DE3530564A1 - METHOD FOR ELECTROCHEMICALLY FORMING A DIELECTRIC OXIDE FILM ON A VALVE METAL, METHOD FORMING VALVE METAL ELECTRODE FOR A CAPACITOR, AND USE OF SUCH A VALVE METAL ELECTRODE IN AN ELECTRODE - Google Patents

Description

Patent attorneys Dipl.-Ing. H. Weickmawn, Dipl.-Phys. Dr. K. Fincke

Dipl.-Ing. RA. ¥ eickmann, Dipl.-Chem. B. Huber Dr.-Ing. H. Liska, DrPL.-PHYs. Dr. J. Prechtel

8000 MUNICH 86 POST BOX 860 820

MÖHLSTRASSE 22 TELEPHONE (089) 98 0352 TELEX 5 22 621 DA TELEGRAM PATENTWEICKMANN MUNICH

Emhart Industries, Inc.

3029 East Washington Street, P.O. Box 706, Indianapolis, Indiana 46206, USA

Process for the electrochemical formation of a

dielectric oxide film on a valve metal, according to the

Process formed valve metal electrode for one

Capacitor and use of such a valve metal electrode in an electrolytic capacitor

The present invention relates to an electrochemical process according to the preamble of the patent claim 1, a valve metal electrode formed according to this process and the use of such a Electrode in an electrolytic capacitor.

Formed valve metals (coated with metal oxide) have been used as electrodes for several decades now used in commercially manufactured electrolytic capacitors. As the electrode coating with a metal oxide acts essentially as an insulator, the electrical properties of capacitors with formed metal electrodes to a large extent by the thickness, the quality, the stability and the dielectric properties the metal oxide layer is determined. It is a significant research and development effort in terms of establishing of improved processes for the formation of valve metals and valve metal alloys. The goal such efforts are in the production of cheaper, more efficient, and more reliable electrolytic capacitors.

fools. Obviously, the achievement of this goal is preceded by the development of efficient formation processes, which are useful in a wide range of valve metals and valve metal alloys to make capacitor electrodes with a thin, cohesive, chemically and thermally stable as well as adhering to the metal surface to produce dielectric metal oxide coating.

The formation of valve metals, i.e. the formation of a dielectric oxide layer on the surface of such Metals are made by chemical or preferably electrochemical oxidation of metal atoms in the area of the metal surface. Numerous electrochemical processes for forming valve metals have been developed. Electrochemical Formation processes are typically carried out in an electrolytic cell such that the Valve metal immersed in an electrolyte (the forming electrolyte) and connected to the positive pole (anode) of a electrical power source is connected. If an electric current is passed through the electrolytic cell, Metal atoms on the surface of the valve metal anode are oxidized, creating a metal oxide coating on the metal surface is formed. The voltage across the electrolytic cell is usually gradually increased to at the Formation of the insulating metal oxide layer on the surface to maintain a current flow.

Such known electrochemical formation processes are usually through the use of protons characterized aqueous formation electrolytes that contain at least one oxide-forming ion former. The majority of such known electrochemical processes for forming valve metals are further through relatively low efficiency and limited applicability with respect to valve metals to be effectively formed marked. For example, for years

tenth for the formation of tantalum and aluminum metals for decades solutions of phosphoric acid and / or Phosphates (e.g. ammonium phosphates) in water or water-ethylene glycol mixtures have been used.

If such solutions are used as forming electrolytes for the formation of titanium, the result is strongly hydrogenated and electrically strongly leaking oxide films. The electrical leakage of such, in aqueous solutions or aqueous Ethylene glycol solutions produced titanium oxide films due to the formation of large amounts of gas at the interface between the oxide and the forming electrolyte. The. Gas formation during formation results in a process that is not very efficient.

It is an object of the present invention to provide one for a wide variety of valve metals and alloys to specify an electrochemical formation process that can be used on the basis of valve metal, with which thin, continuous dielectric oxide films adhered to valve metals and valve metal alloys can be produced.

In a method of the type mentioned at the outset, this object is achieved according to the invention by the features of the characterizing feature Part of claim 1 solved.

Further refinements of this method are characterized in the corresponding subclaims.

In a further development of the invention, valve metal electrodes produced according to the method defined above are used used in electrolytic capacitors. By the formation method according to the invention are uniform and on Oxide films of high quality adhering to valve metals can be produced. Capacitors with: erfinduncfsq ^ mäß formi ^ rtp-n EIoR! clear v-iuij Titan or tiliuu Lt'i | i, Muim aiii Titan Has is / tfhit'ii

BATH ORIGINAL

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Compared to capacitors with anodes made of titanium, which were formed according to known processes (with an aqueous forming electrolyte), a significant capacity advantage.

The invention is explained in more detail below on the basis of exemplary embodiments.

According to the method according to the invention for the electrochemical formation of a dielectric oxide film on a valve metal, this valve metal is subjected to electrolytic anodic oxide formation conditions in an essentially non-aqueous formation electrolyte which contains a polar, proton-free solvent and an ion generator, which is phosphoric acid or an electrolytically soluble one Phosphate salt can act. At 25 ^U C, the electrolyte has a specific resistance between approximately 1000 and approximately 30,000 ohms / ccm.

The process in question can be used to form valve metals or alloys based on valve metals to produce a thin, uniform, dense oxide film adhering to the metal surface. Examples of valve metals for which the method can be used are aluminum, titanium, tantalum, zirconium, and niobium and alloys based on at least one of these metals with other polyvalent metals including known amorphous alloys that can be produced by technologies with rapidly cooled metals. the Metals can be in any desired form, for example as a flexible or rigid sheet or tape, foil, wire or as a porous sintered core. Metal foils formed according to the invention are known per se and metal sheets specifically usable for the manufacture of capacitors of a structure known per se.

The forming process in question is used specifically for anodic oxide production on titanium and on alloys based on titanium. As a material for capacitor electrodes, titanium offers various essential advantages over the more commonly used valve metals aluminum and tantalum. Titanium is cheaper and significantly lighter than tantalum (density of 4.5 compared to 16.6 g / cm ³ ) and can therefore guarantee a far greater capacity per given weight or per given metal cost.

In addition, it is known that titanium is tough capable of forming corrosion-resistant oxide with high dielectric strength. Despite the formed at Potential advantages resulting from titanium electrodes have so far been limited by known formation processes a significant commercial use of titanium electrodes in capacitors is excluded. Becomes titanium using aqueous or aqueous ethylene glycol forming electrolytes, which contain phosphoric acid, formed, result in strongly hydrogenated and electrically strongly leaking oxide films. The "electric Leakage of such titanium oxide films results in poor current efficiencies due to the formation of large quantities of gas at the interface between metal oxide and forming electrolyte.

The inefficiency of known formation processes carried out in aqueous formation electrolytes and the Formation of hydrated leaky oxide films on titanium and titanium alloys are avoided by the method of the present invention avoided using a substantially non-aqueous forming electrolyte. The in Forming electrolyte used in the process in question contains a polar, proton-free solvent as well an ion former in the form of phosphoric acid or an electrolytically soluble phosphate salt. For the invention Purposes, the degree of "proton-free"

• j ^ behavior of a polar solvent by adding a small amount (1 or 2 g) of granular ammonium carbonate to a 1 to 5% concentrated phosphoric acid solution be set in the polar solvent. One containing this percentage of concentrated phosphoric acid Solvent that reacts little or not with ammonium carbonate is useful for the purposes of the present invention sufficiently proton-free. In solvents which are used as polar proton-free solvent components from im in

IQ processes in question used forming electrolytes are not suitable, carbon dioxide is generated in visible quantities. Examples of polar, proton-free solvents, which can be used in the process in question are dimethylformamide, dimethyl sulfoxide,

• each N-methyl-2-pyrolidone and 4-butyrolactone. For practical Purposes, the polar, proton-free solvent should have a relatively high boiling point and a low viscosity Have room temperature.

2Q The term "substantially non-aqueous" used to define of the forming electrolyte used in the process in question, means that the electrolyte should contain less than about 2% water. Regarding the presence of a certain amount of water in the formation electrolyte, that is important for the electrolytic oxide formation process, those amounts of water are sufficient from, which are typically available in conventionally available, as polar proton-free solvent components and in the phosphoric acid component of the forming electrolyte

QQ are present, usually resulting in oxide formation.

Phosphoric acid or more specifically the phosphate ion proves to be the best ion former for use in the in discussion standing process. Phosphoric acid or in the formation electrogg lyten-soluble phosphate salt are added to the forming electrolyte in sufficient quantity to ensure its specific Resistance to values between about 1000 and about

30000 Ohm / cc lower for about 25 ^U C.

The factors governing the selection of a suitable phosphate salt ion former for the forming electrolyte are only the stability of the salt cation during the oxide formation process and the solubility of the phosphate salt in the forming electrolyte and in water. Of course, the phosphate salt must be in the forming electrolyte have sufficient solubility to allow salt concentrations to lower the specific Sufficient resistance of the electrolyte in the range mentioned above.

The phosphate salt should also be sufficiently soluble in water so that salt residues can pass from the surface of the formed metal after the forming process Water can be washed off. Without a certain degree of water solubility, it is difficult, if not impossible, To remove salt residues from etching tunnels of a foil or from internal parts of formed sintered metal bodies.

Suitable phosphate salts are monohydrogen and dihydrogen phosphate salts, the reaction of phosphoric acid with weak amine bases, such as pyridine, Quinoline, aniline, toluidine, semicarbazides and substituted derivatives thereof can be obtained. The nature of the substituents such bases is not critical provided that the phosphate salts of the bases in the forming electrolyte soluble and sufficiently stable, and further provided that they are of a certain degree Have water solubility. Pyridine phosphate is preferred as the phosphate salt which can be used in the process in question. The phosphate salts can be produced by methods known per se and then dissolved in the electrolyte or they can according to a preferred embodiment

γ exemplary embodiment of the invention can be formed on the spot by reaction of phosphoric acid and an amine base in the electrolyte.

c Phosphoric acid is naturally a preferred forming electrolyte ion former in the case in question. They can be used alone or in combination with at least one one of the amine compounds given below can be used, which cause the dissociation of phosphoric acid

- ^ q Lowering of the specific resistance of the electrolyte favor and which the acidity of the essentially non-aqueous polar proton-free formation electro- -lyten buffer. Because of the essentially non-aqueous proton-free nature of the electrolyte ionizes phosphorus

-, j-acid not to the extent that it is proton-containing in aqueous Ionizes electrolytes that are commonly used for oxide formation. The specific resistance of the forming electrolyte is proportional to the degree of ionization of the ion former. The in

2Q at issue are essentially non-aqueous polar proton-free formation electrolytes larger phosphoric acid concentrations required to lower the specific resistance of the electrolyte to values which for practical current densities during the formation process

2g ses are required. Is phosphoric acid alone as an ion generator used in a forming electrolyte in the method in question, such a sufficient one becomes Amount added to adjust the resistivity of the electrolyte in a range from about 10,000 to about 30,000 ohms / cc

Bring OQ.

It is true that a specific resistance of the electrolyte below 10000 Ohm / ccm can be achieved by adding larger quantities can be achieved by phosphoric acid. The advantage of smaller gg specific resistances of the solution (i.e., higher available Formation current densities) must, however, be compensated for against the effect caused by the amounts added of phosphoric acid to the breakdown voltage of the

Electrolytes or, more specifically, the ability of the electrolyte to react with the metal during formation. The breakdown voltage of the forming electrolyte is the voltage at which gas formation and / or sparkling (arcing) can be observed at the anode. As a general rule Speaking of which, with increased phosphoric acid concentration, both the resistivity and the breakdown voltage of the formation electrolyte.

ideally should be the breakdown voltage of the forming electrolyte greater than the formation voltage required to achieve useful dielectric coatings be. For the method in question, the formation electrolyte preferably has a breakdown voltage greater than about 200 V.

In the preferred embodiment of the invention, the forming electrolyte contains phosphoric acid and so on Urea, a water-soluble substituted urea, or up to three moles of an organic amine base per mole Phosphoric acid in the forming electrolyte. The amine bases are selected from amine bases which are used in the electrochemical Formation conditions are stable according to the method in question and which are both in the formation electrolyte as well as form soluble phosphate salts in water. The amine additives are used to give the specific To lower the resistance of the predetermined amounts of forming electrolytes containing phosphoric acid. Thus can the phosphoric acid concentration in the forming electrolyte must be kept to a minimum, i.e. kept in a concentration range that is preferred large breakdown voltage range of the electrolyte is adapted, while at the same time the specific resistance the solution can be lowered in order to ensure greater current densities during the formation process. About that in addition, the addition of an organic amine reduces

γ the "degree of acidity" of the electrolyte and is therefore used to minimize etching of the metal surface during formation.

For forming electrolytes according to the invention Processes are examples of organic amine bases for reducing resistivity and acidity of the electrolyte are pyridine, quinoline, aniline, toluidine, semicarbazides and substituted derivatives thereof, ^ O which both in the formation electrolyte and in water Form soluble phosphate salts.

Is an amine with phosphoric acid in the forming electrolyte used, it is preferred according to the invention that no more than about three moles, preferably about two moles of one Amine base can be used per mole of phosphoric acid in the formation electrolyte. By using any of the foregoing Amine additions to a substantially non-aqueous polar proton-free forming electrolyte containing phosphoric acid Resistances of the solution down to about 1000 Ohm / ccm can be achieved. the Breakdown voltage for the same amine and phosphoric acid containing electrolytes is typically greater than 300 V.

Urea and substituted ureas can advantageously be used in forming electrolytes containing phosphoric acid to reduce their specific resistance also used in the process according to the invention

become gO. Preferably in water and in the forming electrolyte Soluble ureas are urea and methyl substituted ureas. Urea and tetramethyl urea are preferred substances, the amounts of urea or sub-

g ₅ substituted urea are in the range of traces of these substances up to an amount which the solubility limit

of the urea compound in the forming electrolyte.

In practice, the method of the invention is essentially carried out in the same way as known electrochemical formation processes. The formation process The metal to be subjugated is in a substantially non-aqueous polar proton-free forming electrolyte immersed and electrically connected to the positive pole of an electrical power source, which can either deliver a constant current (through voltage regulation) or during the formation process a - supplies constant or programmed increasing voltage for the cell. With a constant current source, the The voltage on the electrolytic cell is gradually increased in order to maintain a preset current density, when a metal oxide layer forms on the anode. The forming process continues until the tension is increased to a predetermined value as high as the breakdown voltage of the formation electrolyte can.

It can be assumed that the current densities are not a critical parameter for the method in question. However, if the method is applied to a more reactive metal, such as titanium or a titanium-based alloy, the current density during formation is preferably kept at a value below about 2 mA per square centimeter and preferably below about 1 mA per square centimeter. The temperature of the formation electrolyte is preferably monitored and ^{kept below about 50 °} C. during the formation process in question. For efficient production of anodic oxide on titanium, the temperature of the formation electrolyte is between about 0 ° C should be about 30 ⁰ C are maintained. Vigorous movement or rapid circulation of the forming electrolyte in the electrolytic cell

-Y Z-

supports the reduction of temperature gradients in the cell and also supports the uniformity of the anodic oxide film.

δ The method in question can preferably be used for Manufacture of capacitor electrodes can be used. Valve metal sheets formed by the present process Sheets have a dense, corrosion-resistant, high quality dielectric oxide film. Formed Valve metal electrodes can be processed according to known construction techniques for capacitors, whereby Capacitors with a long service life in a wide range of operating conditions (applied voltages, temperatures, etc.) arise. Titanium and titanium alloy electrodes become efficient after the process in question formed and have special advantages in terms of unit capacity and oxide quality over Titanium electrodes that have been formed with aqueous forming electrolytes.

The invention is explained in more detail below with the aid of detailed examples.

example 1

Two commercially pure (tico) titanium ribbons with a thickness of 0.127 cm and a width of about 2.38125 cm were made each formed in one of the following two forming electrolytes:

Solution 1:

Ethylene glycol 25 vol.%

Water (deionized) 74% by volume

Phosphoric acid (concentrated) 1 vol.%

Solution 2:

N-methyl-2-pyrrolidone plus concentrated phosphoric acid in an amount necessary to adjust the resistivity to 25000 ohms / ccm at 25 "C. is.

For solution 1, a resistance of about 150 ohms was used found. This value is typical for forming electrolytes that have been used to form tantalum are. The formation of titanium strips was carried out at a current density of 1 mA per square centimeter, The solutions were kept at 25 ° C. with rapid circulation. The breakdown voltage of the solution was 1 after 10 hours at 37 V. No voltage breakdown was observed for solution 2 at 600 V. this shows the disadvantage of known forming solutions compared to solutions according to the invention.

Example 2

The proton-free properties of propylene carbonate were realized by adding ammonium carbonate to a 3% solution of phosphoric acid in propylene carbonate. The propylene carbonate solution of concentrated phosphoric acid reacts - albeit slowly - with ammonium carbonate.

Two commercially pure (tico) titanium bands with a thickness of 0.127 cm and a width of about 2.38125 cm OQ were each in one of the following forming electrolytes formed:

Solution # 1

Propylene carbonate 98% by volume

gg phosphoric acid (concentrated) 2 vol.%

^ Solution # 2

Dimethyl sulfoxide 90% by volume

Phosphoric acid (concentrated) 10% by volume

Solutions 1 and 2 had resistivities of 30,000 ohms / ccm and 200UO ohms / ccm, respectively, at 25 ° C. the
Titanium ribbons were formed in the corresponding solutions at a current density of 1 mA per square centimeter at 25 ° C. with rapid solution circulation. The breakdown voltage of solution # 1 was 330 V. The breakdown voltage of solution # 2 was greater than
600 V.

,, _ Example 3

Ib

The superiority of phosphoric acid as an ion former in formation electrolyte solutions for the formation of Titan shows the following experiment. A titanium band was made in a solution of boric acid and dimethyl sulfoxide a constant current density of 1 mA per square centimeter. There was no increase in voltage. From it it can be concluded that oxide formed in this formation electrolyte is either very conductive or loosens during formation. This experiment was repeated with formation electrolyte solutions, which as Ion formers significant amounts of organic acids such as titric, oxalic, tartaric and salicylic acid included, with solvents, temperatures, specific resistances of the solution and current densities values as with had method according to the invention. Under these conditions, a highly unstable oxide is formed, which after a Period of several minutes to several hours from the base metal.

Example 4

To determine the relative capacitance of anodic oxide films on titanium and tantalum, tapes measuring 2.54 cm from commercially pure (Tico) titanium and fansteel tantalum sheets cleaned with toluene and acetone to make an organic Remove surface contamination. The tapes were then operated at 100 V and a current density of 1 mA formed per square centimeter. The total formation time for the following solutions was as indicated Results one hour:

titanium

Tantalum

4-butyrolactone 90 vol.% Water (deionized) 99 vol.% phosphoric acid 10 vol.% phosphoric acid 1 vol.% specific cons specific cons the solution was: 10,000 ohms / cc the solution was: 61 ohms / cc at 25 ° C at 85 ° C Formation temperature Formation temperature rature: 25 ⁰ C rature: 25 ° C Final current density 80 mA per Final current density 23 mA per Square centimeters

The formed tapes were then rinsed with deionized water and dried at room temperature. the The capacity of the belts was then measured with an H.P. 4261 A bridge at 120Hz (2 wire) using a porous hollow graphite cathode and a 10% phosphoric acid electrolyte measured.

Capacity of formed titanium (6 V bias):

1 microfarad per square centimeter

Capacity of the formed tantalum (2.2 V bias):

0.12 microfarads per square centimeter

The above results show eight times the capacity of the titanium oxide film at this forming voltage.

Example 5

Commercially pure titanium (Tico) was cleaned for one hour in a solution made up of equal volumes Nitric acid (70%} and hydrogen peroxide (30%)

. consists. Tapes of this material were then made into a known forming electrolyte solution and formed in an electrolyte according to the invention.

jg Known electrolyte (a variant of the electrolyte according to

U.S. Patent 2,874,102)

Ethylene glycol 50.0% by volume

deionized water 49.9% by volume

Phosphoric acid 0.1 vol.%

Specific resistance: 5800 Ohm / ccm at 23 ⁰ C

Electrolyte according to the invention:

N-methyl-2-pyrrolidone 500 ml

Phosphoric acid (85%) 10 ml

Pyridine 10 ml

deionized water 2 ml

Specific resistance: 16000 Ohm / ccm at 25 ^U C

The formation was carried out with a constant current and unmixed solutions at 25 ° C.

State of the art invention Current density 1 itiA / cm ^a 0.5 mA / on * Voltage change 5 V / min 6 V / min Tension with tension change _ + 2 V / min 465 V 571 V for returning to Voltage (after 24 hours Idle) required Time at 1 mA / cm ² 285 s to 465 V. 135 s on

The efficiency of the formation with the known solution is only 40% of the efficiency of the invention Solution. The gas formation at the anode is responsible for the additional 60% of the current flow.

Example 6

The electrolyte of the present invention can be specific with one Resistance that is currently used for forming tantalum and aluminum Electrolyte corresponds to:

Dimethylformamide 450.0 ml

Phosphoric acid (85%) 25.0 ml

Pyridine 12.5 ml

Specific resistance: 1000 Ohm / ccm at 30 ⁰ C.

An example 1 prepared in accordance with titanium sheet was formed in the above solution at 25 ⁰ C and a current density of 0.5 mA per square centimeter. The breakdown voltage (undisturbed solution) was 324 V. When the voltage was applied again, the breakdown voltage increased to 335 V. The breakdown voltages given above are those voltages at

where the voltage drops (due to the constant power supply), with a sparkle (arcing) at the anode accompanied gassing was observed. The sparkle is visible in a dark room.

Example 7

A tantalum sheet was formed at 200 V in 1% phosphoric acid at 85 ⁰ C. For 25 square centimeters of formed surface, the capacitance was 1.62 microfarads or about 13 cv / cm * (microfarad volts per g).

A titanium sheet (Tico) was up to 500 V at 0.5 mA per Square centimeters formed in the following solution.

500 ml of N-methyl-2-pyrrolidone

20 ml pyridine

10 ml phosphate acid (85%)

2 ml deionized water

Specific resistance: 11500 Ohm / ccm at 27 ⁰ C

For 25 square centimeters of formed surface, the capacitance was 20.1 microfarads or about 400 cv / cm ² .

This shows a 30-fold cv / area advantage for titanium versus tantalum at 500 V. The above measurements would be made with a H.P. 4261 A bridge with a porous graphite cathode (2 wire connection) and a 10% phosphoric acid electrolyte at 2.2 V bias and 120 Hz measured.

Example 8

A zircon sheet (from Teledyne Wan Change Albany) was cleaned in sulfuric acid / hydrogen peroxide and then formed in the following solution:

450.0 ml of N-methyl-2-pyrrolidone

25.0 ml phosphoric acid (85%)

12.5 ml of pyridine
10

Specific resistance: 3500 Ohm / ccm at 25 ° C. Current density: 0.5 mA per square centimeter

Formation voltage: 300 V

After two hours of voltage, the current density was 10 mA per square centimeter. The capacity of the formed zirconium tape was measured at 1000 Hz and a bias voltage of 2.2 V at 0.06 microfarads / cm ² , 18 microfarads · v / cm ² .

Example 9

A tape made of commercially pure titanium was dipped in nitric acid / hydrogen peroxide cleaned and formed in the following solution:

500 ml of dimethyl sulfoxide

24 ml phosphoric acid (85%)
so g urea

Specific resistance: 8000 ohms / ccm at 25 ° C

The formation was carried out at 25 to 27 ° C. with a current density of 0.5 mA per square centimeter at 500 V.

¹ DC leakage in the formation electrolyte:

70 mA / cm ² after 20 min under voltage 2 mA / cm ⁵ after 9 hours under voltage 5

No corrosion or solid failure occurred. Though also a smaller ratio of urea too Acid is usable, the ratio given was chosen in order to ensure the high solubility of urea in Di-10 methyl sulfoxide to show.

Claims (18)

Patent attorneys Dipl.-Ing. IrJi "Weickm / v · <ϊν, Dipl.-Paiys. Dr. K. Fincke Dipl.-Ing. F.'A.Weickmann, Dipl.-Chem. B. Huber Dr.-Ing. H. Liska, Dipl.-Phys. Dr. J. Prechtel 8000 MUNICH 86 λ η AiIg POSTBOX 860 820 * · '' MO H LSTRASS E 22 TELEFON (089) 980352 TELEX 522621 DA TELEGRAM PATENTWEICKMANN MUNICH Emhart Industries, INc. East Washington Street, P.O. Box 706, Indianapolis, Indiana 46206, USA Process for the electrochemical formation of a dielectric oxide film on a valve metal, according to the Process formed valve metal electrode for one Capacitor and use of such a valve metal electrode in an electrolytic capacitor Claims λ). A process for the electrochemical formation of a dielectric oxide film on a valve metal, characterized in that the valve metal is exposed to electrolytic anodic oxide formation conditions in a substantially non-aqueous formation electrolyte, so that the electrolyte has a specific resistance between about 1000 and about 30,000 ohms per cubic centimeter at 25 ° C , and that the electrolyte contains a polar, proton-free solvent and an ion former in the form of phosphoric acid or an electrolytically soluble phosphate salt. 2. The method according to claim 1, characterized in that the formation electrolyte is phosphoric acid and further Urea, a water-soluble substituted urea or three moles of an amine base per mole of phosphoric acid im Contains forming electrolytes. 3. The method according to claim 1 and 2, characterized in that the forming electrolyte is urea, tetramethyl urea or contains pyridine. . 4. The method according to any one of claims 1 to 3, characterized in that that as a valve metal a metal from the group aluminum, titanium, niobium, tantalum, zirconium and Alloys selected on the basis of these valve metals are. 5. The method according to any one of claims 1 to 4, characterized in, that the polar proton-free solvent from the substances dimethylformamide, dimethyl sulfoxide. , N-methyl-2-pyrrolidone, 4-butyrolactone, propylene carbonate and mixtures thereof. 6. A method according to any one of claims 1 to 7, characterized in that the valve metal is titanium or a titanium-based alloy, and in that the temperature of the formation electrolyte is maintained below about 50 ⁰ C. 25th 7. The method according to any one of claims 1 to 6, characterized in, that the formation electrolyte contains phosphoric acid in a Mehge to reduce its Specific resistance to values between about 10,000 and about 30,000 ohms per cubic centimeter is sufficient. 8. The method according to any one of claims 1 to 7, characterized in that during the electrolytic anodic oxide formation, a current density with a value of not greater than about 2 mA / cm ^s is maintained that the anodic formation voltage on one of the "ΊΝι ' ¹ -, j - Breakdown voltage of the formation electrolyte is not exceeding value is held. 9. The method according to any one of claims 1 to 8, characterized in that the temperature of the formation electrolyte between about 0 and about 30 ⁰ C is kept. 10. The method according to any one of claims 1 to 9, characterized in that the temperature of the formation electrolyte is kept between about 0 and about 30 ⁰ C, and that the current density is not greater than about 1 mA / cm ² . 11. The method according to any one of claims 1 to 10, characterized characterized in that the forming electrolyte contains urea, tetramethyl urea or pyridine, a breakdown voltage greater than about 200 V and a resistivity between about 1000 and about 30,000 Ohms / ccm. 12. The method according to any one of claims 1 to 11, characterized in that for the formation of titanium or alloys based on titanium, the metal is formed at a current density of not more than about 2 mA / cm ² in a substantially non-aqueous polar proton-free forming electrolyte which contains an ion former in the form of phosphoric acid or an electrolytically soluble phosphate salt. 3013. The method according to claim 12, characterized in that the forming electrolyte has a specific resistance between about 1000 and about 30000 ohm / ccm. 14. The method according to claim 12 and 13, characterized in that that the amine base is an electrochemically stable amine base, both in the formation electrolyte as - 4 - also forms phosphate salts which are soluble in water. 15. The method according to any one of claims 12 to 14, characterized characterized in that the formation electrolyte is phosphoric acid and furthermore urea or up to three Contains moles of pyridine per mole of phosphoric acid in the formation electrolyte. 16. The method according to any one of claims 12 to 15, characterized characterized in that the forming electrolyte contains about two moles of pyridine per mole of phosphoric acid. 17. valve metal electrode for a capacitor, characterized in that it is by means of a method according to one of claims 1 to 16 is formed. 18. Use of a valve metal electrode according to claim 17 in an electrolytic capacitor.