U.S. patent application number 16/462618 was filed with the patent office on 2020-02-27 for method for preparing titanium plating solution and method for manufacturing titanium plated product.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. The applicant listed for this patent is Kyoto University, Sumitomo Electric Industries, Ltd.. Invention is credited to Tomoyuki AWAZU, Masatoshi MAJIMA, Toshiyuki NOHIRA, Yutaro NORIKAWA, Koma NUMATA, Mitsuyasu OGAWA, Kouji YASUDA.
Application Number | 20200063281 16/462618 |
Document ID | / |
Family ID | 62195781 |
Filed Date | 2020-02-27 |
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United States Patent
Application |
20200063281 |
Kind Code |
A1 |
NUMATA; Koma ; et
al. |
February 27, 2020 |
METHOD FOR PREPARING TITANIUM PLATING SOLUTION AND METHOD FOR
MANUFACTURING TITANIUM PLATED PRODUCT
Abstract
The titanium plating solution production method including
measuring a titanium plating solution containing fluorine and
titanium by cyclic voltammetry under the following conditions, and
adding titanium to the titanium plating solution so that the
potential difference between the spontaneous potential and the
Ti3.sup.+/Ti.sup.4+ redox potential is 0.75 V or more. Conditions:
when the temperature of the titanium plating solution is
650.degree. C. to 850.degree. C. and when glassy carbon is used as
a working electrode, platinum is used as a pseudo-reference
electrode and titanium is used as a counter electrode, the
potential scanning is repeatedly performed on the working electrode
for at least five times at a scanning speed of 1 mV/sec to 500
mV/sec between a lower potential limit which is the immersion
potential of the working electrode and an upper potential limit
which is a potential that is 2 V to 4 V higher than the lower
potential limit.
Inventors: |
NUMATA; Koma; (Itami-shi,
Hyogo, JP) ; MAJIMA; Masatoshi; (Itami-shi, Hyogo,
JP) ; AWAZU; Tomoyuki; (Itami-shi, Hyogo, JP)
; OGAWA; Mitsuyasu; (Itami-shi, Hyogo, JP) ;
NOHIRA; Toshiyuki; (Kyoto-shi, Kyoto, JP) ; YASUDA;
Kouji; (Kyoto-shi, Kyoto, JP) ; NORIKAWA; Yutaro;
(Kyoto-shi, Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Electric Industries, Ltd.
Kyoto University |
Osaka-shi, Osaka
Kyoto-shi, Kyoto |
|
JP
JP |
|
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
Osaka-shi, Osaka
JP
Kyoto University
Kyoto-shi, Kyoto
JP
|
Family ID: |
62195781 |
Appl. No.: |
16/462618 |
Filed: |
September 12, 2017 |
PCT Filed: |
September 12, 2017 |
PCT NO: |
PCT/JP2017/032796 |
371 Date: |
May 21, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 21/14 20130101;
C25D 3/66 20130101; C25D 21/12 20130101 |
International
Class: |
C25D 3/66 20060101
C25D003/66; C25D 21/12 20060101 C25D021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2016 |
JP |
2016-227050 |
Claims
1. A method for preparing a titanium plating solution comprising:
measuring a titanium plating solution containing fluorine and
titanium by cyclic voltammetry under the following conditions; and
adding titanium to the titanium plating solution so that a
potential difference between the spontaneous potential and the
Ti3.sup.+/Ti.sup.4+ redox potential is 0.75 V or more, conditions:
when the temperature of the titanium plating solution is
650.degree. C. or more and 850.degree. C. or less and when glassy
carbon is used as a working electrode, platinum is used as a
pseudo-reference electrode and titanium is used as a counter
electrode, the potential scanning is repeatedly performed on the
working electrode for at least five times at a scanning speed of 1
mV/sec or more and 500 mV/sec or less between a lower potential
limit which is the immersion potential of the working electrode and
an upper potential limit which is a potential that is 2 V to 4 V
higher than the lower potential limit.
2. The method for preparing a titanium plating solution according
to claim 1, wherein the titanium plating solution is obtained by
dissolving titanium in a molten salt of potassium fluoride and
potassium chloride.
3. The method for preparing a titanium plating solution according
to claim 1, wherein the titanium plating solution is obtained by
dissolving K.sub.2TiF.sub.6 in a molten salt of potassium fluoride
and potassium chloride.
4. The method for preparing a titanium plating solution according
to claim 3, wherein the content of K.sub.2TiF.sub.6 in the titanium
plating solution is 0.1 mol % or more.
5. The method for preparing a titanium plating solution according
to claim 2, wherein the molar mixing ratio between potassium
fluoride and potassium chloride is 10:90 to 90:10.
6. The method for preparing a titanium plating solution according
to claim 1, wherein the titanium added to the titanium plating
solution is titanium sponge.
7. A method for manufacturing a titanium plated product which
includes an electrolyzing step of carrying out a molten salt
electrolysis by using a cathode and an anode provided in a titanium
plating solution containing fluorine and titanium so as to
electrodeposit titanium on the surface of the cathode, the titanium
plating solution being prepared by the method for preparing a
titanium plating solution according to claim 1.
8. The method for manufacturing a titanium plated product according
to claim 7, wherein the titanium plating solution used in the
electrolyzing step is measured by cyclic voltammetry under the
following conditions, and a potential difference between the
spontaneous potential and the Ti3.sup.+/Ti.sup.4+ redox potential
is controlled to be 0.75 V or more, conditions: when the
temperature of the titanium plating solution is 650.degree. C. or
more and 850.degree. C. or less and when glassy carbon is used as a
working electrode, platinum is used as a pseudo-reference electrode
and titanium is used as a counter electrode, the potential scanning
is repeatedly performed on the working electrode for at least five
times at a scanning speed of 1 mV/sec or more and 500 mV/sec or
less between a lower potential limit which is the immersion
potential of the working electrode and an upper potential limit
which is a potential that is 2 V to 4 V higher than the lower
potential limit.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method for preparing a
titanium plating solution and a method for manufacturing a titanium
plated product. The present application claims the benefit of
priority to Japanese Patent Application No. 2016-227050 filed on
Nov. 22, 2016, the entire contents of which are incorporated herein
by reference.
BACKGROUND ART
[0002] Titanium is a metal that is excellent in corrosion
resistance, heat resistance and specific strength. However,
titanium is costly to manufacture and difficult to smelt and work,
which hampers the wide use of titanium. Dry deposition, such as
chemical vapor deposition (CVD) and physical vapor deposition
(PVD), is now partially used in industry as one of the methods that
take advantage of high corrosion resistance, high strength, and
other properties of titanium and titanium compounds. However, the
dry deposition cannot be applied to a complex-shaped substrate. As
a method for depositing titanium that would solve this problem,
electrodeposition of titanium in a molten salt may be adopted.
[0003] For example, Japanese Patent Laying-open No. 2015-193899
(PTL 1) describes that an alloy film of Fe and Ti is formed on a Fe
wire surface by using a molten salt bath of KF--KCl to which
K.sub.2TiF.sub.6 or TiO.sub.2 is added.
CITATION LIST
Patent Literature
[0004] PTL 1: Japanese Patent Laying-open No. 2015-193899
SUMMARY OF INVENTION
[0005] A method for preparing a titanium plating solution according
to an embodiment of the present disclosure includes measuring a
titanium plating solution containing fluorine and titanium by
cyclic voltammetry under the following conditions, and adding
titanium to the titanium plating solution so that the potential
difference between the spontaneous potential and the
Ti3.sup.+/Ti.sup.4+ redox potential is 0.75 V or more, conditions:
when the temperature of the titanium plating solution is
650.degree. C. or more and 850.degree. C. or less and when glassy
carbon is used as a working electrode, platinum is used as a
pseudo-reference electrode and titanium is used as a counter
electrode, the potential scanning is repeatedly performed on the
working electrode for at least five times at a scanning speed of 1
mV/sec or more and 500 mV/sec or less between a lower potential
limit which is the immersion potential of the working electrode and
an upper potential limit which is a potential that is 2 V to 4 V
higher than the lower potential limit.
BRIEF DESCRIPTION OF DRAWINGS
[0006] FIG. 1 is a graph schematically illustrating a measurement
result of a titanium plating solution by cyclic voltammetry;
[0007] FIG. 2 is a schematic view illustrating an example of
defining areas A to E on a titanium plated product in a method of
measuring an average film thickness of a titanium plating film on
the titanium plated product;
[0008] FIG. 3 is a conceptual diagram illustrating an example of a
field of view (i) when the area A of the titanium plated product
illustrated in FIG. 2 is observed with a scanning electron
microscope.
[0009] FIG. 4 is a conceptual diagram illustrating an example of a
field of view (ii) when the area A of the titanium plated product
illustrated in FIG. 2 is observed with a scanning electron
microscope;
[0010] FIG. 5 is a conceptual diagram illustrating an example of a
field of view (iii) when the area A of the titanium plated product
illustrated in FIG. 2 is observed with a scanning electron
microscope.
[0011] FIG. 6 is a graph schematically illustrating a measurement
result by cyclic voltammetry of a titanium plating solution No. 4
prepared in Example 4; and
[0012] FIG. 7 is a graph schematically illustrating a measurement
result by cyclic voltammetry of a titanium plating solution No. A
prepared in Comparative Example 4.
DETAILED DESCRIPTION
Problem to be Solved by the Present Disclosure
[0013] According to the studies conducted by the inventors of the
present disclosure, although an alloy film of Fe and Ti can be
electrodeposited on the surface of a cathode used in the molten
salt electrolysis by the method described in PTL 1, a metal Ti film
cannot be electrodeposited by the method. Specifically, the alloy
film of Fe and Ti is stable in the molten salt bath, whereas the
metal Ti dissolves in the molten salt bath due to a
comproportionation reaction.
[0014] After further studies, the inventors of the present
disclosure have found that it is effective to carry out the molten
salt electrolysis by adding titanium to a titanium plating solution
which is a molten salt containing KF, KCl and K.sub.2TiF.sub.6 in
at least a minimum amount necessary for converting Ti.sup.4+ to
Ti.sup.3+ according to the comproportionation reaction represented
by the following formula (A)
3Ti.sup.4++metal Ti.fwdarw.4Ti.sup.3+ Formula (A):
[0015] According to the above method, it is possible to form a
smooth titanium plating film on the surface of the cathode used in
the molten salt electrolysis.
[0016] However, since it is impossible to confirm whether or not
the comproportionation reaction has sufficiently progressed in the
above method, it is necessary to wait longer than the time required
for the molten salt electrolysis to finish after titanium is added
to the titanium plating solution. In addition, if oxygen is mixed
into the titanium plating solution from the external environment
for some reasons, the titanium ions may be oxidized from Ti.sup.3+
to Ti.sup.4+, and thereby it is impossible to know whether or not
Ti.sup.3+ is sufficiently present in the titanium plating
solution.
[0017] In view of the above problems, it is an object of the
present disclosure to provide a method for preparing a titanium
plating solution in which the concentration ratio between Ti.sup.3+
and Ti.sup.4+ in the titanium plating solution is monitored so that
the concentration of Ti.sup.3+ is maintained sufficiently high.
Advantageous Effect of the Present Disclosure
[0018] According to the present disclosure, it is possible to
provide a method for preparing a titanium plating solution in which
the concentration ratio between Ti.sup.3+ and Ti.sup.4+ in the
titanium plating solution is monitored so that the concentration of
Ti.sup.3+ is maintained sufficiently high.
Description of Embodiments
[0019] First, embodiments of the present disclosure are enumerated
hereinafter.
[0020] (1) A method for preparing a titanium plating solution
according to one embodiment of the present disclosure includes:
measuring a titanium plating solution containing fluorine and
titanium by cyclic voltammetry under the following conditions; and
adding titanium to the titanium plating solution so that the
potential difference between the spontaneous potential and the
Ti3.sup.+/Ti.sup.4+ redox potential is 0.75 V or more, conditions:
when the temperature of the titanium plating solution is
650.degree. C. or more and 850.degree. C. or less and when glassy
carbon is used as a working electrode, platinum is used as a
pseudo-reference electrode and titanium is used as a counter
electrode, the potential scanning is repeatedly performed on the
working electrode for at least five times at a scanning speed of 1
mV/sec or more and 500 mV/sec or less between a lower potential
limit which is the immersion potential of the working electrode and
an upper potential limit which is a potential that is 2 V to 4 V
higher than the lower potential limit.
[0021] According to the embodiment described in the above (1), it
is possible to provide a method for preparing a titanium plating
solution in which the concentration ratio between Ti.sup.3+ and
Ti.sup.4+ in the titanium plating solution is monitored so that the
concentration of Ti.sup.3+ is maintained sufficiently high.
[0022] (2) In the method for preparing a titanium plating solution
described in the above (1), it is preferable that the titanium
plating solution is obtained by dissolving titanium in a molten
salt of potassium fluoride and potassium chloride.
[0023] (3) In the method for preparing a titanium plating solution
described in the above (1) or (2), it is preferable that the
titanium plating solution is obtained by dissolving
K.sub.2TiF.sub.6 in a molten salt of potassium fluoride and
potassium chloride.
[0024] According to the embodiment described in the above (2) or
(3), it is possible to provide a titanium plating solution that can
be maintained in liquid state at a temperature lower than a
titanium plating solution which is obtained by dissolving titanium
in potassium fluoride.
[0025] (4) In the method for preparing a titanium plating solution
described in the above (3), it is preferable that the content of
the K.sub.2TiF.sub.6 in the titanium plating solution is 0.1 mol %
or more.
[0026] According to the embodiment described in the above (4), it
is possible to provide a titanium plating solution enabling the
titanium plating to be carried out stably.
[0027] (5) In the method for preparing a titanium plating solution
described in any one of the above (2) to (4), it is preferable that
the molar mixing ratio between potassium fluoride and potassium
chloride is 10:90 to 90:10.
[0028] According to the embodiment described in the above (5), it
is possible to provide a titanium plating solution enabling the
formation of a smooth titanium plating film.
[0029] (6) In the method for preparing a titanium plating solution
described in any one of the above (1) to (5), it is preferable that
the titanium added to the titanium plating solution is titanium
sponge.
[0030] According to the embodiment described in the above (6), it
is possible to facilitate the progress of the comproportionation
reaction of titanium in the titanium plating solution.
[0031] Note that the titanium sponge refers to a porous metal
titanium having a porosity of 1% or more. The porosity of the
titanium sponge is calculated by the following formula:
100-(the volume calculated from the mass)/(the apparent
volume).times.100.
[0032] (7) A method for manufacturing a titanium plated product
according to one embodiment of the present disclosure includes an
electrolyzing step of carrying out a molten salt electrolysis by
using a cathode and an anode provided in a titanium plating
solution containing fluorine and titanium so as to electrodeposit
titanium on the surface of the cathode, and the titanium plating
solution is prepared by the method for preparing a titanium plating
solution according to any one of the above (1) to (6).
[0033] According to the embodiment described in the above (7), the
method for manufacturing a titanium plated product may be used to
produce a titanium plated product with a smooth titanium plating
film formed on its surface.
[0034] (8) In the method for manufacturing a titanium plated
product described in the above (7), the titanium plating solution
used in the electrolyzing step is measured by cyclic voltammetry
under the following conditions, and the potential difference
between the spontaneous potential and the Ti3.sup.+/Ti.sup.4+ redox
potential is controlled to be 0.75 V or more,
[0035] conditions: when the temperature of the titanium plating
solution is 650.degree. C. or more and 850.degree. C. or less and
when glassy carbon is used as a working electrode, platinum is used
as a pseudo-reference electrode and titanium is used as a counter
electrode, the potential scanning is repeatedly performed on the
working electrode for at least five times at a scanning speed of 1
mV/sec or more and 500 mV/sec or less between a lower potential
limit which is the immersion potential of the working electrode and
an upper potential limit which is a potential that is 2 V to 4 V
higher than the lower potential limit.
[0036] According to the embodiment described in the above (8), the
method for manufacturing a titanium plated product may be used to
continuously and stably produce a titanium plated product with a
smooth titanium plating film formed on its surface.
Details of Embodiment of the Present Disclosure
[0037] Specific examples of the method for preparing a titanium
plating solution and the method for manufacturing a titanium plated
product according to an embodiment of the present disclosure will
be described hereinafter in more detail. It should be noted that
the present invention is not limited to the specific examples but
defined by the scope of the claims, and it is intended that the
present invention encompasses all modifications equivalent in
meaning and scope to the claims.
Method for Preparing Titanium Plating Solution
[0038] In the method for preparing a titanium plating solution
according to an embodiment of the present disclosure, first, a
titanium plating solution containing fluorine and titanium is
prepared. Then, the titanium plating solution is measured by cyclic
voltammetry (hereinafter, abbreviated to "CV" where necessary), and
titanium is added to the titanium plating solution so that the
potential difference between the spontaneous potential and the
Ti3.sup.+/Ti.sup.4+ redox potential is 0.75 V or more.
[0039] The CV measurement may be carried out in a non-oxidizing
atmosphere which does not react with titanium to form a compound.
For example, the CV measurement may be carried out in an inert gas
atmosphere such as argon gas. The CV measurement may be carried out
under such a condition that the temperature is set to 650.degree.
C. or more and 850.degree. C. or less so as to maintain the
titanium plating solution in liquid state and the scanning speed of
the potential scanning is set at 1 mV/sec or more and 500 mV/sec or
less. From the viewpoint of preventing the conductivity of the
titanium plating solution from decreasing, the temperature of the
titanium plating solution is more preferably 650.degree. C. or more
and 850.degree. C. or less, and further preferably 650.degree. C.
or more and 750.degree. C. or less. From the viewpoint of
shortening the measurement time or increasing the measurement
accuracy, the scanning speed of the potential scanning is more
preferably 50 mV/sec or more and 300 mV/sec or less, and further
preferably 100 mV/sec or more and 200 mV/sec or less.
[0040] The working electrode may be, for example, graphite, glassy
carbon or the like.
[0041] The reference electrode may be, for example, Pt, Ni or the
like.
[0042] The counter electrode may be, for example, titanium, glassy
carbon, graphite or the like.
[0043] In the CV measurement, the potential scanning is repeatedly
performed on the working electrode for at least five times between
a lower potential limit which is the immersion potential of the
working electrode and an upper potential limit which is a potential
that is 2 V to 4 V higher than the lower potential limit.
[0044] FIG. 1 illustrates the CV measurement result of a titanium
plating solution. In FIG. 1, the vertical axis represents the
current (mA) and the horizontal axis represents the potential (V)
of the reference electrode.
[0045] The spontaneous potential 1 refers to a potential difference
between the working electrode and the reference electrode when no
current is flowing therethrough.
[0046] The Ti.sup.3+/Ti.sup.4+ redox potential 4 refers to a
midpoint potential between the peak potential 2 resulting from the
oxidation of Ti.sup.3+ to Ti.sup.4+ and the peak potential 3
resulting from the reduction of Ti.sup.4+ to Ti.sup.3+. The peak
potential 2 resulting from the oxidation of Ti.sup.3+ to Ti.sup.4+
is an average value of the potentials obtained by repeating the
potential scanning on the working electrode for at least five
times. Likewise, the peak potential 3 resulting from the reduction
of Ti.sup.4+ to Ti.sup.3+ is an average value of the potentials
obtained by repeating the potential scanning on the working
electrode for at least five times.
[0047] When a titanium plating solution has a potential difference
between the spontaneous potential 1 and the Ti.sup.3+/Ti.sup.4+
redox potential 4 of 0.75 V or more, the concentration of Ti.sup.3+
in the titanium plating solution is much greater than the
concentration of Ti.sup.4+. Therefore, if the molten salt
electrolysis is carried out by using a titanium plating solution
having a potential difference between the spontaneous potential 1
and the Ti.sup.3+/Ti.sup.4+ redox potential 4 of 0.75 V or more, a
titanium plating film which is silvery white and highly smooth can
be formed on the surface of the cathode. On the other hand, when
the molten salt electrolysis is carried out by using a titanium
plating solution having a potential difference between the
spontaneous potential 1 and the Ti.sup.3+/Ti.sup.4+ redox potential
4 of less than 0.75 V, a titanium plating film cannot be formed on
the surface of the cathode. From the viewpoint of forming a smooth
titanium plating film, the potential difference between the
spontaneous potential 1 and the Ti.sup.3+/Ti.sup.4+ redox potential
4 is more preferably 1.0 V or more, and further preferably 1.1 V or
more.
[0048] If the potential difference between the spontaneous
potential 1 and the Ti.sup.3+/Ti.sup.4+ redox potential 4 is known,
the ratio between the concentration of Ti.sup.3+ and the
concentration of Ti.sup.4+ in the titanium plating solution may be
calculated by using the Nernst equation represented by the
following formula (B):
E=E.sub.0-(RT/zF)ln(a.sub.Ti3+/a.sub.Ti4+) Equation (B):
wherein E: electrode potential; E.sub.0: standard electrode
potential; R: gas constant; T: absolute temperature; Z: number of
mobile electrons; F: Faraday constant; and a: activity.
[0049] When using the Nernst equation to calculate the ratio
between the concentration of Ti.sup.3+ and the concentration of
Ti.sup.4+, it is assumed that the electrode potential E in the
formula (B) is dominantly affected by a reaction of oxidizing
Ti.sup.3+ to Ti.sup.4+ and a reaction of reducing Ti.sup.4+ to
Ti.sup.3+, and it is also assumed that the ratio between the
activity of Ti.sup.3+ and the activity of Ti.sup.4+ (Ti.sup.3+
activity/Ti.sup.4+ activity) is the same as the ratio between the
concentration of Ti.sup.3+ and the concentration of Ti.sup.4+
(Ti.sup.3+ concentration/Ti.sup.4+ concentration).
[0050] The titanium plating solution before the CV measurement may
be a molten salt containing fluorine and titanium. For example, the
titanium plating solution may be a molten salt obtained by
dissolving K.sub.2TiF.sub.6 in KF--KCl, a molten salt obtained by
dissolving K.sub.2TiF.sub.6 in LiF--KCl, or a molten salt obtained
by dissolving K.sub.2TiF.sub.6 in NaF--KCl. The titanium compound
to be dissolved in the molten salt is not limited to
K.sub.2TiF.sub.6, it may be TiCl.sub.4 or the like. Among the
molten salts mentioned above, the molten salt obtained by
dissolving K.sub.2TiF.sub.6 in KF--KCl is preferable. The molten
salt obtained by dissolving K.sub.2TiF.sub.6 in KF--KCl is a
titanium plating solution that may be used to form a smooth
titanium plating film.
[0051] When KF--KCl is used in the molten salt, the molar mixing
ratio between KF and KCl is preferably 10:90 to 90:10. If the
content ratio of KF in KF--KCl is 10 mol % or more, a smooth
titanium plating film may be electrodeposited on the surface of the
cathode. If the content ratio of KF in KF--KCl is 90 mol % or less,
the melting point may be made lower than that of the molten salt of
KF alone. From these viewpoints, the molar mixing ratio between KF
and KCl is more preferably 20:80 to 80:20, and further preferably
40:60 to 60:40.
[0052] When carrying out the CV measurement on the titanium plating
solution made of the molten salt, if the potential difference
between the spontaneous potential 1 and the Ti.sup.3+/Ti.sup.4+
redox potential 4 is less than 0.75 V, titanium should be added to
the titanium plating solution so that the potential difference
between the spontaneous potential 1 and the Ti.sup.3+/Ti.sup.4+
redox potential 4 is 0.75 V or more.
[0053] Although the form of Ti to be added to the titanium plating
solution is not particularly limited, it is preferable to use
titanium sponge, titanium powder which is processed as fine as
possible or the like. Since titanium sponge has a higher porosity,
the specific surface area is larger, which makes it easier to be
dissolved in the molten salt bath. Thus, the porosity of titanium
sponge to be used is more preferably 20% or more, and further
preferably 40% or more. Using titanium sponge which has a higher
porosity may facilitate the progress of the comproportionation
reaction in the titanium plating solution.
[0054] If the titanium plating solution obtained by the method for
preparing a titanium plating solution according to an embodiment of
the present disclosure is used to carry out the molten salt
electrolysis, it is possible to manufacture a titanium plated
product with a smooth titanium plating film having a small
thickness distribution on its surface.
Method for Manufacturing Titanium Plated Product
[0055] A method for manufacturing a titanium plated product
according to an embodiment of the present disclosure includes an
electrolyzing step of carrying out a molten salt electrolysis by
using a cathode and an anode provided in the titanium plating
solution which is obtained according to the method for preparing a
titanium plating solution described in the above embodiment so as
to electrodeposit titanium on the surface of the cathode.
Cathode
[0056] In the electrolyzing step, a titanium plating film will be
formed on the surface of the cathode. Thus, a material suitable for
forming the titanium plating film on the surface may be used as the
cathode. As an example, a metal, a conductive sintered body or the
like may be given. Specifically, nickel, iron, SUS304, molybdenum,
tungsten, copper, carbon or the like may be preferably used.
[0057] The base material used as the cathode is simply required to
be conductive at least at its surface. If the base material is made
of a material to be alloyed with titanium, a titanium alloy layer
may be formed on the cathode side of the titanium plating film. On
the other hand, if a high-purity titanium plating film is to be
formed without a titanium alloy layer, a material that cannot be
alloyed with Ti in the titanium plating solution may be used as the
cathode.
Anode
[0058] The anode is not particularly limited, and it may be made of
any conductive material such as glassy carbon or titanium, for
example. From the viewpoint of stably and continuously producing
the titanium plating film, the anode is preferably made of Ti.
Other Conditions
[0059] The atmosphere in which the molten salt electrolysis is
carried out may be vacuum or a non-oxidative atmosphere that does
not form a compound with titanium. For example, the molten salt
electrolysis may be carried out in a glove box filled or circulated
with an inert gas such as argon gas.
[0060] The current density for carrying out the molten salt
electrolysis is not particularly limited, and it may be, for
example, 10 mA/cm.sup.2 or more and 500 mA/cm.sup.2 or less. By
setting the current density to 10 mA/cm.sup.2 or more, it is
possible to stably form a titanium plating film on the surface of
the cathode. By setting the current density to 500 mA/cm.sup.2 or
less, the diffusion of titanium ions in the titanium plating
solution is not a rate-limiting factor, and thus the resulting
titanium plating film can be prevented from becoming black. From
these viewpoints, the current density is more preferably 50
mA/cm.sup.2 or more and 250 mA/cm.sup.2 or less, and further
preferably 100 mA/cm.sup.2 or more and 200 mA/cm.sup.2 or less.
[0061] In the electrolyzing step, the temperature of the titanium
plating solution is preferably 650.degree. C. or more and
850.degree. C. or less. If the temperature of the titanium plating
solution is set to 650.degree. C. or more, it is possible to
maintain the titanium plating solution in liquid state so as to
carry out the molten salt electrolysis stably. If the temperature
of the titanium plating solution is set to 850.degree. C. or less,
it is possible to prevent the titanium plating solution from
becoming unstable due to the evaporation of the components in the
titanium plating solution. From these viewpoints, the temperature
of the titanium plating solution is more preferably 650.degree. C.
or more and 750.degree. C. or less, and further preferably
650.degree. C. or more and 700.degree. C. or less.
[0062] The time for carrying out the molten salt electrolysis is
not particularly limited, and it may be carried out for a period of
time in which the target titanium plating film is sufficiently
formed on the surface of the cathode.
CV Measurement in Electrolyzing Step
[0063] In the electrolyzing step, it is preferable that the
titanium plating solution is measured regularly or irregularly by
cyclic voltammetry and the potential difference between the
spontaneous potential and the Ti.sup.3+/Ti.sup.4+ redox potential
is controlled to be 0.75 V or more.
[0064] If oxygen or water is mixed into the titanium plating
solution from the external environment for some reasons during the
electrolyzing step, the titanium ions may be oxidized from
Ti.sup.3+ to Ti.sup.4+, and thereby a smooth titanium plating film
may not be formed. Further, when an electrode other than the
titanium electrode is used as the anode, the concentration of the
titanium ions in the titanium plating solution may change at
anytime.
[0065] Even under these circumstances, the titanium plating
solution is subjected to CV measurement regularly or irregularly
and controlled so that the potential difference between the
spontaneous potential and the Ti.sup.3+/Ti.sup.4+ redox potential
is 0.75 V or more, which makes it possible to stably and
continuously form a smooth titanium plating film on the surface of
the cathode.
[0066] The conditions for the CV measurement are the same as those
for the CV measurement in the method for preparing a titanium
plating solution according to the embodiment of the present
disclosure described above. When the potential difference between
the spontaneous potential and the Ti.sup.3+/Ti.sup.4+ redox
potential of the titanium plating solution determined by the CV
measurement becomes less than 0.75 V, for example, titanium sponge
or the like may be added and dissolved in the titanium plating
solution.
[0067] According to the method for manufacturing a titanium plated
product according to the embodiment of the present disclosure, it
is possible to manufacture a titanium plated product with a smooth
titanium plating film having a small thickness distribution on its
surface. A smooth titanium plating film having a small film
thickness distribution refers to such a film that either the
maximum thickness or the minimum thickness of the titanium plating
film measured at any of arbitrary five spots is preferably within
.+-.50% of the average film thickness.
[0068] The average film thickness of the titanium plating film is
measured in the following manner. FIG. 2 is a conceptual diagram
for illustrating a method for measuring the average film
thickness.
[0069] First, the titanium plated product with a titanium plating
film formed on its surface is arbitrarily and equally divided into
areas, and five spots (area A to area E) are selected as
measurement spots. Then, the cross section of the titanium plating
film in each area is observed with a scanning electron microscope
(SEM). The magnifying power of the SEM is set in such a manner that
the entire titanium plating film can be observed in the thickness
direction and is enlarged in the thickness direction as much as
possible in one field of view. The maximum thickness and the
minimum thickness of the titanium plating film in each area are
measured at three points by changing the field of view, and the
average value is defined as the average film thickness of the
titanium plating film.
[0070] As an example, FIG. 2 illustrates a schematic view of a
titanium plated product 21 with a titanium plating film formed on
the surface of a substantially square-shaped base material, in
which four corners are defined as areas A to D, and a central
portion is defined as an area E. FIG. 3 illustrates a conceptual
view of a field of view (i) when the area A of the titanium plated
product 21 illustrated in FIG. 2 is observed by SEM. Similarly,
FIG. 4 illustrates a conceptual view of a field of view (ii) of the
area A, and FIG. 5 illustrates a conceptual view of a field of view
(iii) of the area A.
[0071] In each field of view (i) to (iii) for the area A of the
titanium plated product 21 observed by SEM, the maximum thickness
of the titanium plating film 23 (the maximum thickness A(i), the
maximum thickness A(ii), and the maximum thickness A(iii)) and the
minimum thickness of the titanium plating film 23 (the minimum
thickness a(i), the minimum thickness a(ii), and the minimum
thickness a(iii)) are measured. The thickness of the titanium
plating film 23 is defined as the length of the titanium plating
film 23 extending in the vertical direction from the base material
22. In the case where a titanium alloy layer made of titanium and a
base metal is formed between the titanium plating film 23 and the
base material 22, the thickness of the titanium plating film 23 is
defined as the total length of the titanium alloy layer and the
titanium plating film extending in the vertical direction from the
base material 22. Thus, in the area A, the maximum thickness A(i)
to A(iii) and the minimum thickness a(i) to a(iii) are determined
in three fields of view. Regarding the areas B, C, D and E, the
maximum thickness and the minimum thickness of the titanium plating
film are measured in three fields of view in the same manner as the
area A.
[0072] Thus, the average of the maximum thickness A(i) to A(iii),
B(i) to B(iii), C(i) to C(iii), D(i) to D(iii) and E(i) to E(iii)
and the minimum thickness a(i) to a(iii), b(i) to b(iii), c(i) to
c(iii), d(i) to d(iii) and e(i) to e(iii) of the titanium plating
film measured as described above are averaged, and the average
value is defined as the average film thickness of the titanium
plating film.
EXAMPLES
[0073] Hereinafter, the present disclosure will be described in
more detail by examples. It should be noted that the examples are
illustrative, and the method for preparing a titanium plating
solution and the method for manufacturing a titanium plated product
of the present invention are not limited to the examples. The scope
of the present invention is defined by the scope of the claims, and
encompasses all modifications equivalent in meaning and scope to
the claims.
Example 1
Preparation of Titanium Plating Solution
[0074] KCl, KF and K.sub.2TiF.sub.6 were mixed so that the molar
mixing ratio between KCl and KF was 55:45 and the concentration of
K.sub.2TiF.sub.6 was 0.1 mol %, and were heated to 650.degree. C.
to prepare a titanium plating solution.
[0075] While the obtained titanium plating solution was maintained
at 650.degree. C., the CV measurement was carried out at a
potential scanning speed of 200 mV/sec under an atmosphere in which
argon gas was circulated. A graphite rod with a diameter of 3 mm
was used as a working electrode, a Pt wire with a diameter of 1 mm
was used as a reference electrode, and a titanium rod with a
diameter of 3 mm was used as a counter electrode. The potential
scanning was repeatedly performed on the working electrode for five
times.
[0076] According to the CV measurement, the potential difference
between the spontaneous potential and the Ti.sup.3+/Ti.sup.4+ redox
potential of the titanium plating solution was 0.65 V.
[0077] Therefore, 0.3 mg of titanium sponge per 1 g of the titanium
plating solution was added to the titanium plating solution, and
sufficiently dissolved therein. The used titanium sponge has a
porosity of 50%.
[0078] Again, the titanium plating solution was subjected to the CV
measurement under the same conditions, and the potential difference
between the spontaneous potential and the Ti.sup.3+/Ti.sup.4+ redox
potential was 0.75 V. This titanium plating solution was used as
the titanium plating solution No. 1.
Manufacture of Titanium Plated Product
[0079] A cathode and an anode were provided in the titanium plating
solution No. 1, and the molten salt electrolysis was carried out
for 40 minutes.
[0080] The molten salt electrolysis was carried out in a glove box
under an argon flow atmosphere. A Ni plate of 0.5 cm.times.2.5
cm.times.0.1 mm was used as the cathode, and a Ti rod was used as
the anode. A Pt wire was used as a pseudo-reference electrode. The
current density was set to 25 mA/cm.sup.2. The potential of the
pseudo-reference electrode was calibrated with the potential
(K.sup.+/K potential) of metallic potassium electrochemically
deposited on the Pt wire.
[0081] As a result, titanium was electrodeposited on the surface of
the Ni plate serving as the cathode, and a titanium plated product
with a titanium plating film formed on the surface was
obtained.
[0082] After the molten salt electrolyzing step, the titanium
plated product was washed with water. The salt that adhered to the
surface of the titanium plated product was highly soluble in water
and was easily removed. Through the above-described operation, the
titanium plated product No. 1 with a titanium plating film formed
on its surface was obtained.
Example 2
Preparation of Titanium Plating Solution
[0083] Titanium plating solution No. 2 was prepared in the same
manner as Example 1 except that the amount of titanium sponge added
to the titanium plating solution after the CV measurement in
Example 1 was modified to 0.5 mg of titanium sponge per 1 g of the
titanium plating solution. The titanium plating solution No. 2, to
which titanium sponge was added, was subjected to the CV
measurement under the same conditions as Example 1, and the
potential difference between the spontaneous potential and the
Ti.sup.3+/Ti.sup.4+ redox potential was 0.85 V.
Manufacture of Titanium Plated Product
[0084] Titanium plated product No. 2 was manufactured in the same
manner as Example 1 except that the titanium plating solution No. 2
was used in place of the titanium plating solution No. 1 of Example
1.
Example 3
Preparation of Titanium Plating Solution
[0085] Titanium plating solution No. 3 was prepared in the same
manner as Example 1 except that the amount of titanium sponge added
to the titanium plating solution after the CV measurement in
Example 1 was modified to 1 mg of titanium sponge per 1 g of the
titanium plating solution. The titanium plating solution No. 3, to
which titanium sponge was added, was subjected to the CV
measurement under the same conditions as Example 1, and the
potential difference between the spontaneous potential and the
Ti.sup.3+/Ti.sup.4+ redox potential was 1.00 V.
Manufacture of Titanium Plated Product
[0086] Titanium plated product No. 3 was manufactured in the same
manner as Example 1 except that the titanium plating solution No. 3
was used in place of the titanium plating solution No. 1 of Example
1.
Example 4
Preparation of Titanium Plating Solution
[0087] Titanium plating solution No. 4 was prepared in the same
manner as Example 1 except that the amount of titanium sponge added
to the titanium plating solution after the CV measurement in
Example 1 was modified to 1.2 mg of titanium sponge per 1 g of the
titanium plating solution. The titanium plating solution No. 4, to
which titanium sponge was added, was subjected to the CV
measurement under the same conditions as Example 1, and the
potential difference between the spontaneous potential and the
Ti.sup.3+/Ti.sup.4+ redox potential was 1.10 V.
[0088] FIG. 6 illustrates the result of the CV measurement (the
result of the fifth potential scanning) for the titanium plating
solution No. 4. In FIG. 6, the vertical axis represents the current
(mA), and the horizontal axis represents the potential (V) of the
reference electrode.
Manufacture of Titanium Plated Product
[0089] Titanium plated product No. 4 was manufactured in the same
manner as Example 1 except that the titanium plating solution No. 4
was used in place of the titanium plating solution No. 1 of Example
1.
Comparative Example 1
Preparation of Titanium Plating Solution
[0090] Titanium plating solution No. A was prepared in the same
manner as Example 1 except that titanium sponge was not added to
the titanium plating solution after the CV measurement in Example
1. The titanium plating solution No. A was subjected to the CV
measurement under the same conditions as Example 1, and the
potential difference between the spontaneous potential and the
Ti.sup.3+/Ti.sup.4+ redox potential was 0.67 V. FIG. 7 illustrates
the result of the CV measurement (the result of the fifth potential
scanning) for the titanium plating solution No. A. In FIG. 7, the
vertical axis represents the current (mA), and the horizontal axis
represents the potential (V) of the reference electrode.
Manufacture of Titanium Plated Product
[0091] Titanium plated product No. A was manufactured in the same
manner as Example 1 except that the titanium plating solution No. A
was used in place of the titanium plating solution No. 1 of Example
1.
Comparative Example 2
Preparation of Titanium Plating Solution
[0092] Titanium plating solution No. B was prepared in the same
manner as Example 1 except that the amount of titanium sponge added
to the titanium plating solution after the CV measurement in
Example 1 was modified to 0.2 mg of titanium sponge per 1 g of the
titanium plating solution. The titanium plating solution No. B, to
which titanium sponge was added, was subjected to the CV
measurement under the same conditions as Example 1, and the
potential difference between the spontaneous potential and the
Ti.sup.3+/Ti.sup.4+ redox potential was 0.70 V.
Manufacture of Titanium Plated Product
[0093] Titanium plated product No. B was manufactured in the same
manner as Example 1 except that the titanium plating solution No. B
was used in place of the titanium plating solution No. 1 of Example
1.
Evaluation
[0094] The ratio between the concentration of Ti.sup.3+ and the
concentration of Ti.sup.4+ (Ti.sup.3+ concentration/Ti.sup.4+
concentration) in each of the titanium plating solution No. 1
obtained in Example 1, the titanium plating solution No. 2 obtained
in Example 2, the titanium plating solution No. 3 obtained in
Example 3, the titanium plating solution No. 4 obtained in Example
4, the titanium plating solution No. A obtained in Comparative
Example 1, and the titanium plating solution No. B obtained in
Comparative Example 2 was calculated by using the Nernst equation.
The results are listed in Table 1.
[0095] In addition, the surface condition of each of the titanium
plated product No. 1 obtained in Example 1, the titanium plated
product No. 2 obtained in Example 2, the titanium plated product
No. 3 obtained in Example 3, the titanium plated product No. 4
obtained in Example 4, the titanium plated product No. A obtained
in Comparative Example 1, and the titanium plated product No. B
obtained in Comparative Example 2 was visually observed. The
results are listed in Table 1.
[0096] The current efficiency of the cathode in the electrolyzing
step of each of Examples 1 to 4 and Comparative Examples 1 and 2
was calculated by using the following formula (C). The results are
listed in Table 1.
Current efficiency (%)=(actual plating amount)/(theoretical plating
amount).times.100 Formula (C):
TABLE-US-00001 TABLE 1 Titanium plating solution Difference (V)
between Titanium plated product spontaneous Ti.sup.3+/Ti.sup.4+
Surface Current potential and Concen- condition efficiency
Ti.sup.3+/Ti.sup.4- tration of titanium of cathode No. redox
potential ratio No. plating film (%) 1 0.75 10000 1 silvery white
20 2 0.85 40000 2 silvery white 30 3 1.00 290000 3 silvery white 90
4 1.10 1000000 4 silvery white 90 A 0.67 3500 A black plating
impossible B 0.70 7000 B black plating impossible
[0097] As listed in Table 1, when the molten salt electrolysis was
carried out by using the titanium plating solutions No. 1 to No. 4
having a potential difference between the spontaneous potential and
the Ti.sup.3+/Ti.sup.4+ redox potential of 0.75 V or more, it is
possible to obtain the titanium plated products No. 1 to No. 4 each
with a silvery white and smooth titanium plating film formed on its
surface. In particular, when the titanium plating solution No. 3 or
No. 4 having a potential difference between the spontaneous
potential and the Ti.sup.3+/Ti.sup.4+ redox potential of 1.00 V or
more was used, the current efficiency of the cathode could be
improved to 90% or more.
[0098] On the other hand, when the molten salt electrolysis was
carried out by using the titanium plating solution No. A or No. B
having a potential difference between the spontaneous potential and
the Ti.sup.3+/Ti.sup.4+ redox potential of less than 0.75 V, a
titanium plating film could not be successfully formed on the
cathode surface, and the electrodeposited film was black.
REFERENCE SIGNS LIST
[0099] 1: spontaneous potential; 2: peak potential resulting from
the oxidation of Ti.sup.3+ to Ti.sup.4+; 3: peak potential
resulting from the reduction of Ti.sup.4+ to Ti.sup.3+; 4:
Ti.sup.3+/Ti.sup.4+ redox potential; A: arbitrary area on titanium
plated product; B: arbitrary area on titanium plated product; C:
arbitrary area on titanium plated product; D: arbitrary area on
titanium plated product; E: arbitrary area on titanium plated
product; 21: titanium plated product; 22: base material; 23:
titanium plating film; 61: spontaneous potential; 64:
Ti.sup.3+/Ti.sup.4+ redox potential; 71: spontaneous potential; 74:
Ti.sup.3+/Ti.sup.4+ redox potential
* * * * *