High-hardness and high-stability mesogenic aluminum and preparation method thereof

Abstract

The present application relates to a kind of high stability high hardness mesogenic aluminum and its electro-deposition preparation method.The mesogenic aluminum of columnar mesogenic composition prepared by the present application, mesogenic is composed of single nanometer scale aluminum nanocrystalline phase and ionic liquid organic phase, and the nanocrystalline aluminum in columnar mesogenic is close to single crystal orientation.The electro-deposition preparation process of mesogenic aluminum uses the ionic liquid prepared by [BMIM]Cl and AlCl3, and adds the additive methyl nicotinate containing strong electron-withdrawing group, further can be converted into crystal aluminum by adjusting pulse current parameter, and the layered structure composite material containing crystal and mesogenic is prepared by electro-deposition method.Because the electro-deposition preparation method prepared by the mesogenic aluminum coating surface is bright, has hardness up to 2.3GPa and thermal stability up to 320 DEG C (0.63T m ) 0.63T ), the hardness of the mesogenic aluminum is more than seven times higher than that of coarse-grained aluminum, and can be used to replace coarse-grained aluminum coating, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of mesocrystalline metal preparation technology, specifically to a high-hardness, high-stability mesocrystalline aluminum material and its preparation method. Background Technology

[0002] Mesocrystalline materials are unique nanostructures formed from nanocrystals (also known as nanocrystals) through a mineralization-like process, resulting in crystallographically ordered superstructures. Their structural sizes range from 100 nanometers to micrometers, and they typically exhibit single-crystal-like electron diffraction behavior. The synthesis of mesocrystalline materials often involves the extensive use of polymers and surfactants. The aggregation of nanocrystals inevitably generates numerous interstitial spaces, which typically result in mesocrystalline materials with a large specific surface area and high porosity. These pores can be filled with additives and amorphous substances. Therefore, mesocrystalline materials often exhibit unique single-crystal structures and rich nanocrystal matrix-organic interfaces. Mesocrystalline structures are not only widely found in natural minerals, such as pearls and sea urchin teeth, but can also be artificially synthesized for specific applications. Due to their unique structure, such as high internal porosity, small basic units, single-crystal structure, and high crystal defect rate, mesocrystalline materials have wide applications in catalysis, sensing, and optical devices. For example, titanium dioxide mesocrystalline materials, due to their high crystallinity and large specific surface area, possess excellent photocatalytic performance. Furthermore, mesocrystalline materials possess excellent mechanical properties. The interfacial interactions between the organic and inorganic matrices, such as covalent bonds, complex formation, and electrostatic interactions at high-density interfaces, significantly contribute to the material's strength. The extremely fine-interfaced organic-inorganic interface of mesocrystalline materials holds promise for overcoming instability at the single nanoscale and achieving high hardness.

[0003] Methods for preparing mesomorphs mainly include coprecipitation, solvothermal methods, topological transformation methods, dissolution-recrystallization methods, and electrochemical methods. Currently reported mesomorphs primarily focus on salts and metal oxides; pure metal mesomorphs are less common and concentrated in noble metal systems such as Au and Ag, and are all prepared via chemical reduction methods. For example, Heilongjiang University solved the problems of obtaining three-dimensional superlattices and controlling solvent evaporation in existing template-based self-assembled colloidal crystal methods by using organic reduction of noble metal salts, providing a method for preparing noble metal self-assembled colloidal crystals (application number: CN201010207251.9). Fang et al. synthesized two-dimensional single-crystal silver mesomorphs with dimensions of approximately 5-20 mm and a thickness of 70 nm using a simple, non-organic substitution-free reaction system Sn / AgNO3(aq.) (Reference 1: JXFang, BJDing and XPSong, Appl. Phys. Lett., 2007, 91, 083108).

[0004] For electrochemical methods used to prepare mesocrystalline materials, current reports focus on oxide mesocrystalline materials. The main principle is that the anode metal loses electrons to obtain metal ions, while the cathode hydrogen ions lose electrons to obtain hydroxide ions, forming mesocrystalline materials through a precipitation reaction. Electrodeposition, as an electrochemical method, follows the traditional crystallization process. Currently, electrodeposition technology can only form metal materials with polycrystalline structures, which are completely different from mesocrystalline structures. There are currently no reports on the preparation of mesocrystalline pure metals using electrodeposition. Existing methods for preparing pure metal mesocrystalline materials are inefficient and struggle to form mesocrystalline structures with large areas and good surface finishes, making industrialization difficult in fields such as catalysis. Summary of the Invention

[0005] The present invention aims to provide a high-hardness and high-stability mesocrystalline aluminum and its preparation method. The method utilizes electrodeposition to prepare a pure metallic material with a mesocrystalline structure. The resulting mesocrystalline aluminum consists of columnar mesocrystalline phases, which are composed of single-nanoscale aluminum nanocrystalline phases and an ionic liquid organic phase. The nanocrystalline aluminum within the columnar mesocrystalline phases exhibits near-single-crystal orientation, and the low-index facets at the nanocrystalline-organic interface account for more than 50% of the area. These low-index facets are {111}, {100}, and {110}. The ionic liquid accounts for 18%-28% of the volume, and the nanocrystalline-organic interface is dominated by the low-index facets of aluminum. The prepared mesocrystalline aluminum coating has a bright surface, a hardness of up to 2.3 GPa, and a thermal stability of up to 320℃ (0.63 Tm). This preparation method offers advantages such as simplicity, high efficiency, high controllability, and ease of industrialization.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A high-hardness, high-stability mesocrystalline aluminum is disclosed, composed of columnar mesocrystalline phases. These columnar mesocrystalline phases consist of a single-nanoscale nanocrystalline aluminum phase and an ionic liquid organic phase. The nanocrystalline aluminum within the columnar mesocrystalline phases exhibits near-single-crystal orientation, and the low-index facets of the nanocrystalline-organic interface account for more than 50% of the area. The short axis of the columnar mesocrystalline phase is on the order of hundreds of nanometers, and the long axis is on the order of micrometers. The average grain size of the nanocrystalline aluminum is 4.4-6.4 nm. The ionic liquid organic phase is derived from [BMIM]. + AlCl4 － Al2Cl7 － The plating solution uses ionic liquids containing methyl nicotinate, and the organic phase of the ionic liquid accounts for approximately 18%-28% of the volume of the mesocrystalline material. The low-index surfaces of the nanocrystalline-organic interface are {111}, {100}, and {110}. Mesocrystalline aluminum exhibits a hardness of 2.3 GPa and high thermal stability, maintaining its structural dimensions unchanged after annealing at 320°C (0.63 Tm, where Tm is the melting point of aluminum).

[0008] A method for preparing mesocrystalline aluminum according to the present invention is characterized by comprising the following steps: (1) preparing an electroplating solution, wherein the plating solution is a mixture of [BMIM]Cl and AlCl3, then subjected to electrolytic treatment, filtered, and then methyl nicotinate additive is added to obtain an ionic liquid plating solution.

[0009] (2) High-purity aluminum is used as the anode and polycrystalline copper is used as the cathode.

[0010] (3) Place the anode and cathode in the mesocrystalline aluminum electroplating solution prepared in step (1), connect the electrochemical workstation, and electrodeposit mesocrystalline aluminum on the cathode substrate. When using direct current electrodeposition, the current density of direct current electrodeposition is 5 mA-30 mA / cm². 2 Alternatively, when pulsed electrodeposition is used, a single pulsed electrodeposition cycle is divided into two parts: a negative current deposition segment and a positive current deposition segment. The current density in the negative current deposition segment is 10-30 mA / cm². 2 Furthermore, when the time is less than 0.1 s, the deposition positive current is 0.5 mA / cm. 2 The deposition time for the positive current segment should be less than 10 times that for the negative current segment. When the negative current segment is greater than 0.1s, the time for the positive current segment should be greater than 10 times that for the negative current segment. When the time for the negative current segment is greater than 1s, there is no requirement for the time for the positive current segment.

[0011] The concentration of methyl nicotinic acid was 6-10 mmol / L. The positive current range was 0.5 mA / cm. 2 The deposition time for the positive current segment is less than 10 times that for the negative current segment. The positive current can vary within the range of 0.1-2 mA, and the corresponding time changes negatively with the positive current segment. Furthermore, the charge in the positive current segment is less than that in the negative current segment. The molar ratio of [BMIM]Cl to AlCl3 is greater than 1:1 and less than 1:2. Before polycrystalline aluminum is used as the cathode, it needs to undergo pretreatment operations, which include: the pretreatment of the cathode copper substrate includes grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning, and drying. The electrolytic polishing solution is: phosphoric acid: alcohol: water = 1:1:2, the electropolishing temperature is room temperature, and the electropolishing time is 30s. In step (3), the plating solution temperature is room temperature, and the stirring speed is 300-500r / min.

[0012] A method for converting mesocrystalline aluminum into crystalline aluminum according to the present invention includes the following steps: (1) preparing an electroplating solution, wherein the plating solution is a mixture of [BMIM]Cl and AlCl3, and then subjected to electrolytic treatment, filtered, and then methyl nicotinate additive is added to obtain an ionic liquid plating solution; (2) using high-purity aluminum as the anode and polycrystalline copper as the cathode; (3) placing the anode and cathode in the electroplating solution prepared in step (1), connecting an electrochemical workstation, selecting a pulse current deposition mode, and setting the pulse electrodeposition single-cycle deposition to a negative current section with a current density of less than -10 mA / cm. 2The time is less than 0.1s; the positive current range is 0.5mA / cm. 2 The time is in the range of 0.1s-2s; the zero current segment is 0mA / cm. 2 The time is greater than 1 second. The concentration of methyl nicotinic acid is 6-10 mmol / L. The positive current range is 0.5 mA / cm. 2 The time ranges from 0.1s to 2s, during which the positive current can vary from 0.1 to 2mA. The corresponding time changes negatively with the positive current segment, and the amount of charge in the positive current segment is less than that in the negative current segment.

[0013] A method for preparing a composite material containing alternating layered structures of mesocrystalline aluminum and crystalline aluminum as described in this invention using pulsed current electrodeposition technology, the method comprising the following steps: (1) preparing an electroplating solution, wherein the plating solution is a mixture of [BMIM]Cl and AlCl3, then subjected to electrolytic treatment, and then filtered and methyl nicotinic acid additive is added; (2) using high-purity aluminum as the anode and polycrystalline copper as the cathode; (3) placing the anode and cathode in the electroplating solution prepared in step (1), connecting to an electrochemical workstation, and using pulsed current electrodeposition, wherein the pulsed current electrodeposition for forming the crystalline layer is set to a negative current section with a current density of less than -10 mA / cm². 2 The time is less than 0.1s, and the current density in the positive current section is 0.5mA / cm². 2 The time is in the range of 0.1s to 2s, and the zero current is 0mA / cm. 2 The time is greater than 1 second; the electrodeposition of the mesocrystalline layer is set to DC stage B, 5-30 mA / cm 2 Combining multiple cycles of pulsed current single-cycle A and DC electrodeposition B into a composite electrodeposition single-cycle C, and repeating this electrodeposition single-cycle C multiple times, yields a composite material containing alternating layered structures of mesocrystalline aluminum and crystalline aluminum. The positive current range is 0.5 mA / cm². 2 The deposition time ranges from 0.1s to 2s, with the positive current varying from 0.1 to 2mA. The time corresponding to this positive current segment is negatively correlated with the positive current segment, and the charge in the positive current segment is less than that in the negative current segment. Crystalline aluminum deposition is a pulsed deposition process. The pulse single-cycle parameter A and the number of cycles can be set according to the required single-layer crystal thickness based on Coulomb's law. During mesocrystalline aluminum deposition, the current density and time of DC deposition B can be set according to the required crystal layer thickness based on Coulomb's law. The sample thickness is controlled by the number of cycles in electrodeposition C according to Coulomb's law. The deposition order of mesocrystalline layers obtained by DC deposition or crystalline layers obtained by pulse deposition can be interchanged. The concentration of methyl nicotinic acid is 6-10 mmol / L.

[0014] Technical effects of the present invention:

[0015] 1. The mesocrystalline aluminum material of this invention is composed of columnar mesocrystalline phases, which consist of single-nanoscale aluminum nanocrystalline phases and ionic liquid organic phases. The nanocrystalline aluminum within the columnar mesocrystalline phases exhibits near-single-crystal orientation, and the low-index surface area of ​​aluminum at the nanocrystalline-organic interface accounts for more than 50%, such as {111}, {100}, and {110}. The volume percentage of the ionic liquid is 18%-28%, and the nanocrystalline-organic interface is predominantly composed of low-index aluminum surfaces. This microstructure fully conforms to the standards for mesocrystalline materials. The pure aluminum material with a mesocrystalline structure of this invention exhibits superior performance compared to nanocrystalline aluminum and coarse-grained aluminum. Specifically, in terms of hardness, the mesocrystalline aluminum prepared by DC electrodeposition has a hardness value of 2.3 GPa, while the highest reported hardness for nanocrystalline aluminum is 1.7 GPa, and for coarse-grained aluminum is 0.3 GPa. In terms of stability, mesocrystalline aluminum has a thermal stability of up to 320℃ (0.63Tm, Tm: melting point of aluminum), while nanocrystalline aluminum and coarse-grained aluminum are both below 0.5Tm.

[0016] 2. The method for preparing mesocrystalline aluminum in this invention utilizes an electrodeposition process, which offers advantages such as strong controllability and ease of industrialization. It is not only simple and low-cost, but also yields large-area, brightly coated mesocrystalline aluminum. Compared to other pure metal mesocrystalline preparation processes, it has higher preparation efficiency and greater controllability over the mesocrystalline layer. The additives added during the electrodeposition process contain electron-withdrawing groups (-C=O, -C=N-), which are easily adsorbed on the cathode. Furthermore, the additives cannot be desorbed from the surface, thus promoting the formation of a mesocrystalline structure during DC electrodeposition. When a pulsed current is used, the positive current segment promotes the desorption of the additives. As time progresses, the structure spontaneously adjusts, and the structural dimensions change. Further extending the zero-current segment allows the nanocrystals in the mesocrystalline structure to fully fuse and mature, forming crystals.

[0017] 3. The process for controlling the crystal structure of mesocrystalline aluminum in this invention can be used to prepare high-purity crystalline aluminum coatings with the same strong preferred orientation as mesocrystalline materials. Furthermore, this method of controlling the transformation can be used to prepare composite materials with a layered structure that mixes mesocrystalline and crystalline materials. The thickness of each layer of mesocrystalline and crystalline materials can be controlled by bidirectional pulsed current and the time ratio of the DC segment, which broadens the types of coating structures. Moreover, the coating has a coupling between crystalline and mesocrystalline structures, allowing for the design of different crystalline and mesocrystalline layer thicknesses and different compositional forms according to performance requirements. Attached Figure Description

[0018] Figure 1 The image shows the low-magnification microstructure of mesocrystalline aluminum in Example 1; where: (a) is a bright-field image of the surface of the mesocrystalline aluminum, and (b) is a bright-field image of the cross-section of the mesocrystalline aluminum.

[0019] Figure 2The high-magnification microstructure and energy spectrum characterization of mesocrystalline aluminum in Example 1 are shown below: (a) is the bright field image inside the columnar mesocrystalline aluminum, (b) is the nanobeam diffraction result corresponding to the position in (a), (c) is the orientation distribution map of mesocrystalline aluminum, (d) is the HAADF image of mesocrystalline aluminum, and (e) is the energy spectrum distribution map corresponding to the 2d image.

[0020] Figure 3 Example 1: Size evolution and DSC analysis of mesocrystalline aluminum nanocrystalline phase annealed structure; where: (a) shows the change in grain size with annealing temperature, and (b) DSC curves of the mesocrystalline aluminum sample and ionic liquid.

[0021] Figure 4 This is a high-resolution representation of the mesocrystalline nanocrystalline aluminum phase-organic phase interface structure of Example 1; wherein:

[0022] a is the high-resolution result of the

[110] band, with low-index surfaces {111}, {200}, and {220}, and b is... Figure 4 a is the Fourier transform plot; c is the high-resolution result with the

[100] axis, whose low exponent surfaces are {220} and {200}. d is... Figure 4 Fourier transform of c.

[0023] Figure 5 Example 2 shows the mesocrystalline aluminum structure and hardness; where: (a) is a bright-field image of mesocrystalline aluminum with an average nanocrystalline aluminum size of 6.4±1.5 nm, and (b) shows the relationship between the hardness of the mesocrystalline structure and the average size of the nanocrystalline aluminum phase.

[0024] Figure 6 The microstructure and energy dispersive spectral characterization of mesocrystalline aluminum before and after the transformation to crystalline aluminum in Example 3 are shown in (a) for the surface morphology of the mesocrystalline structure, (b) for the bright field image of the mesocrystalline structure, (c) and (d) for the HAADF diagram and corresponding energy dispersive spectral distribution of the mesocrystalline aluminum, respectively, (e) for the surface structure of the crystalline aluminum, (f) for the bright field image of the crystalline aluminum, and (g) and (h) for the HAADF diagram and corresponding energy dispersive spectral distribution of the crystalline aluminum, respectively.

[0025] Figure 7 XRD characterization of mesocrystalline aluminum and its transformation into crystalline aluminum in Example 3.

[0026] Figure 8 The morphology and energy spectrum of the mesocrystalline and crystalline aluminum layered composite material in Example 4 are shown below; where: (a) is the bright field image of the composite material, (b) and (c) are the energy spectrum distribution maps of Al and Cl elements, respectively, and (d) and (e) are the line distribution maps of Al and Cl elements, respectively. Detailed Implementation

[0027] The above solution will be further explained below with reference to the specific accompanying drawings and embodiments.

[0028] Example 1:

[0029] This embodiment describes the preparation of mesocrystalline aluminum containing nanocrystals with an average size of approximately 4.4 nm using direct current electrolytic deposition technology. The preparation process includes the following steps:

[0030] (1) Preparation of mesocrystalline aluminum electroplating solution: Weigh [BMIM]Cl and AlCl3 in a molar ratio greater than 1:1 and less than 1:2. Slowly sprinkle AlCl3 powder into [BMIM]Cl, then perform electrolysis treatment, and finally filter with glass filter paper to obtain the basic plating solution. Add 6-10 mmol of methyl nicotinate as an additive.

[0031] (2) The anode is a pure aluminum plate with a purity of 99.999%. The pretreatment of the cathode copper substrate includes grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning and drying. The electrolytic polishing solution is: phosphoric acid: alcohol: water = 1:1:2 (mass ratio), the electropolishing temperature is room temperature, and the electropolishing time is 30s.

[0032] (3) Electrodeposition preparation parameters: The plating solution temperature in step (1) is room temperature, the stirring speed is 600 r / min, and the DC electrodeposition current density is 10 mA / cm². 2 .

[0033] Figure 1 This is a bright-field image of mesocrystalline material at low magnification. Figure 1 (a) shows a planar structure with a bright-dark contrast region size of approximately 200 nm. Figure 1 (b) shows a bright-field image along the cross-section, with columnar brightness contrast and a long axis greater than 1 μm. Combining the surface and cross-sectional morphology, it can be seen that the mesomorphic crystals are columnar.

[0034] Figure 2 (a) is a bright-field image of the internal structure of the mesocrystalline structure in the plane direction of the sample. The size of the nanocrystals that make up the mesocrystalline structure is 4.4 ± 1.1 nm.

[0035] Figure 2 (b) for Figure 2 (a) shows the results of nanobeam diffraction analysis at four locations. The adjacent nanocrystals are oriented similarly, all along the

[100] zone axis. The diffraction spots on the {200} plane along the upper left and lower right directions form angles of 44.2°, 44°, 49.8°, and 47.9° with the vertical direction, respectively. This indicates that the nanocrystals in the adjacent region have small angular differences.

[0036] like Figure 2 The orientation distribution diagram shown in c indicates that the

[100] zone axis is present in the range of hundreds of nanometers.

[0037] Figure 2d is a high-magnification HAADF image, which has the same structural features as the bright-field image, namely, it is composed of nanocrystals.

[0038] Figure 2 e is a pair Figure 2 The results of energy dispersive spectroscopy analysis at position d show that the mesocrystalline structure consists of two phases: one is a nanocrystalline pure aluminum phase, and the other is a chlorine-containing organic phase.

[0039] Figure 3 a shows the grain size changes of mesocrystalline aluminum samples after annealing at different temperatures (250℃, 300℃, 350℃, 400℃, and 600℃) for 30 minutes. The nanocrystal size of mesocrystalline aluminum did not change when annealed below 320℃ (0.63Tm, Tm: aluminum melting point), but the structure began to coarsen as the temperature increased.

[0040] Figure 3 b shows the DSC analysis results of the mesocrystalline aluminum sample and the ionic liquid. The DSC curves indicate that the endothermic peak of the mesocrystalline aluminum is similar to the endothermic peak of the ionic liquid decomposition, meaning that the mesocrystalline aluminum contains an ionic liquid with a similar organic phase composition. [BMIM] + AlCl4 － Al2Cl7 － And methyl nicotinic acid.

[0041] Figure 4 The results show the high-resolution characterization of the nanocrystalline aluminum phase-organic phase interface structure. In the nanocrystalline aluminum phase-organic phase interface, the low-index surface area accounts for more than 50%.

[0042] Figure 4 a represents the high-resolution result of the

[110] band axis, with low-index surfaces {111}, {200}, and {220}. Figure 4 c is the high-resolution result of the

[100] axis, and its low-index surface is {220}, {200}.

[0043] Based on Faraday's law, the volume percentage of the organic phase was calculated to be approximately 18%-28% using the electrolysis, deposition charge, and sample weight data in Table 1 below.

[0044] Table 1

[0045]

[0046] The Vickers microhardness test of the sample showed a hardness of 2.3 GPa, which is much higher than the 0.3 GPa of coarse-grained aluminum.

[0047] Example 2:

[0048] This embodiment describes the preparation of mesocrystalline aluminum containing nanocrystals with an average size of approximately 6.4 nm using pulsed electrolytic deposition technology. The preparation process includes the following steps:

[0049] (1) Preparation of mesocrystalline aluminum plating solution: Weigh [BMIM]Cl and AlCl3 in a molar ratio greater than 1:1 and less than 1:2. Slowly sprinkle AlCl3 powder into [BMIM]Cl, then perform electrolysis treatment, and finally filter with glass filter paper to obtain the basic plating solution. Finally, add about 8 mmol of methyl nicotinic acid as an additive.

[0050] (2) The anode is a pure aluminum plate with a purity of 99.999%. The pretreatment of the cathode copper substrate includes grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning and drying. The electrolytic polishing solution is: phosphoric acid: alcohol: water = 1:1:2 (mass ratio), the electropolishing temperature is room temperature, and the electropolishing time is 30s.

[0051] (3) Electrodeposition preparation parameters: The plating bath temperature in step (1) is room temperature, the stirring speed is 600 r / min, and the single-cycle negative current segment of the pulse current is -5 mA / cm. 2 (0.1s), positive current range is 0.5mA / cm 2 (0.4s).

[0052] Figure 5 a is the bright-field image of the sample. According to the contrast of the bright-field image, the nanocrystals have the same orientation and their morphology is basically the same as that of the mesocrystalline aluminum characterized in detail in Example 1, indicating that it is also a mesocrystalline structure. The difference is that the size of the nanocrystalline aluminum in this example is 6.4±1.5nm.

[0053] Figure 5 b shows that the Vickers microhardness test of the sample yielded a hardness of 1.9 GPa. The hardness of the mesocrystalline aluminum sample decreased to some extent compared with Example 1. This is because the hardness of the mesocrystalline structure is also related to the size. The hardness decreases as the size of the nanocrystals increases. Moreover, the strengthening effect of the nanocrystalline aluminum-organic interface in the mesocrystalline structure is comparable to the strengthening effect of the grain boundary.

[0054] Example 3:

[0055] This embodiment describes a method for converting mesocrystalline aluminum into crystalline aluminum using pulsed current electrolytic deposition technology. The method includes the following steps:

[0056] (1) Preparation of mesocrystalline aluminum plating solution: Weigh [BMIM]Cl and AlCl3 in a molar ratio greater than 1:1 and less than 1:2. Slowly sprinkle AlCl3 powder into [BMIM]Cl, then perform electrolysis treatment, and finally filter with glass filter paper to obtain the basic plating solution. Finally, add about 8 mmol of methyl nicotinic acid as an additive.

[0057] (2) The anode is a pure aluminum plate with a purity of 99.999%. The pretreatment of the cathode copper substrate includes grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning and drying. The electrolytic polishing solution is: phosphoric acid: alcohol: water = 1:1:2, the electropolishing temperature is room temperature and the electropolishing time is 30s.

[0058] (3) Electrodeposition preparation parameters: The plating bath temperature in step (1) is room temperature, the stirring speed is 600 r / min, and the negative current range for single-cycle pulse electrodeposition is -5 mA / cm. 2 0.1s, positive current range is 0.5mA / cm 2 0.4s, zero current segment 0mA / cm 2 , 2s.

[0059] Figure 6 a represents the surface morphology of a mesocrystalline structure, which has a smooth surface and is composed of tiny nanocrystals.

[0060] Figure 6 b is the bright-field image of the mesocrystalline aluminum sample, which is similar to that in Example 1. Figure 1 The structures are basically the same, consisting of nanocrystalline aluminum phases with consistent contrast (or orientation) over a large range.

[0061] Figure 6 c and 6d are the HAADF of the sample and the corresponding energy dispersive spectroscopy (EDS) results are the same as those in Example 1, and the sample is composed of nanocrystalline aluminum phase and chlorine-containing organic phase.

[0062] Figure 6 e represents the electrodeposition surface morphology of crystalline aluminum. This crystalline aluminum is derived from a mesocrystalline structure. Figure 6 The key step in the electrodeposition process of the mesocrystalline material described in Examples a, b, c, and d is the positive current segment of 0.5 mA / cm. 2 The 0.4s period allows the methyl nicotinic acid additive to desorb from the surface of the electrodeposited aluminum cathode, losing its surface constraint and stabilizing effect, which allows the structure to be adjusted. At this time, it is still a mesocrystalline structure. By utilizing the long zero current period of 2s, the nanocrystalline aluminum phase of the mesocrystalline structure is fully fused and matured, causing the mesocrystalline structure to completely disappear and form a crystalline structure.

[0063] Figure 6 The bright-field image of crystalline aluminum (f) shows that it has a traditional ultrafine grain structure with an average grain size of approximately 420 nm.

[0064] Figure 6 g and 6h are the results of HAADF crystallized aluminum and the corresponding energy dispersive spectroscopy surface scan. The purity is high with only a small amount of residual aluminum impurities.

[0065] Figure 7The XRD results of the mesocrystalline aluminum (Example 1) sample and the sample that was transformed into crystalline aluminum during the electrodeposition process show that they have the same strong {200} preferred orientation.

[0066] Example 4:

[0067] This embodiment describes the preparation of a composite material containing alternating layered structures of crystalline and mesocrystalline aluminum using pulsed current electrolytic deposition technology. The method includes the following steps:

[0068] (1) Preparation of plating solution: Weigh [BMIM]Cl and AlCl3 in a molar ratio greater than 1:1 and less than 1:2. Slowly sprinkle AlCl3 powder into [BMIM]Cl, then perform electrolysis treatment, and finally filter with glass filter paper to obtain the basic plating solution. Finally, add about 8 mmol of methyl nicotinic acid as an additive.

[0069] (2) The anode is a pure aluminum plate with a purity of 99.999%. The pretreatment of the cathode copper substrate includes grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning and drying. The electrolytic polishing solution is: phosphoric acid: alcohol: water = 1:1:2, the electropolishing temperature is room temperature and the electropolishing time is 30s.

[0070] (3) Electrodeposition preparation parameters: The plating bath temperature in step (1) is room temperature, the stirring speed is 600 r / min, and the pulse electrodeposition single-cycle deposition A is set to a negative current range of -10 mA / cm. 2 0.1s, zero current segment is 0mA / cm 2 0.393s, positive current range is 50mA / cm 2 0.007s, zero current segment is 0mA / cm 2 After repeating these four stages for 107 cycles, the DC stage B begins, at -10 mA / cm. 2 The 107 pulse cycles A and the 14.5s DC segment B mentioned here constitute a single electrodeposition cycle C. Repeating this cycle C will yield a structure in which crystals and mesocrystalline layers are arranged alternately.

[0071] Figure 8 Image a is a bright-field image of the composite material of crystalline and mesocrystalline aluminum layered structure, with the positions of the crystalline and mesocrystalline layers marked in the image. The crystalline layer has no obvious features and uniform contrast, while the mesocrystalline layer is quite different, with obvious particle contrast, and the size of each layer is about 50 nm.

[0072] Figure 8 b, 8c, 8d, 8e are the surface and line scan results of the energy dispersive spectroscopy for this sample, respectively. Figure 7 The analysis is consistent because Cl, as a marker element that distinguishes between crystalline and mesocrystalline layers, is distributed in distinct alternating layers, with the layer thickness of both structures being approximately 50 nm.

[0073] Crystalline aluminum deposition is a pulse deposition process. The pulse single-cycle parameters and number of cycles can be set according to the thickness requirements. During the deposition of mesocrystalline aluminum layers, the DC deposition current density and time can be set according to the thickness requirements of the crystal layer. Its approximate thickness can be calculated according to Faraday's law.

[0074] The stability experiment was conducted in a differential scanning calorimeter. The stability experiment consisted of two parts: one was isothermal annealing at different temperatures for 30 min, and the other was DSC testing of mesocrystalline aluminum samples and ionic liquids. The heating rate during the DSC testing process was 20 K / min.

[0075] The hardness test was performed using a Qness Q10 A+ Vickers hardness tester with a measurement load of 25g and a loading time of 10s.

Claims

1. A method for converting mesocrystalline aluminum into crystalline aluminum, characterized in that, The method includes the following steps: (1) Prepare the electroplating solution. The plating solution is made by mixing [BMIM]Cl and AlCl3, then electrolyzing it, filtering it, and adding the additive methyl nicotinate to obtain the ionic liquid plating solution. (2) High-purity aluminum is used as the anode and polycrystalline copper is used as the cathode. (3) Place the anode and cathode in the electroplating solution prepared in step (1), connect the electrochemical workstation, and use pulsed current deposition. The pulsed electrodeposition single-cycle deposition is set to a negative current section with a current density of less than -10 mA / cm². 2 The time is less than 0.1s; the current density in the positive current section is 0.5 mA / cm². 2 The time is in the range of 0.1s-2s; the zero current segment is when the current density is 0 mA / cm². 2 The time is greater than 1 second.

2. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 1, characterized in that: The mesocrystalline aluminum is composed of columnar mesocrystalline phases, which are composed of a single nanoscale nanocrystalline aluminum phase and an ionic liquid organic phase, and the area ratio of the low-index surface of the nanocrystalline-organic interface is greater than 50%.

3. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 2, characterized in that: The columnar mesocrystalline phase has a short axis length in the hundreds of nanometers and a long axis length in the micrometers; the average grain size of the nanocrystalline aluminum phase is 4.4-6.4 nm; the nanocrystalline aluminum within the columnar mesocrystalline phase is single-crystal oriented.

4. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 2, characterized in that: The organic phase of the ionic liquid is derived from [BMIM]. + AlCl4 － Al2Cl7 － The ionic liquid plating solution contains methyl nicotinate, and the volume percentage of the organic phase in the mesocrystalline material is 18%-28%; the low-index surfaces of the nanocrystal-organic interface are {111}, {100}, and {110}.

5. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 1, characterized in that: The method for preparing the mesocrystalline aluminum includes the following steps: (1) Preparation of electroplating solution: First, mix [BMIM]Cl and AlCl3, then perform electrolysis, filter and add methyl nicotinic acid additive to obtain ionic liquid plating solution; (2) High-purity aluminum is used as the anode and polycrystalline copper is used as the cathode; (3) Place the anode and cathode in the electroplating solution prepared in step (1), connect the electrochemical workstation, and electrodeposit mesocrystalline aluminum on the cathode substrate; wherein: when using DC electrodeposition, the current density is 5-30 mA / cm 2 When pulsed electrodeposition is used, a single pulsed electrodeposition cycle is divided into two parts: a negative current deposition segment and a positive current deposition segment. The current density in the negative current deposition segment is 10-30 mA / cm². 2 Furthermore, when the time is less than 0.1 s, the deposition positive current is 0.5 mA / cm. 2 The deposition time for the positive current segment should be less than 10 times that for the negative current segment. When the negative current segment is greater than 0.1s, the time for the positive current segment should be greater than 10 times that for the negative current segment. When the time for the negative current segment is greater than 1s, there is no requirement for the time for the positive current segment.

6. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 5, characterized in that: In step (1), the concentration of methyl nicotinate in the electroplating solution is 6-10 mmol / L; when [BMIM]Cl and AlCl3 are mixed, the molar ratio of [BMIM]Cl to AlCl3 is greater than 1:1 and less than 1:

2.

7. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 5, characterized in that: In step (2), before polycrystalline copper is used as the cathode, it needs to undergo pretreatment operations, which include grinding, electrolytic polishing, ultrasonic cleaning, deionized water cleaning and drying of the polycrystalline copper substrate in sequence; the electrolytic polishing solution used for electrolytic polishing of the polycrystalline copper substrate is a mixture of phosphoric acid, alcohol and water in a ratio of 1:1:2, the electrolytic polishing temperature is room temperature and the electrolytic polishing time is 30s.

8. The method for converting mesocrystalline aluminum into crystalline aluminum according to claim 5, characterized in that: In step (3), the current density in the positive current section is 0.5 mA / cm². 2 The deposition time for the positive current segment is less than 10 times that for the negative current segment. The positive current can vary within the range of 0.1-2mA, and the corresponding time changes negatively with the positive current segment. Furthermore, the amount of charge in the positive current segment is less than that in the negative current segment. In step (3), the plating solution temperature is room temperature, and the stirring speed is 300-500 r / min.

9. A method for preparing a composite material with alternating layered structures of mesocrystalline aluminum and crystalline aluminum using pulsed current electrodeposition technology, characterized in that, The method includes the following steps: (1) Prepare the electroplating solution, which consists of [BMIM]Cl and AlCl. 3 Mix, then electrolyze, then filter and add methyl nicotinic acid as an additive; (2) High-purity aluminum is used as the anode and polycrystalline copper is used as the cathode; (3) Place the anode and cathode in the electroplating solution prepared in step (1), connect them to an electrochemical workstation, and use pulse electrodeposition. The pulse electrodeposition single-cycle A deposition for forming the crystal layer is set to a negative current density of less than -10 mA / cm². 2 The time is less than 0.1s, and the current density in the positive current section is 0.5mA / cm². 2 The time is in the range of 0.1s to 2s, and the zero current is 0mA / cm. 2 The time is greater than 1 second; the electrodeposition of the mesocrystalline layer is set to DC stage B, 5-30 mA / cm 2 By combining multiple cycles of pulsed current single-cycle A and DC electrodeposition B into a composite structure electrodeposition single-cycle C, and repeating the operation of this electrodeposition single-cycle C multiple times, a composite material containing alternating layered structures of mesocrystalline aluminum and crystalline aluminum can be obtained.

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