A thermoelectrically enhanced modified porous oxide film aluminum strand and a method of making

Abstract

This invention discloses a thermoelectrically enhanced modified porous oxide film aluminum stranded wire and its preparation method. The aluminum stranded wire includes an aluminum stranded wire substrate, a nanoscale porous oxide film grown in situ on the surface of the outer layer of aluminum monofilaments, and a surface modification layer formed on the surface of the nanoscale porous oxide film. The method includes pretreatment of the aluminum stranded wire; detection and adjustment of the pH, conductivity, and Al content of the electrolyte. 3+ The concentration of the electrolyte is adjusted to keep it within a preset reuse window. Aluminum stranded wire is then subjected to constant-current anodic oxidation in the electrolyte to form a nanoscale porous oxide film. Subsequent surface modification and post-treatment yield thermoelectrically enhanced modified porous oxide film aluminum stranded wire. This invention improves the consistency of the nanoporous oxide film structure by controlling electrolyte state parameters and adjusts the surface state of the porous oxide film through surface modification. This allows the resulting aluminum stranded wire to maintain the resistance per unit length and minimum breaking force required for overhead conductors while exhibiting lower high-current temperature rise and higher corona initiation voltage.

Description

Technical Field

[0001] This invention relates to the field of surface functionalization modification technology for overhead power transmission conductors, specifically to a thermoelectrically enhanced modified porous oxide film aluminum stranded wire and its preparation method. Background Technology

[0002] Overhead transmission aluminum stranded conductors must simultaneously meet multiple service requirements during long-term operation, including conductivity, heat dissipation, corona control, and mechanical load-bearing capacity. As transmission capacity increases, the current flowing through the conductors rises, making the temperature rise of the aluminum stranded conductors under high-current conditions more pronounced. Higher operating temperatures not only increase line losses but may also accelerate the aging of conductors and hardware connections, affecting the long-term safe operation of the transmission line. Furthermore, overhead transmission conductors are also susceptible to corona discharge under high-voltage operating conditions. Burrs, local defects, or rough, uneven areas on the conductor surface can easily cause local electric field distortion, making the air near the conductor more prone to ionization, thereby reducing the corona initiation voltage. Corona discharge leads to problems such as energy loss, electromagnetic interference, and audible noise.

[0003] To improve the service performance of overhead transmission conductors, existing technologies include surface modification methods such as coatings, plating, and chemical treatments. External coatings can alter the conductor's surface condition to some extent, but their adhesion to the metal substrate typically relies on physical bonding or interfacial bonding. Under long-term service conditions such as wind vibration, rain erosion, dust abrasion, and temperature cycling, they are prone to cracking, peeling, or localized failure. Some coatings may also affect the conductor's conductivity, heat dissipation, or mechanical load-bearing capacity. Therefore, improving the thermal-electrical service performance of aluminum stranded wire remains a problem to be solved.

[0004] Anodizing is an electrochemical treatment method that forms an oxide film in situ on the surface of aluminum and aluminum alloys. Anodizing can form a tightly bonded alumina film on the aluminum substrate surface, and can further form a nanoscale porous oxide film. Compared with simple external coatings, the porous oxide film formed by anodizing originates from in-situ growth on the aluminum substrate surface and has better interfacial bonding stability. This porous oxide film can change the oxidation state and micro / nano rough morphology of the aluminum stranded wire surface, which is beneficial to improving surface heat dissipation conditions and may reduce the adverse effects of local sharp defects on the electric field distribution, thereby improving the high-current heat dissipation capacity and corona initiation voltage of the aluminum stranded wire.

[0005] However, existing anodizing research largely focuses on flat aluminum plates, sheets, or other regular aluminum substrates. Overhead power transmission aluminum stranded wires are typically composed of multiple layers of aluminum monofilaments spirally twisted together, exhibiting surface undulations, grooves, and curvature variations. Their surface morphology, current distribution, and mass transfer conditions differ significantly from those of flat aluminum plates. Current technologies primarily focus on the morphology, anti-icing properties, corrosion resistance, and wettability of porous oxide films, neglecting the comprehensive impact of porous oxide film-coated aluminum stranded wires on key service performance aspects such as high-current temperature rise, corona initiation voltage, resistance per unit length, and minimum breaking force. Therefore, a surface-modified porous oxide film structure and its preparation method suitable for overhead power transmission aluminum stranded wires are still needed, enabling them to maintain conductivity and mechanical load-bearing properties while achieving enhanced heat dissipation and increased corona initiation voltage. Summary of the Invention

[0006] In view of the above-mentioned problems in the existing technology, the technical problem to be solved by the present invention is that the existing surface modification methods for overhead power transmission aluminum stranded wires are difficult to stably construct porous oxide films and surface modification layers under the condition of continuous reuse of electrolyte.

[0007] To address the aforementioned technical problems, this invention provides a thermoelectrically enhanced modified porous oxide film aluminum stranded wire and its preparation method. The porous oxide film aluminum stranded wire comprises an aluminum stranded wire substrate, a porous oxide film in situ grown on the surface of an outer layer of aluminum monofilaments of the aluminum stranded wire substrate, and a surface modification layer formed on the surface of the porous oxide film. The porous oxide film covers the outer surface of the aluminum stranded wire and has a nanoscale porous structure. This porous oxide film originates from the in-situ anodic oxidation reaction on the surface of the outer layer of aluminum monofilaments of the aluminum stranded wire, and has a tight bond with the aluminum stranded wire substrate, which can change the oxidation state and micro / nano roughness morphology of the aluminum stranded wire surface. The surface modification layer is bonded to the surface of the nanoscale porous oxide film and is used to adjust the chemical state and surface structural stability of the porous oxide film surface, while retaining the micro / nano roughness morphology of the porous oxide film without significantly covering the nanopore structure. The combined effect of the porous oxide film and its surface modification layer is beneficial to improving the heat dissipation performance of the aluminum stranded wire under high current conditions and reducing local electric field distortion on the surface, thereby increasing the corona initiation voltage of the aluminum stranded wire. The resulting hot-spot-enhanced modified porous oxide film aluminum stranded wire exhibits a lower temperature rise under high current conditions than the untreated aluminum stranded wire, and a higher corona initiation voltage than the untreated aluminum stranded wire.

[0008] Furthermore, the porous oxide film is an aluminum oxide film layer formed by anodic oxidation. The porous oxide film has a pore wall structure and a channel structure. The pore wall structure and the channel structure together constitute the micro / nano rough morphology of the outer surface of the aluminum stranded wire.

[0009] Furthermore, the surface modification layer is formed by a silane-based modifier. Preferably, the silane-based modifier is heptadecafluorodecyltriethoxysilane. After the surface modification layer is formed, the porous oxide film still maintains its nanoscale pore structure.

[0010] Furthermore, the surface temperature of the porous oxide film aluminum stranded wire is lower than that of the untreated aluminum stranded wire under the same high current carrying conditions, and the corona initiation voltage of the porous oxide film aluminum stranded wire is higher than that of the untreated aluminum stranded wire.

[0011] Furthermore, the unit length resistance and minimum breaking force of the porous oxide film aluminum stranded wire meet the requirements of GB / T1179-2017 "Circular Wire Concentric Stranded Overhead Conductor".

[0012] A method for preparing thermoelectrically enhanced modified porous oxide film aluminum stranded wire includes the following steps:

[0013] S1: Preprocessing

[0014] Aluminum stranded wire is placed in an alkaline solution for degreasing and alkaline washing to remove oil stains and natural oxide layer from the surface of the aluminum stranded wire; then it is ultrasonically cleaned with deionized water to remove residual alkaline solution and reaction products from the surface; after cleaning, it is dried for later use.

[0015] Preferably, the alkaline solution is a 0.8-1.2 mol / L NaOH solution, the alkaline washing time is 4-6 min, the ultrasonic cleaning time is 8-12 min, the drying temperature is 80-110 ℃, and the drying time is 0.5-1.5 h. The concentration of the NaOH solution can be selected from 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, or 1.2 mol / L; the alkaline washing time can be selected from 4 min, 5 min, or 6 min; the ultrasonic cleaning time can be selected from 8 min, 10 min, or 12 min; the drying temperature can be selected from 80 ℃, 90 ℃, 100 ℃, or 110 ℃; and the drying time can be selected from 1 h, 1.2 h, or 1.5 h.

[0016] More preferably, the alkaline solution is a 1 mol / L NaOH solution, the alkaline washing time is 5 min; the ultrasonic cleaning time is 10 min; the drying temperature is 90 ℃, and the drying time is 1 h.

[0017] S2: Electrolyte state parameter detection and control

[0018] During continuous reuse of the electrolyte, the pH, conductivity, and Al content of the electrolyte were measured. 3+ Concentration, and the pH, conductivity and Al 3+ Concentration is used as a parameter for electrolyte reuse status.

[0019] When the electrolyte reuse state parameters are within the preset reuse state window, the electrolyte is used for subsequent constant current anodizing. When at least one of the electrolyte reuse state parameters deviates from the preset reuse state window, the electrolyte state is adjusted by one or more of the following methods: adding fresh electrolyte, partially replacing the electrolyte, re-preparing the electrolyte, or mixing the fresh electrolyte with the reused electrolyte, so that the electrolyte meets the requirements of subsequent constant current anodizing.

[0020] Preferably, the preset reuse state window is: pH 1.283-1.308, conductivity 26.8-28.7 mS / cm, Al 3+ Concentration: 322–523 mg / L. The pH can be 1.283, 1.288, 1.293, 1.298, 1.303, or 1.308; the conductivity can be selected as 26.8 mS / cm, 27.3 mS / cm, 27.8 mS / cm, 28.3 mS / cm, or 28.7 mS / cm; Al 3+ The concentration can be selected as 322 mg / L, 372 mg / L, 422 mg / L, 472 mg / L or 523 mg / L.

[0021] S3: Constant current anodizing

[0022] The pretreated aluminum stranded wire is placed in an electrolyte that has been judged or regulated by S2 for anodic oxidation treatment, forming a nano-scale porous oxide film in situ on the surface of the outer aluminum monofilament of the aluminum stranded wire.

[0023] Preferably, the electrolyte is a phosphoric acid solution with a concentration of 0.2-0.5 mol / L, more preferably 0.3 mol / L.

[0024] Preferably, the anodizing is constant current anodizing, with an anodizing current density of 0.092–0.166 A / cm², an oxidation time of 5–30 min, and an electrolyte temperature of 10–25 °C. Specifically, the current density can be 0.092 A / cm², 0.129 A / cm², or 0.166 A / cm²; the oxidation time can be 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min; and the electrolyte temperature can be 10 °C, 15 °C, 18 °C, 20 °C, or 25 °C.

[0025] More preferably, the anodic oxidation current density is 0.129 A / cm², the oxidation time is 20 min, and the electrolyte temperature is 15 °C.

[0026] S4: Washing and Drying

[0027] The anodized aluminum stranded wire is removed, the residual electrolyte on its surface is cleaned, and then it is dried to obtain an aluminum stranded wire with a porous oxide film on its surface.

[0028] Preferably, the anodized aluminum stranded wire is ultrasonically cleaned with deionized water and then dried at 80-110 °C.

[0029] S5: Surface Finishing

[0030] After being cleaned and dried by S4, the aluminum stranded wire with a porous oxide film on its surface is placed in a surface modification solution for modification, so that the modification molecules are combined with the surface of the nano-porous oxide film to form a surface modification layer.

[0031] Preferably, the surface modification solution is a silane-based modification solution. More preferably, the surface modification solution is a 5-15 wt.% heptadecafluorodecyltriethoxysilane ethanol solution, and even more preferably a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution.

[0032] Preferably, the surface modification is performed by immersion or vacuum immersion, and the modification time is 4-8 hours, more preferably 6 hours.

[0033] S6: Post-processing

[0034] The aluminum stranded wire modified by S5 is taken out and dried or cured to obtain thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0035] Preferably, the post-treatment temperature is 90-110 ℃ and the treatment time is 1-2 h.

[0036] In this invention, the electrolyte reuse state parameters, constant current anodic oxidation current density, and oxidation time are not independent process factors. The constant current anodic oxidation current density mainly determines the charge input intensity per unit area and the field-induced oxidation film formation rate, while the oxidation time mainly determines the duration of charge input and the degree of oxide film growth accumulation; the electrolyte pH, conductivity, and Al... 3+ Concentration affects the electrolyte's conductivity, interfacial chemical dissolution, and the voltage response required to maintain constant current. With continuous reuse of the electrolyte, pH, conductivity, and Al concentration all influence its properties. 3+ Concentration drift can alter the field-induced film formation and chemical dissolution equilibrium on the aluminum stranded wire surface, even when the constant current density and oxidation time remain constant, thus affecting the nanopore size, porosity, and film thickness. Therefore, this invention improves the consistency of nanopore structure construction on the surface of consecutive batches of aluminum stranded wires by controlling the electrolyte reuse state parameters within a preset window to match the constant current anodic oxidation current density and oxidation time.

[0037] The porous oxide film aluminum stranded wire prepared by the above method has an in-situ grown nanoscale porous oxide film on the surface of the outer aluminum monofilament, and a surface modification layer is formed on the surface of the porous oxide film. This porous oxide film, on the one hand, alters the oxidation state and micro / nano rough morphology of the aluminum stranded wire surface, which is beneficial for improving the heat transfer conditions of the aluminum stranded wire surface, resulting in a lower temperature rise under high current conditions; on the other hand, the porous oxide film covering the outer surface of the aluminum stranded wire helps to improve surface micro-defects and local electric field distribution, giving the aluminum stranded wire a higher corona initiation voltage. Simultaneously, the surface modification layer, combined with the nanoscale porous oxide film surface, helps to regulate the surface chemical state and improve surface structural stability, enabling the resulting aluminum stranded wire to achieve more stable thermoelectric performance while maintaining the nanoporous rough structure. Furthermore, since the porous oxide film is formed in-situ grown on the surface of the outer aluminum monofilament, it has minimal impact on the overall conductivity and mechanical load-bearing capacity of the aluminum stranded wire, ensuring that the resistance per unit length and minimum breaking force of the resulting aluminum stranded wire meet the requirements for overhead conductors.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) This invention constructs a nanoscale porous oxide film in situ on the surface of the outer aluminum monofilament of an aluminum stranded wire by controlling the state parameters of the electrolyte. Specifically, this invention uses pH, conductivity, and Al... 3+ Concentration, as a state parameter for electrolyte reuse, is used to determine and regulate acidity, conductivity, and aluminum ion accumulation during continuous electrolyte reuse, thereby reducing the impact of electrolyte state drift on the pore size, porosity, and film thickness consistency of the porous oxide film. This improves the construction stability of the nanoscale porous oxide film on the surface of aluminum stranded wire and provides a structural basis for the uniform formation of subsequent surface modification layers.

[0040] (2) This invention forms an in-situ porous oxide film on the outer surface of aluminum stranded wire through constant current anodizing, which differs from simple external coatings. This porous oxide film originates from the in-situ reaction on the surface of the aluminum substrate and has a tighter bond with the outer aluminum monofilament of the aluminum stranded wire, unlike external coatings which mainly rely on physical adhesion. This improves the bonding stability between the surface modification layer and the aluminum stranded wire substrate, which is beneficial to improving the problems of cracking, peeling, or local failure of existing external coatings during long-term service.

[0041] (3) This invention alters the oxidation state and micro / nano rough morphology of the aluminum stranded wire surface through a porous oxide film, and adjusts the chemical state and structural stability of the porous oxide film surface through a surface modification layer. The porous oxide film and its surface modification layer work together to improve the heat transfer conditions of the aluminum stranded wire surface, which is beneficial to improving the heat dissipation capacity of the aluminum stranded wire surface, enabling the aluminum stranded wire to have a lower temperature rise under high current or overload operation conditions, thereby alleviating the problem of high temperature rise of existing aluminum stranded wires under high current operation.

[0042] (4) By forming an in-situ porous oxide film and its surface modification layer on the outer surface of the aluminum stranded wire, the present invention can improve the microstructure of the aluminum stranded wire surface and reduce the electric field distortion caused by local sharp defects, burrs or uneven areas. This can reduce the degree of local electric field concentration on the surface of the conductor, increase the corona initiation voltage of the aluminum stranded wire under high voltage operating conditions, and thus alleviate the problem of corona discharge caused by local electric field distortion on the surface of existing aluminum stranded wires.

[0043] (5) The thermoelectrically enhanced modified porous oxide film aluminum stranded wire obtained by this invention can still meet the requirements for use in overhead conductors while achieving enhanced heat dissipation and improved corona initiation voltage. This is because the porous oxide film is mainly formed on the surface of the outer aluminum monofilament of the aluminum stranded wire, and the surface modification layer is combined with the surface of the nano-porous oxide film, without changing the main conductive and load-bearing structures of the aluminum stranded wire. Therefore, this invention can improve the thermoelectric service performance of the conductor while taking into account both conductivity and mechanical load-bearing performance, and is suitable for the surface functional modification of overhead transmission line conductors. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the aluminum stranded wire substrate structure.

[0045] Figure 2 This is a schematic diagram of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire structure.

[0046] Figure 3 A schematic diagram of the process for preparing thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0047] Figure 4 The surface nanopore structure morphology of thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0048] Figure 5 A cross-sectional morphology diagram of the porous oxide film on a thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0049] Figure 6 The images show the nanopore morphology of aluminum stranded wire modified with a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution. Figure 6 (a) is a scanning electron microscope image of the modified nanopore morphology; Figure 6 (b) is the energy spectrum elemental analysis of this region.

[0050] Figure 7 Figure 1 shows the temperature rise test results of untreated aluminum stranded wire and thermoelectrically enhanced modified porous oxide film aluminum stranded wire under different current flow conditions.

[0051] Figure 8 The graph shows the corona initiation voltage test results for untreated aluminum stranded wire and thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0052] Figure 9 Figure 1 shows the conductor breaking force test results for untreated aluminum stranded wire and thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0053] Figure 10 Figure 1 shows the test results of the conductivity of untreated aluminum stranded wire and thermoelectrically enhanced modified porous oxide film aluminum stranded wire. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. All equivalent substitutions or transformations made using the inventive concept should fall within the scope of protection of the present invention.

[0055] Example 1

[0056] This embodiment provides a thermoelectrically enhanced modified porous oxide film aluminum stranded wire and its preparation method. The aluminum stranded wire used is JL / LB20A-240 / 30 aluminum-clad steel core aluminum stranded wire for 220 kV overhead lines. The aluminum stranded wire adopts a "24+7" stranding structure, with an outer layer of aluminum monofilaments and an inner layer of aluminum-clad steel core, and an overall diameter of 21.6 mm. Its structural schematic is shown below. Figure 1 As shown.

[0057] The preparation method of this embodiment includes the following steps:

[0058] (1) Pretreatment

[0059] A 0.5 m long aluminum stranded wire sample was cut, and both ends of the aluminum stranded wire were covered with insulating material to ensure that the effective contact length with the electrolyte was 0.4 m. The aluminum stranded wire sample was then placed in a 1 mol / L NaOH solution for 5 min to remove surface oil and the natural oxide layer; after alkali washing, it was ultrasonically cleaned in deionized water for 10 min to remove residual alkali and reaction products; after cleaning, the sample was placed in a 90 ℃ forced-air drying oven for 1 h to dry.

[0060] (3) Electrolyte state parameter detection and control

[0061] A 0.3 mol / L phosphoric acid solution was prepared as the electrolyte. Before anodizing each batch of aluminum stranded wire, the pH, conductivity, and Al content of the electrolyte were measured. 3+ Concentration, and pH, conductivity and Al 3+ Concentration is used as a parameter for electrolyte reuse status.

[0062] In this embodiment, the preset reuse state window is: pH 1.283-1.308, conductivity 26.8-28.7 mS / cm, Al 3+Concentration 322–523 mg / L. When the electrolyte reuse state parameters are within the above window, the electrolyte is used for subsequent constant current anodic oxidation; when at least one of the electrolyte reuse state parameters deviates from the above window, the electrolyte state is adjusted by adding fresh electrolyte, partially replacing the electrolyte, re-preparing the electrolyte, or mixing the fresh electrolyte with the reused electrolyte until its pH, conductivity, and Al are within the specified range. 3+ The concentration returned to the range mentioned above.

[0063] By adjusting the electrolyte state parameters as described above, the acidity, conductivity, and Al content during continuous reuse of the electrolyte can be reduced. 3+ The cumulative state changes affect the constant current anodic oxidation voltage response, field-induced oxidation film formation, and interfacial chemical dissolution equilibrium, thus providing conditions for the subsequent formation of nanoscale porous oxide films with relatively stable pore size, porosity, and film thickness.

[0064] (4) Constant current anodizing

[0065] The pretreated aluminum stranded wire was placed in the phosphoric acid electrolyte, which had been judged or regulated in step (2), for constant current anodizing. During the anodizing process, the aluminum stranded wire was used as the anode, and the ring cathode was used as the cathode. A cold water circulation system was used to control the temperature and stir the electrolyte. The electrolyte temperature was controlled at 15 ℃, the anodizing current density was 0.129 A / cm², and the anodizing time was 20 min.

[0066] Under the above conditions, the electrolyte state parameters, current density, oxidation time and electrolyte temperature are matched with each other, which is conducive to maintaining a relatively stable dynamic balance between field-induced oxidation film formation on the surface of aluminum stranded wire and chemical dissolution process of acidic electrolyte, thereby forming a nano-scale porous oxide film in situ on the surface of the outer aluminum monofilament of aluminum stranded wire.

[0067] (4) Cleaning and drying

[0068] After anodizing, the aluminum stranded wire sample was taken out and ultrasonically cleaned in deionized water for 15 min to remove residual electrolyte on the surface; then it was dried in a 90 ℃ forced-air drying oven for 1 h to obtain aluminum stranded wire with a porous oxide film on the surface.

[0069] The structural diagram of the resulting porous oxide film aluminum stranded wire is shown below. Figure 2 As shown, the preparation process is as follows: Figure 3 As shown. Scanning electron microscopy revealed that a nanoscale porous oxide film formed on the surface of the outer aluminum monofilaments of the aluminum stranded wire, such as... Figure 4 As shown; its cross-sectional morphology is as follows Figure 5As shown, the oxide film is tightly bonded to the aluminum substrate, with a thickness on the micrometer scale and a porous structure distributed along the film growth direction. This porous oxide film, covering the outer surface of the aluminum stranded wire, can alter the oxidation state and micro / nano roughness morphology of the aluminum stranded wire surface.

[0070] (5) Surface finishing

[0071] The aluminum stranded wire with porous oxide film obtained in step (4) was placed in a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution for vacuum impregnation modification for 6 h, so that silane modification molecules were combined with the surface of the nano-porous oxide film to form a surface modification layer.

[0072] (6) Post-processing

[0073] The modified aluminum stranded wire from step (5) was taken out and dried in a 110 ℃ forced-air drying oven for 1 h to obtain thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0074] Scanning electron microscopy revealed that the modified aluminum stranded wire surface retained its nanoscale porous structure, with no obvious blockage or coverage of the nanopores by the modification layer. Figure 6 As shown, the surface modification layer can be bonded to the surface of the nanoscale porous oxide film while retaining the micro / nano rough morphology provided by the porous oxide film. This structure is beneficial for regulating the surface chemical state and surface structural stability of the aluminum stranded wire, and works together with the in-situ porous oxide film to enable the aluminum stranded wire to have a lower temperature rise under high current conditions and a higher corona initiation voltage under high voltage conditions.

[0075] Comparative Example 1

[0076] This comparative example uses JL / LB20A-240 / 30 aluminum-clad steel-core stranded wire of the same model and length as in Example 1, but without anodizing treatment. It is used as an untreated aluminum stranded wire sample to compare its performance with the porous oxide film aluminum stranded wire prepared in Example 1 in terms of high current temperature rise, corona initiation voltage, resistance per unit length, and minimum breaking force.

[0077] Comparative Example 2

[0078] This comparative example is basically the same as Example 1, except that the pH, conductivity, and Al of the electrolyte are not adjusted during the anodizing process. 3+ Instead of using the concentration to determine and control the reuse state window, the electrolyte is continuously reused to directly perform constant current anodic oxidation.

[0079] During continuous anodizing, as the number of experimental batches increases, the H⁺ in the electrolyte is gradually consumed, and Al... 3+As the concentration gradually increases, the conductivity gradually decreases, and the average voltage required to maintain constant current anodizing increases accordingly. When the electrolyte state deviates from the suitable reuse state, the consistency of the nanopore structure on the aluminum stranded wire surface decreases, manifested as a decrease in the average pore size and porosity of the nanopores, an increase in the oxide film thickness, or local pore wall instability. This indicates that in the preparation of thermoelectrically enhanced modified porous oxide film aluminum stranded wires, parameter control of the electrolyte reuse state is beneficial to improving the stability of the nanopore structure and the consistency of subsequent surface modification.

[0080] Comparative Example 3

[0081] This comparative example illustrates the effect of surface modification solution concentration on the retention of nanoscale porous oxide film structure and surface modification effect. This comparative example is basically the same as Example 1, except that the surface modification solution concentration in step (5) is adjusted to 5 wt.% and 15 wt.% heptadecafluorodecyltriethoxysilane ethanol solution, respectively. Other pretreatment, electrolyte state parameter control, constant current anodic oxidation, cleaning and drying, modification time, and post-treatment conditions are the same as in Example 1.

[0082] When the concentration of the heptadecafluorodecyltriethoxysilane ethanol solution is 5 wt.%, the number of silane molecules in the modification solution that can participate in hydrolysis condensation and surface bonding is relatively small, making it difficult to form a sufficiently continuous low surface energy modification layer on the surface of the nanoscale porous oxide film. At this time, there may be insufficiently modified areas on the pore walls, pore openings, and local depressions of the porous oxide film, resulting in insufficient regulation of the chemical state of the oxide film surface and relatively limited improvement in surface structure stability and thermoelectric service performance.

[0083] When the concentration of the heptadecafluorodecyltriethoxysilane ethanol solution is 15 wt.%, the concentration of silane molecules in the modification solution is relatively high, making hydrolysis-condensation reactions more likely to occur in the solution or in localized areas on the pore surface. Excess silane molecules may self-condense and form siloxane aggregates or a thicker organic modification layer, leading to accumulation of the modification layer at the pore openings, walls, or channels of the nanopores. This poses a risk of partially covering, filling, or blocking the nanopore structure. If the nanopore structure is significantly covered, it will weaken the original micro / nano rough morphology and pore structure advantages of the porous oxide film, which is detrimental to maintaining the surface heat transfer conditions and improved local electric field distribution provided by the porous oxide film.

[0084] In contrast, when the concentration of the heptadecafluorodecyltriethoxysilane ethanol solution is 10 wt.%, the concentration of silane molecules in the modification solution is moderate. This is beneficial for forming a sufficient surface modification layer on the surface of the nanoscale porous oxide film, while avoiding significant coverage or blockage of the nanopore structure due to excessive silane condensation. Figure 6It can be seen that after modification with a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution, the surface of the aluminum stranded wire still maintains a relatively clear nanoporous structure, indicating that this concentration condition is conducive to forming a surface modification layer while preserving the micro / nano rough morphology of the porous oxide film. Therefore, this invention preferably uses a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution to modify the porous oxide film on the aluminum stranded wire.

[0085] Comparative Example 4

[0086] This embodiment illustrates the effect of electrolyte temperature on the growth of nanoporous structures during constant current anodizing of aluminum stranded wire.

[0087] During constant-current anodizing, electrolyte temperature simultaneously affects electrolyte conductivity, ion migration rate, interfacial chemical dissolution rate, and oxide film formation rate. For the formation of porous oxide films on aluminum stranded wire surfaces, the growth of nanoporous structures essentially depends on the dynamic balance between field-induced oxidation and acidic electrolyte chemical dissolution. In constant-current mode, the applied current density remains constant, and the power supply maintains the set current by adjusting the voltage. Therefore, when the electrolyte temperature changes, although the input current density remains the same, the electrolyte conductivity, ion migration resistance, and interfacial reaction rate will change, thereby altering the actual voltage response and film growth state.

[0088] When the electrolyte temperature is low, below 10 °C, the ion migration ability in the electrolyte decreases, the interfacial reaction rate slows down, and both oxide film formation and pore bottom dissolution processes are inhibited. At this temperature, the growth of the porous oxide film on the surface of the aluminum stranded wire is slow, the opening of the nanopores is insufficient, and the pore walls are relatively thick, which easily leads to problems such as insufficient pore formation or inadequate pore structure development.

[0089] When the electrolyte temperature is raised to a suitable range of 10–25 °C, the ion migration capacity and interfacial reaction rate in the electrolyte are enhanced, and the field-induced oxidation film formation and chemical dissolution can be better matched. Under these conditions, the oxide film formation rate and the dissolution rate at the pore walls and bottom are in a relatively stable dynamic equilibrium, which is conducive to the formation of nanoscale porous oxide film structures with thinner pore walls, larger pore sizes, and higher porosity.

[0090] When the electrolyte temperature exceeds 25 °C, the chemical dissolution effect of the acidic electrolyte on the alumina film is significantly enhanced. Simultaneously, local Joule heating and interfacial reaction heat accumulate more easily, leading to an imbalance between pore wall dissolution, pore expansion, and film growth. At this point, the aluminum stranded wire surface is prone to phenomena such as localized overgrowth, pore wall collapse, abnormal film thickening, or uneven surface morphology, which are detrimental to obtaining a stable and uniform nanoporous structure. Especially for complex substrates like aluminum stranded wire with helical stranding structures, inter-strand grooves, and curvature variations, the local mass transfer and heat dissipation conditions inherently differ. Excessively high temperatures further amplify the reaction differences between different locations, thereby reducing the consistency of the nanoporous structure.

[0091] Therefore, in this invention, electrolyte temperature is not a single variable independent of electrolyte reuse state parameters, current density, and oxidation time. Electrolyte temperature affects the electrolyte's conductivity and interfacial reaction rate; current density determines the charge input intensity per unit area; oxidation time determines the degree of oxide film growth and accumulation; while pH, conductivity, and Al... 3+ Concentration reflects the acidity, conductivity, and aluminum ion accumulation state of the electrolyte during continuous reuse. These factors collectively determine the dynamic balance between field-induced oxidation film formation and chemical dissolution on the aluminum stranded wire surface.

[0092] Comparative Example 5

[0093] This comparative example illustrates the influence of constant current anodic oxidation current density and oxidation time on the formation of nanoscale porous oxide film structures, and further explains why the present invention preferably uses a current density of 0.129 A / cm² and an oxidation time of 20 min. This comparative example is essentially the same as Example 1, except that: under the condition that the electrolyte reuse state parameters are within a preset reuse state window, constant current anodic oxidation is performed using lower current densities, higher current densities, shorter oxidation times, or longer oxidation times, respectively, to analyze the influence of current density and oxidation time deviating from the preferred matching relationship on the porous oxide film structure.

[0094] During constant-current anodizing, current density determines the charge input intensity per unit area on the aluminum stranded wire surface and the field-induced oxidation film formation rate, while oxidation time determines the duration of charge input and the degree of oxide film growth and accumulation. Both factors jointly influence the alumina film formation rate, the dissolution rate of the oxide film by the acidic electrolyte, and the evolution of the nanopore walls, orifices, and bottom regions. For the nanoporous structure on the aluminum stranded wire surface, only when field-induced oxidation film formation and interfacial chemical dissolution are in a relatively matched dynamic equilibrium state is it conducive to forming a porous oxide film structure with thinner pore walls, larger pore sizes, and higher porosity.

[0095] When the current density is below 0.092 A / cm² or the oxidation time is less than 5 min, the amount of charge input to the surface of the aluminum stranded wire per unit time is insufficient, resulting in slow field-induced oxidation film formation and pore expansion. At this time, the oxide film is still mainly in the initial formation or micropore development stage, with insufficient pore opening, relatively thick pore walls, and the nanoporous structure has not yet fully formed. If subsequent surface modification is carried out in this state, although the modifying molecules can adhere to the surface, due to insufficient pore size, porosity, and micro / nano roughness, it is difficult to fully utilize the improving effect of the porous oxide film on surface heat transfer conditions and local electric field distribution.

[0096] When the current density exceeds 0.166 A / cm² or the oxidation time exceeds 30 min, excessive charge input per unit area or prolonged reaction accumulation time accelerates oxide film formation and pore expansion. However, it also enhances local electric field effects, Joule heat accumulation, and interfacial chemical dissolution effects. At this point, the nanopore walls are prone to over-dissolution, local collapse, or fibrous aggregation, and the originally regular nanopore structure may be covered by irregular overgrown structures. If such structures continue to undergo surface modification, the modified layer is prone to uneven deposition in areas of local depressions, collapsed pore walls, or irregular aggregation, which is detrimental to maintaining stable micro / nano rough morphology and weakens surface heat transfer and local electric field homogenization effects.

[0097] In contrast, when the constant current anodizing current density is 0.129 A / cm² and the oxidation time is 20 min, the charge input intensity and reaction duration are well matched. On the one hand, this current density can provide sufficient field-induced oxidation driving force to allow the porous oxide film to grow fully; on the other hand, the 20 min oxidation time allows the nanoporous structure to develop to a relatively stable stage, without causing large-area collapse of the pore walls or overgrowth due to excessive reaction time. Under these conditions, it is easier to form a nanoscale porous oxide film structure with thinner pore walls, larger pore size, higher porosity, and more uniform distribution on the surface of aluminum stranded wire.

[0098] Therefore, this invention preferably employs a constant current anodizing current density of 0.129 A / cm² and an oxidation time of 20 min, and matches these parameters with the electrolyte reuse window, electrolyte temperature, and subsequent surface modification conditions. This parameter combination facilitates the formation of a stable nanoscale porous oxide film on the aluminum stranded wire surface, providing a structural basis for the uniform bonding of subsequent surface modification layers, and further contributing to obtaining thermoelectrically enhanced modified porous oxide film aluminum stranded wires with lower high-current temperature rise, higher corona initiation voltage, and maintained conductivity and mechanical properties.

[0099] Experimental Example 1: Observation of Nanopore Structure and Modified Morphology

[0100] The aluminum stranded wire after anodizing and the aluminum stranded wire after surface modification in Example 1 were observed by scanning electron microscopy. Figure 4This image shows the morphology of the nanopore structure on the surface of anodized aluminum stranded wire. Figure 5 This is a cross-sectional morphology image of the porous oxide film on the surface of the anodized aluminum stranded wire. Figure 6 The image shows the morphology of the nanoporous structure on the surface of aluminum stranded wire modified with a 10 wt.% heptadecafluorodecyltriethoxysilane ethanol solution.

[0101] Depend on Figure 4 and Figure 5 It can be seen that after electrolyte state parameter regulation and constant current anodizing, a nano-scale porous oxide film is formed on the surface of the outer aluminum monofilament of the aluminum stranded wire, and the oxide film is tightly bonded to the aluminum substrate. Figure 6 It can be seen that after modification with heptadecafluorodecyltriethoxysilane ethanol solution, the surface of the aluminum stranded wire still maintains a clear nanoporous structure, indicating that the surface modification layer did not significantly block or cover the nanoporous structure. This result shows that the present invention can introduce a surface modification layer while retaining the micro / nano rough morphology of the nano-porous oxide film, thereby obtaining thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

[0102] Test Example 2: High Current Temperature Rise Performance Test

[0103] The thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared in Example 1 and the untreated aluminum stranded wire in Comparative Example 1 were subjected to high-current temperature rise tests. The test currents were set sequentially to 300 A, 400 A, 500 A, 600 A, and 700 A, and the stable surface temperature of the samples under different current conditions was recorded. The test results are as follows: Figure 7 As shown.

[0104] Depend on Figure 7 It can be seen that as the current increases from 300 A to 700 A, the surface temperature of both types of aluminum stranded wires gradually increases. However, under the same current conditions, the surface temperature of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared in Example 1 is always lower than that of the untreated aluminum stranded wire. The test results show that under the conditions of 300 A, 400 A, 500 A, 600 A, and 700 A, the surface temperature of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire is reduced by 2.07 ℃, 3.97 ℃, 6.74 ℃, 6.61 ℃, and 10.77 ℃ compared with the untreated aluminum stranded wire, respectively; when the current is 700 A, the surface temperature of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire is 71.55 ℃, and the surface temperature of the untreated aluminum stranded wire is 82.32 ℃.

[0105] The above results indicate that the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared by this invention exhibits a lower temperature rise under high current conditions. This may be because the in-situ porous oxide film and its surface modification layer together alter the oxidation state, micro / nano roughness morphology, and surface chemical state of the aluminum stranded wire surface, which is beneficial for improving the heat transfer conditions of the aluminum stranded wire surface, thus enabling it to exhibit better heat dissipation performance under the same current conditions.

[0106] Experimental Example 3: Corona Induction Voltage Test

[0107] The corona characteristics of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared in Example 1 and the untreated aluminum stranded wire in Comparative Example 1 were tested. The number of corona photons under different applied voltages was recorded using ultraviolet imaging, and a photon count greater than 100 was used as the criterion for significant corona initiation. The test results are as follows: Figure 8 As shown.

[0108] Depend on Figure 8 It can be seen that no obvious corona signal was observed in either type of aluminum stranded wire when the applied voltage was low; as the voltage increased, the number of corona photons gradually increased. The corona initiation voltage of the untreated aluminum stranded wire was between 64 and 66 kV, while the corona initiation voltage of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire was between 68 and 69 kV.

[0109] The above results indicate that the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared by this invention has a high corona initiation voltage. This may be because the in-situ porous oxide film, after covering the outer surface of the aluminum stranded wire, combined with the surface modification layer, improves the microstructure and local electric field distribution of the aluminum stranded wire surface, reducing electric field distortion caused by local defects or uneven regions, thereby increasing the corona initiation voltage of the aluminum stranded wire under high voltage conditions.

[0110] Test Example 4: Resistance per unit length and minimum breaking force test

[0111] To verify the effect of thermoelectrically enhanced modified porous oxide film on the electrical conductivity and mechanical load-bearing capacity of aluminum stranded wire, the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared in Example 1 and the untreated aluminum stranded wire in Comparative Example 1 were subjected to resistance per unit length and minimum tensile force tests, respectively.

[0112] The unit length resistance test results are as follows Figure 10 As shown in the figure. The test results show that the resistivity per unit length of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire and the untreated aluminum stranded wire at 20 °C are 0.1022 Ω / km and 0.1003 Ω / km, respectively, both lower than the standard limit of 0.1131 Ω / km for JL / LB20A-240 / 30 aluminum-clad steel core aluminum stranded wire. The resistivity per unit length of the thermoelectrically enhanced modified porous oxide film aluminum stranded wire increases by only about 1.9% compared to the untreated aluminum stranded wire, indicating that the electrolyte state parameter control, anodizing, and surface modification treatments of this invention have little impact on the overall conductivity of the aluminum stranded wire.

[0113] The minimum tensile strength test results are as follows Figure 9As shown. According to GB / T 1179-2017 "Round Wire Concentric Stranded Overhead Conductors", the minimum breaking force of JL / LB20A-240 / 30 aluminum-clad steel-cored stranded wire is 73.24 kN. During the test, three parallel samples of the same length were cut from the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared in Example 1 and the untreated aluminum stranded wire of Comparative Example 1, respectively, for breaking force testing. Among them, the three parallel samples of thermoelectrically enhanced modified porous oxide film aluminum stranded wire were designated as A1, A2, and A3, and their ultimate loads were 77.12 kN, 76.63 kN, and 73.58 kN, respectively, all higher than the minimum breaking force of 73.24 kN specified in the standard; the three parallel samples of untreated aluminum stranded wire were designated as B1, B2, and B3, and their ultimate loads were 76.89 kN, 73.34 kN, and 78.52 kN, respectively. The average breaking forces of the two types of aluminum stranded wires were 75.78 kN and 76.25 kN, respectively, with little difference, indicating that the thermoelectrically enhanced modified porous oxide film aluminum stranded wire obtained by the present invention can still maintain the mechanical load-bearing performance required for overhead conductors.

[0114] As can be seen from the above tests, the thermoelectrically enhanced modified porous oxide film aluminum stranded wire prepared by the present invention can achieve enhanced heat dissipation and increased corona initiation voltage, while its resistance per unit length and minimum breaking force still meet the requirements for use as an overhead conductor, and can take into account the thermal, electrical, electrical and mechanical service performance of the conductor.

Claims

1. A thermoelectrically enhanced modified porous oxide film aluminum stranded wire, characterized in that, It includes an aluminum stranded wire substrate, a porous oxide film grown in situ on the surface of an outer layer of aluminum monofilaments of the aluminum stranded wire substrate, and a surface modification layer formed on the surface of the porous oxide film; the porous oxide film covers the outer surface of the aluminum stranded wire and has a nanoscale porous structure, and the surface modification layer is bonded to the surface of the porous oxide film.

2. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 1, characterized in that, The porous oxide film is an aluminum oxide film formed by anodic oxidation, and the porous oxide film is in situ bonded to the surface of the outer aluminum monofilament of the aluminum stranded wire.

3. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 1, characterized in that, The porous oxide film has nanoscale pore size and micrometer-scale film thickness.

4. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 1, characterized in that, The porous oxide film includes a pore wall structure and a channel structure, which together form the micro / nano rough morphology of the aluminum stranded wire surface.

5. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 1, characterized in that, The surface modification layer is formed by a silane-based modifier.

6. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 5, characterized in that, The silane modifier is heptadecafluorodecyltriethoxysilane.

7. The thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in claim 1, characterized in that, After the surface modification layer is formed, the porous oxide film still maintains a nanoscale pore structure.

8. A method for preparing thermoelectrically enhanced modified porous oxide film aluminum stranded wire as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Pretreatment, aluminum stranded wire is placed in an alkaline solution for degreasing and alkaline washing to remove surface oil and natural oxide layer; then ultrasonic cleaning with deionized water is performed to remove residual alkaline solution and reaction products on the surface, and then dried for later use. S2: Electrolyte state parameter detection and control, including detection of electrolyte pH, conductivity, and Al. 3+ The concentration is determined, and the electrolyte state is judged or adjusted according to a preset reuse state window; the preset reuse state window is: pH 1.283-1.308, conductivity 26.8-28.7 mS / cm, Al 3+ Concentration 322-523 mg / L; S3: Constant current anodizing. The pretreated aluminum stranded wire is placed in the electrolyte after the S2 judgment for anodizing treatment, and a nano-scale porous oxide film is formed in situ on the surface of the outer aluminum monofilament of the aluminum stranded wire. The current density of constant current anodizing is 0.092-0.166 A / cm², the oxidation time is 5-30 min, and the electrolyte temperature is 10-25 ℃. S4: Cleaning and drying. Take out the anodized aluminum stranded wire, clean the residual electrolyte on its surface, and then dry it to obtain aluminum stranded wire with a porous oxide film on the surface. S5: Surface modification. The aluminum stranded wire after S4 cleaning is placed in a low surface energy modification solution for modification, so that low surface energy molecules are bound to the surface of the nanoporous oxide film. S6: Post-processing, the modified aluminum stranded wire is taken out and dried or cured to obtain thermoelectrically enhanced modified porous oxide film aluminum stranded wire.

9. The preparation method according to claim 8, characterized in that, The electrolyte is a phosphoric acid solution with a concentration of 0.2–0.5 mol / L.

10. The preparation method according to claim 9, characterized in that, The surface modification solution is a heptadecafluorodecyltriethoxysilane-ethanol solution with a mass fraction of 5-15 wt.%.

Images