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 November 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
2TiF
6 or TiO
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
+/Ti
4+ redox potential is 0.75 V or more, conditions: when the temperature of the titanium
plating solution is 650°C or more and 850°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;
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;
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.
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;
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.
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
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]
[0007] 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.
[0008] 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
2TiF
6 in at least a minimum amount necessary for converting Ti
4+ to Ti
3+ according to the comproportionation reaction represented by the following formula
(A):
Formula (A): 3Ti
4+ + metal Ti → 4Ti
3+
[0009] 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.
[0010] 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
3+ to Ti
4+, and thereby it is impossible to know whether or not Ti
3+ is sufficiently present in the titanium plating solution.
[0011] 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
3+ and Ti
4+ in the titanium plating solution is monitored so that the concentration of Ti
3+ is maintained sufficiently high.
[Advantageous Effect of the Present Disclosure]
[0012] 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
3+ and Ti
4+ in the titanium plating solution is monitored so that the concentration of Ti
3+ is maintained sufficiently high.
[Description of Embodiments]
[0013] First, embodiments of the present disclosure are enumerated hereinafter.
[0014]
- (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+/Ti4+ redox potential is 0.75 V or more, conditions: when the temperature of the titanium
plating solution is 650°C or more and 850°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.
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 Ti3+ and Ti4+ in the titanium plating solution is monitored so that the concentration of Ti3+ is maintained sufficiently high.
- (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.
- (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
K2TiF6 in a molten salt of potassium fluoride and potassium chloride.
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.
- (4) In the method for preparing a titanium plating solution described in the above
(3), it is preferable that the content of the K2TiF6 in the titanium plating solution is 0.1 mol% or more.
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.
- (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.
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.
- (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.
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.
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:
- (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).
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.
- (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+/Ti4+ redox potential is controlled to be 0.75 V or more,
conditions: when the temperature of the titanium plating solution is 650°C or more
and 850°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.
[0015] 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]
[0016] 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>
[0017] 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
+/Ti
4+ redox potential is 0.75 V or more.
[0018] 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°C or more and 850°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°C or more and 850°C or less, and further preferably 650°C or more and 750°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.
[0019] The working electrode may be, for example, graphite, glassy carbon or the like.
[0020] The reference electrode may be, for example, Pt, Ni or the like.
[0021] The counter electrode may be, for example, titanium, glassy carbon, graphite or the
like.
[0022] 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.
[0023] 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.
[0024] The spontaneous potential 1 refers to a potential difference between the working
electrode and the reference electrode when no current is flowing therethrough.
[0025] The Ti3
+/Ti
4+ redox potential 4 refers to a midpoint potential between the peak potential 2 resulting
from the oxidation of Ti
3+ to Ti
4+ and the peak potential 3 resulting from the reduction of Ti
4+ to Ti
3+. The peak potential 2 resulting from the oxidation of Ti
3+ to Ti
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
4+ to Ti
3+ is an average value of the potentials obtained by repeating the potential scanning
on the working electrode for at least five times.
[0026] When a titanium plating solution has a potential difference between the spontaneous
potential 1 and the Ti
3+/Ti
4+ redox potential 4 of 0.75 V or more, the concentration of Ti
3+ in the titanium plating solution is much greater than the concentration of Ti
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
3+/Ti
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
3+/Ti
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
3+/Ti
4+ redox potential 4 is more preferably 1.0 V or more, and further preferably 1.1 V
or more.
[0027] If the potential difference between the spontaneous potential 1 and the Ti
3+/Ti
4+ redox potential 4 is known, the ratio between the concentration of Ti
3+ and the concentration of Ti
4+ in the titanium plating solution may be calculated by using the Nernst equation represented
by the following formula (B):
wherein E: electrode potential; E
0: standard electrode potential; R: gas constant; T: absolute temperature; Z: number
of mobile electrons; F: Faraday constant; and a: activity.
[0028] When using the Nernst equation to calculate the ratio between the concentration of
Ti
3+ and the concentration of Ti
4+, it is assumed that the electrode potential E in the formula (B) is dominantly affected
by a reaction of oxidizing Ti
3+ to Ti
4+ and a reaction of reducing Ti
4+ to Ti
3+, and it is also assumed that the ratio between the activity of Ti
3+ and the activity of Ti
4+ (Ti
3+ activity/Ti
4+ activity) is the same as the ratio between the concentration of Ti
3+ and the concentration of Ti
4+ (Ti
3+ concentration/Ti
4+ concentration).
[0029] 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
2TiF
6 in KF-KCl, a molten salt obtained by dissolving K
2TiF
6 in LiF-KCl, or a molten salt obtained by dissolving K
2TiF
6 in NaF-KCl. The titanium compound to be dissolved in the molten salt is not limited
to K
2TiF
6, it may be TiCl
4 or the like. Among the molten salts mentioned above, the molten salt obtained by
dissolving K
2TiF
6 in KF-KCl is preferable. The molten salt obtained by dissolving K
2TiF
6 in KF-KCl is a titanium plating solution that may be used to form a smooth titanium
plating film.
[0030] 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.
[0031] 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
Ti3
+/Ti
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
3+/Ti
4+ redox potential 4 is 0.75 V or more.
[0032] 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.
[0033] 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>
[0034] 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)
[0035] 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.
[0036] 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)
[0037] 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)
[0038] 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.
[0039] The current density for carrying out the molten salt electrolysis is not particularly
limited, and it may be, for example, 10 mA/cm
2 or more and 500 mA/cm
2 or less. By setting the current density to 10 mA/cm
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
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
2 or more and 250 mA/cm
2 or less, and further preferably 100 mA/cm
2 or more and 200 mA/cm
2 or less.
[0040] In the electrolyzing step, the temperature of the titanium plating solution is preferably
650°C or more and 850°C or less. If the temperature of the titanium plating solution
is set to 650°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°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°C or more and 750°C or less,
and further preferably 650°C or more and 700°C or less.
[0041] 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)
[0042] 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
3+/Ti
4+ redox potential is controlled to be 0.75 V or more.
[0043] 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
3+ to Ti
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.
[0044] 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
3+/Ti
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.
[0045] 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
3+/Ti
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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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
[0052] 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
[0053] KCl, KF and K
2TiF
6 were mixed so that the molar mixing ratio between KCl and KF was 55: 45 and the concentration
of K
2TiF
6 was 0.1 mol%, and were heated to 650°C to prepare a titanium plating solution.
[0054] While the obtained titanium plating solution was maintained at 650°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.
[0055] According to the CV measurement, the potential difference between the spontaneous
potential and the Ti
3+/Ti
4+ redox potential of the titanium plating solution was 0.65 V.
[0056] 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%.
[0057] 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
3+/Ti
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
[0058] 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.
[0059] The molten salt electrolysis was carried out in a glove box under an argon flow atmosphere.
A Ni plate of 0.5 cm × 2.5 cm × 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
2. The potential of the pseudo-reference electrode was calibrated with the potential
(K
+/K potential) of metallic potassium electrochemically deposited on the Pt wire.
[0060] 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.
[0061] 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
[0062] 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
3+/Ti
4+ redox potential was 0.85 V.
Manufacture of Titanium Plated Product
[0063] 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
[0064] 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
3+/Ti
4+ redox potential was 1.00 V.
Manufacture of Titanium Plated Product
[0065] 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
[0066] 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
3+/Ti
4+ redox potential was 1.10 V.
[0067] 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
[0068] 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
[0069] 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
3+/Ti
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
[0070] 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
[0071] 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
3+/Ti
4+ redox potential was 0.70 V.
Manufacture of Titanium Plated Product
[0072] 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>
[0073] The ratio between the concentration of Ti
3+ and the concentration of Ti
4+ (Ti
3+ concentration/Ti
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.
[0074] 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.
[0075] 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.
[Table 1]
Titanium plating solution |
Titanium plated product |
No. |
Difference (V) between spontaneous potential and Ti3+/Ti4+ redox potential |
Ti3+/Ti4+ Concentration ratio |
No. |
Surface condition of titanium plating film |
Current efficiency of cathode (%) |
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 |
[0076] 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
3+/Ti
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
3+/Ti
4+ redox potential of 1.00 V or more was used, the current efficiency of the cathode
could be improved to 90% or more.
[0077] 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
3+/Ti
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
[0078] 1: spontaneous potential; 2: peak potential resulting from the oxidation of Ti
3+ to Ti
4+; 3: peak potential resulting from the reduction of Ti
4+ to Ti
3+; 4: Ti
3+/Ti
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
3+/Ti
4+ redox potential; 71: spontaneous potential; 74: Ti
3+/Ti
4+ redox potential