U.S. patent application number 11/817459 was filed with the patent office on 2009-01-08 for method for melting an alloy containing a metal of a high vapor pressure.
This patent application is currently assigned to JAPAN METALS AND CHEMICALS CO., LTD. Invention is credited to Etsuo Akiba, Hirotoshi Enoki, Naoyoshi Terashita, Shigeru Tsunokake.
Application Number | 20090007728 11/817459 |
Document ID | / |
Family ID | 36941358 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090007728 |
Kind Code |
A1 |
Akiba; Etsuo ; et
al. |
January 8, 2009 |
Method For Melting an Alloy Containing a Metal of a High Vapor
Pressure
Abstract
In a method for producing an alloy containing a metal of a low
melting point, a low boiling point and a high vapor pressure such
as Mg, Ca, Li, Zn, Mn, Sr or the like, a helium containing gas is
used as an atmosphere gas for the melting. As a result, the alloy
containing the above metal can be produced as an alloy having a
targeted chemical composition precisely and safely at a low cost
without causing the risk of firing, contamination or the like by
active metal fine powder being vaporized. Furthermore, by using the
helium containing gas as the atmosphere gas, the
quench-solidification of the molten metal can be conducted due to a
high thermal conductivity inherent to the helium gas, so that a
special alloy can be produced even by the usual melting
apparatus.
Inventors: |
Akiba; Etsuo; (Ibaraki,
JP) ; Enoki; Hirotoshi; (Ibaraki, JP) ;
Terashita; Naoyoshi; (Yamagata, JP) ; Tsunokake;
Shigeru; (Tokyo, JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
JAPAN METALS AND CHEMICALS CO.,
LTD
Tokyo
JP
National Institute of Advanced Industrial Science and
Technology
Tokyo
JP
|
Family ID: |
36941358 |
Appl. No.: |
11/817459 |
Filed: |
March 2, 2006 |
PCT Filed: |
March 2, 2006 |
PCT NO: |
PCT/JP2006/304525 |
371 Date: |
August 30, 2007 |
Current U.S.
Class: |
75/392 |
Current CPC
Class: |
B22D 21/007 20130101;
B22D 23/06 20130101 |
Class at
Publication: |
75/392 |
International
Class: |
C22C 1/02 20060101
C22C001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2005 |
JP |
2005-056985 |
Claims
1. A method of melting an alloy containing a metal of a high vapor
pressure characterized in that as the method for melting to produce
an alloy containing one or more of Mg, Ca, Li, Zn, Mn and Sr, a
helium containing gas is used as an atmosphere gas for the
melting.
2. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 1, wherein a helium concentration in
the atmosphere gas is not less than 10 vol %.
3. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 1, wherein the atmosphere gas is a
mixed gas of helium and a gas not reacting with the starting metal
such as nitrogen or argon.
4. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 1, wherein the atmosphere gas has a
pressure of 0.01-1 MPa.
5. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 2, wherein the atmosphere gas is a
mixed gas of helium and a gas not reacting with the starting metal
such as nitrogen or argon.
6. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 2, wherein the atmosphere gas has a
pressure of 0.01-1 MPa.
7. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 3, wherein the atmosphere gas has a
pressure of 0.01-1 MPa.
8. A method for melting an alloy containing a metal of a high vapor
pressure according to claim 5, wherein the atmosphere gas has a
pressure of 0.01-1 MPa.
Description
INDICATION OF THE RELATED APPLICATION
[0001] The present application is an application claiming priority
of JP 2005-56985 filed on Mar. 2, 2005.
TECHNICAL FIELD
[0002] This invention relates to a melting method wherein an alloy
containing a metal of a low melting point, a low boiling point and
a high vapor pressure such as Mg, Ca, Li, Zn, Mn, Sr or the like is
produced by melting.
RELATED ART
[0003] The metal such as Mg, Ca, Zn, Li or the like or an alloy
including such a metal is widely expected for applications as a
structural material or a functional material because the weight is
light and the specific strength is high as compared with a
transition metal such as iron or the like or an alloy thereof.
Among them, Mg and Ca are richly existent in earth crust and sea
water and low in the cost and have no harmful influence upon human
body, so that they are expected to be expanding applications.
[0004] However, the metals such as Mg, Ca, Zn, Li and the like and
alloys thereof are low in the melting point or boiling point and
high in the vapor pressure, so that if it is intended to produce
the alloys containing these metals by a melting method, there is a
problem that the inside of the melting furnace is contaminated with
metal fine powder generated by vaporization. Particularly, since Mg
is very active, if it adheres to an inner wall or the like of the
melting furnace and is exposed to an atmosphere, there is a high
risk of causing fire, explosion or the like.
[0005] Also, there is a problem that the fume of the vaporized
metal fine powder contaminates a window for visual observation of
the melting furnace or shields a visual range and hence whether or
not the alloy is completely melted and whether or not the stirring
is sufficient cannot be visually confirmed or judged. Furthermore,
the estimation of exact vaporization amount becomes difficult, so
that there is a problem that the alloy having a targeted chemical
composition cannot be produced.
[0006] Moreover, the alloy containing Mg, Ca, Zn, Li or the like
can be produced by a mechanical alloying method such as ball
milling or the like in addition to the melting method. Since such a
method is a production method without melting the starting metals,
the above problem will not be caused by the generation of the metal
fine powder, but there is still a problem that the contamination
due to the incorporation of iron and the like from the mill pot and
the deterioration of the alloy homogeneity occur. Also, the long
time is taken in the production, causing a problem that the
production cost is high. Therefore, this method is not suitable in
the mass production.
DISCLOSURE OF THE INVENTION
[0007] As mentioned above, the conventional methods for the
production of the alloys containing Mg, Ca, Zn, Li and the like
have various problems, so that a new production method without such
problems is strongly required. Therefore, it is an object of the
invention to propose a useful melting method for the production of
an alloy containing a metal of a low melting point, a low boiling
point and a high vapor pressure.
[0008] It is another object of the invention to propose a method of
safely producing a greater amount of an alloy having a targeted
chemical composition in a higher precision while reducing the risk
of firing, contamination or the like by active metal fine power
being vaporized.
[0009] The inventors have made various studies in order to achieve
the above objects. As a result, it has been found out that it is
effective to rationalize a gas component constituting the melting
atmosphere, and particularly use helium gas, and the invention has
been accomplished.
[0010] That is, the invention lies in a method of producing an
alloy containing a high vapor pressure metal by melting an alloy
containing one or more of Mg, Ca, Li, Zn, Mn and Sr, characterized
in that a helium containing gas is used as an atmosphere gas for
the melting.
[0011] In the invention, it is preferable that a helium
concentration in the atmosphere gas is not less than 10 vol %, and
the atmosphere gas is a mixed gas of helium and a gas not reacting
with the starting metal such as nitrogen, argon or the like. It is
also preferable that a pressure of the atmosphere gas is 0.01 MPa-1
MPa.
[0012] According to the method of the invention having the above
construction, an alloy containing a low melting point, a boiling
point and a high vapor pressure metal such as Mg, Ca, Li, Zn or the
like, for example, an alloy of the above metal and Al, Ni or the
like can be precisely and safely produced as an alloy having a
targeted chemical composition in a greater amount at a low cost
without causing the risk of firing, contamination or the like by
active metal fine powder being vaporized.
[0013] Furthermore, the melting method of the invention using the
helium containing gas as an atmosphere gas can solve the problems
due to the above active metal fine powder but also has a feature
that the solidification rate of the molten metal is enhanced by a
high thermal conductivity inherent to the helium gas or the effect
of quench-solidification is obtained. Therefore, according to the
method of the invention, a special alloy conventionally produced by
using a melting apparatus for an exclusive use of
quench-solidification can be produced even by using the usual
melting apparatus.
[0014] As seen from the above, the development and practical
application of structural materials or functional materials made
from light weight metal or alloy thereof, which will be used in the
new generation, can be expected to be largely advanced by using the
melting method according to the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a graph showing an influence of a helium gas
concentration in an atmosphere gas upon a melting yield of Mg in
the melting of CaMg.sub.2 alloy.
[0016] FIG. 2 is a view comparing X-ray diffraction curves of
alloys obtained when helium gas and argon gas are used as an
atmosphere gas in the melting of CaMg.sub.2 alloy.
[0017] FIG. 3 is a view comparing pressure-composition isothermal
curves of La--Ni based hydrogen storage alloy melted in a helium
gas atmosphere and La--Ni based hydrogen storage alloy melted in an
argon gas atmosphere.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] The melting method according to the invention will be
described in detail below.
[0019] The melting method according to the invention lies in a
point that a helium containing gas is used as an atmosphere gas for
the melting of an alloy containing at least one metal of a low
melting point, a low boiling point and a high vapor pressure such
as Mg, Ca, Li, Zn and the like. When the helium containing gas is
used as the melting atmosphere, it is possible to prevent metal
fine powder generated by vaporization in the melting from
segregation and the risk of firing or the like due to the segregate
of the metal fine powder or the contamination can be largely
reduced but also the alloy having the target chemical composition
can be safely produced at a greater amount in a high precision.
[0020] It is considered that the above effect of the helium
containing gas can be obtained due to the fact that helium is high
in the thermal conductivity (about 3 times of argon), low in the
density (0.1 times of argon) and long in the average free stroke
(about 3 times of argon) as compared with the other inert gas.
Moreover, hydrogen has the features similar to those of helium, but
hydrogen is not suitable as the melting atmosphere gas because it
may react with the starting metal to form a metal hydride. However,
if it is intended to melt a metal not reacting with hydrogen and
having a low melting point, a low boiling point and a high vapor
pressure, when a hydrogen containing gas is used as an atmosphere
gas, the effect similar to that in the use of helium can be
expected.
[0021] Helium gas is very expensive. Therefore, the helium gas is
preferably replaced partially with a cheap gas not reacting with
the starting metal from a viewpoint of the cost reduction. The
inventors have made experiments of replacing helium with various
other gases and found out that when a part of helium gas is
replaced with a gas not reacting with the starting metal such as
nitrogen, argon or the like, the risk of firing or the like due to
the segregation of the metal fine powder generated by vaporization
and the contamination thereof can be fairly reduced.
[0022] Moreover, as a gas replacing helium gas, an argon gas is
most preferable. Because, the argon gas is cheap and does not react
with Mg, Ca, Li, Zn and the like even at a higher temperature.
[0023] However, it has been confirmed that there is a limit in
replacing helium with the other inert gas. According to the
inventors' knowledge, the helium content in such a mixed gas is
required to be at least 10 vol %, and is preferably not less than
25 vol % and more preferably not less than 50 vol %. It is further
preferably not less than 95 vol %, and may be naturally 90-100 vol
%. Thus, the reason why the lower limit of the ratio of helium
occupied as the atmosphere gas is 10 vol % is due to the fact that
when it is less than 10 vol %, the aforementioned action and effect
of helium are not obtained.
[0024] In the melting method according to the invention, a pressure
of the melting atmosphere comprising the helium containing gas is
preferably 0.01 MPa-1 MPa. When the pressure is less than 0.01 MPa,
the vaporization temperature is considerably decreased, the
vaporization is promoted, and the amount of the metal fine powder
generation cannot be decreased. While, when it exceeds 1 MPa, the
vaporization amount decreases, but the melting point rises and the
melting becomes difficult.
[0025] Moreover, the pressure range of the helium containing gas
means a pressure at room temperature before the melting and there
may be a case exceeding the above range when the temperature inside
the furnace becomes higher in the melting procedure.
[0026] Also, the optimum ranges of the concentration and pressure
of helium used as the atmosphere gas are mainly obtained as a
result of consideration and development from a viewpoint of the
cost.
[0027] In the melting method of the invention, impurity gases such
as oxygen, carbon dioxide, steam and the like may be included in
the helium containing gas supplied as an atmosphere gas within a
scope not damaging the action of the invention. In this case, the
content is preferably not more than 1 mass %. When it exceeds 1
mass %, these gases react with Mg, Ca, Li, Zn and the like to
produce an oxide, a hydroxide, a carbide and the like and hence
there cannot be produced an alloy having a targeted chemical
composition and a compound.
EXAMPLES
[0028] The invention will be described in detail with reference to
the following examples, but the invention is not naturally limited
to these examples.
Invention Example 1
[0029] As a starting material for hydrogen storage alloy
CaMg.sub.2, 1 kg in total of Mg and Ca metals are provided so as to
have a molar ratio of 2:1, and these metals are charged into an
induction melting type melting furnace, and thereafter the interior
of the furnace is evacuated to 8.times.10.sup.-3 Torr and then
helium gas (concentration: 100 vol %) is introduced thereinto up to
600 Torr as an atmosphere gas. Next, the melting furnace is heated
up to a temperature of 1100.degree. C. while filling the inside of
the furnace with the atmosphere gas to melt the starting materials,
and further kept for 30 minutes while maintaining a melting
temperature of the resulting alloy at 1050.degree. C. Thereafter,
the molten alloy is poured onto a water-cooled mold platen and
solidified by cooling at a cooling rate of 1000.degree. C./sec to
prepare CaMg.sub.2 alloy. With respect to thus obtained CaMg.sub.2
alloy, the melting yield and chemical composition are measured by
the following methods (1) and (2).
[0030] (1) Measurement of Melting Yield
[0031] The mass of the starting material before melting and the
mass of alloy after melting to mold are measured to determine the
decreased mass by vaporization and calculate the melting yield.
[0032] (2) Measurement of Chemical Composition
[0033] The chemical composition of the alloy after melting to mold
is quantitatively analyzed by ICP emission spectroscopy.
[0034] The measured results are shown in Table 1. As seen from
these results, in Invention Example 1 using helium gas as a melting
atmosphere gas, the melting yield is as high as not less than
98.2%, and further the alloy can be produced in a high precision
within .+-.1% with respect to the targeted alloy composition.
TABLE-US-00001 TABLE 1 He Analytical concentration Targeted result
of Melting in atmosphere chemical chemical yield gas (vol %)
composition composition (%) Invention 100 CaMg.sub.2 CaMg.sub.1.98
98.25 Example 1 Invention 75 CaMg.sub.2 CaMg.sub.1.96 97.84 Example
2 Invention 50 CaMg.sub.2 CaMg.sub.1.93 97.54 Example 3 Invention
25 CaMg.sub.2 CaMg.sub.1.91 97.27 Example 4 Invention 100
CaAl.sub.2 CaAl.sub.2.02 98.14 Example 5 Invention 100 MgNi.sub.2
MgNi.sub.1.96 97.87 Example 6 Invention 100 CaNi.sub.2
CaNi.sub.2.04 97.81 Example 7 Comparative 0 CaMg.sub.2
CaMg.sub.1.77 96.40 Example 1
Comparative Example 1
[0035] CaMg.sub.2 alloy is prepared in the same manner as in
Invention Example 1 except that argon gas (concentration: 100 vol
%) is used as an atmosphere gas. With respect to this alloy, the
melting yield and chemical composition are measured by the above
methods (1) and (2) to obtain the results shown in Table 1.
Invention Examples 2-4
[0036] CaMg.sub.2 alloys are prepared in the same manner as in
Invention Example 1 except that the concentration of helium gas
introduced as an atmosphere is changed to 75, 50 and 25 vol %
(remainder is argon gas), respectively. With respect to these
CaMg.sub.2 alloys, the melting yield and chemical composition are
measured by the above methods (1) and (2) to obtain the results
shown in Table 1. As seen from these results, when the helium gas
concentration exceeds 50 vol % (Invention Examples 2 and 3), the
melting yield is as high as about 98% and the targeted alloy
composition can be obtained in a high precision. On the other hand,
when the helium gas concentration is 25 vol % (Invention Example
4), the melting yield and the alloy composition are inferior to
those of Invention Examples 1-3, but the melting yield and the
precision of the alloy composition are improved as compared with
the case of using no helium gas (Comparative Example 1), from which
the effect by the introduction of helium gas can be confirmed.
[0037] A relationship between the helium gas concentration and the
melting yield obtained from the results of Invention Examples 1-4
and Comparative Example 1 is shown in FIG. 1. As seen from FIG. 1,
the melting yield is improved as the helium gas concentration
becomes higher.
[0038] Further, the measurement of X-ray diffraction intensity is
carried out with respect to CaMg.sub.2 alloys obtained in Invention
Example 1 and Comparative Example 1 to confirm whether or not the
alloy and compound have a targeted single-phase structure. The
results are shown in FIG. 2. As seen from FIG. 2, the CaMg.sub.2
alloy of Invention Example 1 is an alloy of single CaMg.sub.2 phase
structure, while the alloy of Comparative Example 1 is an alloy of
two mixed phase structure consisting of CaMg.sub.2 phase and Ca
phase.
[0039] As seen from Table 1 and FIGS. 1 and 2, according to the
method of the invention, it is possible to produce a single-phase
alloy having a targeted composition without variations. On the
contrary, according to the method of the comparative example, the
evaporation loss of the starting materials cannot be controlled and
the composition is largely shifted from the targeted composition.
Furthermore, the variations of the alloy composition are
caused.
Invention Example 5
[0040] CaAl.sub.2 alloy is prepared in the same manner as in
Invention Example 1 except that Ca and Al are used as a starting
material, and the melting yield and chemical composition of the
resulting CaAl.sub.2 alloy are measured by the above methods (1)
and (2) to obtain results shown in Table 1. As seen from these
results, in Invention Example 5, the melting yield is as high as
about 98% and the target alloy is obtained in a high precision
within .+-.1% with respect to the targeted Al composition.
Invention Example 6
[0041] MgNi.sub.2 alloy is prepared in the same manner as in
Invention Example 1 except that Mg and Ni are used as a starting
material, and the melting yield and chemical composition of the
resulting MgNi.sub.2 alloy are measured by the above methods (1)
and (2) to obtain results shown in Table 1. As seen from these
results, in Invention Example 6, the melting yield is as high as
about 98% and the target alloy is obtained in a high precision
within .+-.2% with respect to the targeted Ni composition.
Invention Example 7
[0042] CaNi.sub.2 alloy is prepared in the same manner as in
Invention Example 1 except that Ca and Ni are used as a starting
material, and the melting yield and chemical composition of the
resulting CaNi.sub.2 alloy are measured by the above methods (1)
and (2) to obtain results shown in Table 1. As seen from these
results, in Invention Example 7, the melting yield is as high as
about 98% and the target alloy is obtained in a high precision
within .+-.2% with respect to the targeted Ni composition.
Invention Example 8 and Comparative Example 2
[0043] A pressure-composition isothermal curve is measured with
respect to a La--Ni based hydrogen storage alloy produced by
melting in an atmosphere of 100 vol % helium gas according to the
invention (Invention Example 8) and a La--Ni based hydrogen storage
alloy produced by melting in an atmosphere of 100 vol % argon gas
(Comparative Example 2) to obtain results shown in FIG. 3. As seen
from FIG. 3, the alloy of Invention Example 8 is flat and wide in
the plateau region as compared with the alloy of Comparative
Example 2, and the alloy of Invention Example 8 quench-solidified
with the helium gas is an alloy having an excellent
homogeneity.
INDUSTRIAL APPLICABILITY
[0044] The technique of the invention can be utilized as a mass
production technique for alloys containing a metal of a low melting
point, a low boiling point and a high vapor pressure such as Mg,
Ca, Zn, Li or the like but also can be applied to the melting of
single body made of each of these metals, the melting of a compound
used in semiconductors or the like such as gallium-arsenic or other
compounds. Furthermore, the invention is applicable to a melting
technique of structural materials, functional materials,
semiconductor compounds, and other compounds made from a light
metal or alloy used in the new generation.
* * * * *