Method of manufacturing metal material formed of NANO particle layer having water absorption function

Abstract

To provide a method of manufacturing metal material having a nano particle layer useful as a constitution member of a heat pipe of which the heat transport efficiency is improved.SOLUTION: In a device for forming a nano particle layer on a metal substrate which includes a heating section, a boiling section connecting to the heating section, and a condensation section connecting to the boiling section, the metal substrate and dispersion liquid are brought into contact with each other on the boiling section, and such conditions as to reflux liquid on the condensation section and as to return liquid to the boiling section are satisfied. Otherwise, such processes as to take out the metal substrate from the dispersion liquid and as to remove components deposited other than such boiling are added. Removal of the components deposited is performed by such a method as to suck water adhered on the surface of the metal substrate taken out from the dispersion liquid, or is performed by such a method as to blow off water attached onto the surface from the metal substrate taken out from the dispersion liquid. Colloidal particles are at least one kind of the colloidal particles selected from a group composed of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a metal material having a nanoparticle layer, and further relates to a method for manufacturing a metal material having a nanoparticle layer where the metal base material is a component of a heat pipe.

Background Art

[0002] Various techniques have been proposed so far to provide a layer (hereinafter also referred to as a functional layer) having functions according to the purpose and application on the surface of a metal base material. Further, as an improvement thereof, development of a technique for forming the functional layer on a metal base material using particles having a particle diameter from the nano-order to the micro-order has been desired.

[0003] As a technique using the above nano-order particles, a method is disclosed in which a liquid containing nano-sized particles is boiled on the surface of a base material at a temperature higher than its standard boiling point under a pressure higher than atmospheric pressure, and the nano-order particles are deposited on the surface of the base material. This method is disclosed as a technique for forming a surface having good wettability by depositing particles having good wettability (Patent Document 1). Members or base materials having a surface showing good hydrophilicity (wettability) obtained by applying these techniques to the surface of a base material are expected to be applicable as materials for heat exchange elements such as heat pipes and fins.

[0004] The heat pipe is a heat exchange (cooling) device that encloses a wick (capillary structure) and a volatile refrigerant inside a tube and performs heat transport by utilizing the absorption and release of latent heat due to the evaporation and condensation (gas-liquid phase change) of the refrigerant. In recent years, heat pipes have been used as cooling devices for high-heat-generating electronic components in electronic devices, medical devices, and the like.

[0005] With the recent miniaturization and high-performance of electronic devices and medical devices, cooling devices for high-heat-generating electronic components such as the heat pipe have become one of the important technologies in electronic device design. In particular, in smartphones and tablet PCs, the space for cooling devices is limited, and when using high-heat-generation-density electronic elements for high-performance improvement, it is urgent to realize miniaturization and efficiency improvement of the cooling device.

[0006] As members for heat exchange elements such as the heat pipe, various materials and their manufacturing methods have been proposed. For example, a heat pipe (Patent Document 2) has been proposed that uses a monolithic porous body of silica having a three-dimensional network structure and voids as a wick that bears the core of the heat transport principle. Further, as a technique using the aforementioned nano-order particles, a method for manufacturing a heat pipe is disclosed in which the inside of the pipe portion constituting the heat pipe or a mesh having a role as a wick is immersed in a silica nanofluid, the nanofluid is nucleate-boiled, and a nano-particle layer is formed on the inside (inner wall) of the pipe portion or the mesh surface (Patent Document 3).

[0007] A method is disclosed in which a silica sol is brought into contact with a metal substrate, and colloidal silica particles are attached to the substrate in a state where the silica sol is maintained in a nucleate-boiling state near the surface of the metal substrate (Patent Document 4).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a method for producing a metal material having a nanoparticle layer by forming the nanoparticle layer on the surface of a metal substrate. Further, by having a nanoparticle layer having high water absorption performance, the moving speed of water by capillary force is increased, and thereby, an object is to provide a method for producing a metal material having a nanoparticle layer useful as a constituent member of a heat pipe for improving heat transport efficiency.

Means for Solving the Problems

[0010] As a first aspect, the present invention includes the following steps (a0) and (b0), and the steps (a0) and (b0) are sequentially performed in this order, or the steps (a0) and (b0) are performed simultaneously. A method for producing a metal material having a nanoparticle layer, the method including the following Method 1 or Method 2. Method 1: A method in which steps (a0) and (b0) satisfy the following (Condition 1). Method 2: A method in which, following steps (a0) and (b0), a further step (c0) is performed. (a0): A step of bringing a dispersion liquid containing colloidal particles having an average particle diameter (light scattering particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) of 1.0 to 10.0 into contact with a metal substrate. (b0): A step of maintaining the dispersion liquid in a nucleate boiling state in the vicinity of the surface of the metal substrate. (Condition 1): In an apparatus for forming a nanoparticle layer on a metal substrate, which includes a heating section, a boiling section connected to the heating section, and a condensation section connected to the boiling section, the condition comprising bringing the metal substrate into contact with the dispersion liquid in the boiling section, refluxing the liquid in the condensation section, and returning the liquid to the boiling section. (c0): A step of taking out the metal substrate from the dispersion liquid and removing components deposited other than nucleate boiling. As a second aspect, the removal of components deposited other than nucleate boiling in the step (c0) is performed by a method of sucking the surface-attached water of the metal substrate taken out from the dispersion liquid, or by a method of blowing off the surface-attached water from the metal substrate taken out from the dispersion liquid, the method for manufacturing a metal material according to the first aspect, As a third aspect, the colloidal particles are related to the cumulative diameters respectively obtained from the particle size distribution measurement values by the laser diffraction method, the ratio D of the 50% cumulative diameter (D 10 ) to the 10% cumulative diameter (D 50 ) 50 / D 10 is 1.0 or more and less than 2.5, and the ratio D of the 90% cumulative diameter (D 50 ) to the 50% cumulative diameter (D 90 ) 90 / D 50 is 1.0 or more and less than 2.5, the method for manufacturing a metal material having a nanoparticle layer according to the first aspect or the second aspect, As a fourth aspect, the step (a0) is a step of immersing a metal substrate in the dispersion liquid, the method for manufacturing a metal material having a nanoparticle layer according to any one of the first aspect to the third aspect, As a fifth aspect, the colloidal particles are colloidal particles of at least one inorganic oxide selected from the group consisting of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2, the method for manufacturing a metal material having a nanoparticle layer according to any one of the first aspect to the fourth aspect, As a sixth aspect, the metal material is a component of a heat pipe, the method for manufacturing a metal material having a nanoparticle layer according to any one of the first aspect to the fifth aspect, As a seventh aspect, the heat pipe includes a container filled with a working fluid and a metal wick in the container, the method for manufacturing a metal material having a nanoparticle layer according to the sixth aspect, As an eighth aspect, in a heat pipe including a container filled with a working fluid and a metal wick in the container, the metal material is a component of one or both of the wall surface in the container and the metal wick, the method for manufacturing a metal material having a nanoparticle layer according to the sixth aspect, and As a ninth aspect, there is provided a method for manufacturing a metal material having a nanoparticle layer according to any one of the first to eighth aspects, wherein the surface of the metal material is subjected to an etching treatment.

Advantages of the Invention

[0011] It is possible to manufacture a metal substrate having a nanoparticle layer with a high loading amount and enhanced uniformity on the surface of the metal material, and to provide a metal material capable of realizing high water absorption performance in the nanoparticle layer. By using the metal material having a nanoparticle layer formed on the surface obtained by the manufacturing method of the present invention for components such as a container of a heat pipe (the wall surface in the container is provided with the nanoparticle layer) and a metal wick of a heat pipe, it is expected that a heat pipe can be manufactured in which the moving speed of water due to capillary force is improved, the thermal resistance is reduced, and the heat transport efficiency is improved. Furthermore, it is expected that a heat pipe with an improved critical heat transport amount can be manufactured. In addition, the method of the present invention can manufacture a metal material having a nanoparticle layer formed on its surface regardless of the material shape, and a nanoparticle layer with a high loading amount and enhanced uniformity can be formed at a target location such as the wall surface in the container of the heat pipe or on the metal wick, and thus it is expected that a heat pipe with excellent heat transport performance can be manufactured.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] In the present invention, when adhering silica particles in a dispersion liquid (e.g., silica sol) containing colloidal particles in a nucleate boiling state to the surface of a metal material such as a heat pipe, it was found that there is a difference in water supply performance depending on the state of the adhered silica particles. And when forming a nanoparticle layer on a metal material, as a method for manufacturing the metal material, by adopting a method using an apparatus that performs a dispersion liquid containing colloidal particles in a reflux state, it was possible to achieve a state in which the state of the silica particles improves the water absorption performance. When performed in a released state, it is considered that the colloidal particles in the dispersion liquid adhere to the surface of the metal substrate in an aggregated state due to an increase in the concentration of the colloidal particles in the dispersion liquid. By performing it in a reflux state, it is considered that the individual colloidal particles adhere to the surface of the metal substrate in a state having a function. By adhering to the surface of the metal substrate in such a state, a gap is generated between the colloidal particles, and it is considered that a liquid such as water or a refrigerant is sucked up by capillary action through the gap to form a functional layer with high water absorption performance. Also, even after taking out the metal substrate from the apparatus used when manufacturing the metal material according to the present invention, when a dispersion liquid containing colloidal particles remains on the metal substrate, concentration of the colloidal particles in the remaining dispersion liquid occurs due to residual heat. Therefore, it is preferable to promptly remove it from the substrate. As a method for removing the dispersion liquid containing colloidal particles remaining on the metal substrate, methods such as sucking up the surface-attached water of the metal substrate or blowing off the surface-attached water from the metal substrate can be mentioned. At this time, sucking up the adsorbed water under pressure is not preferable because it compresses the surface-attached water, which tends to lead to aggregation of the colloidal particles. Therefore, it is considered that a functional layer with high water absorption performance can be formed by treating the metal substrate taken out from the coating apparatus (apparatus for forming a nanoparticle layer on the metal substrate) by a method that does not cause such a phenomenon. As a method for blowing off the surface-attached water from the metal substrate, a method of removing the surface-attached water with air without applying high pressure can be adopted. can be adopted.

[0014] The present invention focuses on the state of colloidal particles adhering to the surface of a metal material, that is, it focuses on the state of the dispersion liquid before the colloidal particles adhere and the state of the surface-attached water after the colloidal particles adhere, and by a method of avoiding the concentration and aggregation of the colloidal particles, a metal material having a nanoparticle layer with good water absorption performance, and furthermore, a method for manufacturing a component of a heat pipe has been found. It is considered that colloidal particles in an aggregated state have a smaller contact area with water (specific surface area) than colloidal particles in which no aggregated state is formed, resulting in problems with water absorption performance. In non-aggregated colloidal particles, there are gaps between the colloidal particles, and it is considered that capillary action is likely to occur through these gaps.

[0015] The manufacturing method of the metal material having a nanoparticle layer according to the present invention includes the following steps (a0) and (b0), and the steps (a0) and (b0) are sequentially implemented in this order, or the steps (a0) and (b0) are implemented simultaneously. The manufacturing method of the metal material having a nanoparticle layer includes the following Method 1 or Method 2. Method 1: The steps (a0) and (b0) are a method that satisfies the following (Condition 1). Method 2: A method in which, following the steps (a0) and (b0), a further step (c0) is performed. (a0): A step of bringing a dispersion liquid containing colloidal particles having an average particle diameter (light scattering particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) of 1.0 to 10.0 into contact with a metal substrate. (b0): A step of maintaining the dispersion liquid in a nucleate boiling state near the surface of the metal substrate. (Condition 1):: In an apparatus for forming a nanoparticle layer on a metal substrate, which includes a heating section, a boiling section connected to the heating section, and a condensation section connected to the boiling section, the steps (a0) and (b0) are a condition consisting of bringing the metal substrate into contact with the dispersion liquid in the boiling section, refluxing the liquid in the condensation section, and returning the liquid to the boiling section. (c0): A step of removing the metal substrate from the dispersion liquid and removing components deposited other than nucleate boiling.

[0016] [Step (a0)] This step is to bring a metal substrate described below into contact with a dispersion containing colloidal particles having a specific particle size. In the present invention, the contact form between the metal substrate and the dispersion is not particularly limited. For example, a form in which the metal substrate is immersed in the dispersion can be mentioned.

[0017] As an example of the step (a0), a step of bringing the dispersion into contact with a metal substrate heated to, for example, 100°C to 500°C under atmospheric pressure can be mentioned. The heating of the metal substrate can be performed by a hot plate, an electric furnace, etc. Further, the heating temperature can be 100°C to 500°C, or can be in the range of 200°C to 300°C. As the metal used for the substrate for forming the nanoparticle layer used in the present invention, a metal having a high thermal conductivity can preferably be used. For example, silver, copper, gold, aluminum, nickel, iron, zinc, and alloys containing these as main components can be used. Further, as the shape of the metal substrate, those having shapes such as plate shape, linear shape, mesh shape, curved surface shape, pipe shape, and fiber shape can be used. In particular, pipe-shaped or mesh-shaped metal substrates are suitable because they can also be used as components of a heat pipe. Note that the metal substrate may be subjected to an etching treatment on the surface for forming the nanoparticle layer. The colloidal particles used in the present invention can be, for example, colloidal particles of oxides (inorganic oxides) of atoms such as Si, Al, Ti, Zr, Fe, Cu, Zn, Mg, Ca, and Cs. The particles of the inorganic oxide are particles of oxides of atoms with valences of 2 to 6, and these original Examples of the oxides of these atoms include SiO2, Al2O3, TiO2, Fe2O3, CuO, ZnO, ZrO2, etc. The colloidal particles can be used in the form of a sol in which the colloidal particles are dispersed in a liquid medium. The shape of the colloidal particles is not particularly limited, and for example, spherical, chain-like, beaded, string-like, needle-like, rod-like, plate-like, and other non-spherical-shaped colloidal particles can be used. The particle shape can be observed by a transmission electron microscope or the like. Also, the colloidal particles can be produced by known methods (for example, ion exchange method, peptization method, hydrolysis method, reaction method (oxidation method), etc.).

[0018] Among the colloidal particles, in the present invention, colloidal particles of at least one inorganic oxide selected from the group consisting of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2 can be preferably used, and among them, colloidal silica (SiO2) particles can be preferably used. The colloidal silica particles can be used in the form of a dispersion (sol) in which the colloidal silica particles are dispersed in a liquid medium. Also, as the colloidal silica particles, a dispersion of colloidal silica particles produced by a known method (for example, ion exchange method, peptization method, hydrolysis method, reaction method (oxidation method), etc.) can be used. As a dispersion (sol) of colloidal silica particles dispersed in a liquid medium, commercially available products can be used. As an example, Nissan Chemical Industries, Ltd.'s product, trade name Snowtex (registered trademark), organosilica sol can be mentioned, but it is not limited thereto.

[0019] Also, by dispersing silica powder in a liquid medium, a dispersion of colloidal silica particles can be obtained and used as the colloidal particles according to the present invention. The silica powder (SiO2 powder) can be produced by known methods, for example, liquid phase methods (hydrolysis method, sol-gel method, hydrothermal method, coprecipitation method, freeze-drying method, etc.) or gas phase methods (melting method, spray drying method, gas phase reaction method (combustion hydrolysis, etc.)). Also, as described above, after producing colloidal silica particles by a known method (for example, ion exchange method, peptization method, hydrolysis method, reaction method, etc.), drying this to obtain silica powder can also be used. Commercially available silica powders can be used, and examples include, but are not limited to, the following. For example, AEROSIL (registered trademark) series manufactured by Nippon Aerosil Co., Ltd., Cab-O-SIL (registered trademark) series manufactured by Cabot Corporation, Sylysia (registered trademark) series manufactured by Fuji Silysia Chemical Ltd., Rheolosil (registered trademark) series manufactured by Tokuyama Corporation, Excellica (registered trademark) series, HDK (registered trademark) series manufactured by Asahi Kasei Wacker Silicone Co., Ltd., and the like.

[0020] <Average particle diameter (laser diffraction particle diameter), primary particle diameter (BET method particle diameter), and particle size distribution of colloidal particles> In the present invention, it is characterized by using colloidal particles having an average particle diameter (laser diffraction particle diameter) within a predetermined numerical range and a ratio of the average particle diameter (laser diffraction particle diameter) to the primary particle diameter (BET method particle diameter). Further, as described later, it is preferable to use colloidal particles having a cumulative diameter (particle size distribution) within a specific numerical range. In the present invention, by using colloidal particles with a small difference between the average particle diameter (laser diffraction particle diameter) and the primary particle diameter (BET method particle diameter), uniform particle size, high dispersibility, and less aggregation, it is considered that the adhesion amount can be increased and a uniform layer can be formed.

[0021] (Average particle diameter (laser diffraction particle diameter)) The laser diffraction particle diameter refers to the particle diameter measured by a particle diameter measuring device using the laser diffraction method or the dynamic light scattering method as the measurement principle. The average particle diameter (laser diffraction particle diameter) of colloidal particles can be measured by the dynamic light scattering method or the laser diffraction method. In particular, for colloidal particles having an average particle diameter (laser diffraction particle diameter) in the nano order used in the present invention, it is desirable to measure by the dynamic light scattering method. The average particle diameter (light scattering particle diameter) by the dynamic light scattering method (also referred to as the DLS average particle diameter) represents the average value of the secondary particle diameter (dispersion particle diameter). In the dispersion liquid containing colloidal particles before contacting the metal substrate in step (a0), it can be said to be an index for determining whether the colloidal particles in the liquid medium are in a dispersed state or an aggregated state. That is, it can be judged that the larger the DLS average particle diameter, the more the colloidal particles in the liquid medium are in an aggregated state. The colloidal particles used in the present invention have an average particle diameter (light scattering particle diameter) in the range of 5 nm to 800 nm, and for example, those in the range of 10 nm to 500 nm can be used.

[0022] (Primary particle diameter (BET method particle diameter)) The primary particle diameter (BET method particle diameter) of the colloidal particles used in the present invention is the specific surface area diameter (DB [nm]) obtained by measurement by the nitrogen gas adsorption method (BET method). When the particles are spherical, the specific surface area s measured by the nitrogen gas adsorption method and the specific surface area diameter d [nm] satisfy the relationship of s = 6000 / ρd (ρ [g / cm 3 is the density of the particles). That is, the primary particle diameter (BET method particle diameter) referred to in this specification is the particle diameter calculated according to the formula of s = 6000 / ρd using the specific surface area s measured by the nitrogen gas adsorption method. For example, when the colloidal particles are silica particles, the specific surface area diameter can be calculated with the particle density being 2.2 [g / cm 3 . As the primary particle diameter (BET method particle diameter) of the colloidal particles used in the present invention, those in the range of 1 nm to 100 nm, or 3 nm to 80 nm, or 5 nm to 80 nm can be used. As described above, since the average particle diameter (light scattering particle diameter) represents the average value of the secondary particle diameter, the size of the primary particle diameter (BET method particle diameter) does not exceed the average particle diameter (light scattering particle diameter).

[0023] (Average particle diameter (light scattering particle diameter) / Primary particle diameter (BET method particle diameter)) The ratio of the average particle diameter (laser scattering particle diameter) to the primary particle diameter (BET method particle diameter) is the ratio of the average particle diameter (laser scattering particle diameter) and the primary particle diameter (BET method particle diameter) measured by the above method, and can be used as an index of the size of the cluster size in which colloidal particles are formed. The ratio (average particle diameter (laser scattering particle diameter) / primary particle diameter (BET method particle diameter)) of the average particle diameter (laser scattering particle diameter) to the primary particle diameter (BET method particle diameter) of the colloidal particles used in the present invention is 1.0 to 10.0, and for example, those in the range of 1.0 to 8.0, or 1.0 to 6.0 can be used.

[0024] (Cumulative diameter (particle size distribution)) Regarding the cumulative diameter obtained from the particle size distribution measurement by the laser diffraction method, the colloidal particles used in the present invention have a ratio D 10 ) of the 50% cumulative diameter (D 50 ) to the 10% cumulative diameter (D 50 / D 10 of 1.0 or more and less than 2.5, and a ratio D 50 ) of the 90% cumulative diameter (D 90 ) to the 50% cumulative diameter (D 90 / D 50 of 1.0 or more and less than 2.5 is preferable. In this specification, the X% cumulative diameter (D X ) refers to the particle diameter corresponding to the cumulative X volume% from the small particle side of the cumulative particle size distribution (the cumulative value in the volume frequency particle size distribution is X%). The cumulative diameter is determined as follows. First, for a dispersion of particles or the like to be targeted, the particle size distribution is measured using a laser diffraction / scattering particle size distribution measuring device to obtain a volume-based cumulative particle size distribution curve. Then, in the obtained cumulative particle size distribution, the volume particle size at X% cumulative is defined as the X% cumulative diameter (D X ) of the particles or the like. The particle size distribution diameter can be measured using a laser diffraction / scattering particle size distribution measuring device regardless of whether the particle diameter is in the nano order or the micron order. Also, at the time of measurement, the measurement sample may be diluted or concentrated so that the scattering intensity becomes optimal.

[0025] (Dispersion containing colloidal particles) The dispersion containing colloidal particles used in the present invention can be obtained by diluting, if necessary, a dispersion (sol) in which the colloidal particles are dispersed in a liquid medium. In the dispersion containing colloidal particles, the concentration of the inorganic oxide (for example, SiO2 concentration) can be in the range of 0.1% by mass to 10% by mass, or 0.5% by mass to 10% by mass, or 1.0% by mass to 5% by mass. As the liquid medium, for example, an aqueous medium such as water, an organic solvent such as alcohol, glycol, ester, ketone, nitrogen-containing solvent, aromatic solvent, or a mixed solvent of an organic solvent and water can be used.

[0026] [Step (b0)] This step is a step of maintaining a nucleate boiling state in the vicinity of the surface of the metal substrate that has been brought into contact with the dispersion containing colloidal particles in the above step (a0). By this step, a nanoparticle layer composed of the colloidal particles in the dispersion is formed on the surface of the metal substrate.

[0027] The nucleate boiling state of the colloidal dispersion can be realized by heating at least one of the metal substrate (surface) and the dispersion at the time of their contact, that is, by heating one of them (to an extent that causes the dispersion to reach the nucleate boiling state) at the moment of their contact, or by heating one of them (to an extent that causes the dispersion to reach the nucleate boiling state) when they are in contact. This step can be carried out by bringing the metal substrate heated to a high temperature into contact with the dispersion, or by heating the dispersion. For example, as described above, it can be carried out by bringing the dispersion into contact with a metal substrate heated to, for example, 100°C to 500°C. As described above, step (b0) is carried out subsequent to step (a0), or can also be carried out simultaneously with step (a0). For example, when the metal substrate is immersed in the dispersion liquid, a heater is disposed in the vicinity of the metal substrate (for example, in contact with the metal substrate), and the metal substrate is heated, preferably directly heated, so that the dispersion liquid near the surface of the metal substrate can be efficiently brought into a nucleate boiling state.

[0028] (Nucleate boiling) The boiling phenomenon, which is a phenomenon in which a liquid is heated and undergoes a phase change to a gas, can be classified in various ways according to the flow situation of the liquid, the representative temperature of the liquid, the mechanism of boiling, etc. As an example, boiling when the liquid in the system is not forced to flow by a pump or the like is called pool boiling (or natural convection boiling), and in contrast, boiling when the liquid in the system is forced to flow is called forced convection boiling (or forced flow boiling). Pool boiling is a basic form for understanding the mechanism of flow boiling and is an important heat transfer mode in heat treatment of materials. When the heating temperature of the heat transfer surface is gradually increased, using a boiling curve showing how the heat flux transferred from the heat transfer surface to the liquid changes, pool boiling can be roughly divided into the following four regions. That is, the natural convection region (non-boiling) from the start of heating to the boiling start point, the nucleate boiling region from the boiling start point to the maximum heat flux point, the transition boiling region from the maximum heat flux point to the minimum heat flux point, and the film boiling region after the minimum heat flux point. The nucleate boiling used in the present invention is a boiling phenomenon that occurs in the nucleate boiling region. It is considered that air remaining in small depressions (cavities) on the heat transfer surface etc. becomes bubble nuclei and the growth of bubbles starts. In the present invention, it is considered that these bubble nuclei generated on the surface of the metal substrate become the starting points for the precipitation (adhesion) of the colloidal particles constituting the nanoparticle layer. The metal material obtained by the manufacturing method according to the present invention can be suitably used as a constituent member of a heat pipe described later.

[0029] As an example related to this immersion mode, an example of a schematic diagram of a coating device for forming a nanoparticle layer is shown in FIGS. 1 and 2. Figure 1 shows an apparatus used for manufacturing a metal material having a nanoparticle layer, which is performed under reflux and includes a condensation section A. A stainless steel plate 4 is placed on a lower heater (a cartridge heater 8 attached to a heat transfer copper block 7 on top of a brick 9), and a heat transfer member (heat transfer silicon 6) is installed on the stainless steel plate 4. A metal substrate 5 to be coated with the nanoparticle layer is placed on the heat transfer member, which serves as a heating section C. A dispersion liquid 3 containing colloidal particles is introduced into a polycarbonate container 2 having a part of the bottom surface of the metal substrate 5, which serves as a boiling section B. By heating the heater, the dispersion liquid 3 containing colloidal particles is heated through the heated heat transfer member and the metal substrate 5, and the dispersion liquid near the surface of the substrate reaches the nucleate boiling state, thereby forming a nanoparticle layer on the substrate surface. At this time, the liquid is refluxed by the condenser 1 and returned to the boiling section B. The boiling phenomenon in Figure 1 is pool boiling, which will be described later. Figure 2 shows an apparatus used for manufacturing a metal material having a nanoparticle layer, which is performed under open conditions, and includes the same members as in Figure 1 except that it does not include a condensation section A.

[0030] In the method for manufacturing a metal material having a nanoparticle layer of the present invention, it is performed by (Method 1) or (Method 2). (Method 1) is a method in which the (a0) step and the (b0) step satisfy (Condition 1). (Condition 1) is a condition in an apparatus for forming a nanoparticle layer on a metal substrate, which includes a heating section, a boiling section connected to the heating section, and a condensation section connected to the boiling section. In the boiling section, the metal substrate and the dispersion liquid are brought into contact, the liquid is refluxed in the condensation section, and the liquid is returned to the boiling section. In the apparatus for forming a nanoparticle layer on a metal substrate, the boiling section may be connected above, below, or laterally to the heating section, and the condensation section may be connected laterally or above the heating section and the boiling section. As shown in Figure 1, in the apparatus for forming a nanoparticle layer on a metal substrate, it is preferable that the boiling section is connected above the heating section and the condensation section is connected above the boiling section. In the apparatus used for the coating shown in Fig. 1, when the dispersion containing colloidal particles and the metal substrate are brought into contact in the boiling section in the nucleate boiling state, the dispersion medium in the dispersion in the boiling section is returned to the boiling section again by the condenser provided in the condensation section, so there is no significant change in the concentration of the colloidal particles in the dispersion containing the colloidal particles. Since there is little change in the concentration of the colloidal particles in the dispersion, aggregation of the colloidal particles is less likely to occur, and the colloidal particles in that state adhere to the metal substrate. As a result, an appropriate interval is created between the colloidal particles on the substrate surface, and it is considered that the water absorption performance is improved by the capillary phenomenon between the colloidal particles.

[0031] (Method 2) is a method in which, following the (a0) step and the (b0) step, a further (c0) step is performed. The (c0) step is a step of removing the metal substrate from the dispersion and removing the components deposited other than by nucleate boiling. The removal of the components deposited other than by nucleate boiling is performed by a method of sucking the surface-attached water of the metal substrate removed from the dispersion, or by a method of blowing off the surface-attached water from the metal substrate removed from the dispersion. The components deposited other than by nucleate boiling include the liquid remaining on the metal substrate when the metal substrate is removed from the dispersion. Although colloidal particles are present in these residual liquids, concentration of the colloidal particles occurs with the evaporation of the residual liquids, and aggregation of the colloidal particles occurs. This aggregation also inhibits the improvement of the water absorption performance by the capillary phenomenon between the colloidal particles when the nanoparticle layer is formed on the substrate surface, and it is preferable to remove it quickly from the substrate surface. Examples of the removal method include a method of sucking the surface-attached water of the metal substrate, or a method of tilting the metal substrate and dropping it downward. When removing the surface-attached water, there is also a method of wiping with absorbent paper or absorbent cloth, etc., but since pressure applied during wiping applies pressure between the colloidal particles and makes aggregation more likely to occur, a preferable removal method is, for example, a method of sucking using a sponge-like water-removing device. In addition, the method of blowing off the surface-attached water from the metal substrate taken out from the dispersion liquid is a method of removing the surface-attached water from the metal substrate, but it is also possible to blow off the surface-attached water at a low pressure using a gas. At that time, the metal substrate can also be tilted to let the surface-attached water drop off.

[0032] (Heat pipe) The heat pipe according to the present invention refers to a device having a mechanism for transferring heat from a high-temperature side to a low-temperature side. Generally, a heat pipe has a working fluid sealed in a container under vacuum, and also has a structure with a wick (capillary structure) in the container. When a part of the heat pipe is heated, the working fluid evaporates in the heating part and the vapor moves to the low-temperature part. The moved vapor condenses in the low-temperature part, and the condensed working fluid is refluxed to the heating part by the capillary action of the wick. By continuously repeating this mechanism, the function of transferring heat is realized. The shape of the heat pipe applied to the present invention is not particularly limited, and it can take various shapes such as a tube shape and a flat shape.

[0033] The constituent material of the heat pipe can be appropriately selected according to the use temperature range (operating temperature). As the container material of the heat pipe, it is preferably a material having good thermal conductivity, and further being chemically stable and less likely to cause chemical reactions or deterioration with the working fluid filled in the heat pipe. For example, the above-mentioned metal substrates and the like can be mentioned, and among them, materials with high heat conductivity such as copper, copper alloy, aluminum, aluminum alloy, iron, iron alloy, stainless steel, and nickel can be mentioned. Also, the shape of the container can take various shapes such as a round tube, a polygonal tube, a tube with an outer groove, and a tube with an inner groove. The metal material can use a substrate subjected to an etching process. In addition, the surface of the metal substrate may have an oxide of the metal formed thereon. Examples of the material of the wick include the same material as the container material. As its shape (structure), there are those with a structure in which grooves are directly formed on the inner wall surface of the container, and in addition to forms such as metal wires and metal meshes (wire meshes) separate from the container, sintered bodies of metal powders, metal foams, metal felts, etc. can also be mentioned. The working fluid is selected according to the operating temperature range of the heat pipe. When assuming the application locations (room temperature to about 200°C) of the heat pipe according to the present invention, such as electronic devices and medical devices such as smartphones, water and ethanol can be mentioned.

[0034] In the heat pipe according to the present invention, a metal base material to be the object of forming a nanoparticle layer can be applied as one or both of the constituent members of the inner wall surface of the container and the metal wick. That is, the heat pipe of the present invention can have the nanoparticle layer on one or both of the inner wall surface of the container and the surface of the metal wick. At this time, the surface of the metal base material, that is, one or both of the inner wall surface of the container and the surface of the wick can be subjected to etching treatment. The nanoparticle layer is a nanoparticle layer formed of colloidal particles having an average particle diameter (light scattering type particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering type particle diameter) to the primary particle diameter (BET method particle diameter) (average particle diameter (light scattering type particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. In the case where a nanoparticle layer is formed on the inner wall surface of the container in the heat pipe according to the present invention, the nanoparticle layer itself can have capillary force and can serve as a wick (capillary structure) of the heat pipe. Therefore, a separate metal wick may or may not be provided.

[0035] The heat pipe according to the present invention, for example, a heat pipe having a metal container filled with a working fluid, can be manufactured by a procedure including the following steps (a1) and (b1). (a1) The inner wall surface of the container constituting the heat pipe and an average particle diameter (light scattering type particle diameter) of 5 A step of bringing into contact a dispersion liquid containing colloidal particles having an average particle diameter (light scattering particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b1) A step of maintaining the dispersion liquid in a nucleate boiling state in the vicinity of the wall surface inside the container. The step (a1) and the step (b1) can be carried out by reading the metal substrate as the inner wall of the container in the step (a0) and the step (b0) of the above-mentioned [method for forming a nanoparticle layer on a metal substrate surface]. Similar to the step (a0) and the step (b0), the step (a1) and the step (b1) are sequentially carried out in this order, or the step (a1) and the step (b1) are carried out simultaneously.

[0036] In another aspect, a heat pipe according to the present invention, for example, a heat pipe having a metal container filled with a working fluid and a metal wick on the wall surface side inside the container, can be manufactured by a procedure including the following steps (a2) and (b2). (a2) A step of bringing into contact a metal wick constituting the heat pipe with a dispersion liquid containing colloidal particles having an average particle diameter (light scattering particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b2) A step of maintaining the dispersion liquid in a nucleate boiling state in the vicinity of the wick surface. The step (a2) and the step (b2) can be carried out by reading the metal substrate as the metal wick in the step (a0) and the step (b0) of the above-mentioned [method for forming a nanoparticle layer on a metal substrate surface]. Similar to the step (a0) and the step (b0), the step (a2) and the step (b2) are sequentially carried out in this order, or the step (a2) and the step (b2) are carried out simultaneously.

[0037] (Working fluid of the heat pipe) In the heat pipe of the present invention, water or ethanol described above can be used as the working fluid. In addition to these, a dispersion containing colloidal particles can be used as the working fluid. By using such a dispersion as the working fluid, it is expected that the colloidal particles in the dispersion will repair (fill the holes) the deteriorated portions of the nanoparticle layer due to the use of the heat pipe.

[0038] The colloidal particles can be colloidal particles of at least one inorganic oxide selected from the group consisting of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2. Also, colloidal particles containing two or more elements may be used for the purpose of improving the heat resistance of the working fluid. In particular, it is preferable to use a dispersion containing colloidal SiO2 particles, and the colloidal SiO2 particles may contain at least one element selected from Ti, Zr, Zn, Cu, and Al inside and / or on the surface of the particles.

[0039] Colloidal particles having an average particle diameter (light scattering particle diameter) in the range of 5 nm to 80 nm can be used, and the average particle diameter (light scattering particle diameter) can be measured by the dynamic light scattering method. As the average particle diameter (light scattering particle diameter) (DLS average particle diameter) of the colloidal particles in the working fluid used in the heat pipe of the present invention, for example, those having a diameter in the range of 5 nm to 80 nm, 5 nm to 50 nm, or 5 nm to 30 nm can be used. Also, colloidal particles having a primary particle diameter (BET method particle diameter) in the range of 1 nm to 50 nm can be used. The primary particle diameter (BET method particle diameter) is the specific surface area diameter (DB [nm]) obtained by measurement by the nitrogen gas adsorption method (BET method) as described above. Colloidal particles having a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) in the range of 0.8 to 1.5 can be used.

[0040] The dispersion liquid containing colloidal particles used for the working fluid can have a concentration of colloidal particles in terms of inorganic oxide of 0.001 mass% to 5.0 mass%. The concentration in terms of inorganic oxide can be quantified by a firing method. For example, it can be 0.001 mass% to 3.0 mass%, or 0.01 mass% to 3.0 mass%. As the dispersion medium in the dispersion liquid containing colloidal particles used for the working fluid, for example, an aqueous medium such as water, an organic solvent such as alcohol, glycol, ester, ketone, nitrogen-containing solvent, aromatic solvent, or a mixed solvent of an organic solvent and water can be used.

[0041] Also, the dispersion liquid containing colloidal particles used for the working fluid can have a pH in the range of 1 to 14, or 2 to 12. Also, the dispersion liquid containing the colloidal particles can have a viscosity of 0.1 to 5 mPa·s. The viscosity can be measured by the Ostwald method. Note that the dispersion liquid containing colloidal particles used for the working fluid in the heat pipe of the present invention may be the same as or different from the dispersion liquid containing colloidal particles for forming a nanoparticle layer.

[0042] (Evaluation of Heat Pipe) As indicators for performance evaluation of the heat pipe, wickability and the critical heat transport amount (Q max ) can be mentioned.

[0043] (Wickability) Wickability (Wi) is an indicator of water absorption performance (capillary force), and is often used in the study of pool boiling as a performance indicator of the heat transfer surface, which is related to the improvement of the critical heat transport amount (Q max ) described later. The higher the wickability, the higher Q max can be judged to be. Specifically, the liquid (working fluid, such as distilled water) in the capillary tube is sucked onto the heat transfer surface (the nanoparticle layer in the present invention), the decrease rate of the liquid level is measured, and the suction volume flow rate V0 of the liquid is obtained. Substitute V0 into the following formula (1) to calculate the Wickability: Wi.

Number

[0044] (Critical heat transport amount (Q max )) The critical heat transport amount (Q max ) refers to the heat transport amount when the heat flux of the heat transfer surface exceeds a certain value, and the combined bubbles inhibit the heat transfer from the heat transfer surface to the liquid, causing a sharp increase in the superheat degree of the heat transfer surface.

Example

[0045] The present invention will be described in detail with the following examples, but the present invention is not limited to these examples.

[0046] 〔1〕Measurement of the adhesion amount of the nanoparticle layer Let the mass of the copper substrate before nanoparticle layer coating be X0, and the mass of the copper substrate after nanoparticle layer coating be X1. The mass difference: X2 = X1 - X0 is defined as the adhesion amount of the nanoparticle layer to the metal substrate.

[0047] 〔2〕Evaluation of the water absorption performance of the metal substrate with the nanoparticle layer formed; water absorption height Add 1800 mL of pure water to a plastic container with a width of 30 cm × a depth of 30 cm × a height of 30 cm, and lean it against the container so that the end of the short side of the nanoparticle layer-coated substrate is immersed, and measure the height to which the pure water is sucked up. The suction height [mm] after 4200 seconds was evaluated as the water absorption performance. The larger the value of the suction height, the higher the water absorption performance, that is, it can be evaluated that the moving speed of water due to capillary force is faster.

[0048] 〔3〕Evaluation of the water absorption performance of the metal substrate with the nanoparticle layer formed; water absorption speed (V0) A glass capillary tube with an inner diameter of 1.05 mm was filled with distilled water, and the tip of the capillary tube was horizontally brought into contact with the nanoparticle layer surface of each substrate. Using a high-speed camera (High-Speed Camera 500 FPS, manufactured by Photron Ltd.), the process of the distilled water in the capillary tube being absorbed by the nanoparticle layer was photographed, and the rate of decrease in the liquid level in the capillary tube was measured. The volume flow rate V0 of the distilled water was calculated using the following calculation formula. The calculation of V0 was performed three times by changing the measurement site of the nanoparticle layer, and the average value of the obtained V0 was evaluated as the water absorption performance.

Number

[0049] 〔4〕Evaluation of the water absorption performance of the metal substrate with the nanoparticle layer formed; Wickability (Wi) V0 calculated in the above 〔3〕 was substituted into the following calculation formula to calculate Wi. The measurement of V0 and the calculation of Wi were performed three times by changing the measurement site of the nanoparticle layer, and the average value of the obtained Wi values was evaluated as the water absorption performance.

Number

[0050] The metal substrates used in the examples and comparative examples were prepared according to the following procedure. Copper plate with a thickness of 1 mm and dimensions: width 60 mm × length 170 mm (hereinafter referred to as copper substrate). The above copper substrate without surface treatment was used. The copper substrate was degreased in advance, thoroughly washed with pure water, and then dried with an air spray.

[0051] [Example 1] 95.1 g of pure water and 4.9 g of a water-dispersed silica sol (manufactured by Nissan Chemical Industries, Ltd., trade name Snowtex ST-O, solid content 20.5 mass%) were added to a 100 mL polypropylene container, and this was stirred with a magnetic stirrer for 5 minutes to prepare a nanofluid (dispersion containing colloidal particles) (silica concentration: 1.0 mass%). Next, the copper substrate was set in the coating device shown in the schematic diagram of FIG. 1, and 20 mL of the nanofluid was added to the water tank part of the device. It was confirmed that the copper substrate was completely immersed in the nanofluid. After heating to the temperature at which the nanofluid boils, boiling was maintained for 10 minutes. Next, the copper substrate was taken out from the water tank part, and the nanofluid adhering to the substrate was removed with a syringe. Then, the silica that did not adhere to the substrate was removed by blowing air with a hair dryer to obtain a nanoparticle layer-coated substrate. Regarding the produced nanoparticle layer-coated substrate, the evaluations of [1], [2], [3], and [4] were carried out. The evaluation results are shown in Table 1.

[0052] [Example 2] 95.1 g of pure water and 4.9 g of a water-dispersed silica sol (manufactured by Nissan Chemical Industries, Ltd., trade name Snowtex ST-O, solid content 20.5% by mass) were added to a 100 mL polypropylene container, and this was stirred with a magnetic stirrer for 5 minutes to prepare a nanofluid (silica concentration: 1.0% by mass). Next, the copper substrate was set in the coating device shown in the schematic diagram of FIG. 1, and 20 mL of the nanofluid was added to the water tank part of the device. It was confirmed that the copper substrate was completely immersed in the nanofluid. After heating to the temperature at which the nanofluid boils, boiling was maintained for 10 minutes. Next, the copper substrate was taken out from the water tank part, and the substrate was naturally dried. The evaluation was carried out in the same manner as in Example 1.

[0053] [Example 3] 95.1 g of pure water and 4.9 g of a water-dispersed silica sol (manufactured by Nissan Chemical Industries, Ltd., trade name Snowtex ST-O, solid content 20.5% by mass) were added to a 100 mL polypropylene container, and this was stirred with a magnetic stirrer for 5 minutes to prepare a nanofluid (silica concentration: 1.0% by mass). Next, the copper substrate was set in the coating device shown in the schematic diagram of FIG. 2, and 20 mL of the nanofluid was added to the water tank portion of the device. It was confirmed that the copper substrate was completely immersed in the nanofluid. After heating to the temperature at which the nanofluid boils, boiling was maintained for 10 minutes. Next, the copper substrate was taken out from the water tank portion, and the nanofluid adhering to the substrate was removed with a syringe. Thereafter, the silica content not adhering to the substrate was removed by blowing with a hair dryer to obtain a nanoparticle layer-coated substrate. The evaluation was performed in the same manner as in Example 1.

[0054] [Comparative Example 1] 95.1 g of pure water and 4.9 g of a water-dispersed silica sol (manufactured by Nissan Chemical Industries, Ltd., trade name Snowtex ST-O, solid content 20.5% by mass) were added to a 100 mL polypropylene container, and this was stirred with a magnetic stirrer for 5 minutes to prepare a nanofluid (silica concentration: 1.0% by mass). Next, the copper substrate was set in the coating device shown in the schematic diagram of FIG. 2, and 20 mL of the nanofluid was added to the water tank portion of the device. It was confirmed that the copper substrate was completely immersed in the nanofluid. After heating to the temperature at which the nanofluid boils, boiling was maintained for 10 minutes. Next, the copper substrate was taken out from the water tank portion, and the substrate was air-dried. The evaluation was performed in the same manner as in Example 1.

[0055]

Table 1

[0056] In the present invention, in Example 1 and Example 2 in which step (a0) and step (b0) were performed in a reflux state, good results were obtained in terms of the adhesion amount, water absorption height, water absorption rate, and water absorption performance as compared with Comparative Example 1 in which they were not performed. Also, in Example 1 and Example 3 in which step (c0) (in Table 1 above, the nanofluid removal step corresponds to step (c0)) was performed, good results were obtained in terms of the adhesion amount, water absorption height, water absorption rate, and water absorption performance as compared with Comparative Example 1 in which they were not performed. When the steps (a0) and (b0) were carried out in a reflux state and further the step (c0) was carried out, overall good results were obtained in all of the adhesion amount, water absorption height, water absorption rate, and water absorption performance.

Industrial Applicability

[0057] A method for manufacturing a metal material having a nanoparticle layer by forming the nanoparticle layer on the surface of a metal substrate, capable of manufacturing a heat pipe with improved heat transport efficiency.

Explanation of Signs

[0058] A Condensing section B Boiling section C Heating section 1 Condenser 2 Polycarbonate container 3 Nanofluid (dispersion containing colloidal particles) 4 Stainless steel plate 5 Metal substrate 6 Heat transfer silicon 7 Copper block for heat transfer 8 Cartridge heater 9 Brick

Claims

1. A method for manufacturing a metal material having a nanoparticle layer, including the following steps (a0) and (b0), wherein steps (a0) and (b0) are sequentially performed in this order, or steps (a0) and (b0) are performed simultaneously. The method includes Method 1 or Method 2 below. Method 1: A method in which steps (a0) and (b0) satisfy the following (Condition 1). Method 2: A method in which, following steps (a0) and (b0), a further step (c0) is performed. (a0): A step of bringing into contact a dispersion containing colloidal particles having an average particle diameter (light scattering particle diameter) of 5 nm to 800 nm and a ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) of 1.0 to 10.0 with a metal substrate. (b0): A step of maintaining the dispersion in a nucleate boiling state near the surface of the metal substrate. (Condition 1): In an apparatus for forming a nanoparticle layer on a metal substrate, which includes a heating section, a boiling section connected to the heating section, and a condensation section connected to the boiling section, a condition consisting of bringing the metal substrate into contact with the dispersion in the boiling section, refluxing the liquid in the condensation section, and returning the liquid to the boiling section. (c0): A step of removing the metal substrate from the dispersion and removing components deposited other than by nucleate boiling.

2. The method for manufacturing a metal material according to Claim 1, wherein the removal of components deposited other than by nucleate boiling in step (c0) is performed by a method of sucking up the surface-attached water of the metal substrate taken out of the dispersion, or by a method of blowing off the surface-attached water from the metal substrate taken out of the dispersion.

3. The colloidal particles are with respect to the cumulative diameters respectively obtained from the particle size distribution measurement values by the laser diffraction method. 10% cumulative diameter (D １０ ) to 50% cumulative diameter (D ５０ ) ratio D ５０ / D １０ is 1.0 or more and less than 2.5, and Ratio of the 90% cumulative diameter (D ５０ ), to the 50% cumulative diameter (D ９０ ), D ９０ / D ５０ is 1.0 or more and less than 2.5, the method for producing a metallic material having a nanoparticle layer according to claim 1 or claim 2.

4. The method for manufacturing a metal material having a nanoparticle layer according to Claim 1, wherein step (a0) is a step of immersing a metal substrate in the dispersion.

5. The colloidal particles are colloidal particles of at least one inorganic oxide selected from the group consisting of TiO ２ , ZrO ２ , ZnO, CuO, Al ２ O ３ , and SiO ２ , and a method for producing a metal material having a nanoparticle layer according to claim 1.

6. The method for manufacturing a metal material having a nanoparticle layer according to Claim 1, wherein the metal material is a component of a heat pipe.

7. The method for manufacturing a metal material having a nanoparticle layer according to Claim 6, wherein the heat pipe includes a container in which a working fluid is enclosed and a metal wick provided in the container.

8. In a container filled with a working fluid and a heat pipe having a metal wick therein, a method for manufacturing a metal material having a nanoparticle layer according to claim 6, wherein the metal material is a constituent member of one or both of the wall surface in the container and the metal wick.

9. A method for manufacturing a metal material having a nanoparticle layer according to claim 1, wherein the surface of the metal material is subjected to an etching treatment. of the metal material.

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