U.S. patent application number 10/590863 was filed with the patent office on 2007-12-27 for method for producing ti or ti alloy through reduction by ca.
Invention is credited to Masahiko Hori, Tadashi Ogasawara, Kazuo Takemura, Toru Uenishi, Makoto Yamaguchi.
Application Number | 20070295167 10/590863 |
Document ID | / |
Family ID | 34908902 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295167 |
Kind Code |
A1 |
Ogasawara; Tadashi ; et
al. |
December 27, 2007 |
Method for Producing Ti or Ti Alloy Through Reduction by Ca
Abstract
A mixed molten salt containing CaCl.sub.2 and NaCl is held in
the reactor cell 1 at a temperature not more than 600.degree. C.
TiCl.sub.4 which is of a Ti raw material is introduced into the
reactor cell 1 while Na is introduced into the reactor cell 1. Na
introduced into the reactor cell 1 is replaced by Ca, Ca is
dissolved in the molten salt, Ca reduces TiCl.sub.4 introduced into
the reactor cell 1, and thereby Ti particles are generated. The
generated Ti particles are introduced to a separation cell 2 along
with the molten salt, and the Ti particles and Na are separated
from the molten salt. The residual molten salt is introduced to an
electrolytic cell 3 to generate Na by high-temperature electrolysis
at the temperature more than 600.degree. C. The generated Na is
returned to the reactor cell 1 to replenish Na consumed in the
reactor cell 1. The highly reactive Ca is not directly handled, and
Na which is easy to handle is used in a circulating manner.
Therefore, the Ti or Ti alloy can economically be produced by Ca
reduction.
Inventors: |
Ogasawara; Tadashi; (Hyogo,
JP) ; Yamaguchi; Makoto; (Hyogo, JP) ; Hori;
Masahiko; (Hyogo, JP) ; Uenishi; Toru; (Hyogo,
JP) ; Takemura; Kazuo; (Hyogo, JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
34908902 |
Appl. No.: |
10/590863 |
Filed: |
October 13, 2004 |
PCT Filed: |
October 13, 2004 |
PCT NO: |
PCT/JP04/15043 |
371 Date: |
August 28, 2006 |
Current U.S.
Class: |
75/620 |
Current CPC
Class: |
Y02P 10/212 20151101;
C22B 5/04 20130101; Y02P 10/20 20151101; C22B 34/129 20130101; C22B
34/1272 20130101; C22B 34/1295 20130101 |
Class at
Publication: |
075/620 |
International
Class: |
C22B 34/12 20060101
C22B034/12; C25C 3/28 20060101 C25C003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2004 |
JP |
2004-056245 |
Claims
1. A method for producing Ti or Ti alloys through reduction by Ca,
comprising: a Ca generation step by Na introduction, in which Ca is
generated by introducing Na into molten salt containing CaCl.sub.2,
the molten salt being kept at temperatures of not more than
600.degree. C.; a Ti generation step by a reducing reaction, in
which Ti or a Ti alloy is generated in said molten salt by
supplying metallic chloride containing TiCl.sub.4 into said molten
salt to cause the metallic chloride to react with Ca generated in
said molten salt; and a Ti separation step in which said Ti or Ti
alloy generated in said molten salt is separated from said molten
salt.
2. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 1, wherein the Ca generation step by Na
introduction and the Ti generation step by the reducing reaction
are performed in the same reactor apparatus.
3. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 1, further comprising an electrolytic step in
which Na is generated by electrolyzing the molten salt containing
NaCl, wherein Na generated in the electrolytic step is introduced
into said molten salt.
4. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 3, wherein the molten salt is held at
temperatures of more than 600.degree. C. in said electrolytic
step.
5. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 3, wherein the molten salt separated from said
Ti or Ti alloy is supplied to said electrolytic step.
6. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 3, further comprising a chlorination step in
which TiCl.sub.4 is generated by causing a Cl.sub.2 gas to react
with TiO.sub.2, the Cl.sub.2 gas being of by-product in association
with said electrolysis, wherein TiCl.sub.4 generated in the
chlorination step is used for the generation reaction of said Ti or
Ti alloy.
7. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 5, further comprising a Na separation step, in
which a temperature of the molten salt separated from said Ti or Ti
alloy is increased to be more than 600.degree. C. to generate Na
before the molten salt is supplied to said electrolytic step, and
said molten salt is introduced to the electrolytic step after the
generated Na is separated and removed.
8. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 7, wherein the Na separation step also doubles
as said Ti separation step.
9. The method for producing Ti or Ti alloys through reduction by Ca
according to claim 1, wherein said molten salt containing
CaCl.sub.2 is a mixed molten salt containing CaCl.sub.2 and NaCl at
a ratio in which a melting point becomes not more than 600.degree.
C.
10. The method for producing Ti or Ti alloys through reduction by
Ca according to claim 9, wherein said mixed molten salt is a mixed
molten salt containing at least one of KCl, LiCl, and CaF.sub.2 at
a ratio in which a melting point becomes not more than 600.degree.
C.
11. The method for producing Ti or Ti alloys through reduction by
Ca according to claim 1, wherein said metallic chloride containing
TiCl.sub.4 is a mixture containing TiCl.sub.4 and another metallic
chloride.
12. The method for producing Ti or Ti alloys through reduction by
Ca according to claim 1, wherein the generated Ti or Ti alloy is
particulate whose particle diameter ranges 0.5 to 50 .mu.m on an
average.
13. The method for producing Ti or Ti alloys through reduction by
Ca according to claim 1, wherein a Ca concentration is managed to
be not lower than 0.01% in the molten salt used in said Ti
generation step.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing Ti
or Ti alloys through reduction by Ca, in which a metallic chloride
containing TiCl.sub.4 is reduced by Ca to produce metallic Ti or
the Ti alloys.
BACKGROUND ART
[0002] A Kroll method for reducing TiCl.sub.4 by Mg is generally
used as an industrial production method of the metallic Ti. In the
Kroll method, the metallic Ti is produced through a reduction step
and a vacuum separation step. In the reduction step, TiCl.sub.4
which is of a raw material of Ti is reduced in a reactor vessel to
produce the sponge metallic Ti. In the vacuum separation step,
unreacted Mg and MgCl.sub.2 formed as a by-product are removed from
the sponge metallic Ti produced in the reactor vessel.
[0003] In order to explain the reduction step in detail, in the
reduction step, the reactor vessel is filled with the molten Mg,
and the TiCl.sub.4 liquid is supplied from above a liquid surface
of the molten Mg. This allows TiCl.sub.4 to be reduced by Mg near
the liquid surface of the molten Mg to generate the particulate
metallic Ti. The generated metallic Ti sequentially moves downward.
At the same time, the molten MgCl.sub.2 which is of the by-product
is generated near the liquid surface. A specific gravity of molten
MgCl.sub.2 is larger than that of the molten Mg. The molten
MgCl.sub.2 which is of the by-product moves downward due to the
specific-gravity difference, and the molten Mg emerges in the
liquid surface instead. The molten Mg is continuously supplied to
the liquid surface by the specific-gravity difference substitution,
and the reaction is continued.
[0004] In the metallic Ti production by the Kroll method, a
high-purity product can be produced. However, because the product
is produced in a batch manner, production cost is increased and
product becomes remarkably expensive. One of factors of increased
production cost is the difficulty of enhancing a feed rate of
TiCl.sub.4. The following three items are cited as the reason why
the feed rate of TiCl.sub.4 is restricted.
[0005] In order to improve productivity in the Kroll method, it is
effective to increase the feed rate of TiCl.sub.4 which is of the
raw material of Ti, i.e., to increase a supply amount of molten Mg
to the liquid surface per unit area or unit time. However, when the
feed rate is excessively increased, because deprivation of heat is
too late for the reducing reaction created in the liquid surface of
the molten Mg, a temperature of the molten MgCl.sub.2 generated in
the liquid surface by the reaction is increased, and the specific
gravity of the molten MgCl.sub.2 is decreased and brought close to
the specific gravity of Mg. Therefore, the rate of the
specific-gravity difference substitution cannot respond to the
reaction rate, MgCl.sub.2 remains in the liquid surface, and
TiCl.sub.4 is supplied to the MgCl.sub.2, which reduces utilization
efficiency of TiCl.sub.4. As a result, the supplied raw material
becomes unreacted generation gases (referred to as unreacted gas)
such as an unreacted TiCl.sub.4 gas and an unreacted TiCl.sub.3
gas, and the unreacted gas is discharged outside the reactor
vessel. It is necessary to avoid the generation of the unreacted
gas, because a rapid increase in inner pressure of the reactor
vessel is associated with the generation of the unreacted gas.
Because of the above reasons, there is a limit of the feed rate of
TiCl.sub.4 which is of the raw material of Ti.
[0006] When the feed rate of TiCl.sub.4 is increased, a
precipitation amount of Ti is increased in the inner surface of the
reactor vessel above the liquid surface. As the reducing reaction
proceeds, the liquid surface of the molten Mg rises intermittently.
Therefore, the precipitated Ti in the inner surface of the upper
portion of the reactor vessel is immersed in the molten Mg in a
late stage of the reducing reaction, which causes the effective
area of the Mg liquid surface to be decreased to reduce the
reaction rate. In order to suppress the reduction of reaction rate,
it is necessary that the feed rate of TiCl.sub.4 be restricted to
prevent the Ti precipitation in the inner surface of the upper
portion of the reactor vessel. Japanese Patent Application
Publication No. 8-295955 proposes a countermeasure for suppressing
the Ti precipitation in the inner surface of the upper portion of
the reactor vessel. However, the countermeasure proposed in
Japanese Patent Application Publication No. 8-295955 is not
sufficient.
[0007] In the Kroll method, because the reaction is performed only
near the liquid surface of the molten Mg solution in the reactor
vessel, an exothermic area is narrowed. Therefore, when TiCl.sub.4
is supplied at a high rate, cooling cannot keep up with the supply
of TiCl.sub.4 in the reaction area. This also causes the feed rate
of TiCl.sub.4 to be restricted.
[0008] Although the feed rate of TiCl.sub.4 is not directly
affected, in the Kroll method, Ti is generated in the particulate
form near the liquid surface of the molten Mg solution, and Ti
moves downward. However, because of wetting properties (adhesion
properties) of the molten Mg, the generated Ti powder moves
downward while aggregated, and the Ti particles are sintered to
grow in size of the Ti particles due to the temperature of the
molten solution during moving downward, which makes it difficult to
retrieve the Ti particles toward the outside of the reactor vessel.
Therefore, in the Kroll method, the continuous production is
difficult to be performed, and the improvement of the productivity
is blocked. This is the reason why Ti is produced in the batch
manner in the form of the sponge titanium by the Kroll method.
[0009] With reference to the Ti production methods except for the
Kroll method, for example, U.S. Pat. No. 2,205,854 describes that,
in addition to Mg, for example, Ca can be used as the reducing
agent of TiCl.sub.4. U.S. Pat. No. 4,820,339 describes a method for
producing Ti through the reducing reaction by Ca, in which the
molten salt of CaCl.sub.2 is held in the reactor vessel, the
metallic Ca powder is supplied into the molten salt from above, Ca
is dissolved in the molten salt, and the TiCl.sub.4 gas is supplied
from below to react the dissolved Ca with TiCl.sub.4 in the molten
salt of CaCl.sub.2.
[0010] In the reduction by Ca, the metallic Ti is generated from
TiCl.sub.4 by the reaction of the following chemical formula (1),
and CaCl.sub.2 which is of the by-product is also generated at the
same time. Ca has a stronger affinity for Cl than Mg has, and Ca is
suitable for the reducing agent of TiCl.sub.4 in principle.
Particularly, in the method described in U.S. Pat. No. 4,820,339,
Ca is used while dissolved in the molten CaCl.sub.2. When the
reducing reaction by Ca is utilized in the molten CaCl.sub.2, a
reaction field is enlarged compared with the Kroll method in which
TiCl.sub.4 is supplied to the liquid surface of the reducing agent
in the reactor vessel. Therefore, because the exothermic area is
also enlarged to facilitate the cooling, the feed rate of
TiCl.sub.4 which is of the raw material of Ti can be largely
increased, and the remarkable improvement of the productivity can
be also expected. TiCl.sub.4+2Ca.fwdarw.Ti+2CaCl.sub.2 (1)
[0011] However, it is difficult that the method described in U.S.
Pat. No. 4,820,339 is adopted as the industrial Ti production
method. This is because the highly expensive metallic Ca powder is
used in order to dissolve Ca in the molten salt of CaCl.sub.2. That
is, since the production cost is higher than that of the Kroll
method in which the feed rate of TiCl.sub.4 is restricted. In
addition, the highly reactive Ca is extremely difficult to handle,
which can also be the factor of blocking the industrial application
of the method for producing Ti through the reduction by Ca.
[0012] An example of other Ti production methods includes an Olsen
method described in U.S. Pat. No. 2,845,386. The Olsen method is a
kind of oxide direct-reduction method for directly reducing
TiO.sub.2 by Ca, in which TiO.sub.2 is directly reduced by Ca not
through TiCl.sub.4. Although the oxide direct-reduction method is
highly efficient, the oxide direct-reduction method is not suitable
for the production of the high-purity Ti because it is necessary to
use expensive high-purity TiO.sub.2.
DISCLOSURE OF THE INVENTION
[0013] It is an object of the present invention to provide a method
for economically producing a high-purity metallic Ti or a
high-purity Ti alloys with high efficiency without using an
expensive reducing agent.
[0014] In order to achieve the above object, the present inventors
consider that the reduction of TiCl.sub.4 by Ca is indispensable,
and the present inventors propose utilization of Ca dissolved in
the molten salt of CaCl.sub.2 as described in U.S. Pat. No.
4,820,339.
[0015] In the case where Ti is produced by the Ca reduction, Ca in
the molten salt is consumed as the reaction expressed by the
chemical formula (1) proceeds in the reducing reactor vessel, and
it is necessary to continuously supply the metallic Ca powder to
the reducing reactor vessel in the method described in U.S. Pat.
No. 4,820,339.
[0016] In order to industrially establish the method for producing
Ti through reduction by Ca, the present inventors focus on a
reversible reaction shown in chemical formulas (2) and (3) as means
for replenishing Ca in consideration of the fact that it is
necessary that the Ca consumed by the reducing reaction is
economically replenished into the molten salt.
2Na+CaCl.sub.2.fwdarw.Ca+2NaCl (T.ltoreq.600.degree. C.) (2)
Ca+2NaCl.fwdarw.2Na+CaCl.sub.2(T>600.degree. C.) (3)
[0017] A Hunter method in which TiCl.sub.4 is reduced by Na can be
cited as an example of the Ti production method in which the
reduction is utilized. Na and NaCl have low reactivity, and Na and
NaCl are easy to handle compared with Ca and CaCl.sub.2, so that
the NaCl electrolysis and the Na electrolytic production utilizing
the NaCl electrolysis has already industrially been established.
However, in the Hunter method in which Na reduction is used, the
chlorides of bivalent and trivalent Ti are generated by the Na
reduction. The chlorides of bivalent and trivalent Ti decrease
generation efficiency. In addition, because the chlorides of
bivalent and trivalent Ti are dissolved in the molten salt, when
the molten salt is reused in the electrolysis, the oxidation and
reducing reactions are generated between the chlorides of bivalent
and trivalent Ti to largely decrease the generation efficiency
(current efficiency) of Na. Therefore, it is difficult to directly
reduce TiCl.sub.4 by Na, and it is necessary to perform
multi-process treatment, so that Ti is hardly produced at low
cost.
[0018] The present inventors found that the reversible reaction
expressed by the chemical formulas (2) and (3) when the metallic Na
is mixed with CaCl.sub.2. The utilization of this phenomenon
enables the direct reduction of TiCl.sub.4 by Ca without generating
the chlorides of bivalent and trivalent Ti.
[0019] The detail will be described below. That is, in the method
for producing the metallic Ti through the reduction by Ca,
basically CaCl.sub.2 having a melting point of 780.degree. C. is
used as the molten salt. However, like a binary system molten salt
such as CaCl.sub.2--NaCl and CaCl.sub.2--KCl and a ternary system
molten salt such as CaCl.sub.2--NaCl--KCl, at least one of NaCl,
KCl, LiCl, and CaF.sub.2 is mixed into CaCl.sub.2 to form a
multi-system molten salt, which allows the melting point of the
salt to be lowered to decrease the temperature of the molten salt.
As a result, the burden of a reactor material can be reduced to
achieve the cost reduction of the reactor material, and the
vaporization of Ca or salt can also be suppressed from the liquid
surface.
[0020] The mixed molten salt in which NaCl is added to CaCl.sub.2
is particularly distinctive among the multi-system molten salts.
FIG. 2 shows a relationship between a mixture ratio and a melting
point in a binary system molten salt of CaCl.sub.2 and NaCl. The
melting point of CaCl.sub.2 is singly about 780.degree. C., while
the melting point of NaCl is singly over 800.degree. C. However,
when CaCl.sub.2 and NaCl are mixed together, the melting point is
decreased to about 500.degree. C. at the minimum. The melting point
of mixed salt becomes not more than 600.degree. C. when the mixture
ratio of NaCl ranges from about 20% to 45%.
[0021] In the multi-system mixed molten salt such as
CaCl.sub.2--NaCl and CaCl.sub.2--NaCl--KCl containing CaCl.sub.2
and NaCl, as shown in the chemical formulas (2) and (3), Ca
substitutes for the saturated metal at temperatures of not more
than 600.degree. C. while the saturated metal exists as Na at
molten salt temperatures of more than 600.degree. C. When Na is
charged in the CaCl.sub.2 containing molten salt having temperature
of not more than 600.degree. C., Na substitutes Ca to form the
molten salt in which Ca is dispersed in CaCl.sub.2. Then, when the
TiCl.sub.4 is supplied into the molten salt, TiCl.sub.4 is
subjected to the reducing process by the dissolved Ca.
[0022] Thus, when Na is added to the CaCl.sub.2 containing molten
salt which is kept at the temperatures of not more than 600.degree.
C., the highly reactive molten salt in which Ca is dissolved in
CaCl.sub.2 is generated without directly handling the highly
reactive Ca, which allows TiCl.sub.4 to be directly reduced by Ca
without generating the chlorides of bivalent and trivalent Ti.
[0023] The present invention is developed based on the above
consideration, the present invention is a method for producing Ti
or Ti alloys through reduction by Ca, characterized by including a
Ca generation step by Na introduction, in which Ca is generated by
introducing Na into molten salt containing CaCl.sub.2, the molten
salt being kept at temperatures of not more than 600.degree. C.; a
Ti generation step by a reducing reaction, in which Ti or the Ti
alloy is generated in the molten salt by supplying metallic
chloride containing TiCl.sub.4 into the molten salt to cause the
metallic chloride to react with Ca generated in the molten salt;
and a Ti separation step in which the Ti or Ti alloy generated in
the molten salt is separated from the molten salt.
[0024] In the method of the present invention for producing Ti or
Ti alloys through reduction by Ca, for example, the molten
CaCl.sub.2 which is of the molten salt is held in the reactor cell.
However, for example, a mixed molten salt with NaCl is used as the
molten salt such that the melting point becomes not more than
600.degree. C. (see FIG. 2). When Na is charged into the molten
salt (kept at temperatures of not more than 600.degree. C.), Na
substitutes for Ca, and Ca is dissolved in the molten salt
(CaCl.sub.2) unlike Na. In this state of things, for example, when
TiCl.sub.4 is supplied to the molten salt, TiCl.sub.4 is reduced by
Ca dissolved in the molten salt, and powdery and/or particulate
metallic Ti (hereinafter collectively referred to as Ti particles).
The generated metallic Ti is separated from the molten salt to
perform the direct reduction by Ca without generating the chlorides
of bivalent and trivalent Ti.
[0025] Thus, the metallic Ti can extremely economically and
efficiently be produced by the reduction not only without
replenishing the metallic Ca but without solely handling Ca.
[0026] Further, in generating the Ti particles through the
reduction by Ca in the molten salt, the reducing reaction field is
widened and the heat generation area is simultaneously widened. Mg
has vapor pressure of 6.7 kPa (50 mmHg) at 850.degree. C. while Ca
has extremely small vapor pressure of 0.3 kPa (2 mmHg). Therefore,
in the case where Ca is used for the reduction, the Ti
precipitation amount becomes dramatically lessened in the inner
surface of the upper portion of the reactor cell when compared with
the use of Mg. Accordingly, in the method of the present invention
for producing Ti or Ti alloys through reduction by Ca, the feed
rate of TiCl.sub.4 can largely be increased.
[0027] In addition, Ca is inferior in wetting properties (adhesion
properties) to Mg, and Ca adhering to the precipitated Ti particles
is dissolved in CaCl.sub.2, so that the aggregation in the
generated titanium particles and the sintering are significantly
lessened. Therefore, the generated Ti can be taken out in the
particulate state from the reactor vessel, and the Ti production
can continuously be operated.
[0028] In the method of the present invention for producing Ti or
Ti alloys through reduction by Ca, the Ca generation by the Na
introduction and the Ti generation by the reducing reaction can be
performed in the same reactor cell. Therefore, an equipment
configuration is simplified to further improve economic
efficiency.
[0029] Na used for the Ca generation can be generated by
electrolysis (electrolytic step) of the molten salt containing
NaCl. The Na electrolytic production is a technology which has been
already established, and the Na electrolytic production has the
excellent economic efficiency. Accordingly, when the molten salt
which is already used for the Ti generation is introduced to the
electrolytic step (for example, molten salt separated from the
generated Ti), the Ca supply source such as the molten salt
(CaCl.sub.2) and Na can be circulated to economically produce Ti or
the Ti alloys.
[0030] In the Na electrolytic production (electrolytic step), Na is
generated by the reaction shown in chemical formulas (4) and (5).
2Cl.sup.-.fwdarw.2e.sup.-+Cl.sub.2 (anode electrode) (4)
Na.sup.++2e.sup.-.fwdarw.2Na (cathode.sup.-electrode) (5)
[0031] In the electrolytic step, it should be considered that Na is
generated while the temperature of the molten salt is held at more
than 600.degree. C. When the temperature of the molten salt is held
not more than 600.degree. C. in the electrolytic step, Ca is
generated. In the electrolytic step, it should also be considered
that the back reaction is prevented. In the back reaction, Na
generated on the cathode electrode side or the unreacted mixed Na
combines with Cl.sub.2 generated on the anode electrode side to
thereby return to NaCl. When the back reaction is generated,
current efficiency is decreased because electrolytic current is
consumed for the back reaction.
[0032] It is effective that a membrane is provided to partition the
electrolytic cell into the anode electrode side and the cathode
electrode side for preventing the back reaction in which Na
generated on the cathode electrode side combines with Cl.sub.2
generated on the anode electrode side to thereby return to NaCl.
The membrane permits the molten salt to be circulated in the
electrolytic cell while blocking the movement of Na generated on
the cathode electrode side to the anode electrode side. It is
effective to combine the membrane with a unidirectional flow of the
molten salt from the anode electrode side toward the cathode
electrode side in the reactor cell.
[0033] In the case where the molten salt which is already used for
the Ti generation is introduced to the electrolytic step, there is
a fear that the unreacted Ca contained in the molten salt is mixed
into the electrolytic step. When the unreacted Ca is mixed in the
electrolytic step (more than 600.degree. C.), Ca returns to Na to
generate the back reaction in which Na combines with Cl.sub.2
generated on the anode electrode side to return to NaCl. For a
measure against the back reaction, it is effective that the
temperature of the molten salt which is already used for the Ti
generation is temporarily raised to more than 600.degree. C.
outside the electrolytic cell before the molten salt is introduced
to the electrolytic cell. Therefore, in the unreacted dissolved
metal in the molten salt, Ca which is dissolved in the molten salt
is replaced by Na which is hardly dissolved in the molten salt, and
Na can be separated and removed. Then, the molten salt is
introduced to the electrolytic cell after Na is separated and
removed, which prevents the mixture of the unreacted Na and the
back reaction caused by the unreacted Na.
[0034] In the electrolytic step, the molten salt temperature is
also held at more than 600.degree. C., so that the economic
efficiency does not particularly become worsened even if the molten
salt is heated to the temperature of more than 600.degree. C. in
the Na separation step.
[0035] For a supply mode of TiCl.sub.4 to the molten salt, it is
particularly preferable that TiCl.sub.4 be directly supplied in the
gas state to the molten salt because of high contact efficiency of
TiCl.sub.4 with Ca in the molten salt. It is also possible that a
TiCl.sub.4 liquid is supplied to the molten salt, and it is also
possible that the liquid or gaseous TiCl.sub.4 is supplied to the
liquid surface of the molten salt.
[0036] Furthermore, for the supply of TiCl.sub.4, in the method for
reducing TiCl.sub.4 by Ca, there are various advantages compared
with the Kroll method in which the reduction is performed by
Mg.
[0037] In the Kroll method in which the reduction is performed by
Mg, the TiCl.sub.4 liquid is supplied to the liquid surface of the
molten Mg solution. Conventionally it is tried that the TiCl.sub.4
gas is supplied into the molten Mg solution in order to enlarge a
reaction field. However, as described above, since the Mg has the
large vapor pressure, Mg vapor intrudes in a supply nozzle to react
with TiCl.sub.4, and a supply pipe is choked. The problem of nozzle
choking still remains even if the TiCl.sub.4 gas is supplied deep
into the molten salt. This is attributed to the fact that the melt
is agitated by bubbling of TiCl.sub.4 and sometimes the molten Mg
reaches the supply nozzle, although a choking frequency of the
supply pipe is decreased. As much as anything, even if TiCl.sub.4
is supplied to the molten salt, the Ti precipitation reaction is
difficult to occur because Mg is not dissolved in the molten
salt.
[0038] On the contrary, in the method of reducing TiCl.sub.4 by Ca,
the nozzle choking is hardly generated when the TiCl.sub.4 gas is
supplied into the molten salt. Therefore, the TiCl.sub.4 gas can be
supplied into the molten salt. One of the reasons why the nozzle
choking is hardly generated is that the molten Ca has the small
vapor pressure.
[0039] That is, in the method of the present invention for
producing Ti or the Ti alloys which is of a method for reducing
TiCl.sub.4 by Ca, it is preferable that the gaseous or liquid
TiCl.sub.4 be directly supplied into the molten salt, it is
particularly preferable that TiCl.sub.4 be directly supplied in the
gas state into the molten salt, and this supply mode can be applied
with no problem in the actual operation. It is also possible that
the liquid or gaseous TiCl.sub.4 is supplied to the liquid surface
of the molten salt. The supply mode can also be applied with no
problem.
[0040] In handling the Ti particles generated in the molten salt,
it is also possible that the Ti particles are separated from the
molten salt in the reactor cell. In this case, the production mode
becomes the batch manner. In order to improve the productivity, the
Ti particles and the molten salt can be separated from each other
outside the reactor vessel by utilizing the Ti generated in the
particulate form to discharge the Ti particles outside the reactor
vessel along with the molten salt. The Ti particles can simply be
separated from the molten salt by a squeezing operation by
mechanical compression and the like.
[0041] In handling the Cl.sub.2 generated in the electrolysis, it
is preferable that TiCl.sub.4 be used for the Ti generation
reaction in the reactor vessel by causing Cl.sub.2 to react with C
and TiO.sub.2 to form TiCl.sub.4.
[0042] For the raw material of Ti, basically the TiCl.sub.4 is
used. However, Ti can also be produced by mixing TiCl.sub.4 and
another metallic chloride. Because TiCl.sub.4 and another metallic
chloride are simultaneously reduced by Ca, the Ti alloy particles
can be produced by this method.
[0043] For a size of the generated Ti or Ti alloy, it is preferable
that an average particle size ranges from 0.5 to 50 .mu.m. This is
because that the generated Ti or Ti alloy having the average
particle size of 0.5 to 50 .mu.m can flow along with the molten
salt and be easily taken out from the reactor cell. When the
average particle size is lower than 0.5 .mu.m, it is difficult to
separate the molten salt and Ti or the Ti alloy. When the average
particle size is more than 50 .mu.m, it is difficult to take out Ti
or the Ti alloy and the molten salt from the reactor vessel.
[0044] In order to generate Ti or the Ti alloy having the average
particle size of 0.5 to 50 .mu.m, it is effective to manage Ca
concentration to be not lower than 0.01% in the molten salt used in
the Ti generation step. When the Ca concentration is lower than
0.01%, Ti is not generated but chlorides of a divalent or trivalent
Ti are generated, which decreases the Ti generation efficiency. An
upper limit of the Ca concentration is determined according to the
molten salt composition and temperature. It is particularly
preferable that the Ca concentration range be not lower than 0.3%.
When the Ca concentration is not lower than 0.3%, even if the Ca
concentration is locally decreased, Ti is stably generated and the
decrease in Ti generation efficiency caused by the chlorides of
divalent or trivalent Ti does not take place.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a block diagram showing Ti metals production
apparatus according to an example of the present invention; and
[0046] FIG. 2 is a graph showing a relationship between a mixture
ratio and a melting point in a mixed molten salt of CaCl.sub.2 and
NaCl.
BEST MODE FOR CARRYING OUT THE INVENTION
[0047] An example of the present invention will be described below
with reference to the drawings. FIG. 1 is a block diagram showing
Ti metals production apparatus according to an example of the
present invention.
[0048] A reactor cell 1 in which Ti is generated by introducing Na,
a separation cell 2 in which the generated Ti is separated, and an
electrolytic cell 3 in which Na is generated are used in the
example.
[0049] The reactor cell 1 holds a mixed molten salt of CaCl.sub.2
and NaCl, which is of the molten salt. More specifically, in the
mixed molten salt, CaCl.sub.2 and NaCl are mixed together by a
fraction in which a melting point becomes not more than 600.degree.
C., and the reactor cell 1 holds the mixed molten salt at the
temperature ranging from the melting point to 600.degree. C. The
inside of the reactor cell 1 is separated into a Na introduction
side and a raw material introduction side by a partition wall 4
except for a bottom portion.
[0050] In the reactor cell 1, the molten Na is introduced to the Na
introduction side and the gaseous TiCl.sub.4 which is of the Ti raw
material is injected into the molten salt on the raw material
introduction side in a dispersed manner. The molten salt
temperature of not more than 600.degree. C. causes the introduced
Na to react with CaCl.sub.2 in the molten salt to generate Ca
(chemical formula (2)). Ca is dissolved in the molten salt to form
CaCl.sub.2 in which Ca having the high reactivity is dissolved.
[0051] On the raw material introduction side in reactor cell 1, the
particulate metallic Ti is generated by reducing the TiCl.sub.4
supplied to the molten salt with Ca dissolved in the molten salt.
The generated Ti particles moves downward by the specific gravity
difference and accumulated on the bottom on the raw material
introduction side.
[0052] The Ti particles accumulated on the bottom on the raw
material introduction side of the reactor cell 1 are discharged
from the reactor cell 1 along with the molten salt existing on the
bottom of the reactor cell 1, and the Ti particles and the molten
salt are introduced to the separation cell 2. In the separation
cell 2, the Ti particles discharged from the reactor cell 1 along
with the molten salt are separated from the molten salt.
Specifically the Ti particles are compressed to squeeze the molten
salt. The obtained Ti particles are melted to yield a Ti ingot.
[0053] In the separation cell 2, the molten salt temperature is
held at more than 600.degree. C. The molten salt extracted from the
reactor cell 1 is already used, and the molten salt contains some
amount of unreacted Ca although majority of Ca is consumed. When
the molten salt temperature is held at more than 600.degree. C. in
the separation cell 2, the unreacted Ca is replaced by Na which is
hardly dissolved in the molten salt, and Na is separated by Na
floatation on the molten salt (chemical formula (3)).
[0054] The Ti particles and the molten salt in which Na is
separated are introduced to the electrolytic cell 3. In the
electrolytic cell 3, similarly to the separation cell 2, the molten
salt temperature is held at more than 600.degree. C., at which Na
is generated. Therefore, Na is produced by the electrolysis from
NaCl in the molten salt. That is, NaCl in the molten salt is
electrolyzed between an anode electrode 5 and a cathode electrode
6, the Cl.sub.2 gas is generated on the side of the anode electrode
5, and Na is generated on the side of the cathode electrode 6.
[0055] The inside of the electrolytic cell 3 is separated into the
anode electrode side and the cathode electrode side by a membrane
7. The molten salt from the separation cell 2 is introduced to the
anode electrode side in the electrolytic cell 3. The membrane 7
blocks the movement of Na generated on the cathode electrode 6 to
the side of the anode electrode 5 while permitting the molten salt
to flow from the anode electrode side to the cathode electrode
side.
[0056] At this point, when Na is mixed in the molten salt
introduced to the anode electrode side in the electrolytic cell 3,
the back reaction is generated by causing Na to react with the
Cl.sub.2 gas generated on the anode electrode side. However, in the
example, the unreacted Ca in the molten salt and the Ti particles
are removed from the molten salt in the form of Na in the
separation cell 2. Therefore, the back reaction caused by the
mixture of the unreacted Na in the anode electrode side in the
electrolytic cell 3 and the decrease in current efficiency caused
by the back reaction is prevented.
[0057] That is, the separation cell 2 is configured to be used in
both the Ti separation step and the Na separation step, and the
unreacted Ca in the molten salt is previously removed by replacing
the unreacted Ca by Na before the molten salt extracted from the
reactor cell 1 is introduced to the electrolytic cell 3, which
allows the rational and economic operation to be performed. Na
separated from the molten salt in the separation cell 2 is sent
back to the Na introduction side in the reactor cell 1, and returns
to Ca by managing the temperature to be not more than 600.degree.
C., thus enabling to be reused for the reducing reaction.
[0058] On the other hand, the Cl.sub.2 gas generated on the anode
electrode side in the electrolytic cell 3 is sent to a chlorination
step 8. In the chlorination step 8, the chlorination is performed
to TiO.sub.2 with C to generate TiCl.sub.4 which is of the Ti raw
material. The generated TiCl.sub.4 is introduced to the reactor
cell 1, and TiCl.sub.4 is used in a circulating manner to generate
the Ti particles by the Ca reduction. The by-product CO.sub.2 is
discharged to the outside of the system.
[0059] Thus, in the example, the Ti particles are generated by
reducing the molten salt by the dissolved Ca in the reactor cell 1.
Ca consumed in association with the generation of the Ti particles
is replenished into the reactor cell 1 in the form of Na which is
easy to handle. Therefore, it is not necessary that the solid-state
Ca be replenished or taken out, and the high-quality Ti particles
are produced continuously and economically through the Ca
reduction.
[0060] Na is produced by electrolyzing the used molten salt in the
electrolytic cell 3, and Na is used in the circulating manner, so
that Na replenishment is not required from the outside. Accordingly
the method of the present invention is particularly excellent for
the economic efficiency.
[0061] Both the Ti separation and the Na separation are performed
in the separation cell 2 to prevent the mixture of Na in the
electrolytic cell 2, and Na generated on the cathode electrode side
is prevented from flowing in the anode electrode side in the
electrolytic cell 3. Therefore, the back reaction is effectively
prevented in the electrolytic cell 3 to secure the high current
efficiency.
[0062] In the reactor cell 1, the molten salt temperature is held
to be not more than 600.degree. C., so that a reactor material life
can be lengthened to reduce reactor material cost. Because Ca has
the reactivity higher than that of Mg, development of the reactor
material which can withstand Ca for long periods is the important
technological problem in mass production of Ti or the Ti alloys. In
this regard, the operation temperature of the molten salt is
decreased to mitigate the impact on the reactor material by the low
temperature reduction process with the temperature of not more than
600.degree. C., so that the present invention largely contributes
to the solution of the problem of the reactor material life.
[0063] The molten salt temperature in the separation cell 2 is
equalized to the temperature of the reactor cell 1 which is not
more than 600.degree. C.
[0064] In the case where the molten salt temperature is controlled
to be more than 600.degree. C. in the separation cell 2 and the
electrolytic cell 3, it is desirable that the upper limit of the
molten salt temperature be not more than 800.degree. C. from the
viewpoints of thermal efficiency and reactor material durability.
On the other hand, in the case where the molten salt temperature is
managed to be not more than 600.degree. C., the lower limit of the
molten salt temperature is the melting point of the salt to be
used, and it is particularly preferable that the molten salt
temperature be set at the melting point+20.degree. C. in
consideration of existence of a temperature variation in the
cell.
INDUSTRIAL APPLICABILITY
[0065] The method for producing Ti or the Ti alloys through the
reduction by Ca according to the present invention is the method
for reducing TiCl.sub.4, so that the high-purity Ti metals or Ti
alloys can be produced. Ca is used as the reducing agent, and the
metallic chloride containing TiCl.sub.4 which is of the Ti raw
material is caused to react with Ca in the molten salt in which
CaCl.sub.2 is contained and Ca is dissolved. Therefore, the feed
rate of TiCl.sub.4 can be increased. The Ti particles or the Ti
alloy particles can be generated in the molten CaCl.sub.2 solution,
so that the continuous production can be performed. Ca is generated
from Na which is easy to handle and Ca is dissolved in the molten
salt, so that it is not necessary to replenish the expensive
metallic Ca or it is not necessary to handle the single Ca which is
difficult to handle due to the strong reactivity. Accordingly, the
method for producing Ti or the Ti alloys according to the present
invention can effectively be utilized as means for efficiently and
economically producing the high-purity Ti metals or Ti alloys.
* * * * *