In the process of reducing extremely fine metal particles (av. particle size  or = 1000 angstroms) covered with an oxide layer, the metal particles are fluidized by a gas flow contg. H, heated, and reduced. The method uniformly and easily reduces surface oxide layers of the extremely fine metal particles without causing sintering. The metal particles are useful for magnetic recording materials, conductive paste, powder metallurgy materials, chem. reagents, and catalysts

Hayashi, T.

English

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NASA TECHNICAL MEMORANDUM 	 NASA TM-77929
FLUIDIZED REDUCTION OF OXIDES ON FINE METAL POWDERS
WITHOUT SINTERING
Translation of Japan Patent No. 59-116302, July 5, 1984,
Tokyo Japan, pp. 1-3
(l- A3A -T?- 7792Q FLUILIZED 6ELUCTION OF 	 N86-15379
OXIDES 05 FIVE METAL FCWDERS hITHOUT
SINTERING (Naticnal Aeronautics and Space
Adaunistration) 8 p 6C A0z /MF A01 CSCL Alt	 Unclas
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON D.C. 20546
	 NOVEMBER 1985
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Translation of Japan Patent No. S9-116302, July S, 1984,
Tokyo Japan, pp. 1-3
1T► Ab~'
In the process of reducing extremely fine metal particles (ay.
particle size < 1000 A) covered with an oxide layer, the metal
particles are fluidized by a gas flow contg. H, heated, and
reduced. The method uniformly and easily reduces surface
oxide layers of the extremely fine metal particles without
causing sintering. The metal particles are useful for magnetic
recording materials, conductive paste, powder metallurgy
materials, them. reagents, and catalysts.
QRIG1NAL PAGE IS
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Unclassified and Unlimited
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(19) JAPANESE PATENT OFFICE 	 (11) PUBLIC ANNOUNCEMENT OF PATENT
APPLICATION
(12) Public Announcemer
of Patent A	 Sho 59-116302
(51) Int.C1 3
	identification symbol	 Internal process number
B 22F 9/20
	 7141-4K
1/00	 6441-4K
(43) PUBLIC ANNOUNCEMENT (1984) July 5
number of invention 1
request for examination, unrequested
(total 3 pages)
(54) Method of deoxidizing ultrafine metal particles
(21) Patent application Sho 5-7-208500
(22) Date of application November 30, 1982
(72) Inventor Toyoharu Hayashi
Suite B709, Ofuna Parktown
510 1 Kazama-cho
Tozuka-ku, Yokohama City
(71) Applicant Research Development Corp. of Japan
5-2, 2-chome, Nagata-cho
Chiyoda-ku, Tokyo
(71) Applicant Toyoharu Hayashi
Suite B709, Ofuna Parktown
510 Kazama-cho
Tozuka-ku, Yokohama City
(74) Agent	 Patent Attorney, Shin-ichi Hodaka
DETAILS
1. Name of Invention.
Method of deoxidizing ultrafine metal particles.
2. Area covered by the present patent application.
The present method is for deoxidization of ultrafine metal
0
primary particles of diameter less than 1000 A and whose surfaces
are covered with oxide layers. The method is characterized by
fluidizing ultrafine metal particles by a gas flow containing
hydrogen and heating at elevated temperatures.
3. Detailed explanation of the present method.
The present invention is a method of deoxidizing ultrafine
0
metal primary particles of the average diameter less than 1000 A.
1
_	 r
	 k
2It is well known that ultrafine metal particles of the
O
average diameter less than 1000 A have excellent properties for
materials for electronics and magnetic recording, conductive
paste, powder metallurgy, reagents for chemical reaction and
ca'-^.lysts .
In the conventional methods, fine metal powder (for example,
more than 1 micron) is manufactured by mechanically pulverizing
metal or processing metal containing chemical reagents in solution
by appropriate deoxidizers. For manufacturing extremely fine
metal particles (usually the diameter less than 1 u), the vacuum
vaporization method in which metal is heated and evaporated in
vacuum (less than 10 -3 torr) or the method of vaporizing metal
in an environmental (buffer) gas such as argon, nitrogen and
hydrogen, of pressure less than several hundred torrs is used.
In these methods, if the diameter of manufactured metal
particles becomes less than the order of microns, the particles
tend to spontaneously ignite in air because of the high specific
surface area and the strong affinity to oxygen. Therefore, in the
manufacturing process, oxygen is removed from the surface of fine
metal particles and then the particles are stored or transported.
It is, of course, possible to prevent spontaneous ignition by
sealing metals in gases or liquids which do not react with
metals in the manufacturing process. However, it will make manu-
facturing, storage and transportation of the particles very
complex and increase potential dangers. This situation has been
restricting application of ultrafine metal particles. A method
for deoxidizing ultrafine metal particles covered with oxide
layers without spoiling the characteristics (for example, increas-
ing the grain diameter by sintering) will be of great value in
industry.
The present invention aims at solving these problems. In
other words, the purpose of the present invention is to offer a
method of deoxidizing ultrafine metal particles covered with
oxide layers without changing the characteristic features.
4^ 11404W_*
  ..
The present inventor examined many reduction methods in order
to achieve the above mentioned goal. He found a successful method
4
in which ultrafine metal particles are dispersed in solvents such
as water and alcohol, and deoxidizing reagents such as sodium
	 +
boride hydride, hydrazine and hormarine. However, this approach
has several difficulties. For example, reduction reagents may be
too strong or too weak for a particular metal. Also, solvents may
spoil the deoxided surface, and setting the optimal conditions for
reduction temperature and processing time, etc., is rather cumber-
s ome .
Further, it was found that if ultrafine metal particles were
formed into a fixed bed and the temperature was raised in the
buffer gas, localized sintering or insufficiently deoxidized
domains appeared because of imperfect heat removal and uneven gas
flows.
Further study proved that if ultrafine metal particles were
fluidized by a hydrogen containing gas flow and heated, uniform
deoxidization without sintering could be easily accomplished.
The present invention is based on this discovery.
The essence of the present invention is concerned with a
method of deoxidizing ultrafine metal primary particles (the
O
average diameter less than 1000 A) by fluidizing the particles by
a gas flow containing hydrogen and heating.
In the present invention, the primary particles of the average
0
diameter less than 1000 A include the secondary particle forms
which are assemblies of particles of the average diameter less
O
than 1000 A and the particles are combined by physical and
chemical forces to form, for example, fibers.
The method can be applied to all kinds of metal including
noble metals such as silver and others such as copper, nickel and
cobalt.
In the method of the present invention, ultrafine particles
of these metals are sent into a fluidization reactor, and
fluidized by a pure hydrogen gas in normal cases and by a hydrogen
gas diluted by inert gases if the reaction speed is to be slowed.
3
_ _ ---
1
The space speed (the empty tower standard) of the gas flow is 500-
1000 1/hr in GHSV. However, for increasing the gain, the speed
of 1000-5000 1/hr is preferred. The reduction temperature of
100-300 is recommended. If the temperature is lower than this
range, the reaction is too slow and if higher, sintering may
occur. The time duration for the metal particles to stay in the
flow is 0.1-10 minutes and 0.1-1 minute is recommended. These
conditions depend on metals and desired reduction speeds.
Example 1
We sent 0.1 g of ultrafine primary nickel particles of the
0
average diameter 300 A and covered with oxide layers in the
fluidization reactor of the outer diameter 10 mm ^. The air in
the reactor was first replaced by nitrogen gas ar.- then the
particles were fluidized by using a hydrogen gas flow. The
hydrogen gas was supplied at the rate of 120 ml/minutes at the
normal temperature and pressure. The height of the layer was
18 mm. The temperature was increased from the normal to 175°C,
and maintained at the temperature for 0.25 minutes. 	 Then the
outer wall of the reactor was rapidly coo'.ed. The specific surface
area of the obtained deoxidized ultrafine nickel particles was
27.0 m2/g. Comparison with the specific surface area of 27.3
m2/g before deoxidization showed that sintering had been prevented.
Because of the loss of oxygen accompanying the reduction which
generated vapor, the weight loss was 0.005 g.
Example 2
We deoxidized ultrafine
0
diameter of 500 A and covere
method as in example 1. The
after deoxidization were 2.2
nickel particles of the average
3 with oxide layers by the same
specific surface areas before and
m2/g and 2.1 m2/g, respectively.
The weight loss was 0.006 g.
Example 3
We deoxidized ultrafine nickel particles of the average
0
primary particle diameter 1000 A and covered with oxide layers
4
by the same method as in previous examples. The specific surface
areas before and after reduction were 2.2 m 2/g and 2.1 m2/g,
respectively. The weight loss was 0.003 g.
Example 4
We deoxidized ultrafine copper
O
primary particle diameter 500 A and
the same method as in example 1. T1
before and after reduction were 7.6
particles of
covered with
ze specific s-
m2/g and 7.3
the average
oxide layers by
urface areas
m3/g, respectively.
The weight loss was 0.003 g.
As described above, the present method makes it possible to
deoxidize the oxide layers on the surfaces of ultrafine metal
particles uniformly and easily without causing sintering.
Patent applicant	 Research Development Corp. of Japan
Toyoharu Hayashi
Agent	 Patent Attorney, Shin-ichi Hodaka
;1)[2.2 m2/g] in the 6th line of page 6 in the detailed
explanation should be corrected to I20.3 m2/g].
(2) [2.1 m2/g] in the 7th line of the same page should be
[19.7 m2/g].
REVISION OF THE PROCESSING	 January 30, 1984
Head of the patent office	 Kazuo Wakasugi
1. Case: Patent application no. 208500, 1982.
2. Name of invention: Method of deoxidizing ultrafine metal
particles.
3. Revisor:
Relation to the case:	 patent application
Address: 2-go, 5-ban, 2-chome, Nagata-cho
Chiyoda-ku, Tokyo
4. Agent: Phone 356-6090 zip code 160
Address: Suite 602, Shinjuku 0-flat building
1-go, 4-ban, 5-chome, Shinjuku
Shinjuku-ku, Tokyo	 ti
5
141-/
i'
Name:	 Patent Attorney (6515)	 Shin-ichi Hodaka
5. Date of revision	 autonomous revision
6. Increase of invention by revision - none
7. Object of revision
Part of the detailed explanations in the detail of the
invention.
8. Content of correction:
a
6


Fluidized reduction of oxides on fine metal powders without sintering

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