A method for manufacturing an inner tank of a drone-level lightweight composite liquid hydrogen storage tank

Abstract

The application discloses a kind of unmanned aerial vehicle level lightweight composite liquid hydrogen storage tank inner tank manufacturing method.The storage tank inner tank includes composite material pressure-bearing layer (1) from outside to inside in turn, coupling agent treatment layer (2), gradient interface transition layer (5) and functional metal sealing layer (4).The application is decoupled by function design, and the composite material layer is independently pressure-bearing, and the "molecular bridge" chemical bonding is constructed by nanoscale coupling agent, and the thermal shrinkage stress is buffered by combining micrometer grade gradient transition layer.The application is reduced by 60-62.9% compared with traditional metal inner container liquid hydrogen storage tank, and solves the interface peeling problem under the condition of-253 ℃ extreme low temperature cold and hot cycle.

Description

Technical Field

[0001] This invention belongs to the technical field of liquid hydrogen storage and transportation and UAV power system, specifically relating to a high-energy-efficiency, lightweight composite liquid hydrogen storage tank for UAVs and its manufacturing method based on interface modification and gradient layer preparation. Background Technology

[0002] Liquid hydrogen possesses extremely high energy density and holds great promise for applications in aircraft and aviation. However, liquid hydrogen storage faces the severe challenge of extreme low-temperature environments (-253 °C). The extremely low boiling point of liquid hydrogen places extremely high demands on the low-temperature mechanical properties, thermal shrinkage matching, and sealing reliability of the tank materials under long-term thermal cycling. Especially for mobile applications such as drones, the storage tanks must not only withstand the static low temperature of liquid hydrogen but also endure repeated thermal cycles caused by filling, discharging, and changes in ambient temperature. This poses a severe test to the stress compatibility and bonding stability of heterogeneous material interfaces.

[0003] Traditional liquid hydrogen storage typically uses stainless steel, titanium alloys, and other metallic materials as the core structure. While the technology for these materials is mature, their low specific strength results in excessive tank weight, severely limiting the thrust-to-weight ratio and range of the aircraft. To reduce weight, existing technologies have attempted to adopt a "metal inner liner + composite material outer layer" approach in the design of liquid hydrogen storage tanks. However, when attempting to further reduce weight by using an ultra-thin metal inner liner, the ductile-brittle transition of the ultra-thin metal layer at cryogenic temperatures and the interfacial delamination problem caused by the mismatch in the coefficient of thermal expansion (CTE) between the ultra-thin metal layer and the composite material layer become increasingly prominent. This interfacial failure not only damages the structural integrity of the tank but also triggers the propagation of microcracks, leading to severe hydrogen permeation and seal failure.

[0004] In summary, existing technologies struggle to simultaneously achieve extreme lightweight design while maintaining high-strength bonding at heterogeneous material interfaces and ensuring sealing stability under deep cryogenic cycling. Therefore, a novel lightweight storage tank structure and its manufacturing method are needed that can simultaneously meet the requirements of low-temperature resistance, reliable sealing during cryogenic cycling, lightweight design, and manufacturability. Summary of the Invention

[0005] The purpose of this invention: The present invention aims to provide a method for manufacturing an inner tank of a drone-grade lightweight composite liquid hydrogen storage tank, which solves the technical problems of low energy efficiency caused by the excessive weight of the metal inner tank in existing liquid hydrogen storage tanks, and the easy delamination of the composite material and metal layer under deep cryogenic (-253 ℃) thermal cycling.

[0006] The core design concept of this invention: This invention focuses on improving the manufacturing process of the inner tank of a liquid hydrogen storage tank. The composite material tank body bears the majority of the pressure load, while the metal deposition layer on the inner wall serves as a hydrogen sealing barrier. By introducing a nanoscale coupling agent treatment layer and a micron-scale gradient transition layer, a continuous stress transmission system of "organic matrix - molecular bridge - composition gradient - metal seal" is constructed.

[0007] The specific technical solution is as follows: In this invention, the composite material bearing layer (1) bears most of the pressure load, while the functional metal sealing layer (4) serves only as a hydrogen sealing barrier. By introducing a nanoscale coupling agent treatment layer (2) and a micron-scale gradient interface transition layer (5), a continuous stress transmission system is constructed.

[0008] Composite material pressure layer (1): The main body is made of fiber reinforced composite materials such as carbon fiber composite materials, basalt fiber composite materials, glass fiber composite materials, etc., as an independent self-supporting pressure vessel.

[0009] Coupling agent treated layer (2): thickness 1–10 nm. For example... Figure 2 As shown, one end of the coupling agent molecule is connected to the active groups on the surface of the composite pressure-bearing layer (1) through a chemical covalent bond (7), forming a "molecular bridge" structure, which elevates the heterogeneous interface bonding to the level of chemical bonding. The coupling agent can be selected from KH560 or KH550 silane coupling agent, TCA-L97 titanate coupling agent, KEN-REACT zirconate coupling agent, aluminate coupling agent, etc.

[0010] Gradient interface transition layer (5): disposed between the coupling agent treatment layer (2) and the functional metal sealing layer (4). Figure 2 As shown, the layer is composed of an organic resin matrix (6) and a metal powder filler (3) dispersed therein. The characteristic feature is that the volume fraction of the metal powder filler (3) increases gradually from the outside to the inside, allowing for a smooth transition of the coefficient of thermal expansion between the composite material and the metal. Preferably, the metal sealing layer and the metal powder filler are of the same type of metal, specifically stainless steel, titanium alloy, aluminum alloy, etc.

[0011] Functional metal sealing layer (4): 5–500 μm thick, densely deposited on the surface of the gradient interface transition layer (5). Deposition methods include vapor deposition, electroplating, magnetron sputtering, cold spraying, etc.

[0012] Beneficial effects

[0013] Extremely lightweight: Compared with traditional metal-lined liquid hydrogen storage tanks (such as the 2.0 mm aluminum alloy liner solution), the weight reduction of Embodiment 1 of this invention is up to 62.9%, and the weight reduction of Embodiment 2 is up to 60.0%, which is significantly better than the prior art.

[0014] Excellent low-temperature stress compatibility: The ultra-thin metal layer combined with the gradient interface transition layer (5) effectively buffers the thermal shrinkage stress at -253℃.

[0015] High interfacial bonding: The “molecular bridge” formed by chemical covalent bonds (7) upgrades the bonding force from physical adsorption to chemical bonding, ensuring that the bonding does not peel off during hot and cold cycles.

[0016] Unique structure: It breaks away from the traditional thinking that metal liner must be pressure-bearing, and achieves efficient hydrogen barrier through ultra-thin metal deposition. Attached Figure Description

[0017] Figure 1 This is a flowchart of the manufacturing process of the present invention.

[0018] Figure 2 This is a cross-sectional schematic diagram of the inner tank structure of the drone-grade lightweight composite liquid hydrogen storage tank of the present invention.

[0019] Figure 3 This is a design diagram of the gradient interface buffer structure of the present invention.

[0020] Figure 4 This is a schematic diagram of the microscopic mechanism of the "molecular bridge" formed by the coupling agent treatment layer (2) in this invention.

[0021] Explanation of reference numerals in the attached figures: 1. Composite material bearing layer; 2. Coupling agent treatment layer; 3. Metal powder filler; 4. Functional metal sealing layer; 5. Gradient interface transition layer; 6. Organic resin matrix; 7. Chemical covalent bond (or molecular bridge structure). Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings.

[0023] 1. Manufacturing process flow (corresponding) Figure 1 , Figure 2 ): like Figure 1 , 2 As shown, the process mainly includes four key steps, which aim to achieve functional decoupling and interface integration between the composite pressure-bearing layer (1) and the functional metal sealing layer (4): Step S1 (Preparation of pressure-bearing layer): First, the composite pressure-bearing layer (1) is formed by fiber winding or molding process. In this embodiment, a 1 mm thick carbon fiber composite material (CFRP) is selected as the main body of the independent self-supporting pressure vessel.

[0024] Step S2 (Surface Activation and Coupling): Next, the inner surface of the CFRP bearing layer (1) is subjected to plasma treatment to introduce active groups. The plasma treatment time is 3 minutes. Then, KH560 silane coupling agent is sprayed to form a coupling agent treatment layer (2) with a thickness of about 5 nm. This step uses chemical covalent bonds (7) to anchor the coupling agent molecules to the surface of the composite material to construct a "molecular bridge" structure.

[0025] Step S3 (Gradient Transition Layer Construction - Optional Branch): This step is optional and is used to further optimize the thermal stress matching of the interface.

[0026] If a gradient layer is constructed (as in Example 2): on the surface of the coupling agent treated layer (2), resin liquids with different powder loads are coated layer by layer to form a gradient interface transition layer (5) containing metal powder filler (3) and organic resin matrix (6). The selected metal material is 6061 aluminum alloy, and the metal powder is selected with a diameter of 1 micrometer.

[0027] If a gradient layer is not constructed (as in Example 1): skip this step and proceed directly to step S4. In this case, the coupling agent treatment layer (2) is in direct contact with the subsequently deposited metal sealing layer.

[0028] Step S4 (Sealing layer deposition): Finally, based on the selection result of step S3, a functional metal sealing layer (4) is deposited on the surface of the coupling agent treatment layer (2) (without gradient layer scheme) or the gradient interface transition layer (5) (with gradient layer scheme) using a cold spraying process.

[0029] Through the above process, the present invention achieves integrated continuous manufacturing from the pressure-bearing layer to the sealing layer, which ensures both lightweight design and interface reliability at deep and low temperatures.

[0030] Gradient buffer design (corresponding) Figure 3 ): A gradient interface transition layer (5) is filled between the chemical bonding layer and the metal sealing layer. Inside this layer, metal powder fillers (3) (such as stainless steel powder, titanium alloy powder, or aluminum alloy powder) are encapsulated in an organic resin matrix (6). To mitigate stress, the distribution density of the metal powder fillers (3) is not uniform, but rather shows a gradual increase from the outside to the inside, with the powder being most concentrated near the functional metal sealing layer (4).

[0031] 3. Microscopic connection mechanism (corresponding to) Figure 4 ): like Figure 2As shown, this invention constructs a coupling agent-treated layer (2) by applying a coupling agent to the inner surface of the composite pressure-bearing layer (1). The organic end of the coupling agent molecule is anchored to the organic resin matrix of the composite material through chemical covalent bonds (7), while the other end extends towards and binds to the components in the gradient interface transition layer (5). This "molecular bridge" structure effectively avoids physical detachment caused by thermal shrinkage mismatch at deep low temperatures.

[0032] This section demonstrates in detail the impact of the various technical features of the present invention on the performance of the storage tank through comparative experiments.

[0033] Example 1: Basic Lightweight Storage Tank (Functional Decoupling + Interface Coupling)

[0034] This embodiment aims to verify the synergistic effect of "functional decoupling" and "nanoscale coupling layer". A 10 L tank body was prepared using 1 mm thick CFRP as the composite pressure-bearing layer (1); KH560 silane coupling agent was applied to the inner surface to form a 5 nm thick coupling agent treatment layer (2); then a 50 μm thick 6061 aluminum alloy sealing layer was deposited as a functional metal sealing layer (4).

[0035] Example 2: Enhanced lightweight storage tank (functional decoupling + interface coupling + gradient transition layer)

[0036] Based on Example 1, a 50 μm thick gradient interface transition layer (5) was added between (2) and (4), wherein the volume fraction of the metal powder filler (3) was gradually increased from 10% to 50%. Tests showed that it remained intact after 50 cycles of liquid nitrogen heating and cooling (see Table 1).

[0037] Comparative Example 1: Traditional deposition scheme without interface modification

[0038] This comparative example is used to demonstrate the necessity of the interface processing technology of the present invention.

[0039] Tank molding: The same CFRP tank as in Example 1 is used.

[0040] Interface treatment: No coupling agent or gradient layer is used; only simple physical cleaning is performed on the CFRP surface.

[0041] Sealing layer deposition: A 50 μm thick 6061 aluminum alloy sealing layer is directly cold-sprayed onto the inner surface of the CFRP.

[0042] Performance testing: See Table 1.

[0043] Comparative Example 2: Traditional metal-lined storage tank

[0044] This comparative example is used to compare weight loss effects.

[0045] Structural design: The inner liner is made of 2.0 mm thick 6061 aluminum alloy (as one of the independent pressure-bearing components), with an external CFRP reinforcement layer, and a total volume of 10 L.

[0046]

[0047] Table 1 Performance Test Table.

Claims

1. An inner tank for a drone-grade lightweight composite liquid hydrogen storage tank, characterized in that, include: The composite pressure-bearing layer (1) is configured to bear the main pressure load of the storage tank; the functional metal sealing layer (4) is configured to serve only as a hydrogen barrier; wherein, an interface transition structure is provided between the composite pressure-bearing layer (1) and the functional metal sealing layer (4), the interface transition structure includes: a coupling agent treatment layer (2) disposed on the surface of the composite pressure-bearing layer (1); a gradient interface transition layer (5) disposed between the coupling agent treatment layer (2) and the functional metal sealing layer (4), or the coupling agent treatment layer (2) directly contacts the functional metal sealing layer (4); the gradient interface transition layer (5) is composed of an organic resin matrix (6) and metal powder filler (3) dispersed therein, the volume fraction of the metal powder filler (3) is distributed in a gradient increasing direction from the coupling agent treatment layer (2) to the functional metal sealing layer (4).

2. The inner tank of the storage tank according to claim 1, characterized in that: The coupling agent treatment layer (2) is connected to the composite material bearing layer (1) by chemical covalent bonds (7) to form a molecular bridge structure across the heterogeneous interface.

3. The inner tank of the storage tank according to claim 1, characterized in that: The volume fraction of the metal powder filler (3) increases linearly from the side near the coupling agent treatment layer (2) to the side near the functional metal sealing layer (4).

4. The inner tank of the storage tank according to claim 1, characterized in that: The coupling agent treatment layer (2) is selected from one or more of silane coupling agents, titanate coupling agents, zirconate coupling agents or aluminate coupling agents.

5. The inner tank of the storage tank according to claim 1, characterized in that: The thickness of the functional metal sealing layer (4) is 5-500 μm.

6. A method for manufacturing an inner tank of a storage tank as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Prepare a composite pressure-bearing layer (1); S2: Activate the inner surface of the composite pressure-bearing layer (1) and coat it with a coupling agent solution to form a coupling agent treatment layer (2); S3: Optionally, construct a gradient interface transition layer (5) on the surface of the coupling agent treatment layer (2) to control the volume fraction of metal powder filler (3) in the organic resin matrix (6) to be distributed in a gradient; S4: Deposit a functional metal sealing layer (4) on the surface of the coupling agent treatment layer (2) or the gradient interface transition layer (5).

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