U.S. patent application number 14/916650 was filed with the patent office on 2016-07-14 for hydrogen production apparatus, hydrogen production method, silicon fine particles for hydrogen production, and production method for silicon fine particles for hydrogen production.
The applicant listed for this patent is KIT CO, LTD., Hikaru KOBAYASHI, NISSHIN KASEI CO., LTD.. Invention is credited to Toru HIGO, Yayoi KANATANI, Hikaru KOBAYASHI.
Application Number | 20160200571 14/916650 |
Document ID | / |
Family ID | 52628293 |
Filed Date | 2016-07-14 |
United States Patent
Application |
20160200571 |
Kind Code |
A1 |
KOBAYASHI; Hikaru ; et
al. |
July 14, 2016 |
HYDROGEN PRODUCTION APPARATUS, HYDROGEN PRODUCTION METHOD, SILICON
FINE PARTICLES FOR HYDROGEN PRODUCTION, AND PRODUCTION METHOD FOR
SILICON FINE PARTICLES FOR HYDROGEN PRODUCTION
Abstract
An exemplary hydrogen production apparatus 100 according to the
present invention includes a grinding unit 10 configured to grind a
silicon chip or a silicon grinding scrap 1 to form silicon fine
particles 2, and a hydrogen generator 70 configured to generate
hydrogen by causing the silicon fine particles 2 to contact with as
well as disperse in, or to contact with or dispersed in water or an
aqueous solution. The hydrogen production apparatus 100 can achieve
reliable production of a practically adequate amount of hydrogen
from a start material of silicon chips or silicon grinding scraps
that are ordinarily regarded as waste. The hydrogen production
apparatus thus effectively utilizes the silicon chips or the
silicon grinding scraps so as to contribute to environmental
protection as well as to significant reduction in cost for
production of hydrogen that is utilized as an energy source in the
next generation.
Inventors: |
KOBAYASHI; Hikaru; (Kyoto,
JP) ; HIGO; Toru; (Osaka, JP) ; KANATANI;
Yayoi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOBAYASHI; Hikaru
KIT CO, LTD.
NISSHIN KASEI CO., LTD. |
Kyoto
Osaka
Osaka |
|
JP
JP
JP |
|
|
Family ID: |
52628293 |
Appl. No.: |
14/916650 |
Filed: |
August 26, 2014 |
PCT Filed: |
August 26, 2014 |
PCT NO: |
PCT/JP2014/072219 |
371 Date: |
March 4, 2016 |
Current U.S.
Class: |
423/348 ; 241/30;
422/162; 423/648.1 |
Current CPC
Class: |
B01J 8/02 20130101; B01J
2208/00592 20130101; Y02E 60/36 20130101; C01B 33/021 20130101;
C01B 3/06 20130101; B01J 2208/024 20130101; B01J 7/02 20130101;
B01J 8/20 20130101 |
International
Class: |
C01B 3/06 20060101
C01B003/06; C01B 33/021 20060101 C01B033/021; B01J 8/02 20060101
B01J008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2013 |
JP |
2013-184481 |
Feb 28, 2014 |
JP |
2014-038422 |
Claims
1. A hydrogen production apparatus comprising: a grinding unit
configured to grind a silicon chip or a silicon grinding scrap to
form silicon fine particles; and a hydrogen generator configured to
generate hydrogen by causing the silicon fine particles to contact
with as well as disperse in, or to contact with or dispersed in
water or an aqueous solution.
2. The hydrogen production apparatus according to claim 1, further
comprising: a surface oxide film remover configured to cause the
silicon fine particles formed by the grinding unit to contact with
an aqueous hydrofluoric acid solution or an aqueous ammonium
fluoride solution; wherein the hydrogen generator generates
hydrogen by causing the silicon fine particles, which have been
caused to contact with the aqueous hydrofluoric acid solution or
the aqueous ammonium fluoride solution, to contact with as well as
disperse in, or to contact with or dispersed in water or an aqueous
solution.
3. The hydrogen production apparatus according to claim 2, further
comprising: a hydrophilization treatment unit configured to
hydrophilize surfaces of the silicon fine particles having been
caused to contact with the aqueous hydrofluoric acid solution or
the aqueous ammonium fluoride solution; wherein the
hydrophilization treatment unit causes the surfaces of the silicon
fine particles to contact with a surfactant or nitric acid.
4. The hydrogen production apparatus according to claim 1, further
comprising: an additional surface oxide film remover configured to
cause the silicon fine particles extracted from the hydrogen
generator to contact again with an aqueous hydrofluoric acid
solution or an aqueous ammonium fluoride solution; and an
additional hydrogen generator configured to generate hydrogen by
causing the silicon fine particles, which have been caused to
contact again with the aqueous hydrofluoric acid solution or the
aqueous ammonium fluoride solution by the additional surface oxide
film remover, to contact with as well as disperse in, or to contact
with or dispersed in water or an aqueous solution.
5. The hydrogen production apparatus according to claim 1, further
comprising: an adjuster configured to adjust at least one of
hydrogen generation speed and a hydrogen generation amount by
changing a hydrogen ion concentration index (pH) of the water or
the aqueous solution in the hydrogen generator.
6. A hydrogen production method comprising: a grinding step of
grinding a silicon chip or a silicon grinding scrap to form silicon
fine particles; and a hydrogen generating step of generating
hydrogen by causing the silicon fine particles to contact with as
well as disperse in, or to contact with or dispersed in water or an
aqueous solution.
7. The hydrogen production method according to claim 6, further
comprising: a surface oxide film removing step to be executed
before the hydrogen generating step, of causing the silicon fine
particles formed in the grinding step to contact with an aqueous
hydrofluoric acid solution or an aqueous ammonium fluoride
solution; wherein in the hydrogen generating step, hydrogen is
generated by causing the silicon fine particles, which have been
caused to contact with the aqueous hydrofluoric acid solution or
the aqueous ammonium fluoride solution, to contact with as well as
disperse in, or to contact with or dispersed in water or an aqueous
solution.
8. The hydrogen production method according to claim 7, further
comprising: a hydrophilization treatment step to be executed before
the hydrogen generating step, of hydrophilizing surfaces of the
silicon fine particles having been caused to contact with the
aqueous hydrofluoric acid solution or the aqueous ammonium fluoride
solution.
9. The hydrogen production method according to claim 6, further
comprising: an additional surface oxide film removing step to be
executed during or after the hydrogen generating step, of causing
the silicon fine particles to contact again with an aqueous
hydrofluoric acid solution or an aqueous ammonium fluoride
solution; and an additional hydrogen generating step to be executed
after the additional surface oxide film removing step, of
generating hydrogen by causing the silicon fine particles to
contact with as well as disperse in, or to contact with or
dispersed in the water or the aqueous solution again.
10. The hydrogen production method according to claim 6, wherein in
the hydrogen generating step, at least one of hydrogen generation
speed and a hydrogen generation amount is adjusted by changing a
hydrogen ion concentration index (pH) of the water or the aqueous
solution.
11. The hydrogen production method according to claim 8, wherein in
the hydrophilization treatment step, the surfaces of the silicon
fine particles are caused to contact with a surfactant or nitric
acid.
12. The hydrogen production method according to claim 6, wherein
the silicon fine particles have a crystallite diameter of 100 nm or
less.
13. The hydrogen production method according to claim 6, wherein
the aqueous solution used in the hydrogen generating step has a pH
value of 10 or more.
14. A silicon fine particle for hydrogen production, having: an
amorphous shape, a crystallite diameter of 100 nm or less, and a
hydrophilic surface.
15. The silicon fine particle for hydrogen production according to
claim 14, having: a hydrophilic surface.
16. The silicon fine particle for hydrogen production according to
claim 14, including a silicon fine particle obtained by chemically
treating a silicon fine particle that is formed by grinding a
silicon chip or a silicon grinding scrap.
17. A production method for silicon fine particles for hydrogen
production, the method comprising: a grinding step of grinding a
silicon chip or a silicon grinding scrap to form silicon fine
particles.
18. The production method for silicon fine particles for hydrogen
production according to claim 17, the method further comprising: a
surface oxide film removing step of causing the silicon fine
particles formed in the grinding step to contact with an aqueous
hydrofluoric acid solution or an aqueous ammonium fluoride
solution.
19. The production method for silicon fine particles for hydrogen
production according to claim 18, the method further comprising: a
hydrophilization treatment step of hydrophilizing surfaces of the
silicon fine particles having been caused to contact with the
aqueous hydrofluoric acid solution or the aqueous ammonium fluoride
solution.
20. The production method for silicon fine particles for hydrogen
production according to claim 19, wherein in the hydrophilization
treatment step, the surfaces of the silicon fine particles are
caused to contact with a surfactant or nitric acid.
21. The production method for silicon fine particles for hydrogen
production according to claim 17, the method further comprising: a
chemical treatment step of chemically treating the silicon fine
particles that are formed by grinding the silicon chip or the
silicon grinding scrap.
22. A silicon fine particle for hydrogen production, the silicon
fine particle being produced in accordance with the production
method for silicon fine particles for hydrogen production according
to claim 17.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hydrogen production
apparatus, a hydrogen production method, silicon fine particles for
hydrogen production, and a production method for silicon fine
particles for hydrogen production.
BACKGROUND ART
[0002] Fuel cells have recently been attracting attention as one of
possible energy sources in the next generation in terms of resource
exhaustion prevention and environmental protection. Accordingly,
development in technique of producing hydrogen included in fuel
cells as fuel substituting for petroleum will largely influence
success in upcoming development in the fuel cell field. There has
been disclosed a conventional technique of producing hydrogen as
such an energy source by causing silicon fine powder having an
average particle diameter of 2 .mu.m (micron) or less to contact
with water (e.g., Patent Document 1).
[0003] As to silicon powder, the inventors of the present
application have disclosed a method for producing silicon fine
particles, other than grinding a silicon wafer into fine particles,
from silicon particles so-called chip powder that is obtained upon
forming a thin substrate (wafer) from a silicon base material
(ingot). The inventors of the present application have also
disclosed a technique of applying the obtained silicon fine
particles to silicon ink or a solar cell (e.g., Patent Document
2).
PRIOR ART DOCUMENT
Patent Documents
[0004] Patent Document 1: JP 2004-115349 A
[0005] Patent Document 2: JP 2012-229146 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] However, the conventionally disclosed technique of producing
hydrogen achieves a hydrogen gas generation amount only in the
range from 0.2 mmol (millimolar) to 2.9 mmol in a case where 15 g
of silicon powder is caused to react for one hour, and fails to
reach an adequate generation amount for actual industrial
application.
[0007] It is desired, in terms of effective resource utilization
and environmental protection, to effectively utilize silicon
particles that are obtained from chips formed by cutting silicon or
silicon grinding scraps, which are ordinarily dealt as waste.
[0008] The present invention solves at least one of the technical
problems mentioned above, and significantly contributes to
achievement of a hydrogen production apparatus and a hydrogen
production method that effectively utilize silicon waste and are
excellent in economical and industrial efficiency.
Solutions to the Problems
[0009] The inventors of the present application have devoted
themselves to intensive researches in a practically and
industrially excellent hydrogen production technique by focusing on
effective utilization of silicon fine scraps or chips (hereinafter,
also generally called "silicon chips") or silicon grinding scraps,
which are ordinarily discarded as a large amount of waste, in
silicon cutting in a production process of semiconductor products
in the semiconductor field. The inventors finally have found that
silicon waste can be utilized effectively and a large amount of
hydrogen can be produced even under a moderate condition. The
present invention has been devised in view of the above point.
[0010] An exemplary hydrogen production apparatus according to the
present invention includes: a grinding unit configured to grind a
silicon chip or a silicon grinding scrap to form silicon fine
particles; and a hydrogen generator configured to generate hydrogen
by causing the silicon fine particles to contact with as well as
disperse in, or to contact with or dispersed in water or an aqueous
solution.
[0011] This hydrogen production apparatus can achieve reliable
production of a practically adequate amount of hydrogen from a
start material of silicon chips or silicon grinding scraps that are
obtained by silicon cutting in a production process of
semiconductor products or the like and are ordinarily dealt as
waste. This hydrogen production apparatus thus effectively utilizes
silicon chips or silicon grinding scraps ordinarily regarded as
waste so as not only to significantly contribute to environmental
protection, but also to achieve significant reduction in cost for
production of hydrogen that is utilized in a fuel cell or the like
as an energy source in the next generation. This hydrogen
production apparatus can thus markedly improve industrial
productivity in hydrogen production.
[0012] An exemplary hydrogen production method according to the
present invention includes: a grinding step of grinding a silicon
chip or a silicon grinding scrap to form silicon fine particles;
and a hydrogen generating step of generating hydrogen by causing
the silicon fine particles to contact with as well as disperse in,
or to contact with or dispersed in water or an aqueous
solution.
[0013] This hydrogen production method can achieve reliable
production of a practically adequate amount of hydrogen from a
start material of silicon chips or silicon grinding scraps that are
obtained by silicon cutting in a production process of
semiconductor products or the like and are ordinarily dealt as
waste. This hydrogen production method thus effectively utilizes
silicon chips or silicon grinding scraps ordinarily regarded as
waste so as not only to significantly contribute to environmental
protection, but also to achieve significant reduction in cost for
production of hydrogen that is utilized in a fuel cell or the like
as an energy source in the next generation. This hydrogen
production method can thus markedly improve industrial productivity
in hydrogen production.
[0014] An exemplary silicon fine particle for hydrogen production
according to the present invention has an amorphous shape and a
crystallite diameter distribution in the range of 100 nm
(nanometer) or less. Among silicon fine particles formed by
grinding silicon chips or silicon grinding scraps, a silicon fine
particle obtained through chemical treatment (typically, oxide film
removal using an aqueous hydrofluoric acid solution and/or an
aqueous ammonium fluoride solution or hydrophilization using a
fourth liquid in each embodiment to be described later) preferably
exemplify the above silicon fine particles for hydrogen
production.
[0015] An exemplary production method for silicon fine particles
for hydrogen production according to the present invention includes
a grinding step of grinding a silicon chip or a silicon grinding
scrap to form silicon fine particles.
[0016] The silicon fine particles for hydrogen production and the
production method for the silicon fine particles for hydrogen
production can achieve provision of an intermediate material that
enables reliable production of a practically adequate amount of
hydrogen from silicon chips or silicon grinding scraps that are
obtained by silicon cutting in a production process of
semiconductor products or the like and are ordinarily dealt as
waste.
Effects of the Invention
[0017] The exemplary hydrogen production apparatus according to the
present invention and the exemplary hydrogen production method
according to the present invention can achieve reliable production
of a practically adequate amount of hydrogen from a start material
of silicon chips or silicon grinding scraps that are ordinarily
regarded as waste. The hydrogen production apparatus and the
hydrogen production method thus effectively utilize silicon chips
or silicon grinding scraps regarded as waste so as to contribute to
environmental protection as well as to significant reduction in
cost for production of hydrogen that is utilized as an energy
source in the next generation. The exemplary silicon fine particles
for hydrogen production according to the present invention and the
exemplary production method for the silicon fine particles for
hydrogen production can provide an intermediate material that
enables reliable production of a practically adequate amount of
hydrogen from silicon chips or silicon grinding scraps that are
obtained by silicon cutting in a production process of
semiconductor products or the like and are ordinarily regarded as
waste.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a flowchart of respective steps in a hydrogen
production method according to a first embodiment.
[0019] FIG. 2 is a flowchart of respective steps in a hydrogen
production method according to a second embodiment.
[0020] FIG. 3 is a flowchart of respective steps in a hydrogen
production method according to a third embodiment.
[0021] FIG. 4 is an explanatory view depicting a schematic
configuration of a hydrogen production apparatus according to a
fourth embodiment.
[0022] FIGS. 5(a) and 5(b) are sectional TEM (transmission electron
microscope) photographs each depicting a crystal structure of
silicon fine particles after the grinding step in Example 1.
[0023] FIG. 6 is a crystallite diameter distribution graph of
silicon fine particles after the grinding step.
[0024] FIG. 7 is a graph of hydrogen generation amounts according
to Examples 1 to 3.
[0025] FIG. 8 is a graph of hydrogen generation amounts according
to Examples 4 and 5.
[0026] FIG. 9 is a graph of hydrogen generation amounts immediately
after the start of reaction in Examples 4 and 5.
[0027] FIG. 10 is an explanatory view depicting a schematic
configuration of a hydrogen production apparatus according to a
modification example of the fourth embodiment.
[0028] FIG. 11 is a graph of a hydrogen generation amount with
respect to a reaction period in Example 6.
[0029] FIG. 12 is a graph of a difference in maximum hydrogen
generation speed due to a difference in pH value in Example 6.
[0030] FIG. 13 is an XPS spectrography of silicon fine particles
after hydrogen generation reaction in Example 6.
[0031] FIG. 14 is a graph of a hydrogen generation amount per 1 g
with respect to a reaction period in Example 7.
DESCRIPTION OF REFERENCE SIGNS
[0032] 1 Silicon scrap material
[0033] 2 Silicon fine particle
[0034] 3 Silicon fine particle after surface oxide film removal
[0035] 4 Silicon fine particle after hydrophilization treatment
[0036] 5 Hydrogen
[0037] 10 Grinder
[0038] 14 Discharge port
[0039] 15 Filter
[0040] 30 Drying chamber
[0041] 40 Rotary evaporator
[0042] 50 Surface oxide film removal tank
[0043] 57, 67, 77 Agitator
[0044] 58 Centrifuge
[0045] 60 Hydrophilization treatment tank
[0046] 70 Hydrogen generator
[0047] 72 Reaction tank
[0048] 75 Water or aqueous solution
[0049] 79 Transfer pipe
[0050] 80 Water tank
[0051] 87 Hydrogen collector
[0052] 89 Hydrogen pipe
[0053] 90 Hydrogen reservoir
[0054] 100, 200 Hydrogen production apparatus
[0055] 250 Additional surface oxide film removal tank
[0056] 270 Additional hydrogen generator
EMBODIMENTS OF THE INVENTION
[0057] Embodiments of the present invention will now be described
in detail with reference to the accompanying drawings. Common parts
will be denoted by common reference signs in all the drawings in
this disclosure unless otherwise specified. Elements according to
the respective embodiments will not always be depicted at relative
scale ratios. Some of the reference signs may not appear in the
drawings for better visual.
1. Hydrogen Production Method
First Embodiment
[0058] A hydrogen production method according to the present
embodiment includes various steps of using an exemplary start
material of silicon chips or silicon grinding scraps (hereinafter,
also referred to as a silicon scrap material), which are obtained
by silicon cutting in a production process of semiconductor
products and are ordinarily regarded as waste. The silicon scrap
material also includes fine scraps obtained by grinding a waste
wafer. FIG. 1 is a flowchart of the respective steps in the
hydrogen production method according to the present embodiment. As
depicted in FIG. 1, the hydrogen production method according to the
present embodiment includes the following steps (1) to (3).
[0059] (1) Washing step (51)
[0060] (2) Grinding step (S2)
[0061] (3) Hydrogen generating step (S3)
[0062] (1) Washing Step
[0063] The washing step (Si) according to the present embodiment
includes washing the silicon scrap material that is generated in a
process of cutting a monocrystal or polycrystal silicon ingot or
the like. The washing step (Si) is executed mainly for removal of
organic matters adhering to the silicon scrap material, such as
cutting oil and an additive used in the process of cuttings. The
silicon scrap material to be washed is initially weighed, and then
a predetermined first liquid is added and the silicon scrap
material is dispersed in the liquid by using a ball mill. The ball
mill according to the present embodiment is a grinder configured to
grind a steel ball, a magnetic ball, a boulder, and a similar
object. The first liquid according to the present embodiment is,
for example, acetone.
[0064] The silicon scrap material having been treated in the
washing step is caused to pass through a filter for removal of the
first liquid by means of suction filtration. The removed first
liquid is disposed as a waste liquid. The filtrated silicon scrap
material is dried using a drier. The drying temperature according
to the present embodiment is, for example, 40.degree. C. or higher
and 60.degree. C. or lower. The ball mill is used in the washing
step according to the present embodiment, so that it is possible to
markedly improve washing efficiency in comparison to simple
immersion in the first liquid.
[0065] (2) Grinding Step
[0066] The subsequent grinding step (S2) includes grinding washed
silicon sludge to form silicon fine particles having a crystallite
diameter of 100 nm or less. Such silicon fine particles having a
crystallite diameter of 100 nm or less can achieve preferred
effects, or effects similar to those of the present embodiment,
even in a case where the silicon fine particles have an aggregated
particle distribution in the range of 100 nm or more and 5 .mu.m or
less. A predetermined second liquid is then added to the washed
silicon sludge. The second liquid is, for example, propanol. Rough
grinding treatment is subsequently executed using the ball mill.
The roughly ground silicon scrap material is caused to pass through
a filter for removal of relatively coarse particles, and the
remaining silicon scrap material is finely ground using a bead
mill. The second liquid is subsequently removed using a rotary
evaporator to obtain silicon fine particles as a finely ground
object.
[0067] The grinding step (S2) according to the present embodiment
enables formation of silicon fine particles that have amorphous
shapes, a crystallite diameter distribution in the range of 100 nm,
and hydrophilic surfaces. The grinding step (S2) enables grinding
treatment by using any one selected from the grinder group
consisting of a bead mill, a ball mill, a jet mill, and a shock
wave grinder, or using any one of combinations thereof.
[0068] (3) Hydrogen Generating Step
[0069] The subsequent hydrogen generating step (S3) includes
generating hydrogen by causing the silicon fine particles obtained
in the grinding step (S2) to contact with and/or disperse in water
or an aqueous solution. The water used in the hydrogen generating
step is not necessarily pure water but may be water containing an
electrolyte or an organic matter such as ordinary tap water or
industrial water. The aqueous solution according to the present
embodiment is also not particularly limited in terms of its type.
The aqueous solution is not particularly limited in terms of its
hydrogen ion concentration index (pH value), but is more preferred
to have a pH value of 10 or more. It is because, the inventors have
analyzed to find a tendency that a higher pH value leads to faster
hydrogen generation speed and hydrogen generation reaction is
finished in a shorter period of time. Accordingly, in order to
continuously supply a small amount of hydrogen for a long period of
time, the pH value of the aqueous solution is decreased
intentionally in a preferred aspect. In contrast, in order to
temporarily supply a large amount of hydrogen, increase in pH value
of the aqueous solution can achieve hydrogen production compliant
with requests from various industrial fields or users of various
devices.
[0070] The water used in the hydrogen generating step can be set to
an appropriate temperature for achievement of desired hydrogen
generation speed. Measures to cause the silicon fine particles to
contact with and/or disperse in the water or the aqueous solution
can be selected from agitation, water current, shaking, and the
like as necessary. Agitation or the like promotes hydrogen
generation reaction, so that hydrogen production speed can be
increased.
[0071] As described above, the hydrogen production method according
to the present embodiment can achieve reliable production of a
practically adequate amount of hydrogen from a start material of
silicon chips or silicon grinding scraps that are obtained by
silicon cutting in a production process of semiconductor products
or the like and are ordinarily regarded as waste. Accordingly, the
hydrogen production method effectively utilize silicon chips or
silicon grinding scraps regarded as waste so as to contribute to
environmental protection as well as to significant reduction in
cost for production of hydrogen that is utilized as an energy
source in the next generation. It is noted that the present
embodiment can achieve production of a large amount of hydrogen at
the practical level without including a complicated step.
Second Embodiment
[0072] The present embodiment is similar to the first embodiment
except that a surface oxide film removing step of removing oxide
films on the surfaces of silicon fine particles is additionally
executed after the grinding step according to the first
embodiment.
[0073] FIG. 2 is a flowchart of the respective steps in the
hydrogen production method according to the present embodiment. As
depicted in FIG. 2, the hydrogen production method according to the
present embodiment includes the following steps (1) to (4).
[0074] (1) Washing step (T1)
[0075] (2) Grinding step (T2)
[0076] (3) Surface oxide film removing step (T3)
[0077] (4) Hydrogen generating step (T4)
[0078] As mentioned above, the washing step (S1), the grinding step
(S2), and the hydrogen generating step (S3) in the hydrogen
production method according to the first embodiment have the
details overlapped with those in the washing step (T1), the
grinding step (T2), and the hydrogen generating step (T4) according
to the present embodiment. Accordingly, those steps other than the
surface oxide film removing step (T3) will not be described
repeatedly.
[0079] The surface oxide film removing step (T3) will be described
below.
[0080] The surface oxide film removing step (T3) includes causing
the silicon fine particles obtained in the grinding step (T2)
described above to contact with an aqueous hydrofluoric acid
solution or an aqueous ammonium fluoride solution. According to the
present embodiment, the silicon fine particles that are obtained in
the grinding step (T2) and have a crystallite diameter in the range
of 100 nm or less are immersed in the aqueous hydrofluoric acid
solution or the aqueous ammonium fluoride solution. The silicon
fine particles are thus caused to contact with and/or disperse in
the aqueous hydrofluoric acid solution or the aqueous ammonium
fluoride solution. The silicon fine particles and the aqueous
hydrofluoric acid solution are subsequently separated using a
centrifuge. The silicon fine particles are immersed in a third
liquid such as an ethanol solution. The third liquid is then
removed to obtain silicon fine particles for hydrogen
production.
[0081] The surface oxide film removing step according to the
present embodiment includes immersing the silicon fine particles in
the aqueous hydrofluoric acid solution or the aqueous ammonium
fluoride solution, so that the silicon fine particles are caused to
contact with the aqueous hydrofluoric acid solution or the aqueous
ammonium fluoride solution. However, the surface oxide film
removing step according to the present embodiment is not limited
into these modes. It is possible to alternatively adopt the step of
causing the silicon fine particles to contact with the aqueous
hydrofluoric acid solution or the aqueous ammonium fluoride
solution in a different manner. According to a different adoptable
aspect, the aqueous hydrofluoric acid solution or the aqueous
ammonium fluoride solution can be sprayed, in other words,
showered, to the silicon fine particles.
[0082] The subsequent hydrogen generating step (T4) includes
generating hydrogen by causing the silicon fine particles after
surface oxide film removal to contact with and/or disperse in water
or an aqueous solution.
[0083] The hydrogen production method according to the present
embodiment can achieve effects similar to those according to the
first embodiment as well as can achieve increase in hydrogen
production amount by removing the oxide films on the surfaces of
the silicon fine particles.
Third Embodiment
[0084] The present embodiment is similar to the second embodiment
except that a hydrophilization treatment step of hydrophilizing the
surfaces of the silicon fine particles is additionally executed
after the surface oxide film removing step according to the second
embodiment.
[0085] FIG. 3 is a flowchart of the respective steps in the
hydrogen production method according to the present embodiment. As
depicted in FIG. 3, the hydrogen production method according to the
present embodiment includes the following steps (1) to (5).
[0086] (1) Washing step (U1)
[0087] (2) Grinding step (U2)
[0088] (3) Surface oxide film removing step (U3)
[0089] (4) Hydrophilization treatment step (U4)
[0090] (5) Hydrogen generating step (U5)
[0091] As mentioned above, the washing step (T1), the grinding step
(T2), the surface oxide film removing step (T3), and the hydrogen
generating step (T4) in the hydrogen production method according to
the second embodiment have the details overlapped with those in the
washing step (U1), the grinding step (U2), the surface oxide film
removing step (U3), and the hydrogen generating step (U5) according
to the present embodiment. Accordingly, those steps other than the
hydrophilization treatment step (U4) will not be described
repeatedly.
[0092] The hydrophilization treatment step (U4) will be described
below.
[0093] The hydrophilization treatment step (U4) according to the
present embodiment is executed after the surface oxide film
removing step and includes treating the surfaces of the silicon
fine particles with a surfactant or nitric acid. Typical examples
of the surfactant used for the treatment include at least one
selected from the group consisting of an anionic surfactant, a
cationic surfactant, and a nonionic surfactant. According to the
present embodiment, the silicon fine particles are caused to
contact with and/or disperse in a fourth liquid such as propanol,
the surfactant or nitric acid is added, and the resulting liquid is
agitated. The fourth liquid is removed using a rotary evaporator
after the agitation in the present embodiment.
[0094] The subsequent hydrogen generating step (U5) includes
generating hydrogen by causing the silicon fine particles after
hydrophilization treatment to contact with and/or disperse in water
or an aqueous solution.
[0095] The hydrogen production method according to the present
embodiment can achieve effects similar to those according to the
first embodiment as well as can decrease surface tension of the
silicon fine particles by the hydrophilization treatment step to
reliably suppress the silicon fine particles from floating to the
water surface, which is a phenomenon unique to fine particles. The
silicon fine particles are thus well blended with the water or the
aqueous solution to achieve an increase in contact area between the
silicon fine particles and the water or the aqueous solution and
promotion of hydrogen generation reaction. It is thus possible to
markedly increase the hydrogen production amount.
[0096] As described above, among the silicon fine particles formed
by grinding silicon chips or silicon grinding scraps, silicon fine
particles obtained through chemical treatment (typically, oxide
film removal treatment using the aqueous hydrofluoric acid solution
or the aqueous ammonium fluoride solution in the second embodiment,
or hydrophilization treatment using the fourth liquid in the third
embodiment) preferably exemplify the silicon fine particles for
hydrogen production according to each of the above embodiments.
According to a preferred aspect in terms of further promoted
hydrogen generation, each of the above embodiments includes the
chemical treatment step of chemically treating the silicon fine
particles as described above.
2. Hydrogen Production Apparatus
Fourth Embodiment
[0097] A hydrogen production apparatus 100 according to the present
embodiment will be described below. FIG. 4 is an explanatory view
depicting a schematic configuration of the hydrogen production
apparatus 100 according to the present embodiment. As depicted in
FIG. 4, the hydrogen production apparatus 100 according to the
present embodiment mainly includes a grinder 10, a drying chamber
30, a rotary evaporator 40, a surface oxide film removal tank 50, a
centrifuge 58, a hydrophilization treatment tank 60, a hydrogen
generator 70, and a hydrogen reservoir 90. The hydrogen production
apparatus 100 according to the present embodiment is regarded as
including collective devices (treatment units) configured to
execute a plurality of steps to be described later. The hydrogen
production apparatus 100 may be called a hydrogen production
system.
[0098] The grinder 10 according to the present embodiment is a wet
grinder configured to receive a treatment target along with a
liquid and apply grinding, dispersing, and the like to the
treatment target in the liquid. The grinder 10 is configured to be
capable of executing the steps of dispersing, mixing, grinding,
etc., the treatment target and the liquid thus fed. The grinder 10
can be configured by any one selected from the grinder group
consisting of a bead mill, a ball mill, a jet mill, and a shock
wave grinder, or any one of combinations thereof. In the hydrogen
production apparatus 100 according to the present embodiment, the
grinder 10 serves as a washing unit configured to wash a silicon
scrap material such as silicon chips or silicon grinding scraps
generated in a silicon cutting process or the like, and a grinding
unit configured to grind the washed silicon scrap material into
silicon fine particles having a crystallite diameter of 100 nm or
less.
[0099] The grinder 10 initially receives a silicon scrap material 1
as a treatment target and the second liquid according to the first
embodiment through an input port 11 and washes the silicon scrap
material 1. The washed silicon scrap material 1 as well as the
second liquid are caused to pass through a filter 15 provided
adjacent to a discharge port 14, so that the second liquid is
removed as waste liquid by means of suction filtration. The residue
(silicon scrap material 1) is subsequently dried in the drying
chamber 30, and is fed into the grinder 10 through the input port
11 along with the second liquid so as to be ground. Specifically,
the silicon scrap material 1 is roughly ground using a ball mill or
the like and the ground object as well as the second liquid are
caused to pass through the filter 15 for removal of rough
particles. The filtrated ground object is then finely ground using
a bead mill or the like. The finely ground object is subsequently
collected and the second liquid is removed using the rotary
evaporator 40 configured to automatically perform vacuum
distillation, to obtain silicon fine particles 2.
[0100] The surface oxide film removal tank 50 exemplifying a
surface oxide film remover according to the present embodiment
includes an agitator 57 and treats the silicon fine particles 2
supplied from the grinder 10 with an aqueous hydrofluoric acid
solution or an aqueous ammonium fluoride solution 55. The
centrifuge 58 subsequently separates silicon fine particles 3 after
surface oxide film removal from the aqueous hydrofluoric acid
solution. In a case where the surface oxide films on the surfaces
of the silicon fine particles 2 are not removed, the silicon fine
particles 2 are fed to the hydrogen generator 70 to be described
later.
[0101] The hydrophilization treatment tank 60 exemplifying a
hydrophilization treatment unit according to the present embodiment
includes an agitator 67 and causes the silicon fine particles 3
before or after surface oxide film removal to contact with and/or
disperse in a fourth liquid 65 to which a surfactant or nitric acid
is added. In a case where the silicon fine particles 2 are not
subjected to the hydrophilization treatment, the silicon fine
particles before or after surface oxide film removal are fed to the
hydrogen generator 70 to be described later. Silicon fine particles
before surface oxide film removal can be a target of
hydrophilization treatment according to the present embodiment. In
order for more reliable hydrophilization of the silicon fine
particles, hydrophilization treatment is preferably applied to
silicon fine particles after surface oxide film removal.
[0102] The hydrogen generator 70 according to the present
embodiment includes a reaction tank 72 provided with an agitator
77, a water tank 80, a hydrogen collector 87, a transfer pipe 79,
and a hydrogen pipe 89. In the reaction tank 72, at least one
selected from the group consisting of the silicon fine particles 2,
the silicon fine particles 3 after surface oxide film removal, and
silicon fine particles 4 after hydrophilization treatment are
caused to contact with and/or disperse in water or an aqueous
solution 75 to generate hydrogen 5. The generated hydrogen 5 is fed
into water 85 in the water tank 80 via the transfer pipe 79. The
hydrogen 5 collected by the hydrogen collector 87 in accordance
with an exemplary water substitute method is collected into the
hydrogen reservoir 90 via the hydrogen pipe 89.
[0103] The hydrogen production apparatus 100 according to the
present embodiment can achieve relatively fast production of a
practically adequate amount of hydrogen from a start material of
silicon chips or silicon grinding scraps that are obtained by
silicon cutting in a production process of semiconductor products
or the like and are ordinarily regarded as waste.
EXAMPLES
[0104] Examples will be described below for more detailed
description of the above embodiments, but the above embodiments
should not be limited to these examples. Examples 1 to 5 to be
described below refer to results of hydrogen production tests using
the hydrogen production apparatus 100.
Example 1
[0105] In Example 1, the hydrogen production apparatus 100 produced
hydrogen in accordance with the hydrogen production method of the
first embodiment. Specifically, the hydrogen generating step was
executed after the washing step and the grinding step.
[0106] (1) Washing Step
[0107] Two hundred grams (g) of silicon chips was added to 200
milliliters (mL, also expressed as "ml") of acetone, and dispersed
for one hour by using a ball mill. Used as the ball mill was a
Universal BALL MILL manufactured by MASUDA CORPORATION. The ball
mill contained alumina beads having particle diameters of 10
millimeters (mm) and 20 mm. The liquid was then removed by means of
suction filtration and the residue was dried using a drier set to
40.degree. C.
[0108] (2) Grinding Step
[0109] Subsequently, 15 g of washed silicon sludge is weighed and
placed in a plastic container, to which 285 g of 2-propanol was
added. Alumina balls are then placed in a ball mill to perform
rough grinding at a circumferential speed of 80 rpm for two hours.
Used as the ball mill in the present example is a Universal BALL
MILL manufactured by MASUDA CORPORATION. The balls used in the
present example are alumina balls having particle diameters of 10
mm and 20 mm. The resultant obtained in the grinding step was
caused to pass through a mesh filter of 180 .mu.m for removal of
coarse particles.
[0110] Alumina balls were then placed in a bead mill to perform
fine grinding at a circumferential speed of 2908 rpm for four
hours. The bead mill used in the present example is a star mill
LMZ015 manufactured by Ashizawa Finetech Ltd. Used in the present
example were 456 g of zirconia beads having a particle diameter of
0.5 mm. The finely ground particles were then collected and
2-propanol was removed using a rotary evaporator to obtain silicon
fine particles.
[0111] (3) Hydrogen Generating Step
[0112] Immersed in 50.21 g of ultrapure water were 0.86 g of
silicon fine particles for hydrogen production. The test was
executed at normal temperature (about 25.degree. C.) in the present
example.
Example 2
[0113] In Example 2, the hydrogen production apparatus 100 produced
hydrogen in accordance with the hydrogen production method of the
second embodiment. Example 2 was performed in the same manner as in
Example 1 except that the surface oxide film removing step was
additionally executed after the grinding step of Example 1.
Specifically, hydrogen was produced through the washing step, the
grinding step, the surface oxide film removing step, and the
hydrogen generating step in the mentioned order. The surface oxide
film removing step is executed in the following manner.
[0114] In the surface oxide film removing step, the silicon fine
particles obtained in the grinding step of the present example are
dispersed in a 50% aqueous hydrofluoric acid solution.
Subsequently, the silicon fine particles are separated from the
aqueous hydrofluoric acid solution by using a centrifuge. The
obtained silicon fine particles were then immersed in an ethanol
solution. The ethanol solution was subsequently removed to obtain
silicon fine particles for hydrogen production.
Example 3
[0115] In Example 3, the hydrogen production apparatus 100 produced
hydrogen in accordance with the hydrogen production method of the
third embodiment. Example 3 was performed in the same manner as in
Example 2 except that the hydrophilization treatment step of
treating using a surfactant was additionally executed after the
surface oxide film removing step of Example 2.
[0116] Specifically, the washing step, the grinding step, and the
surface oxide film removing step were executed in the same manner
as in Example 2. In the hydrophilization treatment step with use of
the surfactant, 2-propanol as the fourth liquid of the third
embodiment was prepared to include silicon fine particles at a
concentration of 5 wt %. Added to this liquid was 0.05%
polyoxyethylene nonyl phenyl ether ("Nonion NS206" produced by NOF
CORPORATION) as a nonionic surfactant, and the obtained liquid was
agitated for one hour. Subsequently, 2-propanol was removed using a
rotary evaporator.
[0117] In the hydrogen generating step, 50.21 g of ultrapure water
was added to 0.86 g of silicon fine particles for hydrogen
production to immerse the silicon fine particles at normal
temperature.
Example 4
[0118] Example 4 was performed in the same manner as in Example 2
by using the hydrogen production apparatus 100 except that a buffer
solution containing 0.1 mol/L of sodium bicarbonate and 0.1 mol/L
of sodium carbonate was used to adjust the pH value of the aqueous
solution for the hydrogen generating step to 10 in the hydrogen
production method according to the second embodiment.
Example 5
[0119] Example 5 was performed in the same manner as in Example 2
by using the hydrogen production apparatus 100 except that 0.1
mol/L of an aqueous potassium hydroxide solution was used to adjust
the pH value of the aqueous solution for the hydrogen generating
step to 13 in the hydrogen production method according to the
second embodiment.
<Analysis Results of Examples>
1. Crystal Structure Analysis Using Sectional TEM Photographs
[0120] FIGS. 5(a) and 5(b) are sectional TEM (transmission electron
microscope) photographs each depicting a crystal structure of
silicon fine particles after the grinding step in Example 1. FIG.
5(a) depicts a state where the silicon fine particles are partially
aggregated to form slightly larger fine particles in amorphous
shapes. On the other hand, FIG. 5(b) is a TEM photograph focusing
on the individual silicon fine particles. As indicated in a central
circle in FIG. 5(b), there was found a silicon fine particle having
a diameter of about 5 nm or less. It was also found that this
silicon fine particle has a crystalline property.
2. Crystallite Diameter Distribution of Silicon Fine Particles in
Accordance with X-Ray Diffraction Method
[0121] FIG. 6 is a graph of analysis results according to the X-ray
diffraction method, on crystallite diameter distribution of silicon
fine particles after the grinding step. The graph in FIG. 6 as the
transverse axis indicating the crystallite diameter (nm) and the
ordinate axis indicating frequency. The solid line indicates
number-based crystallite diameter distribution whereas the broken
line indicates volume-based crystallite diameter distribution.
According to the number distribution, the crystals had a mode
diameter of 1.97 nm, a median diameter (50% crystallite diameter)
of 3.70 nm, and an average diameter of 5.1 nm. According to the
volume distribution, the crystals had a mode diameter of 13.1 nm, a
median diameter of 24.6 nm, and an average diameter of 33.7 nm. It
was found from these results that the silicon fine particles
obtained after the grinding step according to the bead mill method
are so-called silicon nanoparticles having crystallite diameters
that are in the range of 100 nm or less, and are distributed
particularly in the range of 50 nm or less.
3. Hydrogen Production Amount
[0122] FIG. 7 is a graph of measurement results of hydrogen
generation amounts according to Examples 1 to 3. The graph in FIG.
7 has the transverse axis indicating the immersion period (minute)
and the ordinate axis indicating the hydrogen generation amount
(mL/g) per g of silicon fine particles for hydrogen production.
[0123] As indicated in FIG. 7, in Example 1 not including the
surface oxide film removing step, 10.7 ml of hydrogen was obtained
for the immersion period of 7905 minutes.
[0124] As indicated in FIG. 7, in Example 2 in which the hydrogen
production apparatus 100 produced hydrogen in accordance with the
hydrogen production method of the second embodiment, the reaction
came into an equilibrium state after the immersion period of 5700
minutes (i.e., 95 hours), and about 54.1 mL of hydrogen was
obtained. In Example 1, a large amount as much as 50 mL to 60 mL of
hydrogen was finally produced per g of silicon fine particles for
hydrogen production, as a significantly preferred result.
[0125] In Example 3, 116.7 mL of hydrogen was obtained by immersion
for 9805 minutes (i.e., about 163 hours), as a more preferred
result in comparison to Example 2. It is particularly found that
the hydrogen generation amounts of Examples 2 and 3 for 500 minutes
or 1000 minutes from the start of reaction are much more than the
hydrogen generation amount of Example 1. In other words, it is
found that Examples 2 and 3 achieve extremely fast hydrogen
generation speed for 500 minutes or 1000 minutes from the start of
reaction. FIG. 7 thus indicates the significant effect of the
surface oxide film removing step or the surface oxide film
remover.
[0126] Subsequently studied were results of Examples 4 and 5
including the hydrogen generating step of causing silicon fine
particles to react with an aqueous solution having a high pH value.
FIG. 8 is a graph of measurement results of hydrogen generation
amounts according to Examples 4 and 5. FIG. 9 is a graph of
hydrogen generation amounts for 60 minutes from the start of
reaction in Examples 4 and 5. The graphs in FIGS. 8 and 9 each have
the transverse axis indicating the immersion period (minute) and
the ordinate axis indicating the hydrogen generation amount (mL/g)
per g of silicon fine particles for hydrogen production.
[0127] As indicated in FIG. 8, in Example 4 including the hydrogen
generating step with use of the aqueous solution having a pH value
of 10, the reaction came into a substantially equilibrium state
after 5000 minutes (about 80 hours), and about 720 ml of hydrogen
was obtained per g of silicon fine particles for hydrogen
production. In contrast, in Example 5 including the hydrogen
generating step with use of the aqueous solution having a pH value
of 13, the reaction came into a substantially equilibrium state
after 6254 minutes (about 104 hours), and about 942.1 ml of
hydrogen was obtained per g of silicon fine particles for hydrogen
production. In such a case where the aqueous solution was brought
into an alkaline state so as to have a pH value of 10 or 13, there
was obtained a large amount of hydrogen as much as several to
several ten times in comparison to hydrogen obtained in Examples 1
to 3.
[0128] As indicated in the result of Example 5 in FIG. 9, with use
of the aqueous solution having a pH value of 13 in the hydrogen
generating step, the hydrogen generation amount rapidly increased
immediately after the start of reaction between silicon fine
particles and the aqueous solution. More specifically, about 470 ml
of hydrogen was generated per g of silicon fine particles for
hydrogen production for 10 minutes, and about 590 ml of hydrogen
was generated per g of silicon fine particles for hydrogen
production for 30 minutes. Furthermore, in Example 4 including the
hydrogen generating step with use of the aqueous solution having a
pH value of 10, about 3.5 ml of hydrogen was generated per g of
silicon fine particles for hydrogen production for 13 minutes and
about 15 ml of hydrogen was generated per g of silicon fine
particles for hydrogen production for 30 minutes. Example 4 could
achieve generation of a larger amount of hydrogen in a shorter
period of time in comparison to Examples 1 to 3, although the
reaction of Example 4 is more moderate than that of Example 5.
[0129] It was thus found from FIGS. 8 and 9 that Examples 4 and 5
achieve hydrogen generation speed much faster than that of Examples
1 to 3. Accordingly, it was found that increase in pH value (that
is, adjusted to a pH value of 10 or more) of the aqueous solution
used in the hydrogen generating step achieves reaction promoting
fast hydrogen generation in a short period of time, unlike moderate
hydrogen generation reaction for a long period of time as in
Examples 1 to 3. According to a very preferred aspect, the pH value
of the aqueous solution used in the hydrogen generating step is set
to 10 or more (14 or less) in terms of faster generation of a
larger amount of hydrogen.
[0130] The hydrogen production method and the hydrogen production
apparatus disclosed in each of the above embodiments are largely
expected to be applied to a technical field requiring hydrogen such
as fuel cells. The hydrogen production method and the hydrogen
production apparatus according to each of the above embodiments
have an interesting point that silicon chips or silicon grinding
scraps are utilized as a start material, which are obtained by
silicon cutting in a production process of semiconductor products
or the like and are ordinarily regarded as waste. The cost for
production of hydrogen per unit gram is thus much cheaper than the
cost for production of hydrogen according to a conventional
hydrogen production method. Accordingly, this not only contributes
to environmental protection through effective utilization of waste
but also markedly improves economic efficiency of hydrogen
production. Furthermore, the hydrogen production method and the
hydrogen production apparatus according to each of the above
embodiments do not require any complicated device, facility, or
system, or any complicated step, and can thus significantly
contribute to improvement in industrial productivity.
Other Embodiments
[0131] In the reaction tank 72 of the hydrogen generator 70
according to the fourth embodiment, at least one selected from the
group consisting of the silicon fine particles 2, the silicon fine
particles 3 after surface oxide film removal, and the silicon fine
particles 4 after hydrophilization treatment are caused to contact
with and/or disperse in the water or the aqueous solution 75 to
generate hydrogen. However, the reaction may come into an
equilibrium state with elapse of time to saturate the hydrogen
generation amount or the hydrogen generation speed. Disclosed as a
solution to the problem are the configuration of a hydrogen
production apparatus 200 according to a modification example of the
fourth embodiment as depicted in FIG. 10 as well as Example 6.
[0132] FIG. 10 is an explanatory view depicting a schematic
configuration of the hydrogen production apparatus 200 according to
the modification example of the fourth embodiment. The hydrogen
production apparatus 200 according to the present embodiment is
similar to the hydrogen production apparatus 100 according to the
fourth embodiment except for including an additional hydrogen
generator 270. As indicated by an arrow (R) in FIG. 10, the
additional hydrogen generator 270 executes the step of removing
oxide films on the surfaces of silicon fine particles by extracting
from the reaction tank 72 the silicon fine particles having a
hydrogen generation amount or hydrogen generation speed once
saturated or almost saturated and then introducing the silicon fine
particles into an additional surface oxide film removal tank 250
configuring at least partially an additional surface oxide film
remover in the hydrogen production apparatus 200 (the additional
surface oxide film removing step) and the subsequent step of
generating hydrogen by feeding the silicon fine particles, of which
oxide films are removed, again into the reaction tank 72 (the
additional hydrogen generating step). Accordingly, the overlapped
description may not be disclosed repeatedly.
[0133] In the case where the hydrogen production apparatus 200
depicted in FIG. 10 is used, even if the hydrogen generation amount
or the hydrogen generation speed is saturated or about to be
saturated because the reaction in the reaction tank 72 once comes
into an equilibrium state, the additional surface oxide film
removing step subsequently executed revitalizes hydrogen generation
power of the silicon fine particles. The hydrogen generation power
of the silicon fine particles is revitalized or recovered by
executing the additional surface oxide film removing step of
causing the silicon fine particles to contact again with an aqueous
hydrofluoric acid solution or an aqueous ammonium fluoride solution
during or after the hydrogen generating step in each of the above
embodiments. Accordingly, this markedly improves utilization
efficiency of silicon fine particles for hydrogen generation as
well as significantly contributes to reduction in hydrogen
production cost.
[0134] According to a different adoptable aspect, unlike the
hydrogen production apparatus 200, there can be provided a means
for supplying silicon fine particles into the surface oxide film
removal tank 50 via a flow path connecting the reaction tank 72 and
the surface oxide film removal tank 50 after the silicon fine
particles in the reaction tank 72 are separated from the water or
the aqueous solution 75 by a filter. The silicon fine particles
introduced into the surface oxide film removal tank 50 in such an
aspect are also included in "silicon fine particles extracted from
the hydrogen generator" in the present application. According to a
different adoptable aspect, the hydrophilization treatment step
(the additional hydrophilization treatment step) is executed after
the additional surface oxide film removing step, as in the fourth
embodiment.
[0135] In this aspect, the surface oxide film removing step and the
additional surface oxide film removing step are executed using the
same surface oxide film removal tank, and the hydrogen generating
step and the additional hydrogen generating step are executed using
the same reaction tank 72. However, this aspect is not limited to
this case. The surface oxide film removing step and the additional
surface oxide film removing step may be executed in different
tanks, and the hydrogen generating step and the additional hydrogen
generating step may be executed in different tanks.
Example 6
[0136] In the hydrogen generating step according to Example 6,
immersed in the aqueous solution (0.1 mol/L of an aqueous potassium
hydroxide solution) 75 was 0.86 g of silicon fine particles, which
were formed by grinding p-type silicon chips using a bead mill
including beads made of ZiO.sub.2 in the same manner as in Example
5. Prepared in Example 6 were four types of aqueous solutions 75
having pH values of 12.1, 12.9, 13.4, and 13.9 with different
addition amounts of potassium hydroxide (KOH).
[0137] The constant amount (0.86 g) of silicon fine particles were
immersed in each of the aqueous solutions at normal temperature to
obtain the graph of hydrogen generation amounts with respect to a
reaction period as in FIG. 11. In the case where the pH value is
13.9, it was found that the hydrogen generation amount per gram (g)
of the silicon fine particles reached about 1100 mL or more (i.e.,
about 1100 mL/g or more) within an extremely short period of time
(within about 15 minutes from the start of reaction). It is noted
that the hydrogen generation amount at the pH value of 13.9
exceeded 1000 mL per g of the silicon fine particles in the period
as short as about ten minutes. Neither the additional surface oxide
film removing step nor the additional hydrogen generating step is
executed at this stage.
[0138] FIG. 12 is a graph of a difference in maximum hydrogen
generation speed due to a difference in pH value in Example 6. The
numerical values in FIG. 12 indicate maximum hydrogen generation
speed per g in one minute in the four aqueous solutions having the
different pH values indicated in FIG. 11. It was found from the
result indicated in FIG. 12 that the maximum hydrogen generation
speed per g in one minute is clearly dependent on the pH value and
increases as the pH value is larger. The hydrogen generation speed
can be controlled in accordance with the feature that hydrogen
generation speed is dependent on the pH value of a solution. Again,
neither the additional surface oxide film removing step nor the
additional hydrogen generating step is executed at this stage.
[0139] The silicon fine particles, which have a saturated hydrogen
generation amount or saturated hydrogen generation speed because
reaction comes into an equilibrium state in the case where the pH
value is 13.9, were measured and analyzed using an XPS (X-ray
photoelectron spectroscopy) analyzer. FIG. 13 is an XPS
spectrography of the silicon fine particles after the hydrogen
generation amount or the hydrogen generation speed is saturated in
Example 6.
[0140] As indicated in FIG. 14, there was observed a plurality of
Si.sub.2p peaks belonging to silicon (Si) and silicon dioxide
(SiO.sub.2). It was thus found that the silicon fine particles
already or almost having reacted into an equilibrium state are
formed with silicon dioxide (SiO.sub.2) films on the surfaces of
the particles. According to the peak intensity ratio between (Si)
and (SiO.sub.2) indicated in FIG. 14, it was concluded that the
silicon fine particles are formed with SiO.sub.2 films of about 5
nm thick on the surfaces of the particles.
[0141] Example 6 includes the step of removing the SiO.sub.2 films
by causing the silicon fine particles already or almost having
reacted into an equilibrium state to contact with a 5% aqueous HF
solution (the additional surface oxide film removing step).
Subsequently, the silicon fine particles were immersed again in the
aqueous solution 75 having a pH value of 13.9. The silicon fine
particles then generated further 470 ml/g of hydrogen (per g of the
initial silicon fine particles) (the additional hydrogen generating
step).
[0142] In Example 6, the sum of the initial hydrogen gas generation
amount (until the saturated state) and the hydrogen gas generation
amount after the additional surface oxide film removing step and
the additional hydrogen generating step was about 1570 mL per g of
the silicon fine particles. This is approximate to 1600 mL
(theoretical value) as the maximum generation amount of hydrogen
that can be generated in reaction with 1 g of silicon in the
aqueous solution 75. It was thus found that the additional surface
oxide film removing step and the additional hydrogen generating
step were quite useful measures for generation of an extremely
large amount of hydrogen.
Example 7
[0143] Described next is a different result of a hydrogen
production test by using the hydrogen production apparatus 100. In
the hydrogen generating step according to Example 7, the aqueous
solution 75 includes sodium hydroxide or ammonia. At normal
temperature, 0.86 g of silicon fine particles was caused to contact
with and/or disperse in the aqueous solution 75 so as to be caused
to react.
[0144] FIG. 14 is a graph of the hydrogen generation amount per g
with respect to a reaction period in Example 7. An experiment value
(a) is obtained in a case of using 20 mL of an aqueous solution
having a pH value of 13.4 to which sodium hydroxide (NaOH, also
referred to as caustic soda) is added. An experiment value (b) is
obtained in a case of using 20 mL of an aqueous solution having a
pH value of 11.9 to which ammonia (NH.sub.3) is added. The graph in
FIG. 14 has the transverse axis indicating the immersion period
(minute). The graph in FIG. 14 has the ordinate axis indicating the
hydrogen generation amount (mL/g) per g of silicon fine particles
for hydrogen production.
[0145] When the silicon fine particles are immersed in the aqueous
solution 75 to which ammonia is added, the silicon fine particles
may float on the surface of the solution if the silicon fine
particles are not particularly treated preliminarily. For this
reason, in Example 7, ethanol was added dropwise into the aqueous
solution 75 to precipitate the silicon fine particles to the bottom
of the reaction tank 72. This causes the silicon fine particles to
contact with the aqueous solution 75 to which ammonia is added. On
the other hand, in the case of using the aqueous solution 75 to
which sodium hydroxide is added, the experiment was executed with
the silicon fine particles caused to contact with and/or disperse
in the aqueous solution 75, similarly to the case of using the
solution to which potassium hydroxide is added.
[0146] As indicated in FIG. 14, it was found that the hydrogen
generation amount or the hydrogen generation speed can be
controlled by changing the type or the pH value of the aqueous
solution. According to an adoptable and very preferred aspect, the
hydrogen generation speed and/or the hydrogen generation amount is
adjusted by changing the pH value of the water or the aqueous
solution 75 in the hydrogen generating step in each of the above
embodiments. Similarly, according to an adoptable and very
preferred aspect, the hydrogen generator 70 in the hydrogen
production apparatus 100 or the additional hydrogen generator 270
in the hydrogen production apparatus 200 further includes an
adjuster configured to adjust the hydrogen generation speed and/or
the hydrogen generation amount by changing the pH value of the
water or the aqueous solution 75.
[0147] For example, the adjuster can be configured by a device
provided with a means for dropping a desired amount of the water or
each of the aqueous solutions (the aqueous solution to which NaOH
is added, the aqueous solution to which KOH is added, the aqueous
solution to which NH.sub.3 is added, and the like) having a
variable pH value for a desired period of time, and a control means
for controlling the pH value. More specifically, the dropping means
can be configured to drop a desired amount of a chemical substance
for adjusting the pH value, such as NaOH, KOH, or NH.sub.3, for a
desired period of time so as to achieve a desired pH value, upon
receipt of a feedback measurement result from a measurement unit
configured to measure the pH value of the water or each of the
aqueous solutions 75.
[0148] On the other hand, in consideration of the results of the
examples described above, the pH value is preferably set to 10 or
more and more preferably to 11.9 or more in terms of obtaining a
larger amount of hydrogen in a shorter period of time.
[0149] The silicon fine particles are treated using the aqueous
hydrofluoric acid solution in the surface oxide film removing step
according to each of the above examples. A preferred result similar
to that of each of the examples can be achieved also in a case
where the silicon fine particles are treated using an aqueous
ammonium fluoride solution in place of or along with the aqueous
hydrofluoric acid solution.
[0150] The silicon fine particles are treated using the surfactant
in the hydrophilization treatment step according to the above
example. A preferred result quite similar to that of the example
can be achieved also in a case where the silicon fine particles are
treated using nitric acid in place of or along with the
surfactant.
[0151] In each of the above embodiments, the treatment using the
surfactant or nitric acid may not be performed in the independent
hydrophilization treatment step but can be performed during the
hydrogen generating step by adding the surfactant or nitric acid to
the water or the aqueous solution used in the hydrogen generating
step.
[0152] As described in Example 6, when silicon fine particles are
added into the water or the aqueous solution to be dispersed in the
hydrogen generating step, the silicon fine particles dissolve in
the water or the aqueous solution and are formed with silicic acid
on the surfaces of the particles. The silicic acid is subsequently
oxidized into silicon dioxide (SiO.sub.2), so that hydrogen
generation reaction is inactivated or terminated as time elapses.
In order to suppress formation of silicon dioxide (SiO.sub.2) on
the surfaces of the silicon fine particles to continue hydrogen
generation reaction, according to a different adoptable preferred
aspect, a small amount of hydrofluoric acid is added into the water
or the aqueous solution used in the hydrogen generating step to
cause the silicon fine particles to contact with the water or the
aqueous solution for continuous hydrogen generation reaction.
[0153] Each of the above embodiments adopts the hydrogen generator
70 or the additional hydrogen generator 270 configured to generate
hydrogen from the formed silicon fine particles (or aggregate
thereof) which are not positionally fixed but are caused to contact
with and/or disperse in the water or the aqueous solution 75.
However, the method of causing silicon fine particles to contact
with the water or the aqueous solution 75 is not limited to the
method described above. According to a different adoptable aspect,
the formed silicon fine particles firmly fixed onto a surface of a
solid object (e.g. a sponge body) are caused to contact with the
water or the aqueous solution 75 so as to generate hydrogen. In a
case where the solid object is made of a material that can absorb
and hold a certain amount of liquid like the sponge body,
generation of silicon dioxide (SiO.sub.2) on the silicon fine
particles can be suppressed more possibly by an aqueous
hydrofluoric acid solution or an aqueous ammonium fluoride solution
impregnated into the solid object.
[0154] The above embodiments are disclosed for description of these
embodiments, not for limitation to the present invention.
Furthermore, modification examples within the scope of the present
invention, inclusive of other combinations of the embodiments, are
also included in the claims.
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