U.S. patent application number 10/502732 was filed with the patent office on 2005-07-07 for high-purity sponge titanium material and its production method.
Invention is credited to Wada, Hisayuki.
Application Number | 20050145072 10/502732 |
Document ID | / |
Family ID | 34044589 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145072 |
Kind Code |
A1 |
Wada, Hisayuki |
July 7, 2005 |
High-purity sponge titanium material and its production method
Abstract
The object of the present invention is to economically produce a
high-purity sponge titanium material containing fewer amounts of
oxygen and metal elements. To realize this object the vacuum
separation time t in a vacuum separation step is
t=t.sub.o+(15.about.35) hour where the time t is the vacuum
separation time in a vacuum separation step and t.sub.o is defined
as the time from the start of the vacuum separation till the time
when the temperature of the central part of the material in a
reaction vessel reaches a stable temperature. At and near the
central part of the material where the amounts of metal elements
are small, the specific area measured by the BET method is 0.05
m.sup.2/g or less. Thus, even if the cutting and crushing of the
material are performed in the atmosphere, the amount of oxygen in
the cut and crushed material can be suppressed to a low level.
Inventors: |
Wada, Hisayuki; (Hyogo,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
34044589 |
Appl. No.: |
10/502732 |
Filed: |
March 11, 2005 |
PCT Filed: |
February 8, 2002 |
PCT NO: |
PCT/JP02/01118 |
Current U.S.
Class: |
75/619 |
Current CPC
Class: |
C22B 34/1295 20130101;
C22B 34/1272 20130101 |
Class at
Publication: |
075/619 |
International
Class: |
C22B 034/12 |
Claims
1. A high-purity sponge titanium material produced by Kroll method
wherein a specific area measured by the BET method is set at 0.05
m.sup.2/g or less and the content of respective metal elements of
Fe, Ni, Cr, Al and Si is set at 10 ppm or less.
2. A production method of a high-purity sponge titanium material of
the present invention is one in which when a sponge titanium
material is produced by Kroll method, the vacuum separation time t
in a vacuum separation step is set at t=t.sub.o+(15.about.35) hour
while defining t.sub.o as the time from the start of vacuum
separation till the time when the temperature Tc of the central
part of the material in a reaction vessel reaches a stable
temperature To near the furnace temperature, and after the
completion of vacuum separation, a part at and near the central
part other than the upper part, the lower part and the outer
circumferential part of the material in the reaction vessel is
commercialized.
3. A high-purity sponge titanium material according to claim 1
wherein the amount of oxygen of cut and crushed high purity sponge
titanium material is 200 ppm or less.
4. The production method of the high-purity sponge titanium
material according to claim 2, wherein said high-purity sponge
titanium material has a specific area measured by the BET method of
0.05 m.sup.2/g or less and a content of respective metal elements
of Fe, Ni, Cr, Al and Si of 10 ppm or less.
5. The production method of claim 4, wherein an amount of oxygen of
cut and crushed high purity sponge titanium material is 200 ppm or
less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-purity sponge
titanium material suitable for a crude material of a sputtering
target material and its production method.
BACKGROUND ART
[0002] As an industrial production method of metal titanium, a
method is often used in which after a sponge titanium material
produced by Kroll method was cut and crushed, it is compressed into
briquettes, and the briquettes are melted and cast. The Kroll
method comprises a reduction step in which molten Mg and titanium
tetrachloride are reacted with each other in a reaction vessel and
a vacuum separation step in which after the reduction step,
non-reacted Mg contained in the material in the vessel and
remaining by-products are vaporized to be removed by heating them
under vacuum.
[0003] On the other hand, as a new use of metal titanium, a wiring
material in a semiconductor element such as an LSI or the like is
known. This wiring is formed by sputtering using high-purity metal
titanium as a target material. Lesser impurities are required for
this sputtering target material. Thus, in a sponge titanium
material which is a crude material of the target material, oxygen
content of 200 ppm or less and each content of metal elements of
Ni, Cr, Al and Si of 10 ppm or less are required.
[0004] However, since Kroll method is the one, which gives high
priority in productivity, it is not easy for the method to ensure
such impurity levels as required in the sputtering target material.
Thus, following two methods are proposed. One of them is a center
selection method in which after vacuum separation, a part at and
near the center of a sponge titanium material obtained in a
reaction vessel other than the upper part, lower part and the outer
circumferential part thereof is commercialized (Japanese Patent No.
2863469). The other method is a low humidity crushing method in
which a sponge titanium material taken out of the reaction vessel
is cut and crushed under low humidity atmosphere (Japanese Patent
No. 2921790).
[0005] However, although in the former center selection method, it
is possible for the respective metal elements of Fe, Ni, Cr, Al and
Si to ensure the level required for the sputtering target material,
it is impossible for oxygen to ensure the level. On the other hand,
in the latter humidity crushing method, it is possible for oxygen
to ensure the level required for the sputtering target material, it
is impossible for the respective metal elements of Fe, Ni, Cr, Al
and Si to ensure the level.
[0006] Therefore, to ensure the level required for the sputtering
target material in both of the respective metal elements of Fe, Ni,
Cr, Al and Si, and oxygen, it becomes necessary to combine the
former, center selection method, with the latter, low humidity
crushing method. However, as an actual problem in a case of the
former, implementation of center selection method is easy, but in a
case of the latter, low humidity crushing method, to ensure the
oxygen level actually required for the sputtering target material
stably, a very large partitioned working space which is maintained
at low humidity is needed whereby very large costs are required for
the construction of the space and the maintenance of atmosphere.
These methods are not practical.
[0007] The object of the present invention is to provide a
high-purity sponge titanium material having both small contents of
oxygen and metal elements and which is excellent in cost
effectiveness and its production method.
DISCLOSURE OF THE INVENTION
[0008] To attain the above-mentioned objects, the present inventor
has noted relationships between sample taking positions and oxygen
contents for sponge titanium material made by Kroll method.
[0009] FIG. 1 is a vertical cross-sectional view of a sponge
titanium material in a reaction vessel in a vacuum separation step.
A reaction vessel 20 is contained in a heating furnace 30. A sponge
titanium material 10 in the reaction vessel 20 has a constricted
shape in the middle part since titanium is precipitated on a grate
21 in the reaction vessel 20 and on an inner surface of a side wall
in the reaction vessel 20 in the preceding reduction step.
[0010] In the sponge titanium material 10 obtained after the vacuum
separation step, the respective metal elements of Fe, Ni, Cr, Al
and Si have smaller contents in portions further distant from the
upper surface, the lower surface and the outer circumferential
surface of the reaction vessel 20. This is because the inclusion of
the respective metal elements is mainly due to contamination from
the reaction vessel 20. Thus, while removing the upper part, the
lower part and the outer circumferential part of the sponge
titanium material 10, the remaining part 11 of the material near
the center is taken so that levels of metal elements required for
the sputtering target material can be comparatively easily
ensured.
[0011] However, an oxygen content, particularly, an oxygen content
after cutting and crushing is unexpectedly reduced in a surface
layer region of the sponge titanium material 10. For example,
examining a distribution of the amount of oxygen in each part after
cutting and crushing sponge titanium material 10 from the uppermost
part A to the 1/2 part C at the centerline position, the amount of
oxygen increases more as approaching the 1/2 part C. For example in
a case where an oxygen content of titanium particles obtained from
the uppermost part A is 250 ppm, the amount of oxygen in the 1/4
part B reaches about 300 ppm and the amount of oxygen in the 1/2
part C reaches about 350 ppm. For this tendency of the amount of
oxygen, even if a part 11 near the center of the sponge titanium
material 10 is taken, it becomes impossible for the amount of
oxygen in a cut and crushed material to ensure the level required
for a sputtering target material.
[0012] The present inventor has examined reasons why the amount of
oxygen is reduced at a surface layer region of the sponge titanium
material 10 from both aspects of the physical properties and
production method. As a result the following facts have been
found.
[0013] FIG. 2 shows changes in temperatures of a sponge titanium
material in a vacuum separation step, with respect to the uppermost
part A, the 1/4 part B and 1/2 part C at the centerline position of
the material. The temperatures of each part have a tendency to be
temporarily lowered from the start of vacuum separation, and
increased, and reach stable temperature near the furnace
temperature. This reason is that although the vaporization of
remaining Mg is started together with the start of the vacuum
separation, and temperature is temporarily lowered by its heat of
vaporization, an increase in the temperature is started by
reduction in remaining Mg and a temperature is stabilized at a
level near the furnace temperature.
[0014] This tendency is common even in any part of the uppermost
part A, the 1/4 part B and the 1/2 part C. Nevertheless, the lowest
temperature goes down in the order of the uppermost part A, the 1/4
part B and the 1/2 part C, and both time from the start of the
vacuum separation to the turning point to an increase in
temperature and time from the increase in temperature to a stabled
temperature are further increased in the order of the uppermost
part A, the 1/4 part B and the 1/2 part C. This reason is that
remaining Mg is difficult to be removed at a part nearer the center
of the sponge titanium material. Thus the time when remaining Mg in
the central part where it is difficult to be removed, that is the
1/2 part C, is removed and temperature Tc in this part reaches a
stable temperature To is the finish time of vacuum separation. It
is noted that the reason why stable temperatures become lower in
the order of the 1/2 part C, the 1/4 part B and the uppermost part
A is that heat radiation toward an opening part side (upper side)
of the reaction vessel is remarkable.
[0015] As a result of vacuum separation in such a process, in a
surface layer region far from the center of the sponge titanium
material, heating is continued for a long period of time even after
the vaporization of Mg was finished, resulting in so called
conditions of heating an empty object. The present inventor has
considered that the heating time after vaporization of Mg has
relation to the oxygen content after cutting and crushing the
sponge titanium material, and examined variously. As the results,
the present inventor has found that at a position farther from the
center of the sponge titanium material, sintering is further
advanced while heating under conditions of heating empty object
whereby specific area is decreased; in a part having smaller
specific area is suppressed an increase in oxygen content due to
oxidation in cutting and crushing steps; as a result, the amount of
oxygen in cut and crushed titanium material becomes lower in the
order of the 1/2 part C, the 1/4 part B and the uppermost part A;
and if, after the completion of vaporization of Mg in the 1/2 part
C, heating is continued, sintering of this part is advanced and
specific area is decreased so that low oxygen can be realized.
[0016] The present invention has been completed based on these
knowledge and is a high-purity sponge titanium material produced by
Kroll method wherein a specific area measured by the BET method is
set at 0.05 m.sup.2/g or less and the content of respective metal
elements of Fe, Ni, Cr, Al and Si is set at 10 ppm or less.
[0017] By limiting the specific area of the material measured by
the BET method to 0.05 m.sup.2/g or less, even if cutting and
crushing the material under usual atmosphere the amount of oxygen
of the titanium particle is suppressed to 300 ppm or less.
Preferably the specific area is 0.04 m.sup.2/g or less, and 0.03
m.sup.2/g or less is more preferably. This reduces the amount of
oxygen. Preferable oxygen content after cutting and crushing is 200
ppm or less, and more preferably is 100 ppm or less. As for the
lower limit of the specific area, it is better to be lower from a
viewpoint of reduction in oxygen content. However, when the
specific area is too small, cutting and crushing the material is
difficult. Thus the specific area is preferably 0.01 m.sup.2/g or
more.
[0018] The reason why the respective metal elements of Fe, Ni, Cr,
Al, and Si were limited to 10 ppm or less is to exclude the upper
part, the lower part and the outer circumferential part of a sponge
titanium material. The surface layer region of these parts, for
example an uppermost part A shown in FIG. 1 receives heating in
conditions of heating an empty object so that a specific area
measured by the BET method is decreased. However, in this part the
contents of the respective metal elements exceed 10 ppm. Meantime,
particularly preferable content of the respective metal elements is
7 ppm or less.
[0019] Further, a production method of a high-purity sponge
titanium material of the present invention is one when a sponge
titanium material is produced by Kroll method, vacuum separation
time t in a vacuum separation step is set at
t=t.sub.o+(15.about.35) hour while defining t.sub.o as the time
from the start of vacuum separation till the time when the
temperature Tc of the central part of the material in a reaction
vessel reaches a stable temperature To near the furnace
temperature, and after the completion of vacuum separation, a part
at and near the central part other than the upper part, the lower
part and the outer circumferential part of the material in the
reaction vessel is commercialized.
[0020] By setting the vacuum separation time t as (t.sub.o+15) hour
or more a specific area of a part at and near the center other than
the upper part, the lower part and the outer circumferential part
of the material in the reaction vessel is decreased so that low
oxygen after crushing and crushing material is realized. And by
commercializing the part near the center other than the upper part,
the lower part and the outer circumferential part of the material
in the reaction vessel the contents of the respective metal
elements of Fe, Ni, Cr, Al and Si are suppressed to low levels.
[0021] When the vacuum separation time t exceeds (t.sub.o+35) hour,
the specific area becomes too small to cut and crush the material.
Further, thermal cost efficiency further becomes deteriorated
unnecessarily. A particularly preferable lower limit of the vacuum
separation time t is (t.sub.o+20) hour or more, and a preferable
upper limit thereof is (t.sub.o+30) hour or less.
[0022] It is noted that in an actual operation, the temperature of
the central part in a sponge titanium material is not measured.
Time when the temperature of the central part of the material
should reach a stable temperature is assessed from data of changes
in temperatures obtained by a test operation and a temperature
analysis every operating plant, and heating time in the vacuum
separation step is set with reference to this time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a vertical cross-sectional view of a sponge
titanium material in a reaction vessel in a vacuum separation step,
FIG. 2 is a graph showing time-varying changes in temperatures of
sponge titanium materials in a vacuum separation step with respect
to the uppermost part A, 1/4 part B, and 1/2 part C, FIG. 3 is a
graph showing preferable vacuum separation time in the vacuum
separation step using a diameter of the reaction furnace (retort
diameter) as a parameter, and FIG. 4 is micrographs of samples
taken from the central part of two kinds of sponge titanium
materials, which are different from vacuum separation time.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] Embodiments of the present invention will be described.
[0025] Mg (Magnesium) is melted in a reaction vessel and a titanium
tetrachloride solution is dropped, and thereby produces a sponge
titanium material. When this reduction step is over, it is
transferred to a vacuum separation step. In the vacuum separation
step the inside of the reaction vessel is made in vacuum conditions
and the sponge titanium material is heated at a predetermined
temperature by a heating furnace whereby non-reacted Mg and
by-products are removed.
[0026] This vacuum separation step will be described in detail with
reference to examples of test operations shown in FIG. 2.
Temperature Ta of the uppermost part A of the sponge titanium
material in the reaction vessel is slightly lowered at the start of
the vacuum separation. However, this temperature is immediately
increased and reaches a stable temperature for about 20 to 30 hours
from the start of the vacuum separation. On the other hand,
temperature Tc of the central part (1/2 part C) continues to become
lower for about 30 hours from the start of the vacuum separation,
and after that, the temperature starts rising and reaches to a
stable temperature To after 70 hours from the start of the vacuum
separation.
[0027] The vacuum separation has been conventionally finished for
about 70 hours when the temperature Tc of the central part reaches
a stable temperature To. Although a trial of reducing this time was
performed, but a trial of extending this time has not been
considered. As a result, since heating the material after
vaporization of Mg in conditions of heating an empty object is not
performed in a part at and near the central part where contents of
metal elements are small and sintering does not advance, a specific
area is not sufficiently decreased. Thus even if a part at and near
the center of the material is taken after vacuum separation, an
increase in oxygen content by oxidation becomes remarkable in
cutting and crushing the material in the atmosphere and it was
impossible to realize a low oxygen content's level required for a
sputtering target material.
[0028] Thus, in this embodiment, after the temperature Tc of the
central part reached the stable temperature To, heating is further
continued for 15 to 35 hours, preferably for 20 to 30 hours. Thus,
sintering is advanced even in a part at and near the center of the
material having small contents of metal elements whereby a specific
area by the BET method is reduced to 0.05 m.sup.2/g or less. As a
result, when the part near the center of the material is taken
after vacuum separation, an increase in oxygen content due to
oxidation in the cutting and crushing steps is suppressed so that
in both of oxygen content and contents of metal elements it becomes
possible to realize impurity levels required for the sputtering
target material.
[0029] In taking material from the part near the center of a sponge
titanium material 10 after vacuum separation, following three parts
of the material 10 are cut and removed as shown in FIG. 1. The
first part is an upper part having a thickness h1 from the upper
surface of 0.1 H or more, the second part is a lower part having a
thickness h2 from the bottom surface of 0.25 H or more, and the
third part is an outer circumferential part having a thickness d
from the outer circumferential surface of 0.18 D or more. In this
case the height of the sponge titanium material mass is defined as
H, and the mass diameter thereof is defined as D. After the cutting
and removing the three parts of the material, a remaining part 11
near the center, having less than 30% of the mass weight of the
sponge titanium material 10, is taken.
[0030] The selected part 11 near the center is usually cut and
crushed in the atmosphere to make sponge titanium particles each
having a predetermined particle size. In spite of usually cutting
and crushing in the atmosphere, the amount of oxygen is suppressed
to 300 ppm or less and the content of the respective Fe, Ni, Cr, Al
and Si is suppressed to 10 ppm or less. The particle size of
crushed material is preferably 10 to 300 mm in average.
[0031] A result of examination of preferable vacuum separation time
in a vacuum separation step is shown in FIG. 3. A preferable vacuum
separation time is in a region shown by the slanted lines in FIG.
3.
[0032] The vacuum separation time receives the influence of a
diameter (retort diameter) of a reaction vessel, and the larger
this diameter, the time becomes longer. Conventional vacuum
separation time is shown by a solid line in FIG. 3. The vacuum
separation time of the present invention is +15 to +35 hours to the
conventional vacuum separation time shown by a solid line. A
specific area of the part near the center of the material by the
BET method reaches 0.05 m.sup.2/g or less for +15 hours or more,
and the amount of oxygen after cutting and crushing material
reaches 300 ppm or less. Further, a specific area of the part near
the center of the material by the BET method reaches 0.03 m.sup.2/g
or less for +20 hours or more, and the amount of oxygen after
cutting and crushing material reaches 200 ppm or less. In a case
where the specific area by the BET method is less than 0.01
m.sup.2/g, it is impossible to cut and crush the material.
[0033] A diameter of the reaction vessel (retort diameter) is
preferably 1350 to 2000 mm. In a case of the diameter of less than
1350 mm, even if selection of the part near the center of the
material is performed, metal impurities have a tendency to
increase. In a case where the diameter exceeds 2000 mm there can be
generated a problem in facilities such as thermal deformation or
the like.
[0034] It is noted that in the case of change in temperature shown
in FIG. 2, the diameter (retort diameter) of the reaction vessel is
1700 mm. The time for a conventional vacuum separation is 70 hours
and the time for the present invention in this case is 85 to 105
hours, and preferably 90 to 100 hours.
[0035] In the case where a diameter (retort diameter) of the
reaction vessel is 1700 mm, micrographs of samples taken from the
central part of a sponge titanium material are shown in FIGS. 4(a)
and 4(b) by the same magnification with respect to cases of 70
hours and 90 hours for vacuum separation time respectively.
[0036] A specific area by the BET method is 0.1 m.sup.2/g in the
case of 70 hours of vacuum separation time, and it is 0.03
m.sup.2/g in the case of 95 hours of vacuum separation time. This
difference is clear from FIGS. 4(a) and 4(b). As the results of the
difference between these specific areas the amount of oxygen of cut
and crushed materials having average particle size of 65 mm in the
atmosphere reached 320 ppm in a case of 70 hours of vacuum
separation time and 190 ppm in a case of 95 hours of vacuum
separation time. Further, the contents of the respective metal
elements of Fe, Ni, Cr, Al and Si reached 10 ppm or less in all
cases.
[0037] It is noted that the region shown by slanted lines in FIG. 3
is as follows if it is expressed by a numerical formula.
[0038] Vacuum separation time=(0.0698.times.[retort diameter,
mm]-24).+-.10
[0039] The BET method is a method for calculating a specific area
from an adsorption of liquid nitrogen and is widely used in
adsorbent and the like.
INDUSTRIAL APPLICABILITY
[0040] As described above, in a high-purity sponge titanium
material of the present invention, by limiting the specific area
measured by the BET method to 0.05 m.sup.2/g or less, the amount of
oxygen can be suppressed to a low level even if cutting and
crushing are carried out in the atmosphere. Further, impurity
levels required for the sputtering target material can be
economically ensured by the reduction of metal impurities by
selecting the central part of the material.
[0041] Further, in a production method of the high-purity sponge
titanium material of the present invention, by setting the vacuum
separation time t in a vacuum separation step at
t=t.sub.o+(15.about.35) as the time t.sub.o is defined from the
start of the vacuum separation till the time that the temperature
Tc of the central part of the material in a reaction vessel reaches
to a stable temperature To, the specific area measured by the BET
can be easily limited to 0.05 m.sup.2/g or less. And by a decrease
in the amount of oxygen due to the limitation and reduction of
metal impurities obtained by selecting the central part of the
material, impurity levels required for the sputtering target
material can be economically ensured.
* * * * *