U.S. patent application number 14/403666 was filed with the patent office on 2015-04-09 for porous aluminum body, heat transfer material, and heat exchange device.
The applicant listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Kengo Goto, Akihisa Hosoe, Koutarou Kimura, Junichi Nishimura, Kazuki Okuno, Hideaki Sakaida.
Application Number | 20150099138 14/403666 |
Document ID | / |
Family ID | 51427814 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150099138 |
Kind Code |
A1 |
Nishimura; Junichi ; et
al. |
April 9, 2015 |
POROUS ALUMINUM BODY, HEAT TRANSFER MATERIAL, AND HEAT EXCHANGE
DEVICE
Abstract
Provided is a porous aluminum body capable of being used as a
heat transfer material having a very large specific surface area, a
good heat-exchange efficiency, and a low pressure drop of a gas.
The porous aluminum body contains aluminum as a main component. The
porous aluminum body has a three-dimensional network structure and
has a specific surface area (Y) represented by a (Formula) below.
Y=a.times.exp(0.06X) (Formula) (In the (Formula), Y represents a
specific surface area [m.sup.2/m.sup.3], X represents the number of
cells [per inch], and a represents a number of 100 or more and
1,000 or less.)
Inventors: |
Nishimura; Junichi;
(Osaka-shi, JP) ; Hosoe; Akihisa; (Osaka-shi,
JP) ; Okuno; Kazuki; (Osaka-shi, JP) ; Kimura;
Koutarou; (Osaka-shi, JP) ; Goto; Kengo;
(Osaka-shi, JP) ; Sakaida; Hideaki; (Osaka-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD. |
Osaka-shi, Osaka |
|
JP |
|
|
Family ID: |
51427814 |
Appl. No.: |
14/403666 |
Filed: |
December 17, 2013 |
PCT Filed: |
December 17, 2013 |
PCT NO: |
PCT/JP2013/083703 |
371 Date: |
November 25, 2014 |
Current U.S.
Class: |
428/613 |
Current CPC
Class: |
B22F 3/11 20130101; F28F
13/003 20130101; C22C 1/08 20130101; C22C 1/0416 20130101; F28F
21/084 20130101; C25D 1/08 20130101; Y10T 428/12479 20150115; C25D
3/665 20130101; B22F 5/106 20130101 |
Class at
Publication: |
428/613 |
International
Class: |
F28F 21/08 20060101
F28F021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2013 |
JP |
2013-035481 |
Claims
1. A porous aluminum body comprising aluminum as a main component,
wherein the porous aluminum body has a three-dimensional network
structure and has a specific surface area (Y) represented by a
(Formula) below: Y=a.times.exp(0.06X) (Formula) (where, in the
(Formula), Y represents a specific surface area [m.sup.2/m.sup.3],
X represents the number of cells [per inch], and a represents a
number of 270 or more and 1,000 or less.)
2. The porous aluminum body according to claim 1, wherein the
porous aluminum body has a hollow skeleton.
3. The porous aluminum body according to claim 1, wherein aluminum
contained in the porous aluminum body has a purity of 99.7% by mass
or more.
4. The porous aluminum body according to claim 1, wherein a weight
per volume of the porous aluminum body is 0.1 g/cm.sup.3 or more
and 1.0 g/cm.sup.3 or less.
5. A heat transfer material comprising the porous aluminum body
according to claim 1.
6. A heat exchange device comprising the porous aluminum body
according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a porous aluminum body
having a three-dimensional network structure, a heat transfer
material, and a heat exchange device.
BACKGROUND ART
[0002] Metallic materials having high thermal conductivities are
used as heat transfer materials used in heat exchange devices and
the like. Furthermore, for the purpose of reducing the size of the
devices by increasing the heat-exchange efficiency, an increase in
the surface area of a heat transfer material has been studied. For
example, the surface area of a heat transfer material is increased
by arranging a large number of thin plates composed of a heat
transfer material or by forming grooves in a heat transfer
material.
[0003] For example, Japanese Unexamined Patent Application
Publication No. 07-190664 (PTL 1) has proposed the use of a porous
copper body or a porous copper alloy body as a heat transfer
member. Specifically, this technique uses a property that a copper
oxide powder or a mixed powder of a copper oxide powder and a
powder of another metal such as nickel, aluminum, chromium,
palladium, or silver is sintered as a metal in a reducing
atmosphere and a property that when this sintering is performed on
a metal plate, the resulting sintered product can be integrated
with the metal plate. PTL 1 describes that this technique can
provide a heat transfer tube or a heat transfer plate in which a
porous metal body having a three-dimensional network structure is
integrally adhered to an inner or outer surface of a metal tube or
a surface of a metal plate.
[0004] Electronic components etc. that use semiconductor circuits
generate heat during use, and thus efficient heat dissipation has
been desired. For example, Japanese Unexamined Patent Application
Publication No. 2012-124391 (PTL 2) has proposed a heat transfer
controlling member that controls heat transfer between a heating
element and a peripheral environment thereof, the heat transfer
controlling member including a porous metal layer having a
three-dimensional network structure.
[0005] In the heat transfer controlling member described in PTL 2,
the porous metal layer is composed of a foamed metal having a
three-dimensional network structure in which a plurality of pores
formed by a continuous skeleton are communicated with each other,
and has a porosity of 30% to 98% and a thickness of 0.05 to 50 mm.
This foamed metal is formed by forming a foamable slurry containing
a metal powder, a foaming agent, etc. into a sheet, and foaming the
resulting sheet. Pores in the foamed metal are opened on a front
surface, a back surface, and side surfaces. The foamed metal is
formed so as to be dense in the vicinity of the front and back
surfaces relative to a central portion in the thickness direction.
In addition, one of the front surface and the back surface is
formed so as to be denser than the other surface.
[0006] In a heat transfer material including such a porous metal
body prepared by the sintering method described above, in order to
increase the heat-exchange efficiency in a certain volume, it is
necessary to decrease the cell diameter of the porous metal body so
as to increase the specific surface area. However, when the cell
diameter is decreased in order to increase the heat-exchange
efficiency, there may be a problem in that a pressure drop of a gas
which passes through the porous metal body increases.
CITATION LIST
Patent Literature
[0007] PTL 1: Japanese Unexamined Patent Application Publication
No. 07-190664 [0008] PTL 2: Japanese Unexamined Patent Application
Publication No. 2012-124391
SUMMARY OF INVENTION
Technical Problem
[0009] In view of the above problem, an object of the present
invention is to provide a porous aluminum body capable of being
used as a heat transfer material having a very large specific
surface area, a good heat-exchange efficiency, and a low pressure
drop of a gas.
Solution to Problem
[0010] The inventors of the present invention have conducted
intensive studies in order to solve the above problem. As a result,
it was found that the specific surface area of a porous aluminum
body can be markedly increased by further improving an existing
method for producing a porous aluminum body having a
three-dimensional network structure by a plating method (for
example, Japanese Unexamined Patent Application Publication No.
2011-225950), and this finding led to the completion of the present
invention. Specifically, the present invention has features
described below.
(1) A porous aluminum body containing aluminum as a main component,
in which the porous aluminum body has a three-dimensional network
structure and has a specific surface area (Y) represented by a
(Formula) below.
Y=a.times.exp(0.06X) (Formula)
(In the (Formula), Y represents a specific surface area
[m.sup.2/m.sup.3], X represents the number of cells [per inch], and
a represents a number of 100 or more and 1,000 or less. The
Napier's constant (e) is assumed to be 2.72.)
[0011] The porous aluminum body according to (1) above has very
small irregularities over the entire surface of a skeleton thereof,
and has a specific surface area that is significantly larger than
that of an existing porous aluminum body. Furthermore, since
aluminum is a metal having a high thermal conductivity, the porous
aluminum body can be used as a heat transfer material having a good
heat-exchange efficiency and a low pressure drop of a gas.
[0012] Note that, in the present invention, the phrase "containing
aluminum as a main component" means that the aluminum content in
the porous aluminum body is 90% by mass or more.
(2) The porous aluminum body according to (1) above, in which the
porous aluminum body has a hollow skeleton.
[0013] By producing the porous aluminum body by a plating method,
the skeleton of the porous aluminum body can be made hollow. The
porous aluminum body having such a hollow skeleton can allow a gas
to flow even into the inside of the skeleton, and thus can be used
as a heat transfer material having a higher heat-exchange
efficiency.
(3) The porous aluminum body according to (1) or (2) above, in
which aluminum contained in the porous aluminum body has a purity
of 99.7% by mass or more.
[0014] As described above, aluminum is a metal having a high
thermal conductivity. Accordingly, a porous aluminum body having a
higher thermal conductivity can be obtained by increasing the
purity of aluminum.
(4) The porous aluminum body according to any one of (1) to (3)
above, in which a weight per volume of the porous aluminum body is
0.1 g/cm.sup.3 or more and 1.0 g/cm.sup.3 or less.
[0015] When the weight per volume of the porous aluminum body is
0.1 g/cm.sup.3 or more, the thickness of the skeleton of the porous
aluminum body can be made large and the specific surface area is
increased. Consequently, the heat-exchange efficiency is
improved.
In addition, since the cross-sectional area of the skeleton is
increased, the thermal conductivity is improved. When the weight
per volume of the porous aluminum body is 1.0 g/cm.sup.3 or less,
an increase in the pressure drop can be suppressed. Furthermore, an
excessive increase in the production cost of the porous aluminum
body can be suppressed.
[0016] Note that the term "weight per volume of a porous aluminum
body" in the present invention refers to the mass per unit volume
of the porous aluminum body.
(5) A heat transfer material including the porous aluminum body
according to any one of (1) to (4) above.
[0017] The heat transfer material according to (5) above is a heat
transfer material having a good performance, namely, a very large
specific surface area, a good heat-exchange efficiency, and a low
pressure drop of a gas.
(6) A heat exchange device using the porous aluminum body according
to any one of (1) to (4) above.
[0018] In the heat exchange device according to (6) above, the
porous aluminum body of the present invention is used as a heat
transfer material. Thus, the heat exchange device has a very high
heat-exchange efficiency. Therefore, the size of the heat exchange
device can be reduced as compared with an existing heat exchange
device.
Advantageous Effects of Invention
[0019] According to the present invention, it is possible to
provide a porous aluminum body capable of being used as a heat
transfer material having a very large specific surface area, a good
heat-exchange efficiency, and a low pressure drop of a gas.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a diagram illustrating an equivalent circuit for
evaluating capacitance.
[0021] FIG. 2 is a schematic view illustrating a measurement cell
for measuring alternating current impedance.
DESCRIPTION OF EMBODIMENTS
<Porous Aluminum Body>
[0022] A porous aluminum body according to the present invention
contains aluminum as a main component. The porous aluminum body has
a three-dimensional network structure and has a specific surface
area (Y) represented by a (Formula) below:
Y=a.times.exp(0.06X) (Formula)
(In the (Formula), Y represents a specific surface area
[m.sup.2/m.sup.3], X represents the number of cells [per inch], and
a represents a number of 100 or more and 1,000 or less.)
[0023] As described above, the porous aluminum body according to
the present invention has fine irregularities on the surface of a
skeleton thereof, and has a very large specific surface area. That
is, the specific surface area can be made larger than that of an
existing porous aluminum body without decreasing the cell diameter
more than necessary. Accordingly, by using the porous aluminum body
of the present invention as a heat transfer material, the
heat-exchange efficiency can be improved while the porous aluminum
body has a certain degree of large cell diameter so that the
pressure drop is maintained to be low.
[0024] In the (Formula), X represents the number of cells [per
inch] of the porous aluminum body, and is preferably 6 to 60 per
inch. When the number of cells of the porous aluminum body is 6 per
inch or more, the specific surface area can be made sufficiently
large and the heat-exchange efficiency can be made high. When the
number of cells of the porous aluminum body is 60 per inch or less,
an excessive increase in the pressure drop can be suppressed.
[0025] The number of cells of the porous aluminum body is more
preferably 10 to 33 per inch, and still more preferably 10 to 20
per inch.
[0026] In the present invention, the number (X) of cells of the
porous aluminum body is defined as the number of cells per 1 inch
(25.4 mm). The number of cells can be determined as follows. A
porous aluminum body is sliced in the horizontal direction, and
observed with a microscope to obtain an enlarged image. A straight
line having a length of 1 inch is drawn on the enlarged image, and
the number of cells intersecting the straight line is counted. In
this case, the number of cells is counted at five positions, and
the average of the five positions is determined.
[0027] In the case where a resin body such as urethane foam is used
as a starting material for producing a porous aluminum body, the
number of cells of the porous aluminum body is the same as the
number of cells of the resin body.
The number of cells of the resin foam body can also be determined
as in the case of the porous aluminum body.
[0028] In the (Formula), a represents a number of 100 or more and
1,000 or less. The number a is preferably 200 or more and 1,000 or
less, and still more preferably 600 or more and 1,000 or less.
[0029] In the present invention, the term "specific surface area
(Y)" refers to a value measured by a capacitance method. The
capacitance method is a measurement method that uses a phenomenon
that the capacitance of a metallic material is proportional to the
surface area of the metallic material, as represented by a
theoretical formula described below:
C=.di-elect cons..times.(A/d) (Theoretical formula)
[0030] C: capacitance, .di-elect cons.: dielectric constant, d:
distance between two electrodes, A: surface area of sample
[0031] Specifically, first, a plurality of aluminum plates having
the same purity as a sample and having known surface areas are
prepared. The capacitance of each of the aluminum plates is
evaluated, and a calibration curve of "capacitance" versus "surface
area" is prepared. The capacitance of the sample is then evaluated.
Thus, the surface area of the sample can be determined by a
calibration curve method.
[0032] The capacitance of each of the aluminum plates for preparing
the calibration curve and the capacitance of the sample are
evaluated as follows. First, alternating current impedance is
measured, and the result is then analyzed by using an equivalent
circuit illustrated in FIG. 1. The alternating current impedance
can be measured in a NaCl solution having a concentration of 5% by
mass by using a platinum electrode as a reference electrode, as
illustrated in FIG. 2. In this measurement, the measurement
frequency is set to 100 kHz to 10 Hz in order to confirm that the
effect of a dissolution reaction of aluminum or the like is not
significant. The analysis is then performed by using data in a
range of 10 kHz to 1 kHz, the range being included in the
above.
[0033] The porous aluminum body of the present invention preferably
has a hollow skeleton. With this structure, a gas can pass through
both the inside and the outside of the skeleton, and thus the
porous aluminum body can be used as a heat transfer material having
a good heat-exchange efficiency. Such a porous aluminum body having
a hollow skeleton can be produced by a plating method in which a
surface of a resin body having a three-dimensional network
structure is coated with aluminum by electrolytic plating.
[0034] According to the porous aluminum body of the present
invention, aluminum contained in the porous aluminum body
preferably has a purity of 99.7% by mass or more. In this case, the
porous aluminum body can be used as a heat transfer material having
a higher thermal conductivity. In order to achieve a purity of
99.7% by mass or more of aluminum, the purity of aluminum used as
an anode in the plating method may be 99.7% by mass or more. In
this method, the purity of aluminum contained in the porous
aluminum body can be increased to 99.9% by mass or more, and
further increased to 99.99% by mass or more.
[0035] In the step of performing electrolytic plating, the surface
of a resin body having a three-dimensional network structure may be
subjected to a conductivity-imparting treatment such as carbon
powder coating or plating of Sn or Ni. Note that the purity of
aluminum represents a purity determined by excluding the material
used in the conductivity-imparting treatment, such as carbon, Sn,
or Ni.
[0036] The porous aluminum body according to the present invention
preferably has a weight per volume of 0.1 g/cm.sup.3 or more and
1.0 g/cm.sup.3 or less. When the weight per volume of the porous
aluminum body is 0.1 g/cm.sup.3 or more and 1.0 g/cm.sup.3 or less,
the porous aluminum body can be used as a heat transfer material
having a very large specific surface area and a good heat-exchange
efficiency. The weight per volume of the porous aluminum body is
more preferably 0.1 g/cm.sup.3 or more and 0.6 g/cm.sup.3 or less,
and still more preferably 0.1 g/cm.sup.3 or more and 0.4 g/cm.sup.3
or less.
[0037] In order to obtain a porous aluminum body having a weight
per volume in the above range, the amount of aluminum film formed,
by the plating method, on the surface of the resin body having a
three-dimensional network structure may be appropriately
adjusted.
<Method for Producing Porous Aluminum Body>
[0038] As described above, the porous aluminum body according to
the present invention can be produced by a plating method using a
molten-salt bath. Specifically, a resin body composed of a urethane
foam or the like and having a three-dimensional network structure
provided with continuous pores (hereinafter, also simply referred
to as "resin body") is used as a core material, a
conductivity-imparting treatment is performed on the resin body,
and electrolytic plating of aluminum is then performed in a
molten-salt bath. Subsequently, the resulting resin structure
having an aluminum film thereon is heat-treated so that the resin
is removed by being burnt away. Thus, a porous aluminum body in
which only a metal layer is left can be produced.
[0039] A method for producing a porous aluminum body according to
the present invention will now be described in more detail.
(Preparation of Resin Body Having Three-Dimensional Network
Structure)
[0040] First, a resin body having a three-dimensional network
structure and continuous pores is prepared. Any resin can be
selected as the material of the resin body. Examples of the
material include resin foam bodies composed of polyurethane,
melamine, polypropylene, polyethylene, or the like.
[0041] Urethane foams and melamine foams can be preferably used as
the resin foam bodies because they have high porosities, pore
continuity, and good thermal decomposition properties. Urethane
foams are preferable from the viewpoint of uniformity of pores,
availability, etc., and from the viewpoint that a foam having a
small pore diameter is obtained.
[0042] A resin body often contains residues such as a foaming agent
and an unreacted monomer in the process of producing the foam.
Therefore, a washing treatment is preferably performed for the
subsequent steps. The resin body serving as a skeleton
three-dimensionally forms a network, thereby forming continuous
pores as a whole. The skeleton of a urethane foam has a
substantially triangular shape in a cross section perpendicular to
a direction in which the skeleton extends.
[0043] The resin foam body preferably has a porosity of 80% to 98%
and a pore diameter of 420 to 4,230 .mu.m.
[0044] The porosity is defined by the following formula:
Porosity=(1-(weight of porous material [g]/(volume of porous
material [cm.sup.3].times.density of raw material)).times.100
[%]
[0045] The pore diameter is determined by magnifying a surface of
the resin body by means of a photomicrograph or the like, counting
the number of pores per inch (25.4 mm) as the number of cells, and
calculating an average of the pore diameter as mean pore
diameter=25.4 mm/the number of cells.
(Impartation of Electrical Conductivity to Surface of Resin
Body)
[0046] In order to coat a surface of a resin body with aluminum by
electrolytic plating, the surface of the resin body is subjected to
a conductivity-imparting treatment in advance. The
conductivity-imparting treatment is not particularly limited as
long as a layer having electrical conductivity can be provided by
the treatment on the surface of the resin body. It is possible to
select any method such as electroless plating of a conductive metal
such as nickel, vapor deposition or sputtering of aluminum or the
like, or application of a conductive coating material containing
conducive particles such as carbon particles.
[0047] A method for imparting conductivity by performing a
sputtering process of aluminum and a method for imparting
conductivity to a surface of a resin body by using carbon particles
as conductive particles will now be described as examples of the
conductivity-imparting treatment.
--Sputtering of Aluminum--
[0048] A sputtering process using aluminum is not particularly
limited as long as aluminum is used as a target, and can be
performed by an ordinary method. For example, a resin body is
attached to a substrate holder, and a direct-current voltage is
then applied between the holder and a target (aluminum) while an
inert gas is introduced. The ionized inert gas is thereby caused to
collide with aluminum, and sputtered aluminum particles are
deposited on the surface of the resin body to form a sputtered film
composed of aluminum. The sputtering process is preferably
conducted at a temperature at which the resin body does not melt,
specifically at about 100.degree. C. to 200.degree. C., and
preferably at about 120.degree. C. to 180.degree. C.
--Carbon Coating--
[0049] First, a carbon coating material serving as a conductive
coating material is prepared. A suspension serving as the
conductive coating material preferably contains carbon particles, a
binder, a dispersant, and a dispersion medium. In order to
uniformly apply the conductive particles, it is necessary that the
suspension maintain a uniformly suspended state. For this purpose,
the suspension is preferably maintained at 20.degree. C. to
40.degree. C. This is because when the temperature of the
suspension is lower than 20.degree. C., the uniformly suspended
state is impaired, and only the binder may be concentrated on a
surface of a skeleton forming a network structure of a porous resin
body to form a layer of the binder. In this case, the applied
carbon particle layer is easily separated, and it is difficult to
form a metal plating layer that strongly adheres to the carbon
particle layer. On the other hand, when the temperature of the
suspension exceeds 40.degree. C., the amount of dispersant
evaporated is large. Accordingly, with the lapse of the coating
process time, the suspension is concentrated, and the amount of
carbon applied tends to vary. The carbon particles preferably have
a particle diameter of 0.01 to 5 and more preferably 0.01 to 2
.mu.m. When the particle diameter is excessively large, the carbon
particles may clog cells of the resin body, and disturb flat and
smooth plating. When the particle diameter is excessively small, it
is difficult to ensure sufficient electrical conductivity.
[0050] The carbon particles can be applied onto a resin body by
immersing the target resin body in the suspension, and conducing
squeezing and drying.
(Formation of Aluminum Film on Surface of Resin Body)
[0051] A plating method using a molten-salt bath is employed as a
method for forming an aluminum film on a surface of a resin
body.
--Molten Salt Plating--
[0052] Electrolytic plating is conducted in a molten salt to form
an aluminum film on a surface of a resin body.
[0053] By conducting aluminum plating in a molten-salt bath, an
aluminum film having a large thickness can be uniformly formed
particularly on the surface of a complex skeleton structure, such
as a resin body having a three-dimensional network structure. A
direct current is supplied between the resin body having a surface
to which electrical conductivity is imparted, the resin body
serving as a cathode, and aluminum serving as an anode in a molten
salt.
[0054] The molten salt may be an organic molten salt that is a
eutectic salt of an organohalide and an aluminum halide or an
inorganic molten salt that is a eutectic salt of an alkali metal
halide and an aluminum halide. When an organic molten-salt bath
that melts at a relatively low temperature is used, electrolytic
plating can be performed without decomposition of a resin body
serving as a base. An imidazolium salt, a pyridinium salt, or the
like can be used as the organohalide. Specifically,
1-ethyl-3-methylimidazolium chloride (EMIC) and butylpyridinium
chloride (BPC) are preferred.
[0055] Mixing of moisture or oxygen into the molten salt degrades
the molten salt. Therefore, the plating is preferably conducted in
an inert gas atmosphere such as nitrogen or argon in a closed
environment.
[0056] A bath of a molten salt containing nitrogen is preferred as
the molten-salt bath. Among such bathes, an imidazolium salt bath
is preferably used. In the case where a salt that melts at a high
temperature is used as a molten salt, the rate of dissolution or
decomposition of a resin in the molten salt is higher than the rate
of the growth of a plating film, and thus a plating film cannot be
formed on the surface of the resin body. An imidazolium salt bath
can be used even at a relatively low temperature without affecting
a resin. A salt containing an imidazolium cation having alkyl
groups at the 1- and 3-positions is preferably used as an
imidazolium salt. In particular, aluminum
chloride-1-ethyl-3-methylimidazolium chloride (AlCl.sub.3-EMIC)
molten salts are most preferably used because they have high
stability and are not easily decomposed. Plating on a urethane
resin foam or a melamine resin foam can be performed by using the
molten salt bath. The temperature of the molten salt bath is
10.degree. C. to 100.degree. C., and preferably 25.degree. C. to
45.degree. C. With a decrease in the temperature of the molten salt
bath, the current density range for plating becomes narrow, and
plating on the entire surface of a resin body becomes difficult.
When the temperature of the molten salt bath is a high temperature
of more than 100.degree. C., the shape of the resin body serving as
a base tends to be deformed. Through the above steps, an
aluminum-resin structure including the resin body serving as a core
of the skeleton is prepared.
(Removal of Resin)
[0057] The aluminum-resin structure prepared as described above is
heat-treated by being heated at 500.degree. C. or higher in a
nitrogen atmosphere, air, or the like. The resin is thereby removed
by being burnt away, and a porous aluminum body is thus obtained.
It was found that, in order to produce the porous aluminum body of
the present invention, it is effective to add an improvement to
this step, which has been hitherto performed. Specifically, a
method described below is employed.
--Treatment of Plating Solution Adhering to Resin Structure--
[0058] A plating solution adheres to the surface of the resin body
prepared as described above, the resin body having an aluminum film
on the surface thereof. Therefore, a water washing treatment is
performed, and a heating treatment is then performed.
[0059] In this step, the plating solution is not sufficiently
drained and the water washing step is subsequently performed. Thus,
a porous aluminum body whose skeleton has fine irregularities on
the surface thereof can be obtained. It is believed that this is
because the plating solution containing the molten salt reacts with
water to thereby generate heat, and aluminum and water react with
each other on the surface of the aluminum film to form boehmite. In
general, a dehydration reaction of boehmite occurs at 450.degree.
C. or higher, and boehmite is transformed into .gamma.-alumina
having micropores. Also in the present invention, during combustion
removal of a resin from a resin structure, the resin structure is
exposed to a high temperature of 500.degree. C. or higher.
Consequently, boehmite produced as described above is transformed
into .gamma.-alumina, thereby forming fine irregularities on the
surface of the skeleton.
[0060] In order to obtain, by this method, a porous aluminum body
whose skeleton has fine irregularities on the surface thereof, the
water washing treatment is preferably performed in a state where
the amount of plating solution adhering to the resin structure
becomes 20 to 2,000 mL/m.sup.2. The amount of plating solution
adhering to the resin structure is more preferably 200 to 2,000
mL/m.sup.2, and still more preferably 1,000 to 2,000
mL/m.sup.2.
--Water Washing Treatment of Resin Structure--
[0061] Even in the case where the plating solution is sufficiently
removed in the treatment of the plating solution adhering to the
resin structure, a porous aluminum body whose skeleton has fine
irregularities on the surface thereof can be produced as follows.
As described above, a water washing treatment is performed in order
to remove a plating solution adhering to a resin body having an
aluminum film on the surface thereof. In this step, heat treatment
for removing the resin may be performed without sufficiently
removing water adhering to the resin structure. It is believed
that, also in this case, in the step of heating the resin
structure, aluminum and water react with each other on the surface
of the aluminum film at about 80.degree. C. to produce boehmite,
and the boehmite is then transformed into .gamma.-alumina having
micropores by being further heated.
[0062] In order to obtain, by this method, a porous aluminum body
whose skeleton has fine irregularities on the surface thereof, the
treatment for combustion removal of the resin is preferably
performed in a state where the amount of water adhering to the
resin structure becomes 10 to 1,000 mL/m.sup.2. The amount of water
adhering to the resin structure is more preferably 100 to 1,000
mL/m.sup.2, and still more preferably 500 to 1,000 mL/m.sup.2.
--Combustion Removal of Resin from Resin Structure--
[0063] Besides the two methods described above, there is a method
for producing a porous aluminum body whose skeleton has fine
irregularities on the surface thereof. Specifically, even in the
case where the plating solution is sufficiently drained, and water
that is adhered by the subsequent water washing treatment is also
sufficiently removed, a subsequent step of combustion removal of a
resin may be performed in an atmosphere containing a large amount
of water, i.e., having a high dew point. For this purpose, for
example, heat treatment may be performed by heating to 500.degree.
C. or higher while supplying humidified air. It is believed that,
also in this case, water supplied in the atmosphere in which the
heat treatment is performed and aluminum react with each other at
about 80.degree. C. to produce boehmite, and the boehmite is then
transformed into .gamma.-alumina having micropores by being further
heated.
[0064] In order to obtain, by this method, a porous aluminum body
whose skeleton has fine irregularities on the surface thereof, the
dew-point temperature of the atmosphere in the step of combustion
removal of a resin is preferably 0.degree. C. to 60.degree. C. The
dew-point temperature is more preferably 20.degree. C. to
60.degree. C., and still more preferably 40.degree. C. to
60.degree. C.
<Heat Transfer Material and Heat Exchange Device>
[0065] By using the porous aluminum body of the present invention
as a heat transfer material, a heat transfer material having a very
large specific surface area, a good heat-exchange efficiency, and a
low pressure drop of a gas can be obtained. In addition, since a
heat exchange device produced by using the porous aluminum body of
the present invention as a heat transfer material has a very high
heat-exchange efficiency, the size of the heat exchange device can
be reduced as compared with an existing heat exchange device.
[0066] The heat exchange device is not particularly limited as long
as the porous aluminum body of the present invention is thermally
connected to a heating element or a cooling element and used as a
heat transfer material, and the heat exchange device includes means
for transferring heat transferred to the porous aluminum body to
another medium by air blowing or the like.
[0067] An example of the heat exchange device is the use of the
porous aluminum body of the present invention as a heat dissipation
material of a semiconductor device. For example, the porous
aluminum body of the present invention can be used instead of a
so-called existing heat sink or the like. Specifically, cooling can
be efficiently performed by providing the porous aluminum body of
the present invention on a heating element and supplying wind with
a fan or the like.
[0068] Another example of the heat exchange device is an air
conditioner or the like. In this case, the porous aluminum body of
the present invention may be used instead of a fin provided on a
surface of a heat transfer tube through which a cooling medium or a
heating medium passes. By supplying air to the porous aluminum
body, heat transferred from the heat transfer tube can be
transferred to air.
[0069] Means for providing a porous aluminum body on a surface of a
heat transfer tube is not particularly limited. For example, the
porous aluminum body can be joined by using flux and a brazing
material containing an aluminum alloy powder or the like. In such a
case, the thickness of the porous aluminum body used as a heat
transfer material is not particularly limited, and can be
appropriately changed in accordance with the design of the heat
exchange device. A porous aluminum body having any thickness can be
obtained by appropriately changing the thickness of the resin body
used as a starting material in the production by the plating
method.
[0070] The porous aluminum body of the present invention can be
provided not only on an outer surface of the heat transfer tube but
also on an inner surface of the heat transfer tube. With this
structure, heat from a cooling medium (or a heating medium) that
passes through the heat transfer tube can be more efficiently
transferred to the outside.
EXAMPLES
[0071] The present invention will be described in more detail using
Examples. However, these Examples are only illustrative, and an
apparatus for producing an aluminum powder of the present invention
and the like are not limited thereto. It is to be understood that
the scope of the present invention is defined by the description of
Claims and includes equivalents of the description in Claims and
all modifications within the scope of Claims.
Example 1
Formation of Electrically Conductive Layer
[0072] A urethane foam having a porosity of 97%, a number of cells
of 10 per inch, a pore diameter of about 2,540 .mu.m, and a
thickness of 10 mm was prepared as a resin body and cut into a
rectangle of 80 mm.times.50 mm. Aluminum was deposited on the
surface of the polyurethane foam by sputtering with a weight per
volume of 10 g/m.sup.2 to form an electrically conductive
layer.
(Molten Salt Plating)
[0073] The urethane foam having the electrically conductive layer
on the surface thereof was set, as a workpiece, to a fixture having
a power-supplying function. The fixture to which the workpiece was
set was then placed in a glove box in an argon atmosphere having a
low water content (dew point: -30.degree. C. or lower) and immersed
in a molten salt aluminum plating bath (prepared by adding 0.5 g/L
of 1,10-phenanthroline to 33 mol % EMIC-67 mol % AlCl.sub.3) at a
temperature of 45.degree. C. The fixture to which the workpiece was
set was connected to the cathode side of a rectifier, and an
aluminum plate (purity: 99.99% by mass) serving as a counter
electrode was connected to the anode side.
[0074] Plating was conducted by supplying a direct current at a
current density of 6 A/dm.sup.2 for 60 minutes. As a result, a
structure in which an aluminum film was formed at a mass of 0.15
g/cm.sup.3 on the surface of the urethane foam was obtained.
Stirring was performed with a stirrer using a rotor composed of
Teflon (registered trademark). Note that the current density is a
value calculated on the basis of the apparent area of the urethane
foam.
(Removal of Resin)
[0075] The structure prepared as described above was taken from the
plating bath, and a water washing treatment was conducted in a
state where the amount of plating solution adhering to the
structure became 1,500 mL/m.sup.2. After the water washing
treatment, the structure was sufficiently dried, and in a state
where the amount of water adhering to the structure became 6
mL/m.sup.2, heat treatment was conducted at 600.degree. C. for 30
minutes in air having a dew-point temperature of -15.degree. C.
Through this step, the resin was removed by being burnt away. Thus,
a porous aluminum body 1 of the present invention (purity: 99.99%
by mass) was obtained.
--Evaluation--
<Specific Surface Area>
[0076] The specific surface area of the porous aluminum body 1 was
measured by the capacitance method described above. Specifically, a
plurality of aluminum plates having a purity of 99.99% by mass and
having known surface areas were prepared. The capacitance of each
of the aluminum plates was evaluated, and a calibration curve of
"capacitance" versus "surface area" was prepared. The capacitance
of the porous aluminum body was then evaluated. Thus, the surface
area of the porous aluminum body was determined by a calibration
curve method.
[0077] Table I shows the results.
<Observation with Microscope>
[0078] The porous aluminum body 1 was observed with an electron
microscope. A large number of fine irregularities were formed on
the surface of the porous aluminum body 1.
Example 2
[0079] A porous aluminum body 2 was obtained by the same method as
that used in Example 1 except that, in the method for producing a
porous aluminum body in Example 1, the water washing treatment was
conducted in a state where the amount of plating solution adhering
to the structure became 10 mL/m.sup.2, and subsequently, in a state
where the amount of water adhering to the structure was 800
mL/m.sup.2, heat treatment was conducted in air having a dew-point
temperature of -10.degree. C.
[0080] The evaluation was conducted as in Example 1. Table I shows
the results.
Example 3
[0081] A porous aluminum body 3 was obtained by the same method as
that used in Example 1 except that, in the method for producing a
porous aluminum body in Example 1, the water washing treatment was
conducted in a state where the amount of plating solution adhering
to the structure became 6 mL/m.sup.2, and subsequently, in a state
where the amount of water adhering to the structure was 5
mL/m.sup.2, heat treatment was conducted in air having a dew-point
temperature of 58.degree. C.
[0082] The evaluation was conducted as in Example 1. Table I shows
the results.
Example 4
[0083] A porous aluminum body 4 was obtained as in Example 1 except
that, in the method for producing a porous aluminum body in Example
1, a urethane foam having a number of cells of 30 per inch was
used.
[0084] The evaluation was conducted as in Example 1. Table I shows
the results.
Example 5
[0085] A porous aluminum body 5 was obtained as in Example 2 except
that, in the method for producing a porous aluminum body in Example
2, a urethane foam having a number of cells of 30 per inch was
used.
[0086] The evaluation was conducted as in Example 1. Table I shows
the results.
Example 6
[0087] A porous aluminum body 6 was obtained as in Example 3 except
that, in the method for producing a porous aluminum body in Example
3, a urethane foam having a number of cells of 30 per inch was
used.
[0088] The evaluation was conducted as in Example 1. Table I shows
the results.
Comparative Example 1
[0089] A porous aluminum body 7 was obtained by the same method as
that used in Example 1 except that, in the method for producing a
porous aluminum body in Example 1, the water washing treatment was
conducted in a state where the amount of plating solution adhering
to the structure became 10 mL/m.sup.2, and subsequently, in a state
where the amount of water adhering to the structure was 4
mL/m.sup.2, heat treatment was conducted in air having a dew-point
temperature of -10.degree. C.
[0090] The evaluation was conducted as in Example 1. Table I shows
the results.
Comparative Example 2
[0091] A porous aluminum body 8 was obtained by the same method as
that used in Example 4 except that, in the method for producing a
porous aluminum body in Example 4, the water washing treatment was
conducted in a state where the amount of plating solution adhering
to the structure became 10 mL/m.sup.2, and subsequently, in a state
where the amount of water adhering to the structure was 4
mL/m.sup.2, heat treatment was conducted in air having a dew-point
temperature of -10.degree. C.
[0092] The evaluation was conducted as in Example 1. Table I shows
the results.
Comparative Example 3
[0093] Duocel (registered trademark): material A6061, manufactured
by ERG Aerospace Corporation, the Duocel being produced by a
casting method, was prepared as a porous aluminum body 9.
[0094] The evaluation was conducted as in Example 1. Table I shows
the results.
TABLE-US-00001 TABLE I Production process Amount of Dew-point
Evaluation plating solution Amount of temperature of Fine adhering
to water adhering heat-treatment Specific irregularities structure
to structure atmosphere Number of cells X surface area Y Numerical
on skeleton (mL/m.sup.2) (mL/m.sup.2) (.degree. C.) (per inch)
(m.sup.2/m.sup.3) value a surface Example 1 1500 6 -15 10 1460 806
Formed Example 2 10 800 -10 10 1160 650 Formed Example 3 6 5 58 10
580 305 Formed Example 4 1500 6 -15 30 4700 780 Formed Example 5 10
800 -10 30 3750 615 Formed Example 6 6 5 58 30 1620 270 Formed
Comparative 10 4 -10 10 150 90 Not formed Example 1 Comparative 10
4 -10 30 470 82 Not formed Example 2 Comparative -- -- -- 10 100 52
Not formed Example 3
* * * * *