U.S. patent number 3,718,551 [Application Number 05/086,033] was granted by the patent office on 1973-02-27 for ruthenium coated titanium electrode.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Aleksandrs Martinsons.
United States Patent |
3,718,551 |
Martinsons |
February 27, 1973 |
RUTHENIUM COATED TITANIUM ELECTRODE
Abstract
An anode for the electrolysis of brines is disclosed. The anode
has a titanium base member and an electroconductive coating
thereon. The electroconductive coating comprises a mixture of
amorphous titanium dioxide and a member of the group consisting of
ruthenium and ruthenium oxide.
Inventors: |
Martinsons; Aleksandrs
(Wadsworth, OH) |
Assignee: |
PPG Industries, Inc.
(Pittsburg, PA)
|
Family
ID: |
26774286 |
Appl.
No.: |
05/086,033 |
Filed: |
November 2, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
767281 |
Oct 14, 1968 |
3562008 |
|
|
|
Current U.S.
Class: |
205/505; 205/535;
204/290.14; 204/290.13 |
Current CPC
Class: |
C01B
13/14 (20130101); C25B 11/093 (20210101); C01P
2006/40 (20130101); C01P 2002/02 (20130101); C01P
2002/72 (20130101) |
Current International
Class: |
C01B
13/14 (20060101); C25B 11/00 (20060101); C25B
11/04 (20060101); B01r 003/04 (); B01r
001/00 () |
Field of
Search: |
;204/98-100,128,29F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Fay; Regan J.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser.
No. 767,281 now U.S. Pat. No. 3,562,008, filed Oct. 14, 1968.
Claims
I claim:
1. In a process for the electrolysis of brine comprising
causing an electrical current to pass from an anode to a cathode,
the improvement wherein the anode has a coating consisting
essentially of titanium oxide and ruthenium oxide wherein the
coating shows an X-ray diffraction pattern comprising:
in the range of 26 to 30 degrees two theta a peak having a breadth
at half-maximum intensity of between 1.3 to 2.0 degrees two theta,
said peak having its maximum intensity between 27.80 and 28.00
degrees two theta, and a peak height above background of less than
600 percent of background;
in the range of 34.00 to 38.00 degrees two theta a peak having a
breadth at half -maximum intensity of between 1.3 and 2.0 degrees
two theta, said peak having its maximum intensity between 35.0 and
35.4 degrees two theta, and a peak height above background of less
than 600 per cent of background; and wherein said anode is prepared
by the method comprising applying a mixture of titanium resinate
and ruthenium resinate to a titanium base and heating the coated
base between 300.degree.C and 650.degree.C.
2. An anode having a coating consisting essentially of titanium
oxide and ruthenium oxide wherein the coating shows an X-ray
diffraction pattern comprising:
in the range of 26 to 30 degrees two theta a peak having a breadth
at half-maximum intensity of between 1.3 and 2.0 degrees two theta,
said peak having its maximum intensity between 27.80 and 28.00
degrees two theta, and a peak height above background of less than
700 per cent of background; and
in the range of 34.00 to 38.00 degrees two theta a peak having a
breadth at half-maximum intensity of between 1.3 and 2.0 degrees
two theta, said peak having its maximum intensity between 35.0 and
35.4 degrees two theta, and a peak height above background of less
than 600 per cent of background, prepared by the method comprising
applying a mixture of titanium resinate and ruthenium resinate to a
titanium base and heating the coated base to between 300.degree.C.
and 650.degree.C.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrodes for electrolytic cells and,
more particularly, to a corrosion-resistant, dimensionally-stable
anode for electrolysis of aqueous alkali metal chloride in the
production of elemental chlorine or alkali metal chlorate. Such
electrode has a metallic oxide coating.
The electrolysis of aqueous alkali metal chloride solutions such as
solutions of sodium chloride or potassium chloride is conducted on
a vast commercial scale. In the production of alkali metal
chlorate, anodes and cathodes, or bipolar electrodes which when
arranged in a spaced electrical series in an electrolytic cell may
serve as both anode and cathode, are immersed in an aqueous
solution of the sodium chloride or the like and an electric
potential is established between the electrodes. In the past,
graphite or carbon electrodes have been used as anodes or as the
bipolar electrodes in series. In consequence of the electrochemical
reactions which occur, alkali metal chlorate is produced either
directly in the cell or outside the cell after the solution is
allowed to stand.
The electrolysis of alkali metal chloride to produce elemental
chlorine and alkali metal hydroxide is conducted in two general
types of cells--the diaphragm and the mercury cathode cell. In the
diaphragm cell, the cell is divided into two compartments--the
anode compartment and the cathode compartment--which are separated
by a porous diaphragm usually of asbestos. The cathode is of
perforate metal and the asbestos diaphragm is in contact with the
cathode. The anode, usually of carbon or graphite, is dispersed
centrally in the anode compartment.
In the mercury cathode cell, the cathode is a flowing stream of
mercury which flows along a solid metal base connected to the
negative pole of a power source. The anode, again of carbon or
graphite, is spaced from the mercury cathode and, as electric
current flows, the sodium or like alkali metal is evolved and
collected in the mercury as an amalgam which is removed from the
cell. Outside the cell the mercury amalgam is contacted with water
in a "denuder" to remove the sodium as sodium hydroxide solution
and the mercury is then recycled.
In operating each of the above-described cells, one is confronted
with a common problem; namely, that during the course of the
electrolysis the carbon or graphite electrode erodes and/or
decomposes. Consequently, as the electrodes wear away or erode, the
spacing between the electrodes increases with resulting increase in
voltage between electrodes. This, together with the reactions which
cause degradation of the anode, results in a loss of current
efficiency for the production of the desired product. The graphite
anodes ultimately must be replaced. In all these cells this erosion
increases as the temperature of the electrolyte rises or as the
anode current density is increased. At the same time, the trend of
operation is toward high current density to increase the amount of
product produced per unit cell. Thus it has become necessary to
resort to anodes or bipolar electrodes which remain dimensionally
stable and do not erode appreciably over long periods of cell
operation.
The present invention is directed to an improved stable electrode,
the electrolysis of alkali metal chloride solutions in cells having
the improved electrode, and to electrolytic cells, particularly to
cells of the type described above which contain such electrodes as
the anode or anodic surface thereof.
Electrodes herein contemplated normally should possess a certain
degree of rigidity and, in any event, they must have surfaces which
exhibit good electrolytic characteristics. These characteristics,
particularly in the case of anodes, include low oxygen and chlorine
overvoltage, resistance to corrosion and decomposition in the
course of use as anodes in the electrolytic cell, and minimum loss
of coating during such use. It is well known that certain metals,
metallic oxides, and alloys are stable during electrolysis and have
other superior properties when used as anodes. Such metals
typically include the members of the platinum group; namely,
ruthenium, rhodium, palladium, osmium, iridium, and platinum. These
metals are not satisfactory for construction of the entire
electrode since, for example, their cost is prohibitive. Therefore,
these metals, metallic oxides, and alloys are commonly applied as a
thin layer over a strength or support member such as a base member
comprising titanium, tantalum, niobium, and alloys thereof. These
support members have good chemical and electrochemical resistance
but may be lacking in good surface electroconductivity because of
their tendency to form on their surface an oxide having poor
electroconductivity. Even when the platinum metals are applied in a
thin layer, the cost is still substantial. Therefore, it is highly
desirable to provide a coating having good electrolytic
characteristics as is typical of the platinum metals and yet a
coating which is less expensive.
Various methods have been proposed for applying the layers of metal
to the base member. In the development of this invention, it has
been found that the procedure used in applying the layer of metal,
metallic oxide, or alloy affects the electrolytic characteristics
of the electrode as well as does the particular metal, metallic
oxide, or alloy selected. For example, if platinum is
electrolytically deposited on a titanium electrode, the operating
voltage of a cell containing such electrode as an anode operated at
a particular current density is reduced when the electrode is
heated following the final coating in an attempt to improve
adhesion between the platinum and the titanium.
Furthermore, it has been found that the procedure used in applying
the layer of noble metal, metal oxide, or alloy materially affects
the adhesion between the layer and the titanium base member, thus
affecting the durability and life span of the electrode. One
approach to improving the adhesion between the layer and the base
member is that of etching the base member prior to coating. Another
approach is that of oxidizing the surface of the titanium base
member, thereby forming a porous titanium oxide layer. The adhesion
is greater between the noble metal and titanium oxide than between
the noble metal and the titanium metal. Irregular results can be
obtained with either method.
DESCRIPTION OF THE INVENTION
The present invention provides an electrode having superior
electrolytic characteristics and superior bonding of the noble
metal or noble metal oxide coating on the titanium base member as
well as providing a more economical coating. According to this
invention, a thermally-decomposable organic mixture containing a
noble metal compound and a titanium compound is applied to the base
member. The electrode is heated to decompose and/or to volatilize
the organic matter and other components, leaving a deposit of
amorphous titanium oxide and the noble metal or noble metal oxide.
The titanium oxide being mixed with the noble metal or noble metal
oxide serves to bond the noble metal or noble metal oxide to the
titanium base member. The electrode of the present invention has a
low chlorine and oxygen overvoltage.
IN THE DRAWINGS
FIG. 1 shows an X-ray diffraction pattern made at 35 kilovolts and
15 milliamperes of an electrode of the present invention produced
as described in Example III.
FIG. 2 shows an X-ray diffraction pattern also made at 35 kilovolts
and 15 milliamperes of the electrode of Example IV prior to final
heating.
FIG. 3 shows an X-ray diffraction pattern also made at 35 kilovolts
and 15 milliamperes of another electrode of Example IV following
final heating.
FIG. 4 shows an X-ray diffraction pattern made at 40 kilovolts, 20
milliamperes, and a detector rotation of two degrees two theta per
minute of another electrode of the present invention produced as
described in Example III.
FIG. 5 shows an X-ray diffraction pattern in the range of 26 to 30
degrees two theta of the same electrode shown in FIG. 4. The
diffraction pattern was made at 40 kilovolts, 20 milliamperes, and
a detector rotation of one quarter degree two theta per minute.
The present invention provides an electrode having a layer or
coating which exhibits improved electrolytic characteristics and
improved adhesion. The invention also includes the steps of
applying to the titanium electrode base one or a plurality of
layers of a mixture of certain thermally-decomposable metal organic
compounds such as organic salts and esters of both titanium and a
platinum group metal. Especially useful for this purpose are
mixtures of ruthenium resinate and titanium resinate, or a mixture
of titanium resinate with other platinum resinates. The resulting
coating, if comprising a mixture of ruthenium oxide and titanium
oxide, should have a ruthenium oxide to titanium oxide ratio of at
least 1 to 1 and preferably at least 1.8 to 1 by weight. Resinates
of this type are manufactured by the Hanovia Division of Engelhard
Industries. The metallic resinates may be mixed with an organic
solvent or diluent, such as terpenes and aromatics, typically, oil
of turpentine, xylene, and toluene, before being applied to the
base member for further increasing adhesion.
As a general rule, the coating is applied as a series of thin
layers in order to promote maximum adhesion of the coating to the
base. The layers are then heated between coating operations to
volatilize or drive off the organic matter, solvent, decomposition
products, etc., and to form the oxides of the metals as a thin film
on the base member.
It has been found that if the electrode is heated to a proper
temperature while volatilizing or driving off the organic matter, a
coating is produced comprising an evenly dispersed mixture of
amorphous or essentially noncrystalline titanium oxide and the
noble metal or noble metal oxide. Furthermore, the titanium oxide
extends throughout the coating. The type titanium oxide having only
a minor amount or no crystallinity not only serves to bond the
noble metal or noble metal oxide to the titanium base member but
also provides an exposed surface of high electroconductivity and
low or even substantially no chlorine overvoltage. The electrode
produced has excellent electrolytic characteristics and greatly
improved adhesion. On the other hand, if the electrode is heated to
an unduly high temperature, the titanium is converted to highly
crystalline titanium oxide and a very unsatisfactory electrode is
produced having high chlorine overvoltage and a surface which does
not conduct electricity satisfactorily.
The exact temperature to which the electrode coating should be
heated depends upon the time of heating and temperature at which
the titanium and platinum compounds decompose. It should be high
enough to cause formation of the titanium oxide, normally as
TiO.sub.2, and of the platinum group metal or oxide thereof. At the
same time, crystallinity of the titanium oxide should be low
although it is not necessary that the titanium oxide be completely
noncrystalline. If materials such as silicon, aluminum and boron
are present in the coating, the electrode may be heated to a higher
temperature without adversely affecting the overvoltage
characteristics of the electrode.
The effect on crystallinity of heating is illustrated in the
drawings. The charts are drawings of an X-ray diffraction pattern
obtained by analyzing the particular electrode on a Phillips
Diffractometer. For FIGS. 1, 2, and 3, the X-ray tube was operated
at 35 kilovolts and 15 milliamperes. For FIGS. 4 and 5 the X-ray
tube was operated at 40 kilovolts and 20 milliamperes. Copper
radiation was used and the Phillips Diffractometer was adjusted as
follows: 1.degree. divergence slit, 0.006 inch receiving slit, and
1.degree. scatter slit. For FIGS. 1, 2, 3, and 4, the detector was
rotated at one quarter degree two theta per minute. For FIGS. 1, 2,
3, and 4, the X-ray tube was operated at 1,000 counts per second
full scale and a time constant of 2 seconds. For FIG. 5 the X-ray
tube was operated at 500 counts per second full scale and a time
constant of 5 seconds.
Referring to FIGS. 1, 4, and 5, it will be noted that the charts
show background signal over the entire chart and that there is a
small peak at an angle of about 27.2 to 28.5 degrees two theta and
another at about 34.8 to 36 degrees two theta. These peaks reflect
a ruthenium oxide having a small degree of crystallinity.
Referring to FIG. 1, it is noted that the peak between about 26 to
30 degrees two theta and, more particularly, between about 27.2 and
28.5 degrees two theta, exhibits a median number of counts per
second above background at about 27.80 degrees two theta.
Referring specifically to FIG. 5, it is noted that the peak between
about 27.2 and 28.5 degrees two theta exhibits a median number of
counts per second above background at 27.80 degrees two theta, and
the median number of counts per second above one half maximum
intensity is at 27.85 degrees two theta. The peak itself has a
height above background of about two hundred per cent of background
and a breadth at half maximum intensity of about 1.85 degrees two
theta.
Turning now to the peak between 34 and 38 degrees two theta and,
more particularly, between about 34.8 and 36.0 degrees two theta,
and referring specifically to FIG. 1, it is noted that this peak
exhibits a maximum height above background in the range of about
35.0 to 35.4 degrees two theta and, more particularly, at about
35.2 degrees two theta. This peak exhibits a median number of
counts per second above background at about 35.4 degrees two
theta.
Referring specifically to FIG. 4, it is noted that this peak
exhibits a maximum height above background in the range of about
35.0 to 35.4 degrees two theta, and, more particularly, at about
35.2 degrees two theta, and a median number of counts per second
above background at about 35.4 degrees two theta.
There are also peaks at about 38 to 38.8 and 39.6 to 40.4, both of
which reflect the crystallinity of the titanium metal base. The
chart of FIG. 2 is quite similar to that of FIGS. 1 and 4.
In contrast, however, a very high peak appears at an angle of about
26.8 to 28.4 of FIG. 3. Note that FIG. 3 shows the graph of an
X-ray diffraction pattern of an electrode coated in the same way as
the electrode of FIG. 2 except that whereas the electrode of FIG. 2
was heated only to 550.degree.C. the electrode of FIG. 3 was heated
to 700.degree.C. for 15 minutes after its last coating was applied.
Thus the high peak referred to in FIG. 3 shows higher (and unduly
high) crystallinity. As shown below in the Examples, the anode of
FIG. 3 was substantially poorer in electrical properties than the
anodes of FIGS. 1, 2, and 4.
It is to be noted that the ruthenium oxide shows a small but
detectible degree of crystallization in the electrodes of FIGS. 1,
2, and 4 and masks to a degree a small amount of crystallinity of
TiO.sub.2. However, the TiO.sub.2 crystallinity was raised
substantially by the 700.degree.C. heat treatment as shown by FIG.
3.
While completely amorphous ruthenium oxide coatings have some
value, best results have been obtained in accordance with this
invention when the ruthenium oxide possesses a small amount of
crystallinity which, in general, should correspond to that shown by
the above-described X-ray test method in the range of about 100 to
400 percent above background, and, in any event, less than 700
percent above background in the range of 26 to 30 degrees two
theta, and in the range of about 75 to 300 percent above
background, and, in any event, less than 600 percent above
background in the range of 34 to 38 degrees two theta.
Similarly, the titanium oxide crystallinity, when so measured,
should not be above 700 percent above background and generally
should be below 200 to 400 percent above background. However,
rarely is it below 100 percent above background with the best
bonded electrodes. Such titanium oxide, having a crystallinity as
described above, is referred to herein as being amorphous or
essentially non-crystalline, which terms are used
interchangeably.
To achieve these results and unless heating is conducted for
extremely short periods, the temperature of heating should not
exceed about 650.degree.C. and generally should be 600.degree.C. or
below. In order to obtain decomposition of the titanium and
ruthenium compounds, it is rare that heating below 120.degree.C. is
suitable particularly because of the unduly long periods of heating
which are required and, preferably, heating is conducted at
200.degree.C. to 600.degree.C.
The heating step described above is most advantageously conducted
in an atmosphere containing elemental oxygen such as air or other
oxygen-inert gas mixtures or even in an atmosphere of pure oxygen.
With easily decomposable compounds and at relatively high
temperatures the heating may be conducted in an inert atmosphere.
However, in such a case the tendency is to produce a coating
containing ruthenium metal rather than ruthenium oxide.
The organic compounds may, if desired, be applied by brushing a
coating on the titanium base member or alternatively by any other
method of application such as spraying or dipping. The electrode
must then be heated to a temperature sufficient to drive off the
organic material and to form the ruthenium oxide and the type of
titanium oxide described above.
The temperature of the electrode may be raised at a continuous,
steady rate or raised in a series of incremental steps. For
example, a coating of the metal organic compound may be applied to
the titanium base member while at room temperature. The temperature
may be raised between 25.degree.C. and 75.degree.C. and held at
that point for between 2 and 10 minutes. The temperature may then
be raised a similar increment and held for a like period of time
and repeating until the ultimate temperature is reached. The
following examples are illustrative.
EXAMPLE I
An electrode was prepared starting with a titanium metal strip 53/4
/4 .times. 3/8 .times. 1/16 inch and brushing on a first coating of
a mixture comprising 5 grams ruthenium resinate (4.0 percent
ruthenium), 2 grams titanium resinate (4.2 percent titanium), and 3
grams toluene, thus providing a RuO.sub.2 /TiO.sub.2 ratio of 1.87
by weight. The electrode was then heated to 400.degree.C. by
starting at room temperature and sequentially raising the
temperature 50.degree.C. every 5 minutes. The electrode was held at
400.degree.C. for 10 minutes and then cooled to room temperature.
In like manner, a total of 13 coatings were applied to the titanium
base member. The final layer was further raised to 450.degree.C.
and retained at that temperature for 10 minutes. X-ray
investigation indicated a satisfactory electrode coating.
EXAMPLE II
An electrode was prepared having 23 coats of the mixture used in
Example I. The electrode was heated to 400.degree.C. following each
of the first 22 coatings and then heated to 500.degree.C. following
the final coating. The electrode was 11/2 .times. 11/2 .times. 1/16
inch and the total thickness of ruthenium was a little over 23
micro-inches. The electrode was placed as an anode in series with
other platinum metal surfaced or ruthenium oxide surfaced
electrodes in a cell in which the anode-cathode spacing was
one-half inch. A brine solution having a concentration of 100 to
125 grams per liter NaCl and 500 to 600 grams per liter NaClO.sub.3
was added to the cell. The cell was operated, maintaining the above
NaCl concentration, at a current density of 500 amps per square
foot. The voltage between the anode and the cathode spaced next to
it the first day was 3.18; the 12th day, 3.45; and after 17 days it
was 3.54. This compares with 3.19, 3.49, and 3.64 volts,
respectively, for a platinized titanium anode operated in an
identical cell.
EXAMPLE III
An electrode was prepared by brushing onto a 11/2 .times. 1-1/2
.times. 1/16 inch titanium base member 11 layers of a mixture
comprising 5 grams ruthenium resinate containing 4 per cent by
weight Ru, 2 grams titanium resinate containing 4.2 per cent by
weight Ti, and 3 grams toluene. The electrode was heated to a
temperature of 400.degree.C. following the application of each of
the layers 1 through 6, 8 and 9. The electrode was heated to
500.degree.C. following the application of layers 7 and 10 and then
heated to 550.degree.C. following application of layer 11. An X-ray
analysis disclosed that the apparent ruthenium oxide thickness was
12 micro-inches or 3.8 grams per square meter.
The electrode had an X-ray diffraction pattern as shown by the
chart of FIG. 1. The X-ray diffraction pattern had a broad main
peak for ruthenium dioxide at about 27.2 to about 28.5 degrees two
theta with a breadth at half maximum of approximately 1.3 degrees
two theta. This peak possibly may include some crystalline titanium
dioxide (rutile form), such being hidden in the ruthenium dioxide
peak. No substantial amount of crystalline titanium oxide was
shown. The peak height above background for this main ruthenium
dioxide peak is at about 600 per cent above background.
The X-ray diffraction pattern had a broad second-ary peak at about
34.8 to about 36.0 degrees two theta with a breadth at half maximum
intensity of approximately 1.4 degrees two theta. This peak may
also possibly include some crystalline titanium dioxide (rutile
form), such being hidden in the ruthenium dioxide peak. No
substantial amount of crystalline titanium oxide was shown. The
peak height above background for this secondary ruthenium di-oxide
peak is at about 450 per cent above background.
The other peaks on the chart are ruthenium di-oxide and titanium.
The electrode was tested in a small, high-temperature chlorate
cell, identical to that described in Example II, where it was
compared with a standard plat-inum coated electrode.
The following table shows a comparison of voltages in the cell
using the ruthenium-coated anode and the standard platinum
electrode which is a titanium metal strip coated with platinum.
cell Voltage After 1 day 3 days 49 days
__________________________________________________________________________
Cell with ruthenium coated anode 3.070 3.193 3.670 Cell with
standard platinum metal coated anode 3.260 3.271 3.690
__________________________________________________________________________
Both electrodes were tested by X-ray for loss of coating after 49
days. The ruthenium-coated anode was found to have lost 3.8
micro-inches whereas the platinum-coated anode lost 13.4
micro-inches.
EXAMPLE IV
An electrode was prepared by applying 10 layers of a mixture
comprising 5 grams ruthenium resinate, 2 grams titanium resinate,
and 3 grams toluene. The electrode was heated to a temperature of
400.degree.C. following each of the layers 1 through 6, 8 and 9.
The electrode was then heated to a temperature of 500.degree.C.
following layers 7 and 10 and further heated to 700.degree.C.
following layer 11. An X-ray analysis disclosed that the apparent
thickness of ruthenium was 11.1 micro-inches or 3.5 grams per
square meter. The X-ray diffraction pattern for this electrode
following layer 10, thus prior to heating to 700.degree.C. (FIG.
2), shows a moderate crystalline peak for ruthenium oxide at 28
degrees two theta. This peak has a breadth at half-maximum
intensity of approximately 2.1 degrees two theta. The peak height
above background for this peak is about 400 per cent of background.
The other peaks in FIG. 2 are for ruthenium oxide and titanium. The
X-ray diffraction pattern for this electrode following heating to
700.degree.C. (FIG. 3) shows several changes. The main ruthenium
oxide peak indicates more crystallinity with a half-maximum
intensity of approximately 0.5 degrees two theta. The peak height
above background for this peak is at about 640 per cent of
background. Also, a strong pattern for titanium oxide (rutile form)
has developed of approximately 1,430 per cent. This electrode was
also tested in the above-described, high-temperature chlorate cell
and, after two hours of testing, the electrode was disconnected
because of an excessively-high voltage of 7.02.
In the above description and examples, emphasis has been laid upon
the production of anodes having a titanium dioxide-ruthenium
dioxide coating on a titanium metal base particularly using a
coating composition comprising a mixture of a titanium resinate and
a ruthenium resinate. The composition is very effective in
producing a coated anode or electrode in which the exposed or
outside surface thereof is a mixture of these oxides with a minimum
degree of crystallinity desired as described above. However, other
compounds (usually solids or high body liquids) of titanium and
ruthenium which form a solid or essentially nonvolatile residue
when applied to the base and which decompose or hydrolyze upon
heating in oxygen including inert air to produce the corresponding
metal oxide may be used in lieu of the resinate in the above
examples or in other procedures.
For example, the titanium esters or alcoholates or organic acid
salts thereof or other organo titanates which can be readily
oxidized in air or oxygen at temperatures of 300.degree.C. to
650.degree.C. or below may be used. Such compounds include
tetraethyl titanate, tetra or butyl titanate, tetra stearyl
titanate, tetra (2 ethyl hexyl) titanate, polyoctylene glycol
titanate, diethylene glycol titanates or other titanates or
polytitanates or titanium acylates such as hydroxyl titanium
stearate, isopropoxy titanium stearate, titanium diphthalate,
hydroxyl titanium linseed acylate, isopropoxy titanium oleate, or
polymers of titanium esters such as polymeric tetra-n-butyl
titanate, polymeric tetra isopropyl titanate, and like polymers
including those which may be formed by partial hydrolysis of alkyl
tetracycloalkyl or tetra aryltitanates may be mixed with ruthenium
resinate and the mixture applied to a titanium electrode base with
the resulting coating being heated in oxygen-containing atmosphere
such as air to form the desired oxide coating containing both
ruthenium oxide and titanium oxide. If desired, the
oxygen-containing atmosphere may contain moisture to promote
hydrolysis of the titanium compound and consequent generation of an
oxide coating.
Also, other ruthenium compounds which decompose or hydrolyze on
heating in an oxygen atmosphere in the presence or absence of air
can be applied as a coating to leave a residue or deposit which on
heating converts to oxide, preferably ruthenium dioxide, may be
used in lieu of ruthenium resinate. Such compounds include
ruthenium nitroso bromide, ruthenium trichloride, ruthenium amino
nitride [Ru(NH.sub.3).sub.2 (NO.sub.2).sub.2 ] disulfide,
RuO(OH).sub.2, calcium ruthenate or ruthenite or ruthenium
diiodide, ruthenium triiodide like ruthenate or ruthenate of an
alkaline earth metal, ruthenium titanate, or titanium ruthenium
oxalate, the ruthenium salts of organic acid such as ruthenium
acetate, ruthenium butyrate, ruthenium diphthalate, or the like may
be used in the above examples or in other procedures in lieu of
ruthenium resinate.
It will also be understood that other conductive coatings can be
applied on a titanium anode so long as such coatings comprise a
mixture of titanium oxide, preferably titanium dioxide and the
platinum group metal or platinum group metal oxide. Of special
value are the platinum group resinates including the resinates of
platinum, palladium, osmium, rhodium, and iridium since these
readily form a well bonded coating of excellent conductivity and
electrochemical resistance. However, other platinum group compounds
may be applied with the titanium organic compound including
palladium dichloride, palladium trichloride, platinum
di-n-butylamine nitride, Pt(NH.sub.3).sub.2 NO, pallidium amine,
palladium iodide, palladium selenide, palladium disulfide, and the
organic salts and esters or alcoholates and amino or nitro
compounds of platinum group compounds corresponding to the
ruthenium or titanium compounds listed above may be used in lieu of
part or all of the ruthenium resinate in the above examples.
Where platinum compounds are used, the resulting coating after
heating in air or oxygen at 300.degree.C. to 650.degree.C.
generally contains platinum in metallic state and, in such a case,
the coating is a mixture or intimate mosaic of platinum metal and
titanium dioxide. Where it is desirable to convert the platinum to
oxide, this may be done by immersing the thus-formed electrode in
molten potassium nitrate at 400.degree.C. for 1 to 10 hours.
Typical of formulations which may be used in lie of those set forth
in the above examples include
A B 15 grams isopropyl alochol 5 grams palladium resinate 2 grams
titanium resinate 2 grams titanium resinate 4 grams palladium
chlorate 3 grams toluene 10 grams toluene
The ratio of titanium oxide to platinum group metal oxide in the
coating applied to the titanium base should be sufficiently high to
insure good adhesion of the coating to the titanium but not so high
as to impair the electroconductivity of the coating. Poor
conductibility is achieved when the film contains 60 per cent or
more by weight of titanium (as oxide) based on the total metal
content of the coating or coating composition. However, the
titanium content should, in any event, not be less than 10 per cent
thereof and, in general, best coatings contain 15 to 50 per cent of
Ti as oxide, substantially the entire balance being a platinum
group metal as oxide. Small amounts of other oxides (up to 20 per
cent by weight compacted as the metal of the oxide and based on the
total metal content of the coating) may be incorporated for example
by adding to the coating composition (such as identified above,
particularly in the examples hereof) a resinate of rhenium, lead,
silicon, tantalum, tungsten, molybdenum, calcium, and zirconium,
and heating the coating as described above.
Although the present invention has been described with reference to
the specific details of particular embodiments thereof, it is not
intended thereby to limit the scope of the invention except insofar
as the specific details are recited in the appended claims.
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