|United States Patent
,   et al.
|| February 15, 1977
Method for manufacturing of electrode having porous ceramic substrate
coated with electrodeposited lead dioxide and the electrode
manufactured by said method
An electrode having a lead dioxide coat electrodeposited on a porous
ceramic substrate is manufactured by soaking a porous ceramic substrate in
an aqueous lead (II) salt solution and thereby allowing lead oxide to be
deposited in the porous surface layer and on the surface of the substrate
thereafter soaking said porous ceramic substrate in a persulfate solution
to cause oxidation of the lead oxide so deposited therein and thereon and
effecting electrolysis in an aqueous lead (II) salt solution by using said
lead dioxide-coated substrate as the anode and the aqueous solution as the
electrolyte and thereby causing lead dioxide to the additionally
electrodeposited on said lead dioxide coat.
The electrode manufactured as described above excels in corrosion-resisting
property and therefore proves quite advantageous as an electrode for use
in the electrolysis of aqueous solutions.
Torikai; Eiichi (Yao, JA);
Kawami; Yoji (Kawachi-Nagano, JA)
Agency of Industrial Science & Technology (Tokyo, JA)
August 21, 1975|
U.S. Patent Documents
||204/290R; 204/30; 204/38R; 204/57; 204/291; 429/228 |
||C25B 001/30; C25B 011/16|
|Field of Search:
204/30,57,290 R,290 F,38 R
|2872405||Feb., 1959||Miller et al.||204/290.
|2994649||Aug., 1961||Morrison et al.||204/57.
|3607681||Sep., 1971||Cooke et al.||204/30.
|3668085||Jun., 1972||Kiyohara et al.||204/57.
|Foreign Patent Documents|
Primary Examiner: Edmundson; F.C.
Attorney, Agent or Firm: Oblon, Fisher, Spivak, McClelland & Maier
1. A method for the manufacture of an electrodeposited lead dioxide
electrode incorporating a porous ceramic substrate, which method
soaking a porous ceramic substrate in an aqueous lead (II) salt solution,
removing said substrate from said aqueous solution and drying the
substrate, soaking the dried substrate in one aqueous solution selected
from the group consisting of an aqueous persulfate solution incorporating
an aqueous ammonia and an aqueous persulfate solution incorporating an
alkali metal hydroxide, and subsequently removing the substrate from said
aqueous solution, washing and drying the substrate and thereby obtaining a
composite having said ceramic substrate coated with a layer of lead
dioxide consisting preponderantly of .alpha.-PbO.sub.2 and formed on the
surface and in the porous surface layer of said porous substrate, and
disposing said composite in an electrolytic cell containing an aqueous lead
(II) salt solution as the electrolyte and incorporating, as the cathode, a
piece of a metal selected from the group consisting of lead, copper and
stainless steel, passing a flow of electric current having an anode
current density of 0.5 to 20 A/dm.sup.2 to effect electrolysis and thereby
further coating the composite (ceramic substrate coated lead dioxide) with
a layer of black compact lead dioxide of .alpha. + .beta. form excelling
2. The method according to claim 1, wherein the substance of said porous
ceramic substrate is at least one member selected from the group
consisting of silica, alumina, magnesia, zirconia and calcia.
3. The method according to claim 1, wherein said aqueous persulfate
solution incorporating said aqueous ammonia is an aqueous solution
obtained by adding to an 8 to 10 weight percent aqueous ammonia solution
one persulfate selected from the group consisting of ammonium persulfate,
sodium persulfate and potassium persulfate in an amount to give a
concentration of 5 to 6 percent by weight based on the finally produced
4. The method according to claim 1, wherein said aqueous persulfate
solution incorporating said alkali metal hydroxide is obtained by having
an aqueous alkali metal solution contain therein one persulfate selected
from the group consisting of ammonium persulfate, sodium persulfate and
potassium persulfate, with the pH value adjusted in the range of from 11
5. The method according to claim 1, wherein said aqueous lead (II) salt
solution used as the electrolyte is one member selected from the group
consisting of lead nitrate, lead perchlorate and lead sulfamate.
6. The method according to claim 5, wherein said electrolyte contains 0.5
to 1.0 mole/liter of Pb(NO.sub.3).sub.2 and has a pH value in the range of
6.0 to 2.0 and a liquid temperature of 20.degree. to 60.degree. C.
7. An electrodeposited lead dioxide composite for use as an electrode,
comprising a porous ceramic substrate, a layer preponderantly of .alpha.
-lead dioxide deposited on the surface and in the porous surface layer of
the substrate, and a layer of .alpha. + .beta. lead dioxide deposited on
said deposited layer of .alpha.-lead dioxide.
8. The electrodeposited lead dioxide composite for use as an electrode
according to claim 7, wherein said porous ceramic substrate is at least
one member selected from the group consisting of porous silica, alumina,
magnesia, zirconia and calcia.
BACKGROUND OF THE INVENTION
This invention relates to a method for the manufacture of an electrode
excelling in corrosion-resisting property and having a porous ceramic
substrate coated with electrodeposited lead dioxide and to the electrode
manufactured by said method. There are the following three types of lead
dioxide electrodes known to the art:
A. The type of electrodes produced by having lead dioxide anodically
deposited on the surface of a lead substrate.
B. The type of electrodes formed solely of lead dioxide without using any
C. The type of electrodes produced by having lead dioxide electrodeposited
on the substrate of a corrosion-resisting substance other than lead.
Of these three types, those of types b and c are called electrodeposited
lead dioxide electrodes and they excel over those of type a in terms of
corrosion-resisting property. They have already been put to practical use
as electrodes convenient for the electrolysis of aqueous solutions.
The electrodeposited lead dioxide electrodes generally available on the
market include rectangular lead dioxide electrodes devoid of a substrate
and lead dioxide electrodes possessed of a substrate of graphite, titanium
or tantalum or a substrate of such metal having the surface thereof plated
with platinum, gold or silver. At the present, lead dioxide electrodes
using a titanium substrate are enjoying favorable acceptance in the
The electrodeposited lead dioxide electrodes described above have their
demerits: For example, the type of lead dioxide electrodes using no
substrate are susceptible to fracture and therefore have their shape and
dimensions inevitably limited and the type of electrodes using a graphite,
titanium or tantulum substrate easily sustain cracks. When a crack occurs
in such an electrode in the course of an electrolytic reaction, the
solution undergoing the electrolysis penetrates through the crack and
eventually comes into contact with the underlying substrate, with the
result that the substrate is corroded by the solution. The crack,
therefore, has an adverse effect on the service life of the electrode.
A primary object of the present invention is to provide a method for the
manufacture of an electrodeposited lead dioxide electrode which
incorporates a substrate of high corrosion-resisting property and
therefore permits desired electrolysis to be performed without entailing
troubles for a long time.
Another object of the present invention is to provide electrodeposited lead
dioxide electrodes which enjoy high resistance to corrosion and withstand
use conditions for a long time.
SUMMARY OF THE INVENTION
To accomplish the objects described above, the present invention provides a
method which comprises soaking a porous ceramic substrate in an aqueous
led (II) salt solution, then soaking said substrate desirably in an
aqueous persulfate solution incorporating aqueous ammonia or in an aqueous
persulfate solution incorporating an alkali metal hydroxide and thereafter
drying the wet substrate. In consequence of the treatment described above,
lead dioxide is deposited on the surface and in the porous surface layer
of the porous ceramic substrate.
As the next step, electrolysis is effected by using, as the anode, the
porous ceramic substrate having lead dioxide deposited as mentioned above
and, as the electrolyte, an aqueous lead (II) salt solution. By this
electrolysis, a black, fine-grained coat of lead dioxide excellent in
electroconductivity is additionally formed to coat the lead dioxide layer
covering the porous ceramic substrate.
Consequently, there is obtained an electrodeposited lead dioxide electrode
which is constructed of a ceramic substrate and a layer of lead dioxide
formed to coat the surface of said ceramic substrate. This electrode has
excellent electroconductivity. Even if a crack occurs in the coat of lead
dioxide while the electrode is in use, the electrolysis under way is not
interrupted by the crack because the ceramic substrate offers perfect
resistance to the action of the electrolyte.
BRIEF EXPLANATION OF THE DRAWING
FIG. 1 is an X-ray diffraction diagram indicating the structure of
electrodeposited lead oxide.
FIG. 2 is an X-ray diffraction diagram indicating the structure of lead
dioxide deposited by the soaking process.
DETAILED DESCRIPTION OF THE INVENTION
A ceramic substance is a very poor conductor of electricity. Therefore,
lead dioxide cannot be electrodeposited directly on the ceramic substance.
For the formation of electroconductive films on the surface of ceramic
articles, there have heretofore been proposed methods resorting to
techniques such as chemical plating, vacuum evaporation and thermal
decomposition. The process which comprises plating a given ceramic
substrate in advance such as with platinum or silver by one of such
methods and thereafter causing led dioxide to be electrodeposited thereon
is easy to accomplish. It is, however, not advantageous from the
economical point of view.
The method of the present invention is characterized by first inducing
deposition of lead dioxide by a chemical process or a soaking process so
as to give rise to an electroconductive layer on the surface of a ceramic
substrte which is intrinsically a poor conductor of electricity prior to
causing electrodeposition of lead dioxide on said surface, and
subsequently permitting the formed layer of lead dioxide to achieve growth
by means of electrolysis and thereby producing a fine-grained electrode
excellent in electroconductivity and advantageous for actual uses.
Since the electrode according to the present invention uses a substrate of
ceramic substance, it offers high resistance to corrosion and can be
produced in any desired shape and dimensions.
A porous substance produced by sintering silica, alumina, magnesia,
zirconia, calcia, etc. is used as a ceramic material for the production of
the substrate in the electrode of the present invention. The ceramic
material may be made from either one member or from a mixture of a
plurality of members selected from the group mentioned above. It is quite
easy for such a ceramic material to be molded to any desired shape so as
to suit the purpose for which the finally produced electrode is to be
Since the ceramic substrate thus molded is a poor conductor of electricity,
it is subjected to a treatment to impart desired electroconductivity to
the surface thereof. And this treatment is carried out in accordance with
the method disclosed by the same inventors in Japaneses Patent Publication
No. 20164/1970. To be specific, the porous ceramic substrate molded to a
desired shape is soaked in an aqueous lead (II) salt solution at
temperatures from normal room temperature to 100.degree. C, preferably
from 50.degree. to 80.degree. C, for a period of not less than 5 minutes
and not more than 1 hour. The aqueous lead (II) salt solution is desired
to be an aqueous solution of a water-soluble lead salt such as, for
example, lead nitrate, lead acetate, lead perchlorate or lead sulfamate.
At the end of said soaking, said ceramic substrate is taken out of said
aqueous lead (II) salt solution and dried. This drying may be accomplished
either by allowing the wet substrate to stand at normal room temperature
or by being heated if accelerated drying is required. While the ceramic
substrate is standing in the aqueous lead (II) salt solution, this
solution penetrates into the porous surface layer of the substrate and
adheres to the surface thereof as well. When the substrate is removed from
the solution and then left to stand, the solution deposited in said
surface layer and on the surface dries up to give rise to a uniform
deposit of said lead (II) salt in the form of crystals.
Thereafter, the dried substrate is again soaked in an ammoniacal aqueous
persulfate solution or an alkaline aqueous persulfate solution to cause
oxidation of the lead salt deposited on the surface.
The aqueous persulfate solution incorporating aqueous ammonia to be used
for said oxidation is obtained by preparing an aqueous 8-10% ammonia
solution and adding to this solution such an amount of a persulfate to
give a persulfate concentration of 5 to 6%. The concentrations of ammonia
and persulfate mentioned above may be increased so as to suit the
particular amount of the deposited lead dioxide desired to be oxidized on
the surface of the substrate.
The soaking in the aqueous persulfate solution incorporating the aqueous
ammonia is required to be given for not less than 50 minutes up to 1.5
hours, with the solution temperature kept between normal room temperature
and 60.degree. C, preferably between 50.degree. and 60.degree. C.
Examples of the persulfate, of which the aqueous solution is used for this
oxidation, generally include persulfates of ammonium, sodium, potassium,
The aqueous persulfate solution incorporting an alkali metal hydroxide is
obtained by adding a persulfate such as of ammonium, sodium or potassium
to an aqueous solution of the hydroxide of an alkali metal such as sodium
or potassium in such relative amounts that, in the finally produced
aqueous solution, the alkali metal oxide concentration falls in the range
of from 20 to 40 g/liter and the persulfate concentration in the range of
from 60 to 100 g/liter respectively, with the pH value of the solution
maintained between 13 and 11.
As the result of the aforementioned treatment, crystals of lead dioxide are
deposited on the surface of the substrate and in the pores distributed in
the surface layer to a depth of several millimeters of the substrate.
FIG. 2 is an X-ray diffraction diagram of the lead dioxide crystals
deposited as described above. The horizontal axis is graduated for
diffraction angle 20 and the vertical axis for the intensity of
diffraction ray. From the diffraction diagram, it is seen that the lead
dioxide is substantially composed of .alpha.-lead dioxide. If the formed
layer of deposited lead dioxide does not have sufficient thickness and the
substrate fails to show sufficient electroconductivity, a desired
electroconductive layer can be obtained by repeating the aforementioned
step of oxidative soaking. This soaking process is nothing but an
operation intended to impart sufficient electroconductivity to the
substrate. A layer of lead dioxide having a thickness sufficient for the
purpose of a practical electrode is not obtained, therefore, by merely
repeating this process.
Desired growth of the layer of lead dioxide is accomplished by subsequently
subjecting the substrate to the electrolytic process. This electrolytic
process is effected as follows: In an electrolytic cell which contains, as
the electrolyte, a lead (II) salt such as lead nitrate, lead perchlorate
or lead sulfamate and, as the cathode, a piece of lead, copper or
stainless steel (SUS 304, SUS 316, for example), the ceramic substrate
which has been coated with lead dioxide in consequence of the
aforementioned soaking process is disposed so as to function as the anode
and electrolysis is effected.
For the purpose of this electrolysis, it is desired to use aqueous lead
nitrate solution as the aqueous lead (II) salt solution and to conduct the
electrolysis under the following general conditions: The lead nitrate
concentration is to fall in the range of from 0.5 to 1.0 mole/liter of
Pb(NO.sub.3).sub.2, the pH value in the range of from 3.0 to 2.0, the
solution temperature in the range of from 20.degree. to 60.degree. C and
the anode current density in the range of from 0.5 to 20 A/dm.sup.2.
The surface smoothness of the electrodeposited layer of lead dioxide is
improved by adding to the electrolyte a nonionic surface active agent such
as, for example, polyethylene oxide oleylether at a concentration of 5 to
8 g/liter. The lead ion concentration and the pH value of the electrolyte
can be adjusted by addition of a basic lead carbonate.
Where the aqueous solution of any lead (II) salt other than lead nitrate is
used as the electrolyte, the electrolysis is desired to be carried out
under the following conditions: The lead (II) salt concentration is to
fall in the range of from 0.5 to 1.0 mole/liter of electrolyte, the pH
value in the range of from 2.0 to 3.0, the solution temperature in the
range of from 20.degree. to 60.degree. C and the anode current density in
the range of from 0.5 to 10 A/dm.sup.2. The pH value is adjusted likewise
by using a basic lead carbonate. Addition of a non-ionic surface active
agent has a similar effect in improving the surface smoothness of the
electrodeposited layer of led dioxide to the case of lead nitrate.
The thickness of the electrodeposited layer of lead dioxide to be formed on
the ceramic substrate serving as the anode increases with the increasing
length of the time of electrolysis. For the purpose of an electrode which
is to be used in the electrolysis of ordinary aqueous solutions, the layer
thickness is generally sufficient in the range of from 1 to 3 mm.
When the layer thickness has increased to reach a prescribed value, the
electrolysis is stopped and the product of electrodeposition, namely the
ceramic substrate now coated with the electrodeposited lead dioxide, is
removed from the electrolytic cell and washed with water and dried. The
drying is effected by first allowing it to stand at normal room
temperature to 50.degree. C for preliminary drying and then exposing it to
a heat at 100.degree. C. The layer of electrodeposited lead dioxide thus
finally obtained is a fine-grained black coat excellent in
electroconductivity. FIG. 1 shows an X-ray diffraction diagram of this
product. The diagram clearly indicates that the product is an .alpha. +
.beta. lead dioxide.
A terminal attached at a proper position to the electrodeposited layer
turns the product into a complete electrode ready for use.
A porous round bar of corundum (measuring 15mm in diameter and 300mm in
height) was soaked in a saturated solution of lead (II) nitrate at
90.degree. C for 5 minutes, then removed from the solution and left to dry
at normal room temperature. Subsequently, the dried bar was placed in a
solution which had been prepared by adding 30g of ammonium persulfate to
500ml of aqueous ammonia (obtained by diluting an aqueous 28% ammonia
solution with water of a volume twice as large) and heating the resultant
mixture to 50.degree. to 60.degree. C and left to stand therein and
undergo an oxidation treatment for about 1 hour. At the end of this
treatment, the bar was washed first with dilute nitric acid and then with
water and dried at 100.degree. C. Consequently, the bar was found to be
coated with a layer of .alpha.-lead dioxide penetrating to a depth of 2 to
3mm from the surface of the substrate.
Then, the substrate which had been coated with the layer of .alpha.-lead
dioxide as described above was disposed as an anode and a plate of
stainless steel (SUS 304) was disposed as a cathode respectively in an
electrolytic cell, which was filled with an aqueous 165 g/liter lead
nitrate solution (with the pH value adjusted with nitric acid to 2.0). In
this electrolytic cell, electrolysis was carried out at 25.degree. C. The
anode current density was fixed at 0.5 A/dm.sup.2 in the initial phase of
electrolysis and increased to a final level of 4-5 A/dm.sup.2 within four
hours of electrolysis. After that, the flow of electric current was
continued for 24 hours, with the current density fixed at said final
Subsequently, said substrate used as the anode was taken out, washed with
water and dried at 100.degree. C. There was consequently obtained an
electrodeposited lead dioxide electrode having a corundum substrate coated
with a uniform 2.0-mm layer of blackish gray lead dioxide.
In an electrolytic cell divided into two compartments with an unglazed
diaphragm, the electrodeposited lead dioxide electrode obtained as
described above was disposed in the anode compartment and a lead plate of
the same shape was disposed in the cathode compartment. With this
electrolytic cell, production of iodic acid by electrolysis was tested
under the following conditions: Anode liquid 500ml of 0.6N hydrochloric
acid + 100g of powdered iodine, cathode liquid 500ml of 10% sulfuric acid,
temperature 40.degree. C, voltage 5V, electric current 7A, anode current
density 14 A/dm.sup.2. The flow of current was continued until 110.0 AH.
Then it was discontinued and the anode liquid was evaporated to produce
134g of iodic acid. By calculation, the yield was found to be 96.7%, the
current efficiency to be 92.8% and the anode consumption to be 0.4 g/100g
of HIO.sub.3. These results were substantially the same as those obtained
by using a substrateless lead dioxide electrode.
The fact that the electrodeposited lead dioxide electrode according to the
present invention has greater strength than the substrate-less
electrodeposited lead dioxide clearly indicates that the former excels
over the latter in terms of practical utility.
A porous plate of mullite (measuring 50 .times. 150 .times. 2mm) was soaked
in an aqueous lead (II) nitrate solution by following the procedure of
Example 1. The it was taken out of the solution and immediately dried. The
dried porous plate was then placed in a 30 g/500 ml potassium persulfate
solution and, with the pH value adjusted to 12-13 by incorporation of 2N
aqueous temperatures of hydroxide solution, treated for 1 hour at
temperaturesof from 50.degree. to 60.degree. C. Then the plate was washed
with water and dried similarly to Example 1. The dried plate was found to
be coated with a uniform layer of .alpha.-lead dioxide having the same
thickness as that obtained in Example 1 and penetrating into the surface
layer of the porous substrate to a depth of 2 to 3mm from the surface.
Subsequently, this plate was used to perform electrolysis and then treated
in the same manner as before. Consequently, there was obtained an
electrodeposited lead dioxide electrode having the porous substrate of
mullite coated with a uniform compact layer of blackish gray lead dioxide
having a thickness of 1.5mm.
With this electrode used as the anode, electrolysis was performed by
faithfully following the procedure of Example 1. The electrolysis gave
entirely the same results, indicating that the porous mullite substrate
coated with the layer of lead dioxide served as an excellent
electrodeposited lead dioxide electrode similarly to the electrode
described in Example 1.
A porous plate of zirconia (measuring 50 .times. 150 .times. 3mm) was
soaked in a solution of lead perchlorate (226 g/1000 ml) at 40.degree. to
50.degree. C for 10 minutes, then removed from the solution and dried at
Subsequently, the dried plate was placed in a solution which has been
prepared by adding 30g of ammonium persulfate to 500ml of aqueous ammonia
(obtained by diluting an aqueous 28% ammonia solution with water of a
volume twice as large) and heating the resultant mixture to 50.degree. to
60.degree. C and left to stand therein and undergo an oxidation treatment
for 1 hour. At the end of this treatment, the plate was washed first with
dilute nitric acid and then water and dried at 100.degree. C.
After completion of this chemical treatment, the plate was used to conduct
electrolysis under the same conditions as those described in Example 1.
Consequently, as in Examples 1 and 2, there was obtained an
electrodeposited lead dioxide electrode with a uniform compact layer of
blackish gray lead dioxide having a thickness of 1 to 1.5mm.
* * * * *
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