U.S. patent application number 10/509250 was filed with the patent office on 2005-06-30 for method of purifying metal salt, method of deacidifying titanium material and method of producing the same.
Invention is credited to Shimosaki, Shinji.
Application Number | 20050139483 10/509250 |
Document ID | / |
Family ID | 33307204 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139483 |
Kind Code |
A1 |
Shimosaki, Shinji |
June 30, 2005 |
Method of purifying metal salt, method of deacidifying titanium
material and method of producing the same
Abstract
A purification method of a metal salt which comprises bringing a
metal salt formed by melting an alkali metal salt, an alkaline
earth metal salt or a mixture thereof into contact with titanium or
the like, thereby adsorbing impurities in the metal salt, a
deoxidization method by melting metallic calcium into a molten
product of the metal salt purified by the purification method and
bringing the same into contact with a titanium material, and a
production method of the titanium material which comprises
conducting molten salt electrolysis by using the molten product of
the purified metal salt for an electrolytic bath. Using the
purification or production method the molten metal salt can be
purified simply and conveniently at good efficiency. Then, use of
the purified metal salt can minimize contamination caused by the
metal impurities in the molten salt and the titanium material of
high quality can be produced.
Inventors: |
Shimosaki, Shinji; (Hyogo,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
33307204 |
Appl. No.: |
10/509250 |
Filed: |
September 28, 2004 |
PCT Filed: |
April 21, 2003 |
PCT NO: |
PCT/JP03/05065 |
Current U.S.
Class: |
205/398 |
Current CPC
Class: |
C22B 34/1295 20130101;
C01F 11/32 20130101; C01D 3/20 20130101 |
Class at
Publication: |
205/398 |
International
Class: |
C25C 003/28 |
Claims
1. A method of purifying a metal salt which comprises bringing the
metal salt formed by melting an alkali metal salt, an alkaline
earth metal salt or a mixture thereof into contact with one or more
of titanium, titanium alloy, zirconium and zirconium alloy, thereby
adsorbing impurities in the metal salt.
2. A purification method of a metal salt according to claim 1,
wherein the metal salt is melted in a vessel made of titanium or
titanium alloy, or a vessel lined with titanium or titanium
alloy.
3. A purification method of a metal salt according to claim 1,
wherein foil-like titanium is used as an adsorbent.
4. A method of deoxidizing a titanium material comprising
dissolving metallic calcium to a molten product of a metal salt
purified by the purification method according to claim 1 and
bringing the same into contact with the titanium material.
5. A deoxidization method of a titanium material according to claim
4, wherein calcium chloride is used as the molten salt.
6. A deoxidization method of a titanium material according to claim
4, wherein the exactly same vessel used for the purification of the
metal salt is used.
7. A method of producing a titanium material which comprises
conducting molten salt electrolysis by using a molten product of a
metal salt purified by the purification method according to claim 1
for electrolytic bath.
8. A production method of a titanium material according to claim 7,
wherein an LiCl--KCl system mixed salt is used under electrolysis
as the molten salt.
9. A production method of a titanium material according to claim 7,
wherein the exactly same vessel used for the purification of metal
salt is used.
10. A purification method of a metal salt according to claim 2,
wherein foil-like titanium is used as an adsorbent.
11. A method of deoxidizing a titanium material comprising
dissolving metallic calcium to a molten product of a metal salt
purified by the purification method according to claim 2 and
bringing the same into contact with the titanium material.
12. A deoxidization method of a titanium material according to
claim 5, wherein the exactly same vessel used for the purification
of the metal salt is used.
13. A method of producing a titanium material which comprises
conducting molten salt electrolysis by using a molten product of a
metal salt purified by the purification method according to claim 2
for electrolytic bath.
14. A production method of a titanium material according to claim
8, wherein the exactly same vessel used for the purification of
metal salt is used.
Description
TECHNICAL FIELD
[0001] The present invention concerns a method of purifying a metal
salt, as well as a deoxidization method and a production method of
a titanium material and, more in particular, it relates to a method
of purifying a metal salt, as well as a deoxidization method and a
production method of a titanium material for preventing
contamination from a molten salt in a production step and producing
products of high quality at a good yield.
BACKGROUND ART
[0002] In recent years, titanium has been used also as electronic
materials including target materials for use in sputtering and the
application field thereof has been extending. For generalized use
of titanium as materials for electronic parts requiring high
accuracy, it is necessary for high purity in view of quality.
Recently, further improvement of the quality for use as electronic
parts has been demanded and titanium of higher purity is demanded
for use in them.
[0003] However, since titanium is a metal which is, by nature,
active, particularly at high temperature, it is liable to undergo
contamination from substances in contact therewith in the
production step and it is difficult to produce titanium of high
purity. Therefore, it is an important technical subject to mitigate
contamination due to contact with other substances in the
production step thereof for producing titanium of high purity at a
good yield.
[0004] Further, since titanium is an active metal, it tends to
chemically bond with oxygen to form oxides. As a method of
decreasing oxygen in titanium, a method of melting a salt of an
alkali metal and/or alkaline earth metal and deoxidizing titanium
with metallic calcium melted in the molten salt thereof has been
developed. For example, Publication of Examined Japanese Patent
Application No. 08-14009 describes an invention relating to a
method of producing titanium with a reduced oxygen content. In the
method described in this publication, starting titanium material is
charged in a molten salt (flux), melting metallic calcium in a
molten salt while bringing into contact with the molten salt in a
gaseous or liquidus state, causing the same to react on the
starting titanium material, thereby deoxidizing titanium.
[0005] In the method described in the publication, while oxygen can
be removed effectively, in a case of using a molten salt of low
purity, most of impurities other than oxygen contained in the
molten salt are attracted to titanium and contaminate titanium to
lower the purity of titanium.
[0006] Commercially available salts of alkali metals or alkaline
earth metals of usual grade contain a trace amount of heavy metals
such as iron or nickel as impurities. Accordingly, such impurities
migrate in the titanium deoxidizing process to titanium products to
bring about a problem of contaminating the products.
[0007] While contamination of the products can be mitigated by
using the salts of alkali metals or alkaline earth metals at the
reagent guaranteed class, it industrially requires the use of the
metal salt in a great amount, and use of such expensive salt in a
great amount is not practical from an economical view point of the
cost.
[0008] With an aim of purifying a metal salt of a usual grade,
while a method of bubbling gaseous chlorine in a molten salt to
purify the molten salt has been conducted generally, but this
purification method mainly intends to remove the water content
remaining in the molten salt and can not remove metal
impurities.
[0009] Accordingly, it has been demanded for development of a
purification method starting from the salt of alkali metal or
alkaline earth metal of usual grade as the raw material and forming
the same simply into a salt with less metal impurities. Then, in a
case where the alkali metal salt or alkaline earth metal salt with
less metal impurities can be obtained simply, it is possible for
deoxidizing titanium or producing titanium of high quality by using
such alkali metal salt or alkaline earth metal salt.
DISCLOSURE OF THE INVENTION
[0010] The present invention has been accomplished in view of the
demand for the development of the purification method described
above and it is an object thereof to provide a purification method
of a metal salt capable of simply and effectively purifying. a
molten salt which may possibly form a contamination source in the
production step of titanium, as well as a deoxidization method of a
titanium material and a production method of a titanium material
using the metal salt purified by the purification method.
[0011] The present inventors have noted on titanium and zirconium
as adsorbents for metal impurities. Both titanium and zirconium are
highly active metals at high temperature and tends to chemically
bond with a trace amount of metal impurities such as iron or nickel
contained in molten salts. Further, since titanium alloys and
zirconium alloys are also active metals, a similar effect can be
expected also by using the titanium alloys or the zirconium alloys
instead of titanium and zirconium.
[0012] In view of the above, by adsorbing impurities in the metal
salt by bringing titanium, titanium alloy, zirconium or zirconium
alloy into contact with the molten salt, the molten salt can be
purified. The content of metal impurities is extremely low in the
molten salt of the thus obtained alkali metal and/or alkaline earth
metal.
[0013] Then, when deoxidization or production of a titanium
material of high purity is conducted by using the molten salt
purified as described above, oxygen contained in the titanium
material of high purity can be removed easily with no contamination
caused by the metal impurities, or a titanium material of high
purity having higher quality can be produced.
[0014] The present invention has been accomplished based on the
finding described above and the gist thereof resides in a method of
purifying a metal salt having a feature in the following (1) and
(2), a method of deoxidizing a titanium material having a feature
in the following (3), and a production method for titanium having
the following feature (4).
[0015] (1) A purification method for a metal salt comprising
adsorbing impurities in the metal salt by bringing the metal salt
formed by melting an alkali metal salt, an alkaline earth metal
salt or a mixture thereof into contact with one or more of
titanium, titanium alloy, zirconium and zirconium alloy.
[0016] (2) A method of purifying the metal salt described in (1)
above wherein the metal salt is melted in a vessel made of titanium
or made of titanium alloy, or in a vessel lined with the titanium
or the titanium alloy.
[0017] (3) A method of deoxidizing a titanium material comprising
the step of melting metallic calcium in a molten product of the
metal salt purified by the purification method described in (1) or
(2) above and bringing the same into contact with the titanium
material.
[0018] (4) A method of producing the titanium material comprising
the step of conducting molten salt electrolysis by using the molten
product of the metal salt purified by the purification method
described in (1) or (2) above for the electrolysis bath.
BRIEF EXPLANATION OF DRAWINGS
[0019] FIG. 1 is a view schematically explaining the constitution
of an apparatus for purifying a molten salt, used in the example of
the present invention.
[0020] FIG. 2 is a view showing the progress of the concentration
of iron in calcium chloride when plate-like titanium or foil-like
titanium is used as an adsorbent for metal impurities.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] The content of the present invention comprises, being
classified generally, (A) a purification method of a metal salt,
(B) a deoxidization method of a titanium material and (C) a
production method of the titanium material by molten salt
electrolysis. Accordingly, the content is to be described
specifically while being partitioned into (A), (B) and (C)
respectively.
[0022] (A) Purification Method of Metal Salt
[0023] Purification of a metal salt is conducted by bringing a
metal salt formed by melting an alkali metal salt, an alkaline
earth metal salt or a mixture thereof (hereinafter also referred to
as "molten salt") into contact with one or more of titanium,
titanium alloy, zirconium and zirconium alloy (hereinafter referred
to as "titanium or the like"), thereby adsorbing the impurities in
the metal salt to titanium or the like.
[0024] Contact of titanium or the like means herein mere immersion
of titanium or the like in the metal salt and it is not
accompanied, for example, by a special treatment such as supply of
current to the molten salt.
[0025] As described above, a commercially available salt of an
alkali metal or alkaline earth metal of usual grade contains a
trace amount of heavy metals as impurities. In a case of
deoxidizing a titanium material of high purity or producing a
titanium material of high purity by molten salt electrolysis by
using the molten salt formed by melting such a salt, metal
impurities are taken into the titanium material of high purity to
lower the purity of the titanium material at high purity. In order
to avoid this, the molten salt is previously purified. The type and
the mixing ratio of the metal salts formed by melting the alkali
metal salt, alkaline earth metal salt and a mixture thereof, that
is, the molten salt used herein are not restricted
particularly.
[0026] For the molten salt, one or more of titanium, titanium
alloy, zirconium and zirconium alloy is selected and brought into
contact therewith. Thus, the titanium or the like acts as the
adsorbent for the metal impurities, and the metal impurities in the
molten salt are taken into titanium or the like. Upon contact of
the molten salt and titanium or the like, the titanium or the like
acts as the adsorbent by not only entirely immersing the titanium
or the like but also partially immersing them into the molten
salt.
[0027] Upon purification of the metal salt, it is preferred that
the titanium or the like is disposed in a vessel so that the total
immersing surface area of the titanium or the like is larger. This
can proceed purification at a higher efficiency. Further, for
proceeding purification at a higher efficiency, the molten salt may
be stirred.
[0028] The titanium or the like may be in any form including a
plate-like shape. As described above, since the purification
efficiency is improved as the total immersing surface area in the
molten salt is larger, it is preferably in the form, for example,
of foil, honeycomb, or sponge (porous body). In view of the cost,
since machining chips formed upon machining titanium are available
at a reduced cost and in the form of thin plate, a sufficient
effect can be obtained.
[0029] More specifically, assuming the volume of the metal salt as
V (cm.sup.3) and the total immersing surface area of the titanium
or the like as S (cm.sup.2), it is preferred that the ratio V/S is
10 or less. This is because the content of each of metal impurities
can be lowered to the order of 1 ppm or less in about 50 hrs in a
case where V/S is 10 or less. However, even when V/S is 10 or more,
the content of the metal impurities can be lowered in the same
manner, providing that V/S is 100 or less, by stirring the metal
salt, or shaking or jogging the titanium or the like in the metal
salt.
[0030] The adsorption effect obtained by the contact of the molten
salt with the titanium or the like can be obtained at about
500.degree. C. providing that the temperature of the molten salt is
at or above the melting point. For adsorbing the metal impurities
more efficiently and conducting the purification effectively, the
temperature of the molten salt is preferably 700.degree. C. or
higher. While the upper limit for the temperature of the molten
salt is not defined particularly, it is necessary that the
temperature is at the boiling point of the molten salt or lower and
at the melting point of the titanium or lower.
[0031] The vessel for melting the metal salt is constituted of a
material not leaching ingredients that may form impurities to the
molten salt. For example, oxides such as quartz and alumina,
nickel, titanium, molybdenum or the like can be used as the
material for the vessel. It is not necessary that the vessel is
entirely constituted with the material described above, but the
material may be lined at least to a portion that it is in contact
with the molten salt.
[0032] Considering a case where the titanium of high purity is
deoxidized in the exactly same vessel used for the purification of
the metal salt, it is preferred that at least the portion of the
vessel in contact with the molten salt is made of the titanium or
the titanium alloy. This is because use of the metal identical with
that of the final product in the present invention has no worry of
contamination caused by leaching from the vessel and, further,
titanium or the titanium alloy also has an effect of adsorbing the
impurity metals.
[0033] (B) Deoxidization Method of Titanium Material
[0034] The titanium material can be deoxidized by melting metallic
calcium into a molten salt (molten product of metal salt) purified
by the purification method (A) described above and bringing it into
contact with the titanium material. Deoxidization proceeds when the
calcium melted in the molten salt reacts with oxygen in the
titanium material to form CaO and oxygen is released into the
molten salt.
[0035] In the present invention, since the molten salt purified by
the purification method (A) is used, it is possible to prevent
intrusion of the metal impurities into the titanium material and
prevent degradation of the quality and lowering of the yield caused
by the contamination of the final product.
[0036] The deoxidization of the titanium material can be conducted
successively after practicing the purification method (A) in the
vessel used for the purification method (A). This can efficiently
proceed the production step and is free from the worry of
contamination caused by the impurities intruded upon exchange or
transportation of the vessel.
[0037] (C) Production Process of Titanium Material by Molten Salt
Electrolysis
[0038] The titanium material of high purity can be produced by
conducting the molten salt electrolysis using the molten salt
(molten. metal salt) purified by the purification method (A) for
the electrolytic bath. In the molten salt electrolysis, anodic
melting and cathodic precipitation are conducted in the molten salt
and, in order to purify the titanium material to a higher level,
use of titanium material of high purity as the anode is preferred.
In the present invention, since the molten salt purified by the
purification method (A) is used for the electrolytic bath, it is
possible to prevent the intrusion of the metal impurities into the
titanium material and prevent the degradation of the quality and
the lowering of the yield caused by contamination of the final
products.
[0039] Production of the titanium material by the molten salt
electrolysis can also be conducted successively, like in (B), after
practicing the purification method (A) in the vessel used for the
purification method (A). Also in this case, the production step can
be proceeded efficiently and it is free from the worry of
contamination caused by the impurities intruded upon exchange or
transportation of the vessel.
EXAMPLE
[0040] Descriptions are to be separately made for (A) purification
method of a metal salt, (B) deoxidization method of a titanium
material and (C) production method of a titanium material by molten
salt electrolysis with reference to concrete examples.
[0041] (A) Purification Method of Metal Salt
[0042] At first, for confirming the adsorption effect of metal
impurities by a titanium plate, the titanium plate was charged in a
vessel containing a molten salt and the molten salt was
purified.
[0043] FIG. 1 schematically shows the constitution of an apparatus
for purifying a molten salt used in the example. As shown in FIG.
1, the purification apparatus for the molten salt comprises an
inner vessel 1 for containing the molten salt and an outer vessel 2
for containing the inner vessel 1. A heater 3 is located at the
periphery of the outer vessel 2, so that temperature of a molten
salt 7 can be controlled. Further, an outer vessel 4 is connected
with a vacuum pump 4 and the atmosphere in the outer vessel 2 can
be controlled.
[0044] Purification by a titanium plate 8 was conducted by using
the purification apparatus with the constitution described above.
10 kg of anhydrous calcium chloride (melting point: 772.degree. C.)
and 100 g of titanium in the form of a plate of about 1 mm
thickness were charged in the inner vessel 1 made of quartz, which
were contained in the outer vessel 2 made of stainless steel. A
cover 5 made of quartz was placed for preventing dropping of
contaminants from above and intrusion in the molten salt. Fine
apertures 6 are formed in the cover 5 so as to allow gas to pass
therethrough upon vacuum evacuation, temperature elevation or argon
substitution.
[0045] After containing the inner vessel 1 in the outer vessel 2,
the outer vessel 2 was tightly dosed by a cover and the temperature
inside the vessel was gradually elevated to 700.degree. C. under
vacuum evacuation in order to remove the water content present in
the vessel and hygroscopic moisture content of calcium chloride and
then the evacuation was stopped. Then, argon gas was introduced
such that the pressure in the vessel was equal with the atmospheric
pressure and then the temperature was further elevated to
950.degree. C. At the temperature, calcium chloride is in a molten
state.
[0046] Subsequently, after keeping at 950.degree. C. for 25 hours,
the calcium chloride was sampled and after keeping further for 25
hours, that is, 50 hours in total, it was sampled again. The
sampled specimen was analyzed by ICP after cooling in order to
examine the contained metal impurities. Further, metal impurities
in the titanium plate used for purification was also analyzed by
ICP.
[0047] On the other hand, a test was also conducted without
charging the titanium plate in the inner vessel 1.
[0048] Table 1 shows the content of the metal impurities in the
calcium chloride when the calcium chloride was purified by the
titanium plate.
1 TABLE 1 Content of metal impurities in calcium chloride (ppm)
Specimen Fe Ni Cr Al Mn Before 5 4 1.1 0.8 0.7 purification After
purification 2.2 1.6 0.5 0.5 0.3 at 950.degree. C. .times. 25 hrs
After purification 0.8 0.7 0.2 0.2 0.2 at 950.degree. C. .times. 50
hrs Note) Titanium plate (plate-like titanium) was used as an
adsorbent.
[0049] Table 2 shows the content of the metal impurities in the
titanium plate when calcium chloride is purified by the titanium
plate.
2 TABLE 2 Content of metal impurities in titanium plate (ppm)
Specimen Fe Ni Cr Al Mn Before purification 10 2 <1 1 <1
After purification 420 240 80 60 50
[0050] Table 3 shows the content of the metal impurities in calcium
chloride 50 hrs after the start of melting in a case where calcium
chloride is melted without using the titanium plate.
3 TABLE 3 Content of metal impurities in calcium chloride (ppm)
Specimen Fe Ni Cr Al Mn Before melting 5 4 0.8 0.8 0.7 After
melting 5 4 0.9 0.9 1.0 Note) with no adsorbent
[0051] According to the results in Table 1 and Table 2, the content
of the metal impurities in the calcium chloride was decreased and
the content of metal impurities in the titanium plate was increased
whereas, according to Table 3, the content of metal impurities in
the calcium chloride before melting and after melting was scarcely
changed. In view of the above, it can be seen that the titanium
plate acts as the adsorbent and is effective for purification of
calcium chloride.
[0052] Successively, a similar test was conducted by using 100 g of
foil-shaped titanium. The thickness of the foil-shaped titanium
used herein was about 0.1 mm, which was about {fraction (1/10)} of
the titanium plate described above (about 1 mm thickness).
[0053] Accordingly, the surface area was about ten times more than
the surface area of the plate-like titanium. Other test conditions
than those described above were identical with those for the
titanium plate described above.
[0054] Table 4 shows the content of the metal impurities in calcium
chloride when calcium chloride was purified by the foil-like
titanium.
4 TABLE 4 Content of metal impurities in calcium chloride (ppm)
Specimen Fe Ni Cr Al Mn Before purification 5 4 1.1 0.8 0.7 After
purification 1.1 0.8 0.3 0.3 0.2 at 950.degree. C. .times. 25 hrs
After purification 0.5 0.3 0.2 0.1 0.1 at 950.degree. C. .times. 50
hrs Note) Foil-like titanium was used as an adsorbent.
[0055] As apparent from Table 4, the content of the metal
impurities in the calcium chloride was decreased and it can be seen
that the foil-like titanium acts as an adsorbent and the calcium
chloride can be purified. On the other hand, for demonstrating the
effect when titanium was formed into a foil-like shape, the
impurity metals in the calcium chloride were compared between a
case of using the titanium plate and a case of using the foil-like
titanium.
[0056] FIG. 2 is a graph showing the concentration of iron (Fe) in
the calcium chloride when the plate-like titanium (titanium plate)
or foil-like titanium were used as an adsorbent. As apparent from
FIG. 2, use of the foil-like titanium having a larger surface area
compared with the use of the plate-like titanium is more effective
for decreasing the concentration of iron as the impurity metal
present in the calcium chloride.
[0057] Then, it was examined as to whether the same adsorbing
effect is obtained or not also for a molten salt comprising plural
kinds of metal salts in admixture. Since the melting point of a
mixed salt of anhydrous lithium chloride and anhydrous potassium
chloride, that is, LiCl--KCl system mixed salt is lowered by
eutectics, this is a useful mixed salt frequently used for
electrolytic purification and refining of titanium or
zirconium.
[0058] Then, 4 kg of anhydrous lithium chloride and 6 kg of
anhydrous potassium chloride were used as the metal salt and
purified by 100 g of the foil-like titanium. Also in this case,
other test conditions than the molten salt and the shape of
titanium were identical with those in the case of the titanium
plate described previously.
[0059] Table 5 shows the content of the metal impurities in
LiCl--KCl system mixed salt when LiCl--KCl system mixed salt was
purified by the foil-like titanium.
5 TABLE 5 Content of metal impurities in LiCl--KCl system mixed
salt (ppm) Specimen Fe Ni Cr Al Mn Before purification 5 4 1.1 0.8
0.7 After purification 0.3 0.2 0.1 0.2 0.1 at 950.degree. C.
.times. 50 hrs Note) Foil-like titanium was used as an
adsorbent.
[0060] As apparent from Table 5, it can be seen that the content of
the metal impurities in the LiCl--KCl system mixed salt was
decreased and titanium acted as the adsorbent also to such mixed
salt and the mixed salt can be purified.
[0061] (B) Deoxidization Method of Titanium Material
[0062] Using the calcium chloride purified by the foil-like
titanium in (A) above, that is, the calcium chloride subjected to
the purification treatment for 50 hours in Table 4 was used as the
molten salt and deoxidation of the titanium material was attempted.
The deoxidizing treatment was conducted by melting metallic calcium
by 3% of weight based on the weight of calcium chloride to the
molten salt, dipping 200 g of a titanium material of high purity of
1 mm thickness and keeping the temperature of 950.degree. C. for 10
hours in an argon atmosphere.
[0063] After completing the deoxidizing treatment, the titanium
material of high purity was recovered from the calcium chloride
which was cooled and solidified in the furnace, and the content of
the metal impurities was analyzed by ICP. On the other hand, the
titanium material of high purity applied with the deoxidizing
treatment in the same manner using commercially available anhydrous
calcium chloride was also analyzed by ICP.
[0064] Table 6 shows the content of the metal impurities in the
titanium material before and after the deoxidizing treatment using
the calcium chloride purified by the foil-like titanium as a molten
salt.
6 TABLE 6 Content of metal impurities in titanium plate (ppm)
Specimen Fe Ni Cr Al Mn O Before deoxidizing 5 2 1.0 0.8 0.7 300
treatment After deoxidizing 6 2 1.0 0.8 0.8 30 treatment Note)
Purified calcium chloride was used as a molten salt.
[0065] Table 7 shows the content of the metal impurities in the
titanium material before and after the deoxidizing treatment using
calcium chloride of general or usual grade as a molten salt.
7 TABLE 7 Content of metal impurities in titanium plate (ppm)
Specimen Fe Ni Cr Al Mn O Before deoxidizing 5 2 1.0 0.8 0.7 300
treatment After deoxidizing 240 90 45.0 50 60 30 treatment Note)
Calcium chloride of usual grade was used as a molten salt.
[0066] It can be seen, from the results of Table 6 and Table 7,
that the deoxidization could be attained although the content of
the metal impurities contained in the titanium material were
scarcely changed in a case of using the calcium chloride purified
by the foil-like titanium as a molten salt. On the contrary, the
titanium material was contaminated by the metal impurities in the
molten salt and the content of the metal impurities in the titanium
material was increased in a case of using the calcium chloride of
usual grade.
[0067] (C) Production Method of Titanium Material by Molten Salt
Electrolysis
[0068] Electrolysis was attempted by using the LiCl--KCl system
mixed salt purified in (A) above, that is, the LiCl--KCl system
mixed salt subjected to the purification treatment for 50 hours in
Table 5 were used as the molten salt.
[0069] Electrolysis was conducted by immersing a titanium material
as a cathode and sponge titanium particles contained in a nickel
net as an anode in the molten salt and supplying electric current
between both of the electrodes for 15 hours while keeping the
temperature at 900.degree. C. After completing the electrolysis,
the content of the metal impurities in the titanium material
deposited on the cathode was analyzed by ICP.
[0070] On the other hand, electrolysis was conducted in the same
manner by using the LiCl--KCl system mixed salt before purification
in Table 5 as the molten salt, and the content of the metal
impurities in the titanium material deposited on the cathode was
analyzed by ICP.
[0071] Table 8 shows the content of the metal impurities in the
titanium material deposited on the cathode when electrolysis was
conducted by using the purified LiCl--KCl system mixed salt and the
LiCl--KCl system mixed salt before purification as a molten
salts.
8 TABLE 8 Content of metal impurities in titanium plate (ppm)
Specimen Fe Ni Cr Al Mn O Purified Li--KCl <0.1 <0.1 0.1 0.1
0.3 80 system mixed salt Li--KCl mixed salt 110 40 22 17 20 80
before purification
[0072] As apparent from Table 8, the titanium material of extremely
high purity could be produced in a case of using the purified
LiCl--KCl system mixed salt, whereas the titanium material of high
purity could not be produced being contaminated by the metal
impurities in the mixed salt in a case of using the LiCl--KCl
system mixed salt before purification.
INDUSTRIAL APPLICABILITY
[0073] According to the purification method of the metal salt of
the present invention, a molten metal salt comprising an alkali
metal salt, an alkaline earth metal salt or a mixture thereof can
be purified simply and conveniently at a good efficiency, requiring
no special apparatus leading to an increase in the production cost.
Then, contamination caused by the metal impurities in the molten
salt can be minimized by using the metal salt purified by the
purification method and the titanium material of high quality can
be produced. This can be applied generally as a method of producing
the titanium of high purity used as the material for electronic
parts requiring high accuracy.
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