Field of the Invention
This invention relates to a method and apparatus for producing, in
an economical manner, metal powder offering high purity and uniform granular shape
The invention also relates to a production of titanium powder, among
others, as the aforementioned metal powder.
Background of the Invention
Raw element metals are processed into various forms, such as molded
shapes, sheet, bar, thin wire or foil, according to applications. In recent years
the use of metal powder as molding material is drawing the attention in the fields
of powder metallurgy, thermal spraying and other molding techniques. Particularly,
powder metallurgy is regarded as an important technology offering wide applications,
including production of metal parts, and therefore demand for powder metal―which
is the base material for powder metallurgy―is also growing.
Production of metal powder traditionally used the classic method of
mechanically and directly crushing metal granules into powder form or the method
to blow molten metal with gas pressure to form powder. However, all these and other
methods had difficulty achieving uniform granular shape and size, economy, and so
Electrolysis is one of relatively new methods for metal powder production.
It has been reported that smooth, minute and uniform crystalline structures can
be deposited under appropriate conditions, and that performing electrolysis outside
the range of these conditions produces brittle metal of sponge or powder form.
Still, these newer production methods did not produce metal grains
of satisfactory shape and size uniformity nor did they resolve other problems such
Among other metals, titanium is a relatively new metal compared with
iron, copper and aluminum that have been in use since ancient times. Titanium is
light and offers excellent strength at high temperature as well as corrosive resistance,
and is therefore used widely in industrial applications.
The sample applications of titanium include jet engine material and
structural member for aircraft/spaceship, material for heat-exchangers used in thermal
and nuclear power generation, catalyst material used in polymeric chemical products,
articles of daily use such as eyeglass frame and golf club head, and material for
health equipment, medical equipment and medical/dental material. The applications
of titanium are expected to grow further. Titanium, which is already competing with
stainless steel, duralumin and other high-performance metals in terms of applications,
is likely to surpass its rivals in the future.
Since titanium metal has poor processability and machinability, producing
a mechanical part having complex shape from molten titanium will add to manufacturing
man-hours and costs. It is because use of molten titanium as material will require
cutting and other machining steps following the plastic working process such as
hot forging and rolling.
Therefore, powder metallurgy is widely used in titanium metal processing,
which is the reason for the growing demand for titanium powder, particularly one
offering high purity and good uniformity of granular shape and size. Titanium powder
produced by the conventional powder production methods designed for general metals
is subject to the same problems with other metals; i.e., irregular granular shape
and size, poor economy, and so on. As a result, development of a production method
that can provide titanium powder offering high purity and uniform granular shape
and size is eagerly awaited.
For example, the hydrogenative dewatering method and rotary electrode
method are being put to practical use as improved production methods for titanium
metal powder. The hydrogenative dewatering method uses sponge titanium, molten titanium
or titanium chips generated from cutting/machining as material. The material titanium
is heated in a hydrogen atmosphere to cause it to absorb the hydrogen gas and thus
become brittle. This brittle titanium is then crushed and heated again in vacuum
so that the hydrogen gas will be released and powder formed. In the rotary electrode
method, molten titanium or titanium melted then forged, rolled or otherwise worked
is formed into a round bar to be used as material. This material round bar is turned
at high speed in an atmosphere of argon, helium or other inactive gas, while its
tip is melted by a heat source such as an arc or plasma-arc torch. The drips of
molten metal are then scattered via centrifugal force to produce spherical powder
The grains of titanium powder obtained by the hydrogenative dewatering
method have irregular sphericity. Although this powder can be used in die molding,
the heating process must be repeated twice. A crushing process using a ball mill
or other mechanical means may be incorporated, but oxygen contamination of titanium
powder cannot be avoided. In the rotary electrode method, material titanium is melted
in an inactive gas and made into powder form. Therefore, grains are spherical and
offer good flowability. They are not subject to oxygen contamination, either. However,
the solidification property when molded will be reduced. Both methods are a batch
system, so the power production cost is high.
The atomization method was developed as a titanium powder production
method addressing the aforementioned problems relating to quality and production
cost. In the atomization method, material titanium is melted in a water-cooled copper
crucible using a plasma-arc torch or other heat source, in order to cause molten
titanium to drip continuously from one end of the crucible. Argon, helium or other
inactive gas is then injected onto the molten titanium to atomize it and obtain
powder. However, this method could not reduce the production cost significantly
from the levels of the conventional methods, because molten titanium or melted and
worked titanium had to be used as material.
In the meantime, a method for producing powder titanium offering improved
sphericity and flowability for easier molding, in a manner requiring less cost and
avoiding oxygen contamination, is disclosed in Japanese Patent Application Laid-open
No. 5-93213. In this method, sponge titanium is isostatically pressed cold into
a solid bar. This bar material is then melted in an inactive gas, after which argon,
helium or other inactive gas is injected onto the dripping molten titanium to atomize
it and obtain powder. However, this improved method did not offer good purity or
uniformity of granular shape and size and the production cost was not at a satisfactory
Summary of the Invention
As described above, there is an increasing need and demand for metal
powder, especially titanium metal powder, with the progress of powder metallurgy
and other new molding methods. However, powder production methods that sufficiently
answer such demand were not available and the existing methods had problems, particularly
in regard to the purity of element metal, uniformity of granular sphericity and
size of powder, and production cost
In view of the above, the purpose of the present invention is to provide
element-metal powder material offering excellent uniformity of granular sphericity
and consistency of granule size, for use in powder metallurgy and other types of
The inventors conducted various studies to resolve the problems associated
with the production of element metal powder such as titanium powder, including those
pertaining to the purity of element metal, uniformity of granular sphericity, consistency
of granule size and production cost.
As a result, the inventors resolved these problems by utilizing the
technology relating to a use of titanium material for production of high-function
water containing titanium, as specified in a patent application filed earlier by
the inventors (Japanese Patent Application No. 2000-136932).
The aforementioned invention relating to a production of high-function
water containing titanium (Japanese Patent Application No. 2000-136932), developed
earlier by the inventors, provides a method for producing high-function water in
which molten titanium is dissolved, wherein the method is characterized by the burning
of a mixture gas of oxygen and hydrogen in high-pressure water and the melting of
titanium metal using the combustion gas. By utilizing this technology, powder offering
high purity and excellent uniformity of granular sphericity and size was obtained
for use in the production of element metal powder, especially titanium metal powder,
and the method also reduced the production cost of such powder significantly.
The present invention differs completely from the conventional production
methods for metal powder such as titanium powder, in both concept and structure,
in that a mixture gas of oxygen and hydrogen is burned in high-pressure water and
the combustion gas is used to melt element titanium metal, thereby allowing metal
powder to precipitate in water. It is an improved method for producing metal powder
that adopts an approach completely different from those taken by the conventional
Specifically, the present invention allows for a production of element
metal powder in a very efficient manner without using thermal melting, arc discharge
or laser irradiation to heat material metal and also without a need to let molten
metal drip or inject gas onto it to atomize the metal and produce powder.
The method proposed by the present invention generates virtually no
byproducts or impurities other than the target metal powder. Occurrence of metal
oxidation due to heating of material metal is also very small, and since the obtained
metal powder has excellent uniformity of granular sphericity and consistency of
granule size, the production cost can be reduced significantly. The method also
allows for continuous production in addition to batch production, which opens a
door to mass-production of metal powder having uniform granule size.
In the above production process, a mixture gas of oxygen and hydrogen
is burned in high-pressure water to achieve a high-temperature state, and this heat
is used to melt material element metal, allowing it to instantly disperse in water
and form fine grains. Unlike the preceding invention explained earlier (Japanese
Patent Application No. 2000-136932), in this process the water pressure and degree
of combustion of mixture gas can be adjusted to cause the obtained element metal
powder to precipitate in a short period without floating, thereby yielding titanium
powder aimed by the present invention.
To sum up, the basic structure of the present invention is to burn
a mixture gas of oxygen and hydrogen in high-pressure water and use the combustion
gas to heat material element metal and then convert it into powder form, thereby
producing metal powder of uniform granule size. A schematic drawing of the production
process is shown in the production flow chart given in Fig. 1.
The present invention consists of components (1) through (5) below,
which basically serve to burn a mixture gas of oxygen and hydrogen in high-pressure
water and use the combustion gas to melt material metal and then convert it into
Brief Description of the Drawings
- (1) A method for producing metal powder by burning a mixture gas of oxygen and
hydrogen in high-pressure water, using the combustion gas to heat material element
metal, and converting it into powder form.
- (2) A method for producing metal powder as described in (1) above, wherein the
material element metal is titanium (Ti), zirconium (Zr), germanium (Ge), tin (Sn),
gold (Au), platinum (Pt) or silver (Ag).
- (3) An apparatus for producing metal powder, consisting of a pressure-resistant
container that comprises a high-pressure water tank, an injector nozzle for mixture
gas of oxygen and hydrogen, a material element-metal feeder part, an ignition plug
and a combustion chamber.
- (4) An apparatus for producing metal powder as described in (3) above, wherein
the apparatus has as an adjunct a water electrolyzer for producing a mixture gas
of oxygen and hydrogen.
- (5) A method for producing metal powder as described in (3) or (4) above, wherein
the material element metal takes a shape of bar, sheet, granule or foil.
Description of the Symbols
- Fig. 1: Flow chart of metal powder production as proposed by the present invention
- Fig. 2: An apparatus for producing metal powder as proposed by the present invention
Best Mode for Carrying Out the Invention
- A: Apparatus for producing metal powder
- B: Pressure-resistant container for metal powder production
- C: Electrolyzer
- 1: Mixture-gas injection pump
- 2: High-pressure water tank
- 3: Purified water
- 4: Fine metal grains
- 5: Mixture-gas injector nozzle
- 6: Mixture gas
- 7: Combustion chamber
- 8: Pressure control valve
- 9: Hydrogen-gas feed pipe
- 10: Oxygen-gas feed pipe
- 11: Mixing bar
- 12: Ignition plug
- 13: Metal powder outlet
- 14: Filter system
- 15: Product
- 16: Water
- 18: Partition
- 19: Electrode
- 20: Electrode
- 21: Material element metal
- 22: Metal feeder part
The following explains the present invention by taking a production
of titanium metal powder as an example. Note, however, that the invention is not
limited to production of titanium powder.
According to the present invention, purified water such as distilled
water is filled into the high-pressure water tank inside the pressure-resistant
container for titanium-metal powder production, and material titanium metal such
as a titanium metal bar is fed from the material element-metal feeder part and pressurized
at high pressure. A mixture gas consisting of hydrogen and oxygen is injected from
the nozzle, ignited and let completely bum in the combustion chamber. Upon achievement
of a perfect combustion state leaving an ultrahigh-temperature steam gas, material
titanium is instantly melted in the combustion gas and dispersed in water. At this
time, very fine titanium grains of micron order are produced and dispersed in powder
form. The produced fine titanium powder does not melt or float and precipitates
in a short period.
The present invention can produce titanium powder of high purity at
a very high efficiency. To achieve this, it is important to control the amounts
of gases to be mixed and burned, reaction pressure and feed rate of material titanium
With the production apparatus proposed by the present invention, an
ideal injection amount of mixture gas is approx. 2 to 4 liters per second when the
container can hold one ton of purified water. Applying too high a gas pressure may
damage the apparatus structure, while a low pressure may cause the gas to flow upward
from the nozzle, causing the heated, molten fine metal grains to be encapsulated
in air bubbles and diffused from the water surface. This will reduce the generation
efficiency of fine metal grains. The water pressure in the pressure tank should
be 1.2 to 1.5 atmospheres.
The supplied material titanium metal should preferably have the highest
possible purity, in order to prevent impurities from mixing into the produced titanium
A mixture gas of hydrogen and oxygen provides the most efficient and
stable means of burning titanium metal in water, where high pressure is required
to ensure stable combustion. Physical or chemical explanations as to why element
titanium metal melts instantly and becomes super-fine grains in a combustion gas
in high-pressure water have not been found yet.
Material titanium metal may take a shape of bar, sheet, granule or
foil, and it may be appropriate to feed titanium metal granules instead of bar if
the capacity of the production container is much smaller than one ton.
In addition to titanium, the material element metals that can be used
in the production of metal powder using the production apparatus proposed by the
present invention include, but not limited to, zirconium, germanium, tin, gold,
platinum and silver.
The high-pressure water tank used in the apparatus proposed by the
present invention is a pressure-resistant tank made of metal, or preferably steel,
and ideally other parts such as the combustion chamber should also be made of steel.
The gas pump is installed to blow out a mixture gas at high pressure. Material element
metal is fed continuously in accordance with the melt amount.
Material element metal must be fed into a position where the mixture
gas bums completely and fully turns into a steam gas of ultrahigh temperature. The
combustion chamber is installed to burn the mixture gas to achieve this purpose.
This setup allows for production of pure metal powder free from impurities or byproducts.
High pressure is also required to completely burn a pure mixture gas.
An actual embodiment of the present invention is explained according
to the drawings. Note, however, that the invention is not limited to this example.
Fig. 1 shows a flow chart of metal powder production as proposed by
the present invention, as described earlier. An apparatus for producing metal powder
(A) shown in Fig. 2 consists of a pressure-resistant container (B) that comprises
a high-pressure water tank (2), an injector nozzle for mixture gas of oxygen and
hydrogen (5), a material element-metal feeder part (22), an ignition plug (12) and
a combustion chamber (7).
The apparatus for producing metal powder (A) consists of a pressure-resistant
container for metal powder production (B), and the pressure-resistant container
for metal powder production comprises a gas injection pump (1), a high-pressure
water tank (2), a combustion chamber (7), a pressure control valve (8), a metal
powder outlet (13), purified water (3), material element metal for powder production
(21), an ignition plug (12), a material element-metal feeder part (22) and a mixture-gas
injector nozzle (5). (4) indicates produced metal powder.
Purified water (3) such as distilled water is filled into the high-pressure
water tank (2) of the pressure-resistant container for metal powder production (B),
and material titanium metal (21) such as a titanium metal bar is fed from the material
element-metal feeder part (22), after which the container is pressurized at a high
pressure. Hydrogen and oxygen are injected from the nozzle (5) as a mixture gas
and the mixture gas is ignited by the ignition device (12). The mixture gas is completely
burned in the combustion chamber (7) to obtain a perfect combustion state leaving
an ultrahigh-temperature steam gas, and the material titanium melts instantly in
this combustion gas and disperses in water.
At this time, very fine titanium grains of micron order (4) are produced
and dispersed in powder form. The titanium metal powder does not melt or float and
precipitates as powder in a short period. The separated powder is then released
from the outlet for titanium metal powder (13) and becomes titanium powder.
The supply of mixture gas of hydrogen and oxygen must be precisely
controlled to achieve a hydrogen-to-oxygen ratio of 2 to 1. While a mixture gas
of hydrogen and oxygen is supplied from commercial gas cylinders, adding a water
electrolyzer (C) as an adjunct to produce a mixture gas of hydrogen and oxygen via
electrolysis of water will generate completely pure gases to facilitate an optimal,
efficient supply of mixture gas.
In the present invention, adding a water electrolyzer (C) as an adjunct,
instead of supplying a mixture gas of hydrogen and oxygen from commercial gas cylinders,
will generate completely pure gases via electrolysis of water, thereby facilitating
a supply of mixture gas in a simple and efficient manner. When adding a water electrolyzer
for production of mixture gas of oxygen and hydrogen as an adjunct, the electrolyzer
(C) is considered an optional adjunct unit to produce and supply a mixture gas of
hydrogen and oxygen via electrolysis of water, which consists of feed pipes for
hydrogen and oxygen gases (9, 10), electrodes (19, 20), a partition (18) and water
(16). The electrolyzer causes electrolysis of acid or alkali raw water to generate
oxygen gas at the anode and hydrogen gas at the cathode, and supplies them as a
material mixture gas.
Production Conditions and Results
Pressurized water: 1 ton Pressure: 1.5 kg/m2
Evaluation of Produced Titanium Powder
Internal pressure of production tank: 1.5 atmospheres
Mixture gas: 5 L/sec (2 atmospheres)
Injection period: 1 hour
Feed rate of titanium metal: 25 kg
Production volume of titanium powder: Approx. 25 kg
The element titanium powder contained no byproducts or impurities
and exhibited excellent uniformity of granular sphericity and consistency of granule
size. The production cost was reduced around a half compared with the conventional
Industrial Field of Application
The present invention allows for production of high-purity metal,
especially titanium powder, in a very efficient manner. The production method proposed
by the present invention achieves pure powder free from byproducts or impurities
other than the elemental component, wherein the produced powder offers excellent
uniformity of granular sphericity and size and can be produced at significantly
less cost. Batch production, continuous production and mass production are also