Method and device for accurately controlling freezing printing temperature of three-dimensional graphene preform

Abstract

The invention discloses a method and a device for accurately controlling the freezing printing temperature of a three-dimensional graphene preform, and belongs to the technical field of three-dimensional graphene preform preparation. The method comprises the following steps: injecting a liquid medium into the liquid tank; carrying out hydrophilic treatment on the surface of the printing substrate; the printing substrate is controlled to descend to the initial position in the liquid tank, and the bottom of the printing substrate is immersed in the liquid medium; graphene liquid drops are sprayed on the printing substrate layer by layer through the printing spray head, after spraying of each layer is completed, the printing substrate is driven to descend, the solidified layer graphene part is immersed into the liquid medium, the printing sinking step is repeated till the temperature of the liquid medium is consistent with the set temperature, and the preset number of layers of the three-dimensional graphene prefabricated body is completed. The core advantage of the method is that the problem that the temperature of a printing layer is uncontrollable due to thermal resistance superposition in the prior art is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional graphene preform preparation, and in particular relates to a method and device for accurately controlling the temperature of a three-dimensional graphene preform during cryo-printing. Background Art

[0002] By assembling two-dimensional graphene into three-dimensional graphene preforms to reinforce magnesium-based composites, not only can the graphene agglomeration problem in the matrix be effectively overcome, but it can also construct efficient load transfer, heat conduction, and electron transport networks, thereby significantly improving the overall performance of the material. Traditional three-dimensional graphene manufacturing methods, such as template methods and self-assembly methods, although they have shown certain applicability in various fields, have significant shortcomings in the unified control of macro- and microstructures, process complexity, and complex morphological design. These problems make it difficult to meet the stringent requirements of high-performance composite materials for three-dimensional graphene.

[0003] Cryoprinting combines additive manufacturing with freeze casting. By setting the temperature of a cold source and utilizing the directional growth of ice crystals to form a template, graphene sheets are guided to arrange themselves into a three-dimensional network, while also enabling the printing of complex three-dimensional structures. This technology offers a new strategy for developing three-dimensional graphene materials with high surface area, excellent mechanical properties, and customizable functions, demonstrating significant potential for technological breakthroughs in areas such as flexible electronics and efficient energy storage systems.

[0004] However, current cryoprinting devices generally employ a static cooling mode using a single cryosubstrate, which presents two key issues. Regarding printing efficiency, as the number of printed layers increases, the already solidified layer, due to its inherent low thermal conductivity, creates an insulating effect, leading to a gradual increase in vertical thermal resistance and hindering the conduction of the cooling required for solidification of the upper graphene ink layer. This cumulative effect of heat raises the temperature of the upper printed area, causing the solidification rate of the graphene ink to decrease, resulting in a phenomenon in which printing efficiency decreases with increasing height. Regarding micropore control, the bottom layer of ink rapidly solidifies through direct contact with the cryosubstrate, forming a dense and fine pore structure. However, due to the superimposed effect of thermal resistance, the temperature gradient during ink solidification in the upper layer is significantly reduced, causing the pore size to increase and exhibit lamellar characteristics, ultimately resulting in a pore size gradient distribution along the print height. These issues severely restrict the performance optimization of three-dimensional graphene materials, the controllability of the microstructure, and the improvement of overall printing efficiency.

[0005] Therefore, it is necessary to develop a temperature control method and device suitable for cryo-printing of three-dimensional graphene preforms to accurately control the temperature of printed layers at different heights. Summary of the Invention

[0006] Technical issues to be solved:

[0007] In order to avoid the shortcomings of the prior art, the present invention provides a method and device for precise temperature control of three-dimensional graphene preform cryo-printing. This method uses a temperature control module to accurately set the temperature of the liquid medium in the liquid tank. After the single-layer graphene ink is printed and solidified, the printing substrate is controlled to move downward so that the solidified layer is partially immersed in the liquid medium. After the temperature of the solidified layer reaches the same temperature as the liquid medium, a new ink layer is continuously deposited on the surface of the solidified layer exposed to the liquid surface. By cyclically executing the above steps, the accumulation of thermal resistance between layers can be completely eliminated, ensuring that printed layers of different heights are solidified at a settable temperature. The core advantage of the present invention is that it breaks through the problem of uncontrollable temperature of the printed layer caused by the superposition of thermal resistance in traditional technology.

[0008] The technical solution of the present invention is: a method for accurately controlling the temperature of a three-dimensional graphene preform during cryo-printing, the specific steps of which are as follows:

[0009] The liquid medium is injected into the liquid tank and cooled to a set temperature by a temperature control module, wherein the set temperature is -30°C to 0°C; the surface tension of the liquid medium is 70 to 90 mN / m, the freezing point is lower than -30°C, and the liquid state is maintained within the temperature range of -30°C to 0°C;

[0010] The surface of the printed substrate is treated to be hydrophilic to form a wetting interface with a contact angle of less than 10°;

[0011] Controlling the printing substrate to descend to an initial position in the liquid tank so that its bottom is immersed in the liquid medium, ensuring that the distance between the upper surface of the printing substrate and the surface of the liquid medium is within a set distance range, and waiting for the temperature of the printing substrate to stabilize to the same temperature as the liquid medium;

[0012] Graphene droplets are sprayed layer by layer onto the printing substrate through the print nozzle. After each layer is sprayed, the printing substrate is driven to descend 0.5 to 1.0 mm so that the solidified graphene layer is partially immersed in the liquid medium until its temperature reaches the set temperature. The cooling time of a single printed layer is determined by the thermal resistance of the printing substrate or the single printed layer.

[0013] Repeat the above printing and sinking steps until the preset number of layers of the three-dimensional graphene preform is completed.

[0014] A further technical solution of the present invention is that the liquid medium is a salt solution with a concentration of 20 to 30 wt%, and the ionized ions bind water molecules through hydration to prevent the solidified graphene layer from dissolving.

[0015] A further technical solution of the present invention is: the surface treatment method of the printed substrate is: spraying ethanol dispersed with hydrophilic nano-silica on the surface of the printed substrate, and after the ethanol evaporates, the nano-silica forms a hydrophilic coating on the surface of the printed substrate; the surface roughness of the printed substrate after the hydrophilic treatment is 0.8 to 6.3 μm.

[0016] A further technical solution of the present invention is that the set distance between the upper surface of the substrate and the surface of the liquid medium is 0.5 mm.

[0017] A further technical solution of the present invention is: the calculation formula of the cooling time t(n) of the single-layer printing layer is as follows:

[0018]

[0019] Where n represents the number of printing layers, R sub represents the thermal resistance of the printed substrate, R0 represents the thermal resistance of a single printed layer, m represents the mass of a single printed layer, and c represents the specific heat capacity of the graphene ink.

[0020] A further technical solution of the present invention is that the thickness of the single-layer printing layer is l=0.2-1 mm, and the following conditions need to be met:

[0021]

[0022] Where h represents the surface heat transfer coefficient of air, h = 5W / (m 2 ·K), λ represents the thermal conductivity of the graphene solution in the solidified state, λ=5W / (m·K).

[0023] A precise temperature control device for cryo-printing a three-dimensional graphene preform includes a lifting unit for controlling the periodic immersion movement of a printing substrate in a liquid medium. The printing substrate is located below a printing nozzle and performs cryo-printing in a liquid medium environment of a liquid temperature control unit.

[0024] The liquid temperature control unit includes a liquid tank containing a liquid medium and a temperature control module for controlling the temperature of the liquid tank; the liquid medium is a salt solution with a surface tension of 70 to 90 mN / m, a concentration of 20 to 30 wt%, and a freezing point below -30°C; the temperature of the salt solution in the liquid tank is adjusted to -30°C to 0°C by the temperature control module, with a temperature control accuracy of ±0.5°C;

[0025] The device uses a dynamic immersion mechanism to partially immerse each printed layer in the salt solution in sequence, and direct liquid-solid heat transfer eliminates interlayer thermal resistance, ensuring uniformity of the pore structure and a pore size deviation of ≤10%.

[0026] A further technical solution of the present invention is that the lifting unit includes a first fixed base and a second fixed base symmetrically arranged on both sides of the liquid tank, each of which is equipped with a first stepper motor and a second stepper motor; the output ends of the first stepper motor and the second stepper motor are respectively connected to a first lead screw and a second lead screw arranged in a vertical direction, thereby driving a first slider and a second slider mounted on the first lead screw and the second lead screw to synchronously rise and fall;

[0027] The outer sides of the first slider and the second slider are symmetrically connected to the two sides of the movable bracket; the movable bracket is a U-shaped frame, and the bottom surface of the movable bracket carries the printing substrate to perform reciprocating periodic motion in the vertical direction.

[0028] A further technical solution of the present invention is: the surface of the printing substrate is sprayed with a hydrophilic nano-silicon dioxide coating with a contact angle of less than 10°; the surface roughness is 0.8-6.3 μm, the material is copper or aluminum alloy, and the thickness is 0.3-1.0 mm.

[0029] A further technical solution of the present invention is that the diameter of the droplets sprayed by the printing nozzle is 0.5-1.5 mm, and the layer thickness is 0.3-0.8 mm.

[0030] Beneficial effects

[0031] The beneficial effects of this invention are: through liquid medium optimization, interface modification, dynamic temperature control mechanism, and mathematical model support, this invention systematically solves the problems of thermal resistance accumulation and structural unevenness in traditional cryoprinting. The core of this method lies in the deep integration of physical and chemical regulation (liquid / substrate design) and engineering control (dynamic immersion + mathematical modeling). The specific effects are analyzed as follows:

[0032] 1. This invention utilizes a self-elevating printing substrate in conjunction with the liquid medium within a tank. After the printhead completes a layer, it drives the movable support down to a set height, immersing the solidified layer partially in the liquid medium. A new printed layer is then deposited on the surface of the solidified layer uncovered by the liquid, and the process repeats. This process replaces the traditional interlayer series heat conduction path with direct liquid-solid heat transfer, ensuring a constant equivalent thermal resistance between each newly printed layer and the liquid cooling source. This eliminates the cumulative thermal resistance effect caused by increasing printing height, significantly improving cryoprinting efficiency.

[0033] 2. The present invention uses a temperature control module to regulate the liquid medium at a constant temperature. Combined with the stable thermal boundary conditions formed by the periodic immersion of the printed substrate in the liquid medium, the temperature of each printed layer is consistent with the temperature of the cold source. This method effectively solves the problem of increased temperature gradient in the height direction caused by the accumulation of thermal resistance in traditional printing and freezing printing devices, eliminates the axial gradient change of the pore structure of the graphene material, and realizes the uniform and controllable three-dimensional graphene microstructure. Figure 5 shown.

[0034] 3. The liquid medium designed in the present invention achieves three technical advantages by optimizing key parameters such as surface tension, polarity, substance type, concentration and solidification characteristics: First, the liquid medium will not produce capillary rise after contacting the solidified graphene printing layer, avoiding the failure of the next printing layer to overlap; second, after long-term immersion, the liquid medium will not dissolve the solidified graphene printing layer, ensuring the integrity of the printed part structure; finally, the low freezing point of the liquid medium is well matched with the conventional printing temperature range, providing sufficient control space for the selection of process parameters. Preferably, the liquid medium uses a salt solution to avoid dissolving the graphene layer and ensure the structural integrity of the printed part

[0035] 4. This invention addresses the interfacial behavior between the printed substrate and the liquid medium by applying a surface treatment technique to the printed substrate: grinding the substrate to a smooth, low-roughness surface, combined with spraying a hydrophilic nano-silica coating, creates a wetting interface with a contact angle of less than 10°. This effectively mitigates the capillary phenomenon of the liquid medium rising along the edges of the printed substrate due to excessive surface tension. Compared to traditional liquid formulation modification schemes, this method achieves superior interface control while maintaining the inherent properties of the liquid medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of a device for accurately controlling the temperature of a three-dimensional graphene preform cryo-printing according to an embodiment of the present invention;

[0037] Figure 2 This is a flow chart of a method for accurately controlling the temperature of three-dimensional graphene preform cryo-printing to regulate the temperature of printed layers at different heights according to an embodiment of the present invention;

[0038] Figure 3 This is a diagram showing the calculation results of reducing the printing cooling time by the precise temperature control method for freezing and printing a three-dimensional graphene preform according to an embodiment of the present invention;

[0039] Figure 4 1 is a graph showing the calculation results of accurately controlling the cooling rates of different printed layers using a method for accurately controlling the temperature of a three-dimensional graphene preform cryo-printing according to an embodiment of the present invention;

[0040] Figure 5 The following are photos showing the actual effect of the method and apparatus for precise temperature control of three-dimensional graphene preform cryoprinting on the pores of the printed layer in the embodiments of the present invention: (a) a photo of the pores at the top of three-dimensional graphene using a traditional single cryosubstrate; (b) a photo of the pores at the top of three-dimensional graphene using the precise temperature control method of this embodiment;

[0041] Explanation of the accompanying drawings: 1-first fixed base, 2-first stepper motor, 3-first screw, 4-first slider, 5-movable bracket, 6-liquid tank, 7-liquid medium, 8-temperature control module, 9-printing substrate, 10-printing nozzle, 11-second slider, 12-second screw, 13-second stepper motor, 14-second fixed base. DETAILED DESCRIPTION

[0042] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0043] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0044] The prior art "YU K, GAO Q, LIN Z, et al. Investigation of the temperature gradient control in the printing space for the material extrusion of medical biodegradable hydrogel [J]. Computers in Biology and Medicine, 2024, 168: 107722." proposed superimposing a metal ring on a freezing substrate and using convection heat transfer to adjust the ambient temperature to compensate for the temperature of printed layers at different heights. However, due to the low thermal conductivity of air, this method can only partially slow down the accumulation of thermal resistance and it is difficult to achieve precise control of the temperature of printed layers at different heights. Based on the problems existing in the prior art, the present invention provides a method for precise temperature control of three-dimensional graphene preform cryo-printing, and the specific steps are as follows:

[0045] Step 1: injecting a liquid medium into a liquid tank and cooling it to a set temperature through a temperature control module, wherein the set temperature is -30°C to 0°C; the surface tension of the liquid medium is 70 to 90 mN / m, the freezing point is lower than -30°C, and the liquid medium remains in a liquid state within a temperature range of -30°C to 0°C;

[0046] Step 2: Treat the printed substrate surface with hydrophilicity to form a wetting interface with a contact angle of less than 10°;

[0047] Step 3: Control the printing substrate to descend to the initial position in the liquid tank so that its bottom is immersed in the liquid medium, ensure that the distance between the upper surface of the printing substrate and the surface of the liquid medium is within the set distance range, and wait for the temperature of the printing substrate to stabilize to the same temperature as the liquid medium;

[0048] Step 4: Graphene droplets are sprayed layer by layer onto the printing substrate through the print nozzle. After each layer is sprayed, the printing substrate is driven to descend 0.5 to 1.0 mm so that the solidified graphene layer is partially immersed in the liquid medium until its temperature reaches the set temperature. The cooling time of a single printed layer is determined by the thermal resistance of the printing substrate or the single printed layer.

[0049] Step 5: Repeat the above printing and sinking steps until the preset number of layers of the three-dimensional graphene preform is completed.

[0050] Specifically, the calculation formula for the cooling time t(n) of the single-layer printing layer is as follows:

[0051]

[0052] Where n represents the number of printing layers, R sub represents the thermal resistance of the printed substrate, R0 represents the thermal resistance of a single printed layer, m represents the mass of a single printed layer, and c represents the specific heat capacity of the graphene ink.

[0053] Specifically, the thickness of the single-layer printing layer is l=0.2-1 mm, and the following conditions need to be met:

[0054]

[0055] Where h represents the surface heat transfer coefficient of air, h = 5W / (m 2 ·K), λ represents the thermal conductivity of the graphene solution in the solidified state, λ=5W / (m·K).

[0056] The present invention provides a precise temperature control device for cryo-printing of a three-dimensional graphene preform, comprising a lifting unit for controlling the periodic immersion movement of a printing substrate in a liquid medium. The printing substrate is located below a printing nozzle and performs cryo-printing in a liquid medium environment of a liquid temperature control unit.

[0057] The liquid temperature control unit includes a liquid tank containing a liquid medium and a temperature control module for controlling the temperature of the liquid tank; the liquid medium is a salt solution with a surface tension of 70 to 90 mN / m, a concentration of 20 to 30 wt%, and a freezing point below -30°C; the temperature of the salt solution in the liquid tank is adjusted to -30°C to 0°C by the temperature control module, with a temperature control accuracy of ±0.5°C;

[0058] The device uses a dynamic immersion mechanism to partially immerse each printed layer in the salt solution in sequence, and direct liquid-solid heat transfer eliminates interlayer thermal resistance, ensuring uniformity of the pore structure and a pore size deviation of ≤10%.

[0059] Specifically, the lifting unit includes a first fixed base and a second fixed base symmetrically arranged on both sides of the liquid tank, each of which is equipped with a first stepper motor and a second stepper motor; the output ends of the first stepper motor and the second stepper motor are respectively connected to a first lead screw and a second lead screw arranged in a vertical direction, thereby driving a first slider and a second slider mounted on the first lead screw and the second lead screw to rise and fall synchronously;

[0060] The outer sides of the first slider and the second slider are symmetrically connected to the two sides of the movable bracket; the movable bracket is a U-shaped frame, and the bottom surface of the movable bracket carries the printing substrate to perform reciprocating periodic motion in the vertical direction.

[0061] Specifically, the surface of the printing substrate is sprayed with a hydrophilic nano-silicon dioxide coating with a contact angle of less than 10°; the surface roughness is 0.8 to 6.3 μm, the material is copper or aluminum alloy, and the thickness is 0.3 to 1.0 mm.

[0062] Specifically, the diameter of the droplets sprayed by the printing nozzle is 0.5-1.5 mm, and the layer thickness is 0.3-0.8 mm.

[0063] The above technical solution is further analyzed below with reference to the accompanying drawings and examples:

[0064] In one embodiment, referring to Figure 1 As shown, a precise temperature control device for freezing and printing a three-dimensional graphene preform in this embodiment includes a lifting unit, a liquid temperature control unit, and a printing nozzle.

[0065] The lifting unit includes a first fixed base 1, a first stepping motor 2, a first lead screw 3, a first slider 4, a movable bracket 5, a printing substrate 9, a second slider 11, a second lead screw 12, a second stepping motor 13, and a second fixed base 14;

[0066] The first stepper motor 2 and the second stepper motor 13 are respectively mounted on the top of the first fixed base 1 and the second fixed base 14; the first screw rod 3 and the second screw rod 12 are respectively connected to the first stepper motor 2 and the second stepper motor 13; the first slider 4 and the second slider 11 are respectively threadedly engaged with the first screw rod 3 and the second screw rod 12 for synchronous lifting and lowering movement;

[0067] The movable bracket 5 is a U-shaped frame, with both ends horizontally fixed on the first slider 4 and the second slider 11, with the protruding portion facing downward, for carrying the printing substrate 9 for lifting and lowering; the printing substrate 9 is placed on the upper surface of the protruding portion of the movable bracket 5;

[0068] The liquid temperature control unit includes a liquid tank 6, a liquid medium 7, and a temperature control module 8;

[0069] The temperature control module 8 is located below the protruding portion of the movable bracket 5 and is used to adjust the temperature of the liquid medium 7. The liquid tank 6 is placed on the temperature control module 8 and is used to contain the liquid medium 7.

[0070] The liquid medium 7 is a polar solution with a surface tension ranging from 70 to 90 mN / m. After solidification, the contact angle of the liquid medium 7 on the surface of the graphene printed layer is greater than 90°, showing hydrophobicity, which can effectively suppress the capillary rise phenomenon caused by the liquid medium 7 after contacting the printed layer;

[0071] Preferably, the liquid medium 7 is a polar solution with a surface tension ranging from 70 to 90 mN / m. After solidification, the contact angle of the liquid medium 7 on the surface of the graphene printed layer is greater than 90°, showing hydrophobicity, which can effectively inhibit the capillary rise phenomenon caused by the liquid medium 7 after contacting the printed layer.

[0072] Preferably, the liquid medium 7 is a salt solution with a concentration of 20-30 wt %. The ionized ions bind water molecules through hydration, thereby preventing the liquid medium 7 from dissolving the solidified graphene printed layer.

[0073] Preferably, the freezing point of the liquid medium 7 is lower than -30°C and remains liquid within the temperature range of 0°C to -30°C;

[0074] The surface roughness of the printed substrate 9 is 0.8 to 6.3 μm. The surface of the printed substrate 9 is sprayed with ethanol dispersed with hydrophilic nano-silica. After the ethanol evaporates, the nano-silica forms a hydrophilic coating. After the liquid medium 7 is modified, the contact angle of the surface of the printed substrate 9 is less than 10°.

[0075] The print head 10 is above the printing substrate 9 and is used for jet printing of graphene droplets.

[0076] In one embodiment, referring to Figure 2 As shown, this embodiment provides a method for accurately controlling the temperature of a three-dimensional graphene preform during cryo-printing, and the specific steps are as follows:

[0077] Step 1: injecting a salt solution with a surface tension of 70 to 90 mN / m and a concentration of 20 to 30 wt% into a liquid tank, and cooling the solution to a set temperature of -30°C to 0°C through a temperature control module;

[0078] Step 2: Treat the printed substrate surface with hydrophilicity and spray an ethanol solution containing nano-silica to form a wetting interface with a contact angle of less than 10°.

[0079] Step 3: Control the printing substrate to descend to the initial position in the liquid tank so that its bottom is immersed in the liquid medium, ensure that the distance between the upper surface of the printing substrate and the surface of the liquid medium is 0.5 mm, and wait for the temperature of the printing substrate to stabilize to the same temperature as the liquid medium;

[0080] Step 4: Graphene droplets are sprayed layer by layer onto the printing substrate through the print nozzle. After each layer is sprayed, the printing substrate is driven to descend 0.5 to 1.0 mm so that the solidified graphene layer is partially immersed in the liquid medium until its temperature reaches the set temperature. The cooling time of a single printed layer is determined by the thermal resistance of the printing substrate or the single printed layer.

[0081] Step 5: Repeat the above printing and sinking steps until the preset number of layers of the three-dimensional graphene preform is completed.

[0082] The cooling time derivation process and freezing efficiency verification process of the single-layer printing layer are as follows:

[0083] Define the mass of a single printed layer as m, the specific heat capacity of the graphene ink as c, the temperature difference between the graphene ink and the liquid medium 7 as ΔT, and the total heat Q released by cooling a single printed layer as:

[0084] Q=m·c·ΔT

[0085] Define the total thermal resistance on the heat conduction path as R, and the heat flow φ as:

[0086]

[0087] Define the thermal resistance of the printed substrate 9 as R sub , the thermal resistance of a single printed layer is R0, the number of printed layers is n, and according to the principle of series thermal resistance superposition, the total thermal resistance R is:

[0088]

[0089] Furthermore, according to the actual printing situation, the thickness of a single printing layer is defined as l = 0.2 ~ 1mm, and the surface heat transfer coefficient of air is h = 5W / (m 2 ·K), the thermal conductivity of the graphene solution in the solidified state is λ=5W / (m·K), then the maximum value of the Biot number Bi is:

[0090]

[0091] Furthermore, since the calculated result of the Biot number Bi is much less than 0.1, the internal thermal resistance of the material is much smaller than the surface convection resistance. The lumped parameter method can be used for calculation. The time constant τ for the cooling and solidification of a single printed layer is:

[0092]

[0093] Furthermore, under the conditions of the precise temperature control method in this embodiment, the relationship between the cooling time t(n) of the printed layer and the number of printed layers n is:

[0094]

[0095] Furthermore, the cooling rate v of a single printed layer is defined as:

[0096]

[0097] Furthermore, under the conditions of the precise temperature control method of the present invention, the relationship between the freezing rate v(n) of the printed layer and the number of printed layers n is:

[0098]

[0099] Furthermore, according to the above formula, under the traditional frozen substrate printing conditions, the printing layer cooling time t b The relationship between (n) and the number of printing layers n is:

[0100] t b (n) = mc[R sub +(n-1)R0]n≥1

[0101] Furthermore, according to the above formula, under the traditional freezing substrate printing conditions, the freezing rate v of the printed layer is b The relationship between (n) and the number of printing layers n is:

[0102]

[0103] Reference Figure 3 and Figure 4 As shown, the above formula is normalized, the printed substrate material is copper, and the thermal conductivity is λ sub =400W / (m·K), the thermal conductivity of the graphene solution in the solidified state is λ=5W / (m·K), and the number of printed layers is 20. According to the calculation results, compared with traditional frozen substrate printing, the method and device for precise temperature control of three-dimensional graphene preform freezing printing of the present invention can reduce the time required for printing and freezing to 1 / 10, and can achieve precise control of the cooling rate and temperature of printed layers at different heights;

[0104] In one embodiment, when performing cryo-printing of a three-dimensional graphene preform, the precise temperature control device used in this embodiment achieves precise temperature control of printed layers at different heights in the following specific process:

[0105] Liquid medium 7 is added to liquid tank 6 to a depth of 2 cm. The temperature of temperature control module 8 is set to -20°C, and the liquid medium 7 is allowed to cool to the same temperature. The first stepper motor 2 and the second stepper motor 13 are synchronously controlled to drive the movable bracket 5 to descend, stopping when the upper surface of the printing substrate 9 is 0.5 mm from the liquid surface. After the printing substrate 9 cools to the same temperature as the liquid medium 7, the print head 10 sprays graphene droplets layer by layer on the printing substrate 9, with the droplets having a diameter of 1 mm and a height of 0.5 mm. After the first graphene printed layer solidifies, the printing substrate 9 is lowered 0.8 mm, immersing 3 / 5 of the solidified layer in the liquid medium 7. The print head 10 continues to deposit a new printed layer on the surface of the solidified layer not covered by the liquid medium 7. After the new printed layer cools and solidifies, the printing substrate 9 is lowered 0.5 mm, similarly immersing 3 / 5 of the solidified layer in the liquid medium 7. The printing-descent cycle is repeated continuously, with the printed portion immersed in the liquid medium 7 and remaining solidified, until the three-dimensional graphene preform is printed.

[0106] Reference Figure 5 As shown in the figure, under the same printing parameter conditions, the top layer of three-dimensional graphene printed by the traditional frozen substrate method forms large lamellar pores due to the sudden drop in temperature as the printing height increases. However, the liquid immersion temperature control method and device of the present invention can precisely control the temperature of the printed layers at different heights, so the top of the three-dimensional graphene preform still has honeycomb-shaped uniform pores.

[0107] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for accurately controlling the temperature of a three-dimensional graphene preform during cryo-printing, characterized in that The specific steps are as follows: The liquid medium is injected into the liquid tank and cooled to a set temperature by a temperature control module, wherein the set temperature is -30°C to 0°C; the surface tension of the liquid medium is 70 to 90 mN / m, the freezing point is lower than -30°C, and the liquid state is maintained within the temperature range of -30°C to 0°C; The surface of the printed substrate is treated to be hydrophilic to form a wetting interface with a contact angle of less than 10°; Controlling the printing substrate to descend to an initial position in the liquid tank so that its bottom is immersed in the liquid medium, ensuring that the distance between the upper surface of the printing substrate and the surface of the liquid medium is within a set distance range, and waiting for the temperature of the printing substrate to stabilize to the same temperature as the liquid medium; Graphene droplets are sprayed layer by layer onto the printing substrate through the print nozzle. After each layer is sprayed, the printing substrate is driven to descend 0.5 to 1.0 mm so that the solidified graphene layer is partially immersed in the liquid medium until its temperature reaches the set temperature. The cooling time of a single printed layer is determined by the thermal resistance of the printing substrate or the single printed layer. Repeat the above printing and sinking steps until the preset number of layers of the three-dimensional graphene preform is completed.

2. The method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to claim 1, wherein: The liquid medium is a salt solution with a concentration of 20-30 wt%, and the ionized ions bind water molecules through hydration to prevent the solidified graphene layer from dissolving.

3. The method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to claim 2, wherein: The surface treatment method of the printing substrate comprises: spraying ethanol dispersed with hydrophilic nano-silicon dioxide on the surface of the printing substrate; after the ethanol evaporates, the nano-silicon dioxide forms a hydrophilic coating on the surface of the printing substrate; and the surface roughness of the printing substrate after the hydrophilic treatment is 0.8 to 6.3 μm.

4. The method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to claim 3, wherein: The set distance between the upper surface of the substrate and the surface of the liquid medium is 0.5 mm.

5. The method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to claim 4, wherein: The calculation formula of the cooling time t(n) of the single-layer printing layer is as follows: Where n represents the number of printing layers, R sub represents the thermal resistance of the printed substrate, R0 represents the thermal resistance of a single printed layer, m represents the mass of a single printed layer, and c represents the specific heat capacity of the graphene ink.

6. The method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to claim 5, characterized in that: The thickness of the single-layer printing layer is l = 0.2 ~ 1mm, and the following conditions need to be met: Where h represents the surface heat transfer coefficient of air, h = 5W / (m 2 ·K), λ represents the thermal conductivity of the graphene solution in the solidified state, λ=5W / (m·K).

7. A device for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting, for implementing the method for accurately controlling the temperature of a three-dimensional graphene preform during cryoprinting according to any one of claims 1 to 6; characterized in that: It includes a lifting unit for controlling the periodic immersion movement of the printing substrate in the liquid medium, wherein the printing substrate is located below the printing nozzle and performs cryo-printing in the liquid medium environment of the liquid temperature control unit; The liquid temperature control unit includes a liquid tank containing a liquid medium and a temperature control module for controlling the temperature of the liquid tank; the liquid medium is a salt solution with a surface tension of 70 to 90 mN / m, a concentration of 20 to 30 wt%, and a freezing point below -30°C; the temperature of the salt solution in the liquid tank is adjusted to -30°C to 0°C by the temperature control module, with a temperature control accuracy of ±0.5°C; The device uses a dynamic immersion mechanism to partially immerse each printed layer in the salt solution in sequence, and direct liquid-solid heat transfer eliminates interlayer thermal resistance, ensuring uniformity of the pore structure and a pore size deviation of ≤10%.

8. The device for precise temperature control of three-dimensional graphene preform cryoprinting according to claim 7, characterized in that: The lifting unit includes a first fixed base and a second fixed base symmetrically arranged on both sides of the liquid tank, and is respectively equipped with a first stepper motor and a second stepper motor; the output ends of the first stepper motor and the second stepper motor are respectively connected to a first lead screw and a second lead screw arranged in a vertical direction, driving the first slider and the second slider mounted on the first lead screw and the second lead screw to rise and fall synchronously; The outer sides of the first slider and the second slider are symmetrically connected to the two sides of the movable bracket; the movable bracket is a U-shaped frame, and the bottom surface of the movable bracket carries the printing substrate to perform reciprocating periodic motion in the vertical direction.

9. The device for precise temperature control of three-dimensional graphene preform cryoprinting according to claim 7, characterized in that: The surface of the printing substrate is sprayed with a hydrophilic nano-silicon dioxide coating with a contact angle of less than 10°; the surface roughness is 0.8 to 6.3 μm, the material is copper or aluminum alloy, and the thickness is 0.3 to 1.0 mm.

10. The device for precise temperature control of three-dimensional graphene preform cryoprinting according to claim 7, characterized in that: The diameter of the droplets sprayed by the printing nozzle is 0.5-1.5 mm, and the layer thickness is 0.3-0.8 mm.

Images