U.S. patent application number 11/887511 was filed with the patent office on 2009-04-23 for method for producing ti or ti alloy, and pulling electrolysis method applicable thereto.
Invention is credited to Masahiko Hori, Tadashi Ogasawara, Kazuo Takemura, Makoto Yamaguchi.
Application Number | 20090101517 11/887511 |
Document ID | / |
Family ID | 37053205 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090101517 |
Kind Code |
A1 |
Takemura; Kazuo ; et
al. |
April 23, 2009 |
Method for Producing Ti or Ti Alloy, and Pulling Electrolysis
Method Applicable Thereto
Abstract
In producing Ti or a Ti alloy through reduction by Ca, an
electrolytic-bath salt taken out from a reduction process is
electrolyzed to recover Ca and the electrolytic-bath salt as a
solid substance, and the recovered Ca and electrolytic-bath salt
are delivered to the reduction process. Therefore, heat generation
is suppressed in the reduction process by utilizing latent heat of
fusion possessed by the solid substance, thereby largely improving
production efficiency and thermal efficiency. Additionally, a
reaction temperature is easily controlled, and a raw-material
loading rate can be enhanced to efficiently produce Ti or the Ti
alloy. At this point, using a pulling electrolysis method of the
invention, the solid-state Ca and electrolytic-bath salt can be
obtained at a low voltage and high current efficiency, i.e., with
the relatively small power consumption. When the solid-state Ca and
electrolytic-bath salt is used as a Ca source in producing Ti or
the Ti alloy through reduction by Ca, the Ti or Ti alloy can
efficiently be produced.
Inventors: |
Takemura; Kazuo; (Hyogo,
JP) ; Ogasawara; Tadashi; (Hyogo, JP) ;
Yamaguchi; Makoto; (Hyogo, JP) ; Hori; Masahiko;
(Hyogo, JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
37053205 |
Appl. No.: |
11/887511 |
Filed: |
March 16, 2006 |
PCT Filed: |
March 16, 2006 |
PCT NO: |
PCT/JP2006/305227 |
371 Date: |
September 28, 2007 |
Current U.S.
Class: |
205/557 ;
205/560 |
Current CPC
Class: |
C22B 34/129 20130101;
C25C 3/02 20130101; C22B 5/04 20130101; C22B 34/1268 20130101; C25C
3/28 20130101; C25C 3/26 20130101; C25C 7/00 20130101; C25C 5/04
20130101 |
Class at
Publication: |
205/557 ;
205/560 |
International
Class: |
C25C 1/24 20060101
C25C001/24; C25C 1/06 20060101 C25C001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2005 |
JP |
2005-094205 |
Mar 30, 2005 |
JP |
2005-096690 |
Claims
1. A method of producing Ti or a Ti alloy going through a reduction
process in which a metallic chloride containing TiCl.sub.4 is
caused to react with Ca in a Ca-containing electrolytic-bath salt
to generate Ti or the Ti alloy in the electrolytic-bath salt, the
method comprising feeding the solid-state Ca and electrolytic-bath
salt to the reduction process.
2. The Ti or Ti alloy production method according to claim 1,
wherein a Ca-containing electrolytic-bath salt containing
CaCl.sub.2 is used as the Ca-containing electrolytic-bath salt.
3. A Ti or Ti alloy production method including a reduction process
in which a metallic chloride containing TiCl.sub.4 is caused to
react with Ca in a Ca-containing electrolytic-bath salt to generate
Ti or the Ti alloy in the electrolytic-bath salt and an
electrolysis process in which Ca is generated by electrolyzing the
electrolytic-bath salt taken out from the reduction process, the
method comprising: recovering a solid substance containing Ca and
the electrolytic-bath salt in the electrolysis process; and
delivering the solid substance to the reduction process.
4. The Ti or Ti alloy production method according to claim 3,
wherein the recovery of the solid substance containing Ca and the
electrolytic-bath salt is performed by pulling a cathode while the
solid substance is caused to adhere to and solidified in a cathode
surface.
5. The Ti or Ti alloy production method according to claim 3,
wherein a Ca-containing electrolytic-bath salt containing
CaCl.sub.2 is used as the Ca-containing electrolytic-bath salt.
6. The Ti or Ti alloy production method according to claim 4,
wherein a Ca-containing electrolytic-bath salt containing
CaCl.sub.2 is used as the Ca-containing electrolytic-bath salt.
7. A pulling electrolysis method of recovering a solid-state Ca
using a Ca-containing electrolytic-bath salt, the method
comprising: electrolyzing an electrolytic-bath salt at a bath
temperature of 680 to 900.degree. C., a cathode current density of
0.1 to 200 A/cm.sup.2, and a voltage of 10V or less; and recovering
Ca and the electrolytic-bath salt in a solid state by pulling a
cathode at a pulling rate of 0.05 cm/min or more while a solid
substance is caused to adhere to and solidified in a cathode
surface.
8. The pulling electrolysis method according to claim 7, wherein
the pulling rate satisfies a following equation (1):
V.gtoreq.0.0035.times.t-2.4 (1) where V: cathode pulling rate
(cm/min), and t: bath temperature (.degree. C.).
9. The pulling electrolysis method according to claim 7, wherein a
Ca-containing electrolytic-bath salt containing CaCl.sub.2 is used
as the Ca-containing electrolytic-bath salt.
10. A pulling electrolysis method including a reduction process in
which a metallic chloride containing TiCl.sub.4 is caused to react
with Ca in a Ca-containing electrolytic-bath salt to generate Ti or
the Ti alloy in the electrolytic-bath salt and an electrolysis
process in which Ca is generated by electrolyzing the
electrolytic-bath salt taken out from the reduction process, the Ca
being recovered from the Ca-containing electrolytic-bath salt in
the electrolysis process, the method comprising: electrolyzing an
electrolytic-bath salt at a bath temperature of 680 to 900.degree.
C., a cathode current density of 0.1 to 200 A/cm.sup.2, and a
voltage of 10V or less; and recovering Ca and the electrolytic-bath
salt in a solid state by pulling a cathode at a pulling rate of
0.05 cm/min or more while a solid substance is caused to adhere to
and solidified in a cathode surface.
11. The pulling electrolysis method according to claim 10, wherein
the pulling rate satisfies a following equation (1):
V.gtoreq.0.0035.times.t-2.4 (1) where V: cathode pulling rate
(cm/min), and t: bath temperature (.degree. C.).
12. The pulling electrolysis method according to claim 10, wherein
a Ca-containing electrolytic-bath salt containing CaCl.sub.2 is
used as the Ca-containing electrolytic-bath salt.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for efficiently
producing Ti or a Ti alloy at low costs and a pulling electrolysis
method in which Ca applicable to reduce Ti and other hard-to-reduce
metals can be obtained as a solid-state Ca and an electrolytic-bath
salt.
BACKGROUND ART
[0002] Metals such as Ti, Zr, Ta, Hf, and V each is a useful metal
having excellent properties. These metals are hard to be reduced
and it is necessary to separate coexisting homologous elements and
impurities. Therefore, usually oxides or halides thereof are formed
after the metals are refined through many processing steps, and the
metals are produced by reducing the oxides or halides with a metal
such as Mg and Na having strong reduction power.
[0003] Among others, a metallic Ti and a Ti alloy are excellent in
corrosion resistance and design, and further light in weight and
excellent in mechanical properties. Therefore, the metallic Ti and
Ti alloy are widely used as aircraft materials, heat exchanger
materials, chemical plant materials, roof materials, golf-club
heads, and the like. Particularly, in recent years, the metallic Ti
and Ti alloy are used in instruments of medical fields because of a
nontoxic metal for a human body, and the application of the
metallic Ti and Ti alloy is being increased.
[0004] However, because the metallic Ti is difficult to smelt, the
metallic Ti is extremely expensive as a metal, development of a
method of producing the metallic Ti with high productivity at low
costs is demanded in an industrial scale. That is, in the
conventional metallic Ti smelting method, titanium tetrachloride
(TiCl.sub.4) is reduced to obtain the metallic Ti by the metal such
as Mg and Na having the strong reduction power (reducing metal).
However, in the conventional method, because the production is
performed in a batch manner, there is a problem in that the
improvement in productivity is limited.
[0005] For example, in a Kroll process which is of a typical method
of industrially producing the metallic Ti, molten Mg is loaded in a
reactor vessel, a TiCl.sub.4 liquid is fed from above a liquid
surface thereof, and the metallic Ti is produced by reducing
TiCl.sub.4 with Mg near the liquid surface of the molten Mg.
However, in the Kroll method, a feed rate of TiCl.sub.4 is
restricted because the reaction is generated near the liquid
surface of the molten Mg in the reactor vessel.
[0006] Additionally, Ti granules produced are aggregated because of
an adhesion property between Ti and the molten Mg, and the Ti
granules are sintered to grow in sizes by the heat of the molten
liquid. Consequently, it is difficult to take out the produced Ti
to the outside of the reactor vessel, it is also difficult to
continuously produce Ti, the improvement in productivity is limited
to thereby increase production costs, and a product price becomes
extremely high.
[0007] Therefore, various researches and developments have been
conducted on the Ti production method except for the Kroll process.
For example, U.S. Pat. No. 2,205,854 discloses that Ca can be used
as a reducing agent for TiCl.sub.4 in addition to Mg. Ca has a
stronger affinity for Cl than that of Mg, and Ca is suitable in
principle for the reducing agent for TiCl.sub.4. However, the
metallic Ti production method in which TiCl.sub.4 is reduced with
Ca is not put to practical use yet. This is because that CaCl.sub.2
is hardly electrolyzed.
[0008] Another Ti production method includes an Olson process
disclosed in U.S. Pat. No. 2,845,386. The Olson process is a kind
of oxide direct-reduction process in which TiO.sub.2 is directly
reduced by Ca without going the route of TiCl.sub.4. Although the
oxide direct-reduction process has high efficiency, the oxide
direct-reduction process is not suitable for the high-purity Ti
production at low costs. This is because it is necessary to use
expensive high-purity TiO.sub.2.
[0009] That is, in the Ti production methods disclosed in U.S. Pat.
Nos. 2,205,854 and 2,845,386, unfortunately it is not easy to
refine Ca, and it is difficult to handle Ca because it is easily
oxidized. Additionally, in the oxide direct-reduction process,
there is the problem in that it is necessary to use the expensive
high-purity TiO.sub.2. Therefore, the Ti production methods
disclosed in U.S. Pat. Nos. 2,205,854 and 2,845,386 are not put to
practical use yet.
[0010] However, Ca has the stronger affinity for Cl than that of
Mg, and Ca is suitable in principle for the reducing agent for
TiCl.sub.4. When Ca is obtained at low costs, Ca can be used as the
reducing agent for Ti and hard-to-reduce metals such as Zr and Hf,
and further Ta and V, any of which is caused to form chloride and
then reduced by Mg, thus proving to be industrially-useful.
[0011] Currently, the metallic Ca is mainly produced by a
vaporization reducing method using a carbonated salt as a raw
material. However, a Germany technical document ("HANDBUCH DER
TECHNISCHEN ELEKTRO CHEMIE" DRITTER BAND (1934) p. 128 to p. 164
"Calcium, Strontium, Barium." Von Dr. V. Makow) reports that, in
early stage in which the metallic Ca was industrially produced, the
molten CaCl.sub.2 was electrolyzed and Ca was produced by
separating the attached salt by re-melting.
[0012] However, a voltage becomes extremely high during the
electrolysis in the Ca production by the electrolysis of the molten
CaCl.sub.2, described in the Germany technical reference.
Therefore, it can be predicted that the required electric power
(current.times.voltage) becomes large, huge electric energies are
consumed, and the production costs are increased.
DISCLOSURE OF THE INVENTION
[0013] In view of the foregoing, a first object of the invention is
to provide a method of producing Ti or the Ti alloy through
reduction by Ca, particularly a method of efficiently producing Ti
or the Ti alloy at low costs. A second object of the invention is
to provide a pulling electrolysis method in which Ca applicable for
reducing Ti can be obtained at low electrolytic bath voltage and
high current efficiency in order to be applied to the method of
producing the hard-to-reduce metal, particularly Ti or the Ti
alloy.
[0014] The inventors focus on and study the method of reducing
TiCl.sub.4 by Ca in order to solve the above problems. As a result
of the study, the inventors establish a method (hereinafter the
method is referred to as "the method of producing Ti or the Ti
alloy through reduction by Ca" with inclusion of various examples),
wherein the CaCl.sub.2-containing molten salt in which Ca is
dissolved is retained in the reactor vessel, the metallic chloride
containing TiCl.sub.4 is caused to react with Ca in the molten salt
to generate Ti granules or Ti alloy granules in the molten salt,
and the Ti granules or Ti alloy granules generated in the molten
salt are separated and recovered from the molten salt, whereby
continuously producing Ti or the Ti alloy. Additionally, the
inventors propose a pulling electrolysis method enabling to obtain
a solid-state Ca applicable to the method. The development
background and the obtained findings will be described for each
method while the one is "the method of producing Ti or the Ti alloy
through reduction by Ca" and the other is "the pulling electrolysis
method".
[0015] (Method of Producing Ti or Ti Alloy Through Reduction by
Ca)
[0016] In the method of producing Ti or the Ti alloy through
reduction by Ca, CaCl.sub.2 which is of a by-product in association
with the Ti generation is taken out to the outside of the reactor
vessel and electrolyzed, and the generated Ca can be used in the
reaction for generating the metal such as Ti in the reactor vessel.
In this case, one of large advantages of the method is in that
rigorous separation of Ca and CaCl.sub.2 is not required.
[0017] According to the method of producing Ti or the Ti alloy
through reduction by Ca, the Ti generation reaction proceeds in the
molten CaCl.sub.2. Accordingly, compared with the Kroll process in
which the reaction field is limited to the proximity of the liquid
surface because TiCl.sub.4 is fed to a liquid surface of the
reducing agent (Mg) in the reactor vessel, the reaction field is
enlarged and the heat generation region is also spread to easily
perform the cooling, so that the method holds promise of largely
enhancing a feed rate of TiCl.sub.4 which is of the raw material
for Ti to largely improve productivity.
[0018] However, because the reaction of Ca and TiCl.sub.4 in the
molten CaCl.sub.2 is an exothermic reaction, in order to maintain
the high productivity, it is necessary to cool the heat generation
region to dissipate the heat. Therefore, the production efficiency
is lowered and the thermal efficiency is also lowered because of
the large heat loss.
[0019] In the case where the heat rapidly generated due to the
excessive TiCl.sub.4 feed rate exceeds the cooling capacity, the
reaction field (region where the reaction of Ca and TiCl.sub.4 is
generated) gets to an excessively high temperature and the reactor
vessel is severely worn. On the contrary, when the temperature is
excessively lowered, the reaction rate is decreased. Therefore, in
the TiCl.sub.4 reduction process, it is necessary to finely control
the temperature to maintain the high productivity.
[0020] In order to solve the problem, the inventors further study
measures to overcome the difficulty in the reaction-field
temperature control while suppressing the decrease in production
efficiency and energy loss caused by repetition of the heat
generation and heat dissipation as much as possible. As a result,
the inventors have an idea in which the molten CaCl.sub.2 solution
is electrolyzed while taken out from the reactor vessel and the
generated Ca is not returned into the reactor vessel along with the
molten CaCl.sub.2 solution (i.e., as the CaCl.sub.2 solution whose
Ca concentration is increased), but Ca and the molten CaCl.sub.2
solution are recovered in the form of the solid substance and the
solid substance is returned to the reduction process.
[0021] The realization of the method can absorb the heat generated
by the reaction of Ca and TiCl.sub.4 by utilizing latent heat of
fusion possessed by the solid substance containing Ca and
CaCl.sub.2. Therefore, the thermal efficiency is largely improved,
the reaction temperature is easily controlled, and the method of
producing Ti or the Ti alloy through reduction by Ca can be
performed further efficiently.
[0022] The Germany technical reference reports that a rod-shape Ca
is obtained by the electrolysis of the molten CaCl.sub.2.
[0023] FIG. 1 is a view showing a schematic configuration of a main
part of a calcium furnace for producing Ca by the electrolysis of
the molten CaCl.sub.2, disclosed in the Germany technical document.
In the calcium furnace (electrolytic apparatus) having the
schematic configuration shown in FIG. 1, a calcium chloride
(CaCl.sub.2) 16 which is of an electrolyte is loaded in a graphite
crucible 15 (cooled steel vessel coated with a graphite plate), and
is melted and heated. A part of the electrolyte is solidified to
form a solidified electrolyte 20 by cooling in a bottom portion and
an inner wall portion of the crucible 15.
[0024] Then, electricity is turned on between an anode (positive
electrode) 17 and a cathode (negative electrode) 18 to perform the
electrolysis. At this point, the cathode 18 is pulled such that
variations in current and voltage are decreased according to a
degree of depositing Ca on the cathode 18, and Ca 19 is grown in a
rod shape. Because the solidified salt adheres to the surface of
the calcium rod, the solidified salt is re-melted and separated in
the calcium chloride. The Germany technical reference reports that,
during the electrolysis, a cathode current density is set to 125
A/cm.sup.2, the voltage ranges from 35 to 40V, and purity of the
re-melted metallic Ca ranges from 98 to 99%.
[0025] Although Ca is generated by the electrolysis in the Germany
technical reference, the inventors perform experiments and studies
on the recovery of the solid substance containing Ca and the
electrolytic-bath salt (CaCl.sub.2 is used) in the electrolysis
process. As a result, the inventors obtain the following findings:
Ca generated by the electrolysis is deposited on the cathode
surface by gradually pulling the cathode during the electrolysis,
and a phenomenon in which CaCl.sub.2 adheres as solidified
substance near the deposited Ca is repeatedly generated to obtain
the solid substance in which the Ca and the electrolytic-bath salt
are mixed.
[0026] (Pulling Electrolysis Method)
[0027] In order to develop a pulling electrolysis method of being
able to obtain the hard-to-reduce metal, particularly Ca usable in
the Ti reduction, the inventors conducts comprehensive study for
finding an electrolysis condition that, using the electrolytic-bath
salt containing CaCl.sub.2, the tank voltage (hereinafter simply
referred to as "voltage") is decreased while the high current
efficiency (i.e., high Ca recovery efficiency) is obtained during
the electrolysis. As a result, the inventors obtain the following
findings for the bath temperature, the cathode current density
(hereinafter referred to as "cathode current density" or simply
"current density"), and the cathode pulling rate.
[0028] (a) Because the voltage is increased when the cathode
current density is increased, in order to decrease the voltage, the
cathode and the anode are brought close to each other to shorten a
distance between the electrodes (inter-electrode distance), whereby
decreasing the current efficiency. On the contrary, when the
inter-electrode distance is lengthened, the current efficiency is
improved while the voltage is increased. That is, it is difficult
to balance the decrease in voltage with the improvement of the
current efficiency.
[0029] (b) When the electrodes are brought close to each other to
decrease the voltage while the current density is set within a
predetermined range (0.1 to 200 A/cm.sup.2), the inter-electrode
distance becomes not more than 7 cm and the voltage becomes not
more than 10V.
[0030] (c) When the cathode pulling rate is enhanced while the
condition (b) is satisfied, the current efficiency is increased.
This effect is observed when the pulling rate is not less than 0.05
cm/min. The solid-state "Ca and electrolytic-bath salt" containing
Ca generated (deposited) by the electrolysis and the
electrolytic-bath salt which adheres to the surface of Ca and is
solidified is recovered by pulling the cathode.
[0031] (d) When the bath temperature is raised under the condition
(c), a Ca concentration in the recovered Ca and electrolytic-bath
salt is increased. In the case of the high-temperature
electrolytic-bath salt, although the current efficiency is slightly
decreased, the current efficiency is increased by enhancing the
cathode pulling rate. The super current efficiency is obtained in
the case where the pulling rate satisfies the following equation
(1):
V.gtoreq.0.0035.times.t-2.4 (1)
[0032] where V: cathode pulling rate (cm/min), and
[0033] t: bath temperature (.degree. C.).
[0034] The following unique advantage is generated by being able to
recover Ca in the form of the solid-state "Ca and electrolytic-bath
salt".
[0035] As described above, instead of the Kroll process in which
the continuous production is hardly performed, the inventors
establish the method, wherein the CaCl.sub.2 containing molten salt
in which Ca is dissolved is retained in the reactor vessel, the
metallic chloride containing TiCl.sub.4 is caused to react with Ca
in the molten salt to generate the Ti granules or the Ti alloy
granules in the molten salt, and the Ti granules or the Ti alloy
granules are separated and recovered from the molten salt to
continuously produce Ti or the Ti alloy.
[0036] As described above, in the production method, CaCl.sub.2
which is of the by-product in association with the Ti generation is
taken out to the outside of the reactor vessel and electrolyzed,
and the generated Ca can be used in the reaction for generating the
metal such as Ti in the reactor vessel. In this case, one of the
large advantages of the method is in that rigorous separation of Ca
and CaCl.sub.2 is not required.
[0037] According to the method of producing Ti or the Ti alloy
through reduction by Ca, the Ti generating reaction proceeds in the
molten CaCl.sub.2. Accordingly, compared with the Kroll process
(reaction field is limited to the neighbor of the Mg liquid
surface), the region where the reducing reaction is generated
(i.e., reaction field) is remarkably enlarged and the heat
generating region is also spread to easily perform the cooling, so
that the TiCl.sub.4 feed rate can largely be enhanced to remarkably
improve the productivity.
[0038] However, because the reaction of Ca and TiCl.sub.4 in the
molten CaCl.sub.2 is the exothermic reaction, in order to maintain
the high productivity, it is necessary to cool the heat generating
region to dissipate the heat. Therefore, the thermal efficiency is
also lowered because of the large heat loss.
[0039] In the case where the heat, rapidly generated due to the
excessive TiCl.sub.4 feed rate, exceeds the cooling capacity, the
reaction field becomes an excessively high temperature, and the
reactor vessel is severely worn. On the contrary, when the
temperature is excessively lowered, the reaction rate is decreased.
Therefore, in the TiCl.sub.4 reduction process, it is necessary to
finely control the temperature to maintain the high
productivity.
[0040] In order to solve the problem, the inventors further study
the measures to overcome the difficulty of the reaction-field
temperature control while suppressing the decrease in energy loss
caused by repetition of the heat generation and heat dissipation.
As a result, the inventors hit on an idea, in which the molten
CaCl.sub.2 solution is electrolyzed while taken out from the
reactor vessel, the generated Ca and the molten CaCl.sub.2 solution
are recovered in the form of the solid substance, and the solid
substance is returned to the reduction process.
[0041] The realization of the method can absorb the heat generated
by the reaction of Ca and TiCl.sub.4 by utilizing latent heat of
fusion possessed by the solid substance containing Ca and
CaCl.sub.2. Therefore, the production efficiency and thermal
efficiency are largely improved, the reaction temperature is easily
controlled, and the method of producing Ti or the Ti alloy through
reduction by Ca can be performed further efficiently.
[0042] Additionally, in producing Ti or the Ti alloy through
reduction by Ca, when the solid-state Ca and electrolytic-bath salt
are fed as the Ca source to the molten salt containing CaCl.sub.2
in the reactor vessel, unlike the case in which the solid-state
metallic Ca is fed as the Ca source, the solid-state Ca and
electrolytic-bath salt are dissolved rapidly and evenly, and the
reaction of Ca and the metallic chloride containing TiCl.sub.4 can
be caused to proceed evenly in a wide range inside the reactor
vessel.
[0043] Thus, in the method of producing Ti or the Ti alloy through
reduction by Ca, the large effect is obtained by utilizing the
solid-state Ca and electrolytic-bath salt as the Ca source.
[0044] The invention is made based on study result on the method of
producing Ti or the Ti alloy through reduction by Ca, the
involvement with the technique of producing Ti or the Ti alloy
through reduction by Ca, and the findings (a) to (d). The summary
of the invention includes the following Ti or Ti alloy production
methods (1) to (3) and pulling electrolysis methods (4) and
(5).
[0045] (1) A method of producing Ti or a Ti alloy going through a
reduction process in which a metallic chloride containing
TiCl.sub.4 is caused to react with Ca in a Ca-containing
electrolytic-bath salt to generate Ti or the Ti alloy in the
electrolytic-bath salt, the method is characterized in that the
solid-state Ca and electrolytic-bath salt are fed to the reduction
process.
[0046] (2) A Ti or Ti alloy production method including a reduction
process in which a metallic chloride containing TiCl.sub.4 is
caused to react with Ca in a Ca-containing electrolytic-bath salt
to generate Ti or the Ti alloy in the electrolytic-bath salt and an
electrolysis process of generating Ca by electrolyzing the
electrolytic-bath salt taken out from the reduction process, the
method is characterized in that, in the electrolysis process, a
solid substance containing Ca and the electrolytic-bath salt is
recovered and the solid substance is delivered to the reduction
process.
[0047] (3) In the Ti or Ti alloy production method of (1) and (2),
the recovery of the solid substance containing Ca and the
electrolytic-bath salt may be performed by pulling a cathode while
the solid substance is caused to adhere to and solidified in a
cathode surface. Additionally, when a Ca-containing
electrolytic-bath salt containing CaCl.sub.2 is used as the
Ca-containing electrolytic-bath salt, desirably the method of
producing Ti or the Ti alloy through reduction by Ca proposed by
the inventors can further efficiently be performed.
[0048] (4) A pulling electrolysis method of recovering a
solid-state Ca using a Ca-containing electrolytic-bath salt, the
method is characterized in that a electrolytic-bath salt is
electrolyzed at a bath temperature of 680 to 900.degree. C., a
cathode current density of 0.1 to 200 A/cm.sup.2, and a voltage of
10V or less, and Ca and the electrolytic-bath salt is recovered in
a solid state by pulling a cathode at a pulling rate of 0.05 cm/min
or more while a solid substance is caused to adhere to and
solidified in a cathode surface. The pulling electrolysis method
can be applied as the electrolysis method of recovering Ca from the
Ca-containing electrolytic-bath salt in the electrolysis process
described in the Ti or Ti alloy production methods (1) and (2).
[0049] (5) In the pulling electrolysis method (4), desirably the
pulling rate satisfies the following equation (1):
V.gtoreq.0.0035.times.t-2.4 (1)
[0050] where V: cathode pulling rate (cm/min), and
[0051] t: bath temperature (.degree. C.).
[0052] Additionally, when a Ca-containing electrolytic-bath salt
containing CaCl.sub.2 is used as the Ca-containing
electrolytic-bath salt, desirably Ti or the Ti alloy production can
further efficiently be performed in the case of adopting the Ti or
Ti alloy production methods (1) and (2).
[0053] As used herein, "solid-state" defined in the invention shall
mean that the solid substance in the cathode surface is apparently
in the solid state (including the state in which the surface is
wetted during solidification) at a time when the cathode is pulled.
Specifically, "solid-state" shall mean both the case in which the
whole of the solid substance is in the solid state (i.e., the
solidification is completed) and the case in which, although the
solid substance is apparently in the solid state, actually the
solid substance is partially solidified and the electrolytic-bath
salt or the like in the molten state exists in the solid
substance.
[0054] The Ti or Ti alloy production methods (1) and (2) each is
the method in which, in producing Ti or the Ti alloy through
reduction of TiCl.sub.4 by Ca in the electrolytic-bath salt, the
electrolytic-bath salt taken out from the reduction process is
electrolyzed to recover Ca and the electrolytic-bath salt as the
solid substance, and the recovered Ca and electrolytic-bath salt
are delivered to the reduction process. In the Ti or Ti alloy
production methods (1) and (2), heat generation is suppressed in
the reduction process to largely improve production efficiency and
thermal efficiency, a reaction temperature is easily controlled,
and Ti or the Ti alloy can efficiently be produced at low cost.
[0055] The pulling electrolysis methods (4) and (5) are the method
of recovering Ca by regulating the bath temperature, the cathode
current density, the voltage, and the pulling rate of the cathode
in predetermined ranges. According to these methods, Ca can be
obtained as the solid-state Ca and electrolytic-bath salt at low
voltage and high current efficiency, i.e., with relatively small
electric power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a view showing a schematic configuration of a main
part of a calcium furnace for producing Ca by electrolysis of a
molten CaCl.sub.2, disclosed in a Germany technical document;
[0057] FIG. 2 is a view for explaining a pulling electrolysis
method according to the invention;
[0058] FIG. 3 is a view illustrating relationships between a
cathode pulling rate and current efficiency when the electrolysis
method according to the invention is implemented;
[0059] FIG. 4 is a view showing relationships between a bath
temperature and a cathode pulling rate in the pulling electrolysis;
and
[0060] FIG. 5 is a view showing a configuration example of an
apparatus for producing a metallic Ti through reduction by Ca.
BEST MODE FOR CARRYING OUT THE INVENTION
[0061] A Ti or Ti alloy production method according to the
invention, a pulling electrolysis method which can be applied
thereto, and an optimum production process of the invention in
which these methods are combined will be individually described
below.
[0062] 1. Ti or Ti Alloy Production Method
[0063] The Ti or Ti alloy production method of the invention is a
method of producing Ti or a Ti alloy going through a reduction
process in which a metallic chloride containing TiCl.sub.4 is
caused to react with Ca in a Ca-containing electrolytic-bath salt
to generate Ti or the Ti alloy in the electrolytic-bath salt, the
method being characterized in that the solid-state Ca and
electrolytic-bath salt are fed to the reduction process.
[0064] A specific configuration as an example is "a Ti or Ti alloy
production method including a reduction process in which a metallic
chloride containing TiCl.sub.4 is caused to react with Ca in a
Ca-containing electrolytic-bath salt to generate Ti or the Ti alloy
in the electrolytic-bath salt and an electrolysis process of
generating Ca by electrolyzing the electrolytic-bath salt taken out
from the reduction process, the method being characterized in that,
in the electrolysis process, a solid substance containing Ca and
the electrolytic-bath salt is recovered and the solid substance is
delivered to the reduction process.
[0065] That is, the Ti or Ti alloy production method of the
invention is characterized in that the solid substance containing
Ca and the electrolytic-bath salt is recovered in the electrolysis
process and the recovered solid substance is delivered to the
reduction process in the method of producing Ti or the Ti alloy by
reducing TiCl.sub.4 by Ca in the electrolytic-bath salt.
[0066] A molten salt is used as the electrolytic-bath salt. Usually
the molten salt containing CaCl.sub.2 is preferably used. However,
the molten salt is not limited to the molten salt containing
CaCl.sub.2. Any molten salt can be used as the electrolytic-bath
salt, because the reducing reaction by Ca proceeds unless the
molten salt having conductivity has extremely small solubility for
Ca. There is no limitation in a solid substance recovering method.
Ca generated in the electrolysis process is taken out from the
electrolytic bath as the solid substance containing the
electrolytic-bath salt, and Ca is delivered to the reduction
process (namely, Ca is loaded in a reactor vessel in which the
reduction process proceeds).
[0067] At this point, the whole amount of Ca generated in the
electrolysis process may be delivered in the form of the solid
substance to the reduction process, or Ca may partially be
delivered in the form of the solid substance to the reduction
process while the residue may be returned in the form of the
CaCl.sub.2 solution Whose Ca concentration is increased. Even in
this case, the above effects (such as the improvement of the
production efficiency and thermal efficiency and the improvement of
the reaction temperature control) are obtained depending on an
extent of the delivered solid substance.
[0068] Adopting the "solid substance recovery-delivery" method can
decrease heat loss to largely improve the thermal efficiency while
absorb the heat generation to enhance the production efficiency by
utilizing latent heat of fusion possessed by the solid substance
containing Ca and CaCl.sub.2. Because cooling capability in the
reaction system is increased as a whole, the reaction temperature
is easily controlled, and the raw-material loading rate can be
enhanced to further efficiently produce Ti or the Ti alloy through
the reduction by Ca at low costs. The compact apparatus can also be
realized.
[0069] In the method of producing Ti or the Ti alloy through
reduction by Ca, the reaction rates in the reduction process and
electrolysis process are possibly changed during operation (or the
reaction rates are inevitably changed). In such cases, an added
effect that the solid substance containing Ca and CaCl.sub.2 is
retained (temporarily stored) as the Ca source and used according
to need can be sufficiently expected.
[0070] That is, the solid substance containing Ca and CaCl.sub.2
can act as a buffer in adjusting the reaction rates in the
reduction process and electrolysis process. When the CaCl.sub.2
solution whose Ca concentration is increased is kept in a
high-temperature state, or when CaCl.sub.2 solution is regained to
be in a dissolution state when in use after cooled once, the energy
loss becomes extremely large. In addition, because the solid
substance containing the high-concentration Ca can be recovered, an
amount of Ca transported to the reduction process can be decreased
compared with the case in which Ca is returned to the reduction
process along with CaCl.sub.2 solution.
[0071] In the Ti or Ti alloy production method of the invention,
the recovered Ca and the Ca concentration in the solid substance
containing the electrolytic-bath salt can be adjusted by
controlling the temperature of the Ca-containing electrolytic-bath
salt. For example, the Ca concentration in the solid substance can
be adjusted to 20% by weight by setting the electrolytic
temperature to 720.degree. C., and the Ca concentration in the
solid substance can be adjusted to 30% by weight by setting the
electrolytic temperature to 800.degree. C.
[0072] That is, the Ca concentration in the solid substance
containing Ca and the electrolytic-bath salt can be controlled by
managing the electrolytic temperature. For example, in the case
where a temperature in a reaction field where the reducing reaction
is generated is lowered, the electrolytic temperature is lowered to
decrease the Ca concentration in the solid substance. On the other
hand, in the case where a reaction rate is enhanced in the
reduction process, the electrolytic temperature is raised to
increase the Ca concentration in the solid substance. Thus, the
solid substance containing Ca and the electrolytic-bath salt can be
suitably selectively used as the operation situation demands.
[0073] 2. Pulling Electrolysis Method
[0074] As described above, the pulling electrolysis method of the
invention is a method characterized in that an electrolytic-bath
salt is electrolyzed at a bath temperature of 680 to 900.degree.
C., a cathode current density of 0.1 to 200 A/cm.sup.2, and a
voltage of 10V or less, and the electrolytic-bath salt and Ca is
recovered in a solid state by pulling a cathode at a pulling rate
of 0.05 cm/min or more while a solid substance is caused to adhere
to and solidified in a cathode surface.
[0075] FIG. 2 is a view for explaining the pulling electrolysis
method of the invention. As shown in FIG. 2, an electrolytic-bath
salt 2 is retained in an electrolytic tank 1, and a positive
electrode 3 and a cathode 4 are provided. When electricity is
passed between the electrodes to start the electrolysis, chlorine
(Cl.sub.2) is generated at the anode 3 and Ca is deposited at the
cathode 4.
[0076] At this point, when the cathode 4 is gradually pulled upward
as shown by an arrow in FIG. 2, because the temperature is rapidly
lowered in an exposed portion above the liquid surface of the
electrolytic-bath salt 2, the electrolytic-bath salts adhering to
Ca generated (deposited) by the electrolysis start the
solidification one after another. On the other hand, because the
conductivity is maintained, Ca is continuously deposited while the
electrolytic-bath salt is solidified.
[0077] The deposition of Ca and the adhesion and solidification of
the electrolytic-bath salt near the deposited Ca repeatedly undergo
as the cathode 4 is pulled, and the solid-state Ca and
electrolytic-bath salt 5 in which Ca and the electrolytic-bath salt
are contained in a mixed state are formed downward from the portion
which is dipped in the electrolytic-bath salt 2 in starting the
electrolysis of the cathode 4.
[0078] In the solid-state Ca and electrolytic-bath salt, Ca is
dispersed in fine granules, and Ca has an extremely large surface
area. Accordingly, in the method of producing Ti or the Ti alloy
through reduction by Ca, the solid-state Ca and electrolytic-bath
salt have a property of being easily dissolved in the molten salt
containing CaCl.sub.2 in the reactor vessel when the solid-state Ca
and electrolytic-bath salt are used as the Ca source. For the
"state in which Ca and the electrolytic-bath salt are mixed", a
mixing ratio and unbalance of the mixing are not particularly
defined. Any solid-state Ca and electrolytic-bath salt may be used
as long as they are rapidly and evenly dissolved in the molten salt
containing CaCl.sub.2 when fed into the molten salt as the Ca
source.
[0079] In the electrolysis method of the invention, the
electrolytic-bath salt having any composition can be used as long
as the temperature of the electrolytic-bath salt can be adjusted
within the above-described temperature range and Ca is generated by
the electrolysis. Usually a mixture of a halogenated salt of Ca is
used. Examples of the mixture of a halogenated salt of Ca includes
a binary-system mixed salt such as a calcium fluoride and a calcium
chloride and the calcium chloride and a potassium chloride and a
ternary-system mixed salt such as the calcium chloride, the calcium
fluoride, and the potassium chloride. Because a melting point of
the electrolytic-bath salt can be changed by the use of the mixed
salt, the electrolytic-bath salt can be selected according to the
setting bath temperature.
[0080] The bath temperature is set to a range of 680 to 900.degree.
C. When the bath temperature is lower than 680.degree. C., the
electrolytic generation of Ca is hardly performed due to the
excessively low reaction temperature. On the other hand, when the
bath temperature exceeds 900.degree. C., it is difficult to obtain
high current efficiency (i.e., Ca recovery efficiency) because a
dissolution amount of generated Ca in the electrolytic-bath salt is
increased.
[0081] The cathode current density is set in the range of 0.1 to
200 A/cm.sup.2. A lower limit of the current density depends on a
rate at which Ca generated by the electrolysis is re-dissolved.
When the current density is less than 0.1 A/cm.sup.2, because the
rate at which Ca is dissolved in the electrolytic-bath salt is
faster than the Ca generation rate, Ca cannot be recovered. On the
other hand, the reason why an upper limit of the current density is
set to 200 A/cm.sup.2 is that, when the electrolysis is performed
at the current density exceeding 200 A/cm.sup.2, the voltage cannot
be decreased even if the inter-electrode distance is adjusted, and
the electric power consumption is increased.
[0082] When the cathode current density is set in the range of 0.1
to 70 A/cm.sup.2, the voltage can be set to 5V or less to largely
reduce the electric power consumption, which is desirable. Further,
when the cathode current density is set to the range of 10 to 50
A/cm.sup.2, at least 90% current efficiency can be obtained in
addition to the large reduction of the electric power
consumption.
[0083] That is, the demands of the decrease in voltage and the
current efficiency improvement, which conflict with each other, can
be satisfied. Accordingly, the above range is the compatible range
for the cathode current density, and desirably the commercial
operation is performed while the cathode current density is set in
the range of 10 to 50 A/cm.sup.2.
[0084] The reason why the voltage is set to 10V or less during the
electrolysis is that the increase in electric power consumption is
suppressed as much as possible. In the description of the Germany
technical document, it is considered that the electrolysis is
performed at high voltage (35 to 40V) in order to deposit the
metallic Ca. However, the high voltage is not required in the
electrolysis method of the invention, because Ca is recovered as
the solid substance in which the Ca and the electrolytic-bath salt
are mixed. Although the lower limit of the voltage is not
particularly determined, it is necessary that the voltage be higher
than at least a decomposition voltage (about 3.2V) of the molten
CaCl.sub.2 in order that the electrolysis proceeds to deposit
Ca.
[0085] The cathode pulling rate is set to 0.05 cm/min or more. When
the pulling rate is slower than 0.05 cm/min, it is difficult to
cause the generated Ca to adhere to the cathode surface. This is
because the generated Ca is dissolved and widely spread into the
bath.
[0086] The upper limit of the pulling rate is not particularly
defined. As regulated in the electrolysis method of the invention,
when a manipulation for pulling the cathode while the solid
substance is caused to adhere to and solidified in the cathode
surface is performed, the upper limit of the pulling rate is
determined by itself. That is, when the pulling rate is excessively
fast, the pulled solid substance has an excessively small sectional
area (i.e., becomes excessively thin) and the pulled solid
substance is cut in the middle, so that the pulling cannot
continuously be performed. In consideration of the restriction on
the pulling manipulation, desirably the pulling rate is set to 10
cm/min or less.
[0087] In the electrolysis method of the invention, when the
pulling rate further satisfies the equation (1), Ca and the
electrolytic-bath salt can be recovered at good current
efficiency.
[0088] FIG. 3 is a view illustrating relationships between the
cathode pulling rate and the current efficiency when the pulling
electrolysis method of the invention is implemented. FIG. 3 shows
electrolysis examples at the voltage of 10V or less and the
interelectrode distance of 7 cm or less. In FIG. 3, a mark
".diamond-solid." and a solid line indicate the case in which bath
temperature is set to 720.degree. C. during the electrolysis
(electrolysis at 720.degree. C.), the mark ".diamond-solid." and a
broken line indicate the case in which the bath temperature is set
to 800.degree. C. (electrolysis at 800.degree. C.), a mark
indicates the case in which a columnar cathode whose diameter is 8
mm is used, a mark " " indicates the case in which a columnar
cathode whose diameter is 5 mm is used, and a mark ".largecircle."
indicates the case in which a columnar cathode whose diameter is 15
mm is use d.
[0089] At this point, the current efficiency is expressed by a
ratio (percentage) of the Ca amount in the solid substance (i.e.,
solid-state Ca and electrolytic-bath salt) of the cathode surface
to the Ca deposition amount (theoretical deposition amount)
determined from the electricity amount based on a Faraday's law.
Because Ca in the solid substance does not include Ca which is
dissolved or peeled off after once deposited on the cathode
surface, the current efficiency used herein is synonymous with Ca
recovery efficiency.
[0090] As is clear from FIG. 3, the cathode pulling rate is closely
related with the current efficiency, the current efficiency is
improved when the pulling rate is increased irrespective of the
bath temperature. This is attributed to the fact that, although the
generated Ca is partially dissolved and spread in the bath from the
neighbor of the cathode, the generated Ca is exposed from the
surface of the electrolytic-bath salt before dissolved in the bath
by increasing the pulling rate, which allows the dissolution to be
suppressed to enhance the Ca recovery efficiency (i.e., current
efficiency). In the electrolysis at 800.degree. C., an influence of
the shape (diameter in section) of the cathode is not observed as
far as the investigation is performed.
[0091] In the case of the high bath temperature, the current
efficiency is slightly lowered. In the example shown in FIG. 3, the
electrolysis at 800.degree. C. is lower than the electrolysis at
720.degree. C. in the current efficiency over the whole range of
the pulling rate. This is attributed to the fact that the
dissolution amount of generated Ca into CaCl.sub.2 is increased to
decrease the Ca recovery amount when the bath temperature becomes
higher. Accordingly, in the case where the electrolytic-bath salt
is used at a particularly high temperature, desirably the pulling
rate is increased to perform the electrolysis on the condition that
the current efficiency is enhanced.
[0092] As the bath temperature is increased, the Ca concentration
is increased in the recovered solid-state Ca and electrolytic-bath
salt. For example, the Ca concentration is 30% by weight at
800.degree. C. while the Ca concentration is 20% by weight at
720.degree. C. Although the detailed phenomenon is unknown, this is
attributed to the fact that, in the case of the high bath
temperature, the electrolytic-bath salt adhering to the cathode
surface (deposited Ca surface) during the pulling runs off to be
easily separated from Ca before the electrolytic-bath salt is
solidified and Ca in the recovered solid substance is
condensed.
[0093] Accordingly, the Ca concentration can be controlled in the
recovered solid-state Ca and electrolytic-bath salt by adjusting
the bath temperature, and the Ca concentration can be learned and
arbitrarily determined when the solid-state Ca and
electrolytic-bath salt are used as the Ca source.
[0094] In the equation (1), the relationship between the bath
temperature and the pulling rate in which the good current
efficiency is obtained is determined based on the relationship
among the bath temperature, the cathode pulling rate, and the
current density during the electrolysis shown in FIG. 3. In the
electrolysis method of the invention, when the equation (1) is
satisfied, Ca can efficiently be recovered as the solid-state Ca
and electrolytic-bath salt.
[0095] FIG. 4 is a view showing a relationship between the bath
temperature and the cathode pulling rate in the pulling
electrolysis. A portion hatched in FIG. 4 is a region, where the
pulling rate is not lower than 0.05 cm/min and the good current
efficiency (i.e., good Ca recovery efficiency) expressed by the
equation (1). The lower limit of the region is expressed by an
equation (V=0.0035.times.t-2.4, where 700<=t<=900) in the
case where both sides of the equation (1) are equal to each
other.
[0096] In the electrolysis method of the invention, Ca and the
electrolytic-bath salt are recovered in the solid state. As
described above, "solid-state" means that the Ca and the
electrolytic-bath salt are apparently in the solid state. For
example, in the case where a large difference is made between the
bath temperature and the melting point of the electrolytic-bath
salt due to the high bath temperature, sometimes the molten
electrolytic-bath salt exists inside the solid substance on the
cathode surface. The electrolytic-bath salt adhering to the pulled
cathode surface is hardly solidified, and Ca generally has the
melting point higher than that of the electrolytic-bath salt.
Therefore, Ca is deposited in the form of the solid substance from
the beginning, or Ca becomes immediately the solid substance even
if Ca is initially in the molten state, so that the unsolidified
electrolytic-bath salt is taken into the solid substance.
[0097] In the case of the small difference between the bath
temperature and the melting point of the electrolytic-bath salt,
because the electrolytic-bath salt is easily solidified, the whole
of the solid substance on the cathode surface is recovered as the
solid state.
[0098] Thus, according to the electrolysis method of the invention,
Ca can be obtained as the solid-state Ca and electrolytic-bath salt
at low voltage and high current efficiency (i.e., with the
relatively small electric power consumption). The solid-state Ca
and electrolytic-bath salt is extremely effectively used as the Ca
source when the method of producing Ti or the Ti alloy through
reduction by Ca is implemented.
[0099] 3. Production Process
[0100] A production process into which the pulling electrolysis
method of the invention is incorporated in producing Ti or the Ti
alloy through reduction by Ca will be described below.
[0101] The production process is a method in which solid-state Ca
and electrolytic-bath salt recovered by the pulling electrolysis
method of the invention is used as Ca caused to react with a
metallic chloride containing TiCl.sub.4 in implementing the method
of producing Ti or the Ti alloy through reduction by Ca, i.e., the
Ti or Ti alloy production method including a reduction process of
causing a metallic chloride containing TiCl.sub.4 to react with Ca
in a Ca-containing electrolytic-bath salt to generate Ti or the Ti
alloy in the electrolytic-bath salt and an electrolysis process of
generating Ca by electrolyzing the electrolytic-bath salt taken out
from the reduction process.
[0102] FIG. 5 is a view showing a configuration example of an
apparatus for producing the metallic Ti through reduction by Ca. In
the example, TiCl.sub.4 is used as the raw material, and the
Ca-containing electrolytic-bath salt containing CaCl.sub.2 is used
as the Ca-containing electrolytic-bath salt. In the example, a
separation process and a chlorination process are included in
addition to the reduction process (below-mentioned process
proceeding in the reactor vessel 6) and the electrolysis process.
In the separation process, the generated metallic Ti is separated
and recovered. In the chlorination process, TiCl.sub.4 is produced
by utilizing the chlorine (Cl.sub.2) generated through the
electrolysis.
[0103] Referring to FIG. 5, a reducing agent feed pipe 7 for
feeding Ca (in this case, feeding the solid-state Ca and
electrolytic-bath salt) which is of a reducing agent is provided in
a ceiling portion of a reactor vessel 6. A bottom of the reactor
vessel 6 is tapered downward while a diameter of the reactor vessel
6 is gradually reduced in order to promote discharge of produced Ti
granules. A Ti discharge pipe 8 is provided in a central portion at
lower end of the reactor vessel 6 to discharge the produced Ti
granules.
[0104] On the other hand, a cylindrical separation wall 9 is
disposed inside the reactor vessel 6 while a predetermined gap is
provided between the separation wall 9 and an inner surface of a
straight body portion of the reactor vessel 6. A molten salt
discharge pipe 10 is provided in an upper portion of the reactor
vessel 6 to discharge CaCl.sub.2 in the vessel to the side. A raw
material feed pipe 11 for feeding TiCl.sub.4 which is of a raw
material to Ti is provided in a lower portion of the reactor vessel
6 while piercing through the separation wall 9 to reach a central
portion of the vessel.
[0105] The molten CaCl.sub.2 solution in which Ca is melted is
retained as the molten salt in the reactor vessel 6. A level of the
molten CaCl.sub.2 solution is set higher than the molten salt
discharge pipe 10 and lower than an upper end of the separation
wall 9. In this state of things, a TiCl.sub.4 gas is supplied to
the molten CaCl.sub.2 solution located inside the separation wall 9
through the raw material feed pipe 11. This enables TiCl.sub.4 to
be reduced by Ca in the molten CaCl.sub.2 solution inside the
separation wall 9 to produce the granular metallic Ti in the molten
CaCl.sub.2 solution.
[0106] The Ti granules produced in the molten CaCl.sub.2 solution
located inside the separation wall 9 in the reactor vessel 6 moves
downward through the molten CaCl.sub.2 solution and deposited on
the bottom of the reactor vessel 6. The deposited Ti granules are
appropriately taken out downward from the Ti discharge pipe 8 along
with the molten CaCl.sub.2 solution and delivered to a separation
process 12.
[0107] The molten CaCl.sub.2 solution whose Ca is consumed by the
reducing reaction inside the separation wall 9 rises along the
outside of the separation wall 9 though the bottom of the
separation wall 9, and the molten CaCl.sub.2 solution is discharged
from the molten salt discharge pipe 10. The discharged molten
CaCl.sub.2 solution is delivered to an electrolysis process 13.
[0108] Inside the separation wall 9, Ca is replenished by feeding
the solid-state Ca and electrolytic-bath salt to the molten
CaCl.sub.2 solution from the reducing agent feed pipe 7.
[0109] On the other hand, in the separation process 12, the Ti
granules taken out of the reactor vessel 6 along with the molten
CaCl.sub.2 solution are separated from the molten CaCl.sub.2
solution. Specifically, the Ti granules are compressed by squeezing
the molten CaCl.sub.2 solution. The molten CaCl.sub.2 solution
obtained in the separation process 12 is delivered to the
electrolysis process 13.
[0110] In the electrolysis process 13, a molten CaCl.sub.2 solution
13b introduced into an electrolytic tank 13a from the reactor
vessel 6 and the separation process 12 are separated into Ca and
the Cl.sub.2 gas through the electrolysis.
[0111] Ca generated on the side of a cathode 13d is recovered by
the manipulation for pulling the cathode 13d in the form of
solid-state Ca and electrolytic-bath salt 13e in which Ca and the
electrolytic-bath salt are mixed, and the solid-state Ca and
electrolytic-bath salt 13e are returned into the reactor vessel 6
to replenish Ca. The total of Ca may be replenished (fed) with the
solid-state Ca and electrolytic-bath salt, or part of Ca may be
replenished with the solid-state Ca and electrolytic-bath salt
while the residue is replenished with the CaCl.sub.2 solution whose
Ca concentration is increased.
[0112] The solid-state Ca and electrolytic-bath salt 13e delivered
in the reactor vessel 6 are easily dissolved, so that they are
rapidly and evenly dissolved in the reactor vessel. In the case
where the molten electrolytic-bath salt exists in the solid-state
Ca and electrolytic-bath salt, because the dissolution proceeds
further rapidly, the even reaction between TiCl.sub.4 and Ca
proceeds effectively in the wide range of the vessel.
[0113] Additionally, the solid-state Ca and electrolytic-bath salt
13e are melted by absorbing the heat generated in association with
the reaction between TiCl.sub.4 and Ca, which allows the production
efficiency and the thermal efficiency to be largely improved.
Because the cooling capability in the reaction system is enhanced
as a whole, the reaction temperature is easily controlled, and
raw-material loading rate can be enhanced to produce further
efficiently Ti or the Ti alloy through reduction by Ca. The latent
heat of fusion can maximally be utilized when the whole of the
solid-state Ca and electrolytic-bath salt are in the solid
state.
[0114] In the method of producing Ti or the Ti alloy through
reduction by Ca, the reaction rates in the reduction process and
electrolysis process are possibly changed during operation (or the
reaction rates are inevitably changed). In such cases, an added
effect that the solid-state Ca and electrolytic-bath salt are
retained (temporarily stored) as the buffer of the Ca source and
used according to need can sufficiently be expected.
[0115] The Cl.sub.2 gas generated on the side of a positive
electrode 13c in the electrolysis process 13 is delivered to a
chlorination process 14. In the chlorination process 14, TiO.sub.2
is chlorinated to produce TiCl.sub.4 in the presence of carbon
powders (C). Oxygen which is of a by-product is discharged in the
form of CO.sub.2 by simultaneously using the carbon powders (C).
The produced TiCl.sub.4 is introduced into the reactor vessel 6
through the raw material feed pipe 11. Thus, Ca and Cl.sub.2 gas
which are of the reducing agent are circulated by the circulation
of CaCl.sub.2.
[0116] As described above, according to the production process, the
metallic Ti can continuously be produced only by actually
replenishing TiO.sub.2 and C. At this point, the solid-state Ca and
electrolytic-bath salt which are recovered by the electrolysis
method of the invention can suitably used as the Ca source.
INDUSTRIAL APPLICABILITY
[0117] According to the production method of the invention, in
producing Ti or the Ti alloy through reduction by Ca, the
electrolytic-bath salt taken out from the reduction process is
electrolyzed to recover the Ca and electrolytic-bath salt in the
form of the solid substance, and the recovered Ca and
electrolytic-bath salt is delivered to the reduction process.
Therefore, the heat generation in the reduction process is
suppressed by utilizing the latent heat of fusion possessed by the
solid substance, the production efficiency and the thermal
efficiency are largely improved, the reaction temperature is easily
controlled, and the raw-material loading rate can be enhanced to
efficiently produce Ti or the Ti alloy at low cost. In the pulling
electrolysis method of the invention, Ca is recovered while the
bath temperature, the cathode current density, the voltage, and the
cathode pulling rate are regulated within the predetermined ranges.
Therefore, the solid-state Ca and electrolytic-bath salt can be
obtained at low voltage and high current efficiency, i.e., with the
relatively small power consumption. When the solid-state Ca and
electrolytic-bath salt are used as the Ca source in producing Ti or
the Ti alloy through reduction by Ca, the solid-state Ca and
electrolytic-bath salt are dissolved rapidly and evenly in the
reactor vessel, and the excessive heat generated by the reaction of
the metallic chloride containing Ca and TiCl.sub.4 is suppressed by
melting the Ca and electrolytic-bath salt during the reducing
reaction, so that Ti or the Ti alloy can efficiently be
produced.
* * * * *