|United States Patent
|Caldwell , et al.
||January 18, 1983 |
Substituted cobalt oxide spinels
Electroconductive substrates are coated with an interface layer and then with
cobalt oxide spinels conforming substantially to the empirical formula where M
represents at least one metal from the Groups IB, IIA, IIB, where Z represents
at least one metal from Group IA where x is equal to or greater than zero but
not greater than 1, where y is equal to or greater than zero but not greater
than 0.5, and where (x plus 2y) is equal to or greater than zero but not greater
than 1. The composites are prepared by thermally oxidizing metal oxide
precursors in-situ on the substrate, including, optionally, modifier metal oxide
materials as a separate dispersed phase in the contiguous spinel structure. The
interface layer comprises at least one oxide of Pb, Sn, Sb, Al, In, or mixtures
||Caldwell; Donald L. (Lake Jackson,
TX), Hazelrigg, Jr.; Mark J. (Lake Jackson, TX) |
||The Dow Chemical Company (Midland, MI)
||March 25, 1981|
|Current U.S. Class:
||204/290.02 ; 204/290.1;
204/290.12; 204/290.13; 204/290.14; 204/291; 427/126.5; 427/126.6;
|Current International Class:
||C25B 11/04 (20060101); C25B
|Field of Search:
427/126.5,126.6 429/218,222 |
References Cited [Referenced
U.S. Patent Documents
Primary Examiner: Edmundson; F.
||Hazelrigg et al.|
||Lewis et al.|
Attorney, Agent or Firm: Lee; W. J.
1. An electrically-conductive composite comprising an
electrically-conductive substrate, an interface coating, and a monometal or
polymetal cobalt spinel outer coating,
said interface coating comprising
a layer of at least one metal oxide of the group consisting of lead oxide, tin
oxide, antimony oxide, aluminum oxide, and indium oxide,
or polymetal cobalt spinel comprising at least one substituted cobalt oxide
spinel conforming substantially to the empirical formula M.sub.x Z.sub.y
where M is at least one metal of the Groups IB,
IIA, and IIB,
where Z is at least one metal of Group IA,
is greater than or equal to zero, but not greater than 1,
where y is
greater than or equal to zero, but not greater than 0.5,
where (x+2y) is
greater than or equal to zero, but not greater than 1, and where the amounts of
M, Z, and Co are sufficient to substantially satisfy the valence requirements of
oxygen in the spinel structure.
2. The composite of claim 1 wherein the
substrate comprises a valve metal selected from the group consisting of
titanium, tantalium, zirconium, molybdenum, niobium, tungsten, hafnium, and
vanadium and alloys thereof.
3. The composite of claim 1 wherein the
substrate comprises titanium or alloys thereof.
4. The composite of
claim 1 wherein the composite comprises an electrode material.
composite of claim 1 wherein the composite comprises an anode material.
6. The composite of claim 1 wherein the composite comprises an anode in
a brine electrolysis cell.
7. The composite of claim 1 wherein M
represents one metal, Z represents one metal and (x+2y) equals a value in the
range of about 0.5 to about 1.0.
8. The composite of claim 1 wherein M
represents two metals and y is zero.
9. The composite of claim 1 where Z
represents one metal and x is zero.
10. The composite of claim 1 where Z
represents two metals and x is zero.
11. The composite of claim 1
wherein the polymetal cobalt spinel is substantially represented by the
empirical formula ZnCo.sub.2 O.sub.4.
12. The composite of claim 1
wherein the polymetal cobalt spinel is substantially represented by the
empirical formula Li.sub.0.5 Co.sub.2.5 O.sub.4.
13. The composite of
claim 1 wherein the coating of monometal or polymetal cobalt spinel contains
dispersed therein up to about 50%, on a metal-to-metal molar basis, of at least
one modifier selected from the oxides of metals of Groups IIIB, IV-B, V-B, VI-B,
VII-B, III-A, IV-A, V-A, Lanthanides, and actinides.
14. The composite
of claim 1 wherein the coating of monometal or polymetal cobalt spinel contains
dispersed therein up to about 50%, on a metal-to-metal molar basis, a modifier
metal oxide comprising ZrO.sub.2.
15. The composite of claim 1 wherein
the polymetal cobalt spinel coating comprises ZnCo.sub.2 O.sub.4 containing
dispersed therein a minor amount of a modifier metal oxide comprising ZrO.sub.2.
16. The composite of claim 1 wherein the interface coating comprises tin
oxide, indium oxide, a mixture of tin oxide and antimony oxide, or a mixture of
indium oxide and antimony oxide.
17. The composite of claim 1 wherein
the interface coating comprises a mixture of indium oxide and antimony oxide and
the spinel coating comprises ZnCo.sub.2 O.sub.4 containing dispersed therein a
minor amount of a modifier metal oxide comprising ZrO.sub.2.
composite of claim 17 wherein the composite is an anode in a brine electrolysis
19. The composite of claim 17 wherein the composite is an anode
material in an electrolytic chloralkali cell.
20. The composite of claim
1 wherein the composite is an electrode.
BACKGROUND OF THE INVENTION
Various cobalt oxide spinels coated
onto electrically-conductive substrates, especially for use as anodes in brine
electrolysis, are known. Of particular relevancy are U.S. Pat. Nos. 3,977,958;
4,061,549; and 4,142,005; all of which are incorporated herein by reference.
Also of various degrees of relevancy are U.S. Pat. Nos. 4,073,873;
3,711,382; 3,711,397; 4,028,215; 4,040,939; 3,706,644; 3,528,857; 3,689,384;
3,773,555; 3,103,484; 3,775,284; 3,773,554; 3,632,498; and 3,663,280.
SUMMARY OF THE INVENTION
An insoluble anode for electrolysis,
especially electrolysis of brine solutions, is prepared by coating an
electroconductive substrate with a first coating comprising one or more oxides
of the group of metals consisting of Sn, Pb, Sb, Al, and In, and then an outer
coating comprising an effective amount of a monometal or polymetal oxide having
a spinel structure conforming substantially to the empirical formula comprising
M.sub.x Z.sub.y Co.sub.3-(x+y) O.sub.4, where O.ltoreq.x.ltoreq.1,
O.ltoreq.y.ltoreq.0.5, O.ltoreq.(x+2y).ltoreq.1, where M represents at least one
metal of Groups IB, IIA, and IIB of the Periodic Table and where Z represents at
least one metal of Group IA. The spinel coating optionally contains a modifier
metal oxide. The coating is prepared by applying a fluid mixture of the metal
oxide precursors to the substrate and heating under oxidizing conditions at a
temperature in a range effective to form the first coating and the second
(spinel) coating in-situ on the substrate. A "polymetal" cobalt spinel is used
herein to describe a spinel containing a plurality of metals, of which cobalt is
FIG. 1 illustrates data from only certain embodiments described
DESCRIPTION OF THE INVENTION
Cobalt oxide based
anode coatings of the spinel type are sensitive to preparation temperature.
Anodes prepared at temperatures above 450.degree. C. tend to have high operating
potentials in service; furthermore, these potentials tend to increase more
rapidly than those of anodes prepared at lower temperatures. It has unexpectedly
been found that the anodes of the present invention are more tolerant of high
preparation temperatures than are those of the prior art. A high temperature
yields a tougher, more highly sintered active coating, and is thus desirable, if
low operating potentials can be maintained.
It is believed that the
cobalt oxide based anode coatings of the spinel type are sufficiently permeable
to oxygen at elevated temperatures that oxidation of the electroconductive
substrate (typically a valve metal such as titanium) can take place during the
coating operation. It is well known that valve metal oxides are poor electrical
conductors in the anodic direction; thus such high-temperature anodes have
undesirably high resistances and thus high operating potentials.
believed that the interface layer of the present invention functions by reacting
with the valve metal oxide as it is formed on the surface of the substrate,
rendering it electrically conductive. The mechanism by which this is
accomplished is uncertain. Trivalent metals such as indium may function as
conventional semi-conductor dopants in the (tetravalent) valve metal oxide
lattice; tetravalent metals such as tin may form conductive solid solutions with
the valve metal oxide, analogous to RuO.sub.2 -TiO.sub.2 solid solutions.
One feature that distinguishes the present invention from interface
layers of platinum group metals and/or oxides is that the interface materials of
the present invention cannot in themselves form the basis of an operable anode
coating: tin oxide can be used as a dopant in solid solution anode coatings but
is insufficiently stable to be used alone, and antimony and indium oxides are
highly reactive in typical brine electrolysis anolyte. It is thus unexpected
that their presence in interface layers stabilizes the operation of anodes in
In general, the first metal oxide coating is
prepared on a cleaned, oxide-free, electroconductive substrate, such as
titanium, by applying to the substrate a layer of precursor metal compound
which, when thermally decomposed in air, yields the oxide of the metal affixed
in-situ on the substrate. More than one metal oxide precursor may be used
simultaneously, so long as the precursor compound is at least one thermally
decomposable compound of Sn, Pb, Sb, Al, In or mixtures of these. The precursor
may be a metal-organic, or otherwise contain organic moieties, but is preferably
an inorganic compound. It is preferred that the precursor metal compound be
carried in a liquid medium, such as water, alcohol, water/alcohol,
water/acetone, and the like; preferably the precursor metal compound is soluble
in the liquid medium. During the heating step of the process the liquid carrier
is boiled away and plays no further part in the process. The steps of applying
the metal oxide precursors, followed by heating to create the metal oxides, is
beneficially repeated one or more times, thereby assuring that a contiguous
well-adhered coating of the metal oxide is obtained, though only one coat is
operable. It is best if this metal oxide underlayer has a thickness in the range
of about 20-400 A, coatings as thin as about 10 A demonstrate operability as to
coatings thicker than 400 A but there are no additional benefits to be derived
from such thicker coatings which are commensurate with the expense of laying
down such thicker coatings. The temperature used in forming the metal oxide
underlayer may be from the decomposition temperature (in air) of the metal oxide
precursor to as high as several hundred degrees centigrade, preferably a
temperature in the range of about 200.degree. C. to about 450.degree. C., most
preferably about 250.degree.-450.degree. C. The baking time is generally in the
range of about 1.5 to about 60 minutes, the higher temperatures requiring the
lesser times. Excess time at the higher temperatures can lead to unwanted
oxidation of the substrate.
In general, the spinel coating is prepared
in-situ on the so-coated electroconductive substrate by applying a fluid mixture
(preferably a solution) of the spinel-forming precursors along with, optionally,
any modifier metal oxide precursors desired, to the coated substrate, then
heating at a temperature and for a time effective to produce the spinel
structure as a layer or coating on the pre-coated substrate. The spinel coating
is found to form a contiguous, well-adhered layer on the undercoating of metal
oxide applied first.
The temperature effective in producing the spinel
structure is generally in the range of about 200.degree. C. to about 475.degree.
C., preferably in the range of about 250.degree. C. to about 400.degree. C. At
temperatures below about 200.degree. C. the formation of the desired spinel
structure is likely to be too slow to be feasible and it is likely that
substantially no spinel will be formed, even over extended periods of time. At
temperatures above about 475.degree. C. there is likely to be formed other
cobalt oxide structures, such as cobaltic oxide (Co.sub.2 O.sub.3) and/or
cobaltous oxide (CoO), whether substituted or not. Any heating of the spinel
above about 450.degree. C. should be of short duration, say, not more than about
5 minutes, to avoid altering the desired spinel structures to other forms of the
metal oxides. Any modifier metal oxides present, being contained in the spinel
structure as a different phase, will be formed quite well at the spinel-forming
temperatures and any variations in the oxide form of the modifier metal oxides
are not significant in the present invention. By using the undercoat prescribed
in the present invention, the preferred temperature range for formation of the
spinel topcoat becomes about 400.degree. C.-450.degree. C., most preferably
about 400.degree. C.-425.degree. C.
The length of time at which the
heating is done to form the spinel structure is, generally, inversely related to
the temperature. At lower temperatures within the prescribed range, the time may
be as much as 8 hours or more without destroying the spinel structure or
converting substantial amounts of it to other oxide forms. At the upper end of
the prescribed heating range, the time of heating should not be extended beyond
the time needed to form the desired spinel structure because extended heating
times may destroy or convert a substantial amount of the spinel to other oxide
forms; at the upper end of the range a heating time in the range of about 1
minutes to about 5 minutes is generally satisfactory in forming the spinel
without forming other oxide forms.
The substrates of interest in the
present invention are electroconductive metals comprising the valve metals or
film-forming metals which includes titanium, tantalum, zirconium, molybdenum,
niobium, tungsten, hafnium, and vanadium or alloys thereof. Titanium is
especially preferred as a substrate for preparing anodes to be used in
electrolysis of brine.
The precursor cobalt compounds used in making the
present spinel structures may be any thermally-decomposable oxidizable compound
which, when heated in the prescribed range, will form an oxide of cobalt. The
compound may be organic, such as cobalt octoate or cobalt 2-ethyl hexanoate and
the like, but is preferably an inorganic compound, such as cobalt nitrate,
cobalt hydroxide, cobalt carbonate, and the like. Cobalt nitrate is especially
The precursor metal compounds of Groups IA, IB, IIA, and IIB
and of the modifier metal oxides (if used) may be any thermally-decomposable
oxidizable compound which, when heated in the prescribed range, will form
oxides. Organic metal compounds may be used, but inorganic metal compounds are
Modifier oxides may be incorporated into the
substituted or unsubstituted Co.sub.3 O.sub.4 coating to provide a tougher
coating. The modifier oxide is selected from among the following listed groups:
Group III-B (Scandium, Yttrium)
Group IV-B (Titanium, Zirconium,
Group V-B (Vanadium, Niobium, Tantalum)
(Chromium, Molybdenum, Tungsten)
Group VII-B (Manganese, Technetium,
Lanthanides (Lanthanum through Lutetium)
(Actinium through Uranium)
Group III-A Metals (Aluminum, Gallium,
Group IV-A Metals (Germanium, Tin, Lead)
V-A Metals (Antimony, Bismuth).
The modifier oxide is, preferably, an
oxide of cerium, bismuth, lead, vanadium, zirconium, tantalum, niobium,
molybdenum, chromium, tin, aluminum, antimony, titanium, or tungsten. Mixtures
of modifier oxides may also be used.
Most preferably, the modifier oxide
is selected from the group consisting of zirconium, vanadium, and lead, or
mixtures of these, with zirconium being the most preferable of these.
The amount of modifier oxide metal or metals may be in the range of zero
to about 50 mole %, most preferably about 5 to about 20 mole % of the total
metal of the coating deposited on the electroconductive substrate. Percentages,
as expressed, represent mole percent of metal, as metal, in the total metal
content of the coating. The modifier oxide is conveniently prepared along with
the substituted or unsubstituted Co.sub.3 O.sub.4 from thermally decomposable
oxidizable metal compounds, which may be inorganic metal compounds or organic
The carrier for the precursor metal compounds is
preferably water, a mixture of water/acetone, or a mixture of water and a
water-miscible alcohol, e.g., methanol, ethanol, propanol, or isopropanol. The
carrier is one which readily evaporates during spinel formation. The precursor
metal compounds are preferably soluble in the carrier or at least in very
finely-divided form in the carrier. Solubilizing agents may be added to the
mixture, such as ethers, aldehydes, ketones, tetrahydrofuran, dimethylsulfoxide,
and the like. In some instances, adjustments to the pH of the mixture may be
made to enhance the solubility of the metal compounds, but attention should be
given to whether or not the pH adjuster (acid or base) will add any unwanted
metal ions. Ammonia is generally the best alkalizer since it does not add metal
The procedure for preparing the coatings comprises starting with a
clean substrate with surface oxides and contaminants substantially removed, at
least on the surface(s) to be coated, then applying the interface coating as
described above. The mixture of metal oxide spinel precursors in a liquid
carrier is applied to the substrate, such as by dipping, spraying, brushing,
painting, or spreading. The so-coated substrate is subjected to a temperature in
the prescribed range for a period of time to thermally oxidize the metal
compounds to oxides, thereby forming, on the interface coating, the spinels of
the present invention, along with any modifier metal oxides or second-phase
metal oxides which may be co-prepared but which are not part of the expanded
cobalt oxide spinel crystal structure. Generally, the first such application
(which usually gives a relatively thin layer) is done quickly to avoid the risk
of excessive oxidation of the substrate itself. Then as additional applications
are made (i.e., applications of the precursor liquid carrier containing the
metal compounds, followed by thermal oxidation) the thickness of the coating
builds up, becomes tighter and denser, and there is a substantially reduced risk
of excessively oxidizing the substrate under the interface coating and the
spinel coating. Each subsequent layer is found to combine quite readily to
preceding layers and a contiguous spinel coating is formed which is adhered
quite well to the interface on the substrate. It is preferred that at least 3
such layer-applications are employed, especially from about 6 to about 12 such
It is best to charge the initial mixture of metal
compounds into the liquid carrier in such a way that the desired ratio of metals
are present on a molar basis to satisfy the stoichiometry of the desired
polymetal cobalt spinel, also referred to herein as expanded cobalt spinel or
substituted cobalt spinel.
The following enumerated paragraphs are
presented to offer a simplified explanation, based on belief and experience, of
what transpires when one or more monovalent or divalent metal ions replace a
portion of the cobalt ions in a cobalt oxide spinel, but the invention is not
meant to be limited by, or confined to, this simplified explanation. This
explanation is intended to cover metals of Groups IA, IIA, IB, and IIB insofar
as replacement of cobalt ions in a cobalt oxide spinel structure is concerned.
1. A "single-metal" cobalt oxide spinel, Co.sub.3 O.sub.4, is understood
as having, per molecule, one Co.sup.++ ion and two Co.sup.+++ ions to satisfy
the valence requirements of four O.sup.-- ions; thus the single metal cobalt
spinel may be illustrated by the emprical formula Co.sup.++ Co.sub.2.sup.+++
O.sub.4.sup.-- to show the stoichiometric valence balance of cobalt cations with
2. When divalent metal ions are substituted into the
cobalt oxide spinel structure, they tend to replace divalent cobalt ions. For
example when Mg.sup.++ is substituted into the Co.sub.3 O.sub.4 spinel
structure, it replaces Co.sup.++ giving a spinel illustrated by the empirical
formula Mg.sup.++ Co.sub.2.sup.+++ O.sub.4.sup.--.
3. When monovalent
metal ions are substituted into the cobalt oxide spinel structure they tend to
replace divalent cobalt ions. The maximum monovalent ion substitution may be
illustrated as, for example, Li.sub.0.5.sup.+ Co.sub.2.5.sup.+++ O.sub.4, to
show stoichiometric valence balance. The empirical formula may be illustrated
as, for example, Li.sub.y Co.sub.3-y O.sub.4, where y is not more than 0.5, 3-y
is at least 2.5, and where (y times Li valence) plus (3-y times cobalt valence)
4. When two or more divalent metal ions are substituted into
the cobalt oxide spinel structure, then the structure can be written,
empirically, as M.sub.x M'.sub.x' Co.sub.3-(x+x') O.sub.4 or as, e.g., M.sub.x
M'.sub.x' M".sub.x" Co.sub.3-(x+x'+M") O.sub.4.
5. When two or more
monovalent metal ions are substituted into the cobalt oxide structure, then the
structure can be written, empirically, as Z.sub.y Z'.sub.y' Co.sub.3-(y+y')
O.sub.4 or as, e.g., Z.sub.y Z'.sub.y' Z".sub.y" Co.sub.3-(y+y'+y") O.sub.4.
6. When at least one monovalent metal ion and at least one divalent ion
are substituted into the cobalt oxide spinel structure, then the structure can
be written, empirically, as M.sub.x Z.sub.y Co.sub.3-(x+y) O.sub.4 or as, e.g.,
M.sub.x M'.sub.x' Z.sub.y Co.sub.3-(x+x'+y) O.sub.4 or, e.g., as M.sub.x
M'.sub.x' Z.sub.y Z'.sub.y' Co.sub.3-(x+x'+y+y') O.sub.4.
7. If an
excess of monovalent and/or divalent metal ions are present in the mixture from
which the substituted cobalt oxide structures are prepared, the excess metal
values tend to form a separate metal oxide phase which is not a spinel structure
but which is present with the spinel structure.
8. It will be understood
by practitioners of these arts that there may be some degree of imperfect spinel
crystals which, if they could be isolated and measured separately may not
conform exactly to the empirical structures written in this disclosure, but the
spinel products prepared according to this invention can be said to conform
substantially to the empirical formulae shown.
9. If metal values are in
the mixture (from which the spinel structures are formed) which do not
effectively replace cobalt ions in the cobalt oxide spinel structure, these
metals tend to form separate metal oxide phases which act as modifiers of the
spinel structures. For instance, where the spinel structures are formed by
building up a contiguous layer of the spinel on a substrate by repeated
applications of spinel-forming ingredients, each application being followed by
the heating step, the modifier metal oxides are beneficial in providing
toughness and abrasion-resistance to the layer. The amount of modifier metal
oxides should be limited so that the desired spinel is the predominant
ingredient of the coating.
The metals of the relevant groups of the
Periodic Table are as follows:
IIA IB IIB ______________________________________ Li Be Cu Zn Na Mg Ag Cd K Ca
Au Hg Rb Sr Cs Ba Fr Ra ______________________________________
upper limits for molar percentage of the M and Z metals which form polymetal
spinels with cobalt are, based on total metal content of the spinel:
M.ltoreq.33.3%, Z.ltoreq.16.7%, and M+Z.ltoreq.33.3%. Any excess of M and Z will
form a separate phase of the metal oxide amongst the spinel crystals. When M
metals are used in the coating, it is preferred that on a molar metal basis M is
at least 8%. When Z metals are used in the coating, it is preferred that on a
molar metal basis Z is at least 4%.
The following examples are to
illustrate the invention, but the invention is not limited to the particular
The type of test cell utilized
here was a conventional vertical diaphragm chlorine cell. The diaphragm was
deposited from an asbestos slurry onto a foraminous steel cathode in the
conventional manner. Anode and cathode were each approximately 3".times.3" (7.62
cm.times.7.62 cm). Current was brought to the electrodes by a brass rod brazed
to the cathode and a titanium rod welded to the anode. The distance from the
anode to the diaphragm face was approximately 1/4 inch (0.635 cm). Temperature
of the cell was controlled by means of a thermocouple and heater placed in the
anolyte compartment. A 300 gpl sodium chloride solution was fed continuously to
the anolyte compartment via a constant overflow system. Chlorine, hydrogen, and
sodium hydroxide were withdrawn continuously from the cell. Anolyte and
catholyte levels were adjusted to maintain an NaOH concentration in the
catholyte of about 110 gpl. Power was supplied to the cell by a
current-regulated power supply. Electrolysis was conducted at an apparent
current density of 0.5 ampere per square inch (6.45 cm.sup.2) anode area.
The etching solution employed in the examples below was prepared by
mixing 25 ml analytical reagent hydrofluoric acid (48% HF by weight), 175 ml
analytical reagent nitric acid (approximately 70% HNO.sub.3 by weight), and 300
ml deionized H.sub.2 O.
Anode potentials were measured in a laboratory
cell specifically designed to facilitate measurements on 3".times.3"
(7.62.times.7.62 cm) anodes. The cell is constructed of plastic. Anode and
cathode compartments are separated by a commercial PTFE membrane. The anode
compartment contains a heater, a thermocouple, a thermometer, a stirrer, and a
Luggin capillary probe which is connected to a saturated calomel reference
electrode located outside the cell. The cell is covered to minimize evaporative
losses. Electrolyte is 300 gpl sodium chloride brine solution. Potentials are
measured with respect to saturated calomel at ambient temperature
(25.degree.-30.degree. C.). Lower potentials imply a lower power requirement per
unit of chlorine produced, and thus more economical operation.
Fifteen pieces of ASTM Grade I titanium expanded mesh approximately
3".times.3".times.0.063" (7.62.times.7.62.times.0.16 cm) were dipped in
1,1,1-trichloroethane, air dried, dipped in HF-HNO.sub.3 etching solution
approximately 30 seconds, rinsed with deionized water, and air dried. The mesh
was blasted with Al.sub.2 O.sub.3 grit to a uniform rough surface and blown
clean with air. Two interface coating precursor solutions were prepared as
follows: Solution (A) contained 15.1 g of SnCl.sub.4.5H.sub.2 O dissolved in 5
ml concentrated reagent HCl and 30 ml technical isopropyl alcohol; Solution (B)
contained 2.03 g SbCl.sub.3 and 15.1 g SnCl.sub.4.5H.sub.2 O dissolved in 5 ml
concentrated reagent HCl and 30 ml technical isopropyl alcohol. The active
spinel coating precursor, Solution (C), was prepared by mixing appropriate
quantities of Co(NO.sub.3).sub.2.6H.sub.2 O, Zn(NO.sub.3).sub.2.6H.sub.2 O,
aqueous ZrO(NO.sub.3).sub.2 solution and deionized H.sub.2 O to give a mole
ratio of 10 Co:5 Zn:1 Zr.
Five sets of anodes were prepared, each
containing three samples. Sample (a) of each set contained no interface coating,
and thus serves as a comparative example. Sample (b) contains an interface
coating of tin oxide obtained from Solution (A). Sample (c) contains an
interface coating of tin and antimony oxides obtained from Solution (B).
All interface coatings were prepared at 450.degree. C. For all samples
(b) and (c) the specimens were brushed with the appropriate interface solution,
baked in a 450.degree. C. convection oven for about ten minutes, removed and
cooled in air about ten minutes. One additonal interface coat was applied in a
similar manner. For sets (1) and (2) Sample (a) was given two coats of active
spinel at 450.degree. C. while Samples (b) and (c) were being given their two
All fifteen anodes were given eight coats of active
spinel in the following manner: the substances treated as described above were
brushed with solution (C), placed in a convection oven heated to the temperature
listed in Table I below, baked for about ten minutes, removed, and cooled in air
about ten minutes. Seven additional coats were applied in a similar manner.
After all coats were applied and baked, the anodes were given a final bake at
375.degree. C. for about one hour.
Potentials of the fifteen anodes were
measured in the laboratory cell described above. The cell was heated to about
70.degree. C. and electrolysis was conducted at an apparent current density of
0.5 ampere per square inch (6.45 cm.sup.2) anode area. Results are shown in
Table I and FIG. 1. It is apparent that the anodes of the present invention are
much less sensitive to preparation temperature than are those of the comparative
TABLE I ______________________________________ Bake Temperature
(.degree.C.) Interface SET/ Interface Active Final Coat Anode SAMPLE Coat.sup.1
Spinel.sup.2 Bake Oxides Potential.sup.3 ______________________________________
1 a* 450.sup.4 450 375 NA** 1340 b 450 450 375 Sn 1125 c 450 450 375 Sn + Sb
1112 2 a* 450.sup.4 425 375 NA 1188 b 450 425 375 Sn 1098 c 450 425 375 Sn + Sb
1089 3 a* NA 400 375 NA 1102 b 450 400 375 Sn 1097 c 450 400 375 Sn + Sb 1092 4
a* NA 375 375 NA 1095 b 450 375 375 Sn 1097 c 450 375 375 Sn + Sb 1089 5 a* NA
350 375 NA 1090 b 450 350 375 Sn 1094 c 450 350 375 Sn + Sb 1094
______________________________________ *Comparative example. **NA means not
applied. .sup.1 Two coats. .sup.2 Eight coats. .sup.3 Anode potential is
measured in millivolts at 0.5 ASI, 70.degree. C VS SCE at 25-30.degree. C.
.sup.4 Two coats of active spinel precursor.
of ASTM Grade 1 titanium expanded mesh approximately 3".times.3".times.0.063"
(7.62.times.7.62.times.0.16 cm) was dipped in 1,1,1-trichloroethane, air dried,
dipped in HF-HNO.sub.3 etching solution approximately 30 seconds, rinsed with
deionized water, and air dried. The mesh was blasted with Al.sub.2 O.sub.3 grit
to a uniform rough surface and blown clean with air. An interface coating
precursor solution was prepared as follows: 1.30 g of InCl.sub.3.4H.sub.2 O and
0.009 g SbCl.sub.3 were dissolved in 3.2 g concentrated reagent HCl and 20.5 g
technical isopropyl alcohol. An active spinel coating precursor, Solution (C),
was prepared by mixing appropriate quantities of Co(NO.sub.3).sub.2.6H.sub.2 O,
Zn(NO.sub.3).sub.2.6H.sub.2 O, aqueous ZrO(NO.sub.3).sub.2 solution, and
deionized H.sub.2 O to give a mole ratio of 10 Co:5 Zn:1 Zr.
specimen was brushed with the interface solution, baked in a 400.degree. C.
convection oven for about ten minutes, removed, and cooled in air about ten
minutes. The specimen was then given twelve coats of spinel. Each coat was
applied by brushing with spinel coating precursor, baking at 400.degree. C. ten
minutes, removed from the oven, and cooling in air about ten minutes. After the
twelfth spinel coat had been baked the anode was given a final bake at
375.degree. C. for about one hour.
The anode was placed in a diaphragm
chlorine cell as described above and operated for over 1.5 years. The cell was
shut down from time-to-time for measurement of the anode potential in the
laboratory cell, also described above. The potential of the anode at 0.5 ampere
per square inch (6.45 cm.sup.2) apparent current density and 70.degree. C.,
measured versus saturated calomel at 30.degree. C., was 1082 mv prior to
start-up, 1104 mv after 0.15 yr. operation, and 1093 mv after 1.5 yr. operation.
It thus demonstrated stable operation in long-term service as a chlorine anode.
Other polymetal spinel outer coatings (especially
containing ZrO.sub.2 dispersed therein) which are effective as anodic material
for brine electrolysis and which benefit from the interface layer of oxides of
Sn, Sb, Pb, Al, In, or mixtures of these include, for example (approx. values):
______________________________________ Li.sub.0.5 Co.sub.2.5 O.sub.4
Li.sub.0.125 Zn.sub.0.5625 Cu.sub.0.1875 Co.sub.2.125 O.sub.4 Li.sub.0.375
Zn.sub.0.25 Co.sub.2.375 O.sub.4 Li.sub.0.125 Mg.sub.0.75 Co.sub.2.125 O.sub.4
Li.sub.0.375 Co.sub.2.625 O.sub.4 Li.sub.0.25 Zn.sub.0.50 Co.sub.2.25 O.sub.4
Li.sub.0.25 Co.sub.2.75 O.sub.4 Li.sub.0.125 Zn.sub.0.5625 Mg.sub.0.1875
Co.sub.2.125 O.sub.4 Li.sub.0.125 Zn.sub.0.75 Co.sub.2.125 O.sub.4 Li.sub.0.125
Co.sub.2.875 O.sub.4 Li.sub.0.125 Cu.sub.0.75 Co.sub.2.125 O.sub.4 ZnCo.sub.2
O.sub.4 Zn.sub.0.75 Mg.sub.0.25 Co.sub.2 O.sub.4 Zn.sub.0.25 Ag.sub.0.375
Co.sub.2.375 O.sub.4 Zn.sub.0.5 Co.sub.2.5 O.sub.4 Zn.sub.0.25 Co.sub.2.75
O.sub.4 Zn.sub.0.5 Ba.sub.0.5 Co.sub.2 O.sub.4 Zn.sub.0.5 Mg.sub.0.5 Co.sub.2
O.sub.4 Zn.sub.0.5 Sr.sub.0.5 Co.sub.2 O.sub.4 Zn.sub.0.5 Ca.sub.0.5 Co.sub.2
O.sub.4 Zn.sub.0.5 Cu.sub.0.5 Co.sub.2 O.sub.4 Zn.sub.0.5 Cd.sub.0.5 Co.sub.2
* * * * *