Preparation method of micro-nano composite structure wick of titanium water ultrathin plane heat pipe

Abstract

The invention discloses a preparation method of a micro-nano composite structure wick of a titanium water ultrathin plane heat pipe, and belongs to the field of plane heat pipe wick. The invention aims to solve the problem of hydrophobicity of a planar heat pipe wick micron structure. On the basis of a rolling forming method, a regular micron-sized wick microstructure is manufactured; and then a hydrophilic nano structure is prepared on the surface of the microstructure through a strong alkali solution hydrothermal method, and the wick of the micro-nano composite structure capable of achieving bubble nucleation density increase and strong capillary action at the same time is manufactured. The micron-level wick is obtained through rolling, so that the capillary force of the heat pipe and the machining efficiency of the microstructure are greatly improved. Meanwhile, the titanium dioxide nanotubes are obtained in a strong alkali solution through a hydrothermal method, and the hydrophilicity of the wick is improved. Therefore, the wick of the ultrathin planar heat pipe can be stably and effectively prepared.

Description

Technical Field

[0001] The present invention belongs to the field of wick structures for planar heat pipes, and more particularly, relates to a wick structure for a titanium-water ultra-thin planar heat pipe with a micro-nano composite structure and a preparation method thereof. Background Art

[0002] With the continuous development of high-end equipment such as microelectronic devices, radars, laser weapons, and nuclear power plants in the direction of high integration and high power, the power of the equipment is gradually developing from the current kilowatt level to the megawatt level, and may even reach the megawatt level in the future. If the instantaneous high-density heat flux generated by its power heat source cannot be dissipated in time, it is extremely easy to cause equipment failures or malfunctions. The vapor chamber can utilize the huge latent heat provided by the evaporation / boiling and condensation phase changes to effectively evacuate the high heat flux density, and has currently been applied in fields such as chip heat dissipation and integrated microelectronic devices. However, with the continuous development of China's aerospace technology, spaceborne electronic components and space-based weapons also face severe heat dissipation problems. The wick inside the vapor chamber is a key component. The main function of the wick is to achieve heat transfer and liquid transportation, and ultimately achieve efficient heat dissipation through the gas-liquid cycle. Specifically, the liquid first absorbs heat and undergoes a phase change at the wick at the bottom of the vapor chamber and turns into a gas. Then the gas liquefies at the condensation end at the top of the vapor chamber and releases heat. Subsequently, the liquid at the condensation end is sucked to the evaporation end by the strong capillary force of the wick to achieve heat transfer and working fluid circulation. Currently, in order to improve the capillary force of the existing vapor chamber wicks, microstructures are usually processed on the surface of the wicks, and most of them are manufactured by methods such as laser processing and chemical etching. These processing methods have a long processing cycle and low efficiency. The plastic forming process has the advantages of high production efficiency and high material utilization rate. In particular, the roll forming process can quickly manufacture a large number of neatly arranged microstructures on the surface of the wick, which can improve the capillary force of the wick. However, the wicks with micron-scale microstructures have poor hydrophilic properties, resulting in poor droplet spreading and poor bubble nucleation ability, which is not conducive to improving the boiling heat transfer ability of the planar heat pipe wick. Summary of the Invention

[0003] The present invention proposes a manufacturing method for a super-hydrophilic micro-nano composite structure of a titanium-water ultra-thin planar heat pipe wick. By means of roll pressing, a wick with micro-grooves is processed on the surface of pure titanium. Subsequently, a layer of titanium dioxide nanotubes is prepared on the surface of the micro-grooves by means of a strong alkali solution hydrothermal method and subsequent heat treatment methods to achieve surface modification from hydrophobic to hydrophilic. This method solves the problem of the hydrophobicity of the micron-scale structure of the planar heat pipe wick, realizes the hydrophilicity requirement of the micro-nano composite structure wick, and thus realizes the rapid spreading of water droplets on the wick, which is beneficial to the formation of large-area film condensation and improves the heat dissipation ability at the evaporation end. Therefore, through this method, a wick with a micro-nano composite structure that can simultaneously increase the bubble nucleation density and has strong capillary action can be manufactured, and finally, excellent phase change heat transfer performance is imparted to the titanium planar heat pipe.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention aims to provide a method for preparing a wick of a micro-nano composite structure titanium-water ultra-thin planar heat pipe, comprising the following steps:

[0006] Step 1: Roll rectangular micro-grooves on a pure titanium plate, and place it in acetone for ultrasonic cleaning to fully remove the oil stains on the surface;

[0007] Step 2: Then place it in a mixed solution of nitric acid and hydrofluoric acid to remove the oxide film on the surface, and then wash it thoroughly with clean water;

[0008] Step 3: Then place it in a high-temperature and high-pressure reaction kettle filled with a NaOH solution with a concentration of 3M - 10M, and seal it;

[0009] Step 4: Then place it in an oven, heat it at 160 ± 2 °C for 4 hours, take it out after cooling, pickle it with dilute hydrochloric acid, rinse it with deionized water, and thoroughly remove Na + , vacuum dry it, and calcine it to complete.

[0010] Further defined, in step 1, the thickness of the pure titanium plate is 2 mm; the purity of the titanium plate is 99.9 wt.%.

[0011] Further defined, in step 1, the width of the rectangular groove is 200 ± 10 μm, and the depth is 140 μm - 150 μm.

[0012] Further defined, in step 2, the concentration of nitric acid is 68%, the concentration of hydrofluoric acid is 40%, and the volume fraction ratio of nitric acid to hydrofluoric acid is (4 - 5):1.

[0013] Further defined, in step 4, the concentration of the dilute hydrochloric acid is 0.4M - 0.5M.

[0014] Further defined, in step 4, the pickling time is 6h - 7h.

[0015] Further defined, in step 4, dry it in the oven at 50 °C for 0.5h - 1h.

[0016] Further defined, in step 4, the calcination process: heat it in a muffle furnace to 500 °C at a rate of 5 °C / s, keep it warm for 2 hours, and cool it to room temperature with the furnace.

[0017] Another object of the present invention is to provide a wick of a micro-nano composite structure titanium-water ultra-thin planar heat pipe prepared by any of the above methods.

[0018] Further defined, having a micro-nano composite structure, CA = 3.6°.

[0019] Although microgrooves can be prepared by methods such as machining, stamping, and laser processing, their production efficiency is low and the production cycle is long. Although nanostructures can be achieved by anodic oxidation, the processing parameters and experimental conditions of anodic oxidation fluctuate greatly, the structural parameters of the prepared titanium dioxide nanotubes are unstable, and the production efficiency is low.

[0020] The closest prior art solution (Xie Jie, Xu Zhiming, Yang Biqi, Ding Chaogang, Liu Gang, Shan Debin, Song Bingke, Guo Bin, A vapor chamber wick structure and its preparation method [P]. Application number: 202410743598.7, 2022-03-29.) is to prepare carbon nanotubes on the micro-pits processed by laser using chemical vapor deposition, which can simultaneously increase the bubble nucleation site density and enhance capillary action. However, this method has low processing efficiency, a cumbersome process, and great preparation difficulty. Since the metal substrate and carbon nanotubes are not in-situ prepared from the same material, the bonding ability between the carbon nanotubes and the metal substrate is poor, resulting in poor stability of the micro-nano composite structure. The present invention proposes a method for preparing a micro-nano structure that can simultaneously improve the capillary action and nucleation sites of the liquid-absorbing core of a flat heat pipe. Based on the roll forming method, regular micron-scale liquid-absorbing core microstructures are manufactured. Subsequently, hydrophilic nanostructures are prepared by hydrothermal method in a strong alkali solution, and a liquid-absorbing core of a micro-nano composite structure that can simultaneously increase the bubble nucleation density and has strong capillary action is manufactured, finally endowing the titanium flat heat pipe with excellent phase change heat transfer performance. The processing size of the sheet material of the present invention can meet the manufacturing requirements of the liquid-absorbing core of an ultra-thin flat heat pipe, and the macroscopic size will reach 100×100mm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention applies rolling to obtain a liquid-absorbing core at the micron level, which greatly improves the processing efficiency. At the same time, titanium dioxide nanotubes are obtained by hydrothermal method in a strong alkali solution, improving the hydrophilicity of the liquid-absorbing core. This can stably and effectively prepare the liquid-absorbing core of an ultra-thin flat heat pipe.

[0023] The surface nanostructures prepared by traditional technologies have poor bonding ability with the substrate and will be washed away by the heat transfer working fluid during the heat transfer process. The present invention can successfully solve the problem of poor fixation of the product and the carrier;

[0024] Although the electrochemical method can control the thickness and morphology of the deposition layer by changing the current parameters, for plates of different sizes, there will be phenomena such as uneven deposition even with the same parameters; the present invention can ensure the uniformity of the morphology and performance of the surface micro-nano structure.

[0025] Although the crystals prepared by chemical vapor deposition have good quality, the deposition efficiency of its products is low, and the reaction gases are usually flammable, explosive, toxic, and corrosive. The micro-nano composite structure prepared by the present invention has high efficiency, stable performance, and lower requirements for reaction conditions.

[0026] In order to further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the accompanying drawings are only provided for reference and illustration purposes and are not used to limit the present invention. Description of the Drawings

[0027] Figure 1(a) is the three-dimensional morphology of micron-scale microgrooves prepared by the rolling method;

[0028] Figure 1(b) is the three-dimensional morphology of micron-scale microgrooves prepared by the rolling method;

[0029] Figure 1(c) is the cross-sectional size of micron-scale microgrooves prepared by the rolling method;

[0030] Figure 2 (a) is the hydrophilicity test of the wick of an ultra-thin planar heat pipe without structure;

[0031] Figure 2 (b) is the hydrophilicity test of the wick of an ultra-thin planar heat pipe with microstructures;

[0032] Figure 3 (a) and (b) are the surface morphologies of the wicks with nanostructures prepared by the hydrothermal method in a rolling-3M sodium hydroxide solution, Figure 3 (b) is Figure 3 a high-magnification enlarged view of (a);

[0033] Figure 3 (c) and (d) are the surface morphologies of the wicks with micro-nano composite structures prepared by the hydrothermal method in a rolling-3M sodium hydroxide solution, Figure 3 (d) is Figure 3 a high-magnification enlarged view of (c);

[0034] Figure 4 (a) and (b) are the surface morphologies of the wicks with nanostructures prepared by the hydrothermal method in a rolling-5M sodium hydroxide solution, Figure 4 (b) is Figure 4 a high-magnification enlarged view of (a);

[0035] Figure 4 (c) and (d) are the surface morphologies of the wicks with micro-nano composite structures prepared by the hydrothermal method in a rolling-5M sodium hydroxide solution, Figure 4 (d) is Figure 4 a high-magnification enlarged view of (c);

[0036] Figure 5(a) and (b) are the surface morphologies of the absorbent cores with nanostructures prepared by the hydrothermal method in a 7M sodium hydroxide solution under rolling; Figure 5 (b) is Figure 5 a high-magnification view of (a);

[0037] Figure 5 (c) and (d) are the surface morphologies of the absorbent cores with micro-nano composite structures prepared by the hydrothermal method in a 7M sodium hydroxide solution under rolling; Figure 5 (d) is Figure 5 a high-magnification view of (c);

[0038] Figure 6 (a) and (b) are the surface morphologies of the absorbent cores with nanostructures prepared by the hydrothermal method in a 10M sodium hydroxide solution under rolling; Figure 6 (b) is Figure 6 a high-magnification view of (a);

[0039] Figure 6 (c) and (d) are the surface morphologies of the absorbent cores with micro-nano composite structures prepared by the hydrothermal method in a 10M sodium hydroxide solution under rolling; Figure 6 (d) is Figure 6 a high-magnification view of (c);

[0040] Figure 7(a) shows the hydrophilicity test of the absorbent core with nanostructures prepared by the hydrothermal method in a 3M sodium hydroxide solution under rolling;

[0041] Figure 7(b) shows the hydrophilicity test of the absorbent core with micro-nano composite structures prepared by the hydrothermal method in a 3M sodium hydroxide solution under rolling;

[0042] Figure 7(c) shows the hydrophilicity test of the absorbent core with nanostructures prepared by the hydrothermal method in a 5M sodium hydroxide solution under rolling;

[0043] Figure 7(d) shows the hydrophilicity test of the absorbent core with micro-nano composite structures prepared by the hydrothermal method in a 5M sodium hydroxide solution under rolling;

[0044] Figure 7(e) shows the hydrophilicity test of the absorbent core with nanostructures prepared by the hydrothermal method in a 7M sodium hydroxide solution under rolling;

[0045] Figure 7(f) shows the hydrophilicity test of the absorbent core with micro-nano composite structures prepared by the hydrothermal method in a 7M sodium hydroxide solution under rolling;

[0046] Figure 7(g) shows the hydrophilicity test of the absorbent core with nanostructures prepared by the hydrothermal method in a 10M sodium hydroxide solution under rolling;

[0047] Figure 7(h) shows the hydrophilicity test of the absorbent core with micro-nano composite structures prepared by the hydrothermal method in a 10M sodium hydroxide solution under rolling; Detailed implementation manners

[0048] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and at the same time do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0049] Example 1: The preparation method of the micro-nano composite structure titanium-water ultra-thin planar heat pipe wick in the present invention is carried out according to the following steps:

[0050] Step 1: Roll rectangular micro-grooves on one side of a pure titanium plate (the micro-grooves are shown in Figures 1(a-c)), and place it in acetone for ultrasonic cleaning for 5 minutes to fully remove the oil on the surface.

[0051] Step 2: Then place it in a mixed solution of nitric acid and hydrofluoric acid (the concentration of nitric acid is 68%, the concentration of hydrofluoric acid is 40%, nitric acid volume fraction: hydrofluoric acid volume fraction = 4:1) to remove the surface oxide film, and then wash it thoroughly with clean water to wash away the residual acid solution on the surface.

[0052] Step 3: Then place it in a high-temperature and high-pressure reaction kettle filled with a 3M sodium hydroxide solution and seal it.

[0053] Step 4: Then place it in a high-temperature oven, heat it at 160 °C for 4 hours, take it out after cooling, sodium titanate is formed on the surface of the titanium plate with micro-structures (sodium titanate is unstable), and then pickled with 0.4M dilute hydrochloric acid for 6-7 hours. + Replace Na + fully to generate titanic acid, and then rinse it with deionized water to thoroughly remove Na + , and then place it in a drying oven, dry it at a temperature of 50 °C for 1 h, heat it to 500 °C at a rate of 5 °C / s (to obtain titanium dioxide nanotubes), keep it warm for 2 hours, and cool it to room temperature with the furnace, and finally obtain the micro-nano composite structure titanium-water ultra-thin planar heat pipe wick with a micro-nano composite structure.

[0054] Example 2: The difference between this example and Example 1 is that the concentration of the sodium hydroxide solution is 5M. Other reaction steps and parameters are the same as those in Example 1.

[0055] Example 3: The difference between this example and Example 1 is that the concentration of the sodium hydroxide solution is 7M. Other reaction steps and parameters are the same as those in Example 1.

[0056] Example 4: The difference between this example and Example 1 is that the concentration of the sodium hydroxide solution is 10M. Other reaction steps and parameters are the same as those in Example 1.

[0057] The three-dimensional morphology of the wick with micron-scale microgrooves obtained by rolling on a pure titanium plate is shown in Fig. 1(a). It can be found that its overall arrangement is neat and orderly. Fig. 1(b) is a partial enlarged view, from which it can be seen that the surface quality is flat and smooth. Fig. 1(c) is the sectional dimension diagram marked in Fig. 1(a), and it can be found that the width of the microgroove is about 200 microns, and the width of the microgroove remains at about 150 microns. The above research results show that high-quality microstructures can be manufactured through the rolling forming process.

[0058] The hydrophilicity test of the initial plate (unstructured pure titanium plate) is as Figure 2 (a) shows that the measured contact angle is 55.9°, showing a certain degree of hydrophilicity. However, after rolling, the hydrophilicity test of the wick of the ultra-thin planar heat pipe with microstructures shows that the contact angle is 152.2°, showing great hydrophobicity.

[0059] Figure 3 is the surface morphology diagram obtained by SEM analysis of the sample prepared under 3M sodium hydroxide solution. Among them Figure 3 (a)-(b) are nanostructures, Figure 3 (c)-(d) are micro-nano composite structures. It can be found that at this time, due to the low concentration of the sodium hydroxide solution, sodium hydroxide is not sufficient to cause the pure titanium to undergo a continuous reaction to generate a sufficient amount of sodium titanate, which will result in only a very thin layer of titanium dioxide being formed after subsequent replacement with hydrochloric acid. Moreover, network-like voids can be clearly seen in some areas, which are some unreacted areas where no titanium dioxide is formed. In addition, the morphology of the titanium dioxide at this time is fluffy and elongated linear. Figure 4 is the surface morphology diagram obtained by SEM analysis of the sample prepared under 5M sodium hydroxide solution. Among them Figure 4 (a)-(b) are nanostructures, Figure 4 (c)-(d) are micro-nano composite structures. It can be found that at this time, due to the increase in the concentration of the sodium hydroxide solution, sodium hydroxide can cause the pure titanium to undergo a continuous reaction to generate a sufficient amount of sodium titanate, which will result in the formation of cluster-like titanium dioxide after subsequent replacement with hydrochloric acid. At this time, some voids can still be seen in some areas, but the number of voids is not Figure 3 many. At this time, the titanium dioxide also gradually grows in the thickness direction, and the titanium dioxide has a certain thickness. The morphology of the titanium dioxide gradually grows into a needle shape.

[0060] Figure 5 and Figure 6 are respectively the surface morphology diagrams obtained by SEM analysis of the samples prepared under 7M and 10M sodium hydroxide solutions. Among them Figure 5 (a)-(b) and Figure 5 (a)-(b) are nanostructures, Figure 6(c)-(d) and 6(c)-(d) are micro-nano composite structures. It can be found that at this time, due to the high concentration of sodium hydroxide solution, sodium hydroxide can cause the pure titanium to undergo a continuous reaction to generate a sufficient amount of sodium titanate, which will lead to the formation of a dense titanium dioxide layer after subsequent displacement with hydrochloric acid. The layered structure of titanium dioxide is composed of short and thick titanium dioxide wires. In some areas, the voids can no longer be seen at all. The growth trend of titanium dioxide in the thickness direction is also getting better, and titanium dioxide has a certain thickness.

[0061] Figure 7 shows the hydrophilicity test of the wicking cores of micro-nano composite structures prepared by hydrothermal method with different concentrations of sodium hydroxide solution after rolling. The results show that for the nanostructures, when the concentration of sodium hydroxide is 3M, the contact angle decreases compared to the original structure without any structure, which is 44.4°. As the concentration of sodium hydroxide increases, the hydrophilicity gradually decreases. After reacting in a 10M sodium hydroxide solution, the contact angle decreases to 17.6°, which has reached the standard of superhydrophilicity. For the micro-nano composite structures, the contact angle is 100.3° when the concentration of sodium hydroxide is 3M. Although it still shows hydrophobicity, the contact angle decreases compared to the microstructures. When the concentration of sodium hydroxide is 5M, the contact angle decreases to 20.1°; when the concentration of sodium hydroxide further increases to 10M, the water droplet even completely spreads on the surface of its micro-nano structure, which is superhydrophilic. This meets the performance requirements of this design.

[0062] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A method for preparing a micro-nano composite structure wick of a titanium-water ultra-thin planar heat pipe, characterized in that, It includes the following steps: Step 1: Roll rectangular micro-grooves on a pure titanium plate, and place it in acetone for ultrasonic cleaning to fully remove the oil stains on the surface; Step 2: Then place it in a mixed solution of nitric acid and hydrofluoric acid to remove the surface oxide film, and then wash it thoroughly with clean water; Step 3: Then place it in a high-temperature and high-pressure reactor filled with a sodium hydroxide solution with a concentration of 3M - 10M, and seal it; Step 4: Then place it in an oven, heat it at 160 ± 2 °C for 4 hours, take it out after cooling, pickle it with dilute hydrochloric acid, rinse it with deionized water to completely remove Na + , dry it, and calcine it to complete.

2. The method according to claim 1, wherein The thickness of the pure titanium plate is 2 mm.

3. The method according to claim 1, wherein The width of the rectangular groove is 200 ± 10 microns, and the depth is 140 - 150 microns.

4. The method according to claim 1, wherein The concentration of nitric acid is 68%, the concentration of hydrofluoric acid is 40%, and the volume fraction ratio of nitric acid to hydrofluoric acid is (4 - 5):

1.

5. The method according to claim 1, wherein The concentration of dilute hydrochloric acid is 0.4M - 0.5M.

6. The method according to claim 1, wherein The pickling time is 6h - 7h.

7. The method according to claim 1, wherein Dry at 50°C for 0.5h - 1h.

8. The method according to claim 1, wherein Calcination process: Heat up to 500°C at a rate of 3°C / s - 5°C / s, hold for 2 hours, and cool to room temperature with the furnace.

9. A micro-nano composite structure titanium / water ultra-thin planar heat pipe wick prepared by the method according to any one of claims 1 - 8.

10. The wick according to claim 9, characterized in that, It has a micro-nano composite structure, and CA = 3.6°.

Images