Method for manufacturing a metal substrate having a nanoparticle layer

Abstract

[Problem] To provide a method for forming a nanoparticle layer on the surface of a metal substrate, thereby manufacturing a metal substrate having the nanoparticle layer, and to consequently provide a method for manufacturing a heat pipe having improved heat transfer efficiency through use of the abovementioned method to form a nanoparticle layer with a high water absorption capacity on the surface of a metal substrate, i.e., manufacturing / providing a metal substrate having a nanoparticle layer with a high water absorption capacity, to increase the speed of migration of water due to capillary force. [Solution] A method for manufacturing a metal substrate having a nanoparticle layer, the method including steps (a0) and (b0) below, and in which steps (a2) and (b2) are sequentially carried out in the order listed, or steps (a2) and (b2) are simultaneously carried out. (a0) A step for bringing a dispersion and a metal substrate into contact with each other, the dispersion containing colloidal particles for which the average particle diameter (light-scattering particle diameter) is 5 nm to 800 nm and the ratio (average particle diameter (light-scattering particle diameter) / primary particle diameter (BET-method particle diameter)) between the average particle diameter (light-scattering particle diameter) and the primary particle diameter (BET-method particle diameter) is 1.0 to 10.0; and (b0) a step for maintaining the dispersion in a nucleate boiling state in the vicinity of the surface of the metal substrate.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a metal substrate having a nanoparticle layer, and more particularly to a method for manufacturing a metal substrate having a nanoparticle layer in which the metal substrate is a component of a heat pipe. [Background technology]

[0002] Various technologies have been proposed to date to create layers on the surface of metal substrates that impart functions according to their purpose and application. As a further improvement, there is a need for the development of a technology that uses particles with particle sizes ranging from nano-order to micro-order to form these functional layers on metal substrates. For example, a technique for forming an anti-corrosion layer on metal surfaces such as zinc and aluminum has been disclosed, which involves treating the metal surface with an agent containing nanoparticles with an average particle size of less than 500 nm, obtained by treating an aqueous solution containing metal oxocations and halogen complex anions (Patent Document 1). Furthermore, as a technology for ceramic coatings that improve scratch resistance and thermal conductivity, a ceramic coating is disclosed on a metal support containing a matrix containing reactive silane and particles such as diamond or silicon carbide with a size of 0.01 to 50 μm (Patent Document 2).

[0003] Furthermore, as an example of a technology for forming a functional layer on a metal substrate, a technique is known in which hydrophilicity is imparted to the surface of the metal substrate, thereby increasing the affinity between polar liquids such as water and the article (metal substrate). For example, an aluminum-based hydrophilic member is disclosed in which a portion of the surface layer of aluminum or an alloy is made into a mesh-like porous structure, and hydrophilic fine particles such as kaolinite or silica are supported and fixed to this structure (Patent Document 3). One technique using the nano-order particles described above involves boiling a liquid containing nanometer-sized particles on a substrate surface at a temperature higher than its standard boiling point under pressure higher than atmospheric pressure, thereby depositing the nano-order particles on the substrate surface. This technique is disclosed as a method for forming a surface with good wettability by depositing particles with good wettability (Patent Document 4). By applying these technologies to the surface of a substrate, components and substrates having surfaces exhibiting good hydrophilicity (wetting properties) are expected to be applicable as materials for heat exchange elements such as heat pipes and fins.

[0004] The aforementioned heat pipe is a heat exchange (cooling) device that transports heat by utilizing the absorption and release of latent heat through the evaporation and condensation (gas-liquid phase change) of the ventilator, which contains a wick (capillary structure) and a volatile refrigerant inside the tube. In recent years, heat pipes have been used as cooling devices for high-heat-generating electronic components in electronic equipment and medical devices. With the recent trend towards miniaturization and increased performance of electronic and medical devices, cooling devices for high-heat-generating electronic components such as heat pipes have become an important technology in electronic device design. In particular, in smartphones and tablet PCs, space for cooling devices is limited, and miniaturization and efficiency improvements of these cooling devices are urgently needed when using high-performance electronic elements with high heat density. As members for heat exchange elements such as the above heat pipes, various materials and their manufacturing methods have been proposed. For example, a heat pipe (Patent Document 5) has been proposed that uses a monolithic porous body of silica having a three-dimensional network structure skeleton and voids as a wick responsible for the core of the heat transport principle. Further, as a technique using the above-described nano-order particles, a method for manufacturing a heat pipe is disclosed in which the inside of a 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 6). Non-Patent Document 1 discloses that a nano-particle layer of TiO2 (Aeroxide TiO2P25), Al2O3 (Aeroxide Alu C), and SiO2 (Aeroxide 90G) is formed on the surface of a copper substrate by nucleate boiling of a nanofluid.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a method for manufacturing a metal substrate having a nanoparticle layer by forming a nanoparticle layer on the surface of a metal substrate. As a result, by forming a nanoparticle layer having high water absorption performance on the surface of a metal substrate, that is, by manufacturing and providing a metal substrate 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 manufacturing a heat pipe with improved heat transport efficiency.

Means for Solving the Problems

[0008] [[ID=,17]]As a result of earnestly studying to solve the above problems, the inventors of the present invention have found that in the vicinity of the surface of a metal substrate, by maintaining a dispersion liquid containing 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 a nucleate boiling state, a metal substrate having a nanoparticle layer with high uniformity and a high loading amount on the surface can be obtained, and the metal substrate having the nanoparticle layer on the surface has high water absorption performance and is useful as a material for a wick of a heat pipe, thus completing the present invention.

[0009] Specifically, the first aspect relates to a method for manufacturing a metal substrate having a nanoparticle layer, comprising the following steps (a0) and (b0). Here, steps (a0) and (b0) are carried out sequentially in this order, or steps (a0) and (b0) are carried out simultaneously. (a0) A step of bringing a metal substrate into contact with 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) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b0) A step of maintaining the dispersion in a nucleation boiling state near the surface of the metal substrate. From a second perspective, the colloidal particles, with respect to the cumulative diameter determined from the particle size distribution measurements by laser diffraction, 10% cumulative diameter (D 10 ) 50% cumulative diameter (D 50 ) ratio D 50 / D 10 The value is 1.0 or greater and less than 2.5, and 50% cumulative diameter (D 50 ) 90% cumulative diameter (D 90 ) ratio D 90 / D 50 The present invention relates to a method for manufacturing a metal substrate having a nanoparticle layer as described in the first aspect, wherein the ratio is 1.0 or greater and less than 2.5. The third aspect relates to a method for manufacturing a metal substrate according to the first or second aspect, wherein step (a0) is a step of bringing the dispersion liquid into contact with a metal substrate heated to 100 to 500°C in the gas phase. The fourth aspect relates to a method for manufacturing a metal substrate as described in the third aspect, wherein the gas phase consists of one or more gases selected from the group consisting of air, nitrogen, and argon. The fifth aspect relates to a method for manufacturing a metal substrate according to the third or fourth aspect, wherein step (a0) is a step of bringing droplets of the dispersion into contact with the metal substrate. The sixth aspect relates to the manufacturing method described in the first or second aspect, wherein step (a0) is a step of immersing a metal substrate in the dispersion. The seventh aspect relates to a method for producing a metal substrate having a nanoparticle layer according to any one of the first to sixth aspects, wherein 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 eighth aspect relates to a method for manufacturing a metal substrate having a nanoparticle layer according to any one of the first to seventh aspects, wherein the metal substrate is a component of a heat pipe. The ninth aspect relates to a method for manufacturing a metal substrate having a nanoparticle layer as described in the eighth aspect, wherein the heat pipe is a heat pipe comprising a container filled with a working fluid and a metal wick on the inner wall side of the container. The tenth aspect relates to a method for manufacturing a metal substrate having a nanoparticle layer according to any one of the first to ninth aspects, wherein the metal substrate is a component of one or both of the inner wall of the container and the metal wick in a heat pipe comprising a container filled with a working fluid and a metal wick on the inner wall side of the container. The eleventh aspect relates to a method for manufacturing a metal substrate having a nanoparticle layer according to any one of the first to eighth aspects and the tenth aspect, wherein the surface of the metal substrate is etched. The twelfth aspect is a method for manufacturing a heat pipe having a metal container filled with a working fluid, comprising the following steps (a1) and (b1), wherein steps (a1) and (b1) are carried out sequentially in this order, or steps (a1) and (b1) are carried out simultaneously. (a1) A step of bringing the inner wall of a container constituting a heat pipe into contact with 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) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b1) The process relates to maintaining the dispersion in a nucleation boiling state near the surface of the inner wall of the container. The thirteenth aspect relates to a method for manufacturing a heat pipe according to the twelfth aspect, wherein step (a1) is a step of bringing the dispersion liquid into contact with the inner wall of the container heated to 100 to 500°C in the gas phase. The 14th aspect relates to a method for manufacturing a heat pipe according to the 12th aspect, wherein step (a1) is a step of immersing the inner wall of the container in the dispersion. The 15th aspect relates to a method for manufacturing a heat pipe according to any one of the 12th to 14th aspects, wherein the inner wall of the container is etched. The 16th aspect relates to a method for manufacturing a heat pipe comprising a metal container filled with a working fluid and a metal wick on the inner wall side of the container, The present invention relates to a method for manufacturing a heat pipe, comprising the following steps (a2) and (b2), wherein steps (a2) and (b2) are performed sequentially in this order, or steps (a2) and (b2) are performed simultaneously. (a2) A step of bringing a metal wick constituting a heat pipe into contact with 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) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b) A step of maintaining the dispersion in a nucleation boiling state near the surface of the metal wick. The 17th aspect relates to a method for manufacturing a heat pipe according to the 16th aspect, wherein step (a2) is a step of bringing the dispersion liquid into contact with the metal wick heated to 100 to 500°C in the gas phase. The 18th aspect relates to a method for manufacturing a heat pipe according to the 16th aspect, wherein step (a2) is a step of immersing the metal wick in the dispersion. The 19th aspect relates to a method for manufacturing a heat pipe according to any one of the 16th to 18th aspects, wherein the surface of the metal wick is etched. The 20th aspect relates to a method for manufacturing a heat pipe according to any one of the 12th to 19th aspects, wherein the working fluid is a dispersion containing colloidal particles. The 21st aspect relates to a method for manufacturing a heat pipe according to any one of the 12th to 20th aspects, wherein the working fluid is a dispersion containing colloidal particles of at least one inorganic oxide selected from the group consisting of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2. From the 22nd perspective, a heat pipe comprising a metal container filled with a working fluid, The present invention relates to a heat pipe having a nanoparticle layer formed on the inner wall surface of the container, which is made of colloidal particles with 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. From the 23rd perspective, a heat pipe comprising a metal container filled with a working fluid and a metal wick on the inner wall side of the container, The surface of the inner wall of the container and the surface of the metal wick, or both, have a nanoparticle layer formed from 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. Regarding heat pipes. The 24th aspect relates to the heat pipe according to the 23rd aspect, wherein the nanoparticle layer is provided on one or both of the etched inner wall surface of the container and the etched surface of the metal wick. The 25th aspect relates to a heat pipe according to any one of the 22nd to 24th aspects, wherein the working fluid is a dispersion containing colloidal particles. The 26th aspect relates to a heat pipe according to any one of the 22nd to 25th aspects, wherein the working fluid is a dispersion containing colloidal particles of at least one inorganic oxide selected from the group consisting of TiO2, ZrO2, ZnO, CuO, Al2O3, and SiO2. [Effects of the Invention]

[0010] According to the present invention, it is possible to manufacture a metal substrate having a nanoparticle layer on the surface of the metal substrate with a high loading amount and enhanced uniformity, and to provide a metal substrate that can achieve high water absorption performance in the nanoparticle layer. Therefore, by using a metal substrate with a nanoparticle layer formed on its surface, obtained by the manufacturing method of the present invention, as a component of a heat pipe such as a heat pipe container (with the nanoparticle layer on the inner wall surface of the container) or a heat pipe metal wick, it is expected that the capillary action of water will be improved, thermal resistance will be reduced, and heat transport efficiency will be improved in the manufacture of a heat pipe. Furthermore, it is expected that a heat pipe with improved critical heat transport capacity will be manufactured. Furthermore, the method of the present invention can produce a metal substrate on which a nanoparticle layer is formed on its surface regardless of the substrate shape. This allows for the formation of a nanoparticle layer with high load capacity and improved uniformity in target locations such as the inner wall of a heat pipe container or on a metal wick, and is expected to enable the production of a heat pipe with excellent heat transport performance. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram of the coating apparatus used in the example. [Figure 2] Figure 2 shows an example of a heat pipe according to the present invention, where (a) is a partial side cross-sectional view of the heat pipe, and (b) is a partial enlarged view of A shown in (a). [Figure 3] Figure 3 is a graph showing the amount (mg) of nanoparticle layer attached to the substrates of the examples and comparative examples. [Figure 4]Figure 4 is a graph showing the results of the water absorption performance evaluation (absorption height (after 4200 seconds) (mm)) for the substrates of the examples and comparative examples. [Figure 5] Figure 5 is a schematic diagram of the coating apparatus used in the example to form a nanoparticle layer on the inner wall of a copper pipe. [Figure 6] Figure 6 shows a photograph taken from the inner wall side of a heat pipe in an embodiment, which has a nanoparticle layer formed on its inner wall surface, after it has been cut along the longitudinal direction of the pipe. [Figure 7] Figure 7 is a schematic diagram of the apparatus used to evaluate the performance of the heat pipe in the embodiment. [Modes for carrying out the invention]

[0012] As mentioned above, a technology has been proposed to form functional layers on a metal substrate using nano-order size particles, and as one such technology, it has been proposed to use a material with hydrophilic properties on the surface of a metal substrate as a material for heat exchange elements such as heat pipes. For example, as cited in Patent Document 4 and Non-Patent Document 1, a method for forming a nanoparticle layer on the surface of a metal substrate using nucleation boiling of nanofluids has been proposed. Non-Patent Document 1 states that the particle size distribution of oxide particles such as TiO2 is 80-800 nm in the nanofluid, which is significantly larger than the primary particles of the oxide (~20 nm), and it is speculated that this is a result of the particles forming clusters in the nanofluid. The formation of these particle clusters is expected to hinder the formation of a uniform layer when forming a nanoparticle layer on the substrate surface. While investigating methods for forming a nanoparticle layer on the surface of a metal substrate, the inventors investigated a method for manufacturing a metal substrate having a nanoparticle layer that can form more uniformly and in a larger quantity on the surface of the metal substrate, in order to further improve the desired function. The inventors focused on the average particle size (light scattering particle size) of the nanoparticles, as well as the ratio of the average particle size (light scattering particle size) to the primary particle size (BET particle size), and concluded that by employing highly dispersible colloidal particles and bringing the dispersion of these colloidal particles into a nucleated boiling state, the amount of adhesion can be increased, and a uniform nanoparticle layer can be formed, thus completing the present invention. Furthermore, by applying this technology to heat pipes, specifically to improve the heat transport efficiency and critical heat transport capacity of heat pipes, the present invention was completed by forming a nanoparticle layer more uniformly and in greater quantity on the surface of metal substrates such as the heat pipe container (inner wall) and metal wick, thereby enhancing the water absorption performance of the nanoparticle layer and improving the water movement speed by capillary action.

[0013] The present invention relates to a method for forming a nanoparticle layer on the surface of a metal substrate using nucleation boiling, that is, a method for manufacturing a metal substrate having a nanoparticle layer, and further relates to a method for manufacturing a metal substrate having a nanoparticle layer, in which a nanoparticle layer is formed on the surface of a metal substrate that is a component of a heat pipe. The present invention also relates to a heat pipe having a nanoparticle layer on the inner wall of a container or on the surface of a wick, and to a method for manufacturing a heat pipe using nucleation boiling.

[0014] [Method for manufacturing a metal substrate having a nanoparticle layer] The present invention provides a method for manufacturing a metal substrate having a nanoparticle layer, comprising the following steps (a0) and (b0). Steps (a0) and (b0) are carried out sequentially in this order, or steps (a0) and (b0) are carried out simultaneously. (a0) A step of bringing a metal substrate into contact with 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) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.0. (b0) A step of maintaining the dispersion in a nucleation boiling state near the surface of the metal substrate.

[0015] [(a0) process] This process involves bringing a metal substrate, described later, into contact with a dispersion containing colloidal particles having a specific particle size. In the present invention, the form of contact between the metal substrate and the dispersion is not particularly limited, but examples include a form in which the dispersion and the metal substrate are in contact in the gas phase (such as a form in which droplets of the dispersion are brought into contact with the metal substrate (spraying the dispersion), or a form in which the dispersion is applied to the metal substrate), or a form in which the metal substrate is immersed in the dispersion. In this invention, contact between the metal substrate and the dispersion is sufficient if the surface of the metal substrate forming the nanoparticle layer is in contact with the dispersion, and it is not necessary for the surface of a substrate that is not intended to form a nanoparticle layer to be in contact with the dispersion.

[0016] As an example of the above (a0) step, one can cite the step of bringing the dispersion liquid into contact with a metal substrate heated to, for example, 100°C to 500°C in the gas phase. The metal substrate can be heated using a hot plate, electric furnace, or the like. The heating temperature can be set to 100°C to 500°C, or to a range of 200°C to 300°C. The aforementioned gas phase can be selected from one or more gases, for example, consisting of air, nitrogen, and argon. While inert gases such as nitrogen and argon can be used as the gas phase to prevent oxidation of the metal substrate, air may also be used as the gas phase from the viewpoint of handling the dispersion and substrate. When contacting the dispersion and metal substrate in a gas phase other than air, this can be done using a gas-purged electric furnace with a constant supply of inert gas. The contact in the gas phase described above is preferably, for example, contact between the metal substrate and droplets of the dispersion. The droplets of the dispersion can be in the form of a sprayed dispersion, and one method of forming droplets of the dispersion is to pressurize the liquid to make it into a mist and then use a known sprayer that can spray it into the gas phase from a nozzle. Examples of such sprayers include spray guns, spray dryers, atomizers, dispensers (liquid metering devices), and electrostatic sprayers. Depending on the contact area, the power source for pressurization, such as manual power, electric motors, or power engines, can be appropriately selected. The average particle size (light scattering particle size) of the droplets is not particularly limited, but by using the above-described sprayer, droplets with an average particle diameter of several μm to several hundred μm can be sprayed in a mist-like manner.

[0017] <Metal substrate: Substrate for forming a nanoparticle layer> As the metal used for the substrate on which the nanoparticle layer used in the present invention is formed, a metal with 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. Furthermore, the metal substrate can be in various shapes, such as plate-like, linear, mesh-like, curved, pipe-like, or fibrous. In particular, pipe-like and mesh-like metal substrates are suitable because they can be used as components of heat pipes. The surface of the metal substrate that forms the nanoparticle layer may be etched.

[0018] <Colloidal particles> The colloidal particles used in this 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 inorganic oxide particles are particles of oxides of atoms with a valence of 2 to 6, and examples of oxides of these atoms include SiO2, Al2O3, TiO2, Fe2O3, CuO, ZnO, ZrO2, etc. The above-mentioned 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 described above is not particularly limited, and colloidal particles of spherical, chain-like, bead-like, string-like, needle-like, rod-like, plate-like, and other non-spherical shapes can be used. The particle shape can be observed using a transmission electron microscope or the like. Furthermore, the above-mentioned colloidal particles can be produced by known methods (for example, ion exchange, gelatinization, hydrolysis, reaction methods (oxidation), etc.).

[0019] Among the above 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 these, colloidal silica (SiO2) particles can be preferably used. Colloidal silica particles can be used in the form of a dispersion (sol) in which colloidal silica particles are dispersed in a liquid medium. Alternatively, a dispersion of colloidal silica particles produced by known methods (e.g., ion exchange, papular lysis, hydrolysis, reaction (oxidation), etc.) can be used as the colloidal silica particles. A commercially available product can be used as the dispersion (sol) of colloidal silica particles dispersed in a liquid medium. One example is, but is not limited to, OrganoSilicaSol, manufactured by Nissan Chemical Corporation, trade name Snowtex®.

[0020] Furthermore, 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 above-mentioned silica powder (SiO2 powder) can be produced by known methods, such as liquid-phase methods (hydrolysis, 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.)), etc.). Alternatively, as described above, colloidal silica particles can be produced by known methods (for example, ion exchange method, papular dissolution method, hydrolysis method, reaction method, etc.), and then dried to obtain silica powder. Commercially available silica powder can be used, and examples include, but are not limited to, the following. For example, the AEROSIL® series from Nippon Aerosil Co., Ltd., the Cab-O-SIL® series from Cabot Corporation, the Sylysia® series from Fuji Silysia Chemical Co., Ltd., the Rheoroseal® series and Excelica® series from Tokuyama Corporation, and the HDK® series from Asahi Kasei Wacker Silicone Co., Ltd.

[0021] <Average particle diameter (light scattering particle diameter), primary particle diameter (BET method particle diameter), and particle size distribution of colloidal particles> The present invention is characterized by using colloidal particles having an average particle diameter (light scattering particle diameter) within a predetermined numerical range, and a ratio between the average particle diameter (light scattering particle diameter) and the primary particle diameter (BET method particle diameter). Furthermore, as described later, it is preferable to use colloidal particles having a cumulative diameter (particle size distribution) within a specific numerical range. In this invention, by using colloidal particles that have a small difference between the average particle size (light scattering particle size) and the primary particle size (BET particle size), uniform particle size, high dispersibility, and low aggregation, it is believed that the amount of adhesion will be increased, leading to the formation of a uniform layer.

[0022] 《Average particle size (light scattering particle size)》 The light-scattering 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 (light-scattering particle diameter) of colloidal particles can be measured by the dynamic light scattering method or the laser diffraction method. In particular, for the colloidal particles with an average particle diameter (light-scattering particle diameter) in the nano order used in the present invention, it is desirable to measure them by the dynamic light scattering method. The average particle diameter (light-scattering particle diameter) (also referred to as DLS average particle diameter) by the above dynamic light scattering method represents the average value of the secondary particle diameter (dispersion particle diameter), and can be said to be an index for judging 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 colloidal particles in the liquid medium are in an aggregated state as the DLS average particle diameter becomes larger. 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.

[0023] 《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 measuring by the nitrogen gas adsorption method (BET method). When the particles are assumed to be 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 assuming the density of the particles is 2.2 [g / cm 3 . The primary particle diameter (BET particle diameter) of the colloidal particles used in this invention can be in the range of 1 nm to 100 nm, 3 nm to 80 nm, or 5 nm to 80 nm. As mentioned above, since the average particle diameter (light scattering particle diameter) represents the average value of the secondary particle diameters, the size of the primary particle diameter (BET particle diameter) will not exceed the average particle diameter (light scattering particle diameter).

[0024] 《Average particle size (light scattering method particle size) / primary particle size (BET method particle size)》 The ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) is the ratio of the average particle diameter (light scattering particle diameter) and the primary particle diameter (BET method particle diameter) measured by the above method, and can be used as an indicator of the size of the cluster formed by colloidal particles. The ratio of the average particle diameter (light scattering particle diameter) to the primary particle diameter (BET method particle diameter) of the colloidal particles used in this invention (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) 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.

[0025] 《Cumulative diameter (particle size distribution)》 The colloidal particles used in this invention have a cumulative diameter of 10% (D) as determined by particle size distribution measurement by laser diffraction. 10 ) 50% cumulative diameter (D 50 ) ratio D 50 / D 10 The value is 1.0 or greater and less than 2.5, and the 50% cumulative diameter (D 50 ) 90% cumulative diameter (D 90 ) ratio D 90 / D 50 It is preferable that the value is between 1.0 and less than 2.5. In this specification, the above X% cumulative diameter (D X ) refers to the particle size corresponding to the cumulative X volume % (the cumulative value in the volume frequency particle size distribution) from the small particle side of the cumulative particle size distribution. The cumulative diameter is determined as follows: First, the particle size distribution of the dispersion of the target particles is measured using a laser diffraction scattering particle size distribution analyzer to obtain a volume-based cumulative particle size distribution curve. Then, in the obtained cumulative particle size distribution, the volume particle size at X% accumulation is defined as the X% cumulative diameter (D) of the particles. X ) The above particle size distribution can be measured using a laser diffraction scattering particle size distribution analyzer, regardless of whether the particle size is on the nano-order or the micron-order. Furthermore, the measurement sample may be diluted or concentrated to optimize the scattering intensity during measurement.

[0026] <Dispersion containing colloidal particles> The dispersion containing colloidal particles used in the present invention can be used by diluting a dispersion (sol) in which the colloidal particles are dispersed in a liquid medium as needed. In a dispersion containing colloidal particles, the concentration of inorganic oxides (e.g., SiO2 concentration) can be in the range of 0.1% to 10% by mass, 0.5% to 10% by mass, or 1.0% to 5% by mass. Examples of the liquid mediums that can be used include aqueous media such as water, organic solvents such as alcohols, glycols, esters, ketones, nitrogen-containing solvents, and aromatic solvents, as well as mixed solvents of organic solvents and water.

[0027] [(b0) process] This step involves maintaining a nucleated boiling state near the surface of the metal substrate that has come into contact with the dispersion of colloidal particles in step (a0) above. This step forms a nanoparticle layer consisting of colloidal particles in the dispersion on the surface of the metal substrate.

[0028] The nucleated boiling state of the colloidal dispersion can be achieved by heating at least one of the metal substrate (surface) and the dispersion at the time of contact between them; that is, by heating one of them (to the extent that it causes the dispersion to reach a nucleated boiling state) at the moment of contact, or by heating one of them (to the extent that it causes the dispersion to reach a nucleated boiling state) while they are in contact. This process can be carried out by bringing the metal substrate, which has been heated to a high temperature, into contact with the dispersion, or by heating the dispersion. For example, as mentioned above, this can be carried out by bringing the dispersion into contact with a metal substrate heated to, for example, 100°C to 500°C (by spraying the dispersion onto the heated metal substrate). As mentioned above, step (b0) is performed following step (a0), or simultaneously with step (a0).

[0029] Furthermore, for example, when the metal substrate is immersed in the dispersion, by placing a heater near the metal substrate (for example, in contact with the metal substrate) and heating the metal substrate, preferably by directly heating the metal substrate, the dispersion near the surface of the metal substrate can be efficiently brought to a nucleation boiling state. As an example of the implementation of step (b0) related to this immersion method, Figure 1 shows an example of a schematic diagram of a coating apparatus for forming a nanoparticle layer. Figure 1 shows a cross-sectional view of the coating apparatus 1. A heat transfer member 3 and a rubber sheet 5 are placed on top of the heater 2 at the bottom, and the metal substrate 4 to be coated with a nanoparticle layer is placed on top of the heat transfer member 3. The rubber sheet 5 is arranged around the metal substrate 4 to form a tank-like shape with the metal substrate 4 as the bottom surface, and a stainless steel block 6 is placed on top of the rubber sheet 5. Then, the dispersion liquid N (nanofluid) containing the colloidal particles is poured into the tank-shaped apparatus with the metal substrate 4 as the bottom surface and the rubber sheet 5 and stainless steel block 6 as the inner surfaces. The heater 2 may be, for example, a copper block with a cartridge heater attached, and a copper block may be used as the heat transfer member 3. When heater 2 is heated, the dispersion N is heated through the heated heat transfer member 3 and metal substrate 4, causing the dispersion near the substrate surface to enter a nucleation boiling state, thereby forming a nanoparticle layer on the substrate surface. The boiling phenomenon shown in Figure 1 is pool boiling, which will be described later.

[0030] <Nuke boiling> Boiling, the phenomenon in which a liquid undergoes a phase change to a gas when heated, can be classified in various ways depending on the liquid's flow conditions, its typical temperature, and the boiling mechanism. For example, boiling that occurs when the liquid in a system is not forced to flow by a pump or other means is called pool boiling (or natural convection boiling), while boiling that occurs when the liquid in the system is forced to flow is called forced convection boiling (or forced flow boiling). Pool boiling is a fundamental form for understanding the mechanism of fluid boiling and is an important mode of heat transfer in the heat treatment of materials. Using a boiling curve that shows how the heat flux transferred from the heat transfer surface to the liquid changes as the heating temperature of the heat transfer surface is gradually increased, pool boiling can be broadly divided into the following four regions: the natural convection region (non-boiling) from the start of heating to the boiling point, the nucleation boiling region from the boiling 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 nucleated boiling used in this invention is a boiling phenomenon that occurs in the nucleated boiling region. It is believed that air remaining in small depressions (cavities) on the heat transfer surface acts as bubble nuclei, initiating bubble growth. In this invention, these bubble nuclei formed on the surface of the metal substrate are considered to be the starting point for the deposition (adhesion) of colloidal particles that constitute the nanoparticle layer.

[0031] The metal substrate obtained by the manufacturing method according to the present invention can be suitably used as a component of a heat pipe, as described later.

[0032] <Heat pipe> The heat pipe according to the present invention refers to a device that has a mechanism for transferring heat from a high-temperature side to a low-temperature side. Generally, a heat pipe has a structure that includes a working fluid sealed under vacuum inside a container, and a wick (capillary structure) on the inner wall of the container. When a part of the heat pipe is heated, the working fluid evaporates in the heated section and the vapor moves to the colder section. The vapor then condenses in the colder section, and the condensed working fluid is returned to the heated section by the capillary action of the wick. This mechanism is repeated continuously to achieve the function of transferring heat. The shape of the heat pipe to which this invention applies is not particularly limited and can take various shapes, such as a tube shape or a flattened shape.

[0033] The materials used in a heat pipe can be appropriately selected depending on the operating temperature range. The container material for the heat pipe described above is preferably a material that has good thermal conductivity and is chemically stable, so as not to undergo chemical reactions or degradation with the working fluid filled inside the heat pipe. Examples include the metal substrates mentioned above, and among these, materials with high heat conductivity such as copper, copper alloys, aluminum, aluminum alloys, iron, iron alloys, stainless steel, and nickel can be cited. Furthermore, the shape of the container can take various forms, such as round tubes, polygonal tubes, tubes with grooves on the outside, and tubes with grooves on the inside. Furthermore, the surface of the metal substrate may have an oxide of the metal formed on it. The materials for the wick mentioned above are the same as those for the container. In terms of shape (structure), examples include structures with grooves directly applied to the inner wall surface of the container, as well as metal wires or metal meshes (wire mesh) separate from the container, and also sintered metal powders, metal foams, and metal felts. The working fluid is selected according to the operating temperature range of the heat pipe. When considering application locations of the heat pipe according to the present invention (room temperature to approximately 200°C), such as electronic devices like smartphones and medical devices, water or ethanol can be used.

[0034] In the heat pipe according to the present invention, a metal substrate on which the nanoparticle layer is formed can be applied as a component of either or both of the inner wall of the container and the metal wick. That is, the heat pipe of the present invention may have the nanoparticle layer on either or both of the surface of the inner wall of the container and the surface of the metal wick. In this case, the surface of the metal substrate, i.e., either or both of the surface of the inner wall of the container and the surface of the wick, may be etched. The nanoparticle layer is a nanoparticle layer formed from 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. Furthermore, in the heat pipe according to the present invention, if a nanoparticle layer is formed on the inner wall of the container, the nanoparticle layer itself may have capillary action and can function as a wick (capillary structure) for the heat pipe. Therefore, a separate metal wick may or may not be provided.

[0035] A 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) A step of bringing the inner wall of a container constituting a heat pipe into contact with 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) (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 in a nucleation boiling state near the surface of the inner wall of the container. Steps (a1) and (b1) described above can be carried out by substituting the metal substrate with the inner wall of the container in steps (a0) and (b0) of the aforementioned [method for forming a nanoparticle layer on the surface of a metal substrate]. Also, similar to steps (a0) and (b0), steps (a1) and (b1) can be carried out sequentially in this order, or steps (a1) and (b1) can be carried out simultaneously.

[0036] In another embodiment, the heat pipe according to the present invention, for example, a heat pipe comprising a metal container filled with a working fluid and a metal wick on the inner wall side of the container, can be manufactured by a procedure including the steps (a2) and (b2) below. (a2) A step of bringing a metal wick constituting a heat pipe into contact with 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) (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 in a nucleation boiling state near the surface of the wick. Steps (a2) and (b2) described above can be carried out by substituting a metal wick for the metal substrate in steps (a0) and (b0) of the aforementioned [method for forming a nanoparticle layer on the surface of a metal substrate]. Also, similar to steps (a0) and (b0), steps (a2) and (b2) can be carried out sequentially in this order, or steps (a2) and (b2) can be carried out simultaneously.

[0037] Figure 2 shows an example of an embodiment of the heat pipe according to the present invention. Note that the heat pipe embodiment shown below is an exemplary embodiment of the present invention, and the heat pipe of the present invention is not limited to this example. In Figure 2, Figure 2(a) shows a partial side cross-sectional view of the heat pipe, and Figure 2(b) shows a magnified view of section A shown in Figure 2(a). As shown in Figure 2, the heat pipe HP according to this embodiment comprises a copper container C filled with a working fluid (not shown) and a wick (capillary structure, not shown) provided on the inner wall side of the container C, forming a liquid flow path (not shown) for the working fluid. The wick is formed of a nanoparticle layer NL for forming the liquid flow path. In this embodiment, the nanoparticle layer NL is attached to the entire inner wall surface of the container C.

[0038] <Working fluid for heat pipes> In the heat pipe of the present invention, while water or ethanol as described above can be used as the working fluid, a dispersion containing colloidal particles can also 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 in) the deteriorated parts of the nanoparticle layer caused by the use of the heat pipe.

[0039] 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. Alternatively, colloidal particles containing two or more elements may be used to improve the heat resistance of the working fluid. In particular, it is preferable to use a dispersion containing colloidal SiO2 particles, and these 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.

[0040] The colloidal particles can have an average particle diameter (light scattering particle diameter) in the range of 5 nm to 80 nm, and this average particle diameter (light scattering particle diameter) can be measured by dynamic light scattering. In the heat pipe of the present invention, for example, colloidal particles with an average particle diameter (light scattering particle diameter) (DLS average particle diameter) of 5 nm to 80 nm, 5 nm to 50 nm, or 5 nm to 30 nm can be used as the working fluid. Furthermore, the colloidal particles can be those with a primary particle size (BET method particle size) of 1 nm to 50 nm. The primary particle size (BET method particle size) is the specific surface area diameter (DB [nm]) obtained by measuring using the nitrogen gas adsorption method (BET method), as described above. The colloidal particles used have a ratio of average particle diameter (light scattering particle diameter) to primary particle diameter (BET method particle diameter) in the range of 0.8 to 1.5.

[0041] The dispersion containing colloidal particles used as the working fluid can have a concentration of 0.001% to 5.0% by mass of colloidal particles in terms of inorganic oxides. The concentration in terms of inorganic oxides can be quantified by calcination. For example, it can be 0.001% to 3.0% by mass or 0.01% to 3.0% by mass. As the dispersion medium in the dispersion liquid containing colloidal particles used in the working fluid, for example, an aqueous medium such as water, an organic solvent such as alcohol, glycol, ester, ketone, nitrogen-containing solvent, or aromatic solvent, or a mixed solvent of an organic solvent and water can be used.

[0042] Furthermore, the dispersion containing colloidal particles used as the working fluid may have a pH in the range of 1 to 14 or 2 to 12. Furthermore, the dispersion containing the colloidal particles may have a viscosity of 0.1 to 5 mPa·s. The viscosity can be measured by the Ostwald method. Furthermore, the dispersion containing colloidal particles used as the working fluid in the heat pipe of the present invention may be the same as, or different from, the dispersion containing colloidal particles used for forming the nanoparticle layer.

[0043] <Evaluation of heat pipes> As indicators for evaluating the performance of heat pipes, wickability and critical heat transport capacity (Q) are used. max ) can be cited.

[0044] Wickability Wickability (Wi) is an indicator of water absorption performance (capillary force), and is related to the critical heat transport capacity (Q), which will be discussed later. max It is often used in pool boiling studies as a performance index of the heat transfer surface, related to the improvement of ). The higher the wickability, the higher the Q max It can be determined that the value is high. Specifically, the liquid in the capillary tube (working fluid, e.g., distilled water) is drawn onto the heat transfer surface (the nanoparticle layer in this invention), the rate at which the liquid level decreases is measured, and the volumetric flow rate V0 of the drawn liquid is determined. V0 is substituted into the following equation (1) to calculate the wickability: Wi.

number

[0045] 《Critical heat transport capacity (Q max )》 Critical heat transport capacity (Q max This refers to the amount of heat transported when the heat flux on the heat transfer surface exceeds a certain value, causing the coalesced bubbles to obstruct the transfer of heat from the heat transfer surface to the liquid, resulting in a rapid increase in the superheating degree of the heat transfer surface. [Examples]

[0046] The present invention will be described in detail with reference to the following embodiments, but the present invention is not limited to these embodiments.

[0047] The metal substrates and silica particles (colloidal particles and powder particles) used in the examples and comparative examples were prepared according to the following procedure. The average particle size (light scattering particle size) of the colloidal particles and powder particles was also measured according to the following procedure. (1) The following metal substrates were prepared. (1-1) An aluminum plate with a thickness of 1 mm and dimensions of 44 mm in width and 155 mm in length (hereinafter referred to as the aluminum base material). The aforementioned aluminum substrate was pre-treated using a commercially available etching solution. (1-2) A copper plate with a thickness of 1 mm and dimensions of 60 mm in width and 170 mm in length (hereinafter referred to as the copper base material). The copper substrate used was one that had not undergone any surface treatment. The copper substrate was degreased beforehand, thoroughly washed with pure water, and then dried with an air spray. (2) The following silica particles (colloidal particles A and B, and powder particles C) were prepared. • Colloidal silica particles A: Water-dispersed silica sol (manufactured by Nissan Chemical Corporation, product name Snowtex ST-O, solid content 20.5% by mass) • Colloidal silica particles B: Water-dispersed silica sol (manufactured by Nissan Chemical Corporation, product name Snowtex ST-OUP, solid content 15.3% by mass) • Powdered silica particles C: Fumed silica (manufactured by Evonik, product name AEROSIL90G, solids content 100%) (3) The average particle size (light scattering particle size) and particle size distribution of the silica particles were measured according to the following procedure. Powdered silica particles C were dispersed in pure water and used as a dispersion. However, if the average particle size (light scattering particle size) obtained by the dynamic light scattering method described in (3-1) below was on the order of microns, the particle size measured according to (3-2) below was taken as the average particle size (light scattering particle size). (3-1) The average particle diameter (light scattering particle diameter) of the particles was measured by dynamic light scattering. After diluting the dispersion containing the silica particles with pure water, the average particle size (light scattering particle size) of each silica particle was measured using a dynamic light scattering measurement device: a zeta-sizer manufactured by Malvern Instruments Ltd., with silica (SiO2) parameters. (3-2) The particle size distribution (and average particle diameter (light scattering particle diameter)) of the particles was measured by laser diffraction. After diluting the dispersion containing the silica particles with pure water, the particle size distribution (and average particle diameter (light scattering particle diameter)) of the silica particles was measured using a Shimadzu Corporation SALD-7500nano. Here, [1.45-0.00i] was used as the substitute value for the refractive index. (3-3) The particle size distribution of the particles was measured by laser diffraction. When the average particle size (light-scattered particle size) obtained by the dynamic light scattering method described in (3-1) above was on the order of nanometers, the particle size distribution (and average particle size (light-scattered particle size)) of the silica particles was measured using a dispersion containing the silica particles with a Shimadzu Corporation SALD-7500nano. Here, [1.45-0.00i] was used as the substitute value for the refractive index. (4) Primary particle size of silica particles (BET method particle size) The average primary particle diameter (BET particle diameter) of the aforementioned particles was measured using the BET method. The specific surface area of ​​the dried powder or silica powder of the dispersion containing the aforementioned silica particles was measured using a Monosorb specific surface area analyzer manufactured by Yuasa Ionics Co., Ltd., and the average primary particle diameter (BET method particle diameter) of the silica particles was measured.

[0048] [Example 1] 91.8 g of pure water and 8.2 g of colloidal silica particles A (water-dispersed silica sol) were added to a 100 mL polypropylene container, and the mixture was stirred with a magnetic stirrer for 5 minutes to prepare nanofluid A (silica concentration: 1.7% by mass). Next, the aluminum substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 30 mL of nanofluid A was added to the water tank of the apparatus. After confirming that the aluminum substrate was completely immersed in nanofluid A, the apparatus was heated to the boiling point of nanofluid A. By maintaining the heating until the water in nanofluid A had completely evaporated, a nanoparticle layer was formed on the aluminum substrate. After the water in nanofluid A evaporated, 30 mL of nanofluid A was added again to the water tank, and the water was evaporated by heating and holding the tank, repeating this process five times. Then, the substrate was removed from the water tank, and the silica that was not attached to the substrate was removed (detached) by blowing air with a hairdryer to obtain nanoparticle layer coated substrate A.

[0049] [Example 2] 88.8 g of pure water and 11.2 g of colloidal silica particles B (water-dispersed silica sol) were added to a 100 mL polypropylene container, and the mixture was stirred with a magnetic stirrer for 5 minutes to prepare nanofluid B (silica concentration: 1.7% by mass). Next, the aluminum substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 30 mL of nanofluid B was added to the water tank of the apparatus. After confirming that the aluminum substrate was completely immersed in nanofluid B, the apparatus was heated to the boiling point of nanofluid B. By maintaining the heating until the water in nanofluid B had completely evaporated, a nanoparticle layer was formed on the aluminum substrate. After the water in nanofluid B evaporated, 30 mL of nanofluid B was added again to the water tank, and the water was evaporated by heating and holding the tank, repeating this process five times. Then, the substrate was removed from the water tank, and any silica that was not attached to the substrate was removed by blowing air with a hairdryer to obtain nanoparticle layer coated substrate B.

[0050] [Comparative Example 1] Nanofluid C was prepared by adding 295g of pure water and 5g of powdered silica particles C to a 300mL beaker and ultrasonically dispersing them for 3 hours using an ultrasonic stirrer (silica concentration: 1.7% by mass). Next, the aluminum substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 30 mL of nanofluid C was added to the water tank of the apparatus. After confirming that the aluminum substrate was completely immersed in nanofluid C, the apparatus was heated to the boiling point of nanofluid C. By maintaining the heating until the water in nanofluid C had completely evaporated, a nanoparticle layer was formed on the aluminum substrate. After the water in nanofluid C evaporated, 30 mL of nanofluid C was added again to the water tank, and the water was evaporated by heating and holding the tank, repeating this process five times. Then, the substrate was removed from the water tank, and any silica not adhering to the substrate was removed by blowing air with a hairdryer to obtain nanoparticle layer coated substrate C.

[0051] The nanoparticle layer coated substrates A to C obtained in Examples 1 and 2, and Comparative Example 1, were subjected to the tests described in (5) to (7) below. The aluminum substrate without the nanoparticle layer coating was designated as Comparative Example 2, and the test described in (7) below was performed on it. The obtained results, along with the measurement results of (3) average particle diameter (light scattering particle diameter) and particle size distribution, and (4) primary particle diameter (BET method particle diameter), are shown in Table 1, Figure 3, and Figure 4.

[0052] (5) Evaluation of the uniformity of the nanoparticle layer The uniformity of the nanoparticle layer formed on the surface of the metal substrate was evaluated visually according to the following evaluation criteria. <Evaluation Criteria> ◎: The coverage ratio of the nanoparticle layer (visually observed) is 80% or more of the substrate area. ○: The coverage ratio of the nanoparticle layer (visually observed) is 50% or more and less than 80% of the substrate area. ×: The coverage ratio of the nanoparticle layer (visually observed) is less than 50% of the substrate area.

[0053] (6) Measurement of the amount of nanoparticle layer attached The mass of the aluminum substrate before coating with the nanoparticle layer was denoted as X0, and the mass of the aluminum substrate after coating with the nanoparticle layer was denoted as X1. The difference in mass, X2 = X1 - X0, was defined as the amount of nanoparticle layer attached to the metal substrate. Figure 3 shows a graph illustrating the amount of attachment (mg) for each example.

[0054] (7) Evaluation of water absorption performance of metal substrates on which a nanoparticle layer is formed. 1800 mL of pure water was added to a plastic container measuring 30 cm wide x 30 cm deep x 30 cm high. A nanoparticle-coated substrate or an aluminum substrate was then propped up in the container so that its short edge was immersed in the water, and the height to which the pure water was absorbed was measured. The absorbance height [mm] after 4200 seconds was evaluated as the water absorption performance. Figure 4 shows a graph of the absorbance height (after 4200 seconds of immersion) (mm) for each example. The larger the suction height value, the higher the water absorption performance, which in turn indicates a faster water movement speed due to capillary action.

[0055] [Table 1]

[0056] As shown in Table 1, the nanoparticle layer coated substrates A and B obtained in Examples 1 and 2 had a nanoparticle layer coverage ratio (formation ratio) of 80% or more relative to the substrate area, and an adhesion amount exceeding 150 mg. Compared to the nanoparticle layer coated substrate C obtained in Comparative Example 1, which used a dispersion liquid (nanofluid C) outside the scope of the present invention (coverage ratio: less than 50%, adhesion amount: 50 mg or less), it was confirmed that these substrates were metal substrates having a nanoparticle layer with a high support amount and exhibiting high uniformity. Furthermore, regarding water absorption performance, nanoparticle-coated substrates A and B obtained in Examples 1 and 2 showed approximately 2 to 5 times higher water absorption height values ​​compared to nanoparticle-coated substrate C obtained in Comparative Example 1 and Comparative Example 2, which was a non-coated substrate (aluminum substrate). This confirmed that the nanoparticle-coated substrates of the examples are metal substrates with high water absorption performance.

[0057] [Example 3] 80.5 g of pure water and 19.5 g of colloidal silica particles A (water-dispersed silica sol) were added to a 100 mL polypropylene container, and the mixture was stirred with a magnetic stirrer for 5 minutes to prepare nanofluid D (silica concentration: 0.04 mass%). Next, the copper substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 40 mL of nanofluid D was added to the water tank of the apparatus. After confirming that the copper substrate was completely immersed in the nanofluid D, the apparatus was heated to the boiling point of the nanofluid D. By maintaining the heating until the water in the nanofluid D had completely evaporated, a nanoparticle layer was formed on the copper substrate. After the water in nanofluid D evaporated, 40 mL of nanofluid D was added again to the water tank, and the water was evaporated by heating and holding the tank, repeating this process five times. Then, the substrate was removed from the water tank, and any silica that was not attached to the substrate was removed by blowing air with a hairdryer to obtain nanoparticle layer coated substrate D.

[0058] [Example 4] 95.1 g of pure water and 4.9 g of colloidal silica particles A (water-dispersed silica sol) were added to a 100 mL polypropylene container, and the mixture was stirred with a magnetic stirrer for 5 minutes to prepare nanofluid E (silica concentration: 1.0 mass%). Next, the copper substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 20 mL of nanofluid E was added to the water tank of the apparatus. After confirming that the copper substrate was completely immersed in the nanofluid E, the apparatus was heated to the boiling point of the nanofluid E. By maintaining the heating until the water in the nanofluid E had completely evaporated, a nanoparticle layer was formed on the copper substrate. After the water in nanofluid E evaporated, 20 mL of nanofluid E was added to the water tank again, and the water was evaporated by heating and holding the tank, a process that was repeated 10 times. Then, the substrate was removed from the water tank, and any silica that was not attached to the substrate was removed by blowing air with a hairdryer to obtain nanoparticle layer coated substrate E.

[0059] [Example 5] 4345.1g of pure water and 654.9g of colloidal silica particles B (water-dispersed silica sol) were added to a 100mL polypropylene container, and the mixture was stirred with a magnetic stirrer for 5 minutes to prepare nanofluid F (silica concentration: 2.0% by mass). Next, polyimide tape was applied 1 cm from the edge of the copper substrate to mask the surface so that the coating area was 150 mm x 40 mm, thereby obtaining a masked copper substrate. The masked copper substrate was placed on a hot plate set to 450°C, and the surface temperature was measured with a non-contact thermometer. Heating was continued until the temperature reached 250°C. 700 mL of nanofluid B was poured into the tank of a spray gun (HVLP electric spray gun, manufactured by MonotaRO Co., Ltd.). After confirming that the surface temperature of the masked copper substrate reached 250°C, the entire substrate was sprayed with the spray gun, and spraying was stopped when the surface temperature reached 100°C. After confirming that the surface temperature of the masked copper substrate reached 250°C, the spraying process was repeated 7 times to form a nanoparticle layer on the copper substrate. Subsequently, the polyimide seal was removed, and any silica not adhering to the substrate was removed by air blowing to obtain a nanoparticle layer coated substrate F.

[0060] [Comparative Example 3] Nanofluid G was prepared by adding 299.8g of pure water and 0.12g of powdered silica particles C to a 300mL beaker and ultrasonically dispersing them for 3 hours using an ultrasonic stirrer (silica concentration: 0.04 mass%). Next, the copper substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 20 mL of nanofluid G was added to the water tank of the apparatus. After confirming that the copper substrate was completely immersed in the nanofluid G, the apparatus was heated to the boiling point of the nanofluid G. By maintaining the heating until the water in the nanofluid G had completely evaporated, a nanoparticle layer was formed on the copper substrate. After the water in nanofluid G evaporated, 20 mL of nanofluid G was added to the water tank again, and the water was evaporated by heating and holding the tank, a process that was repeated 10 times. Then, the substrate was removed from the water tank, and any silica that was not attached to the substrate was removed by blowing air with a hairdryer to obtain nanoparticle layer coated substrate G.

[0061] [Comparative Example 4] Nanofluid C was prepared by adding 295g of pure water and 5g of powdered silica particles C to a 300mL beaker and ultrasonically dispersing them for 3 hours using an ultrasonic stirrer (silica concentration: 1.7% by mass). Next, the copper substrate was placed in the coating apparatus shown in the schematic diagram of Figure 1, and 20 mL of nanofluid C was added to the water tank of the apparatus. After confirming that the copper substrate was completely immersed in nanofluid C, the apparatus was heated to the boiling point of nanofluid C. The heating was maintained until the water in nanofluid C had completely evaporated, but a nanoparticle layer could not be formed on the copper substrate.

[0062] The nanoparticle layer coated substrates D to F obtained in Examples 3 to 5 and Comparative Example 3 were subjected to the tests described in (5), (6) above and (8) below. The results obtained are shown in Table 2, along with the measurement results of (3) average particle diameter (light scattering particle diameter) and particle size distribution, and (4) primary particle diameter (BET method particle diameter).

[0063] (8) Evaluation of water absorption performance (Wickability) of metal substrates on which a nanoparticle layer is formed. Wickability (Wi) was measured as a performance indicator for the heat pipe. Distilled water was filled into a glass tube with an inner diameter of 1.05 mm, and the tip of the tube was brought into horizontal contact with the nanoparticle layer surface of each substrate. Using a high-speed camera (500 FPS high-speed camera, manufactured by Photron Co., Ltd.), the absorption of distilled water into the nanoparticle layer by capillary force was filmed, and the rate of decrease in the liquid level inside the tube was measured to calculate the volumetric flow rate V0 of the distilled water. Wi was calculated by substituting V0 into the following formula. Vo was measured and Wi was calculated three times by changing the measurement location of the nanoparticle layer, and the average value of the obtained Wi values ​​was used as the evaluation of water absorption performance (wickability).

number

[0064] [Table 2]

[0065] As shown in Table 2, the nanoparticle layer coated substrates D to F obtained in Examples 3 to 5 had a nanoparticle layer coverage ratio (formation ratio) of 80% or more relative to the substrate area, and the adhesion amount exceeded 20 mg, demonstrating high uniformity and confirming that they were metal substrates with a nanoparticle layer at a high load capacity. Furthermore, all nanoparticle layer coated substrates in Examples 3 to 5 had a water absorption performance (wickability) of 7 or higher. On the other hand, the nanoparticle layer coated substrate G of Comparative Example 3, obtained using a dispersion liquid (nanofluid G) outside the scope of the present invention, had a water absorption performance (wickability) of 9, but compared to Examples 3 to 5, it was significantly inferior in the uniformity of the nanoparticle layer and also had a smaller amount of adhesion (coating ratio: less than 50%, adhesion amount: 15 mg or less). Furthermore, the nanofluid C used in Comparative Example 1 was able to form a nanoparticle layer, albeit non-uniformly, on the aluminum substrate (Comparative Example 1), but it did not form a nanoparticle layer on the copper substrate (Comparative Example 4).

[0066] [Example 6] Fabrication of a heat pipe The heat pipe HP for Example 6 was fabricated using the following procedure. The heat pipe fabricated in this example has a length of 100 mm, an outer diameter of 8 mm, and an inner diameter of 7 mm.

[0067] Figure 5 shows a schematic diagram of a coating apparatus 30 that forms a nanoparticle layer on the inner wall of a copper pipe constituting a heat pipe. The device 30 has a configuration in which a nichrome wire heater 32 is wound around the outside of a copper pipe P. A heat-resistant polyimide tape 34 is placed between the conduit P and the nichrome wire heater 32, and a fluorine tape 36 is placed on the outside of the nichrome wire heater 32. These tapes 34 and 36 provide electrical insulation and heat insulation.

[0068] Using the aforementioned copper cylindrical tube as the copper tube P, and filling the inside of the copper tube P with the nanofluid D (SiO2 concentration: 0.04 mass%), the inner wall of the copper tube P is immersed in the nanofluid D. Then, using a bolt slider (not shown), the AC power supplied to the nichrome wire heater 30 is set to 180 kW / m². 2 The temperature was adjusted to induce nucleation boiling on the inner surface of the copper pipe P, forming a nanoparticle layer NL (see Figure 6, described later) across the entire inner wall surface of the container. The amount of nanoparticles attached to the heat pipe of Example 6 produced by this method was 1.3 g / m². 2 That was the case. Figure 6 shows the inner surface of the copper tube P on which the nanoparticle layer NL is formed. Note that the partially white areas in Figure 6 are due to light reflection.

[0069] Using a copper tube on which the nanoparticle layer NL obtained above was formed, pure water was sealed as the working fluid to fabricate the heat pipe of Example 6.

[0070] [Example 7] The heat pipe of Example 7 was fabricated in the same manner as in Example 6, except that a nanoparticle layer was formed using silica nanofluid E (SiO2 concentration: 1.0 mass%) instead of nanofluid D.

[0071] [Comparative Example 5] A heat pipe for Comparative Example 5 was fabricated in the same manner as in Example 6, except that the copper pipe before the nanoparticle layer was formed was used, and a brass mesh (wire diameter 85 μm, thickness 170 μm, no nanoparticle layer) was used as a wick and inserted into the copper pipe (neither the copper pipe nor the mesh had a nanoparticle layer coating).

[0072] [Comparative Example 6] The heat pipe of Comparative Example 6 was fabricated in the same manner as in Example 6, except that a nanoparticle layer was formed using silica nanofluid G (SiO2 concentration: 1.7 mass%) instead of nanofluid D.

[0073] [Example 8] The heat pipe of Example 8 was fabricated using the same procedure as in Example 7, except that silica nanofluid E was used as the working fluid instead of pure water.

[0074] (9) Heat transfer characteristics test of heat pipes The heat transfer characteristics of the heat pipes fabricated in Examples 6-8 and Comparative Examples 5-6 were evaluated using the following procedure.

[0075] Figure 7 shows a schematic diagram of the experimental apparatus (heat transfer characteristic test apparatus 40) used for conducting heat transfer characteristic experiments on heat pipes (HP). As shown in Figure 7, the device 40 has a configuration in which a nichrome wire heater 42 is wound around the outside of one end of a heat pipe 43 to heat it, and the outside of the other end is cooled with water 46 in a water tank 45. The part around which the nichrome wire heater is wound corresponds to the evaporation part of the heat pipe 43, and the part cooled by water 46 corresponds to the condensation part of the heat pipe 43. Insulation material 41 is placed on the outside of the nichrome wire heater 42 and on the outside of the heat pipe 43 leading to the water tank 45, and the temperature of the water 46 in the water tank 45 is controlled by a cooler 44 and a temperature control heater 47. Nine K-type thermocouples T1 to T18 are spot-welded to the evaporation section and condensation section of the heat pipe 43 (evaporation section: T1 to T9, condensation section: T10 to T18), and the temperature is measured and recorded by the data logger 48. Heating of the heat pipe 43 is performed by supplying power (not shown) to the nichrome wire heater 42, and the input heat quantity (power supplied) Q input Adjust the power within the range of 3W to 140W.

[0076] (9-1) Thermal resistance R Input heat quantity Q input The temperature difference ΔT = Te - Tc between the evaporation section (thermocouples T1 to T9) and the condensation section (thermocouples T10 to T18) was experimentally investigated when the temperature was changed and a steady state was reached (the state in which the temperature inside the heat pipe system becomes constant after the temperature change). The thermal resistance R of the heat pipe is the heat transport amount Q of the heat pipe (i.e., the input heat amount Q). input The input heat quantity Q is increased in stages, and each heat transport quantity Q (input heat quantity Q) is increased. input The following equation was used to define the steady state, using the temperature difference ΔT at which the value of ) was reached. R = ΔT / Q input (Formula 2)

[0077] (9-2) Limiting heat transport Q max Input heat quantity Q input When the value of is sufficiently small, the value of R is approximately constant, and ΔT and Q input A roughly linear relationship exists between them. On the other hand, the input heat quantity Q input Q is the limiting heat transport amount. max When it exceeds this value, the value of ΔT increases sharply, deviating from the linear relationship. Therefore, the relationship between ΔT and Q obtained experimentally is not clear. input Investigate the relationship and determine Q when it clearly deviates from a linear relationship. input The value of the critical heat transport quantity Q max That's what I decided. Furthermore, the region where ΔT does not change abruptly (the region with a linear relationship) can be considered to be the heat pipe operating normally, i.e., a high input heat quantity Q. input Even in this case, ΔT does not deviate from the linear relationship, that is, the limiting transport quantity Q max The higher the value, the better the heat pipe can be considered to be, as it can transport more heat.

[0078] The results obtained are shown in Tables 3 and 4. [Table 3] [Table 4]

[0079] The lower the thermal resistance R, and the lower the critical heat transport capacity Q. max A higher value indicates superior heat transfer characteristics. As shown in Tables 3 and 4, in the heat pipes (Examples 6-8) in which a nanoparticle layer was formed on the inner wall of the copper pipe using nanofluid D or nanofluid E, a reduction in thermal resistance R of about half was observed compared to a heat pipe (Comparative Example 5) that had a metal wick (mesh) but did not have a nanoparticle layer on either the inner wall of the copper pipe or the mesh, even without using a separate metal wick. On the other hand, in a heat pipe (Comparative Example 6) in which a nanoparticle layer was formed using a dispersion liquid (nanofluid G) outside the scope of the present invention, the thermal resistance R was reduced to about half compared to a heat pipe (Comparative Example 5) without a nanoparticle layer, but the critical heat transport amount Q was reduced. max The result was inferior. Thus, the fact that better heat transfer performance was obtained than existing specifications, even without installing a metal wick (mesh), is considered useful for developing small-scale heat transport devices. [Explanation of Symbols]

[0080] 1. Coating device 2. Heater 3. Heat transfer components 4...Metal base material 5. Rubber sheet 6. Stainless steel block N...Dispersion containing colloidal particles (nanofluid) HP Heat Pipe NL... Nanoparticle layer C...Container P... Copper pipe 30. Coating equipment 32. Nichrome wire heater 34. Heat-resistant polyimide tape 36. Fluorine tape 40. Heat transfer characteristics testing equipment 41...Insulation 42. Nichrome wire heater (heating section) 43. Heat pipe 44...Cooling pipe 45... Aquarium 46...Water 47. Temperature-controlled heater 48. Data logger T1~T18... Thermocouples (T1~T9: Thermocouples (heat pipe evaporation section), T10~T18: Thermocouples (heat pipe condensation section))

Claims

1. A method for manufacturing a metal substrate having a nanoparticle layer, comprising the following steps (a0) and (b0), wherein steps (a0) and (b0) are carried out sequentially in this order, or steps (a0) and (b0) are carried out simultaneously, (a0) A step of bringing a metal substrate into contact with 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) (average particle diameter (light scattering particle diameter) / primary particle diameter (BET method particle diameter)) of 1.0 to 10.

0. (b0) A step of maintaining the dispersion in a nucleation boiling state near the surface of the metal substrate, The aforementioned colloidal particles, with respect to the cumulative diameter determined from the particle size distribution measurement by laser diffraction, The ratio of the 50% cumulative diameter (D50) to the 10% cumulative diameter (D10), D50 / D10, is 1.0 or greater and less than 2.5, and The ratio of the 90% cumulative diameter (D90) to the 50% cumulative diameter (D50), D90 / D50, is 1.0 or greater and less than 2.

5. A method for producing a metal substrate having a nanoparticle layer.

2. The method for producing a metal substrate according to claim 1, wherein step (a0) is a step of bringing the dispersion liquid into contact with a metal substrate heated to 100 to 500°C in the gas phase.

3. The method for producing a metal substrate according to claim 2, wherein the gas phase consists of one or more gases selected from the group consisting of air, nitrogen, and argon.

4. The method for manufacturing a metal substrate according to claim 2 or 3, wherein step (a0) is a step of bringing droplets of the dispersion into contact with the metal substrate.

5. The manufacturing method according to claim 1, wherein step (a0) is a step of immersing a metal substrate in the dispersion.

6. The colloidal particles are TiO ２ , ZrO ２ , ZnO, CuO, Al ２ O ３ , and SiO ２ A method for producing a metal substrate having a nanoparticle layer according to claim 1, wherein the nanoparticle layer is at least one colloidal particle of an inorganic oxide selected from the group consisting of the following.

7. A method for manufacturing a metal substrate having a nanoparticle layer according to claim 1, wherein the metal substrate is a component of a heat pipe.

8. The method for manufacturing a metal substrate having a nanoparticle layer according to claim 7, wherein the heat pipe is a heat pipe comprising a container filled with a working fluid and a metal wick on the inner wall side of the container.

9. A method for manufacturing a metal substrate having a nanoparticle layer according to claim 1, wherein the metal substrate is a component of one or both of the inner wall of the container and the metal wick in a heat pipe comprising a container filled with a working fluid and a metal wick on the inner wall side of the container.

10. A method for producing a metal substrate having a nanoparticle layer according to claim 1, wherein the surface of the metal substrate is etched.

11. A method for manufacturing a heat pipe having a metal container filled with a working fluid, comprising the following steps (a1) and (b1), wherein steps (a1) and (b1) are carried out sequentially in this order, or steps (a1) and (b1) are carried out simultaneously. (a1) A step of bringing the inner wall of the container constituting the heat pipe into contact with 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) (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 in a nucleation boiling state near the surface of the inner wall of the container.

12. The method for manufacturing a heat pipe according to claim 11, wherein step (a1) is a step of bringing the dispersion liquid into contact with the inner wall of the container heated to 100 to 500°C in the gas phase.

13. The method for manufacturing a heat pipe according to claim 11, wherein step (a1) is a step of immersing the inner wall of the container in the dispersion.

14. A method for manufacturing a heat pipe according to any one of claims 11 to 13, wherein the inner wall of the container is etched.

15. A method for manufacturing a heat pipe comprising a metal container filled with a working fluid and a metal wick on the inner wall side of the container, A method for manufacturing a heat pipe, comprising the steps (a2) and (b2) below, wherein steps (a2) and (b2) are performed sequentially in this order, or steps (a2) and (b2) are performed simultaneously. (a2) A step of bringing a metal wick constituting a heat pipe into contact with 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) (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 in a nucleation boiling state near the surface of the metal wick.

16. The method for manufacturing a heat pipe according to claim 15, wherein step (a2) is a step of bringing the dispersion liquid into contact with the metal wick heated to 100 to 500°C in the gas phase.

17. The method for manufacturing a heat pipe according to claim 15, wherein step (a2) is a step of immersing the metal wick in the dispersion.

18. A method for manufacturing a heat pipe according to any one of claims 15 to 17, wherein the surface of the metal wick is etched.

19. The method for manufacturing a heat pipe according to claim 11 or claim 15, wherein the working fluid is a dispersion containing colloidal particles.

20. The working fluid is a dispersion containing 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 The method for manufacturing a heat pipe according to claim 11 or claim 15, which is a dispersion containing colloidal particles of at least one inorganic oxide selected from the group consisting of

21. A heat pipe comprising a metal container filled with a working fluid, A heat pipe having a nanoparticle layer formed on the inner wall surface of the container, which consists of colloidal particles with 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.

22. A heat pipe comprising a metal container filled with a working fluid and a metal wick on the inner wall side of the container, The surface of the inner wall of the container and the surface of the metal wick, or both, have a nanoparticle layer formed from 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. Heat pipe.

23. The heat pipe according to claim 22, wherein the nanoparticle layer is provided on one or both of the etched inner wall surface of the container and the etched surface of the metal wick.

24. The heat pipe according to any one of claims 21 to 23, wherein the working fluid is a dispersion containing colloidal particles.

25. The working fluid is TiO ２ , ZrO ２ , ZnO, CuO, Al ２ O ３ , and SiO ２ A heat pipe according to any one of claims 21 to 23, comprising a dispersion containing colloidal particles of at least one inorganic oxide selected from the group consisting of the following.

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