freezing was performed using low-temperature physical technology to form a one-dimensional nanostructure.
It has achieved the preparation of high-purity and stable nanowires and angstroms, avoiding catalyst residue, and has the potential for large-scale production. It has good structural stability, is suitable for large-scale and efficient preparation, and is green and environmentally friendly.
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Figure CN121107436A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to methods for preparing nanowires and angstroms, particularly methods for preparing nanowires and angstroms using an extrusion-stretching-freezing method. Background Technology
[0002] Nanowires are a product of "nanotechnology," while angstrom chains are the beginning of "atomic technology." The shift from nanometers to angstroms represents not only a reduction in scale but also a paradigm shift from classical physics to quantum physics.
[0003] Nanowires are quasi-one-dimensional nanostructures confined to the nanoscale in two dimensions, yet freely extending in the third dimension. They are among the most important and common one-dimensional nanomaterials. Nanowires can be single-crystal, polycrystalline, or amorphous. Metal nanowires are used for transparent conductive electrodes, semiconductor nanowires for transistors, lasers, and photodetectors, insulating nanowires for templates or support structures, and polymer nanowires for flexible electronics. Limitations in existing nanowire fabrication methods may pose practical challenges to nanowire research and applications. Inhomogeneous structure and composition can lead to performance fluctuations, such as inconsistent electrical, optical, or magnetic properties, making it difficult to achieve uniform and stable device performance. Impurities such as catalyst or template residues can alter the intrinsic properties of nanowires or introduce unnecessary defects, thus affecting the efficiency and reliability of the final device. Poor process repeatability makes it difficult to guarantee batch-to-batch consistency, hindering comparative analysis in basic research and impeding large-scale production and commercial applications.
[0004] Some methods rely on expensive equipment or complex processes, resulting in high production costs and low yields, making it difficult to meet the demand for large quantities of low-cost nanowires in practical applications.
[0005] An angstrom chain specifically refers to a one-dimensional atomic chain with a diameter of 1 angstrom. This is the limit of one-dimensional structures being explored, typically only a few atoms thick, or even a chain-like structure composed of a single atom linked together. Its stability often requires special terminal atoms or a specific substrate environment to maintain. At this scale, the physical properties of materials are entirely dominated by quantum mechanical effects, resulting in many novel phenomena not found in macroscopic bulk materials. The absence or addition of a single atom significantly alters its properties. Fabricating angstrom chains is extremely difficult, requiring atomic-level precision manipulation. For example, in an ultra-high vacuum environment, material growth is precisely controlled, and the chain is broken using the tip of a scanning probe microscope. Currently, angstrom chains are primarily in the stage of fundamental physics research, but their application prospects are revolutionary, providing an excellent platform for studying one-dimensional physics, quantum confinement effects, and quantum transport. As the ultimate interconnects for future integrated circuits, angstrom chains can theoretically achieve minimal resistance and energy consumption, potentially used to construct connections between qubits or as novel quantum devices. Stability is the biggest challenge. Atomic chains are extremely fragile and prone to breakage; their electrical properties are extremely sensitive to the environment, making them difficult to control and integrate. Summary of the Invention
[0006] This invention provides a method for preparing nanowires and angstroms using an extrusion-stretching-freezing technique. This method represents a highly imaginative physical preparation concept that departs from traditional chemical synthesis approaches. It ingeniously combines macroscopic machining techniques (extrusion and stretching), low-temperature physics (freezing), and microscopic nanotechnology, making it distinctly different from current mainstream preparation methods.
[0007] This invention is based on the following fundamental principles: (1) Extrusion: First, a substrate-precursor-substrate sandwich structure is constructed using the extrusion method. The precursor contains polar molecules and ionic compounds, which are not suitable for nonpolar molecules and metal systems. This is because polar molecules have non-coincident positive and negative charge centers, and ionic compounds have positive and negative ions. Their electrostatic attraction is the core factor in the formation of one-dimensional nanowires and angstrom chains. The substrate should be as flat as possible, and materials such as molybdenum disulfide, mica, silicon, sapphire, and specific crystal exposure directions of metals can be selected. For example, a layer of graphene can be grown directly on a copper surface using chemical vapor deposition, or graphene sheets can be laid flat on an atomically flat substrate. Polar molecular droplets or salt powder are added to the substrate surface, and another substrate is placed on top of the precursor. The temperature is controlled to treat the precursor into a malleable state, such as liquid water or molten salt. The two substrates are slowly brought closer together using the extrusion method, and the precursor is gradually flattened and thinned, with excess precursor overflowing from the edge of the substrate. Extrusion is stopped when the thickness of the precursor tends to be a few molecular layers. The purpose of this step is to use the fluidity of the precursor to retain nanoscale-thick water molecules between the substrates, which also serve a protective function.
[0008] (2) Heating: The substrate perimeter is sealed to ensure complete isolation from the external environment while maintaining nanoscale degrees of freedom of movement. The substrate is then heated to a temperature preferably higher than the boiling point of the precursor, allowing sufficient time to conduct heat to the precursor between layers, ensuring the precursor temperature is within the range where it can transition to a gaseous state or is capable of sufficient movement. The purpose of this step is to prepare for subsequent spatial stretching; preheating the precursor to a high temperature allows it to quickly diffuse throughout the space after stretching.
[0009] (3) Stretching: The substrate is kept away from the other substrate at a distance of 10-1000 nm, causing the precursors between layers to expand and resulting in a decrease in density. The degree of density decrease should not be too large, preferably 2-7 times. Excessive density decrease will lead to too low density of the material between the substrates, thus affecting the temperature control time and effect. Existing piezoelectric nanopositioning stages can achieve sub-nanometer precision and can handle sample weights ranging from a few grams to hundreds of kilograms. Appropriate instrument parameters can be selected based on a trade-off between precision and load. The purpose of this step is to provide space for the formation of a one-dimensional structure of the precursors in the later stage.
[0010] (4) Rapid freezing: When the precursor is stretched to the target size and density, it is immediately rapidly frozen at a temperature controlled between 1 and 150 K. The most common method is liquid nitrogen cooling. Rapid freezing can instantly form nanowires and angstroms in the precursor within 300 ps, solidifying the current morphology of the material, locking its nanoscale structure, greatly inhibiting grain growth and coarsening, thereby obtaining ultrafine nanowires and angstroms, resulting in unique mechanical and physical properties.
[0011] (5) Separation, Preservation, Observation, and Application: The sealing around the substrate is removed, leaving the nanowires and angstroms encapsulated and protected by the substrate material, while also being in a cryogenically locked state, thus preserving their structure. The substrate simultaneously performs the functions of preparation and protection. This structural stability allows for easier separation, preservation, observation, and application of the prepared materials. Theoretically, any polar molecule or ionic compound material with plasticity or capable of being formed into a precursor solution / melt can potentially be prepared into nanowires and angstroms using this method, excluding metals and their alloys. Precise control of the mechanical parameters (speed, force) during extrusion and stretching allows for precise regulation of the nanowire length range. This is a catalyst-free physical method, resulting in nanowires with extremely high purity and no catalyst residue, which is crucial for electrical and optical applications. This method is essentially a continuous process, and once matured, it is highly suitable for large-scale, high-efficiency nanowire preparation.
[0012] The present invention adopts the following technical solution: The preparation of nanowires and angstroms by extrusion-stretching-freezing method includes the following steps: (1) Select a material with atomic-level flatness, chemical inertness and appropriate affinity for polar molecules and ionic compounds as a substrate. One substrate is used as the bottom substrate and the other is used as a movable top substrate. Polar molecules and ionic compounds are used as precursors. The precursors are placed on the surface of the bottom substrate and the other substrate is placed on top of the precursors. The temperature is controlled to process the precursors into a plastic state. The top substrate is moved slowly and accurately downward by piezoelectric ceramics to reduce the spacing between the substrates and force the excess precursors to be discharged. The remaining precursors and the substrate form a substrate-precursor-substrate sandwich structure. The substrate also has a protective function. (2) Use flexible corrugated pipe to seal the periphery of the substrate, control the temperature control component outside the substrate to heat the base, and conduct the heat to the precursor between the layers. The time should be sufficient to ensure that the temperature of the precursor is within the range where it can change to gaseous state or can move sufficiently. (3) Controlling the top base away from the bottom base, the expansion of the precursor between the upper and lower base layers leads to a decrease in density; (4) The temperature control components outside the substrate are controlled to rapidly freeze the substrate, and the interlayer precursors form nanowires and angstroms. The substrate-nanowire / angstrom chain-substrate sandwich structure exists stably and can be used for observation and application after being taken out.
[0013] The substrates selected in step (1) include graphene, hexagonal boron nitride, molybdenum disulfide, mica, silicon, sapphire, and metals.
[0014] The thickness of the precursor in the substrate-precursor-substrate step (1) is on the order of angstroms or nanometers.
[0015] The temperature reached in step (2) must be higher than the boiling point of the precursor but lower than the melting point of the substrate. The heating process can be carried out slowly.
[0016] In step (3), the distance between the upper and lower substrate layers is 10-1000 nm, and the precursor density must not be less than one-tenth of its normal state.
[0017] The freezing temperature in step (4) is controlled at 1-150 K, and the cooling process must be completed rapidly within a short time. For salts with higher melting points, the freezing temperature can be extended to 1-300 K.
[0018] This invention has the following advantages: (1) The method described in this invention combines macroscopic machining technology (extrusion and stretching), low-temperature physics (quick freezing), and microscopic nanotechnology to prepare nanowires and angstrom chains. Graphene is obtained by tearing graphite with tape to obtain a two-dimensional film. The extrusion-stretching-quick freezing method controls the amount of precursors by extrusion, controls the volume and density by stretching, and transforms the precursors into one-dimensional nanowires and angstrom chains by quick freezing.
[0019] (2) The precursors include polar molecules and ionic compound systems, which means that countless substances and mixtures thereof, such as water, ammonia, sulfur dioxide, ethanol, formaldehyde, sodium chloride, potassium chloride, calcium chloride, copper sulfate, sodium nitrate, potassium bromide, ferric chloride, and ferric sulfate, can form nanowires and angstroms. From this perspective, the method described in this invention will be a revolutionary technological advancement and can serve as a universal method for preparing one-dimensional nanowires and angstroms.
[0020] (3) The method system described in this invention adopts existing mature technologies to construct a substrate-precursor-substrate sandwich structure during the extrusion process. The mass of the precursor can be controlled by the distance between the substrates, which is beneficial to the subsequent preparation process. The mass of the interlayer precursor can also be indirectly calculated by the amount of overflow material.
[0021] (4) The nanowires and nanochains are encapsulated and protected by the substrate material and are in a low-temperature locked state, so the structure can be maintained. The substrate simultaneously undertakes the functions of preparation and protection, and the prepared materials can be more easily separated, stored, observed and applied.
[0022] (5) The method described in this invention uses physical methods throughout and does not involve chemical reactions, making it green and environmentally friendly.
[0023] (6) The method described in this invention has a clear principle, simple steps, a wide range of material selection, strong versatility, and potential for large-scale application. Attached Figure Description
[0024] Figure 1 This is a temperature-dependent schematic diagram illustrating the method for preparing ionic compound nanowires and angstrom chains according to the present invention. The interlayer spacing of nickel is 56.384 angstroms, the density of all interlayer materials is 0.25 g / cm³, and the atomic ratio of chloride ions to sodium ions is 1:1. 1 is the lower nickel substrate, 2 is the upper nickel substrate, and 3 is sodium chloride. Figure 1 All parts together present the variation of the same system under different temperature parameters.
[0025] Figure 2 This diagram illustrates the temperature-dependent principle for preparing polar molecular nanowires and angstrom chains using the method of this invention. The Ni interlayer spacing is 56.384 Å, and the density of sodium chloride is 0.3 g / cm³. 3 3 represents the nickel substrate, 4 the nickel top substrate, and 5 the water molecule. Figure 2 All parts together present the variation of the same system under different temperature parameters.
[0026] Figure 3 This is a schematic diagram of the extrusion process in the method of the present invention. 6 is the lower graphene substrate, 7 is the temperature control station of the lower substrate, 8 is the ionic crystal, 9 is the upper graphene substrate, 10 is the temperature control station of the upper substrate, 11 is the molten state of the ionic crystal, and 12 is the molten state of the two-dimensional ionic crystal.
[0027] Figure 4 This is a schematic diagram of the stretching process in the method of the present invention. 13 is the lower substrate temperature control component, 14 is the copper support layer, 15 is the graphene lower substrate, 16 is the upper substrate temperature control component, 17 is the copper support layer, 18 is the graphene upper substrate, and 19 is two-dimensional water.
[0028] Figure 5 This represents the structural transformation of sodium chloride under rapidly varying temperatures. The transformation temperatures are 300K to 1K, 600K to 300K, 600K to 1K, and 2000K to 1K. The interlayer spacing of nickel is 56.384 Å, the density of all interlayer material is 0.25 g / cm³, the atomic ratio of chloride to sodium ions is 1:1, and the time is 0–100 ps. Figure 5 The diagram clearly shows the structural changes during the cooling process, with comparisons of all parts.
[0029] Figure 6 Schematic diagrams of the sodium chloride angstrom chain structure and physical state. (a) Schematic diagram of the stable structure of the sodium chloride angstrom chain, (b) Internal perspective view of the stable structure of the sodium chloride angstrom chain, (c) Hamiltonian of the sodium chloride angstrom chain, (d) Pressure change of the sodium chloride angstrom chain, (e) Density change of the sodium chloride angstrom chain, (f) Temperature change of the sodium chloride angstrom chain. The interlayer spacing of nickel is 56.384 angstroms, the density of all interlayer materials is 0.25 g / cm³, the atomic ratio of chloride ions to sodium ions is 1:1, and the system temperature is 200 K. Figure 6 All parts collectively embody the characteristics of various parameters within the same system.
[0030] Figure 7 Let g(r) represent the radial distribution function of sodium chloride from high temperature to low temperature. (a) Radial distribution function g(r) of Cl-Cl, (b) Radial distribution function g(r) of Na-Cl, (c) Radial distribution function g(r) of Na-Na. The nickel interlayer spacing is 56.384 Å, the density of all materials in the interlayer is 0.25 g / cm³, the atomic ratio of chloride ions to sodium ions is 1:1, and the temperature conditions are 200 K and 2000 K, respectively. Figure 7 It describes the radial distribution characteristics among elements in the same system.
[0031] Figure 8 Schematic diagrams of the angstrom chain structure and physical state of sodium chloride and copper chloride. (a) Schematic diagram of the stable angstrom chain structure, (b) Internal perspective view of the stable angstrom chain structure, (c) Hamiltonian, (d) Pressure change, (e) Density change, (f) System temperature change. The interlayer spacing of nickel is 56.384 angstroms, the density of all interlayer materials is 0.50 g / cm³, the atomic ratio of sodium ions, copper ions and chloride ions is 1:1:3, and the system temperature is 200 K. Figure 8 All parts collectively embody the characteristics of various parameters within the same system.
[0032] Figure 9 Let g(r) represent the radial distribution function of sodium chloride from high temperature to low temperature. (a) Radial distribution function g(r) of Cl-Cl, (b) Radial distribution function g(r) of Cu-Cu, (c) Radial distribution function g(r) of Na-Na, (d) Radial distribution function g(r) of Cu-Cl, (e) Radial distribution function g(r) of Cu-Na, and (f) Radial distribution function g(r) of Na-Cl. The nickel interlayer spacing is 56.384 Å, the density of all materials in the interlayer is 0.50 g / cm³, the atomic ratio of sodium, copper, and chloride ions is 1:1:3, and the temperature conditions are 200 K and 2000 K, respectively. Figure 9 It describes the radial distribution characteristics among elements in the same system. Detailed Implementation
[0033] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention. Example
[0034] (1) Graphene was selected as the substrate. One substrate was fixed as the bottom substrate and the other was a movable top substrate. Liquid water droplets were added to the surface of the bottom substrate. The top substrate was moved slowly and precisely downward by piezoelectric ceramics to reduce the spacing between the substrates to 40 nm, which forced the excess water molecules to be discharged. The remaining water and the substrate formed a substrate-water-substrate sandwich structure, and the substrate also had a protective function.
[0035] (2) A flexible corrugated pipe is used to seal the periphery of the substrate, and the temperature control component outside the substrate is controlled to heat the substrate to 500 K for 10 min, so that the heat is conducted to the water molecules between the layers, ensuring that the water molecules are in the range where they can change to gas.
[0036] (3) By controlling the top substrate to be far away from the bottom substrate through piezoelectric ceramics, the distance between the upper and lower substrate layers is 100 nm, and the water molecules expand, resulting in a decrease in density.
[0037] (4) Liquid nitrogen was injected into the temperature control component outside the substrate to rapidly freeze the substrate for 10 minutes, and water molecules in the interlayer formed nanowires and angstrom chains. Example 1
[0038] (1) Molybdenum disulfide was selected as the substrate. One substrate was fixed as the bottom substrate and the other was a movable top substrate. Liquid water droplets were added to the surface of the bottom substrate. The top substrate was moved slowly and precisely downward by piezoelectric ceramics to reduce the spacing between the substrates to 40 nm, which forced the excess water molecules to be discharged. The remaining water and the substrate formed a substrate-water-substrate sandwich structure, and the substrate also had a protective function.
[0039] (2) A flexible corrugated pipe is used to seal the periphery of the substrate, and the temperature control component outside the substrate is controlled to heat the substrate to 500 K for 10 min, so that the heat is conducted to the water molecules between the layers, ensuring that the water molecules are in the range where they can change to gas.
[0040] (3) By controlling the top substrate to be far away from the bottom substrate through piezoelectric ceramics, the distance between the upper and lower substrate layers is 100 nm, and the water molecules expand, resulting in a decrease in density.
[0041] (4) Liquid nitrogen was injected into the temperature control component outside the substrate to rapidly freeze the substrate for 10 minutes, and water molecules in the interlayer formed nanowires and angstrom chains. Example 2
[0042] (1) Select nickel as the substrate, one as the bottom substrate and the other as the movable top substrate. Add sodium chloride powder crystals to the surface of the bottom substrate and heat to 1100 K.
[0043] (2) By precisely driving the top substrate with piezoelectric ceramics, the spacing between the substrates is reduced to 40nm, which forces the excess sodium chloride to be discharged. The remaining sodium chloride forms a substrate-sodium chloride-substrate sandwich structure with the substrate, and the substrate also has a protective function.
[0044] (3) A flexible corrugated pipe is used to seal the periphery of the substrate, and the temperature control component outside the substrate is controlled to heat the substrate to 1750 K for 10 min, so that the heat is transferred to the sodium chloride between the layers.
[0045] (4) By controlling the top substrate to be far away from the bottom substrate through piezoelectric ceramics, the spacing between the upper and lower substrate layers is 100 nm, and the sodium chloride expands, resulting in a decrease in density.
[0046] (5) Liquid nitrogen was injected into the temperature control component outside the substrate to rapidly freeze the substrate for 10 minutes, and sodium chloride formed nanowires and angstrom chains in the interlayer. Example
[0047] (1) Select nickel as the substrate, one as the bottom substrate and the other as the movable top substrate. Add sodium chloride powder crystals to the surface of the bottom substrate and heat to 1100 K.
[0048] (2) By precisely driving the top substrate with piezoelectric ceramics, the spacing between the substrates is reduced to 40nm, which forces the excess sodium chloride to be discharged. The remaining sodium chloride forms a substrate-sodium chloride-substrate sandwich structure with the substrate, and the substrate also has a protective function.
[0049] (3) A flexible corrugated pipe is used to seal the periphery of the substrate, and the temperature control component outside the substrate is controlled to heat the substrate to 2000 K for 10 min, so that the heat is transferred to the sodium chloride between the layers.
[0050] (4) By controlling the top substrate to be far away from the bottom substrate through piezoelectric ceramics, the spacing between the upper and lower substrate layers is 100 nm, and the sodium chloride expands, resulting in a decrease in density.
[0051] (5) Liquid nitrogen was injected into the temperature control component outside the substrate to rapidly freeze the substrate for 10 minutes, and sodium chloride formed nanowires and angstrom chains in the interlayer. Example 3
[0052] (1) Select nickel as the substrate, one as the bottom substrate and the other as the movable top substrate. Add sodium chloride powder crystals to the surface of the bottom substrate and heat to 1100 K.
[0053] (2) By precisely driving the top substrate with piezoelectric ceramics, the spacing between the substrates is reduced to 50nm, which forces the excess sodium chloride to be discharged. The remaining sodium chloride forms a substrate-sodium chloride-substrate sandwich structure with the substrate, and the substrate also has a protective function.
[0054] (3) A flexible corrugated pipe is used to seal the periphery of the substrate, and the temperature control component outside the substrate is controlled to heat the substrate to 2000 K for 10 min, so that the heat is transferred to the sodium chloride between the layers.
[0055] (4) By controlling the top substrate to be far away from the bottom substrate through piezoelectric ceramics, the spacing between the upper and lower substrate layers is 200 nm, and the sodium chloride expands, resulting in a decrease in density.
[0056] (5) Liquid nitrogen was injected into the temperature control component outside the substrate to rapidly freeze the substrate for 10 minutes, and sodium chloride formed nanowires and angstrom chains in the interlayer.
[0057] The applicant declares that the detailed process equipment and process flow of this invention are illustrated through the above embodiments, but this invention is not limited to the above detailed process equipment and process flow, that is, it does not mean that this invention must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the products of this invention, additions of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.
Claims
1. Preparation of nanowires and angstroms by extrusion-stretching-freezing method, comprising the following steps: (1) Select a material with atomic-level flatness, chemical inertness and appropriate affinity for polar molecules and ionic compounds as a substrate. One substrate is used as the bottom substrate and the other is used as a movable top substrate. Polar molecules and ionic compounds are used as precursors. The precursors are placed on the surface of the bottom substrate and the other substrate is placed on top of the precursors. The temperature is controlled to process the precursors into a plastic state. The top substrate is moved slowly and accurately downward by piezoelectric ceramics to reduce the spacing between the substrates and force the excess precursors to be discharged. The remaining precursors and the substrate form a substrate-precursor-substrate sandwich structure. The substrate also has a protective function. (2) Use flexible corrugated pipe to seal the periphery of the substrate, control the temperature control component outside the substrate to heat the base, and conduct the heat to the precursor between the layers. The time should be sufficient to ensure that the temperature of the precursor is within the range where it can change to gaseous state or can move sufficiently. (3) Controlling the top base away from the bottom base, the expansion of the precursor between the upper and lower base layers leads to a decrease in density; (4) The temperature control components outside the substrate are controlled to rapidly freeze the substrate, and the interlayer precursors form nanowires and angstroms. The substrate-nanowire / angstrom chain-substrate sandwich structure exists stably and can be used for observation and application after being taken out.
2. The preparation method according to claim 1, characterized in that, The substrate selection in step (1) includes graphene, hexagonal boron nitride, molybdenum disulfide, mica, silicon, sapphire, and metal.
3. The preparation method according to claim 1, characterized in that, The thickness of the precursor in the substrate-precursor-substrate step (1) is on the order of angstroms or nanometers.
4. The preparation method according to claim 1, characterized in that, The temperature reached in step (2) must be higher than the boiling point of the precursor but lower than the melting point of the substrate. The heating process can be carried out slowly.
5. The preparation method according to claim 1, characterized in that, In step (3), the distance between the upper and lower substrate layers is 10-1000 nm, and the precursor density must not be less than one-tenth of its normal state.
6. The preparation method according to claim 1, characterized in that, The freezing temperature in step (4) is controlled at 1-150K, and the cooling process must be completed quickly within a short time. For salts with higher melting points, the freezing temperature can be extended to 1-300K.