Copper powder liquid wick and preparation method thereof

Abstract

The present invention discloses a copper powder wick and a preparation method thereof. The method comprises the following steps: oxidizing water-atomized copper powder, then partially reducing it at a temperature lower than the oxidation temperature to obtain semi-reduced copper powder with a reduced surface and a certain amount of residual oxygen inside. The method further comprises sintering the copper powder at a large temperature increase to reduce the residual oxygen inside the copper powder to form micropores. A large number of reduced pores still exist on the surface of the wick after sintering, thereby obtaining a copper powder wick with a higher porosity and a higher capillary climbing rate. The capillary climbing rate can be increased to 17.9 s / 100 mm, while maintaining a certain sintering strength. This effectively prevents the wick from breaking during the heat pipe preparation process and ensures stable heat pipe performance.

Description

Technical Field

[0001] The invention relates to the technical field of material preparation, and in particular to a method for improving the capillary climbing rate and porosity of a copper powder liquid-absorbing core. Background Art

[0002] With the advent of the 5G era, electronic devices are developing towards miniaturization, integration, and higher operating frequencies. Their heat generation per unit volume can reach 10 times or even higher than that of 4G devices. Heat dissipation modules with heat pipes are often used in engineering to conduct heat away from electronic devices. Therefore, higher requirements are placed on the thermal conductivity limit of heat pipes.

[0003] It is usually desirable to use copper powder wicks with higher porosity and higher capillary climbing rate to prepare "copper-water sintered heat pipes" to make the heat pipe's thermal conductivity capillary limit stronger. The capillary limit of a heat pipe is proportional to the amount of capillary reflux water. A capillary wick with high porosity absorbs more liquid and has a larger capillary reflux water volume. At the same time, a wick with high capillary climbing rate has a higher capillary reflux speed, which is also beneficial to improving the capillary limit of the heat pipe. Copper powder wicks with high capillary climbing rate and high porosity are the basis for the preparation of heat pipes with high thermal conductivity. During the preparation of the heat pipe, the outer copper powder is pulled when bent and is prone to breakage. This causes the working liquid to stop flowing at the break of the wick, greatly affecting the capillary performance of the heat pipe and causing a sharp drop in the thermal conductivity of the heat pipe. Therefore, the wick also needs to have sufficient tensile strength.

[0004] It should be noted that the wicks sintered from different types of copper powder have different capillary climbing rates, porosity and mechanical properties. Generally speaking, the wicks obtained by sintering copper powder with lower bulk density have higher capillary climbing rates and porosity, but the tensile strength of the wicks is reduced; the copper powder with smaller particle size has a higher capillary climbing rate, but the porosity is reduced. Copper powder with lower bulk density is more suitable for the preparation of high-power heat pipes, but there is a limit to the bulk density of copper powder prepared by water atomization process. Many researchers and engineers have begun to develop some copper powder post-processing processes to obtain copper powder with different properties to prepare heat pipes with better thermal conductivity. There are currently two main copper powder processing processes. One is to mix and sinter different types of copper powder, and the other is to add a pore-forming agent.

[0005] Chinese patent CN201610781175.X obtains thermally conductive copper powder by mixing copper oxide powder and electrolytic copper powder, sintering and crushing them, and its bulk density can reach 1.6 g / cm 3 The prepared wicks have a porosity of 57-80% and a high capillary creep rate of 13 s / 100 mm. This significantly increases the capillary creep rate by utilizing the unique dendritic structure of electrolytic copper powder. However, the high cost of electrolytic copper powder makes it unsuitable for large-scale industrial production.

[0006] Chinese patent CN202110799135.9 mixes and sinters 10% to 60% of non-dense copper powder (core-shell structure copper powder generated by oxidation-reduction) and 40% to 90% of dense copper powder (copper powder not subjected to oxidation-reduction treatment). The bulk density of the copper powder raw material used is 2.4 g / cm 3 The copper powder particle size ranged from 60 to 250 μm, resulting in a wick porosity of 50% to 57.9% and a capillary creep rate of 38.0 to 46.9 s / 100 mm. Common sintering methods involve increasing the temperature in the furnace, which causes the surface microporous structure to disappear. Consequently, the resulting wick porosity and capillary creep rate are low, making them unsuitable for industrial applications.

[0007] The literature "Cheng Qijun. Preparation of copper-based porous core materials for sintered heat pipes and research on their microstructure and properties [D]. Central South University, 2011." reports that using pore-forming agents such as CuCl2·2H2O to increase the porosity of the liquid-absorbing core can increase the porosity of the ball powder by about 7%, but the addition of pore-forming agents greatly reduces the strength of the sintered core.

[0008] In engineering applications, a simple manufacturing process is desirable. Water-atomized copper powder is commonly used as a filler powder in heat pipes because it is less expensive than electrolytic copper powder. In the 5G era, heat pipes are becoming increasingly thinner and have more stringent bending angles. It is desirable for the sintered wick to have a certain tensile strength to prevent wick breakage during heat pipe preparation. However, when the external dimensions of the heat pipe are extremely demanding, a reduction in powder strength is undesirable, and the use of pore-forming agents is no longer applicable. Therefore, in industrial heat pipe manufacturing, the key issue currently lies in how to use a low-cost, simple copper powder post-processing process that significantly improves heat pipe performance to achieve wicks with high capillary creep rates, high porosity, and high tensile strength. Summary of the Invention

[0009] The present invention aims to overcome the shortcomings of the prior art and provide a method for improving the capillary climbing rate and porosity of a copper powder absorbent wick. The method comprises the following steps: firstly, water-atomized copper powder is subjected to sufficient oxidation treatment, and then the oxidized copper powder is reduced at a temperature below the oxidation temperature to form a semi-reduced copper powder with a reduced surface and residual oxygen inside. The semi-reduced copper powder is then sintered in a reducing atmosphere to obtain a copper powder absorbent wick with high porosity and high capillary climbing rate. The core concept of the present invention is that the reduced portions of the semi-reduced copper powder surface contact each other during the sintering process, forming a sintering neck immediately. Heat is released when copper oxide is reduced to pure copper, which is conducive to forming a wick with high sintering strength and preventing the wick from breaking during the heat pipe preparation process. The residual oxygen element within the semi-reduced copper powder is used to delay the sintering process, reduce the wick shrinkage rate, and prevent over-sintering, thereby obtaining a wick with high porosity. The sintering parameters are adjusted so that the rough structure formed by the escape of residual oxygen during the reduction process is retained, and reduced pores are present on the surface of the wick after sintering, which is conducive to improving the capillary climbing rate of the wick, thereby obtaining a wick with a high capillary climbing rate.

[0010] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0011] A method for preparing a copper powder liquid wick comprises the following steps:

[0012] Step 1: oxidize the water-atomized copper powder raw material in an air atmosphere at a temperature not lower than 400° C. for more than 30 minutes, and increase the mass percentage by more than 3% after oxidation;

[0013] Step 2: First, heat to the reduction temperature, then add copper powder and perform surface reduction in a reducing atmosphere. The reduction temperature is 350-600°C and the time is 10-20 minutes. The reduction temperature is lower than the oxidation temperature in step 1 (not complete reduction, to ensure that only the oxygen elements on the surface of the copper powder are reduced, and the oxygen elements inside remain). After reduction, the surface of the copper powder is glossy, and some oxygen elements remain inside. The mass of the copper powder after oxidation and reduction increases by more than 1% compared to the mass of the copper powder raw material.

[0014] Step 3: After the sintering furnace is heated to above 650°C, the oxidized and reduced copper powder is placed in the furnace. The subsequent sintering furnace heating rate is 8-15°C / min. Sintering is carried out in a reducing atmosphere above 800°C for 20-60 minutes to obtain a copper powder wick. The copper powder sintering in step 3 should have a high heating rate. This method is the key to generating a microporous rough structure on the copper powder surface. The reason is that the reduction temperature of the oxidized copper powder is much lower than the sintering temperature of the copper powder. If the copper powder is heated with the furnace temperature, the residual oxygen inside the copper powder obtained in step 2 will be reduced first, and the effect of reducing the sintering shrinkage rate will not be obvious. In addition, the formed micropores are very easy to fuse and disappear during the subsequent sintering process, which fails to achieve the purpose of forming reduced micropores to increase the capillary climbing rate.

[0015] The copper powder sintering time should not be too long, otherwise the reduced pores produced cannot be retained, and the purpose of increasing the capillary climbing rate cannot be achieved. After sintering, if the copper powder does not fall off, it is considered a successful sintering. If the sintering is successful, the sintering time should be reduced to ensure that sufficient micropores remain.

[0016] Preferably, the bulk density of the water atomized copper powder is 1.7-2.2 g / cm 3 , particle size is 50~100 mesh.

[0017] Preferably, the oxidation temperature in step 1 is 450-700° C., the oxidation time is 40-120 min, and the mass increase percentage after oxidation is 6%-20%. According to the energy spectrum EDS test, the mass percentage of oxygen on the surface of the copper powder after oxidation is 15%-25%, which basically reaches the limit oxygen storage capacity of copper.

[0018] Preferably, the reduction temperature in step 2 is at least 50° C. lower than the oxidation temperature in step 1, and the mass increase percentage of the treated copper powder compared to the copper powder raw material is 1% to 5%.

[0019] Preferably, step 1 adopts dynamic oxidation to prevent the copper powder from sintering into agglomerates.

[0020] Preferably, the dynamic oxidation is to oxidize the copper powder for 20±10 min, stir the copper powder to a loose state after cooling, and then continue oxidation under the same conditions.

[0021] Preferably, the sintering temperature of the copper powder in step three is 860±40° C., and the mass percentage of oxygen in the sintered liquid wick tested by EDS energy spectrum is less than 0.5%.

[0022] Preferably, the reducing atmosphere in step 2 and step 3 is a nitrogen-hydrogen mixture, wherein the mass percentage of hydrogen is 5%; and the sintering time in step 3 is 30±10 min.

[0023] Preferably, the oxidation temperature in step 1 is 500±100°C, the reduction temperature in step 2 is 400±100°C, and the copper powder feeding temperature in step 3 is 100-200°C lower than the sintering temperature.

[0024] The principle of the present invention is as follows: sintering copper powder with a certain amount of residual oxygen inside it results in a lower sintering shrinkage, a higher porosity of the wick, a higher capillary climbing rate, and comparable tensile strength of the sintered body compared to sintering pure copper powder. Oxidized copper powder has a high melting point. If sintered directly at the original temperature, the rate of sintering neck formation is extremely low, resulting in a wick with low tensile strength, easy breakage, and easy powder shedding. Reducing the surface of the oxidized copper powder is beneficial to the formation of a sintering neck, ensuring comparable tensile strength of the sintered body. The residual oxygen inside the powder also slows down the sintering rate, thereby reducing the sintering shrinkage and increasing the porosity of the sintered body. During the sintering process, the residual oxygen inside the copper powder is reduced to form micropores. Under appropriate sintering process parameters, the micropores can be retained, which increases the roughness of the copper powder surface and helps improve the capillary climbing rate of the wick.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1) The present invention does not require the use of other auxiliary raw materials such as pore-forming agents and electrolytic copper powder, and can achieve a significant increase in the porosity and capillary climbing rate of the liquid absorbent core, which has the advantages of simple process and low cost.

[0027] 2) The copper powder sintered liquid absorbent core obtained by the method of the present invention has the characteristics of higher porosity and stronger capillary action. 3 , 70~80 mesh copper powder raw materials, according to this post-treatment process, the shrinkage rate of the wick can be reduced by up to 6%, the porosity can be increased by up to 5.93%, and the capillary climbing rate can be increased from 27.0 s / 100 mm to 17.9 s / 100 mm.

[0028] 3) The present invention adopts a large temperature increase range for sintering, such as adding copper powder for sintering after the furnace temperature reaches 700°C, which successfully retains the pore structure generated by the reduction process. The operation is simple and the capillary climbing rate is significantly improved.

[0029] 4) The porosity of the copper powder wick of the present invention is continuously adjustable, limited by the inhibitory effect of oxygen on the sintering process. The deeper the residual oxygen depth and the higher the residual oxygen content, the greater the wick porosity. Specifically, when other parameters remain constant, at the same oxidation temperature, the lower the reduction temperature, the greater the wick porosity; at the same reduction temperature, the higher the oxidation temperature, the greater the wick porosity.

[0030] 5) The present invention ensures sufficient sintering strength of the liquid wick, effectively prevents the problem of the liquid wick breaking during the heat pipe preparation process, and ensures stable performance of the heat pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1These are low-magnification scanning electron microscope images of the copper powder raw materials used in Examples 1 to 5.

[0032] Figure 2 These are high-magnification scanning electron microscope images of the copper powder raw materials used in Examples 1 to 5.

[0033] Figure 3 This is the surface morphology of the copper wick directly sintered from the copper powder raw material in Example 1.

[0034] Figure 4 This is the surface morphology of the copper powder in Example 2 after oxidation.

[0035] Figure 5 This is the surface morphology of the copper powder in Example 2 after oxidation and reduction.

[0036] Figure 6 This is the surface morphology of the copper powder after sintering that has undergone oxidation-reduction treatment in Example 2.

[0037] Figure 7 This is the surface morphology of the copper powder in Example 3 after oxidation.

[0038] Figure 8 This is the surface morphology of the copper powder in Example 3 after oxidation-reduction.

[0039] Figure 9 This is the surface morphology of the copper powder after sintering after oxidation-reduction treatment in Example 3.

[0040] Figure 10 The tensile strength distribution diagram of the absorbent cores of Examples 1 to 5 is shown. DETAILED DESCRIPTION

[0041] The present invention is further described below with reference to examples, and the scope of protection claimed in the present invention is not limited to the scope shown in the examples.

[0042] In this example, the bulk density is 2.08 g / cm 3 , 70~80 mesh copper powder is used as raw material, the powder morphology photo is as follows Figure 1 and Figure 2 shown.

[0043] The bulk density test method is based on GB / T 1479.1-2011 "Metal powders - Determination of bulk density - Part 1: Funnel method". The copper powder used is obtained by sieving. In the examples, 70-80 mesh copper powder is used to obtain more stable and reliable results.

[0044] The porosity and shrinkage test methods are as follows: a powder cake block is sintered in a graphite box with an inner chamber diameter of 25 mm and a depth of 8 mm; the porosity of the powder cake is calculated using the density method, and the shrinkage rate of the powder cake diameter is used as the shrinkage rate.

[0045] The capillary rise rate test method involves placing a 100 mm long, 20 mm wide copper powder sintered body into 10 mm deep pure water and recording the time it takes for the water to rise to the top. As the wick height increases, the capillary rise rate slows, with a value of 27.0 s / 100 mm indicating an acceptable capillary rise rate. Currently, there is no standardized method for testing the capillary rise rate of copper powder wicks. The test method used in this invention is similar to that in the literature and patents, providing good comparability.

[0046] The tensile strength test method is as follows: a cylindrical liquid-absorbing core sintered in a graphite mold with an inner chamber diameter of 10 mm and a depth of 150 mm is used to test its tensile strength using a universal mechanical testing machine.

[0047] All data are the average of the test results of three samples, and all samples are prepared from the same batch to ensure that the sample preparation conditions are absolutely the same.

[0048] Example 1

[0049] Example 1 was used as a control group experiment, in which copper powder raw materials were directly sintered. Figure 3 The microscopic surface morphology of the copper powder wick is shown in the figure, which shows a smooth surface and rounded corners.

[0050] Procedure: Copper powder raw material was sintered in a tube furnace at 860°C for 30 minutes in a nitrogen-hydrogen mixture flow rate of 20 L / min. The copper powder was fed into the furnace at 700°C (at a heating rate of 10°C / min). The target product was obtained after cooling to room temperature. The sintering shrinkage was 9.32%, the wick porosity was 57.36%, and the capillary creep rate was 27.0 s / 100 mm.

[0051] Example 2

[0052] A method for improving the capillary climbing rate and porosity of a copper powder wick comprises the following steps:

[0053] Step 1: Oxidize the copper powder in a tube furnace at 450°C with an air flow rate of 50 L / min for 20 minutes. After cooling, stir the copper powder until it is loose and then oxidize it under the same conditions for another 40 minutes. This effectively prevents the formation of sintering necks. The mass increase of the copper powder after oxidation is 6.04%. Figure 4 The microscopic surface morphology of the oxidized copper powder is shown.

[0054] Step 2: The copper powder obtained in step 1 was reduced in a tube furnace at 350°C with a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 10 min. Compared with the copper powder raw material, the mass increase percentage after oxidation-reduction was 2.19%, and the surface of the copper powder showed luster. Figure 5 Shows the microscopic surface morphology of incompletely reduced copper powder.

[0055] Step 3: The copper powder obtained in step 2 is sintered in a tubular furnace at 860°C and a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 30 min. The copper powder is fed into the furnace at a temperature of 700°C (heating rate of 10°C / min). The target product is obtained after cooling to room temperature.

[0056] According to EDS testing, the mass percentage of oxygen on the surface of copper powder after oxidation is 18.7%, the mass percentage of oxygen on the surface of copper powder after reduction is 2.53%, and the mass percentage of oxygen on the surface of copper powder after sintering is less than 0.2%. Figure 6 The microscopic surface morphology of the sintered copper powder is shown, with residual reduced microporous (~2 um) structure.

[0057] The tests showed that the porosity of the copper powder sintered body was 59.76%, the sintering shrinkage was 7.93%, and the capillary climbing rate of the wick was 21.4 s / 100 mm.

[0058] Example 3

[0059] A method for improving the capillary climbing rate and porosity of a copper powder wick comprises the following steps:

[0060] Step 1: Oxidize the copper powder in a tube furnace at 550°C and an air flow rate of 50 L / min for 20 minutes. After cooling, stir the copper powder until it is loose and then oxidize it under the same conditions for another 40 minutes. This effectively prevents the formation of sintering necks. The mass increase of the copper powder after oxidation is 9.61%. Figure 7 The microscopic surface morphology of the oxidized copper powder is shown.

[0061] Step 2: The copper powder obtained in step 1 was reduced in a tube furnace at 400°C with a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 10 min. Compared with the copper powder raw material, the mass increase percentage after oxidation-reduction was 3.51%, and the surface of the copper powder showed luster. Figure 8 Shows the microscopic surface morphology of incompletely reduced copper powder.

[0062] Step 3: The copper powder obtained in step 2 is sintered in a tube furnace at 860°C and a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 30 min. The copper powder is fed into the furnace at a temperature of 700°C (heating rate of 10°C / min). The target product is obtained after cooling to room temperature.

[0063] According to EDS testing, the mass percentage of oxygen on the surface of copper powder after oxidation is 19.9%, the mass percentage of oxygen on the surface of copper powder after reduction is 2.13%, and the mass percentage of oxygen on the surface of copper powder after sintering is less than 0.2%. Figure 9 The microscopic surface morphology of the sintered copper powder is shown, showing a large number of reduced micropores (~2 um) and a small number of cracks.

[0064] Testing revealed a porosity of 63.29% and a sintering shrinkage of 5.27% for the copper powder sintered body. The capillary rise rate was 17.9 s / 100 mm, meaning it took 17.9 s to rise 100 mm.

[0065] Compared with Example 2, in Example 3, the oxidation and reduction temperatures are higher, the mass percentage of residual oxygen elements is higher, the residual depth of oxygen elements is deeper, and the delaying effect on sintering is stronger, so the sintering shrinkage rate is smaller, and more reduced micropores formed during the sintering process are retained, which increases the capillary climbing rate of the liquid-absorbing core.

[0066] Example 4

[0067] A method for improving the capillary climbing rate and porosity of a copper powder wick comprises the following steps:

[0068] Step 1: Oxidize the copper powder in a tube furnace at 550°C and an air flow rate of 50 L / min for 20 minutes. After cooling, stir the copper powder until it is loose and then oxidize it under the same conditions for another 40 minutes. This effectively prevents the formation of sintering necks. The mass increase of the copper powder after oxidation is 9.61%.

[0069] Step 2: The copper powder obtained in step 1 was reduced in a tube furnace at 500°C and a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 10 min. Compared with the copper powder raw material, the mass increase percentage after oxidation-reduction was 2.04%, and the surface of the copper powder showed luster.

[0070] Step 3: The copper powder obtained in step 2 is sintered in a tubular furnace at 860°C (heating rate of 10°C / min) and a nitrogen-hydrogen mixed gas flow rate of 20 L / min for 30 min. The copper powder inlet temperature is 700°C. After cooling to room temperature, the target product can be obtained.

[0071] The tests showed that the porosity of the copper powder sintered body was 60.86%, the sintering shrinkage was 6.77%, and the capillary climbing rate of the wick was 18.7 s / 100 mm.

[0072] Compared with Example 3, the reduction temperature in Example 4 is higher, the mass percentage of residual oxygen element is lower, and the delay effect on sintering is weaker, so the sintering shrinkage rate is larger and the reduced pore structure can be well retained, resulting in a capillary climbing rate comparable to that of Example 3.

[0073] Example 5

[0074] Example 5 illustrates the necessity of reducing the oxidized copper powder, and the implementation steps are as follows:

[0075] Step 1: Oxidize the copper powder in a tube furnace at 550°C and an air flow rate of 50 L / min for 20 minutes. After cooling, stir the copper powder until it is loose and then oxidize it under the same conditions for another 40 minutes. This effectively prevents the formation of sintering necks. The mass increase of the copper powder after oxidation is 9.61%.

[0076] Step 2: The copper oxide powder obtained in step 1 is sintered in a tubular furnace at 860°C (heating rate of 10°C / min) and a nitrogen-hydrogen mixed gas flow rate of 20L / min for 30 min. The copper powder is fed into the furnace at a temperature of 700°C. After cooling to room temperature, the target product is obtained.

[0077] After testing, the shrinkage rate of the copper powder sintered body is extremely low, at 3.35%. There is black unreduced copper oxide powder in the sintered block, the sintering neck is not formed in large quantities, the sintering strength is low, the powder is easy to fall off, and it cannot be used.

[0078] For special pore structures such as wicks, the tensile strength test results are relatively discrete, such as Figure 10 As shown, the tensile strengths of the samples obtained in Examples 1 to 4 ranged from 1.81 to 3.23 MPa. The average tensile strength of Example 2 was the highest, at 2.73 MPa, and the average tensile strength of Example 1 was 2.53 MPa. This indicates that the tensile strength of the wick is substantially not weakened after treatment according to the present invention. The tensile strength of Example 5 was all below 1.59 MPa, fully demonstrating that the tensile strength of the copper powder without surface reduction decreased significantly after sintering, which could cause the problem of split breakage during the heat pipe preparation process.

[0079] Table 1 Process parameters and product performance test results of Examples 1 to 5 (average value)

[0080]

[0081] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a copper powder liquid wick, characterized in that: The following steps are involved: Step 1: oxidizing the water-atomized copper powder raw material, wherein the copper powder after oxidation increases in mass by more than 3% compared to the water-atomized copper powder raw material; Step 2: First, the temperature is raised to the reduction temperature, and then the oxidized copper powder is added and the surface is reduced in a reducing atmosphere. The reduction temperature is 350-600 ° C and the time is 10-20 minutes. The reduction temperature is lower than the oxidation temperature in step 1. After the reduction, the surface of the copper powder is glossy and some oxygen elements remain inside. The mass of the copper powder after oxidation and reduction increases by more than 1% compared with the mass of the water-atomized copper powder raw material. Step 3: After the sintering furnace is heated to above 650°C, the oxidized and reduced copper powder is added. The subsequent sintering furnace heating rate is 8~15°C / min, and sintering is carried out in a reducing atmosphere above 800°C for 20~60 minutes to obtain the copper powder liquid absorbent core.

2. The preparation method according to claim 1, characterized in that The bulk density of the water atomized copper powder is 1.7-2.2 g / cm 3 , particle size is 50~100 mesh.

3. The preparation method according to claim 1, characterized in that The oxidation temperature in step 1 is 450-700 °C, and the oxidation time is 40-120 min. The mass increase of the oxidized copper powder compared with the water-atomized copper powder raw material is 6%-20%. The EDS test shows that the mass percentage of oxygen on the surface of the oxidized copper powder is 15%-25%.

4. The preparation method according to claim 3, characterized in that The reduction temperature in step 2 is at least 50° C. lower than the oxidation temperature in step 1, and the mass of the copper powder after oxidation-reduction increases by 1% to 5% compared to the mass of the water-atomized copper powder raw material.

5. The preparation method according to claim 4, characterized in that Step one uses dynamic oxidation.

6. The preparation method according to claim 5, characterized in that The dynamic oxidation is to oxidize the copper powder for 20±10 minutes, stir the copper powder to a loose state after cooling, and then continue oxidation under the same conditions.

7. The preparation method according to any one of claims 1 to 6, characterized in that The sintering temperature in step 3 is 860±40° C., and the mass percentage of oxygen in the sintered liquid wick tested by EDS energy spectrum is less than 0.5%.

8. The preparation method according to claim 7, characterized in that The reducing atmosphere in step 2 and step 3 is a nitrogen-hydrogen mixture, wherein the mass percentage of hydrogen is 5%; and the sintering time in step 3 is 30±10 min.

9. The preparation method according to claim 8, characterized in that The oxidation temperature in step 1 is 500±100°C, the reduction temperature in step 2 is 400±100°C, and the copper powder feed temperature after oxidation-reduction in step 3 is 100~200°C lower than the sintering temperature.

10. The copper powder liquid wick prepared by the method according to any one of claims 1 to 9.

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