USRE28015E - Aluminum electrode electrolytic capacitor construction - Google Patents

Aluminum electrode electrolytic capacitor construction Download PDF

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USRE28015E
USRE28015E US28015DE USRE28015E US RE28015 E USRE28015 E US RE28015E US 28015D E US28015D E US 28015DE US RE28015 E USRE28015 E US RE28015E
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electrolytic capacitor
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
    • C23C22/33—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also phosphates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/004—Details
    • H01G9/04—Electrodes or formation of dielectric layers thereon

Definitions

  • FIG. 2 ALUMI NUM ELECTRODE ELECTROLYT I C CAPACITOR GONSTRUCT ION F/GI Original Filed Dec. 3, 1969 FIG. 2
  • Pretreatment of etched aluminum foil includes the combined steps of immersion in a boiling aqueous solution containing CrO and H PO, followed by a 3-minute immersion in a boiling solution of controlled pH containing H POf, SiO and CrO
  • Pretreatment of aluminum in a wet electrolytic capacitor is afforded by the addition of a concentration of at least one of the following inhibiting ions to the liquid electrolyte: phosphate, phosphite, periodate, arsenate, tungstate, silicate vanadate [vandadate], tellurate, tellurite, antimonate, arsenite, selenate, sulfite and germanate.
  • the capacity of an electrolytic capacitor is determined primarily by the area of the electrode (usually the anode) surface and the thickness of the dielectric film covering this surface.
  • the typical wet electrolytic capacitor employs an etched surface electrode structure and a number of methods have been developed to produce the desired roughening of the electrode surface. The most effective of these methods is the electrolytic etching of the electrode foil, while the foil is immersed in an etching solution e.g. sodium chloride (followed in some cases, e.g. for highvoltage applications by etching in nitric acid).
  • an etching solution e.g. sodium chloride
  • the foil is made the positive electrode with respect to a second electrode immersed in the same etching solution.
  • the resulting attack upon the aluminum develops pores extending into the foil, these pores ranging from about 1-5 microns in lateral dimension and penetrating to a depth of from about 100- 500 microns.
  • the electrodes are cleaned, usually by rinsing in water, to remove all traces of any contaminating or foreign materials, which might either affect forrnation of the requisite dielectric film or affect the performance of the finished capacitor.
  • the aluminum foil to be used as the anode is anodized to form an anodic oxide (predominately amorphous A1 0 layer thereon using either a basic or an acidic anodizing electrolyte.
  • anodic oxide predominately amorphous A1 0 layer thereon using either a basic or an acidic anodizing electrolyte.
  • Numerous electrolytes for the formation of anodic films are listed on page 55 of the test book Electrolytic Capacitors by Paul McKnight Deeley (Recorder Press 1938). The most commonly used anodizing electrolytes are boric acid and inorganic phosphates.
  • the anodic oxide layer formed substantially uniformly covers all of the etched surface (both sides) of the aluminum foil even extending into and covering the inside surfaces of the small pores.
  • a typical electrode assembly (anode/paper spacer/cathode/paper spacer) is prepared. This assembly is rolled into a cylindrical configuration and impregnated with (as by immersion) a fill electrolyte for aging.” During the aging process a potential is applied to the electrode assembly equal to or slightly in excess of the rated operating voltage for the completed capacitor for a predetermined period of time. The aging, or reforming, potential tends to repair any breakage or cracking, which may have occurred in the anodic film during the handling and assembly.
  • the electrode assembly is inserted into an aluminum can and the can is capped and sealed.
  • Fill electrolytes are either nonaqueous (organic solvent) or have a low-water content. Ethylene glycol is frequently used, because of its solvent characteristics and low freezing point.
  • the anodic oxide layer is constantly subject to attack by water deliberately or spuriously present in the fill electrolyte. This degradation according to the aluminum/water reaction can reduce the dielectric strength of the capacitor to such a level that the imposition of a normal electrical load may cause failure of the capacitor.
  • passivation and inhibition are employed. These terms are defined as follows:
  • Passivation is the rendering of a metallic or metallic oxide surface relatively immune to corrosive attack in a normally hostile environment.
  • Inhibition is the rendering innocuous of a normally hostile environment by the addition of substances to the environment.
  • the instant invention introduces into the sequence of steps in preparing a wet electrolytic capacitor (a) a modified pretreatment of the etched aluminum foil to passivate the etched surface in order to delay the initiation of hydroxide formation from reaction of the aluminum with water and/or (b) the addition of one or more substances of a specific class, which provide inhibitor ions, to the fill electrolyte such that the completed electrolytic capacitor is afforded protection against dissolution of the dielectric oxide during periods of electrical inactivity.
  • FIG. 1 is an exploded view of an example of an electrolytic capacitor to which the instant invention applies and
  • FIG. 2 is a diagrammatic representation of the process of preparation of electrolytic capacitors according to the invention.
  • capacitor 10 comprises cooperating electrodes 11, 12 in the form of thin aluminum foils. These electrodes have a thin film of aluminum oxide thereon. Between electrodes 11 and 12 as they are arranged in the electrode assembly are disposed spacers 13 consisting of sheets of absorbent material. Spacers 13 are, or become, impregnated with electrolytic composition. Terminal tabs 14, 16 are provided for establishing electrical contact to the electrodes. After preparation, the electrode assembly is placed in aluminum can 17, which is sealed with cap 18 provided with external terminals 14a, 16a (connected to the tabs 14, 16, respectively) and vent plug hole 19 for the release of excess internal pressure.
  • the aluminum foil is subjected to a sequence of two steps, which produces substantial passivation of the aluminum foil.
  • the etched aluminum foil is immersed in a boiling aqueous solution containing Cro and H PO This immersion reduces the thickness of the thin A1 layer (normally present on the surface of aluminum) after which a complex region develops at the surface of the A1 0 layer as this layer reaches an equilibrium condition, when the rate of layer buildup equals the rate of layer dissolution.
  • the complex region at the surface of the A1 0 layer contains CrO and P0 but is incapable of rendering the system highly passive. It is essential that this stripping operation be accomplished first and be followed by the second step.
  • the second step may be conducted.
  • the stripped etched aluminum foil is immersed in a boiling aqueous solution containing CrO H PO and SiO (with pH adjusted to a value ranging from 4 to 6) which exposure changes the complex layer at least by including SiO as a component thereof.
  • a conventional stripping solution (20 grams CrO and 35 milliliters of concentrated H PO per liter of water) may be used with the immersion lasting from 1 to 5 minutes followed by a 3 minute immersion in an aqueous solution of adjusted pH containing from about to 10- moles per liter of each of NaH PO Na SiO and CrO
  • Use of this pretreatment sequence has shown that initiation of hydroxide formation according to the aluminum/water reaction is delayed by at least a factor of 10 as compared to untreated foil and by at least a factor of 10 compared to aluminum foil subjected to the first, but not the second, step of this sequence.
  • the passivated aluminum foil may be stored at considerably reduced risk until ready for the anodizing step preparatory to constructing the electrolytic capacitor.
  • the corrosion process (which will otherwise occur within the sealed capacitor between the exposed aluminum surfaces and liquid water in the electrolyte and between the anodic oxide layer and liquid Water) may be inhibited by introducing certain inorganic substances into the capacitor can dissolved in the fill electrolyte.
  • inhibition will be strong when (a) in the oxyanion of the inhibitor the centrally located, positively charged component (for example, phosphorous in the H PO ion) has a radius between 0.24 and 0.5 times the radius of oxygen and when (b) the inhibiting oxyanion has a proton level of 0.4 to 0.7 ev. relative to that of a proton in H 0
  • the structure and proton level of the inhibitor ion should be close to the structure and proton level of aluminum oxide.
  • the substances which have the required structure and proton level are tellurate, tellurite, tungstate, antimonate, vanadate, arsenate, arsenire, [aresenate, aresenite] selenate, sulfite, periodate, phosphate, phosphite, germanate and silicate ions. All of these substances are effective inhibitors, the strongest being phosphate, phosphite, periodate, arsenate, tungstate, silicate and vanadate in the order given.
  • the pH of maximum effectiveness is about 5:1.
  • the oxyanion concentration dissolved in the fill electrolyte should be in the range of from about l() to 10 weight percent of the electrolyte solution with the preferred range being from about 0.1 to about 1.0 weight percent.
  • the fill electrolyte soluble salts which are compatible with the fill electrolyte and which provide concentrations of ions of one or more of the above materials (eg the sodium, potassium, calcium, ammonium salts thereof) so that the concentration of requisite ions remains within the sealed electrolytic capacitor, initiation of the corrosion process is delayed by at least a factor of compared to electrolytic capacitors, which do not contain the aforementioned inhibiting ions.
  • fill electrolytes are as follows (percentages are by weight).
  • oxyanions dissolving in the fill electrolyte a water-soluble source of inhibiting oxyanions, said oxyanions being present in a concentration in the range of from about 10- to about 10 percent by weight of the electrolyte solution and being selected from the group consisting of tellurate, tellurite, tungstate, antimonate, vanadate, arsenate, arsenite, selenate, sulfite, periodate, phosphate, phosphite, germanate and silicate ions.
  • the improvement of claim 4 wherein the pH of the fill electrolyte is in the range of from 4 to 6.
  • step (a) immersing the cleaned etched foil in a first boiling aqueous solution containing CrO, and H -PO and b. immersing the foil as modified by step (a) in a second boiling aqueous solution containing from about 10* to 10*" moles per liter of each of H POF, SiO and CrO;
  • etched aluminum foil may be stored without substantial deterioration prior to the anodizing step.
  • a method for the passivation of an aluminum surface comprising the steps of:
  • step (a) immersing the aluminum surface in a first boiling aqueous solution containing CrO and H PO and b. immersing the aluminum surface as modified by step (a) in a second boiling aqueous solution containing from about 10- to 10* moles per liter of each of H PO [and] SiO and CrO [10.
  • a water-soluble source of inhibitive ions is disposed in said housing with said electrolyte, said inhibitive ions being present in said electrolyte in a concentration in the range of from about 10* to about 10 percent by weight of electrolyte solution and being selected from the group consisting of tellurate, tellurite, tungstate, antimonate, arsenate, arsenite, selenate, sulfite, periodate, and germanate ions] 11.
  • the pH of the fill electrolyte is in the range of from 4 to 6.

Abstract

BOTH THE PASSIVATION OF ALUMINUM FOIL PARTICULARLY FOR USE AS ELECTRODE IN WET ELECTROLYTIC CAPACITORS AND THE INHIBITION OF THE ALUMINUM-WATER-REACTION WITHIN THE COMPLETED CAPACITOR ARE DESCRIBED. PRETREATMENT OF ETCHED ALUMINUM FOIL INCLUDED THE COMBINED STEPS OF IMMERSION IN A BOILING AQUEOUS SOLUTION CONTAINING CRO3 AND H3PO4 FOLLOWED BY A 3-MINUTE IMMERSION IN A BOILING SOLUTION OF CONTROLLED PH CONTAINING H2PO4-, SIO2= AND CRO3,

INHIBITION OF ALUMINUM IN A WET ELECTROLTIC CAPACITOR IS AFFORDED BY THE ADDITION OF A CONCENTRATION OF AT LEAST ONE OF THE FOLLOWING INHIBITING IONS TO THE LIQUID ELECTROLYTEL ; PHOSPHATE, PHOSPHITE, PERIODATE, ARSENATE, TUNGSTATE, SILICATE VANADATE (VANDADATE), TELLURATE, TELLURITE, ANTIMONATE, ARSENITE, SELENATE, SULFITE AND GERMANATE.

Description

May 21, 1974 o. A. VERMILYEA Er AL Re. 28,015
ALUMI NUM ELECTRODE ELECTROLYT I C CAPACITOR GONSTRUCT ION F/GI Original Filed Dec. 3, 1969 FIG. 2
ALUMINUM FOIL CLEANED A/VD ETC'HED FOIL IMMERSED //v BOILING 61 0 /11 P04 501. U T ION FG/L IMMERSED l/V BOILING SOLl/T/O/V OF H POLS/O ,603
ELECTRODE ASSEMBLY PREPARED ASSEMBL V IMPREGWA TED WITH F/LL ELECTROLYTE CO/V T A l/V/IVG 0X YA N/O/V SOURCE IMPRE'GNA r50 ASSEMBL r AGED ASSEMBL Y CANNED A/VD SEALED IN VE N TORS" 04 W0 4. VERM/L YEA 00mm R. OCHAI? W/L L EM VEDDER bra-4 THE/R ATTORNEY United States Patent 28,015 ALUMINUM ELECTRODE ELECTROLYTIC CAPACITOR CONSTRUCTION David A. Vermilyea, Schenectady, N.Y., Donald R. Ochar, Columbia, S.C., and Willem Vedder, Albany, N.Y., by General Electric Co., New York, N.Y. Original No. 3,622,843, dated Nov. 23, 1971, Ser. No. 881,853, Dec. 3, 1969. Application for reissue Sept. 13, 1972, Ser. N 0. 288,508
Int. Cl. H01g 13/00 US. Cl. 29-570 6 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.
ABSTRACT OF THE DISCLOSURE Both the passivation of aluminum foil particularly for use as electrodes in wet electrolytic capacitors and the inhibition of the aluminum-water reaction Within the completed capacitor are described. Pretreatment of etched aluminum foil includes the combined steps of immersion in a boiling aqueous solution containing CrO and H PO, followed by a 3-minute immersion in a boiling solution of controlled pH containing H POf, SiO and CrO Inhibition of aluminum in a wet electrolytic capacitor is afforded by the addition of a concentration of at least one of the following inhibiting ions to the liquid electrolyte: phosphate, phosphite, periodate, arsenate, tungstate, silicate vanadate [vandadate], tellurate, tellurite, antimonate, arsenite, selenate, sulfite and germanate.
BACKGROUND OF THE INVENTION The capacity of an electrolytic capacitor is determined primarily by the area of the electrode (usually the anode) surface and the thickness of the dielectric film covering this surface. The typical wet electrolytic capacitor employs an etched surface electrode structure and a number of methods have been developed to produce the desired roughening of the electrode surface. The most effective of these methods is the electrolytic etching of the electrode foil, while the foil is immersed in an etching solution e.g. sodium chloride (followed in some cases, e.g. for highvoltage applications by etching in nitric acid). In the process of electrolytic etching the foil is made the positive electrode with respect to a second electrode immersed in the same etching solution. The resulting attack upon the aluminum develops pores extending into the foil, these pores ranging from about 1-5 microns in lateral dimension and penetrating to a depth of from about 100- 500 microns.
It has been found that aluminum foil etched for usage as electrodes in electrolytic capacitors loses capacitance during storage. This loss in capacitance is believed to be the result of blockage of some or all of the small pores by the formation therein of aluminum hydroxide, a corrosion product of the aluminum/water reaction. Water for this destructive reaction is most often present in the atmosphere of the storage facilities and in event of temperature cycling liquid water may condense within these small pores. Aluminum oxidation in liquid water produces a layer of amorphous oxide, which dissolves and reprecipitates as a porous layer of hydroxide of (AlOOH), which may grow to a thickness of several microns depending upon the temperature. Development of this corrosion product within the small pores, therefore, decreases the available electrode area. Prevention of the aluminum hydroxide formation would, therefore, be beneficial to minimizing reduction in capacitance during storage.
ice
After etching, the electrodes are cleaned, usually by rinsing in water, to remove all traces of any contaminating or foreign materials, which might either affect forrnation of the requisite dielectric film or affect the performance of the finished capacitor. After cleaning, the aluminum foil to be used as the anode is anodized to form an anodic oxide (predominately amorphous A1 0 layer thereon using either a basic or an acidic anodizing electrolyte. Numerous electrolytes for the formation of anodic films are listed on page 55 of the test book Electrolytic Capacitors by Paul McKnight Deeley (Recorder Press 1938). The most commonly used anodizing electrolytes are boric acid and inorganic phosphates.
The anodic oxide layer formed substantially uniformly covers all of the etched surface (both sides) of the aluminum foil even extending into and covering the inside surfaces of the small pores.
When the active dielectric film of aluminum oxide has been formed, a typical electrode assembly (anode/paper spacer/cathode/paper spacer) is prepared. This assembly is rolled into a cylindrical configuration and impregnated with (as by immersion) a fill electrolyte for aging." During the aging process a potential is applied to the electrode assembly equal to or slightly in excess of the rated operating voltage for the completed capacitor for a predetermined period of time. The aging, or reforming, potential tends to repair any breakage or cracking, which may have occurred in the anodic film during the handling and assembly.
When the aging has been completed, the electrode assembly is inserted into an aluminum can and the can is capped and sealed.
Fill electrolytes (as distinguished from anodizing lectrolytes) are either nonaqueous (organic solvent) or have a low-water content. Ethylene glycol is frequently used, because of its solvent characteristics and low freezing point.
During sustained periods, when the completed capacitor is stored or is standing on open circuit, the anodic oxide layer is constantly subject to attack by water deliberately or spuriously present in the fill electrolyte. This degradation according to the aluminum/water reaction can reduce the dielectric strength of the capacitor to such a level that the imposition of a normal electrical load may cause failure of the capacitor.
It is to this problem of open circuit dielectric degradation as well as to the problem of degradation of etched aluminum foil during storage that the instant invention is directed for the purpose of optimizing electrolytic capacitor construction.
In describing this invention the terms passivation and inhibition" are employed. These terms are defined as follows:
Passivation is the rendering of a metallic or metallic oxide surface relatively immune to corrosive attack in a normally hostile environment.
Inhibition is the rendering innocuous of a normally hostile environment by the addition of substances to the environment.
SUMMARY OF THE INVENTION The instant invention introduces into the sequence of steps in preparing a wet electrolytic capacitor (a) a modified pretreatment of the etched aluminum foil to passivate the etched surface in order to delay the initiation of hydroxide formation from reaction of the aluminum with water and/or (b) the addition of one or more substances of a specific class, which provide inhibitor ions, to the fill electrolyte such that the completed electrolytic capacitor is afforded protection against dissolution of the dielectric oxide during periods of electrical inactivity.
3 BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention as Well as objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:
FIG. 1 is an exploded view of an example of an electrolytic capacitor to which the instant invention applies and FIG. 2 is a diagrammatic representation of the process of preparation of electrolytic capacitors according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT As is shown in FIG. 1, capacitor 10 comprises cooperating electrodes 11, 12 in the form of thin aluminum foils. These electrodes have a thin film of aluminum oxide thereon. Between electrodes 11 and 12 as they are arranged in the electrode assembly are disposed spacers 13 consisting of sheets of absorbent material. Spacers 13 are, or become, impregnated with electrolytic composition. Terminal tabs 14, 16 are provided for establishing electrical contact to the electrodes. After preparation, the electrode assembly is placed in aluminum can 17, which is sealed with cap 18 provided with external terminals 14a, 16a (connected to the tabs 14, 16, respectively) and vent plug hole 19 for the release of excess internal pressure.
As is described in FIG. 2, after etching and cleaning and prior to storage or anodizing, the aluminum foil is subjected to a sequence of two steps, which produces substantial passivation of the aluminum foil.
In the first step of the sequence the etched aluminum foil is immersed in a boiling aqueous solution containing Cro and H PO This immersion reduces the thickness of the thin A1 layer (normally present on the surface of aluminum) after which a complex region develops at the surface of the A1 0 layer as this layer reaches an equilibrium condition, when the rate of layer buildup equals the rate of layer dissolution. The complex region at the surface of the A1 0 layer contains CrO and P0 but is incapable of rendering the system highly passive. It is essential that this stripping operation be accomplished first and be followed by the second step.
Once equilibrium has been reached the second step may be conducted. In this step the stripped etched aluminum foil is immersed in a boiling aqueous solution containing CrO H PO and SiO (with pH adjusted to a value ranging from 4 to 6) which exposure changes the complex layer at least by including SiO as a component thereof.
In a typical passivation sequence a conventional stripping solution (20 grams CrO and 35 milliliters of concentrated H PO per liter of water) may be used with the immersion lasting from 1 to 5 minutes followed by a 3 minute immersion in an aqueous solution of adjusted pH containing from about to 10- moles per liter of each of NaH PO Na SiO and CrO Use of this pretreatment sequence has shown that initiation of hydroxide formation according to the aluminum/water reaction is delayed by at least a factor of 10 as compared to untreated foil and by at least a factor of 10 compared to aluminum foil subjected to the first, but not the second, step of this sequence.
The above-described procedure for passivating aluminum foil may be applied to either etched or plain foil. however, the prime object has been to prevent destruction during storage of the high-surface area developed by the etching process.
The passivated aluminum foil may be stored at considerably reduced risk until ready for the anodizing step preparatory to constructing the electrolytic capacitor.
In addition, when the internal construction of the electrolytic capacitor 10 has been prepared, rolled, aged and inserted into the aluminum can 17, the corrosion process (which will otherwise occur within the sealed capacitor between the exposed aluminum surfaces and liquid water in the electrolyte and between the anodic oxide layer and liquid Water) may be inhibited by introducing certain inorganic substances into the capacitor can dissolved in the fill electrolyte.
Thus, it has been determined that inhibition will be strong when (a) in the oxyanion of the inhibitor the centrally located, positively charged component (for example, phosphorous in the H PO ion) has a radius between 0.24 and 0.5 times the radius of oxygen and when (b) the inhibiting oxyanion has a proton level of 0.4 to 0.7 ev. relative to that of a proton in H 0 In essence, the structure and proton level of the inhibitor ion should be close to the structure and proton level of aluminum oxide. The substances which have the required structure and proton level are tellurate, tellurite, tungstate, antimonate, vanadate, arsenate, arsenire, [aresenate, aresenite] selenate, sulfite, periodate, phosphate, phosphite, germanate and silicate ions. All of these substances are effective inhibitors, the strongest being phosphate, phosphite, periodate, arsenate, tungstate, silicate and vanadate in the order given. The pH of maximum effectiveness is about 5:1. The oxyanion concentration dissolved in the fill electrolyte should be in the range of from about l() to 10 weight percent of the electrolyte solution with the preferred range being from about 0.1 to about 1.0 weight percent.
Thus, by adding to the fill electrolyte soluble salts, which are compatible with the fill electrolyte and which provide concentrations of ions of one or more of the above materials (eg the sodium, potassium, calcium, ammonium salts thereof) so that the concentration of requisite ions remains within the sealed electrolytic capacitor, initiation of the corrosion process is delayed by at least a factor of compared to electrolytic capacitors, which do not contain the aforementioned inhibiting ions.
Examples of fill electrolytes are as follows (percentages are by weight).
A. Organic solvent electrolyte (with organic and inorganic salts) Ethylene glycol 1 49.8 Boric acid 10.0 Pyrogallol 10.0 Methylamine 30.0 Sodium phosphate 0.2
B. Organic solvent electrolyte (with organic salts) Dimethylformamide 98.7 Oxalic acid 1.0 Ammonium oxalate 0.1 Ammonium phosphate 0.2
C. Organic solvent electrolyte (with inorganic salts) Ethylene glycol 89.8 Ammonium biborate 10.0 Ammonium phosphite 0.2
D. Aqueous electrolyte (organic salt+water) Ammonium tartrate 10.0 Water 89.8 Ammonium periodate 0.2
What we claim as new and desire to secure by Letters Patent of the United States:
1. In the preparation of a wet electrolytic capacitor wherein the following steps are performed: etching aluminum foil; cleaning said etched foil; anodizing said etched, cleaned foil; preparing an electrode assembly wherein anode and cathode layers are separated by spacers, said anode layer being made of said anodized foil; irnpregnating said electrode assembly with a fill electrolyte; aging said electrode assembly by the application of electrical potential thereto; introducing said "aged electrode assembly into a cam; and capping and sealing said can, the improvement in said series of steps comprising:
a. immersing the cleaned etched foil in a first boiling aqueous solution containing Cr0 and H PO b. immersing said foil so modified in a second boiling aqueous solution containing from about to 10- moles per liter of each of HgPOf', Si0 and CrO and c. dissolving in the fill electrolyte a water-soluble source of inhibiting oxyanions, said oxyanions being present in a concentration in the range of from about 10- to about 10 percent by weight of the electrolyte solution and being selected from the group consisting of tellurate, tellurite, tungstate, antimonate, vanadate, arsenate, arsenite, selenate, sulfite, periodate, phosphate, phosphite, germanate and silicate ions.
2. The improvement of claim 1 wherein the second boiling solution contains NaH PO Na SiO and CrO 3. The improvement of claim 1 wherein the pH of the boiling solution is adjusted in the range of from 4 to 6.
[4. In the preparation of a wet electrolytic capacitor wherein the following steps are performed: etching aluminum foil; cleaning said etched foil; anodizing said etched, cleaned foil; preparing an electrode assembly wherein anode and cathode layers are separated by spacers, said anode layer being made of said anodized foil; impregnating said electrode assembly with a fill electrolyte; aging said electrode assembly by the application of electrical potential thereto; introducing said aged electrode assembly into a can; and capping and sealing said can, the improvement in said series of steps comprising:
a. dissolving in the fill electrolyte a water-soluble source of inhibiting oxyanions, said oxyanions being present in a concentration in the range of from about l0- to about 10 percent by weight of the electrolyte solution and being selected from the group consisting of tellurate, tellurite, tungstate, antimonate, arsenate, arsenite, selenate, sulfite, periodate, and germanate ions] [5. The improvement of claim 4 wherein the pH of the fill electrolyte is in the range of from 4 to 6.]
[6. The improvement of claim 4 wherein the concentration of dissolved oxyanions is in the range of from about 0.1 to about 1.0 percent by weight of the electrolyte solution] 7. In the preparation of a wet electrolytic capacitor wherein the following steps are performed: etching aluminum foil; cleaning said etched foil; anodizing said etched, cleaned foil; preparing an electrode assembly wherein anode and cathode layers are separated by spacers, said anode layer being made of said anodized foil; impregnating said electrode assembly with a fill electrolyte; aging said electrode assembly by the application of electrical potential thereto; introducing said "aged electrode assembly into a can; and capping and sealing said can, the improvement in said series of steps comprising:
a. immersing the cleaned etched foil in a first boiling aqueous solution containing CrO, and H -PO and b. immersing the foil as modified by step (a) in a second boiling aqueous solution containing from about 10* to 10*" moles per liter of each of H POF, SiO and CrO;
whereby etched aluminum foil may be stored without substantial deterioration prior to the anodizing step.
8. The improvement of claim 7 wherein the second boiling solution contains NaH PO Na SiO and CrO 9. A method for the passivation of an aluminum surface comprising the steps of:
a. immersing the aluminum surface in a first boiling aqueous solution containing CrO and H PO and b. immersing the aluminum surface as modified by step (a) in a second boiling aqueous solution containing from about 10- to 10* moles per liter of each of H PO [and] SiO and CrO [10. In a wet electrolytic capacitor wherein a housing contains an anodized aluminum anode and a liquid electrolyte and means are attached to said housing for the forming of an external electrical connection thereto, said housing being sealed to prevent leakage of the electrolyte therefrom, the improvement in said combination wherein a water-soluble source of inhibitive ions is disposed in said housing with said electrolyte, said inhibitive ions being present in said electrolyte in a concentration in the range of from about 10* to about 10 percent by weight of electrolyte solution and being selected from the group consisting of tellurate, tellurite, tungstate, antimonate, arsenate, arsenite, selenate, sulfite, periodate, and germanate ions] 11. The improvement of claim 6 wherein the pH of the fill electrolyte is in the range of from 4 to 6.]
[12. The improvement of claim 10 wherein the concentration of dissolved ions is in the range of from about 0.1 to about 1.0 percent by weight of the electrolyte solution.]
References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.
UNITED STATES PATENTS 3,329,873 7/1967 Hagihara et a1 317-230 2,890,394 6/1959 Stephenson et al. 317-230 2,875,384 2/1959 Wallmark 317-234 3,345,544 10/1967 Metcalfe 317-230 3,502,947 3/1970 Hand 317-230 2,965,816 12/1960 Ross 317-230 3,547,423 12/1970 Jenny et al 317-230 2,019,154 4/1936 Emmens et a1 317-230 2,757,140 7/1956 Bush 317-230 X 2,934,682 4/1960 Schwartz et al. 317-230 2,994,809 8/1961 Jenny et al. 317-230 3,003,089 10/1961 Bernard et al. 317-230 3,138,746 6/1964 Burger et al. 317-230 2,934,681 4/1960 Ross 317-230 OTHER REFERENCES Periodic Table of the Elements, E. H. Sargent & Co., Chicago, 1964.
RUDOLPH V. ROLINEC, Primary Examiner W. D. LARKINS, Assistant Examiner US. Cl. X.R.
US28015D 1972-09-13 1972-09-13 Aluminum electrode electrolytic capacitor construction Expired USRE28015E (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4204919A (en) 1979-05-02 1980-05-27 Sprague Electric Company Treating etched aluminum electrolytic capacitor foil
US4470885A (en) 1983-02-07 1984-09-11 Sprague Electric Company Process for treating aluminum electrolytic capacitor foil
US5219617A (en) * 1989-09-19 1993-06-15 Michigan Chrome And Chemical Company Corrosion resistant coated articles and process for making same
US6256188B1 (en) * 1996-02-10 2001-07-03 Asea Brown Boveri Jumet S.A. (Abb) Power capacitor
US6307735B1 (en) * 1998-01-28 2001-10-23 Matsushita Electric Industrial Co., Ltd. Electrolytic capacitor and its manufacturing method

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4204919A (en) 1979-05-02 1980-05-27 Sprague Electric Company Treating etched aluminum electrolytic capacitor foil
US4470885A (en) 1983-02-07 1984-09-11 Sprague Electric Company Process for treating aluminum electrolytic capacitor foil
US5219617A (en) * 1989-09-19 1993-06-15 Michigan Chrome And Chemical Company Corrosion resistant coated articles and process for making same
US6256188B1 (en) * 1996-02-10 2001-07-03 Asea Brown Boveri Jumet S.A. (Abb) Power capacitor
US6307735B1 (en) * 1998-01-28 2001-10-23 Matsushita Electric Industrial Co., Ltd. Electrolytic capacitor and its manufacturing method
US6962612B1 (en) * 1998-01-28 2005-11-08 Matsushita Electric Industrial Co., Ltd. Electrolytic capacitor and its manufacturing method
USRE45994E1 (en) * 1998-01-28 2016-05-03 Panasonic Corporation Electrolytic capacitor and its manufacturing method

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