CA1056769A - Cathode for electrolytic systems - Google Patents
Cathode for electrolytic systemsInfo
- Publication number
- CA1056769A CA1056769A CA232,349A CA232349A CA1056769A CA 1056769 A CA1056769 A CA 1056769A CA 232349 A CA232349 A CA 232349A CA 1056769 A CA1056769 A CA 1056769A
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- CA
- Canada
- Prior art keywords
- cathode
- titanium
- sheet
- cathodes
- central core
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Novel electrolytic cells and electrodes, e.g. cathodes and bipolar cathodes/anodes therefor are provided. The electrode comprises titanium base metal in self-sustaining form, e.g., in flat sheet form the surfaces of which having a high surface area, any pores or apertures in the central core being smaller than pores or apertures at the surface, so that the central core is less porous or more dense, the sheet being in accordion-type form, of mesh-like form, of grid-like form, or of expanded metal form. The exposed cathodically active surfaces are of high surface area, i.e., being microporous and more porous than the surface of the sheet in which it is provided. They may e.g. be provided by grit blasting the base titanium, or by subjecting the base titanium to electrolysis, or by sintering or by fus-ing powered titanium. The cathode has the advantages of a steel or carbon cathode and yet does not suffer the disadvantages thereof. The electrolytic cell comprises a plurality of anodes and cathodes, preferably m the form of end-to-end bipolar electrodes the cathodes each being as described above, namely, comprising titanium base metal in self-sustaining form, whose exposed cathodically active surfaces are of high surface area.
Novel electrolytic cells and electrodes, e.g. cathodes and bipolar cathodes/anodes therefor are provided. The electrode comprises titanium base metal in self-sustaining form, e.g., in flat sheet form the surfaces of which having a high surface area, any pores or apertures in the central core being smaller than pores or apertures at the surface, so that the central core is less porous or more dense, the sheet being in accordion-type form, of mesh-like form, of grid-like form, or of expanded metal form. The exposed cathodically active surfaces are of high surface area, i.e., being microporous and more porous than the surface of the sheet in which it is provided. They may e.g. be provided by grit blasting the base titanium, or by subjecting the base titanium to electrolysis, or by sintering or by fus-ing powered titanium. The cathode has the advantages of a steel or carbon cathode and yet does not suffer the disadvantages thereof. The electrolytic cell comprises a plurality of anodes and cathodes, preferably m the form of end-to-end bipolar electrodes the cathodes each being as described above, namely, comprising titanium base metal in self-sustaining form, whose exposed cathodically active surfaces are of high surface area.
Description
This invention relates to novel titanium base cathodes for use in electrolytic systems. More particularly, it is directed to such cathodes which are specifically suited for electrolytic systems such as chloride oxidation where conventional cathode material usually is found to have inherent problems in maintaining performance.
In electrolytic cells for the production of hypochlorites, chlorates, perchlorates and hydrox des it is conventional to employ steel as a cathode material for monopolar type cells, and to employ a graphite material as a cathode for bipolar type cells. Although these materials have a proven commercial performance and provide generally satisfactory cathode materials in the new development of electrolytic cells, these conventional cathodes do limit the performance of the elec-trolytic system. In the case of bipolar cells, ma~or disadvantages inherent in the use of graphite include the relative poor conductance, thus often requiring a large number of cathodes, and have problematic connections between the graphite cathodes and the electric current leads.
In the case of monopolar cells using steel cathodes, while steel is a relatively good conductor, it corrodes at the interphase of the elec-trolyte and gas. Such corrosion is very significant when foaming is experienced in the cell. The contact joint for electric current leads to the cathodes usually gives a poorer performance with time. Also!this type of cell employing steel cathodes requires cathodic protection when the electrolytic process is shut off. Another disadvantage is that the electrolyte at times is high in iron contamination due to failure of the cathodic protection and/or the failure of the cathodes for other reasons.
It would therefore be highly desirablé to provide a cathode which is based on a material which has the advantages of carbon or steel and yet does not suffer to any deleterious extent, the disadvantages pointed out above.
It is known that suitable cathodic materials for electrolytic cells should be electrically conductive, substantially insoluble in the electrolyte under cathodic conditions, resistant to reduction and either -1- ~
` 105676g substantially impermeable with respect to H2, or, if permeable by ~2~ be di-mensionally stable with respect to H2. It is known that, in addition to steel, it would be possible to use copper, chromium, cobalt, nickel, lead, tin, iron or alloys thereof. However, these latter metals suffer the same disadvantages as steel.
While titanium sheet has been used as an anode in electrolytic cells, its use as a cathode has been discouraged by the fact that titanium sheeting has too high an overvoltage which makes it unsuitable for commercial use as a cathode. Attempts have been made to take advantage of the desirable characteristics of titanium sheet as a cathode ~hile minLmizing the overv~l-tage problem by applying cathode layers of platinum metal or layers of iron or steel thereon (see United States Patent No. 3,219,563 issued November 23, 1965 to Collins or Canadian Patent No. 760,427 issued June 6, 1967 to Ino et al). Yet, the iron or steel layers provided the same disadvantage as for solid steel cathodes. The platinum coating has been found to be unsuitAhle since the platinum coating has been found to ~7ear away in a matter of days, and this then results in a titanium sheet cathode suffering fr~m the original disadvantages of titanium sheet cathodes.
Accordingly, it would h~ very advantageous to provide a cathode which ~70uld have the advantages of titanium, i.e. chemical inertness to elec-trolyte and the feasibility for achieving a ~7elded joint to adjacent cell ano es and/or electrical current leads, while avoiding the deficiency of titanium, i.e. high overv~ltage.
It has surprisingly been found that titanium sheet which has been surface treated may be used as a cathode in electrolytic cells without suf-fering the disadvantage of high overvoltage.
Thus, by a broad aspect of this invention, a cathode is provided for an electrolytic cell, comprising: (a) a titanium sheet having a central core and surfaces having high surface are, ~ - 2 -`` 1056769 any pores or apertures in the central core being of lesser diameter than the pores at the surfaces, thereby providing a central core of less porosity than the surfaces; and (b) the exposed surfaces of at least tWD side faces thereof being microporous titanium, the titanium having pores of greater dia-meter than those of the core and thus being more porous than the surface of the titanium sheet on which it is provided.
Ey one variant thereof, the core is sintered micro size po~Jder.
By another variant, the cathode comprises a sintered mocroporous titanium sheet having a central core and t~o side faces, the central core formed from smaller size titanium powder than the tw~ side faces, and having a lower porosity than the two side faces.
By variations thereof, the pore size may be 3-30 microns, the porosity of the core may be 20%~
By other variants, the titanium sheet may ke in flat sheet form, in accordian-type form, in mesh-like form, in grid-like form or of expanded metal form.
By still another varian~, the high surface area of the exposed side faces may be provided by grit blasting the base titanium, e.g., with aluminum oxide; ot by subjecting the base titanium to electrolytic dissolving, e.g., in a chloride electrolyte at a v~ltage slightly above deaomposition voltage; or by sintering or fusing powdered titanium.
By a further variant, the cathode may be anodized, e.g. in chloride water solution or in caustic solution.
By another aspect of this invention, an electrolytic cell is provided comprising a plurality of alternating anodes and the cathodes as described above. - r Thus, an improved and novel cathode is provided herein which is made of titanium base metal. This provides a number of advan-
In electrolytic cells for the production of hypochlorites, chlorates, perchlorates and hydrox des it is conventional to employ steel as a cathode material for monopolar type cells, and to employ a graphite material as a cathode for bipolar type cells. Although these materials have a proven commercial performance and provide generally satisfactory cathode materials in the new development of electrolytic cells, these conventional cathodes do limit the performance of the elec-trolytic system. In the case of bipolar cells, ma~or disadvantages inherent in the use of graphite include the relative poor conductance, thus often requiring a large number of cathodes, and have problematic connections between the graphite cathodes and the electric current leads.
In the case of monopolar cells using steel cathodes, while steel is a relatively good conductor, it corrodes at the interphase of the elec-trolyte and gas. Such corrosion is very significant when foaming is experienced in the cell. The contact joint for electric current leads to the cathodes usually gives a poorer performance with time. Also!this type of cell employing steel cathodes requires cathodic protection when the electrolytic process is shut off. Another disadvantage is that the electrolyte at times is high in iron contamination due to failure of the cathodic protection and/or the failure of the cathodes for other reasons.
It would therefore be highly desirablé to provide a cathode which is based on a material which has the advantages of carbon or steel and yet does not suffer to any deleterious extent, the disadvantages pointed out above.
It is known that suitable cathodic materials for electrolytic cells should be electrically conductive, substantially insoluble in the electrolyte under cathodic conditions, resistant to reduction and either -1- ~
` 105676g substantially impermeable with respect to H2, or, if permeable by ~2~ be di-mensionally stable with respect to H2. It is known that, in addition to steel, it would be possible to use copper, chromium, cobalt, nickel, lead, tin, iron or alloys thereof. However, these latter metals suffer the same disadvantages as steel.
While titanium sheet has been used as an anode in electrolytic cells, its use as a cathode has been discouraged by the fact that titanium sheeting has too high an overvoltage which makes it unsuitable for commercial use as a cathode. Attempts have been made to take advantage of the desirable characteristics of titanium sheet as a cathode ~hile minLmizing the overv~l-tage problem by applying cathode layers of platinum metal or layers of iron or steel thereon (see United States Patent No. 3,219,563 issued November 23, 1965 to Collins or Canadian Patent No. 760,427 issued June 6, 1967 to Ino et al). Yet, the iron or steel layers provided the same disadvantage as for solid steel cathodes. The platinum coating has been found to be unsuitAhle since the platinum coating has been found to ~7ear away in a matter of days, and this then results in a titanium sheet cathode suffering fr~m the original disadvantages of titanium sheet cathodes.
Accordingly, it would h~ very advantageous to provide a cathode which ~70uld have the advantages of titanium, i.e. chemical inertness to elec-trolyte and the feasibility for achieving a ~7elded joint to adjacent cell ano es and/or electrical current leads, while avoiding the deficiency of titanium, i.e. high overv~ltage.
It has surprisingly been found that titanium sheet which has been surface treated may be used as a cathode in electrolytic cells without suf-fering the disadvantage of high overvoltage.
Thus, by a broad aspect of this invention, a cathode is provided for an electrolytic cell, comprising: (a) a titanium sheet having a central core and surfaces having high surface are, ~ - 2 -`` 1056769 any pores or apertures in the central core being of lesser diameter than the pores at the surfaces, thereby providing a central core of less porosity than the surfaces; and (b) the exposed surfaces of at least tWD side faces thereof being microporous titanium, the titanium having pores of greater dia-meter than those of the core and thus being more porous than the surface of the titanium sheet on which it is provided.
Ey one variant thereof, the core is sintered micro size po~Jder.
By another variant, the cathode comprises a sintered mocroporous titanium sheet having a central core and t~o side faces, the central core formed from smaller size titanium powder than the tw~ side faces, and having a lower porosity than the two side faces.
By variations thereof, the pore size may be 3-30 microns, the porosity of the core may be 20%~
By other variants, the titanium sheet may ke in flat sheet form, in accordian-type form, in mesh-like form, in grid-like form or of expanded metal form.
By still another varian~, the high surface area of the exposed side faces may be provided by grit blasting the base titanium, e.g., with aluminum oxide; ot by subjecting the base titanium to electrolytic dissolving, e.g., in a chloride electrolyte at a v~ltage slightly above deaomposition voltage; or by sintering or fusing powdered titanium.
By a further variant, the cathode may be anodized, e.g. in chloride water solution or in caustic solution.
By another aspect of this invention, an electrolytic cell is provided comprising a plurality of alternating anodes and the cathodes as described above. - r Thus, an improved and novel cathode is provided herein which is made of titanium base metal. This provides a number of advan-
- 2 a -ii-` ?
tages: firstly, it provides for the feasibility of a ~lelded joint to adjacent cell anode and~or electrical current leads; secondly, it provides chemical inertness to the electrolyte; and thirdly, by specification of the type of surface, the required perform~nc~ for discharging electr~ns frGm the electro-lyte onto the cathode surface is enhanced.
Titanium cathodes having a large surface area, with an apparent density for surfaces down to 0.010 inches of depth, of less than 50% of the specific weight of titanium may be provided in a number of ways according to variants of this invention. Firstly, they may be prepared by a grit blast-ing. The grit may be aluminum oxide or silica sand, using conventionalblasting techniques which need not be described further.
On the other hand, the cathode may be surface treated by electro-chemical dissolving, using chloride electxolyte, and a vDltage slightly above decomposition voltage. Such voltage varies depending on the purity of the chloride solution, but normally is below 15 volts, maintaining a 1~^~
current density, less than 0.1 amps/in.2.
- Yet another procedure of preparing the cathode is by employing pcwdered titanium which has keen sintered and/or pressed to a porous or semi-porous member. This provideEs a cathode having a large surface area by the pcwdered metallurgy technique. It has been found, moreover, that a smaller pore size is desirable for better cathode performance. The range ~ _ 3 _ -` 10~i6769 tested was 3 to 30 microns with 70% porosity of the surface. The cathDde vDltage was slightly improved when the porous sheet was ~nodized by operating the sheet anodically for a few d~ys at 10 milliamperes per square inch in chloride water solution
tages: firstly, it provides for the feasibility of a ~lelded joint to adjacent cell anode and~or electrical current leads; secondly, it provides chemical inertness to the electrolyte; and thirdly, by specification of the type of surface, the required perform~nc~ for discharging electr~ns frGm the electro-lyte onto the cathode surface is enhanced.
Titanium cathodes having a large surface area, with an apparent density for surfaces down to 0.010 inches of depth, of less than 50% of the specific weight of titanium may be provided in a number of ways according to variants of this invention. Firstly, they may be prepared by a grit blast-ing. The grit may be aluminum oxide or silica sand, using conventionalblasting techniques which need not be described further.
On the other hand, the cathode may be surface treated by electro-chemical dissolving, using chloride electxolyte, and a vDltage slightly above decomposition voltage. Such voltage varies depending on the purity of the chloride solution, but normally is below 15 volts, maintaining a 1~^~
current density, less than 0.1 amps/in.2.
- Yet another procedure of preparing the cathode is by employing pcwdered titanium which has keen sintered and/or pressed to a porous or semi-porous member. This provideEs a cathode having a large surface area by the pcwdered metallurgy technique. It has been found, moreover, that a smaller pore size is desirable for better cathode performance. The range ~ _ 3 _ -` 10~i6769 tested was 3 to 30 microns with 70% porosity of the surface. The cathDde vDltage was slightly improved when the porous sheet was ~nodized by operating the sheet anodically for a few d~ys at 10 milliamperes per square inch in chloride water solution
- 3 a -~056769 or in a caustic solution.
Another advantage of a titanium cathode is that it may be used in conjunction with the anodes and/or elec-trical current leads disclosed in copending application Serial No. 213,586 filed November 13, 1974 and assigned to the same assignee as the present application.
Comparative Test A
Conventional titanium sheet was used as a cathode in a test using an electrolyte containing 500 GPL NaC103 and 100 GPL NaCl at pH 7 over the range of 0.5 to 2.5 amperes per square inch. This showed 0.2 to 0.3 volt potential higher than that of a mild steel cathode.
It was found that a similar result, i.e. overvoltage, was obtained in electrolysis of water using an alkaline water electrolyte.
Example-l -Titanium sheet which was grit blasted using aluminum oxide was used as a cathode in an electrolysis of an electrolyte containing 500 g/l NaC103 and 100 g/l NaCl at pH 7 over the range or 0.5 to 2.5 amperes/in2. There was no evidence of the ahove recited overvoltage of 0.2 to 0.3 volt potential.
There was no significant change in voltage over several months of operation and no apparent loss of titanium hydride even under conditions at numerous times of no induced current potential.
A test repeated using a cathode of titanium sheet with a mild blasted surface employing silica sand gave no improvement in voltage compared to an unblasted surface.
Repeated blasting on the same surface gave improved voltage, but not equal to that achieved employing aluminum oxide grit as the blasting agent.
Example 2 A similar example was conducted using cathodes hav-ing pore sizes of 3 microns, 10 microns and 30 microns.
It was found that a cathode of 3 microns pore size has 0.3 volt lower voltage compared to mild steel; lO micron cathode was 0.05 volt higher than the 3 micron sheet; and 30 micron pore size showed 0.1 volt higher than mild ste21. If the porous members are anodized, the overvoltage was lower for all pore sizes by approximately 0.1 volt.
Test B
Test A was repeated using a cathode of grit blasted titahium sheet having a surface coating of platinum. It was found that such cathode did not show any improvement in voltage, i.e. it was the same as a grit blasted electrode.
Thus, it has been common practice that the overvol-tage was the determining factor why titanium was not employed as cathodes. It has now been found that this overvoltage is eliminated if the titanium is surface treated to increase-its surface area.
It has been found, however, that the titanium sheet-like cathodes of aspects of this invention form hydrides dur-ing electrolysis. Therefore, substantially the same cur-rent density should be maintained for both sides of the sheets to avoid significant bowing caused by a change in density of the metal when hydride is formed.
The inherent property of titanium metal minimizes the tendency for reversible current at no induced electric power load condition of the electrolytic cell. Thus, the cathode of aspects of this invention has successfully been employed with voltage performance of at least equal to that i of low carbon mild steel. No corrosion was evident and furthermore there was no apparent contamination of the elec-trolyte.
In addition, the use of the cathodes of aspects of this invention enables the operation of electrolytic cells at high temperatures, e.g. in the case of chlorate eaectrolysis, above 60C., and as high as near the boiling temperature of the slectrolyte to yield a high strength of finished pro-duct liquor by the significant amount of evaporation of ~ater during electrolysis at the elevated temperatures.
A cell so operated showed no deterioration in operating performance over a period of several months and no apparent wear of t4e grit blasted titanium cathodes.
The "sheet" titanium may be solid sheet, mesh-like sheet, grids, expanded metal or accordion-folded titanium metal pl~ate.
SUPPIE~3~C~RY ~ISCLOSURE
me Principal Disclosure pr~vided novel cathodes and novel electro-lytic cells containiny such cathodes. The cathode comprised titanium sheet metal in self-sustaining form having a central core and whose exposed cathodi-cally active surfaces were of high surface area and whose surfaces had an apparent density less than that of the titanium core. The electrolytic cell included a plurality of interleaved anodes and such cathodes. Examples of sui~hle self-sustaining titanium cores included flat sheet form, accordian- r type form, mesh-like form, grid-like form, or expanded metal form, while examples of suitable cathodically active surfaces included those provided by sintering powdered titanium.
An important variant in the form of an end-to-end bipolar electrode has now been provided through the use of an expanded titanium sheet as the core.m us, by the present invention as now provided by this Supplementary Disclosure,a bipolar electr~de is provided comprising: an expanded titanium cathodic core, having a coating acting as a cathode on both its faces along a portion of its length, the coating comprising a pressed and sintered powdered titanium, and a surface acting as an anode on both its faces along the remaining portion of its length.
By a variant thereof, the anode portion of the bipolar electrode provided the expanded titanium sheet is provided with a oonventional anodic surface coating, e.g. a platinum sheet surface.
By another variant, the end face of the cathode portion of the bi-polar electrode is provided with an electrically non-conductive electrcde spacer, e.g., of a synthetic plastics material.
mus, by the present invention as now provided by this Supplementary Disclosure, a bipolar electrode is now provided which is of titanium. m is provides a number of advantages: firstly, it provides an end-to-end combined ..
......
cathode/anode of cell-liquor-inert material and facilitates joining the elec-trode to adjacent cell electrical current leads; secondly, it provides chemical inertness to the electrolyte, thirdly, by specification of the type of sur- _ face, the required performance for discharging electrons from the electrolyte onto the cathode surface is enhanced fourthly, it provides extra thickness for the porous surface thereby providing sufficient structural rigidity for use as such.
The cathode portion of the bip31ar electrode may be prepared by em-ploying Fowdered titanium which has been pressed and sintered to a porous or semi-porous member. This provides a cathode portion having a large area by the powdered metallurgy technique. It has been found, n~reover, that a smaller pore s ze is desirable for better cathode performance. me range tested was 3 to 30 microns with 70% porosity. The cathode voltage was slightly improved when the porous sheet was anodized by operating the sheet anodically for a few days at 10 milliamperes per square inch in chloride water solution or in a caustic solution.
The anode portion of the bipolar electrode may simply be expanded titanium surface, or it may be surh surface which has been coated with platinum to improve anode performance.
In the accompanying drawing, the-single figure is a central longi-tudinal section of an end-to-end bipolar electrode of an aspect of this inven-tion.
The electrode 10 includes a cathode portion 12 and an anode portion 14, and is provided by a core of self-sustaining titanium 11, which is an expanded titanium sheet. mis sheet ll provides a dense core and provides im-proved longitudinal current conductance. On koth side faces of cathode portion 12 of the electrode 10 is a surface 13 acting as a cathode of high surface area. This surface is preferably pressed and sintere powdered titanium.
1(~56769 The titanium core 11 extends beyond one end 16 of the cathode portion 12 as anode ~ortion 14. The anode 14 may be the expanded titanium sheet, or may be a solid, unexpanded titanium sheet coated with platinum.
The cathode at end 17 is capped with an electr~de spacer 15, e.g., of a synthetic plastic material to assist in the assembly of electrodes in an electrolyzer. A suitable material for such spacer is one made of polyvinyl-dichloride (PVDC). Other suit~ble electricalLy non-conductive plastics materials are those known by the Trade Marks of Kynar, Kel-F or Teflon.
By this embodiment of the invention, the bipolar electrode is rigid and can be used for an extended period of time before bowing and warpage may develop. With this embodlment, the bipolar electrode should perform for at least a five-year period. One :mbodiLent of the bipolar electrode of this aspect of the invention uses a 1/16" exp~nded titanium core with a total cathodic area thickness of 3/8".
f, ,~,
Another advantage of a titanium cathode is that it may be used in conjunction with the anodes and/or elec-trical current leads disclosed in copending application Serial No. 213,586 filed November 13, 1974 and assigned to the same assignee as the present application.
Comparative Test A
Conventional titanium sheet was used as a cathode in a test using an electrolyte containing 500 GPL NaC103 and 100 GPL NaCl at pH 7 over the range of 0.5 to 2.5 amperes per square inch. This showed 0.2 to 0.3 volt potential higher than that of a mild steel cathode.
It was found that a similar result, i.e. overvoltage, was obtained in electrolysis of water using an alkaline water electrolyte.
Example-l -Titanium sheet which was grit blasted using aluminum oxide was used as a cathode in an electrolysis of an electrolyte containing 500 g/l NaC103 and 100 g/l NaCl at pH 7 over the range or 0.5 to 2.5 amperes/in2. There was no evidence of the ahove recited overvoltage of 0.2 to 0.3 volt potential.
There was no significant change in voltage over several months of operation and no apparent loss of titanium hydride even under conditions at numerous times of no induced current potential.
A test repeated using a cathode of titanium sheet with a mild blasted surface employing silica sand gave no improvement in voltage compared to an unblasted surface.
Repeated blasting on the same surface gave improved voltage, but not equal to that achieved employing aluminum oxide grit as the blasting agent.
Example 2 A similar example was conducted using cathodes hav-ing pore sizes of 3 microns, 10 microns and 30 microns.
It was found that a cathode of 3 microns pore size has 0.3 volt lower voltage compared to mild steel; lO micron cathode was 0.05 volt higher than the 3 micron sheet; and 30 micron pore size showed 0.1 volt higher than mild ste21. If the porous members are anodized, the overvoltage was lower for all pore sizes by approximately 0.1 volt.
Test B
Test A was repeated using a cathode of grit blasted titahium sheet having a surface coating of platinum. It was found that such cathode did not show any improvement in voltage, i.e. it was the same as a grit blasted electrode.
Thus, it has been common practice that the overvol-tage was the determining factor why titanium was not employed as cathodes. It has now been found that this overvoltage is eliminated if the titanium is surface treated to increase-its surface area.
It has been found, however, that the titanium sheet-like cathodes of aspects of this invention form hydrides dur-ing electrolysis. Therefore, substantially the same cur-rent density should be maintained for both sides of the sheets to avoid significant bowing caused by a change in density of the metal when hydride is formed.
The inherent property of titanium metal minimizes the tendency for reversible current at no induced electric power load condition of the electrolytic cell. Thus, the cathode of aspects of this invention has successfully been employed with voltage performance of at least equal to that i of low carbon mild steel. No corrosion was evident and furthermore there was no apparent contamination of the elec-trolyte.
In addition, the use of the cathodes of aspects of this invention enables the operation of electrolytic cells at high temperatures, e.g. in the case of chlorate eaectrolysis, above 60C., and as high as near the boiling temperature of the slectrolyte to yield a high strength of finished pro-duct liquor by the significant amount of evaporation of ~ater during electrolysis at the elevated temperatures.
A cell so operated showed no deterioration in operating performance over a period of several months and no apparent wear of t4e grit blasted titanium cathodes.
The "sheet" titanium may be solid sheet, mesh-like sheet, grids, expanded metal or accordion-folded titanium metal pl~ate.
SUPPIE~3~C~RY ~ISCLOSURE
me Principal Disclosure pr~vided novel cathodes and novel electro-lytic cells containiny such cathodes. The cathode comprised titanium sheet metal in self-sustaining form having a central core and whose exposed cathodi-cally active surfaces were of high surface area and whose surfaces had an apparent density less than that of the titanium core. The electrolytic cell included a plurality of interleaved anodes and such cathodes. Examples of sui~hle self-sustaining titanium cores included flat sheet form, accordian- r type form, mesh-like form, grid-like form, or expanded metal form, while examples of suitable cathodically active surfaces included those provided by sintering powdered titanium.
An important variant in the form of an end-to-end bipolar electrode has now been provided through the use of an expanded titanium sheet as the core.m us, by the present invention as now provided by this Supplementary Disclosure,a bipolar electr~de is provided comprising: an expanded titanium cathodic core, having a coating acting as a cathode on both its faces along a portion of its length, the coating comprising a pressed and sintered powdered titanium, and a surface acting as an anode on both its faces along the remaining portion of its length.
By a variant thereof, the anode portion of the bipolar electrode provided the expanded titanium sheet is provided with a oonventional anodic surface coating, e.g. a platinum sheet surface.
By another variant, the end face of the cathode portion of the bi-polar electrode is provided with an electrically non-conductive electrcde spacer, e.g., of a synthetic plastics material.
mus, by the present invention as now provided by this Supplementary Disclosure, a bipolar electrode is now provided which is of titanium. m is provides a number of advantages: firstly, it provides an end-to-end combined ..
......
cathode/anode of cell-liquor-inert material and facilitates joining the elec-trode to adjacent cell electrical current leads; secondly, it provides chemical inertness to the electrolyte, thirdly, by specification of the type of sur- _ face, the required performance for discharging electrons from the electrolyte onto the cathode surface is enhanced fourthly, it provides extra thickness for the porous surface thereby providing sufficient structural rigidity for use as such.
The cathode portion of the bip31ar electrode may be prepared by em-ploying Fowdered titanium which has been pressed and sintered to a porous or semi-porous member. This provides a cathode portion having a large area by the powdered metallurgy technique. It has been found, n~reover, that a smaller pore s ze is desirable for better cathode performance. me range tested was 3 to 30 microns with 70% porosity. The cathode voltage was slightly improved when the porous sheet was anodized by operating the sheet anodically for a few days at 10 milliamperes per square inch in chloride water solution or in a caustic solution.
The anode portion of the bipolar electrode may simply be expanded titanium surface, or it may be surh surface which has been coated with platinum to improve anode performance.
In the accompanying drawing, the-single figure is a central longi-tudinal section of an end-to-end bipolar electrode of an aspect of this inven-tion.
The electrode 10 includes a cathode portion 12 and an anode portion 14, and is provided by a core of self-sustaining titanium 11, which is an expanded titanium sheet. mis sheet ll provides a dense core and provides im-proved longitudinal current conductance. On koth side faces of cathode portion 12 of the electrode 10 is a surface 13 acting as a cathode of high surface area. This surface is preferably pressed and sintere powdered titanium.
1(~56769 The titanium core 11 extends beyond one end 16 of the cathode portion 12 as anode ~ortion 14. The anode 14 may be the expanded titanium sheet, or may be a solid, unexpanded titanium sheet coated with platinum.
The cathode at end 17 is capped with an electr~de spacer 15, e.g., of a synthetic plastic material to assist in the assembly of electrodes in an electrolyzer. A suitable material for such spacer is one made of polyvinyl-dichloride (PVDC). Other suit~ble electricalLy non-conductive plastics materials are those known by the Trade Marks of Kynar, Kel-F or Teflon.
By this embodiment of the invention, the bipolar electrode is rigid and can be used for an extended period of time before bowing and warpage may develop. With this embodlment, the bipolar electrode should perform for at least a five-year period. One :mbodiLent of the bipolar electrode of this aspect of the invention uses a 1/16" exp~nded titanium core with a total cathodic area thickness of 3/8".
f, ,~,
Claims (23)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A cathode for an electrolytic cell comprising (a) a titanium sheet having a central core and surfaces having high surface areas, any pores or apertures in the central core being of lesser diameter than the pores at the surfaces, thereby providing a central core of less porosity than the surfaces; and (b) the exposed surfaces of at least two side faces thereof being microporous titanium, the titanium having pores of greater diameter than those of the core and thus being more porous than the surface of the titanium sheet on which it is provided.
2. A cathode according to claim 1, wherein the core is sintered micro sized powder.
3. A cathode as claimed in claim 1 comprising a sintered micro-porous titanium sheet having a central core and two side faces, the central core formed from smaller size titanium powder than the two side faces, and having a lower porosity than the two side faces.
4. A cathode according to claim 3, wherein the central core has a porosity of 20% and the two side faces have a porosity of 75%.
5. The cathode of claim 1 wherein the pore size is 3-30 microns.
6. The cathode of claims 1 or 5 wherein the porosity of the sur-face is 70%.
7. The cathode of claims 1 or 2 wherein said titanium sheet is in flat sheet form.
8. The cathode of claims 1 or 2 wherein said titanium sheet is in accordian-type form.
9. The cathode of claims 1 or 2 or 3 wherein said titanium sheet is of mesh-like form.
10. The cathode of claims 1 or 2 wherein said titanium sheet is of grid-like form.
11. The cathode of claims 1 or 2 wherein said titanium sheet is of expanded metal form.
12. The cathode of claims 1, 2 or 3 wherein the high surface area is provided by grit blasting said titanium sheet.
13. The cathode of claims 1, 2 or 3 wherein said surfaces having high surface-areas are provided by grit blasting the base titanium and wherein the grit used in grit blasting is aluminum oxide.
14. The cathode of claims 1, 2 or 3 wherein said surfaces having high surface areas are provided by subjecting the base titanium to electro-lytic dissolving.
15. The cathode of claims 1, 2 or 3 wherein said surfaces having high surface areas are provided by subjecting the base titanium to electro-lytic dissolving and wherein the electrochemical dissolving is effective in a chloride electrolytic at a voltage slightly above decomposition voltage.
16. The cathode of claims 1, 2 or 3 wherein the cathode has a microporous surface provided by sintering or fusing powdered titanium.
17. The cathode of claims 1, 2 or 3 which has additionally been anodized.
18. The cathode of claims 1, 2 or 3 which has additionally been anodized in chloride water solution or in caustic solution.
19. An electrolytic cell comprising a plurality of alternating anodes and cathodes, each of said cathodes comprising the cathode as claimed in claims 1, 2 or 3.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
20. An electrode as claimed in claim 1 comprising an expanded titanium cathode core, having a coating acting as a cathode along a portion of its length, on both sides thereof, said coating comprising a pressed and sintered powdered titanium porous coating, and a surface acting as an anode on both sides thereof along the remaining portion of its length.
21. The electrode as claimed in claim 17 wherein the portion of the titanium sheet acting as an anode is provided with a coating on the sur-face thereof acting as an anode.
22. The electrode as claimed in claim 18 wherein the coating acting as an anode is formed of platinum.
23. The electrode as claimed in claim 17 wherein the end face of the portion of the electrode acting as a cathode is provided with an electrically non-conductive electrode spacer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA232,349A CA1056769A (en) | 1975-07-28 | 1975-07-28 | Cathode for electrolytic systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA232,349A CA1056769A (en) | 1975-07-28 | 1975-07-28 | Cathode for electrolytic systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1056769A true CA1056769A (en) | 1979-06-19 |
Family
ID=4103715
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA232,349A Expired CA1056769A (en) | 1975-07-28 | 1975-07-28 | Cathode for electrolytic systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1056769A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4456518A (en) * | 1980-05-09 | 1984-06-26 | Occidental Chemical Corporation | Noble metal-coated cathode |
-
1975
- 1975-07-28 CA CA232,349A patent/CA1056769A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4456518A (en) * | 1980-05-09 | 1984-06-26 | Occidental Chemical Corporation | Noble metal-coated cathode |
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