US 3816293 A
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United States Patent 1191 Ueda et al. June 11, 1974 [5 ELECTRODE CONSTRUCTION AND 3,284,333 ll/l966 Parsi et al. 204/290 R 3,625,851 12/1971 Geld 204/196 METHOD OF MAKING AN ELECTRODE lnventors: Kenji Ueda; Akihiro Tanaka, both of Nagasaki, Japan Assignee: Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed: Mar. 29, 1972 Appl. No.: 239,160
[1.8. CI 204/290 R, 204/ 196, 204/284, 204/292 Int. Cl. B0lk 3/04, BOlk 3/06, C23f l3/OO Field of Search 29/199; 204/293, 292, 290 R,
References Cited UNITED STATES PATENTS 5/l954 Fischbach ct al 136/36 Primary Examiner-F. C. Edmundson Attorney, Agent, or Firm-McClew and Tuttle 1571 ABSTRACT An electrode comprises a lead base which is covered by a silver material on at least a portion of the surface which is in the form of a net or grid. The lead base itself, may include some percentage of silver and the net or grid may be in the form of a bandage or of a netting which is applied over the surface and then secured to the surface. The securement may be effected such as by mechanical pressure joining with or without additional securement elements or by heat joining such as by welding.
11 Claims, 8 Drawing Figures PATENTEDJuu 11 1914 I 3.816293 'SHEET 1UFV2.
Potential (V) Electrolyzing Time (Day) Q (PriorAfl') FIG.|
PATENTEDJUN 1 1 1914 slalslzsa SHEET 20F 2 FIG.3
ELECTRODE CONSTRUCTION AND METHOD OF MAKING AN ELECTRODE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relatesin general to the construction of electrodes and, in particular, to a new and useful electrode having a-net-like covering of silver on at least a portion of its surface and to a method of making the electrode.
Electrodes which are made of lead which contains a small percentage of silver, have been utilized for a long period of time for the purpose of cathodic protection for the electrolysis apparatus which is used in sea water. Since chlorine is generated in the electrolysis of sea water, the known electrodes have disadvantages. Even slight variations of electrical potential affects the electrolysis efficiency and such potential increases during the electrolysis time up to a point at which it is impossible to continue the electrolysis. In addition, blisters are produced on the electrode surface which may cause contact with the opposed electrode. In general, the known or conventional lead silver electrodes have an uneven or nonuniform distribution of the silver so that the surface current density is extremely uneven as is shown upon microscopic examination during the early phase of electrolysis. This allows many reactions to take place between the lead andthe anions, (such as Cl", OH", SO 1, etc.). These reactions take place in the solution so that it is typical to form lead dioxide of uniform texture. Therefore, many attempts have been made to carry out electrolysis in the case where the reaction anions can easily take place by lowering the current density and producing lead dioxide slowly over a long period of time so as to form a compact crater-free layer of lead dioxide. Such attempts, however, are still unsatisfactory because distributions of lead and silver are non-uniform.
SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an electrode which includes a lead base or a lead base having some silver and which is covered by a symmetrically arranged and uniform grid or netting of silver. The netting is arranged over at least a portion of the surface of the electrode and is secured in position thereon such as by mechanical press securement or by heat bonding such as welding. The invention provides an improved electrode construction for electrolysis of sea water which has a uniform surface distribution of silver and which can operate in a stable condition for a long period of time and which can be manufactured at low costs. The construction of the electrode of the invention produces an electrode having a low electrode potential and no blistering of the electrode is likely. The silver in the form of a net is placed in contact with the surface of the lead base or lead silver alloy base in order to increase the silver density on the surface of the base. The lead dioxide layer on the electrode surface is made into acrater-free compact structure by using amechanical joining of the netting structure to the surface. Because the silver is limited to the surface layer alone, the surface density can be remarkably raised as compared with the prior art devices with the same amount ofsilver.
Accordingly, it is an object of the invention to provide an improved electrode construction which comprises a lead base having a covering of silver arranged in a grid pattern and preferably uniformly distributed over the surface and symmetrically arranged.
A further object of the invention is to provide an electrode which includes a net of silver over a lead base with means for securing the net to the base which advantageously may comprise a separate clamping element embedded into the base.
A further object of the invention is to provide a method of making an electrode which comprises applying a net of silver over a lead base, and advantageously securing the net to the base such as by heat bonding or by mechanical pressure clamping.
A further object of the invention is to provide an electrode which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to theaccompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:
FIG. I is a curve indicating the changes of electrical potention with time for the known (PRIOR ART) lead silver electrodes;
FIG. 2 is a cross-sectional view of the prior art silver electrode indicating the tendency to crack formation;
FIG. 3 is a front elevational view of an electrode constructed in accordance with the invention;
FIG. 4 is a section taken along the line IV-IV of FIG. 3;
FIG. 5 is a view similar to FIG. 3 of another embodiment of the invention;
FIG. 6 is a partial sectional view taken along the lines VI-VI of FIG. 5; 7
FIG. 7 is a perspective view of another embodiment of electrode; and
FIG. 8 is an end elevational view of still another embodiment of electrode.
DESCRIPTION OF THE PRIOR ART SHOWN IN FIGS. 1 AND 2 As shown in FIG. 1, curves A and B indicate the changes of potential for an ordinary lead silver electrode with a silver content of 4 percent electrolizing time for electrolizing sea water at a current density of 5 A/dm. The distinct curves A and B show that for lead silver electrodes, even when they are cast under the same conditions, there is a wide variation of potential, and thus they are not suitable for use in electrolysis. The curves C and D represent electrodes of a silver content of 2 and 1 percent respectively. In these cases, the potential rise takes place faster and hence, an inoperative situation is brought about much earlier than in the case of an electrode using 4 percent silver content.
As shown in FIG. 2, the lead silver alloy electrodes which include a lead base 2 forms a lead dioxide layer 3 when it is used for anodic electrolysis in sea water. 7
This layer 3 is formed with a plurality of cracks l which permits the sea water to enter and to react with the lead base 2. Thus, the reactions between the lead dioxide layer 3 and sea water and the lead 2 and sea water takes place simultaneously at both internal and external interfaces thus giving rise to blistering particularly where the current density is high.
GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawingsin particular, the invention embodied therein in FIGS. 3 and 4, comprises a lead base 5, which may comprise lead or a lead and silver alloy, and which is provided with a surface covering in the form of a silver net 6. The net 6, in accordance with the invention, is secured to the lead base surface such as by pressure or by heat bonding, such as welding. In the embodiment shown, the silver net includes a plurality of substantially parallel equally spaced vertical net elements 6a which 6a which are interwoven with a plurality of substantially parallel and equally spaced horizontal elements 6b. In the method indicated in FIG. 4, the longitudinal elements 60 are pressure embedded into the surface of the base 5. With the inventive construction, the silver density of the surface of the lead base 5 can be raised far higher than is possible with a construction in which the silver is disbursed throughout the base 5. In addition, a compact lead dioxide structure is formed on the electrode surface which is contacted by the electrolyte. The lead base 5 may comprise a lead silver alloy containing a minor percentage of silver.
With the inventive construction, electric current flows mostly from the silver with only a very limited amount of current flowing in the lead during the early phase of the electrolysis reaction. Therefore, the reaction of the lead in the initial stage of electrolysis are limited to those of a low level. The lead is gradually oxidized by catalytic action of the regularly arranged vertical and horizontal elements 6a and 6b. Silver sulfide is generated on the surface and the flow of electrical current is substantially stopped allowing the current to flow only through the oxide layer which is produced on the surface of the lead base 5. In the meantime, the layer of lead oxide swells up to fill the meshes of the silver net 6.
In general, lead dioxide acts as an n-type (excess type) semiconductor (electron conductor), so that if lead oxide is of a compact texture, it is possible to check erosion of lead.
Experiments were conducted with two types of silver net 6, one type being 2001A in line diameter and 400p. in interval, and the other being 250p. in line diameter and 835p. in interval. As a result, it was found that, although the electric current was applied at the rate of 5 A/dm from the beginning, no generation of blister and no rise of electrode potential (average -l.32 V) took place even 300 days after the start of the test.
It was found that the porosity which serves as a yardstick in determining the presence of craters in the surface layer was almost zero or near the ideal level as compared with over 10 percent usually observed in the ordinary 4 percent lead-silver alloy electrodes. Also, the current efficiency was as high as 80 percent on the average at 5 A/dm which can well compare with that of platinum.
The bonding of the net 6 to the base 5 may be effected by a fusion method utilizing heat diffusion, but in such a case, a control of the temperature and time is very important and care must be used so as not to break the meshes by alloying.
In the arrangement of FIGS. 5 and 6, there is provided a silver netting, generally designated 6, which is arranged over a lead base, generally designated 5', which may include some percentage of silver. The netting 6' is secured to the base 5 by driving securing elements or clamping bars 7 of a material such as a noble metal for example, silver, platinum, or the like, into the assembly. According to this arrangement, electrical current flows through the noble metal bar 7 so that blockade of electrical current flow by self-oxidation of the lead structure 5 owing to the generation of lead oxide on its surface is eliminated.
Of course, it is possible to preclude a current blockade due to self-oxidation of the lead base either by en larging the diameter of the net 6 or by arranging the silver cross element 6a and 6b such that they are embedded or partially embedded into the base 5'. The degree at which the silver is embedded into the lead is detennined by taking into account the life expectancy of the electrode.
In the method of the invention in which the netting 6' is secured to the base 5' using securing bars 7,as shown in FIGS. 5 and 6, the diameter in the spacing of the bar 7 is chosen to maintain the proper current distribution.
In the embodiment shown in FIG. 7, a silver net 6" is applied over a base 5" of lead or lead and silver alloy. The net 6" is in the form of a pouch or bag and a conductor wire 8 is shown as extending out through the top thereof. A similar construction is shown in FIG. 8 but with a base 5 having a rounded bottom portion.
With the inventive method, the nets 6 and 6 may be secured to the bases 5 and 5, respectively, by first arranging the individual gear elements over the surface and the calking them into the base by hammering. At least a part of the wires which constitute the netting 6 and 6' may be made of a non-metallic oxidation-proof material, such as-a glass fiber or synthetic fiber, in order to minimize the amount of silver which is required for the net. In such a case, the nonmetallic oxidation-proof material serves as a reinforcement of the lead dioxide which is formed, while the silver wires play a role in the improvement of the lead dioxidegenerating characteristics. However, with this construction, a heat bonding cannot be used for securing the netting to the lead base 5.
The invention thus provides an electrode with a base which may contain silver in smaller quantities and which is at least partially covered with a gauze or network of silver wires so that as compared with the invention, silver lead electrodes in which silver is disbursed throughout the lead structure, the silver density in the lead base surface is markedly increased. In addition, by use of the netting structure 6, 6', 6" and 6", the lead dioxide layer generated on the electrode surface can be made into a compact crater-free texture. Consequently, the electrode potential remains stabilized for a long time and no blisters are produced and thus, there is provided an electrode with extremely high performance and reliability.
When an electrode of the invention is used in sea water, in an electrolysis apparatus for prevention of deposition of marine organisms, for example, it allows a long time continuous operation of the apparatus, thus, greatly contributing to reduction of the electrolizing costs. In addition, the base of the electrode can be made not only from a lead silveralloy formation, but also of lead alone and thhis has been impossible with the conventional techniques employed. Even in a case when a lead silver alloyis employed, the silver may be concentrated on the surface so that the surface density of silver with the netting thereon is far higher than possible with conventional techniques using the same amount of silver. In general, the silver accounts for a major portion of the entire costs of lead silver electrode so that the arrangement of the inventionprovides a substantial cost reduction. This coupled with the fact that the lead alone may be used as the base structure, permits the extremely inexpensive manufacture of the electrode of the invention.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
What is claimed is:
1. In an electrode for cathodic protection of electrolysis apparatus which is used in sea water, the improvement which comprises an electrode having a base of lead and a coating of lead dioxide thereon, and, as an essential element thereof, a net of silver completely covering and partially embedded in the surface of said base and forming a composite positive electrode therewith, at least a portion of said electrode being in contact with sea water, whereby an even distribution of silver over the lead base is achieved with a uniform surface current density resulting during electrolysisand further whereby said coating of lead dioxide is maintained substantially free from cracks due to distortion owing to formation of the lead dioxide layer on the base of lead.
2. An electrode, according to claim 1, wherein said net is welded to said base.
3. An electrode, according to claim 1, including clamping means clamping said net to said base.
4. An electrode, according to claim 3, wherein said clamping means comprises a noble metal bar embedded into said base.
5. An electrode, according to claim 1, wherein said net comprises evenly spaced longitudinal elements.
6. An electrode, according to claim 5, wherein said longitudinal and transverse elements are interweaved.
base by embedding a portion of the net in the base.
10. A method of making an electrode, according to claim 9, wherein the net is at least partially secured to the base by separately applied clamping elements which are embedded into the base.
11. A method of making an electrode, according to claim 9, wherein the net is partially secured to the base by welding.