JP2010248586A - Diamond coating structure and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide diamond coating structure which can be manufactured with successful productivity, in which there is no void or extremely few void between a diamond coating and the porous substrate surface, and continuous coatings of diamond are formed on the porous substrate surface, and a method for manufacturing the same. <P>SOLUTION: In the diamond coating structure, a porous substrate is coated by the diamond coating which grows by using nanodiamond particles whose primary grain diameters are 1-20 nm as the nucleus. The diamond coating structure is manufactured by growing the nanodiamond particles as the nucleus after sticking dispersion solution based on the nonodiamond particles whose primary particle diameters are 1-20 nm to the porous substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a diamond-coated structure and a method for producing the same.

  Since diamond has the largest hardness and elastic modulus among the substances on the earth, a structure in which a porous substrate is coated with diamond can be expected to have a high hardness and elastic modulus.

  Further, since diamond is excellent in thermal conductivity and insulation, a structure in which a porous substrate is coated with diamond can be expected to be applied as a heat dissipation material or an electrical insulation material.

  As a method for coating with such a diamond, “a method for chemical vapor deposition of diamond on a shaped article, (a) polishing powder in liquid (diamond powder, particle size: about 0.25 Placing the shaped article in a suspension of ˜1 μm, wherein the powder material has a hardness greater than that of the shaped article material, (b) the shaped Agitating the suspension containing the shaped article for a time sufficient for the surface of the shaped article to become polished; (c) removing the shaped article from the suspension; A method comprising the steps of: removing and drying the shaped article; and (d) depositing the diamond on the shaped article by chemical vapor deposition. Reference 1). In fact, Patent Document 1 discloses that a suspension of a 0.25 μm diamond paste was used, and graphite fibers or silicon carbide fibers were coated with diamond by a CVD method.

  However, even if an attempt is made to cover the surface of a substrate such as graphite fiber by the method disclosed in Patent Document 1, voids are likely to occur between the diamond powder and the surface of the substrate, so that a desired electrical insulation performance can be obtained. There wasn't. Moreover, since it is difficult to form a continuous film on the substrate surface by the method disclosed in Patent Document 1, it has been difficult to obtain sufficient heat dissipation performance. In order to form a continuous film, the deposition time by the CVD method can be increased, but in this case, the productivity of the diamond-coated structure is deteriorated.

Japanese National Patent Publication No. 8-503026 (Claims 1, 4, 5 and Examples)

  The present invention has been made to solve the above-mentioned problems, and there is no or very little void between the diamond coating and the porous substrate surface, and the continuous surface of diamond on the porous substrate surface. An object of the present invention is to provide a diamond-coated structure that can be manufactured with high productivity and a manufacturing method thereof.

  The invention according to claim 1 of the present invention is “a diamond-coated structure in which a porous substrate is coated with a diamond film grown using nanodiamond particles having a primary particle diameter of 1 to 20 nm as a nucleus”.

  The invention according to claim 2 of the present invention is "the diamond-coated structure according to claim 1, wherein the surface roughness of the structure is 50 nm or less."

  The invention according to claim 3 of the present invention is “the diamond-coated structure according to claim 1 or 2, wherein the porous substrate is a fiber sheet made of fibers having a diameter of 10 μm or less”.

  The invention according to claim 4 of the present invention includes: (1) a step of preparing a dispersion solution mainly composed of nanodiamond particles having a primary particle diameter of 1 to 20 nm, and (2) applying the dispersion solution to a porous substrate. And (3) growing the nanodiamond particles as nuclei and coating the porous substrate with a diamond film, thereby producing a diamond-coated structure. Method. "

  In the invention according to claim 1 of the present invention, when the primary particle diameter of the nanodiamond particles serving as the growth nucleus is as very small as 1 to 20 nm, voids are formed between the porous base material and the diamond film when grown. It is difficult to generate, and the primary particle size of nanodiamond particles is very small, so that the number of nanodiamond particles that can adhere to the porous substrate is very large and the density can be increased. It has been found that a typical diamond film can be formed.

  In the invention according to claim 2 of the present invention, since the surface roughness of the structure is as smooth as 50 nm or less, the amount of diamond film is small, and the structure can be produced with good productivity. In other words, since nano-diamond particles having a primary particle size of 1 to 20 nm are used as the core, the surface roughness exceeding 50 nm means that the grains constituting the diamond film have been coarsened and a dense diamond film has been formed. This means that when the surface roughness of the structure is 50 nm or less, it is a diamond-coated structure manufactured with high productivity and coated with a minimum amount of a dense diamond film.

  In the invention according to claim 3 of the present invention, since the porous substrate is a fiber sheet made of fibers having a diameter of 10 μm or less, the characteristics of diamond can be sufficiently exhibited. That is, the fiber having a diameter of 10 μm or less has a very large surface area, and the surface area of the diamond film coated with this fiber is also very large, so that the characteristics of diamond can be sufficiently exhibited.

  Since the invention according to claim 4 of the present invention uses a dispersion solution mainly composed of nanodiamond particles having a primary particle diameter of 1 to 20 nm, the diamond-coated structure according to claim 1 can be produced.

Typical sectional drawing explaining the neutralization spinning method in an Example (A) Plan view of the creeping discharge element used in the example (b) Cross-sectional view of the creeping discharge element used in the example Schematic cross-sectional view explaining the heat dissipation test method

  The diamond-coated structure of the present invention (hereinafter sometimes simply referred to as “coated structure”) is particularly characterized in that nanodiamond particles having a primary particle diameter of 1 to 20 nm are used as nuclei. . By using such very fine nanodiamond particles as the core, when the diamond film grows, it is difficult for voids to form between the porous substrate and the number of nanodiamond particles that can adhere to the porous substrate. Since it can be deposited on a porous substrate at a high density, a continuous diamond film can be formed with high productivity.

  The nanodiamond particles have a primary particle diameter of 1 to 20 nm so as to exhibit the above-described action, but preferably have a primary particle diameter of 1 to 10 nm so as to exhibit the above-described action. More preferably, it is 3 to 5 nm. The “primary particle diameter” refers to the size of the nanodiamond particles, and a dispersion solution of nanodiamond particles having a concentration of 2 mass% is used with a concentrated particle size analyzer FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.) The value obtained by measuring the particle size distribution by dynamic light scattering.

  Such nanodiamond particles can be obtained, for example, by a method in which nanodiamond coarse agglomerates produced by an explosion method are crushed by high-speed rotary wet milling using ceramic beads or metal beads.

  The coated structure of the present invention is a porous base material coated with a diamond film, and the diamond film is grown using nanodiamond particles as a nucleus as described above. The growth can be performed, for example, by a CVD method. Examples of the CVD method include a hot filament method, a plasma method (eg, direct current, high frequency, microwave, etc.), an electron cyclotron resonance plasma method, and the like.

  Since the base material constituting the coating structure of the present invention is porous, the diamond performance can be sufficiently exhibited. In other words, the porous base material has a large surface area due to the porous base material, and the coated structure coated with the diamond film has a large surface area of the diamond film. . The porous substrate is not particularly limited, and examples thereof include fiber sheets such as woven fabrics, knitted fabrics, and nonwoven fabrics, foams, and porous films. Among these, a fiber sheet having a large surface area is preferable. If the fiber sheet is made of fibers having a diameter of 10 μm or less, the surface area of the diamond film is increased due to the large surface area of the fiber, and the fiber sheet is a non-woven fabric. If there is, there is an appropriate gap between the fibers, and a diamond film on the fiber surface can be used effectively, which is more preferable. In addition, since the surface area becomes wider as the fiber diameter is smaller, it is more preferably 5 μm or less, further preferably 2 μm or less, and further preferably 1 μm or less. In addition, although the minimum of a fiber diameter is not specifically limited, It is preferable that it is 10 nm or more from the point of handleability. In addition, L / D [= length (unit: μm) / fiber diameter (unit: μm)] is 100 or more so that the fibers constituting the fiber sheet are excellent in performance (for example, thermal conductivity) by the diamond film. Long fibers are preferred. Therefore, a nonwoven fabric made of long fibers having a diameter of 2 μm or less is preferred, and a nonwoven fabric made of long fibers having a diameter of 1 μm or less is most preferred. Such a nonwoven fabric composed of long fibers having a diameter of 2 μm or less is manufactured by, for example, an electrostatic spinning method, a method in which a gas is applied to a spinning solution, and the spinning solution is stretched by a shearing force of the gas to be fiberized. can do. In the present invention, “fiber diameter” means the diameter when the cross-sectional shape of the fiber is circular, and means the diameter of a circle having the same area as the cross-sectional area when the cross-sectional shape is non-circular. .

  The coated structure of the present invention preferably has a surface roughness of 50 nm or less and is smooth to some extent. In the present invention, since nano-diamond particles having a primary particle diameter of 1 to 20 nm are used as the core, the surface roughness exceeding 50 nm means that the grains constituting the diamond film are coarsened, and a dense diamond film is formed. This means that it is not formed, but if the surface roughness of the structure is 50 nm or less, it is a diamond-coated structure manufactured with high productivity and coated with a minimum amount of a dense diamond film. . More preferable surface roughness is 20 nm or less, and further preferably 10 nm or less. Although the minimum of surface roughness is not specifically limited, Since the primary particle diameter of a nano diamond particle is 1-20 nm, it is 1 nm or more. The surface roughness (Sa) of the present invention was measured using an atomic force microscope (Nano-R: manufactured by Pacific nanotechnology) in a non-contact mode in a 200 nm × 200 nm area of a diamond-coated structure with a Si probe (nanoworld). Means the average roughness measured using When the diamond covering structure is inclined or has a curvature, leveling is performed, and the average roughness is measured after correcting the surface of the diamond covering structure to a horizontal plane.

  Such a covering structure of the present invention can be manufactured, for example, by the following method.

  First, (1) a step of preparing a dispersion solution mainly composed of nanodiamond particles having a primary particle diameter of 1 to 20 nm is performed. Such a dispersion solution can be obtained, for example, by a method of crushing nano-diamond coarse agglomerates produced by an explosion method by high-speed rotary wet milling using ceramic beads or metal beads. Note that “mainly” means that 90% by mass or more of diamond particles having a primary particle diameter of 1 to 20 nm are included. As the number of diamond particles having a primary particle diameter of 1 to 20 nm increases, voids are less likely to be generated between the porous substrate and the diamond substrate when the diamond film grows. Since it can adhere to the surface and a diamond film having a uniform thickness can be formed, it is preferably 95 mass% or more, more preferably 98 mass% or more, and further preferably 99.9 mass% or more.

  The “explosion method” is a method of collecting soot generated by decomposing oxygen-deficient military explosive composition Composition B in an inert medium such as water and removing amorphous carbon by oxidation with hot concentrated nitric acid. . Therefore, the solvent constituting the dispersion solution is an inert medium such as water used in producing the nanodiamond coarse aggregate.

  The concentration of the nanodiamond dispersion solution of the present invention is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 1 mass% or less so that the dispersion solution exists stably. Further, in order to attach the nanodiamond particles to the porous substrate at a high density, it is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, and 0.05 mass% or more. More preferably.

  Next, (2) a step of applying the dispersion solution to the porous substrate and attaching nanodiamond particles to the porous substrate is performed. In this step, for example, a method in which the porous substrate is dried after being immersed in the dispersion solution, a method in which the dispersion solution is coated on the porous substrate by a pulling method or the like, and a method in which the dispersion solution is dried are sprayed on the porous substrate. It can implement by the method of drying later. From the viewpoint of attaching the nanodiamond particles to the porous substrate at a high density, it is preferable to attach the porous substrate by dipping in the dispersion solution and then drying. The drying is not particularly limited as long as the method can be performed while maintaining the state in which the nanodiamond particles are adhered at a high density. For example, a hot air dryer, oven, vacuum oven, microwave irradiation Can be implemented.

  When the porous substrate is immersed in the dispersion solution, it is preferable to apply ultrasonic waves so that the dispersed state of the nanodiamond particles in the nanodiamond dispersion solution can be maintained. The ultrasonic wave is not particularly limited as long as it can maintain the dispersed state of the nanodiamond particles. For example, an ultrasonic cleaning device, a horn type high output ultrasonic device, or the like can be used.

  Then, (3) a process of growing the nanodiamond particles as nuclei and coating the porous substrate with a diamond film can be performed to produce the coated structure of the present invention. In the present invention, since the nano-diamond particles having a primary particle diameter of 1 to 20 nm are grown as nuclei, they grow without generating voids between the diamond film and the porous substrate. This step can be performed by, for example, a CVD method. Examples of the CVD method include a hot filament method, a plasma method (eg, direct current, high frequency, microwave, etc.), an electron cyclotron resonance plasma method, and the like.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
(1) Water-dispersed nanodiamond colloid containing 98.8 mass% of primary particles of 4.6 ± 0.8 nm and 1.2 mass% of aggregates of 59.4 ± 22.8 nm (Nanoamando 5 manufactured by Nanocarbon Laboratory Co., Ltd.) 0.0 mass%) was diluted 100 times to prepare a 0.05 mass% nanodiamond aqueous dispersion.

(2) Tetraethoxysilane, ethanol, water and 1N hydrochloric acid are mixed at a molar ratio of 1: 5: 2: 0.003 and refluxed at a temperature of 78 ° C. for 10 hours. After removing by an evaporator and concentrating, it was heated to a temperature of 60 ° C. to form a sol solution having a viscosity of 2 poise. Using the obtained sol solution as a spinning solution, a gel-like silica fiber web was prepared using the electrostatic spinning device 1 disclosed in JP-A-2005-264374. That is, the creeping discharge element 25 shown in FIGS. 2A and 2B was used as the counter electrode 5 shown in FIG. Details are shown below.

Spinning nozzle 2: Metal injection needle with 0.4mm inner diameter (tip cut)
Distance between spinning nozzle 2 and counter electrode 5: 200 mm
Counter electrode 5 and ion generating power source (also serving as both electrodes): An alumina film (dielectric substrate 26) having a thickness of 1 mm is sprayed on a stainless steel plate (induction electrode 28), and a tungsten wire (discharge electrode) having a diameter of 30 μm thereon. 27) creeping discharge elements 25 stretched at equal intervals of 10 mm (tungsten wire surface is opposed to the spinning nozzle 2 and grounded, and an AC high voltage of 50 Hz is applied between the stainless steel plate 26 and the tungsten wire by an AC high voltage power supply 29. )
First high voltage power supply 7: -16 kV
Second high-voltage power supply 8: ± 5 kV (peak voltage along the AC surface: 5 kV, 50 Hz)
Horizontal air flow 30a: 25 cm / sec.
Vertical air flow 30b: 15 cm / sec.
Spinning chamber 31 atmosphere: temperature 25 ° C., humidity 40% RH or less Continuous spinning time: 30 minutes or more

  Next, the obtained silica gel fiber web was fired at a temperature of 500 ° C. to prepare a silica fiber web.

  On the other hand, as an inorganic sol solution for bonding used for interfiber bonding, tetraethoxysilane, ethanol, water and 1N nitric acid are mixed at a molar ratio of 1: 7.2: 7: 0.0039, and the temperature is 25 ° C. The mixture was reacted for 15 hours at 300 rpm with stirring conditions. After the reaction, it was diluted with ethanol so that the solid content concentration of silicon oxide was 0.25%, and a diluted silica sol solution (adhesive inorganic sol solution) was obtained.

  Next, after the silica fiber web was immersed in this silica sol dilute solution, the excess sol solution was removed by suction to produce a silica sol dilute solution-containing silica fiber web.

Subsequently, the silica fiber web containing the silica sol dilute solution is kept in an atmosphere of 110 ° C. for 30 minutes and then baked at 800 ° C. to thereby form a nonwoven fabric composed of silica long fibers (= porous substrate, basis weight: 23 g / m ^2). , Fiber diameter: 1 μm).

  And after cut | disconnecting this silica long fiber nonwoven fabric to a magnitude | size of 20x20 mm, it was immersed in the said nanodiamond aqueous dispersion, and ultrasonic treatment was performed for 30 minutes. After the treatment, the silica long fiber nonwoven fabric (porous substrate) is taken out from the nanodiamond aqueous dispersion, washed with 100 ml of pure water, dried in a hot air dryer at 120 ° C. for 1 hour, and the silica long fiber nonwoven fabric (porous base) Nanodiamond particles were adhered to the material.

(3) Next, the silica long fiber nonwoven fabric (porous substrate) to which the nanodiamond particles are adhered is coated with a diamond coating by a microwave plasma CVD method to produce the diamond coated structure of the present invention. did. The conditions of this CVD method are as follows: raw material gas flow rate: CH ₄ = 0.1 sccm, H ₂ = 100.0 sccm, synthesis pressure: 7 kPa, microwave output: 400 W, time: 30 min. It was.

(Comparative Example 1)
A diamond-coated structure was produced in the same manner as in Example 1 except that a 0.05 mass% aqueous dispersion of an explosion-method nanodiamond aggregate (manufactured by Amati International) having a particle size of 106.0 ± 41.1 nm was used. . In this structure, the number of nanodiamond particles fixed on the silica long fiber nonwoven fabric was small, and a continuous diamond film could not be formed.

(Comparative Example 2)
A diamond-coated structure was produced in the same manner as in Comparative Example 1 except that the diamond film formation time by the microwave plasma CVD method was 12 hours. A continuous diamond film could be formed by performing CVD for a long time.

(Comparative Example 3)
A diamond-coated structure was produced in the same manner as in Example 1 except that a 1.0 mass% aqueous dispersion of an explosion-method nanodiamond aggregate (manufactured by Amati International) having a particle size of 106.0 ± 41.1 nm was used. . In this structure, the number of aggregates fixed on the silica long-fiber nonwoven fabric increased, and a continuous diamond film could be formed.

(Comparative Example 4)
An attempt was made to produce a diamond-coated structure by the same method as in Example 1 except that a 0.05 mass% aqueous dispersion of microdiamond (manufactured by EID) having a particle size of 0.25 to 1 μm was used. Could not be fixed.

(Evaluation of surface roughness)
Using an atomic force microscope (Nano-R: manufactured by Pacific nanotechnology), the surface roughness (Sa) in the 200 nm × 200 nm area of the diamond-coated structures of Example 1 and Comparative Examples 1 to 4 was measured. The results are shown in Table 1. The measurement was performed in a non-contact mode, and a Si probe (manufactured by Nanoworld) and a back surface aluminum coated PPP-NCHR were used as the probe.

(Evaluation of electrical insulation)
First, 5 parts by weight of dicyandiamide (DICY) as a curing agent was added to 100 parts by weight of a bisphenol type epoxy resin having an epoxy equivalent of 450 to 500 to prepare a varnish.

Then, after immersing Example 1, Comparative Examples 1 to 4 and silica long-fiber nonwoven fabric (Comparative Example 5) to which no nanodiamond particles were adhered, this varnish was dried at 145 to 160 ° C. for 2 hours to prepare a prepreg. Prepared. Thereafter, a pressure of 3 kgf / cm ² was uniformly applied to the entire prepreg to prepare composite samples having a thickness of 0.23 ± 0.03 mm.

  Each composite sample is sandwiched between a pair of cylindrical electrodes (diameter: 10 mm, the periphery of the surface in contact with the sample is rounded with a radius of 3.0 mm) at a pressure of 200 gf, and each composite sample is in a horizontal state. Then, an AC voltage of 60 Hz is used as the applied voltage, and 10 kV / 60 sec. The voltage was applied to the pair of cylindrical electrodes at a speed of 5 to measure the breakdown voltage. The results are shown in Table 1. In addition, when a void is generated between the silica long-fiber nonwoven fabric and the diamond film, or when a void is generated between the diamond-coated structure and the varnish, the electrical insulating property is deteriorated and the insulation is reduced. The breakdown voltage is lowered.

(Evaluation of thermal conductivity)
Thermal conductivity was evaluated by the method shown in FIG. That is, on the water cooling apparatus C, as the composite sample H using Example 1 and Comparative Examples 1 to 5 and the resistance R, stainless steel (SUS304) having a length of 10 mm, a width of 10 mm, and a height of 10 mm is sequentially placed. did.

  Next, using a constant current source, the rising temperature of the resistance R after 10 minutes when a heat amount of 100 W was applied to the resistance R was measured with a radiation thermometer. The results are shown in Table 1. Note that the higher the thermal conductivity of the composite sample, the lower the temperature at which the resistance R rises because it is cooled by the water cooling device C.

  As apparent from Table 1, the coating structure of the present invention had a high dielectric breakdown voltage and an excellent electrical insulation performance. This is because voids are not generated between the silica long-fiber non-woven fabric and the diamond coating, and voids are generated between the diamond coated structure and the varnish due to the smooth surface of the diamond coated structure. It was thought that it was not.

  In addition, the coated structure of the present invention has a low resistance rise temperature and excellent thermal conductivity. This was thought to be because the surface of the silica long fiber nonwoven fabric was densely covered with a continuous diamond film.

  Since the diamond-coated structure of the present invention is excellent in electrical insulation performance, thermal conductivity, etc., it can be suitably used as a heat dissipation material or an electrical insulation material.

DESCRIPTION OF SYMBOLS 1 Electrostatic spinning apparatus 2 Spinning nozzle 3 Fiber collection container 4 Collection member 5 Counter electrode 5a Ion 6 Sol solution supply machine 7 1st high voltage power supply 8 2nd high voltage power supply 9 Suction machine 25 Creeping discharge element 26 Dielectric substrate 27 Discharge electrode 28 Induction electrode 29 AC high voltage power supply 30a Horizontal airflow 30b Vertical airflow 31 Spinning chamber H Complex sample C Water cooling device R Resistance

Claims (4)

A diamond-coated structure in which a porous substrate is coated with a diamond film grown using nanodiamond particles having a primary particle diameter of 1 to 20 nm as a nucleus. The diamond-coated structure according to claim 1, wherein the surface roughness of the structure is 50 nm or less. The diamond covering structure according to claim 1 or 2, wherein the porous substrate is a fiber sheet made of fibers having a diameter of 10 µm or less. (1) a step of preparing a dispersion solution mainly composed of nanodiamond particles having a primary particle diameter of 1 to 20 nm;
(2) A step of applying the dispersion solution to a porous substrate and attaching nanodiamond particles to the porous substrate;
(3) growing the nanodiamond particles as nuclei and coating a porous substrate with a diamond film;
A method for producing a diamond-coated structure.

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